• 한국세라믹학회지
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• 제35권10호
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• pp.1030-1039
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• 1998

In fly ash-lime system the effects of reaction condition amounts of gypsum and cement and CaO/SiO2 ratio on the hydrates by hydrothermal reaction were investigated. The tobermorite phases were not observed in hy-drothermal reaction of fly ash lime because of the hydrate rate was very slow. The compressive strength and the hydration rate increased with increasing the amount of gypusm and cement and the optimum amounts of gypsumo and cement were 5wt and 20wt% respectively. The specimen which CaO/SiO2 ratio is 0.85 was shown the maximum compressive strength and the tobermorite phase within reaction time 2 hours.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.184-184
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• 2011

Using first-principles density-functional calculations, we investigate the chain reaction mechanism of allyl alcohol (ALA) molecules on the H-terminated Si(001)-2${\times}$1 surface. Recently, it was reported [1] that allyl mercaptan (ALM) molecules show a self-directed line growth across the dimer rows through a chain reaction involving several reaction processes: (i) The created radical at the C atom is transferred to the S atom, (ii) the resulting S-centered radical easily abstracts an H atom from the neighboring dimer row, and (iii) the generated S-H group further reacts with the neighboring dimer row to produce the Si-S bond on the neighboring dimer row, accompanying the associative desorption of H2. This H2-desorption process creates a new DB on the neighboring dimer row, setting off the chain reaction across the dimer rows. In the present study, we find that although the structure of ALA with -OH functional is analogous to that of ALM with -SH functional, ALA and ALM lines show a difference in their growth direction. We predict that ALA undergoes the chain reaction to show a line growth along the dimer row, contrasting with the ALM line growth across the Si dimer rows. Our analysis shows that the different growth direction of ALA is due to the strong instability of oxygen radical intermediate, which prevents from growing across the dimer rows. Thus, we demonstrate that the stability of the radical intermediate plays a crucial role in determining the direction of molecular line growth.

• 한국세라믹학회지
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• 제37권5호
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• pp.505-510
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• 2000

In this investigation, we fabricated RBSN (Reaction Bonded Silicon Nitride) using the static nitriding system which could be advantageous for commercialization. Firstly, Si compacts of different sizes were made, and then nitridation rates were investigated as a function of added static gas pressure. The reaction schedule was obtained by pre-experiments. In case of small samples, the variation of ${\alpha}$, ${\beta}$ phases between the inside and the outside region of the specimens was examined after the samples were nitrided under 1 bar and 1.5 bar reaction pressure. On the other hand, large samples of Si compact with the size of 36 mm for diameter and 23 mm for thickness were nitrided for 26 hours of the total nitridation time, which showed a complete and homogeneous nitriding reaction from the outside to the inside of the samples, although the time was considerably shorter than that needed for convertional nitridation. Nitridation rates obtained at the early stage of reaction were proportional to the reaction gas pressures. The sequences of the nitridation reaction with the thickness were as follows 1) the outside, 2) the inside and 3) the intermediate area of the specimen. These results wer eobtained from the coloration of cross sectioned specimens that had various nitridation rates. Total nitriding reaction kinetics was controlled by chemical reaction, not by diffusion of the nitrogen gas.

• 한국세라믹학회지
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• 제32권4호
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• pp.419-428
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• 1995

Polycrystalline silicon carbide (SiC) thick films were depostied by low pressure chemical vapor deposition (LPCVD) using CH3SiCl3 (MTS) and H2 gaseous mixture onto isotropic graphite substrate. Effects of deposition variables on the SiC film were investigated. Deposition rate had been found to be surface-reaction controlled below reactor temperature of 120$0^{\circ}C$ and mass-transport controlled over 125$0^{\circ}C$. Apparent activation energy value decreased below 120$0^{\circ}C$ and deposition rate decreased above 125$0^{\circ}C$ by depletion effect of the reactant gas in the direction of flow in a horizontal hot wall reactor. Microstructure of the as-deposited SiC films was strongly influenced by deposition temperature and position. Microstructural change occurred greater in the mass transport controlled region than surface reaction controlled region. The as-deposited SiC layers in this experiment showed stoichiometric composition and there were no polytype except for $\beta$-SiC. The preferred orientation plane of the polycrystalline SiC layers was (220) plane at a high reactant gas concentration in the mass transfer controlled region. As depletion effect of reactant concentration was increased, SiC films preferentially grow as (111) plane.

• 한국분말재료학회지
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• 제5권4호
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• pp.250-257
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• 1998

The synthesis of titanium silicides ($Ti_3Si$, $TiSi_2$, $Ti_5Si_4$, $Ti_5Si_3$ and TiSi) by mechanical alloying has been investigated. Rapid, self-propagating high-temperature synthesis (SHS) reactions were observed to produce the last three phases during room-temperature high-energy ball milling of elemental powders. Such reactions appeared to be ignited by mechanical impact in an intimate, fine powder mixture formed after a critical milling period. During the high-energy ball milling, the repeated impact at contact points leads to a local concentration of energy which may ignite a self-propagating reaction. From in-situ thermal analysis, each critical milling period for the formation of $Ti_5Si_4$, $Ti_5Si_3$ and TiSi was observed to be 22, 35.5 and 53.5 min, respectively. $Ti_3Si$ and $TiSi_2$, however, have not been produced even till the milling period of 360 min due to lack of the homogeneity of the powder mixtures. The formation of titanium silicides by mechanical alloying and the relevant reaction rates appeared to depend upon the critical milling period, the homogeneity of the powder mixtures, and the heat of formation of the products involved.

• 한국표면공학회지
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• 제38권3호
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• pp.89-94
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• 2005

We investigate the reaction stability of cobalt and nickel with side-wall materials of $SiO_2\;and\;Si_3N_4$. We deposited 15nm-Co and 15nm-Ni on $SiO_2(200nm)/p-type$ Si(100) and $Si_3N_4(70 nm)/p-type$ Si(100). The samples were annealed at the temperatures of $700\~1100^{\circ}C$ for 40 seconds with a rapid thermal annealer. The sheet resistance, shape, and composition of the residual materials were investigated with a 4-points probe, a field emission scanning electron microscopy, and an AES depth profiling, respectively. Samples of annealed above $1000^{\circ}C$ showed the agglomeration of residual metals with maze shape and revealed extremely high sheet resistance. The Auger depth profiling showed that the $SiO_2$ substrates had no residual metallic scums after $H_2SO_4$ cleaning while $Si_3N_4$ substrates showed some metallic residuals. Therefore, the $SiO_2$ spacer may be appropriate than $Si_3N_4$ for newly proposed Co/Ni composite salicide process.

• 한국재료학회지
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• 제14권11호
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• pp.780-785
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• 2004

The degradation mechanism of soft magnetic properties of $Fe-Hf-N/Cr/SiO_2$ thin films reacted with a bonding glass was investigated. When $Fe-Hf-N/Cr/SiO_2$ films were annealed under $600^{\circ}C$ without the bonding glass, the compositions and the soft magnetic properties of Fe-Hf-N layers were not changed. However, after reaction with the bonding glass at $550^{\circ}C$, the soft magnetic properties of the film were degraded. At $600^{\circ}C$, the saturation magnetization of the reacted film decreased to 13.5 kG, and its coercivity increased to 4 Oe, and its effective permeability decreased to 700. It was founded that O diffused from the glass into the Fe-Hf-N layers during the reaction and generated $HfO_2$ phases. It was considered that the soft magnetic properties of the $Fe-Hf-N/Cr/SiO_2$ films reacted with the bonding glass were primarily degraded by the formation of the Fe-Hf-O-N layer of which the Fe content was below 60 $at\%$, and secondarily degraded by the Fe-Hf-O-N layer above 70 $at\%$.

• Bulletin of the Korean Chemical Society
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• 제34권12호
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• pp.3738-3742
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• 2013

The reaction mechanism of $SiF_2$ radical with HNCO has been investigated by the B3LYP method of density functional theory(DFT), while the geometries and harmonic vibration frequencies of reactants, intermediates, transition states and products have been calculated at the B3LYP/$6-311++G^{**}$ level. To obtain more precise energy result, stationary point energies were calculated at the CCSD(T)/$6-311++G^{**}$//B3LYP/$6-311++G^{**}$ level. $SiF_2+HNCO{\rightarrow}IM3{\rightarrow}TS5{\rightarrow}IM4{\rightarrow}TS6{\rightarrow}OSiF_2CNH(P3)$ was the main channel with low potential energy, $OSiF_2CNH$ was the main product. The analyses for the combining interaction between $SiF_2$ radical and HNCO with the atom-in-molecules theory (AIM) have been performed.

• Bulletin of the Korean Chemical Society
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• 제23권6호
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• pp.845-851
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• 2002

The synthesis of the intramolecular donor - stabilized silyl and germyl complexes of the type ($Cab^c.p) MMe_2X$ (2a:M=Si, X=Cl;2b;M= Ge, X=Cl;2e;M=Si,X=H) was achieved by the reaction of $LiCab^c,p$ (1) with $Me_2SiClX$ and $Me_2GeCl_2$ respectively. The intramolecular M←P interacion in 2a-2c is provided by $^1H$, $13^C.$, $31^P$ and $29^Si$ NMR spectroscopy. The salt elimination reactions of dichlorotetramethyldisilane and -digermane with 1 afforded the $bis(\sigma-carboranylphosphino)disilane$ and disgermane [$(Cab^C.P)MMe_2]_2(4a;M$ = Si;4b: M=Ge). The oxidative addition reaction of 4a-4b with $pd_2(dba)_3CHCl_3afforded$ the bis(silyl)-and bis(germyl)-palladium complexes. The chloro-bridged dipalladium complexes were obtained by the reaction of 2a-2b with $pd_2(dba)_3CHCl_3$ The crystal structures of 5a and 7b were determined by X-ray structural studies.

• 한국세라믹학회지
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• 제46권5호
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• pp.515-519
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• 2009

Carbon layers were fabricated on silicon carbide by chlorination reaction at temperatures between $1000^{\circ}C$ and $1500^{\circ}C$ with $Cl_2/H_2$ gas mixtures. The effect of reaction temperature on the micro-structures and tribological behavior of SiC derived carbon layer was investigated. Tribological tests were carried out ball-on-disk type wear tester. Carbon layers were characterized by X-ray diffractometer, Raman spectroscopy and surface profilometer. Both friction coefficients and wear rates were maintained low values at reaction temperature up to $1300^{\circ}C$ but increased suddenly above this temperature. Variation of surface roughness as a function of reaction temperature was dominant factor affecting tribological transition behavior of carbon layer derived from silicon carbide at high temperature.