Inorganic pigments, determination

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 procedure of determination of metals in the thin layer without elimination of the non-volatile organic components for different paints containing inorganic pigments was developed. Several techniques of sampling from paint-and-lacquer materials for X-ray fluorescence analysis were proposed. For the study of nonhomogenity of metal distribution in the thin layer we used additionally the local method of X-ray fluorescence analysis. 

In this article, we will discuss the use of physical adsorption to determine the total surface areas of finely divided powders or solids, e.g., clay, carbon black, silica, inorganic pigments, polymers, alumina, and so forth. The use of chemisorption is confined to the measurements of metal surface areas of finely divided metals, such as powders, evaporated metal films, and those found in supported metal catalysts. 

When determining the tinting strength of inorganic pigments, the tristimulus value Y (lightness) is usually used [1.37]. 

Powder diffraction patterns have three main features that can be measured spacings, peak intensities, and peak shapes. Because these patterns are a characteristic fingerprint for each crystalline phase, a computer can quickly compare the measured pattern with a standard pattern from its database and recommend the best match. Whereas the measurement of spacings is quite straightforward, the determination of peak intensities can be influenced by sample preparation. Any preferred orientation, or presence of several larger crystals in the sample, makes the interpretation of the intensity data difficult. The most common structures of inorganic pigments are rutile, anatase, and spinel. 

Chemically, inorganic pigments are quite simple materials and include elements, their oxides, mixed oxides, sulfides, chromates, silicates, phosphates, and carbonates. The application usefulness of inorganic pigments is determined by physical as well as chemical properties. 

The particle sizes relevant for inorganic pigments stretch between several tens of nanometers for transparent pigment types to approximately two micrometers. For practical applications it is very desirable to determine not only the mean particle size but also the whole distribution. These parameters must not be confused with the crystal size determined by X-ray diffraction, as pigment particles usually are not monocrystals. 

The determination of the particle size distribution is a complex issue and the subject of voluminous monographs [1.15] so only an introduction to the questions relevant for applications concerning inorganic pigments can be given. 

Two methods are mainly used for the determination of particle size of inorganic pigments Sedimentation methods (centrifuges) and Fraunhofer diffraction with additional correction due to Mie scattering. 

Thermal UV spectroscopy has been used to identify and determine organic and inorganic pigments in polymers. 

Third International Radiocarbon Intercomparison (TIRI) standard wood samples (5,6,8) and four different archaeological charcoal samples (2,3J8) for comparison with dates previously determined at other laboratories using standard combustion methods. These measurements were utilized to demonstrate the viability of the plasma extraction technique for dating rock paintings from around the world with charcoal and inorganic pigments. 

Other applieations are examination of porous and pigmented or filled polymers (size, shape, distribution and orientation of pores or dispersed components), and the study of multicomponent and weathered materials. Examples are the determination of the distribution of rubber particles in ABS, the distribution of inorganic pigments or fillers in the surfaee (produetion of specks, irregular gloss) or in the layer proximate to the surface (haze) [135], The method is also suitable for quantitative eharacteri-sation of reinforeed composites. Mills et al. [151]... 

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