Reaction of Silicate Glasses and Mullite with Hydrogen Gas

The increasing order of corrosion resistance to H₂ gas flowing fast enough to ensure that the reaction is the slow step is fused silica, aluminosilicate glass, and mullite at T =1300° to 1500° C; the activation energies are 347.3, 358.6, and 389.1 kj/mol (83.0, 85.7, and 93.0 kcal/mol), respectively. No detectable reaction with a-Al₂O₃ was observed. Addition of a small amount of CaO to the glass reduced its activation energy (283.7 kj/mol (67.8 kcal/mol)) and made its reactivity with H₂ similar to that of mullite at high temperatures. The reaction product for the glasses consisted of a porous zone composed of an intermediate layer close to mullite in composition and an outer layer of a-AI₂O₃. The reaction product for mullite consisted of a porous a-Al₂O₃ residue layer.     

Reaction of Hydrogen with Optical Defects in Glasses

A kinetic model for the removal of optical defects in glasses by exposure to hydrogen or deuterium gas is presented. Since annealing involves a chemical reaction at low temperatures, it is called "chemical annealing" to distinguish it from the common, higher-temperature, thermal annealing processes. As an example, this model is applied to the elimination of the aluminum/oxygen hole center in irradiated vitreous silica at 73°C in 93 kPa of D₂.     

Reaction of Glasses with Hydrofluoric Acid Solution

The gravimetric method was used to study the reaction between fused silica and silicate glasses with HF acid solution. The reaction was found to be transport-controlled. Additions of Al₂O₃, CaO, or both to fused silica caused a reduction in corrosion resistance of the resulting glasses.     

Hydrogen Permeability of Borosilicate Glasses

Borosilicate glass-forming compositions R₂O – B₂O₃ – SiO₂ – R_aO_b (R — Li, Na, K; R_a — Zn, PbO) are investigated. A correlation-regression analysis of the criteria (the silicate modulus, the oxygen number, the structure cohesion factor, the relative molar volumes of the components) affecting the hydrogen permeability of glasses is carried out. The tendency for permeability variations depending on the component composition and the above specified criteria is identified.     

Spectroscopic Investigation of the Coloration and Fabrication Conditions of Medieval Blue Glasses

Potash‐ and soda‐lime‐stained glasses from the 12th–13th centuries, blue‐colored by cobalt, have been investigated by Mn, Fe, and Cu K‐edge X‐ray and optical absorption spectroscopies in order to determine the oxidation state of these elements and their impact on the blue color. Remelting these historical glasses in air at 1200°C, the estimated temperature of medieval furnaces, revealed that these four glasses are more reduced before remelting. This favors Mn as weakly absorbing Mn²⁺, Fe as Fe²⁺ and Cu as colorless Cu⁺. Therefore Fe²⁺ is the second blue chromophore and copper was not intentionally used by glassmakers to obtain a blue color. A colorimetric analysis indicates that these specific melting conditions have a limited effect on the blue color of these glasses. Based on the spectroscopic determination of the redox state of Fe, Mn, and Cu, we estimate the oxygen partial pressure in medieval furnaces to be 10^?7–10^?9 and 10^?5 bar for the potash‐ and soda‐lime samples, respectively. The comparison with previous results enables to prove the evolution of furnace technology over centuries.     

Chemical Durability of Fluoride Glasses: II, Reaction of Barium-Thorium-Based Glasses with Water

The aqueous leaching behavior of three Ba-Th-based fluoride glasses was studied. Results of solution analysis, SEM, and IR spectroscopy are reported and compared with earlier studies on fluorozirconate-based glasses. Leaching appears to be by matrix dissolution dominated by component solubility. No hy-drated leach layer was seen to form on the surface. Only a mild drift In solution pH, resulting from a limited hydrolysis of, dissolved thorium fluoride, was observed. The reduced pH drift away from neutral, coupled with lower component solubilities, is credited with the 100-fold improvement in chemical durability of the Ba-Th-based fluoride glasses over the fluorozirconate-based glasses reported previously.     

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.     

Effect of Temperature on the Relaxation of Radiation-Induced Coloration in Optical Glasses

Optical and radiation-resistant crown and flint glasses exposed to gamma irradiation at room temperature are investigated. The relaxation of radiation-induced absorption in irradiated glasses is examined prior to and after short-term or long-term heat treatment at different temperatures in the range 20–150°C. It is established that an increase in the heat treatment temperature by even several tens of degrees leads to a drastic increase in the relaxation rate of radiation-induced coloration and a decrease in the time of complete bleaching of irradiated glasses by several orders of magnitude.     

EPR and Kinetic Studies of Hydrogen Centers in Aluminoborate Glasses

Barium aluminoborate glasses containing hydrogen as an impurity, irradiated at 77 K with X rays, show the characteristic doublet of atomic hydrogen in the EPR spectra when measured at T<200 K. The hfs constant of the H^o_i center is smaller than that of free atomic hydrogen, indicating that the attractive van der Waals interaction is more important than the repulsive Pauli exclusion forces in that glassy matrix. It is suggested on the basis of isochronal and isothermal annealing experiments that there are at least three different sites for hydrogen, each one contributing with Ist-order decay kinetics. The activation energies found in 30 mol% BaO, 60 B₂O₃, 10 Al₂O₃ glass are, respectively, equal to E₁=(0.5±0.1), E₂=(0.24±0.03), and E₃=(0.16±0.03)×lO⁻¹⁹ J.     

氢键对有机取代反应和加成反应的影响

取代反应和加成反应是有机化学中最基础、最重要、也是研究最多的反应。影响取代反应和加成反应的因素很多,文章从氢键的形成、类型、键能大小出发,分析讨论了其对饱和碳原子上亲核取代反应、苯环上C-F键的亲核取代反应、亲电加成反应及羰基化合物亲核加成反应的影响,所得结论对有机化学理论教学和有机合成具有一定的指导意义。     

Flash Photolysis of Hydrogen Peroxide I: The Reaction of Ozonide with Hydrogen Peroxide

The photochemistry of basic aqueous solutions containing hydrogen peroxide and oxygen has been investigated by the flash photolysis method. The decay of O₃^? was followed at 4300 Å over the pH range 13 – 13.7 as a function of hydrogen peroxide and oxygen concentrations. The decay was found to be of the first order under all conditions ?[d(O₃)^?/dt] = k_obs[O₃^?]. The pseudo first-order rate constant k^obs was found to be dependent on H₂O₂ and O₂ concentrations. A mechanism which is consistent with the experimental results is suggested.     

Reaction of Hydrogen Bromide with Long Chain 1,2-Diols

The reactions of 1,2-hexadecanediol and 1,2-octadecanediol with hydrogen bromide in the presence of acetic anhydride have been investigated. The treatment of hydrogen bromide (48%) in acetic anhydride with 1,2-hexadecanediol gives mainly 1-bromo-2-acetoxy hexadecane (66%), 2-acetoxy hexadecanol (26%), and 1,3-hexadecanediol (8%). Similar products result from 1,2-octadecanediol. The structures of the products are based on combustion data, spectroscopic, and chemical evidences. The mechanism of the reaction has been discussed.     

Limiting Phenomena in the Reaction of Fluorine with Hydrogen

Reactions involving energy branching and deceleration by the end product were studied using as an example the reaction of fluorine with hydrogen. It has been shown that for such reactions, entrance into the autoignition region determined by static conditions (reagent concentration, pressure, and temperature) due to variation in the pressure of the mixture may be or may not be accompanied by mixture autoignition. The parameter determining the behavior of a particular mixture is the rate of variation in the mixture pressure. A process of fast (in the range of seconds) preparation of fluorocarbon mixtures with minimal yield of hydrogen fluoride is substantiated.     

加氢操作反应机理及装置功能特性

通过反应物传质模型论述了加氢反应装置的反应机理;分析了反应阻力与其影响因素之间的关系;介绍了搅拌槽型加氢反应装置的结构形式和操作过程;以混合型加氢反应器和自吸式搅拌槽为例,论述了加氢反应器的性能特征、主要功能和技术管理要点。     

Reaction of Terminal and Non-terminal Dihydroxy Fatty Acids with Hydrogen Bromide

The action of hydrogen bromide on non-terminal glycol acids (threo and erythro-6,7-dihydroxystearic acids) leads to the formation of 6(7)–7(6)-bromoacetoxystearic and 6(7)-ketostearic acids as major and minor products of the reaction. On the other hand the same reaction on a terminal glycol acid, 10,11-dihydroxyundecanoic yielded only one bromoacetoxy acid (10-acetoxy-11-bromoundecanoic) and a diacetoxy derivative (10,11-diacetoxyundecanoic) as minor and major products. Assignment of configuration and structures of reaction products are based on the I. R., N. M. R. and mass spectral studies. It is evident that hydrogen bromide reaction of the terminal glycol acid takes a different course from that observed in the nonterminal dihydroxy acids.     

Effects of Radiation and Hydrogen on the Fracture Resistance of Borosilicate Glasses

In this study, short bar fracture toughness samples were used to determine the effects of radiation and hydrogen on the resistance to fracture of vitreous silica and four commercial borosilicate glasses. The results showed that neither exposure to 10¹⁰ rads of γ-radiation nor saturation to a room-temperature-equivalent exposure of 408 atm of hydrogen had an effect on fracture resistance. Nevertheless, when samples were saturated with hydrogen and then exposed to radiation, resistance to fracture increased significantly in some of the glasses. The increase in the resistance to fracture correlated directly with the increase in concentration of hydroxyl and hydride groups created by exposure to radiation and hydrogen. The concentration of these groups differs with glass composition and accounts for the difference in behavior between the types of glass studied.     

过氧化氢氧化苯甲醛反应的研究

研究了在无催化剂及以硫酸铜、金属铜、浓硫酸为催化剂的不同条件下,过氧化氢对苯甲醛的氧化反应。考察了苯甲醛和过氧化氢的摩尔投料比、温度、浓硫酸用量和反应时间对反应的影响．结果表明：温度60℃、反应时间36h、加浓硫酸2滴(以25mL苯甲醛为基准)、投料比为2时,苯甲酸的产率可达86．5％。     

含甲醛废水的过氧化氢湿式氧化及其反应动力学

在连续流釜式反应器中,以过氧化氢为氧化剂,辅以温度和压力,研究了湿式氧化法处理甲醛模拟废水的工艺条件:过氧化氢供氧量为废水理论需氧量的110%时为宜;160~180℃为甲醛湿式氧化的适宜温度范围;甲醛初始浓度在480~1500mgL-1范围内能保持较高的去除率。建立了该反应的指数型经验动力学模型方程,得出基于甲醛和COD的表观活化能分别是38.67kJmol-1和53.02kJmol-1。 反应产物的紫外光谱分析表明中间产物甲酸的进一步氧化是甲醛彻底降解的限速步骤。     

Reaction of Fused Silica With Hydrogen Gas

Fused silica and flowing hydrogen gas react in the experimental temperature range of 1200° to 1400°C to form SiO and H₂O vapors. Above a critical flow rate of hydrogen gas, the reaction rate is independent of gas flow rate and is not transport-controlled. The apparent activation energy for the overall process was 343±33 kj /mol (82±8 kcal/mol). The rate-limiting step is deduced to be desorption of the product from the glass surface.