Zirconia-based Ceramics Research Articles

Colloidal Processing and Superplastic Properties of Fine-Grained Zirconia-Based Ceramics

Colloidal Processing and Superplastic Properties of Fine-Grained Zirconia-Based Ceramics

Time-dependent transformation in zirconia-based ceramics

The present observation of compressive stress relaxation for 8mol%CeO 2–0.5mol%Y 2O 3–TZP shape memory ceramics provides a new evidence of a gradual reverse transformation (m→t) accompanying a volume contraction of about 5% during the natural aging, resulting in continuous increase of the length of the specimen.

Atomic Scale Analysis of a YSZ Bicrystal Grain Boundary

Yttria-stabilized zirconia (YSZ) has been the subject of many experimental and theoretical studies, due to the commercial applications of zirconia-based ceramics in solid state oxide fuel cells. Since the grain boundaries usually dominate the overall macroscopic performance of the bulk material, it is essential to develop a fundamental understanding of their structure-property relationships. Previous research has been performed on the atomic structure of grain boundaries in YSZ, but no precise atomic scale compositional and chemistry characterization has been carried out. Here we report a detailed analytical study of an [001] symmetric 24° bicrystal tilt grain boundary in YSZ prepared with ∼10 mol % Y2O3 by Shinkosha Co., Ltd by the combination of Z-contrast imaging and electron energy loss spectroscopy (EELS).The experimental analysis of the YSZ sample was carried out on a 200kV Schottky field emission JEOL 201 OF STEM/TEM4.

High-quality zirconia powder resulting from the attempted separation of acetic acid from acrylic acid with zirconium oxychloride

Both acetic and acrylic acids are low molecular weight carboxylic acids with very similar physical and chemical properties. As a result it is difficult to separate these two acids by the now commercially significant separation techniques such as distillation, solvent extraction, adsorption, ion exchange, calcium salt precipitation, and membrane processes. We propose a metal–organic precipitation process using zirconium oxychloride to separate acetic acid from acrylic acid in the effluent of an acrylic acid plant. The process developed is based on the selective precipitation of acrylic acid, at suitable pH values, by the addition of zirconium oxychloride to the effluent. The resulting precipitate is a precursor that can yield a pure, ultrafine, and partially-stabilized zirconia powder which has been characterised using thermal analysis, infrared spectroscopy, and X-ray diffraction. Environmental, technological and cost advantages will make the present process feasible for the manufacture of advanced zirconia-based ceramics.

211 ジルコニア系セラミックス板材の超塑性成形に関する研究(機械材料・材料加工IV)

211 ジルコニア系セラミックス板材の超塑性成形に関する研究(機械材料・材料加工IV)

Domain switching in monoclinic YNbO 4-modified ZrO 2(3Y)

Behaviors of domain switching in zirconia-based ceramics are observed only on the tetragonal phase. Despite the presence of domain switching in monoclinic hafnia ceramics, the similar behavior of monoclinic zirconia have frequently been considered impractical since zirconia ceramics are prone to fracture when they contain a large amount of the monoclinic phase. YNbO{sub 4} is a compound having a monoclinic structure at room temperature and a tetragonal structure at temperatures exceeding 900 C. A related investigation proposed that introducing YNbO{sub 4} into ZrO{sub 2} ceramics, either as a minor second phase or as a solid solution, would more easily promote the nucleation of monoclinic ZrO{sub 2}. Extra high fracture toughness has been observed in Zirconia doped with YNbO{sub 4}. Their studies observed ferroelastic domain switching in tetragonal YNbO{sub 4}-modified ZrO{sub 2}(3Y), similar to those of previous studies. However, their results also indicated an extraordinary elastic behavior of monoclinic YNbO{sub 4}-modified ZrO{sub 2}(3Y) under uniaxial compression. Therefore, the authors investigate the effect of incorporating YNbO{sub 4} into ZrO{sub 2}(3Y) and the ferroelastic domain switching behavior in the monoclinic phase of this material system.

Superplasticity and Joining of Zirconia-Based Ceramics

AbstractSteady-state creep and joining of alumina/zirconia composites containing alumina volume fractions of 20, 60, and 85% have been investigated between 1250 and 1350°C. Superplasticity of these compounds is controlled by grain-boundary sliding and the creep rate is a function of alumina volume fraction, not grain size. Using the principles of superplasticity, pieces of the composite have been joined by applying the stress required to achieve 5 to 10% strain to form a strong interface at temperatures as low as 1200°C

Development of ceramic waste forms for actinide-rich waste— Radiation stability of perovskite and phase and chemical stabilities of ZR-and AL-based ceramics

Ceramics are considered as most promising materials for conditioning of long-lived radionuclides because of their outstanding durability for long term. The Japan Atomic Energy Research Institute (JAERI) has developed ceramic waste forms, e.g. Synroc and zirconia-based ceramics, for the actinide-rich wastes arising from partitioning and transmutation processes. In the present study, α-decay damage effects on the density and leaching behavior of perovskite (one of three main minerals forming Synroc) were investigated by an accelerated experiment using the actinide doping technique. A decrease in density of Cm-doped perovskite reached 1.3 % at a dose of 9 × 10 17 α-decays·g −1. The leach rates (MCC-1 leach test inpH ∼ 2 solution at 90°C for 2 months) of perovskite specimens with accumulated doses of 1.6 × 10 17, 4.0 × 10 17 and 8.3 × 10 17 α-decays·g −1 were 1.7, 2.3 and 3.0 μ·m −2·day −1, respectively. Application of zirconia- and alumina-based ceramics for incorporating actinides was also investigated by the experiments using non-radioactive elements (Ce and Nd) with an emphasis on crystallographic phase stability and chemical durability. The yttria-stabilized zirconia was stable crystallographically in the wide ranges of Ce and/ or Nd content and had excellent chemical durability.

Densification and Grain Growth of Nanocrystalline Zirconia-Based Ceramics

The sintering behavior of ZrO 2 -14 wt. % Al 2 O 3 nanocomposites between 1000 and 1200 °C was investigated and compared with the results obtained for pure nanocrystalline ZrO 2 . The highest density found in pure nanocrystalline ZrO 2 was 92 % with a grain size of 72 nm at 1000°C. Nanocrystalline ZrO 2 -Al 2 O 3 composites reached densities of 97 % with a corresponding grain size of 35 nm at 1200°C. The results are discussed in terms of the level of agglomeration of the initial powders compacts and the pinning of grain boundaries by dispersed nanoparticles. Pure nanocrystalline ZrO 2 is monoclinic at all temperatures; the nanocrystalline composite exhibits a transformation from the monoclinic to the tetragonal phase with a maximum volume fraction of approx. 80 % at 1050 °C.

Elastic modulus in rigid Al 2O 3/ZrO 2 ceramic laminates

Layered ceramics have recently attracted a great deal of interest. This is because of their capability to tailor materials with anisotropic properties to satisfy the complex requirements of emerging technologies [1], such as the electronics and microelectronics industry [2–5] and structural applications [6–14]. Particularly Zirconia-based composite ceramics have received most attention due to the possibility of improving mechanical properties by microscopic effects. The latter includes, for instance, a stress-induced transformation of the metastable tetragonal inclusions and microcracking around the unstabilized monoclinic inclusions [15,16], or interfacial mechanisms acting at a macroscopic scale in multilayer composites. Internal stresses, developed as a consequence of the different thermal contractions in laminated Zirconia-based materials, provoke a deviation of the propagating cracks at the interface, and so an improved toughness is obtained in these materials [17–19]. Recent studies have shown that multilayered composites of Al2O3 and Ce-ZrO2 exhibit especially high fracture toughness because of the influence of the laminar microstructure on the shape of the crack tip transformation zone [20].

Resistance of Mg-PSZ ceramics to thermal damage

The stability of two types of zirconia-based structural ceramics partially stabilized with magnesium oxide with a different initial content of the monoclinic phase is determined on certified samples. The data obtained make it possible to plot a diagram of resistance to thermal damage (RTD). The materials with a high initial content of the monoclinic phase of ZrO2 (33.5%) cannot be classified as heat-resistant. An x-ray study of samples of two materials with a different initial content of the monoclinic phase of ZrO2 showed that the dependences of the monoclinic-hase content and the bending strength on the temperature of the heat treatment prior to hardening are virtually identical to the course of the RTD curves and demonstrate a difference between the materials studied.

Zirconia-base ceramics for drawing tools

Results of an investigation and fabrication of a ceramic drawing tool based on zirconia partially stabilized by yttrium oxide and the combined stabilizing additives Y2O3 + CeO2 and Y2O3 + MgO, which increase the heat resistance of the materials, are presented. The developed ceramics based on ZrO2 and stabilized by 2% Y2O3 by chemical coprecipitation with a CeO2 additive has the following parameters: an open porosity of 2.1%, an apparent density of 5.60 g/cm3, an ultimate bending strength of 450 MPa. In a ceramic based on ZrO2 and stabilized by 5% Y2O3 by the method of ceramic sintering the corresponding parameters are 3%, 5.62 g/cm3, and 271 MPa. An experimental batch of zirconia drawing matrices has been produced and tested in tube drawing. Mandrel-free drawing of tubes made of stainless steel of grades 08Kh18N10, 12Kh18N10T, and EI702, copper of grade M1, and titanium alloy of grade VT1-0 and long-mandrel drawing of steel of grade 12Kh18N10T occurred stably and without sticking of the metal to the die or any damage to the tubes or dies.

The role of a threshold stress in the superplastic deformation of fine-grained yttria-stabilized zirconia polycrystals

Zirconia-based ceramics have been studied extensively over the past two decades because of their excellent properties of strength and toughness, which derive from the stress-induced martensitic transformation of the metastable tetragonal phase to a phase with monoclinic symmetry. In this paper the authors present a detailed study of the superplastic behavior of 4 mol% yttria-stabilized zirconia polycrystals as a function of the stress. The observed variation in the apparent creep parameters n and p have been rationalized in terms of the presence of a threshold stress below which grain boundary sliding cannot operate.

Evaluation of the properties of some kinds of zirconia-based structural ceramics

Zirconia-based ceramic articles produced by the Klein and Syntek Keramik firms (Germany) are investigated by the methods of x-ray, luminescent, and ultrasound analyses. The density, the porosity, ultimate bending strength at room temperature, Weibull's modulus, crack resistance, and Young's modulus are investigated for specimens cut from the articles and are compared with the properties of domestic specimens based on zirconia partially stabilized by Y2O3. The structure and the composition are investigated by the methods of scanning electron microscopy, petrography, and x-ray and chemical analyses. The high-temperature strength is measured and the structure of fractures caused by these tests is investigated by the method of scanning electron microscopy.

Preparation of Multicomponent Powders by Alkoxide Hydrolysis. 1. Chemical Processing

A series of chemical processes, based on alkoxide hydrolysis, has been developed as a general technique for preparing multicomponent, ceramic-precursor powders. The basic approach for preparing such powders (where coprecipitation, cohydrolysis, or sol−gel preparation involving all components is difficult, or impossible) involves (i) preparation of an initial homogeneous hydrolysate containing as many components as possible and (ii) sorption of any additional components, as soluble species or as sols, onto the surface of the hydrolysate. This hydrolysate/sorption technique has been used to produce powders with such varied compositions as titanate-based dielectrics, lead zirconate titanate, lead lanthanum zirconate titanate, mullite, zirconia-based ceramics, etc. An example of this approach is provided by the preparation of the multicomponent titanate ceramic, Synroc, which has been produced on a 100 kg scale. The method involves the base-catalyzed hydrolysis of a concentrated solution of titanium, zirconiu...

Applied crystallography solutions to problems in industrial solid-state chemistry. Case examples with ceramics, cements and zeolites

We show that a number of processes involved in the field of industrial solid-state chemistry can be successfully studied in situ, using a range of crystallographic and related techniques. The adaptation of relevant equipment to reproduce the process environment at the sample is a crucial part of the approach. Examples are given, involving the synthesis of zirconia-based ceramics, hydration of cements, and dehydration of zeolites, where successful applications of this approach have uncovered new structural/kinetic aspects concerning seemingly well established industrial processes.

Regulation of sintering temperature of zirconia-based ceramics

The results on regulation of the sintering temperature of ceramics by treating the surface of powder particles with organic liquids are presented. It is established that in some cases the sintering temperature is reduced by 350°C.

Deformation and fracture of zirconia ceramics stabilized by CeO2. II. Crack resistance

Investigations of crack resistance of four types of zirconia-base ceramics stabilized by 9% CeO2 are described. In three types of ceramics cracks develop against the background of the formation of a wide zone of transformation transitions, whose size decreases with decrease in the grain size of the materials. In the ceramics with the finest grain composition (1.14 µm) such a zone is absent. The measured results are highly divergent as a function of the method used for estimating the length of the cracks, namely, visual examination and determining the compliance of the specimens. It is assumed that the divergence can be attributable to the presence of a zone of transformation transitions at the tip of a crack and along it.

Deformation and strength of engineering ceramics and single crystals

A comparative investigation has been performed of the laws of deformation and strength of engineering silicon nitride-, alumina, and zirconia-based ceramics, as well as zirconia crystals. The specimens were tested in four-point bending in air over a temperature range from ambient to 1400 °C. The materials' mechanical behaviour was analyzed by load versus deflection diagrams (deformation diagrams). It has been found that above the brittle-to-ductile transition temperature, T BD, for the ceramics studied it is possible to choose such combinations of temperature and deformation rate, which would ensure the same path of deformation diagrams, i.e. equivalent influence of those two parameters on the mechanical behaviour of ceramics is observed. The mechanism of inelastic deformation of the ceramics studied is shown to be associated with the development of two processes: viscous flow of the grain boundary phase and crack propagation to a critical size, with one of them prevailing at different load levels. In contrast to ceramics, the strength of zirconia crystals remained practically unchanged (partially-stabilized crystals) up to 1400 °C or even increased (fully-stabilized crystals). For all the crystals, static elasticity moduli were independent of the number of repeated-static loading cycles at high temperatures (their values remained constant), while for ceramics a reduction was observed. Partially-stabilized zirconia crystals, as compared to other investigated materials, exhibited practically no creep up to 1400 °C at loads close to limiting ones. This allows them to be considered as a promising engineering material for high-temperature application.

Deformation and fracture of CeO2-stabilized zirconia ceramics. I. Strength and deformability

Investigations of the strength and deformability of four types of zirconia-base ceramics stabilized by 9% CeO2 (9Ce — TZP) and having different grain sizes (from 1.4 to 3.0 µm) are described. Under mechanical loads these materials exhibit “avalanche” formation of wide transformation zones. A correlation is established between the special features of the formation of such zones, the deformability of specimens, the the acoustic emission in them, and the grain composition of the material.