|Monthly Tech-Tip |
Ceramic materials are among the hardest and most heat resistant materials known. Ceramics spans the spectrum from ancient terra cotta to modern hi-tech materials.
A solid produced by the fusion of non-metallic mineral or man-made mineral-like substances in a kiln. Or, in simpler terms, it is grinding minerals and rocks into a powder then firing the powder in a kiln to stick it back together again as a rock! Technically, mother nature makes ceramics: Metamorphic and igneous rocks. In contrast with metals, which oxidize over decades, ceramics are bonded oxide compounds, making them durable over millenniums. Often the only objects that have endured from ancient cultures are their ceramics.
The term 'ceramic industry' is subjective and can mean very different things in different circles (e.g. tableware, sanitaryware, structural, hi-tech, tile, wear parts, abrasives, glass). The term 'ceramic materials' is also subjective, materials used in traditional ceramics are very different from those used in refractory, wear resistant or thermal shock resistant products. At this site we generally deal with 'traditional ceramics', products like tableware and pottery (porcelain, stoneware, terra cotta), porcelain bathroom products (sanitaryware), brick, tile, sculpture and architectural items. All of these have been made for milleniums and are well understood and their manufacture is within the reach of even hobbyists. That being said, in all of these sectors large-scale manufacture has become very high-tech, putting a great divide between it and traditional small-scale methods.
Ceramics distinguish themselves in their hardness and durability (accompanied by brittleness). And their ability to do that at high temperatures. Specific properties include insensitivity to acids and alkalis, bio-compatibility, insulating effect when exposed to heat or electrical currents, porosity control, etc.
In recent years a wide range of new ceramic processes have been developed, many owing to the development of much better kilns (with abilities to accurately control temperature, pressure and atmosphere). Industries have learned to form ceramics in many new ways and even how to machine and 3D print them. And materials are being processed to much finer particle sizes, better purity and more specific property profiles.
The fired ceramic matrix is composed of crystalline particles (mainly of clays, feldspars and quartz) that begin to bond at points of contact at lower firing temperatures (forming porous solids of low strength). As temperatures rise glass can form as feldspar particles begin to melt, that cements other particles together (filling voids between them, densifying the matrix and increasing strength). Higher temperatures also cause transformations in mineral particles, they can change shape, react with each other and form better bonding (even in the absense of glass). Ceramic matrixes often contain aggregate particles that act as fillers and modify drying and firing behavior and the physical properties of the fired material.
Glass vs. Crystalline
In ceramics, understanding the difference between what a glass and crystal are provides the basis for understanding the physical presence of glazes and clay bodies.
In the ceramic industry, refractory materials are those that can withstand a high temperature without deforming or melting. Refractories are used to build and furnish kilns.
A densification process occurring within a ceramic kiln. With increasing temperatures particles pack tighter and tighter together, bonding more and more into a stronger and stronger matrix.