Papers by Keyword: Zro₂

Abstract: Ceramic/ metal functionally graded materials (FGMs) have been promising to sustain coating structures working under super high temperature as well as high temperature gradient conditions. Compositional gradients in the FGMs can be engineered according to functional performance requirements. This study aims to fabricate Al₂O₃/ZrO₂/SUS304 hybrid FGMs with continuous compositional gradient manners using a combination of centrifugal slurry methods and spark plasma sintering (SPS). The compositional gradients in the FGMs were investigated on microstructures with elemental distributions and hardness on the cross sections of the FGMs. It was demonstrated that the compositions of ZrO₂ and SUS304 continuously varied in the FGMs, while Al₂O₃ resided only on ZrO₂-rich sides, which can effectively enhance the fracture toughness of the ZrO₂-rich layer. Ball milling treatments can make the Al₂O₃ layer more formed in the ZrO₂-rich layer. With increasing the amount of Al₂O₃, the Al₂O₃ layer resided closer to the top of the ZrO₂ surfaces in the FGMs subject to ball milling treatments, which can prevent the crack propagation from the ZrO₂ top surfaces.

Abstract: The structural, physical and mechanical properties of alumina composites reinforced with various zirconia contents were studied. Zirconia with specific stress-induced toughness mechanisms (from tetragonal to monoclinic) can improve its mechanical properties. The raw materials were commercial products of alumina (Al₂O₃) and zirconia (ZrO₂) with gamma alumina (γ-Al₂O₃) and monoclinic zirconia (m-ZrO₂) phases, respectively. In this study, alumina and zirconia powders containing 0, 10, 20, 30, and 40 wt% were mechanically activated and sintered at 1400°C for 3 h. Fourier transform infrared spectroscopy (FTIR) characterization was used to confirm the functional groups in the sample. Phase analysis of the sintered samples was carried out via X-ray diffraction (XRD). Composite characterization includes diameter shrinkage, density, and Vickers hardness. Corundum (α-Al₂O₃), monoclinic zirconia (m-ZrO₂) and tetragonal zirconia (t-ZrO₂) phases were the observed phases in the sintered sample. The Al₂O₃/ZrO₂ 60:40 sample had the largest shrinkage in pellet diameter, apparent density, and Vickers hardness, at 8%, 4.35 g/cm³, and 1.33 HVN, respectively.

Abstract: CaCO₃ is one of abundant minerals in nature, which is a promising material in thermochemical energy storage (TCES). In this work, we have succeeded in synthesizing CaCO₃/ZrO₂ composites by physical mixing with a magnetic stirrer using CaCO₃ from natural limestone. The mixing was carried out by mechanical stirring with various molar percentages of CaCO₃:ZrO₂ of 100:0, 85:15, 70:30 and 50:50. The phase and structure of the CaCO₃/ZrO₂ composites were characterized by x-ray diffraction (XRD). Thermal properties were characterized by thermogravimetri analyzer. Morphology of the composites was observed by scanning Electron microscopy (SEM) with energy dispersive x-ray (EDX). Based on the XRD results, the peak intensity of CaCO₃ at the crystalline plane of (104) decreased with increasing percentage of ZrO₂. The lattice volume of CaCO₃ also relatively decreases with increasing percentage of ZrO₂. The increase in the percentage of ZrO₂ in the CaCO₃/ZrO₂ composites makes the decomposition temperature also decreases. This is probably due to heat and mass transfer of ZrO₂.

Abstract: Ceramic-metal functionally graded materials (FGMs) are advantageous to two dissimilar materials joined directly together, which includes smoothing of thermal stress distributions, minimization or elimination of stress concentrations and singularities at the interface corners and increase in bonding strength. In this study, ZrO₂/ 304 stainless steel (SUS304) FGMs with continuous gradient manners, not stepwise manners, were fabricated by a combination of centrifugal slurry methods and spark plasma sintering (SPS). The size and surface smoothness of the powders of SUS304 highly affected formation of compositional gradient patterns in the FGMs. Effects of ball milling time and ball sizes on such conditions of the powders as well as compositional gradients in the FGMs were investigated by microstructure observations with element analysis and hardness probing on the cross sections of the FGMs.

Abstract: In this work, we fabricated ZrO₂ based resistive random access memory by sol-gel spin coating technique and investigated its structural, optical and resistive switching properties. The X-ray diffraction pattern revealed that 400 °C annealed ZrO₂ thin film has tetragonal structure. The optical band gap value of ZrO₂ thin film obtained was 5.51 eV. The resistive switching behaviour of W/ZrO₂/ITO capacitor like structure was studied. It was found that no initial electroforming process required for the device. The fabricated devices show a self-compliance bipolar resistive switching behaviour and have high on off ratio (>10²). Our result suggests that solution processed ZrO₂ has great potential to develop transparent and flexible resistive random access memory devices.

Abstract: In present work, the structure, absorption and energy gap of films prepared from biodegradable polymer doped ZrO₂-SiC NPs for UV-shielding, biomedical fields and optoelectronics approaches were investigated. The nanocomposites films were fabricated by casting method. The absorption spectra was measured in range (200-800) nm. Results indicated to enhance in absorption and energy gap of biopolymer by adding of ZrO₂-SiC NPs ratios, this behavior make it suitable for various applications like antibacterial films, anti-UV light, diodes, solar cell, transistors and other fields. Keywords: biodegradable polymer, UV-shielding, absorption, energy gap, ZrO₂.

Abstract: Bentonite was modified through intercalation and calcination using a ZrOCl₂ pillaring solution. To create nano Ni/ZrO₂-bentonite catalyst, ZrO₂ pillared bentonite was impregnated using Ni(NO₃)₂•6H₂O precursor first, then followed by calcination and reduction. The physical-chemical properties of the catalyst was characterized by XRD (X-ray Diffractometer), FT-IR (Fourier Transform Infrared), surface acidity with NH₃ vapor adsorption method, SAA (Surface Area Analyzer) and TEM (Transmission Electron Microscope). The results of characterization with XRD showed specific peaks for montmorillonite minerals with a monoclinic crystalline type and its chemical composition (Ca)(Al,Mg)₆(Si₄O₁₀)₃(OH)₆.nH₂O and after pillarization showed a shift in basal spacing d₀₀₁ to the left (angle 2θ <5°). The typical peak indicating basal spacing d₀₀₁ shift towards a smaller angle of 2θ was not very apparent after impregnation with nickel metal. Qualitative determination of acidity after adsorption of ammonia showed characteristics at 1404-1635 cm^-1 wavenumbers with increasingly sharp spectra indicating increased acidity of the catalyst (Brǿnsted and Lewis acids). Surface area showed a significant increase from 27.385 m²/g to 174.208 m²/g after pillarization and impregnation of nickel metal.

Abstract: Zirconia (ZrO₂) powders doped with cobalt were prepared by sol-gel method using inorganic salt of zirconium (IV) chloride (ZrCl₄) as precursor. The amount of cobalt was varied in the range of 4–16% weight percent to study the effect to structural properties. X-ray diffraction (XRD) analysis suggested the resulting phases were zirconium oxide (Baddeleyite) with monoclinic crystal system along with cobalt oxide as secondary phase. The increasing cobalt content caused the XRD peaks to shift into lower angle due to substitution of Zr atom to smaller Co atom in crystal lattice. Scanning electron microscope (SEM) images showed the samples with higher Co content had smoother surface. Generally, the microstructures of Co doped zirconia powders consisted of large agglomerates with small particles on the surface.

Abstract: Sol-gel technology allows the synthesis of powders and nanoporous materials with a complicated structure and morphology, improving the reactivity of the synthesized material. Nanoparticles of ternary oxide ZrO₂-SiO₂-TiO₂ system have properties ascendant to those of the pure components. In the present work, the powders of the ZrO₂-SiO₂-TiO₂ system were obtained by a sol-gel technology. The powder particles were homogenized with a high energy milling process for 1 or 6 hours. The acquired particles and nanoporous ceramic materials, after sintering at 800 ^OC and 1000 ^OC, were characterized by X-ray diffraction, particle size distribution, compressive strength tests, BET specific surface area and porosity analysis.

Abstract: The ZrO₂ nanoparticles for highly refractive index nanocomposite are synthesized according to reaction temperature, zirconium precursor concentration, and kinds of precursor such as zirconium iso-propoxide (ZIP) and zirconium n-propoxide (ZNP). At lower reaction temperature the monoclinic phase is formed, whilst higher temperature favors the tetragonal and cubic phases. As the precursor concentration increased, the particle size of ZrO₂ nanoparticle slightly increased. TEM images prove that the ZrO₂ nanoparticles are spherical and monodisperse with a diameter of about 4 nm. The synthesized ZrO₂ was modified methacryloxy propyltrimethoxy silane (MPS) for dispersibility in organic solvent. Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA) illustrate that MPS are chemically attached to the surface of the ZrO₂. The ZrO₂ synthesized from ZNP and ZIP dispersed in o-phenylphenoxyethyl acrylate (OPPEA) is the highly transparent and the refractive index of this nanocomposite is 1.649 and 1.670, respectively.