Ceramic Crucible Corrosion by Heavy Metal Oxide Glasses, Part II: Diffusion Study

Due to their low cost and high resistance to corrosion, ceramic crucibles can be used for the melting of PBG glasses (PbO-BiO 1.5GaO 1.5). These glasses present good window transmission from ultra-violet to infrared, making their use as optical fibres promising. However, their disadvantage is the high reactivity, leading to the corrosion of different crucibles, including gold and platinum ones. In this work, the corrosion of Al 2O 3, SnO 2 and ZrO 2 crucibles after melting at temperatures varying from 850 to 1000°C, was evaluated by Scanning Electronic Microscopy (SEM) in conjunction with microanalysis by EDS. The lead diffusion profile in the crucible material was obtained. Diffusion coefficients were calculated according to the Fick and Fisher theories. Results indicated that the different crucibles presented similar behaviour: in the region near the interface, diffusion occurs in the volumetric way and in regions away from the interface, diffusion occurs through grain boundary.

Use of high energy ball milling on the sintering optimization of alumina ceramics

In this work, the effect of the milling time on the densification of the alumina ceramics with or without 5wt.%Y 2O 3, is evaluated, using high-energy ball milling. The milling was performed with different times of 0, 2, 5 or 10 hours. All powders, milled at different times, were characterized by X-Ray Diffraction presenting a reduction of the crystalline degree and crystallite size as function of the milling time increasing. The powders were compacted by cold uniaxial pressing and sintered at 1550°C-60min. Green density of the compacts presented an increasing as function of the milling time and sintered samples presented evolution on the densification as function of the reduction of the crystallite size of the milled powders. © (2010) Trans Tech Publications.

Shear bond strength of resin cement bonded to alumina ceramic after treatment by aluminum oxide sandblasting or silica coating

Purpose: To evaluate the shear bond strength and bond durability between a dual-cured resin cement (RC) and a high alumina ceramic (In-Ceram Alumina), subjected to two surface treatments. Materials and Methods: Forty disc-shaped specimens (sp) (4-mm diameter, 5-mm thick) were fabricated from In-Ceram Alumina and divided into two groups (n = 20) in accordance with surface treatment: (1) sandblasting by aluminum oxide particles (50 μm Al 2O 3) (SB) and (2) silica coating (30 μm SiO x) using the CoJet system (SC). After the 40 sp were bonded to the dual-cured RC, they were stored in distilled water at 37°C for 24 hours. After this period, the sp from each group were divided into two conditions of storage (n = 10): (a) 24 h-shear bond test 24 hours after cementation; (b) Aging-thermocycling (TC) (12,000 times, 5 to 55°C) and water storage (150 days). The shear test was performed in a universal test machine (1 mm/min). Results: ANOVA and Tukey (5%) tests noted no statistically significant difference in the bond strength values between the two surface treatments (p= 0.7897). The bond strengths (MPa) for both surface treatments reduced significantly after aging (SB-24: 8.2 ± 4.6; SB-Aging: 3.7 ± 2.5; SC-24: 8.6 ± 2.2; SC-Aging: 3.5 ± 3.1). Conclusion: Surface conditioning using airborne particle abrasion with either 50 μm alumina or 30 μm silica particles exhibited similar bond strength values and decreased after long-term TC and water storage for both methods. © 2011 by The American College of Prosthodontists.

Influência de protocolos de jateamento na rugosidade da superfície de uma cerâmica de zircônia tetragonal parcialmente estabilizada por ítria

Objective: To evaluate the influence of different air abrasion protocols on the surface roughness of an yttria-stabilized polycrystalline tetragonal zirconia) (Y-TZP) ceramic, as well as the surface topography of the ceramic after the treatment. Method: Fifty-four specimens (7.5×4×7.5mm) obtained from two ceramic blocks (LAVA, 3M ESPE) were flattened with fine-grit sandpaper and subjected to sintering in the ceramic system's specific firing oven. Next, the specimens were embedded in acrylic resin and the surfaces to be treated were polished in a polishing machine using sandpapers of decreasing abrasion (600- to 1,200-grit) followed by felt discs with 10μm and 3μm polishing pastes and colloidal silica. The specimens were then randomly assigned to 9 groups, according to factors particle and pressure(n=6): Gr1- control; Gr2- Al 2O 3(50μm)/2.5 bar; Gr3- Al 2O 3(110μm)/2.5 bar; Gr4- SiO 2(30μm)/2.5 bar; Gr5- SiO 2(30μm)/2.5 bar; Gr6- Al 2O 3(50μm)/3.5 bar; Gr7- Al2O3(110μm)/3.5 bar; Gr8- SiO 2(30μm)/3.5 bar; Gr9- SiO 2(30μm)/3.5 bar. After treatments, surface roughness was analyzed by a digital optical profilometer and the morphology was examined by scanning electron microscopy (SEM). Data (μm) were subjected to statistical analysis by Dunnett's test (5%), two-way ANOVA and Tukey's test (5%). Results: The type of particle (p=0.0001) and the pressure (p=0.0001) used in the air abrasion protocols influenced the surface roughness values among the experimental groups (ANOVA). The mean surface roughness values (μm) obtained for the experimental groups (Gr2 to Gr9) were, respectively: 0.37 D; 0.56 BC; 0.46 BC; 0.48 CD; 0.59 BC; 0.82 A; 0.53B CD; 0.67 AB. The SEM analysis revealed that Al 2O 3, regardless of the particle size and pressure used, caused damage to the surface of the specimens, as it produced superficial damages on the ceramic, in the form of grooves and cracks. Conclusion: Al2O3 (110 μm/3.5 bar) air abrasion promoted the highest surface roughness on the ceramics, but it does not mean that this protocol promotes better ceramic-cement union compared to the other air abrasion protocols.

Characteristics of PbO-BiO1.5-GaO1.5 glasses melted in SnO2 crucibles

PbO-BiO 1.5-GaO 1.5-based glasses are good candidates for optical applications, because of some of their interesting characteristics, such as high refraction indices and high transmission in the ultraviolet (UV), visible (VIS), and infrared (IR) regions. A limited stage in the processing of these glasses is the corrosion that is caused by the melt in all currently used conventional crucibles, such as noble metals (platinum or gold) and Al 2O 3. The absorption of crucible material by the glass composition may reduce the transmission level, the cutoff in the UV-VIS, and IR regions, and the thermal stability. In this study, a SnO 2 crucible has been tested for PbO-BiO 1.5-GaO 1.5 molten glass. Optical and thermal analyses show, in some cases, advantages over the use of platinum and Al 2O 3 crucibles. A visible cutoff value of 474 nm has been measured, and a longer melting time (850°C for 4 h) results in a significant reduction of the O-H absorption band at 3.2 μm.

Strong visible up-conversion emissions and thermometric applications of Er3+-Yb3+ codoped Al2O3 prepared by the sol-gel method

The Er3+-Yb3+ codoped Al2O3 has been prepared by the sol-gel method using the aluminium isopropoxide [Al(OC3H7)(3)]-derived Al2O3 sols with addition of the erbium nitrate [Er(NO3)(3) center dot 5H(2)O] and ytterbium nitrate [Yb(NO3)(3) center dot 5H(2)O]. The phase structure, including only two crystalline types of doped Al2O3 phases, theta and gamma, was obtained for the 1 mol% Er3+ and 5 mol% Yb3+ codoped Al2O3 at the sintering temperature of 1,273 K. By a 978 nm semiconductor laser diodes excitation, the visible up-conversion emissions centered at about 523, 545, and 660 nm were obtained. The temperature dependence of the green up-conversion emissions was studied over a wide temperature range of 300-825 K, and the reasonable agreement between the calculated temperature by the fluorescence intensity ratio (FIR) theory and the measured temperature proved that Er3+-Yb3+ codoped Al2O3 plays an important role in the application of high temperature sensor.

Tris[4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dionato]aluminium(III)-tris[4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dionato]iron(III) (3/1)

In the title compound, [Al(C8H4F3O2S)3]3[Fe(C8H4F3O2S)3], the metal centre is statistically occupied by AlIII and FeIII cations in a 3:1 ratio. The metal centre is within an octahedral O6 donor set defined by three chelating substituted acetoacetonate anions. The ligands are arranged around the periphery of the molecule with a mer geometry of the S atoms.

Performance of an Al-Si-graphite particle composite piston in a diesel engine

Al-Si-graphite particle composite alloy pistons containing different percentages of about 80 μm uncoated graphite particles were successfully cast by foundry techniques. Tests with a 5 hp single-cylinder diesel engine show that Al-Si-graphite particle composite pistons can withstand an endurance test of 500 h without any apparent deterioration and do not seize during the running-in period. The use of the Al-Si-3% graphite particle composite piston also results in (a) up to 3% reduction in the specific fuel consumption, (b) considerable reduction in the wear of all four piston rings, (c) a reduction in piston wear, (d) a 9% reduction in the frictional horsepower losses of the engine as determined by the motoring test and (e) a slight increase in the exhaust gas temperature. These reductions (a)–(d) appear to be due to increased lubrication from the graphite particles which are smeared on the bearing surface, the higher damping capacity of the composite pistons and the reduced coefficient of thermal expansion of the composite pistons. Preliminary results indicate that aluminum-graphite particle composite alloy is a promising material for automotive pistons.

Tris(methyl 3-oxobutanoato-kappa O-2,O `)aluminium(III)

In the title compound, [Al(C5H7O3)(3)],three acac-type ligands(methyl 3-oxobutanoate anions) chelate to the aluminium(III)cation in a slightly distorted AlO6 octahedral coordination geometry.Electron delocalization occurs within the chelating rings.

Tris(tert-butyl 3-oxobutanoato-kappa O-2(1),O- )-aluminium(III) at 153 K

In the title complex, [Al(C8H13O3)(3)], a potential metal-organic chemical vapour deposition (MOCVD) precursor, three bidentate ligand molecules are bound to the metal atom, forming an octahedral geometry. Two non-planar six-membered chelate rings adopt screw-boat conformations, while the third ring has a conformation that lies about halfway between an envelope and a screw-boat.

碱金属和碱土金属氟化物对掺Er^3＋氟磷酸盐玻璃光谱性质的影响

研究了碱金属和碱土金属离子修饰的掺Er^3＋氟磷酸盐玻璃的光谱性质，讨论了碱金属和碱土金属对铒氟磷玻璃的吸收和发射截面、荧光半高宽，Judd-Ofelt强度参数和上转换发光强度等光谱性质的影响，并与一些传统氧化物玻璃系统进行了比较．研究表明碱金属K^＋和碱土金属Sr^2＋掺杂高的玻璃更适宜用作光放大器基质．含12mol％K^＋的氟磷玻璃展现出7．83×10^-21cm^2的高发射截面和最小的荧光上转换强度；含23mol％Sr^2＋的氟磷玻璃则有7．58×10^-21cm^2的高发射截面、65nm的荧光半高

Validation of a lattice Boltzmann model for gas-solid reactions with experiments

A lattice Boltzmann method is used to model gas-solid reactions where the composition of both the gas and solid phase changes with time, while the boundary between phases remains fixed. The flow of the bulk gas phase is treated using a multiple relaxation time MRT D3Q19 model; the dilute reactant is treated as a passive scalar using a single relaxation time BGK D3Q7 model with distinct inter- and intraparticle diffusivities. A first-order reaction is incorporated by modifying the method of Sullivan et al. [13] to include the conversion of a solid reactant. The detailed computational model is able to capture the multiscale physics encountered in reactor systems. Specifically, the model reproduced steady state analytical solutions for the reaction of a porous catalyst sphere (pore scale) and empirical solutions for mass transfer to the surface of a sphere at Re=10 (particle scale). Excellent quantitative agreement between the model and experiments for the transient reduction of a single, porous sphere of Fe 2O 3 to Fe 3O 4 in CO at 1023K and 10 5Pa is demonstrated. Model solutions for the reduction of a packed bed of Fe 2O 3 (reactor scale) at identical conditions approached those of experiments after 25 s, but required prohibitively long processor times. The presented lattice Boltzmann model resolved successfully mass transport at the pore, particle and reactor scales and highlights the relevance of LB methods for modelling convection, diffusion and reaction physics. © 2012 Elsevier Inc.

First-principles study of p-type transparent conductive oxides CuXO2 (X=Y, Sc, and Al)

Using first-principles methods we have calculated electronic structures, optical properties, and hole conductivities of CuXO2 (X=Y, Sc, and Al). We show that the direct optical band gaps of CuYO2 and CuScO2 are approximately equal to their fundamental band gaps and the conduction bands of them are localized. The direct optical band gaps of CuXO2 (X=Y, Sc, and Al) are 3.3, 3.6, and 3.2 eV, respectively, which are consistent with experimental values of 3.5, 3.7, and 3.5 eV. We find that the hole mobility along long lattice c is higher than that along other directions through calculating effective masses of the three oxides. By analyzing band offset we find that CuScO2 has the highest valence band maximum (VBM) among CuXO2 (X=Y, Sc, and Al). In addition, the approximate transitivity of band offset suggests that CuScO2 has a higher VBM than CuGaO2 and CuInO2 [Phys. Rev. Lett. 88, 066405 (2002)]. We conclude that CuScO2 has a higher p-type doping ability in terms of the doping limit rule. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2991157]

On the acid-base stability of Keggin Al-13 and Al-30 polymers in polyaluminum coagulants

The acid-base stabilities of Al-13 and Al-30 in polyaluminum coagulants during aging and after dosing into water were studied systematically using batch and flow-through acid-base titration experiments. The acid decomposition rates of both Al-13 and Al-30 increase rapidly with the decrease in solution pH. The acid decompositions of Al-13 and Al-30 with respect to H+ concentration are composed of two parallel first-order and second-order reactions, and the reaction orders are 1.169 and 1.005, respectively. The acid decomposition rates of Al-13 and Al-30 increase slightly when the temperature increases from 20 to ca. 35 A degrees C, but decrease when the temperature increases further. Al-30 is more stable than Al-13 in acidic solution, and the stability difference increases as the pH decreases. Al-30 is more possible to become the dominant species in polyaluminum coagulants than Al-13. The acid catalyzed decomposition and followed by recrystallization to form bayerite is one of the main processes that are responsible for the decrease of Al-13 and Al-30 in polyaluminum coagulants during storage. The deprotonation and polymerization of Al-13 and Al-30 depend on solution pH. The hydrolysis products are positively charged, and consist mainly of repeated Al-13 and Al-30 units rather than amorphous Al(OH)(3) precipitates. Al-30 is less stable than Al-13 upon alkaline hydrolysis. Al-13 is stable at pH < 5.9, while Al-30 lose one proton at the pH 4.6-5.75. Al-13 and Al-30 lose respective 5 and 10 protons and form [Al-13] (n) and [Al-30] (n) clusters within the pH region of 5.9-6.25 and 5.75-6.65, respectively. This indicates that Al-30 is easier to aggregate than Al-13 at the acidic side, but [Al-13] (n) is much easier to convert to Alsol-gel than [Al-30] (n) . Al-30 possesses better characteristics than Al-13 when used as coagulant because the hydrolysis products of Al-30 possess higher charges than that of Al-13, and [Al-30] (n) clusters exist within a wider pH range.

熔盐电解法制备Al-Li合金的应用基础研究及其工艺初探

Al-Li合金是近年发展起来的新型航空材料，具有低密度、高强度的特点。目前世界上正就如何进一步提高其断裂韧性，使Al-Li合金尽早走出实验室，获得实际用进行广泛，深入的研究。熔盐电解法就是在这种情况下发展起来的。虽然此法现在尚处于研究的初级阶段，但已以其能够在较简单的设备上制备低Na高纯Al-Li合金的特点受到广泛的重视，是一种很有前途的发展方向。针对我国的技术、设备现状，在参考国外研究结果的基础上，采用熔盐电解法制备Al-Li母合金 → 应用合金的制备方法是可以尽快赶上世界发步伐的有效途径。因此，本文作为整个熔盐电解制备Al-Li合金系统研究的一部分，针对目前在此领域中很多应用基础问题，诸如：作为新的电解体系正在探索中的LiCl-KCl-LiF三元相图，Li在液体Al阴极中的扩散系数，利用熔盐电解法制备低Na高纯Al-Li合金的热力学基础及如何克服LiCl强烈的吸水性给电解工艺带来的种种不便等均未得到系统研究的现状，设计完成了一系列有关熔盐电化学和热力学实验，填补了本领域的一些研究空白，并为进一步系统研究工艺条件提供了重要的参考数据。1．用NH_4Cl氯化Li_2CO_3的研究 根据热力学从理论上论证了在200 ℃左右下述氯化反应：Li_2CO_3 + 2NN_4Cl = 2LiCl + 2NH_3~↑ + H_2O~↑ + CO_2~↑可以进行完全。利用DSC方法测定反应产物LiCl的纯度，并用离子色谱法分析反应产物中CO_3~=的含量，结果均证明：在Li_2CO_3:NH_4Cl = 1:4 (mol)时，Li_2CO_3可以定量转化为LiCl，剩余的NH_4Cl完全分解。根据热重分析结果推测NH_4Cl氯化Li_2CO_3的反应历程为：Li_2CO_3 + 2NH_4Cl = 2LiCl + 2NH_3~↑ + H_2O~↑ + CO_2~↑ NH_4Cl = HCl~↑ + NH_3~↑ 而并非是想像中的：NH_4Cl = HCl~↑ + NH_3~↑ 2HCl + Li_2CO_3 = 2LiCl + H2O~↑ + CO_2~↑利用X－射线衍射方法分析产物，结果亦说明氯化可以成功。将1:4（mol）= Li_2CO_3:NH_4Cl混合样品在差热分析反应炉中直接加热测定反应产物LiCl的溶点，并与纯LiCl样品熔点的测定结果相比较，二者完全一致。以上结果说明：不仅可用此氯化反应产物代替LiCl应用于熔盐电解制备Al-Li合金中，而且还可将其应用于LiCl体系的相图测定中。因Li_2CO_3，NH_4Cl均不吸水，极易处理，因此以上研究结果无论对于Al-Li合金的工艺研究还是其他有关LiCl体系的基础研究都是很有价值的。2．直接氯化法制备LiCl-KCl-LiF三元相图的研究。LiCl-KCl-LiF三元相图是研究此体系电解机制的重要基础。为将以上直接氯化法应用于差热分析中制作此三元体系相图，首先用直接氯化法测定了三个已知二元LiCl体系相图：LiCl－KCl；LiCl-LiF；LiCl-NaCl。与文献结果吻合很好。说明将此法应用于差热分析中制作LiCl体系相图结果是可靠的。在LiCl-KCl-LiF三元相图的测定中共做出七个垂直截面，在各截面上读出等温条件下的相界点投影到浓度三角形中，得到等温投影图。结果说明LiCl-KCl-LiF是固态完全不互溶的三元共晶体系，共有三个液－固两相区；三个液－固－固三相区；一个液－固－固－固四相区，（三元共晶平面）和一个固－固－固三相区。四相点温度为348 ℃，其组成在三相平衡线的交点处，在实验上测出近似等于：41.4KCl + 57.3LiCl + 1.3LiF (mol)。3．氯化物体系中Li~+, Na~+析出电位的比较及其去极化作用的研究。在正常电化序中，Li~+应先于Na~+析出。但在以Al作阴极电解LiCl体系时，则由于Li~+在Al上有较强的去极化作用而提前析出。这是熔盐电解法可以制备低Na，高纯Al-Li合金的基础。本文在理论上对此问题进行了较深入的研究。具体内容包括（1）。测定Li~+, Na~+在二元氯化物体系中的析出电位。通过在Al阴极，Mo阴极上二离子析出电位的比较，确认了Li~+在Al阴极上产生很强的去极化作用是能利用电解法制备低Na高纯Al-Li合金的根本原因。并为在工艺研究中选择合适的电流密度提供了参考依据。（2）．根据热力学理论推导出合金化反应产生的自由焓变化与去极化作用的关系：ΔG_x + ΔG_m = -nFΔE。揭示了产生去极化作用的原因。并根据ΔG_x（偏摩尔过剩自由焓）与合金结构的关系提出可以利用二元合金相图推测极化类型及极化大小。并根据动力学原理对温度对极化的影响提出了自己的看法。（3）．求出合金化反应的热效应，认为在一定条件下亦可利用此值作为判断去极化作用大小的标准。（4）．测定Li~+, Na~+在Al-Cu, -Al-RE合金上的析出电位。结果表明Cu，RE的存在均可加强Li~+在阴极上的去极化作用，进一步加大了Li~+, Na~+析出电位之间的差别，有利于制备更纯的Al-Li 使金。为直接生产Al-Cu-Li, Al-RE-Li三元母合金奠定了基础。（5）测定Li~+在不同组成配比的LiCl-KCl熔体中，在Al阴极上的析出电位，并求出LiCl的离子平均活度系数γ＝0.71 (T = 740 ℃), 熔体对理想状态产生负偏离。4．利用阳极计时电位法测定T＝720 ℃时Li在液体Al中的扩散系数D_(Li/Al) = 4.94 * 10~(-5)cm~2·s~(-1)，与利用Stocks-Einstan公式计算出的理论值D_(Li/Al) = 4.85 * 10~(-5)cm~2·s~(-1)吻合较好。5．在上述理论研究的基础之上进行了工艺初探，所得初步结论有：（1）．加入LiF可以提高电效。（2）．采用电流密度为1 A/cm~2时，不加搅拌亦可制备出成份均匀，含Li量为10％（w.f）的Al-Li合金。（3）．根据实验结果提出 Li在熔体中的熔解可能是影响电流效果的主要原因。