| 1. |
- Ekström, Thommy, et al.
(författare)
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Dense single-phase β-sialon ceramics by glass-encapsulated hot isostatic pressing
- 1989
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Ingår i: Journal of Materials Science. - 0022-2461. ; 24:5, s. 1853-1861
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Tidskriftsartikel (refereegranskat)abstract
- Single phase-sialon ceramics, Si6–z Al z O z N8–z , have been prepared from carefully balanced powder mixtures, also taking account of any excess oxygen in the starting materials. Sintering powder compacts in a nitrogen atmosphere (0.1 MPa) at 1800° C or higher transforms the starting mixture into a-sialon solid solution atz-values up to about 4.3, but the sintered material has an open porosity. Addition of 1 wt% Y2O3 to the starting mix improved the sintering behaviour somewhat and the density of the sintered compacts reached 95% of the theoretical value. By glass-encapsulated hot isostatic pressing at 1825° C, however, sintered materials of virtually theoretical density could be obtained, with or without the 1 wt% Y2O3 addition. These latter samples have been studied by X-ray diffraction and electron microscopy, and their hardness and indentation fracture toughness have been measured. It was found that the maximum extension of the-sialon phase composition at 1825° C and 200 MPa pressure is slightly below 4,z 3.85 and about 4.1 at atmospheric pressure, and that the hexagonal unit cell parameters are linear functions of thez-value. The single-phase-sialon ceramics had no residual glassy grain-boundary phase. The grain shape was equi-axed and the grain size increased from about 1m at lowz-values to 5m at highz-values. At lowz-values the hardness at a 98 N load was 1700 and the fracture toughness 3, whereas an increase inz above 1 caused both the hardness and fracture toughness to decrease significantly. Addition of 1 wt % Y2O3 to the starting mix prior to the HIP-sintering gave rise to a small amount of amorphous intergranular phase, changes in grain size and shape, a clear increase in fracture toughness and a moderate decrease in hardness.
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| 2. |
- Gibson, L.J., et al.
(författare)
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Structure and mechanics of the iris leaf
- 1988
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Ingår i: Journal of Materials Science. - 0022-2461 .- 1573-4803. ; 23:9, s. 3041-3048
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Tidskriftsartikel (refereegranskat)abstract
- The structure of the iris leaf resembles that of a sandwich beam with fibre composite faces separated by a low-density foam core. Such structures have a high specific stiffness because the separation of the faces by the lightweight core increases the moment of inertia of the section with little increase in weight. In this paper we examine the structure of the leaf of the bearded iris and show that its flexural stiffness can be explained in terms of the mechanics of sandwich beams
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| 3. |
- Lindberg, Henrik, et al.
(författare)
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Chlorine loss and mass loss from Polyvinylchloride and polyvinylidenchloride under the electron beam
- 1985
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Ingår i: Journal of Materials Science. - 0022-2461 .- 1573-4803. ; 20:6, s. 2225-2232
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Tidskriftsartikel (refereegranskat)abstract
- The loss of chlorine during the irradiation of PVC and PVDC in the electron microscope has been measured by the decay of the X-ray chlorine Kα signal. A number of factors affecting the measured beam damage curves have been considered and the experimental errors reduced to ±10%. The results show that the chlorine decay curves can be best described by the sum of two exponentials, corresponding to the two different chlorine decay processes, these being: the dehydrochlorination of the polymer molecules and the dehydrochlorination of the polyene structure formed by the beam damage. The higher initial chlorine content of PVDC compared to PVC will result in a larger amount of chlorine atoms reacting with the polyene structure, which is more stable in the electron beam than the undamaged polymer. The chlorine loss, measured by X-ray analysis, has been compared to the mass loss, measured by energy loss analysis, and also with the volume changes of isolated spherical PVC particles. It has been concluded that the mass loss is almost entirely due to chlorine loss and that the residual structure has a density similar to the undamaged PVC.
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| 4. |
- Lindberg, Henrik, et al.
(författare)
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Electron beam damage of some chlorine containing polymers and PVC blends
- 1989
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Ingår i: Journal of Materials Science. - 0022-2461 .- 1573-4803. ; 24:8, s. 2825-2832
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Tidskriftsartikel (refereegranskat)abstract
- The electron beam damage of PVC, PVDC, chlorinated PE, chlorosulphonated PE (Hypalon) and chloroendic acid polyester has been studied by chlorine loss and mass loss measurements. The mass loss decay curves have been recalculated for true mass loss and correlated with the X-ray measurements of chlorine loss. It is shown that the major mechanism of degradation in these polymers is dehydrochlorination. The rate of dehydrochlorination is dependent on the chemical structure of the polymer, and in particular on the availability of hydrogen for HCl formation. However, in case of chloroendic acid polyester, more complicated volatile chlorinated compounds are also formed. The dehydrochlorination rate and mass loss of miscible PVC blends, namely PVC with organotin stabilizer, PMMA, PCL and SAN have been studied. The rate of chlorine loss from PVC was found to be unchanged for all blends except for PMMA and PCL, where it slightly increased due to the chemical reaction between the molecular fragments of both polymers. The differences between the thermal degradation and electron beam damage are also discussed.
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