Effect of Organic Acids on E-Glass Fabric

E-glass fabric was treated with organic acids. Acid treatment leaches nonsiliceous ions from the glass structure via ion exchange. The degree of removal is determined by the strength of the acid and leaching time. The results, which are compared with those for mineral acids, show that the acid anion is involved in the leaching process.     

Effect of Stress and Temperature During Forming on Strength of Glass

The effect of mechanical stress during the drawing process on the strength obtained was determined for large-diameter fibers of soda-lime-silica glass. Fibers were formed by down-drawing cane at a constant rate, using loads of from 100 to 8000 gm. Tensile strength was determined by transverse loading on annealed specimens. The results showed that the variation of temperature and load during forming increased the strength of the drawn fiber as much as 62%. The tendency toward increased strength persisted, but to a lesser extent, after the surface of the fibers was abraded.     

Effect of Hydrogen-Water Atmospheres on Corrosion and Flexural Strength of Sintered α-Silicon Carbide

Sintered α-SiC was exposed for 10 h to H₂ containing various partial pressures of H₂O ( P _H2O from 5×10⁻⁶ to 2×10⁻² atm; 1 atm≅10⁵ Pa) at 1300° and 1400°C. Weight loss, surface morphology, and room-temperature flexural strength were strongly dependent on P _H2O. The strength of the SiC was not significantly affected by exposure to dry H₂ at a P _H2O of 5×10⁻⁶ atm; and following exposure at P _H2O >5×10⁻³ atm, the strength was even higher than that of the as-received material. The increase in strength is thought to be the result of crack blunting associated with SiO₂ formation at crack tips. However, after exposure in an intermediate range of water vapor pressures (1×10⁻⁵< P _H2O <1×10⁻³ atm), significant decreases in strength were observed. At a P _H2O of about 1×10⁻⁴ atm, the flexural strength decreased approximately 30% and 50% after exposure at 1300° and 1400°C, respectively. The decrease in strength is attributed to surface defects caused by corrosion in the form of grain-boundary attack and the formation of pits. The rates of weight loss and microstructural changes on the exposed surfaces correlated well with the observed strength changes.     

Effect of Sulfur Dioxide Atmospheres on Efflorescence

The effect of sulfurous atmospheres on the efflorescence of structural clay materials was studied. An efflorescing shale and a nonefflorescing clay were fired in 5 and 0.5% sulfur dioxide atmospheres. The efflorescing tendency was determined by a wick-action type of test, and the efflorescing salts were analyzed by microchemical techniques. The effects of additions of calcium carbonate and magnesium carbonate to the nonefflorescing material were studied. Sulfate development in the drier was investigated by drying specimens in a sulfurous atmosphere. Efflorescence was obtained on specimens prepared from a normally nonefflorescing material when this material was fired in a sulfurous atmosphere; the efflorescence tendency was increased, however, by drying in an atmosphere containing sulfur dioxide.     

Adsorption of Water Vapor on E-Glass

The thermodynamics of a water-vapor-E-glass system were studied by adsorption-isotherm analysis. The seven isotherms completed were Brunauer type IV with permanent hysteresis. The first adsorbed water layer could not be removed by pumping, indicating permanent hydrolysis. Application of heat removed the remaining water to close the hysteresis loop. Calculation of isosteric heat of adsorption indicates that the adsorbed state is between the solid and the liquid states, equivalent to the loss of one vibrational and one translational degree of freedom. A new plot of energy vs thickness is proposed which describes the adsorption independent of surface area, as contrasted to the usual energy-vs-volume plot which was found to depend on surface area. A modified Clausius-Clapeyron equation is proposed for computing the isosteric heat of adsorption.     

Leaching of E-Glass

The extraction of acid-soluble oxide constituents in E-glass fibers was studied as a function of acid strength and time. Leaching was found to be diffusion controlled. Surface area, moisture adsorption, and weight loss measurements show that the porous structure that results on leaching is controlled by acid strength and time. Polymerization occurring on leaching and aging accounts for structural changes in the porous product.     

Sintering Alumina: Effect of Atmospheres

Two effects of atmosphere on the sintering of alumina powder compacts were investigated. Changing the oxidizing conditions during early-stage sintering measurements showed that, within the range −70°F dew point oxygen to −70°F hydrogen equilibrated with alumina, there was no observable effect on sintering rate. The effect of trapped atmosphere on closure of pores was determined from apparent density limits obtained at high sintering temperatures and long sintering times. The complete elimination of porosity during sintering of alumina was possible if discontinuous grain growth was controlled and if the ambient atmosphere was hydrogen, oxygen, or vacuum. Porosity could not be completely eliminated when the ambient atmosphere was helium, argon, or nitrogen (or therefore air).     

Effect of Various Atmospheres on Thermal Con ductance of Refractories

The thermal conductance of insulating firebrick was measured in gas atmospheres other than air. The effect of using insulating firebrick in gases of thermal conductivity higher or lower than that of air was correlated with porosity. Curves are presented that permit direct computation of the thermal conductance of these brick in any gas atmosphere of known thermal conductivity. An equation is given for estimating the thermal conductance of a clay-based brick using only its porosity and thermal conductance in air.     

聚乳酸热老化和生物降解性能的影响研究

研究了添加氧化镁(MgO)对聚乳酸(PLA)性能的影响.结果表明:MgO的存在对PLA的结构影响不明显,使PLA结晶度降低,一定程度上抑制了PLA的老化,并且对PLA的降解有促进的作用.MgO对PLA力学性能下降有所抑制;同时也加快了PLA的降解速度.     

Strength of Epoxy/Glass Interfaces after Hygrothermal Aging

The stability of epoxy/glass interfaces subjected to hygrothermal aging was assessed using a fracture-mechanics approach. An epoxy system consisting of diglycidyl ether of bisphenol F cured with 2-ethyl-4-methyl-imidazole was bonded to borosilicate glass adherends that were treated with various types of adhesion promoters to provide a variety of interfaces. Adhesive strength was measured under dry, as-processed conditions and as a function of exposure time to an 85°C/85% relative humidity (RH) environment. As expected, the strain-energy-release rate, G_c, dropped significantly with aging time for the bare epoxy/glass interface. The drop in G_c is assumed to be due to a loss of interfacial forces. The use of two silane-based adhesion promoters, 3-aminopropyltriethoxysilane (APS) and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (ECH) resulted in improved adhesive strength both before and after hygrothermal aging. The improvement in adhesive strength can be explained by the introduction of chemical bonds at the interface. The drop in G_c is assumed to be due to a loss of interfacial forces and hydrolysis of siloxane bonds. In addition to the use of organosilane-based adhesion promoters, a series of polyhydroxyaminoethers (PHAE) thermoplastic adhesive resins was also investigated as potential adhesion promoters. It was found that 2% PHAE in Dowanol® PM, a hydroxyl-group-containing solvent, was the best system for the PHAE-based adhesion promoters. Interestingly, both the acetic acid concentration in the solvent and maleic anhydride content in the PHAE resin were shown to affect the adhesive strength.     

Strength of Epoxy/Glass Interfaces after Hygrothermal Aging

The stability of epoxy/glass interfaces subjected to hygrothermal aging was assessed using a fracture-mechanics approach. An epoxy system consisting of diglycidyl ether of bisphenol F cured with 2-ethyl-4-methyl-imidazole was bonded to borosilicate glass adherends that were treated with various types of adhesion promoters to provide a variety of interfaces. Adhesive strength was measured under dry, as-processed conditions and as a function of exposure time to an 85°C/85% relative humidity (RH) environment. As expected, the strain-energy-release rate, G _c , dropped significantly with aging time for the bare epoxy/glass interface. The drop in G _c is assumed to be due to a loss of interfacial forces. The use of two silane-based adhesion promoters, 3-aminopropyltriethoxysilane (APS) and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (ECH) resulted in improved adhesive strength both before and after hygrothermal aging. The improvement in adhesive strength can be explained by the introduction of chemical bonds at the interface. The drop in G _c is assumed to be due to a loss of interfacial forces and hydrolysis of siloxane bonds. In addition to the use of organosilane-based adhesion promoters, a series of polyhydroxyaminoethers (PHAE) thermoplastic adhesive resins was also investigated as potential adhesion promoters. It was found that 2% PHAE in Dowanol® PM, a hydroxyl-group-containing solvent, was the best system for the PHAE-based adhesion promoters. Interestingly, both the acetic acid concentration in the solvent and maleic anhydride content in the PHAE resin were shown to affect the adhesive strength.     

炭黑对三元乙丙橡胶耐湿热老化和热空气老化性能的影响

研究了半补强(SRF)、高耐磨(HAF)、快压出(FEF)、喷雾(SCB)和导电炭黑(CCB)等5种炭黑对三元乙丙橡胶(EPDM)的补强作用、耐湿热老化性能和耐热空气老化性能的影响。结果表明,在加入炭黑后,随着炭黑粒径减小,炭黑对EPDM的补强效果得到提高。其中小粒径的CCB和HAF能使EPDM硬度和拉伸强度上升幅度较大,同时拉断伸长率降低。而它们良好的补强效果能在EPDM的老化过程中起到显著的稳定作用。EPDM/CCB和EPDM/HAF硫化胶的物理机械性能,均在湿热老化(40℃/93%相对湿度)和热空气老化(120℃)中表现稳定。     

老化条件对HDPE性能的影响

以高密度聚乙烯(HDPE)为主要研究对象,在其中添加一定量的纳米ZnO制成复合材料,并用傅里叶红外变换仪和熔融指数仪,分析其在人工加速真空老化、湿热老化、紫外老化条件下的宏观性能变化和微观结构变化.实验结果表明,纳米ZnO的加入能抑制HDPE的老化,添加量为1.5％(质量分数)时效果最佳;各种老化条件中,紫外老化对材料性能影响最大.     

Effect of Aging on Glaze Suspensions Rheology

The rheological behavior of glaze suspensions has to be closely controlled to obtain an adequate final product. In this work, we have studied glaze suspensions produced with a range of industrial frits. The main objective was to establish a correlation between changes in rheological behavior with aging and modifications in the ionic composition of the liquid phase, as a consequence of frit dissolution. Suspension rheology was followed through flow and dynamic oscillatory tests. It was found that frits releasing Ca²⁺, B³⁺, and Pb²⁺ can pose handling problems. To better understand the effect of cations' presence on glaze rheology, industrial glazes were compared with simulated glazes produced with inert silica and several cations. These suspensions reproduced the behavior of the industrial glazes and may be used in the future in stabilization tests.     

Equilibrium and Transport Properties of Gases in E-Glass Melts

The solubility and diffusion coefficients of oxygen, sulfur dioxide, and water were determined (and those for nitrogen, carbon dioxide, and argon were estimated) in commercial E-glass melts as a function of melt temperature and atmosphere. Knowledge of these fundamental constants of gases in glass melts is required for the development of models for bubble growth and elimination within the melt. The effectiveness of fining agents can be traced to the production of those gases in the melt which possess the greatest variation in solubility and diffusion as a function of the temperature and atmosphere. Accordingly, oxygen through multivalent elements and sulfur are the best fining agents for glass production.     

拉伸强度与弯曲强度的关系及弯曲强度尺寸效应

本文研究了材料的破坏发生区、拉伸强度与弯曲强度的关系及弯曲强度的尺寸效应。拉伸及弯曲强度的关系为σ_t=σ_b(1-△/h),弯曲强度尺寸效应表现为σ_(bo)/σ_b=(1-△/h)/(1-△/h_0)。本文研究为精确测试材料拉伸强度提供了简便的方法,同时提供了破坏发生区的测试方法。     

Influence of Surface Conditioning Protocols on Glass-Fiber Post Adhesion Performance After Aging and Flexural Strength

The effect of surface-conditioning of fiber-posts on the flexural strength of the post and on the adhesion between the root dentin and cement and between the fiber-post and the composite core were assessed. The fiber-posts were subjected to cleaning with alcohol (AL), treatment with AL + silane (SIL), sandblasting with Al₂O₃ particles + SIL, H₂O₂ etching + SIL, hydrofluoric acid etching + SIL, and H₃PO₄ etching + SIL. For comparison, another group of specimens was left unconditioned (control group). The conditioned fiber-posts were cemented to bovine roots, and standardized cylindrical resin cores were fabricated. The specimens were subjected to 10⁶ mechanical pulses and then sectioned perpendicular to the long axis of the root. Push-out tests were conducted on the sliced root sections, and microtensile testing was applied to the trimmed sliced core sections. The posts were also subjected to three-point bending tests. The surface-conditioning did not have any significant effect on the push-out strength. However, silanization increased the microtensile strength at the resin core. Sandblasting significantly decreased the flexural strength as compared to other surface treatments. Our study indicates that post surface-conditioning did not improve the post retention in the root canal, although silanization enhanced the adhesion to the core resin. Sandblasting with 125-µm alumina particles should be avoided.     

酸性溶液对聚碳酸酯结构和性能的影响

研究了聚碳酸酯经过酸性溶液老化后结构和性能的变化,力学性能测试,结果表明:酸性溶液老化后,冲击强度下降,拉伸强度先上升后下降,弯曲强度没有明显的变化;扫描电镜(SEM)断口形貌分析显示老化后PC以剪切屈服破坏机理为主;差示扫描量热分析(DSC)显示老化后玻璃化转变温度向高温区偏移;傅里叶变换红外光谱(FTIR)分析显示老化后PC的基本结构没有变化。