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In the Sol–Gel Laboratory at the Institute of Nuclear Chemistry and Technology (INCT), studies of synthesis of various advanced ceramic materials by the sol–gel method have been carried out for 50 years. The ceramics products, such as metal oxides, homogeneous mixtures of metal oxides, cermetals and metals, were obtained in various shapes, as irregular powders, monoliths, coatings, fibers or spherical particles with various diameters. A new method using a water-in-oil technique – the ICHTJ Process (INCT in English) was elaborated to synthesize spherical particles of metal oxide or mixture of metal oxides, with diameters below 100 µm. Through years, the method has been evaluated and optimized. Prepared sol solutions of metal cations are emulsified in 2-ethylhexanol-1 containing 1 volume % of the surfactant sorbitol monooleate. Drops of emulsion are gelled by extracting their water with this organic solvent. The main parameters e.g. flow rate; gelation time, syringe, sol solution etc. that have a strong influence on the optimization of the synthesis method and features of the spherical particles are described in this article through an example of synthesis of uranium oxycarbide – mixture of uranium dioxide with uranium carbide.

Synroc (Synthetic Rocks) materials have been regarded as the second generation of high level waste forms in the world. It allows incorporating into their crystal structures almost all of the elements present in high-level radioactive waste. One of the components of Synroc-C is perovskite (CaTiO 3) which immobilize mainly fission products, but also allow immobilizing in his structure long-lived actinides such as plutonium (Pu). Perovskite phase has been fabricated by a sol-gel route. In the present work complex sol-gel process (CSGP Polish Patent PL 172618, 1997) and method of synthesis Me-titanates (Polish Patent PL 198039, 2001) were adapted to prepare of perovskite. Additions of 10 % molar Sr, Co, Cs and Nd into Ti-Ca-nitrate sols were carried out by CSGP. Gels obtained by evaporation of sols under reduced pressure were thermal treated according thermogravimetric (TG, DTA) analysis. Transformation of ascorbat-nitrate gels into doped orthorhombic perovskite phases was definitely lower (about 650 C) than those pure nitrate gels (approx. 700 C). All structures were confirmed by X-ray diffraction analyses. Surrogates were homogeneously distributed into crystalline structure of perovskite. It means that elaborated process can be applied for synthesis Synroc materials and it might be competitive to vitrification process. © 2013 Akadémiai Kiadó, Budapest, Hungary.

A new method for synthesis of uranium oxide microspheres (diameter

For synthesis of silica glasses designed to contain high-level nuclear wastes，a patented complex sol-gel process has been used. Surrogates of the nuclear waste elements Cs, Sr, Co, and Nd (generically denoted Me) were used. Gels in the forms of powders and sintered compacts were prepared by hydrolysis and polycondensation of tetraethoxide/Me nitrate solutions, which contained ascorbic acid as a catalyst. Transformation to final products was studied by thermogravimetric analysis, infrared spectroscopy, and X-ray diffraction. Preliminary testing of Me leaching was also completed in water. Most of the final products were porous; only a single dense form was resistant to leaching.

Medium sized spherical particles of Li2TiO3 (with diameters below 100 μm) can be prepared from peroxy lithium titanate solution (stabilized with citric acid) by a modified INCT (Institute of Nuclear Chemistry and Technology) variant of the sol–gel process. The process consists of the following main steps: (I) formation of aqueous phase emulsion in 2-ethylhexanol-1; (II) gelation of emulsion drops by extraction of water with partially dehydrated EH; (III) filtration and washing with carbon tetrachloride or acetone; (IV) non-destructive thermal treatment. The medium size particles can be used for increasing pebble bed density by infiltration them into bed larger spheres (1 mm diameter). The tritium release from sol–gel process preparation of Li2TiO3 microspheres was found very close to that observed for other traditional material however, the new process is more efficient than other processes because of the morphology of the sintered specimens.

The spinel LiMn2O4 and layered oxides LiNi x Co1 − x O2 (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.

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.

Zirconolite (CaZrTi2O7) is one of the components of Synroc materials, which are regarded throughout the world nuclear as the second generation of high-level nuclear waste forms. The zirconolite phase was synthesized by a sol-gel method, with one variant of the method making use of ascorbic acid as a strong complexing agent. Into the structure of the zirconolite was incorporated 10 mol% Sr. Undoped and doped samples were examined by thermal analyses and X-ray diffraction. Addition of ascorbic acid to the sols lowered the firing temperature and promoted formation of the zirconolite phase.

A powder of nominal composition 4 mol (Bi-2212) + 1 mol was prepared from acetates by a sol - gel method. When compared with a conventional Bi-2212 powder, the composite powder was less phase pure, containing significant concentrations of , Cu-free phases, and CuO. Electron microscopy revealed the presence of nanometre-scale precipitates within many of the superconductor grains in the composite powder. Although these precipitates were uniformly distributed in only some of the superconducting grains, enhancement of flux pinning at 6 K was attributed to their presence.

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.

Fully and partially stabilized ZrO[sub 2] solid solutions are one of the most extensively studied solid oxide electrolyte systems due to the many practical applications of these materials. Spherical powders (with diameters 95% of the theoretical density) and showed both tetragonal and/or cubic X-ray phases. The bulk density values of these ceria-doped zirconia sintered pellets are much higher than those obtained for the CaO- or Y[sub 2]O[sub 3]- doped zirconia samples prepared by the same process.

A modified complex sol-gel process was developed to synthesize LiMn2O4 and LiNixCo1-xO2 powders. Sols were prepared from 1.5 M of Mn2+ or 1 M of xNi2+ and (1-x)Co2+ acetates plus ascorbic acid aqueous solutions by alkalizing them with LiOH and NH4OH. Ascorbic acid was added to prevent precipitation in the precursor solutions. When the sols were concentrated to one-third of their initial volume under reduced pressure and then gelled by drying for 10 days, heat treatment to ≥700 °C was accompanied by foaming, violent self-ignition, and formation of carbonates in the Ni-containing species. Significant improvements to the process and resulting powders were gained by modifying the gelation step. When gelation and drying were carried out under reduced total pressure, subsequent heating produced self-ignition, but no foaming, for all heating rates. The resulting products were determined to be nearly phase pure and carbonate free by thermogravimetric, differential thermal, X-ray, and infrared spectroscopy methods.

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.

Hydroxyapatite (HA) microspheres of diameter 3–4. On average, ≈1/20 moles of metal reacted with 1 mole of HA. Adsorbed metals could be desorbed with efficiencies of 60–90%. In addition, nuclear-waste-saturated beds of HA could be transformed to insoluble ceramics by thermal treatment. The cost of producing HA microspheres was estimated to be comparable to current prices of irregularly shaped commercial hydroxyapatite powders. For radioactive contaminants such as U, for which resorption need not be considered, porous monoliths were produced by use of industrial reagents. The retention capacity was determined to be 30 mg of U per 1 mg of monolith.

The major disadvantage of Ni/NiO cathodes for a Molten Carbonate Fuel Cells (MCFC) application is dissolution of NiO in K/Li electrolyte that significantly decreases the cell lifetime. Thin films of LiCoO2 or LiMg0.05Co0.9502 were prepared on a cathode body in order to protect them against dissolution. For preparation of starting sols the Complex Sol-Gel Process (CSGP) has been applied. These sols have been prepared by adding of LiOH to aq. acetates solution of Co 2+(Mg2+) with ascorbic acid and then by alkalizing them with aqueous ammonia to pH=8. The cathode plates of various dimensions (to several hundreds cm2) have been dipped in these sols and withdrawn at rate a 1.7 cm/s. Commercially sintered Ni plates were always initially oxidized by heating at various temperatures. Their microstructure and mechanical properties as a function of temperature were observed. Heat treatment should be carried out under the dead load of the ceramic plates in order to avoid their waving. The best non-folded plates were obtained by treating them for lh at 550°C. The covered substrates were calcined for lh at 650°C, using low heating ratel°C/min. The presence of LiCoO2 in a deposited coating has been proved by EDS patterns. The resultant film thicknesses were measured by scanning electron microscopy (SEM) on the fractured cross-sections; they ranged from 0.5 to 2νm and depended on sol concentration and viscosity. A 350 hundred hours test in molten carbonates, proved that the cathode bodies covered with LiCoO2 are completely prevented from dissolution of Ni in a molten K/Li electrolyte. Dissolution of LiCoO2 coating was not observed as well. After treatment in a molten electrolyte SEM observations did not show any changes in microstructures and morphology of the covered cathodes.

The layered oxides, among the wide family of intercalation compounds, have received considerable attention as positive electrode materials in high-energy density lithium and lithium ion batteries. Within this frame LiNiO2 and LiCoO2 oxides and their solid solutions have been extensively studied as they (and the LiMn2O4 spinels) are the only known materials able to intercalate reversibly lithium at high cell voltage (3.5-4 V). Recently, solid solutions such as LiNi1-xCoxO2 have attracted the attention as alternative cathodes to the state of art LiCoO2 in commercial rechargeable Li-ion batteries. Here we have used the Complex Sol-Gel Process (CSGP) to prepare LiNi1-xCoxO2 (x= 0, 0.25, 0.5, 0.75, 1). Starting sols were prepared from Li+-(1-x)Ni2+-xCo2+ acetate aqueous solution in two different routes. According to route-A aqueous ammonia was added to a starting solution containing 0.2M ascorbic acid (ASC) on 1 M total Me. According to route B the starting acetate solutions were first alkalized by ammonia and then the ascorbic acid was added. Regular sols were concentrated to 1/3 of their initial volume and dried slowly up to 170°C. Thermal transformation of the gels to solids was studied by XRD and IR. The electrochemical properties of the compound LiNi0.75Co0.25O2 prepared by the Route-A were evaluated and reported.

Complex Sol-Gel Process (CSGP) was applied to the preparation of LiNi0.5Co0.5O2. Starting sol-solutions were prepared in two different ways: I, in which aqueous ammonia was added to a starting solution of Li+-Ni2+-Co2+ acetate-ascorbate, and II in which LiOH was added to a solution of Ni2+- Co2+ and NH4+ acetate-ascorbate. It was found that in the absence of ascorbic acid, or at its lower content (≤0.2 M on 1M σ Li+- Ni2+- Co2+) precipitation of Ni hydroxides occurred. Regular sols were concentrated ∼3 times, gelled and dried at 140°C. Intensive foaming was observed for samples during further heating. Consequently for scaling up to 200g in a run a preliminary long drying procedure followed by self-ignition step (∼400°C) was introduced. Thermal transformation of the gel to solid was studied by TG, DTA, XRD and IR. The main feature of this step is carbonate formation. The final structure LiNi0.5Co0.5O2 is observed after heating for Ih at 800°C. For larger scale production the extension of firing time was necessary. Electrochemical properties of the LiNi0.5Co0.5O2 compound, prepared by the CSGP were evaluated and considered satisfactory.

Direct Methanol Fuel Cells (DMFC) have been recognized as one of the most promising systems of energy sources for automotive area. Oxidation of methanol in these cells is catalyzed by Pt (often mixed with other metals or/and oxides, e.g., Ru, Au, Os, Ir, Pd, Sn, Pb, Bi, Cr, Cu, Fe and W) on carbon black support. The catalysts can be applied either to electrodes (generally Teflon bonding) or to membranes. In this work the CSGP was applied for preparation of Pt-WO{sub x} and its coatings on carbon black, silver and titanium substrates. Saturated tungsten sol (0.15M) was prepared by dissolving (NH{sub 4}){sub 4}W{sub 5}O{sub 17}2.5 H{sub 2}O in ascorbic acid solution. To this solution H{sub 2}PtCl{sub 6} was added to obtain the molar ratio Pt:W=1. After evaporation and heating at 700 C for 2h homogeneous yellow-green powders were obtained. Another part of this solution was diluted with ethanol and after ultrasonic mixing used for preparation of coatings on Ag and Ti substrates by the immersion technique. Gel layers were dried at 200 C for 20h and then calcined at 700 C for 2h. The resulting white colored layers (thickness 10--65{micro}m) were very adherent. Ascorbate aqueous tungsten-platinum sol diluted to 0.03more » or 0.06 M {Sigma}Me was used for preparation of Pt-W (10 and 20%) catalyst by impregnation of carbon black Vulcan XC-72, followed by thermal treatment in air, argon and hydrogen atmospheres.« less

Medium sized spherical particles (with diameters below 100 μm) of ceramic materials (Al203 and Al203 +8%TiO2) were produced in the following steps: (1) preparation of concentrated hydroxide sols of cations by extraction of anions using Primene JMT, (2) formation of sol emulsion in 2-ethylhexanol-1 containing various amounts of surfactants (EH), (3) gelation of emulsion drops by extraction of water with partially dehydrated EH, (4) non-destructive thermal treatment. Principal properties of the sol depend on the temperature of the extraction process. For preparation of lowanionic sols a two step extraction process, separated by digestion of the aqueous phase at boiling point, was necessary. It was found that the parameters of emulsion formation as well as the properties of the sols significantly influence the particle size distribution. It was concluded that lowering of the sol- EH interracial tension by the surfactant does not influence the process. On the contrary the “anti-clustering” effect of surfactants is essential for preparation of perfect spherical powders. The thermal decomposition of gels to oxides is determinant for densities, specific surface area and carbon content. Medium sized spherical powders are free flowing. The compactibility and sinterability of those powders are poor. However drastic reduction of particle size by milling (connected with their transformation to irregular shape) significantly improves the sinterability.

A method of preparation of spherical powders (with particle diameters

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 NH4OH 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.

The starting sols were prepared by addition of ammonium hydroxide to acidic solutions of Y-Ba-Cu acetates or by dissolving solid Ba9CO9 or CuCO9.CuCOH)2H2O in acetates of the remaining components. The sols were then gelled to spherical particles with diameter below 50μm by extracting water with 2-ethyl-l-hexanol or to shard by evaporation of water. After thermal treatment of both powders amorphous and then crystalline YBa2Cu,9O7−x were obtained. Formation of these compounds is strongly improved by aging the gel at 200°C. Green and sintered pellets exhibit excellent superconductivity properties.

Titanium oxide and titanates based on Ba, Sr and Ca were prepared from commercial solutions of TiCl4 and HNO3. The main preparation steps for the sols consisted of elimination of chloride anions by distillation with nitric acid and addition of metal hydroxides for the titanates. Resulting sols were gelled and used to (1) prepare irregularly shaped powders by evaporation; (2) produce by a dipping technique thin films on glass, Ag, or Ti substrates; and (3) produce spherical powders (diameters