Use of polypropylene fibres to increase the resistance of reinforcement to chloride corrosion in concretes

Concrete with the addition of polypropylene fibres is more cohesive and has better adhesion, deformability and tightness because the fibres “bind” the concrete matrix together and prevent large pores from forming in the concrete mix and limit the formation and spread of shrinkage cracks. Therefore, it can be assumed that polypropylene fibres affect the effectiveness of the concrete cover as a layer protecting steel bars against corrosion. This article presents the results of tests allowing us to estimate the effect of addition of polypropylene fibres on the reduction of reinforcing bars corrosion in concrete caused by the action of chlorides. Evaluation of the degree of corrosion of the reinforcement was analysed using the electrochemical polarisation galvanostatic pulse technique. The use of such a method allowed for the quantitative estimation of the effect of the addition of polypropylene fibre on the reduction of corrosion activity of the reinforcement in concrete.

Microstructure and corrosion characteristics of cast silicon bronze in ammonia environment

Refrigerating systems operating on either the open re-circulation or chilled water circuits are proned to corrosion attacks. Often, the ensued corrosion products foul and inhibit efficient heat transfer within the system causing leaks resulting in catastrophic failures. Thus, the imperative to search for a material that can be an effective substitute for the conventional copper pipe used in most refrigerating systems. In this study, the microstructure and corrosion susceptibility of cast silicon bronze in anhydrous ammonia environment was investigated. The silicon bronze was produced by sand casting with the silicon varied from 1-4 wt. %. An accelerated electrochemical polarisation technique was employed to simulate the corrosion behavior of the cast alloy. The results show relatively low corrosion susceptibility, 0.75 mm/yr of the alloy in anhydrous ammonia. This may be attributed to the silicon dioxide (SiO2) passive film formed on the surface of the alloy. The effectiveness of the SiO2 passive film increases as the wt. % of silicon addition increased. The potential for drastic reduction in maintenance cost and frequency of call-backs of refrigerating units is enhanced by the outcome of this study.Kathmandu University Journal of Science, Engineering and TechnologyVol. 13, No. 1, 2017, Page: 56-65

Electrocrystallization and solubility of mercury in alkaline solution

The chemical thermodynamics of mercury in aqueous sodium hydroxide solution has been investigated through electrochemical polarisation and solubility experiments. A review of thermodynamic data allowed determination of the Hg/HgO electrode potential. Cyclic voltammetry revealed a complex anodic reaction beginning with aqueous dissolution of elemental mercury and subsequent electrocrystallization of mercuric oxide. Cathodic sweeps showed dual reduction reactions, attributed to the presence of aqueous mercury and mercuric oxide. The solubility and hence activity of elemental mercury in sodium hydroxide solution was determined, otherwise known as the Sechenov salt effect. Sodium hydroxide salted mercury out of solution.

Significance of formed adherent complex by use of phosphorylated polyphenol coating

Purpose The purpose of this paper is to report on the use of phosphorylated polyphenol (PP)-coated galvanised iron (GI) surface to study the degradation of coating with different time intervals and long-term exposure in different salty media. Design/methodology/approach The as-obtained PP complex on GI was evident by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The coated coupons were exposed to different salty media such as 3.5 per cent NaCl, 1.5 per cent Na2SO4 and tap water at set time intervals. Electrochemical polarisation was performed to study the anodic and cathodic polarisation behaviour at each time interval. Findings The adherent foliolate nanopattern of iron zinc phosphate and zinc dihydrogen phosphate on GI surface was evident by SEM, FT-IR, EDS and XRD. The coated coupons exhibited good corrosion resistance. This coating performs as an alternative to time-consuming multistep operations of phosphating treatment. Originality/value The mode of the experiment treatment using modified PP coating especially on GI in different corrosive exposures at set time intervals is a novel approach in this research.

Synthesis and Characterization of TiO2 Dispersed Al 7075 Micro- and Nanocomposite

Micro-TiO2and nanoTiO2dispersed Al 7075 composites have been synthesized by mechanical milling followed by cold compaction and sintering. The compressibility of the nanocomposites is less than the micro composite, but sintered density of the nanocomposite is higher that the microcomposite. Nanocomposite shows better hardness than microcomposite. However, both types of composites do not show artificial ageing characteristics like unreinforced Al 7075 alloy. Microstructural analysis through XRD and TEM reveals that the formation of MgTiO3and ZnO near TiO2-Al 7075 matrix interface causes depletion of Mg and Zn in the Al 7075 matrix. This suppresses GP zone formation and shows almost no age hardenable characteristic. Potentiodynamic electrochemical polarisation study shows that the corrosion potential (Ecorr) has shifted towards noble direction with the addition of TiO2in the composite.

Depth-Profiles of Corrosion Properties of Carbonitrided AISI 405 Steel

Depth-Profiles of Corrosion Properties of Carbonitrided AISI 405 SteelElectrochemical polarisation characteristics of AISI 405 type stainless steel, carbonitrided in fluid flow, are presented. The evaluation of the corrosion resistance of carbonitrided stainless steel was carried out by using the so called progressive thinning method, consisting in determination of polarisation characteristics on increasingly-deeper situated regions of the top layer. This method made it possible to determine changes in particular corrosion parameters read out from potentiokinetic polarisation curves, thus enabling the depth profiles of these parameters. The resistance of the AISI 405 steel against acid corrosion was determined in acidified 0.5M sulphate solutions having three different pH values, namely 1, 2 and 4. The thickness of the carbonitrided layer has been evaluated on the basis of the spectrophotometric analysis of carbon content and microhardness on the cross section of the surfacial layer.