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The aim of this paper is to study the corrosion protection behavior of water‐borne inorganic zinc‐rich coatings based on potassium silicate/nanosilica developed with various zinc and micaceous iron oxide (MIO) contents during cathodic protection stage.

The formulated coatings were applied on carbon steel panels and were subjected to electrochemical impedance spectroscopy (EIS) and free corrosion potential measurements for characterization of corrosion protection behavior. Also atomic force microscopy (AFM) and optical microscopy were used to investigate the surface topography of coatings.

All of the coatings preserved the cathodic protection ability throughout 75 days of exposure to 3.5% NaCl solution. Supporting results of electrochemical tests and microscopic observations revealed that replacement of zinc by MIO particles reduced both the rate of reactivity and the duration of cathodic protection of inorganic zinc‐rich coatings. It was observed that the coatings demonstrated a reactivation step after a dry‐wet cycle implying that cyclic immersion can change the overall duration of cathodic protection stage.

The paper describes formulation and investigation of corrosion protection behavior of an environmentally friendly zero‐VOC coating as well as providing an insight into EIS of zinc‐rich coatings.

A barrier type of finish coat on zinc‐rich primers can effectively prevent corrosion on mild steel structures in marine environments. Chlorinated rubber is well known for its impermeability of water vapours and corrosive ions. Micaceous iron oxide (MIO) and titanium dioxide (Ti0₂) are the best barrier pigments available in the world. The chlorinated rubber based top coatings have been prepared by incorporating these two pigments separately and applied over three types of zinc‐rich primers (ZRP) (butyl titanate ZRP, cashew nut shell liquid ZRP and epoxy polyamide ZRP). The electro chemical aspects of protection afforded by these coating systems have been evaluated on mild steel substrate in 3 percent NaCI solution by potential‐time, polarisation and impedance techniques. This study revealed an interesting correlation between the polarisation and impedance observations. The inorganic ZRP with top coated systems behave differently to organic ZRP with top coated systems. The MIO pigmented finish coat affords equally higher duration of protection of steel substrate from corrosive saline environment, even though the PVC value is considerably lower than the TiO₂ pigmented top coat systems.

In connection with the launching as a new British Standard of the revised “Code of Practice for Protective Coating of Iron and Steel Structures Against Corrosion”, the Association of Metal Sprayers published a “Plain Guide to BS 5493: 1977”. The “Plain Guide” introduces the new Code of Practice to owners and managers of structures, consulting engineers, designers, architects and all specifiers of protective systems for steel; it enables them to take advantage of the wealth of information which has been assembled in BS 5493 and which initially might appear to the engineer not intimately involved in corrosion protection. The Guide, main details of which are published below, charts the way through the Standard and should enable everybody more readily to make full use of the information and advice contained within BS 5493. Full copies of “Plain Guide to BS 5493” can be obtained from the Association of Metal Sprayers, Chamber of Commerce, Ward Street, Walsall WS1 2AG, at a cost of 40p each including postage.

The purpose of this paper is to measure the apparent and complex viscosities of the zinc‐rich coatings derived from sodium silicate solution modified with aluminium chloride (AlCl₃), and then theoretically analyse the relation between viscosity behaviour and physiochemical mechanisms.

According to the different dosages of AlCl₃, five coatings were prepared. The apparent viscosities as functions of shear rate, time and temperature, complex viscosity with variations of temperature and heating rate of these coatings were measured using an AR500 rheometer.

Results showed that the zinc‐rich coatings possessed the typical shear thinning behaviour and the apparent viscosity increased with time until solidification. Complex results showed that the complex viscosity depended strongly on heating rate. Both apparent and complex viscosities initially decreased to minimum and then started to increase, while temperature was ramped from 0 to 70°C.

It is believed that there is no published literature about the apparent and complex viscosities of the zinc‐rich coatings from sodium silicate solution modified with AlCl₃. This paper presents the first attempt to obtain the rheological data of these zinc‐rich coatings.

There are many ways of protecting ferrous metals with zinc, and coating them with paint incorporating metallic zinc powder as a pigment is the most versatile. Although hot dip galvanizing remains the standard by which other forms of protection are judged, zinc paints have some very great advantages:— they are easy to apply, which may be in factory or on site; the thickness of coating can be controlled to that required for a given duration of protection; there is no limit on the size or weight of the object which can be protected (both the world's biggest ship and largest building are protected with zinc rich paints). They are preferable to galvanizing where welding or flame cutting operations are carried out subsequently, and can be made to withstand temperatures up to dull red heat.

Maintenance coatings have several functions but certainly one of their most important is to combat corrosion. Corrosion protection is important in both maintenance and industrial coatings and this is stressed in an article in Chemical Marketing Reporter (June 6 (1983) p. 5, 20). According to this article, which quotes results from a marketing research firm, Margolis Marketing and Research, corrosion resistance will provide the objectives for an important segment of the coatings industry in highway construction and in the automotive industry. The use of salt on highways to melt snow and ice is increasing and this causes billions of dollars of damage to iron and steel each year. U.S. roads are covered with over 10 million tons per year of salt. In the industrial area galvanised steel has become an important component of items subject to rust such as the automobile.

In this special feature details are given of those British paints which can be described as corrosion‐resistant primers, both one‐ and two‐pack. The materials are generally classified according to the base or pigment which actively prevents corrosion—e.g. metallic zinc in zinc/epoxy formulations— or by the base which produces a barrier action against corrosion, e.g. bitumen in bituminous paints. Exceptions to this are the etching primers, which are separately classified. About 300 primers are described, the manufacturers' names and addresses being cross‐indexed and listed separately on page 48.

METALLIC ZINC has been used for many years as a pigment in paints. If the zinc content of the paints is higher than 90%, the paints are generally called zinc rich paints; this paper deals with this type.

THIS ARTICLE presents just a sample of the work that we do. We shall start by looking at our laboratory work and then detail the steps required from the preparation of test samples to the performance of the paints when applied industrially.

Economics of surface coatings on metals are discussed with emphasis on surface preparation, especially when large scale coating operations are conducted. Relative cost and other parameters affecting the choice between manual and machine blasting are considered, including the area cost of surface preparation, health and safety factors, incidental pollution, and other variations. Advantages of high build surface and multi‐purpose primer application are related along with comparisons of cost between initial and manual recoating of structures after erection. Importance of proper coating maintenance is emphasised. Economic case histories are given, including large scale surface preparation of tank plates and piping, differences between sand abrasive and centrifugal blasting, factors related to intercoat adhesion, cost of Zn rich with epoxy or alkyd topcoats, and the high cost of repainting when scaffolding is necessary. Regulations on surface preparations, ecological controls, and safety are discussed. Two coat simplified systems are recommended, along with automatic and semiautomatic surface preparation when the size of the job makes either one possible. Tabulated data on area costs of various modes an locations for surface preparation and coating costs for various metal configurations are provided.