Zirconia Powders Research Articles

Alkali-Treated Alumina and Zirconia Powders Decorated with Hydroxyapatite for Prospective Biomedical Applications.

The alumina and zirconia surfaces were pretreated with chemical etching using alkaline mixtures of ammonia, hydrogen peroxide and sodium hydroxide, and followed with application of the powder layer of Ca-deficient hydroxyapatite (CDH). The influence of etching bath conditions time and concentration on surface development, chemical composition and morphology of medicinal ceramic powders were studied. The following analyses were performed: morphology (scanning electron microscopy), phase composition (X-ray diffraction analysis), changes in binding interactions and chemical composition (FT-Infrared and Energy dispersive spectroscopies). Both types of etchants did not expose the original phase composition changes or newly created phases for both types of ceramics. Subsequent decoration of the surface with hydroxyapatite revealed differences in the morphological appearance of the layer on both ceramic surfaces. The treated zirconia surface accepted CDH as a flowing layer on the surface, while the alumina was decorated with individual CDH aggregates. The goal of this study was to focus further on the ceramic fillers for polymer-ceramic composites used as a biomaterial in dental prosthetics.

Synthesis and sintering of refractory calcium zirconate for high temperature applications in contact with titanium and titanium alloys

The publication provides general information about CaZrCh, discusses synthesis methods and main application areas. Based on the analysis of sources, it was found that the least expensive and easiest technique is solid-phase synthesis from natural carbonate powder and zirconium dioxide. The morphology of powders of micromarble brand KM-2, monoclinic zirconium dioxide brand CrO-1 and calcium metazirconate of domestic production is investigated. To determine the temperature of calcium zirconate synthesis from the initial powders of zirconium dioxide and calcium carbonate, a differential thermal analysis was used. The temperature of the chemical compound formation is approximately 1230 oC. Calcination of a mixture of initial powders was carried out at temperatures of 1100, 1200, 1300 and 1400 oC. X-ray phase and microscopic analysis of the obtained powders was conducted. It is established that at a temperature of 1100 oC solid-phase synthesis does not occur, at 1200 oC it does not pass completely, at 1300 oC and 1400 oC it is fully completed. However, the powder synthesized at 1400 oC is dense aggregated, the destruction of which requires mechanical action. And the powder synthesized at 1300 oC consists of friable particles that can be easily desegregated and is sinter active. A comparison between cera mics obtained from synthesized powder and from calcium meta zirconate of domestic production was carried out. The material made of the synthesized powder has a denser structure and greater strength. The crucible from the synthesized powder was successfully tested under vacuum heating conditions to a temperature of 1600 oC in contact with of Ti – Ni – Hf and Ti – Zr – Nb preforms.

Effect of Y2O3 additive on morphology and phase composition of zirconia solid solutions

Zirconia and zirconia-yttria solid solution powders within the range of 0–8 mol.% Y2O3 concentration were precipitated and crystallized in NaOH aqueous solution under hydrothermal conditions. The resulting powders were characterized using X-ray diffraction, specific surface area measurements and infrared and Raman spectroscopy. It has been found that morphology and phase composition of the obtained powders are strongly influenced by the Y2O3 concentration in the system. Low yttria content of 0 and 1 mol. % leads to the elongated particles with monoclinic symmetry. Moreover, an order of magnitude smaller isometric particles appear when Y2O3 content reaches 2 mol.% and more. They are characterized by tetragonal or even cubic symmetry. It has been shown that Y2O3 forms solid solution in each zirconia polymorph, i.e. monoclinic, tetragonal and cubic symmetry one.

Characterization and Hydrodynamic Evaluation of the Relationship between Permeability and Microstructure Parameters Ceramic Membranes for the Separation of Oil-in-water Emulsion

Ceramic membranes for wastewater treatment are usually fine filters prepared by sintering of alumina, titania or zirconia powders at ultra-high temperatures and have an asymmetric cross-section using the same material or a combination of the three giving a base support and an active layer forming the membrane. The Carman–Kozeny (C–K) and Hagen–Poiseuille (H–P) transport equations have been used to predict water permeability of ceramic membranes and can be adapted to take account of the effects of microstructural parameters (porosity, and tortuosity) of ceramic membranes on pure water flux. The hydrodynamics of the membranes were evaluated by gas transport to obtain equivalent water permeability which was then used to obtain the porosity and tortuosity respectively. Gas permeability experiments showed good correspondence with the calculated water flux. Characterization of the membranes was carried out using scanning electron microscopy (SEM) imaging to determine the morphological aspects of the sample including shape and size of membranes while the electron diffraction with x-rays analysis (EDAX) was used to obtain information on the elemental composition.

Few-layered-graphene/zirconia composites: Single-step powder synthesis, spark plasma sintering, microstructure and properties

The chemical vapor deposition of carbon is performed onto a commercial yttria-stabilized zirconia (3YSZ) powder bed. This produces few-layered-graphene (FLG) film uniformly covering the 3YSZ grains, without the manipulation of any pre-existing nanocarbon in the form of graphene platelets. The powders are then consolidated by spark plasma sintering, producing specimens where FLG is located along the grain boundaries of the 3YSZ matrix, which is below 0.3 μm in grain size. The samples are characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy. The pure 3YSZ exhibits higher toughness and fracture strength compared to composites, but the trend is that their toughness increases upon the increase in carbon content. Crack-deflection and crack-bridging are observed. The composites are electrically conducting with a percolation threshold between 1.48 and 1.98 vol.% of carbon, reflecting the continuous nature of the FLG film over very long distances.

Evaluation of the effect of adding zirconium or titanium oxide powder to heat cured acrylic resin on the fracture resistance of denture base of the mandibular implant supported overdenture. An invitro study

Evaluation of the effect of adding zirconium or titanium oxide powder to heat cured acrylic resin on the fracture resistance of denture base of the mandibular implant supported overdenture. An invitro study

Oxide Ion Conductivity of Mechanically produced Calcia Stabilised Zirconia for Oxygen Sensing Applications

Cryo-milling was used to make calcia stabilized zirconia (CSZ) powders with 9 mol%, 12 mol%, and 15 mol% of calcia. Powder X-ray diffraction was done to examine the phase growth in prepared powders over the course of 80h of mechanical alloying (MA) in cryogenic environment at 300rpm. The calcined powders were hydraulically pressed into cylindrical shaped sensor elements in a uniaxial press and then sintered for 4h at 1400°C. The microstructure of sintered pellets were studied using Scanning Electron Microscope (SEM). Electrical Conductivity measurements of the prepared stabilized zirconia at various temperatures over a temperature range of 200°C to 500°C using a dual-probe impedance analyzer is carried out and the effects of composition and temperature on the grain boundary impedance of CSZ were analyzed. Conductivity is discussed in terms of ionic vacancies in the bulk due to calcium ion substitution and available grain boundary paths. Ionic Conductivity of prepared CSZ is compared for suitability in oxygen sensing applications.

Nano-Dispersed 8 Mol% Yttria Stabilized Zirconia Powder: Phase, Morphology and Conductivity Investigation with Different Chelating Agents Via Modified Sol-Gel Method

Nano-Dispersed 8 Mol% Yttria Stabilized Zirconia Powder: Phase, Morphology and Conductivity Investigation with Different Chelating Agents Via Modified Sol-Gel Method

39 - Properties of Printed Zirconia Using Suspension Enclosing Projection Stereolithography

To evaluate the feasibility of using suspension enclosing projection stereolithography (SEPS) in printing zirconia dental restorations. Different from most AM processes, this technique is capable of printing overhanging shapes without the need of support structures. A zirconia material (3 M Lava Esthetic, 5%mol zirconia), commonly used to mill zirconia dental restorations, and two experimental printed zirconia groups were analyzed regarding flexural strength, hardness, and microstructure. Thirty-two bar-shaped (n=16) specimens were printed using SEPS from 5% mol yttria zirconia powder (Zpex-Tosoh, Japan) and a photopolymerizable resin from an STL file, at a 70:30, and at a 75:25 ratio. Specimens were cured for 10 minutes, then debinded and sintered. Sixteen specimens were sectioned from zirconia pucks (control) and sintered using a heating, holding, and cooling cycle. Three-point bending test was performed for all 48 specimens using a universal testing machine at 0.5mmm/min cross-head speed. Knoop hardness measurements were performed, using a load of 200 g for 15 s for both groups (n=8). The average of two measurements was recorded. An Independent-Samples Kruskal-Wallis Test was performed to test the flexural strength among the groups. A statistically significant difference was observed for the milled group(p<0.003). The microhardness was not significantly different among groups (p= 0.29, One-way ANOVA). SEPS showed to be a feasible technique to produce zirconia specimens. SEPS produced zirconia showed favorable microhardness properties for dental application. However, SEPS specimens had significantly reduced flexural strength when compared to the control, in particular for the 75% group. Further research is necessary to optimize the debinding and sintering settings when using SESP to print zirconia structures.

Effect of spraying ceramic powder pore structure on thermophysical properties of plasma-sprayed thermal barrier coatings

Pore structure is one of the major factors influencing the failure mechanisms of thermal barrier coatings (TBCs) during high-temperature service. Powders exhibiting different pore structures have been produced using the plasma spheroidization technique. To improve the strain tolerance of an aircraft engine's hot sections, the preparation method of the TBCs material—8-wt% yttria-stabilized zirconia powders—has been continuously optimized. In this paper, the constrained effects of pores on the ceramic top coating of plasma-sprayed lamellar TBCs were investigated. Furthermore, the crystal phase structures, thermophysical properties, porosity, microstructures, and synthesis mechanism of powders and coatings were analyzed. Results revealed that the top ceramic coating, which was made from powders cooled by air and distilled water, can influence the coating porosity. Moreover, thermal insulation was substantiated by the finite element analysis method. Consequently, dense powders cooled by water can be used on the top surface in direct contact with high temperature flame flow to resist the diffusion of oxides, and the porous powder cooled by air can be applied in the middle coating to decrease the thermal conductivity. Hence, TBCs with various layers of different porosities can prolong the service life of thermal barrier coatings.

Production and Physico-Chemical Properties of Calcium-Thermal Zirconium Powder as a Component of Pyrotechnical Compositions

Production and Physico-Chemical Properties of Calcium-Thermal Zirconium Powder as a Component of Pyrotechnical Compositions

Aggregation and disaggregation of highly dispersed zirconium powder particles

Aggregation and disaggregation of highly dispersed zirconium powder particles

Study on the effect of ZrO2 and SiO2 additions type on the properties of high alumina crucibles for melting heat-resistant alloys and steels

The technology of vibrocasting high-quality refractories from granular masses of different chemical composition, size, configuration and weight of products, in particular crucibles for induction melting of heat-resistant alloys was developed and introduced by JSC “URIR named after A. S. Berezhnoy”. According to the developed technology, mullite-alumina zircon-containing crucibles contain ZrO2 ~ 8 %, zirconia-containing crucibles — ~ 17 %, alumina zircon-containing crucibles — ~ 8 %, ~ 8—10 % and ~ 25 %, have open porosity &lt; 20 %, cold crushing strength depending on the used raw materials and firing temperature within ~ 50—230 N/mm2, thermal shock resistance&gt; 20 thermal cycles (1300 °C — water).&#x0D; The article studies the effect of ZrO2 and SiO2 additives type introduced with zircon or zirconia in combination with a silica-containing additive on the main properties of vibrocasting samples after firing at 1580 °C.&#x0D; As a result of the studies the high alumina samples with 10 % ZrO2, introduced by zircon or zirconia powder, were produced, which are characterized by apparent density of 3.12 and 3.08 g/cm3, open porosity of 14.4 and 15.5 %, cold crushing strength 145 and 210 N/mm2, thermal shock resistance &gt; 20 thermal cycles and 6 thermal cycles (1300 °C — water) respectively. That is, with practically the same chemical composition, samples with zircon have better indicators of apparent density and especially thermal shock resistance than samples with zirconia in combination with silica. The high thermal shock resistance of samples with zircon can be explained by a nature of the pores which long irregular in configuration and connected to each and, as well as microfractured structure due to the decomposition of zircon and the formation of microcrystalline monoclinic zirconia while in the structure of the samples, which included zirconia powder and silica and a mixture of joint grinding of alumina and a silica-containing additive, the pores are predominantly round isolated. Considering also that zircon is a domestic material and is cheaper than imported ZrO2, it is more expedient to use zircon for crucibles.

Crystal structure and morphology of CeO2 doped stabilized zirconia ceramics under high-frequency microwave field sintering

Under high-frequency microwave irradiation, zirconia ceramics were prepared by sintering nano-CeO2 (Ce = 7 mol%) doped zirconia powder. The different effects of temperature environment on the phase structure transformation, surface functional groups, microstructure, growth process, and density of doped zirconia were analyzed, and the optimized microwave sintering process for zirconia was determined. The experimental results reveal that the tetragonal phase of zirconia is positively correlated with the temperature when the temperature reaches about 1100 °C in the studied range. The reason is that the grain grows with the increase of sintering temperature, and the surface energy of grain decreases, which leads to the fluctuation of tetragonal phase content. The density of zirconia reaches 98.03% at 1300 °C, and the growth activation energy is 27.40 kJ/mol. There is no abnormal growth of zirconia particles, and the phase transition temperature decreases, which is attributed to the efficient heating of microwave and the incorporation of nano-ceria stabilizer.

ВОЗМОЖНОСТЬ ПРИМЕНЕНИЯ ТИГЛЕЙ ZrO2-MgO-CaO ДЛЯ ПОЛУЧЕНИЯ СПЛАВА U-10 % Zr

It is known that the thermal shock resistance of ceramic crucibles is insufficient for melting uranium alloys in them. Typically, crucibles withstand one or more heats and then break down. The possibility of using nanostructured ceramic crucibles based on ZrO2-MgO-CaO to obtain a U-10 % Zr alloy in an induction electric furnace has been substantiated at IPPE. Crucibles were made in JSC “ONPP “Tekhnologiya” named after A.G. Romashin” from a mixture of zirconium dioxide powders, partially stabilized with nanocrystalline CaO and MgO in a ratio of 30 and 70 wt. %, using two-stage sintering. Such crucibles have a sufficiently high resistance to thermal shock in contact with melts of metals and alloys and withstand 1-3 melts without destruction. Crucibles with various densities (from 5.206 to 5.29 g/cm3) and porosity (from 5 to 9 %) were tested under conditions of heating the melt at a rate of 12 to 19 °C/min to a maximum temperature of 1455 to 1560 °C. The tested crucible ZrO2-MgO-CaO was inserted into a graphite crucible to prevent leakage of the melt in the electric furnace in case of destruction of the ceramic crucible. There was no complete destruction of the crucibles; some crucibles with small cracks could be reused. The best result (three melts) was obtained when using such a crucible with a porosity of about 5 % for melting a charge containing uranium and zirconium. In order to determine the degree of interaction of a uranium-zirconium melt with a crucible based on ZrO2-MgO-CaO, the microstructure and microhardness of the crucible surface in contact with the melt were studied at an elevated temperature of 1600 °C. The surface of all tested crucibles is not wetted by liquid uranium-zirconium melt, and there is no chemical interaction. Nanostructured ceramic crucibles based on ZrO2-MgO-CaO are suitable for melting uranium-containing materials in an electric induction furnace.

PHASE ANALYSIS AND PHYSICAL PROPERTIES OF B2O3-ADDED ZIRCON CERAMICS SINTERED AT 1300 °C

This study was aimed to know the effect of B2O3(boria) addition on the phase composition and physical properties of zircon ceramics.The raw zircon powder used in the study was a purified natural zircon sand from Kereng Pangi, Central Kalimantan, Indonesia. The zircon ceramics were prepared by a solid state reaction method with variation of B2O3 addition of 3 wt%, 6 wt% and 9 wt% and sintered at 1300 °C for 5h. The phase composition, density and microstructure were characterized using X-ray diffraction (XRD), densimeter and Scanning Electron Microscope (SEM), respectively. Vickers Hardness measurement was perfomed at the polished surface of the ceramics. Results showed that all samples contained pure zircon phase, i.e. there was no effect of B2O3 addition on the phase composition. In general, the density and hardness increased with increasing B2O3 addition, but addition up to 9 wt% is not optimum to achieve ultra-dense zircon ceramics. Furthermore, the SEM image also showed no significant difference in average grain size. The crystallite size has grown nearly eight times (325 nm) of its original powder. The Vickers hardness of the ceramics is not significantly influenced by the addition of boria. It appears that the boria failure to increase densification also results in the extent of contact between grains which then produces relatively large zircon grains.

Development of 3D Slurry Printing Technology with Submersion-Light Apparatus in Dental Application

This study proposes an innovative three-dimensional printing technology with submersion-light apparatus. A zirconia powder with an average particle size of 0.5 µm is mixed with 1,6-Hexanediol diacrylate (HDDA) and photo-initiator to form a slurry. The weight percentage of zirconia powder to HDDA is 70:30 wt.%. A light engine box is submerged in a slurry and emits a layered pattern to induce photopolymerization and transform a slurry into a printed green body. Green body sintering parameters for the first and second stages are 380 °C with a holding time of 1.5 h and 1550 °C with a holding time of 2 h. The sintered parts’ length, width, and height shrinkage ratios are 29.9%, 29.7%, and 30.6%. The ball milling decreases the powder particle size to 158 ± 16 nm and the mean grain size of the sintered part is 423 ± 25 nm. The sintered part has an average hardness of 1224 (HV), a density of 5.45 g/cm3, and a flexural strength of 641.04 MPa. A three-unit zirconia dental bridge also has been fabricated with a clinically acceptable marginal gap.

Alumina-Toughened-Zirconia with Low Wear Rate in Ball-on-Flat Tribological Tests at Temperatures to 500 °C.

An alumina-toughened zirconia (ATZ) material, fabricated using a procedure consisting of the common sintering of two different zirconia powders, was tested using the ball-on-disc method in a temperature range between room temperature and 500 °C. Corundum balls were used as a counterpart. The ATZ composite behaviour during tests was compared with that of commonly used α-alumina and tetragonal zirconia sintered samples. At temperatures over 350 °C, a drastic decrease in the wear rate of the material was detected. SEM analyses proved that, in such conditions, nearly the whole surface of the sliding material was covered with a layer of deformed submicrometric grains, which limited contact with the part of material that was not deformed. The mentioned layer was relatively strongly connected with the material, increased its resistance, and decreased its coefficient of friction. As a reference, commonly used materials, namely commercial alumina and tetragonal zirconia, were tested. The wear parameters of the composite were significantly better than those registered for the materials prepared of commercial powders.

Zirconia nano-powders with controllable polymorphs synthesized by a wet chemical method and their phosphate adsorption characteristics & mechanism

Adsorption is a simple and efficient phosphorus removal method used to control the eutrophication of water bodies. A simple and gentle atmospheric pressure hydrothermal method by adjusting the dosage of ammonium chloride and sodium hydroxide was used to synthesize amorphous, monoclinic, and tetragonal zirconia nano-powders with high specific surface areas (383.91 m2/g, 330.01 m2/g, and 234.36 m2/g) and particle size of about 40 nm for phosphate adsorption. When pH = 6.3, the phosphate adsorption capacity of the amorphous monoclinic phase and the tetragonal phase respectively reached 102.58 mg P/g, 68.11 mg P/g, and 37.25 mg P/g and the adsorption process of the three crystal forms of zirconia powders conformed to the Langmuir adsorption model. In the first 2 min of rapid adsorption, amorphous zirconia completed 76.23% of the adsorption process and the monoclinic phase also completed more than 60%. The adsorption process of the three crystal forms of zirconia was completed within 240 min and conformed to the pseudo-second-order kinetic model. Their adsorption characteristics of the three crystal forms of zirconia decreased with the increase in pH. While the pH was above than the isoelectric point of the solution, the adsorption capacity was significantly reduced. The large specific surface area and high hydroxyl content of the zirconia nano-powder made a great contribution to the adsorption process.

The densification and diametral compression strength of Hydroxyapatite-Zirconia bioceramics: Experimental and modelling studies

In the present work, hydroxyapatite (HAP) and zirconia (ZrO2) powders have been used to elaborate HAP-ZrO2 composite for biomedical applications. X-ray diffraction (XRD), and scanning electron microscopy (SEM)), were used to characterize the as-obtained samples. The aim of this study was to evaluate the morphology, densification and mechanical strength of the produced ceramics sintered at 1200 °C and 1250 °C. The relative density and mechanical strength of the HAP-ZrO2 ceramics reached their height values at 1250 °C. Experimental results were modeled by the finite element method to determine the stress distribution in the compacted samples. In addition, the stress intensity factors in produced ceramics for different geometrical dimensions of the notch was evaluated numerically.