Growth Of Reaction Layer Research Articles

Compatibility of a V-15Cr-5Ti alloy with SiC at high temperatures

To clarify the chemical compatibility between a V-15Cr-5Ti alloy and silicon carbide, the extent of reaction, the reaction products and the structure of reaction layer were studied at temperatures ranging from 1423 to 1523 K in an argon gas stream. The reaction layers formed in the interfacial reactions consisted of the suicides, V 5Si 3 and V 3Si, and minor amounts of TiC over the temperature range, and a remarkable internal titanium carbide was also observed. The enrichment of chromium in the alloy matrix adjacent to the reaction layer was caused by the preferential diffusion of vanadium toward the SiC side. The growth of reaction layers followed a parabolic rate law. The parabolic growth rate constant was expressed by k p ( m 2 s −1) = 1.8 × 10 −8 exp(−197 kJ mol −1/ RT).

Reaction layer formation in nitride ceramics(Si3N4 and AlN) to metal joints bonded with active filler metals.

Bonding of nitride ceramics (Si3N4 and AlN) to metals was carried out in a vacuum of about 6 mPa using Cu-base active filler metals. Reaction layers existed at the interfaces between Si3N4 or AlN and insert layers, and Cu enriched layers were found in the bonding layers. Reaction layers in Si3N4 to W joints were composed of nitrides and silicides of active metals, and those in AlN-Cu joints were composed of nitrides of active metals. The thermodynamic calculation suggested that these products were formed by the reactions between nitride ceramics and the melted active filler metals. It was elucidated that the growth behavior of the reaction layer in Si3N4-W joints could be expressed by the Johnson-Mehl type equation with a time exponent 'n' of 1/2. It was deduced that the growth of reaction layers were controlled by the diffusion process of active metals in the reaction layers.

耐熱性ファインセラミックスの接合に関する研究 第８報 Ｓｉ３Ｎ４と金属接合界面における反応層成長に関する速度論的検討

Kinetics of the reaction layer growth in Si3N4-W brazed joints was investigated using Cu-5%Cr, Cu-I%Nb, Cu-3%V, Cu-5%Ti and Cu-10%Zr liquid insert metals. It was elucidated that the reaction layer growth could be expressed by Johnson-Mehl type equation with time exponent 'n' of 1/2. EPMA analysis of elements in the reaction layer revealed that Cr, Nb, V, Ti and Zr contents slightly decreased toward Si3N4, and that N content was almost constant. From the consideration of activation energy for reaction layer growth, it may be deduced that the reaction layer growth was controlled by diffusion of Cr, Nb, V, Ti and Zr in the reaction layer from the melted insert metal to Si3N4.

耐熱性ファインセラミックスの接合に関する研究 第７報 Ｓｉ３Ｎ４と金属接合部における反応層およびＣｕ富化層の形成現象

Bonding of Si3N4 to W using Cu-5%Cr, Cu-1%Nb, Cu-3%V, Cu-5%Ti and Cu-10%Zr insert metals was conducted in a vacuum chamber. Thickness of the reaction layer formed at the interface between Si3N4 and insert layers was increased with increasing bonding temperature and holding time. SEM observation revealed that reaction layer grew toward the both sides of bonding interface. Growth of reaction layer toward the Cu enriched layer was attributed to the reaction between N and Cr, Nb, V, Ti or Zr, and that toward Si3N4 was attributed to the solid state reaction between Si3N4 and Cr, Nb, V, Ti or Zr in the reaction layer. Formation of Cu enriched layer was explained as a consequence of decrease in the contents of Cr, Nb, V, Ti and Zr in the melted insert metal by the reaction with Si3N4.

The Influence of Impurities of the Kinetics and Morphology of Reaction Layers in Diffusion Couples

The growth and morphology of reaction layers in diffusion couples is probably more frequently influenced by impurities than is generally realized. We found drastic effects of impurities on the reaction between Cu and Si and on the reaction between Cu20 and Ni or Co. In the first case the always present thin Si02-film on Si plays an important role: it hampers the reaction between Cu and Si, giving rise to an incubation period. This reaction barrier can be removed completely by only a few ppm of phosphorus in the copper starting material, which enables the formation of Cu3Si at much lower temperatures than in the absence of phosphorus. In the latter example the presence of chloride ions prevents NiO or CoO, which is formed during the displacement reaction, from building up a continuous, closed and rate-limiting layer. Instead, precipitates of these oxides in a matrix of copper are formed . This results in a much higher reaction rate since then the much faster diffusion of oxygen through copper becomes rate-limiting.

高温高圧下におけるモリブデン‐炭化物系セラミックスの固相界面反応とその接合技術への応用

Diffusion couples of molybdenum with several carbides, i.e. SiC, B4C, TiC, ZrC, HfC and TaC, were heated at various temperatures ranging from 1500 to 1840°C under high pressures of 3GPa and 100MPa for up to 4hr. The couples were then examined for the composition of reaction products, the growth rate of reaction layers, interfacial structures, and tensile strength. In case of Mo-transition metal carbides, Mo2C layer was mainly formed, so that the carbides, which had supplied carbon, resulted in having the nonstoichiometric composition near the interface. The activation energy for the growth of Mo2C layer in Mo-TiC system was 332kJ/mol, and that in Mo-TaC system was 366kJ/mol. In Mo-SiC system, Mo2C layer, the mixed phase of Mo2C and Mo5Si3, and Mo5Si3C layer were formed in order from the Mo side. In Mo-B4C system, the mixed phase of Mo2B and MoB, and Mo2BC layer appeared. The decomposed graphite from B4C was also observed between B4C and Mo2BC phase. The activation energy for the growth of total reaction layer in Mo-SiC system was 531kJ/mol, and that in Mo-B4C system was 183kJ/mol. It can be said that the growth of reaction layers is controlled by diffusion. The orientation of crystals was observed in all reaction products except for Mo2BC phase in Mo-B4C system and (Mo, Ta)2C phase in Mo-TaC system. In HIPed couples, the magnitude of tensile strength was dependent on the difference in thermal expansion coefficient between Mo and carbides. HIPed Mo-TaC couple had the best weldability among the systems examined in the present investigation.

模擬高レベル放射性廃棄物を含んだガラス粉末の水熱固化反応

The lithification of borosilicate glass powder containing simulated high level radioactive waste with the hot pressing technique under hydrothermal conditions was investigated. The glass powder was easily formed to hardened body with a little distilled water (5-10w/0). This glass body showed a high compressive strength above 2, 500 kg/cm2. The lithification occur-red at 240-270°C with the rapid shrinkage. The initial shrinkage kinetics were examined in consideration of the dissolution core model: 1-(1-x)1/3=kt1/2, 1-(1-x)1/3=k't, where x is the shrinkage ratio, k and k' the constants and t the reaction time. The apparent activation energy of shrinkage below 250°C was found to be about 20 kcal/mol, which was good agreement with that of the growth of surface reaction layer in hydrothermal solution. It was suggested that the initial stage of lithification followed the dissolution-deposition model.

Growth of Beta Alumina on Aluminum Oxide

The rate of growth of a beta alumina reaction layer at an interface between alpha alumina and sodium aluminate was determined. The data for the growth of this reaction layer were found to obey a parabolic rate law. Further analysis of the data indicated that the reaction is controlled by oxygen diffusivity in beta alumina.