No abstract

No abstract

Mullite is one of the most promising engineering materials for applications at elevated temperatures, but has poor mechanical properties at ambient temperature; therefore, it is usually reinforced with particles, fibres or whiskers to improve its properties. Among particles added to mullite are ZrO 2 particles which improve its fracture toughness through the well known process of phase transformation from tetragonal to monoclinic in zirconia particles. The aim of the present work is to explore the utilisation of Algerian kaolin, a-Al 2 O 3 and ZrO 2 to synthesise mullite-ZrO 2 composites through reaction sintering and investigate phase transformation and sintering behaviour of the composites. The raw materials were mixed through planetary ball milling followed by attrition milling. Compacted samples were sintered at temperatures between 1100 and 1600uC for 2 h. The bulk density was measured by the water immersion method. X-ray diffraction (Rietveld method) was used to characterise phases present in the sintered samples. It was found that the zirconia phase retained its tetragonal structure with the addition of up to 16% zirconia. The formation of primary mullite in all samples was complete at 1250uC. The cristobalite started to form at 1150uC, and disappeared at 1300uC in the samples of mullite, and at 1250uC when ZrO 2 was added. The zircon compound ZrSiO 4 started to form at 1250uC and completely disappeared at 1400uC. The increase in ZrO 2 ratio promoted the formation of grains with spherical shape.

No abstract

The aim of this work is the substitution of the bovine bone by the natural phosphate from Djebelel-Onk (Tébessa, East of Algeria). We prepared two composites (bone/Al2O3 and natural phosphate/Al2O3) by reaction sintering. Different experimental techniques, including density, porosity, X-rays diffraction, and SEM techniques, were used to analyze the formation and transformation of phases at different temperatures. From the X-ray diffraction patterns, we put in evidence the formation of several phases. Through these results, we lighted the possibility of preparing bioceramics from natural phosphate (bone and natural phosphate). The presence of the different materials was confirmed by the micrographic observations.

The kinetics of spinel (Al-Si) crystallization from Algerian halloysite (DD1) was investigated using differential thermal analysis. Experiments were carried out on samples between room temperature and 1400• C with constant heating rate from 2 to 20The activation energies measured from isothermal and non-isothermal treatments were 1054.85 and 1140 kJ mol −1 , respectively, for the spinel (Al-Si) formation. The Avrami constant n obtained by the Ligero method and the m parameter obtained by the Matusita method were about 2 for spinel crystallization. This value indicates that the crystallization mechanism of Al-Si spinel phase proceeds by bulk nucleation of the phase formation with a constant number of nuclei and that the three-dimensional growth of crystals is controlled by diffusion.

No abstract

No abstract