Zirconia ceramics have become increasingly widely used in recent years and are favored by relevant enterprises. From the traditional dental field to aerospace, parts manufacturing has been used, but there is limited r...Zirconia ceramics have become increasingly widely used in recent years and are favored by relevant enterprises. From the traditional dental field to aerospace, parts manufacturing has been used, but there is limited research on the deformation and damage process of zirconia ceramics. This article analyzes the acoustic emission characteristics of each stage of ceramic damage from the perspective of acoustic emission, and explores its deformation process characteristics from multiple perspectives such as time domain, frequency, and EWT modal analysis. It is concluded that zirconia ceramics exhibit higher brittleness and acoustic emission strength than alumina ceramics, and when approaching the fracture, it tends to generate lower frequency acoustic emission signals.展开更多
Inspired by structures of natural shells,zirconia-carbon nanocomposites were obtained by using natural chitin from shrimp shells as templates via the sol-gel route in this study.Chitin was dispersed in the water and c...Inspired by structures of natural shells,zirconia-carbon nanocomposites were obtained by using natural chitin from shrimp shells as templates via the sol-gel route in this study.Chitin was dispersed in the water and chelated with the zirconia precursors by amidogen.After a heat treatment for carbonization,nacre-like structures of carbon-zirconia nanocomposites were successfully synthesized.Due to the toughening mechanism of tetragonal zirconia,the mechanical properties of carbon-zirconia composites are further improved.The as-received zirconia/carbon nanocomposite with best mechanical property has a hardness of 5.88GPa and an elastic modulus of 80.6 GPa,which is even stronger than natural shells.This work might facilitate a versatile platform for developing green nanocomposites with reasonably good mechanical properties.展开更多
Zirconia has been extensively used in aerospace,military,biomedical and industrial fields due to its unusual combination of high mechanical,electrical and thermal properties.However,the fundamental and critical phase ...Zirconia has been extensively used in aerospace,military,biomedical and industrial fields due to its unusual combination of high mechanical,electrical and thermal properties.However,the fundamental and critical phase transition process of zirconia has not been well studied because of its difficult first-order phase transition with formidable energy barrier.Here,we generated a machine learning interatomic potential with ab initio accuracy to discover the mechanism behind all kinds of phase transition of zirconia at ambient pressure.The machine learning potential precisely characterized atomic interactions among all zirconia allotropes and liquid zirconia in a wide temperature range.We realized the challenging reversible first-order monoclinic-tetragonal and cubicliquid phase transition processes with enhanced sampling techniques.From the thermodynamic information,we gave a better understanding of the thermal hysteresis phenomenon in martensitic monoclinic-tetragonal transition.The phase diagram of zirconia from our machine learning potential based molecular dynamics simulations corresponded well with experimental results.展开更多
The sintering behavior and mechanical properties of zirconia doped with 2.0mol%-3.0mol%Y_(2)O_(3)were studied by pressure-less sintering.The experimental results show that the densification temperature of zirconia cer...The sintering behavior and mechanical properties of zirconia doped with 2.0mol%-3.0mol%Y_(2)O_(3)were studied by pressure-less sintering.The experimental results show that the densification temperature of zirconia ceramics increases gradually with the decrease of Y_(2)O_(3)doping content by which decreases the sintering driving force due to the lower oxygen vacancy concentration of the systems.Furthermore,the bending strength and fracture toughness of the prepared zirconia ceramics increase with the decrease of Y_(2)O_(3)doping content.It can be attributed to the fact that the phase stability of tetragonal zirconia decreases with the decrease of Y_(2)O_(3)doping content,which is easier to induce"phase transformation toughening"and dissipate impact energy.The relative density,bending strength and fracture toughness of 2.0 mol%Y_(2)O_(3)doped zirconia ceramics(2.0Y-ZrO_(2))sintered at 1525℃are 99.00%,1256.65±20.82 MPa and 9.85±0.13 MPa·m^(1/2),respectively.展开更多
In order to investigate the effect of zirconia corundum on the preparation of chrome corundum castables,samples were prepared using tabular corundum,white fused corundum,active alumina micropowder,chromium oxide micro...In order to investigate the effect of zirconia corundum on the preparation of chrome corundum castables,samples were prepared using tabular corundum,white fused corundum,active alumina micropowder,chromium oxide micropowder and fused ziconia corundum particles as the main raw materials,and pure calcium aluminate cement as the binder.The effects of the fused zirconia corundum particles addition(1-0.5 mm,0,4.5%,9%,and 18%,by mass)on the linear change rate,the apparent porosity,the cold modulus of rupture,and the thermal shock resistance of chrome corundum castables were studied,and the microstructure of the samples was analyzed.The results show that:(1)with the zirconia corundum addition increasing,the permanent linear change on heating of the samples gradually increases,the apparent porosity gradually increases,the cold modulus of rupture gradually decreases,and the thermal shock resistance gradually increases;(2)according to SEM,it can be found that the phase transformation of ZrO2 after heat treatment leads to a large number of microcracks in the material.On one hand,the cold modulus of rupture of the material is reduced;on the other hand,the thermal shock resistance of the material is improved.展开更多
Advances in metal-free materials and the popularization of Computer-Aided Design and Manufacturing (CAD/CAM) have led to the wide clinical use of all-ceramic crowns for esthetic restorations. A 72-year-old woman prese...Advances in metal-free materials and the popularization of Computer-Aided Design and Manufacturing (CAD/CAM) have led to the wide clinical use of all-ceramic crowns for esthetic restorations. A 72-year-old woman presented to our hospital with unesthetic restorations on the right upper and lower posterior teeth. Intraoral examination revealed poorly fitting metal crown margins. Defective prostheses were removed, and provisional restorations were provided to stabilize the mandibular position. Optical impressions and the maxillomandibular relationship were recorded using an intraoral scanner, and monolithic zirconia crowns were fabricated using CAD/CAM technology for complete veneer crown restorative treatment. Occlusal examination revealed an improvement in occlusal force distribution at initial examination (right side: 33.5%, left side: 66.5%) after placement of the zirconia crowns (right side: 54.9%, left side: 45.1%). Occlusal force and occlusal force distribution area also showed an increasing trend. The Oral Health Impact Profile short form (OHIP-14) score decreased from 7 points at initial examination to 0 points after prosthodontic treatment. Appropriate diagnosis and treatment planning contributed to the increased occlusal force and balanced occlusal force distribution. Therefore, the present case indicates the potential of monolithic zirconia crowns to achieve both esthetic and stable functional outcomes.展开更多
Ni-Al_(2)O_(3)cermet supported tubular SOFC was fabricated by thermal spraying.Flame-sprayed Al_(2)O_(3)-Ni cermet coating plays dual roles of a support tube and an anode current collector.4.5mol.%yttria-stabilized zi...Ni-Al_(2)O_(3)cermet supported tubular SOFC was fabricated by thermal spraying.Flame-sprayed Al_(2)O_(3)-Ni cermet coating plays dual roles of a support tube and an anode current collector.4.5mol.%yttria-stabilized zirconia(YSZ)and 10mol.%scandia-stabilized zirconia(ScSZ)coatings were deposited by atmospheric plasma spraying(APS)as the electrolyte in present study.The electrical conductivity of electrolyte was measured using DC method.The post treatment was employed using nitrate solution infiltration to densify APS electrolyte layer for improvement of gas permeability.The electrical conductivity of electrolyte and the performance of single cell were investigated to optimize SOFC performance.The electrical conductivity of the as-sprayed YSZ and ScSZ coating is about 0.03 and 0.07 S·cm^(-1)at 1000℃,respectively.The ohmic polarization significantly influences the performance of SOFC.The maximum output power density at 1000℃increases from 0.47 to 0.76 W·cm^(-2)as the YSZ electrolyte thickness reduces from 100μm to 40μm.Using APS ScSZ coating of about 40μm as the electrolyte,the test cell presents a maximum power output density of over 0.89 W·cm^(-2)at 1000℃.展开更多
Aim To evaluate the interactive effects of different self- adhesive resin cements and tribochemical treatment on bond strength to zirconia. Methodology The following self-adhesive resin cements for bonding two zirconi...Aim To evaluate the interactive effects of different self- adhesive resin cements and tribochemical treatment on bond strength to zirconia. Methodology The following self-adhesive resin cements for bonding two zirconia blocks were evaluated： Maxcem （MA）, Smartcem （SM）, Rely X Unicem Aplicap （UN）, Breeze （BR）, Biscem （BI）, Set （SE）, and Clearfil SA luting （CL）. The specimens were grouped according to conditioning as follows： Group 1, polishing with 600 grit polishing paper; Group 2, silica coating with 110 μm Al2O3 particles which modified with silica; and, Group 3, tribochemical treatment - silica coating ＋ silanization. Specimens were stored in distilled water at 37℃ for 24 hours before testing shear bond strength. Results Silica coating and tribochemical treatment significantly increased the bond strength of the MA, UN, BR, B1, SE and CL to zirconia compared to #600 polishing. For both #600 polished and silica coating treatments, MDP- containing self-adhesive resin cement CL had the highest bond strengths to zirconia. Conclusion Applying silica coating and tribochemical treatment improved the bond strength of self-adhesive resin cement to zirconia, especially for CL.展开更多
Despite its unique high efficiency and good environmental compatibility, the water-soluble binder system still encounters problems achieving a desired sintered part via ceramic injection molding because of the poor co...Despite its unique high efficiency and good environmental compatibility, the water-soluble binder system still encounters problems achieving a desired sintered part via ceramic injection molding because of the poor compatibility and the powder-binder segregation between ceramic powders and binders. The objective of this study was to obtain a sintered part with excellent properties by introducing a small quantity of oleic acid to the surface of zirconia powders before the mixing process. As opposed to many previous investigations that focused only on the rheological behavior and modification mechanism, the sintering behavior and densification process were systematically investigated in this study. With the modified powders, debound parts with a more homogeneous and smaller pore size distribution were fabricated. Also, a higher density and greater flexural strength were achieved in the sintered parts fabricated using the modified powders.展开更多
Zirconia-mullite-corundum composites were successfully prepared from fly ash,zircon and alumina powder by a reaction sintering process.The phase and microstructure evolutions of the composite synthesized at desired te...Zirconia-mullite-corundum composites were successfully prepared from fly ash,zircon and alumina powder by a reaction sintering process.The phase and microstructure evolutions of the composite synthesized at desired temperatures of 1 400,1 500 and 1 600°C for 4 h were characterized by X-ray diffractometry and scanning electronic microscopy,respectively.The influences of sintering temperature on shrinkage ratio,apparent porosity and bulk density of the synthesized composite were investigated.The formation process of the composites was discussed in detail.The results show that the zirconia-mullite-corundum composites with good sintering properties can be prepared at 1 600°C for 4 h.Zirconia particles can be homogeneously distributed in mullite matrix,and the zirconia particles are around 5μm.The formation process of zirconia-mullite-corundum composites consists of decomposition of zircon and mullitization process.展开更多
To overcome the photochemical activity of rutile used as a pigment and improve its durability in application, hydrous zirconia-coated TiO2 was prepared by the precipitation method. High-resolution transmission electro...To overcome the photochemical activity of rutile used as a pigment and improve its durability in application, hydrous zirconia-coated TiO2 was prepared by the precipitation method. High-resolution transmission electron microscope （HRTEM） and X-ray photoelectron spectroscopy （XPS） were used to characterize the morphology and surface structure of hydrous zirconia-coated TiO2. The ζ-potential and ultraviolet （UV） absorption of both coated and uncoated rutile were examined. The results show that hydrous zirconia can not only improve the durability but also raise the lightness. A suitable ZrO2 content of hydrous zirconia-coated TiO2 is about 1.0wt%, and a dense film on the surface of rutile can be formed with better pigmentary properties. Based on the thermodynamic analysis, the zirconia-coating process and the film growth mechanism were discussed.展开更多
An efficient ZrO2-doped Cu/SiO2 catalyst was fabricated through hydrolysis precipitation method(HP)and used to produce ethylene glycol(EG)through dimethyl oxalate(DMO)hydrogenation.The states for zirconia on copper ca...An efficient ZrO2-doped Cu/SiO2 catalyst was fabricated through hydrolysis precipitation method(HP)and used to produce ethylene glycol(EG)through dimethyl oxalate(DMO)hydrogenation.The states for zirconia on copper catalyst and roles in DMO hydrogenation were investigated through various characterization tools,including N2 physical adsorption,XRD,H2-TPR,Methyl glycolate-TPD-MS,XPS,XAES as well.Compared with common ammonia evaporation and co-precipitation methods used in catalyst preparation,this HP method is found to effectively suppress the agglomeration and further size growth of copper nanoparticles by enhancing the interactions between copper and zirconia species.More importantly,uniform distribution of ZrO2 dopant is achieved due to the pseudo-homogeneous reactions in the mixing step of catalyst preparation.A proper amount of zirconium dopant helps achieve the desirable proportion of Cu+/(Cu++CuO)for surface copper species,especially promotes the production of Cu+species originated from Cu-ZrO2 species at the interface of copper and zirconia particles.In comparison with Cu+species formed from copper phyllosilicates reduction,the Cu+sites derived from Cu-ZrO2 species show higher adsorption ability of MG,an important intermediate species in ethylene glycol production.These adsorbed MG molecules further react with atomic hydrogen shifted from adjacent metallic copper surface,leading to a higher catalytic behavior.For the EG production via DMO hydrogenation,the turnover frequency(TOF)normalized by CuO species on CuZr/SiO2 catalyst is 1.8 times than that of traditional Cu/SiO2 counterpart.Due to the enhanced synergy effect between Cu+and Cuo active sites,a lower activation energy of ester hydrogenation on this ZrO2-doped Cu/SiO2 catalyst is believed to be responsible for the significant improvement.展开更多
The influences of adding sodium to zirconia on the acid-base properties of the surface and on the catalytic conversion of ethanol and acetone were investigated. The rates of ethanol dehydration, dehydrogenation and co...The influences of adding sodium to zirconia on the acid-base properties of the surface and on the catalytic conversion of ethanol and acetone were investigated. The rates of ethanol dehydration, dehydrogenation and coupling were evaluated in a fixed-bed flow reactor operating at temperatures from 613 to 673 K. The rate of acetone condensation was evaluated in the same reactor operating at 473-573 K. Addition of 1.0 wt% Na to ZrO2 decreased the rate of ethanol dehydration by more than an order of magnitude, which was consistent with a neutralization of acid sites evaluated by ammonia adsorption microcalorimetry. Addition of 1.0 wt% Na to ZrO2 also increased the base site density quantified by carbon dioxide adsorption microcalorimetry and the rate of acetone condensation. Although the rate of ethanol coupling was not increased by the addition of Na, the overall selectivity of ethanol to butanol was improved over the 1.0 wt% Na/ZrO2 sample because of the significant inhibition of ethanol dehydration.展开更多
In order to investigate the effect of piles on tooth restoration and their service life, micro-computed tomography （CT） was used to scan the first maxillary canines by establishing a three-dimensional finite element...In order to investigate the effect of piles on tooth restoration and their service life, micro-computed tomography （CT） was used to scan the first maxillary canines by establishing a three-dimensional finite element model for pile restoration. The stress distributions after tooth restoration with different pile materials were analyzed using a 100 N bite force. Then, the S-N fatigue characteristic curve of zirconia material was obtained using experimental data. The fe-safe fatigue analysis software was used to study the service life of zirconia piles in teeth. The static analysis results demonstrate that when fiber piles are used to repair, the stress from the dentin neck is larger than that by zirconia piles, but the stress from the apical of the dentin is smaller than that by zirconia piles. Besides, the stress exerted by fiber piles is lower than that by zirconia piles. Furthermore, the fatigue analysis results indicate that under normal conditions, zirconia piles can be used in teeth for over 20 years. Compared with fiber piles, zirconia piles have a better effect on the repair of tooth defects.展开更多
As for ceramic stereolithography technique,the preparation of suitable resin-based ceramic slurry is of primary importance.In this study,the effects of powder characteristics such as specific surface area,particle siz...As for ceramic stereolithography technique,the preparation of suitable resin-based ceramic slurry is of primary importance.In this study,the effects of powder characteristics such as specific surface area,particle size and distribution,particle morphology on the rheological behavior of zirconia resin-based suspensions were investigated intensively.Results show that the specific surface area of the powder is the most important factor affecting slurry viscosity.Choosing low specific surface area and quasi-spherical shaped powder is more likely to obtain low viscosity slurries.In addition,the influence of solid loading on the flow behavior were also studied using Krieger-Dougherty model.Zirconia samples with the relative density of(97.83±0.33)%were obtained after sintering at 1550℃.No obvious abnormal grain growth in the microstructure of the sintered body is observed.Results indicate that after the optimization of the processing parameters with the help of rheology characterization,complex-shaped high-quality zirconia parts can be obtained using the stereolithography technique.展开更多
C1 chemistry based on synthesis gas, methane, and carbon dioxide offers many routes to industrial chemicals. The reactions related to the synthesis of gas can be classified into direct and indirect approach for making...C1 chemistry based on synthesis gas, methane, and carbon dioxide offers many routes to industrial chemicals. The reactions related to the synthesis of gas can be classified into direct and indirect approach for making such products, such as acetic acid, dimethyl ether, and alcohol. Catalytic syngas processing is currently done at high temperatures and pressures, conditions that could be unfavorable for the life of the catalyst. Another issue of C1 chemistry is related to the methane-initiated process. It has been known that direct methane conversions are still suffering from low yields and selectivity of products resulting in unprofitable ways to produce products, such as higher hydrocarbons, methanol, and so on. However, many experts and researchers are still trying to find the best method to overcome these barriers, for example, by finding the best catalyst to reduce the high-energy barrier of the reactions and conduct only selective catalyst-surface reactions. The appli- cation of Yttria-Stabilized Zirconia （YSZ） and its combination with other metals for catalyzing purposes are increasing. The existence of an interesting site that acts as oxygen store could be the main reason for it. Moreover, formation of intermediate species on the surface of YSZ also contributes significantly in increasing the production of some specific products. Understanding the phenomena happening inside could be necessary. In this article, the use of YSZ for some C1 chemistry reactions was discussed and reviewed.展开更多
A mesoporous sulfated zirconia-silica catalyst bearing only Br？nsted acid sites converted glycerol to acrolein in 81%yield with 82% selectivity.Space time yield as high as 9.0 mmol h^（-1） g_（cat）^（-1） was achie...A mesoporous sulfated zirconia-silica catalyst bearing only Br？nsted acid sites converted glycerol to acrolein in 81%yield with 82% selectivity.Space time yield as high as 9.0 mmol h^（-1） g_（cat）^（-1） was achieved even at a low reaction temperature of 523 K.The catalytic activity and selectivity were higher than those of typical sulfated zirconia.It is proposed that the milder acidity due to dilution of zirconium species by silica and large pore size for faster diffusion contributed towards the better catalytic performance.展开更多
Mesoporous tetragonal sulfated zirconia with high surface area and narrow pore-size distribution was prepared using Zr（O-nPr）4 as zirconium precursor, sulfuric acid as sulfur source and triblock copolymer poly（ethy...Mesoporous tetragonal sulfated zirconia with high surface area and narrow pore-size distribution was prepared using Zr（O-nPr）4 as zirconium precursor, sulfuric acid as sulfur source and triblock copolymer poly（ethylene glycol）-poly（propylene glycol）- poly（ethylene glycol） （P123） as the template. The samples were characterized by X-ray diffraction, N2 sorption, TEM, and NH3- TPD. A phase transformation from monoclinic sulfated zirconia to tetragonal sulfated zirconia is observed. The product shows strong acidity.C2009 Bin Yue. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.展开更多
A novel method to prepare mesoporous nano-zirconia was developed. Thesynthesis was carried out in the presence of PEO surfactants via a solid-state reaction. Thematerials exhibit a strong diffraction peak at low 2θ a...A novel method to prepare mesoporous nano-zirconia was developed. Thesynthesis was carried out in the presence of PEO surfactants via a solid-state reaction. Thematerials exhibit a strong diffraction peak at low 2θ angle and their nitrogenadsorption/desorption isotherms are typical of type IV with H1 hysteresis loops. The pore structureimaged by TEM can be described as wormhole domains. The tetragonal zirconia nanocrystals are uniformin size (around 1.5 nm) and their mesopores focus on around 4.6 nm. The zirconia nanocrystal growthis tentatively postulated to be the result of an aggregation mechanism. This study also revealsthat the PEO surfactants can interact with the Zr-O-Zr framework to reinforce the thermal stabilityof zirconia. The ratio of NaOH to ZrOCl_2, crystallization and calcination temperature play animportant role in the synthesis of mesoporous nano-zirconia.展开更多
Mesoporous zirconia was synthesized by a new and simple method. Zirconium n-propoxide was used as the zirconium source. A small, inexpensive nonsurfactant, triethanolamine, was used as the template. The template was r...Mesoporous zirconia was synthesized by a new and simple method. Zirconium n-propoxide was used as the zirconium source. A small, inexpensive nonsurfactant, triethanolamine, was used as the template. The template was removed by thermal treatment in air and supercritical fluid extraction using CO2. The structure of the resulting materials was characterized by X-ray diffraction, transmission electron microscopy, and N2 adsorption-desorption analyses. The materials are found to have narrowly distributed average pore diameters and wormhole-like pore channels. However, higher surface area and larger pore volume are exhibited after supercritical fluid extraction with CO2. The removal of the template by thermal treatment also leads to condensation and mild shrinkage of the zirconia framework.展开更多
文摘Zirconia ceramics have become increasingly widely used in recent years and are favored by relevant enterprises. From the traditional dental field to aerospace, parts manufacturing has been used, but there is limited research on the deformation and damage process of zirconia ceramics. This article analyzes the acoustic emission characteristics of each stage of ceramic damage from the perspective of acoustic emission, and explores its deformation process characteristics from multiple perspectives such as time domain, frequency, and EWT modal analysis. It is concluded that zirconia ceramics exhibit higher brittleness and acoustic emission strength than alumina ceramics, and when approaching the fracture, it tends to generate lower frequency acoustic emission signals.
基金the National Key Research and Development Program of China(No.2021YFA0715700)the National Natural Science Foundation of China(Nos.51521001 and 51832003)the 111 Project(No.B18038)。
文摘Inspired by structures of natural shells,zirconia-carbon nanocomposites were obtained by using natural chitin from shrimp shells as templates via the sol-gel route in this study.Chitin was dispersed in the water and chelated with the zirconia precursors by amidogen.After a heat treatment for carbonization,nacre-like structures of carbon-zirconia nanocomposites were successfully synthesized.Due to the toughening mechanism of tetragonal zirconia,the mechanical properties of carbon-zirconia composites are further improved.The as-received zirconia/carbon nanocomposite with best mechanical property has a hardness of 5.88GPa and an elastic modulus of 80.6 GPa,which is even stronger than natural shells.This work might facilitate a versatile platform for developing green nanocomposites with reasonably good mechanical properties.
基金the Creative Research Groups of National Natural Science Foundation of China(Grant No.51921006)National Natural Science Foundation of China(Grant No.52322803)。
文摘Zirconia has been extensively used in aerospace,military,biomedical and industrial fields due to its unusual combination of high mechanical,electrical and thermal properties.However,the fundamental and critical phase transition process of zirconia has not been well studied because of its difficult first-order phase transition with formidable energy barrier.Here,we generated a machine learning interatomic potential with ab initio accuracy to discover the mechanism behind all kinds of phase transition of zirconia at ambient pressure.The machine learning potential precisely characterized atomic interactions among all zirconia allotropes and liquid zirconia in a wide temperature range.We realized the challenging reversible first-order monoclinic-tetragonal and cubicliquid phase transition processes with enhanced sampling techniques.From the thermodynamic information,we gave a better understanding of the thermal hysteresis phenomenon in martensitic monoclinic-tetragonal transition.The phase diagram of zirconia from our machine learning potential based molecular dynamics simulations corresponded well with experimental results.
基金Funded by the National Key Research and Development Plan of China(No.2021YFB3701401)the National Natural Science Foundation of China(Nos.92163208,51902233,51972243,51521001,and 51832003)。
文摘The sintering behavior and mechanical properties of zirconia doped with 2.0mol%-3.0mol%Y_(2)O_(3)were studied by pressure-less sintering.The experimental results show that the densification temperature of zirconia ceramics increases gradually with the decrease of Y_(2)O_(3)doping content by which decreases the sintering driving force due to the lower oxygen vacancy concentration of the systems.Furthermore,the bending strength and fracture toughness of the prepared zirconia ceramics increase with the decrease of Y_(2)O_(3)doping content.It can be attributed to the fact that the phase stability of tetragonal zirconia decreases with the decrease of Y_(2)O_(3)doping content,which is easier to induce"phase transformation toughening"and dissipate impact energy.The relative density,bending strength and fracture toughness of 2.0 mol%Y_(2)O_(3)doped zirconia ceramics(2.0Y-ZrO_(2))sintered at 1525℃are 99.00%,1256.65±20.82 MPa and 9.85±0.13 MPa·m^(1/2),respectively.
文摘In order to investigate the effect of zirconia corundum on the preparation of chrome corundum castables,samples were prepared using tabular corundum,white fused corundum,active alumina micropowder,chromium oxide micropowder and fused ziconia corundum particles as the main raw materials,and pure calcium aluminate cement as the binder.The effects of the fused zirconia corundum particles addition(1-0.5 mm,0,4.5%,9%,and 18%,by mass)on the linear change rate,the apparent porosity,the cold modulus of rupture,and the thermal shock resistance of chrome corundum castables were studied,and the microstructure of the samples was analyzed.The results show that:(1)with the zirconia corundum addition increasing,the permanent linear change on heating of the samples gradually increases,the apparent porosity gradually increases,the cold modulus of rupture gradually decreases,and the thermal shock resistance gradually increases;(2)according to SEM,it can be found that the phase transformation of ZrO2 after heat treatment leads to a large number of microcracks in the material.On one hand,the cold modulus of rupture of the material is reduced;on the other hand,the thermal shock resistance of the material is improved.
文摘Advances in metal-free materials and the popularization of Computer-Aided Design and Manufacturing (CAD/CAM) have led to the wide clinical use of all-ceramic crowns for esthetic restorations. A 72-year-old woman presented to our hospital with unesthetic restorations on the right upper and lower posterior teeth. Intraoral examination revealed poorly fitting metal crown margins. Defective prostheses were removed, and provisional restorations were provided to stabilize the mandibular position. Optical impressions and the maxillomandibular relationship were recorded using an intraoral scanner, and monolithic zirconia crowns were fabricated using CAD/CAM technology for complete veneer crown restorative treatment. Occlusal examination revealed an improvement in occlusal force distribution at initial examination (right side: 33.5%, left side: 66.5%) after placement of the zirconia crowns (right side: 54.9%, left side: 45.1%). Occlusal force and occlusal force distribution area also showed an increasing trend. The Oral Health Impact Profile short form (OHIP-14) score decreased from 7 points at initial examination to 0 points after prosthodontic treatment. Appropriate diagnosis and treatment planning contributed to the increased occlusal force and balanced occlusal force distribution. Therefore, the present case indicates the potential of monolithic zirconia crowns to achieve both esthetic and stable functional outcomes.
基金The present project was supported by Foundation of China Education Ministry for Talented Young ScholarEducation Promotion ProjectDoctoral Thesis Foundation of Xi'an Jiaotong University.
文摘Ni-Al_(2)O_(3)cermet supported tubular SOFC was fabricated by thermal spraying.Flame-sprayed Al_(2)O_(3)-Ni cermet coating plays dual roles of a support tube and an anode current collector.4.5mol.%yttria-stabilized zirconia(YSZ)and 10mol.%scandia-stabilized zirconia(ScSZ)coatings were deposited by atmospheric plasma spraying(APS)as the electrolyte in present study.The electrical conductivity of electrolyte was measured using DC method.The post treatment was employed using nitrate solution infiltration to densify APS electrolyte layer for improvement of gas permeability.The electrical conductivity of electrolyte and the performance of single cell were investigated to optimize SOFC performance.The electrical conductivity of the as-sprayed YSZ and ScSZ coating is about 0.03 and 0.07 S·cm^(-1)at 1000℃,respectively.The ohmic polarization significantly influences the performance of SOFC.The maximum output power density at 1000℃increases from 0.47 to 0.76 W·cm^(-2)as the YSZ electrolyte thickness reduces from 100μm to 40μm.Using APS ScSZ coating of about 40μm as the electrolyte,the test cell presents a maximum power output density of over 0.89 W·cm^(-2)at 1000℃.
文摘Aim To evaluate the interactive effects of different self- adhesive resin cements and tribochemical treatment on bond strength to zirconia. Methodology The following self-adhesive resin cements for bonding two zirconia blocks were evaluated： Maxcem （MA）, Smartcem （SM）, Rely X Unicem Aplicap （UN）, Breeze （BR）, Biscem （BI）, Set （SE）, and Clearfil SA luting （CL）. The specimens were grouped according to conditioning as follows： Group 1, polishing with 600 grit polishing paper; Group 2, silica coating with 110 μm Al2O3 particles which modified with silica; and, Group 3, tribochemical treatment - silica coating ＋ silanization. Specimens were stored in distilled water at 37℃ for 24 hours before testing shear bond strength. Results Silica coating and tribochemical treatment significantly increased the bond strength of the MA, UN, BR, B1, SE and CL to zirconia compared to #600 polishing. For both #600 polished and silica coating treatments, MDP- containing self-adhesive resin cement CL had the highest bond strengths to zirconia. Conclusion Applying silica coating and tribochemical treatment improved the bond strength of self-adhesive resin cement to zirconia, especially for CL.
基金financially supported by the National Natural Science Foundation of China (Nos. 51572035 and 51502041)
文摘Despite its unique high efficiency and good environmental compatibility, the water-soluble binder system still encounters problems achieving a desired sintered part via ceramic injection molding because of the poor compatibility and the powder-binder segregation between ceramic powders and binders. The objective of this study was to obtain a sintered part with excellent properties by introducing a small quantity of oleic acid to the surface of zirconia powders before the mixing process. As opposed to many previous investigations that focused only on the rheological behavior and modification mechanism, the sintering behavior and densification process were systematically investigated in this study. With the modified powders, debound parts with a more homogeneous and smaller pore size distribution were fabricated. Also, a higher density and greater flexural strength were achieved in the sintered parts fabricated using the modified powders.
基金Project(N100302002)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(20100471467)supported by the China Postdoctoral Science Foundation
文摘Zirconia-mullite-corundum composites were successfully prepared from fly ash,zircon and alumina powder by a reaction sintering process.The phase and microstructure evolutions of the composite synthesized at desired temperatures of 1 400,1 500 and 1 600°C for 4 h were characterized by X-ray diffractometry and scanning electronic microscopy,respectively.The influences of sintering temperature on shrinkage ratio,apparent porosity and bulk density of the synthesized composite were investigated.The formation process of the composites was discussed in detail.The results show that the zirconia-mullite-corundum composites with good sintering properties can be prepared at 1 600°C for 4 h.Zirconia particles can be homogeneously distributed in mullite matrix,and the zirconia particles are around 5μm.The formation process of zirconia-mullite-corundum composites consists of decomposition of zircon and mullitization process.
基金supported by the National Key Technologies R&D Program of China (No.2006BAC02A05)the Major State Ba-sic Research and Development Program of China (No.2007CB613501)the Knowledge Innovation Program of the Chinese Academy of Sciences (No.KGCX2-YW-214)
文摘To overcome the photochemical activity of rutile used as a pigment and improve its durability in application, hydrous zirconia-coated TiO2 was prepared by the precipitation method. High-resolution transmission electron microscope （HRTEM） and X-ray photoelectron spectroscopy （XPS） were used to characterize the morphology and surface structure of hydrous zirconia-coated TiO2. The ζ-potential and ultraviolet （UV） absorption of both coated and uncoated rutile were examined. The results show that hydrous zirconia can not only improve the durability but also raise the lightness. A suitable ZrO2 content of hydrous zirconia-coated TiO2 is about 1.0wt%, and a dense film on the surface of rutile can be formed with better pigmentary properties. Based on the thermodynamic analysis, the zirconia-coating process and the film growth mechanism were discussed.
基金financial support from the National Natural Science Foundation of China(21878227,U1510203)。
文摘An efficient ZrO2-doped Cu/SiO2 catalyst was fabricated through hydrolysis precipitation method(HP)and used to produce ethylene glycol(EG)through dimethyl oxalate(DMO)hydrogenation.The states for zirconia on copper catalyst and roles in DMO hydrogenation were investigated through various characterization tools,including N2 physical adsorption,XRD,H2-TPR,Methyl glycolate-TPD-MS,XPS,XAES as well.Compared with common ammonia evaporation and co-precipitation methods used in catalyst preparation,this HP method is found to effectively suppress the agglomeration and further size growth of copper nanoparticles by enhancing the interactions between copper and zirconia species.More importantly,uniform distribution of ZrO2 dopant is achieved due to the pseudo-homogeneous reactions in the mixing step of catalyst preparation.A proper amount of zirconium dopant helps achieve the desirable proportion of Cu+/(Cu++CuO)for surface copper species,especially promotes the production of Cu+species originated from Cu-ZrO2 species at the interface of copper and zirconia particles.In comparison with Cu+species formed from copper phyllosilicates reduction,the Cu+sites derived from Cu-ZrO2 species show higher adsorption ability of MG,an important intermediate species in ethylene glycol production.These adsorbed MG molecules further react with atomic hydrogen shifted from adjacent metallic copper surface,leading to a higher catalytic behavior.For the EG production via DMO hydrogenation,the turnover frequency(TOF)normalized by CuO species on CuZr/SiO2 catalyst is 1.8 times than that of traditional Cu/SiO2 counterpart.Due to the enhanced synergy effect between Cu+and Cuo active sites,a lower activation energy of ester hydrogenation on this ZrO2-doped Cu/SiO2 catalyst is believed to be responsible for the significant improvement.
基金the Chemical Sciences,Geosciences and Biosciences Division,Office of Basic Energy Sciences,Office of Science,U.S.Department of Energy,grant no.DEFG0295ER14549
文摘The influences of adding sodium to zirconia on the acid-base properties of the surface and on the catalytic conversion of ethanol and acetone were investigated. The rates of ethanol dehydration, dehydrogenation and coupling were evaluated in a fixed-bed flow reactor operating at temperatures from 613 to 673 K. The rate of acetone condensation was evaluated in the same reactor operating at 473-573 K. Addition of 1.0 wt% Na to ZrO2 decreased the rate of ethanol dehydration by more than an order of magnitude, which was consistent with a neutralization of acid sites evaluated by ammonia adsorption microcalorimetry. Addition of 1.0 wt% Na to ZrO2 also increased the base site density quantified by carbon dioxide adsorption microcalorimetry and the rate of acetone condensation. Although the rate of ethanol coupling was not increased by the addition of Na, the overall selectivity of ethanol to butanol was improved over the 1.0 wt% Na/ZrO2 sample because of the significant inhibition of ethanol dehydration.
基金The National Numerical Control Equipment Major Projects(No.2013ZX09008011)
文摘In order to investigate the effect of piles on tooth restoration and their service life, micro-computed tomography （CT） was used to scan the first maxillary canines by establishing a three-dimensional finite element model for pile restoration. The stress distributions after tooth restoration with different pile materials were analyzed using a 100 N bite force. Then, the S-N fatigue characteristic curve of zirconia material was obtained using experimental data. The fe-safe fatigue analysis software was used to study the service life of zirconia piles in teeth. The static analysis results demonstrate that when fiber piles are used to repair, the stress from the dentin neck is larger than that by zirconia piles, but the stress from the apical of the dentin is smaller than that by zirconia piles. Besides, the stress exerted by fiber piles is lower than that by zirconia piles. Furthermore, the fatigue analysis results indicate that under normal conditions, zirconia piles can be used in teeth for over 20 years. Compared with fiber piles, zirconia piles have a better effect on the repair of tooth defects.
基金National Key Research and Development Program of China(2017YFB0310400)National Natural Science Foundation of China(51572277,51702340)+1 种基金Shanghai Sailing Program(17YF1428800)Natural Science Foundation of Shanghai(17ZR1434800)。
文摘As for ceramic stereolithography technique,the preparation of suitable resin-based ceramic slurry is of primary importance.In this study,the effects of powder characteristics such as specific surface area,particle size and distribution,particle morphology on the rheological behavior of zirconia resin-based suspensions were investigated intensively.Results show that the specific surface area of the powder is the most important factor affecting slurry viscosity.Choosing low specific surface area and quasi-spherical shaped powder is more likely to obtain low viscosity slurries.In addition,the influence of solid loading on the flow behavior were also studied using Krieger-Dougherty model.Zirconia samples with the relative density of(97.83±0.33)%were obtained after sintering at 1550℃.No obvious abnormal grain growth in the microstructure of the sintered body is observed.Results indicate that after the optimization of the processing parameters with the help of rheology characterization,complex-shaped high-quality zirconia parts can be obtained using the stereolithography technique.
基金Project supported by the Global R&D Program of the Korea Foundation for International Cooperation of Science and Technology (KICOS)
文摘C1 chemistry based on synthesis gas, methane, and carbon dioxide offers many routes to industrial chemicals. The reactions related to the synthesis of gas can be classified into direct and indirect approach for making such products, such as acetic acid, dimethyl ether, and alcohol. Catalytic syngas processing is currently done at high temperatures and pressures, conditions that could be unfavorable for the life of the catalyst. Another issue of C1 chemistry is related to the methane-initiated process. It has been known that direct methane conversions are still suffering from low yields and selectivity of products resulting in unprofitable ways to produce products, such as higher hydrocarbons, methanol, and so on. However, many experts and researchers are still trying to find the best method to overcome these barriers, for example, by finding the best catalyst to reduce the high-energy barrier of the reactions and conduct only selective catalyst-surface reactions. The appli- cation of Yttria-Stabilized Zirconia （YSZ） and its combination with other metals for catalyzing purposes are increasing. The existence of an interesting site that acts as oxygen store could be the main reason for it. Moreover, formation of intermediate species on the surface of YSZ also contributes significantly in increasing the production of some specific products. Understanding the phenomena happening inside could be necessary. In this article, the use of YSZ for some C1 chemistry reactions was discussed and reviewed.
基金supported by Grant-in-Aid for Research Activity Start-up(KAKENHI,21860004)for Young Scientists(KAKENHI,26709060) from Japan Society for the Promotion of Science(JSPS)
文摘A mesoporous sulfated zirconia-silica catalyst bearing only Br？nsted acid sites converted glycerol to acrolein in 81%yield with 82% selectivity.Space time yield as high as 9.0 mmol h^（-1） g_（cat）^（-1） was achieved even at a low reaction temperature of 523 K.The catalytic activity and selectivity were higher than those of typical sulfated zirconia.It is proposed that the milder acidity due to dilution of zirconium species by silica and large pore size for faster diffusion contributed towards the better catalytic performance.
基金supported by the National Basic Research Program of China(No.2009CB623506)the National Science Foundation of China(Nos.20633030,20721063 and 20873027),STCSM(Nos.08DZ2270500 and075211013)Shanghai Leading Academic Discipline Project(No.B108).
文摘Mesoporous tetragonal sulfated zirconia with high surface area and narrow pore-size distribution was prepared using Zr（O-nPr）4 as zirconium precursor, sulfuric acid as sulfur source and triblock copolymer poly（ethylene glycol）-poly（propylene glycol）- poly（ethylene glycol） （P123） as the template. The samples were characterized by X-ray diffraction, N2 sorption, TEM, and NH3- TPD. A phase transformation from monoclinic sulfated zirconia to tetragonal sulfated zirconia is observed. The product shows strong acidity.C2009 Bin Yue. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
文摘A novel method to prepare mesoporous nano-zirconia was developed. Thesynthesis was carried out in the presence of PEO surfactants via a solid-state reaction. Thematerials exhibit a strong diffraction peak at low 2θ angle and their nitrogenadsorption/desorption isotherms are typical of type IV with H1 hysteresis loops. The pore structureimaged by TEM can be described as wormhole domains. The tetragonal zirconia nanocrystals are uniformin size (around 1.5 nm) and their mesopores focus on around 4.6 nm. The zirconia nanocrystal growthis tentatively postulated to be the result of an aggregation mechanism. This study also revealsthat the PEO surfactants can interact with the Zr-O-Zr framework to reinforce the thermal stabilityof zirconia. The ratio of NaOH to ZrOCl_2, crystallization and calcination temperature play animportant role in the synthesis of mesoporous nano-zirconia.
基金Supported by the Natural Science Foundation of Ningxia ProvinceInnovation Team Projects in Ningxia Teachers University
文摘Mesoporous zirconia was synthesized by a new and simple method. Zirconium n-propoxide was used as the zirconium source. A small, inexpensive nonsurfactant, triethanolamine, was used as the template. The template was removed by thermal treatment in air and supercritical fluid extraction using CO2. The structure of the resulting materials was characterized by X-ray diffraction, transmission electron microscopy, and N2 adsorption-desorption analyses. The materials are found to have narrowly distributed average pore diameters and wormhole-like pore channels. However, higher surface area and larger pore volume are exhibited after supercritical fluid extraction with CO2. The removal of the template by thermal treatment also leads to condensation and mild shrinkage of the zirconia framework.
