Tribological Behaviour of Alumina Ceramics with Nano TiO2 as a sintering aid in Non-Conformal Contact

The study emphasized the sintering behaviour and tribo-mechanical properties of alumina ceramics by nano TiO2 addition as a sintering aid. With increase in sintering temperature, the bulk density of alumina has increased gradually and optimized at 1600°C. The optimizing effect of densification at 1600°C is 98.25% by the addition of 1 wt.% nano TiO2. The maximum solid solubility of titania in alumina grains was at 1600°C, causes optimisation of densification by 1 wt. % addition. The excess addition of TiO2 formed low dense Al2TiO5, appear as a secondary phase at grain boundaries and does not significantly improved densification. Fracture toughness increases and coefficient of friction decreases with the addition of nano TiO2 in alumina matrix. The 1wt.% nano TiO2 addition improved hardness to 8.82% and reduces specific wear rate to 45.56%. The 1wt.% nano TiO2 addition greatly influenced the microstructure of sintered Al2O3. The morphology was sharply changed from hexagonal columnar shape to order sub round orientation which also directly impact the tribo-mechanical properties of sintered alumina. The 1wt.% addition substantially decreases wear track depth as observed by 3D surface profilometer. Microscopic observation of the worn-out surface showed that wearing is majorly caused by plastic deformation and abrasion.

The use of fluorinated alumina as a support of the sulfated zirconia catalyst for isomerization of hexane

The study considers the effect of fluorine doping of the alumina matrix used for the synthesis of supported sulfated zirconia catalysts. Hydrofluoric acid served as a fluorinating agent. The addition of fluorine was shown to affect the textural characteristics of the Al2O3 matrix and hence the surface area of sulfated zirconia catalysts based on the doped systems. It was found that the introduction of fluorine into the catalysts increases their activity (the conversion of hexane) and the yield of high-octane isomer 2,2-dimethylbutane.

The promotion of supported sulfated zirconia catalysts by iron and manganese sulfates

The study considers the effect of iron and manganese introduction on the textural characteristics and phase composition of the alumina matrix used as a support for sulfated zirconia catalysts in hexane isomerization. The additives introduced during plasticization of aluminum hydroxide essentially enhance the catalytic activity, which is expressed in terms of hexane conversion, and the selectivity of isomerization toward the formation of hexane isomers. The distinctive feature of the doped catalysts is the formation of acid sites with LAS/BAS ≥ 2, which promote an increase in the yield of isomers and particularly the yield of high-octane 2,2-dimethylbutane.

Ablation of Al2O3f/Al2O3 Composites Under Oxyacetylene Torch Flame

Continuous alumina fibers reinforced alumina matrix composites (Al2O3f/Al2O3 composites) were produced by following the sol-gel process effectively, while the ablation behavior was analyzed and compared by means of oxyacetylene torch flame test. The results suggested that Al2O3f/Al2O3 composites showed excellent ablation resistance, but no obvious cracks, pits or holes after ablation. The mass and thickness of the sample were barely changed after ablation. After ablation for 120s at 1800℃, the surface morphology of composite material showed no significant change. With the increase of ablation temperature, there were visible signs of high-temperature and high-pressure gas erosion found on the surface of composites. Then, the molten black material began to appear on the surface, and the delamination phenomenon occurred finally. After ablation at 2200℃, the surface of composites became uneven, manifesting large-scale black molten particles, and the area affected by ablation was increasing obvious.