| 1. |
- Azhdar, Bruska, et al.
(author)
-
A new method for assessing the efficiency of stabilizers in polyolefins exposed to chlorinated water media
- 2009
-
In: Polymer testing. - : Elsevier BV. - 0142-9418 .- 1873-2348. ; 28:6, s. 661-667
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Journal article (peer-reviewed)abstract
- The chlorine used as disinfectant in tap water degrades most materials, including polyethylene. The most adequate (functional) test method, the pressure test, is complicated and expensive because the chlorinated aqueous media (Cl-2 or ClO2 in water) are unstable and they undergo reactions that are dependent on the pH. A new method which assesses the protection efficiency of phenolic antioxidants in polyolefins was developed. The method uses a liquid hydrocarbon analogue, squalane, in which antioxidants are dissolved. The organic phase was dispersed in the aqueous chlorinated phase (containing 10 ppm of either Cl-2 or ClO2; pH=6.8) at 70 degrees C by intense stirring. The depletion of antioxidant (Irganox 1010) was monitored by standard DSC determination of the oxidation induction time. It was shown that 300 min of exposure was sufficient to obtain useful data.
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| 2. |
- Azhdar, Bruska, et al.
(author)
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Determination of dynamic and sliding friction, and observation of stick-slip phenomenon on compacted polymer powders during high-velocity compaction
- 2006
-
In: Polymer testing. - : Elsevier BV. - 0142-9418 .- 1873-2348. ; 25:8, s. 1069-1080
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Journal article (peer-reviewed)abstract
- Dynamic friction, sliding friction, and the stick-slip phenomenon have been studied on compacted polymer powders during high-velocity compaction. It is particularly important from a practical point of view to distinguish the stick-slip mechanism and the sliding mechanism which occur concurrently. A practical experimental system has been successfully developed to study the dry frictional force and to measure the sliding coefficient between the polymer powder particles and the die wall during high-velocity compaction. Two new components have been introduced as relaxation assists to improve the compaction process by reducing the frictional forces. It was found that the relaxation assist device leads to an improvement in the polymer powder compaction process by giving a more homogeneous opposite velocity and a better locking of the powder bed in the compacted form with less change in dimensions. The subsequent movement of the particles can be reduced and the powder bed attains a higher density with a minimum total elastic spring-back. The relative time of the stick-slip phenomenon during the compacting stage is also reduced so that the time needed to transfer from an intermittent stick-slip state to a smooth sliding state is reduced and the powder bed slides smoothly. It was found that the dynamic, dry frictional force is intermittent (stick-slip mechanism) at low compaction rates but that at high compaction rates is becomes more smooth (sliding mechanism). Both mechanisms depend on the nature of the powder and on the compaction conditions. At the beginning of the compaction stage, the sliding coefficient decreases due to an increase in the radial to axial stress ratio until the maximum pressure has been reached. During the reorganization stage, more time is needed for large particles to move, rotate and slide due to their relatively large diameter and mass. As a result, the reorganization stage is extended and the stick-slip phenomenon is observed more with increasing particle size. Much better transfer of the pressure throughout the powder bed and less loss of pressure lead to a higher sliding coefficient due to the overall friction during the compaction process. It was found that the sliding coefficient is proportional to the density. A more homogeneous density distribution in the compacted powder and a smaller pressure loss during compaction has a major influence on the sliding coefficient and on the quality of the compacted material
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| 3. |
- Azhdar, Bruska, et al.
(author)
-
Determination of springback gradient in the die on compacted polymer powders during high-velocity compaction
- 2006
-
In: Polymer testing. - : Elsevier BV. - 0142-9418 .- 1873-2348. ; 25:1, s. 114-123
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Journal article (peer-reviewed)abstract
- A uniaxial high-velocity compaction process for polymer powder using a cylindrical, hardened steel die and a new technique with relaxation assist was tested with various heights. The influences of the relaxation assist device on the process characteristics are discussed. Two bonded strain gauges and a high-speed video camera system were used to investigate the springback phenomenon during the compaction process. It was found that the relaxation assist improves the compaction of the polymer powder by locking the powder bed in the compacted form. It is shown that the high-velocity compaction process is an interruption process and that the delay times between the pressure waves can be reduced by increasing the height of the relaxation assist device. The delay times between the pressure waves are also strongly dependent on the strain rate. If the height of the relaxation assist device is increased, the first gross instantaneous springback, and the total elastic springback, are reduced. In addition, the density of the powder bed is increased. The relative times of the compacting stage, decompacting stage and the reorganisation of the particles can be also controlled by altering the height of the relaxation assist.
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| 4. |
- Azhdar, Bruska, et al.
(author)
-
Development of a High-Velocity Compaction process for polymer powders
- 2005
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In: Polymer testing. - : Elsevier BV. - 0142-9418 .- 1873-2348. ; 24:7, s. 909-919
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Journal article (peer-reviewed)abstract
- The High-Velocity Compaction (HVC) process for powder polymers has been studied, with a focus on the compactibility characteristics and surface morphology of the compacted materials, with and without relaxation assists, by increasing compacting quantity and direction. The basic phenomena associated with HVC are explained and the general energy principle is introduced to explain pull-out phenomena during the decompacting stage. Polyamide-11 powders with different particle size distributions have been compacted with the application of different compaction profiles, e.g. different energies and velocities. Scanning electron microscopy (SEM) and image computer board camera, (IC-PCI Imaging Technology) have been used to the study the morphological characteristics, the limit of plastic deformation and particle bonding by plastic flow at contact points, and pull-out phenomena. The relative green density is influenced more by the pre-compacting (primary compaction step) than by the post-compacting (secondary compaction step). The pressure and density distribution differences between the upper and lower surface are not uniform. Projectile supports or 'relaxation assists' are presented as a new technique to reduce pull-out phenomenon. Experimental results for different compaction profiles are presented showing the effect of varying the opposite velocity during the decompacting stage, and how to improve the homogeneous densification between the upper and lower surface and the evenness of the upper surface of the compacted powder bed by using relaxation assists.
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| 5. |
- Azhdar, Bruska
(author)
-
Improved high velocity cold copaction processing : polymer powder to high performance parts
- 2005
-
Licentiate thesis (other academic/artistic)abstract
- A uniaxial High-Velocity Compaction (HVC) process for polymer powder using a cylindrical, hardened steel die and a new technique with relaxation assist was tested with a focus on the compactibility characteristics and surface morphology of the compacted materials using various heights of relaxation assist device with different compacting profiles. Relaxation assist device was presented as a new technique to reduce springback, pull-out phenomenon and to improve the compaction process. The basic phenomena associated with HVC are explained and the general energy principle is introduced to explain pull-out phenomenon during the decompacting stage. In this study, polyamide-11 powders with different particle size distributions have been compacted with the application of different compaction profiles, e.g. different energies and velocities. It was found that the relative green density is influenced more by the pre-compacting (primary compaction step) than by the post-compacting (secondary compaction step). Experimental results for different compaction profiles were presented showing the effect of varying the opposite velocity during the decompacting stage and how to improve the homogeneous densification between the upper and lower surface and the evenness of the upper surface of the compacted powder bed by using relaxation assists, and the influences of the relaxation assist device on the process characteristics. It was found that the relaxation assist improves the compaction of the polymer powder by locking the powder bed in the compacted form. In addition, the relative times of the compacting stage, decompacting stage and the reorganisation of the particles can be controlled by altering the height of the relaxation assist. It was found that the high-velocity compaction process is an interruption process and that the delay times between the pressure waves can be reduced by increasing the height of the relaxation assist device. Furthermore, the first gross instantaneous springback and the total elastic springback are reduced. Two bonding strain gauges and a high-speed video camera system were used to investigate the springback phenomenon during the compaction process. Scanning electron microscopy (SEM) and image computer board Camera (IC-PCI Imaging Technology) were used to the study the morphological characteristics, the limit of plastic deformation and particle bonding by plastic flow at contact points, and pull-out phenomena.
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| 6. |
- Azhdar, Bruska, 1965-
(author)
-
Novel Technique to Improve High-Velocity Cold Compaction : Processing of Polymer Powders and Polymer-Based Nanocomposite High Performance Components
- 2006
-
Doctoral thesis (other academic/artistic)abstract
- Compaction of polymer powders and polymer-based nanocomposites by uniaxial high-velocity cold compaction (HVC), by high-energy ball milling (HEBM) and using a novel technique, relaxation assists, was investigated with a focus on the process parameters, the compactibility characteristics, surface morphology and friction. The basic phenomena associated with HVC are explained and the general energy principle is introduced to explain the pull-out phenomenon, springback gradient, delay time, relative time of the pressure wave, and stick-slip phenomenon during the compaction process. Experimental results for different compaction profiles, different particle size distributions and different milling system for polymer-based nanocomposite are presented, showing the effect of varying the process parameters on the compacted material; the compactibility in the compacted bed, the uniformity of the compacted surface, the pull-out phenomenon, the springback gradient, the stick-slip phenomenon and the homogeneity of the dispersions of nanoparticles in the polymer powders in the solid state. It was found that the high-velocity compaction process is an interruption process and that the opposite velocity and pressure loss during the compaction process have a major influence on the quality of the compacted material. The relaxation assist device is a novel technique that has been successfully developed to improve the compaction process. The relaxation assists are parts of the piston and they are regarded as projectile supports. They are constructed of the same material as the piston, and the diameters are the same but the lengths are different. The relaxation assist device leads to an improvement in the compaction of powders, polymer powders and polymer-based nanocomposites by giving a more homogeneous opposite velocity and a better locking of the powder bed in the compacted form during the compaction process with less change in dimensions in the case of both homogeneous and heterogeneous materials. If the movement of the particles is restricted the powder bed attains a higher density and the total elastic springback is minimized. In addition, there is a more homogeneous dispersion of nanoparticles in the case of a heterogeneous material. A much better transfer of the pressure through the powder bed and a smaller loss of pressure lead to a more homogenous stick-slip of the particles and a higher sliding coefficient due to the overall friction during the compaction process.
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| 7. |
- Azhdar, Bruska, et al.
(author)
-
Polymer-nanofiller prepared by high-energy ball milling and high velocity cold compaction
- 2008
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In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 29:3, s. 252-261
-
Journal article (peer-reviewed)abstract
- High-energy ball milling using comilling in a solid state by low-temperature mechanical alloying to prepare nickel-ferrite (NiFe2O4) nanopowders and ultrafine poly(methyl methacrylate) (PMMA), dispersing nanoparticles in a polymer matrix, and a uniaxial high-velocity cold compaction process using a cylindrical, hardened steel die and a new technique with relaxation assists have been studied. The focus has been on the particle size distributions of the nanocomposite powder during the milling and on the surface morphology of the nanocomposite-compacted materials after compaction with and without relaxation assists. Experimental results for different milling systems are presented showing the effects of milling time and material ratio. It was found that a longer mixing time give a higher degree of dispersion of the nanopowder on the PMMA particle surfaces. Furthermore, with increasing content of NiFe2O4 nanopowder, the reduction of the particle size was more effective. Different postcompacting profiles, i.e. different energy distributions between the upper and lower parts of the compacted powder bed, lead to different movements of the various particles and particle layers. Uniformity, homogeneity, and densification on the surfaces in the compacted powder are influenced by the postcompacting magnitude and direction. It was found that the relaxation assist device leads to an improvement in the polymer powder compaction process by reducing the expansion of the compacted volume and by reducing the different opposite velocities, giving the compacted composite bed a more homogeneous opposite velocity during the decompacting stage and reducing the delay time between the successive pressure waves.
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| 8. |
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| 9. |
- Ekelund, Maria, et al.
(author)
-
Evaporative loss kinetics of di(2-ethylhexyl)phthalate (DEHP) from pristine DEHP and plasticized PVC
- 2010
-
In: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 95:9, s. 1789-1793
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Journal article (peer-reviewed)abstract
- The migration of di(2-ethylhexyl)phthalate (DEHP) from poly(vinyl chloride) (PVC) to a surrounding gas phase at temperatures below 120 degrees C kinetically is controlled by evaporation. The effects on the DEHP loss rate of nitrogen flow rate, relative humidity and degradation of the plasticizer at 100 degrees C was assessed. The sample mass decreased linearly with time for both pristine DEHP and plasticized PVC at comparable rates, suggesting that a thin film of DEHP was present on the jacketing insulation during desorption. The latter hypothesis was supported by infrared spectroscopy and by the fact that DEHP is an amphiphilic molecule that will tend to aggregate at the surface with the hydrophobic 2-ethylhexyl units at the air interface. The effect on the migration rate of moisture present in the gas phase was negligible. The DEHP loss rate increased in a retarding non-linear fashion with increasing gas flow rate. In one of the experiments, DEHP was accidently degraded as revealed by discoloration, the presence of low molar mass degradation products (liquid chromatography) containing additional carbonyl groups (infrared spectroscopy) and an increase in the evaporation rate at temperatures between 100 and 130 degrees C. (C) 2010 Elsevier Ltd. All rights reserved.
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| 10. |
- Ekelund, Maria, et al.
(author)
-
Long-term performance of poly(vinyl chloride) cables, Part 2 : Migration of plasticizer
- 2008
-
In: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 93:9, s. 1704-1710
-
Journal article (peer-reviewed)abstract
- Cable samples with plasticized poly(vinyl chloride) insulations were aged in air at temperatures between 80 and 155 degrees C. The concentrations of the plasticizer (di-(2-ethylhexyl) phthalate, DEHP) in the insulations of the aged cables were determined by extraction of samples in tetrahydrofuran followed by analysis of the extract by liquid chromatography. The plasticizer concentration data for different ageing times were analysed by numerical methods, fitting Fick's second law with a concentration-dependent diffusivity. The analysis showed that the transport of the plasticizer to the surrounding air phase was controlled by diffusion at 120 and 155 degrees C with an activation energy of 89 kJ mol(-1). The evaporation of the plasticizer from the outer boundary was rate controlling at lower temperatures (<= 100 degrees C), The rate of evaporation was initially constant and independent of the plasticizer concentration at both 80 and 100 degrees C. The activation energy for the initial DEHP loss rate from PVC at these temperatures was the same as that obtained for evaporation of pure DEHP on a glass plate at 60-100 degrees C measured by thermogravimetry, 98 2 kJ mol-1. Furthermore, the evaporation rate of pure DEHP on a glass plate was also of the same order of magnitude as the rate of plasticizer loss from the cable insulation. Extrapolation of the plasticizer loss rate data (from the cable at 80 degrees C and from pure liquid DEHP at temperatures between 60 and 100 IQ to 25 degrees C predicted a maximum loss of plasticizer of 1% over 25 years. This is in accordance with earlier presented data and with the data presented in this report.
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| 11. |
- Jäverberg, Nadejda, 1977-, et al.
(author)
-
Dielectric properties of alumina-filled poly(ethylene-co-butyl acrylate) nanocomposites
- 2010
-
In: 2010 Annual Report Conference on Electrical Insulation and Dielectric Phenomena (CEIDP). - : IEEE. - 9781424494705 ; , s. 5724031-
-
Conference paper (peer-reviewed)abstract
- The dielectric properties of poly (ethylene-co-butyl acrylate) with 13 wt% of butyl acrylate (EBA) filled with alumina nanoparticles (diameter < 50 nm) were studied as a function of particle coating and filler content (2, 6 and 12 wt%). The particles were either unmodified or surface treated either with aminopropyl triethoxysilane or octyltriethoxysilane. The complex permittivity was measured with an IDA200 dielectric spectroscopy analyzer at applied voltage of 200 Vpeak with frequencies varying between 1 mHz and up to 1 kHz at different temperatures (25, 45 and 65°C). Measurements are performed in dry conditions. Pure EBA shows two regions of frequency dispersion in the complex permittivity: a broad relaxation peak in the order of MHz and a characteristic low frequency dispersion that likely is a Maxwell-Wagner response due to a barrier blocking conduction process. Obtained data fits well to a sum of two Havriliak-Negami expressions. Adding nanoparticles to the EBA matrix changes the low frequency dispersion behaviour significantly. Differences in dielectric losses between nanocomposites with different surface treatment seem to be small. The differences in dielectric constant, however, are more pronounced and seem to indicate better dispersion with octylthriethoxysilane surface treatment.
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| 12. |
- Jäverberg, Nadejda, 1977-, et al.
(author)
-
Dielectric Properties of Alumina-filled Poly (ethylene-co-butyl acrylate) Nanocomposites Part I - Dry Studies
- 2012
-
In: IEEE transactions on dielectrics and electrical insulation. - 1070-9878 .- 1558-4135. ; 19:2, s. 383-390
-
Journal article (peer-reviewed)abstract
- The dielectric properties of poly (ethylene-co-butyl acrylate) with 13 wt% of butyl acrylate (EBA) filled with alumina nanoparticles were studied as a function of particle size, particle coating, filler content (2, 6 or 12wt%) and temperature. The particles were either unmodified or surface-treated with either aminopropyltriethoxy silane or octyltriethoxy silane. The complex permittivity was measured with frequencies varying between 1 mHz and up to 1 kHz at different temperatures (25, 45 and 65 degrees C). Measurements were performed in dry conditions. From the dielectric spectroscopy measurements it can be seen that the tan delta for the dry samples is almost independent of the type of the particle coating used. It does, however, depend on the particle size, filler content and temperature.
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| 13. |
- Jäverberg, Nadejda, 1977-, et al.
(author)
-
Dielectric Properties of Alumina-filled Poly (ethylene-co-butyl acrylate) Nanocomposites Part II - Wet Studies
- 2012
-
In: IEEE transactions on dielectrics and electrical insulation. - 1070-9878 .- 1558-4135. ; 19:2, s. 391-399
-
Journal article (peer-reviewed)abstract
- The influence of moisture on the dielectric properties of different types of poly (ethylene-co-butyl acrylate) filled with alumina nanoparticles was systematically investigated by varying the type of aluminum oxide, particle surface treatment and filler content (2, 6 and 12 wt%). The nanoparticles were either unmodified or surface-treated with either aminopropyl triethoxysilane or octyltriethoxy silane. The complex permittivity was measured with an IDA200 dielectric spectroscopy analyzer at applied voltage of 200 V-peak with frequencies varying between 1 mHz and 1 kHz. The measurements were performed at 25 degrees C and relative air humidities of 24, 54 and 86 %. In order to expand the frequency range the HP 4284A precision LCR meter was used for measuring sample impedance at the frequency range of 100 Hz to 1 MHz. From the frequency dependence of dielectric losses it can be seen that absorbed water plays a significant role in determining the dielectric properties of the nanocomposites. The magnitude of tan delta seems to be determined primarily by the particle size and filler content, while the peak frequency is mostly influenced by the amount of absorbed water and the type of particle coating.
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| 14. |
- Nawaz, Sohail, et al.
(author)
-
Stabilizer activity in Al2O3/ poly(ethylene-co-butylacrylate) nanocomposites
-
In: Polymer degradation and stability. - 0141-3910 .- 1873-2321.
-
Journal article (other academic/artistic)abstract
- The stabilizer activity of polymer nanocomposites based on poly(ethylene-co-butylacrylate) and 0.5 - 3 vol. % of two different types of Al2O3 nanoparticles was investigated. The nanoparticles were either functionalized using octyl- or amino-terminated silanes, or used as received. The nanocomposites also contained 0.2 wt. % of Irganox 1010, a hindered phenolic stabilizer. The activity of the stabilizer in the samples was analyzed by Differential Scanning Calorimetry (assessment of Oxidation Induction Time (OIT)), and compared those obtained for the pristine polymers. The stabilizer was adsorbed to the untreated Al2O3 nanoparticles resulting in a significant reduction in OIT. The reduction increased with increasing total surface area of the particles. Surface silanization of the nanoparticles resulted in an increase in OIT, compared to the untreated particles. The activity of the stabilizer was evaluated by OIT after thermal ageing of the nanocomposites in hot-air oven at 90C up to 30 days. No surface oxidation was observed on any of the samples using reflection infrared spectroscopy. The ageing showed that the stabilizer was not irreversibly adsorbed to the particle surfaces, resulting in a gradual release with the ageing time. This resulted in a slower reduction in OIT as function of aging time for the nanocomposites, compared to the pristine polymer. In order for the nanocomposites to exhibit similar or higher OIT values after thermal ageing, compared to unfilled EBA, > 0.5 mg of stabilizer per m2 of octyl- or amine-coated Al2O3 nanoparticles was needed. The loss of stabilizer was controlled by the evaporation rate of the stabilizer from the surface of the samples to the surrounding air.
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| 15. |
- Nordell, Patricia, et al.
(author)
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Preparation and characterization of aluminum oxide-poly(ethylene-co-butyl acrylate) nanocomposites
- 2012
-
In: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628. ; 125:2, s. 975-983
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Journal article (peer-reviewed)abstract
- This article describes the preparation and characterization of composites containing poly(ethylene-co-butyl acrylate) (EBA13 and EBA28 with 13 and 28 wt % butyl acrylate, respectively) and 212 wt % (0.53 vol %) of aluminum oxide nanoparticles (two types differing in specific surface area and hydroxyl-group concentration; uncoated and coated with, respectively, octyltriethoxysilane and aminopropyltriethoxysilane). A greater surface coverage was obtained with aminopropyltriethoxysilane than with octyltriethoxysilane. An overall good dispersion was obtained in the EBA-13 composites prepared by extrusion compounding. Composites with octyltriethoxysilane-coated nanoparticles showed the best dispersion. The addition of the nanoparticles to EBA28 resulted in poor dispersion, probably due to insufficiently high shear forces acting during extrusion mixing which were unable to break down nanoparticle agglomerates. The nanoparticles had no effect on the crystallization kinetics in the EBA13 composites, but in the EBA28 composites the presence of the nanoparticles led to an increase in the crystallization peak temperature, suggesting that the nanoparticles had a nucleating effect in this particular polymer.
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| 16. |
- Qadeer, Muhammad I., et al.
(author)
-
Anomalous high temperature oxidation of Sm 2(Fe,Co,Cu,Zr) 17 particles
- 2012
-
In: Corrosion Science. - : Elsevier BV. - 0010-938X .- 1879-0496. ; 65, s. 453-460
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Journal article (peer-reviewed)abstract
- Sm 2Co 17 alloys are attractive as high temperature permanent magnets; however their magnetic properties are prone to degrade by oxidation. The oxidation mechanism is not clearly understood, and inconsistent results are reported in the literature.This work correlates the oxidation of Sm 2(Co,Fe,Cu,Zr) 17 with microstructural and microchemical changes as a consequence of chemical reaction of alloy particles with their environment at high temperature. Thermogravimetric analysis suggests a change in oxidation mechanism occurs at 550°C. Energy dispersive X-ray spectroscopy suggests this is related to the loss of Sm by sublimation.
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| 17. |
- Qadeer, Muhammad Ifran, et al.
(author)
-
Improved oxidation resistance of SmCo magnetic alloy powders by silanization
- 2013
-
In: Progress in organic coatings. - : Elsevier BV. - 0300-9440 .- 1873-331X. ; 76:1, s. 94-100
-
Research review (peer-reviewed)abstract
- The thermal stability of Sm2Co17 powders coated with four different silanes was studied between 25 degrees C and 500 degrees C and isothermally at 400 degrees C. Thermogravimetry data indicated that the silane-based coatings provided improved oxidation resistance. The microstructural analysis of uncoated powders oxidized for 10 h at 400 degrees C revealed the formation of a featureless ca. 10 mu m thick shell, surrounding the unreacted core. The development of this shell was attributed to the inward diffusion of oxygen, decomposition of intermetallic phases and redistribution of alloying elements. The EDS elemental maps revealed that the shell was rich in O, Fe and Co, and depleted in Sm, Zr and Cu. In the presence of the silane-based coatings the thickness of the shell was reduced by more than 80% (to less than 2 mu m) and the redistribution of alloying elements was insignificant. Based on the thermogravimetric analysis at or above ca. 400 degrees C and the nnicrostructural analysis it was possible to assess the relative effectivity of the different silanes in preventing the oxidation of the SmCo powder. Methyltrimethoxysilane (MTMS), which also formed the thinnest coating, was the best silane. (3-Glycidyloxypropyl)trimethoxysilane, forming a thicker coating, was less effective than MTMS, but superior to the two amine-functionalized silanes ((3-aminopropyl)triethoxysilane and (3-aminopropyl)trimethoxysilane).
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| 18. |
- Qadeer, Muhammad Ifran, et al.
(author)
-
The Effect of Silanisation on Microstructural Stability and Magnetic Properties of the Intermetallic Sm2(Co, Fe, Cu, Zr)17
- 2011
-
In: Materials Research Society Symposium Proceedings. - : Springer Science and Business Media LLC. - 0272-9172 .- 1946-4274. ; 1295, s. 443-448
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Journal article (peer-reviewed)abstract
- The effects of silanising using the coupling agent γ-glycidoxpropyltrimethoxysilane on microstructural stability and magnetic properties of Sm-Co powder particles have been investigated. The silanisation provides structural stability by improving the oxidation resistance at 400oC for 10 hours. The untreated particles undergo microchemical changes by redistribution of alloying elements which mainly accumulate in parallel black and grey streaks in the interior of the particles. The silanised particles after heat treatment show coercivity of 836 Oe and the untreated particles show a much lower coercivity of 376 Oe. The difference in magnetic properties of uncoated particles is caused by diffusion of oxygen and microstructural instability.
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| 19. |
- Shoaib, Muhammad
(author)
-
Discrete element simulation of elasto-plastic shock waves in high-velocity compaction
- 2011
-
Doctoral thesis (other academic/artistic)abstract
- Elasto-plastic shock waves in high-velocity compaction of spherical metal particles are the focus of this thesis which consists of four papers (A-D). The compaction process is modeled by a discrete element method while using elastic and plastic loading, elastic unloading and adhesion at contacts. Paper A investigates the dynamic compaction of a one-dimensional chain of homogenous particles. The development of the elasto-plastic shock waves, its propagation and influence on the compaction process are examined. Simulations yield information on the contact behavior, velocity of the particle and its deformation during dynamic compaction. Effects of changing loading parameters on the compaction process are also discussed. Paper B addresses the non-homogeneity in a chain having; particles of different sizes and materials, voids between the particles and particles with/without adhesion between them. Simulations show transmission and reflection of elasto-plastic shock wave during compaction process. The particle deformation during incident and reflected shocks and particle velocity fluctuations due to voids between particles are simulated. The effects of adhesion on particles separation during unloading stage are also discussed. Paper C develops a simulation model for a high-velocity compaction process with auxiliary pistons, known as relaxation assists, in a compaction assembly. The simulation results reveals that the relaxation assists offer; smooth compaction during loading stage, prevention of the particle separation during unloading stage and conversion of higher kinetic energy of hammer into particles deformation. Furthermore, the influence of various loading elements on compaction process is investigates. These results support the findings of experimental work. Paper D further extends the one-dimensional case of Paper A and B into two-dimensional assembly of particles while adding friction between particles and between particles and container walls. Three particular cases are investigated including closely packed hexagonal, loosely packed random and a non-homogenous assembly of particles of various sizes and materials. Consistent with the one-dimensional case, primary interest is the linking of particle deformation with the elasto-plastic shock wave propagation. Simulations yield information on particle deformation during shock propagation and change in overall particles compaction with the velocity of the hammer. The force exerted by particles on the container walls and rearrangement of the loosely packed particles during dynamic loading are also investigated. Finally, the effects of presence of friction and adhesion on both overall particles deformation and compaction process are simulated.
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| 20. |
- Shoaib, Muhammad, et al.
(author)
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Simulation of high-velocity compaction process with relaxation assists using the discrete element method
- 2012
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In: Powder Technology. - : Elsevier. - 0032-5910 .- 1873-328X. ; 217, s. 394-400
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Journal article (peer-reviewed)abstract
- The discrete element method is used to investigate the high-velocity compaction process with additional piston supports known as relaxation assists. It is shown that by incorporating the relaxation assists in the piston-die assembly, particles can be better locked during the compaction process. The simulation results reveal that relaxation assists offer; smooth compaction during loading stage, prevention of the particle separation during unloading stage and conversion of higher kinetic energy of hammer into particle deformation. Finally, the influences of various loading elements on compaction process and effects of presence of adhesion during unloading stage are investigated. The results support the findings of experimental work.
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| 21. |
- Yu, Wenbin, et al.
(author)
-
Deterioration of polyethylene pipes exposed to water containing chlorine dioxide
- 2011
-
In: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 96:5, s. 790-797
-
Journal article (peer-reviewed)abstract
- Chlorine species used as disinfectants in tap water have a deteriorating effect on many materials including polyethylene. There are only very few scientific reports on the effect on polyethylene pipes of water containing chlorine dioxide. Medium-density polyethylene pipes stabilized with hindered phenol and phosphite antioxidants were pressure tested with water containing 4 ppm chlorine dioxide at 90 degrees C and pH = 6.8 as internal medium. The stabilizers were rapidly consumed towards the inner pipe wall; the rate of consumption was four times greater than in chlorinated water (4 ppm, pH = 6.8) at the same temperature. The depletion of stabilizer occurred far into the pipe wall. A supplementary study on a polymer analogue (squalane) containing the same stabilizer package showed that the consumption of the phenolic antioxidant was 2.5 times faster when exposed water containing chlorine dioxide than on exposure to chlorinated water. The subsequent polymer degradation was an immediate surface reaction. It was confirmed by differential scanning calorimetry, infrared spectroscopy and size exclusion chromatography that in the surface layer which came into contact with the oxidising medium, the amorphous component of the polymer was heavily oxidized leaving a highly crystalline powder with many carboxylic acid chain ends in extended and once-folded chains. Scanning electron microscopy showed that propagation of cracks through the pipe wall was assisted by polymer degradation.
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