Acid-base interfaces in fiber-reinforced polymer composites

The role of Lewis acid-base interactions at the fiber-matrix interface in composites is studied with both glass and Teflon fibers. In the glass fiber case, surface chemistry is modified with amino-, methacryloxy- and glycidoxy-silane coupling agents (A-1100, A-174 and A-187, respectively). Silane adsorption mechanisms as well as the properties of filament-wound, unidirectional epoxy and polyester composites are explained by a combination of X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and flow microcalorimetry. The heats of adsorption of pyridine and phenol prove that the coupling agents add acidic sites to the glass fiber surface as well as stronger basic sites. The subsequent adhesion of the matrix polymers and the short beam shear strengths of composites are explained on this basis. The Teflon fibers are first etched with sodium naphthalene solutions, and then sequentially hydroborated and acetylated, producing approximately monofunctional hydroxyl (acidic) and ester (basic) groups on the surfaces, as determined by XPS, FTIR, and electrophoretic mobility analyses. Composites prepared with the acetylated fibers and a chlorinated polyvinyl chloride (acidic) matrix are superior in tensile properties, and SEM fractography shows PTFE fibrillation, indicative of good fiber-matrix adhesion and stress transfer, in this case only.     

Acid-base character of carbon fiber surfaces

The acid-base character of the surfaces of commercially available carbon fibers used in advanced composites is determined using both pulsed and continuous flow microcalorimetry techniques. The carbon fibers investigated include unsized versions of AS4, IM6, IM7X, T300, and several Apollo fibers with different levels of surface treatment. All of these carbon fiber surfaces are amphoteric and energetically heterogeneous. In general, the heats of preferential adsorption in the pulsed flow mode of bases dissolved in n-heptane are larger than for acids. While most of the adsorbates used are reversibly and physically adsorbed onto the carbon fibers, some primary and secondary amines exhibit irreversible binding to a portion of the surface. In continuous flow experiments the adsorption heat isotherms for several bases on T300 display a sharp jump at low probe concentrations, reflecting the energetically heterogeneous nature of these surfaces. Comparisons between the flow microcalorimetry data and other measures of the surface chemistry are made. Pulsed flow adsorption heats correlate with the amount of oxidized carbon species on the fiber surfaces as detected using ESCA, and recently reported results of inverse gas chromatography and programmed thermal desorption (S. Wesson, Textile Research Institute). Calorimetry results are also compared with fracture mechanical measures of fiber-resin adhesion in manufactured composites. Adsorption heats of both acids and bases on selected carbon fibers correlate with edge delamination and 90° flexural strengths of composites composed of these fibers in both epoxy and bismaleimide resins. This supports a causal connection between carbon fiber surface adsorption heats and a practical measure of fiber-resin adhesion.     

Enzyme flow microcalorimetry—a useful tool for screening of immobilized penicillin G acylase

Screening of a representative series of immobilized penicillin G acylase biocatalysts (enzyme, cells) using enzyme flow microcalorimetry is described. Immobilized penicillin G acylase biocatalysts were either prepared in the laboratory by various techniques or obtained from four commercial manufacturers. An industrial strain of Escherichia coli was entrapped in (poly)acrylamide gel or hardened calcium pectate gel. Semi-purified enzyme was immobilized in various ways—either by covalent binding to oxirane-acrylic beads or chlorotriazine bead cellulose or by entrapment in (poly)acrylamide gel. The validity of the enzyme flow microcalorimetry results was corroborated by a pH-stat method, showing enzyme flow microcalorimetry to be a suitable method for rapid screening of immobilized biocatalysts regardless of the immobilization technique, carrier type or the biocatalyst source. © 1998 Society of Chemical Industry     

A calorimetric examination of coal surfaces

This communication reports the results of some exploratory experiments to examine the surface of coal by (i) flow microcalorimetry (FM) and (ii) vapour sorption calorimetry (VSC). Excepting differential scanning calorimetry, calorimetric methods have not been widely-exploited in coal structure research. The intent of this short communication is to demonstrate that hitherto neglected calorimetric methods are very rewarding when applied to the study of coal surfaces.     

The influence of surface acidity and basicity on adhesion of poly (ethylene-co-acrylic acid) to aluminum

This work demonstrates the usefulness of flow microcalorimetry for surface characterization of metal foils (aluminum) and polymer [poly (ethylene-co-acrylic acid)] fibers. It shows that the polymer to aluminum adhesion is dominated by Lewis acid/Lewis base type interactions. These interactions are predictable from the measured heats of surface adsorption and desorption of probe molecules from dilute solution. The heats of interaction are a measure of the strengths of these sites. Adhesion between basic aluminum foil and acidic polymer resin increases with increasing numbers of either acidic sites on the polymer or basic sites on the foil. The calorimetry and adhesion results are in good agreement. This study supports recent observations vide infra that wettability of the aluminum is much less important for polymer/aluminum adhesion than chemical bonding.     

Kinetic model and effect of surface impurities on the crack healing of BK7 glass

When BK7 glass material is heated under appropriate conditions, surface cracks heal spontaneously under the action of viscous flow and capillary forces. In this paper, based on the theories of viscous fluid and capillary flow, a kinetic model for crack healing is established. A series of thermal healing experiments with different parameters are conducted on Vickers indentation radial cracks on BK7 glass, and the effects of surface impurities, heating temperature, crack size, and ambient humidity are studied. The results show that the surface impurities and humidity can promote crack healing. Upon combining the experimental results and relevant theories, the initial kinetic model is modified to accurately predict the healing process of the BK7 glass and describe the relationships among the crack healing length and these factors. In addition, the proposed model can be used for the healing of other materials with the mechanism of viscous capillary flow.     

E玻璃窑炉液流速度计算及案例分析

从运行窑炉中存在的跑料问题入手,引入E玻璃窑炉表面液流速度计算方法。通过计算玻璃液流速度,优化窑炉工艺制度,提高窑炉表面液流速度,很好解决了窑炉跑料问题,确保了拉丝作业的稳定性,促进了生产。     

Heat Flow Calorimetry of Propellants – Effects of Sample Preparation and Measuring Conditions

Isothermal microcalorimetry measurements were performed on the double base ball propellant K 6210. The influence of different sample preparation techniques and measuring conditions is discussed. The most important parameter is the atmosphere above the propellant. If air is replaced by nitrogen a reduction of primary effects can be observed. A replacement by oxygen leads to a complete different decomposition reaction. Comparable effects are achieved when the ampoules are only filled to 25%. In this case oxidation reactions can be observed. Also using ampoules that are not tightly closed changes the decomposition reaction. All experiments were accompanied by stabiliser analyses (HPLC) that demonstrate the different decomposition reactions as well. Changing the temperature but leaving the sample preparation and measurement conditions unchanged heat flow curves are observed that are similar in shape. That means that the decomposition reactions are comparably activated. Reducing the volume to lower the sample amount is not possible by adding glass balls because absorption/desorption reactions cover the first part of the decomposition reaction. If a glass rod is taken there is no change in the shape of the curve.     

Quantum-mechanical approach to understanding acid-base interactions at metal-polymer interfaces

Molecular orbital theory is presented as a means to understanding metal-polymer interfacial chemistry. While the systems used in molecular orbital studies tend to be rather idealized, much insight may be gained from such studies. Three different investigations are cited as examples of the applicability of molecular orbital theory in describing how functional groups of an adsorbate bond to a metal surface as well as how quantum-mechanical calculations may be used to interpret experimental data, e.g. photoelectron spectra. Experimental techniques (nucleophilic displacement, isoelectric points, flow microcalorimetry, and temperature-programmed desorption) for determining acid-base interactions are also discussed briefly.     

浮法玻璃表面锡类颗粒污染物起源及治理措施分析

通过对浮法玻璃生产线渣箱内部污染物的分析、污染物与锡槽内气流分析,确定了浮法玻璃板表面锡类污染物颗粒主要来源于锡槽内锡液的汽化蒸发产生的锡液滴,提出了通过采取措施减少锡槽内锡液的汽化蒸发量,减少锡槽空间内气流中的锡液滴浓度来预防浮法玻璃锡类污染物,达到减少玻璃板表面污染的目的。     

Observation of Cell Structures Developed by Marangoni Convection in Glass Thick Films

Cell structures developed by convection in glass thick films have been studied with special emphasis on the effects of material parameters and heating conditions on the cell structure. Borosilicate glass films from 10 to 30 μm thick were prepared on alumina substrates by printing and firing at temperatures between 750° and 950°C up to 2 h, and surface flow patterns were observed with an optical microscope under dark-field illumination. In most cases a flow pattern developed and changed with time, finally reaching a steady state. Cell structures with regular polygons of four to seven sides from 15 to 150 μm across developed, depending on the glass composition. The effects of heating time, temperature, film thickness, and glass chemistry on the cell structure have been examined. From observations of cell structures, the driving force for the convection in glass thick films has been identified to be the gradient in surface tension due to small temperature fluctuations on the surface. Hence, it is concluded that the convection in glass thick films is of Marangoni type.     

丝网印刷艺术装饰玻璃的方法

通过对在玻璃上丝网印刷艺术装饰玻璃所需要的原稿的选择,四色分色片底版的制作方法,丝印网版的制作方法,玻璃钢化油墨的选择,玻璃表面的预处理方法,以及如何在玻璃表面进行印刷和玻璃如何进行钢化的实践和探索,对在生产中影响产品质量的各重要工艺参数进行了具体的实践和分析,初步总结出了一套适合于进行丝网印刷艺术装饰玻璃的工艺流程和实施作业的具体方法。     

阳光控制镀膜玻璃表面缺陷的观察与分析

采用常压化学气相沉积法在浮法玻璃上制备了阳光控制镀膜玻璃。用扫描电镜和能谱仪对镀膜玻璃表面的缺陷进行了观察,分析了产生缺陷的原因。结果表明:镀膜玻璃样品表面存在典型的孔洞、翘曲和皱褶等缺陷,缺陷的尺寸不超过100μm,孔洞缺陷发生在薄膜与基体之间。缺陷的形成与制备工艺条件,如:反应气体的配比、流量、玻璃板的厚度与玻璃基体的化学成分等因素有关。     

A comparative physico-chemical study of bioactive glass and bone-derived hydroxyapatite

This study aimed at comparing the physico-chemical properties of bioactive glass and bone-derived hydroxyapatite (HA). 63S bioglass particles were obtained by sol-gel process and HA samples were derived from bovine bone. The chemical composition and the crystalline structure of both bioceramics were evaluated. Then the zeta potential in physiological saline and at different pH values was determined. It was found that the negativity of zeta potential for 63S bioglass is higher than that of bone-derived HA. The exothermal behavior through the hydration process was evaluated by isothermal microcalorimetry. The results showed that the librated heat during bioactive glass hydration process and its rate are almost ten times higher than HA. It could be related to different hydration mechanisms of bioglass and HA. However, for both bioglass and HA, this value is in the safe range and cannot be harmful for the adjacent tissues in the body.     

Kinetic Processes Involved in the Sintering and Crystallization of Glass Powders

Viscometry, crystal growth kinetics, and glass powder sintering were used to determine the activation energies of viscous flow, crystal growth, and sintering behavior of a standard NBS 710 glass and two crystallizable glass powders in the calciaaluminosilicate system. In a system which sintered successfully to zero porosity, the activation energy for sintering was comparable to the activation energy of viscous flow. When the apparent activation energy for the sintering process was lower than that of viscous flow, sintering was found to proceed at a slower rate because the precipitated crystalline phase retarded viscous flow and the shrinkage of the pores. Initial crystallization appeared to occur on the surfaces of coalesced particles. A chemical treatment was partially successful in suppressing the onset of surface nucleation of the precursor powder.     

等离子体射流载气流量大小对玻璃纤维改性效果影响的研究

通过大气压等离子体射流在玻璃纤维（GF）表面沉积氧化硅（SiOx）纳米颗粒的方法改善玻璃纤维增强聚丙烯（GFRP）复合材料的界面结合性能,利用扫描电子显微镜、原子力显微镜和X射线光电子能谱等表征分析了改性纤维的表面形貌、化学成分、润湿性能和复合材料的界面结合性能,并考察了等离子体射流载气流量大小对GF改性效果的影响。结果表明,当载气流量为40 mL/min时,GF的改性效果最好,且此时GF的表面能相比对照组提高了43.18%,GFRP复合材料的层间剪切强度提高了30.79%;经过等离子体处理后,GF的表面粗糙度增大,极性官能团增多,复合材料的界面结合性能提升。     

Simplified Mathematical Model Simulating Heat Transfer in Glass-Forming Molds

Heat transfer in glass-forming operations depends on many factors, e.g. the properties of the glass, heat-transfer coefficients at the glass/mold and mold/air interfaces, the characteristics of the mold material, and the glass/mold contact time. Using a computer model developed for one-dimensional heat flow, the influences of these factors were calculated. The heat-transfer parameters, which were analyzed individually, include e.g. the glass surface temperature, the peak inner mold surface temperature, the quantity of heat transferred from glass to mold during a steady-state cycle, and the amplitude of mold surface temperature oscillation at steady state. Comments are given on the significance of the results.     

Performance of floating cum tilted-wick type solar still with the effect of water flowing over the glass cover

A simple transient performance of floating cum tilted-wick type solar still has been presented by incorporating the effects of water flowing over a glass cover, heat capacity of tilted-wick water surface and floating-wick water surface. Explicit expressions for flowing water, glass, tilted-wick water surface and floating-wick water surface temperature and efficiency of the system have been derived. Numerical calculations have been carried out for a typical day in the month of March 2004. The relative standard deviations between the numerical and experimental results of different temperature components of the proposed still have been found. The results indicate that the relative standard deviations between theoretical and experimental results are less than 8% (glass cover), 2% (tiltedwick water surface), 1% (floating-wick water surface) and 2% (flowing water at the lower end of the glass cover) an average for the working hours of the day. Moreover, based on the numerical results, the following conclusions have been drawn: (i) glass cover temperature decreases significantly; (ii) the effect of water flowing over the glass cover has a fascinating effect on the production of distillate output during peak sunny hours; (iii) water flow rate of 1.5 m/s is optimum, and beyond it the efficiency decreases. Experimental investigations have been performed at Sri Ramakrishna Mission Vidyalaya College of Arts and Science, Coimbatore, India.     

Effect of surface morphology on the flow of entrained fine particles by ascending gas through packed beds

Coarse particles of glass or cokes were packed in vertical columns, 1- and 2-m in height, and fine particles of glass or coke were entrained through the columns by the ascending gas flow. These systems were used as a model to investigate the flow of fine coal particles introduced into a blast furnace. The effects of properties of packed particles, as well as fines, on the static and dynamic holdups of fines were then investigated. The static holdup of fines was strongly affected by the surface roughness of the packed particles, while the dynamic holdup of fines was not. These results suggest that the fine particles are trapped in the form of static holdup in the isolated narrow spaces bounded with packed particles, and that they remain on the surface of the packed particles which are exposed to the gas flow for only a short period of time.