Thermal pigment decomposition

Thermal stability is always a system-dependent property. It is a function not only of the chemical composition of the medium but also of the processing conditions, degree of dispersion, and pigment concentration. For most practical purposes, for instance, the color change due to pigment decomposition in a highly pigmented system is hardly noticeable and can thus be tolerated. 

Synthetic Iron Oxides. Iron oxide pigments have been prepared synthetically since the end of the seventeenth century. The first synthetic red iron oxide was obtained as a by-product of the production of sulfuric acid from iron sulfate containing slate. Later, iron oxide pigments were produced direcdy by the thermal decomposition of iron sulfates. In the 1990s, about 70% of all iron oxide pigments consumed are prepared synthetically. 

The mauve colored cobalt(II) carbonate [7542-09-8] of commerce is a basic material of indeterminate stoichiometry, (CoCO ) ( (0 )2) H20, that contains 45—47% cobalt. It is prepared by adding a hot solution of cobalt salts to a hot sodium carbonate or sodium bicarbonate solution. Precipitation from cold solutions gives a light blue unstable product. Dissolution of cobalt metal in ammonium carbonate solution followed by thermal decomposition of the solution gives a relatively dense carbonate. Basic cobalt carbonate is virtually insoluble in water, but dissolves in acids and ammonia solutions. It is used in the preparation of pigments and as a starting material in the preparation of cobalt compounds. 

The most important synthetic routes to iron oxide pigments involve either thermal decomposition or aqueous precipitation processes. A method of major importance for the manufacture of a-Fe203, for example, involves the thermal decomposition in air of FeS04-7H20 (copperas) at temperatures between 500 °C and 750 °C. The principal method of manufacture of the yellow a-FeO(OH) involves the oxidative hydrolysis of Fe(n) solutions, for example in the process represented by reaction (1). 

Fig. 49 Thermal decomposition of azo pigments in the solid phase. Results of differential thermoanalysis performed on pigment powders in a nitrogen atmosphere.

The assumption is that thermal decomposition starts as soon as the diarylide yellow pigment begins to dissolve in the polymer. This means that the decomposition process proceeds via the dissolved state of the pigment. This assumption, if true, also explains why these pigment powders are heat resistant up to temperatures as high as 340°C, as shown by differential thermoanalysis (DTA). 

P.Y.17 is also frequently used in polyolefins, sometimes in the form of pigment preparations. Its heat stability in these media was said to be about 220 to 240°C, but must now, as a result of the detected thermal decomposition of diarylide yellow pigments in plastics, be limited to 200°C. This tendency to decompose excludes P.Y.17 from recommendation for use in polystyrene, in which the pigment largely dissolves under the processing conditions. The same is true for ABS. 

Solid state transformations including thermal decomposition of iron salts and oxide-hydroxides. This method produces red, black and brown pigments. ... 

Thermal decomposition of iron pentacarbonyl. Very finely divided red iron oxide is obtained by atomizing iron pentacarbonyl, Fe(CO)5, and burning it in excess of air. The size of the particles depends on the temperature (580-800 °C) and the residence time in the reactor. The smallest particles are transparent and consist of 2-line ferri-hydrite, whereas the larger, semi-transparent particles consist of hematite (see Chap. 19). The only byproduct of the reaction is carbon dioxide, hence, the process has no undesirable environmental side effects. Magnetite can be produced by the same process if it is carried out at 100-400 °C. Thermal decomposition of iron pentacarbonyl is also used to coat aluminium powder (in a fluidized bed) and also mica platelets with iron oxides to produce interference or nacreous pigments. 

SQWVs of green paint layers confirmed the presence of azurite and azurite plus smalt mixtures accompanied by tenorite (CuO) in several samples as a result of thermal decomposition of azurite. Since azurite decomposition starts at 345°C with a loss of CO2 and water, slowly yielding CuO which is then converted to cuprite (Cu2 O) at 840°C [175], and since no traces of this last mineral were detected in any sample, one can conclude that the effective temperature reached by the pigments in such samples ranged from 350 to 840°C. 

Polyvinyl chloride is processed into a number of forms by including additives. Additives are used to vary the properties of PVC so that it can be made soft and flexible or hard and rigid. Additives are also used to inhibit decomposition as a result of exposure to sunlight, ozone, and chemicals. Plasticizers are the primary additive included in PVC materials. Di(2-ethylhexyl) phthalate (DEHP) and a host of other phthalates are the most common plasticizers. Plasticizers impart flexibility, thermal stability, strength, and resilience to PVC compounds. PVCs without plasticizers are classified as UPVC the letters stand for unplasticized polyvinyl chloride. UPVC is rigid and used for conduit, containers, gutters, and floor tiles. Other common PVC additives are biocides, lubricants, and pigments. 

High-quality pigments called copperas reds are obtained by the thermal decomposition of FeS047 H20 in a multistage process (Fig. 22). If an alkaline-earth oxide or carbonate is included during calcination, the sulfate can be reduced with coal or carbon-containing compounds to produce sulfur dioxide, which is oxidized with air... 

Reduction of Ammonium Dichromate. Chromium(III) oxide can be obtained by thermal decomposition of ammonium dichromate. Above ca. 200 °C, a highly voluminous product is formed with elimination of nitrogen [3.48]. The pigment is obtained after addition of alkali salts (e.g., sodium sulfate) and subsequent calcination [3.49]. 

Various methods have been suggested to deposit a thin active layer of material on a support. Those most commonly employed are (i) electroplating (ii) thermal decomposition (iii) in situ formation. Pigmented Ni matrixes have also been proposed [508]. As one can expect, a range of activation has been observed the electrochemical and mechanical stability is also varied. As for the nature of the active material, it seems clear that Ni-Mo based materials show superior qualities. The... 

The term carbon black describes a group of industrial carbons created through the partial combustion or the thermal decomposition of hydrocarbons. Carbon black is unique in that it possesses the smallest particle size and highest oil absorption among the commercially available pigments for plastics. These characteristics help explain carbon black s excellent color strength, cost-effectiveness, and ultraviolet (UV) performance and place it as the most widely used black pigment for thermoplastic applications. 

Polybenzazole fibers have been prepared containing blended organic pigments that are heat, moisture, and light resistant with thermal decomposition temperatures exceeding 200°C. These materials are useful as fibers for high-strength rope, cement/concrete reinforcers, and bullet proof vests. 

Payakoff carried out the synthesis of various oxalate complexes by mechanical activation of the solid oxalic acid with hydroxides and basic salts [35], He demonstrated that the synthesis proceeded with the formation of honey-like mass from which solid complex crystal hydrates are crystallized relatively easily under aging of activating mixtures at room temperature. Ultrafine and highly reactive catalysts, pigments and other compounds of practical importance were obtained by thermal decomposition of the mentioned complexes. 

The metal oxides produced by thermal decomposition contain all the elements initially present in the raw material apart from the titanium, which has been converted into pigment. The mixture of metal oxides, mainly iron oxide, can be used as an additive in the construction materials or cement industry. 

Transparent red iron oxide is manufactured by thermal decomposition of yellow iron oxide and elimination of water at temperatures of300 to 500 °C. It is best to start from the dried, crushed filter cake. The pigment is subsequently ground. Pigments with particularly low conductivity values are obtained by additional treatment [5.186]. 

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