Pigment Quality

The quality of the TiOz pigment is influenced by vario us factors. Reaction temperature, excess oxygen, and flow conditions in the reactor affect particle size and size distribution. Therefore, optimum conditions must be established for every reactor design. Caking of the TiOz on the walls of the reactor leads to impairment of quality. 

The quality of the Ti02 pigment is influenced by various factors. Reaction temperature, excess oxygen, and rheologic conditions in the reactor affect particle size and 

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A higher quality a-modification with enhanced tinctorial strength and transparency is prepared from the leuco form of bromoisoviolanthrone. This intermediate in turn is manufactured by vatting crude bromoisoviolanthrone with sodium dithionite/aqueous sodium hydroxide. The product is separated and oxidized in an aqueous alkaline medium in the presence of surfactants. Application of shearing forces, preferably by means of a sand or pearl mill, and maintaining a temperature of 50°C produces improved pigment quality [26]. 

The process can be accelerated by operating at 150 °C under pressure this technique also improves pigment quality [3.19]. Rapid heating of a suspension of iron oxide hydroxide with the necessary quantity of Fe(OH)2 to ca. 90 °C also produces black iron oxide of pigment quality [3.20], [3.21],... 

A pigment-grade zinc oxide rotary kiln uses high temperature to produce pigment-quality zinc oxide and makes possible higher recovery than a grate furnace. 

These reactions are carried out continuously in furnaces. The reacted mixture is leached with water to remove soluble products, filtered, dried and ground. Very pure chromium(III) oxide (99%) of pigment quality is thereby obtained. 

Legodi, M.A. de Waal, D. (2007). The preparation of magnetite, goethite, hematite and maghemite of pigment quality from mill scale iron waste. Dyes and Pigments, 74(1), 161-168. doi ... 

M, 2 equiv.) were mixed using a range of flow rates (10, 30, and 50 ml min-1) and the reaction products were collected in a beaker of distilled water. After 5 min, a resin solution was added to the beaker and stirring continued for an additional 16 h prior to filtration and assessment of the pigment quality, using a commercially available sample of 166 as a benchmark. Using this approach, the authors obtained a... 

Figure 16.9 Pigment quality scaling-up (batch synthesis) versus numbering-up of CPC microreactors for small-scale production of a yellow model pigment. Courtesy of Elsevier [20].

These preliminary experiments indicate that a combination of both lower firing temperatures and better pigment quality is possible. The colloidal route can render the sol-gel process economically more attractive, but it seems that the major edge of the sol-gel technology lies in the superior quality of the pigments produced. 

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