Whisker mixing

The method for bismaleimide resin filled with whiskers is similar to the preceding. The mass ratio of BMI (bismaleimide) and BA (diallyl bisphenol A) is 1 0.8. First, heat BA to 130°C, then add BMI slowly, prepolymerize for 20 minutes, add the whisker, mix uniformly, pour into a glass mold coated with a release agent, vacuum and deaerate at 120-130°C for 15 minutes, and cure according to the following sequence l45°C/2 h + l60°C/2 h + 180°C/2 h + 200°C/2 h. Finally, posttreat at 220°C for 6 h. 

Ceramic matrix composites are produced by one of several methods. Short fibers and whiskers can be mixed with a ceramic powder before the body is sintered. Long fibers and yams can be impregiated with a slurry of ceramic particles and, after drying, be sintered. Metals (e.g., aluminum, magnesium, and titanium) are frequently used as matrixes for ceramic composites as well. Ceramic metal-matrix composites are fabricated by infiltrating arrays of fibers with molten metal so that a chemical reaction between the fiber and the metal can take place in a thin layer surrounding the fiber. 

Naturally occurring fibers such as cotton, cellulose, etc., have short whiskers protruding from the surface, which help to give a physical bond when mixed with rubber. Glass, nylon, polyester, and rayon have smooth surfaces and adhesion of these fibers to the rubber matrix is comparatively poor. In addition, these synthetic fibers have chemically unreactive surfaces, which must be treated to enable a bond to form with the mbber. In general, the fibers are dipped in adhesives in the latex form and this technology is the most common one used for continuous fibers. The adhesion between elastomers and fibers was discussed by Kubo [128]. Hisaki et al. [129] and Kubo [130] proposed a... 

More recently, Stanicioiu, Chinta Hartner (1959) attempted to reinforce the cement with glass fibres, but this was not successful. The most serious study on the reinforcement of dental silicate cement was made by J. Aveston (in Wilson et al., 1972). Silicon carbide whiskers, carbon fibres and alumina powder were introduced into the cement mix. Unfortunately, the glass powder/liquid ratio had to be reduced, and the strength gained by reinforcement was thereby lost. It is clear that dental silicate cement cannot be strengthened by fibre or particulate reinforcement. 

Whiskers can be easily mixed with powders and processed as such. Composites are formed with metal (utilization in automobile construction e.g. pi.stons of whisker-reinforced aluminum), ceramic or polymer matrices for frictional applications (e.g. brake and clutch linings). Small quantities command prices of 1500 to 2000 DM/kg. For larger quantities prices of 100 to 150 DM/kg are expected. 

The pyrolysis reactions take place at temperatures between 800 and 3000°C, both in the gas phase and on the substrate surface. Their property mix can be varied within wide limits by appropriate choice of process parameters. The production of an isotropic structure is just as possible as the obtaining of spiral, columnar or extremely anisotropic laminar structures. Graphite whiskers can also be produced. 

The disadvantage of this method is the high manufacturing cost of whiskers and the difficulties associated with processing them into homogeneous composites, e.g., mixing and densification. As a result, the whisker volume present in the composites is practically limited to 30 to 40 vol % when pressure-assisted densification techniques are employed and to be-... 

Kamijo et al. [54] discovered that other metals and alloys consisting of Ni, Co, Cr, Ti, Ta, W, and Mo can accelerate whisker formation similarly to Fe. For SiC or Si3N4 powders mixed with sintering additives, whisker formation agents containing Si, Si02, C, and one of the metal catalysts, resulted in composites with SiC or Si3N4 whiskers when heated between 1300 and 1750°C. 

Whisker growth of hexagonal jS-HfP, cubic a-ZrP, and hexagonal /3-TiP is possible via a mixed-metal, impurity-activated chemical vapor deposition (CVD) process from HfCH/ZrCR/TiCH - - PCI3 - - H2 -L Ar gas mixtures at 1050 °C. Si-b Pd and Si-l-Pt were used as mixed-metal impurity components. Such whiskers are stable in concentrated... 

UnHomi, Mixed Colloidai Suspension olAbPySiCW with Submicron Particies attached to SiC whisker via Heterointeraction... 

This is simply an extension of the powder route for producing monolithic ceramics. A powder of the matrix constituent is mixed with the toughening constituent, which is in particulate or whisker form, together with a binder. The mixture is then pressed and fired or hot pressed. 

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