Solvent effect on microstructure of yttria-stabilized zirconia (YSZ) particles in solvothermal synthesis

Using methanol or methanol/2-propanol mixtures as reaction media, yttria-stabilized zirconia (YSZ) particles were synthesized with a solvothermal route. The particles were characterized with X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), laser diffraction technique, and nitrogen adsorption isotherms. Results indicated that cubic/tetragonal YSZ nanocrystals with crystal size lower than 5 nm were obtained and the crystal size depends on solvent composition, reaction temperature and reaction time. For the same reaction temperature and reaction time, the solvent composition also controls YSZ crystal agglomeration behaviour. According to the DLVO theory and analysis of experimental results, the solvent effect on microstructures of YSZ particles in solvothermal synthesis has been discussed. In addition, the mechanism of particle microstructure evolution during solvothermal synthesis has been suggested.     

Effect of DC and AC electric fields on crack healing behavior in 8 mol% yttria-stabilized cubic zirconia polycrystal

The effect of the flash event (FE) on microcrack healing behavior in 8 mol% yttria-stabilized zirconia was examined at healing temperatures of 1040 and 1230°C under the direct and alternating (DC and AC) electric fields. The crack healing behavior changed depending on the factors of the electric field, healing temperature, and crack length. Although the crack healing proceeded with the temperature, the healing rate increased with the crack length, suggesting that the external energy stored as crack surface energy would provide a driving force for the crack healing. Although the crack healing occurs even under the static annealing without the electric field, the healing rate was accelerated by FE significantly more under the AC field than under the DC field. The microcracks with a length of ≈20 μm were fully healed at 1230°C only for 10 min by the FE treatment under the AC field, and the flash healing behavior was four times faster than that of the static annealing. These results suggest that the enhanced healing behavior cannot be explained only by thermal effects, and the accelerated diffusivity caused additionally by nonthermal effect under FE might contribute to the enhanced healing behavior, especially in the AC electric field.     

On the role of the pore morphology on the electrical conductivity of porous yttria-stabilized zirconia

Yttria Stabilized Zirconia ceramics with well-controlled porosity, pore size and shape were prepared using well-calibrated poly-methyl-methacrylate (PMMA) micro-beads (MB) as a pore-forming agent. The microstructure was observed by Scanning Electron Microscopy. Impedance spectroscopy was used to evaluate the effect of pore morphology (pore size, pore size distribution, pore shape and interconnectivity) on the electrical properties of YSZ ceramics. Archie's law based analyzes to express the dependence of conductivity on porosity have shown that Archie's law is independent of pore size for a pore diameter of between 1 and 7 μm. The Bruggeman model could be used to predict the bulk conductivity if the porosity was less than 25%, thus showing that the impedance response included the effect of sinuousness and constriction induced by pores. Therefore, the tortuosity factor calculated from the bulk conductivity was higher than that predicted by the Bruggeman model for porosities greater than 25% and spherical pores wide (>20 μm). Another point relates to the comparison between tortuosity factors obtained for pore samples fabricated with pore-forming PMMA or by sub-sintering.     

Effects of laser surface remelting on the molten salt corrosion resistance of yttria-stabilized zirconia coatings

In the present study, atmospheric plasma-sprayed yttria-stabilized zirconia coatings were post-remelted by a continuous diode laser to improve the hot corrosion resistance for as-sprayed coatings. The coating surfaces were covered with a salt mixture (V₂O₅ and Na₂SO₄) and then subjected to a hot corrosion test at 1100?°C in air. The influence of laser parameters including power and scanning rate on the coating microstructure and corrosion resistance was investigated. Results showed that the hot corrosion resistance can be improved by producing a dense and smooth surface and reducing the coating permeability to the molten salt. The transformation of the hot corrosion mechanisms was clarified on the basis of the observed corrosion behaviors. A laser power of 1500?W and scanning rate of 9?mm/s can produce minimal surface roughness with few segmented cracks, which can provide improved performance of the hot corrosion resistance.     

Effect of waste-derived MA spinel on sintering and stabilization behavior of partially stabilized double phase zirconia

Cubic-stabilized zirconia ceramic composites have been synthesized by conventional sintering, starting from commercial m-ZrO₂, Y₂O₃, and waste-derived magnesium aluminate spinel (MA) powders. In this work, the effect of sintering temperature and MA content on stabilization and densification properties of YSZ have been duly considered. MA-free YSZ0 composite sintered at 1600°C-1700°C revealed m- and t-ZrO₂ dual-phase structure where its m-ZrO₂ was partially stabilized upon temperature rising into tetragonal phase by Y³⁺ diffusion inside zirconia structure. YSZ10-50 composites containing 10-50 wt% MA demonstrated dissimilar behavior where their m-ZrO₂ was transformed and stabilized into a cubic form by diffusion of Y³⁺, Mg⁺², and Al⁺³ inside zirconia lattice. Furthermore, densification of YSZ10-50 powder mixtures by conventional sintering at 1600°C for 2 hours resulted in fully dense compacts with micrometer-sized grains. The outcomes indicate that MA has a significant effect on m-ZrO₂ stabilization into the cubic phase structure at room temperature. In this respect, this study offers huge potentials for developing fully stabilized c-ZrO₂ ceramics that could be possibly used as industrial ceramics for structural applications of harsh chemical and thermal environmental conditions.     

粒度对硝铵类炸药静电火花感度的影响

采用喷射细化法和滴加法分别制备了3种粒度的RDX、HMX、PETN粉末。采用激光粒度分析仪和扫描电子显微镜（SEM）对样品进行了表征,并对其进行了静电火花感度实验。结果表明,随着粒度的减小,RDX、HMX、PETN 3种样品的静电火花感度均逐渐升高。从理论上分析了硝铵类炸药粒度对其静电火花感度的影响。     

Bismuth oxide-coated (La,Sr)MnO3 cathodes for intermediate temperature solid oxide fuel cells with yttria-stabilized zirconia electrolytes

Taking Y₂O₃ stabilized Bi₂O₃ (YSB) as an example, bismuth oxide-added (La,Sr)MnO₃ (LSM) is evaluated as a cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs) with 8 mol% Y₂O₃ stabilized ZrO₂ (YSZ) electrolytes. YSB was added to LSM cathodes using an impregnation method, dramatically improving the electrode performance. The interfacial polarization resistance R_p, at 700 °C for the electrode coated with 50 wt.% of YSB is 0.14 Ω cm², which is only 0.2% of the value for a pure LSM electrode. The high oxygen ionic conductivity and the catalytic activity of YSB, as well as the favorable electrode microstructure are likely reasons for the dramatic reduction of R_p. The YSB-added LSM cathodes also exhibited lower overpotential and higher exchange current density than the pure LSM cathode. Moreover, these electrodes show much lower R_p than that of parallel-fabricated LSM electrodes with samaria-doped-CeO₂ as well as other LSM-based electrodes reported in the literature, demonstrating the superiority of the of YSB as the ionic conduction component in composite LSM electrodes. The superior performance of the single cell further demonstrates that the bismuth oxide-added LSM cathode is an excellent candidate for IT-SOFCs.     

Wall effects on the velocities of a single sphere settling in a stagnant and counter-current fluid and rising in a co-current fluid

Experimental results were obtained on the steady settling of spheres in quiescent media in a range of cylindrical tubes to ascertain the wall effects over a relatively wide range of Reynolds number values. For practical considerations, the retardation effect is important when the ratio of the particle diameter to the tube diameter (λ) is higher than about 0.05. A new empirical correlation is presented which covers a Reynolds number range Re = 53-15,100 and a particle to tube diameter ratio λ < 0.88. The absolute mean deviation between the experimental data and the presented correlation was 1.9%. The well-known correlations of Newton, Munroe and Di Felice agree with the presented data reasonably well. For steady settling of spheres in a counter-current water flow, the slip velocity remains practically the same as in quiescent media. However, for rising spheres in a co-current water flow, the slip velocity decreases with increasing co-current water velocity, i.e., the wall factor decreases with increasing co-current water velocity. Consequently, the drag coefficient for rising particles in co-current water flow increases with increasing water velocity.     

高压喷涂偶联剂对氧化锆表面微观形貌及粘接效果的影响

探讨使用不同压力气体喷涂偶联剂对氧化锆表面形貌及氧化锆-树脂粘合剂粘接强度的影响。烧结、喷砂后的氧化锆瓷片,按偶联剂种类(CP;ZP)和喷涂气体压力的高低(L 0.1 MPa;H 0.3 MPa)随机分为CPL、CPH、ZPL、ZPH 4个实验组及无偶联剂处理的对照组NP(n=15)。各组处理后的氧化锆瓷片利用激光共聚焦显微镜观察5组氧化锆表面形貌并测量粗糙度,并与树脂粘合剂(SA luting)粘接并测试微剪切强度。激光共聚焦显微镜观察显示,CPL和ZPL组中氧化锆表面光滑平坦,CPH、ZPH组的氧化锆表面则保留了高低不平的微观形貌,平均粗糙度明显高于低压气体喷涂组。CPH组的微剪切粘接强度最高(24.82±7.34)MPa,其次为CPL组(17.93±1.53)MPa、ZPL组(15.67±3.39)MPa和ZPH组(9.59±5.97)MPa,对照组最低(8.77±3.12)MPa。偶联剂喷涂压力显著影响氧化锆-树脂粘合剂的粘接强度。,,     

基于感应式静电传感器的流化床中颗粒循环时间的测量

引言流化床在石油加工、结晶硅生产、烯烃气相聚合、矿物的热解与焙烧等工业生产过程中有着广泛的应用。在流化床中,颗粒的循环时间是描述流化质量的重要参数,其对气固两相之间的热量和质量传递速率有着重要影响[1]。目前,流化床内颗粒循环时间的检测可以采用示踪技术、高速摄影CCD技术、光导纤维和激光多普勒仪等方法[2-4],但这     

Effect of monolithic zirconia on the degree of conversion of two resin cements analyzed by FT-IR/ATR spectroscopy

Objective: This study aimed to evaluate the degree of conversion (DC) of two different resin cements polymerized under the monolithic zirconia specimens in different thicknesses and colors.

Material and methods: Partially stabilized monolithic zirconia blocks (inCoris TZI) were cut into three different thicknesses (0.5, 1.0, and 2.0 mm) and the specimens were divided into four color groups (A1, A2, A3, and A4). The light transmittance of each specimen was measured. Panavia F 2.0 or Variolink N resin cement was applied into teflon mold and irradiated using the light emitting diode curing unit for 20 s under monolithic zirconia specimen (n = 10). The resin cement specimens were stored at room temperature under dry conditions. The DC of each specimen was measured by Fourier transform infrared-attenuated total reflection (FT-IR/ATR) spectroscopy after the 1st and 10th day. Data were analyzed with two-way analysis of variance (ANOVA), two-way repeated measures ANOVA, three-way repeated measures ANOVA, and the Tukey least significant difference (LSD) tests (α = 0.05).

Results: The light-cure resin cement groups showed higher DC than the dual-cure resin cement groups (p < 0.05). The DC of both resin cements reduced with an increase in the thickness and darkening of the color of monolithic zirconia specimens. There was a statistically meaningful increase in the 10th-day values for dual-cure resin cement (p < 0.05), whereas there were no significant differences between the 1st- and 10th-day values for light-cure resin cement (p > 0.05).

Conclusion: The use of light-cure resin cement can be suggested for the luting of monolithic zirconia restorations.     

Testing the application of Free Flapping Foils (FFF) as a method to improve adhesion in an electrostatic wall-climbing robot

In this paper, extensive testing on an electrostatic wall-climbing robot is carried out to examine the electrostatic adhesion force when using the Free Flapping Foils (FFF) method. This method is successfully applied to an electrostatic robot to enable it to stick more firmly, by about three times, on walls with different materials, including wood, plaster, granite, glass and climb wall with a continuous movement. The innovation in this paper is that successful tests were carried out, when using thin flexible electrodes made from aluminium foil and free movement of those electrodes. The FFF electrodes are flexible enough to get the shape and roughness of the wall and increases the contact surface. Thus, they increase the adhesion force and would also improve performance of the robot in rough surfaces. The experimental parameters including charging voltage, charging time, number of electrodes, area of electrodes, wall material (permittivity) and surface finishing of wall that affect the electrostatic carrying force were investigated. The robot could cross obstacles with different heights. The final robot was 1.27?Kg and able to convey 14?N extra load when sticking and climbing vertical walls.     

The role of platinum oxide in the electrode system Pt(O2)/yttria-stabilized zirconia

The existence and role of platinum oxide in the solid state electrode system Pt(O₂)/yttria-stabilized zirconia is discussed. Covering and porous model-type Pt film electrodes on YSZ single crystals are investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and in situ scanning photoelectron microscopy. The formation of Pt oxide and its amount strongly depend on the experimental conditions, such as temperature, oxygen partial pressure, and oxygen flux towards the electrode during anodic polarization. Electrode activation and deactivation processes can be explained by formation and decomposition of Pt oxide, which is reducing or inhibiting the oxygen exchange rate.     

Ca2+对序批式生物反应器活性污泥性能的影响

二价阳离子能够中和活性污泥表面负电荷,影响微生物活性和生物絮凝性能。本文采用序批式生物反应器（SBR）考察Ca²⁺对污泥活性和污泥絮体表面性质的影响,利用红外光谱和三维荧光光谱分析胞外聚合物（EPS）组分和结构的变化,揭示Ca²⁺与污泥疏水性和zeta电位之间的联系,明确Ca²⁺在生物絮凝中的作用。结果表明：在进水COD、TN和NH₄⁺-N分别为420mg/L、40mg/L和35mg/L的条件下,当Ca²⁺浓度达到160mg/L时,COD、NH₄⁺-N和TN去除率最高（分别为96.7%、90.02%和73.2%）,DHA活性和耗氧呼吸速率（OUR）达到最大,分别为124mgTF/L和3.1mg/（min·L）。Ca²⁺促进了污泥微生物EPS的生成,增大了EPS中蛋白质含量。Ca²⁺与EPS表面带负电的官能团形成架桥,吸附桥联的Ca²⁺中和EPS表面的负电荷,减少了污泥表面负电荷之间的静电斥力,使污泥絮体保持稳定;同时增大了污泥表面的疏水性,改善了污泥的絮凝性和沉降性。     

On the role of the calcination step in the preparation of active (superacid) sulfated zirconia catalysts

In the preparation of active SO₄-ZrO₂ catalysts, several steps involving various chemical and/or physical processes are necessary. In particular it has been reported that, after sulfation of amorphous Zr hydrates, a calcination atT _calc>773 K is needed to guarantee the crystallization of ZiO₂ in the tetragonal phase. By the use of a stabilized tetragonal ZrO₂, it is here demonstrated that a calcination atT _calc>773 K is indeed necessary for all SO₄-ZrO₂ systems, and that its actual role is the selective elimination of sulfates from highly energetic crystallographic defects. The calcination step atT _calc>773 K so creates the conditions for the formation of strong Lewis acid centres, that are necessary in the catalytic process, and the presence of which is here monitored spectroscopically by the reversible adsorption of carbon monoxide.     

Effect of low gas velocity on the nanoparticle collection performance of an electrostatic precipitator

Gas velocity is a critical operational variable in the electrostatic precipitation process. However, studies concerning the collection of nanoparticles have ignored the effect of low gas velocities. Therefore, the aim of this work was to use a wire-plate electrostatic precipitator to investigate the effects of atypical gas velocities under different electric fields on the efficiency. Increasing of both variables enhanced the efficiency, under the conditions used. Unusual behaviors of the grade efficiency curves were associated with diffusional effects. The experimental overall efficiency data were compared with the Deutsch model, and effective migration velocity curves with maximum points were obtained.     

The influence of chlorine on the dispersion of Cu particles on Cu/ZnO(0001) model catalysts

One of the ways in which chlorine is thought to poison metal catalysts on oxide supports is by altering their dispersion. The effect of chlorine on Cu/ZnO(0001) model catalysts was studied by vapor‐depositing Cu onto Zn‐terminated ZnO(0001), both with and without preadsorbed Cl₂, using XPS, ion scattering spectroscopy (ISS), temperature‐programmed desorption (TPD), work function, and band bending measurements. A disordered, but nearly close‐packed overlayer of Cl adatoms forms at saturation with ∼0.30 Cl adatoms per Zn site. Without Cl, vapor‐deposited Cu grows in two‐dimensional islands that cover ∼33% of the ZnO, after which these islands thicken (i.e., as 3D Cu particles) while the clean ZnO between these Cu islands gets covered with Cu only very slowly. Preadsorbed Cl decreases the fraction of the surface that is covered by Cu islands by a factor of three, so Cl(a) either decreases the number of 2D Cu islands or their critical area before thickening. Both are consistent with weaker binding of Cu to the Cl‐covered surface than to the clean ZnO. The TPD features for formate decomposition after HCOOH adsorption onto Cu/ZnO(0001) were suppressed with preadsorbed Cl, but the CO₂ : CO selectivity increased. When Cu was deposited onto Cl‐presaturated ZnO, neither the Zn‐ nor Cu‐formate peaks were observed, showing that Cl covers both the Zn sites and the growing Cu islands, as suggested by ISS also. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of additives on the purity of tetragonal phase and grain size of ceria-stabilized tetragonal zirconia polycrystals (Ce-TZP)

A comprehensive study on the influence of typical additives on zirconia (ZrO₂) crystallization was presented. Zirconium nitrate pentahydrate (Zr(NO₃)₄·5H₂O) and cerium(III) nitrate hexahydrate (Ce(NO₃)₃·6H₂O) were employed as reagents, ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) or glycerol were adopted as additives, and ammonia water was adopted as pH regulator. The ZrO₂ powders were prepared by hydrothermal method. The crystal phase purity, grain size and micro morphology of the ZrO₂ powders were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS) to investigate the influence of EDTA-2Na, glycerol and Ce⁴⁺ content on the purity of tetragonal phase and the grain size of ceria-stabilized tetragonal zirconia polycrystals (Ce-TZP). It was found that EDTA-2Na could decrease the purity of tetragonal phase and alter the grain size of Ce-TZP nonlinearly, while glycerol could not decrease the purity of tetragonal phase and the grain size of Ce-TZP, and the grain size was not linear with the amount of glycerol; Doping Ce⁴⁺ could increase the purity of tetragonal phase of zirconia but could not decrease the grain size, and the grain size was not linear with the Ce⁴⁺ content; In addition, it was indicated that EDTA-2Na and glycerol could not improve the distribution uniformity of Ce⁴⁺. This study is expected to have provided a novel path to achieve tailored ZrO₂ crystals with reduced low-temperature degradation.     

Role of grain constraint on the martensitic transformation in ceria-doped zirconia

Zirconia polycrystals have historically suffered from catastrophic cracking during the tetragonal-monoclinic martensitic transformation. Recently, transformation-induced cracking has been avoided by doping to achieve crystallographic compatibility between the transforming phases. However, these materials showed depressed transformation temperatures and incomplete transformation, the causes for which are yet unknown. In this work, we probe these phenomena by performing a comparative study of sintered pellets and powders. We characterize the thermally induced transformation in a series of ZrO₂-CeO₂ compositions by in situ diffraction and calorimetry and develop a thermodynamic model of the system. In compositions exhibiting reduced cracking, we find that transformation temperatures are depressed in pellets but not in powders. Correspondingly, we measure significant compressive strains in pellets consistent with thermodynamically expected transformation temperature depression, demonstrating the influence of grain constraint and the resultant pressure build-up. However, we find that both pellets and powders exhibit incomplete transformation. In pellets, this is attributed to early exhaustion of autocatalysis caused by grain constraint, whereas in powders, this is attributed to insufficient driving force for distributed heterogeneous nucleation.