Search results

This paper aims to study the growth and properties of potentiostatic passive films formed on iron electrodes immersed in pH 8.9‐11.0 phosphate solutions.

First, passive films were grown potentiostatically on pure iron electrodes under different experimental conditions (namely the Na₂HPO₄ concentration, time and potential of polarization, solution pH and temperature). Subsequently, the properties of the resulting passive layer were evaluated by electrochemical measurements (open circuit potential and potentiodynamic polarization measurements) and scanning electron microscopy.

The formation of passive films on iron electrodes immersed in weak‐alkaline phosphate solutions was found to occur in three main steps, being the Na₂HPO₄ concentration a very important parameter to promote reduction of iron dissolution. Films with protective properties could be obtained within at least 30 s of polarization at +0.50 V/SCE. The effect of the polarization potential was interpreted according to previous potentiodynamic data and the influences of solution pH and temperature follow thermodynamic laws.

In‐situ surface analytical techniques such as extended X‐ray absorption fine structure (EXAFS) and elipsometry coupled to electrochemical measurements can elucidate more information on the film growth process, and in turn on resulting properties.

This contribution provides useful insights into the potentiostatic behaviour of iron in alkaline phosphate solutions.

The phosphate treatment of metals has been in industrial use for over 50 years and is the most widely used method of treating light‐gauge steel as a preparation for painting; in addition, during the last 20 years, its use as an aid in the cold forming of steel in such operations as tube and wire drawing has been established. As a result of these trends, phosphating is now a very significant part of the whole metal finishing industry. This review includes advancements in operation, composition and use.

It has long been recognised that the durability of a paint finish is largely dependent on the condition of the metal surface beneath it. Complaints of poor durability, blistering and formation of rust are often the result of inadequate surface preparation and have no direct bearing on the quality of the paint itself. Good preparation of a metal surface is known to be essential prior to metal spraying or electroplating, and very quick failure by flaking will occur if the surface is not correctly prepared. Unfortunately, with paint, it is possible to ‘get away with it’ temporarily and hide surface defects; but before many months have passed the paint will fail and complaints are likely to be made against its quality. This comprehensive article surveys present‐day techniques in the preparation of metals for painting and includes sections on the testing of results, economics and design considerations.

Copper-graphite (Cu/C) is a type of seal material that has been widely used in liquid rocket engines and with normal metal pairs, has a high wear rate under liquid oxygen lubrication. In this study, bearing steel disks were subjected to a high-temperature oxidization and phosphating progress to create an oxidized tricresyl phosphating film (OTCP) film, using tricresyl phosphate (TCP) as the phosphating solvent. It is hoped that the surface wear rate and friction coefficient can be reduced by this method.

This study aim to form an anti-wear film on the surface of bearing steel, which can significantly improve the lubrication performance of Cu/C and bearing steel. The surfaces of bearing steel disks were dried to remove surface water and then put on a heating plate with a magnetic stirrer and a blue glazed oxide film obtained by heating the disks in the air at 200°C for 1 h. To create the OTCP film, bearing steel disks with a blue glazed oxide film were cleaned ultrasonically three times in ethanol and then placed in baths of TCP. After heating for 2 h at 120°C, excess TCP liquid was removed from the disks using ethanol, leaving an OTCP film on the disk surface.

It was found that steel coated with an OTCP film demonstrated better tribological performance (lower coefficient of fiction and wear rate) when pairing with Cu/C than either oxidized or untreated bearing steel. Additional chemical reactions occur when the oxide disk is immersed in TCP and the FePO₄ film is formed after heating. Additionally, the OTCP film coated steel displayed good corrosion resistance, as confirmed by electrochemical corrosion tests. This finding demonstrates the potential for this process in the aerospace industry.

The preparation of OTCP films via high-temperature oxidization and phosphating of bearing steel was demonstrated, with the tribological properties of the OTCP film being investigated alongside those of the original surface and an oxidized film surface. The fabrication of OTCP films is easily scaled up and exhibits significant advantages as a new technology for applications in mechanical contact seal lubrication.

Jenolite Division of Duckhams Oils, Rusham Road, Egham, Surrey, have made an addition to their range of phosphates. Kleenfos 100 ST is a degreaser/phosphate which is claimed to be capable of producing iron phosphate coatings by spray or immersion. The manufacturers state that it can be employed to phosphate iron and steel, galvanised metal and also aluminium and deposits coating weights of up to 100 mg/sq. ft.

Transmission Mossbauer Spectroscopy of corrosion products of mild steel immersed in 3 per cent NaCl and 3 per cent NaCl containing 0.03 M concentrations of different inhibitors viz. sodium nitrite, sodium molybdate, sodium tungstate, sodium meta borate and sodium hexameta phosphate were carried out to understand the corrosion process occurring under these conditions. All corrosion products showed the presence of γ‐FeOOH and superparamagnetic (SPM) α‐FeOOH. However, the corrosion product obtained on mild steel in presence of nitrite showed non‐stoichiometric magnetite (Fe_3−xO₄) along with oxyhydroxides. The corrosion products of steel in presence of phosphate inhibitor showed the presence of ferrous phosphate. The Mossbauer results were supported by FTIR studies. Electrochemical studies showed a high polarisation resistance (Rp) in ease of nitrite inhibitors. Therefore, it can be concluded that an inhibitor which promote the formation Fe_3−xO₄ can provide better protection for steel substrate.

A new zinc phosphating bath, which produces coatings at relatively lower temperatures within a reasonable time by using of chemical accelerators has been devised. Improvement of the bath performance by the addition of divalent cations like calcium, manganese and magnesium has been studied. Bath formulation and operating conditions have been optimized by coating weight determinations. Corrosion resistance property of the resultant coatings has been evaluated in 1,000 ppm Cl⁻ by electrochemical methods such as potentiodynamic polarization and impedance measurements. Results of the electrochemical techniques have been complemented by salt spray, humidity and immersion tests. Porosity and roughness of the coatings have also been studied. Results show that the phosphating bath with manganese addition gives good coatings within 30 min. Studies have shown that the corrosion resistance of the resultant coatings are much superior than the conventional coatings.

Preparation of the surface is just as important when a powder coating is to be applied as with any other method of finishing. In the case of a metallic surface it should be first cleaned so that any corrosion products, heat treatment scale, oil, grease or any other foreign matter is removed and then, preferably, chemically treated so that it is converted to a non‐metallic coating.

The purpose of this paper is to show impacts of household wastes handling on some physicochemical parameters of surface water, soil, sediments and borehole water samples in Port Harcourt. Waste generated from the households are indiscriminately dumped on roads, stream channels, bush lands and open spaces thus defacing the landscape of the city, flooding and spreading vector-borne diseases. As a result there is unsustainable and wasteful utilisation of resources which gives rise to pollution of the environment. The research determines the pollution profile of some dumpsites, surface water bodies that act as recipients of household waste from result of analysis of physicochemical parameters.

Major dumpsites in the city were selected for sampling. Three sampling stations at upstream, discharge point and downstream were selected for water and sediments. Water samples were collected in one-litre plastic containers, and then labelled and transported to laboratory for analysis. Sediment samples were collected at a depth of 5-10 m under water and preservation, handling and analysis were based on standard principles and procedures. Soil samples were dug with auger at both top (0-15 cm) and bottom (15-30 cm) in radial coordinates. The soil and sediment samples were first digested using the wet oxidation method before analysis with atomic absorption spectrophotometry.

The physicochemical analysis of surface water samples showed that conductivity, salinity, turbidity, sulphate, phosphate, magnesium, total hardness and lead exceeded the World Health Organization and Nigerian Industrial Standard limits for drinking water qualities at the sampled areas. The same parameters in addition to pH and manganese also exceeded the limits for sediment samples. The soil pH showed acidity at the sampling stations for both top and bottom depths. Conductivity, sulphate, iron, manganese, phosphate and lead also exceeded the FMEnv Guidelines and standards for soil quality. The continuous discharge of household wastes on water and soil resulted in elevated levels of some measured parameters.

The research was limited by funds. The cost of sampling and analysis was enormous and limited the study to parameters that available funds could carry. This factor also stretched the period of study. The non-availability of sponsorship made it difficult to extend the research to soil particle size distribution and the underground water movement of the study areas. Another limitation was logistics as the study covered vast areas of the metropolis demanding steady means of mobility that was not available. Epileptic supply of power delayed the timely delivery of result of analysis.

The results of the analysed physicochemical parameters of water, sediments, soil and borehole water samples indicated spatial variations in their values at the study area, with higher values at the discharge points and downstream than the upstream, while for the borehole water analysis, the effect was more pronounced at stations with appreciable quantity of degradable household wastes. The levels of some physicochemical variables exceeded standard limits as a result of continuous discharge of household wastes .The implication is that household waste handling influenced the physicochemical variables negatively and constant monitoring serves as a useful tool of abatement.

This work is original and has not been published before in any book or journal article locally or internationally. The research related waste handling lifestyles with concentrations of measurable parameters, which is an additional work to what other authors have done. The value is that data generated will be a reference material to other researchers, city planners, government agencies and institutions that are involved with environmental management. Furthermore it has added a new dimension to the discipline of waste management in terms of scope and contribution to knowledge.

The aim of this study was to evaluate the corrosion inhibition efficiency of steel samples in different environments before and after the treatment with rust metamorphose (RM), which is formulated in this research study and shows excellent adherence over the rusted surface of substrate because of the presence of the P-O-Fe bond.

An RM solution (phosphorylated polyphenol) was synthesised and characterised using Fourier transform infrared spectroscopy (FT-IR), and then the degree of protection offered by it to steel surfaces with and without the treatment with the RM solution in different atmospheres was evaluated;. Before and after treating with the RM solution, the corroded steel samples were characterised using X-ray diffraction (XRD), FT-IR, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The study of the passive behaviours of the corroded steel samples and RM-treated steel samples was done in different simulated atmospheres.

This RM solution is phosphorylated polyphenol solution (proved by FT-IR), which acts as a corrosion inhibitor on corroded steel surfaces because of the formation of a passive and symmetric adherent layer of phosphorylated polyphenol–iron complex (confirmed by FT-IR, XRD, EDS, SEM and adhesion X test). The significant improvement in corrosion resistance in splash conditions of 3.5 per cent NaCl, tap water and 1.5 per cent Na₂SO₄ was found with the treatment of phosphorylated polyphenol-based RM.

The development of RM and its characterisation with performance evaluation in different atmospheres is a novel approach in this research.