Aluminum Pigments Research Articles

Corrosion protection of aluminum pigments by sol–gel coatings

New sol–gel coatings for the corrosion protection of aluminum pigments were developed. To this end, the pigment particles are first coated with a silica layer by phosphoric acid-catalyzed sol–gel processing of Si(OEt) 4, to which either hexadecyltrimethoxysilane or dimethyldimethoxysilane is condensed. The coated pigments have excellent anticorrosive properties in alkaline solutions as well as under boiling water conditions.

Epoxy ester resins as corrosion inhibitors for aluminium and zinc pigments

The hydrogen evolution of aluminium and zinc pigments in aqueous media at pH 10 is inhibited by several epoxy ester resins. One certain epoxy ester resin (EPE b) is an excellent corrosion inhibitor both for aluminium and zinc pigment. An increase of resin addition effects a decreasing hydrogen evolution, i.e., an increase of corrosion inhibition. Moreover, corrosion inhibition of aluminium and zinc pigments by the epoxy ester EPE b is not significantly affected by other added paint resins. Furthermore, the mobility of resins dissolved in a liquid medium seems to be a requirement for corrosion inhibition.

Silica fume – formed during the manufacture of ferrosilicon alloys – as an extender pigment in anticorrosive paints

PurposeThis paper is concerned with the study of silica fume that arises in tonnage amounts during the manufacture of ferrosilicon alloys; this was done in order to maximize productivity and to create new market for industrial by‐product and/or waste material.Design/methodology/approachThe structure and particle shape of silica fume were identified using X‐ray diffraction and electron microscope, respectively. Standard methods were used for the identification of chemical analyses, solubility, hydrogen ion concentration, specific gravity, bulking value, oil absorption, chemical resistance and particle size. The characterized and evaluated silica fume was applied in several paint formulations. The physico‐mechanical, chemical and corrosion protective properties of the paint films were measured according to standard methods.FindingsThe silica fume under investigation was a fine lightweight fluffy amorphous powder. It has a grayish‐white color that makes it suitable for use as a filler and extender pigment in a wide variety of different fields of application; its amorphous nature favors safe use from a standpoint of industrial hygiene. It can be used as an economic pigment that possesses suitable values of specific gravity, bulking value and oil absorption. It also is inert, neutral and of an excellent chemical resistance. The material can be used successfully as an extender pigment in different paint formulations; taking into consideration that alkyd resin based paints should not be used in alkaline environments or mixed with basic pigments, or the paint film will deteriorate. Silica fume particles in the pigment mixture may offer a suitable opportunity for the voids formed by the larger particles to be occupied by smaller ones to produce a condition of maximum packing. It can be successfully used with the flaky aluminum or stainless steel anticorrosive pigments to produce a highly efficient corrosion protective film.Originality/valueThere is increasing environmental concern with regard to excessive volumes of solid waste hazards accumulation. Silica fume that arises – as a disposal material – in tonnage amounts during the manufacture of ferrosilicon alloys can find a new market in paint industry. It can be used successfully for anticorrosive paints to provide well backed paint films.

Ciba Specialty Chemicals acquires Wolstenholme's Metasheen line of high-reflectance aluminum pigments

Ciba Specialty Chemicals acquires Wolstenholme's Metasheen line of high-reflectance aluminum pigments

Citric acid as corrosion inhibitor for aluminium pigment

Aluminium pigments corrode in aqueous alkaline media (e.g., water-borne paints) with the evolution of hydrogen. The hydrogen corrosion of aluminium pigment can be inhibited by the chelating agent citric acid, which is a renewable raw material and absolutely non-toxic. At pH 8 more hydrogen is evolved as at pH 10 which can be explained with the isoelectric point of aluminium oxide (pH 9) and a chemical reaction of citrate with aluminium. The product of this reaction should be an aluminium(III)–citric acid-chelate which is assumed to be the actual corrosion inhibitor. This assumption can be corroborated by tests with aluminium(III)–citric acid-chelates. With increasing addition of citric acid the hydrogen volumes evolved increase, which could also be explained with a chemical reaction of citrate with aluminium. Agaric acid (α-hexadecyl-citric acid) can be considered as a surfactant with the chelating agent citric acid as hydrophilic group and inhibits the corrosion reaction of aluminium pigment better when compared to citric acid.

Influence of additives segregation on surface composition of automotive coatings: effects of an ethanol cleaning

The automotive topcoat is constituted of a pigmented basecoat, covered by a transparent and shiny clearcoat. This layer protects the basecoat from the environment damage and determines the paint appearance. For white plain colour, the basecoat/clearcoat system is replaced by a layer of lacquer. The surface analyses are used to determine the influence of the topcoat composition on the adhesion of pressure-sensitive adhesives. X-ray photoelectron spectroscopy (XPS) and secondary ions mass spectrometry (ToF-SIMS) study the automotive topcoats chemistries. These analyses point out that polysiloxane additives are detected on the clearcoats but not on the lacquers. The impact of the different additives families (anti-UV agents and surface levelling additives) on the topcoat surface chemistry is identified. Moreover, the aluminium pigments do not appear on the metallic basecoat surface because of a siloxane additives layer, which also covers the polyester–polyurethane network. XPS studies on the basecoats covered by a clearcoat formulated without additive bring to the fore that the basecoat siloxane additives segregate towards the clearcoat/air interface during the curing process. The clearcoats additives can be removed with an ethanol cleaning according to the XPS analyses but this solvent cleaning is not able to remove all the additives from the basecoat surface, which seem to be partly cross-linked with the basecoat polyurethane network.

Resistance of metallic substrates protected by an organic coating containing aluminum powder

The corrosion behavior of an epoxy primer containing aluminum powder (10 vol.%) applied on carbon steel and on galvanized steel was examined by electrochemical impedance spectroscopy (EIS). The data show that this coating is more protective when applied onto carbon steel substrates, and that on galvanized steel thicker coatings allow to achieve similar protection levels as those obtained for carbon steel. These effects are probably due to aluminum pigments providing a cathodic protection of the substrate, and to the resulting products precipitating inside the pores of the polymeric coating. Three stages can be distinguished during exposure of the coated specimens. Upon immersion of the coated samples in the test solution, a pre-saturated stage is observed. After a certain period of immersion, which strongly depends on the thickness of the applied coating, a saturation stage is reached in which an effective protection of the metallic substrate against corrosion is achieved. Finally, at sufficiently long exposure times, swelling through the coating eventually leads to the detachment of the coating.

Influence of Pigment Particle Size and Packing Volume on Printability of Glossy Inkjet Paper Coatings

The optical properties and printability of ink jet coated papers are influenced by smoothness, surface chemistry and pore structure of the surface coating layer. To control these properties, the coating formulator must select the proper pigment(s) and binder(s), the two main components of any coating. For glossy ink jet papers, small particle, large surface area fumed silica and aluminum pigments have been shown to provide the desired properties for high quality glossy ink jet coated papers. However, their high cost and low make-down solids, in comparison to conventional pigments, has limited their use by the industry to these specialty grades.The focus of this study was to determine if the costs and application solids of fumed silica and alumina coatings could be improved by extending the pigments with less expensive compatible pigments. The effects of the resultant change in packing volume and particle size distribution on the optical properties and printability were determined. Blends capable of providing equal or better gloss and printability, at a reduced cost, were sought.It was determined that up to 30 parts of the fumed silica and alumina could be replaced with less expensive compatible pigments, without significant loss to the optical and printing properties of the glossy ink jet paper.

Coloured paints based on iron oxide and silicon oxide coated flakes of aluminium as the pigment, for energy efficient paint: optical and thermal experiments

Energy efficient coloured paint coatings utilising flaky aluminium pigment with either single layer (Fe2O3) or double layer (Fe2O3 on SiO2) interference coatings are optically and thermally characterised. Similar pigments with coatings on flaky dielectric particles and standard paints of similar colour are compared. Data presented includes hemispherical and specular reflectance spectra across visible and infra red wavelengths, thermal emittance from an emissometer and light spreading data from a photogoniometer. Solar absorptance, and colour show that, as theoretically predicted, and provided flaky metal pigments are used, a wide range of colours combined with a much lower solar absorptance than traditional paints of similar colour is achieved. Superior thermal performance to ordinary paints with similar colour is thus possible and is demonstrated for two such coloured layers via controlled heating-cooling studies under both an indoor lamp and outdoor clear sky solar illumination. It is seen that heat gains from the sun and associated cooling loads can be reduced by up to 50% for most colours, which is of some benefit for cars and metal roofs in hot climates.

Corrosion inhibited metal pigments

Flake-shaped particles of aluminium are well known in the coatings and printing ink industry as “silver bronze pigments”. For their use in waterborne coatings or outdoor applications, an effective corrosion protection of the highly reactive aluminium surfaces is required. The traditional stabilization techniques for aluminium pigments are based on the addition of corrosion inhibitors or on chromate passivation. This publication presents new developments in the encapsulation of metallic pigments that are based on modern sol-gel techniques. All products are heavy metal-free and provide excellent applicational properties.

Corrosion inhibition and adsorption of resins on aluminium pigment

The hydrogen evolution from aqueous alkaline media due to aluminium pigment is inhibited by various styrene-maleic acid anhydride resins (SMA) and thermosetting phenolic resins (PF). The determination by the quantities of aluminium, oxygen and carbon on the aluminium sheet surfaces by x-ray photoelectron spectroscopy (XPS) leads to the assumption that a chelate complex of PF and aluminium(III) should be formed on the aluminium surface.

Amino and polyamino acids as corrosion inhibitors for aluminium and zinc pigments

A severe problem with water‐borne paints containing aluminium or zinc pigments is hydrogen corrosion of these metals in the aqueous alkaline paint media. The subject of the present study is the examination of corrosion inhibition of aluminium and zinc pigments in aqueous alkaline media by different amino and polyamino acids. Aspartic acid inhibits this corrosion reaction of aluminium pigment only at pH 8 (protection factor 96 per cent) whereas polyaspartic acids do not. In contrast, aspartic acid stimulates the corrosion reaction of zinc pigment whereas polyaspartic acids show a moderate corrosion inhibiting effect. So, corrosion inhibition by aspartic and polyaspartic acids is completely different on aluminium and zinc pigment.

Harmful Substances on the Opera Stage: Possible Negative Effects on Singers' Respiratory Tracts

Objective, quantitative information is lacking in the medical community about actual working conditions for professional singers onstage, and moreover, about which conditions are safe. Physicians, speech-language pathologists, and speech scientists focusing on laryngology should have relevant information about the opera as workplace and the medical sequelae of unhealthy environments. We describe five toxic substances to which singers presenting to our clinics were exposed while working professionally on the opera stage: (1) aromatic diisocyanates, (2) penicillium frequentans in cork granulate, (3) formaldehyde in cork granulate, (4) cobalt and aluminum (pigment components), and (5) quartz sand capable of entering the alveolae. Biological considerations and clinical data for some subjects suggest a direct causal link between the exposures and the patients' complaints and findings. Our observations suggest that whenever singers complain about deleterious conditions such as dry and hot onstage climate or suspicion of the presence of harmful substances, the specific conditions existing in the theater in question should be investigated. Harmful substances are not only poorly tolerated by singers, but also they should be preventable.

Corrosion inhibition of aluminium and zinc pigments by saccharides

Both aluminium and zinc pigments react in aqueous alkaline media (e.g., water-borne paints) with the evolution of hydrogen which can be measured gas volumetrically. The hydrogen corrosion of aluminium pigment can be inhibited with addition of the reducing saccharides fructose and mannose as well as with addition of the reducing ascorbic acid whereas the non-reducing saccharose did not inhibit this corrosion reaction. With increasing addition of fructose or ascorbic acid the hydrogen volumes evolved increase; this observation leads to the assumption that reaction products of aluminium and fructose or ascorbic are the actual corrosion inhibitors. The hydrogen corrosion of zinc pigment is inhibited by ascorbic acid only. So, the most efficient of the examined natural corrosion inhibitors both for aluminium and zinc pigment is ascorbic acid. But corrosion inhibition of ascorbic acid on zinc pigment is much less effective when compared to aluminium.

Amphiphilic Esters of Gallic Acid as Corrosion Inhibitors for Aluminium and Zinc Pigments

Amphiphilic Esters of Gallic Acid as Corrosion Inhibitors for Aluminium and Zinc Pigments

Interaction of resins and metal pigments in water‐borne printing inks

In aqueous alkaline ink media aluminium pigments react with the evolution of hydrogen, whereas the more noble copper and brass pigments react by the absorption of oxygen, which can be measured gas‐volumetrically. These different corrosion reactions can be inhibited with addition of certain binders for printing inks, such as styrene‐maleic acid resins, maleic resins and to some extent styrene‐acrylate resins. So, certain ink resins inhibit corrosion reactions of different noble metal pigments in a reducing hydrogen atmosphere (aluminium) as well as in an oxidizing oxygen atmosphere (copper and brass). The overall best resin is that with the lowest acid number. Atomic absorption spectroscopy measurements showed that a lower acid number pruduces a lower solubility of copper and zinc in the medium.

Stabilization of aluminum pigment in waterborne paints

The corrosion of aluminum pigments in aqueous alkaline paint media, which results in the evolution of hydrgen, can be inhibited by certain substances. The combination of noninhibiting paint resins with three corrosion inhibitors (salicylic acid, a fluorinated phosphate surfactant, and an epoxy ester resin) has been studied. The presence of the resins does not significantly affect the stabilization of the aluminum pigment at pH 10 by the corrosion inhibitors. With the addition of corrosion inhibitors, the hydrogen volume evolved from aqueous aluminum pigment dispersions is surprisingly reduced by stirring. However, when heated to +40°C aqueous aluminum pigment dispersions with inhibitors evolve more hydrogen; at pH 8 the results are still satisfactory even at +40°C.

Epoxy esters as corrosion inhibitors for aluminium pigment

The hydrogen evolution caused by aluminium pigment in aqueous alkaline media is inhibited by several epoxy ester resins. At pH 8 less hydrogen is evolved than at pH 10. One particular epoxy ester resin (EPE b) is an excellent corrosion inhibitor especially at the high pH value of 10. An increase of epoxy ester addition results in a decreased hydrogen evolution, ie, an increase of corrosion inhibition. Corrosion inhibition of aluminium pigment by the epoxy ester EPE b is not significantly affected by the addition of paint resins, saturated polyester or melamine resin.

Corrosion inhibition of different metal pigments in aqueous alkaline media

In aqueous alkaline media aluminium and zinc pigments react with the evolution of hydrogen whereas the more noble copper and brass pigments react by the absorption of oxygen. All these different corrosion reactions can be inhibited with addition of the chelating agent 2-hydroxy benzoic acid (2-HBA). So, 2-HBA works in a reducing hydrogen atmosphere as well as in an oxidizing oxygen atmosphere. In contrast, the chelating 2-mercapto benzoic acid only inhibited the hydrogen evolution of zinc pigment, which can be explained with “Pearson’s principle of hard and soft acids and bases”. The non-chelating 4-hydroxy benzoic acid only inhibited the oxygen absorption of copper and brass pigments. So, for aluminium pigment chelation seems to be a basic requirement for corrosion inhibition whereas for copper and brass pigments chelation is not essential.

Corrosion inhibition of aluminium and zinc pigments by copolymers

Aluminium and zinc pigments corrode in aqueous alkaline paint media with the evolution of hydrogen. Maleic acid‐styrene‐acrylic ester copolymers were synthesized by copolymerisation of maleic acid anhydride, styrene and different (meth)acrylic esters. Three acrylic esters (ethyl, n‐butyl, n‐hexyl) and two methacrylic esters (n‐dodecyl, n‐octadecyl) were used; the copolymers with long‐chain acrylic esters are amphiphilic. Additionally, a commercial (non‐amphiphilic) styrene‐maleic acid copolymer (SMA) with similar molecular mass and acid number was tested. The corrosion reaction of aluminium and zinc pigments in aqueous alkaline media can be inhibited by addition of these copolymers. But aluminium and zinc pigments react completely differently with the examined copolymers. With addition of the amphiphilic maleic acid‐styrene‐acrylic ester copolymers to aluminium pigment dispersions the evolved hydrogen volumes decrease with increasing chain‐length of the acrylate monomer in the copolymers, whilst with zinc pigment the hydrogen volumes increase, which is just the opposite compared with aluminium. Furthermore, there exist mathematical correlations between the number of carbon atoms of the ester alcohol of the acrylate monomer in the copolymers and the hydrogen volumes evolved.