X ferrites

The non-stoichiometric Ca2LaFe308+x ferrite was also studied by measuring the electrical conductivity variation with oxygen partial pressure, p02, at various temperatures (Fig. 18). In each curve, three ranges of variation are observable as represented for the imaginary temperature tp... 

ASTM A763, Practice X Ferritic stainless steels Intergranular attack associated with Cr carbides, Cr nitrides, and intermetallic phases such as a-phase... 

Iron oxide is also used for nonpigmentary applications, eg, ferrites (qv) and foundry sands making total world demand for iron oxide close to 1 X 10 t. The principal worldwide producers of iron oxide pigments are Bayer AG (ca 300,000 t/yr worldwide), and Harcros Pigments Inc., a subsidiary of Harrisons Crosfield PLC. In the United States, Bayer produces the Bayferrox line of iron oxide pigments in New Martinsville (see Iron compounds). 

A number of ferrites have been subjected to shock modification and studied with x-ray diffraction as well as static magnetization and Mossbauer spectroscopy [87V01], Studies were carried out on cobalt, nickel, and copper ferrites as well as magnetite (iron ferrite). 

Minchener el al. report that the bubble phase of atmospheric fluidised bed combustion has a pOi in the range 2 x 10 to 2 x 10 Combustion in the dense phase is sub-stoichiometric, with the /Oj as low as 10 and SO2 and SO3 present in the range 500-5 000ppm. Low Cr-Mo steels show heavy scaling in these conditions, whereas 9-12% Cr steels show good resistance to sulphidation up to 650°C. Roberts et however, report that for pressurised fluidised-bed combustion, ferritic steels at or below 9% Cr show heavy general corrosion above 540-560°C. 

Oxides play many roles in modem electronic technology from insulators which can be used as capacitors, such as the perovskite BaTiOs, to the superconductors, of which the prototype was also a perovskite, Lao.sSro CutT A, where the value of x is a function of the temperature cycle and oxygen pressure which were used in the preparation of the material. Clearly the chemical difference between these two materials is that the capacitor production does not require oxygen partial pressure control as is the case in the superconductor. Intermediate between these extremes of electrical conduction are many semiconducting materials which are used as magnetic ferrites or fuel cell electrodes. The electrical properties of the semiconductors depend on the presence of transition metal ions which can be in two valence states, and the conduction mechanism involves the transfer of electrons or positive holes from one ion to another of the same species. The production problem associated with this behaviour arises from the fact that the relative concentration of each valence state depends on both the temperature and the oxygen partial pressure of the atmosphere. 

The above techniques have a wide array of applications, including those that are both analytical and physicochemical (such as bonding) in nature. Typical examples of research include the surface chemistry of ferrite minerals (38) and the valence states of copper in a wide array of copper (39) minerals. Other areas of bonding that have been studied include the oxidation state of vanadium (40) in vanadium-bearing aegirities (also using x-ray photoelectron spectroscopy) and the. surface features of titanium perovskites (41). ... 

The spinel ferrites were fabricated by solid state reaction technique. Cobalt and Zinc ferrites CoxZnyFe204,(x=0.7,0.3,0.4,0.2 and y=0.3,0.7,0.6,0.8) were prepared by solid state reaction technique. The crystalline structure of the sample was investigated by X-ray diffraction(XRD). All samples show cubic spinel structure. The lattice parameter decreases with increasing cobalt content. Magnetic properties shows that the prepared sample exhibit ferromagnetic behaviour at room temperature. The saturation magnetization increases with increasing cobalt content. Curie temperature... 

Ni-Co ferrites with the general formula Nii cCoxFe204 were tested for the methylation of pyridine [110]. It was observed that the systems possessing x values >0.5 are selective for 3-picoline formation, whereas the ones with x values 0 and 0.2 give a mixture of 2- and 3-picolines. Pyridine conversion increased with the progressive substitution of Ni ions by Co ions. The cation distribution in the spinel lattice influences their acidic and basic properties, and these factors have been considered as helpful to evaluate the activity of the systems. 

I.I The prediction of transformation diagrams after Kirkaldy et al. (1978). A model for the calculation of ferrite and pearlite was first presented by Kirkaldy et al. (1978) based on Zener-Hillert type expressions (Zener 1946, Hillert 1957). In this first effort, no attempt was made to differentiate between the diffusive and displacive transformations and a overall C curve was produced of the type shown schematically in Fig. 11.14. Kirkaldy ettd. (1978) used the formalism below where the general formula for the time (r) to transform x fraction of austenite at a temperature T is given by... 

Feltz, A. Martin, A. (1987) Solid-state reactivity and mechanisms in oxide systems. 11 Inhibition of zinc ferrite formation in zinc oxide - a-iron(lll) oxide mixtures with a large excess of a-iron(lll) oxide. In Schwab, G.M. (ed.) Reactivity of solids. Elsevier, 2 307—313 Fendorf, S. Fendorf, M. (1996) Sorption mechanisms of lanthanum on oxide minerals. Clays Clay Miner. 44 220-227 Fendorf, S.E. Sparks, D.L. (1996) X-ray absorption fine structure spectroscopy. In Methods of Soil Analysis. Part 3 Chemical Methods. Soil Sd. Soc. Am., 377-416 Fendorf, S.E. Eick, M.J. Grossl, P. Sparks, D.L. (1997) Arsenate and chromate retention mechanisms on goethite. 1. Surface structure. Environ. Sci. Techn. 31 315-320 Fendorf, S.E. Li,V. Gunter, M.E. (1996) Micromorphologies and stabilities of chromiu-m(III) surface precipitates elucidated by scanning force microscopy. Soil Sci. Soc. Am. J. 60 99-106... 

Lithium ferrite itself (x = 0.5) has a high Curie temperature and can be fabricated so as to give a square hysteresis loop satisfactory for digital-computer memory cores. In this application, the dielectric losses connected with the presence of mobile charge carriers can cause a dramatic loss in core quality. The mobile carriers may be introduced by... 

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

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