Powder Impregnation Research Articles

Effect of surface treatment of pitch‐based carbon fiber on mechanical properties of polyethernitrile composites

AbstractThe effect of surface treatment of pitch‐based carbon fiber on a new engineering thermoplastic resin, polyethernitrile, was investigated. Pitch‐based carbon fiber (CF) was treated in two separate oxidizing solutions. In the first method, a nitric acid solution was used as an oxidizing agent. In the second method, a hydrogen peroxide solution was used. Both methods demonstrated that each of these solutions was a satisfactory oxidizing agent for the pitch‐based CF. These treated fibers were combined with polyethernitrile polymer by the powder impregnation method, and unidirectional laminates were obtained. Improvements in both interlaminar shear strength and transverse flexural strength were achieved. The laminates fabricated from the treated CF maintained the same longitudinal flexural strength as laminates from the untreated control. In addition, scanning electron micrographs of composite fracture surfaces also showed excellent bonding of the treated fiber.

Manufacture of Powder-Impregnated Thermoplastic Composites

The use of thermoplastic composites has been limited by the lack of reliable techniques to make prepregs of consistent quality. Dry powder impregnation methods offer a new approach to the solution of this problem. This paper discusses the features that are essential to the development of an acceptable dry powder process The physical principles that govern the manufacture of thermoplastic prepreg tapes of controllable fiber-matrix volume fractions and the consolidation of these tapes to make void-free composite parts are presented A novel powder prepregging process suitable for the manufacture of high-quality powder-impregnated tapes and their subsequent consolidation to make void-free parts is discussed. It is shown that a well-designed dry powder process can achieve fine control over both fiber-matrix composition in the prepreg tape and intimate wetting between in dividual fibers and the thermoplastic matrix Powder prepreg tapes can be consolidated into void-free specimens with simple consolidation cycles developed for a specific fiber- matrix combination

Tribological Properties of Alumina-boria-silicate Fabric From 25°C to 850°C

Demanding tribological properties are required of the materials used for the sliding seal between the sidewalls and the lower wall of the variable area hypersonic engine. Temperatures range from room temperature and below to operating temperatures of 1000 C in an environment of air, hydrogen, and water vapor. Candidate sealing materials for this application are an alumina-boria-silicate, ceramic, fabric rope sliding against the engine walls which may be made from copper- or nickel-based alloys. Using a pin-on-disk tribometer, the friction and wear properties of some of these potential materials and possible lubrication methods are evaluated. The ceramic fabric rope displayed unacceptably high friction coefficients (0.6 to 1.3) and, thus, requires lubrication. Sputtered thin films of gold, silver, and CaF2 reduced the friction by a factor of two. Sprayed coatings of boride nitride did not effectively lubricate the fabric. Static heat treatment tests at 950 C indicate that the fabric is chemically attacked by large quantities of silver, CaF2, and boron nitride. Sputtered films or powder impregnation of the fabric with gold may provide adequate lubrication up to 1000 C without showing any chemical attack.

Manufacture and some properties of iron-chromium-nickel alloy powders

1. Techniques have been developed for the preparation of iron-chromium-nickel alloy powders representing a wide range of chemical compositions. In the preparation of such powders, use was made of the following processes: a) diffusion impregnation with chromium of iron-nickel alloy powders prepared by the coreduction of oxides of the metals involved; b) simultaneous interimpregnation of iron, nickel, and chromium powders; c) diffusion impregnation with chromium of an iron-nickel powder mixture prepared by the hydrogen reduction of nickel carbonate in the presence of iron powder. 2. A study of the properties of iron-chromium-nickel powders yielded by various processes has shown that homogeneous alloy powders in the range of compositions corresponding to Kh18N9, Kh18N15, and Kh23N18 austenitic steels can be prepared only by the method of diffusion impregnation of iron-nickel alloy powders with chromium. Such powders exhibit excellent compressibility, while sintered materials produced from them possess mechanical properties greatly superior to those of materials produced from powders prepared by other technological variants of the diffusion impregnation process.

Thermodiffusion impregnation of iron and nickel powders with manganese

A study was carried out on the thermodiffusion impregnation of iron and nickel powders with manganese from point sources at temperatures of 773–1373°K and holding durations of 2, 6, and 10 h, using charges containing 2–30% ammonium chloride. Manganese in the form of ferromanganese or metallic manganese was added to the charge in amounts ranging from 8 to 30%. It was demonstrated that the presence of excessive amounts of ammonium chloride in the charge leads to substantial manganese losses and is therefore undesirable. The optimum conditions have been established for the impregnation of iron and nickel powders with manganese.