J. Tatami

Synthesis of Mg-α SiAlON powders from talc and halloysite clay minerals

Abstract Carbothermal reduction and nitridation (CRN) of SiO 2 is an attractive method to manufacture Si 3 N 4 powders with controlled grain morphology. Some inexpensive raw materials were previously used to synthesize β-sialon powder, resulting in cheaper products to be useful for some engineering applications. In this work, Mg-α sialon (Mg x Si 12− m − n Al m + n O n N 16− n ) powders were achieved by CRN of mixtures of talc (Mg 3 (Si 2 O 5 ) 2 (OH) 2 ) and NZ halloysite clay (Al 2 Si 2 O 5 (OH) 4 ) minerals. The final products consisted mainly of α-sialon and β-sialon phases. Small amounts of 15R AlN-polytypoid and SiC were also identified in the synthesized powder. By adding a small amount of α-Si 3 N 4 powder as seeds to the starting composition, the conversion rate of α-sialon phase was significantly enhanced and powders with up to 90 wt% of α-sialon were produced.

Inhomogeneous grain growth and elongation of Dy-α sialon ceramics at temperatures above 1800°C

Abstract A series of samples with dysprosium α-sialon compositions and different amounts of sintering additives has been fabricated from α-Si 3 N 4 , AlN, Al 2 O3 and Dy 2 O 3 starting powders, using pressureless sintering (PLS) at 1800°C plus gas pressure sintering (GPS) at the same and higher temperatures under a relatively low gas pressure of 0.9 MPa N 2 . The resultant α-sialon grains show significantly different features, such as regularly fine and equiaxed, elongated, and even a few extraordinarily large with high aspect ratio grains in the fine matrix, which has rarely been observed in α′ ceramics. It is suggested that the temperature strongly influences the grain morphologies of α-sialon, playing an important role particularly in the latter stage of the “nucleation-growth” process. Such a kind of microstructural morphology as mixed with equiaxed and elongated grains toughens the α-sialon ceramics and leaves them still hard as usual. Overly high temperature treatment leads to the preferential growth of a few grains which become excessively large and long, and do not significantly improve the materials toughness.

An improvement of thermal conduction of activated carbon by adding graphite

This study was performed to improve thermal conduction of granular activated carbon by adding graphite powder. Granular activated carbons were fabricated from anthracites and graphite powders using a binder pitch, and then activated in a nitrogen-carbon dioxide gas at 850°C. Additions of graphite from 20 to 30 wt% were considered to be suitable for thermal conductivity and n-butane adsorption power. The thermal conductivities of such granular activated carbons were 20 times those of activated carbons without graphite. A fixed bed filled with the granular or powder activated carbons containing graphite were never ignited even though the inside of the bed was directly heated.