Effects of oxidation of SiC aggregates on the sintering behaviour and microstructures of SiC-CaAl12O19 composite refractories

In order to develop chrome-free refractory materials applicable in coal slurry gasification, SiC-CaAl12O19 (SiC-CA6) composite refractories were developed and prepared by using SiC aggregates and CA6 powders as main raw materials. The sintering behaviour of the composites was investigated. After firing at different temperatures under CO atmosphere, the effects of oxidation of SiC aggregates on the sintering behaviour and microstructures of SiC-CA6 composite refractorieswere investigated. SiC-CA6 composites could not be sintered when firing temperature was lower than 1500?C. SiC had a passive oxidation and the oxidation components were able to react with CA6 to form CaAl2Si2O8. The CaAl2Si2O8 melted into liquid when sintering temperature was in the range of 1500-1600?C, which promoted the sintering process of the SiC-CA6 composites. At temperatures above 1600 ?C, an active oxidation of SiC occurred. Simultaneously, SiC could also reacted with the SiO2(s,l) to form SiO, leading to the precipitation of Al2O3 and CaO in the liquid to generate plate-like CA6. Above this temperature, the sintering of the SiC-CA6 composite refractories was affected by the growth of CA6 and oxidation of SiC. This work demonstrates that the optimal sintering temperature for the SiC-CA6 composite refractories was 1600?C.

Enhanced removal of chromium(vi) by Fe(iii)-reducing bacterium coated ZVI for wastewater treatment: batch and column experiments

To effectively destroy the structure of the passive oxidation film covering zero-valent iron (ZVI), an Fe(iii)-reducing strain, Morganella sp., was isolated from anaerobic activated sludge and coated on the ZVI.

Gel Oxidation of Titanium at Low Concentration of Sodium Hydroxide (NaOH)

Gel oxidation is an effective thermochemical method for the preparation of bioactive titanium surfaces. This study aims to investigate the effect of low concentration of NaOH on gel oxidation of titanium when subjected to various temperatures. Titanium foils were soaked in NaOH aqueous solutions with the concentration of 0.5 M or 1.0 M, followed by oxidation in the range of 400°C to 800°C. The crystallinity of the film was determined using glancing angle X-ray diffraction (GAXRD). The microstructures were examined using field emission scanning electron microscope (FESEM). Focused ion beam milling (FIB) was used for cross-sectional imaging. At low NaOH concentration, the amount of sodium titanate hydrogel, if present, was too low to detect after gelation. Subsequent oxidation at 400°C was insufficient to form sufficient anatase and/or rutile to be detectable by GAXRD. Oxidation at 600°C and 800°C resulted in the detection of rutile. The concentration of the NaOH solution was important that it affected the dissolution or retention of the anatase passive oxidation layer whereby low concentrations of the NaOH solution (0.5 M and 1.0 M) resulted in a low degree of dissolution.

Stability of SiC and SiO2 in Helium with Little Water Vapor

The stability of SiC and SiO2 in helium with little water vapor is studied in this paper in order to confirm whether they can service as anti-oxidation layers on the surface of fuel elements of high temperature gas-cooled reactor (HTR) under water-ingress accident. Through thermodynamic analysis, it is found that the influence factor controlling the critical temperature of passive oxidation for SiC in He-H2O is the partial pressure of H2O; the critical temperature of passive oxidation for SiC increases with the partial pressure of H2O. The influence factors controlling the critical temperature of decomposition for SiO2 are the partial pressure of H2O and the amount of H2O in gas for 1 mol SiO2, the critical temperature of decomposition for SiO2 increases with the partial pressure of H2O while it decreases with the amount of H2O in gas for 1 mol SiO2. SiO2/SiC composite coating is more suitable than SiC coating in He-H2O with little H2O.