Strength loss in E-glass fibres after exposure to hydrochloric,hydrobromic and hydriodic acids

The corrosion of E-glass fibres by hydrochloric, hydrobromic, and hydriodic acids has been investigated by measuring the loss of mechanical strength of the fibres following immersion in solutions of the acids. Corrosion is greatest in hydrochloric acid and least in hydriodic acid. Curves of percentage strength retention against concentration show well-defined minima for hydrochloric and hydrobromic acids, but not for hydriodic acid. This phenomenon has been attributed to complex ion formation by metal ions in the glass with chloride or bromide ions in the corroding solution. Spectroscopic evidence suggests that ferric ions play an important role in the corroding process.     

Understanding physical changes and strength loss of E-glass fibres following exposure to elevated temperatures

The strength loss of glass fibres (GFs) following exposure to elevated temperatures is a long-established phenomenon, yet the mechanism or mechanisms responsible for the strength decrease are not fully understood, aside from acknowledgement that surface flaws must become more severe by some means. As disposal of GF-based composite materials by landfill has become untenable in many regions, interest in composite recyclability has increased. Separation of GFs from thermosetting polymers generally requires the use of high temperatures, which produces very weak fibres with minimal commercial value. In this context, an understanding of the strength loss mechanisms is of importance in terms of efforts to mitigate fibre damage or to recover the strength of previously heated fibres. In addition to fibre strength loss, numerous other physical and chemical changes to heat treated or recycled GF have been described in the literature.

This review was chosen as a runner up of the 2016 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining, run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged.     

Chemical corrosion of E-glass fibres in neutral phosphate solutions

Following local reports of failure of glass reinforced plastic (GRP) tanks used for the storage of ammonium orthophosphate fertilizer, the effect of phosphate solutions on the strength retention of E-glass fibre was investigated. Although solutions (1 to 5 mol dm^–3) of mineral acids are known to corrode E-glass fibre, phosphoric acid solution (3 mol dm^–3; pH 1.55) is essentially inert and strength retention of the glass fibre after 15 days exposure is the same as the water control. However, as the pH is raised strength retention is diminished and a minimum is observed around pH 7 to 8. A chemical explanation of this behaviour is put forward in terms of leaching and complex formation with calcium and magnesium ions. Although not nearly as corrosive as other agents, evidence suggests that phosphate solutions do corrode E-glass fibre and this should be borne in mind when GRP materials are used in such chemical environments.     

Diffusion behaviour of the core-sheath structure in E-glass fibres exposed to aqueous HCl

The existence of a characteristic core-sheath morphology in E-glass fibres undergoing acid corrosion is well known. This effect is attributed to the removal of calcium and aluminium ions from the glass structure. Sheath growth measurements indicate that this abstraction involves a two-stage diffusion process, with a room-temperature diffusion coefficient of 1.4×10^–16 m ² sec^–1 initially, slowing to 1.5×10^–17 m² sec^–1 at later times. This two-stage process is related to fibre structure. It is also shown that there is an initial delay, during which the core-sheath structure does not develop.     

The kinetics of corrosion of E-glass fibres in hydrochloric acid

The corrosion of glass fibres in acid solution is well known and is thought to be responsible for many instances of failure in glass reinforced plastic materials. Although it is generally accepted that cations are leached from the glass matrix into the acid solution, the precise chemical mechanism and rates of corrosion are still not fully understood. For example, it is not simply the hydrogen ion concentration of the corroding medium that affects the rate of corrosion, but in many cases the anion associated with the acid plays a major role. Anions that can form insoluble salts or complexes with cations in the glass matrix can increase the rate of leaching and hence accelerate the corrosion process. In the case of hydrochloric acid, it has been suggested that chloride anions form complexes with iron(III) ions leached from the glass and this in part increases the rate of corrosion. This paper investigates the corrosion rate of glass fibres exposed to hydrochloric acid at different concentrations and temperatures by measuring the residual strength of the fibres before and after exposure. The leaching rate of cations into solution is also measured using atomic absorption spectroscopy. As expected, increase in temperature increases the rate of corrosion and this can be modelled using a simple Arrhenius plot to determine the activation energy of the process. Strength retention and rates of leaching of individual cations are compared in an attempt to explain the mechanism of corrosion.     

Comparative evaluation of N-glass and E-glass fibres with special reference to their use in FRP composites

The abilities of E-glass and N-glass fibres and of composites based on them to withstand degradative effects in boiling water or in boiling aqueous solutions of HCl (10%), NaOH (0.5%) and NaCl (10%) have been evaluated on a comparative basis by following the loss or retention of strength properties (tensile/flexural) with the time of the respective degradative exposure. The degradative effects under different chemical environments for the composites were also analysed with the help of SEM micrographs of the composites before and after the specific degradative treatments. Analysis of strength properties and retention of strength and of the micrographs clearly indicates that N glass is highly superior to E glass, and the former imparts a much higher order of stability to composites in different chemical environments despite substantial initial advantages in the strength properties for E-glass fibre and composites based on this fibre.     

An acoustic emission study of failure by stress corrosion in bundles of E-glass fibres

Fibre failures in bundles of parallel E-glass fibres loaded from their ends and immersed in aqueous HCl solutions or in water are detected using acoustic emission. In constant load and constant stress tests the times to failure of the fibres and the bundles are accounted for on the basis of a theory which assumes a Weibull distribution of initial strengths, and that the velocity (v) of subcritical stress-corrosion cracks in the fibres depends on the stress intensity (K _l) according to a power law (VK _l ⁿ ). The crack growth parameter (n) is measured by three methods, and its variation with acid strength is correlated with other corrosion studies. The stress corrosion measurements also allow a determination of the Weibull modulus of the fibres.     

Physical characterization of E-glass fibres treated with alkylphenylpoly(oxyethylene) alcohol — fibres conditioned in solutions of different pH

The adsorption of alkylphenylpoly(oxyethylene)alcohol on E-glass fibres was characterized by X-ray photoelectron spectroscopy, by the Wilhelmy plate method and by streaming-potential measurements. In this study, the glass fibres were conditioned in solutions of different pH. The acid resistance of the E-glass fibres was studied by treating the material with H₂SO₄. During the acid treatment the surface composition, namely the Si/Al-ratio, was changed, presumably because the aluminium ions were leached out of the glass structure. The alkaline resistance was studied by treating the material with NaOH. The Si/Al-ratio was unaffected by these moderate alkaline solutions. The effect of the surface conditioning in solutions of different pH seemed to be greatest for the acidic solutions giving rise to an increased adsorption of the surfactant on the glass-fibre surface.     

Strength retention of silicon nitride after long-term oil immersion exposure

Two commercial grade silicon nitride ceramics (Honeywell GS44 and Kyocera SN235) were exposed to an oil ash to evaluate the long-term corrosion/oxidation resistance in a simulated diesel engine environment. The exposure condition was at 850 °C for 1000 h in air. Subsequently, the exposed specimens were tested in flexure for strength degradation at room temperature and 850 °C at stressing rates of 30 MPa/s and 0.003 MPa/s in air, respectively. A similar set of specimens not exposed to the oil ash was also tested in flexure for purpose of comparison. Little change in strength was measured after 1000 h exposure in the oil ash environment. Also, the values of Weibull modulus obtained for all of the exposed silicon nitride materials were similar to those with the unexposed specimens whose strength were obtained under the same conditions. However, both exposed and unexposed GS44 specimens exhibited a low fatigue exponent, suggesting a susceptibility to slow crack growth at test temperature. In addition, detailed SEM/EDAX analyses indicated that no oil ash elements (e.g., Zn, Ca, P, Na, and S) were detected beneath a thin layer in the surface; thus, there were no changes in the chemistry of the secondary phase(s) within the bulk. These elements were detected only in a region about 1–3 μm below the exposed surface, but no apparent changes in microstructure observed. Results of mechanical properties and microstructural characterizations indicated that these candidate silicon nitride materials exhibited excellent corrosion/oxidation resistance in the simulated diesel engine environment and, based on their excellent mechanical strengths, would be ideal candidates for diesel engine exhaust valve applications.     

Attack of cement pastes exposed to organic acids in manure

Manure such as silage effluents and liquid manure contains organic acids which constitute a severe chemical threat toward the concrete of agricultural structures. The purposes of this study were to identify the chemical composition parameters that influence durability by analysing the behaviour of the chemical elements of the cement paste (Ca, Si, Al, Fe and Mg) in organic acid solutions and to compare the intensity of the chemical attack by the different acids found in liquid manure. This study was carried out on cement pastes made from four binders (ordinary Portland cement, slag cement, OPC blended with silica fume and OPC blended with fly ash). The hardened cement pastes were first crushed, then immersed in solutions made of five organic acids with an initial pH of 4 and constantly stirred. The pH and the concentrations of major elements were monitored over time.

The results show that Si, Al, and Fe appear to be favourable elements for the chemical resistance of binders whereas the amount of Ca should be limited. Moreover, it is shown that the four acids found in liquid manure (acetic, propionic, butyric, iso-butyric) are equally aggressive. Lactic acid, present with acetic acid in silage effluent, is more aggressive according to the value of its pK_a.     

Modelling the loss in strength of AR-glass fibres in textile-reinforced concrete

AR-glass-reinforcement in concrete, which for example is used in the new composite material textile-reinforced concrete, loses strength in the long term as a consequence of weathering. The knowledge of this time-dependant development of strength loss is an essential aspect for the application of textile-reinforced components in structurally relevant areas. The present work describes investigations about the development of strength loss of AR-glass-reinforcement in concrete caused by weathering. First of all, the main reason for the loss in strength of AR-glass in concrete was determined [1]. Based on this, a mathematical approach to describe the loss in strength was derived for constant climatic conditions. This model was verified with numerous test results acquired by various investigation methods. The influence of humidity, temperature, pH-value and glass composition on the loss in strength of the AR-glass-reinforcement was investigated. The loss in strength of the reinforcement starts above a critical humidity and increases exponentially with higher temperatures. Additionally combined loads were analysed to finally derive a basis for a durability-model which can take arbitrarily complex weathering into account. Pull-out investigations underline that the bond between AR-glass-reinforcement and matrix is independent of the long-term weathering.     

An investigation of the mechanisms for strength gain or loss of geopolymer mortar after exposure to elevated temperature

When fly ash-based geopolymer mortars were exposed to a temperature of 800 °C, it was found that the strength after the exposure sometimes decreased, but at other times increased. This paper shows that ductility of the mortars has a major correlation to this strength gain/loss behaviour. Specimens prepared with two different fly ashes, with strengths ranging from 5 to 60 MPa, were investigated. Results indicate that the strength losses decrease with increasing ductility, with even strength gains at high levels of ductility. This correlation is attributed to the fact that mortars with high ductility have high capacity to accommodate thermal incompatibilities. It is believed that the two opposing processes occur in mortars: (1) further geopolymerisation and/or sintering at elevated temperatures leading to strength gain; (2) the damage to the mortar because of thermal incompatibility arising from non-uniform temperature distribution. The strength gain or loss occurs depending on the dominant process.     

Corrosion of electrodeposited copper by exposure to volatile organic compounds

In this paper we investigate the corrosive behaviour of various volatile organic compounds (VOCs) on electroplated copper. The VOCs we considered were of the following types: (i) aromatic and substituted-aromatic compounds (benzene, toluene and ethyl benzene); (ii) a chlorine-substituted hydrocarbon (dichloromethane) and (iii) an aliphatic alcohol (isopropyl alcohol). Contamination by VOCs is typical of ULSI (Ultra Large Scale Integration) manufacturing environments, and exposure of Cu to VOC-contaminated clean room air has been pinpointed as a serious cause of interconnects failure. SEM observation highlighted corrosion signature that are typical of the different classes of molecules. In particular, the corrosion of copper is almost absent following exposure to isopropyl alcohol, very slow in the case of aromatic molecules and severe in the case of dichloromethane. The obtained results can be interpreted in terms of a crevice corrosion mechanism under droplets, enhanced by pitting in the presence of chlorinated solvents.     

茶叶中有机酸的测试方法概述

针对茶叶中有机酸测定前处理分析测试条件等不统一,导致测试结果无可比性的问题,该文在参阅1907年以来国内外关于茶叶中有机酸分析的30余篇文献的基础上,对茶叶中有机酸的分析方法做了较系统的归纳阐述,并对目前常用的分析方法包括高效液相色谱法、离子色谱法以及毛细管电泳色谱法等进行了评述,提出了茶叶中有机酸测定应进行标准化,以确保测试结果的可比性。