Effect of processing parameters on the deposition rate of Si3N4/Si2N2O by chemical vapor infiltration and the in situ thermal decomposition of Na2SiF6

AbstractThree different methods of preparing Mosi2 and composites reinforced with ceramic fibers by reactive in-situ processing are described. Reactive powder sintering (co-synthesis) of elemental powders, chemical vapor infiltration/deposition and reactive vapor infiltration are examined. Monolithic Mosi2, SiC particle-reinforced Mosi2 or fibrous Mosi2 composites reinforced with Nicalon fiber were prepared. The advantages and disadvantages of these processes relative to more traditional processing techniques such as HIPing of prealloyed powders, mechanical alloying and a reported in-situ displacement reactions are discussed.

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Thermal decomposition of methyltrichlorosilane/ hydrogen/ inert mixtures at conditions relevant for chemical vapor infiltration of SiC ceramics

International Journal of Chemical Kinetics ◽

10.1002/kin.21550 ◽

2022 ◽

Author(s):

Khanh Dang ◽

Harsha K. Chelliah

Keyword(s):

Thermal Decomposition ◽

Chemical Vapor ◽

Chemical Vapor Infiltration ◽

Sic Ceramics ◽

Vapor Infiltration

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Model of chemical vapor infiltration using temperature gradients

Journal of Materials Research ◽

10.1557/jmr.1997.0107 ◽

1997 ◽

Vol 12 (3) ◽

pp. 724-737 ◽

Cited By ~ 10

Author(s):

Daniel J. Skamser ◽

Hamlin M. Jennings ◽

D. Lynn Johnson

Keyword(s):

Ceramic Matrix Composite ◽

Chemical Vapor ◽

Processing Parameters ◽

Chemical Vapor Infiltration ◽

Temperature Gradients ◽

Macroscopic Model ◽

Optimum Conditions ◽

Microstructure Model ◽

Process Diagrams ◽

Vapor Infiltration

An optimized chemical vapor infiltration (CVI) process has conditions that promote complete densification at the fastest allowable reaction rate. In order to help define optimum conditions, a model has been developed to simulate the CVI of a fibrous specimen for determining the effects of temperature gradients along with the other processing parameters such as pressure, size, chemistry, rate of reaction, and porosity on the resulting deposition profiles. This model simulates the deposition of alumina matrix within fibers wrapped around a tube. This symmetry reduces the model to a simple one-dimensional problem. Parameters for transport properties, calculated using a local microstructure model, are used in this macroscopic model. The model is applied as a guideline for choosing optimum conditions for producing a dense ceramic matrix composite. From this model, process diagrams are constructed that can help an experimentalist to choose the best conditions for the CVI process using temperature gradients.

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Formation of hierarchical Si3N4 foams by protein-based gelcasting and chemical vapor infiltration

Journal of Advanced Ceramics ◽

10.1007/s40145-020-0431-4 ◽

2021 ◽

Vol 10 (1) ◽

pp. 187-193

Author(s):

Junsheng Li ◽

Qiuping Yu ◽

Duan Li ◽

Liang Zeng ◽

Shitao Gao

Keyword(s):

Silicon Nitride ◽

Multiple Scales ◽

Gas Permeability ◽

Retention Rate ◽

Chemical Vapor ◽

Chemical Vapor Infiltration ◽

Porous Bodies ◽

Hierarchical Porous ◽

Vapor Infiltration

AbstractSilicon nitride foams with a hierarchical porous structure was formed by the combination of protein-based gelcasting, chemical vapor infiltration, and in-situ growth of silicon nitride nanowires. The porosity of the foams can be controlled at 76.3–83.8 vol% with an open porosity of 70.2– 82.8 vol%. The pore size distribution was presented in three levels: < 2 μm (voids among grains and cross overlapping of silicon nitride nanowires (SNNWs)), 10–50 μm (cell windows), and >100 μm (cells). The resulted compressive strength of the porous bodies at room temperature can achieve up to 18.0±1.0 MPa (porosity = 76.3 vol%) while the corresponding retention rate at 800 ℃ was 58.3%. Gas permeability value was measured to be 5.16 (cm3·cm)/(cm2·s·kPa). The good strength, high permeability together with the pore structure in multiple scales enabled the foam materials for microparticle infiltration applications.

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