Monoclinic zirconium oxide nanostructures synthesized by a hydrothermal route

Zirconium oxide (ZrO(2)) nanostructures were synthesized by a hydrothermal route. Surface morphology analysis depicts the formation of rice-grain-like and fiber-like ZrO(2) nanostructures at different synthesis conditions. The structural analysis confirms that the as-synthesized ZrO(2) product is of pure monoclinic phase (m-ZrO(2)). The clear and equally spaced lattice fringes in high-resolution transmission electron microscopy (HRTEM) images and discrete spot pattern of selected area electron diffraction (SAED) confirm the high quality of the synthesized product. The product consists of monodispersed nanoparticles of uniform composition, high purity, and crystallinity. The Raman spectra are quantitatively analyzed and the observed peaks are attributed to various vibration modes of m-ZrO(2).     

Growth and characterization of hydroxyapatite crystals by hydrothermal method

Hydroxyapatite crystals were grown by hydrothermal method using dicalcium phosphate dihydrate crystals as a starting material. The grown crystals were found to be free from carbonate inclusion. Two distinct morphologies were obtained by following two different growth methods. Controlled slow growth process and rapid growth process results in hexagonal and whisker like morphologies.     

Synthesis of ZrO2 and TiO2 nanocrystalline powders by hydrothermal process

In present work, nanocrystalline zirconia and titania were synthesized by hydrothermal treatment of zirconyl ZrO(NO₃)₂ and titanyl TiO(NO₃)₂ nitrates aqueous solutions and amorphous gels of the corresponding hydroxides. The hydrothermal synthesis was performed in a wide range of temperatures (150–250 °C), concentration of starting solutions (0.25–0.5 M) and duration of the process (from 10 min to up to 24 h). The hydrothermal treatment at high pressure about 2.0–4.0 GPa was also carried out. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and BET. Particle sizes, morphology and properties of the products were investigated. The influence of hydrothermal synthesis conditions on ZrO₂ and TiO₂ phase compositions were established.     

Growth of oxide single crystals by topotactic reaction

Single crystals of MgO have been heated with crystals of Al₂O₃, Fe₂O₃ and TiO₂ on cut and polished faces, in known relative crystallographic orientations. The initial product in every case was a spinel phase witha ₀=8.38 Å, oriented with its axes parallel to those of MgO. Crystals reacted in different orientations gave the same product, but kinetic rates appeared to differ. CaO and TiO₂ crystals, treated in the same way, gave an unoriented product.     

Preparation of ZrO2-Al2O3 powder by thermal decomposition of gels produced from an aluminium chelate compound and zirconium butoxide

Organic precursors containing Al and Zr atoms were synthesized from an aluminium chelate compound and zirconium n-butoxide. A ZrO₂-Al₂O₃ composite powder was prepared by the thermal decomposition of these precursors. An amorphous phase exists to higher temperatures for this ZrO₂-Al₂O₃ powder than for a comparable powder prepared from aluminium sec-butoxide and zirconium n-butoxide. In addition the tetragonal ZrO₂ phase was stabler in this ZrO₂-Al₂O₃ powder than in a comparison powder. The ZrO₂ grains were 50–500 nm in diameter and were homogeneously dispersed in the Al₂O₃ matrix after heating at 1400 °C.     

Synthesis of zirconium oxide by hydrolysis of zirconium alkoxide

Submicrometre particles have been prepared from hydrolysis-polycondensation of zirconium alkoxide [Zr(n-C₃H₇O)₄] in ethanolic solution. The properties of these particles (morphology, specific surface area, S _BET, crystal phase and size distribution) after calcination at 450 °C for 5 h were found to depend on the conditions of synthesis, i.e. alkoxide concentration and mole ratio water/alkoxide.     

Mechanical behavior of zirconium dioxide crystals partially stabilized with yttrium oxide

The results are given of a composite investigation of the mechanical behavior of single crystals of zirconium dioxide partially stabilized with yttrium oxide and ytterbium oxide at temperatures up to 1400°C. It is shown that the elastic modulus of these materials lies in the 150–350 GPa range and their tensile strengths may reach 1,688 MPa. These materials have a nonincreasing relationship of the stress intensity factor to crack length (flat R-curves). The stress intensity factors determined on specimens with a sharp crack are significantly lower than on specimens with a notch. The picture of fracture of single crystals in penetration of an indentor, etc. differs significantly in relation to the stabilizing addition.Translated from Problemy Prochnosti, No. 1, pp. 73–77, January, 1991.     

Growth of transition metal oxide crystals by halide vapour hydrolysis

Single crystals of NiO, CoO, FeO, Co₃O₄, and Fe₃O₄ have been epitaxially deposited on MgO single-crystal substrates by the hydrolysis of anhydrous metal bromides in the gaseous phase. All of the crystals were grown at temperatures below 700° C and at a total pressure of less than 25 torr. The deposition was usually complete after approximately 30 min, and the crystals were of uniform thickness with a glassy-clear, smooth surface. Depending on the number of depositions, these crystals can be formed in various thicknesses ranging from approximately 5 m to 1 mm. The crystals were found to deposit in parallel alignment with the (100) cleavage plane of MgO. A substantial increase in chemical purity is observed, and only 10³ to 10⁵ dislocations/cm² were observed in all NiO crystals. A reaction mechanism is proposed which involves: (i) the formation of a hydroxybromide transport phase with fluid properties; (ii) adsorption of the transport phase on the MgO substrate; followed by (iii), the chemical disproportionation-crystallisation of the intermediate phase to the oriented, solid oxide phase.Also associated with the Department of Geochemistry and Mineralogy.     

Growth of gallium orthophosphate single crystals in acidic hydrothermal solutions

The hydrothermal growth of GaPO₄ single crystals has been studied in several solutions. Among many solutions, H₃PO₄, HCl and H₂SO₄ solutions were found to be effective solvents for the growth of GaPO₄ single crystals. Single crystals have been hydrothermally grown at temperatures over the range 210 to 290 °C in these solutions with seed crystals. HCl solution was found to be the most effective solvent in which to grow large single crystals. Morphologies of crystals grown at temperatures below 200 °C tended to be bounded by small major rhombohedral (1 0 ˉ1 1) faces. In the temperature range from 210 to 430°C, the crystals have morphologies bounded by prism (1 0 ˉ1 0), small major rhombohedral (1 0 ˉ1 1) and minor rhombohedral (0 1 ˉ1 1) faces, and grew with well developed basal (0 0 0 1) faces with increase in the growth temperature. Single crystals of GaPO₄ with lower dislocation density have been hydrothermally grown at 210 to 290°C in 3m H₃PO₄ solution.     

Low temperature hydrothermal synthesis of ZrO2-CaO solid solutions

Nanosized powders of ZrO₂-CaO solid solutions have been synthesized by hydrothermal treatment at 110°C. Amorphous hydrous ZrO₂, CaO freshly prepared by thermal decomposition of CaCO₃ and MOH (M = Na, Li) mineralizer solutions were employed as precursors for the hydrothermal synthesis. Calcia-stabilized zirconia (CSZ) with different CaO content and characterized by different crystal sizes have been produced by changing the hydrothermal treatment temperature, the reaction time and the mixture composition of precursors. The combined effect of both MOH and CaO on the crystallization-stabilization of zirconia at low temperature of hydrothermal treatment is discussed.     

水热法制备MoO_2纳米棒的自组装生长机理研究

水热条件下,以双氧水和钼粉制备的过氧钼酸溶胶为钼源,乙醇为还原剂制备得到Mo O2纳米棒。利用X射线衍射(XRD)、扫描电子显微镜(SEM)以及场发射高分辨透射电子显微镜(HRTEM)对产物的结构与形貌进行表征。结果表明,水热反应初期过氧钼酸溶胶首先生成Mo3纳米带,随后在还原剂的作用下,纳米带逐渐劈裂成扇形Mo8O23,最后在乙醇的还原下,扇形Mo8O23纳米片进一步劈裂形成结晶良好的Mo O2纳米棒。     

Preparation of ultrafine zirconium dioxide particles by thermal decomposition of zirconium alkoxide vapour

Ultrafine zirconia particles are produced by thermal decomposition of zirconium tetratertiary butoxide (ZrTB) vapour. The introduction of ZrTB vapour into the cylindrical electric furnace, is achieved by three different methods: (evaporator, pressurized nebulizer and ultrasonic nebulizer). The properties of the fine particles obtained by these methods are mainly analysed by X-ray diffraction and transmission electron microscopy. It is found that ultrafine zirconia particles produced at relatively low temperatures from 600 to 700° C are spherical in the diameter range 0.035 to 0.15 μm and of tetragonal phase. Furthermore, two-component fine particles of zirconia-ilver are generated by putting the silver solid inside the furnace containing alkoxide vapour, and are deposited by inertia on to a glass substrate under low pressure to form films having a thickness of 17 to 33 μm. The electrical characteristics of the films are evaluated, and the conductance of the film is found to increase with the content of the silver component.     

Preparation of copper-cobalt oxide spinels by thermal decomposition of copper-cobalt basic nitrate mixed crystals

Copper-cobalt oxide spinels with a common formula Cu _x Co_3–x O₄ (0x1.0) have been prepared by thermal decomposition at 350° C in air of single-phase mixed basic nitrate precursors (Cu, Co)₂(OH)₃NO₃. The formation of the oxide phase during the thermal treatment has been associated with a diffusionless mode of transformation, established for some hydroxides and hydroxysalts with a layer-type structure.     

Calcium phosphate formation on nanocrystalline ZrO2 thin film prepared by using a zirconium naphthenate

To investigate the calcium phosphate forming ability of ZrO₂ thin film, we prepared ZrO₂/Si structure by a chemical solution deposition with a zirconium naphthenate as a starting material. Precursor sol was spin-coated onto the cleaned Si substrate and prefired at 500 °C for 10 min in air, followed by final annealing at 800 °C for 30 min in air. Surface morphology and surface roughness of the annealed layer were characterized by field emission-scanning electron microscope and atomic force microscope. After soaking for 5 days in a simulated body fluid, formation of the calcium phosphate on nanocrystalline ZrO₂ layer annealed at 800 °C was observed by energy dispersive X-ray spectrometer. Fourier transform infrared spectroscopy revealed that carbonate was substituted into the calcium phosphate.     

Mechanical treatment of TiO2 and ZrO2 oxide mixtures

The mixed ZrO2-TiO2 system (5-50 wt% of ZrO2) has been studied to investigate the influence of the mechanical treatment on its physicochemical properties depending on the composition, time of milling (5, 10 and 20 min, r.p.m. 82) and temperature (400, 550 and 700 degrees C). Samples were characterized by Raman spectroscopy, X-ray powder diffraction, Scanning Electron Microscopy coupled with Energy Dispersion X-ray analyzer, High Resolution-Transmission Electron Microscopy and nitrogen adsorption porosimetry. Results show that srilankite (TiZrO4) phase has been produced. No influence of the milling time and temperature on the phase composition is observed. The presence of zirconia increases the thermal stability of anatase phase up to 700 degrees C hindering the anatase rutile phase transformation.     

Homogeneity of triglycine sulphate crystals

Powder suspensions in silicone oil have been used for decorating slices of TGS grown from aqueous solutions by conventional means, and by a spinning disc technique. The method provides a quick means of assessment of crystal quality and uniformity and has helped in the interpretation of some of the phenomena observed in electrical measurements on both undoped and doped TGS crystals. Sections of crystals grown with alanine as dopant — which gives the crystals an internal polarization bias — show a markedly non-uniform decoration pattern, indicative of a variation of polarization in different growth sectors. Much improved uniformity is demonstrated in crystals grown on a single surface under controlled conditions of solution flow.