In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences


Volume 49 No. 1 March 2000

Foreword; 3–4
Studies on thermochemistry and thermal processing of apatite; 5–18
Abstract. A summary of the results obtained by studies on thermochemistry of synthetic and natural apatites and thermal processing of apatites in the presence of various inorganic compounds or natural minerals is presented. The studies resulted in the development of new methods for thermal processing of phosphate rocks with the purpose of their enrichment or production of feed phosphates and phosphorus fertilizers.
Key words: apatite, synthetic, natural, thermochemistry, thermal processing, defluorinated phosphates, thermophosphates, sulphur dioxide.

Reaction chemistry of hydroxyapatite: Formation and decomposition; 19–28
Takafumi KANAZAWA, Hideki MONMA, and Yusuke MORIYOSHI
Abstract. The solid state formation of stoichiometric hydroxyapatite (HAp) was investigated in detail by heating the Ca3(PO4)2–CaO mixture and Ca4(PO4)2O in the presence of water vapour. HAp was an exceptionally thermally stable hydroxide even at high temperatures above 1000 °C and at low water vapour pressures. New cementing materials consisting of a -Ca3(PO4)2, a -Ca3(PO4)2 + CaHPO4×2H2O, and CaHPO4× 2H2O + CaCO3 were found and clarified with respect to the hardening accompanying the formation of calcium-deficient hydroxyapatite (DAp), hydration reactions with and without additives, and mechanical strength of hardened products. The conversion of sparingly water-soluble CaHPO4×2H2O and CaSO4× 2H2O and a calcium silicate mixture into DAp was successfully conducted. Thermal decomposition characteristics of DAp, HAp, HAp + SiO2, and HAp + Ca2P2O7 were elucidated in detail.
Key words: hydroxyapatite, solid state formation, thermal decomposition, apatitic cement.

Synthesis and structure of double phosphates of titanium and alkali metals; 29–35
Abstract. Interaction of powdered titanium with the polyphosphoric acid melt containing cations of alkali metals was studied at 350 °C. For the first time double condensed phosphates of titanium and alkali metals with a composition Na3TiIIIP8O23 and Cs2TiIVP4O13 were obtained and studied by XRD. Ultraphosphates Na3TiIIIP8O23 with framework structure contain cage-type anions. Tetraphosphate Cs2TiIVP4O13 is of a layer structure.
Key words: phosphates, crystal structure.

Preparation and thermal behaviour of oxovanadium(IV) phosphates and hydrogenphosphates; 36–43
Dietmar FRATZKY, Thomas GÖTZE, Horst WORZALA, and Manfred MEISEL
Abstract. The results of a systematic study on the conditions of the formation of different oxovanadium(IV) hydrogenphosphate and orthophosphate hydrates in dependence on the concentration, temperature, and pressure in the system V2O5/H3PO4/ (COOH)2/H2O are reported. Some structural data and the thermal dehydration of different oxovanadium(IV) orthophosphate hydrates are discussed.
Key words: oxovanadium(IV) hydrogenphosphate hydrates, oxovanadium(IV) orthophosphate hydrates, hydrothermal synthesis, X-ray powder diffraction, DTA.

Thermal analysis of Israeli phosphorites; 44–52
Kaia TÕNSUAADU, Mihkel VEIDERMA, Mihkel KOEL, and Yaacov NATHAN
Abstract. Thermal analysis of Israeli phosphorites from Nahal Zin and Arad deposits was performed using the TG/DTA method complemented with titrimetric and thermogaschromatographic determination of the evolved gases. The amounts and temperature intervals of H2O, CO2, and SO2 evolvement were established, both in the oxygen-containing flow and in the inert gas atmosphere, where additionally the organic compounds were established.
Key words: phosphorites, thermal analysis, evolved gases, thermogaschromatography, Israel.

Modelling SO2 capture by Estonian limestones and dolomites; 53–70
Abstract. Sulphation of several chemically and physically different Estonian limestone and dolomite samples was studied by thermogravimetric analysis, accompanied by Hg-porosity, X-ray, and SEM measurements. The SO2 binding capacity of the samples (particle size 125–160 mm) was analysed isothermally at 850 °C and at 1 or 15 bar in a gas mixture of 4% O2, 15% CO2, 0.5% SO2, and N2. The final values of conversion under these conditions were in the range of 32–66%, the amount of bound SO2 being 15.5–34 mg per 100 mg of initial sample. An attempt was made to apply an unreacted shrinking core model with variable effective diffusivity to the CaO and CaCO3 sulphation data under atmospheric and pressurized conditions. The rate parameters were calculated for the sulphation reaction and the limiting stages for the binding process were established.
Key words: sulphur binding, thermogravimetric analysis, flue gas desulphurization.

Mihkel Veiderma 70; 71–73
Ilmar Koppel 60; 74–75
Instructions to authors; 76–78
Copyright Transfer Agreement; 79