Al2O3-ZrO2 System Research Articles

Structure Formation of a Ceramic Composite of the Al2O3–ZrO2 System During Strontium Hexaaluminate Synthesis During Firing

Structure Formation of a Ceramic Composite of the Al2O3–ZrO2 System During Strontium Hexaaluminate Synthesis During Firing

Characterization of Zr-bearing crystalline phases from Rb-bearing model matrix materials

As part of the synthesis of new matrix materials for vitrifcation of highly active radioactive wastes, the crystalline phases formed during rapid cooling from melts of the Na2O–Rb2O–SrO(Ba)–B2O3– SiO2–Al2O3–ZrO2 system with a high Rb and Zr content (up to 10 mol. %) are found and studied. The presence of numerous Zr and Rb-bearing crystals in samples is established by electron microscopy, X-ray diffraction and Raman spectroscopy; their morphology, chemical composition and spectral characteristics are studied. It is concluded that these crystalline phases form due to the excessive content of individual components of the melt and their formation is responsible for the undesirable fnal local heterogeneity and crystallization of matrix materials.

Aero acoustic levitation to unveil the solidification of complex oxides: Case study of the system Al2O3–ZrO2

Binary or multi-component phase mixtures are of particular technical importance. Despite the wide field of application of Al2O3 and ZrO2 composites, the literature reveals contradictions about the liquidus region. Containerless processing avoids typical problems of conventional techniques like melt contamination or lack of suitable container materials. Composition ranging from 0–80 mol% ZrO2 were melted and solidified in an aero acoustic levitator. A high-speed camera recorded the crystallization, allowing a direct correlation with the observed microstructures. Due to homogeneous nucleation, all samples exhibited significant undercooling before crystallization. The nucleation temperature of the different compositions roughly followed the slope of the liquidus line. Undercooling, solidification kinetics, and local reheating played a considerable role in microstructure formation. A lamellae eutectic microstructure was created over a large compositional range from 36–48 mol% ZrO2. On the hypoeutectic side, the effect was attributed to solidification within the coupled zone. However, hypereutectic samples also exhibit a zirconia-rich eutectic as well. We assume impaired ZrO2 nucleation or growth favors alumina precipitation from the melt. Aero acoustic levitation proved to be an excellent technique for studying complex high melting oxide systems, enabling a better understanding of their crystallization process.

Formation of the structure of a ceramic composite of the Al<sub>2</sub> O<sub>3</sub> ‒ZrO<sub>2</sub> system during the synthesis of strontium hexaaluminate during firing

Experimental results of the formation of the structure of a ceramic composite of the Al2O3‒ZrO2 system with the formation of strontium hexaaluminate, a reinforcing element of the material, during firing, are presented. It is shown that a uniform distribution of lamellar crystals of strontium hexaaluminate over the volume of the structure and a 30 % increase in strength is achieved during its synthesis during the firing of ceramics with the introduction of pre-synthesized strontium zirconate (precursor) into the charge. The introduction of pre-synthesized strontium hexaaluminate into the composition of the composite charge, followed by mixing and grinding, does not provide the effect of hardening the composite.

Phase diagram study and thermodynamic modeling of the Na2O–Al2O3–ZrO2 system

AbstractThe phase diagram of the Na2O–Al2O3–ZrO2 system was experimentally studied at 1500°C–1650°C by a classical equilibration/quenching method and differential thermal analysis followed by X‐ray diffraction phase analysis and electron probe micro‐analysis. A sealed Pt crucible was utilized to prevent the volatile loss of Na2O during high‐temperature phase equilibrium experiments and the hydration upon quenching. The phase diagram of the Na2O–Al2O3–ZrO2 system was revealed for the first time. Based on the present experimental data and available binary modeling results in literature, the thermodynamic modeling of the ternary system was performed using the Calculation of Phase Diagram method and the phase diagram of the entire the Na2O–Al2O3–ZrO2 system was constructed and the optimized thermodynamic properties for all solids and liquid phase within the ternary system were obtained.

THERMODYNAMIC ANALYSIS OF OXIDE-CARBON AND CARBON MONOXIDE CHEMICAL REACTIONS IN ORDER TO SELECT ADDITIVES FOR CARBON NANOTUBE REINFORCED CORUNDUM CERAMICS

The calculation of Gibbs energy for reactions of interaction of ZrO2, Al2O3, SiO2, TiO2, CaO and MnO with carbon and carbon monoxide in temperature range 1273 – 2273 К (1000 – 2000 ?С) is made to select eutectic additive for structural ceramics in Al2O3–ZrO2–eutectic additive–carbon nanotube system. Considering the multi-component structure of the ceramic matrix composite in the system Al2O3–ZrO2–eutectic additive–carbon nanotube system, it is necessary to consider the process of possible carbidization, worsening the strength characteristics of the synthesized material. As a result of the analysis, it was found that eutectic additives containing Al2O3, SiO2, TiO2, CaO.

КЕРАМИЧЕСКИЕ МАТЕРИАЛЫ НА ОСНОВЕ ОКСИДОВ АЛЮМИНИЯ И ЦИРКОНИЯ, ПОЛУЧЕННЫЕ ЗОЛЬ-ГЕЛЬ МЕТОДОМ

The rheological properties, processes of structure and phase formation of the Al2O3–ZrO2 system compositions obtained by the sol-gel method have been investigated. The temperature range of crystallization of the compositions is 900–1100 °C. With an increase in the concentration of zirconium dioxide in the system, the temperature of the transition from the tetragonal to the monoclinic phase decreases. The effect of the ratio of the components in the initial solutions and the temperature regime of heat treatment of gels on the physicochemical properties of nanopowders and sintered materials has been studied. Ceramic materials of eutectic composition give the highest density and lower values of porosity and water absorption.

Механоструктурные свойства керамоматричных композитов Al2O3—ZrO2, армированных поликристаллическими волокнами на основе Al2O3.

The article considers the production of composite materials in the Al2O3—ZrO2system by free and vacuum sintering methods, as well as the effectof the introduction of an additive of polycrystalline fibers based on Al2O3on the strengthening of the composites.

Methodology for Measurement of Density of Liquid Oxides

Abstract Measurement of physical properties of materials in extreme conditions, such as high temperature, is limited by technological challenges. Nevertheless, modeling of several phenomena relies on the existence of experimental data for their validation. In this study, a method suitable for determination of density in a liquid phase at high temperature is proposed and tested on Al2O3–ZrO2 system. A methodology for acquiring the temperature dependence of density for radioactive materials is proposed and is aimed to refine severe nuclear accidents modeling. The oxide was melted in an induction furnace with a cold crucible. The measurement was based on evaluation of the volume of the melt at different temperatures, in a range from 2100 to 2400 °C. The densities of the oxide in the solid-state and the skull-layer were measured using a pycnometer. A temperature dependence of the density was established and the results were compared with literature. The difference between existing data and the measured values in this work was less than 5%. Thus, the proposed methodology provides reliable density values in extreme conditions.

Effect of Co2+ on the Phase Formation, Mechanical Properties, and In Vitro Behavior of Ceramics in the ZrO2–Al2O3 System

Effect of Co2+ on the Phase Formation, Mechanical Properties, and In Vitro Behavior of Ceramics in the ZrO2–Al2O3 System

Increasing the Sintering Rate and Strength of ZrO2–Al2O3 Ceramic Materials by Iron Oxide Additions

We have prepared powders and ceramic composite materials in the ZrO2–Al2O3 system containing 10 and 20 wt % Al2O3 and examined the effect of ferric oxide additions on the linear shrinkage, phase composition, porosity, microstructure, and mechanical properties of the ZrO2–Al2O3 ceramic materials. The results demonstrate that the addition of ferric oxide leads to a considerable increase in linear shrinkage and ensures porosity as low as under 1% even at a sintering temperature of 1450°C in both composite materials. Moreover, small amounts of the additive stabilize the tetragonal phase of ZrO2, whereas increasing the Fe content to 3 mol % leads to an increase in the amount of the monoclinic phase. We have obtained densely sintered ZrO2–10% Al2O3 and ZrO2–20% Al2O3 ceramic materials at 1450°C, with a bending strength of up to 760 and 475 MPa, respectively.

The effect of transition metal oxides on the sintering and properties of ceramics in the ZrO2-Al2O3 system

The paper presents the results of the investigation of the transition metals oxides – cobalt and iron additives influence on the sintering and properties of the ceramic material based on ZrO2- Al2O3 system with 10 wt.% Al2O3. It is shown that the addition of the oxides resulted in the significant increase of the sintered ceramic materials ZrO2-10%Al2O3 strength and decrease of sintering temperature. The maximum bending strength was more than 800 MPa (sintered at 1450 °C) and porosity was less than 1%.

Medical Ceramics from Powders of the System Al2O3–ZrO2–Y2O3 Obtained on an Installation of Nanospray Drying

This work shows the possibility of obtaining Al2O3–ZrO2–Y2O3 medical ceramics from powders synthesized by nanospray drying. The powder is spheres with a uniform distribution of components: mixed oxides. It is shown that yttrium oxide, in addition to stabilizing the tetragonal phase of zirconium oxide in ceramics, causes a more deagglomerated structure of particles and, as a result, increases the degree of shrinkage of ceramics and the final temperature of active sintering from 1252 to 1468°C. The ceramics obtained by cold pressing with subsequent sintering have a hardness of 15.31 GPa and density of 92.8%; those obtained by the sintering method in spark discharge plasma have a hardness of 16.05 GPa and density of 99.21%.

Waste-Free Recycling of Secondary Bacor Resources1

Technology is developed for two-stage processing of secondary zirconium-containing mineral resource. A production scheme includes mechanical treatment of bacor waste and subsequent chemical leaching of impurities. The main processes in the first (mechanical) stage are crushing and selective grinding with separation of high-zircon concentrate (Al2O3–ZrO2 system) and aluminum-zirconia product leaner with respect to ZrO2 (R 2O–Al2O3–ZrO2–SiO2 system). In the second stage the latter are leached with a fluoric acid solution. The waste-free technology proposed for enrichment makes it possible to use valuable secondary resources entirely with preparation of two end products: enriched bacor refractory and a slag-forming mixture for steel smelting production.

ZERO-WASTE RECYCLING OF THE SECONDARY BACOR MATERIALS

The two-stage processing for the secondary zirconiumcontaining mineral raw materials was developed in the article. The process flow sheet includes both the Bacor scrap mechanical treatment and the subsequent chemical leaching of impurities. The main processes of the first (mechanical) stage are the crushing and selection extraction of the high-zirconium concentrate (Al2O3‒ZrO2 system) and more poor in ZrO2 alumina-zirconium product (R2O‒Al2O3‒ZrO2‒SiO2 system). At the second stage this product is leached by means of the hydrogen fluoride water solution. The zero waste enrichment technology proposed allows the full utilization of the valuable secondary raw materials with the two resulting products: the concentrated refractory Bacor and the slag-forming mixture for the steel making industry. Ill. 1. Ref. 6.

Thermal Expansion of Composite Ceramic of the Zirconium Dioxide – Aluminum Oxide System

The change in LTEC is analyzed on heating and cooling ceramic materials of the Al2O3–ZrO2 system in the range 200 – 1500°C. The effect of structural and phase components and measurement regime (heating/cooling) on form of the relationship Δl/l 0 = f(t), and also the dependence of LTEC on composite chemical composition are established. Results obtained are discussed from the point of view of material phase composition and published data are analyzed. Data are provided for average and true LTEC values.

Sintering and microstructure of materials based on the fluorohydroxyapatite–ZrO2–Al2O3 system

We have studied the influence of the sintering temperature and modifying additives on the phase composition, microstructure, and mechanical strength of a fluorohydroxyapatite-based composite ceramic material containing 20 wt % zirconia. The addition of 5 wt % alumina has been shown to prevent recrystallization processes and contribute to phase composition stabilization. Moreover, the addition of a sintering aid (2 wt %) has made it possible to lower the sintering temperature to 1200°C and raise the bending strength of the material to 143 MPa.

Influence of matrix replacement on consolidation processes of composite ceramic materials of ZrO2-Al2O3 system

This paper studies the influence of the introduction of alumina Al(OH)3 as a hydrogel on the consolidation processes and the formation of the microstructure of the composite material of the ZrO2-Al2O3 system under matrix replacement. It is found that the densification processes of the composite material during sintering with the matrix replacement decelerate owing to the occurring polymorphic transformation γ → α-Al2O3.

Electrical conductivity of NaF–AlF3–CaF2–Al2O3–ZrO2 molten salts

The electrical conductivity of NaF–AlF3–CaF2–Al2O3–ZrO2 system was studied by a tube-type cell with fixed cell constant. The results show that the electrical conductivity of NaF–AlF3–3%Al2O3–3%CaF2–ZrO2 molten salt system decreases with increase of ZrO2 content in an interval of 0–5%. The increase of 1% ZrO2 results in a corresponding electrical conductivity decrease of 0.02 S/cm, and the equivalent conductivity increases with the increase of molar ratio of NaF to AlF3. When the temperature increases by 1 °C, the electrical conductivity increases by 0.004 S/cm. At last, the regression equations of electrical conductivity relative to temperature and ZrO2 are obtained by quadratic regression analysis.

Coordination nature of phase separation in oxide melts

The behavior of uranium oxide-silica, zirconia-alumina, zirconia-iron oxide, uranium oxideiron oxide, zirconia-alumina-iron oxide, and uranium oxide-iron oxide-zirconia melts was experimentally investigated in the air. The existence of two-phase fluids in these systems was confirmed. It is proposed that the reason for the phase separation is the formation of complexes with the general formula x[M3+O8/2] [Me4+O8/2]. The influence of a complex concentration on the density and surface tension of melts in the ZrO2-Al2O3 system was demonstrated.