• Applied Microscopy
• /
• v.26 no.3
• /
• pp.379-388
• /
• 1996

Structure of premartensite in $Ti_{50}Ni_{49}Fe_1\;and\;Ti_{50}Ni_{50}$ prepared by self-propagating high temperature synthesis (SHS) method has been investigated by a detailed transmission electron microscopy. $Ti_{50}Ni_{49}Fe_1$ consists of microdomain area and needle type domain area. On the other hand, $Ti_{50}Ni_{50}$ consists of microdomain-free and microdomain area, and needle type domain area. Various types of extra superreflections, such as 1/2<100>, 1/2<110> and 1/4<210> type superreflection have been observed in the selected area electron diffractions from microdomain area. Such extra superreflections are due to transformation from B2 structure to distorted B2 structure or premartensite. The present study shows that incommensurate phase forms as an intermediate phase during martensitic transformation. Particularly, in Fe-free $Ti_{50}Ni_{50}$, two types of matrix phases have been observed, microdomain and microdomain-free area. Types of extra superreflections in $Ti_{50}Ni_{50}$ are different from those in $Ti_{50}Ni_{49}Fe_1$, i.e. 1/7<321> type superreflections have been observed, instead of 1/2<110>, 1/2<100>, 1/4<210> types in $Ti_{50}Ni_{49}Fe_1$.

• Journal of Powder Materials
• /
• v.20 no.5
• /
• pp.332-337
• /
• 2013

Recently, self-propagating high-temperature synthesis (SHS), related to metallic and ceramic powder interactions, has attracted huge interest from more and more researchers, because it can provide an attractive, energy-efficient approach to the synthesis of simple and complex materials. The adiabatic temperature $T_{ad}$ and apparent activation energy analysis of different thermit systems plays an important role in thermodynamic studies on combustion synthesis. After establishing and verifying a mathematic calculation program for predicting adiabatic temperatures, based on the thermodynamic theory of combustion synthesis systems, the adiabatic temperatures of the NiO/Al aluminothermic system during self-propagating high-temperature synthesis were investigated. The effect of a diluting agent additive fraction on combustion velocity was studied. According to the simulation and experimental results, the apparent activation energy was estimated using the Arrhenius diagram of $ln(v/T_{ad}){\sim}/T_{ad}$ based on the combustion equation given by Merzhanov et al. When the temperature exceeds the boiling point of aluminum (2,790 K), the apparent activation energy of the NiO/Al aluminothermic system is $64{\pm}14$ kJ/mol. In contrast, below 2,790 K, the apparent activation energy is $189{\pm}15$ kJ/mol. The process of combustion contributed to the mass-transference of aluminum reactant of the burning compacts. The reliability of the simulation results was experimentally verified.

• Journal of the Korean Ceramic Society
• /
• v.32 no.9
• /
• pp.1085-1091
• /
• 1995

Molybdenum disilicide (MoSi2) was synthesized from Mo, MoO3, Si and Al powders by self-propagating high temperature synthesis (SHS). The effect of processing parameters such as Mo/MoO3 molar ratio, Ar gas pressure in the reactor and pressing pressure of compacts in synthesis of MoSi2 were investigated. h-MoSi2 was transformed into t-MoSi2 with increasing the Mo/MoO3 mole ratio, and only t-MoSi2 phase was identified above 3.5 : 1 (molar ratio). The synthesized phases did not change with the variation of Ar gas pressure and pressing pressure of compacts. It was found that the combustion temperature was above 2,50$0^{\circ}C$. The products were separated into MoSi2 (s) and $\alpha$-Al2O3 by the difference of their specific grativities. Bending strength, hardness and density of sintered specimen exhibited 82 MPa, 5.368 GPa and 5.43 g/㎤, respectively.

• Journal of the Korean Ceramic Society
• /
• v.33 no.10
• /
• pp.1089-1094
• /
• 1996

In this study the formation mechanism of AlN synthesized by SHS(Self-propagating high-temperature Syn-thesis) was studied in order to obtain uniform AlN powder size and morphology. Based on the morphology of AlN synthesized and the calculation of the temperature of Al powder as a function AlN layer thickness the formation mechanism of AlN was proposed.

• Journal of the Korean Ceramic Society
• /
• v.31 no.11
• /
• pp.1283-1292
• /
• 1994

Ultra-fine $\beta$-SiC powders were fabricated by self-propagating high temperature synthesis process (SHS) using chemical furnace. The dependences of the C powders with different surface areas, the molar ratios of C/Si, the weight ratios of chemical fuel content, and pellet diameter-size on synthesis were investigated. Compositional and structural characterization of these powders was carried out by scanning electron micrograph and X-ray diffraction. The $\beta$-SiC powders which had C/Si mole ratio=1.05, 3 times chemical fuel contents, and pellet diameter=20 mm were optimum for synthesis efficiency. By optimizing process-variables, it is possible to fabricate $\beta$-SiC powders which have little secondary phases ($\alpha$-SiC).

• Journal of the Korean Ceramic Society
• /
• v.44 no.3 s.298
• /
• pp.152-156
• /
• 2007

Tungsten carbide powder was synthesized by SHS (self-propagating high-temperature synthesis). Except $WO_{3}$, each concentration of raw material ($WO_{3},\;Mg,\;NaCl,\;Na_{2}CO_{3},\;C$) was investigated. Final product was characterized by XRD and SEM. X-ray data demonstrated that the $NaCl+Na_{2}CO_{3}$ combined mixture has superiority in the WC formation process. Single phase and submicrometer WC powder was synthesized at the temperature below $1600^{\circ}C$. The role of sodium salts in combustion process was discussed, and chemical mechanism of WC formation was proposed. WC powder prepared by salt-assisted combustion synthesis has a size $0.2{\sim}3\;{\mu}m$ and low agglomeration degree.

• Journal of the Korean Ceramic Society
• /
• v.30 no.8
• /
• pp.685-693
• /
• 1993

Boron cabride was prepared from the mixture of metal boron and graphite powders in Argon atmosphere by Self-propagating High-temperature Synthesis Chemical furnace. The most excellent mechanical properties were in the case that Fe was added as a sintering agent before the synthesis of the B4C in the Chemical furnace. Sintered B4C-5wt% Fe specimen showed the relative density of 95%, of theoretical value, and 3-point-flexural strength of 380MPa.

• Journal of the Korean Ceramic Society
• /
• v.33 no.9
• /
• pp.961-968
• /
• 1996

The aluminum nitride was synthesized by the self-propagating high-temperature synthesis(SHS). The synthe-sis was used aluminum powder mixed with AlN powder as reactant and the control factors affected to synthesis were considered compact density pressure of reaction gas AlN diluent content and aluminum powder size. The SHS reaction conducted with a reactant containing 50% AlN diluent under 0.8MPa nitrogen gas pressure yielded a complete conversion of aluminum powder to AlN powders. The size and purity of AlN produced were found to be comparable with that of AlN produced by the carbothermal nitrogen method.

• Journal of the Korean Ceramic Society
• /
• v.33 no.1
• /
• pp.41-48
• /
• 1996

Self-propagating High-temperature Synthesis of Ti+N system has been investigated using the cylindrical high pressure reactor. The nitrogen pressure was varied from 40 to 80 atmosphere and TiNx(x=0.55) powder produced by SHS process was used as a diluent in order to control the reaction. Both the velocity of surface reaction and the ratio of TiN synthesis increased with increasing the nitrogen pressure. As the amount of diluent increases the degree of conversion to titanium nitride increases. Homogenious TiN powder was obtained in the composition 50Ti+50TiN0.94(diluent)

• Journal of the Korean Ceramic Society
• /
• v.28 no.3
• /
• pp.234-242
• /
• 1991

Ti-B system ceramics were prepared by the self-propagating high-temperature synthesis method from the mixture of metal titanium and boron powders The major crystalline phase as a function of boron content was TiB for mixtures containing 0.5 or 1.0mol B, and TiB2 for these containing over 1.3mol B. The combustion mode observed by a high-speed camera was steady-state. The Combustion velocity increased with increasing the boron content. Sintered TiB2 specimen showed the density of 97% of theoretical valve, Vicker's hardness of 2250kg/㎟ for 0.2kg load and three-point-flexure strength of 500MPa.