Chromites and Ferrites

Three main groups of CICPs are commercially produced. Titanates, which use a titanium dioxide base, aluminates, which use an aluminum oxide base, and chromites and ferrites, which have chromium and/or iron oxide bases. 

Table S-3 Common aluminate-, chromite-, and ferrite-based CICPs.

Chromite and ferrite pigments have physical properties similar to those of the titanates and aluminates. Nearly all pigments of this variety are of brown and black shades, with just a few greens and green-blues. Some have unique infrared spectral properties that make them of interest in addition to their durability and color stability. 

There are three types of black chromites and ferrites. These contain copper, cobalt, and nickel. The copper-containing blacks include C.I. Pigments Black 23, Black... 

In order to have more infoimation on the nature of the oxygen species active in partial and total oxidation we investigated the interaction of the hydrocarbons with the pre-oxidized surfaces of oxides where different types of surface oxygen species are formed. In particular we investigated p-type semiconductors like chromia, chromites and cobalt oxide C03O4. Moreover, we studied n-type metal oxides like FezOs, metal ferrites and CuObased catalysts. 

Cobalt monoxide is a well-defined chemical entity, but the existence ol monoxides of rhodium and iridium has not as yet been satisfactorily demonstrated. All three metals yield sesquioxides, of the type R203, and dioxides, of the type R02. The last named exhibit weak acidic tendencies in that they can unite with bases to form cobaltites, rhodites, and iridites respectively, analogous to the ferrites, ruthenites, and osmites mentioned in the previous section, and exhibiting an interesting relationship to the chromites and manganites. 

Among the cuprous compounds which have been studied by X-ray methods, linear coordination is quite rare but it does occur in cuprite, Cu20 (100), which is isostructural with argentous oxide, and in cuprous chromite (33) and ferrite (127). In these three linearly coordinated oxide structures,... 

The proportion of metal added should be from about 0.01 to 5% by volume, based on the silica. It will be understood that this proportion is the total amount of modifying metal present but that more than a single metal can be used to attain this proportion. In such instances there can be found in the final supported catalysts of this invention, mixed oxides of the metals, compounds of two or more of the metals present with each other such as chromites, maganites, molybdates, tungstates, vanadates, cerates, stannates and ferrites. 

A = Mg, Fe, NT, Co, and Zn and trivalent cations B = Al, Fe, Cr, and V L Hence two types of spinel structure must be distinguished normal spinels withx = 0, meaning that all the divalent cations occupy tetrahedral sites, and inverse spinels with x = 1. Of these, rods of pure magnetite (Fe OJ or its doped form" obtained by casting molten iron oxides have been used as industrial anodes since 1870. Apart from magnetite and ferrites, today other classes of spinels have been investigated such as cobaltites and chromites. Due to their better electrocatalytic properties and fewer health and safety issues, cobaltites (e.g., MCo O with M= Mg, Cu, and Zn) are now preferred and are the only ones being developed. 

A large number of CICPs contain transition metal oxides without a significant amount of a colorless base oxide. These pigments, listed in Table 5-3, employ either green chromium(III) oxide, red iron(III) oxide, or a combination of the two as a base. They are thus referred to as chromites or ferrites, for the chromium and iron bases, respectively. Most adopt the spinel configuration, with the other important structures being those of corundum and hematite. 

Synthesis of Nano-Cobaltites, -Ferrites, -Chromites, and -Manganites... 

The most extensively studied rate processes in this group are those which yield spinels [1] (ferrites, chromites, etc.), molybdates and tungstates, and complex iodides. These types are conveniently exemplified by the representative systems... 

Pigments. Pigments employed include TiONA Ti02, SCM Chemicals, lot 25-JKSJ, Baltimore, MD 21202 lampblack, lot 97 Pfizer Minerals and Pigments Div., New York, NY 10017 manganese ferrite and copper chromite, Ferro Colors, Ferro Corp., Pittsburgh, PA 15204. 

Ferrimagnetism Positive Large x = f H) Ferrites (MnFc204, ZnFe204) and chromites... 

The hydroxide V(OH)3 is distinguished from the corresponding hydroxides of phosphorus, arsenic and antimony in that it is wholly basic. It is insoluble in alkalis, so that there do not exist any compounds of vanadium which would correspond to the phosphites, arsenites, and antimonites, or to the ferrites, aluminates, and chromites. 

The spinels are a class of double oxide of general formula AB204 industrially important members of this class include aluminates (e.g. MgAl204), ferrites (e.g. MgFe204) and chromites (e.g. MgCr204). 

Chromia Chromite Cr2Fe04 is the most commonly used chromium-containing mineral for ceramic formulations. This mineral has a spinel crystal structure, where the iron may be replaced by magnesium and aluminum. Chromite is used in ceramics largely as a refractory in the form of burned and chemically bonded bricks. For this purpose, a low-silica material is desired. When low silica is desired, chromic oxide is extracted from chromite by dissolution in add, removal of the iron impiu-ity by liquid—liquid extraction, and precipitation of the hydroxide, which is subsequently calcined to the oxide. Chromic oxide is used as a color additive to azes and enamels and in ferrite production to give magnetic materials. 

---