T. Olczak

Preparation of spherical powders of hydroxyapatite by sol-gel process

Abstract Spherical powders of hydroxyapatite with particle diameters below 100 μm were prepared using the water extraction variant of the sol-gel process. A freshly prepared solution of calcium acetate and phosphoric acid (molar ratio Ca/P = 1.67) was emulsified in dehydrated 2-ethyl-1-hexanol. Drops of the emulsion were solidified by extraction of water with this solvent. The process was carried out continuously. The separated gel particles were calcined to hydroxyapatite particles with preservation of the spherical shape. This process was studied using differential thermal analysis, thermal gravimetric analysis, X-ray diffraction analysis and infrared spectroscopy. During thermal treatment, the formation of calcium carbonates is observed first. Above 400°C, the formation of hydroxyapatite starts and then at 580°C formation of carbonate hydroxyapatite starts. The last step, decomposition to hydroxyapatite, proceeds above 750°C.

Fabrication of Li2TiO3 spherical microparticles from TiCl4 by a classical, inorganic sol-gel route; characteristics and tritium release properties

Medium sized spherical particles of Li2TiO3 (with diameters below 100 μm) can be fabricated by a classical, inorganic sol-gel process, from commercially available TiCl4. Elaborated process consists of the following main steps: (1) dissolving of TiCl4 in concentrated aqueous HCl; (2) formation of sol emulsion in 2-ethylhexanol-1 containing the surfactant SPAN-80 (EH); (3) gelation of emulsion drops by extraction of water with partially dehydrated EH; (4) impregnation of gel to Li : Ti molar ratio (MR) = 2; (5) thermal treatment at 1200°C. This temperature can be significantly lowered (to 750°C) by chemical treatment of chloride precursors (gels or starting solution TiCl4) with aq. ammonia or better with nitric acid. Tritium release from sol-gel made Li2TiO3 micro-spheres were found very close to that observed for other traditional materials, however for the first sample process starts slightly earlier.

Preparation of thin SnO2 layers by inorganic sol-gel process

SnO2 sols were prepared in the following way: (1) precipitation of metastannic acid with aqueous ammonia from aqueous solutions of SnCl4, (2) washing the precipitates with NH4NO3 solution and water, (3) peptization of precipitates in water, sometimes with an addition of HNO3, at elevated temperature using mechanical stirring. In those sols, sometimes diluted with water or ethanol, substrates (glass or silica derived wafers) were dipped and withdrawn at various rates. Gel coatings were converted into crystalline SnO2 by thermal treatment at 600°C. Coatings with thickness between 300–2000 Å were prepared.

Inorganic Sol-Gel Preparation of Medium Sized Microparticles of Li2TiO3 from TiCl4 as Tritium Breeding Material for Fusion Reactors

Microspheres of Li2TiO3 were fabricated by a classical, inorganic sol-gel process from commercially available TiCl4. Elaborated process consists of the following main steps: (1) dissolving of TiCl4 in concentrated aqueous HCl and addition of LiOH; (2) formation of sol emulsion in 2-ethylhexanol-1 containing the surfactant SPAN-80 (EH); (3) gelation of emulsion drops by extraction of water with partially dehydrated EH; (4) impregnation of gel to Li:Ti molar ratio MR = 2; (5) thermal treatment at 1200°C in order to receive chloride free product. This temperature can be significantly lowered (to 750°C) by dechlorination starting solution TiCl4 by chemical treatment of the with nitric acid to form of nitrate-stabilized titania sols. Tritium release from sol-gel made Li2TiO3 microspheres were found very close to that observed for other traditional materials, however for the first sample process starts slightly earlier.

Thermal Conversion of Gels Prepared by the Complex Sol-Gel Process (CSGP) from Li+-Me2+-CH3COO−-Ascorbic Acid (ASC)-NH4+-OH−-H2O Systems to LiMn2O4 and LiNixCo1 − xO2

The spinel LiMn2O4 and layered oxides LiNixCo1 − xO2 (x = 1; 0.75; 0) have been prepared by Complex Sol-gel Process (CSGP). The appropriate sol compositions were obtained from acetate aqueous solution of metals containing ascorbic acid by alkalizing it with aqueous ammonia. Gels were produced from the systems by evaporation of water and other volatilies at elevated temperatures. A very intense foaming was observed during the heating at the temperatures higher than 140°C. To avoid foaming in the course of the final thermal treatment, a very long (lasting several days) soaking step was found necessary. However pretreated materials exhibit self-ignition at temperature range 320–500°C dependent on socking conditions. The dependence of self-ignition temperature on carbon content in bed as well as on specific surface has not been proved. Final thermal transformation of gel to solid was studied by TG, DTA, XRD, and IR methods. It was observed that final compounds are formed faster from precursors which did not contain Ni (e.g. LiMn2O4 and LiCoO2), while Li carbonate is not formed in these systems. In contrast, in Li-Ni(Co)-O the formation of Li(or Ni)CO3 was always proved. In addition, during the thermal treatment Ni species are partially reduced even to metallic phase. This effect evidently restrains the formation of pure layered oxides phase. Electrochemical properties of carbonate free compounds are definitely better than of those containing CO3.

Sol-gel process for preparation of YBa2Cu4O8 from acidic acetates/ammonia/ascorbic acid systems

YBa{sub 2}Cu{sub 4}O{sub x} sols were prepared by addition of ammonia to acidic acetate solutions of Y{sup 3+}, Ba{sup 2+}, and Cu{sup 2+}. Ascorbic acid was added to part of the sol. The resultant sols were gelled to a shard or a coating by evaporation at 60 C. Addition of ethanol to the sols facilitated formation of gel coatings, fabricated by a dipping technique, on Ag or glass or substrates. At 100 C, gels formed in the presence of ascorbic acid were perfectly amorphous, in contrast to crystalline acetate gels. The quality of coatings prepared from ascorbate gels was superior to that of acetate gel coatings.

Some aspects of thermal conversion of gels to YBCO and BSCCO superconductors. Removal of carbonates from intermediate phases

Abstract The thermal transformation of acetate derived gels: YBCO and BSCCO to respective superconductors has been studied using thermogravimetry, XRD and i.r. techniques. Formation of carbonates was observed during the thermal treatment of all the materials examined. Thermal decomposition of the carbonates turned out to be more difficult in the YBCO than in BSCCO compounds. Nevertheless the negative effect of carbonates on the formation of BSCCO phases has been observed. Removal of carbonates from intermediate phases by low-temperature treatment with nitric acid strongly accelerates formation of the 2223 BSCCO superconducting phase.

Preparation of BSCCO Precursors by Water Extraction Variant of Sol-Gel Process

The starling acetate sols of molar compositions of Bi:Pb:Sr:Ca:Cu=I-2:O:2:l: 2, 11–2:0:2:2:3 and 111–1.6:0.4:2:2:3 were prepared by NH 4 OH addition at various rates, followed by evaporation. Sols were gelled by further evaporation to shard or to microspheres (diameter below 100 μm) by water extraction from the sol emulsion drops formed in 2-ethyl-l-hexanol. The gels were converted to BSCCO phases by thermal treatment. The processes were characterized by XRD and IR examinations. The influence of the sol preparation step connected with formation of polynuclear cations on the following stages of the process was examined.

Preparation of titanium hexacyanoferrate microspheres (diameter < 70 {micro}m) by water extraction variant of sol-gel process and its application to sorption of {sup 137}Cs from nuclear reactor cooling water

Titanium hexacyanoferrate microspheres (diameter < 70{micro}m) were obtained in the following steps: (1) extraction of chlorides from an aqueous solution of TiCl{sub 4} with long chain amine -- Primene JMT -- in paraffin diluent (the resulting sol has the concentration 320 g TiO{sub 2}/dm{sup 3} and the mole ratio Cl{sup {minus}}:Ti{sup 4+} = 1.83); (2) blending of titania sol with an aqueous solution of K{sub 4}Fe(CN){sub 6}{center_dot}3H{sub 2}O (280 g/dm{sup 3}) in order to obtain final sols with Fe(CN){sub 6}{sup 4{minus}}:Ti{sup 4+} mole ratio of 0.05--0.1; (3) formation of multicomponent sol emulsion in 2-ethylhexanol-1 containing 1 vol. % of Ethomen S/15 (EH), (4) gelation of emulsion drops by extraction of water with partially dehydrated EH; (5) filtration and washing with acetone; (6) drying at 140 C using a special procedure elaborated on the basis of TG and DTA studies. The final product is insoluble in water and exhibits high sorption efficiency of {sup 137}Cs.