Amorphous ZrO2 Research Articles

Alkoxide-derived amorphous ZrO 2 coatings

Pure and transparent ZrO 2 coatings on microscopic glass slides, ranging in thickness from 250 to about 1500 Å, were prepared from (i) zirconium n-propoxide in dry cyclohexane, and (ii) zirconium n-propoxide in isopropanol with additions of acetic acid and water. A dipping technique was used. A baking temperature of 450°C was chosen for the conversion of as-prepared gel films into the pure oxide state. The coatings were X-ray amorphous. The dependence of coating thickness on lifting speed and concentration of zirconium n-propoxide in solution was examined. The coating profile showed that these films were fairly smooth beyond a “trouble zone” (appearing along the boundary between the coated and non-coated parts of a slide and extending up to about 1 mm) where a relatively high and irregular profile was observed.

A high resolution transmission electron microscopy study of ZrO 2-CaO films

The structure of ZrO 2-CaO films, which were prepared by vacuum deposition and crystallized by electron beam heating, was investigated by high resolution electron microscopy. In an amorphous ZrO 2 film obtained from the deposition of pure ZrO 2, monoclinic ZrO 2 crystals which are stable below 1170°C were obtained on heating in vacuum. In a film obtained from the deposition of ZrO 2 and CaCO 3, Zr(Ca)O 2− x crystals grew in a solid solution of ZrO 2 with CaO. It was observed that, in ZrO 2-20mol.%CaO films, ordered CaZrO 3 crystals and CaZr 4O 9 (Φ 1 phase) crystals were precipitated in the Zr(Ca)O 2− x crystals. Not only the lattice orientation relationship but also the atom configuration relationship of these crystals with the Zr(Ca)O 2− x crystal were established. Calcium ion walls with anion vacancies were found along the (001), (1̄10) and (1̄11) planes in the Zr(Ca)O 2− x crystals.

Synthesis of solid superacid of tungsten oxide supported on zirconia and its catalytic action for reactions of butane and pentane

A solid superacid catalyst with an acid strength of H0⩽–14.52 was obtained by impregnating Zr(OH)4 or amorphous ZrO2 with aqueous ammonium metatungstate followed by calcining in air at 800–850 °C (13 wt.% W); this catalyst was active for the isomerisations butane to isobutane at 50 °C, and pentane to isopentane at 30 °C.

Low-temperature oxidative degradation of low-dimensional zirconium and hafnium tellurides

The penta-, tri- and ditellurides of zirconium and hafnium easily take up oxygen and become partly oxidized at and below room temperature. Complete oxidation of these phases to (amorphous) ZrO 2 or HfO 2 and (crystalline) Te is attained at some 320 to 500K (depending on compound, sample characteristics and experimental conditions) provided sufficient amounts of oxygen are available. Explanations for the different anomalies in ZrTe 5 are advanced as adsorbed/absorbed oxygen in the voids of the structure, partial oxidation, partial destruction of the Te III-Te III zig-zag chains in the structure and decomposition to the corresponding tritelluride and Te.

Crystallization process of cubic ZrO2 in calcium acetate solution

Ultrafine powders of cubic ZrO2 were obtained at about 270° C by heating hydrated amorphous ZrO2 in greater than 0.2 molal calcium acetate solutions. Ca2+ ions played a role as nucleii for crystallization and were introduced into distinct sites of the crystalline phases, that is, substituted for Zr4+ ions. Mn2+ ions produced almost the same effects on the crystallization of ZrO2·EPR spectra for powder samples containing Mn2+ ions apparently showed two types as follows: for tetragonal ZrO2 with a trace of monoclinic ZrO2, the central fine structure transitions (M=+1/2↔−1/2) showed a well-resolved hyperfine structure. In addition to the Δm=0 transition, forbidden Δm=±1 transitions were observed. For cubic ZrO2, the broad underlying response was observed as well as the hyperfine structure composed of six main peaks.

Preparation of amorphous ZrO2 coatings from metal-organic solutions

Conditions de preparation et proprietes de transmission optique des revetements transparents et amorphes de ZrO 2 des substrats de verres sodocalciques

Preparation of amorphous ZrO 2 fibers by unidirectional freezing of gel

Zirconia hydrogel was prepared by dialyzing 1∼3M ZrOCl 2 solution partially neutralized with an alkline solution for 96 ∼192 h. The gel was placed in a plastic cylinder and unidirectionally frozen by lowering the cylinder into a −78°C cold bath at 4 or 6 cm/h. A bundle of parallel fibers longer than 8 cm and 10∼60 μm in diameter was obtained after thawing. The fibers were amorphous and porous as-dried at 25°C. Their pores were greatly eliminated by a heat treatment in a vacuum at 290°C for 2 days. The chemical composition of the heat-treated fibers was approximately ZrO 2·H 2O.

ChemInform Abstract: CRYSTALLIZATION AND TRANSFORMATION OF ZIRCONIA UNDER HYDROTHERMAL CONDITIONS

AbstractWährend gleichmäßigen Au?ieizens auf 350°C in konz. NaOH‐Lösungen kristallisiert hydratisiertes amorphes ZrO2 kubisch.

Crystallization and Transformation of Zirconia Under Hydrothermal Conditions

During constant-rate heating to 350°C in concentrated NaOH solutions, cubic ZrO2 crystallized at ∼120°C from hydrated amorphous ZrO2; these One cubic ZrO2 particles abruptly changed into needlelike monoclinic ZrO2 single crystals at 300°C. Crystallization and phase transformation were studied by XRD, TEM, and EPMA. Cubic ZrO2 appears to crystallize via collapse of the ZrO2−nH2O structure and subsequent slight rearrangement of the lattice. The abrupt formation of mono-clinic ZrO2 was considered to result when the very fine cubic ZrO2 particles coagulated in a highly oriented fashion.

Thermal decomposition of zirconium hydroxide

The thermal decomposition of zirconium hydroxides prepared from aqueous ammonium hydroxide solutions on the addition of potassium fluorozirconate, K 2ZrF 6, under various conditions has been examined by thermogravimetry, differential thermal analysis, X-ray diffraction study and infrared spectrophotometry. As a result, it is found that the thermal decomposition of zirconium hydroxide proceeds according to ▪ In this process, the transformation of amorphous ZrO 2 to either the metastable tetragonal or monoclinic form depends on the composition of the original starting material as an hydrated oxyhydroxide, ZrO 2− x (OH) 2 x · y H 2O where x ⩽ 2 and y ⋍ 1.

ChemInform Abstract: RAMAN SCATTERING STUDY OF THE CRYSTALLIZATION AND PHASE TRANSFORMATIONS OF ZRO2

X-ray diffraction, electron diffraction, and Raman scattering measurements are presented for dehydrated amorphous ZrO2. Although the material lacks sufficient crystallinity to diffract X rays, electron diffraction patterns indicate a microcrystallinity with a grain size of 15 to 30 A. Raman spectra characteristic of the metastable tetragonal polymorph were obtained from these materials. Heating the amorphous materials induces recrystallization into first a metastable tetragonal phase and then the stable monoclinic phase.

Raman Scattering Study of the Crystallization and Phase Transformations of ZrO2

X‐ray diffraction, electron diffraction, and Raman scattering measurements are presented for dehydrated amorphous ZrO2. Although the material lacks sufficient crystallinity to diffract X rays, electron diffraction patterns indicate a microcrystallinity with a grain size of 15 to 30 A. Raman spectra characteristic of the metastable tetragonal polymorph were obtained from these materials. Heating the amorphous materials induces recrystallization into first a metastable tetragonal phase and then the stable monoclinic phase.

Irradiation effects in amorphous ZrO2

Abstract Amorphous ZrO2 was irradiated in order to study respectively electronic excitation and displacement cascade-induced thermal effects. We have first studied the crystallization of amorphous ZrO2 by heating it in a furnace. We have then compared these thermal effects with radiation induced thermal effects. Tracks, of non-crystalline structure, have been observed in amorphous ZrO2 irradiated with fission fragments at low dose. The threshold stopping power of fission fragments leaving a track was determined to be 1300 eV/A. White spots have also been observed in amorphous ZrO2 irradiated with 1 MeV Kr+ ions. They exhibit, in electron microscopy, a more intense transmission than the amorphous matrix. It is shown that displacement spikes are responsible for these spots and that the atomic order is higher in these spots than in the amorphous matrix. The threshold energy, for a primary to create a displacement spike able to induce such a spot, was found to be 50 keV.

The crystallization of amorphous ZrO 2 by thermal heating and by ion bombardment

Thin films of amorphous ZrO 2 suitable for transmission electron microscopy were prepared by sputtering anodized Zr with 6-keV Kr or O 2 ions and collecting the deposit on unheated KC1. In a first group of experiments, thermal heating of the amorphous films was shown to lead to crystallinity at a temperature dependent on the heating time, for example 520–540 °C in 5 min. The crystallized films consisted mainly of an apparently cubic form of ZrO 2 together with a certain amount of the monoclinic form, though only the latter persisted to higher temperatures. In further experiments, in which the amorphous films were bombarded with 2 to 35 keV Kr ions, crystallized regions with mean diameters of 250–750 Å were found. At currents above about 20 μA/cm 2 such crystallization is probably in part an impact effect and in part due to beam heating. At lower currents, however, beam heating is insufficient and it is necessary to assume that either displacement spikes, thermal spikes, or radiation-enhanced diffusion plays a role.

Infrared Spectra Study on the Oxidation Film of Zirconium

An investigation was made of the infrared absorption spectra of various zirconium oxides, The spectra of hydrated ZrO2 had four absorption bands at 2.9, 6.5, 7.5, and 20 mu . An amorphous ZrO2 had an absorption band at 20 mu . The tetragonal ZrO2 had three absorption bands at 17.5, 20, and 27 mu. The monoclinic ZrO2 had five absorption bands at oxide films on several grades of zirconium and zirconium alloys had five absorption bands similar to the reference monoclinic ZrO2. Although a consistent relation was not found between the oxidation rate and the infrared absorption frequency, an appreciable difference of infrared absorption frequency was found between the oxide films, which have no difference in the lattice constant by x-ray analysis.