The effect of the sintering atmospheres (vacuum, N_2, Ar) on the microstructures and properties of the TiC based cermets was studied using XRD, SEM/BSE and energy dispersive spectrometer. Compared with the alloy sinte...The effect of the sintering atmospheres (vacuum, N_2, Ar) on the microstructures and properties of the TiC based cermets was studied using XRD, SEM/BSE and energy dispersive spectrometer. Compared with the alloy sintered in vacuum, the carbon content of the specimen sintered in N_2 and Ar is lower by 0.5%; and the nitrogen content is higher by 0.3% when sintered in nitrogen. The central part of the ring structure may be carbide with either a high W or Ti content. The ring structures are (Ti, W, Ta, Mo, Co, Ni)C solid solutions with different metallic elements and distributions. The composition of the binder phase is (Co, Ni) solid solution with different Ti, W, Ta, Mo, C contents. The structures are uniform for the cermets sintered in vacuum and the properties are the best. When sintered in Ar or N2, the O_2 and N2 in the atmosphere take part in the sintering reaction to break the carbon balance in the cermets to form a shell structure and defects, which results in poor density, microhardness (HV) and transverse rupture strength (TRS).展开更多
For further understanding of self-heating of coal, we tested the reactions of seven different ranks of coal under inert atmosphere. In the test, 50-gram of coal sample ranged from 0.18 mm to 0.38 mm was put into a spe...For further understanding of self-heating of coal, we tested the reactions of seven different ranks of coal under inert atmosphere. In the test, 50-gram of coal sample ranged from 0.18 mm to 0.38 mm was put into a special designed copper reaction vessel and let pure nitrogen to flow into the coal sample from the bottom at a rate of 100 mL/min. The programmed temperature enclosure was run at a programmed rate of 0.8 ~C/min. The concentration of the carbon oxides and the coal temperature were tested. The results show that the coal reactions under inert atmosphere can generate CO and C02. The reactions under inert atmosphere are affected by coal ranks, initial pore structure of coal and sulfur content. For low ranks of coal, the productions of carbon oxides are piecewise. The coal temperature is lower than the surrounding temperature throughout the reactions under inert atmosphere, but it rises quickly and reaches a crossing point temperature in the later stage under dry-air atmosphere. Based on the analysis, it indicates the self-reaction of initial active groups exists in the self-heating of coal besides the reactions in the two parallel reactions model. Spontaneous combustion of coal is due to both the oxidation heat accumulation and the chain reaction. A new reaction model of self-heating of coal was orooosed.展开更多
基金Foundation item: Project(2002AA331090) supported by the Hi-tech Research and Development Program of China Project(06D073) supported by Scientific Research Fund of Education Department of Hunan Province
文摘The effect of the sintering atmospheres (vacuum, N_2, Ar) on the microstructures and properties of the TiC based cermets was studied using XRD, SEM/BSE and energy dispersive spectrometer. Compared with the alloy sintered in vacuum, the carbon content of the specimen sintered in N_2 and Ar is lower by 0.5%; and the nitrogen content is higher by 0.3% when sintered in nitrogen. The central part of the ring structure may be carbide with either a high W or Ti content. The ring structures are (Ti, W, Ta, Mo, Co, Ni)C solid solutions with different metallic elements and distributions. The composition of the binder phase is (Co, Ni) solid solution with different Ti, W, Ta, Mo, C contents. The structures are uniform for the cermets sintered in vacuum and the properties are the best. When sintered in Ar or N2, the O_2 and N2 in the atmosphere take part in the sintering reaction to break the carbon balance in the cermets to form a shell structure and defects, which results in poor density, microhardness (HV) and transverse rupture strength (TRS).
基金Financial supports for this research provided by the National Natural Science Foundation of China (No. 50927403)the Fundamental Research Funds for the Central Universities (No.2011RC06)the Jiangsu Natural Science Foundation (No.BK2009004)
文摘For further understanding of self-heating of coal, we tested the reactions of seven different ranks of coal under inert atmosphere. In the test, 50-gram of coal sample ranged from 0.18 mm to 0.38 mm was put into a special designed copper reaction vessel and let pure nitrogen to flow into the coal sample from the bottom at a rate of 100 mL/min. The programmed temperature enclosure was run at a programmed rate of 0.8 ~C/min. The concentration of the carbon oxides and the coal temperature were tested. The results show that the coal reactions under inert atmosphere can generate CO and C02. The reactions under inert atmosphere are affected by coal ranks, initial pore structure of coal and sulfur content. For low ranks of coal, the productions of carbon oxides are piecewise. The coal temperature is lower than the surrounding temperature throughout the reactions under inert atmosphere, but it rises quickly and reaches a crossing point temperature in the later stage under dry-air atmosphere. Based on the analysis, it indicates the self-reaction of initial active groups exists in the self-heating of coal besides the reactions in the two parallel reactions model. Spontaneous combustion of coal is due to both the oxidation heat accumulation and the chain reaction. A new reaction model of self-heating of coal was orooosed.