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The state of the art in synthetic sapphire for windows and small domes (one foot in diameter) was described in a 2004 review for the military.
Synthetic sapphire production in 2003 was 250 tons per year worldwide.
Current issues for sapphire production for windows and domes include:
(1) The cost of sapphire is high. Much of the cost is in machining and polishing.
(2) There is a need for larger area windows. The EFG method can make inherently large windows. The Heat Exchanger method has been scaled up to 38-cm-diameter, but larger sizes would be desirable. Materials Systems, Inc. has demonstrated a way to bond sapphire panes to each other to make large windows, but the bond lines are not as strong as sapphire and they provide an optical discontinuity.
(3) Optical fabrication is not well enough controlled to give reproducible mechanical properties. It is virtually impossible to know the mechanical strength of a particular sapphire part unless it is proof tested. In the absence of proof testing, designs must be conservative to be reliable
Exotic Electro-Optics, Inc., (EEO), is the world’s largest producer of large format sapphire windows. EEO has an 8,000 sq-ft facility dedicated to sapphire window fabrication and will be expanding into a 24,000 square foot building scheduled for completion in mid-2010.
With regard to future developments, a European consortium of companies and institutions has been working to develop a transparent alumina Al2O3. The main objective is the development of significantly improved alumina ceramic nanomaterials with an extremely reduced grain size. These components must exhibit the following physical properties: exceptional mechanical strength ~700 MPa; high optical transparency; improved corrosion resistance (e.g. against metal halides); and a complex hollow shape (vs. cylindrical). The improved material should solve problems in existing applications (e.g. metal halide lamps) and may lead to new applications such as scratch-resistant windows for bar-code scanners (now sapphire). Improvements in metal halide lamps could lead to substantial energy savings up to 7 billion kWh in Europe, which corresponds to one big power station or 4.5 million tons of CO2 production.
Researchers at OSU have made significant advances in the emerging science of transparent electronics, creating transparent copper oxide (CuO) based semiconductors which exhibit more than 200 times the conductivity of previously competitive materials. This basic research is opening the door to new types of electronic circuits which, when deposited onto glass, are literally invisible. The studies are so cutting edge that the products which could emerge from them have not yet been invented—although they may find applications ranging everywhere from flat-panel displays (e.g. automobile dashboard displays) to invisible circuits on screens and visors
Sapphire sensors could help enable the gasification of coal and manage processes in gasified coal power plants. The gasification process can increase the efficiency to more than 45 percent from the current 37% efficiency. No sensor has been developed that’s tough enough to withstand the intense environment inside a gasifier, where temperatures can surpass 3,000 degrees Fahrenheit. Sapphire sensors can take the heat.
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