Yttria-stabilized Zirconia Powders Research Articles

Ferroelastic and Plastic Behaviors in Pseudo-Single Crystal Micropillars of Nontransformable Tetragonal Zirconia

The orientation-dependent micromechanical properties of nontransformable tetragonal (t') zirconia, which diffusionlessly transformed from the fluorite cubic phase and does not show stress-induced phase transformation, were characterized via pseudo-single crystal micropillar compression and electron microscopy. The t' zirconia sample was obtained via atmospheric plasma spraying of 4.5 mol% yttria-stabilized zirconia (YSZ) powders into liquid nitrogen and consolidated into a bulk state via hot pressing at 1100°C. Dense and cylindrical micropillars were fabricated using a focused ion beam from pseudo-single crystalline regions, which had a nanodomain microstructure of three t' variants partitioned by {1 0 1}c twin boundaries with 90° symmetry, and were compressed using a flat-end diamond indenter. Near- c compressions were attributed to ferroelastic domain switching and subsequent {1 0 1}c and/or {1 1 1}c slips. In ferroelastic deformation, a certain t' variant diminished and a binary domain microstructure developed with c axes perpendicular to the compressive direction. Near- c compressions were governed by {0 0 1}c slips accompanied by strain hardening with negligible ferroelasticity, resulting in buckling deformation with rotational kinking. Crack-tolerant plasticity was ascribed to ferroelastic toughening, where t' variants with c axes across crack planes developed to relieve stress concentrations around the crack tips in both orientations. In contrast, pseudo-cleavage fractures on low-index planes were observed in near- c compressions. Crack-tolerant behavior was not observed in the cubic counterpart with a domain-free microstructure (8.0 mol% YSZ), which demonstrated catastrophic fractures. Hence, ferroelastic toughening is viewed as the origin of enhanced toughness in t' zirconia.

Cellular Nickel-Yttria/Zirconia (Ni-YSZ) Cermet Foams: Manufacturing, Microstructure and Properties.

Open-celled ceramic composite foams were prepared from NiO and yttria-stabilized zirconia (YSZ) powders by the polymer sponge replication (Schwartzwalder) technique using the respective aqueous dispersions. Mechanically stable NiO–YSZ foams with an average porosity of 93 vol.% were obtained. After chemical reduction of the NiO phase with hydrogen, cellular Ni–YSZ cermet structures were obtained. They are characterized by an electric conductivity up to 19∙103 S∙m−1 which can be adjusted by both, the Ni volume fraction, and the sintering/reduction procedure. The NiO–YSZ ceramic foams, as well as the cellular Ni–YSZ cermets prepared therefrom, were characterized with respect to their microstructure by scanning electron microscopy, confocal Raman microscopy and X-ray diffraction with Rietveld analysis. In addition, the compressive strength, the electric conductivity and the thermal conductivity were determined. The collected data were then correlated to the sample microstructure and porosity and were also applied for modelling of the mechanical and electric properties of the bulk Ni–YSZ strut material.

Bi-Material Micro-Part of Stainless Steel and Zirconia by Two-Component Micro-Powder Injection Molding: Rheological Properties and Solvent Debinding Behavior

From the micro-powder injection molding (μPIM) process, a two-component micro-powder injection molding (2C-μPIM) process has evolved due to the growing demand for multi-functional micro-components in avant-garde applications. 2C-μPIM technology provides the opportunity to conjugate distinct materials within one part. Stainless steel (SS 17-4PH) and 3 mol.% yttria-stabilized zirconia (3YSZ) are characteristically recognized for their corrosion resistance and high hardness. In this work, the obtained critical powder volume concentration (CPVC) of SS 17-4PH and 3YSZ powders were 71.7 and 47.1 vol.%, respectively. Solid loadings of 2 and 3 vol.% less than the CPVC were considered as the optimal content for both powders. Feedstocks were obtained by mixing SS 17-4PH and 3YSZ powders with a binder system comprised of palm stearin (PS) and low-density polyethylene (LDPE). The rheological behaviors of the prepared feedstocks were assessed to figure out the feedstocks having the best rheological properties. The feedstocks of SS 17-4PH and 3YSZ with powder loadings of 69 and 44 vol.% were eventually injected to produce bi-material micro-parts. The optimal solvent debinding temperature of the green bi-material micro-part was then investigated, and it was found that 73.3% soluble binder was removed when bi-material was immersed in acetone at 70 °C for 40 min.

Printed Miniaturized Platinum Heater on Ultra-Thin Ceramic Membrane for Mox Gas Sensors

Introduction The progress of the Internet of Things stimulates the development of sensors of small size and low power consumption. Miniaturized metal-oxide semiconductor (MOX) gas sensors (e.g. methane, hydrogen or carbon monoxide detection) can be integrated into agro-industrial facilities such as livestock facilities, fish farming, forestry, food-storage and horticulture, where they support future-oriented plant production (smart agriculture). The central part of a MOX gas sensor is a micro-hotplate, which is mainly responsible for the sensor power consumption at operating temperatures of 450 to 600°C. Under harsh environmental conductions, ceramic materials are the best choice for the micro-hotplate substrate and sensor housing (ceramic MEMS) in combination with platinum metallization for the heater. To realize such gas sensors with low power consumption (< 200 mW@4500C) the development of miniaturized printable heaters on ultra-thin ceramic membranes is needed. Methods Yttria-stabilized zirconia (3YSZ) powders were evaluated for the preparation of casting slurries and tape casting of thin tapes < 40 µm (present on Fig.1). After thermal treatment the substrates were characterized by density, thickness, flatness, roughness and mechanical bending stability. To reduce the thermal mass of the hotplate, the ceramic substrate was cut by a developed micro-milling process to realize free standing membranes of 280 µm size in diameter (present on Fig.2). Platinum particle (20 wt.-% and 30 wt.-%) as well as Pt-SiO2-composite inks were synthesized and ink properties like viscosity, surface tension and sedimentation stability characterized. Printing tests of miniaturized heater layouts (2.0x0.5 mm2 and 40 µm line width in hot spot) were performed by aerosol-jet (Optomec M3D 150 µm nozzle) and piezoDoD inkjet (Dimatix DMP 10 pL). The printed microheater were characterized (photo of experiment present on Fig.5) after sintering by film thickness, resistivity and microstructure (SEM). The applicability is demonstrated by heating tests, where temperature and power consumption is monitored in dependence of the heater driving voltage.The all parts of gas sensor was fabricated by totally digital technological flow with using pre-developed in STL format 3D model like as is customary in rapid prototyping way. For material of sensor package was used inexpensive Al2O3 monolithic ceramics. As a form factor for sensor was using SOT-23 package (3.0x1.4x1.0 mm), which give possibility to dissipate 350 mW heating power at room temperature. Parts of sensor package was fabricated by 20W fiber laser with a wavelength of 1.064 μm and tunable pulse duration from 50 to 200 ns with using especially developed software (present on Fig.7) combined process of micronilling and on-line comparisons fabricating geometrical parameters with 3D model. Results and Conclusions Mechanical flexible 3YSZ substrates of 5x5 cm2 size with thickness of 20 to 40 µm and a high density of 6.1 g/cm3 (equals theoretical density) were achieved (Fig.1a). The choice of raw material powders correlates to the substrates surface roughness (250 to 600 nm) and mechanical stability. The developed Pt-particle inks show a good print compatibility and a high sedimentation stability of < 0.2 mm per month. Miniaturized heater layouts with a narrow line width down to 40 µm were only achieved by aerosol-jet printing (Fig.4). Too large ink droplets and a pronounced ink wetting on the substrates leads to line width > 100 µm by using inkjet. The sintered Pt-heater show a suitable resistance of 10 to 30 Ohm and were successfully evaluated by heating tests up to 450-600°C by micro melting technique [1] with using micro powder of polyamide with dependence of power consumption vs. working temperature on surface of microhotplate present on Fig.6. Acknowledgement This research was sponsored by the Federal Ministry of Education and Research (BMBF) in Germany founding No. 02P15B520, the Israel Innovation Authority and the Ministry of Science and Higher Education of the Russian Federation founding with unique identifier RFMEFI58718X0054 in frame of MANUNET project MNET17/ADMA-1147.

Catalytic characteristics of Ni(B)-coated YSZ powder by neutral electroless plating

In this study, an eco-friendly, electroless, and neutral (pH 7.0) process of nickel plating at low temperature (40 °C) was used to develop an anode catalyst for a solid oxide fuel cell (SOFC). Electroless Ni(B) plating on yttria-stabilized zirconia (YSZ) particles resulted in the formation of a Ni(B)/YSZ core–shell. We examined the crystallinity and uniformity of the Ni(B) layer on the plated core–shell powder and found that it had an amorphous-like structure. In addition, we evaluated the rate of carbon deposition and characteristics of the SOFC anode catalyst: the carbon deposition rate was 19.42%, H2 selectivity was nearly 88% at 800 °C, and methane conversion was maintained at 100% at temperatures above 850 °C. It was ascertained that in the high-temperature region, which is the main operating temperature of SOFCs, the amorphous-like microstructure of the Ni(B) layer on the Ni(B)–YSZ core–shell powder played an important role in enhancing these properties.

Microstructural study and hot corrosion behavior of bimodal thermal barrier coatings under laser heat treatment

In this study, nanostructured YSZ powders were deposited on the Hastalloy X Superalloy substrate coated with a metallic bond coat by plasma spraying to produce a nanostructured thermal barrier coating with bimodal microstructure. After that, the coated samples were heat-treated using a Nd:YAG laser. Then, the microstructures of the conventional and nanostructured TBCs before and after the laser glazing process were examined using a scanning electron microscope (SEM). The coating phases were studied by X-ray diffractometry (XRD). The high-temperature corrosion behavior of the nanostructured plasma sprayed coating in the presence of Vanadium pentoxide and Sodium sulfate molten salt was compared with that of the conventional coatings before and after laser treatment at 1050 °C. The hot corrosion results showed that the coatings had a similar degradation mechanism based on which the corrosive molten salt reacted with the stabilizer of YSZ, producing hot corrosion products such as YVO4. It led to an unwanted phase transformation from tetragonal (t) to monoclinic (m) Zirconia and the final degradation of the TBC system. However, reducing molten salt penetration, decreasing surface roughness and, reduction of the specific surface area are three important mechanisms that improved hot corrosion resistance, finally extending the lifetime of the glazed samples. The results also showed that the nanostructured TBC had higher hot corrosion resistance in comparison with other samples.

Design of core-shell structured YSZ@Cu cermet powders with thermal conductivity anisotropy by electroless deposition

Core-shell structured cermet powders with thermal conductivity anisotropy have been brought into focus because they have a great potential application as the horizontal thermal diffusion layer material in multilayer thermal protective coating (TPC). In this contribution, core-shell structured YSZ@Cu cermet powders were fabricated by electroless deposition (ED) of Cu on yttria-stabilised zirconia (YSZ) powder. The surface of YSZ powder was uniformly coated with a thin Cu shell of approximately 2 μm. Through X-ray photoelectron spectra (XPS) analysis, it was found that trace CuO and Cu2O oxides formed on the surface of Cu shell. Results of thermal spraying adaptability analysis show the flowability of core-shell structured YSZ@Cu cermet powder improved to 56.8 s/50 g, which conforms better to the basic requirements of thermal spraying material. By differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests, the YSZ@Cu powder had good thermal stability. In particular, between 25 and 500 °C, the anisotropy thermal conductivity rose higher than 1.8 and it remained stable at approximately 1.6 with temperature as high as 900 °C. All these features promise it a high-performance thermal conductivity anisotropy material.

Hot corrosion mechanism of yttria-stabilized zirconia powder in the presence of molten Na2SO4 + V2O5 salts

The hot corrosion behavior of yttria-stabilized zirconia (YSZ) powder specimens exposed to Na2SO4/V2O5 salts mixtures at high temperature was evaluated. Initial tests were carried out at 1000 °C for 10 h, the salt concentrations varied from 0.1 wt% to 1.00 wt%, and the Na2SO4/V2O5 mass ratios were between 0.20 and 0.44 following a factorial design 22. X-ray diffraction (XRD) analyses of the tested samples showed with a confidence of 95% that the mixture composed of 32 wt% Na2SO4 + 68 wt% V2O5, and 1.00 wt% salt concentration led to high destabilization of the t′-YSZ phase and formation of YVO4 products. A second set of experiments were conducted to assess the influence of temperature on the hot corrosion response of the YSZ in the range between 490 and 1100 °C. Thermogravimetric analysis (TGA) experiments and Rietveld adjustments of XRD patterns showed that the mass loss of the samples varied with testing temperature and also that the major destabilization of tetragonal phase occurred at 900 °C.

Effect of powder composition upon plasma spray-physical vapor deposition of 8YSZ columnar coating

Agglomerated 8YSZ nano-powders for thermal barrier coating (TBC) were prepared by spray drying method. The morphology and diameter of 8YSZ powders were adjusted through controlling the solid content of the suspensions. Using prepared agglomerated 8YSZ nano-powders, columnar-structured coatings were obtained on Ni-based superalloy substrates by plasma spray-physical vapor deposition (PS-PVD). The experimental results proved that the spray dried powders characteristics were related to the solid content of suspensions. During the PS-PVD process, the deposition efficiency of the powders was improved with the increase of powder diameter due to the existence of thermophoresis. Moreover, it can be concluded by mathematical derivations that the top area of the plasma flame was sufficient for powder evaporation.

Thermal resistance determination of Sm2Zr2O7 + 8YSZ composite type of TBC

The determination of thermal resistance related to splat boundaries in composite TBC (thermal barrier coating) systems and expressed as splat-to-splat heat transfer coefficient was analyzed. Sm2Zr2O7 and conventional 8YSZ powders were used for coatings deposition by atmospheric plasma spraying. Two types of internal morphology were deposited: monolayered type (Sm2Zr2O7, 8YSZ) and composite TBCs (Sm2Zr2O7 + 8YSZ with weight ratios of 75/25, 50/50 and 25/75). The primary investigation was related to microstructural characterization of ceramic layers (pores and cracks architecture description), thermal diffusivity and conductivity characterization by laser flash analysis and theoretical models. The thermal conductivity was initially calculated on the basis of thermal diffusivity, heat capacity and density measurement as a function of temperature. Those values were corrected due to the presence of pores (microstructural analysis) and effective vales of thermal conductivity were calculated. These values were used as the basis for additional calculations based on the Hasselman-Johnson model of thermal conductivity for composite materials. Based on quantitative data from image analysis and porosity corrected thermal conductivity for monolayered and composite TBC systems, the thermal boundary conductivity (splat-to-splat heat transfer coefficient) was calculated as a function of temperature for Sm2Zr2O7 + 8YSZ composite systems.

Synthesis, Characterization and Optimization of Electrophoretic Deposition (EPD) Parameters of YSZ Layer on Ti-6Al-4V Alloy substrate

The objective of present work is to study the effect of electrophoretic deposition (EPD) parameters (voltage, time and concentration) using DC current based on the thickness, porosity and coating characterizations of YSZ layer on Ti-6Al-4V alloy substrate. The Taguchi approach was used in order to determine the optimal conditions for EPD and different criteria were applied for the deposit of biochemical coatings. Yttria stabilized zirconia powder (YSZ) was deposited on Ti-6Al-4V alloy substrate by electrophoresis using ethanol as a solvent under DC, to improve the quality of alloy surface and meet the requirements of biological orthopedic application activity. Ethanol was used as solvent to precipitate chitosan and YSZ on the alloy substrate. The composition of the surface and the cross section of coatings have been described by this electrode-enabled cathodic deposition for characterization. Many tests and inspections; zeta potential, water contact angle, XRD, SEM and optical microscopes were used to characterize surface morphology of YSZ layer. Optimum conditions for deposition of YSZ layer were used at 40 volt, 2 min and 1g / l for suspension being at room temperature. The contact angles values of coatings were changed between hydrophilic 67.489°C and 35.914°C Suitable percentages of porosity with pores size of 56.601-83.505 μm were obtained.

Effect of oxygen partial pressure on the phosphorescence of different lanthanide ion (Ln3+)-doped yttria-stabilised zirconia

In this study, the effect of oxygen partial pressure on phosphorescence was investigated for different lanthanide ion-doped (Ln = Eu, Dy, Sm, Er) yttria-stabilized zirconia (YSZ). Samples of YSZ powders doped with 1 mol% Ln3+ were prepared using the sol-gel method. A measurement system comprising a pressure and temperature calibration chamber, a 405 nm laser, a spectrometer, a photo-multiplier tube (PMT) and related optics was established. The phosphor emission spectra were measured first to verify the sample fabrication method. Then, the phosphorescence lifetime of the Ln3+-doped YSZ (YSZ:Ln) were obtained at different oxygen partial pressures and temperatures. These data showed that all the YSZ:Ln aside from the YSZ:Er exhibited a negative correlation between phosphorescence lifetime and oxygen partial pressure in high-temperature environments. The oxygen sensitivity was enhanced as temperature increased, and further analysis showed that this oxygen sensitivity was related to the energy levels of the phosphor‘s excited state and charge transfer state. That is, an excited state at a high energy level and a change transfer state at a low energy level would lead to oxygen sensitivity. These findings not only provide a useful reference for the evaluation of the oxygen effect on YSZ:Ln3+-based phosphor thermometry but may also serve as a basis for developing optical pressure sensors suitable for high-temperature environments.

A study of mechanical properties of alumina–zirconia composite films prepared by a combination of tape casting and solution impregnation method

Zirconia-toughened alumina (ZTA) ceramics are one of the most important engineering ceramics with high bending strength and fracture toughness. ZTA ceramics have found important applications in catalysts, implants, wear resistance tools, and electric circuit substrate. The near net shape method based on impregnation of porous body with desired solution has been used to prepare composites with improved properties. In this paper alumina–zirconia composite thin film has been prepared by a combination of aqueous tape casting and solution impregnation methods to improve sintering behavior and mechanical properties. At first, porous 3 mol% yttria-stabilized zirconia was prepared using aqueous tape casting, followed by impregnation with aluminum nitrate solution. Then, the rheological behavior was studied. The microstructure and phase content of samples were studied by SEM and XRD. Microhardness, nanohardness, Young’s modulus, and fracture toughness were measured by Vickers microhardness and nanoindentation methods, respectively. It was found that alumina–zirconia composites with homogeneous distribution of phases and high density can be obtained by solution impregnation method. The mechanical properties of composite thin films prepared by solution impregnation method have been improved compared to those of the composite prepared by tape casting of mixture of alumina and 3YSZ powders.

Thermal shock resistance behaviour of multilayered Gd2O3 doped YSZ on Inconel-718 substrate

Inconel 718 is a Nickel-based super alloy which is used in the high temperature sections of gas turbine engines in the aerospace industry due to its corrosion resistance and strength at high temperatures. Further improvements of properties are achieved by applying thermal barrier coatings on the material. NiCrAly is sprayed as the bond coat over the substrate for a thickness of 100 µm. After the bond coating, pure YSZ, mixture of YSZ and Gd2O3 powder prepared by ball milling process with various proportions are plasma sprayed on the substrate over the bond coat with a thickness of 300 μm which acts as the top coat. Similarly for multi layer coating, a sequence of bond coat, pure YSZ, combinations of Gd2O3 and YSZ and finally pure YSZ is sprayed over the substrate with thickness of 100 µm each. Thermal shock test was conducted on the coated to study the optimum composition of coating and the layer arrangement of coatings which can withstand the high temperature shock. In this all the specimens withstood the thermal cyclic test and the higher concentration of Gadolinium oxide in YSZ as an intermediate layer failed at 440 cycles.

Synthesis of Yttria-Stabilized Zirconia Nano Powders for Plasma Sprayed Nano Coatings

Abstract Plasma sprayed Yttria Stabilized Zirconia (YSZ) coatings, with few microns sized microstructure/grain morphology has been well researched, reported and established as an industrial Thermal Barrier Coatings (TBC) material/system. However, nano structured YSZ coatings possess improved characteristics when compared with their micron sized counterparts. However, due to their nano sizes, light weight, and low density, plasma spray coating process of nano powders suffers from flowability issues due to lack of nano powder inertia/momentum, leading to poor deposition/ uneven coating thickness. In this research work, nano structured YSZ coatings were synthesized by using an Atmospheric Spray Coating (APS) facility. Nano powders of YSZ were used as the starting materials to prepare micron sized plasma sprayable powders. 80μm thick NiCrAlY bond coat (commercial) and 200μm thick YSZ top coat with nano microstructure (lab synthesized) were built on steel substrates. The starting nano crystalline (YSZ) powders, measuring 30-70 nanometers (nm) were synthesized in the laboratory via chemical method (sol-gel) by employing zirconium oxy chloride hexa-hydrate and yttrium nitrate as precursors, citric acid as chelating agent and ethylene glycol for the diversification reaction followed by calcination @ 1000°C. They were then re-constituted into micron sized (53-106 μm) plasma sprayable powders by agglomerating with polyvinyl alcohol (PVA) binders. The nano crystallite morphology of powders and coatings were analyzed by Scanning Electron Microscope (SEM), chemical composition by Energy Dispersive spectroscopy (EDS) and crystal structural phase by X-ray diffraction (XRD). The influence of calcination temperature of 1150°C on nano crystallite morphology was also studied.

Modifiye Sol-Jel Yöntemi Kullanılarak İtriya Katkılı Zirkonya Sentezi

Zirconia is widely used ceramic powders as a biomaterial in medical applications due to its similarity with tooth color, good mechanical and bioinert properties. Its high temperature forms can be fully or partially stabilized by the addition of oxides such as MgO, CaO and Y 2 O 3 . Recently, yttria stabilized zirconia has been mostly studied because of its lots of advantages. In this study, 3% mol and 8% mol yttria stabilized zirconia powders have been synthesized using a simple sol-gel process. ZrO(NO 3 ) 2 .xH 2 O and Y(NO 3 ) 3 .6H 2 O was dissolved in ethylene glycol and pure water, respectively and mixed together. After mixing pH was adjusted to 3.5 using HNO 3 . Final suspension was stirred until it becomes homogenized. Homogeneous mixture dried at 120°C and then sintered at 1200°C. Crystallite sizes and mineralogical composition were determined by XRD. Surface area was measured by BET method and particle size was calculated. Density of powders was measured by ultrapicnometer. Also, morphological structure was examined by SEM. Tetragonal ZrO 2 and tetragonal ZrO 2 -Y 2 O 3 phases were observed. Current studies showed that YSZ powder can be effectively synthesis with the present method.

Microstructure and mechanical property of dense yttria-stabilized zirconia coating fabricated by an axial bi-cathode plasma torch under very low pressure

Very low-pressure plasma spray is a promising technique for preparing dense metal/ceramic coatings due to the high-speed plasma jet. However, at the same time, the low-pressure environment weakens the ability of the plasma jet to heat sprayed materials. In order to improve this shortcoming, a novel bi-cathode plasma torch was firstly designed in this study, which could enhance the plasma power from 40 kW to 81 kW and realize the axial powder feeding. By using this torch under 6 mbar, a dense and uniform yttria-stabilized zirconia coating with a porosity of 2.7% was fabricated, which had a hybrid microstructure that deposited with the form of unmelted particles, melted droplets, and vapor clusters. Meanwhile, 40% of the zirconia phase changed from the monoclinic type to the tetragonal type, indicating that the yttria-stabilized zirconia powder was melted well. The microhardness and elastic modulus of the coating was high compared with those prepared with other plasma spraying processes, which was 11.7 ± 0.6 GPa and 167.8 ± 4 GPa, respectively. The high density and mechanical property of the YSZ coating demonstrated that using the bi-cathode plasma torch at low pressure has the potential for the preparation of SOFC electrolytes.

X-ray diffraction analysis of the yttria stabilized zirconia powder by mechanical alloying and sintering

In the present work, monoclinic zirconia was mechanically alloyed with yttria (6–14 mol%) via ball milling at the different ball-to-powder mass ratios (BPMRs) for 3–24 h, and then, the mixed powders were sintered at 1100 °C and 1500 °C. Line profile analysis of the X-ray diffraction (XRD) patterns, using the Alexander-Klug, Adam-Cox, Rietveld, and Scherrer methods, was systematically used to investigate the effects of the milling time, BPMRs, sintering temperature, sintering time and zirconia-to-yttria ratio. The experimental results indicate that the yttria-stabilized zirconia (YSZ) appears in the mixed powder after a milling time longer than 8 h. In addition, the ZrO2 content will decrease with the milling time or amount of BPMRs. The XRD patterns demonstrate that the intensity of the YSZ diffraction peaks was greatly improved after sintering. However, even if sintering at 1100 °C for 10 h, m-ZrO2 still remained in the mixed powder. When the temperature rose to 1500 °C, only the cubic phase of YSZ (c-YSZ) was found in the zirconia-14 mol% yttria powder. Based on the above results, combined with other related research, the possible mechanism of the phase transformation in the ball milling and sintering process is discussed in this paper.

Mechanical Properties and Fabrication of 4YSZ-BN Composites by Pulsed Current Activated Sintering

4YSZ is generally used in fuel cells, oxygen sensors, hip and knee joint replacements and thermal barriers because of it excellent properties, including low density, high biocompatibility, good resistance against corrosion, hard phase and high melting point, and high ionic conductivity. However, 4YSZ with large grain has low resistance to abrasion and wear because of its low fracture toughness and low hardness at room temperature. The hardness and fracture toughness of 4YSZ can be improved by the addition of a second hard phase to form a nanostructured composite. Nanostructured materials have received considerable attention because they possess a high hardness and fracture toughness. Recently, nano-crystalline YSZ powder was fabricated by several methods. However, nanosized sintered YSZ has not been obtained due to fast grain growth during the conventional sintering method. In this study, nanostructured 4YSZ-BN composites with nearly full density were achieved using pulsed current activated sintering for 80 sec at a pressure of 80 Mpa. The addition of hexagonal BN to 4YSZ caused the nano scale structure to be retained in the ceramic by deterring grain growth. The crystalline size of the 4YSZ was reduced by the addition of BN. The addition of BN to 4YSZ greatly improved its mechanical properties (hardness and fracture toughness). Key words: sintering, nanomaterials, bn, fracture toughness, hardness

Characterization of Zirconia for Ceramic Dental Implant Coated with Carbonate Apatite

Zirconia-based dental implant in Indonesia is rarely used, especially due to low demand. High production cost makes the price of each zirconia dental implant piece become expensive. The fabrication process of the dental implant using 3 mol% Yttria-stabilized Zirconia (3YSZ) as a starting powder, or being synthesized using ZrCl3 and YCl4 precursor were costly and complicated. The aim of this study is to investigate morphology and phase analysis in the ceramic dental implant which coated with carbonate apatite (CO3Ap). The industrial 3YSZ powder was compacted using a manual hydraulic press and sintered at 1500°C approximately to 11 mm pellet size. Specimens were pre-treated using 9% hydrofluoric acid (HF) before coated by CO3Ap, while others without treatment as a control. Then, the specimens were dipped into CO3Ap suspension and heat treated with temperature variable of 300°C or 500°C. The fabrication of specimen using manual hydraulic press creates monoclinic phase more than expected, while SEM discovered that the particle size of the specimen was 130-500nm. In conclusion, the effective method to coat the ceramic dental implant with CO3Ap was using 9% HF as a pre-treatment and calcinate in 300°C as confirmed in XRD and EDS.