Spinel color

For hematites and (inverse) spinels, color is also influenced by the calcination temperature. However, the main driving factor is the actual chemical composition, including the use of mineralizing agents. This opens numerous possibilities to obtain colored pigments with different shades. 

The major ceramic applications for spinels are the magnetic ferrospinels (ferrites), chromite brick and spinel colors (see table). Magnetic recording tape coated with a-CrjOj is a relatively recent development. Also used as a porous protective coating in oxygen sensors for automotive emission controls. 

Several gemstone species occur in various colors, depending on the presence of impurities or irradiation-induced color centers. Examples are the beryl, comndum, and quart2 families. Quart2 has poor optical properties (RI = 1.55, DISP = 0.013), but becomes of gemological interest when it exhibits attractive colors. Any material can have its color modified by the addition of various impurities synthetic mby, sapphires, and spinel are produced commercially in over 100 colors (2). Synthetic cubic 2irconia has been made in essentially all colors of the spectmm (11), but only the colorless diamond imitation is produced commercially in any quantity. 

Another desirable property for a ceramic color is a high refractive index. For example, valuable pigments are based on spinels [1302-67-6] ( 2jj = 1.8) and on zircon ( 2j = 1.9), but no valuable pigments are based on apatite ( 2j = 1.6), even though the lattice of apatite is as versatile for making ionic substitutions as that of spinel. 

Rubin, m. ruby, -balas, m. balas ruby (ruby spinel), -blende, /. pyrargyrite. -farbe, /. ruby color, ruby. 

Chrome alumina pink spinel, formula and DCMA number, 7 348t Chrome Antimony Titanate Buff, pigment for plastics, 7 369t Chrome brick, 6 495 Chrome dyes, 9 468 26 396 Chrome green, 6 554 color, 7 331... 

Fourcroy predicted that this mineral would give chemists the opportunity to make a more thorough study of the properties of chromium and perhaps to discover compounds of it which, because of their rich and varied colors, would be useful in painting and in the manufacture of glass and enamel (90). He also encouraged study of the chromium alloys. The chrome-iron ore is now known as chromite. It is not a chromate, but has the spinel composition, Fe(Cr02)2-... 

Fe304, magnetite [1309-38-2], spinel structure, ferrimagnetic, color black... 

Many spinel phases have been used as colorants for ceramics and porcelain enamels. The most important pigments based on spinel phases used in paints, plastics, and building materials are given in Table 25. 

Zinc Iron Brown. Variation of the zinc to iron ratio in red-brown iron spinel (ZnFe204), or replacement of some of the iron ions by aluminum and titanium ions, gives light to medium brown pigments. Inclusion of a small proportion of lithium ions considerably improves stability towards reducing agents, e.g., when the pigments are used to color plastics [3.87]. The partial replacement of iron ions by chromium(III) ions yields dark brown products [3.88]. 

Emery is a mixture of granular corundum of dark color, magnetite and hematite, sometimes with spinel. Quartz may be present For a long time emery was supposed to be an ore of iron. Until the introduction of artificial abrasives, emery was much used for such purposes. 

Several gemstone species occur in various colors, depending on the presence of impurities or irradiation-induced color centers. Any material can have its color modified by the addition of various impurities synthelic ruby, sapphires, and spinel are produced commercially in over 100 colors. 

Spinel. Colorless (pure), blue (Co), and olher colored synthelic spinels made by the Vemeuil process are widely seen in class rings and in other jewelry uses, where the blue is often mislabeled as synthetic sapphire. 

Intercalation of cations into a framework of titanium dioxide is a process of wide interest. This is due to the electrochromic properties associated with the process (a clear blue coloration results from the intercalation) and to the system s charge storage capabilities (facilitated by the reversibility of the process) and thus the potential application in rocking-chair batteries. We have studied alkali-metal intercalation and ion diffusion in the Ti02 anatase and spinel crystals by theoretical methods ranging from condensed-phase ab initio to semiempirical computations [65, 66]. Structure relaxation, electron-density distribution, electron transfer, diffusion paths and activation energies of the ion intercalation process were modeled. 

Figure 7.25. Positions of Mg atoms (larger, light color) are shown in a fee cell and in one set of T positions for spinel, MgAl204. Al4 tetrahedra are in the other T positions. Oxygen atoms are omitted.

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