Paint systems formulated with ion-exchange pigments applied on carbon steel: Effect of surface preparation

Ion exchange pigments are a scientifically very interesting alternative to chromates that have not yet been fully explored. This study considers the following candidate anticorrosive pigments: calcium-exchanged silica (Si/Ca), hydrotalcite/vanadate (HT/V) and calcium bentonite (Bentonite/Ca).     

The assessment of a smart anticorrosive coating by the electrochemical noise technique

Zinc phosphate and related compounds are convenient replacements for chromates. However, more eco-compatible pigments are being investigated. The objective of this research was to develop a modified zeolitic rock which is intended to replace phosphate pigments in anticorrosive paints. The modified zeolitic rock was obtained by grinding the rock followed with ionic exchange with molybdenyl ions. This “composite” has an intelligent behavior because molybdenum compounds are leached from the zeolite particle by corrodent species. The anticorrosive properties of this zeolitic rock were studied by electrochemical techniques, employing inhibitor suspensions, and formulating anticorrosive coatings. Coatings performance was evaluated by accelerated tests (humidity chamber and salt spray) and electrochemical noise measurements (ENM). Electrochemical noise data were analyzed in the time domain. The noise resistance (R_n) was compared, as far as possible, with the polarization resistance.     

Effect of insulation on the fire behaviour of steel floor trusses

This paper describes a study into the fire behaviour of open‐web steel trusses supporting concrete floor slabs, exposed to a range of realistic design fires. This study is intended to give some insight into the possible structural behaviour of the floor trusses in the World Trade Center (WTC) towers. The analysis was carried out using a non‐linear finite element program SAFIR. The trusses were analysed with and without protective insulation for several different fires, each with three types of connections; pinned at both ends, simply supported, and simply supported with an axial spring. This paper shows that the likely failure mode of the floor truss depends on the connection strength, and emphasizes the importance of ensuring that the insulation remains intact. Unlike the actual event in the WTC with multiple floors exposed to fire, this analysis only considers a single floor, hence the results from this analysis do not confirm the actual behaviour of the buildings while they collapsed. Copyright © 2004 John Wiley & Sons, Ltd.     

Surface potential distribution over a zinc/steel galvanic couple corroding under thin layer of electrolyte

In this study, surface potential and surface pH changes over a zinc/steel galvanic couple corroding in artificial seawater (ASW) at 60 and 90% RH have been investigated. The results from surface potential and surface pH measurements were substantiated by the surface observation of the corroded sample during and after the corrosion test. The potential difference over the zinc and steel surface in 90% RH was very low (less than 200 mV) showing that whole steel surface was under galvanic protection. On the other hand, in 60% RH, after several days of corrosion the potential difference between the zinc coating and the steel surface was very high (more than 500 mV) and hence the galvanic protection was limited to interface region. The X-ray analysis of the sample corroded in 60% RH has shown that the zinc corrosion products were deposited on the steel surface near the interface, the same region has shown a low pH compared to than in other part of the steel surface. This led to conclude that with the progress of corrosion, the coating surface of zinc coated steel acidifies by the hydrolysis reaction of the dissolved zinc ions, and the iron surface showed the alkalinity by the oxygen reduction reaction. Moreover, the parts of the steel surface covered with zinc corrosion products had developed relatively less noble potential than other parts indicating that zinc corrosion products took a role to protect the base steel against corrosion. It was assumed that this behavior was related to a combination of the water absorbing capability of zinc corrosion products and adsorption of zinc ion on the steel surface due to low pH.     

SKP and FT-IR microscopy study of the paint corrosion de-adhesion from the surface of galvanized steel

Scanning Kelvin Probe (SKP) and FTIR microscopy were applied to study the atmospheric corrosion of galvanized steel coated by electrophoretic epoxy resin (ED) at a defect.     

Study of the anticorrosive properties of polypyrrole/polyaniline bilayer via electrochemical techniques

In this work, using electrochemical techniques the authors investigated the protective properties of a polypyrrole/polyaniline bilayer as a conductive polymer. A polypyrrole/polyaniline bilayer was deposited on carbon steel substrate by potentiostatic method. The electric capacitance and resistance of the films were monitored with the immersion time in a corrosive solution to investigate the water permeability of the films. Polypyrrole/polyaniline bilayer has a relatively low permeability and good catalytic behavior in passivation of carbon steel in longer periods. The results show that the bilayer has a better anticorrosive behavior compared to homopolymers (polypyrrole and polyaniline).     

Electrochemical behaviour of an AISI 304L stainless steel implanted with nitrogen

In this paper the electrochemical behaviour of AISI 304L stainless steel implanted with nitrogen is studied in alkaline media and chloride-containing media, and it is compared with the behaviour of the unimplanted material. Implantation was done at a saturation dose (4 × 10¹⁷ ions cm⁻²) at an acceleration voltage of 150 keV. The results show a clear improvement of the corrosion resistance for the implanted specimens. No pitting potential is observed in the alkaline media or in the neutral media containing high chloride concentration. The improved corrosion resistance is presumed to be due to the modifications that N⁺ implantation induces in the passive layer that is naturally formed on the alloy. XPS analysis reveals Ni⁰ and Cr³⁺ enrichment in this passive layer. Moreover, a carbon-rich layer is found at the outermost part of the passive layer. The presence of this outermost layer is verified with electrochemical impedance measurements and SEM observations.     

Evaluation of the anticorrosive behaviour of organic coatings applied on galvanised steel surfaces

Conclusions  The study of the anticorrosive behaviour of the four systems of organic coatings — two with coal tar epoxy layer and two with zinc rich epoxy layer and external coating with epoxy paint — which were applied to galvanised steel specimens and were exposed to NaCl solution leads to the following conclusions:

Effect of molecular weight of phenalkamines on the curing,mechanical, thermal and anticorrosive properties of epoxy based coatings

The present investigation deals with the study of effect of molecular weight and structures of phenalkamine curing agents on the curing, mechanical, thermal and anticorrosive properties of epoxy based coatings. The phenalkamines were prepared by varying the composition of formaldehyde and diamine in the formulation. The structural characterization confirmed successful preparation of high molecular weight phenalkamines. These were then used as curing agents for air drying and thermally curable epoxy coatings. The effect of these phenalkamines on curing properties of epoxy resin as well as mechanical, chemical, thermal and dynamic thermo-mechanical properties of the resultant coatings was studied and compared with commercial phenalkamine. The anticorrosive properties of the coatings were evaluated by salt spray test and electrochemical impedance spectroscopy. The study revealed that high molecular weight phenalkamines resulted in faster surface drying due to rapid molecular weight build-up. The anticorrosive performance also improved as indicated by higher modulus and electrochemical potential values.     

Influence of heavy metal contaminants at variable pH regimes on rheological behaviour of bentonite

Long-term competent performances of clays as barrier and liner systems for waste landfills are dependent on both the physico-mechanical properties and attenuation characteristics of the clay soils. The presence of heavy metal ions in the pore water will alter the physico-chemical characteristics of the clay–water system, resulting in changes in the short- and long-term mechanical and chemical behaviour of the clay soil barrier materials. This study investigates bentonite–contaminant interaction at different pH levels and heavy metal ion concentrations, and their resultant effect on the mechanical behaviour of bentonite soil. A set of physico-chemical experiments including Atterberg limits, precipitation testing, pH measurement and consolidation were performed to investigate the fundamental mechanism of soil–contaminant interaction from a rheological point of view. Consolidation tests were performed to study volume change behaviour with respect to the control exercised by mechanical and osmotic stresses. The impact of multiple aspects of heavy metal ion interaction on the osmotic compressibility and consolidation of bentonite is investigated. It is shown that while the selectivity phenomenon governs the adsorption characteristics of contaminated bentonite, the microstructural change due to the lower pH level and the high concentration of HMs, the different onset of precipitation for Zn and Pb, and the osmotic phenomenon control the rheological performance of compacted bentonite. The theoretical aspect of the experimental investigation is addressed and the restrictions of classical double layer theory for heavy metal/clay soils interaction are illustrated.     

Effect of Al on the galvanic ability of Zn-Al coating under thin layer of electrolyte

The effect of Al on the galvanic ability of Zn-Al coating has been studied under thin electrolyte layers by measuring surface potential and surface pH. The changes of surface potential and surface pH over Zn-Al/steel galvanic couple corroding in artificial sea water (ASW) were measured at 60% and 90% RH at 298 K. In the initial stage of corrosion, Zn-55Al coating has shown better galvanic protection ability than Zn-5Al coating in both 60% and 90% RH. However, Zn-5Al coating was better in long term corrosion. The better galvanic ability of Zn-55Al coating in the initial stage of corrosion was related to the observation of pH as low as low as 2 on its surface. The low pH value was due to hydrolysis of Zn²⁺ and Al³⁺ ions. The low pH value was further confirmed by observing evolution of gas due to H⁺ reduction on the Zn-55Al coating. With the progress of corrosion, the low pH region of coating layer extended towards the base steel. This helped expand the deposition of zinc corrosion products on the steel surface. The enhanced dissolution of zinc in Zn-55Al coating led to the formation of a barrier layer which limited the galvanic protection of remaining steel. This was not the case in Zn and Zn-5Al coating. The X-ray analyses of the corroded samples have shown the deposition of zinc corrosion products on the steel surface, which greatly depended on the RH value. The part of the steel surface covered with zinc corrosion products has shown relatively less noble potential than other part indicating that zinc corrosion products took a role to protect the base steel against corrosion. The results from surface potential and surface pH measurements were substantiated by the surface observation of the corroded sample during and after the corrosion test.     

钢—热塑性树脂界面之间粘合的耐水性研究

研究钢/粘合剂/聚乙烯层状复合材料在自来水中的耐水性能。使用两种钢基材进行比较;一种未经任何表面处理(So),另外一种经过磷酸化表面处理(S_1)。粘合剂是聚乙烯接枝马来酸酐(PE-g-MAH)。采用剥离强度测试来定量分析钢/粘合剂/聚乙烯之间的粘接性能。结果表明,经磷酸化处理的层状物的耐水性好。     

EIS study of the effect of high levels of SO2 on the corrosion of polyester-coated galvanised steel at different relative humidities

The effect of SO₂ on the degradation of polyester-coated galvanised steel at different relative humidities was investigated using electrochemical impedance spectroscopy. Measurements were performed on specimens which had been tested in an accelerated gaseous corrosion test. For this purpose the samples were subjected to SO₂ gas for 16 days in atmospheric test cells with adjusted relative humidity (RH) from 60 to 100%. Subsequently, the impedance response of the coated material was measured and evaluated. The results indicated that the coating performance varies with RH. Thus, under condensing conditions, the organic coating and galvanised layer was totally removed, the impedance response being interpreted as the formation of an iron sulphide film on the surface. At lower RH, remarkably, the coating remained effectively intact with the coating resistance varying inversely with RH. This work is relevant to the application of such organic-coated products adjacent to combustion flues where high levels of SO₂ occur in association with high humidity.     

一种新型不锈钢常温化学除锈剂的研制

研制一种用于不锈钢表面锈蚀常温快速清洗的除锈剂,基础配方由盐酸和硝酸以18%∶18%的质量比组成,加入一定量的磷酸、柠檬酸、焦硝酸钠等,可以提高除锈效率和不锈钢的表面光亮度。研究十二烷苯磺酸钠、JFC渗透剂、乌洛托品的添加对除锈效果的影响,结果表明,配方中不宜添加十二烷苯磺酸钠,JFC渗透剂和乌洛托品的最佳添加量分别为1.5 g/L和6 g/L。     

ISO12944《色漆和清漆 钢结构防腐涂层保护体系》浅述

简要介绍了ISO12944《色漆和清漆钢结构防腐涂层保护体系》标准8部分内容:ISO12944-1基本介绍;ISO12944-2环境分类;ISO12944-3设计考虑原则;ISO12944-4表面类型和表面处理;ISO12944-5涂层保护体系;ISO12944-6试验室性能测试方法;ISO12944-7涂装管理和检查;ISO12944-8新建与维修时规格书的制订。     

Electrochemical behaviour of haemoglobin at the liquid/liquid interface

The electrochemical behaviour of haemoglobin (Hb) at the liquid/liquid interface was investigated. Based on ion transfer cyclic voltammetry and bulk ionolysis experiments, it is proposed that Hb adsorbs at the liquid/liquid interface and forms a multi-layer deposit thereafter repetitive cycling. However Hb does not cross the interface. The transfer peak current measured increased non-linearly with the bulk concentration of Hb in the aqueous phase but it did vary linearly with the square root of the scan rate. This diffusion-controlled process is ascribed to the Hb-facilitated transfer of the anion of the organic phase electrolyte. The electrochemical signal also increases with time suggesting a conformational re-arrangement of Hb at the liquid/liquid interface. The transfer peak potential was seen to vary with the nature of the anion, in agreement with the trend in hydrophobicity of the anions examined. Furthermore, at pH values ≥pI of Hb, no transfer peak was observed, suggesting that neutral or negatively charged Hb does not facilitate the transfer process.     

Surface relaxation at the metal/electrolyte interface

X-ray diffraction is an ideal technique for the in situ study of single crystal metal surfaces in an electrochemical environment. In this paper, measurements of the low-index surfaces of Au and Pt are described, in particular with reference to surface expansion effects. Surface expansion can be probed potentiodynamically to correlate expansion with the adsorption/desorption of solution species. In general, the results are in good agreement with recent theoretical calculations. The X-ray technique can also give insight into electrocatalytic reactions as shown by the results for the adsorption and oxidation of CO on Pt(111).     

喷漆铸钢件表面锈蚀分析与研究

为了解决喷漆后的铸钢件和结构件中的铸钢件部位在存放过程中表面提早发生锈蚀的问题,从底材处理、涂料性能、涂装工艺等方面对锈蚀原因进行了全面的分析和研究.结果发现,铸钢件表面涂膜厚度达不到设计要求是锈蚀的原因.由于铸钢件表面较粗糙,而测厚时未能根据其特点对测厚仪进行正确校准,使测出的漆膜厚度比实际厚度大l0～30 μm.为...     

Effect of high temperatures on the dielectric behaviour of viscose fibres at low frequency

Commercial and purified viscose fibres exhibit dielectric dispersion and a loss peak within the frequency range 0.05–1 k c/s and at temperatures of 80–140°C. Such high temperature relaxation is local in nature and is attributed to side group motion. The characteristics of the absorption bands of these samples are compared and the results obtained are interpreted. The variation of the dielectric constant with temperature showed a second order transition at about 110°C with these samples, which disappears on hydrolysis.