Лако-красочные материалы — производство

Calcination causes some oxidation of the product, resulting in the formation of soluble cadmium sulfate. Prevailing regulations require pigments or pigmented articles to pass tests for the extraction of heavy metals. In order to meet these tests any soluble cadmium must first be removed. This is achieved by acidification with dilute mineral acid, followed by […]

Calcined cadmium pigments are relatively soft and easily form a slurry. Passing the slurry through a pin mill or hammer mill will break aggregates down. The slurry can then be passed through a fine mesh to exclude oversize agglomerates and ensure a product which disperses well when used in the desired application. 3.4.10

The filter cake can be oven dried, after which it requires crushing into small lumps prior to calcination. To reduce manual handling, the cake is often extruded into noodles onto a belt drier, where a flow of hot air through the pigment bed dries the product into small pellets. 3.4.8 Calcination Calcination is one of […]

Separation of the solid particles from the liquid is most likely to be done by a filter press or belt filter, although decantation can be used for washing, as the product settles well. Soluble sulfate and/or nitrate salts, depending on the acid used to dis­solve the cadmium, will also need washing out. This step is […]

During precipitation, the above solutions are intimately mixed so as to form a mixture of stoichiometrically balanced sulfides that will form a pigment on firing. It must be remembered that the initial products formed on precipitation do not possess final pigmentary properties. Batch-wise production is the more common route for precipitation, although continuous precipitation has […]

Solutions of sodium sulfide are normally made from sodium sulfide flakes (Na2S. H2O). If lithopones are required, a solution of barium sulfide is also neces­sary. The latter can be purchased as “black ash”, which owes its name to a gray appearance, having been made from the reduction of barium sulfate with carbon. It is difficult […]

While cadmium will dissolve in sulfuric, hydrochloric and nitric acids, a mixture of sulfuric and nitric acids is preferred, to obtain a controllable reaction rate to avoid producing noxious fumes. Sulfuric acid on its own does not dissolve cadmium metal well, as hydrogen bubbles produce a coating which prevents further attack. Typically, cadmium moss or […]

Not all manufacturers produce cadmium oxide, as some prefer to dissolve cad­mium metal directly in acid. However cadmium oxide is used in many other ap­plications, including nickel cadmium batteries and stabilizers for polymers. The oxide can be produced by first melting the metal, then allowing it to flow into a carbon or silicon carbide crucible […]

3.4.1 General Points Today’s high-performance pigments require the use of high grade starting materi­als and a controlled process to ensure the production of consistent colors. Early methods for cadmium pigments would appear crude by modern techniques, and would not be capable of producing the commercially required products of today. The process route to cadmium pigments […]

It is the very property that cadmium and sulfur can be lattice substituted to a con­siderable extent by members of their own periodic groups that gives rise to the broad range of colors possible in the cadmium palette. This property, coupled with excellent insolubility and outstanding heat resis­tance, makes them truly high-performance pigments. The replacement […]