Papers by Author: Li Qun Ma

Abstract: Failure analysis of fracture of 35CrMo bolt was investigated. It was analyzed by means of morphology and microstructure analysis, chemical composition analysis, hydrogen content analysis, scanning electron microscope (SEM) micro-morphology of fracture surface, electronic differential system (EDS) corrosion products analysis. The results showed that the cause of fracture of 35CrMo bolt was stress corrosion cracking. Working stress of the bolt，H2S in surroundings and the high hardness of the bolt combined caused cracking of the bolt. Suitable heat treatment for the 35CrMo bolt is suggested.

Abstract: The properties and precipitation rules of secondary phases generated during isothermal aging of duplex stainless steels and factors affecting the precipitates were reviewed in this article. These secondary phases include carbides(M23C6,M7C3), nitrides(Cr2N,CrN) and intermetallic phases(σ-phase, χ-phase, Fe3Cr3Mo2Si2, R-phase, π-phase, α′-phase). With the right understanding about the phases, the aim is the suitable heat-treating processes would be chose to avoid the unfavorable influences of secondary phases.

Abstract: Cu₂O/Cu composite particles were successfully synthesized by a novel facile template-free chemical reduction route at room temperature. X-ray diffraction (XRD) results showed that the sample mainly consisted of the Cu₂O phase coexisting with a few Cu phases. Scanning electron microscopy (SEM) images indicated that the regular particles with a cubic shape about 2-3 μm is Cu₂O. In addition, the electrochemical behavior of the Cu₂O/Cu composite electrode and copper electrode during the charging and discharging process were both investigated. It was found that the first discharge capacity of Cu₂O/Cu composite electrode was up to 650 mAh•g^-1, which is much higher than the theoretical capacity of Cu₂O (about 375 mAh•g^-1). The additional capacity is attributed to the electrodeposition of lithium on pure copper, confirmed by the electrochemical property of copper as the anode material of the lithium-ion battery. The copper electrode presented a high discharge capacity of 280 mAh•g^-1 during the first cycle. However, a large irreversible capacity as same as the cuprous oxide electrode was observed during the first charging process. It is indicated that deposition of lithium on the Cu particle surface acts as a barrier preventing the contact between the Cu and the electrolyte. Furthermore, the Cu₂O/Cu composite electrode can exhibit reversible capacity of 210 mAh•g^-1 at a charge-discharge rate of 30 mA•g^-1 after 40 cycles.