Processing, ceramic materials

However, there have been a number of reports of athermal effects in processing ceramic materials, where the sintering rate or the microstructure evolution (grain size and/or porosity) resulting from microwave heating differed from that obtained by a conventional heat treatment at the same temperature. Thus, athermal effects refer to mechanisms that operate in addition to the conventional thermal effects and may be a function of, for example, the electric field intensity or the frequency. 

In extrusion the existence of a homogenous tribosystem caimot be assumed. As a rule, distinct variations in material and of an energetic nature have to be considered in processing ceramic materials. Even if there are no phase changes, the material parameters vary considerably in respect to their mechanical, thermal, rheological, tribological and chemical characteristics as a result of the effects created by temperature, pressure and speed. It is thus impossible to analyse an extruder as a comprehensive tribosystem in its entirety. 

We usually process ceramic materials in the solid state (although small amounts of liquid may be present) either... 

Recently Degussa announced that they have developed Separion separators for lithium batteries by combining the characteristics of flexible polymeric separators with the advantages of chemical and thermally resistant and hydrophilic ceramic materials. Separion is produced in a continuous coating process. Ceramic materials, e.g., alumina, silica, and/or zirconia, are slip-coated and hardened onto a support. ... 

Fabrication technologies for ah electronic ceramic materials have the same basic process steps, regardless of the appHcation powder preparation, powder processing, green forming, and densiftcation. 

Mixing. The most widely used mixing method is wet ball milling, which is a slow process, but it can be left unattended for the whole procedure. A ball mill is a barrel that rotates on its axis and is partially filled with a grinding medium (usually of ceramic material) in the form of spheres, cylinders, or rods. It mixes the raw oxides, eliminates aggregates, and can reduce the particle size. 

Sol—Gel Technology. The sol—gel process involves conversion of a metal alkoxide or mixture of metal alkoxides, dissolved in an organic solvent (generally the patent alcohol) into a hydroxooxyalkoxide sol, followed by gelation and sintering to give the desired ceramic material. 

The piopeities of a ceramic material that make it suitable for a given electronic appHcation are intimately related to such physical properties as crystal stmcture, crystallographic defects, grain boundaries, domain stmcture, microstmcture, and macrostmcture. The development of ceramics that possess desirable electronic properties requires an understanding of the relationship between material stmctural characteristics and electronic properties and how processing conditions maybe manipulated to control stmctural features. 

Alternative Thin-Film Fabrication Approaches. Thin films of electronic ceramic materials have also been prepared by sputtering, electron beam evaporation, laser ablation, chemical beam deposition, and chemical vapor deposition (CVD). In the sputtering process, targets may be metal... 

In the broad range of ceramic materials that are used for electrical and electronic apphcations, each category of material exhibits unique property characteristics which directiy reflect composition, processing, and microstmcture. Detailed treatment is given primarily to those property characteristics relating to insulation behavior and electrical conduction processes. Further details concerning the more specialized electrical behavior in ceramic materials, eg, polarization, dielectric, ferroelectric, piezoelectric, electrooptic, and magnetic phenomena, are covered in References 1—9. 

The electrical characteristics of ceramic materials vary gteady, since the atomic processes ate different for the various conduction modes. The transport of current may be because of the motion of electrons, electron holes, or ions. Electrical ceramics ate commonly used in special situations where reftactoriness or chemical resistance ate needed, or where other environmental effects ate severe (see Refractories). Thus it is also important to understand the effects of temperature, chemical additives, gas-phase equilibration, and interfacial reactions. 

Dielectric Constant The dielectric constant of material represents its ability to reduce the electric force between two charges separated in space. This propei ty is useful in process control for polymers, ceramic materials, and semiconduc tors. Dielectric constants are measured with respect to vacuum (1.0) typical values range from 2 (benzene) to 33 (methanol) to 80 (water). TEe value for water is higher than for most plastics. A measuring cell is made of glass or some other insulating material and is usually doughnut-shaped, with the cylinders coated with metal, which constitute the plates of the capacitor. 

Ceramic or carbon-brick linings are frequently used as facing linings over plastic or membrane linings when surface temperatures exceed those which can be handled by the unprotected materials or when the membrane must be protec ted from mechanical damage. This type of construction permits processing of materials that are too corrosive to be handled in low-cost metal constructions. 

This book has been written as a second-level course for engineering students. It provides a concise introduction to the microstructures and processing of materials (metals, ceramics, polymers and composites) and shows how these are related to the properties required in engineering design. It is designed to follow on from our first-level text on the properties and applications of engineering materials," but it is completely self-contained and can be used by itself. 

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