Commercial Oxide Powders Research Articles

Microstructural, thermal characterization and CMAS corrosion resistance of novel quaternary (Y0,25Er0,25Tm0,25Yb0,25)2Si2O7 high entropy disilicate material

A novel (Y0,25Er0,25Tm0,25Yb0,25)2Si2O7 high entropy disilicate quaternary composition was synthesized from commercial oxide powders using ball milling and sintering processes as a candidate material for environmental barrier coatings (EBC). As-synthesized high entropy disilicate powders were sintered at different durations (12, 18, and 24 h) at 1600 °C in a muffle furnace before characterization. The XRD and SEM analyses revealed the single-phase monoclinic structure (β-type) with homogeneous elemental distribution for the sintered samples. The (Y0,25Er0,25Tm0,25Yb0,25)2Si2O7 samples exhibited low thermal diffusivity coefficient, low thermal conductivity, a close coefficient of thermal expansion (CTE) to SiC and a high temperature stability. The (Y0,25Er0,25Tm0,25Yb0,25)2Si2O7 samples were subjected to CMAS corrosion tests at 1300 °C with different durations (2, 12, and 24 h) to evaluate CMAS corrosion resistance. Additionally, Yb2Si2O7 samples were prepared and subjected to molten CMAS in the same way for comparison. Based on the results, the CMAS corrosion resistance was improved with (Y0,25Er0,25Tm0,25Yb0,25)2Si2O7 composition.

Spectroscopy of solid-solution transparent sesquioxide laser ceramic Tm:LuYO3

We report on a detailed spectroscopic study of a Tm3+-doped transparent sesquioxide ceramic based on a solid-solution (lutetia – yttria, LuYO3) composition. The ceramic was fabricated using commercial oxide powders by hot isostatic pressing at 1600°C for 3 h at 190 MPa argon pressure. The most intense Raman peak in Tm:LuYO3 at 385.4 cm-1 takes an intermediate position between those for the parent compounds and is notably broadened (linewidth: 12.8 cm-1). The transition intensities of Tm3+ ions were calculated using the Judd-Ofelt theory; the intensity parameters are Ω2 = 2.537, Ω4 = 1.156 and Ω6 = 0.939 [1020 cm2]. For the 3F4 → 3H6 transition, the stimulated-emission cross-section amounts to 0.27 × 10−20 cm2 at 2059nm and the reabsorption-free luminescence lifetime is 3.47 ms (the 3F4 radiative lifetime is 3.85 ± 0.1 ms). The Tm3+ ions in the ceramic exhibit long-wave multiphonon-assisted emission extending up to at least 2.35 µm; a phonon sideband at 2.23 µm is observed and explained by coupling between electronic transitions and the dominant Raman mode of the sesquioxides. Low temperature (12 K) spectroscopy reveals a significant inhomogeneous spectral broadening confirming formation of a substitutional solid-solution. The mixed ceramic is promising for ultrashort pulse generation at >2 µm.

Effect of Yb3+ doping level on the structure and spectroscopic properties of ZnO optical ceramics

Zinc oxide optical ceramics with hexagonal structure doped with 0.6 –5.0 wt% Yb were fabricated by uniaxial hot pressing of commercial oxide powders at 1180 °C in vacuum. The ceramics were characterized by X-ray diffraction, SEM, EDX, X-ray and optical spectroscopy. It is shown that Yb3+ ions are distributed between C-type Yb2O3 sesquioxide crystals and ZnO grain boundaries. The Yb3+ doping of ZnO ceramics enhances the near-band-edge emission of zinc oxide. ZnO:Yb optical ceramics are promising for optoelectronic applications.

Structure and spectral-luminescent properties of Er3+:ZnO optical ceramics

Transparent zinc oxide ceramics, undoped and doped with 0.1-2.0 wt% Er3+ ions were fabricated by uniaxial hot pressing of commercial oxide powders. The ceramics were characterized by X-ray diffraction, SEM, EDX, Raman, X-ray and optical spectroscopy. The analysis of morphology of Er3+:ZnO ceramics reveals that the main components of texture are hexagonal prism planes similar to those for undoped ceramic. The ZnO grain size decreases with addition of Er2O3. The Er3+ ions are distributed between the ZnO grains and the Er2O3 crystals and do not enter the zinc oxide structure. The luminescence spectra of Er3+:ZnO ceramics contain emission bands originating from the intra-4f shell transitions of Er3+ ions and bands assigned to defect states at ZnO. The X-ray luminescence spectra indicate the possible energy-transfer between the ZnO grains and Er3+ ions. The defect luminescence band becomes weaker and the X-ray luminescence decay time decreases as the erbium concentration is increased.

Preparation of In-doped Y2O3 ceramics through a sol-gel process: Effects on the structural and electronic properties

The Pechini-type sol-gel (PSG) process has been used for the preparation of doped oxides due to its capability to overcome most of the difficulties that frequently occur by using other producing methods. In this work we analyze the case of samples of pure and In-doped yttria (Y2O3) prepared by the PSG process. We experimentally characterize the synthesized samples by x-ray diffraction, micro-Raman spectroscopy, electrochemical impedance spectroscopy (EIS), and time-differential perturbed γ-γ angular correlation (PAC) spectroscopy, and we compare these results with those obtained starting from commercial oxide powders. We found that the PSG process can be used to successfully produce doped yttria in the cubic phase, with the impurities substitutionally located at the cationic sites of the structure. By the proposed PSG route, the inclusion of impurities does not affect the particle size nor the resistivity. However, when we compare the PSG samples with other samples produced from commercial powder, we found that the first have lower resistivities at grain interiors. On the other hand, PAC spectroscopy in 111In(→111Cd)-doped yttria allows the study of the dynamic hyperfine interactions observed by the radioactive 111Cd impurity-probe, which can be used to “sense” the host electron availability near the impurities after the electron-capture decay of 111In. Differences between PAC spectra for PSG samples and the commercial powder suggest that the PSG process introduces additional donor defects into the yttria electronic structure, which is consistent with the lower resistivity observed in the PSG samples by EIS spectroscopy.

Fabrication and luminescence of Ce-doped GGAG transparent ceramics, effect of sintering parameters and additives

Ce-doped garnets find their use as scintillators as well as phosphors. Among synthetic garnets, gallium gadolinium aluminium garnet (GGAG) is a relatively new and interesting material, a mixed garnet that has displayed very good scintillation and luminescence properties. In the presented work Ce-doped GGAG ceramic samples were produced by reaction sintering from commercial oxide powders. The mixed powders were pressed into pellets and sintered. In order to achieve transparency of a ceramic material, it is crucial to eliminate porosity. Therefore, a number of process parameters and their influence on the microstructure and optical quality of the ceramics were studied: starting powders, sintering additives and sintering conditions. The sintering process consisted of two steps, viz. pressureless sintering in air followed by hot isostatic pressing. Luminescence properties of the sintered ceramics were studied by means of photo-luminescence and correlated to the fabrication process parameters.

Green synthesis of UV and visible light active TiO2/WO3 powders and films for malachite green and ethylene photodegradation

Powder nanocomposites of TiO2/WO3 are prepared by a simple solid-state thermal procedure from commercial oxide powders and cast thereafter as a film coating on TLC substrate. The WO3 content in the powder composites is varied from 0.5 to 50%. The phase composition and morphology of titania/tungsten composites and films is characterized by SEM and X-ray analysis. The photocatalytic activity of TiO2/WO3 powders is tested in the degradation of malachite green dye in aqueous solutions under UV and visible light irradiation. The effect of preparation temperature on the photocatalytic activity is also investigated. It is found out that the mixed powder of 5%WO3 manifests the best photocatalytic performance. The prepared powder photocatalyst is deposited as a film coating on TLC sheet for gas-phase application. The as-obtained composite coated photocatalysts with 5%WO3 are tested for air purification from ethylene contamination under UV and visible light illumination. The TiO2/WO3 coated photocatalysts show always a higher efficiency in comparison to that of the pure TiO2.

Diffusion-controlled solid-state reactive sintering of Nd:YAG transparent ceramics

Diffusion-controlled solid-state reactive sintering is one of the most important steps in fabrication of highly transparent Nd:YAG ceramics using commercial oxide powders as starting materials. The difference in raw powders, especially for the characteristic of Y2O3 powder, will seriously influence the sintering behavior and finally lead to the large difference in microstructure and optical property. Thus, interactions between commercially available α-Al2O3 submicron particles and severely agglomerated Y2O3 nanoparticles during vacuum sintering were investigated in details in the present paper. Upon examining the influence of solid-state reactive diffusion in Nd:YAG ceramics, by optimizing the sintering parameters, highly transparent Nd:YAG ceramics were fabricated by solid-state reactive sintering of Y2O3, α-Al2O3 and Nd2O3 powders. The in-line transmittances of the ceramics achieved 83.8% and 81% at 1064nm and 400nm, respectively.

Densification and microstructural evolution of yttria transparent ceramics: The effect of ball milling conditions

Abstract Ho:Y2O3 ceramics were prepared by using solid-state reaction method with commercial oxide powders. The effect of ball milling condition, specifically slurry concentration (CS), on densification, microstructure evolution and transmittance of the Ho:Y2O3 ceramics was studied. Ho:Y2O3 powders were ball milled with slurry concentrations of 33.2–17.4 vol%. The samples were vacuum sintered between 1400 and 1850 °C. Over the CS range of 33.2–18.4 vol%, decreasing slurry concentration improved the densification, normal grain growth and optical transmittance of the Ho:Y2O3 ceramics. The 18.4 vol% Ho:Y2O3 powders showed the lowest agglomeration and highest densification rate, from which the ceramics prepared have the best transmittance. The grain growth exponents of the Ho:Y2O3 ceramics during final-stage of sintering were also studied.

Biofouling of various metal oxides in marine environment

Biofouling has induced serious problems in various industrial fields such as marine structures, bio materials, microbially induced corrosion (MIC) etc. The effects of various metals on biofouling have been investigated so far and the mechanism has been clarified to some extent(1,2), and we proposed that Fe ion attracted lots of bacteria and formed biofilm very easily(3). In this study, we investigated the possibility for biofouling of Pseudomonas aeruginosa on various metal oxides such as Fe2O3, TiO2, WO3, AgO, Cr2O3 etc. And in addition of such a model experiment on laboratory scale, they were immersed into actual sea water as well as artificial sea water. As for the preparation of metal oxides, commercial oxide powders were used as starting material and those whose particle sizes were under 100 micrometers were formed into pellets by a press. Some of them were heated to 700 °C and sintered for 10 hours at the temperatures. After the calcinations, they were immersed into the culture of P. aeruginosa at 35 °C in about one week. After the immersion, they were taken out of the culture and the biofouling behaviors were observed by optical microscopy, low pressure scanning electron microscopy (low pressure SEM) etc. Biofouling is generally classified into several steps. Firstly, conditioning films composed of organic matters were formed on specimens. Then bacterial were attached to the specimen's surfaces, seeking for conditioning films as nutrition. Then bacteria formed biofilm on the specimens. In marine environment, more larger living matters such as shells etc would be attached to biofilms. However, in the culture media, only biofilms were formed.

Preparation of Ternary Rare Earth Sulfide Ln<sub>x</sub>Gd<sub>2-x</sub>S<sub>3</sub> (Ln: La, Tb)

We investigated the formation behavior of ternary rare earth sulfide LnxGd2-xS3 (Ln: La, Tb). Ternary rare earth sulfide LnxGd2-xS3 (Ln: La, Tb) was synthesized via the sulfurization of their commercial oxide powders using CS2 gas for short sulfurization time. It was found that ternary rare earth sulfide LnxGd2-xS3 (Ln: La, Tb) could be synthesized for a short sulfurization time of 3 h at 1100°C. For LaxGd2-xS3, it crystallizes in α phase (Orthorhombic phase), the crystal structure is different from rare earth sulfide La10S14-xOx which crystallizes in β phase (Tetragonal phase) but is same with rare earth sulfide α-Gd2S3. TbxGd2-xS3 also crystallizes in α phase, the crystal structure is same with rare earth sulfide α-Tb2S3.

Recent Advances in Microwave, Millimeter-Wave and Plasma-Assisted Processing of Materials

We present results on microwave, millimeter-wave, and millimeter-wave-driven plasma-assisted processing of materials. The research is primarily based on two systems- a 2.45 GHz, 6 kW S-band system and an 83 GHz, 15 kW gyrotron-based quasi-optical system. The S-Band system is used to synthesize nanophase metals, metal mixtures, and metal oxides by our patented continuous microwave polyol process, which has potential for large scale and low cost production. This system is also being investigated to develop techniques for titanium melting and sintering. The 83-GHz system is used for rapid sintering of ceramic powder compacts to produce polycrystalline materials with limited grain growth. An important application is to the development of polycrystalline laser host materials for high power solid-state lasers, where the requirement is for transparency with high optical quality and good lasing efficiency. We are currently investigating solid-state reactive sintering of Nd-doped YAG (Yttrium Aluminum Garnet) from commercial oxide powders. This has thus far yielded translucent samples with good fluorescence lifetime of the lasing state. Techniques for further reducing light scattering by residual pores are being investigated. Finally, the millimeter-wave system is being used in the development of millimeter-wave plasma-assisted diamond deposition, as the quasi-optical system has significant advantages over conventional microwave plasma-assisted diamond deposition systems. The results and implications of this wide range of materials processing experiments are presented and discussed.

Synthesis of rare earth sulfides and their UV-vis absorption spectra

Rare earth sulfides were systematically synthesized via the sulfurization of their commercial oxide powders using CS 2 gas to shorten sulfurization time, and their UV-vis absorption spectra were investigated. The appropriate sulfurization conditions were studied. For the rare earth sulfides with the same crystal structure, the sulfurization temperature showed increasing tendency with the decrease of rare earth element atomic radii. The UV-vis absorption spectra of rare earth sulfides did not depend on the crystal structure of rare earth sulfides, but on the 4f electronic structure of rare earth element. The data showed that the optical band gaps of rare earth sulfides were irregular, and the values ranged from 1.65 to 3.75 eV.

Characteristics of Nd 3+-doped Y 3ScAl 4O 12 ceramic laser

Highly transparent Nd 3+-doped Y 3ScAl 4O 12 (YSAG) ceramics with up to 5.0 at.% Nd 3+-concentration ( C Nd) were synthesized from commercial oxide powders with purity of >99.99% by a solid-state reaction method. Absorption, fluorescence, and decay properties of these materials were evaluated. Considering the influence of increasing C Nd on these spectroscopic characteristics, it became clear that Nd:YSAG ceramics is suitable for the microchip laser or the mode-locked laser. We demonstrated microchip laser operation using highly concentrated Nd:YSAG. One-micron laser output power of 165 mW (37.0% optical-to-optical overall efficiency) and 49.5% slope efficiency were obtained under direct pumping into the emitting levels by a Ti:Sapphire laser from uncoated ceramic gain medium. Short-pulse generation from a passively mode-locked Nd 3+-doped YSAG ceramic laser was also demonstrated, and this laser generated pulses of ∼10 ps with 560 mW average power (35% optical-to-optical efficiency) under cw mode-locking operation.

Interactions of LiBr with calcite and calcium oxide powders

The interaction of LiBr with calcite and calcium oxide powders have been studied with and without the calcite decomposition reaction, using DTA and TG analysis plus SEM and RX observations. Interactions in LiBr  CaCO 3 system show two possible phase transformations at the temperature of 748 K and 786 K. The second one is due to the formation of an eutectic liquid phase in the LiBr-rich region. The rate of decomposition of calicite powders was measured in dry nitrogen and in a high partial pressure of CO 2 with and without LiBr. The addition of LiBr causes the decomposition reaction occur at a lower temperature. The LiBr changes the mechanism of the reaction. The decomposition process occurs through a liquid-phase path given by the eutectic of LiBrCaCO 3. The total rate of reaction as well as the temperature dependence are related to the liquid phase. The CaCO 3 powders obtained have a very dense structure with a high degree of crystallization. Probably the LiBrCaO eutectic provides a solution path for CaO recrystallization. The effectiveness of salt addition in lowering the decomposition temperature of carbonates seems promising in saving energy, as well as in promoting changes in morphology of important commercial oxide powders.

Ageing of some commercial oxide powders on storage

AbstractSome samples of technical grade silica and titania on storage for several years at room temperature show loss of apparent surface. The loss is attributed to dehydration of surface hydroxy‐groups. This can cause adhesion and aggregation of particles whereby the surface measured both by nitrogen and by dyes decreases, and, in some cases, causes a loss of surface reactivity.With heating at temperatures up to 250°, the loss of apparent surface of silica is increased, but that of titania is partly restored. It is suggested that these effects may influence specific surface measurements made by vapour phase adsorption if high temperature out‐gassing is employed.