摘要:

Molybdenum and titanium silicides (MoSi2and Ti5Si3) and their composites have been processed by reaction hot pressing of stoichiometric ratios of mixtures of powders of Mo/Si and TiH2/Si without and with reinforcement powders, respectively at 1500°C in vacuum. MoSi2and Ti5Si3formin situby diffusion of Si atoms (in liquid state) under external pressure into the Mo and Ti lattice, respectively, followed by chemical reaction. The processing parameters and particle sizes of the raw materials affect the density, microstructure, grain size and other properties of the composite. In the MoSi2/20 vol% SiC composite, most of the MoSi2/SiC interfaces are atomically abrupt. However, a few interfaces contain a layer of amorphous SiO25–8 nm thick Fracture toughness and flexural strengths increase with the decrease in grain sizes. Ti5Si3and Ti5Si3/20 vol% TiC composite having similar grain size show a higher hardness and fracture toughness in the composite.

ISSN:0371-750X    

DOI:10.1080/0371750X.1997.10804797

出版商:Taylor & Francis    

年代:1997

数据来源: Taylor

摘要:

An attempt has been made to prepare stoichiometric mullite powders by mixing aluminium nitrate and TEOS in different solvents like distilled water, ethanol and methanol. The sol obtained was spray dried and the powders were calcined in the range 850°-1000°C and sintered at 1600°C. XRD patterns of these powders calcined at 1000°C showed mullite formation in all the solvent systems. Thermal analysis data indicated mullite exotherm below 1000°C. A 10% increase in density was observed on sintering at 1600°C preferentially for methanol derived powder. Fractographs of the sintered mullite generally showed localised densification indicating the inhomo-geneity in the precursor. A controlled hydrolysis of the precursor under different solvent media was indicated to influence the gelation characteristics and bring down the extent of inhomogeneity. A correlation has been presented with respect to history of gelation and the formation of a mullite phase as well as development of sintered microstructure.

ISSN:0371-750X    

DOI:10.1080/0371750X.1997.10804798

出版商:Taylor & Francis    

年代:1997

数据来源: Taylor

摘要:

Alumina membranes for gas separation were made using chelated alkoxide, through the sol-gel route. Use of chelated alkoxides prevents the uncontrolled hydrolysis of aluminium alkoxides and gives rise to a modified precursor that gives finer particle size and lower alumina crystallization temperature. However, chelated alkoxide membranes crack extensively. The type of chelating agent and the amount of chelating agent and water used for hydrolysis were found to affect crack formation. Crack-free membranes could be successfully prepared with alkoxide/chelating agent ratios less than 1: 0.75 using ethylacetoacetate as the chelating agent. These membranes were tested for their integrity using scanning electron microscopy and nitrogen permeability measure-ments. Cracked membranes showed considerably high permeability compared to uncracked ones.

ISSN:0371-750X    

DOI:10.1080/0371750X.1997.10804799

出版商:Taylor & Francis    

年代:1997

数据来源: Taylor

摘要:

Porous and electrically conducting Ni-YSZ cermet is used as fuel electrode for solid oxide fuel eel (SOFC). The synthesis of NI-YSZ cermet through a solution chemistry route is discussed in this paper. The Ni concentration is varied between 10 and 60 volume percent (v/o). Porous structure of these cermets is obtained by proper control of sintering schedule. Electrical properties are evaluated as a function of nickel content. At around 30 v/o of Ni a sudden change in electrical conductivity takes place due to formation of a continuous Ni-chain.

ISSN:0371-750X    

DOI:10.1080/0371750X.1997.10804800

出版商:Taylor & Francis    

年代:1997

数据来源: Taylor

摘要:

An attempt was made to fabricate different ceramic items made of common clays. The fast depletion of higher grade china clays and progressive increase in the cost of fuel necessitated the development of ceramic bodies by incorporating abundantly available low-cost, inferior grade ceramic clays fired at a low temperature but without compromising with the desired properties. With preliminary processing, the physical properties of the clay—both unfired and fired, were systematically investigated in detail. The utilisation of the common clay along with other ceramic ingredients in right proportion in the production of various types of semi-vitreous and vitreous articles was found to be quite viable.

ISSN:0371-750X    

DOI:10.1080/0371750X.1997.10804801

出版商:Taylor & Francis    

年代:1997

数据来源: Taylor

ISSN:0371-750X    

DOI:10.1080/0371750X.1997.10804802

出版商:Taylor & Francis    

年代:1997

数据来源: Taylor