What is CMC?

These are conductive Ceramics.

Some times they are reinforced by different functional materials to increase ionic conductivity of the material, far greater than Semiconductors and then material works like high temperature metal conductor, far beyond metal melting point temperatures.

It happens due to highly organized structural arrangement inside the ceramic metrix which otherwise is flash frozen fluid like random space structure. It is more closer to crystal structure in functional materials that gives new property. It is no longer a glassy material.

I believe your reference to CMC's relates to Ceramic MATRIX Composites. A Polymer Matrix Composite is made from fibers (carbon, glass, etc) that are cast (in a 'matrix) in a polymer (epoxy, polyester, etc.). So, a Ceramic Matrix Composite is made from fibers (carbon, glass, ceramic, etc.) in a ceramic matrix.

These products generally have much higher thermal stability than polymer matrix composites and may be stronger and/or more durable than ceramics. But, processing can be difficult and costly, so please do your homework assessing your materials options.

For more information: http://www.the-infoshop.com/study/bc5207_ceramic_matrix_composite.html

Do you have an application you ar considering that we could discuss in this forum?

I do not know about CMC, however, you seem to have two different, but equally valid answers already.

I do know about Ceramic Coating technology, at least as it pertains to coating metals with a Ceramic material. This is really several different technologies. The most common and oldest technology to coat metal with ceramic is where a "green" ceramic slurry is applied to the surface of a metal part, usually in finished or near finished form, because working the coated metal is problematic. The slurry is a mix of ceramic powders and powdered glass with water to form a (usually) thixotropic mixture. The mix is applied either by spray or dip. Excess water will often drain off once the solids settle. The coating material must be dried slowly before firing in a furnace similar to other ceramics. However, the time and temperature must take into consideration the dissimilar thermal expansion of the ceramic and metal, which should be matched as closely as possible. The glass portion of the "mud" will vitrify (melt and become "glassy"), and act as a bond betwen the metal and the ceramic as well as providing a nice shiny finish which is often desirable. Some ceramics will also "vitrify" as they change to a glassy state. This is the process used for hundreds of year to make so-called "porcelain" metal goods and most consumer stoves, washers, and dryers, Although plastics and other corrosion resistant metals have been making gains in those areas, ceramic coated steel is still prevalent in those products. Traditionally, vitreous enamel has been mostly glass, however glass-ceramic coatings are finding new applications due to a wider range of properties.

Another type of ceramic coating on metals is a plasma-coating process. Usually a high temperature ceramic powder, like alumina, (Aluminum Oxide, Al₂O₃) is melted in a superheated gas stream which is then directed at the metal substrate, initially "sticking" to the metal due to a static electric charge, but then fusing to the metal as it cools. Plasma-coatings can be very thin or built up with several layers to be very thick. They can be used for their thermal or electrical insulating properties. Whereas ceramic materials alone might be very fragile and expensive, ceramic coated metals have greater strength and usually lower cost, although sometimes at a price of reduced temperature capability as compared to ceramics alone

Some ceramic coatings may be brushed or sprayed on cold and simply allowed to dry without firing. These will often have excellent strength and electrical insulating qualities, but might not hold up in high temperatures, due to bonding agents which might be substituted for the vitrifying elements. One example of this is the way that modern "chalk boards" are made, using a high-ceramic paint instead of traditional slate sheet "black boards". This paint can be used on either metal or wood composite surfaces.

These same porocesses are used to produce vitrious and ceramic coatings in the electronics industry Ceramic coated resistances. also where high temperature insulators are required. Your answer gives plenty of good info.

metal composite can be either structural or surface composite

what line you are looking for.

aarshi

I think glass is glass and not structured like crystals. Perhaps only some amount of polymer formation may be structured or tightly bonded or even directionally bonded.