Ferric oxide, 4.35

Ferric oxide (Fe203) occurs naturally and is often used as a red pigment employed in paints and primers, as well as in rubber formulation. Because of durability, the iron oxide pigments are used in barn and freight car paints. The synthetic pigment is made by heating iron sulfate. 

Venetian red is a mixture of ferric oxide with up to an equal amount of the pigment extender, calcium sulfate. This pigment is manufactured by heating ferrous sulfate with quicklime in a furnace. Venetian red is a permanent and inert pigment, particularly on wood. The calcium sulfate content, which furnishes corrosion-stimulating sulfate ions, disqualifies this pigment for use on iron. 

Indian red is a naturally occurring mineral whose ferric oxide content may vary from 80 to 95%, the remainder being clay and silica. It is made by grinding hematite and floating off the fines for use. 

Ferric Oxide. - Hydrolysis of Fe salts may lead either to a-FeaOa (haematite) or FeOOH (both in the )3- and a-form), depending on the nature of precipitating agent, the pH and the type of salt. a-FeOOH (goethite) was studied in the mid-seventies to some extent but its interest as a catalyst is very limited, as it transforms into haematite at 180°C. Crystallites of goethite terminate by the (100) face, as confirmed by the adsorption of phosphate and sulphate groups. The adsorption of some test molecules has been studied. 

The 7-Fe203 (maghemite), which converts into the a-form at 400 °C has not been studied. Haematite is widely used as a catalyst. Unfortunately, it is difficult to obtain samples in a stable form for the characterization of 

---

Fixed-bed noncatalytic reactors. Fixed-bed reactors can be used to react a gas and a solid. For example, hydrogen sulfide can be removed from fuel gases by reaction with ferric oxide ... 

Uptake at saturation by a ferric oxide gel at 25°C, calculated as a volume of liquid (v,)... 

A detailed study of the physical and chemical adsorption of water on three xerogels, ferric oxide, alumina and titania, as well as on silica (cf. p. 272) has been carried out by Morimoto and his co-workers. Each sample was outgassed at 600°C for 4 hours, the water isotherm determined at or near 20°C, and a repeat isotherm measured after an outgassing at 30 C. The procedure was repeated on the same sample after it had been evacuated at a... 

Physisorption and chemisorption of water on alumina, titania and ferric oxide selection of results (Morimoto ef a/. )... 

Titanium dioxide-ferric oxide coated mica... 

Another sol—gel abrasive, produced by seeding with a-ferric oxide or its precursors, has been patented (30). A magnesium-modified version of this abrasive, also called Cubitron, is being produced as a replacement for the earlier type. Yttria [1314-36-91-vnc>A V eA sol—gel abrasives have also been patented (31), as well as rare earth oxide modified materials (32). These abrasives are all produced by 3M Corporation they have performed very well ia various applications such as ia coated abrasives for grinding stainless steel and exotic alloys. 

Iron Sponge. An old method for removal of sulfur compounds involves contacting gases containing H2S and H2O with CC- or y-ferric oxide... 

Iron. As with copper, some dozen or more materials are used as fertilizer Hon sources. These include ferrous and ferric oxides and sulfides and ferrous ammonium phosphate [10101 -60-7] ferrous ammonium sulfate [10045-89-3] frits, and chelates. In many instances, organic chelates are more effective than inorganic materials. Recommended appHcation rates range widely according to both type of micronutrient used and crop. Quantities of Fe range from as low as 0.5 kg/hm as chelates for vegetables to as much as a few hundred kg/hm as ferrous sulfate for some grains. 

Alkali metal haHdes can be volatile at incineration temperatures. Rapid quenching of volatile salts results in the formation of a submicrometer aerosol which must be removed or else exhaust stack opacity is likely to exceed allowed limits. Sulfates have low volatiHty and should end up in the ash. Alkaline earths also form basic oxides. Calcium is the most common and sulfates are formed ahead of haHdes. Calcium carbonate is not stable at incineration temperatures (see Calcium compounds). Transition metals are more likely to form an oxide ash. Iron (qv), for example, forms ferric oxide in preference to haHdes, sulfates, or carbonates. SiHca and alumina form complexes with the basic oxides, eg, alkaH metals, alkaline earths, and some transition-metal oxidation states, in the ash. 

Parasitic ferromagnetism is a weak ferromagnetism that accompanies antiferromagnetism, eg, in a-ferric oxide [1309-37-1], a-Fe202. Possible causes include the presence of a smaU amount of ferromagnetic impurities, defects in the crystal, and slight deviations in the directions of the plus and minus spins from the original common axis. 

Particulate Materials. There are three principal classes of particulate magnetic materials y-ferric oxide, y-Fe202, and its modifications chromium dioxide [12018-01 -8] and iron [7439-89-6]. A comparison of the remanent magnetization, and coercivity, for several y-Fe202... 

In the double-neutralization process, Na2SiFg is precipitated and removed by filtration at a pH of 3—4 (9). Upon raising the pH to 7—9, insoluble phosphates of Fe, Al, Ca, and Mg form and separate. Iron can be precipitated as hydrous ferric oxide, reducing the phosphate loss at the second filter cake. Both the fluorosihcate and metal phosphate filter residues tend to be voluminous cakes that shrink when dewatered recovery of soluble phosphates trapped within the cakes is difficult. 

In the direct precipitation process, the seeds of iron(III) oxide are added to an iron salt solution, most often iron(II) sulfate, which is subsequendy oxidized by air. The released sulfuric acid is removed by the addition of metallic iron with which it reacts to iron(II) sulfate. The overall reaction shows that ferrous sulfate is not consumed during the process. It only helps to oxidize metallic iron to ferric oxide ... 

The Penniman-Zoph process involves the preparation of seeds or nucleating particles by the alkaU precipitation of ferrous sulfate. The reaction is carried out at alow temperature using an excess of ferrous ions. The hydroxide is then oxidized to the seeds of hydrated ferric oxide ... 

Iron Browns. Iron browns are often prepared by blending red, yellow, and black synthetic iron oxides to the desired shade. The most effective mixing can be achieved by blending iron oxide pastes, rather than dry powders. After mixing, the paste has to be dried at temperatures around 100°C, as higher temperatures might result in the decomposition of the temperature-sensitive iron yellows and blacks. Iron browns can also be prepared directiy by heating hydrated ferric oxides in the presence of phosphoric acid, or alkaU phosphates, under atmospheric or increased pressure. The products of precipitation processes, ie, the yellows, blacks, and browns, can also be calcined to reds and browns. 

Catalytic alkylation of aniline with diethyl ether, in the presence of mixed metal oxide catalysts, preferably titanium dioxide in combination with molybdenum oxide and/or ferric oxide, gives 63% V/-alkylation and 12% ring alkylation (14). 

Strontium Hexaferrite. Strontium hexaferrite [12023-91 -5] SrO-6 Fe2 03, is made by combining powdered ferric oxide, Fe203, and strontium carbonate, SrCO, and calcining the mixture at ca 1000°C in a rotary kiln (9). The material is cmshed, mixed with a binder, and pressed or extmded into... 

Styrene. Commercial manufacture of this commodity monomer depends on ethylbenzene, which is converted by several means to a low purity styrene, subsequendy distilled to the pure form. A small percentage of styrene is made from the oxidative process, whereby ethylbenzene is oxidized to a hydroperoxide or alcohol and then dehydrated to styrene. A popular commercial route has been the alkylation of benzene to ethylbenzene, with ethylene, after which the cmde ethylbenzene is distilled to give high purity ethylbenzene. The ethylbenzene is direcdy dehydrogenated to styrene monomer in the vapor phase with steam and appropriate catalysts. Most styrene is manufactured by variations of this process. A variety of catalyst systems are used, based on ferric oxide with other components, including potassium salts, which improve the catalytic activity (10). 

Iron Titanates. Ferrous metatitanate [12168-52-4] FeTiO, mp ca 1470°C, density 472(0), an opaque black soHd having a metallic luster, occurs in nature as the mineral ilmenite. This ore is used extensively as a feedstock for the manufacture of titanium dioxide pigments. Artificial ilmenite may be made by heating a mixture of ferrous oxide and titanium oxide for several hours at 1200°C or by reducing a titanium dioxide/ferric oxide mixture at 450°C. 

Ferrous orthotitanate [12160-20-2] Fe2Ti04, is orthorhombic and opaque. It has been prepared by heating a mixture of ferrous oxide and titanium dioxide. Ferrous dititanate [12160-10-0] FeTi20, is orthorhombic and has been prepared by reducing ilmenite with carbon at 1000°C. The metallic ion formed in the reaction is removed, leaving a composition that is essentially the dititanate. Ferric titanate [1310-39-0] (pseudobrookite), Fe2TiO, is orthorhombic and occurs to a limited state in nature. It has been prepared by heating a mixture of ferric oxide and titanium dioxide in a sealed quartz tube at 1000°C. 

D. A. D2ombak and P. M. M. Morel, Suface Complexation Modeling Hydrous Ferric Oxide, Wiley-Interscience, New York, 1990. 

In the presence of oxygen (air), the thermal decomposition of amphiboles is associated with an oxidation of divalent iron to trivalent iron, which may lead to an increase in the sample weight the oxidation process also induces an obvious color alteration, the fibers acquire the characteristic ferric oxide... 

---