Carbon-Coated Nanopowder as Sintering Aid for Water-Atomized Iron Powder

The influence of carbon coating on the nanopowder when used as a sintering aid for water-atomized iron powder is explored. Iron nanopowder without such a coating was used as a reference sintering aid to isolate and depict the influence of the carbon coating. Both nanopowder variants were characterized using XPS and HRTEM, and the results showed a core-shell structure for both nanopowder variants. Iron nanopowder is covered by a 3-4 nm thick iron oxide layer, while the carbon-coated nanopowder is encapsulated with a number of nanometric carbon layers. Thermogravimetry carried out in a pure hydrogen environment shows a multipeak behaviour for carbon-coated nanopowder, while a single peak behaviour is observed for the iron nanopowder. This difference was correlated with chemical analysis. Two types of micro/nanobimodal powders were obtained by mixing the nanopowder with water-atomized iron powder. An improved linear shrinkage was observed when carbon-coated iron nanopowder was added. This can be explained by the reduced surface diffusion in the nanopowder due to the carbon coating, which allows the nanopowder to sinter at higher temperatures and improves densification.

Effect of Carbon Source on Synthesis of Carbon Coated Lithium Titanate

Carbon coated lithium titanate (Li4Ti5O12/C) was obtained by a facile solid state approach in inert Ar atmosphere. The composition, morphology, residual carbon content and Ti valence of the samples were systematically investigated. The carbon content of Li4Ti5O12/C should be optimized, since excess carbon in the composite leads to the reduction of Ti (IV) to form Ti (III), which results in large irreversible capacity of Li4Ti5O12/C. With an optimal carbon content of 0.68wt%, the Li4Ti5O12/C sample shows high rate capabilities and good cycling ability, delivering discharge capacities of 160.8 mAh/g at 5C. The superior high rate properties are ascribed to the specific nanostructures, which enables fast electronic and ionic transport by introducing carbon coating and decreasing the particle size of lithium titanate.