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The purpose of the present study is to use an amino-functional polysiloxane for the surface modification of red iron oxide (Fe₂O₃) pigment particles for their improved dispersion stability and hydrophobicity and to study the chemical interactions of polysiloxanes with the particle surface.

Surface-treated red Fe₂O₃ pigment particles were prepared by treatment of the particles with different quantities of the (aminopropylmethylsiloxane)-dimethylsiloxane copolymer in concentrated suspensions in water. The samples were analysed with different instrumental and spectroscopic techniques to study the interaction of the polysiloxane with the particle surface and the effect of the surface treatment of the particles on their dispersion stability and hydrophobicity.

Chemisorption of the amino-polysiloxane onto the surface of Fe₂O₃ particles resulted in stable layers which turned out to be helpful in improving greatly the dispersion stability of the particles as shown by the Static Light Scattering and Dynamic Light Scattering results. Formation of a polysiloxane coating onto the surface of the pigment particles was confirmed by studying the interactions of the polymer molecules with Fe₂O₃ surfaces by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy techniques.

The surface-treated red Fe₂O₃ particles with improved dispersion stability can be important components of various formulations in applications such as the colouring of the cement or inorganic pigment-based paint formulations.

The study provides mechanistic insights about the interactions of amino-polysiloxane with the red Fe₂O₃ particles. The process of surface modification of red Fe₂O₃ particles with the amino-functional polysiloxane showed increased hydrophobicity and dispersion stability which is an important requirement of the pigment-based formulations in real applications.

The specific influence of calcium and sodium cations on the rate of deposition of a‐Fe2O3 (a main corrosion product in boilers and heat exchangers) has been experimentally studied. A deposition model based on the microlayer evaporation and dryout phenomena that occur in the nucleate boiling bubble is put forward for interpretation of the deposited layer. It has been found that the rate of deposition of Fe2O3 increases with the increase in valency of the soluble cations. With calcium, the deposition rate increases linearly with the increase in its ionic concentration, whereby the rate is increased by 5.9, 6.8 and 7.6 with 200, 400 and 600 ppm calcium respectively. Development of the deposition layer takes place in the valleys of the surface contour according to a micro‐layer evaporation mechanism. Successive deposition is performed at the periphery of the first deposit. Reduction in cation content in the crude solution and selecting smooth heated surfaces are recommended to reduce the ∝‐Fe2O3 deposition on heated surfaces in boiling water.

This study aims to perform the surface treatment of synthetic α-Fe₂O₃ red iron oxide pigment with hydrolysate 3-aminopropyl silane (A) and colloidal silica (CS) and investigate the effects of surface-treated pigment on the styrene acrylic (SA) emulsion and polyurethane (PU) dispersion.

For this purpose, firstly red iron oxide particles were modified with A and CS separately in an aqueous medium. After isolation of the modified iron oxide were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS). Moreover, the degree of the dispersion stability of the modified pigment in coatings with SA emulsion and PU dispersion was investigated by using an oscillation rheometer. Loss (G''), storage (G') modulus, loss factor [tan(δ)] and yield stress (τ⁰) values were determined by performing amplitude and frequency sweep tests.

The τ⁰ in SA coatings decreases with the amount of used A and increases with the amount of used CS. The τ⁰ decreases as the amount of used A and CS in PU coatings increases. The use of CS on red iron oxide pigments causes storage modulus to increase in SA coatings at low angular frequencies, while it causes a decrease in PU coatings.

To the best of the authors’ knowledge, for the first time, the suspended state of the iron oxide hybrid pigment formed with CS in the coating was investigated rheologically in this study.

Because of rationalisation and demands for improved quality, the surface coatings industry makes ever‐increasing demands for micronised pigments. Micronised pigments permit quicker dispersion and increased output, coincident with decreased production costs. Such factors as the superior dispersibility of micronised pigments have frequently been mentioned, and it is not easy to quote new aspects of this. Therefore, this article will primarily cover other technical advantages of micronised iron oxide pigments‐advantages hitherto neglected in favour of the main advantage, better dispersibility.

The need for environmentally acceptable anti‐corrosive pigments to replace those based on lead and chromates in priming paints has stimulated the emergence of phosphate, molybdate and borate types and many others. However there are widespread doubts about the ability of these “non‐toxic” alternatives to provide the same degree of corrosion‐resistance as the lead and chrome pigments. This has encouraged a search for ways and means of boosting the inhibitive action of the newer pigments, for instance by mixing with other ingredients that might promote a synergistic effect. There has been a growing interest in utilising inert “barrier” pigments for this purpose and the development of synthetic iron oxide with a flake‐like crystalline structure is a significant step forward in this context.

DISCUSSION The chromium coating thicknesses used in this work were comparable to those used commercially, being between 70 and 170 micrometres approximately. Even after oxidation for the temperatures and times stated the chromium concentrations at the metal‐oxide interface were between 20% and 60%. These concentrations fell steadily to approximately 13% over the approximate depth stated above before reducing sharply to zero at what was the ferrite‐austenite transformation boundary during the coating process. This is contrary to the structure observed in aluminized stainless steels where a complex structure is produced due to the existence of intermetallic phases. Hence during all the oxidation experiments performed the chromium level of the surface offered for oxidation was never below 13% and complete oxidative breakdown therefore did not occur, excluding spalling effects. Many workers have shown that the oxidation rate of iron‐chromium alloys initially drops sharply with increasing chromium but eventually reaches a minimum of about 20% chromium and then rises for more chromium rich alloys. From the graph of oxidation rate in pure oxygen against chromium content given by Mortimer et al., from 13% chromium to 100% chromium the oxidation rate increases by approximately 6 × 10−9 g.cm−2 sec.−1 It is reasonable to assume that for a diffusion coating the oxidation behaviour will be markedly affected by the composition at its outer surface layer and much less by the composition gradient. If oxidation was continued for sufficiently long periods the latter could affect the general availability of chromium ions for the oxidation process. Over the first 5?m the average chromium levels were between 63% and 20% for the chromised and chrome‐aluminized respectively. From the figures given by Mortimer et al the oxidation rate of the 63% chromium coating would be expected to be 0.5 × 10−9 g.cm−2 sec−1 greater than the 20% chromium coating on the chrome‐aluminized specimens at 600°C, on the basis of the chromium content alone. The results obtained here vary in this manner, hence it is reasonable to conclude that the general oxidation behaviour of the coatings will be very similar to that of pure iron‐chromium alloys containing the same chromium content as in the outer few micrometres of the respective coatings. Even though the true surface area is greater with diffusion treated specimens their oxidation rates are lower that for the corresponding pure alloys.

If a weather‐beaten structural steelwork, protected by a full system of anticorrosive coatings, will show a lifetime of over 20 years without any maintenance during this time, we will speak of a ‘longterm Corrosion Protection.’ These 20 years often seem to be too long, but many case‐histories of structural steelworks over the whole of Europe, such as bridges, tankfarms, cranes etc. will prove it. By the way, the German Railway Administration foresees a major repainting of their objects only every 20 years, the Swiss Federal Railway Administration only after 25–30 years. The most parts of these protective coatings are pigmented with Micaceous Iron Oxide (MIO), a pigment with the highest life expectance.

Whilst accepting the economic necessity for adding extenders to zinc rich paints, there are several problems which need careful consideration.

Vinyl coating systems provide an outstanding combination of properties—toughness, flexibility, abrasion resistance, adhesion, weatherability, water resistance and chemical resistance—that have enabled such coatings to have a proven record of long term performance unsurpassed by any other type of coating. Fifteen or twenty years are quite common terms of satisfactory protection, with only occasional spot touch‐ups needed; this means low maintenance costs per year of life for the protection of structural steel. Since the labour costs for adequate metal preparation, such as blast cleaning, and for applying the coatings is estimated to cover some 80% of the total cost of a job, the importance of a good, long term protection can be readily appreciated.

One of the problems in the production of narrow hot‐rolled mild steel strip is the formation, at the edges of the strip, of scale that can be extremely resistant to pickling; This extreme resistance to pickling of ‘hard edge scale’ sometimes requires repickling of a considerable percentage of coils with consequent loss of production and deterioration of surface finish. The paper considers in detail the correlation between the microstructure of scale on the strip and its pickling behaviour. It is shown that certain characteristics of the microstructure, peculiar to ‘hard edge scale’, i.e. increased thickness, the presence of a primary magnetite layer, greater degree of wüstite transformation and the nature and presence of haematite, can be suppressed to a greater or lesser degree by variations in the cooling cycle. It is considered that no single one of these structural differences between hard edge scale and that which is removed readily from the centre of the strip would, by itself, interfere with pickling, but when these characteristics occur together repickling is made necessary. The above observations and conclusions are supported by results obtained from pickling tests carried out in the laboratory on samples taken from a wide range of coils.