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Numrering	Referens	Omslagsbild	Hitta
1.	Ahlen, N., et al. (författare) On the carbothermal vapour-liquid-solid (VLS) mechanism for TaC, TiC, and TaxTi1-xC whisker growth 2000 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 20:14-15, s. 2607-2618 Tidskriftsartikel (refereegranskat)abstract The growth of TaC, TiC and TaxTi1-xC whiskers has been studied in some detail. The whiskers were synthesised via a vapour-liquid-solid (VLS) growth mechanism in the temperature range 1220-1400 degreesC. The starting materials were Ta2O5, TiO2, C, NaCl, and a catalyst metal (Ni, Co, Fe, and Cu were tested). The main reaction during synthesis was a carbothermal reduction of Ta2O5 and TiO2, and NaCl was added to form the oxochlorides and chlorides of Ta and Ti that account for the transport to the catalyst metal. The syntheses were made in a protecting Ar atmosphere. From experiments interrupted after different times at the synthesis temperature it is clear that sodium tantalates form as intermediate products, whereas sodium titanates cannot be identified. Only metals that are able to dissolve the elements building up the whiskers work as catalysts. Whisker growth starts either from a catalyst droplet in contact with carbon or from an oxide particle in contact with both catalyst metal and carbon. For TaC and TaxTi1-xC the only growth direction observed is [100], while TiC may grow either along [100] or along [111].
2.	Alkebro, J, et al. (författare) Mechanical alloying of alumina-yttria powder mixtures 2000 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 20:12, s. 2169-2174 Tidskriftsartikel (refereegranskat)abstract Mechanical alloying has been used to prepare powder mixtures of alumina and yttria as a means to create composites with a dominant matrix phase together with small particles of a dispersed second phase. The yttria-alumina system, containing five possible phases, has the potential for creating eight combinations of matrix and dispersed phases. Here compositions designed to give YAlO3(YA) dispersed in Y3Al5O12(Y3A5 i.e. YAG) or Y4Al2O9(Y2A) were studied. After milling with steel tools for times up to 8 h, the powders were subjected to thermal cycles up to 1500 °C during which the phase evolution was monitored using X-ray diffractometry (including high-temperature XRD) and differential thermal analysis. During milling the original crystal structures were quickly broken down, in some cases partially replaced by an intermediate structure after milling. Upon subsequent heating the milled mixtures crystallized to give the expected phases, YA in Y3A5 and YA in Y2A respectively, but the reaction route was seen to be different depending on the amount of amorphization of the yttria. Contamination by iron was seen to affect the phase distribution and the lattice parameters.
3.	Antti, Marta-Lena, et al. (författare) Thermal degradation of an oxide fibre (Nextel 720)/aluminosilicate composite 2004 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 24:3, s. 565-578 Tidskriftsartikel (refereegranskat)abstract The effect of thermal exposure on the microstructure and tensile stress-strain behaviour has been investigated for composites of woven continuous oxide fibres (Nextel 720) in a porous aluminosilicate matrix. The tensile tests were carried out on straight-sided, centre hole notched plates with 0/90° and ±45° orientations. The as-received material was slightly notch sensitive in that the net section fracture stress decreased somewhat with increasing hole diameter but much less than predicted for an ideally elastic, fully notch-sensitive material. After exposure at 1100°C and for long time at 1000°C in air the composite was embrittled. In the 0/90 composite this resulted in a reduced fracture strength, a reduced strain to failure as well as a reduced fracture toughness and damage zone size. After exposure for 100 h at 1100 °C (the most extreme exposure applied) the material also became significantly more notch sensitive and had failure characteristics similar to those of a monolithic ceramic. The ±45 composite was also embrittled which resulted in a reduced strain to failure but an increase in fracture strength. Density measurements and observations on the microstructure and fracture surfaces indicated that the embrittlement was due mainly to localised densification of the matrix and an increase in fibre/matrix bonding.
4.	Ashkin, A., et al. (författare) At-temperature observation of phase development in yttrium α-Sialon 1995 Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 15:11, s. 1101-1109 Tidskriftsartikel (refereegranskat)abstract A powder mixture of α-Si3N4, AlN and Y2O3 corresponding to an yttrium α-sialon composition, Y0.4Si10.2Al1.8O0.6N15.4, was sintered both in a high temperature X-ray diffraction unit and in a regular sintering furnace. X-ray analysis was performed and it was shown that high temperature X-ray diffraction can be used to monitor the kinetics of the α-sialon phase formation during sintering at temperatures between 1450 and 1580 °C as the reactions take place. A variety of yttrium-rich intermediate and secondary phases are formed during sintering; those formed in the HT-XRD unit were not the same as those formed in the regular sintering furnace, but they do not significantly influence the overall reaction sequence or the amount of α-sialon formed. Quantitative analysis of the acquired data was used to evaluate the kinetics of the α-sialon phase formation; the estimated activation energy of the initial stage α-sialon formation was 330kJ/mol. After this initial stage of relatively rapid α-sialon formation the process became inhibited
5.	Ashkin, Daniel (författare) Nitridation Behaviour of Silicon with Clay and Oxide Additions: Rate and Phase Development 1997 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 17:13, s. 1613-1624 Tidskriftsartikel (refereegranskat)abstract Samples pressed from fine powders of Si, Si + SiO2, Si + kaolinite and Si + SiO2 + Al2O3 were nitrided by both the nitrogen demand method and a constant rate of heating using a graphite resistance furnace at temperatures of 1100 to 1450 °C. The nitridation rate for different compositions and input parameters were determined by continuously monitoring the time, temperature and pressure within the furnace. By comparing the different compositions, the effect of impurities, silica and particle size on nitriding rate, phase composition and percent theoretical weight gain were determined. Compositions containing high purity additives were found to nitride at higher temperatures and to be more susceptible to weight loss during nitridation. The prime cause for low weight gains was determined to be volatilization of silicon out of the samples. Si2N2O/O′ Sialon was formed in all compositions containing the as-used additives and acted to retain the oxygen within the sample.
6.	Babushkin, O., et al. (författare) Kinetic Aspects of the Formation of Lead Zirconium Titanate 1996 Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 16:12, s. 1293-1998 Tidskriftsartikel (refereegranskat)abstract The kinetics of the second calcination step in the formation of PZT solid solution (with perovskite ABO3 lattice) has been investigated by using two different particle sizes of the B-site precursor (1·91 and 5·08 μm), the finer size being obtained by prolonged milling. In-situ analysis performed by high-temperature X-ray diffractometry in a non-isothermal mode (20-800°C) revealed a reduction of the calcination temperature by 100°C with a decrease in particle size of the precursor. In order to clarify the mechanism of the solid-state reaction to PZT, isothermal heat treatment of the mixtures was performed in the temperature range 540-700°C. The activation energies for the fine and the coarse powders were estimated as 150 and 210 kJ mol 1 respectively, and the reaction was found to follow the Jander model for diffusion-controlled solid-state reaction kinetics
7.	Babushkin, O., et al. (författare) PZT phase formation monitored by high-temperature X-ray diffractometry 1997 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 17:6, s. 813-818 Tidskriftsartikel (refereegranskat)abstract The crystallisation kinetics of amorphous sol-gel PZT thin films were investigated using high-temperature X-ray diffraction. Crystallisation for different isotherms was monitored as a function of time. Phase transformation data were obtained from integrated X-ray peak intensities which were calibrated based on image analysis of the surface microstructure of the samples at the end of the isothermal treatments. An activation energy of 310 kJ/mol was obtained without assuming a specific kinetic model. From the transformation data, a TTT diagram was constructed for the ranges studied.
8.	Babushkin, Oleg, et al. (författare) Reaction sequence in the formation of perovskite Pb(Zro0.48Ti0.52)O3-Pb(Nb2/3Ni1/3)O3 solid solution : Dynamic heat-treatment 1998 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 18:7, s. 737-744 Tidskriftsartikel (refereegranskat)abstract The sequence of the solid state reactions in the PbOZrO 2-TiO2-Nb2O5-NiO system has been investigated. The oxide mixing route utilised in sample preparation was selected in order to determine the basic reaction path in the formation of the PZTPNN perovskite phase. It has been established that the main intermediate phases formed prior to PZTPNN are PbTiO3 and pyrochlore Pb-Nb-based phases. The sequence in the pyrochlore formation was from tetragonal Pb3Nb2O8 (500 °C) to rhombohedral Pb2Nb2O7 (600-750 °C) and finally to cubic Pb3Nb4O13 (650-850 °C). The formation of the perovskite phase proceeded from mutual solubility of PbTiO3 and pyrochlore Pb3Nb4O13 phases, accompanied by dissolving of residuals (PbZrO3 and NiO) in the perovskite solid solution formed
9.	Casellas, D., et al. (författare) On the transformation toughening of Y-ZrO2 ceramics with mixed Y-TZP/PSZ microstructures 2001 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 21:6, s. 765-777 Tidskriftsartikel (refereegranskat)abstract Heat treatment of Y-TZP at high temperatures produces materials with a mixed Y-TZP/PSZ phase assemblage, which exhibit a unique combination of high mechanical strength and fracture toughness, uncommon in zirconia ceramics. The microstructure and crack growth resistance of the Y-TZP/PSZ materials developed by treating at 1650°C in air a fine-grained Y-TZP was studied. XRD as well as Raman spectroscopy results indicate that the obtained microstructure allow the retention of large tetragonal grains (up to ˜4 μm), resulting in both phase transformability enhancement and pronounced R-curve behavior. The large transformation zone, discerned from accurate measurements with Raman microprobe spectroscopy, sustains the above assessment and points out tetragonal to monoclinic phase transformation as the main toughening mechanism in the investigated Y-TZP/PSZ microstructures. This was confirmed by satisfactory agreement between the transformation toughening estimated from numerical analysis and the crack shielding experimentally determined from the R-curve measurements.
10.	Deng, Shiqiang, et al. (författare) Creep properties of single crystal oxides evaluated by a Larson-Miller procedure 1995 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 15:6, s. 513-520 Tidskriftsartikel (refereegranskat)abstract A collation of published results of compressive and tensile creep studies of single and binary oxide single crystals is presented. For the purposes of comparison the results were normalised by means of a Larson-Miller procedure. This method proved to be effective in providing a ranking of the oxides in terms of their creep resistance. Binary oxides with complex crystal structures exhibited the highest creep strengths; no direct correlation with the melting point could be found.
11.	Grins, Jekab, et al. (författare) High-resolution electron microscopy of a Sr-containing sialon polytypoid phase 1999 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 19, s. 2723-2730 Tidskriftsartikel (refereegranskat)abstract A new type of Sr-containing sialon polytypoid phase with the structural formula SrSi10-xAl18+xN32-xOx (x approximate to l) has been found in the Sr-Si-Al-O-N system. The phase was characterised by X-ray powder diffraction (XRPD), and its structure was investigated by electron diffraction (ED) and high resolution electron microscopy (HREM). It is considerably disordered, but the average structure has a rhombohedral unit cell with a=5.335(5)approximate to root 3.a(AIN) and c= 79.1(1)Angstrom approximate to 30.c(AIN). The Sr atoms ave located in layers M-Sr-M, M=(Si/Al), at the origin of the unit cell with 12 X= (O,N) atoms around it, at distances of similar to 3 Angstrom, forming a cubo-octahedron. The X atoms that form a hexagon around the Sr atom in the ab plane are corner shared by M = (Si/Al) tetrahedra with opposite polarity in adjacent layers in which 2/3 of the tetrahedra are occupied. The M-Sr-M layers alternate with normally eight-layer-thick AIN type blocks, although the thickness of these blocks frequently varies. The structural model obtained from the HREM images includes a polarity reversal of the tetrahedra in the AIN blocks, similar to that proposed to occur in Si-Al-O-N polytypoid phases. The model with one Sr layer and 10 M = (Si,Al) layers per 1/3 of the repeat unit agrees with the composition of the phase and experimental HREM images.
12.	Hansson, T., et al. (författare) High temperature fracture of a SiC whisker-reinforced alumina in air and vacuum 1994 Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 13:5, s. 427-436 Tidskriftsartikel (refereegranskat)abstract The fracture behaviour of a SiCw/alumina composite was studied between room temperature and 1320°C in vacuum by four-point bend testing of specimens pre-cracked by bridge indentation. The results are compared to those of earlier work on a similar material in air. In vacuum, the composite begins to exhibit stable crack growth (SCG) and increasing apparent toughness at about 1100°C. Between 1100 and 1320°C, the extent of SCG increases and the toughness rises to almost three times the room temperature fracture toughness. The toughness enhancement is due mainly to such processes as crack deflection, crack branching, microcrack zone formation and crack tip blunting rather than any temperature-related increase in intrinsic fracture resistance of the material. In air, the fracture processes are similar to those in vacuum but the toughness increase is delayed by about 100°C and the level of toughening is lower. These differences arise from the formation of a glass phase in air which delays microcrack formation but reduces the resistance to stable crack growth.
13.	Harrysson, Ralph, et al. (författare) Glass formation in the system Y2O3-Al2O3-SiO2 under conditions of laser melting 1994 Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 14:4, s. 377-381 Tidskriftsartikel (refereegranskat)abstract Glass formation in the Y2O3---Al2O3---SiO2 system was investigated by means of laser melting using a CO2 laser source (wavelength 106 μm) with a maximum output power of 1700 W. The glass-forming region was found to be more extensive than that observed by other investigators. No glassy phase formed in compositions with less than 20 wt% SiO2. A non-equilibrium phase diagram corresponding to the conditions of laser-induced rapid melting and self-quenching was also determined. All the phases reported in the relevant binary diagrams with the exception of yttrium silicate 2Y2O3.3SiO2 were observed.
14.	Käll, Per-Olov, et al. (författare) Sialon Ceramics Made with Mixtures of Y2O3-Nd2O3 as Sintering Aid 1990 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 6:2, s. 119-127 Tidskriftsartikel (refereegranskat)abstract Sialon ceramics have been prepared by pressureless sintering at 1775 and 1825°C, using mixtures of Y2O3---Nd2O3 as sintering aids. It was found that at 1775°C less dense materials were obtained, but by raising the sintering temperature to 1825°C fully dense materials could be produced, even when pure neodymia was used. The hardness of the Nd-sialon ceramics was found to be slightly lower than for the corresponding Y-sialon ceramics, but the fracture toughness was approximately the same. It was also observed that the amount of intergranular phase increased when yttria was replaced by neodymia.
15.	Laarz, Eric, et al. (författare) Colloidal processing of Al2O3-based composites reinforced with TiN and TiC particulates, whiskers and nanoparticles 2001 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 21:8, s. 1027-1035 Tidskriftsartikel (refereegranskat)abstract A colloidal processing route has been developed for the preparation of dense and homogeneous Al2O3–TiN/TiC composites. The dispersion and rheological properties of mixtures of TiN or TiC particulates and Al2O3 particles were investigated using electrokinetics and steady-shear rheology. We found that well-dispersed aqueous suspensions with low viscosity could be prepared by adding a poly(acrylic acid) dispersant and controlling pH in the alkaline range. This processing scheme was also suitable for preparation of whisker and nanoparticle composite suspensions. The alumina-based composite suspensions with a secondary-phase concentration of 25 vol.% were freeze-granulated and hot-pressed, and the resulting bodies were fully densified with well-dispersed secondary phases. Homogeneous Al2O3–TiN nanoparticle composites could only be prepared with additions of up to 5 vol.% nanoparticles; higher additions resulted in agglomeration and subsequent grain growth of the nanoparticles.
16.	Larker, Hans T, et al. (författare) Near net shape production of monolithic and composite high temperature ceramics by hot isostatic pressing (HIP) 1999 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 19:13-14, s. 2367-2373 Tidskriftsartikel (refereegranskat)abstract Improved properties of high temperature ceramics in general are achieved by compositional and processing research and development-compatible with sintering and forming needs. Pressure can be used to increase the driving force for densification and with hot isostatic pressing (HIP) the form can be closely controlled, even of complex shaped parts, like turbine wheels. Recent development within the EUREKA-AGATA hybrid electric car gas turbine project shows that improved high temperature material properties can be achieved, while at the same time fabricating components like combustion parts and turbine wheels, to near-net-shape. For such components a highly uniform green powder body is desired. Combined with a type of encapsulation during HIP, which does not create shear stresses at the surface of the green body during the shrinkage/sintering to full density, but at the same time prevents penetration into the body, optimal near-net-shape results can be achieved. Recent studies, e.g. by TEM, have confirmed that some encapsulation glass constituents can form new compounds with silicon nitride, at the very surface, which appear to help develop these desired characteristics. Non-homogeneous and non-isotropic ceramics, like fiber reinforced composites, may be fabricated using rigid, shape controlling tools on one or several sides. Particularly for large (and curved) panels such use of a hot isostatic press can be an advantage.
17.	Lei, B., et al. (författare) Nitridation study of reaction-bonded silicon nitride in situ by high temperature X-ray diffraction 1997 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 17:9, s. 1113-1117 Tidskriftsartikel (refereegranskat)abstract The reaction-bonded silicon nitride (RBSN) nitriding process has been studied using a high temperature X-ray diffractometer (HT-XRD) under isothermal conditions in the temperature interval 1300-1400°C. With HT-XRD, the nitridation reaction and phases formed could be monitored almost instantaneously at temperature. The experimentally observed kinetics of the nitriding reaction were found to be in fair agreement with a theoretical model which predicts that the nitriding reaction occurs predominantly by Knudsen diffusion of nitrogen molecules through channels in a layer of growing Si3N4. However, no single rate law is likely to describe the whole nitridation process. Observation of the microstructure after nitridation indicates that the process occurs partly by reaction of Si vapour with nitrogen gas but that inward diffusion of nitrogen into particles also contributes significantly to the overall nitridation. The phase analysis showed that α-Si3N4 formation predominates over β-Si3N4 formation but the proportion of β-Si3N4 increases as nitridation continues
18.	Li, W.B., et al. (författare) A kinetic model for reaction bonding process of silicon powder compact 1997 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 17:9, s. 1119-1129 Tidskriftsartikel (refereegranskat)abstract In order to obtain detailed information about the kinetics and the reaction nature of a complex reaction process like reaction bonding of silicon nitride, mathematical modelling of the process is necessary. The previous quantitative models for this process have been based only on the mechanism that the nitrogen diffuses through the solid silicon nitride without taking into account the multiple reaction mechanisms. In the present study, a comprehensive kinetic model, which is based on analysis of the multiple mechanisms in a silicon powder compact reacting with nitrogen gas and forming silicon nitride, is constructed for a solid-gas reaction bonding process with specific application to the reaction-bonding of silicon nitride. The model will incorporate the rate equation for each mechanism into a constitutive equation from which more complete information of process kinetics can be predicted. The results predicted by the present model have been compared with previous experimental results and satisfactory agreement obtained
19.	Li, Wen Bin, et al. (författare) Stresses developed in reaction-bonded ceramics 1999 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 19:3, s. 277-283 Tidskriftsartikel (refereegranskat)abstract A physical model is presented that predicts the stress distribution created in a particle during its reaction with a surrounding reactant to form a uniform layer of reaction product on its surface, when the reaction involves a volume change. The results of the model are applied specifically to the case of silicon reacting with nitrogen to form Si3N4. The model predicts the generation of a high, tensile hydrostatic stress in the Si core as well as high tensile radial stress and compressive tangential stress in the nitride layer. Although the model is restricted to elastic deformation only and therefore predicts unrealistically high stresses in some cases, the results are anyway of relevance in the consideration of possible non-elastic processes such as creep and fracture and also in assessing the possible effect of stress on the reaction equilibrium. It is predicted that the nitride reaction layer would fracture during the nitridation process. A second model is also presented predicting the residual stresses arising during cooling of a partially reacted particle as a result of the difference in thermal expansion of the reactant core and the reaction product layer. In the case of the reaction of silicon to silicon nitride these thermal expansion mismatch stresses are significant but small compared to the stresses due to the chemical reaction.
20.	Osso, D., et al. (författare) Mechanical-thermal synthesis of Al2O3-Cr composite powders 1995 Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 15:12, s. 1207-1212 Tidskriftsartikel (refereegranskat)abstract Three different approaches have been investigated to synthesize alumina-chromium composites by displacement reactions between aluminium and chromia. The reactions have been performed either by pure mechanosynthesis or pure thermal ignition or also by a combined mechanical and thermal activation process. Differential thermal analysis, dilatometry and high temperature X-ray diffraction have been used to show the various reaction mechanisms and chemical transformations. High-energy milling of the powder modifies the reactivity of the system. A partial pre-milling treatment not only reduces the reaction temperature but can also induce a different reaction path. It has been shown that an appropriate mechanical-thermal treatment leads to the synthesis of an alumina-chromia composite by a pure solid-state process: intermediate reaction stages exhibit little if any liquid phases.
21.	Persson, Jeanette, et al. (författare) Oxidation Behaviour and Mechanical Properties of β- and Mixed α-β Sialons Sintered with Additions of Y2O3 and Nd2O3 1993 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 11:4, s. 363-373 Tidskriftsartikel (refereegranskat)abstract Sialon ceramics have been prepared from two different Si3N4 powders obtained from different commercial sources, using Y2O3 and/or Nd2O3 as sintering aid. Although both powders were high-purity and high-quality silicon nitrides, surprisingly different phase compositions were obtained for the same overall starting compositions upon sintering at 1825°C. The phase compositions, densities, microstructures and mechanical properties of the samples obtained from the two powders have been compared. The samples prepared from one of the powders were oxidized at 1350°C for 20 h in dry oxygen in a TG unit. The oxidation curves obtained have been interpreted within the framework of a new rate law. The new rate law covers the observation that the oxidation behaviour of Si3N4-based ceramics is often non-parabolic, probably as a result of crystallization processes and the formation of cracks and/or bubbles within the oxide scale or at the scale/matrix interface during oxidation.
22.	Persson, Jeanette, et al. (författare) Parabolic-Non-Parabolic Oxidation Kinetics of Si3N4 1993 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 12:3, s. 177-184 Tidskriftsartikel (refereegranskat)abstract The isothermal oxidation behaviour of Si3N4, HIP sintered without additives, has been investigated thermogravimetrically in the temperature range 1250–1500°C. The formed oxide scales were found to be partly crystalline, and the obtained weight gain curves followed the parabolic rate law after a certain time, t0, but not during the entire oxidation experiment. In the time interval t<t0 the curves have been interpreted with the rate law , which is developed with the assumption that the cross-section area available for oxygen diffusion decreases during the experiment, due to a crystallization process and to formation of nitrogen bubbles within the oxide scale. The rate constants, Kp were calculated from the constants in the arctan function, and the activation energy could be determined to be 310±25 kJ/mol. The oxygen diffusion rates found are in fair agreement with those obtained for amorphous silica.
23.	Ratko, A., et al. (författare) Sorption and gas sensitive properties of In2O3 based ceramics doped with Ga2O3 1998 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 18:14, s. 2227-2232 Tidskriftsartikel (refereegranskat)abstract The process of structure formation in In2O3 based ceramics doped with Ga2O3 was investigated. The data obtained demonstrated the profound influence of Ga-dopands both on the crystallization path of solids produced by coprecipitation and on their final physical and electrical properties. The limited solubility of Ga2O3 dopands in cubic In2O3 lattice which lies within the 11-12 wt% was also noted. Ga2O3-dopands caused the formation of a porous structure in the In2O3-based ceramics, providing an active interaction surface in the semiconductor for reducing gases. Ga-doped ceramics demonstrated better gas sensor properties then pure In2O3.
24.	Sørensen, Bent F., et al. (författare) Toughness of damage tolerant continuous fibre reinforced ceramic matrix composites 1995 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 15:11, s. 1047-1059 Tidskriftsartikel (refereegranskat)abstract A simple shear-lag model is used to estimate the toughness of a unidirectional fibre reinfored ceramic matrix composite. In the model, which includes the residual axial stresses, the stress transfer across the fibre/matrix interface is by a constant shear stress. The estimates from the model are compared to experimental measurements for four composites and good agreement is found. The effects of distributed and localized energy uptake on fracture stability are discussed, and it is concluded that for most applications the toughness, rather than the pull-out energy absorption, should be maximized
25.	Vomacka, P., et al. (författare) Crystallization of Y3Al5O12 from an Oxynitride Glass Monitored by High-Temperature X-Ray Diffractometry 1996 Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 16:11, s. 1263-1269 Tidskriftsartikel (refereegranskat)abstract It is well established that the glassy phase in a β-SiAlON material, with addition of Y2O3, can be crystallized to yttrium aluminium garnet (Y3Al5O12-YAG) by a post-sintering heat treatment. The crystallization of the YAG phase from an oxynitride glass with composition 46·1 wt% Y2O3, 26·3 wt% Al2O3, 21·6 wt% SiO2 and wt% Si3N4 was studied by means of high-temperature X-ray diffractometry. The kinetics of the crystallization were monitored in terms of the (420)) YAG peak area versus isothermal soaking time at 1150 °C during different heat treatments. The crystallization of the YAG phase was found to proceed as a surface crystallization. The results are relevant to developing improved crystallization treatments for glasses with potential for crystallization to YAG-based glass-ceramics and for heat treatments of YAG/β-SiAlON materials
26.	Vomacka, P., et al. (författare) Influence of Zirconia Addition on the Crystallization Kinetics of a Y-Si-Al-O-N Glass 1996 Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 16:11, s. 1253-1262 Tidskriftsartikel (refereegranskat)abstract The crystallization behaviour of YSiAlON glasses with and without ZrO2 additives, prepared by melting at 1700 °C, were studied by means of differential scanning calorimetry, scanning microscopy and X-ray powder diffraction analysis. The optimum nucleation temperatures were determined to be Tg + 65°C and Tg + 50 °C for the ZrO2-free and the ZrO2-containing glass, respectively. The crystallization of the glasses was found to be dominated by the surface mechanism of nucleation and growth. The added zirconia acted as a growth modifier rather than a nucleating agent.
27.	Vomacka, P., et al. (författare) Influence of ZrO2 Addition on Melting Kinetics of a YSiAlO Glass-Ceramic 1996 Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 16:11, s. 1245-1251 Tidskriftsartikel (refereegranskat)abstract A ZrO2-free YSiAlO glass of composition 27Y: 42Si:31Al in equivalent % and one with the addition of wt% ZrO2 were prepared in a nitrogen atmosphere at 1700 °C. These glasses were treated in a nitrogen atmosphere at a controlled rate, during which the glass partially crystallizes to form a glass-ceramic. Under continued heating melting occurs. This behaviour was monitored by differential thermal analysis, scanning electron microscopy and X-ray diffraction. The original dendritic appearance of the crystallized microstructures changed to a blocky one in the early stages of the melting process. The ZrO2 addition was found to increase the kinetics of the phase transformations occurring during the melting.
28.	Vomacka, P. (författare) Influence of ZrO2 addition on the crystallization of yttrium oxynitride glasses to Y3Al5O12-based glass-ceramics 1997 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 17:4, s. 615-621 Tidskriftsartikel (refereegranskat)abstract The influence of a ZrO2 addition (6 wt%) on the crystallization behaviour of a glass with potential for crystallization to Y3Al5O12-based glass-ceramics has been investigated. Differential thermal analysis, X-ray diffraction and scanning electron microscopy were used to assess the crystallization process. Vickers hardness was used to monitor changes in the crystallized volume fraction at different heat treatment temperatures. The results indicate that the addition of ZrO2 to the investigated glass composition promotes the formation of the y- Y2Si2O7 and inhibits the crystallization of the Y3Al5O12 phase
29.	Vomacka, P., et al. (författare) Yttria-alumina-silica glasses with addition of zirconia 1995 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 15:9, s. 921-928 Tidskriftsartikel (refereegranskat)abstract ZrO2-free glasses and glasses containing ZrO2 in the system Y2O3-Al2O3-SiO2 have been investigated. Properties of compositions fired in nitrogen at 1600, 1650 and 1700 °C have been assessed. The solubility limit of ZrO2 in yttrium aluminosilicate liquids with a high content of Y2O3 at 1700 °C was determined to be 6 wt%. The hardness and density of the ZrO2-containing glasses were slightly increased compared to the ZrO2-free glass; y- Y2Si2O7 (at temperatures < 1300 °C) and β- Y2Si2O7 (at temperatures >1300 °C) monoclinic phases are the main products formed during the crystallization. An unidentified intermediate phase rich in Y, Al and Si was observed to undergo a transformation at temperatures ≥1200 °C resulting in the formation of the β-Y2Si2O7 phase.
30.	Vomacka, P., et al. (författare) Zirconia as a nucleating agent in a yttria-alumina-silica glass 1995 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 15:11, s. 1111-1117 Tidskriftsartikel (refereegranskat)abstract The crystallization behaviour of a ZrO2-containing glass and a ZrO2-free glass in the Y2O3-Al2O3-SiO2 system prepared at 1700°C were compared in order to study the influence of ZrO2 on the nucleation and growth processes. Techniques used included SEM, DTA and XRD analysis. The microstructural development of the ZrO2-containing material during crystallization was more complex than that of the ZrO2-free material. In the crystallization treatments no phase separation prior to crystallization could be observed and no precursor crystalline phase was observed to form in the ZrO2-containing glass. Thus the added zirconia could be considered to act as a growth modifier rather than a catalyst nucleating agent.
31.	Westman, Anna-Karin, et al. (författare) Chemical reactions in the system Si3N4-SiO2-B2O3 1998 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 18:6, s. 633-640 Tidskriftsartikel (refereegranskat)abstract Chemical interactions in the system of silicon nitride with borosilicate glass have been studied as part of an evaluation of glass encapsulated HIP. Theoretical calculations have been performed to predict the thermodynamically stable phases under conditions reflecting different stages in a HIP-cycle. Experimental studies were made on heat treated mixtures of the silicon nitride and the silicate glass. These samples were evaluated with X-ray diffraction. At temperatures commonly used for densification, the system reacted to BN and Si2N2O in agreement with the theoretical calculations. At typical temperatures for pressure application no chemical reactions could be detected but the theoretical calculations showed that BN and, for larger amount of silicon nitride, also silicon oxynitride were stable. Minor amounts of the phases may have formed or non-equilibrium conditions could be explanations for the absence of the expected phases
32.	Westman, Anna-Karin, et al. (författare) Interaction of encapsulation glass and silicon nitride ceramic during HIPing 1999 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 19:16, s. 2739-2746 Tidskriftsartikel (refereegranskat)abstract Interaction between ceramic compacts and the encapsulation glass during the HIP process has been studied in a model system of silicon nitride and borosilicate glass. Attention has been focused on what happens when the pressure is first applied in the HIP-cycle, i.e. between about 1200 and 1500°C. At this stage the pore system of the ceramic green body is still rather unaffected by sintering. The model system was characterised to evaluate a possible viscous flow of glass into the green body. Two glass compositions, one with high and one with low viscosity, were used, measurements being made of their viscosity and their contact angle on the nitride. Applying Darcy's law it was predicted that the encapsulation glass with the lowest viscosity should penetrate about 1200 microns into the still open pore structure at 1450°C, but this was not observed experimentally. In the calculations no chemical reactions were assumed to take place. However, increases in hardness of heat-treated mixture of glass and silicon nitride powder indicates that nitrogen dissolves in the glass. It is known that nitrogen increases the viscosity of the glass and this would result in a more limited glass intrusion. After HIP the surface region of the dense ceramic exhibited a phase composition gradient of silicon oxynitride, down to approximately 100-200 microns into the bulk
33.	Westman, Anna-Karin, et al. (författare) Ultra-micro indentation technique used for examination of mechanical properties close to a HIPed surface of silicon nitride 1998 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 18:7, s. 879-890 Tidskriftsartikel (refereegranskat)abstract Ultra-micro indentation using both pointed and spherical tipped indenters has been used to characterize mechanical properties of silicon nitride densified by glass encapsulated hot isostatic pressing (HIP). Young's modulus and hardness have been studied as a function of distance to the interface between silicon nitride and the encapsulation glass. The Young's modulus values are 10 to 20% lower in the close vicinity of the silicon nitride surface compared to bulk values. At distances of 75 to 150 microns from the glass-silicon nitride interface, bulk values are measured. The differences in hardness values between the region close to the surface and the bulk is less pronounced. A possible explanation for these gradients is formation of new phases at the surface of the silicon nitride. Routines for the calibration of both the pointed and spherical tipped indenters are presented
34.	Adamopoulos, Othon, et al. (författare) A nanophase oxygen storage material : Alumina-coated metal-based ceria 2009 Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 29:4, s. 677-689 Tidskriftsartikel (refereegranskat)abstract Nanoparticles of Ce1-xMxO2-delta (M = Ca or Zr) coated with Al2O3 with average crystallite size of 10 nm have been synthesised via solution chemistry approach under controlled chemical and hydrodynamic conditions. Their synthesis has been accomplished in three major steps: (1) simultaneous co-precipitation of cations, (2) sequential precipitation of Al(OH)(3) over the former particles and (3) calcination of the precipitated precursors to the corresponding oxides. Several compositions have been synthesised and their physicochemical properties are compared with commercial state-of-the-art material. The Al2O3-coating hinders the particles growth at high temperatures, resulting in materials with a large specific surface area and a restrain in the decrease of their oxygen storage capacity.
35.	Adolfsson, Erik, et al. (författare) Effects of granule density on strength and granule related defects in zirconia 2012 Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 32:11, s. 2653-2659 Tidskriftsartikel (refereegranskat)abstract A suspension of zirconia powder (TZ3YSE) with a solids loading of 50 vol% was prepared by ball milling. Binders were added and some of the suspension was diluted to 40, 30 and 20 vol% before freeze granulation was performed. A spray dried material (TZ3YSEB) was used as a reference. The pore size distribution of the different granules was evaluated and from the microstructure it was shown that inhomogeneities were present in both the freeze granulated as well as in the spray dried granules. In addition, the density, microstructure as well as the strength of sintered materials prepared from the granules were studied. The results showed that a high green density or sintered density was not sufficient in order to achieve a high strength material. It was further shown that the strength was significantly influenced by the granule density and not by the inhomogeneities found in the granules.
36.	Adolphsen, Jens Q., et al. (författare) Characterisation and processing of aqueous LaNi0.6Fe0.4O3 Suspensions into Porous Electrode Layers for Alkaline Water Electrolysis 2019 Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 39:4, s. 1271-1278 Tidskriftsartikel (refereegranskat)abstract The colloidal properties and processing of aqueous LaNi0.6.Fe0.4O3 suspensions into electrode layers with hierarchical pore sizes has been investigated by light scattering, electron microscopy and rheology. We found that the colloidal stability of the oxide particles and the resulting microstructure of the electrode layers were similar when dispersing the particles at their intrinsic pH, or when adding polyvinylpyrrolidone. The addition of the ammonium salt of poly(methaacrylic acid) resulted in a poor colloidal stability and the concentrated suspensions became viscoelastic during processing. Addition of rice starch resulted in an increase of the porosity but the cast electrode layers cracked and delaminated.
37.	Akhtar, Farid, et al. (författare) Structuring adsorbents and catalysts by processing of porous powders 2014 Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 34:7, s. 1643-1666 Tidskriftsartikel (refereegranskat)abstract Microporous materials such as zeolites, metal organic frameworks, activated carbons and aluminum phosphates are suitable for catalysis and separation applications. These high surface area materials are invariably produced in particulate forms and need to be transformed into hierarchically porous structures for high performance adsorbents or catalysts. Structuring of porous powders enables an optimized structure with high mass transfer, low pressure drop, good heat management, and high mechanical and chemical stability. The requirements and important properties of hierarchically porous structures are reviewed with a focus on applications in gas separation and catalysis. Versatile powder processing routes to process porous powders into hierarchically porous structures like extrusion, coatings of scaffolds and honeycombs, colloidal processing and direct casting, and sacrificial approaches are presented and discussed. The use and limitations of the use of inorganic binders for increasing the mechanical strength is reviewed, and the most important binder systems, e.g. clays and silica, are described in detail. Recent advances to produce binder-free and complex shaped hierarchically porous monoliths are described and their performance is compared with traditional binder-containing structured adsorbents. Needs related to better thermal management and improved kinetics and volume efficiency are discussed and an outlook on future research is also given.
38.	Ali, Sharafat, Associate Professor, 1976-, et al. (författare) A novel approach for processing CaAlSiON glass-ceramics by spark plasma sintering : Mechanical and electrical properties 2022 Ingår i: Journal of the European Ceramic Society. - : Elsevier. - 0955-2219 .- 1873-619X. ; 42:1, s. 96-104 Tidskriftsartikel (refereegranskat)abstract Lithium containing glassy materials can be used as solid electrolytes or electrode materials for lithium-ion batteries due to their high energy density. Conventional melt-quenched Ca11Al14Si16O49N10 glass powder containing 24 e/o N, doped with Li-ions (1, 3, and 6 wt. %) and sintered by spark plasma sintering technique (SPS) was studied. The benefits of using SPS to produce glass-ceramics are rapid heating rates compared to conventional consolidation techniques and tuning of properties, adjusting the temperature, holding time (closed to Tg temperature), heating rate (solidification), and pressure (densification) profile during the heat treatment using SPS. Pure glass and glass-ceramic were obtained under identical SPS conditions and compared with pristine oxynitride and soda-lime-silicate (float) glasses. XRD and SEM analysis confirmed that increasing the amount of Li increases the crystallinity in the glass matrix. Nano-indentation analysis showed a decreased hardness and reduced elastic modulus values with the addition of Li-ions. The direct current conductivity increases with the addition of Li due to the high mobility of Li-ions. However, the float glass sample doped with 6 wt.% of Li exhibits even higher values of D.C. conductivity, than the analogously doped Ca11Al14Si16O49N10 glass. The magnitude of activation energy (more than 1 eV) is typical for an ion hopping mechanism and the D.C. conduction mechanism is dominated by Li+ hopping.
39.	Ali, Sharafat, 1976-, et al. (författare) Compositional effects on the properties of high nitrogen content alkaline-earth silicon oxynitride glasses, AE = Mg, Ca, Sr, Ba 2011 Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 31:4, s. 611-618 Tidskriftsartikel (refereegranskat)abstract A series of alkaline-earth element containing high nitrogen content oxynitride glasses (AESiON), with AE = Mg, Ca, Sr, Ba, were prepared in order to investigate the compositional effects on the physical properties of the alkaline-earth element. The physical properties were found to change linearly with the concentration of AE elements. The density of the glasses increases substantially with an increase in the AE atomic mass and slightly with an increase in nitrogen ratio. Ba containing glasses shows the value of density 4.16 g/cm3. Glass transition temperatures are found to be higher for Mg glasses, ca. 1020 °C, in comparison with Ba glasses, ca. 895 °C. The hardness of Mg containing glasses shows high values, up to 12.2 GPa and decreases for Ca, Sr and Ba containing glasses. Ba, containing glasses shows high values of refractive index in comparison with the Sr, Ca and Mg containing glasses.
40.	Andersson, Linnéa, et al. (författare) Gas-filled microspheres as an expandable sacrificial template for direct casting of complex-shaped macroporous ceramics 2008 Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 28:15, s. 2815-2821 Tidskriftsartikel (refereegranskat)abstract Expandable microspheres have been used as a sacrificial template to produce macroporous ceramic materials by a gel-casting process. The temperature range for the gel-casting process has been tuned to allow the gas-filled polymer spheres to expand prior to the setting of the powder body. It is demonstrated that by controlling the amount and size of the expandable microspheres it is possible to tune and tailor the porosity up to 86% and the pore size distribution from 15 up to 150 mu m. The expandable microspheres add a relatively low amount of organic material that allows rapid and facile burn-out. The temperature-induced expansion of the microspheres and the associated volume increase of the suspension has been used as a simple zero-pressure near-net shaping method to yield complex-shaped macroporous alumina bodies.
41.	Andersson, Linnéa, et al. (författare) Three-dimensional structure analysis by X-ray micro-computed tomography of macroporous alumina templated with expandable microspheres 2010 Ingår i: Journal of the European Ceramic Society. - Amsterdam, Netherlands : Elsevier. - 0955-2219 .- 1873-619X. ; 30:12, s. 2547-2554 Tidskriftsartikel (refereegranskat)abstract The three-dimensional (3D) structures of macroporous alumina, produced by a novel method that combines gel casting with expandable polymericmicrospheres as a sacrificial templating material, have been characterised by X-ray micro-computed tomography (µ-CT). The grey-scale intensitytomogram data produced by the X-ray µ-CT was segmented into porous and solid phases and the individual pores were identified. We comparedtwo-dimensional slices of the analysed data with the corresponding scanning electron microscopy images and showed that the structural featuresof the pores were well reproduced in the X-ray µ-CT images. 3D visualisations of the pore structure and the pore network were also shown. Theopen porosity obtained from X-ray µ-CT corresponded well with the porosity derived from mercury porosimetry for pores larger than the voxeldimension (3 µm). The quantitative analysis also yielded information on the spatial variations in porosity and the number of connected neighboursof pores. The 3D data was used to relate the calculated permeability to the open porosity.
42.	Azina, Clio, et al. (författare) Microstructural and compositional design of Cr2AlC MAX phases and their impact on oxidation resistance 2024 Ingår i: Journal of the European Ceramic Society. - : ELSEVIER SCI LTD. - 0955-2219 .- 1873-619X. ; 44:8, s. 4895-4904 Tidskriftsartikel (refereegranskat)abstract The oxidation of MAX phases has largely been investigated, but the effect of secondary phases and microstructure is still unclear. We report on the effect of reactive and non-reactive sintering, and starting powders, on the microstructure, phase formation, and chemical composition of Cr2AlC MAX phases. The grain sizes are shown to be sensitive to both the processing method and the starting powders. Secondary phases were observed mostly in reactively sintered samples as Cr7C3 and AlCr2 were identified, and Al contents varied between 24.4 and 28.0 at %. Finally, the oxidation behavior of the produced MAX phases was evaluated after 60 and 120 min at 1100 degrees C. The Al content, the average grain size of the as-sintered samples, and the presence of secondary phases affected the decomposition of the MAX phase into Cr-carbides in the vicinity of the oxide scale and the composition of the oxide scale, respectively.
43.	Azina, Clio, et al. (författare) Oxidation behaviour of V2AlC MAX phase coatings 2020 Ingår i: Journal of the European Ceramic Society. - : ELSEVIER SCI LTD. - 0955-2219 .- 1873-619X. ; 40:13, s. 4436-4444 Tidskriftsartikel (refereegranskat)abstract We report on the oxidation behaviour of V2AlC coatings up to 800 degrees C, in air. The coatings were deposited at 580 degrees C using magnetron sputtering from a powder metallurgical composite V2AlC target and were subsequently oxidised for 5, 15 and 30 min. The microstructural evolution of the samples was investigated, and X-ray diffraction patterns were collected to track the formation of oxides. The first indications of oxidation appear after just 15 min at 500 degrees C, as V-based oxides grew on the surface of the coatings. Later, the presence of mostly V-based oxides and ternary (V, Al)-oxides was observed starting after 5 min at 600 degrees C. Further analyses confirmed outward diffusion of V and inward diffusion of O, while Al tends to sublimate. alpha-A12O3 was only indexed after 5 min at 800 degrees C. Ex-situ electrical resistivity measurements allowed tracking the oxidation progress of the V2AlC coating.
44.	Barick, Prasenjit, et al. (författare) Spray-freeze-dried nanosized silicon carbide containing granules : Properties, compaction behaviour and sintering 2016 Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 36:16, s. 3863-3877 Tidskriftsartikel (refereegranskat)abstract Spherical granules comprising silicon carbide nanoparticles have been produced with the help of sprayfreeze-drying (SFD) technique. The effect of solid loading of slurries on rheological properties, flowability and morphology of the resulting SFD granules has been studied. Further, a systematic study has been performed to investigate the effect of applied pressures and granule density on the relative densities and microstructures of the green compacts. A marginal increase in viscosity is noted as the solid content of slurries increases from 5 to 15 vol% with significant increase in viscosity being observed in case of 18 vol% slurry. The granules prepared from SiC slurries are spherical in shape with their mean size, density, gravimetric flow rate, and yield strength increasing with the increase in solid content. The mechanical properties of sintered SiC produced from SFD granules are found relatively superior to that made from commercially available spray-dried (SD) granules.
45.	Bergström, L, et al. (författare) Temperature induced flocculation of concentrated ceramic suspensions: rheological properties 1999 Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 19, s. 2117-2123 Tidskriftsartikel (refereegranskat)abstract Concentrated, sterically stabilised ceramic suspensions have been reversibly flocculated by changing the temperature. Using an amphiphilic polymer, Hypermer KD3, as dispersant for alumina and alumina-silicon carbide whisker composite mixtures in pentanol resulted in a transition from dispersed to flocculated state close to room temperature. The collapse of the adsorbed polymer layer with decreasing solvency (temperature) in the marginal solvent pentanol induces flocculation when the long-range van der Waals force overcomes the remaining steric repulsion. Temperature induced flocculation (TIF) has a drastic effect on the rheological properties. At high temperatures, T>30 °C, the suspensions have a low viscosity and neglible elasticity. When the temperature is lowered below 20 °C, the viscosity increases significantly and the viscoelastic behaviour becomes predominatly elastic. The elasticity and the associated particle network strength are sufficiently high for a highly concentrated gelled suspension to support its own weight. The potential use of TIF as a novel forming method was discussed with relation to other new shaping techniques.
46.	Buscaglia, V., et al. (författare) Raman and AFM piezoresponse study of dense BaTiO3 nanocrystalline ceramics 2005 Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 25:12, s. 3059-3062 Tidskriftsartikel (refereegranskat)abstract Dense nanocrystalline BaTiO3 (BT) ceramics with grain sizes (GSs) below 100 nm obtained by spark plasma sintering (SPS), were investigated by micro-Raman spectroscopy in order to obtain information about the changes in the local order induced by size effects. The obtained spectra in the range 80-700 K showed the presence of all the crystalline phases of BaTiO3, even in the finest structure (50 nm grain size ceramic), with particularities attributed to the high density of non-ferroelectric grain boundaries. The AFM piezoresponse study incontestably proved the ferroelectric switching at local scale in nanocrystalline BaTiO3 ceramics at room temperature.
47.	Cabioch, Thierry, et al. (författare) Structural investigation of substoichiometry and solid solution effects in Ti2Al(C-x,N1-x)(y) compounds 2012 Ingår i: Journal of the European Ceramic Society. - : Elsevier. - 0955-2219 .- 1873-619X. ; 32:8, s. 1803-1811 Tidskriftsartikel (refereegranskat)abstract The milling, cold compaction and thermal annealing (4 h-1400 degrees C-Ar flow) of Ti, TiC, Al and AlN powders were used to produce Ti2Al(CxN(1-x))(y) compounds with x = 0, 0.25, 0.5, 0.75, 1 and 0.7 andlt;= y andlt;= 1. X-ray diffraction analysis, scanning electron microscopy observations combined with microanalysis confirmed the formation of the almost pure Ti(2)A/CxN(1-x) carbonitrides for y=1 whereas increasing amounts of titanium aluminides were formed when y decreases. Proportions of the different phases deduced from Rietveld refinements of the X-ray diffractograms indicate that no or very poor substoichiometry in carbon was possible in carbide whereas C and N deficiency can be achieved in nitrides and carbonitrides Ti2AlCxN(1-x). Electron Energy Loss Spectroscopy investigations confirm that carbonitrides can have at least 20% of vacancies on the C or N site. The a lattice parameter varies linearly with x whereas it is not the case for the c lattice parameter, its values being lower for the carbonitrides. Furthermore, a strong broadening of the carbonitrides XRD peaks is observed, a phenomenon that can be mainly attributed to C and N concentration gradients inside the samples.
48.	Cabioch, Thierry, et al. (författare) Tailoring of the thermal expansion of Cr2(Alx,Ge1−x)C phases 2013 Ingår i: Journal of the European Ceramic Society. - : Elsevier. - 0955-2219 .- 1873-619X. ; 33:4, s. 897-904 Tidskriftsartikel (refereegranskat)abstract We report thermal expansion coefficients of the end members and solid-solution compounds in the Cr2(Alx,Ge1−x)C system. All samples studied were essentially phase-pure Cr2AlxGe1−xC except the Cr2GeC sample, which contained a substantial fraction of Cr5Ge3Cx. X-ray diffraction performed in the 25–800 °C temperature range shows that the in-plane thermal expansion remains essentially constant at about 14 ± 1 × 10−6 K−1 irrespective of Al content. The thermal expansion of the c axis decreases monotonically from 17 ± 1 × 10−6 K−1 for Cr2GeC to ∼12 ± 1 × 10−6 K−1 with increasing Al content. At around the Cr2(Al0.75,Ge0.25)C composition, the thermal expansion coefficients along the two directions are equal; a useful property to minimize thermal residual stresses. This study thus demonstrates that a solid-solution approach is a route for tuning a physical property like the thermal expansion. For completeness, we also include a structure description of the Cr5Ge3Cx phase, which has been reported before but is not well documented. Its space group is P63/mcm and its a and c lattice parameters are 7.14 Å and 4.88 Å, respectively. We also measured the thermal expansion coefficients of the Cr5Ge3Cx phase. They are found to be 16.3 × 10−6 K−1 and 28.4 × 10−6 K−1 along the a and c axes, respectively. Thus, the thermal expansion coefficients of Cr5Ge3Cx are highly anisotropic and considerably larger than those of the Cr2(Alx,Ge1−x)C phases.
49.	Cai, Yanbing, et al. (författare) Thermal Properties of Nitrogen-Rich Ca-α-Sialons 2009 Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 29:16, s. 3409-3417 Tidskriftsartikel (refereegranskat)abstract Nitrogen-rich Ca-α-Sialon (CaxSi12−2xAl2xN16 with x = 0.2, 0.4, and 0.8, 1.2 and 1.6) ceramics were prepared from the mixtures of Si3N4, AlN and CaH2 powders in a hot press at 1800 °C using a pressure of 35 MPa and a holding time of 4 h, and then were investigated with respect to reaction mechanism, phase stability and oxidation resistance. In addition the sample with x = 1.6 was prepared in the temperature range 600–1800 °C using a pressure of 35 MPa and a holding time of 2 h. The α-Sialon phase was first observed at 1400 °C but the α-Si3N4 and AlN phases were still present at 1700 °C. Phase pure Ca-α-Sialon ceramics could not be obtained until the sintering temperature reached 1800 °C. The phase pure nitrogen-rich Ca-α-Sialon exhibited no phase transformation in the temperature range 1400–1600 °C. In general, mixed α/β-Sialon showed better oxidation resistance than pure α-Sialon in the low temperature range (1250–1325 °C), while α-Sialons with compositions located at α/β-Sialon border-line showed significant weight gains over the entire temperature range tested (1250–1400 °C). The phases formed upon oxidation were characterized by X-ray, SEM and TEM studies.
50.	Candelario, Victor M., et al. (författare) Aqueous colloidal processing of nano-SiC and its nano-Y3Al5O12 liquid-phase sintering additives with carbon nanotubes 2015 Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 35:13, s. 3363-3368 Tidskriftsartikel (refereegranskat)abstract Carbon nanotubes (CNTs) have occasionally been observed to benefit the aqueous colloidal processing of nano-SiC with its nano-Y3Al5O12 liquid-phase-sintering additives. Experimental evidence is here presented for a broad set of CNTs with different morphology and/or surface functionalization confirming that CNTs (7 vol.% addition), regardless of their features, prevent the coagulation of these nanoceramic suspensions, whence it is inferred that aqueous colloidal processing is well-suited for the environmentally friendly preparation of the homogeneous mixtures of nanoceramic particles and CNTs required for the fabrication of CNT-reinforced ceramic matrix nanocomposites. Furthermore, it is shown that surface-functionalized CNTs seem to work better than deflocculated CNTs for the preparation of stable concentrated colloidal suspensions, whose rheological properties are in general very close, but with thinner CNTs being nonetheless preferable. Finally, the feasibility is demonstrated of fabricating SiC/CNT nanocomposites by aqueous colloidal processing followed by liquid-phase assisted spark-plasma sintering.

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