X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) techniques at both Fe and Co K-edges were used to investigate the formation of CoFe2O4 nanoparticles embedded in a silica aerogel matrix as a function of calcination temperature and CoFe2O4 content. In particular, nanocomposite aerogels containing relative CoFe2O4 amounts of 5 and 10 wt % and calcined at 450, 750, and 900 °C were studied. The evolution of the nanophase with calcination temperatures depends on the composition. In the sample containing 10 wt % of nanophase, results indicate that CoFe2O4 nanocrystals were formed after calcination at 750 °C, whereas in the sample containing 5 wt % of nanophase, they were obtained only after calcination at 900 °C. Quantitative determination of the distribution of the iron and cobalt phase in the octahedral and tetrahedral sites of the spinel structure shows that cobalt ferrite prepared by sol−gel has a partially inverted spinel structure with a degree of inversion around 0.70.

X-ray Absorption Investigation of the Formation of Cobalt Ferrite Nanoparticles in an Aerogel Silica Matrix

This study investigated the feasibility of producing reactive MgO cement from reject brine obtained from a desalination plant and evaluated its use as a binder in comparison to a commercial MgO. The mechanical performance of the samples cured under carbonation conditions for up to 28 days were further supported by x-ray diffraction (XRD), thermogravimetric analysis/differential scanning calorimetry (TGA/DSC) and field emission scanning electron microscopy (FESEM) analyses. Samples involving synthetic MgO revealed higher strengths than those with commercial MgO, in line with the higher reactivity of the former. The increased dissolution of synthetic MgO led to its enhanced hydration and carbonation, resulting in samples with denser structures and improved performances. The findings highlighted issues regarding the large-scale production of MgO from reject brine and CO2 emissions of this process. The major environmental impact was associated with the production of the alkali base (NaOH), which could be improved via the identification of sustainable alkali sources used during production. Overall, the production of MgO from reject brine can save natural resources and pave the way for the sequestration of CO2 as stable carbonates in cement-based mixes.

Production of reactive magnesia from desalination reject brine and its use as a binder

Stoichiometric cobalt ferrite was synthesised in the laboratory using a standard ceramic method and the crystal structure was identified by X-ray diffraction using FeKalpha radiation. The oxidation states of the cations were determined by studying the chemical shifts. The degree of inversion in this ferrite was estimated by studying the shape and structure of the K-absorption discontinuities of cations as absorbing atoms together with the nature of extended fine structures associated with these discontinuities.

X-ray spectroscopic study of cobalt ferrite

The crystallinity in UO2 powders prepared by the ADU route at different calcination temperatures (600°-1600°C) and its influence on their sintering behaviour (sintering temperature 1000°-1600°C) in hydrogen were studied by X-ray difiraction techniques. Powder patterns were made for the loose powders and back reflection for the sintered pellets. It was noticed that higher the calcination temperature, the greater was the degree of crystallinity developed in the powders and poorer was their sinterability. The crystallinity of the sintered pellets was mainly dependent on the sintering temperature and crystallinity of the original powder and is not directly related to the sintered density. By sintering pellets of poorly crystalline powders at low temperatures (about 1200°C) sintered pellets of near theoretical density but with poorly developed crystallinity could be obtained.

Role of Crystallinity in the Sintering of Urania Powders

Isothermal grain growth and sintering in pure ThO2 and ThO2-CaO compositions

Thoria powders of different origins and thermal history have been shown to have different sintering characteristics. The difference in the sintering behaviour could not be completely accounted for by the physical characteristics of the powder.The development of “crystallinity” with rise in temperature was studied in case of thoria powders prepared at 600°C from oxalate, carbonate and tannate, and those derived from the compound in situ, using a high temperature X-ray camera. Marked differences in “crystallinity” were noticed for powders of different origins and for those of the same origin but subjected to different calcination treatments. The shapes of the particles of different origins and calcination treatments were studied by electron microscopy. An attempt has been made to explain differences in the sintering behaviour of thoria, of different origins and thermal history on the basis of the “crystallinity” of the powders.

Sintering of Thoria Powders—Part IV Development of Crystallinity in Thoria Powders During Heating and its Influence on their Sintering Behaviour

An attempt was made to study the influence of origin and calcination treatments on the development of crystallinity, surface area and the morphology of magnesia powders. Magnesia powders were prepared by thermal decomposition/calcination of different parent compounds namely, magnesium hydroxide, oxalate, carbonate, salicylate and succinate. Calcination temperatures upto 900°C in either air or vacuum and soaking time from half to 16 hrs were used. The development of crystallinity in the resultant magnesia powders was studied at room temperatures by X-ray line broadening techniques. The surface areas of the magnesia powders were determined by the BET method. A limited study was made on the morphology of the powders using electron microscope.It was found that at the decomposition temperature of the parent compound, the crystallinity of the resultant magnesium oxide was very poor, and the surface area extremely high. With an increase in calcination temperature, the crystallinity of the oxide powders improved ...

Influence of Origin and Calcination Treatments on the Physical Properties of Magnesia Powders

Studies on the influence of various fabrication parameters viz., calcination temperature, grinding period, sintering temperature and soaking time, on the initial a.c. permeability and Q-factor of Nickel-Zinc-Ferrite (Ni0.3Zn0.7 Fe2O4 samples, were made with a view to develop ferrite cores, for use at high frequencies. A higher calcination temperature, a lower sintering temperature and a shorter soaking period have been found desirable to attain reasonably high density coupled with a low initial permeability and high Q. Repeated calcinations interspaced with wet grinding resulted in further improvement of the properties.

Influence of Conditions of Preparation on the Properties of Nickel-Zinc-Ferrite

Barium titanate is commonly used for the preparation of high permittivity capacitors and for transducer applications. Dielectric properties developed in titanate capacitors are markedly influenced by the raw materials used and the conditions of manufacture. In the present investigation, the influence of techniques of preparation and minor additions on the sinterability and the dielectric properties of the barium titanate bodies have been studied. An addition of 1 to 3% titania promoted the sinterability and resulted in the development of high dielectric constant (about 2000). Dissipation factor of the order of 0.02 which is acceptable for commercial use was obtained only when the density exceeded 5 gm/cc.

Development of Barium Titanate Capacitors

The influence of amount of calcia addition and calcination temperature on the sintering characteristics of zirconia was studied. The extent of stabilization was studied by X-ray diffraction. It was noticed that the optimum amount of calcia addition to obtain high density without cracking was 0.50 to 0.75 wt%. Higher amount of calcia addition and higher calcination temperature resulted in lowered density.Stabilization of zirconia with calcia addition, i.e. the formation of cubic phase, is found to be a function of amount of calcia added. The cubic solid solution formation took place mainly between 1000° and 1200°c. With the addition of 5.0 wt% of CaO, about 85% of cubic phase is formed at 1200°C and 100% at 1700°C.

V. K. Moorthy

Papers

Sintering of Thoria Powders—Part IV Development of Crystallinity in Thoria Powders During Heating and its Influence on their Sintering Behaviour

Influence of Origin and Calcination Treatments on the Physical Properties of Magnesia Powders

Influence of Conditions of Preparation on the Properties of Nickel-Zinc-Ferrite

Development of Barium Titanate Capacitors

Influence of calcia addition and calcination temperatures on sintering and stabilization of zirconia