Sun Jun-cai

Low pressure plasma arc source ion nitriding compared with glow-discharge plasma nitriding of stainless steel

Abstract The nitrided layers produced by low temperature conventional d.c. glow discharge plasma nitriding and low pressure plasma arc source ion nitriding on AISI 304 austenitic stainless steel were studied using X-ray diffraction (XRD), transmission electron microscopy (TEM) and microhardness testing. The surface nitrogen content was determined by electron probe microanalysis (EPMA) and energy dispersive X-ray analysis (EDX). The nitrogen content in the nitrided layer obtained using a low pressure plasma arc source is higher than that in the nitrided layer obtained by d.c. glow discharge plasma nitriding at 420°C. Microstructural analyses by XRD show that both treatments at the same temperature of ∼400°C lead to predominant formation of the f.c.c. nitrogen [N] solid solution phase γ N . However, the concentrations of N and the layer thickness of this phase are clearly different for the various treatments. There are substantial differences in microstructures and phases detected by TEM, which showed that the pure expanded austenite phase with a f.c.c. structure was formed in the nitrided layer for the low pressure plasma arc source, but for glow discharge plasma nitriding, the CrN+γ mixture was present in the nitrided layer even when nitriding at temperatures below 450°C. The reason for this is not clear. When the temperature was increased to 480–500°C, there was no evident difference in the microstructures and phases in nitrided layers obtained by both treatments. The nitrided layers all consisted of CrN+α-Fe phases. Both nitriding methods are able to harden the surface of austenitic stainless steel by nitrogen diffusion forming nitrided layers.

Electrical Properties and Microwave Synthesis of Mixed Rare Earth Oxide Ln0.7Sr0.3-x Cax Co0.9Fe0.1 O3-δ

Abstract In order to lower the raw materials cost and develop a novel cathode materials for intermediate temperature solid oxide fuel cell(ITSOFC), using mixed rare earth replacing the expensive pure La 2 O 3 as the raw materials, the powders of Ln 0.7 Sr 0.3-x Ca x Co 0.9 Fe 0.1 O 3-δ (Ln = the mixed rare earth, x = 0.05, 0.10, 0.15) for the applications as the cathode materials were prepared by microwave sintering process. The crystal structure and the particles morphology of the obtained powders were characterized by XRD and SEM, the electrical conductivity of all samples sintered at 1200 °C for 3 h was also measured as the function of the temperature from 100 to 800 °C by DC four-probe method in air. The experimental results show that due to the influence of mixed rare earth the powders of Ln 0.7 Sr 0.3-x Ca x Co 0.9 Fe 0.1 O 3-δ synthesized at 1200 °C for 0.5 h with the mean particle size of 1 ∼ 20 μm was of perovskite and cubic fluorite phase as well a little SrO phase, the electrical conductivity of the samples decreases with the adding Ca 2+ content, and are all higher than 100 S·cm −1 from 500 to 700 °C when x≤0.10. Ln 0.7 Sr 0.3-x Ca x Co 0.9 Fe 0.1 O 3-δ . can meet the demand of the electrical properties for the cathode materials in ITSOFC.