Ceramic powders binder mixture

Metal powder—glass powder—binder mixtures are used to apply conductive (or resistive) coatings to ceramics or metals, especially for printed circuits and electronics parts on ceramic substrates, such as multichip modules. Multiple layers of aluminum nitride [24304-00-5] AIN, or aluminay ceramic are fused with copper sheet and other metals in powdered form. The mixtures are appHed as a paste, paint, or slurry, then fired to fuse the metal and glass to the surface while burning off the binder. Copper, palladium, gold, silver, and many alloys are commonly used. 

The plastic forming of ceramic shapes is based on the application of external forces to a mixture of ceramic powder and binder. The plastic mixture deforms and flows under applied stresses. The external forces cause the plastic mix to be adjusted to any die or mold, which dictates the eventual shape. Therefore, the flow behavior of such mixes during plastic forming has a major effect on the quality of the ceramic parts. Again, the flow stability of the mix during forming depends on the homogeneity of the ceramic powder and binder mixture. 

The primary focus of this chapter is to describe the factors that influence flow behavior and mix homogeneity of a plastic mixture containing a high volume fraction of ceramic powder as a filler and a relatively small volume fraction of organic polymeric binder. The emphasis is placed on mixes in which flowability is achieved only above the ambient temperature. 

Because of the exponential form of the viscosity equation, mixtures of ceramic powder in thermoplastic binder are only significantly sensitive to temperature change above 70°C [3]. In an injection molding operation, it is usual to plot In q versus T for a constant shear rate, not a In q versus l/T plot at a... 

Dispersive mixing An important application of dispersive mixing is the incorporation of the ceramic powder into the molten organic binder. During dispersion, the agglomerates of the constituent elements of the secondary component of the mixture are ruptured. 

In thermal debinding, the binder is removed as a vapor by heating at ambient pressure in an oxidizing or nonoxidizing atmosphere or under a partial vacuum. The process is influenced by both chemical and physical factors. Chemically, the composition of the binder determines the decomposition temperature and the decomposition products. Physically, the removal of the binder is controlled by heat transfer into the body and mass transport of the decomposition products out of the body. In practice, binder systems consist of a mixture of at least two components that differ in volatility and chemical decomposition. The ceramic powder may alter the decomposition of the pure polymer. In view of the complexity of real systems, we first consider the basic features of thermal debinding for a simplified system consisting of a powder compact with a single binder, e.g., a thermoplastic polymer such as poly(methyl methacrylate) or polyethylene. Later,... 

In plastic forming, the ceramic powder is mixed with a binder or a plasticizer. This incorporation of a binder makes the mixture plastic and makes it possible to be formed under the use of pressure. This method again is used in powder metallurgy. 

Barium titanate is made by sintering a finely powdered mixture of barium carbonate and titanium dioxide in a furnace at 1,350°C. The calcined mass is finely ground and mixed with a binder (plastic). The mixture is subjected to extrusion, pressing or film casting to obtain ceramic bodies of desired shapes. Plastic is burnt off by heating and the shaped body is sintered by firing and then pobshed. 

As discussed earlier, aluminides have been used as binders for carbide- and boride-based cermets, for example, by adding Ni and Al powders to exothermic mixtures of Ti with C or B. On the other hand, some intermetallic compounds (e.g., NiAl, Ni3Al, TiAl) possess high enough heats of formation so that composites with intermetallic matrices can be produced either in the VCS or SHS regimes. The ceramic components are added either in the green mixture or synthesized in situ during the reaction. 

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