Low-temperature oxidation behavior of MoSi_2 powders

The oxidation behavior of molybdenum disilicide （MoSi2） powders at 400, 500, and 600℃ for 12 h in air were investigated by using X-ray diffraction （XRD） and transmission electron microscopic （TEM） techniques. Significant changes were observed in volume, mass, and color. Especially at 500℃, the volume expansion was found to be as high as 7-8 times, the color changed from black to yellow-white, and the mass gain was about 169.34% after 8 h, with SiO2 and MoO3 as main reaction products. The gains in volume and mass were less at 400 and 600℃ compared with those at 500℃, probably due to the less reaction rate at 400℃ and the formation of silica glass scale at 600℃, which would protect the matrix and restrain the diffusion of oxygen and molybdenum. Thus, the accelerated oxidation behavior of MoSi2 powder appeared at 500℃ and the volume expansion was the sign of accelerated oxidation.

Kinetic of Forced Oxidation of Grape Seeds, Walnuts and Corn Germs Oils in the Presence of Antioxidants

The present study aimed to investigate the effectiveness of the use of some antioxidants-α-tocopherol, n-octyl gallate, L-ascorbic acid 6-palmitate and matcha extract (green tea) as inhibitors of grape seeds, walnuts and corn germ oils oxidation. The oxidation was studied in a forced regime during 700 h, by the addition of hydrogen peroxide and Cu2+ ions. The optimal conditions of the accelerated oxidation process in the analysed systems were established. The progress of lipid oxidation was evaluated by measuring the peroxide value (PV) and conjugated dienes and trienes (CD, CT). A series of secondary products of the lipid oxidation were identified: hexanal, octanal and hydroxy-nonadienal. The intensity of the formation of these compounds during oxidation was monitored. The results of this study showed that the oil samples with the addition of antioxidants showed considerably lower oxidation values compared to the control sample. More effective was the action of L-ascorbic acid 6-palmitate and n-octyl gallate, the optimum concentration was 0.1%. An inhibitory effect of the oxidation process was noted for α-tocopherol and matcha extract, the optimal addition concentration was 1%.

Effects of Different Oxidants on HCl-based Pickling Process of 430 Stainless Steel

To shorten the time required for the pickling process and to enhance the quality of ferritic stainless steel plates,the effects of oxidants including hydrogen peroxide（H2O2）,potassium permanganate（KMnO4）,and potassium chlorate（KClO3）on the pickling behavior in HCl-based electrolyte as well as the surface quality of hot-rolled and blasted 430 stainless steel（430-SS）were studied.Experiments were conducted using mass-loss tests,microstructure analyses,potentiodynamic polarization curves,and electrochemical impedance spectroscopy measurements.The results showed that the addition of oxidants substantially accelerated the pickling process of 430-SS by enhancing the cathodic reaction rate and reducing the charge transfer resistance.In electrolytes comprising 5-8mass% HCl at a temperature of 40-60 ℃ and at the same concentration within the range from 0to 2mass%,H2O2 was demonstrated to be superior to KMnO4 and KClO3in accelerating the pickling process.The surface quality of 430-SS pickled in the presence of H2O2 was better than those of specimens pickled in the presence of KMnO4 and KClO3 when the removal of the oxide layer,intergranular corrosion,and surface roughness were collectively considered.When 1mass% H2O2 was added,the mass loss rate of 430-SS was increased by 629%and no residual oxide layer or intergranular corrosion was observed on the surface of the steel;in addition,the roughness was only 1.7μm.H2O2 was determined to be a better oxidant than KMnO4 and KClO3 when the pickling process,surface quality,solution recycling,and environment protection were considered as a whole.