Editing Ceramic (section)

===Optical properties===
[[File:cermax.jpg|thumb|upright|Cermax [[xenon arc lamp]] with [[synthetic sapphire]] output window]]
[[Optics|Optically transparent materials]] focus on the response of a material to incoming light waves of a range of wavelengths. [[Optical filter|Frequency selective optical filters]] can be utilized to alter or enhance the brightness and contrast of a digital image. Guided lightwave transmission via frequency selective [[waveguides]] involves the emerging field of fiber [[optics]] and the ability of certain glassy compositions as a [[transmission medium]] for a range of frequencies simultaneously ([[multi-mode optical fiber]]) with little or no [[adjacent-channel interference|interference]] between competing [[wavelengths]] or frequencies. This [[resonant]] [[normal mode|mode]] of [[energy]] and [[data transmission]] via electromagnetic (light) [[wave propagation]], though low powered, is virtually lossless. Optical waveguides are used as components in [[Integrated optical circuit]]s (e.g. [[light-emitting diodes]], LEDs) or as the transmission medium in local and long haul [[optical communication]] systems. Also of value to the emerging materials scientist is the sensitivity of materials to radiation in the thermal [[infrared]] (IR) portion of the [[electromagnetic spectrum]]. This heat-seeking ability is responsible for such diverse optical phenomena as [[night-vision]] and IR [[luminescence]].

Thus, there is an increasing need in the [[military]] sector for high-strength, robust materials which have the capability to transmit [[light]] ([[electromagnetic waves]]) in the [[visible spectrum|visible]] (0.4 – 0.7 micrometers) and mid-[[infrared]] (1 – 5 micrometers) regions of the spectrum. These materials are needed for applications requiring [[transparency and translucency|transparent]] armor, including next-generation high-speed [[missile]]s and pods, as well as protection against improvised explosive devices (IED).

In the 1960s, scientists at [[General Electric]] (GE) discovered that under the right manufacturing conditions, some ceramics, especially [[aluminium oxide]] (alumina), could be made [[translucent]]. These translucent materials were transparent enough to be used for containing the electrical [[plasma (physics)|plasma]] generated in high-[[pressure]] [[sodium]] street lamps. During the past two decades, additional types of transparent ceramics have been developed for applications such as nose cones for [[heat-seeking]] [[missiles]], [[window]]s for fighter [[aircraft]], and [[scintillation counter]]s for computed [[tomography]] scanners. Other ceramic materials, generally requiring greater purity in their make-up than those above, include forms of several chemical compounds, including:

#[[Barium titanate]]''':''' (often mixed with [[strontium titanate]]) displays [[ferroelectricity]], meaning that its mechanical, electrical, and thermal responses are coupled to one another and also history-dependent. It is widely used in [[electromechanics|electromechanical]] [[transducer]]s, ceramic [[capacitor]]s, and [[Ferroelectric RAM|data storage]] elements. [[crystallite|Grain boundary]] conditions can create [[positive temperature coefficient|PTC]] effects in [[heating element]]s.
#[[Sialon]] (silicon aluminium oxynitride) has high strength; resistance to thermal shock, chemical and wear resistance, and low density. These ceramics are used in non-ferrous molten metal handling, weld pins, and the chemical industry.
#[[Silicon carbide]] (SiC) is used as a [[susceptor]] in microwave furnaces, a commonly used abrasive, and as a [[refractory|refractory material]].
#[[Silicon nitride]] (Si<sub>3</sub>[[nitrogen|N]]<sub>4</sub>) is used as an [[abrasive]] powder.
#[[Magnesium silicide|Steatite (magnesium silicates)]] is used as an [[electrical insulator]].
#[[Titanium carbide]] Used in space shuttle re-entry shields and scratchproof watches.
#[[Uranium oxide]] ([[uranium|U]]O<sub>2</sub>), used as [[nuclear fuel|fuel]] in [[nuclear reactor]]s.
#[[Yttrium barium copper oxide]] (Y[[barium|Ba]]<sub>2</sub>[[copper|Cu]]<sub>3</sub>[[oxygen|O]]<sub>7−x</sub>), a [[high-temperature superconductor]].
#[[Zinc oxide]] ([[zinc|Zn]]O), which is a [[semiconductor]], and used in the construction of [[varistor]]s.
#[[Zirconium dioxide]] (zirconia), which in pure form undergoes many [[phase transition|phase changes]] between room temperature and practical [[sintering]] temperatures, can be chemically "stabilized" in several different forms. Its high oxygen [[ion conductivity]] recommends it for use in [[fuel cell]]s and automotive [[oxygen sensor]]s. In another variant, [[metastable]] structures can impart [[fracture toughness|transformation toughening]] for mechanical applications; most [[ceramic knife]] blades are made of this material. Partially stabilised zirconia (PSZ) is much less brittle than other ceramics and is used for metal forming tools, valves and liners, abrasive slurries, kitchen knives and bearings subject to severe abrasion.<ref>{{cite journal |doi=10.1038/258703a0 |volume=258 |issue=5537 |title=Ceramic steel? |year=1975 |last1=Garvie |first1=R. C. |last2=Hannink |first2=R. H. |last3=Pascoe |first3=R. T. |journal=Nature |pages=703–704 |bibcode=1975Natur.258..703G |s2cid=4189416}}</ref>