Pigment inorganic

Two of the most important inorganic pigments are the white opaque titanium dioxide and carbon black. However, in this text we will only consider those pigments which are used for their colour, i.e. a specific absorption in the visible spectmm. The origin of the colour in inorganic pigments is due to one of the three following effects  

Ligand field effects e.g. iron oxide reds and yellows) Charge transfer e.g. chromates, ultramarines) 

Pure semi-conductors e.g. cadmium yellows and oranges) 

It should be noted that the use of certain inorganic pigments, especially those derived from cadmium derivatives and lead chromates, pose considerable toxicological risks and their use is now subject to legislation in most countries. 

Iron oxides may be natural or synthetic. Synthetic oxides are preferred for their high pigmentation capacity, and their chemical and color purities. Natural oxides are cheaper in cost but they contain impurities that may interfere with some of the polymer properties. Iron oxides are used as yellow, red, black, brown shaded, and light-tan pigments. 

Cadmium pigments, mainly cadmium reds, are often used, but their high cost and their poisoning effect limit their practical applications, in spite of their very good light and heat stability. 

Other interesting inorganic pigments are white zinc, aluminum hydrate (green), white lead, cinnabar, and chromium oxide, hydrated or dehydrated, used in the production of some transparent colored plastic materials. 

Ultramarine blues are used as pigments to produce reddish blue violet shades they have good heat and light stabilities and a good resistance to humidity, but they are sensitive to acids and may be responsible for polymer oxidation. 

Titanates are used as yellow, green, and blue pigments [2] they are stable but their low tinctorial strength and their high cost reduce their application range. 

Titanium dioxide Iron oxide Aluminum Blanc fixe 

Zinc oxide Red lead Zinc Paris white 

Antimony oxide White lead Lead sulfate Cadmium red Lead silicochromate Lead chromates Zinc chromates Cadmium yellow Calcium plumbate Chromium oxide Prussian blue Ultramarine blue Lead Barytes whiting China clay Mica Talc 

Characteristics Anatase Titanium dioxide Rutile Zinc oxide White lead Basic lead carbonate 

400- to 500-nm region, giving a yellowish undertone, whereas anatase absorbs almost no light. The color of rutile coatings can be adjusted by tinting with a violet pigment. 

There is other regional legislation that is outside the scope of this book. 

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Chemical Properties. Elemental analysis, impurity content, and stoichiometry are determined by chemical or iastmmental analysis. The use of iastmmental analytical methods (qv) is increasing because these ate usually faster, can be automated, and can be used to determine very small concentrations of elements (see Trace AND RESIDUE ANALYSIS). Atomic absorption spectroscopy and x-ray fluorescence methods are the most useful iastmmental techniques ia determining chemical compositions of inorganic pigments. Chemical analysis of principal components is carried out to determine pigment stoichiometry. Analysis of trace elements is important. The presence of undesirable elements, such as heavy metals, even in small amounts, can make the pigment unusable for environmental reasons. 

The most common stmctures of inorganic pigments ate mtile, anatase, and spinel. 

Whereas the production flow charts of inorganic pigments appear to be simple, the actual processes can be very compHcated. Many pigments are not pure chemical compounds, but can be multiphase systems contaminated with various impurities and modifiers. Because pigments are fine powders, the physical properties are as critical to their appHcation performance as are the chemical properties. 

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