Hello everyone! I am interested in working on processing (fabrication)of transparent ceramic (bulk), but have not yet decided on which specific materials to focus on. I browsed the google and found out some candidate materials, such as ALON, Mg-Al spinel, sapphire, etc. Could anyone give me some suggestions? (I am in a university research lab and want to tackle a topic that is also attractive to industry.)
Thanks in advance.
Transparent BULK ceramics.
Single crystals of many different crystalline sturctures are optically transparent, but may be anisotropic.
If you want polycrystalline bulk transparent ceramics, you should stick with the cubic based crystal structures (MgO and so on). The cubic crystals are optically isotropic and there in no refractive index mismatch between adjacent crystals or grains.
Not certain about the possibliity of grain boundary scattering which could reduce transparency.
The topic has been popular periodically since the 1960's when I first became interested in ceramics .....
Probably a god time to retreat to the library and actually dig up some data.
In thin films, which is not your stated interest, the crystal symmetry requirements are less restrictive.
Jim
Thank you for the information. I will do some more literature survey.
I don't know the details but, Casio has developed a ceramic lens using "LUMICERA", for its line of digital cameras.
Carl Sachs
Yung-Jen L> Hello everyone!
A key question should be whether or not you want to work with single crystals which usually involve melt or gas vapor growth, not easily accomplished unless you have some $$$$ for equipment. Al raised a good point, just how transparent does this need to be. AlON and spinel are only made optically transparent through hot pressing or Hipping, and only translucent through pressureless sintering. (this is usually due to pore scattering and in the case of AlON dependent upon stoichiometry) Even alumina sintered in hydrogen is fairly translucent. If you want an industry attractive topic look at ways to pressureless sinter these polycrystalline ceramics to improve the transmission. Sylvania uses oodles of these translucent alumina envelopes for high pressure gas lights. The more transparent and more resistance to clouding are a good target.
Also, a crystal is likely to exhibit birefringence (also called double refraction). This is a difference in the index of refraction along crystal axes.
I do not have equipment for single crystal growing. Basically, I am looking into "conventional" methods to make it. A company in the US (called Surmet) marketed ALON as transparent ceramic for military applications. The company claims that 2 mm thick piece can have transmittance ~ 75-80%. Most amazing is that it claims that the bulk pieces can be fabricated by pressureless sintering or slip casting. If polycrystalline spinels can be made transparent by pressureless sintering, it would be very attractive. Now, AlON can be pressureless sintered to transparency. it is quite possible for other spinels too.
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