Ferrites colour

Dehydroxylation of goethite produces the ferrite reds - extremely colour fast and pure hematite. With low temperature calcination the acicular shape of the goethite precursor is retained, whereas high temperatures lead to a sintered product. 

Portland cement clinker emerges from a dry process kiln as rounded pellets, or from a wet process kiln as irregularly shaped lumps, in either case typically of 3-20 mm dimensions. Typical clinkers are greenish black, the colour being due to ferrite phase that contains Mg (Ml8) in the absence of Mg , they are buff. Reducing conditions in the kiln typically produce clinkers that are yellowish brown, especially in the centres of the lumps, where less reoxidation has occurred. Light colours can also arise from underburning. 

Nitroanthranylazo (formula 5.1) has been proposed for the determination of Li [47]. The colour reaction is carried out in aqueous acetone made alkaline with KOH. The absorbance is measured at 530 nm (e= 1.2-10 ). The colour intensity depends on the medium used (water-acetone, dioxan, methanol, DMF), excess of Nitroanthranylazo, and ionic strength. In the determination of 2 pg of lithium, there is no interference of 200 pg Rb, 100 pg Mg or Ca, 50 pg Ba, Sr, or Na, The method has been applied for determination of lithium in ferrites [48]. 

Nevertheless, several general papers have been published on stealth technology applied to aircraft such as LOCKHEED F 117 [5,6] or others [7,8,9]. The description of radar absorbing materials is restricted to iron or ferrite loaded paints or elastomers except the case of retinyl Schiff base salts [10,11]. This molecule attracted interest of many scientists in 1987. In fact this material which is a charge transfer salt derived from the A vitamin, never exhibited high-frequency dielectric constant due to its intrinsic conductivity, despite its beautiful orange colour Moreover, reference books as the one of Knott el al. [12] do not mention the use of conductive polymers for this purpose. 

Reaction of ferrite and water Ferrite and water react very slowly. Moderate amounts of heat are evolved - about 300 J per gram. The product is not attacked by sulphate and is beneficial mainly to the strength of the cement. However, the main importance of ferrite is cosmetic, as it influences the colour of the product. 

The two mineral sources for strontium are the sulfate (celes-tite) and carbonate (strontianite). The main use of strontium is as a component in colour television faceplate glass ( 8% SrO is incorporated into the glass) where its function is to stop X-ray emissions from the cathode ray tube (CRT). However, the increasing market for CRT-free flat-screen televisions is having a dramatic effect on the demand for strontium. Other uses of strontium include ferrite ceramic magnets and pyrotechnics (see Flame tests in Section 12.3). 

The grey colour of Portland cements is due to the presence of the names ferrite phases in absence of elements other than calcium, aluminium, iron and oxygen, calcium... 

On the two oxides, a different phase was formed. With zirconia, homogeneously coloured, olive green pellets were obtained, which changed to light brown very rapidly upon exposure to atmospheric air. This indicates the formation of a potassium ferrite phase. On titania, this phenomenon was not observed, as the brownish colour was present already immediately after calcination. 

When potassium is applied also, a different behaviour is observed for the two oxides. In titania-supported catalysts a mixed compound containing titanium, iron and potassium is formed, probably the non-stoichiometric oxide K(,gFej, jTi, 204 [16]. Since the colour of the samples supported on zirconia after calcination indicated the formation of potassium ferrite (KFeOj), which is known to decompose readily in atmospheric air, diffractograms were recorded excluding air. In these catalysts, however, only excess potassium carbonate was observed, and no diffraction lines emanating from other phases than zirconia were detected. In combination with the results from TEM, it is concluded that a finely distributed phase, most probably potassium ferrite, was formed, in which iron and potassium are intimately mixed. 

According to the Colour Index (1971 Cl 77495/Pigment Brown 11) magnesium ferrite , iron magnesium oxide, has a composition of 79% Fe203 and 19% MgO. It is prepared by heating a stoichiometric mixture of iron(III) and magnesimn oxides at 1000°C. 

So-called magnesium and zinc ferrites (Mg0.Fe203 and ZnO. Fe203) have also been used as pigments Colour Index, 1971 Cl 77495/Pigment Brown 11 and Pigment Yellow 119 Fuller). 

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