Conventional Zirconia Research Articles

Oxygen Measurement System using Optical Communication Devices

Concentration measurement of oxygen gas is required for better monitoring and control of various types of combustion systems. As compared with conventional zirconia oxygen sensors, tunable diode laser absorption spectroscopy can provide faster response, with smaller interference of inflammable gases. In this paper we report the concentration measurement of oxygen molecules using the absorption band (A-band) of 760 nm wavelength. A periodically poled LiNbO3 crystal (PPLN) is employed for the frequency doubling of 1520 nm light from a distributed feedback laser, resulting in the 760 nm output power of 1.8 mW. The wavelength modulation spectroscopy with dual beam configuration enables the cancellation of the common mode noise from diode laser as well as excess etalon noise that arises from optical paths including the PPLN module. With the cell length of 200 mm, the absorption measurement using the R11Q12 line at 760.445 nm has led to a minimum detectable absorbance of 3.7×10-4 m-1. A dynamic response faster than 1 s was seen when the oxygen concentration was changed between 0% and 24% while the laser wavelength was fixed at the absorption peak.

Shear Bond Strength Comparison between Conventional Dental Nano Zirconia Combinations and New Functionally Graded Nano Zirconia Combinations after Thermal-Mechanical Cycling

The aim of the study was to evaluate the core veneer bond strength of graded zirconia combinations and compared those to conventional zirconia combinations after thermal and mechanical tests. Conventional zirconia-veneer combinations and graded zirconia-veneer combinations were made into cylinders. Prior to shear bond testing, half of each group was subjected to thermal and mechanical cycling testing at three conditional levels. All specimens were thereafter subjected to a shear force. The fractured surfaces were visually analyzed with scanning electron microscopy. The shear bond strength values of functionally graded zirconia combinations were signi cantly higher than zirconia combinations, irrespective of the fatigue conditions (P < 0.05). The shear bond strength values of graded zirconia combinations and zirconia combinations before thermal-mechanical cycling were higher than after (P < 0.05). The shear bond strength values of graded zirconia combinations was 40.99±2.22MPa, 39.44±2.36MPa, 37.45±2.06MPa, and 36.87±2.18MPa for conditions 0 to 3, respectively. The shear bond strength values were 26.75±2.16 MPa, 23.95±2.16 MPa, 21.65±2.14 MPa, and 20.49±2.16 MPa for zirconia combinations from conditions 0 to 3, respectively. The functionally graded zirconia combinations exhibited greater shear bond strength than zirconia combinations, irrespective of the fatigue conditions. Thermal-mechanical cycling had an impact on the shear bond strength of both graded zirconia combinations and conventional zirconia combinations.

Influence of coping design on the cervical color of ceramic crowns

The replication of natural teeth, especially with single-tooth restorations, represents a challenge. Similar to metal ceramic crowns, different designs of zirconia substructures have been suggested to improve the esthetic results of zirconia ceramic crowns. The purpose of the study was to analyze the color of the cervical portion of single zirconia ceramic crowns fabricated with different zirconia coping designs. The color, measured on the CIELAB color scale, of 3 different groups of restorations (n=10) fabricated with zirconia coping (Lava) and feldspathic porcelain (Noritake Super Porcelain) was analyzed with a spectrophotometer. Conventional zirconia crowns with zirconia facial margins were compared with ceramic crowns with porcelain facial margins and either a horizontal reduction of the zirconia coping (1.0 mm reduction) or an additional vertical reduction (1.0 mm additional reduction). The 3 groups, each with a different coping extension, were examined with a 1-way ANOVA and the Fisher exact test, and the differences of the groups were evaluated by applying ΔE thresholds (α=.05). The mean color difference among all the groups was not clinically significant (ΔE<3.7). Reduced color differences were present between the 2 porcelain butt margin groups of crowns (ΔE=1.06, between group H and V). Increased differences were present between the zirconia margin group and the porcelain butt margin group (ΔE=2.54 between group C and H; ΔE=2.41 between group C and V). Lab* values were examined in all the groups of crowns to determine the clinical implications. Within the limitation of the study, no significant differences were present among the tested groups of crowns. Nevertheless, although some differences were present between the zirconia margin group and the porcelain butt margin group, reduced differences were present between the 2 different cutback designs.

Applying microwave technology to sintering dental zirconia

When sintering zirconia, conventional processing may not provide uniform heating and consumes more energy than an alternative method using microwave energy. The purpose of this study was to compare the surface quality, mechanical and physical properties, and dimensional stability obtained by sintering yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) in a conventional furnace versus a microwave furnace. Twenty bars of Y-TZP were prepared from Zircad blocks. Ten specimens were used for sintering in a conventional furnace. The remaining 10 specimens were sintered in a microwave furnace. The sintering temperature used for both techniques was 1500°C. The flexural strength of all specimens was measured with the 3-point bend test with a universal testing machine with a cross head speed of 1.0 mm/min. Density was measured by applying the Archimedes method, and specimen length, width, and thickness were measured with a digital micrometer. The phase composition and average grain size of these ceramics were examined by using X-ray diffraction, and microstructure characteristics were studied with scanning electron microscopy. Data obtained were analyzed by using independent t tests (α=.05). No significant difference between conventional and microwave sintering for either flexural strength, t18=0.49 (P=.63) or density, t18=0.07 (P=.95) was found. Specimens in both groups exhibited a uniform firing shrinkage of approximately 24.6% in all dimensions. The surface of selected specimens examined with a scanning electron microscope showed no visible difference in grain shape or porosity size between the 2 sintering methods. Under the conditions of this study, it appears that either microwave or conventional zirconia sintering may be used for processing zirconia for dental use. However, microwave energy provides uniformity of heating, allowing the use of higher heating rates, which can increase productivity and save energy.

Structure and Tribological Performance of Nanostructured ZrO2-3 mol% Y2O3 Coatings Deposited by Air Plasma Spraying

In this study, nanostructured ZrO2-3 mol% Y2O3 coatings were deposited by air plasma spray using reconstituted feedstock. The coating structures were characterized by x-ray diffractometer, micro-Raman spectrometer, field emission scanning electron microscope, and transmission electron microscope. It is revealed that the as-sprayed coating is mainly composed of columnar grains with diameters <100 nm and demonstrates the better toughness, higher microhardness, and lower porosity. It consists only of nontransformable tetragonal ZrO2 phase. The tribological performance of the coating was examined with a ball-on-disk apparatus under dry sliding conditions. The results show that the friction coefficient of as-sprayed coating was approximately one-fifth of the conventional zirconia coating and wear rate was lower one order of magnitude than the conventional zirconia coating. The dominant wear mechanism is abrasive wear. The improved wear resistance can be attributed to the increased mechanical properties of as-sprayed coating.

Esterification of 4-methoxyphenylacetic acid with dimethyl carbonate over mesoporous sulfated zirconia

Abstract Mesoporous zirconia was synthesized using cetyltrimethylammonium bromide as template under hydrothermal conditions. The surfactant was removed by ethanol extraction. The resultant mesoporous material was further treated with sulfuric acid and calcined in air at 450 °C for 5 h to obtain mesoporous sulfated zirconia (MSZ). The mesoporous sulfated zirconia was characterized by XRD and N 2 adsorption and desorption measurements. Esterification of 4-methoxyphenylacetic acid (4-MPAA) with dimethyl carbonate was carried out in a batch reactor under autogeneous pressure over this catalyst as a function of reaction temperature, catalyst loading and the results are also compared with conventional sulfated zirconia (CSZ). More than 98% selectivity for methyl 4-methoxyphenylacetate was observed in all the experiments. The CSZ catalyst shows very low conversion when compared to that of MSZ. This may be attributed to its low surface area, presence of micropores and non-uniform pore size distribution. The mesoporous sulfated zirconia comprises of large surface area and uniformly distributed mesopores, which facilitates the reaction of bulky organic molecules like 4-MPAA with DMC. In addition, MSZ catalyst shows higher acidity than that of CSZ catalyst and in turn a higher catalytic activity. The kinetics of the reaction over both the catalysts was studied. The rate constant for the reaction was found to be 4.7 × 10 −3 min −1 and 0.5 × 10 −3 min −1 for MSZ and CSZ, respectively. The activation energy of the reaction is 18.0 kcal/mol over MSZ catalyst.

Comparison of thermal shock behaviors between plasma-sprayed nanostructured and conventional zirconia thermal barrier coatings

NiCoCrAlTaY bond coat was deposited on pure nickel substrate by low pressure plasma spraying(LPPS), and ZrO 2-8%Y 2O 3 (mass fraction) nanostructured and ZrO 2-7%Y 2O 3 (mass fraction) conventional thermal barrier coatings(TBCs) were deposited by air plasma spraying(APS). The thermal shock behaviors of the nanostructured and conventional TBCs were investigated by quenching the coating samples in cold water from 1 150, 1 200 and 1 250 °C, respectively. Scanning electron microscopy(SEM) was used to examine the microstructures of the samples after thermal shock testing. Energy dispersive analysis of X-ray(EDAX) was used to analyze the interface diffusion behavior of the bond coat elements. X-ray diffractometry(XRD) was used to analyze the constituent phases of the samples. Experimental results indicate that the nanostructured TBC is superior to the conventional TBC in thermal shock performance. Both the nanostructured and conventional TBCs fail along the bond coat/substrate interface. The constituent phase of the as-sprayed conventional TBC is diffusionless-transformed tetragonal( t′). However, the constituent phase of the as-sprayed nanostructured TBC is cubic( c). There is a difference in the crystal size at the spalled surfaces of the nanostructured and conventional TBCs. The constituent phases of the spalled surfaces are mainly composed of Ni 2.88Cr 1.12 and oxides of bond coat elements.

Lost Mold Rapid Infiltration Forming of Mesoscale Ceramics: Part 1, Fabrication

Free-standing mesoscale (340 mum x 30 mum x 20 mum) bend bars with an aspect ratio over 15:1 and an edge resolution as fine as a single grain diameter ( approximately 400 nm) have been fabricated in large numbers on refractory ceramic substrates by combining a novel powder processing approach with photoresist molds and an innovative lost-mold thermal process. The colloid and interfacial chemistry of the nanoscale zirconia particulates has been modeled and used to prepare highly concentrated suspensions. Engineering solutions to challenges in mold fabrication and casting have yielded free-standing, crack-free parts. Molds are fabricated using high-aspect-ratio photoresist on ceramic substrates. Green parts are formed using a rapid infiltration method that exploits the shear thinning behavior of the highly concentrated ceramic suspension in combination with gelcasting. The mold is thermally decomposed and the parts are sintered in place on the ceramic substrate. Chemically aided attrition milling disperses and concentrates the as-received 3Y-TZP powder to produce a dense, fine-grained sintered microstructure. Initial three-point bend strength data are comparable to that of conventional zirconia; however, geometric irregularities (e.g., trapezoidal cross sections) are present in this first generation and are discussed with respect to the distribution of bend strength.

Transesterification of soybean oil catalyzed by sulfated zirconia

Two sulfated zirconias were synthesized and characterized by X-ray diffraction and infrared spectroscopy. They were used as catalysts in the alcoholysis of soybean oil and in the esterification of oleic acid. Using sulfated zirconia prepared by the solvent-free method (S–ZrO 2) as catalyst, the alcoholysis conversions of soybean oil under optimized conditions (120 °C, 1 h and 5 wt% of catalyst) were 98.6% (methanolysis) and 92% (ethanolysis), respectively. The esterification of oleic acid with methanol was complete after 2 h. Zirconia sulfated by standard methods (SZ) had low activity in the methanolysis of soybean oil (conversion of 8.5%) and conventional zirconia (NS) was inactive for methanolysis under the conditions optimized for S–ZrO 2.

Novel Low Thermal Conductivity Ceramic Materials for Thermal Barrier Coatings

The increase of the efficiency for gas turbines leads to the increasing combustion-chambertemperatures. Rapid degradation of the conventional yttria-stabilized zirconia coatings does not fulfill therequirements at these temperatures for a reliable thermal barrier coatings (TBCs) due to the phasetransformation of zirconia and the sintering behaviour. Therefore, it is very important to develop novelceramic materials for TBCs with low thermal conductivity and long-term stability at high temperatures.In this paper, the developments of potential novel ceramic materials for TBCs with low thermalconductivity are reviewed.

Synthesis of Gadolinium Zirconate by Coprecipitaiton and Its Properties for TBC Application

The increase of the efficiency for gas turbines leads to the increasing combustion-chambertemperatures. Rapid degradation of the conventional yttria-stabilized zirconia coatings does not fulfill therequirements at these temperatures for a reliable thermal barrier coatings (TBCs) due to the phasetransformation of zirconia and the sintering behaviour. Therefore, it is very important to develop novel ceramic materials for TBCs with low thermal conductivity and long-term stability at high temperatures.In this paper, the developments of potential novel ceramic materials for TBCs with low thermalconductivity are reviewed.

Wear behaviour of nanostructured and conventional 8 wt-%Y2O3–ZrO2 coatings against Si3N4 ball

The aim of the present paper is to investigate and compare the wear and tribological behaviour of two types of yttria–partially stabilised zirconia coatings, i.e.nanostructured and conventional zirconia. The coatings, 8 wt-%Y2O3–ZrO2, were produced using an air plasma spraying (APS) technique. Substrates used were made from AISI 304 stainless steel. To perform the wear tests, a pin on disc wear testing machine, using a 10 mm silicon nitride (Si3N4) ball as the pin, was employed. Coatings produced were characterised before and after being subjected to wear testing, using optical microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry and X-ray diffraction. Regarding the wear tests, effects of various parameters, such as wear distance, substrate temperature, disc rotating speed (sliding velocity) and applied normal load, were investigated. Results obtained (weight loss, wear rate, coefficient of friction and worn surface microstructure) revealed that under the wear conditions applied, the nanostructured zirconia coating exhibited a better wear resistance and tribological properties than the conventional one. Also it was observed that the difference in wear resistance between both coatings tested is a function of wear testing parameters such as wear distance, substrate temperature, disc rotating speed and applied normal load.

Microstructural feature, thermal shock resistance and isothermal oxidation resistance of nanostructured zirconia coating

Nanostructured and conventional zirconia coatings on superalloys have been deposited to show thermal shock resistance and oxidation resistance by atmospheric plasma spraying. The results showed that the nanostructured zirconia coating mainly contained two kinds of microstructures, nanosized zirconia particles embedded in the matrix and micrometer-sized columnar grain structures of zirconia similar to those of conventional zirconia coating. Compared with the conventional zirconia coating, the nanostructured coating is denser and has finer and less porous structure and fewer microcracks with higher thermal shock resistance and isothermal oxidation resistance. With increasing zirconia coating thickness from 100 to 500 μm, the thermal shock resistance of both nanostructured and conventional coatings decreased. The increased properties of nanostructured zirconia coating are related to improved toughness and decreased porosity and microcrack of the coating.

Evaluation of unlubricated wear properties of plasma-sprayed nanostructured and conventional zirconia coatings by SRV tester

Atmospheric plasma spraying method was used to deposit nanostructured and conventional zirconia coatings using spray-dried nanostructured zirconia powder and conventional zirconia powder as feedstock, respectively. Their wear properties were evaluated comparatively by a sliding, reciprocating and vibrating (SRV) tester under dry conditions. The obtained results show that the wear properties of the plasma sprayed zirconia coatings deposited from spray-dried nanostructured zirconia powder were greatly improved compared with those of plasma sprayed zirconia coatings produced from conventional powder. The wear rates of nanostructured zirconia coatings are approximately half of those of conventional zirconia coatings. Under dry conditions, the wear mechanism for the plasma-sprayed nanostructured zirconia coatings is abrasive wear. Whilst in the case of plasma sprayed conventional zirconia coatings, it is a combination of abrasive wear and brittle fracture, the former is dominant wear mechanism. Their wear properties were explained in terms of their microstructure as well as mechanical properties and compared with the wear properties obtained under distilled-water lubricated conditions. Based on the experimental results, it is concluded that the finer debris is a critical factor for the improvement of wear properties of plasma-sprayed nanostructured zirconia coating under dry conditions. The wear properties of plasma sprayed zirconia coatings can be increased by the presence of water during the SRV testing.

Thermal shock resistances of nanostructured and conventional zirconia coatings deposited by atmospheric plasma spraying

Nanostructured and conventional zirconia coatings were deposited by atmospheric plasma spraying and the thermal shock resistances of as-sprayed coatings were investigated by the water quenching method. The results showed that the nanostructured as-sprayed coating possessed better thermal shock resistance than the conventional coating. This phenomenon is explained in terms of the difference in microstructure and microstructural changes occurring during thermal shock cycling.

High-Pressure NMR Studies on the Alternating Copolymerization of Styrene with Carbon Monoxide Catalyzed by a Palladium(II)−(R,S)-BINAPHOS Complex

The asymmetric copolymerization of styrene with CO catalyzed by Pd−(R,S)-BINAPHOS complexes has been studied using in situ NMR spectroscopy under both diffusion- and reaction-controlled conditions. While a study conducted in a conventional zirconia tube suffered from gas diffusion limitation, use of a high-pressure NMR flow cell allows the observation of potential catalytic intermediates. The formation of Pd−alkyl complexes via 1,2-insertion of styrene into Pd−acyl complexes is confirmed to be the most active catalytic pathway. The 2,1-insertion complexes were found to be quite inactive to further insertion and remarkably stable toward β-hydride elimination, in contrast to our previous expectations.

Influence of feedstock and spraying parameters on the depositing efficiency and microhardness of plasma-sprayed zirconia coatings

In this work, nanostructured and conventional zirconia coatings were deposited by atmospheric air plasma spraying (APS) under different spraying conditions using spray-dried nanostructured powders and conventional powders as feedstocks, respectively. The microstructures of the feedstocks were characterized by TEM and SEM. The depositing efficiencies for both nanostructured and conventional zirconia coatings deposited under different spraying parameters were comparatively measured. The obtained results revealed that the spray-dried nanostructured powders possessed higher deposition efficiency than that of conventional powders. It is significant from economic view of reducing cost. In addition, the influence of spraying parameters on microstructure and microhardness of zirconia coatings were discussed also. It was found that the microhardness of nanostructured zirconia coatings was larger than that of its counterparts.

Synthesis of thermally stable tetragonal zirconia with large surface area and its catalytic activity in the skeletal isomerization of 1-butene

Thermally stable zirconia with a large BET surface area was prepared by using zirconium atrane derivatives and commercial alkyltrimethylammonium bromide. The zirconia samples were characterized by wide-angle X-ray diffraction, thermal analysis and N2 adsorption/desorption analysis. The results showed that the present zirconia existed as a thermally stable tetragonal crystallite and consisted of mesoporous material with microporous contribution. The BET surface area was found larger than 240 m2/g even after calcination at 600 °C. The present zirconia after sulfation was applied to the skeletal isomerization of 1-butene, and its catalytic activity was found superior to that of the conventional sulfated zirconia.

Mesostructured sulfated zirconia with high catalytic activity in n-butane isomerization

A mesostructured sulfated zirconia with a large surface area (189 m2/g) has been successfully prepared using a triblock copolymer as a structure-directing agent. The resulting material was characterized by XRD, TEM, nitrogen adsorption, FTIR and TG/DTA, which suggested that the mesostructured sulfated zirconia was tetragonal crystalline. Catalytic testing showed that the mesostructured sulfated zirconia was much more active than conventional sulfated zirconia for n-butane isomerization.

Limits in the use of pyridine adsorption, as an analytical tool to test the surface acidity of oxidic systems. The case of sulfated zirconia catalysts

When high-area oxidic systems carry surface anionic species (in the present case: stable sulfate groups at the surface of sulfated zirconia catalysts), pyridine adsorption leads to an overestimated and thus partly artefact evaluation of the surface Lewis acidity. IR spectroscopic evidence is presented for the existence of a ligand competition at surface cationic centres (Lewis acid sites) between strong Lewis bases (pyridine) and surface sulfates. In the case of weak Lewis bases, like CO, there is no competition. The use of a “model” sulfated zirconia system, obtained by sulfation of an yttria-stabilized tetragonal zirconia preparation, turned out to be vital for obtaining the mentioned evidence, as this preparation allowed to compare the surface Lewis acidity in an homogeneous series of non-sulfated, sulfated, and sulfated-and-calcined systems of virtually unchanged crystal phase, surface area and crystal morphology. Also the conventional sulfated zirconia catalysts, prepared from an amorphous hydrate precursor, present the same type of surface ligand competition and the partly artefact evaluation of surface Lewis acidity, but in that case a piece of information is missing in that physical and chemical properties of the non-sulfated amorphous precursor cannot be compared with those of the crystalline sulfated systems.