Color in Ceramics

F centers in crystals in Section 11.9, and the origins of color in glass in Section 21.8 we will discuss color more in Chapter 36. 

Most dielectric ceramics and glasses are colorless because of their large g. They become colored when energy states are added within the band gap. These new levels allow electron transitions to occur within the visible 

The most common way to color a ceramic is by adding transition metals (TM), particularly Ti, V, Cr, Mn, Fe, Co, and Ni, where the 3d is partly fllled. 

FIGURE 32.9 (a) Splitting of the d orbitals in a ligand field, (b) Splitting of d orbitals in a distorted octahedral ligand field in corundum. 

Other sources of color in ceramics include the following  

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Cobalt as a Colorant in Ceramics, Glasses, and Paints. Cobalt(II) ion displays a variety of colors in soHd form or solution ranging from pinks and reds to blues or greens. It has been used for hundreds of years to impart color to glasses and ceramics (qv) or as a pigment in paints and inks (see CoLORANTS FOR CERAMICS). The pink or red colors are generally associated with cobalt(II) ion in an octahedral environment and the chromophore is typically Co—O. The tetrahedral cobalt ion, Co—chromophore, is sometimes green, but usually blue in color. 

Cuprous Iodide, Cu.O. cubic while crystals, practically insoluble in H 0 or alcohol, soluble in NHjOH. potassium iodide, or potassium cyanide. Used in Sandmeyer s reaction lo synthesize aryl chlorides. Cupric Oxide. CuO, black cubic crystals, insoluble in IFO. soluble in HCI. NHjOH. or ammonium chloride. Used as a green and blue colorant in ceramics. 

Data obtained from Denio, Allen A. 2001. The joy of color in ceramic glazes with the help of redox chemistry. Journal of Chemical Education. 78 No 10. 

Nassau, K. (1983) The Physics and Chemistry of Color The Eifteen Causes of Color, Wiley, New York. The classic book on the sources of color in ceramics. 

Rare earth element impurities are also used as commercial colorants in ceramics. In this case, these ions possess partially filled f orbitals. Similar effects occur as with the 3d transition elements however, the electronic transitions occur between the energetically split f orbitals. Some ions commonly found to induce color are Ce ", Pr, and Nd. ... 

Bloor, D. and R. W. Khan. 1994. Encyclopedia of Advanced Materials. (4 vols.) Oxford, UK./ Tarrytown, NY Pergamon Press. Advanced materials are artificially produced to meet the requirements of particular applications. The rapid developments in this field are covered in more depth than was possible in the standard Encyclopedia of Materials Science and Engineering (1986) and its supplements. Examples of topics covered include aerogel catalysts, bicmiedical polymers, color in ceramics, fast ion conduction in ceramics, hydrogels, metal matrix composites, and oligomers. There is an excellent subject index and a wealth of illustrations. 

Lead antimonate [13510-89-9] (Naples yellow), Pb2(Sb0 2> mol wt 993.07, d = 6.58g/cm, is an orange-yeUow powder that is insoluble in water and dilute acids, but very slightly soluble in hydrochloric acid. Lead antimonates are modifiers for ferroelectric lead titanates, pigments in oil-base paints, and colorants for glasses and glazes (see Colorants for ceramics). They are made by the reaction of lead nitrate and potassium antimonate solutions, followed by concentration and crystallization. 

Most talc sold to paper, ceramics, and other industrial customers is manufactured to specifications agreed to between the producer and consumer. In paper, properties such as color, abrasion, surface area, and tint ate most important, whereas in ceramics, oxide chemistry, fired color, pressing characteristics, and alkaH metal content ate mote important. There ate some military specifications for talc used in corrosive coatings (6) and for cosmetic talc products used for cleaning of personnel in chemical warfare zones (7). 

This dissociated zircon is amenable to hot aqueous caustic leaching to remove the siHca in the form of soluble sodium siHcate. The remaining skeletal stmcture of zirconia is readily washed to remove residual caustic. Purity of this zirconia is direcdy related to the purity of the starting zircon since only siHca, phosphate, and trace alkaHes and alkaline earth are removed during the leach. This zirconia, and the untreated dissociated zircon, are both proposed for use in ceramic color glazes (36) (see Colorants for ceramics). 

Cadmium hydroxide is the anode material of Ag—Cd and Ni—Cd rechargeable storage batteries (see Batteries, secondary cells). Cadmium sulfide, selenide, and especially teUuride find utiUty in solar cells (see Solarenergy). Cadmium sulfide, Hthopone, and sulfoselenide are used as colorants (orange, yellow, red) for plastics, glass, glazes, mbber, and fireworks (see Colorants for ceramics Colorants forplastics Pigments). 

Cobalt pigments are usually produced by mixing salts or oxides and calcining at temperatures of 1100—1300°C. The calcined product is then milled to a fine powder. In ceramics, the final color of the pigment maybe quite different after the clay is fired. The materials used for the production of ceramic pigments are... 

There are a number of ways to obtain color in a ceramic material (1). First, certain transition-metal ions can be melted into a glass or dispersed in a ceramic body when it is made. Although suitable for bulk ceramics, this method is rarely used in coatings because adequate tinting strength and purity of color caimot be obtained this way. 

R. A. Eppler and D. R. Eppler, Color in Eead andEead-free Glacis, presented at the M. E. Whitewares EaU Meeting, American Ceramic Society, Asheville, N.C., Sept. 26,1991 Ceram. Eng. Sci. Proc. to be pubhshed 1992. 

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