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

• 한국세라믹학회지
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• 제35권10호
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• pp.1078-1084
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• 1998

금속 질산염과 urea를 사용하여 연소합성법에 의해 LaCrO3 분말을 제조하고, 용액의 pH를 HNO3와 NH4OH로 조절한 후, 용매의 가열방법에 따른 연소 생성물인 LaCrO3의 형상을 고찰하였다. 연소생성물의 수율은 용액의 pH에 의해 크게 좌우되었다. 용액의 pH가 0.7~4 사이에서는 90% 이상의 수율이 얻어졌으나, 5 이상 또는 0.5 이하의 pH에서는 수율이 크게 감소하였다. 한편, 연소생성물의 형상은 용액의 pH에 무관하였고 용액의 가열방법에 좌우되었다. 용액을 저항가열법으로 가열하여 연소반응시킨 경우의 분말은 미세한 일차입자들이 2차원적으로 연결된 응집체를 형성하고 있었으나, 마이크로파를 인가하여 가열한 경우에는 용액의 pH에 관계없이 미세한 LaCrO3 분말이 얻어졌다. BET 분석 결과, 마이크로파 가열에 의해 얻어진 입자의 비표면적은 25~32m2/g으로 저항가열법으로 가열한 경우의 10-14m2/g에 비해 더 큰 값을 보였다. 이러한 결과는 마이크로파에 의한 연소반응물의 균일한 가열이 연소생성물의 2차원적인 강항 응집체 형성을 억제할 수 있음을 보여 주었다.

• 대한기계학회논문집B
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• 제32권9호
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• pp.659-668
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• 2008

Combustion instability has been considered as very important issue for developing gas turbine and rocket engine. There is a need for fundamental understanding of combustion instability. In this study, combustion instability was numerically and experimentally investigated in a dump combustor with bluff body. The fuel and air mixture had overall equivalence ratio of 0.9 and was injected toward dump combustor. The pressure oscillation with approximately 256Hz was experimentally obtained. For numerical simulation, the standard k-$\varepsilon$ model was used for turbulence and the hybrid combustion model (eddy dissipation model and kinetically controlled model) was applied. After calculating steady solution, unsteady calculation was performed with forcing small perturbation on initial that solution. Pressure amplitude and frequency measured by pressure sensor is nearly the same as those predicted by numerical simulation. Furthermore, it is clear that a combustion instability involving vortex shedding is affected by acoustic-vortex-combustion interaction. The phase difference between the pressure and velocity is $\pi$/2, and that between the pressure and heat release rate is in excitation range described by Rayleigh, which is obvious that combustion instability for the bluff body combustor meets thermoacoustic instability criterion.

• The Korean Journal of Ceramics
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• 제6권1호
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• pp.47-52
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• 2000

Lanthanides such as La, Gd and Ce have recognized as elements of high level radioactive wastes immobilized by forming solid solution with $CaTiO_3$. For easy forming solid solution between $CaTiO_3$and lanthanides, the combustion synthesis process was applied and the powder characteristics and sinterability were investigated. The proper selection of the type and the composition of fuels are important to get the crystalline solid solution of $CaTiO_3$and lanthanides. When glycine or the mixtures of urea and citric acid with stoichiometric composition was used as a fuel, the solid solution of $CaTiO_3$with $La_2O_3$or $Gd_2O_3$or $CeO_2$was produced very well by the combustion process. The combustion synthesized powder seemed to have a good sinterability with the linear shrinkage of more than 25% up to $1500^{\circ}C$, while that of the solid state reacted powder was less than 10% at the same condition.

• 한국재료학회지
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• 제33권10호
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• pp.385-392
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• 2023

A solution combustion process for the synthesis of hollandite (BaAl₂Ti₆O₁₆) powders is described. SYNROC (synthetic rock) consists of four main titanate phases: perovskite, zirconolite, hollandite and rutile. Hollandite is one of the crystalline host matrices used for the disposal of high-level radioactive wastes because it immobilizes Sr and Lns elements by forming solid solutions. The solution combustion synthesis, which is a self-sustaining oxi-reduction reaction between a nitrate and organic fuel, generates an exothermic reaction and that heat converts the precursors into their corresponding oxide products in air. The process has high energy efficiency, fast heating rates, short reaction times, and high compositional homogeneity. To confirm the combustion synthesis reaction, FT-IR analysis was conducted using glycine with a carboxyl group and an amine as fuel to observe its bonding with metal element in the nitrate. TG-DTA, X-ray diffraction analysis, SEM and EDS were performed to confirm the formed phases and morphology. Powders with an uncontrolled shape were obtained through a general oxide-route process, confirming hollandite powders with micro-sized soft agglomerates consisting of nano-sized primary particles can be prepared using these methods.

• 한국세라믹학회지
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• 제39권1호
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• pp.74-78
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• 2002

본 연구에서는 전구체 용액의 산화환원 발열반응을 이용하여 다성분계 산화물을 제조할 수 있는 용액연소합성법을 이용하여 페로브스카이트 구조 PZT 세라믹스를 합성하고자 하였다. 산화제/환원제 전구체 혼합물의 열분석(DTA/TG) 결과 산화제와 환원제의 열분해 거동의 차이로 인해 214$^{\circ}C$와 35$0^{\circ}C$에서 발열 피크가 나타났다. PZT세라믹스 합성을 위한 승온 과정에서는 37$0^{\circ}C$에서 연소반응이 일어났으나, 페로브스카이트로의 상전이는 일어나지 않았다. 용액연소과정 중 산화제와 연료의 열분해 거동을 고려하여 $600^{\circ}C$에서 제조한 생성물은 결정크기가 50nm인 정방정의 단일상으로 이루어진 PZT세라믹스이었다. 격자상수를 측정한 결과 a는 3.997$\pm$0.001 $\AA$이었으며, c는 4.147$\pm$0.001 $\AA$으로 나타났다.

• 한국연소학회지
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• 제13권1호
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• pp.17-22
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• 2008

A partly implicit/quasi-explicit method is introduced for the solution of detailed chemical kinetics with stiff source terms based on the standard fourth-order Runge-Kutta scheme. Present method solves implicitly only the stiff reaction rate equations, whereas the others explicitly. The stiff equations are selected based on the survey of the chemical Jaconian matrix and its Eigenvalues. As an application of the present method constant pressure combustion was analyzed by a detailed mechanism of hydrogen-air combustion with NOx chemistry. The sensitivity analysis reveals that only the 4 species in NOx chemistry has strong stiffness and should be solved implicitly among the 13 species. The implicit solution of the 4 species successfully predicts the entire process with same accuracy and efficiency at half the price.

• 한국재료학회지
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• 제25권9호
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• pp.492-496
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• 2015

Hydroxyapatite (HA), which is an important calcium phosphate mineral, has been applied in orthopedics, dentistry, and many other fields depending upon its morphology. HA can be synthesized with different morphologies through controlling the synthesis method and several parameters. Here, we synthesize various morphologies of HA using two simple methods: hydrothermal combustion and solution combustion. The phase purity of the synthesized HA is confirmed using X-ray diffractometry. It demonstrates that pure phased hydroxyapatite can be synthesized using both methods. The morphology of the synthesized powder is examined using scanning electron microscopy. The effects of pH and temperature on the final powder are also investigated. At $140^{\circ}C$, using the hydrothermal method, nano-micro HA rods with a hexagonal crystal structure can be synthesized, whereas using solution combustion method at $600^{\circ}C$, a dense cubic morphology can be synthesized, which exhibits monoclinic crystal structures.

• 한국재료학회지
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• 제11권9호
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• pp.797-801
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• 2001

In this study, the solution combustion method was employed to synthesize stoichiometric mullite, and hence the attrition process was employed to prepare ultrafine mullite particles with nano size. The thermal decomposition behavior and partial pressure of equilibrium species of both oxidizer and fuel were considered during solution combustion process. The synthesized product was mullite phase with 40 nm crystalline size, and the alumina contents of the product by TEM/EDS quantity analysis was 3.12$\pm$04 mole. The result showed that the synthesized mullite was almost close to the it's stoichiometric composition. For attrition process, the dispersion behavior of the mullite suspension was controlled and was comminuted with the condition of 800 rpm for 4 hours using 0.3 mm zirconia ball media. As a result of comminution, the mean particle size was 80 nm.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2012년도 제45회 KOSCO SYMPOSIUM 초록집
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• pp.195-198
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• 2012

Numerical simulation is performed to evaluate the conditional moment closure (CMC) models for spray development, ignition, and turbulent combustion for the Engine Combustion Network (ECN) test cases. The CMC model is implemented in the open source code, OpenFOAM, to provide conditional flame structures through the solution of Eulerian as well as Lagrangian conditional transport equations. In spite of more accurate treatment of the convective term, Eulerian CMC provides similar ignition delays and lift-off lengths with Lagrangian CMC.