| 1. |
- Björk, Emma M., 1981-
(author)
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Mesoporous Building Blocks : Synthesis and Characterization of Mesoporous Silica Particles and Films
- 2013
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Doctoral thesis (other academic/artistic)abstract
- Catalyst supports, drug delivery systems, hosts for nanoparticles, and solar cells are just some examples of the wide range of exciting applications for mesoporous silica. In order to optimize the performance of a specific application, controlling the material’s morphology and pore size is crucial. For example, short and separated particles are beneficial for drug delivery systems, while for molecular sieves, the pore size is the key parameter.In this thesis, mesoporous silica building blocks, crystallites, with hexagonally ordered cylindrical pores were synthesized, with the aim to understand how the synthesis parameters affect the particle morphology and pore size. The synthesis of the particles is performed using a sol-gel process, and in order to increase the pore size, a combination of low temperature, and additions of heptane and NH4F was used. By variations in the amounts of reagents, as well as other synthesis conditions, the particle morphology and pore size could be altered. Separated particles were also grown on or attached to substrates to form films. Also, a material with spherical pore structure was synthesized, for the first time using this method.It was found that a variation in the heptane concentration, in combination with a long stirring time, yields a transition between fiber and sheet morphologies. Both morphologies consist of crystallites, which for the fibers are joined end to end, while for the sheets they are attached side by side such that the pores are accessible from the sheet surface. The crystallites can be separated to a rod morphology by decreasing the stirring time and tuning the HCl concentration, and it was seen that these rods are formed within 5 min of static time, even though the pore size and unit cell parameters were evolving for another 30 min. Further studies of the effects of heptane showed that the shape and mesoscopic parameters of the rods are affected by the heptane concentration, up to a value where the micelles are fully saturated with heptane. It was also observed that the particle width increases with decreasing NH4F concentration, independent of heptane amount, and a platelet morphology can be formed. The formation time of the particles decrease with decreasing NH4F, and the growth mechanism for platelets was further studied. The pore sizes for various morphologies were altered by e.g. variations in the hydrothermal treatment conditions, or the method for removing the surfactants.The separated particles can be attached to substrates, either during the particle synthesis or by post grafting prior to calcination. The film formation during the one-pot-synthesis was studied and a formation mechanism including nucleation of elongated micelles on the substrate was suggested. During the post grafting film synthesis, the medium in which the particles are dispersed, as well as functionalization of both particle and substrate are crucial for the post grafting process. The pores are easily accessible independent of the method, even though they are aligned parallel to the substrate when the one-pot-method is used, while post grafting gives a perpendicular pore orientation.In summary, this work aims to give an understanding for the formation of the synthesized material, and how to tune the material properties by alterations in parameter space. Successful syntheses of four different particle morphologies and two new types of films were performed, and the pore size could easily be tuned by various methods.
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| 2. |
- Abrikosov, Igor, et al.
(author)
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Phase Stability and Elasticity of TiAlN
- 2011
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In: Materials. - : MDPI. - 1996-1944. ; 4:9, s. 1599-1618
-
Journal article (peer-reviewed)abstract
- We review results of recent combined theoretical and experimental studies of Ti1−xAlxN, an archetypical alloy system material for hard-coating applications. Theoretical simulations of lattice parameters, mixing enthalpies, and elastic properties are presented. Calculated phase diagrams at ambient pressure, as well as at pressure of 10 GPa, show a wide miscibility gap and broad region of compositions and temperatures where the spinodal decomposition takes place. The strong dependence of the elastic properties and sound wave anisotropy on the Al-content offers detailed understanding of the spinodal decomposition and age hardening in Ti1−xAlxN alloy films and multilayers. TiAlN/TiN multilayers can further improve the hardness and thermal stability compared to TiAlN since they offer means to influence the kinetics of the favorable spinodal decomposition and suppress the detrimental transformation to w-AlN. Here, we show that a 100 degree improvement in terms of w-AlN suppression can be achieved, which is of importance when the coating is used as a protective coating on metal cutting inserts.
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| 3. |
- Ballem, Mohamed Ali, et al.
(author)
-
Growth of Gd2O3 nanoparticles inside mesoporous silica frameworks
- 2013
-
In: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 168, s. 221-224
-
Journal article (peer-reviewed)abstract
- Gadolinium oxide (Gd2O3) nanoparticles with very small size and narrow size distribution were synthesized by infiltration of Gd(NO3)(3)center dot 6H(2)O as an oxide precursor into the pores of SBA-15 mesoporous silica using a wet-impregnation technique. High resolution transmission electron microscopy and X-ray diffraction show that during the hydrothermal treatment of the precursor at 550 degrees C, gadolinium oxide nanoparticles inside the silica pores are formed. Subsequent dissolution of the silica framework in aqueous NaOH resulted in well dispersed nanoparticles with an average diameter of 3.6 +/- 0.9 nm. If GdCl3 center dot 6H(2)O is used as precursor, GdOCl is formed instead of Gd2O3. The Gd2O3 nanoparticles showed a weak antiferromagnetic behavior, as expected.
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| 4. |
- Ballem, Mohamed A., et al.
(author)
-
Influence of synthesis temperature on morphology of SBA-16 mesoporous materials with a three-dimensional pore system
- 2010
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In: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 129, s. 106-111
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Journal article (peer-reviewed)abstract
- Spherical particles of mesoporous silica SBA-16 with cubic Im3m structure were synthesized at low pH using Pluronic F127 as template and TEOS as silica source. The diameter of the spherical particles can be controlled in the range of 0.5–8 μm by varying synthesis temperature from 1 °C up to 40 °C. A sharp transition from large particle sizes at approximately 20 °C to smaller ones is observed when the temperature is increased. It is suggested that this morphology transition is due to a change in hydrolysis and condensation rate of the silica source and as a result the assembly of F127 micelles will differ. The SBA-16 samples were characterized using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption techniques.
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| 5. |
- Ballem, Mohamed A., et al.
(author)
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Low Temperature Nanocasting of Ultrafine Hematite Nanoparticles using Mesoporous Silica Molds
- 2012
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In: Powder Technology. - : Elsevier. - 0032-5910 .- 1873-328X. ; 217, s. 269-273
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Journal article (peer-reviewed)abstract
- Iron oxide (α-Fe2O3) nanoparticles with very small size, high crystallinity, and narrow size distribution were synthesized by infiltration of Fe(NO3)3.9H2O as an oxide precursor into mesoporous silica (SBA-15 and SBA-16) molds using a wetimpregnation technique. High resolution transmission electron microscopy shows that during the hydrothermal treatment of the precursor at 140 °C for 2 days, stable α-Fe2O3 nanoparticles inside the silica pores are formed. Subsequent leaching out of the silica template by NaOH resulted in well dispersed nanoparticles with an average diameter of ~ 4 nm.
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| 6. |
- Ballem, Mohamed A., et al.
(author)
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Mesoporous silica templated zirconia nanoparticles
- 2011
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In: Journal of nanoparticle research. - : SpringerLink. - 1388-0764 .- 1572-896X. ; 13:7, s. 2743-2748
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Journal article (peer-reviewed)abstract
- Nanoparticles of zirconium oxide (ZrO2)were synthesized by infiltration of a zirconia precursor(ZrOCl28H2O) into a SBA-15 mesoporous silicamold using a wet-impregnation technique. X-raydiffractometry and high-resolution transmission electronmicroscopy show formation of stable ZrO2nanoparticles inside the silica pores after a thermaltreatment at 550 C. Subsequent leaching out of thesilica template by NaOH resulted in well-dispersedZrO2 nanoparticles with an average diameter of*4 nm. The formed single crystal nanoparticles arefaceted with 110 surfaces termination suggesting it tobe the preferred growth orientation. A growth modelof these nanoparticles is also suggested.
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| 7. |
- Ballem, Mohamed A.
(author)
-
Synthesis of Mesoporous Silica and their Use as Templates for Metal and Metal Oxide Nanoparticles
- 2011
-
Doctoral thesis (other academic/artistic)abstract
- This thesis covers the synthesis and characterization of two types of mesoporous silica, SBA-15 silica with two-dimensional hexagonal arrangement, and SBA-16 silica with three-dimensional cubic arrangement. The obtained mesoporous materials were then used as hard templates for synthesizing of different types of nanostructures. In the first part, the effects of some synthesis parameters on the morphology and texture properties of the mesoporous silica have been studied. By varying the synthesis temperature solid spheres of SBA-16 with different sizes were synthesized and by additions of heptane as a swelling agent, SBA-16 in a hollow-sphere morphology with a large pore size was obtained. In the case of SBA-15, dispersed rods were synthesized in the presence of heptane and NH4F in a low-temperature synthesis. The length of the rods was varied by changing the concentration of HCl, and the pore size was tuned by changing the hydrothermal treatment time and temperature. Furthermore, the reaction time was decreased with a well-retained pore size and morphology. This work has resulted in SBA-15 rods with large pore sizes for this morphology. In the second part, SBA-15 and SBA-16 silica were used to synthesize different nanostructured materials such as metal and metal oxide nanoparticles. In fact, most of the work in this part is focused on the use of mesoporous silica as hard templates for synthesis of different types of nanoparticles. The synthesis of these nanoparticles was carried out by infiltration of a suitable precursor in the pores of the silica template. The mesoporous frameworks act as molds controlling the size and the final shape of the formed nanostructures. Subsequent dissolution of the silica templates by NaOH resulted in e.g., monodispersed zirconia, hematite, and cobalt nanoparticles with narrow size distributions. Functionalization of the SBA-15 surfaces was carried out in the synthesis of cobalt nanoparticles. This functionalization plays a crucial role on the infiltration and reaction of the reagents in the pores of the silica. By functionalization of the external surface, a highly hydrophobic surface was achieved, which proved to be sufficient to avoid formation of large cobalt particles outside the silica channels, while the internal functionalization enhances the attraction of cobalt ions to the silica pores, and as a result the nanoparticles grew inside these pores.
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| 8. |
- Ballem, Mohamed, et al.
(author)
-
Synthesis of hollow silica spheres SBA-16 with large-pore diameter
- 2011
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In: Materials letters (General ed.). - : Elsevier Science B.V., Amsterdam.. - 0167-577X .- 1873-4979. ; 65:7, s. 1066-1068
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Journal article (peer-reviewed)abstract
- Hollow silica SBA-16 spheres with cubic ordered mesoporous shells were synthesized by an emulsion-templating method, using Pluronic F127 as a structure-directing agent. tetraethyl orthosilicateas as a silica source and heptane as a cosolvent in the presence of NH4F. The size of these spheres is in the range of 10 to 30 mu m. The shell is about 700 nm thick and consists of large pores, similar to 9 nm in diameter, arranged in a cubic order. After calcination, the spheres maintain their mesoporosity and show a high surface area of 822 m(2)/g. The formation mechanism of the silica hollow spheres is discussed.
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| 9. |
- Barrirero, Jenifer, et al.
(author)
-
Comparison of segregations formed in unmodified and Sr-modified Al-Si alloys studied by atom probe tomography and transmission electron microscopy
- 2014
-
In: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 611, s. 410-421
-
Journal article (peer-reviewed)abstract
- The mechanical properties of Al-7 wt.% Si can be enhanced by structural modifications of its eutectic phase. Addition of low concentrations of certain elements, in this case 150 wt-ppm Sr, is enough to cause a transition from a coarse plate-like Si structure to a finer coralline one. To fully understand the operating mechanism of this modification, the composition of the eutectic Si phase in unmodified and Sr-modified alloys was analysed and compared by atom probe tomography and (scanning) transmission electron microscopy. The unmodified alloy showed nanometre sized Al-segregations decorating defects, while the Sr-modified sample presented three types of Al-Sr segregations: (1) rod-like segregations that promote smoothening of the Al-Si boundaries in the eutectic phase, (2) particle-like segregations comparable to the ones seen in the unmodified alloy, and (3) planar segregations favouring the formation of twin boundaries. Al and Sr solubilities in Si after solidification were determined to be 430 +/- 160 at-ppm and 40 +/- 10 at-ppm, respectively. Sr predominantly segregates to the Si phase confirming its importance in the modification of the eutectic growth.
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| 10. |
- Björk, Emma M., et al.
(author)
-
Grafting mesoporous silica particles to substrates : a method for synthesizing mesoporous films with cylindrical pores perpendicular to the substrate
- 2013
-
Other publication (other academic/artistic)abstract
- A method for synthesizing mesoporous silica films with cylindrical pores perpendicular to the substrate has been developed. The films consist of SBA-15 platelets that are grafted on glass substrates. The grafting is studied in terms of parameters such as pH, substrate functionalization, salt additions, time for TEOS prehydrolysis, and calcination. The best coverage of particles on the substrate was achieved for a low pH in combination with OTS-treated glass substrate. Furthermore, the prehydrolysis time of the TEOS was found to be a key parameter in order to bind the particles to the substrate. These porous films have potential in applications such as catalysis, drug delivery, and as a template for nanoparticle or nanorod, growth.
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| 11. |
- Björk, Emma M., et al.
(author)
-
Single-pot synthesis of ordered mesoporous silica films with unique controllable morphology
- 2014
-
In: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 413, s. 1-7
-
Journal article (peer-reviewed)abstract
- Mesoporous silica films consisting of a monolayer of separated SBA-15 particles with unusually wide and short pores grown on silicon wafers have been fabricated in a simple single-pot-synthesis, and the formation of the films has been studied. A recipe for synthesizing mesoporous silica rods with the addition of heptane and NH4F at low temperature was used and substrates were added to the synthesis solution during the reaction. The films are ∼90 nm thick, have a pore size of 10.7–13.9 nm depending on the hydrothermal treatment time and temperature, and a pore length of 200–400 nm. All pores are parallel to the substrate, open, and easy to access, making them suitable for applications such as catalyst hosts and gas separation. The growth of the films is closely correlated to the evolution of the mesoporous silica particles. Here, we have studied the time for adding substrates to the synthesis solution, the evolution of the films with time during formation, and the effect of hydrothermal treatment. It was found that the substrates should be added within 30–60 s after turning off the stirring and the films are formed within 10 min after addition to the synthesis solution. The study has yielded a new route for synthesizing mesoporous silica films with a unique morphology.
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| 12. |
- Björk, Emma M., et al.
(author)
-
Tuning the shape of mesoporous silica particles by alterations in parameter space : from rods to platelets
- 2013
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 29:44, s. 13551-13561
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Journal article (peer-reviewed)abstract
- The knowledge of how to control the pore size and morphology of separated mesoporous silica particles is crucial for optimizing their performance in applications, such as molecular sieves and drug delivery systems. In this work, we have systematically studied the effects of various synthesis parameters to gain a deeper understanding of how particle morphologies can be altered. It was found that the morphology for isolated particles of SBA-15 type, with unusually short and wide pores, could be altered from rods to platelets by variations in the NH4F concentration. The pore length is nearly constant (similar to 300 nm) for the different morphologies, but the particle width is increasing from 200 nm to >3 mu m when decreasing the amount of NH4F, and the pore size can be tuned between 10 and 13 nm. Furthermore, other synthesis parameters such as heptane concentration, pH, silica precursor, and additions of ions have also been studied. The trend regarding particle width is independent of heptane concentration, at the same time as heptane increases the particle length up to a plateau value of similar to 500 nm. In all, parameters controlling particle width, length, and pore size have been separated in order to evaluate their function in the particle formation. Additionally, it was found that the formation time of the particles is strongly affected by the fluoride ion concentration, and a mechanism for particle formation for this system, where micelles transform from a foam, to multilamellar vesicles, and finally to cylindrical micelles, is suggested.
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| 13. |
- Cordoba Gallego, Jose Manuel, et al.
(author)
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Growth of single crystalline dendritic Li(2)SiO(3) arrays from LiNO(3) and mesoporous SiO(2)
- 2011
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In: Journal of Solid State Chemistry. - : Elsevier Science B.V., Amsterdam. - 0022-4596 .- 1095-726X. ; 184:7, s. 1735-1739
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Journal article (peer-reviewed)abstract
- A solution based wet chemistry approach has been developed for synthesizing Li(2)SiO(3) using LiNO(3) and mesoporous silica as starting materials at 550 degrees C. A reaction path where NO and O(2) are formed as side-products is proposed. The crystals synthesized exhibit dendritic growth where the as-prepared nanodendrite is a typical 1-fold nanodendrite composed of one several microns long and some tenth of nanometers wide trunk with small branches, which are several hundreds of nanometers long and up to 70 nm in diameter. The effect of the structure of the mesoporous silica for the final morphology is discussed.
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| 14. |
- Eriksson, Anders, et al.
(author)
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Arc deposition of Ti–Si–C–N thin films from binary and ternary cathodes — Comparing sources of C
- 2012
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In: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 213, s. 145-154
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Journal article (peer-reviewed)abstract
- Ti–Si–C–N thin films with composition of 1–11 at.% Si and 1–20 at.% C have been deposited onto cemented carbide substrates by arcing Ti–Si cathodes in a CH4 + N2 gas mixture and, alternatively, through arcing Ti–Si–C cathodes in N2. Films of comparable compositions from the two types of cathodes have similar structure and properties. Hence, C can be supplied as either plasma ions generated from the cathode or atoms from the gas phase with small influence on the structural evolution. Over the compositional range obtained, the films were dense and cubic-phase nanocrystalline, as characterized by X-ray diffraction, ion beam analysis, and scanning and transmission electron microscopy. The films have high hardness (30–40 GPa by nanoindentation) due to hardening from low-angle grain boundaries on the nanometer scale and lattice defects such as growth-induced vacancies and alloying element interstitials.
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| 15. |
- Eriksson, Anders, et al.
(author)
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Layer Formation by Resputtering in Ti-Si-C Hard Coatings during Large Scale Cathodic Arc Deposition
- 2011
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In: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 205:15, s. 3923-3930
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Journal article (peer-reviewed)abstract
- This paper presents the physical mechanism behind the phenomenon of self-layering in thin films made by industrial scale cathodic arc deposition systems using compound cathodes and rotating substrate fixture. For Ti-Si-C films, electron microscopy and energy dispersive x-ray spectrometry reveals a trapezoid modulation in Si content in the substrate normal direction, with a period of 4 to 23 nm dependent on cathode configuration. This is caused by preferential resputtering of Si by the energetic deposition flux incident at high incidence angles when the substrates are facing away from the cathodes. The Ti-rich sub-layers exhibit TiC grains with size up to 5 nm, while layers with high Si-content are less crystalline. The nanoindentation hardness of the films increases with decreasing layer thickness.
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| 16. |
- Eriksson, Anders, et al.
(author)
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Ti-Si-C-N Thin Films Grown by Reactive Arc Evaporation from Ti3SiC2 Cathodes
- 2011
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In: Journal of Materials Research. - : Cambrdige University Press. - 0884-2914 .- 2044-5326. ; 26, s. 874-881
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Journal article (peer-reviewed)abstract
- Ti-Si-C-N thin films were deposited onto WC-Co substrates by industrial scale arc evaporation from Ti3SiC2 compound cathodes in N2 gas. Microstructure and hardness were found to be highly dependent on the wide range of film compositions attained, comprising up to 12 at.% Si and 16 at.% C. Nonreactive deposition yielded films consisting of understoichiometric TiCx, Ti and silicide phases with high (27 GPa) hardness. At a nitrogen pressure of 0.25-0.5 Pa, below that required for N saturation, superhard, 45-50 GPa, (Ti,Si)(C,N) films with a nanocrystalline feathered structure were formed. Films grown above 2 Pa displayed crystalline phases of more pronounced nitride character, but with C and Si segregated to grain boundaries to form weak grain boundary phases. In abundance of N, the combined presence of Si and C disturb cubic phase growth severely and compromises the mechanical strength of the films.
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| 17. |
- Escalera, Edwin, et al.
(author)
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High temperature phase evolution of Bolivian kaolinitic-illitic clays heated to 1250 degrees C
- 2014
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In: Applied Clay Science. - : Elsevier. - 0169-1317 .- 1872-9053. ; 101, s. 100-105
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Journal article (peer-reviewed)abstract
- The thermal behaviour of two types of clays collected from different locations in Bolivia has been studied. The clays contain kaolinite, illite, quartz and small amounts of microcline. The phase evolutions have been characterized from room temperature to 1250 degrees C. For both clays, kaolinite is completely transformed into metakaolinite when heated up to 650 degrees C. During further heating to 1050 degrees C, illite undergoes total dehydroxylation. Mullite is formed in the temperature interval of 1050-1150 degrees C and its formation rate is dependent on the amount of K and Fe present in the clays. The clay with higher amounts of K (3.2 mass %) and Fe (5.6 mass%) has an onset temperature for sintering at about 900 degrees C and an onset temperature for liquid formation at 1080 degrees C. This is about 50 degrees C lower onset temperature for sintering and 94 degrees C lower onset temperature for liquid formation when compared with the clay with lower amounts of K (2.3 mass %) and Fe (1.6 mass %).
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| 18. |
- Escalera, Edwin, et al.
(author)
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High temperature phase evolution of Bolivian kaolinitic–illitic clays heated to 1250 °C
- 2014
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In: Applied Clay Science. - : Elsevier BV. - 0169-1317 .- 1872-9053. ; 101, s. 100-105
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Journal article (peer-reviewed)abstract
- The thermal behaviour of two types of clays collected from different locations in Bolivia has been studied. The clays contain kaolinite, illite, quartz and small amounts of microcline. The phase evolutions have been characterized from room temperature to 1250 °C. For both clays, kaolinite is completely transformed into metakaolinite when heated up to 650 °C. During further heating to 1050 °C, illite undergoes total dehydroxylation. Mullite is formed in the temperature interval of 1050–1150 °C and its formation rate is dependent on the amount of K and Fe present in the clays. The clay with higher amounts of K (3.2 mass %) and Fe (5.6 mass%) has an onset temperature for sintering at about 900 °C and an onset temperature for liquid formation at 1080 °C. This is about 50 °C lower onset temperature for sintering and 94 °C lower onset temperature for liquid formation when compared with the clay with lower amounts of K (2.3 mass %) and Fe (1.6 mass %).
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| 19. |
- Escalera, Edwin, et al.
(author)
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Synthesis of homogeneously dispersed cobalt nanoparticles in the pores of functionalized SBA-15 silica
- 2012
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In: Powder Technology. - : Elsevier. - 0032-5910 .- 1873-328X. ; 221:S1, s. 359-364
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Journal article (peer-reviewed)abstract
- Cobalt nanoparticles were prepared at room temperature by reducing cobalt sulfate heptahydrate with sodium borohydride and using functionalized SBA-15 mesoporous silica as a hard template. It was found that both external and internal fuctionalization of silica walls play a crucial role on the infiltration and reaction of the reagents in the silica framework. Subsequent heat treatment of the impregnated silica at 500 °C in air or nitrogen atmospheres leads to growth of crystals of the deposited cobalt and formation of cobalt and cobalt oxide nanoparticles, respectively. Dissolution of the silica template by NaOH resulted in well dispersed Co and Co3O4 nanoparticles ranging in size from 2 to 4 nm. The functionalization of the silica was studied by FTIR, N2-physisorption, and thermogravimetric techniques and the obtained nanoparticles were characterized by XRD, TEM and EDX analysis.
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| 20. |
- Escalera, Edwin, et al.
(author)
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Thermal treatment and phase formation in kaolinite and illite based clays from tropical regions of Bolivia
- 2012
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In: 6th EEIGM International Conference Advanced Materials Research. - Bristol : IOP Publishing Ltd.
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Conference paper (peer-reviewed)abstract
- The aim of this study was to compare the thermal behaviour of clays containing illite and kaolinite in various proportions. The clays contained small amounts of K and Fe, which act as fluxing agents. In order to investigate the phase formations during heating, the samples were examined in a differential scanning calorimeter at temperatures up to 1300°C. The thermal expansion of the samples was determined by dilatometer measurements from room temperature up to 1150°C. Phases were identified using x-ray diffraction and scanning electron microscopy. In all samples, most of the kaolinite was transformed into metakaolinite during heating up to 650°C, while illite remained unchanged up to 950°C. There was no influence of K and Fe on dehydroxylation. Metakaolinite formed at temperatures above 950°C leading to a Si-Al spinel. Furthermore, mullite was formed in the temperature interval 1050-1150°C. In this temperature range, the mechanism of mullite formation depended on the amount of K and Fe in the samples, changing the temperature of formation of mullite. It was observed by x-ray diffraction that most of the illite was transformed into a Si-Al spinel phase at 1050°C, and during further heating transformed into mullite. An increased amount of illite in the clays slightly decreased the melting temperature. The dilatometer measurements showed expansion and shrinkage for the dehydroxylation and spinel-phase formation, respectively.
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| 21. |
- Fager, Hanna
(author)
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Growth and Characterization of Amorphous TiAlSiN and HfAlSiN Thin Films
- 2012
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Licentiate thesis (other academic/artistic)abstract
- This Thesis explores amorphous transition metal nitrides for cutting tool applications. The aim is to extend the knowledge on amorphous nitride thin lms, to describe the growth process, and to explore ways of characterizing these novel complex materials.Thin lms of Ti-Al-Si-N and Hf-Al-Si-N were fabricated using industrial cathodic arc evaporation and magnetically-unbalanced reactive magnetron sputtering, respectively. The microstructure of the lms was studied using x-ray diraction (XRD) and transmission electron microscopy (TEM), while compositional analysis of the lms was performed by spectroscopic techniques (EDS, SIMS, and RBS). The mechanical properties were investigated by nanoindentation.The Ti-Al-Si-N lms were grown on cemented carbide substrates using Ti-Al-Si compound cathodes in an N2 atmosphere. High Al and Si concentrations in the lms (i.e., 12 at% Si and 18 at% Al) promote renucleation and result in x-ray amorphous lms. High resolution TEM (HRTEM) reveals isolated grains, ~2 nm in size, embedded in an amorphous matrix. Annealing experiments show that the lms are thermally stable up to 900 oC. They exhibit age hardening, with an increase in hardness from 21.9 GPa for as-deposited lms to 31.6 GPa at 1000 oC. At 1100 oC severe out-diusion of Co and W from the substrate occurs, and the lms recrystallize into c-TiN and w-AlN.The single layer Hf-Al-Si-N and multilayer Hf-Al-Si-N/HfN lms were grown on Si(001) substrates from a single Hf0:60Al0:20Si0:20 alloy target in an N2/Ar atmosphere. The composition and nanostructure of the lms was controlled during growth by independently varying the ion energy (Ei) and the ion-to-metal flux ratio (Ji=JMe). With Ji/JMe=8, the nanostructure and composition of the lms changes from x-ray amorphous with a Hf content of 0.6, to an amorphous matrix with encapsulated nanocrystals with 0.66≤Hf≤0.84, to nanocrystalline with 0.96≤Hf≤1.00, when increasing Ei from 15 to 65 eV. Varying Ji=JMe with Ei=13 eV yields electron-diraction amorphous lms at substrate temperatures of 100 oC. Hf-Al-Si-N/HfN multilayers with periods Λ=2-20 nm exhibit enhanced fracture toughness compared to polycrystalline VN, TiN, and Ti0:5Al0:5N reference samples; multilayer hardness values increase from 20 GPa with Λ=20 nm to 27 GPa with Λ=2 nm.̴
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| 22. |
- Fager, Hanna, et al.
(author)
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Growth of Hard Amorphous Ti-Al-Si-N Thin Films by Cathodic Arc Evaporation
- 2013
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In: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 235:25, s. 376-385
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Journal article (peer-reviewed)abstract
- Ti(1−x−y)AlxSiyNz (0.02≤x≤0.46, 0.02≤y≤0.28, and 1.08≤z≤1.29) thin films were grown on cemented carbide substrates in an industrial scale cathodic arc evaporation system using Ti-Al-Si compound cathodes in a N2 atmosphere. The microstructure of the as-deposited films changes from nanocrystalline to amorphous by addition of Al and Si to TiN. Upon incorporation of 12 at% Si and 18 at% Al, the films assume an x-ray amorphous state. Post-deposition anneals show that the films are thermally stable up to 900 ◦C. The films exhibit age hardening up to 1000 ◦C with an increase in hardness from 21.9 GPa for as-deposited films to 31.6 GPa at 1000 ◦C. At 1100 ◦C severe out-diffusion of Co and W from the substrate occur, and the films recrystallize into c-TiN and w-AlN.
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| 23. |
- Fehrman-Ekholm, Ingela, 1947, et al.
(author)
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Post-nephrectomy development of renal function in living kidney donors: a cross-sectional retrospective study
- 2011
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In: Nephrology, dialysis, transplantation : official publication of the European Dialysis and Transplant Association - European Renal Association. - : Oxford University Press (OUP). - 1460-2385 .- 0931-0509. ; 26:7, s. 2377-2381
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Journal article (peer-reviewed)abstract
- BACKGROUND: Increasing numbers of living donor kidney transplantations calls for better knowledge about long-term donor outcomes and risks. METHODS: To explore long-term kidney donor outcomes and risks, we conducted a cross sectional retrospective study. To this end, we analysed renal function using measured glomerular filtration rate (mGFR) and estimated glomerular filtration rate (eGFR) as well as microalbuminuria, blood pressure (BP), body mass index, haemoglobin, albumin and parathyroid hormone in kidney donors nephrectomized between 1965 and 2005. RESULTS: A total number of 573 kidney donors agreed to undergo medical follow-up examinations. The mean age (standard deviation) at donation was 47 (11) years and the mean time since donation was 14 (9) years. Both mean mGFR [68 (15) mL/min/1.73m(2) body surface; P = 0.028] and mean eGFR [71 (16) mL/min/1.73m(2) body surface; P < 0.001], based on modified diet renal dysfunction and iohexol or Cr-EDTA clearance, respectively, were found to decrease with age and to increase with time since donation. Special multivariable regression analyses reveal that for 30-year old donors, the median eGFR typically increases during the first 17 years, then remains constant for ∼8 years and slowly declines thereafter. For 50-year-old donors, the median eGFR is expected to increase during the first 15 years or so and then to enter a phase of slight progressive decline. In total, 23% (126/546) of the donors were on antihypertensive medication. An additional 22% (117/543) of the donors were found to suffer from hitherto undiagnosed hypertension (BP >140/90 mm Hg). CONCLUSION: Renal function of the remaining kidney in living donors is expected to improve for many years but will show signs of slight deterioration in the longer run.
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| 24. |
- Forsén, Rikard, et al.
(author)
-
Alloying as a tool for structure and thermal stability engineering of hard coatings
- 2014
-
Other publication (other academic/artistic)abstract
- A large range of (ZrxAly Cr(100-x-y))1N1 coatings have been deposited using cathodic arc evaporation and annealed at temperatures up to 1100 ºC. The coatings can be divided into three different characteristic categories based on their structure, thermal stability and hardness.The first category of coatings, (Al < ~30 % and ~40 % < Zr), are stable cubic solid solutions up to 1100 ºC. The hardness decreases upon annealing because of defect annihilation.In the second category, (40 % < Al < 60 % and Zr < 15 %), the coatings decompose into ZrCr- and Al-rich nanometer-sized domains when annealed, which results in a hardness increase.In the third category (~67 % < Al), the microstructure contain a mixture of 1-2 nanometer-sized nano-crystalline hexagonal (AlN) and cubic (ZrCrN) phases. These coatings have a significantly lower hardness in the as deposited state but upon annealing the hardness increases significantly.
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| 25. |
- Forsén, Rikard, et al.
(author)
-
Coherency strain engineered decomposition of unstable multilayer alloys for improved thermal stability
- 2013
-
In: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 114:24, s. 244303-
-
Journal article (peer-reviewed)abstract
- A concept to improve hardness and thermal stability of unstable multilayer alloys is presented based on control of the coherency strain such that the driving force for decomposition is favorably altered. Cathodic arc evaporated cubic TiCrAlN/Ti 1−x Cr x N multilayer coatings are used as demonstrators. Upon annealing, the coatings undergo spinodal decomposition into nanometer-sized coherent Ti- and Al-rich cubic domains which is affected by the coherency strain. In addition, the growth of the domains is restricted by the surrounding TiCrN layer compared to a non-layered TiCrAlN coating which together results in an improved thermal stability of the cubic structure. A significant hardness increase is seen during decomposition for the case with high coherency strain while a low coherency strain results in a hardness decrease for high annealing temperatures. The metal diffusion paths during the domain coarsening are affected by strain which in turn is controlled by the Cr-content (x) in the Ti 1−x Cr x N layers. For x = 0 the diffusion occurs both parallel and perpendicular to the growth direction but for x > =0.9 the diffusion occurs predominantly parallel to the growth direction. Altogether this study shows a structural tool to alter and fine-tune high temperature properties of multicomponent materials.
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| 26. |
- Forsén, Rikard, et al.
(author)
-
Decomposition and phase transformation in TiCrAlN thin coatings
- 2012
-
In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 30:6
-
Journal article (peer-reviewed)abstract
- Phase transformations and mechanisms that yield enhanced high temperature mechanical properties of metastable solid solutions of cubic (c)-(TixCryAlz)N coatings are discussed in this paper. Coatings grown by reactive arc evaporation technique with metal composition range y<17 at. % and 45h)-AlN is formed compared to TiAlN. The improved thermal stability is discussed in terms of a lowered coherency stress and a lowered enthalpy of mixing due to the addition of Cr, which results in improved functionality in the working temperature range of 850-1000 ºC of for example cutting tools. Upon annealing up to 1400 ºC the coatings decompose into c-TiN, bcc-Cr and h-AlN. The decomposition takes place via several intermediate phases, c-CrAlN, c-TiCrN and hexagonal (β)-Cr2N. The microstructure evolution investigated at different stages of spinodal decomposition and phase transformation is correlated to the thermal response and mechanical hardness of the coatings.
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| 27. |
- Forsén, Rikard, et al.
(author)
-
Effects of Ti alloying of AlCrN coatings on thermal stability and oxidation resistance
- 2013
-
In: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 534, s. 394-402
-
Journal article (peer-reviewed)abstract
- Quaternary cubic (TixCr1 − xAl~ 0.60)1 N1 coatings with 0 < x < 0.33 have been grown using reactive cathodic arc evaporation. When adding Ti the hardness was retained after annealing up to 1100 °C which is a dramatic improvement compared to CrAlN coatings. The coatings showed an age hardening process caused by spinodal decomposition into coherent TiCr- and Al-rich cubic TiCrAlN domains and the formation of hexagonal AlN precipitates and cubic TiCrN domains in the vicinity of the grain boundaries. The improved hardness was attributed to the stabilization of the cubic structure suppressing the formation and growth of hexagonal AlN. Furthermore, the presence of Ti atoms generated incoherent nanometer-sized crystallites within the hexagonal AlN precipitates disrupting the hexagonal lattice during the coarsening process.The addition of Ti promoted the formation of a TiO2 layer over Al2O3 resulting in a lower oxidation resistance. However, by tuning the composition it is possible to design coatings to have both good oxidation resistance and good high temperature mechanical stability.
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| 28. |
- Forsén, Rikard, 1985-
(author)
-
Mechanical properties and thermal stability of reactive arc evaporated Ti-Cr-Al-N coatings
- 2012
-
Licentiate thesis (other academic/artistic)abstract
- This licentiate thesis reports experimental and theoretical work on the high temperature mechanical properties and the thermal stability of cubic (c)-(Ti-Cr-Al)1-N1 coatings. It is demonstrated that it is possible to tailor and improve the properties of hard nitride coatings by different degrees of multicomponent alloying. When Cr is added to Ti-Al-N the coatings exhibit age hardening up to 1000 ºC which is higher compared to what is observed for Ti-Al-N. In addition, the coatings show a less pronounced hardness decrease when hexagonal (h)-Al-N is formed compared to Ti-Al-N. The improved thermal stability is discussed in terms of a lowered coherency stress and a lowered enthalpy of mixing due to the addition of Cr. When Ti is added to Cr-Al-N the formation and growth of the detrimental h-Al-N phase is suppressed and delayed improving the mechanical properties. This is discussed in terms of kinetic effects where the Ti atoms obstruct the Al diffusion and consequently the growth of h-Al-N precipitates. The microstructure evolution investigated at different stages of spinodal decomposition, coarsening and phase transformations are correlated to the thermal responses and the mechanical hardness of the coatings. Upon annealing up to 1400 ºC the coatings decompose into c-TiN, bcc-Cr and h-AlN. The decomposition takes place via several intermediate phases, c-CrAlN, c-TiCrN and hexagonal (β)-Cr2N. The oxidation resistance of (Tix-Cry-Al60)1-N1 is also investigated and presented for different x/y ratios. The results show that it is possible to generate coatings with both excellent mechanical properties and oxidation resistance improving the functionality in the working temperature range of 850-1100 ºC of for example cutting tools.
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| 29. |
- Forsén, Rikard
(author)
-
Multicomponent Alloying for Improved Hard Coatings
- 2014
-
Doctoral thesis (other academic/artistic)abstract
- Coatings are vital to protect and to increase the productivity of cutting tools in high speed and dry cutting applications. During the cutting operation the temperature may exceed 1000 ºC it is therefore necessary that the coatings withstand high temperatures. A lot of development and research has been carried out during the last 30 years on finding new coating material systems providing enhanced properties such as adhesion, hardness and oxidation resistance at elevated temperatures. This thesis is based on multicomponent alloying of quaternary transition metal nitride hard coatings with a main focus on Ti-Cr-Al-N coatings. Many different coatings and compositions have been deposited using an industrial scale cathodic arc evaporation deposition system. All deposited coatings contain Al as this element is known to increase the hardness and the oxidation resistance of nitride coatings. The deterioration of the hardness in Al-containing nitride coatings is generally attributed to the transformation of cubic Al-N into hexagonal Al-N and the consequent domain coherency relaxation. This thesis investigates these phenomena on an atomic level providing a deeper understanding of and a way to engineer improved hard nitride coatings. The essence of this thesis is that by adding a third metal to a ternary nitride material system, for example one of the most frequently used Ti-Al-N, it is possible to tune and engineer the thermal stability of the cubic structure and the coherency strain which in turn affects the hardness and the oxidation resistance. The key point is that new intermediate phases in the decomposition process are generated so that the eventual detrimental phases are suppressed and delayed. More specifically, when Cr is added to the Ti-Al-N material system the coatings exhibit an age hardening process up to 1000 ºC caused by spinodal decomposition into coherent TiCr- and AlCr-rich cubic Ti-Cr-Al-N domains. This means that the unstable cubic Ti-Cr-Al-N phase decomposes via yet another unstable cubic Cr-Al-N phase before the detrimental hexagonal transformation of AlN takes place. The hardness is therefore retained up to a higher temperature compared to Ti-Al-N coatings.By utilizing multicomponent alloying through addition of Ti to Cr-Al-N coatings the hardness is retained after annealing up to 1100 ºC. This is a dramatic improvement compared to Cr-Al-N coatings. Here the Ti addition promotes the competitive spinodal decomposition into TiCr- and Al-enriched domains suppressing the detrimental hexagonal AlN formation.To investigate the effect of multicomponent alloying for other material systems with different mixing free energies and atomic sizes, Zr-containing, Zr-Cr-Al-N and Zr-Ti-Al-N, quaternary nitride coatings have also been deposited. For high Al- and high Zr-containing coatings the cubic solid solution structure is disrupted into a mix of nano-crystalline hexagonal and cubic phases with significantly lower hardness. The results show that the structure and hardness of these coatings are sensitive to the composition and in order to optimize the hardness and thermal stability the composition has to be fine-tuned. Altogether it is shown that through multicomponent alloying and through the control of the coherency strain it is possible to enhance the hardness and the oxidation resistance compared to the ternary system which may lead to new improved functional hard coatings.
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| 30. |
- Forsén, Rikard, et al.
(author)
-
Nanostructuring and coherency strain in multicomponent hard coatings
- 2014
-
In: APL Materials. - : American Institute of Physics (AIP). - 2166-532X. ; 2:11, s. 116104-
-
Journal article (peer-reviewed)abstract
- Lattice resolved and quantitative compositional characterizations of the microstructure in TiCrAlN wear resistant coatings emerging at elevated temperatures are performed to address the spinodal decomposition into nanometer-sized coherent cubic TiCr- and Al-rich domains. The domains coarsen during annealing and at 1100 ºC, the Al-rich domains include a metastable cubic Al(Cr)N phase containing 9 at.% Cr and a stable hexagonal AlN phase containing less than 1 at.% Cr. The cubic and the hexagonal phases form strained semi-coherent interfaces with each other.
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| 31. |
- Frodelius, Jenny, 1978-, et al.
(author)
-
Annealing of thermally sprayed Ti2AlC coatings
- 2011
-
In: INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY. - : Blackwell. - 1546-542X. ; 8:1, s. 74-84
-
Journal article (peer-reviewed)abstract
- Phase transformations during annealing of coatings sprayed with the High Velocity Oxy-Fuel technique using Ti2AlC powder have been investigated by in-situ x-ray diffraction. The asdeposited coatings, consisting of Ti2AlC, Ti3AlC2, TiC, Ti-Al, and oxides, are stable up to 500 °C. Ti3AlC2 forms above 550 °C and Ti2AlC forms above 700 °C by intercalation of Al into TiCx. For temperatures between 900 and 1100 °C, Ti3AlC2 and Ti2AlC decompose by losing Al to the surrounding matrix resulting in TiCx, and Al2O3. The thermal expansion coefficient between ambient and 700°C is 11.9·10-6 K-1. The thermal diffusivity at room temperature is 1.9·10-6 m2/s.
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| 32. |
- Ghafoor, Naureen, et al.
(author)
-
Anomalous epitaxial stability of (001) interfaces in ZrN/SiNx multilayers
- 2014
-
In: APL Materials. - : American Institute of Physics. - 2166-532X. ; 2:4, s. 046106-
-
Journal article (peer-reviewed)abstract
- Isostructural stability of B1-NaCl type SiN on (001) and (111) oriented ZrN surfaces is studied theoretically and experimentally. The ZrN/SiNx/ZrN superlattices with modulation wavelength of 3.76 nm (dSiNx similar to 0.4 nm) were grown by dc-magnetron sputtering on MgO(001) and MgO(111). The results indicate that 0.4 nm thin SiNx layers utterly influence the preferred orientation of epitaxial growth: on MgO(001) cube-on-cube epitaxy of ZrN/SiNx superlattices were realized whereas multilayers on MgO(111) surface exhibited an unexpected 002 texture with a complex fourfold 90 degrees-rotated in-plane preferred orientation. Density functional theory calculations confirm stability of a (001) interface with respect to a (111) which explains the anomaly.
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| 33. |
- Ghafoor, Naureen, et al.
(author)
-
Nanolabyrinthine ZrAlN thin films by self-organization of interwoven single-crystal cubic and hexagonal phases
- 2013
-
In: APL Materials. - New York, USA : American Institute of Physics (AIP). - 2166-532X. ; 1:2, s. 022105-1-022105-6
-
Journal article (peer-reviewed)abstract
- Self-organization on the nanometer scale is a trend in materials research. Thermodynamic driving forces may, for example, yield chessboard patterns in metal alloys[Y. Ni and A. G. Khachaturyan, Nature Mater. 8, 410–414 (2009)] or nitrides [P. H.Mayrhofer, A. Horling, L. Karlsson, J. Sj ¨ ol¨ en, T. Larsson, and C. Mitterer, Appl. ´Phys. Lett. 83, 2049 (2003)] during spinodal decomposition. Here, we explore theZrN-AlN system, which has one of the largest positive enthalpies of mixing amongthe transition metal aluminum nitrides [D. Holec, R. Rachbauer, L. Chen, L. Wang,D. Luefa, and P. H. Mayrhofer, Surf. Coat. Technol. 206, 1698–1704 (2011); B.Alling, A. Karimi, and I. Abrikosov, Surf. Coat. Technol. 203, 883–886 (2008)].Surprisingly, a highly regular superhard (36 GPa) two-dimensional nanolabyrinthinestructure of two intergrown single crystal phases evolves during magnetron sputter thin film synthesis of Zr0.64Al0.36N/MgO(001). The self-organization is surfacedriven and the synergistic result of kinetic limitations, where the enthalpy reductionbalances both investments in interfacial and elastic energies.
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| 34. |
- Gustafsson, Hanna, 1982, et al.
(author)
-
Immobilization of lipase from Mucor miehei and Rhizopus oryzae into mesoporous silica - The effect of varied particle size and morphology
- 2012
-
In: Colloids and Surfaces B: Biointerfaces. - : Elsevier BV. - 0927-7765 .- 1873-4367. ; 100, s. 22-30
-
Journal article (peer-reviewed)abstract
- Immobilization of enzymes usually improves the recyclability and stability and can sometimes also improve the activity compared to enzymes free in solution. Mesoporous silica is a widely studied material as host for immobilized enzymes because of its large internal surface area and tunable pores. It has previously been shown that the pore size is critical both for the loading capacity and for the enzymatic activity; however, less focus has been given to the influence of the particle size. In this work the effect of particle size and particle morphology on the immobilization of lipase from Mucor miehei and Rhizopus oryzae have been investigated. Three kinds of mesoporous silica, all with 9 nm pores but with varying particle size (1000 nm, 300 nm and 40 nm) have been synthesized and were used as host for the lipases. The two lipases, which have the same molecular size but widely different isoelectric points, were immobilized into the silica particles at varied pH values within the interval 5 to 8. The 300 nm particles were proven to be the most suitable carrier with respect to specific activity for both enzymes. The lipase from Mucor miehei was more than four times as active when immobilized at pH 8 compared to free in solution whereas the difference was less pronounced for the Rhizopus oryzae lipase.
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| 35. |
- Hedström, Peter, et al.
(author)
-
Load partitioning between single bulk grains in a two-phase duplex stainless steel during tensile loading
- 2010
-
In: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 58:2, s. 734-744
-
Journal article (peer-reviewed)abstract
- The lattice strain tensor evolution for single bulk grains of austenite and ferrite in a duplex stainless steel during tensile loading to 0.02 applied strain has been investigated using in situ high-energy X-ray measurements and finite-element modeling. Single-grain X-ray diffraction lattice strain data for the eight austenite and seven ferrite grains measured show a large variation of residual lattice strains, which evolves upon deformation to the point where some grains with comparable crystallographic orientations have lattice strains different by 1.5 x 10(-3), corresponding to a stress of similar to 300 MPa. The finite-element simulations of the 15 measured grains in three different spatial arrangements confirmed the complex deformation constraint and importance of local grain environment.
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| 36. |
- Johansson, Emma M.
(author)
-
Controlling the Pore Size and Morphology of Mesoporous Silica
- 2010
-
Licentiate thesis (other academic/artistic)abstract
- Mesoporous silica with a hexagonally ordered pore structure (SBA-15) has been synthesized. Through variations in the synthesis conditions several morphologies, such as fibers, sheets and separate rods, have been realized. Furthermore, additions of heptane and NH4F make it possible to synthesize SBA-15 with pores as large as 18 nm in the sheet morphology. Mechanisms for the formation of different morphologies have been suggested. In the case of fibers and sheets, the amount of heptane present during the synthesis determines the final morphology. For low concentrations, the heptane enters the micelles and increases the pore size while the particles (crystallites) attaches to each other end to end. When the heptane concentration increases, the heptane droplets increase in size, and above a critical droplet size the crystallites attach with one short end towards the droplet, forming the sheet morphology. The crystallites can also be separated. This is the case of the rod morphology. The separation is performed by shortening the stirring time and increasing the HCl concentration. The increased amount of HCl increases the hydration rate of the silica precursor, which can be used to control the thickness and length of the rods. Furthermore, the reaction time has been decreased from 20 h for all morphologies to less than 4 hours. The materials have been characterized with nitrogen sorption, electron microscopy and x-ray diffraction. Also, thermogravimetric analysis and fourier transformed infrared spectroscopy have been used for studying the removal of surfactants.
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| 37. |
- Johansson, Emma, et al.
(author)
-
Rapid Synthesis of SBA-15 Rods with Variable Lengths, Widths, and Tunable Large Pores
- 2011
-
In: Langmuir. - : ACS American Chemical Society. - 0743-7463 .- 1520-5827. ; 27:8, s. 4994-4999
-
Journal article (peer-reviewed)abstract
- Dispersed SBA-15 rods have been synthesized with varying lengths, widths, and pore sizes in a low-temperature synthesis in the presence of heptane and NH4F. The pore size of the material can systematically be varied between 11 and 17 nm using different hydrothermal treatment times And/or temperatures. The particle length (400-600 nm) and width (100-400 nm) were tuned by varying the HCl concentration. All the synthesized materials possess a large surface area of 400-600 m(2)/g And a pore volume of 1.05-1.30 cm(3). A, mechanism for the effect of the HCl concentration on the particle morphology is suggested. Furthermore, it is shown that the reaction time an be decreased to 1 h, with well-retained pore size and morphology. This work has resulted in SBA-15 rods with the largest pore size reported for this morphology.
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| 38. |
- Johansson, Emma, et al.
(author)
-
The effects on pore size and particle morphology of heptane additions to the synthesis of mesoporous silica SBA-15
- 2010
-
In: Microporous and Mesoporous Materials. - : Elsevier Science B.V., Amsterdam.. - 1387-1811 .- 1873-3093. ; 133:01-Mar, s. 66-74
-
Journal article (peer-reviewed)abstract
- The effect of heptane on the particle morphology and pore size in the synthesis of SBA-15 is presented. Heptane in the presence of NH4F works as a pore swelling agent, resulting in 13-18 nm sized pores in 400 nm long and 200-1000 nm wide crystallites. The pores are hexagonally arranged and run through the crystallites. Increasing the heptane to P123 molar ratio changes the morphology of SBA-15 from fibers to sheets when the crystallites rearrange during the synthesis. The pore order in the sheets is controlled by changing the molar ratio of water to P123. The surface areas of these materials are 500-800 m(2)/g with pore volumes of 1.2-1.7 cm(3)/g. The sheets have accessible pores with a size of 18 nm running parallel to the sheet normal, which makes them suitable for membranes.
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| 39. |
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| 40. |
- Johansson, Helena, 1981, et al.
(author)
-
High serum adiponectin predicts incident fractures in elderly men: Osteoporotic fractures in men (MrOS) Sweden
- 2012
-
In: Journal of Bone and Mineral Research. - : Wiley. - 1523-4681 .- 0884-0431. ; 27:6, s. 1390-1396
-
Journal article (peer-reviewed)abstract
- Adipocytes and osteoblasts share a common progenitor, and there is, therefore, potential for both autocrine and endocrine effects of adiponectin on skeletal metabolism. The aim of the present study was to determine whether high serum adiponectin was associated with an increased risk of fracture in elderly men. We studied the relationship between serum adiponectin and the risk of fracture in 999 elderly men drawn from the general population and recruited to the Osteoporotic Fractures in Men (MrOS) study in Gothenburg, Sweden. Baseline data included general health questionnaires, lifestyle questionnaires, body mass index (BMI), bone mineral density (BMD), serum adiponectin, osteocalcin, and leptin. Men were followed for up to 7.4 years (average, 5.2 years). Poisson regression was used to investigate the relationship between serum adiponectin, other risk variables and the time-to-event hazard function of fracture. Median levels of serum adiponectin at baseline were 10.4 mu g/mL (interquartile range, 7.714.3). During follow-up, 150 men sustained one or more fractures. The risk of fracture increased in parallel with increasing serum adiponectin (hazard ratio [HR]/SD, 1.46; 95% confidence interval [CI], 1.231.72) and persisted after multivariate-adjusted analysis (HR/SD, 1.30; 95% CI, 1.091.55). Serum adiponectin shows graded stepwise association with a significant excess risk of fracture in elderly men that was independent of several other risk factors for fracture. Its measurement holds promise as a risk factor for fracture in men. (C) 2012 American Society for Bone and Mineral Research.
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| 41. |
- Johansson, Helena, 1981, et al.
(author)
-
Low bone mineral density is associated with increased mortality in elderly men : MrOS Sweden
- 2011
-
In: Osteoporosis International. - : Springer Science and Business Media LLC. - 0937-941X .- 1433-2965. ; 22:5, s. 1411-1418
-
Journal article (peer-reviewed)abstract
- We studied the nature of the relationship between bone mineral density (BMD) and the risk of death among elderly men. BMD was associated with mortality risk and was independent of adjustments for other co-morbidities. A piecewise linear function described the relationship more accurately than assuming the same gradient of risk over the whole range of BMD (p = 0.020). Low BMD was associated with a substantial excess risk of death, whilst a higher than average BMD had little impact on mortality. Previous studies have demonstrated an association between low BMD and an increased risk of death among men and women. The aim of the present study was to examine the pattern of the risk in men and its relation to co-morbidities. We studied the nature of the relationship between BMD and death among 3,014 elderly men drawn from the population and recruited to the MrOS study in Sweden. Baseline data included general health questionnaires, life style questionnaires and BMD measured using DXA. Men were followed for up to 6.5 years (average 4.5 years). Poisson regression was used to investigate the relationship between BMD, co-morbidities and the hazard function of death. During follow-up, 382 men died (all-cause mortality). Low BMD at all measured skeletal sites was associated with increased mortality. In multivariate analyses, the relationship between BMD and mortality was non-linear, and a piecewise linear function described the relationship more accurately than assuming the same gradient of risk over the whole range of BMD (p = 0.020). Low BMD is associated with a substantial excess risk of death compared to an average BMD, whereas a higher than average BMD has a more modest effect on mortality. These findings, if confirmed elsewhere, have implications for the constructing of probability-based fracture risk assessment tools.
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| 42. |
- Johansson, Helena, 1981, et al.
(author)
-
Low serum vitamin D is associated with increased mortality in elderly men: MrOS Sweden
- 2012
-
In: Osteoporosis International. - : Springer Science and Business Media LLC. - 1433-2965 .- 0937-941X. ; 23:3, s. 991-999
-
Journal article (peer-reviewed)abstract
- In elderly man, low serum 25-hydroxyvitamin D (25(OH)D) was associated with a substantial excess risk of death compared to 25(OH)D values greater than 50-70 nmol/l, but the association attenuated with time. The aim of the present study was to determine whether poor vitamin D status was associated with an increase in the risk of death in elderly men. We studied the relationship between serum 25(OH)D and the risk of death in 2,878 elderly men drawn from the population and recruited to the MrOS study in Sweden. Baseline data included general health and lifestyle measures and serum 25(OH)D measured by competitive RIA. Men were followed for up to 8.2 years (average 6.0 years). Mortality adjusted for comorbidities decreased by 5% for each SD increase in 25(OH)D overall (gradient of risk 1.05; 95% confidence interval 0.96-1.14). The predictive value of 25(OH)D for death was greatest below a threshold value of 50-70 nmol/l, was greatest at approximately 3 years after baseline and thereafter decreased with time. Low serum 25(OH)D is associated with a substantial excess risk of death compared to 25(OH)D values greater than 50-70 nmol/l, but the association attenuates with time. These findings, if causally related, have important implications for intervention in elderly men.
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| 43. |
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| 44. |
- Johansson, Helena, 1981, et al.
(author)
-
Waning predictive value of serum adiponectin for fracture risk in elderly men: MrOS Sweden
- 2014
-
In: Osteoporosis International. - : Springer Science and Business Media LLC. - 0937-941X .- 1433-2965. ; 25:7, s. 1831-1836
-
Journal article (peer-reviewed)abstract
- Serum adiponectin is a risk factor for fracture. The predictive value attenuates with time in elderly men so that its use for the risk assessment in the long term is questionable. The study underlines the importance of testing the long-term stability of potential risk factors. High serum adiponectin is associated with an increased risk of fracture in elderly men. The aim of the present study was to determine the impact of adiponectin on the probability of fracture as a function of time. The probability of osteoporotic fracture was computed in 989 elderly men from the MrOS study in Sweden. Baseline data included clinical risk factors for fracture, femoral neck BMD and serum adiponectin. Men were followed for up to 7.4 years with a mean follow up of 5.3 years (range 0.0-7.4 years). Poisson regression was used to model the hazard function for osteoporotic fracture and death to determine the 10 year probability of fracture. During follow up, 124 men sustained one or more osteoporotic fracture. There was a significant interaction between adiponectin and time since baseline (p = 0.026) such that the longer time since baseline, the lower the gradient of fracture risk. When using this interaction in the calculation of 10-year probability of fracture, the probabilities of osteoporotic fracture varied little over the range of adiponectin values. Serum adiponectin is a risk factor for fracture. Nevertheless, the predictive value attenuates with time so that its use for the risk assessment in the long term is questionable. This study underlines the importance of testing the long-term stability of potential risk factors that might be used in fracture risk assessment.
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| 45. |
- Johansson Jöesaar, Mats P., et al.
(author)
-
Anisotropy effects onmicrostructure and properties in decomposed arc evaporated Ti1-xAlxN coatings during metal cutting
- 2013
-
In: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 235:25, s. 181-185
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Journal article (peer-reviewed)abstract
- Anisotropy effects on the spinodal decomposition in cathodic arc evaporated cubic “phase c-Ti1−xAlxN coatingshave been studied with respect to composition, microstructure and hardness properties before and after a continuousturning operation. Coatings are simultaneously being exposed to both a high temperature and high pressureduring the metal cutting process. As evident from the current results, a high Al content coating, x = 0.66,when exposed to such extreme conditions decomposes into cubic c-AlN and c-TiN-rich domains. In this case,the evolving microstructure comprises interconnected spatially periodic, elongated and coherent cubic c-AlNand c-TiN-rich regions aligned along elastic compliant b100N crystal direction. A significantly different microstructurewith randomly oriented domains is observed for a coating with an elemental composition closer tothe isotropic limit, x = 0.28, exposed under the same conditions. From a coating hardness perspective, thenanoindentation results display a minor age hardening effect for the c-Ti1−xAlxN coating grown at x = 0.28while the coating grown with x = 0.66 exhibits a significant age-hardening effect of about 18%. We concludethat both microstructure and age hardening behavior during spinodal decomposition of c-Ti1−xAlxN correlateto the relative amount ofmetal Ti/Al ratio and consequently to the elastic anisotropy of the as-grown coatingmaterial.These results provide newinsights to the understanding of improvedwear resistance of c-Ti1−xAlxN withAl content during metal cutting.
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| 46. |
- Johnson, Lars, et al.
(author)
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Blind deconvolution of time-of-flight mass spectra from atom probe tomography
- 2013
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In: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 132, s. 60-64
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Journal article (peer-reviewed)abstract
- A major source of uncertainty in compositional measurements in atom probe tomography stems from the uncertainties of assigning peaks or parts of peaks in the mass spectrum to their correct identities. In particular, peak overlap is a limiting factor, whereas an ideal mass spectrum would have peaks at their correct positions with zero broadening. Here, we report a method to deconvolute the experimental mass spectrum into such an ideal spectrum and a system function describing the peak broadening introduced by the held evaporation and detection of each ion. By making the assumption of a linear and time-invariant behavior, a system of equations is derived that describes the peak shape and peak intensities. The model is fitted to the observed spectrum by minimizing the squared residuals, regularized by the maximum entropy method. For synthetic data perfectly obeying the assumptions, the method recovered peak intensities to within +/- 0.33 at%. The application of this model to experimental APT data is exemplified with Fe-Cr data. Knowledge of the peak shape opens up several new possibilities, not just for better overall compositional determination, but, e.g., for the estimation of errors of ranging due to peak overlap or peak separation constrained by isotope abundances. (C) 2013 Elsevier By. All rights reserved.
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| 47. |
- Johnson, Lars, 1983-
(author)
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Inside The Miscibility Gap : Nanostructuring and Phase Transformations in Hard Nitride Coatings
- 2012
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Doctoral thesis (other academic/artistic)abstract
- This thesis is concerned with self-organization phenomena in hard and wear resistant transition-metal nitride coatings, both during growth and during post deposition thermal annealing. The uniting physical principle in the studied systems is the immiscibility of their constituent parts, which leads, under certain conditions, to structural variations on the nanoscale. The study of such structures is challenging, and during this work atom probe tomography (apt) was developed as a viable tool for their study. Ti0.33Al0.67N was observed to undergo spinodal decomposition upon annealing to 900 °C, by the use of apt in combination with electron microscopy. The addition of C to TiSiN was found to promote and refine the feather-like microstructure common in the system, with an ensuing decrease in thermal stability. An age-hardening of 36 % was measured in arc evaporated Zr0.44Al0.56N1.20, which was a nanocomposite of cubic, hexagonal, and amorphous phases. Magnetron sputtering of Zr0.64Al0.36N at 900 °C resulted in a self-organized and highly ordered growth of a two-dimensional two-phase labyrinthine structure of cubic ZrN and wurtzite AlN.The structure was analyzed and recovered by apt, although the ZrN phase suffered from severe trajectory aberrations, rendering only the Al signal useable.The initiation of the organized growth was found to occur by local nucleation at 5-8 nm from the substrate, before which random fluctuations in Al/Zr content increased steadily from the substrate. Finally, the decomposition of solid-solution TiB0.33N0.67 was found, by apt, to progress through the nucleation of TiB0.5N0.5 and TiN, followed by the transformation of the former into hexagonal TiB2.
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| 48. |
- Johnson, Lars, 1983-, et al.
(author)
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Microstructure evolution and age hardening in (Ti,Si)(C,N) thin films deposited by cathodic arc evaporation
- 2010
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In: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 519:4, s. 1397-1403
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Journal article (peer-reviewed)abstract
- Ti1 − xSixCyN1 − y films have been deposited by reactive cathodic arc evaporation onto cemented carbide substrates. The films were characterized by X-ray diffraction, elastic recoil detection analysis, transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron-energy loss spectroscopy and nanoindentation. Reactive arc evaporation in a mixed CH4 and N2 gas gave films with 0 ≤ x ≤ 0.13 and 0≤y≤0.27. All films had the NaCl-structure with a dense columnar microstructure, containing a featherlike pattern of nanocrystalline grains for high Si and C contents. The film hardness was 32–40GPa. Films with x > 0 and y > 0 exhibited age-hardening up to 35–44 GPa when isothermally annealed up to 900 °C. The temperature threshold for over-ageing was decreased to 700 °C with increasing C and Si content, due to migration of Co, W and Cr from the substrate to the film, and loss of Si. The diffusion pathway was tied to grain boundaries provided by the featherlike substructure.
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| 49. |
- Johnson, Lars, et al.
(author)
-
Spinodal decomposition of Ti0.33Al0.67N thin films studied by atom probe tomography
- 2012
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In: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 520:13, s. 4362-4368
-
Journal article (peer-reviewed)abstract
- Details of the phase decomposition in NaCl-structure Ti0.33Al0.67N thin films deposited by cathodic arc evaporation are studied by atom probe tomography. We demonstrate that as-deposited films are in the earliest stage of decomposition for which electron microscopy and x-ray diffraction indicate a single-phase solid solution. Annealing at 900 degrees C further activates spinodal decomposition of the films, although pockets of unde-composed material remain after 2 h. N preferentially segregates to the AlN and TiN domains, causing the TiAlN matrix to be understoichiometric, by the energetics of N vacancies in TiAlN. The corresponding modulation in stoichiometry implies a Kirkendall effect, caused by different Al and Ti diffusivities.
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| 50. |
- Knutsson, Axel, et al.
(author)
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Machining performance and decomposition of TiAlN/TiN multilayer coated metal cutting inserts
- 2011
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In: SURFACE and COATINGS TECHNOLOGY. - : Elsevier Science B.V., Amsterdam.. - 0257-8972. ; 205:16, s. 4005-4010
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Journal article (peer-reviewed)abstract
- The wear resistance of metal cutting inserts coated with metastable Ti0.34Al0.66N/TiN multilayers was tested in continuous turning of an AISI 316L stainless steel. The multilayers had periods of 25 + 50, 12 + 25 and 6 + 12 nm (Ti0.34Al0.66N + TiN) with a total multilayer stack thickness of 2 mu m. Inserts coated with monolithic TiN and Ti0.34Al0.66N deposited under similar conditions were used as references. The multilayer coated inserts show a decrease of wear with decreased multilayer period, both on the rake and flank face. The wear on the rake face was lower on all the multilayer coated tools compared to the references. Scanning transmission electron imaging and energy dispersive spectroscopy elemental mapping of a worn multilayer coating show decomposition of the Ti0.34Al0.66N to domains rich of Al and Ti. High resolution transmission electron micrography shows preserved epitaxy between the TiN and Ti0.34Al0.66N layers. The improved wear resistance of the multilayer coated inserts is discussed in terms of an improved thermal stability of the multilayer stacks.
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