V. Zapletal

Behaviour of α-Fe2O3 (hematite), prepared by oxidation precipitation of ferrous sulphate, on heating

The effects of heatingα-Fe2O3 (hematite) prepared by oxidation precipitation of ferrous sulphate, at temperatures up to 700° C were studied. It was found that, in the course of heating, losses of structurally-bound water occured, accompanied by the formation and removal of pores, the lattice constants changed and the optical properties were modified, an effect which is important from the standpoint of the use of hematite as ferric pigment. With increasing annealing temperature, the complementary wavelength was shifted to higher values and the spectral purity of the pigment colour was decreased.

Preparation of high-temperature superconductors by controlled double-jet precipitation

Abstract Controlled double-jet precipitation has been used to synthesize high-temperature superconductors (HTSCs). The cation and oxalic anion solutions were simultaneously separately introduced into the crystallizer with a stirred solution of gelatin under conditions where the temperature, excess of oxalic anions in solution, pH, reactant addition rate, type and amount of the growth restrainer were tightly controlled. The suspensions with submicron average grain size, narrow grain size distribution, and with high sinterability were used to prepare bulk specimens and films on various substrates. The sintered oxides were characterized by electrical resistivity and ac-susceptibility measurement. The superconducting properties of these samples were found to be comparable, if not superior, to those observed for samples produced by other conventional methods.

Reactivity of finely dispersed iron (III) oxides and oxide hydroxides in solid-state reactions

The kinetics of the reaction ofα-Fe2O3 (hematite) with K2CO3 was studied at 600–800 °C for hematite samples prepared in different ways. The results demonstrated that the hematite reactivity is not a simple function of the specific surface area (or particle size), but depends significantly on the sample preparation history, especially at lower reaction temperature. The effect of low-temperature sintering on the hematite reactivity is discussed.ZusammenfassungDie Kinetik der Reaktion unterschiedlich präparierterα-Fe2O3- (Hämatit-) Proben mit K2CO3 bei 600–800 °C wurde untersucht. Die Ergebnisse zeigen, dass die Reaktivität des Hämatits keine einfache Funktion der spezifischen Oberfläche (bzw. Teilchengrösse) ist, sondern deutlich von der Vorgeschichte der Probe, insbesondere bei tieferer Temperatur, abhängt. Der Einfluss des Tieftemperatursinterns auf die Reaktivität des Hämatits wird diskutiert.РезюмеПри температуре 600–800° и зучена кинетика реак ции взаимодействия полу ченного различными способам и гематита (а-Ге2О3) с ка рбонатом калия. Результаты пок азали, что реакционная способн ость гематита являет ся не просто функцией его удельно й площади поверхности (или разм ера частиц), а в значите льной мере зависит, особенно при более низкой температуре реакции, от «истории» получен ия образца. Обсуждено влияние ни зкотемпературного спекания на реакцион нуюспособность гема тита.

Preparation of silver doped high temperature super-conductors by the controlled double-jet precipitation

Chemical precursors of high temperature superconductors were prepared by the controlled double-jet precipitation of their oxalates to obtain suspensions with submicron average crystal size, narrow crystal size distribution, desired chemical composition and internal structure. To improve mechanical and electrical properties of HTSC layers the chemical precursors of HTSC were doped by silver oxalates using the same method. This technique enables to achieve better mixing of reagents in compare with mixed oxide processing. The suspensions were coagulated, washed and coated on various substrates. During carefully controlled heat treatment the grains readily sintered and formed HTSC layers. The layers prepared by this technique showed some improvements in mechanical and electrical properties. When coated on silver substrate, high density layer and a strong bond between the HTSC layer and substrate were achieved