R. Romagnoli, R.O. Batic, V.F. Vetere, J.D. Sota, I.T. Lucchini and R.O. Carbonari
Hardened cement paste is a heterogeneous system resulting from the grouping of particles, films, microcrystals and other solid structural elements bounded in a porous mass. The…
Abstract
Hardened cement paste is a heterogeneous system resulting from the grouping of particles, films, microcrystals and other solid structural elements bounded in a porous mass. The cement paste microstructure must be understood firstly due to its influence on concrete properties. The behaviour of concrete greatly depends on the conformation of localised special structures rather than on general structures found in the mass cement paste. The objective of this paper was to study the cement paste microstructure, as a function of the water–cement ratio, in order to interpret the variations of the steel–mortar bond strength and the developing of the corrosion process in steel–mortar specimens kept in tap water and 3 percent sodium chloride solutions for 1 year. A description of the steel–mortar interface was also provided.
M. Deyá, V.F. Vetere, R. Romagnoli and B. del Amo
The efficiency of two anticorrosive pigments containing aluminium polyphosphate was studied. Pigments were analysed by current analytical techniques and characterised by FT‐IR…
Abstract
The efficiency of two anticorrosive pigments containing aluminium polyphosphate was studied. Pigments were analysed by current analytical techniques and characterised by FT‐IR spectrometry. The anticorrosive properties of the selected pigments were evaluated following the electrochemical behaviour of a steel electrode in pigments suspensions. In a second stage, solvent‐borne paints with 30 and 10% v/v of the pigment and PVC/CPVC (pigment volume concentration/critical pigment volume concentration) ratio 0.8 were formulated. Three resins were chosen as film forming materials: an alkyd, an epoxy and a vinyl. The performance of the resulting anticorrosive paints was assessed by accelerated (salt spray cabinet and humidity chamber) and electrochemical tests (corrosion potential, ionic resistance and polarisation resistance). The anticorrosive performance of the tested paints was closely related with pigment composition. The nature of the resin was also of importance; in this sense, epoxy paints showed the best anticorrosive performance. Good correlation has been obtained between accelerated and electrochemical tests.
L.S. Hernández, B. del Amo and R. Romagnoli
Substitution of zinc chromate or zinc yellow, traditionally used as anticorrosive pigment, for other phosphate‐based pigments that are not hazardous to health and have the same…
Abstract
Substitution of zinc chromate or zinc yellow, traditionally used as anticorrosive pigment, for other phosphate‐based pigments that are not hazardous to health and have the same anticorrosive behaviour or even better, is studied in this paper. Four alkyd paints were specially prepared; two of them contained calcium acid phosphate or micronised zinc phosphate as anticorrosive pigments respectively. A paint containing zinc chromate was used as reference and a paint without anticorrosive pigments was used as a blank, in which the other ingredients were increased proportionally to attain the desired PVC relationship. The corrosion behaviour of low carbon steel panels coated with these paints in a 3 per cent NaCl solution was assessed by electrochemical impedance spectroscopy (EIS). In addition, other painted panels were evaluated by salt spray and humidity chamber tests. Results of all tests showed that the paint with calcium acid phosphate and especially that with micronised zinc phosphate exhibited better behaviour than paint with zinc chromate. Analysis of impedance parameters (ionic resistance and capacitance of the paint film) against immersion time allowed the paints to be ranked in the same order as that obtained with salt spray and humidity chamber tests.
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P. Mošner, A. Kalendova´ and L. Koudelka
Twelve pigment compositions derived from the xCaO·(50−x)ZnO·20B2O3·30P2O5·(x=10, 20, 30) and yMgO·(50−y)ZnO·20B2O3·30P2O5·(y=10, 20, 30) systems were prepared. The synthesis was…
Abstract
Twelve pigment compositions derived from the xCaO·(50−x)ZnO·20B2O3·30P2O5·(x=10, 20, 30) and yMgO·(50−y)ZnO·20B2O3·30P2O5·(y=10, 20, 30) systems were prepared. The synthesis was carried out either by the medium‐temperature process or by the high‐temperature process followed by cooling in air and an isothermal crystallisation of the glass obtained. The pigments prepared by the medium‐temperature process achieved better corrosion results in styrene‐acrylate coating formulations, whereas those prepared by the high‐temperature process achieved better results in alkyd‐resin coating formulations. The anti‐corrosion results for the Ca‐Zn pigments were better than those for the Mg‐Zn pigments.
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Nivin M. Ahmed and Mohamed M. Selim
The purpose of this paper is to introduce a new method of pigment preparation, which is economic and highly efficient in corrosion protection properties, known as the core‐shell…
Abstract
Purpose
The purpose of this paper is to introduce a new method of pigment preparation, which is economic and highly efficient in corrosion protection properties, known as the core‐shell method. According to this method, a cheap core (an extender) is covered with only a surface layer of effective pigments. Following this method of preparation, a new group of pigments is prepared in this research using the Egyptian kaolin ore as the core covered with single and mixed zinc, magnesium, and zinc‐magnesium phosphates as a shell to replace the original phosphates. These new pigments combine the properties of both its core and shell counter‐parts exhibiting improved corrosion protection properties that exceed both of kaolin and zinc phosphate individually.
Design/methodology/approach
Pigments concerned in this paper are prepared using simple chemical techniques, and then they are characterised using X‐ray diffraction, scanning electron microscopy combined with energy‐dispersive X‐ray analysis, and transmission electron microscopy. These pigments are incorporated in solvent‐based paint formulations based on medium oil alkyd resin. The physico‐mechanical properties of dry films and their corrosion properties are tested using accelerated laboratory test in 3.5 percent NaCl for 28 days, according to ASTM.
Findings
The prepared kaolin‐phosphate (core‐shell) pigments are based essentially on Egyptian kaolin ore, which is an abundant cheap ore in Egypt, and then the kaolin is covered with a surface layer of phosphates that are proved to be efficient anticorrosive pigments. These pigments are easily prepared, economically feasible and can successfully replace ordinary phosphate pigments with superior corrosion protection behaviour.
Practical implications
These pigments can be applied in other polymer composites, e.g. rubber and plastics as reinforcing agent.
Originality/value
Prepared pigments are environmentally friendly and can replace hazardous pigments (e.g. chromates) and ordinary phosphates. The main advantages of these pigments are that they combine both the properties of their core and shell counter‐parts, and they are of lower cost with similar and maybe in some cases better efficiency in corrosion protection of metals. Also, they can be applied in industries other than paints, e.g. paper, rubber and plastics composites.
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Walaa M. Abd El-Gawad, Nivin M. Ahmed, Mohamed M. Selim, E. Hamed and Eglal R. Souaya
In recent years, zeolites have been highlighted as a new component in many industrial applications owing to their unique properties. The purpose of this study is to apply three…
Abstract
Purpose
In recent years, zeolites have been highlighted as a new component in many industrial applications owing to their unique properties. The purpose of this study is to apply three prepared types of zeolites Na-X, Na-Y and hydroxysodalite (Na-HS) in anticorrosive paint formulations to be evaluated as a partial replacement to zinc phosphate in anticorrosive paint formulations to protect carbon steel.
Design/methodology/approach
The three types of zeolites were characterized using different instrumental analysis such as X-ray diffraction, scanning electron microscopy and X-ray fluorescence. Evaluation of zeolites was done using American society for material and testing. Then, they were incorporated in paint formulations based on medium oil-modified soya-bean dehydrated castor oil alkyd resin in the presence and absence of zinc phosphate. Their corrosion behavior was estimated using both immersion test and electrochemical impedance measurements in 3.5% NaCl.
Findings
Generally, the prepared zeolites exhibited good corrosion protection performance, but in presence of zinc phosphate the performance was better. This proves that, zeolites by themselves can resist corrosion but not efficiently, while in presence of zinc phosphate and owing to a synergistic effect between them, the performance was better. This opens the way to partial replacement of zinc phosphate with another safer and cheaper ingredient, which is zeolite.
Practical implications
The three zeolites can be applied in many industries besides the paint industry, such as reinforcing filler in rubber, plastics and ceramic composites, also can be applied in paper filling, paper coatings and electrical insulation.
Originality/value
The three zeolites are environmentally friendly materials that can partially replace other expensive anticorrosive pigments (e.g. zinc phosphate).
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M.A. Abd El‐Ghaffar, E.A.M. Youssef and N.M. Ahmed
Historically, paints designed to protect steel and other metals have been formulated using anticorrosive chromate pigments, which are currently under environmental restrictions…
Abstract
Historically, paints designed to protect steel and other metals have been formulated using anticorrosive chromate pigments, which are currently under environmental restrictions. During the investigation reported here, various phosphate compounds. The pigments prepared were characterised using a variety of chemical and spectrophotometric methods of analysis including emission atomic absorption, transmission electron microscope, X‐ray diffraction, in addition to thermal gravimetric analysis. The pigments were also evaluated according to relevant international standard testing methods. The phosphates prepared were incorporated into anticorrosive paint formulations, to replace the imported zinc phosphate pigment, containing medium oil alkyd resin, and melamine formaldehyde resin. Paint films obtained were tested in artificial seawater for 28 days for anticorrosion properties. The results indicated that the paint films had good anticorrosive protection properties that could be attributed to the pigments prepared and the resins used.
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Petr Mošner, Andrea Kalendová, Ladislav Koudelka and Petr Kalenda
Four pigments derived from the SrO–ZnO–B2O3–P2O5 system were tested in a solvent coating system based on a modified alkyd resin and water‐borne system based on a styrene–acrylate…
Abstract
Four pigments derived from the SrO–ZnO–B2O3–P2O5 system were tested in a solvent coating system based on a modified alkyd resin and water‐borne system based on a styrene–acrylate dispersion. The pigments pastes were applied on activated steel panels and after conditioning standard corrosion tests were performed comprising the determination of resistance to humid atmospheres containing SO2 and also the resistance to a neutral salt fog. Test results were compared with those performed on the coatings prepared with standard anticorrosion pigments of Zn3(PO4)2.2H2O, Ca(BO2)2, Zn(BO2)2 a Ba(BO2)2. Some tested pigments revealed at least comparable corrosion‐inhibition properties with standard pigments. Coatings based on alkyd resins gave better results than those prepared form water‐borne system.
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M.A. Abd El‐Ghaffar, E.A.M. Youssef and Nivin M. Ahmed
Owing to the ongoing demand for the elimination of chromate‐ and lead‐based pigments and the need to identify effective replacements, phosphate and molybdate are finding…
Abstract
Purpose
Owing to the ongoing demand for the elimination of chromate‐ and lead‐based pigments and the need to identify effective replacements, phosphate and molybdate are finding increasing application in coating industry. In the study reported here, phosphomolybdates, the newest of the second generation of molybdate and phosphate pigments had been prepared, characterised and evaluated as anti‐corrosive pigments for coating applications.
Design/methodology/approach
In this study, Ca, Zn and Ca‐Zn phospomolybdates were prepared and characterised by chemical analysis and spectrophotometric measurements, X‐ray diffraction (XRD) and scanning electron microscopy (SEM), in addition to thermal gravimetric analysis (TGA). The pigments were also evaluated according to international standard testing methods. The conditions for the preparation of the phosphomolybdate pigments were established. Their anticorrosive properties were evaluated by incorporation in anticorrosive paint formulations using medium oil alkyd resin as a binder. The paint films were tested in artificial seawater for 28 days.
Findings
The results showed superior anticorrosive protection properties of the pigments prepared over their phosphate and molybdate counterparts, in addition to the high tinting strength of their golden yellow colours.
Practical implications
The method for enhanced production of the eco‐friendly phosphomolybdate pigments was novel and economically feasible.
Originality/value
Phosphomolybdates, the newest of the second generation of molybdate pigments incorporate a synergistic combination of phosphate and molybdate compounds and are believed to have exceptional corrosion inhibiting activity, which has allowed for more optimised applications in specific types of coatings. They are considered the best known and most frequently utilised non‐toxic eco‐friendly inhibitive pigments.
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P. Mošner, D. Veselý, L. Koudelka and A. Kalendová
The purpose of this paper is to synthesise glassy and crystalline Ca‐Zn and Sr‐Zn borophosphates.
Abstract
Purpose
The purpose of this paper is to synthesise glassy and crystalline Ca‐Zn and Sr‐Zn borophosphates.
Design/methodology/approach
Anticorrosion pigments on the basis of glassy and crystalline borophosphates formulated as 20CaO‐30ZnO‐20B2O3‐30P2O5 and 20SrO‐30ZnO‐20B2O3‐30P2O5 were synthesised. The pigments prepared were characterised by means of X‐ray diffraction and their physical‐chemical properties were determined. The pigments synthesised were used to prepare water‐borne styrene‐acrylate coatings with a 10 per cent anticorrosion pigment content. The coatings underwent corrosion tests in a humid environment with SO2 content and a test in a salt mist environment. The corrosion tests results were compared with industrially produced pigments.
Findings
As the glassy phase reduces the anticorrosion efficiency of the coatings with the Sr‐Zn borophosphate content decreases too. In case of the Ca‐Zn borophosphates, the maximum anticorrosion efficiency was detected with regard to a pigment containing 75 wt% of the glassy phase.
Practical implications
The pigments synthesised can be conveniently used in water‐borne coatings to protect metal bases from corrosion.
Originality/value
The application of the synthesised glassy‐crystalline borophosphate pigments in anticorrosion water‐borne coatings to protect metal bases from corrosion presents a new method. The use and the method of synthesising these anticorrosion pigments are beneficial.