Papers by Keyword: Low Temperature Oxidation

Abstract: This paper reveals the relationship between the changes of active functional groups in coal and gaseous products. Intelligent coal heating and oxidation trial furnace and GC-4085 series gas chromatograph are used for heating and gas analyzing, then use Fourier-transform infrared spectrophotometer instrument (FTIR) tests the reactive functional groups of coal under different temperatures. Analyzing result shows that: alkane side chains of aliphatic react in the whole process of heating and oxidation. -CH₂-, -CH₂-CH₂- and other bridged linkages crack into free radical groups when they are heated. CO, CO₂ and alkane gases are formed in the reaction. At about 110°C, ethane gas appears; stretching vibration of aromatics, carbonyl acid in the plane and unsaturated hydrocarbon key in aromatic hydrocarbon are relatively stable, which start to react after 140°C with very small amounts of ethylene and propylene gases produced. CO, CO₂ and alkane gases, which are produced by the reaction that peripheral side chains of coal adsorb surface complexes and the gases break away from the coal, are important parts for CO, CO₂ and alkane, etc. to generate in low temperature.

Abstract: The paper studied the change of the coal characteristics based on the influence of lignite naturally oxidated in air. The original lignite and lignite naturally oxidated under different time were analyzed by the FTIR technology. The reason that metamorphism of lignite was vulnerable by oxygen was analyzed from the side of coal molecular structure. It indicates that lignite of a low rank coal easily oxidated is mainly because lignite has more active groups in coal molecular such as methyl, methylene, hydroxyl, aromatic ether, oxygen button and ether key. In lignite molecular, side chains of aromatic ring structure unit is firstly oxidized. The bridge button or side chains of coal molecular structure unit are easily oxidized at the same time with the structure of the bridge between units fracturing oxidation. Number of aromatic hydrocarbons remains stable after oxidation. General trend of cycloparafin hydrocarbon as well as aliphatic hydrocarbon are gradually reduced over the oxidized time.

Abstract: Coal spontaneous combustion is a complex procedure of physical and chemical changing, in which the macro characters is the reflection of micro changes of coal molecule structure in low temperature oxidation. In order to understand the essence of coal-oxygen composition, the Fourier transform infrared spectrum apparatus is used to test and analyze different kinds of coal samples in different oxidation temperature. According to main characteristic spectrum peaks, the activity of coal functional groups is studied. The difference and change of the type and quantity of functional groups in different kinds of coal sample in different temperature are analyzed. The relation between the macro structure change and spontaneous combustion property of coal in low temperature oxidation process is discussed.

Abstract: The oxidation of (W,Mo)Si2 powders has been examined at 400, 500 and 600°C for 12.0 hours in air. It was shown that the low temperature oxidation resistance of (W,Mo)Si2 was worse than that of MoSi2, and they showed great changes in mass, volume and colour. At 500°C, the amount of volume expansion of (W,Mo)Si2 was as high as about 7~8 times and color changed from black to yellow after 4.0h with MoO3, WO3, (W,Mo)O3 and amorphous SiO2 as main reaction products. It took about 8.0h to obtain the same results for MoSi2. The mass gain and oxidation rate were relatively slower at 400°C and 600°C than that at 500°C. These were probably due to the lower oxidation rate at 400°C and the protective silica glass on surface of powders formed from the volatilization of MoO3, WO3 and (W,Mo)O3 at 600°C, which would restrain the diffusion of molybdenum from matrix to exterior and oxygen from outside to inside and the further accelerated oxidation.

Abstract: In this paper, single crystals, around 8mm in diameter, of MoSi2 and NbSi2 have been grown by optical heating floating zone method. X-ray analysis confirmed that the as-grown ingots were single phase and single crystalline material. Oxidation behavior of the poly-crystalline and single crystalline MoSi2 and NbSi2 were characterized by measuring their weight changes as a function of exposure time. For arc-melted poly-crystalline samples, MoSi2 and NbSi2 fully turned into white powders after 160 and 3hrs exposure at 773K and 1023K respectively, which is known as the “pesting” phenomenon. As a comparison, no pesting was found in the dense spark plasma sintered (SPS) poly-crystalline samples and single crystals. The weight change of single crystals during exposure is found to be much lower than that of the SPS sample, indicating grain boundary plays an important role in the low temperature oxidation behavior of these two silicides.