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An adiabatic calorimeter has been used to measure heat capacities and heats of transformation for iron-eobalt alloys over the temperature range 700-1500K. Estimates of the entropy associated with magnetic and configurational disorder suggestthat f'V 75% of the magnetic order is lost by the Curie temperature and that although the Bragg-Williams theory correctly predicts the entropy of disordering FeCo, it overestimates the entropy of disordering alloys away from the ideal ordering compositions. Phase-diagram information for the oc-+y transformation, the ordering reaction, and the Curie temperature are given.This investigation was initiated at a time when the data available on the heat capacities l -4 and heats of transformation of iron-cobalt alloys5 were limited to early studies over restricted ranges of temperature. More recently, four more studies of heat capacities have become available,6-9 but the majority of the effort has been concentrated on alloys close to the FeCo composition, whereas this study covers the range from xco=0·018 to 0·942. The present results form part of a programme of thermodynamic' measurements on solid alloys of iron with transition elements which is being carried out in the Department of Metallurgy at Sheffield University with the long-term objectives of improving the understanding of alloying behaviour and of developing models to predict thermodynamic quantities in ternary and more complex iron alloy systems as well as obtaining phase-diagram information.There is good agreement between Yokoyama, 3 Masumo'to et al.,5 Castanet anti Ferrier,6 and the present study in defining the order-disorder temperature for the FeCo compositions as 999-1002 K. Mills,9 Ansano et al.,4 and Kaya et al.I favour a higher value of 1006-1009 K whereas Pepperhoff and Ettwig 8 record a lower value of 983 K.Heat-capacity effects associated with the order-disorder transformations have been observed over the composition range xco=0'29 to 0.70 2 ,4,9 and a second maximum in the heat-capacity curves at-f'V 823 K has been reported for alloys in the range xco=0·35 to 0'67.1,2 This second peak is reported to be very sensitive to heat-treatment and to become very much smaller in furnace-cooled specimens than in material which had been rapidly cooled.The present study is connected with previous investigations of pure iron ll and pure cobalt 12 carried out by Sale and by Normanton. ExperimentalThe spherical adiabatic calorimeter and its mode of operation have been fully described in previous publications. 1l -14 Alloys were prepared by vacuum melting electrolytic iron and electrolytic cobalt. As the oxygen content of the iron was comparatively high ( f'V 550 ppm by weight), this was deoxidized y vacuum melting with a small amount of carbon to prepare a suitable melting stock for the preparation of the alloys. These were generally cast as 750 g ingots into 25 mm dia. chill moulds, but in the case of the alloy xco=0'495, a 75 mm ingot was cast from an 8 kg melt. \ The 25 mm ingots were hot rolled to 19 mm dia. from an init...

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Two iron ore samples from Nigeria have been examined using TG, DTA, EGA, XRD, and optical and electron microscopy. Itakpe iron ore is hematite-rich, this mineral being intergrown with magnetite, and silica is the major impurity. Agbaja ore is an acidic oölite ore consisting of goethite and magnetite, with alumina, silica and phosphorus as major impurities. Itakpe is typical of a rich ore formed by magmatic segregation whilst Agbaja is a lean ore of sedimentary origin. Isothermal mass-change measurements in hydrogen and carbon monoxide in the range 800–1100°C show Agbaja to be less reducible than Itakpe; in particular, Agbaja is very irreducible at 1100°C because of sintering of the ore. Characterization and reducibility experiments were also carried out on Corby (Northamptonshire, UK) iron ore for comparison.

Fine, homogeneous lead zirconate titanate (PZT) powders have been prepared by the thermal decomposition of metalorganic complexes derived from nitrate solutions using ethylenediaminetetraacetic acid (EDTA) as a complexing agent. It has been shown that nitrate ions accelerate the decomposition of the precursor and the crystallization of the PZT phase initiates at temperatures as low as 250°C. No intermediate phases, other than PbO, were found. The coexistence region of the rhombohedra1 and tetragonal phases in the sintered ceramic was found to be a little over 1 at.%. The chloride-EDTA precursor did not form the desired PZT phase, even after calcination at 1000°C. The segregation and loss of lead was observed for this material, due to the formation and evaporation of PbC12. DTA/TGA, SEM, and XRD were employed to characterize the powders. The use of TEM with nanoprobe energy dispersive X-ray analysis (EDX), allowed the identification of the phase segregation in the chloride-EDTA derived powder. A possible reaction mechanism for this phase segregation is suggested. [