• 한국재료학회지
• /
• 제18권3호
• /
• pp.123-127
• /
• 2008

The production of tin oxide ($SnO_2$) microrods on iridium (Ir)-coated substrates was achieved through the thermal evaporation of Sn powders in which a sufficiently high $O_2$ partial pressure was employed. Scanning electron microscopy revealed that the product consisted of microrods with diameters that ranged from 0.9 to $40\;{\mu}m$. X-ray diffraction, high-resolution transmission electron microscopy, and selected area electron diffraction indicated that the microrods were $SnO_2$ with a rutile structure. As the microrod tips were free of metal particles, it was determined that the growth of $SnO_2$ microrods via the present route was dominated by a vapor-solid mechanism. The thickening of rod-like structures was related to the utilization of sufficiently high $O_2$ partial pressure during the synthesis process, whereas low $O_2$ partial pressure facilitated the production of thin rods.

• 한국세라믹학회지
• /
• 제31권6호
• /
• pp.637-642
• /
• 1994

Using SHS(Self-propagating High-temperature Synthesis) method, the optimum synthetic condition of titanium carbonitride was established by controlling the parameters such as relative density of mixture (Ti+C), nitrogen pressure, additive amounts of titanium hydride(TiH1.924) and protecting heat loss. Under 1 atm nitrogen pressure, nitridation ratio with changing relative density of the sample compacts has a maximum (87.2%) at about 55%, and in the case of enveloping the pellet with a quartz tube, the highest nitridation ratio of 90% was obtained at about 68%. At relative density of 55%, nitridation ratio with the nitrogen pressure has a miximum (87.3%) at 7 atm. As the amounts of additive titanium hydride increased, nitridation ratio decreased at below 7 atm nitrogen pressure and, increased at above this pressure until percent of addition percent reached 15 wt% and decreased abruptly upon futher increases in titanium hydride. In the synthesis of TiCxNy by combustion reaction, heat transfer from combustion zone to preheating zone and nitrogen gas penetration into the compact were found to be important factors affecting the TiCxNy formation. It was difficult to obtain high nitridation ratio when the conbustion temperature was either too high or too low, and it seems that the retention of high temperature after a combustion wave sweeped through the reactant mixture pellet is critical to obtain a satisfactory nitridation ratio.

• 한국초전도학회:학술대회논문집
• /
• 한국초전도학회 2000년도 High Temperature Superconductivity Vol.X
• /
• pp.1-1
• /
• 2000

The infinite layer compound $ACuO_2$, (A-Alkaline earth) consists of infinite stacking of $CuO_2$ planes separated only by alkaline earth ions. This compound attracted much attention because it contains only key ingredient of all cuprate high temperature superconductor; $CuO_2$ plane with controllable carrier concentration without charge reservoir block. High pressure synthesis method has been found to be preferable for this system due to its ability of doping various lanthanide ion into A site with larger superconducting volume fraction. But rigorous study on this rudimentary compound has been hindered by insufficient quality of sample. Especially superconductlng volume fraction was often too small to identify its origin. In this presentation, we report high pressure synthesis of $Sr_{0.9}Ln_{0.1}CuO_2$ (Ln=La, Sm). By controlling the heating temperature precisely during high pressure synthesis we could have superconductors with quite high superconducting volume fraction for this compound. The magnetic properties of the graln aligned samples show very different behavior compared to the cuprate high temperature superconductors. Details will be discussed.

• 한국분말재료학회지
• /
• 제2권2호
• /
• pp.158-164
• /
• 1995

Synthesis of the NiTi shape memory alloy using the thermal explosion mode of the self-propagating high-temperature synthesis has been investigated. The significant fractions of intermetallics phases were found to form at the Ti/Ni powder interface during the heating to the ignition temperature and seemed to influence the relative fraction of phases in the final products. As the heating rate to the ignition temperature was increased, the combustion temperature and the fraction of NiTi in the final reaction products were increased. The synthesis reaction under 70 MPa compressive pressure yielded a reaction product with 98% theoretical density.

• The Korean Journal of Ceramics
• /
• 제6권3호
• /
• pp.250-257
• /
• 2000

The feasibility of synthesizing SiC-AlN solid solution by field-activated combustion synthesis was demonstrated. At lower fields of 8-16.5V/cm, composites of AlN-rich and SiC-rich phases were synthesized, but at fields of 25-30 V/cm, the product was a 2H structure solid solution. Combustion synthesis of the solid solution by nitridation of aluminum with silicon carbide under a nitrogen gas pressure of 4-8 MPa was also investigated. The maximum combustion temperature and wave propagation velocity were found to be influenced by the electric field in the field-activated combustion synthesis, and by the green density and nitrogen pressure in the combustion nitridation. In both cases the formation of solid solutions is complete within seconds, considerably faster than in conventional methods which require hours.

• 한국광물학회지
• /
• 제10권1호
• /
• pp.18-32
• /
• 1997

Analysis of geological data, relating to occurrence and formation of diamonds as well as host rocks, inclined author to have different outlook on the diamond genesis and to establish a proposition on their formation at pneumatolytic-hydrothermal conditions near superficial Earth zones. Based on that theoretical foundations and experimental works, the first low-pressure and low-temperature hydrothermal diamond synthesis from water solution in pressure autoclave was executed. As a result, the natural diamond seed crystal grew bigger ad coupling of the synthetic diamond single-crystalline grains were obtained. SEM documentation proofs that parallely paragenetic crystallization of quartz and diamond, and nucleation of new octahedral diamond crystals brush take place on the seed crystal surface. Forecast of none times growth of diamond industrial application at 2000 and seventeen times at 2010 with reference to 1995, needs technology of large and pure single-crystals diamond synthesis. Growth of the stable and destressed diamond single-crystals in the pseudo-metastable diamond plot, may be realized with processes going through the long time and with participation of free radicals catalysts admixtures only. Sol-gel colloidal processes are an example of environment which form stable crystals in thermodynamically unstable conditions through a long time. Paper critically discusses a whole way of studies on the diamond synthesis, from high-pressure and high-temperature processes through chemical vapour deposition up to hydrothermal experiments.

• The Korean Journal of Ceramics
• /
• 제3권3호
• /
• pp.187-190
• /
• 1997

The aluminum-magnesium (Al-Mg) aklloys have been proved to be an effective solvent for synthesis of cubic-phase boron nitride (cBN) from hexagonal-phase boron nitride (hBN) at the conditions of high pressures and high temperatures (HP/HT). Various kinds of hBN powders having different crystallinity have been tested for cBN synthesis with Al-Mg solvents. The conversion ratio from hBN to cBN and the shape of synthesized cBN crystals appeared to be affected strongly by chemical composition and added amount of Al-Mg solvents as well as crystallinity of BN powders. As the magnesium content increased in the Al-Mg solvents, the conversion ratio increased and the size of cBN crystals became larger. The crystal facets developed well in the specimens with solvents having high Mg content. It was observed that a hBNlongrightarrowcBN transformation occurred more easily in the specimens having well crystallized hBN powders. Amorphous BN having much $B_2O_3$ impurity exhibited a low threshold temperature for transformation to cBN, which was attributed to crystallization of amorphous BN to well crystallized hBN prior to transformation into cBN with help of $B_2O_3$.

• 한국분말재료학회지
• /
• 제12권1호
• /
• pp.17-23
• /
• 2005

Dense $WSi_2$-20vol.%SiC composite was synthesized by high-frequency induction-heated combustion synthesis(HFIHCS) method within 2 minutes in one step from elemental powder mixture of W, Si and C. Simultaneous combustion synthesis and densification were accomplished under the combined effects of an induced current and mechanical pressure. Highly dense $WSi_2$-20vol.%SiC with relative density of up to 97% was produced under simultaneous application of 60MPa pressure and the induced current. The average grain size of $WSi_2$ was about $5.2{\mu}m$. The hardness and fracture toughness values obtained were 1700kg/$mm^2$ and $4.4MPa{\cdot}m^{1/2}$, respectively.

• 한국분말재료학회지
• /
• 제10권2호
• /
• pp.108-117
• /
• 2003

WC and dense WC-10 vol%Co materials with grain size of~1${\mu}m$ were synthesized by high-frequency induction heated combustion synthesis (HFIHCS) method in one step from elemental powders of W, C and Co within several minutes. Simultaneous combustion synthesis and densification were accomplished under the combined effects of an induced current and mechanical pressure. In the absence of cobalt additive, WC can be formed, but its relative density was low (about 73%) under simultaneous application of a 60 MPa pressure and the induced current. However, in the presence of 10 vol.%Co, the relative density increased to 99% under the same experimental condition. The percentages of the total shrinkage occurring before and during the synthesis reaction of WC-10 vol.%Co were 5% and 51%, respectively. The fracture toughness and hardness values of WC-10 vol.%Co were 10 MPa . m$^{1/2}$ and 1840 kg/$mm^2$, respectively.

• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
• /
• pp.1136-1137
• /
• 2006

The ultrahigh pressure process for synthesizing diamond grits is due to make a quantum leap: the raw materials will incorporate diamond seeds with a predetermined pattern. The result is doubling the diamond yield with a narrower size distribution. Moreover, the shape of diamond crystals can be precisely tuned. For example, diamond octahedra or diamond cubes, that are not available today, can be mass-produced. The new technology is now being implemented worldwide so the future diamond grits will have improved quality at reduced prices.