Ceramic paste formation

Part II. Ceramic Powder S5mthesis Part III. Ceramic Paste Formation Mise-en Pate Part IV. Green Body Formation Mise-en Forme Part V. Presintering Heat Treatments of Drying and Binder Burnout... 

Part in Ceramic Paste Formation—Mise-En Pdte... 

The third part of this hook describes the formation of a ceramic paste. This process involves the following steps ... 

Extrusion can be defined as paste flow and extrudate formation from ceramic paste [1]. A membrane support must provide a high mechanical resistance and permeability. Tubular configurations correspond to this criterion and are adapted to the tangential filtration. 

Freudenberg produces its separator by impregnating a polyester (PET) nonwoven with an organic/ceramic paste. It aims to use this technology to produce material that increases the safety of the ceU without compromising cell production and multiple performance requirements. Table 11.3 below outlines its lithium-ion nonwoven battery separator, for use in cylindrical, prismatic, and pouch formats ... 

These relate mainly to the degree of purity of the powders and the nature of the particles surface. Purity depends on the source of the raw materials and the transformation processes that give rise to impurities (iron, heavy metals, salts, carbon, etc.). It will determine to a large extent the sintering reactivity, with the possible formation of a second intergranular phase and the final properties of the piece (mechanical, chemical, electric, etc.). The surface properties of the particles determine the mechanisms of species adsorption and dissolution. They will control the dispersion properties, homogenity and the rheological behavior of the suspensions and ceramic pastes (section 5.3). 

Friction and Adhesion. The coefficient of friction p. is the constant of proportionality between the normal force P between two materials in contact and the perpendicular force F required to move one of the materials relative to the other. Macroscopic friction occurs from the contact of asperities on opposing surfaces as they sHde past each other. On the atomic level friction occurs from the formation of bonds between adjacent atoms as they sHde past one another. Friction coefficients are usually measured using a sliding pin on a disk arrangement. Friction coefficients for ceramic fibers in a matrix have been measured using fiber pushout tests (53). For various material combinations (43) ... 

Properties of CBCs lie between ceramics and cements. These materials are formed at room temperature like cements, or may be synthesized at slightly elevated temperatures, but their structure is highly crystalline or glass-crystalline composite. The particles in CBCs are bonded by a paste formed by chemical reaction, as in cements, but the particles themselves are mostly crystalline. Their strengths are higher than those of cements but fall short of sintered ceramics. Their corrosion resistance is close to ceramics, but at the same time, they may be vulnerable to erosion like cements. The ease of formation of these ceramics, their rapid setting behavior and low cost make them very attractive for the various applications discussed in this book. 

CBPCs may have an important role even in the production of artificial implants. Typically, one may exploit rapid-prototyping to produce exact shapes of the implants. From a practical standpoint, formation of a ceramic out of a paste would appear to be most suitable for rapid-prototyping processes [11]. Thus, coupling CBPC with rapidprototyping should lead to artificial body parts that not only match the namral bones in their composition, but in structure as well. The science of CBPCs paves the way for their use not only as dental cements and bioceramics for the 21st century, but as discussed in earlier chapters, many other applications as well. 

Sol-gel chemistry has been extensively studied during the past decade. The basic reactions, hydrolysis, condensation, and complexation, involved in the formation of oxide networks from molecular precursors are now quite well described. The sol-gel process brings new opportunities in the field of materials science. It allows a powderless processing of glasses and ceramics. Coatings can be easily deposited directly from the solution onto a wide variety of substrates. Many patents have been taken and several products are now on the market. Other industrial applications will undoubtedly be developed during the next few years. 

---