Corrosion of Lead Glasses in Acid Media: II, Concentration Profile Measurements

Lead concentration profiles were measured in a binary lead silicate glass corroded by acid using ahd a-backscattering technique. These profiles were characteristic of those predicted for an interdiffusion process and revealed a surface layer deficient in lead. Diffusion coefficients for Pb²⁺ were calculated, together with values of the total amount of lead removed at the various experimental temperatures and times. Good agreement was found between these data and those previously obtained experimentally. All diffusion coefficient values were high and, correspondingly, activation energy values were low compared with those predicted by the literature for similar glass compositions. This difference was justified from consideration of the leaching process.     

Kinetics of Leaching of Lead Glass by Ethylenediaminetetraacetic Acid

Treatment of lead glass with a hot basic solution of the sodium salt of ethylenediaminetetraacetic acid (EDTA) was shown to remove lead from the glass surface. A mechanism is proposed whereby lead is removed by a two-step reaction involving hydroxyl ions and EDTA. The rate constant and the overall heat of activation were estimated for this reaction. Potassium and silicon are also removed from the glass surface and show a dependence similar to that of lead removal. Potassium and silicon, however, do not form complexes with EDTA. Thus, it appears that lead removal weakens the silicate structure of the glass surface, allowing the potassium and silicon to be attacked and removed by hydroxyl ions and/or water. Experimental results indicate that the silicon released from the glass surface is in the form of silica.     

Leaching of Lead and Connectivity of Plumbate Networks in Lead Silicate Glasses

The formation of a plumbate network in binary lead silicate glasses was examined based on the leaching behavior of Pb²⁺ in lead silicate glasses over a wide composition region. The effective diffusion coefficient of Pb²⁺ at 40°C was on the order of 10⁻¹⁷ m²/s for PbO<35 mol% glasses, and increased three orders of magnitude for 35–50 mol% PbO contents. Such a steep composition dependence is considered to be because of changes in the medium or longer range structure. That is, it is proposed that the plumbate network forms a percolative 3D network in the composition region to form diffusion paths for the lead ions. In addition, the present results indicate that the lead ion exists as a network former over the entire glass forming composition range of the binary silicate glasses.     

Corrosion of Zinc-Containing Cabal Glasses by Various Leaching Solutions

The corrosion behavior of some cabal glasses (CaO-B₂O₃-Al₂O₃) containing ZnO was evaluated both as a bulk specimen and as grain powder. Different leaching solutions were used including HCI, H₂SO₄, and NaOH for varying temperatures or periods of exposure. Zinc oxide replacing calcium oxide in cabal glasses of constant 40 mol% B₂O₃, 30 mol% Al₂O₃, caused a decrease in chemical durability in all leaching solutions used. The corrosion was found to be linear with time in the limit of investigation (1–4 h) but with different rates depending on the type of leaching solution or temperature.     

Kinetics of the Reduction of Lead Compounds and Glasses

The kinetics of the gas–solid reduction reactions of high purity dry hydrogen with selected lead compounds and glasses was investigated. Materials studied were PbO, Pb₂SiO₄, PbSiO₃, PbZrO₃, PbTiO₃, lead zirconate titanate (54/46, Zr/Ti ratio), lead orthosilicate glass, and lead metasilicate glass. A constant pressure (1 atm) hydrogen flow (2 liters per minute) system was used in reacting the powdered materials at specified constant temperatures. The extent of reduction was quantitatively determined by (1) weight loss of the reacted specimen, and (2) dew point of the reaction atmosphere. Expressions are presented for relating both the weight loss and the dew point to the fraction of reduction, a. The activation energies for the reduction reactions were calculated from plots of log h (reaction rate constant) versus 1/T °K. Activation energies obtained were 18.4, 19.9, 21.0, 34.6, 46.5, and 47.0 kcal per mole, respectively, for the first six compounds. The lead glasses, which reacted below their melting ranges, were reduced appreciably less than the lead compounds.     

Interaction Kinetics of Bismuth Borate Glasses and Orthophosphoric Acid

Glass and Ceramics - The interaction of orthophosphoric acid with the bismuth borate glasses having the compositions (weight content, %) 70Bi2O3 - 30B2O3, 70Bi2O3 - 27B2O3 - 3MoO3, 70Bi2O3 -...     

含铅玻璃及其无铅化的研究

介绍了铅对人体的危害,综述了一些为限制铅的使用及排放而制定的相关法规,详细介绍了铅玻璃在现阶段中的一些主要用途和目前人们对这些玻璃的无铅化方面的工作。指出电子产品无铅化的迫切性。     

赤泥中钇浸出行为及动力学研究

采用盐酸浸出提取赤泥中的钇,考察了盐酸浓度、浸出温度、液固比和反应时间对钇浸出率的影响.分析了赤泥盐酸浸出提钇过程的物相变化和表面形貌变化.根据钇浸出动力学参数,确定了关键控制步骤和表观活化能.结果表明:在盐酸体积浓度30％,浸出温度为80℃,液固比为7 mL/g,反应时间为60 min的条件下,钇的浸出率为82.57％.酸浸过程赤泥中钙霞石和方解石全部溶解,赤铁矿和钙钛矿部分溶解,酸浸渣的粒度变小,颗粒粘结现象消失.在低浓度盐酸介质中,钇的浸出过程主要受化学反应控制,在高浓度盐酸介质中,主要受内扩散控制.不同浸出温度条件下,赤泥酸浸提钇过程均主要受内扩散模型控制,浸出提钇过程的表观活化能为19.8 kJ·mol-1.     

Microseparation in Lead Borate Glasses

The microstructure of a series of lead borate glasses was studied by electron microscopy and small-angle X-ray scattering techniques. Although the glasses were optically homogeneous, microheterogeneities of the order of 2000 to 3000 A were detected in glasses with compositions near the region of two-liquid stability. The size of these heterogeneities increased as the composition approached the region of immiscibility.     

Strengthening of Glasses by Partial Leaching

A technique for strengthening certain alkali borosilicate glasses is described. Porous surface layers of a desired thickness are created on an article, taking advantage of the phase separation and leaching phenomena in such glasses. The semiporous composite is then heated to sinter the high-silica clad about the borosilicate core. On cooling, residual compressive stresses develop within the cladding. The mechanical properties of cylindrical specimens prestressed by this method were characterized by photoelastic measurements and moduius-of-rupture tests. Residual stresses as high as —410 MPa were observed and found to be in reasonable agreement with the form of a previously developed thermal-stress model. The roles played by thermal tempering and stress-relaxation effects are also discussed.     

攀西高锰稀土矿泥盐酸浸取稀土动力学

采用盐酸浸取攀西高锰稀土矿泥,考察了浸取反应温度、矿石粒度及盐酸浓度对浸取速率的影响. 结果表明,当盐酸浓度为2 mol/L时,浸取过程符合缩核模型,表观活化能为9.59 kJ/mol,属内扩散控制,宏观动力学方程为：K=(4.15?10–4)/r02 · exp(9590/RT); 当盐酸浓度大于2 mol/L时,矿石中的锰被大量浸出,其结构被破坏,浸取过程为混合控制.     

Properties of Lead Fluorosilicate Glasses

Lead fluorosilicate glasses containing up to 25 mol% PbF₂ were prepared. The dc electrical conductivity, thermal expansion, and transformation-range viscosity of these glasses indicate that they are anionic conductors and that fluorine significantly decreases the continuity of the vitreous network.     

Sintering of Low-Density Glasses: I, Theory

An analysis is presented which describes the rate at which a cubic array of cylinders densifies by viscous flow driven by surface energy reduction. The cubic array is proposed as a model for the microstructure of low-density, open-pore materials such as gels and flame-hydrolysis preforms. The parameters of the model structure (cylinder length and radius) can be deduced from Hg penetration porosimetry.     

Controlled-Potential Coulometry of Lead, Cadmium, and Zinc in Glasses

A controlled-potential coulometric determination of lead, cadmium, and zinc in glasses is reported. The method consists of reducing or oxidizing the various ions at appropriate potentials. The integrated current resulting from the electrolysis is used to calculate the amount of substance present. The lower limit of detection, without background corrections, is approximately 0.2 millifaradays for each ion. The method is accurate and more rapid than the usual classical methods of analysis.     

Study of Optical Glass Surfaces by Leaching with Nitric Acid: I, Polishing Lines

A study was made of the origin of fine lines that appeared on polished glass surfaces after leaching with nitric acid. The results were considered on the basis of theories of nonreflecting films and the polishing lines developed by hydrofluoric acid etching. The conclusions reached are compatible with the existence of deep fields of compression where the ionic exchange is enhanced.     

Anionic Conduction in Lead Halosilicate Glasses

Electrical conductivity due to halide ions has been measured for the glasses in the system 30SiO₂· (70 − x )PbO · x PbX₂ (0 < x < 17.2 mol%; X = F, Cl). The conductivity increases with x by several orders of magnitude for both series of glasses. The contribution of principal factors to the conductivity has been examined. The analysis of the activation energy on the basis of the Anderson-Stuart model shows that the strain energy is a predominant term in the Cl glasses, while both the strain energy and the electrostatic energy have a comparable contribution in the F glasses. The decrease in the activation energy with increasing PbX₂ content is related to the decrease in the shear modulus for the Cl glasses and to the increase in the permittivity for the F glasses.     

废糖蜜-硫酸溶液中软锰矿的浸出动力学

用收缩芯模型研究了硫酸介质中废糖蜜还原浸出软锰矿的动力学,考察了软锰矿粒度、反应温度、浸出时间、硫酸浓度和废糖蜜浓度对锰浸出速率的影响. 结果表明,提高反应温度、硫酸浓度、废糖蜜浓度和减小软锰矿颗粒的初始平均半径,均可提高锰的浸出速率. 废糖蜜还原浸出软锰矿属界面化学反应控制,表观活化能为45.6 kJ/mol,硫酸和废糖蜜的反应级数分别为0.52及0.28.     

Chemical Durability of Fluoride Glasses: I, Reaction of Fluorozirconate Glasses with Water

The chemical durability of five flouarozirconate glass compositions was studied. Measurements of leachant composition and solution chemistry by plasma emission spettroscopy, pH, and fluoride analysis are reported. Changes in surface structure were monitored by scanning electron microscopy, electron-probe X-ray analysis, and X-ray diffraction. The modifer additives with high aqueous solubility (A1F₃, NaF, LiF, PbF₂) exhibited the highest leach rates with ZrF₄, BaFs₂, and LaF₃ exhibiting lower rates. The leaching order of Zr > Ba > La was maintained for all samples. The leaching process consists of the dissolution of the glass matrix, leaving a thick and porous layer containing Zr, Ba, La, and molecular water. Hydroxylation of the Zr species to form a hydroxyfluoride complex in solution dominated a decrease in pH to moderately acidic values. The resulting increase in component solubility (particularly zirconium fluoride) in the acidic solutions accelerated the glass dissolution rate and demonstrated that, if no buffer is present to avert the pH drift, the chemical durability of these glasses in aqueous environments is extremely poor, being roughly equivalent to that of Na₂O 2SiO₂.