Search Results for chemical vapor infiltration

This article focuses on the process methods and matrix chemistries of ceramic-matrix composites. These methods include pressure-assisted densification, chemical vapor infiltration, melt infiltration, polymer infiltration and pyrolysis, and sol-gel processing. The article discusses the use of a ceramic, preceramic, or metal phase as a fluid or vapor phase reactant to form the matrix. Emphasis is placed on microstructural features that influence ultimate composite properties.

This article describes the manufacture, post-processing, fabrication, and properties of carbon-carbon composites (CCCs). Manufacturing techniques with respect to the processibility of different geometries of two-directional and multiaxial carbon fibers are listed in a table. The article discusses matrix precursor impregnants, liquid impregnation, and chemical vapor infiltration (CVI) for densification of CCCs. It presents various coating approaches for protecting CCCs, including pack cementation, chemical vapor deposition, and slurry coating. Practical limitations of coatings are also discussed. The article concludes with information on the mechanical properties of CCCs.

This article presents the principles of chemical vapor deposition (CVD) with illustrations. It discusses the types of CVD processes, namely, thermal CVD, plasma CVD, laser CVD, closed-reactor CVD, chemical vapor infiltration, and metal-organic CVD. The article reviews the CVD reactions of materials related to hard, tribological, and high-temperature coatings and to free-standing structures. It concludes by reviewing the advantages, disadvantages, and applications of CVD.

This article describes the various pure forms of carbon matrices and the corresponding methods used to create them or incorporate them into a matrix of a composite. These forms include graphite, diamond, fullerenes, and nanotubes. The article discusses the three types of liquid precursors, namely, thermoplastic, thermosetting, and evaporative or solvent carriers. It provides a description of the advantages and limitations of various methods involved in chemical vapor infiltration. The article concludes with a discussion on matrix contribution to composite properties.

Ceramic-matrix composites (CMCs) have ability to withstand high temperatures and have superior damage tolerance over monolithic ceramics. This article describes important processing techniques for CMCs: cold pressing, sintering, hot pressing, reaction-bonding, directed oxidation, in situ chemical reaction techniques, sol-gel techniques, pyrolysis, polymer infiltration, self-propagating high-temperature synthesis, and electrophoretic deposition. The advantages and disadvantages of each technique are highlighted to provide a comprehensive understanding of the achievements and challenges that remain in this area.

This article is a compilation of abbreviations, symbols, and tradenames for terms related to the properties, selection, processing, and applications of the most widely used nonmetallic engineering materials.

Ceramic-matrix composites (CMCs) are being developed for a number of high-temperature and high-performance applications in industrial, aerospace, and energy conservation sectors. This article focuses on processing, fabrication, testing, and characterization methods of CMCs, namely, discontinuously reinforced composites and continuous-fiber-reinforced composites. Processing methods include cold pressing, sintering, hot pressing, reaction bonding, melt infiltration, directed metal oxidation, sol-gel and polymer pyrolysis, self-propagating high-temperature synthesis and joining. A table summarizes the properties of various ceramic reinforcements and industrial applications of these composites.

The applications of discontinuously reinforced ceramic-matrix composites (CMCs) fall into four major categories, namely, cutting tool inserts; wear-resistant parts; aerospace and military applications; and other industrial applications, including engines and energy-related applications. This article provides examples for these four categories, with an emphasis on those applications/materials that have achieved commercial viability. The applications for continuous fiber ceramic composites are also summarized.

This article identifies the coatings applied to many substrates for both beautification and protection, and the inherent conflicts that exist between the coatings and the buildings they are designed to protect; emphasis is placed on masonry walls. It provides information on the purposes of the coatings in the commercial buildings. The article briefly describes some of the most common types of substrates found in buildings and the coatings commonly associated with each substrate. The selection of the coating system depends on the substrate and service expectations. The article addresses the primary causes of masonry coating problems and also provides a detailed discussion on the wall design considerations, moisture considerations, and coating system challenges in the masonry buildings.

In general, metal-matrix composites (MMCs) are classified into three broad categories: continuous fiber-reinforced composites, discontinuous or short fiber-reinforced composites, and particle-reinforced composites. This article focuses on stir casting and melt infiltration as the two main methods of MMC solidification processing. It describes the MCC casting methods, such as sand and permanent mold casting, centrifugal casting, compocasting, and high-pressure die casting. The article discusses the MMC infiltration processes in terms of pressure infiltration casting and liquid metal infiltration. It reviews the powder metallurgy processing of aluminum MMCs and deformation processing of discontinuously reinforced aluminum composites. The article concludes with a discussion on the processing of fiber-reinforced aluminum.

The residual porosity in sintered refractory metal ingots is usually eliminated by different densification processes, such as thermomechanical processes. This article focuses on thermomechanical processing of tungsten, molybdenum, and tantalum. It provides an overview of liquid-phase sintering of tungsten heavy alloys and describes the infiltration of tungsten and molybdenum for attaining full density. The article concludes by providing information on hot isostatic pressing of refractory metal alloys to full density.