The Formation of Nial Phase and Layered Carbon Precipitates During Ni3Al/SiC Solid State Reactions

1990 ◽  
Vol 213 ◽  
Author(s):  
T. C. Chou ◽  
T. G. Nieh
Keyword(s):  
Solid State ◽  
Reaction Zone ◽  
Solid State Reactions ◽  
Growth Rate Constant ◽  
Reaction Products ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Nial Phase ◽  
Carbon Precipitation ◽  
Rate Limiting

ABSTRACTSolid state reactions of Ni3A1 with SiC have been studied at 1000°C. Three layered reaction products consisting of NiAl Ni5,4Al1Si2, and Ni(5.4−x)A11Si2+C were formed in the reaction zone. The Ni5.4AllSi2 layer showed carbon precipitation free, while modulated carbon bands were formed in the Ni(5.4−x)A11Si2+C layer. Carbon precipitates were found to exist in either a disordered or partially ordered (graphitic) state, depending upon their locations from the SiC reaction interface. The NiAl layer showed dramatic contrast difference compared to the Ni3Al and Ni5.4Al1Si2 layers, and was bounded by the Ni3Al/NiAl and NiAl/Ni5.4A1lSi2 phase boundaries. The kinetics of the NiAl formation was limited by diffusion, and the growth rate constant was measured to be 2 × 10−10cm2/s. The thickness of the reaction zone on the Ni3Al side was always greater than that on the SiC side, suggesting that the decomposition of the SiC may be a rate limiting step for the SiC/Ni3Al reactions. An Al-rejection model, based on a lower solid solubility of Al in the Ni-Al-Si ternary phase than in the Ni3A1 intermetallic compound, is proposed to explain the formation of NiAl phase. The rate limiting step for the Ni3Al/SiC reactions is discussed in light of discontinuous decomposition of SiC, which leads to the formation of alternating C and Ni(5 4−x)Al1Si2 layers in the reaction zone. Preliminary results on C precipitation behavior in NiAl/SiC system are reported.

Solid state reactions between Ni3Al and SiC

1990 ◽  
Vol 5 (9) ◽  
pp. 1985-1994 ◽  
Author(s):  
T. C. Chou ◽  
T. G. Nieh
Keyword(s):  
Growth Rate ◽  
Solid State ◽  
Solid State Reactions ◽  
Growth Rate Constant ◽  
Cross Sectional ◽  
Rate Limiting Step ◽  
Nial Phase ◽  
Reaction Zones ◽  
Carbon Precipitation ◽  
Terminal Component

Solid state reactions between SiC and Ni3Al were studied at 1000°C for different times. Multi-reaction-layers were generated in the interdiffusion zone. Cross-sectional views of the reaction zones show the presence of three distinguishable layers. The Ni3Al terminal component is followed by NiAl, Ni5.4Al1Si2, Ni(5.4−x)Al1Si2 + C layers, and the SiC terminal component. The Ni5.4Al1Si2 layer shows carbon precipitation free, while modulated carbon bands were formed in the Ni(5.4−x)Al1Si2 + C layer. The NiAl layer shows dramatic contrast difference with respect to the Ni3Al and Ni5.4Al1Si2 layers, and is bounded by the Ni3Al/NiAl and Ni5.4Al1Si2/NiAl phase boundaries. The kinetics of the NiAl formation is limited by diffusion, and the growth rate constant is measured to be 2 ⊠ 10−10 cm2/s. The thickness of the reaction zone on the SiC side is always thinner than that on the Ni3Al side and no parabolic growth rate is obeyed, suggesting that the decomposition of the SiC may be a rate limiting step for the SiC/Ni3Al reactions. The carbon precipitates were found to exist in either a disordered or partially ordered (graphitic) state, depending upon their locations from the SiC interface. The formation of NiAl phase is discussed based on an Al-rejection model, as a result of a prior formation of Ni–Al–Si ternary phase. A thermodynamic driving force for the SiC/Ni3Al reactions is suggested.

Solid state reactions of SiC with Co, Ni, and Pt

1991 ◽  
Vol 6 (4) ◽  
pp. 796-809 ◽  
Author(s):  
T.C. Chou ◽  
A. Joshi ◽  
J. Wadsworth
Keyword(s):  
Solid State ◽  
Solid State Reactions ◽  
Dendritic Microstructure ◽  
Sic Ceramics ◽  
Rate Limiting Step ◽  
Metal Silicides ◽  
Metal Ceramic ◽  
Reaction Zones ◽  
Ceramic Interfaces ◽  
Rate Limiting

Solid state reactions between SiC ceramics and Co, Ni, and Pt metals have been studied at temperatures between 800 and 1200 °C for various times under He or vacuum conditions. Reactions between the metals and SiC were extensive above 900 °C. Various metal silicides and carbon precipitates were formed in layered reaction zones. Interfacial melting was also observed at certain temperatures; teardrop-shaped reaction zones, porosity, and dendritic microstructure resulting from melting/solidification were evident. The metal/ceramic interfaces exhibited either planar or nonplanar morphologies, depending upon the nature of the metal/ceramic reactions. Concave interfacial contours were observed when interfacial melting occurred. By contrast, planar interfaces were observed in the absence of interfacial melting. In all cases, the decomposition of SiC was sluggish and may serve as a rate limiting step for metal/ceramic reactions. Free unreacted carbon precipitates were formed in all the reaction zones and the precipitation behavior was dependent upon the metal system as well as the location with respect to the SiC reaction interface. Modulated carbon bands, randomly scattered carbon precipitates, and/or carbon-denuded bands were formed in many of the reaction zones, and the carbon existed in a mixed state containing both amorphous and graphitic forms.

Kinetics and mechanism of solvolysis of substituted phenyl N-phenylbenzimidoesters

1987 ◽  
Vol 52 (5) ◽  
pp. 1285-1297
Author(s):  
Jaromír Kaválek ◽  
Ludmila Hejtmánková ◽  
Vojeslav Štěrba
Keyword(s):  
Hydrochloric Acid ◽  
Kinetics And Mechanism ◽  
Reaction Products ◽  
Phenol Content ◽  
Aqueous Methanol ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Kinetics Of

Kinetics of hydrochloric acid-catalyzed solvolysis of substituted phenyl and methyl N-phenylbenzimidoesters have been studied in methanol, 50 vol. % aqueous methanol, and 50 vol. % aqueous tetrahydrofurane, and the composition of the reaction products has been determined. The rate-limiting step consists in addition of water or methanol to the protonated substrate. The reaction of methyl N-phenylbenzimidoester with both water and methanol and that of substituted phenyl N-phenylbenzimidoesters with methanol produce aniline, the ester (or orthoester) and the corresponding phenol. The reaction of substituted phenyl N-phenylbenzimidoesters with water gives both the neutral tetrahedral intermediate (which is decomposed into phenol and anilide) and the protonated intermediate (which produces aniline and the ester). At the same proton concentration the phenol content increases with increasing value of the σ constant of the substituent.

Ornithine Decarboxylase Activity in Cultured Endothelial Cells Stimulated by Serum, Thrombin and Serotonin

1978 ◽  
Vol 39 (02) ◽  
pp. 496-503 ◽  
Author(s):  
P A D’Amore ◽  
H B Hechtman ◽  
D Shepro
Keyword(s):  
Endothelial Cells ◽  
Ornithine Decarboxylase ◽  
Decarboxylase Activity ◽  
Aortic Endothelial Cells ◽  
Ornithine Decarboxylase Activity ◽  
Rate Limiting Step ◽  
Bovine Aortic Endothelial Cells ◽  
Limiting Step ◽  
Rate Limiting ◽  
Serum Serotonin

SummaryOrnithine decarboxylase (ODC) activity, the rate-limiting step in the synthesis of polyamines, can be demonstrated in cultured, bovine, aortic endothelial cells (EC). Serum, serotonin and thrombin produce a rise in ODC activity. The serotonin-induced ODC activity is significantly blocked by imipramine (10-5 M) or Lilly 11 0140 (10-6M). Preincubation of EC with these blockers together almost completely depresses the 5-HT-stimulated ODC activity. These observations suggest a manner by which platelets may maintain EC structural and metabolic soundness.

Dynamics of hepatic and peripheral insulin effects suggest common rate-limiting step in vivo

Diabetes ◽  
1993 ◽  
Vol 42 (2) ◽  
pp. 296-306 ◽  
Author(s):  
D. C. Bradley ◽  
R. A. Poulin ◽  
R. N. Bergman
Keyword(s):  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting
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