Lead chromate pigments properties

Bismuth V n d te. The use of lead chromate pigments has been slowly phased out of many appHcations. Thus a search for more environmentally acceptable relatively inexpensive yeHow pigments having exceHent coloristic properties has been ongoing. 

As far as carcinogenic effects are concerned, extensive epidemiological investigations have given no indication that the practically insoluble lead chromate pigments have any carcinogenic properties [3.139, 3.140]. Such properties have been reported for the more soluble zinc chromate and strontium chromate pigments. 

As mentioned in Section 5.2.5.1, zinc phosphate, while having many desirable properties as an anticorrosive pigment, does not demonstrate the degree of corrosion protection offered by lead and chromate pigments [5.55]. Therefore the pigment industry has concentrated on developing phosphate-based pigments with improved... 

Because of the property of lead pigments to chalk, and therefore provide an endlessly renewable surface, they were also noted for the brightness of color they produced. Even today, lead chromate is the constituent of the yellow paint that marks curbstones, fire hydrants, and highway guidelines. Sadly, little did anyone realize at the time that, in addition to flaking and peeling, the chalking of lead paint would produce deadly layers of lead chips and dust inside painted homes. 

HISTORY. Chromium was discovered by the French chemist Vauquel in 1797, while he was studying the properties of crocoite, an ore which is rich in lead chromate, its common name of chrome was derived from the Creek word chroma, which means color, because the element is present in many different colored compounds. These compounds have long been used as pigments in dyeing, and in the tanning of leather. In the early 1900s, chromium became... 

Primrose chrome This is a pale, greenish-yellow pigment with a metastable orthorhombic crystal structure containing a solid solution of lead chromate and lead sulfate. The crystals are normally stabilized by additives. Due to a less-stable crystal form, they have poorer fastness properties compared to other monoclinic chrome pigments. 

Mechanical and Chemical Properties. Colorants, especially pigments, can affect the tensile, compressive, elongation, stress, and impact properties of a polymer (5). The colorants can act as an interstitial medium and cause microcracks to form in the polymer colorant matrix. This then leads to degradation of the physical properties of the system. Certain chemicals can attack colorants and there can be a loss of physical properties as well as a loss of the chromatic attributes of the colorant. Colorants should always be evaluated in the resin in which they will be used to check for loss of properties that ate needed for the particular appHcations. 

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