Weiping SHEN
,
Fei WANG
,
Zhuohui WU
,
Changchun GE
材料科学技术（英）
This paper presents results of combustion synthesis (Self-Propagating High Temperature Synthesis, SHS) of Si3N4 under nitrogen with argon, hydrogen or ammonia. Higher percentages of α-Si3N4 content were obtained in large size cakes in SHS with hydrogen and ammonia than those with argon. Effect of the auxiliary gases for combustion synthesis of Si3N4 on α phase content, on phase transformation of α-Si3N4 to β-Si3N4 in SHS Si3N4 and on oxygen content in SHS Si3N4 were investigated.
关键词:
Combustion synthesis
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Wojciech Kicinski
材料科学技术（英）
The catalytically assisted self-propagating high-temperature synthesis of carbon fibrous nanostructures, where the iron-doped colloidal carbon xerogel is proposed as a catalyst system, was examined. The carbon xerogel was prepared through carbonization of an iron doped organic xerogel at temperatures ranging from 600 to 1050°C. The reaction between calcium carbide and hexachloroethane in the presence of sodium azide is exothermic enough to proceed at a high temperature, self-sustaining regime. The combustion reactions of those mixtures enriched with iron-doped carbon xerogels were conducted in a stainless steel reactor|calorimetric bomb under an initial pressure of 1 MPa of argon. Scanning electron microscopy analysis of the combustion products revealed low yield of various type of carbon fibers (presumably nanotubes), which grew via the tip-growth mechanism. The fibrous nanostructures were found in the vicinity of the spot of ignition, while in the outer and cooler area of the reactor, dusty products with soot-like morphology dominated. No significant correlation between the pyrolysis temperature of the carbon xerogel and the morphology of the obtained carbon fibrous nanostructures was observed.
关键词:
Combustion synthesis
Weiping SHEN
,
Wenbin CAO
,
Changchun GE
,
E.H.Grigoryan
,
A.E.Sytschev
,
A.S.Rogachev
材料科学技术（英）
The effects of Cu and Ni (x=0, 10, 20 and 40 wt pct) and compaction pressures (12, 24, 84 and 108 MPa) on combustion wave velocity and wave front shape for Ti-2B-Cu/Ni and 3Ti-2BN-Cu/Ni bilayered cermets were investigated by a video camera. Since the boiling point of Cu is lower, the wave velocities of specimens are slower. Due to the higher specific heat of Ni than that of Cu, the wave velocities of specimens was slowed down a lot with increasing the Ni diluent. The wave velocity differences of the specimens containing Ni are more than that of the bilayered specimens containing Cu. Wave velocities of the specimens containing Ni increased more than that of the specimens containing Cu when higher pressure was employed for green mixture. The more the wave velocity difference of the bilayer, the more curved the specimen.
关键词:
Combustion synthesis
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null
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G.S.Cho
,
J.H.Yang
,
K.H.Choe
,
K.W.Lee
,
A.Ikenaga
材料科学技术（英）
We focused on the surface reinforcement of ligth weight casting alloys with Ni-Al intermetallic compounds by in-situ combustion reaction to improve the surface properties of non-ferrous casting components. In our previous works, green compact of elemental Ni and Al powders were reacted to form Ni3Al intermetallic compound by SHS (Self-propagating high temperature synthesis) reaction with the heat of molten Al alloy and simultaneously bonded with Al casting alloy. But some defects such as tiny cracks and porosities were remained in the reacted compact. So we applied pressure to prevent thermal cracks and fill up the pores with liquid Al alloy by squeeze casting process. The compressed Al alloy bonded with the Ni3Al intermetallic compound was sectioned and observed by optical microscopy and scanning electron microscopy (SEM). The stoichiometric compositions of the intermetallics formed around the bonded interface and in the reacted compact were identified by energy dispersive spectroscopy (EDS) and electron probe micro analysis (EPMA). Si rich layer was formed on the Al alloy side near the bonded interface by the sequential solidification of Al alloy. The porosities observed in the reacted Ni3Al compact were filled up with the liquid Al alloy. The Si particles from the molten Al alloy were detected in the pores of reacted Ni3Al intermetallic compact. The Al casting alloy and Ni3Al intermetallic compound were joined very soundly by applying pressure to the liquid Al alloy.
关键词:
Joining
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