Magnetic oxides

The magnetic properties of oxides and related compounds have been tabulated in comprehensive data collections [3.4]. A review of the basic magnetic properties of garnets (A3 [B2](Si3)Oi2 and spinel ferrites Me0Fc203 or Me Fe 04 is given by Guillot in [3.3]. 

The fact that the site occupation in magnetite is opposite to that of spinel arises from the interaction of the d elecU ons on die cations with the suiTound-ing anions. The energy for the exchange 

In this approximation it is assumed drat die endialpy of exchange is equal to the energy of exchange, and the thermal entropy of exchange is equal to zero. Both of diese imply that there is no change in heat capacity when this exchange is carried out, which is not normally the case, although the effect is small. 

Results of quantum-mechanical calculations (Dunitz and Orgel, 1957) have given values for the OSPEs of a number of transitional metal ions and the degree of inversion of mixed spinels 

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The term ferrite is commonly used generically to describe a class of magnetic oxide compounds which contain iron oxide as a principal component. In metallurgy (qv), however, the term ferrite is often used as a metaHographic indication of the a-iron crystalline phase. 

Unalloyed steel can be directly oxidized by steam at temperatures over 750 °F (399 °C). Extensive cracks may occur, the steel surface may resemble tree bark, and magnetic oxide deposits are generated at the failure site. Intergranular oxidation may take place. In the thermal oxidation reaction, hydrogen is directly released as shown ... 

J. E. Greedan, Magnetic Oxides, in Encyclopedia of Inorganic Chemistry, 2nd ed., Wiley, Hoboken, NJ, 2006. 

Corundum-type Magnetic Oxide Surfaces. The substrate hematite with the corundum-type crystal structure is an antiferromagnet below 963 K. In the corundum-type structure of hematite, pairs of ferric ions are in a row spaced by single vacant sites along the <111> direction. The positions of ferric ions in each pair are shifted slightly upward or downward in the <111> direction. We denote these lattice positions as up and down sites (Au and A ), respectively. 

With Iron.—If metallic iron is heated in the presence of water under very high pressure, hydrogen is evolved and magnetic oxide formed, in accordance with the following equation —... 

After the completion of the reaction the pressure can be let off from the generator and the magnetic oxide of iron produced removed and reduced by water gas to the metallic state, when it can again be employed in die process... 

Theoretically, to produce 1000 cubic feet of hydrogen 30 inches barometric pressure and 40° F., ii6 5 lb. iron and 49 95 lb of steam are required however, in actice these figures are not closely approached because e magnetic oxide of iron formed tends to shield the stallic iron from the action of the steam indeed, the action may be regarded as merely a surface one. 

The advantage of this procedure is that a spongy coating of metallic iron is obtained on the refractory iron oxide, with the result that the iron and the resulting magnetic oxide tend to be held together, and so keep the material open, and therefore free from back pressure to tile passage of the steam and water gas. 

Triiron tetroxide occurs in nature as the mineral magnetite, the magnetic oxide of iron. This mineral along with hematite is used as the starting material for producing iron, steel and other ferro-alloys. 

At the Bine]ting works of Sweden and Norway, the principal ores from which the iron is manufactured are the magnetic oxide, the composition of which has been already given. According to M. Jars, the smelting flimaces. of Sweden and Norway are about thirty feet, high from the tuyere-hole to the base... 

The magnetic oxide of iron or the lodestone by its attraction at a distance made a great impression on the minds of the ancients and there was a natural tendency to exag-... 

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