Oxide-based Ceramics Research Articles

Self-propagating high-temperature synthesis of Lu2O3 powders for optical ceramics

A technique has been developed for the self-propagating high-temperature synthesis of lutetium oxide (Lu2O3) powders using citric acid, glycine, and lutetium acetate as fuels. We have carried out thermodynamic analysis of synthesis conditions and examined the effect of the nature of the fuel on the properties of the resultant powders. Using vacuum sintering at a temperature of 1780°C and powders prepared with glycine as a fuel and containing 25 mol % yttrium oxide and 5 mol % lanthanum oxide as sintering aids, we have obtained transparent lutetium oxide-based ceramics.

Development and evaluation of magnesium oxide-based ceramics for chamber parts in mass-production plasma etching equipment

In mass-production plasma etching equipment, the corrosion of ceramic chamber parts reduces the production yield of LSI and overall equipment effectiveness (OEE) owing to contamination, short useful life, and particle generation. Novel ceramics that can improve the production yield and OEE are highly required. We develop magnesium oxide (MgO)-based ceramics and evaluate them under mass-production plasma etching conditions. The results of this study indicate that the developed MgO-based ceramics with high mechanical properties and low electric resistivity have a higher resistance to corrosion in plasma etching using CF4 gas than Si and conventional ceramic materials such as aluminum oxide and yttrium oxide.

Clinical Performance of All-Ceramic Dental Restorations

The study aims to assess the current scientific evidence on the clinical performance of all-ceramic dental restorations. Silica-based and oxide-based ceramics provide esthetic treatment alternatives but rely on proper case selection and handling. Clinical long-term success rates are generally high for both tooth-supported and implant-supported restorations. Due to limited flexural strength and high brittleness, silica-based ceramics are limited in respect to clinical indications and their success greatly depends on resin bonding for final insertion. High-strength oxide-based ceramics can be inserted with conventional cements and reveal high success rates. More recently developed materials, such as resin matrix ceramics, zirconia-reinforced silicate ceramics, and monolithic translucent zirconia, reveal promising properties in the laboratory. However, they lack scientific validation through long-term clinical trials. Established silica-based and oxide-based ceramic materials demonstrate high long-term clinical survival rates; however, recently developed ceramics need further assessment.

(Invited) Non-Thermal Plasmas for the Production of Sustainable Functional Materials

This talk will highlight the potential of non-thermal plasmas as a viable synthetic approach for materials that are difficult to produce using other techniques. Materials such as titanium and zirconium nitride are impossible to produce in nanoparticle form using liquid phase chemistry techniques, and are not compatible with approaches such as flame and spray pyrolysis because they are not oxide-based ceramics. At the same time, they are quickly attracting interest because they are predicted to show plasmonic response in the visible, making them great candidates for the replacement of silver and gold-based plasmonics. Our recent investigation in this material system confirms that low-temperature, non-thermal plasma processes are compatible with the synthesis of titanium and zirconium nitride nanocrystals. Particles are produced using metal chlorides and ammonia as precursors. The plasma reactor is designed in a continuous flow configuration, where precursors are continuously fed into the plasma volume and nanoparticles are continuously collected downstream of the plasma by filtering. This technique allows producing TiN and ZrN nanocrystals with average size below 10 nm, with narrow size distribution (all particles are within 5 nm and 15 nm) and with perfect stoichiometry. In partial agreement with the theoretical predictions, such particles show plasmon resonance in the visible and in the near-infrared part of the spectrum. Yet the plasmon energy is lower than theoretically predicted, a behavior that has not been observed before and that we attribute to the presence of a native oxide shell. This observation is justified by simple experiments in which the particles are annealed in air at moderate temperature (<300°C), leading to the progressive growth of an oxide shell, as confirmed by elemental analysis and by XPS. The plasmon peak energy continuously red shifts during the annealing process, suggesting that a strategy for limiting oxide growth needs to be developed to enable the use of these nanomaterials for refractory plasmonic applications. In addition to discussing the properties of these novel plasma-produce nanomaterials, this talk will summarize our most recent findings with respect of their nucleation and growth. A combination of in-situ FTIR and optical emission spectroscopy measurements suggests that the nucleation process is initiated via atomic hydrogen-induced dissociation of the chlorine-based metal precursor, in this case titanium tetrachloride. This talk will also cover our most recent studies on the interaction between nanoparticles and plasmas. Despite operating near room temperature, and despite the short residence time (tens to hundreds of milliseconds) these systems are capable of producing nanocrystals of high melting point materials. Moreover, there is mounting evidence that such systems are compatible with the production of a broad range of high melting point materials. Therefore it is necessary to achieve a detailed understanding of the phenomena occurring in such reactors to fully take advantage of their capabilities as a nanomaterial synthetic approach. Using the silane-based chemistry as a testbed, we have performed careful in-situ FTIR characterization of the surface of silicon nanoparticles immersed in a non-thermal plasma. The hydrogen surface coverage decreases as the input power density increases. We attribute this to plasma-induced heating of nanoparticles to temperatures sufficiently high to lead to hydrogen desorption. This observation confirms the prediction of several theoretical studies that there is a non-equilibrium between nanoparticle temperature in a dusty plasma and the background gas temperature.

Tin oxide-based ceramics of high density obtained by pressureless sintering

Abstract Dense tin oxide-based ceramic semiconductors have a high potential as electrodes for aluminum production, glass industry, sputtering targets for transparent conducting thin films, varistors, and thermoelectrics due to their specific electrical properties, high corrosion resistance and ability to withstand high temperatures. The application of these ceramics is still limited because of the necessity to reach density of 99% of TD or greater and high electrical conductivity, and because of the manufacturing difficulties to produce components of different shapes and sizes with low cost. The paper reviews the results of the works conducted towards obtaining tin oxide-based ceramics with density up to 99.5+% of TD through low-temperature pressureless sintering. The selected sintering aids/dopants and firing conditions promoted both liquid phase sintering and electrical conductivity. The uniform microcrystalline structure is obtained.

Sodium bismuth titanate-based lead-free RAINBOW piezoelectric devices

The piezoelectric properties of lead-free piezoelectric ceramics are normally lower than those of lead oxide-based ceramics. In order to enhance the electromechanical performance of lead-free piezoelectric ceramics, an asymmetric chemical reduction was applied to sodium bismuth titanate (NBT)-based piezoelectric ceramics. Similar to the lead-containing ceramics, a curvature structure can be induced by the reduction in the NBT-based materials and lead-free RAINBOW (reduced and internally biased oxide wafer) devices can be fabricated. A large displacement (approximately 17μm) under an electric field of 900V/mm and high piezoelectric sensitivity (>4000pC/N) under a stress, which are related to the reduction induced curvature, can be measured in the NBT-based devices. The apparent piezoelectric response of the lead-free RAINBOW devices is comparable to that of Pb(Zr,Ti)O3-based devices. We proposed that apart from the piezoelectric properties, flexoelectric effect could also be a contributing mechanism for the observed apparent piezoelectric response in RAINBOW devices.

Pseudobrookite-type MgTi2O5 water purification filter with controlled particle morphology

Pseudobrookite-type oxide-based ceramics, such as Al2TiO5 and MgTi2O5, have recently been studied as porous ceramic membranes. Here, the effect of LiF doping on the morphology of MgTi2O5 particles is presented in detail. Water purification filters were produced using porous MgTi2O5, with different particle morphologies. MgCO3 (basic) and TiO2 powders with various LiF contents were wet-ball milled, dried, and then, calcined in air at 1100 °C to obtain the MgTi2O5 powders. The powder compacts were sintered at 1000–1200 °C to produce the MgTi2O5 disk filters. The 0.5 wt.% LiF-doped MgTi2O5 disk filter, with elongated grains, showed well-balanced performance removing boehmite particles with diameter of 0.7 μm. Non-doped MgTi2O5 disk filter with equiaxed grains was suitable for precise filtration.

Marginal bone loss of two implant systems with three different superstructure materials: a randomised clinical trial

Marginal bone level is a criterion for implant success. The aetiological factors of bone loss have not been clarified. The aim of this study was to evaluate the influence of implant systems and prosthetic materials on the marginal bone loss. Twenty-three patients participated; two implant systems and three superstructure materials were used in this study. Twenty-two of the implants were restored with porcelain fused to base metal alloy (BMA), 25 with porcelain fused to noble metal alloy (NMA) and 20 with zirconium oxide-based ceramics. Radiographs were taken at baseline and 3, 6 and 12 months after loading. Crestal bone-level changes were assessed with digital subtraction radiographs. The effects of superstructure materials and implants were evaluated with one-way anova and independent samples t-test, respectively (α = 0·05). The mean crestal bone loss was found 0·483 mm in 3 months, 0·622 mm in 6 months and 0·816 mm in 12 months. Prosthetic materials were found to have greater effect (β = 0·575, P = 0·015) on crestal bone loss than implant systems (P > 0·05). The porcelain fused to BMA restorations showed higher crestal bone loss than NMA-based restorations (P = 0·003) at 3 months, (P = 0·038), at 6 months and (P = 0·00) at 12 months; however, crestal bone loss differences between NMA and zirconia were not significant (P = 0·629) at 3 months, (P = 0·974) at 6 months and (P = 1) at 12 months. Within the limitations of this study, our results revealed that rather than the implant systems, prosthetic materials seemed to have an effective role on crestal bone.

A prospective evaluation of zirconia posterior fixed dental prostheses: Three-year clinical results

Although the favorable mechanical properties of zirconium oxide-based ceramics have increased the acceptance of fixed dental prostheses for use in the posterior regions of the mouth in recent years, there are few clinical studies documenting the longevity of these restorations. Furthermore, certain complications must be resolved before the material is used more extensively. The purpose of this randomized prospective study was to evaluate the clinical performance of zirconia (Lava) 3-unit posterior fixed dental prostheses. Twenty 3-unit fixed dental prostheses were placed in 17 participants to replace a second premolar or a first molar. Eleven were placed in the maxilla and 9 in the mandible. All abutment teeth were prepared with a chamfer finish line of 0.8 to 1 mm, and frameworks were prepared with the Lava system. Restorations were cemented with a resin cement. Two calibrated examiners independently evaluated the fixed dental prostheses 1 week (baseline) and 1, 2, and 3 years after placement with the California Dental Association quality evaluation system. The periodontal parameters: the gingival index, plaque index, margin index, and the probing depths of abutment teeth and contralateral teeth were assessed. Data were analyzed by using descriptive statistics and the Wilcoxon signed-rank test (α=.05). All fixed dental prostheses were rated satisfactory after 3 years, and no fracture of the framework was observed during the observation period. One fixed dental prostheses was lost because of a biological complication at the 3-year examination, and a small degree of chipping of the veneering ceramic was observed in 2 participants. No significant differences among the periodontal parameters of the test and control teeth were observed except for the margin index. The results of a 3-year evaluation suggest that posterior zirconia 3-unit fixed dental prostheses are a reliable treatment.

Machinability Evaluation in the Ultrasonic Drilling (USD) Process of Aluminum Oxide-based Ceramics

The ultrasonic drilling (USD) has been used in the manufacture of the hard, fragile, difficult to cut, nonconductive ceramic materials. In this study, the mathematical models of material removal rate (MRR) and surface roughness (SR) have been obtained for the machinability evaluation in the USD process of aluminum oxide-based ceramic material. The experimental plan adopts the face centered central composite design (CCD). The mathematical models using the response surface methodology (RSM) are developed so as to investigate the influences of three machining parameters, including the power rating, grit size and slurry concentration on the performance characteristics of MRR and SR. It has been proved that the proposed mathematical models in this study would fit and predict values of the performance characteristics, which would be close to the readings recorded in experiment with a 95% confidence level. The significant parameters that critically affect the performance characteristics are examined.

Nonlinear electrical properties and aging characteristics of (NiO, MgO, Cr2O3)-doped Zn-Pr-Co-R (R = Y, Er) oxide-based varistors

The electrical properties and stability of the varistors, which composed of (NiO, MgO, Cr2O3)-doped Zn-Pr-Co-R (Y, Er) oxide-based ceramics, were investigated for different additives. The breakdown voltage of the varistors increased in order of NiO→undoped→MgO→Cr2O3: 1200→1551→1691→1959 V/cm for ZPCY system and undoped→NiO→MgO→Cr2O3: 1024→1041→1500→1668 V/cm for ZPCE system, respectively. The nonlinear coefficient value increased in order of undoped→NiO→MgO→Cr2O3: 21→25→38→50 in ZPCY system and NiO→undoped→MgO→Cr2O3: 27→32→35→38 in ZPCE system, respectively. In ZPCY and ZPCE systems, the Cr2O3-additives most greatly improved the nonlinear properties. In Cr2O3-doped system, ZPCY system exhibited higher nonlinear properties than that of ZPCE system. The stability against d.c. accelerated aging stress was higher in Cr2O3-additives than in NiO- and MgO-additives for ZPCY system and was higher in NiO-additives than in MgO- and Cr2O3-additives for ZPCE system.

Microstructure and electrical properties of Tb-doped zinc oxide-based ceramics

The microstructure and electrical properties of Zn–Pr–Co–Cr–Tb oxide-based ceramics were investigated for different Tb4O7 amounts. The increase of Tb4O7 amount led to more densified ceramics, increasing from 5.73 to 5.85g/cm3 in sintered density. The average grain size decreased from 13.1 to 5.0 μm with the increase of Tb4O7 amount. It increased in the range of 8.9–42.0 in the nonlinear coefficient and in the range of 1026–6514V/cm in the breakdown field. The highest nonlinear coefficient (42) was obtained for 1.0 mol% Tb4O7. As Tb4O7 amount increased, the donor density decreased in the range of 1.23×1018–0.70×1018/cm3, whereas the barrier height at grain boundaries increased in the range of 0.73–0.93eV.

Effect of sintering temperature electrical properties of ZNR doped with Pr–Co–Cr–La

The microstructure, electrical properties, and dielectric characteristics of the ZNR (zinc oxide-based nonlinear resistors), which are composed of zinc oxide-based ceramics doped with Pr–Co–Cr–La, were investigated at different sintering temperatures (1240, 1245, 1250, 1255, 1260, and 1300 °C). The increase of sintering temperature led to more densified ceramics, whereas it decreased the nonlinear properties and breakdown voltage. The highest nonlinearity was obtained from 1240 °C, with 79.3 in nonlinear coefficient and 0.3 μA in leakage current. As the sintering temperature increased, the donor density increased from 0.90 × 10 18 to 2.59 × 10 18/cm 3, and the barrier height decreased from 1.90 to 0.67 eV, and the dielectric dissipation factor increased from 0.0874 to 0.2839.

Thermoluminescence properties of [formula omitted] nanopowder

Titanium oxide ( TiO 2 ) -based ceramics have many desirable and potential applications. Their mechanical properties are strongly affected by composition and microstructure, and can thus be tailored. The optical properties of TiO 2 are useful, being colorless, transparent, and possessing a high refractive index. These properties and the ability to tailor the structure make TiO 2 -based ceramics suitable for a wide range of applications. Interest in titanium oxide-based ceramics has increased considerably in recent years as possible thermoluminescence (TL) dosimeters which could be used in a wide variety of research activities and applications of ionizing radiation dosimetry. The aim of this work is to investigate some dosimetric properties of manganese doped titanium oxide ( TiO 2 : Mn ) nanopowder concerning the TL phenomenon related to its structural, morphological, and luminescent characteristics. Powder of TiO 2 : Mn was prepared using a co-precipitation method from titanium oxysulfate–sulfuric acid complex ( TiOSO 4 × H 2 SO 4 × H 2 O ) and manganese ( II ) chloride · 6 H 2 O . Formation of the compound was confirmed by studying the X-ray diffraction patterns. Diffraction patterns obtained suggested a mixture of anatase and rutile structure of the TiO 2 powder analyzed. Assuming the particles are stress-free, the size was estimated from a single diffraction peak using Scherrer's equation. Powder with the average nanopolycrystalline sizes from 10 nm up to about 80 nm was obtained. The glow curve of TiO 2 : Mn nanopowder exposed to gamma radiation exhibited one main peak centered at 240 ∘ C and a lower intensity peak at about 258 ∘ C . The intensity of the main peak increases as the dose increases. TL glow curve intensity of TiO 2 : Mn powder submitted to 1000 ∘ C was found to be more intense than that of the amorphous material, with the intensity increasing with the increase of crystallization temperature.

Effect of sintering temperature on microstructure and electrical properties of Zn·Pr·Co·Cr·La oxide-based varistors

The microstructure and electrical properties of varistors, which are composed of Zn·Pr·Co·Cr·La oxide-based ceramics, were investigated with different sintering temperatures. The increase of sintering temperature led to more densified ceramics, whereas it decreased the varistor voltage and nonlinear properties. The highest nonlinearity was obtained from 1230 °C, with 77.9 in nonlinear exponent and 0.4 μA in leakage current. As the sintering temperature increased, the donor concentration and density of interface states increased in the range of 0.90 × 10 18 to 2.59 × 10 18/cm 3 and 3.98 × 10 12 to 4.04 × 10 12/cm 2, respectively. The barrier height decreased with increasing sintering temperature, reaching a minimum (0.67 eV) at 1300 °C.

Comparative characteristics of silver and copper electrodes on ZnO varistor ceramics

The current–voltage characteristics of zinc oxide-based ceramics with silver electrodes created by silver baking and with copper electrodes obtained by electrodeposition of copper have been investigated in wide region of electric current. For ZnO varistors with copper electrodes the leakage current in 3–4 times is less than for varistors with silver electrodes. The reason of it is a thermal influence on ceramics at creation of silver electrodes. The transition layer between ceramics and the copper electrode, which has a negative influence on current–voltage characteristic at region of high electric current was not detected. The raster electronic microscopy indicates a good contact between ceramics and the copper electrode. The tearing strength for copper electrode is (8.21±3.03)×10 6 newton·m −2 and is close to similar magnitude for a silver electrode.

The Thermal and Elastic Properties of Zinc Oxide-Based Ceramics at High Temperatures

The thermal conductivity, thermal expansion coefficient (TEC), and the propagation velocity of longitudinal and transverse ultrasonic waves in ZnO-based ceramics are investigated in the temperature range from 300 to 1200 K with a porosity from 1.5 to 21%. The Young, shear, and bulk moduli and the Poisson ratio are calculated from the data on the propagation velocities of ultrasonic waves. Formulas are suggested to calculate the investigated parameters as a function of temperature and porosity.

Massive transformation in bismuth oxide-based ceramics

The massive transformation in metallic alloys has been investigated in considerable detail over the past three decades, both theoretically as well as experimentally. Rapid atomic transport, however, usually makes it difficult to experimentally investigate the kinetics of the massive transformation in metallic alloys under isothermal conditions. In ceramics, on the other hand, diffusion is generally much slower and can be manipulated through defect chemistry by the addition of an aliovalent dopant (that is, a dopant of a valence different from that of the host ion), and/or by altering the atmosphere. This, in principle, makes it possible to investigate the kinetics of the massive transformation in ceramics under isothermal conditions. The present manuscript reports on a study of the massive transformation in Bi2O3-based ceramics. Samples in the Bi2O3-RE2O3 systems, where RE is Y or a rare-earth ion, were fabricated in a dense from by consolidating requisite powder mixtures and sintering compacts in air. The high-temperature form of Bi2O3 is isostructural with CaF2, with 25 pct of the oxygen sites being vacant. This makes it an excellent oxygen ion conductor, thus affording the measurement of oxygen ion conductivity as a technique to investigate the kinetics of the massive transformation. The kinetics of the massive transformation was investigated under isothermal conditions using a number of techniques, including X-ray diffraction (XRD), reflected optical microscopy, transmission optical microscopy, transmission electron microscopy (TEM), electron-probe microanalysis (EPMA), and the measurement of ionic conductivity. The studies demonstrated that the cubic → rhombohedral transformation (during cooling) in Bi2O3-based ceramics is a massive transformation, and the rhombohedral → cubic reverse transformation (during heating) is also a massive transformation. A study of the Gd2O3-Bi2O3 system also showed that a massive transformation occurs inside a two-phase field, thus possibly shedding some light on a controversial point, much debated in the literature on metallic alloys. The sluggishness of the transformation kinetics suggests that ceramic systems are perhaps better suited to investigate salient features of the massive transformation (and, for that matter, many other diffusional transformations), theories for which have been developed for metallic alloys.

Erratum: “Synthesis of aluminum oxide-based ceramics by laser photoinduced reactions from gaseous precursors” [J. Mater. Res. 12, 774–782 (1997)

Erratum: “Synthesis of aluminum oxide-based ceramics by laser photoinduced reactions from gaseous precursors” [J. Mater. Res. 12, 774–782 (1997)

Catalytic properties of yttria doped bismuth oxide ceramics for oxidative coupling of methane

Fluorite structured bismuth oxide-based ceramics are potential membrane materials for oxygen separation and membrane reactor applications. In this work, the catalytic properties of the surface of several bismuth oxide-based ceramics for oxidative coupling of methane were studied using a conventional tubular reactor operated in the cofeed mode. A most commonly studied catalyst, 5 wt% Li/MgO ( Li/MgO), was selected as a reference catalyst. 30 mol% Y 2O 3 doped Bi 2O 3 (BY30) exhibits C 2 yield (18%) and selectivity (50%) similar to Li/MgO at 800–850°C, but the former has a C 2 space-time yield 15 times higher than the latter. Like Li/MgO, BY30 also yields more C 2H 4 and CO 2 than C 2H 6 and CO in its products. The comparison studies on Bi 2O 3, BY25, BY30 and Y 2O 3 show that doping yttria in Bi 2O 3 results in an increased C 2 yield and a slightly decreased C 2 selectivity. A decrease in the surface area of the bismuth oxide-based ceramics gives a larger C 2 selectivity and a lower C 2 yield.