Liu Yi-han

Preparation and Characterization of Graphite Powder Covered with CeO2

Abstract In order to improve the wetting properties of graphite with Al melt and reduce the oxidation of the graphite, by which the segregation of components during the liquid-stir-casting process could be prevented. In this paper, a uniform thin nano-film of CeO 2 , about 20 nm thick, was successfully prepared onto graphite powder surface by heterogeneous nu-cleation process. The results show that an obvious chemical reaction did exit between CeO 2 film and graphite with the formation of Ce-O-C bond, leading to a shift of the binding energy of C and Ce. The cover with CeO 2 film illustrates a distinct change of surface state of graphite with a decrease of angle of contact.

Effect of MnO2 Addition on Early‐Stage Sintering Behavior and Properties of NiFe2O4 Ceramics

The samples with small amounts of MnO2 (0, 0.5, 1.0, 2.5 wt%, respectively) were prepared via ball-milling process and two-step sintering process from commercial powders (i.e. Fe2O3, NiO and MnO2). Microstructure features, phase transformation, the early-stage sintering behavior and mechanical properties of Mn-doped NiFe2O4 samples have been investigated. Results indicate that the reduction of MnO2 into Mn2O3 and following the reduction of Mn2O3 into MnO existed in sintering process. No new phases are detected in the matrix, the crystalline structures of ceramic matrix are still NiFe2O4 spinel structure. MnO2 addition can promote the sintering process. The temperature for 1 wt% MnO2-doped samples to reach the maximum shrinkage rate is 59 °C lower than that of un-doped samples.