• S RAY

Articles written in Bulletin of Materials Science

• Fracture of particulate composites

A thermodynamic analysis of the process of fracture in elastically deformable composites is formulated. The critical dimensions leading either to particle fracture or to matrix-particle decohesion are identified. Fracture in plastically deformable composites is discussed in the light of the experimental evidence regarding void or cavity nucleation. Models of void growth under the application of stress and the role of void growth in causing failure are described in brief.

• Electron microscopy study of chemically deposited Ni-P films

The structure of electroless thin films of Ni-P has been studied. The microstructure and the selected area diffraction pattern of the samples reveal that certain samples transform to crystalline Ni with P in solid solution by nucleation and growth, whereas others transform to crystalline state by growth alone. The former set of thin films having a P-content of 19–21 at.% is characterized as amorphous. Films with a P-content of 13–15 at.% fall in the latter category and are characterized as microcrystalline. Those with a P-content of 16–18 at.% contain both amorphous and microcrystalline regions.

• Deformation behaviour of materials—A phenomenological approach

The quantitative description of stress-strain behaviour through appropriate models for structural evolution of materials has been fairly successful in explaining both the monotonic and transient stress-strain behaviour of materials. Further exploration of this approach may lead to detailed understanding of evolution parameters and the influence of metallurgical variables. Thus, a quantitative method for alloy design for the purpose of structural applications at ambient and elevated temperature may emerge.

• Degana tungsten project—present plant practice and future scenario

Experiments/testworks were carried out on Degana tungsten ore by various R & D organizations to recover the strategic mineral wolframite. Process flowsheet developed after tests on the dump ore assaying 0·151% WO3 is being tried on a very small scale till the 150 tpd pilot beneficiation plant is commissioned. Tungsten bearing granite samples were also found amenable to physical benefication. Hence 168 Mt granitic resources analysing 0·08% WO3 has ushered a hope for large scale exploitation subject to detailed exploration. By-product recovery of lithium, caesium, rubidium and some other trace elements, if feasible, will be of added advantage.

• Chemical nature of catalysts of oxide nanoparticles in environment prevailing during growth of carbon nanostructures by CCVD

Carbon nanostructures (CNS) are often grown using oxide nanoparticles as catalyst in chemical vapour deposition and these oxides are not expected to survive as such during growth. In the present study, the catalysts of cobalt- and nickel oxide-based nanoparticles of sizes varying over a range have been reduced at 575$^{\circ}$C under environment resulting from the introduction of C$_2$H$_2$ $+$ NH$_3$ during growth of CNS as well as under introductionof C$_2$H$_2$ and NH$_3$ separately. The structure of the reduced nanoparticles is often different from the equilibrium structure of the bulk. Nanoparticles of cobalt oxide with and without doping by copper oxide are reduced to cobalt alloy or cobalt nanoparticles having fcc structure, but the rate of reduction is relatively less in NH$_3$ environment. However, reduced nickel oxide nanoparticles with and without doping shows a mix of fcc and hcp phases. The presence of hydrogen and nitrogen in the environment appears to discourage the formation of hcp nickel as inferred from the results in NH$_3$ environment. Cobalt carbide forms when the 10 wt.% or less doped cobalt oxide is reduced in C$_2$H$_2$ $+$ NH$_3$ environment. At higher level of doping of 20 wt.%, separate metallic phase of copper appears andcarbide formation gets suppressed.

• # Bulletin of Materials Science

Volume 44, 2021
All articles
Continuous Article Publishing mode

• # Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020