Andrea Kalendova, Martina Hejdová and David Vesely
The purpose of this paper is to synthesize anticorrosion pigments of the perovskite type, YXO3, where X = Ti, Zr, Mn or Al and Y = Ca, Sr, La or Fe, for coating materials intended…
Abstract
Purpose
The purpose of this paper is to synthesize anticorrosion pigments of the perovskite type, YXO3, where X = Ti, Zr, Mn or Al and Y = Ca, Sr, La or Fe, for coating materials intended for corrosion protection of metals. Also, to synthesize pigments containing hexavalent Mo and W (double perovskites).
Design/methodology/approach
The anticorrosion pigments were synthesized from oxides or carbonates by a high-temperature process. The following pigments were synthesized: CaTiO3, SrTiO3, CaZrO3, SrZrO3, LaTiO3, LaMnO3, CaMnO3, SrMnO3, LaFe2O3, SrFe2O3, LaAlO3, Ca2ZnWO6 and Ca2ZnMoO6. The pigments were characterized by the physico-chemical properties of the powders, by X-ray diffraction analysis and by scanning electron microscopy. Epoxy-ester coating materials containing the pigments at a volume concentration PVC = 10 per cent were prepared and subjected to tests examining their physico-mechanical properties and tests in simulated corrosion atmospheres.
Findings
The perovskite structure was identified in the majority of the pigments. The pigments were found to impart good corrosion inhibiting properties to coating materials. The highest calculated anticorrosion efficiency was found for paints containing CaMnO3 or SrMnO3 as the pigments.
Practical implications
The pigments synthesized can be used with advantage in paints intended for corrosion protection of the substrate metals.
Originality/value
The use of the above pigments in anticorrosion coating materials to protect metals is new. Especially beneficial are the uses and procedures for the synthesis of anticorrosion pigments which do not contain heavy metals and are acceptable from the environmental protection aspect.
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Eva Schmidova, Pavel Svanda, David Vesely and Andrea Kalendova
The purpose of this paper is to verify the capability of pigmented coatings to mitigate the effects of thermal sensitisation of 430 stainless steel.
Abstract
Purpose
The purpose of this paper is to verify the capability of pigmented coatings to mitigate the effects of thermal sensitisation of 430 stainless steel.
Design/methodology/approach
Experimental weld joints of non‐stabilised ferritic corrosion resistant steel type AISI 430 were prepared. Protective coatings in several variants were applied to a number of weldments, subsequently subject to corrosion tests in SO2 and NaCl. The anticorrosive efficiency of the coatings was evaluated by means of normative visual assessment and metallographic analysis of the mechanism and depth of corrosion damage.
Findings
Anticorrosive efficiency of the tested coatings was experimentally established under conditions where differences were identified in structural changes caused by welding, or resulting from mechanical damage to the coating. Differences in the progress of corrosion damage caused by phase changes in the heat‐affected zone were established.
Practical implications
Tests of anticorrosive efficiency of coatings of selected types provided information about possible reduction in sensitisation of welded non‐stabilised steel. The effect of the investigated processes on degradation of anticorrosive resistance was identified.
Originality/value
A specific effect of phase changes accompanying welding on the corrosion mechanism was described and so were the reasons underlying development of corrosion damage at visually identical character of surface damage.
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Eva Schmidova, Pavel Svanda, David Vesely and Andrea Kalendova
The purpose of this paper is to clarify the destabilisation mechanism that occurs with two types of ferritic corrosion‐resistant steel during the welding cycle.
Abstract
Purpose
The purpose of this paper is to clarify the destabilisation mechanism that occurs with two types of ferritic corrosion‐resistant steel during the welding cycle.
Design/methodology/approach
A series of experimental weld joints was made to verify the actual response of non‐stabilised corrosion‐resistant steel, and of the same steel that had been stabilised by added titanium. The character and extent of the ensuing structural changes were analysed. The essential characteristics of degradation in the heat‐affected zone are evaluated using optical and scanning electron microscopy; individual phases are identified by means of EDX microanalysis. The underlying mechanism for the loss of stability is induced experimentally in several stages; depending on the thermal doping level and interaction with the environment during the welding process, phases of various types are precipitated. These phases subsequently are studied in connection with the original microstructural characteristics of the steel and the induced grain boundary decohesion of the surface layer. The scope and character of the damage are analysed and the results verified by analysing the actual operating damage to the weldment.
Findings
A degradation mechanism of stabilised corrosion‐resistant steel 1.4510 is induced that is associated with destabilisation of titanium phases. The importance is demonstrated of ensuring that a protective atmosphere is maintained during welding, and various phase changes in the surface layers are identified that can delimit the use of appropriate post‐weld passivation procedures.
Practical implications
Identification of the mechanism underlying the damage to the surface layer in welded stabilised ferritic steel will find application in development of welding technology, specifically in designing a technology process and subsequent surface treatment.
Originality/value
The results bring new knowledge of material response of steel 1.4510 under specific material processing conditions; a destabilisation mechanism related to precipitation of several titanium‐containing phases is identified. The result enables the fatigue limit of the welded material as a function of the welding technology employed, which offers increased service life under specific application conditions.
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A. Kalendová, D. Veselý and P. Kalenda
The purpose of this paper is to synthesise X2TiO4 spinel‐type anticorrosion pigments and YTiO3, perovskite‐type anticorrosion pigments, where X = Zn, Mg, Ca, Sr; Y = Ca for metal…
Abstract
Purpose
The purpose of this paper is to synthesise X2TiO4 spinel‐type anticorrosion pigments and YTiO3, perovskite‐type anticorrosion pigments, where X = Zn, Mg, Ca, Sr; Y = Ca for metal protective paints.
Design/methodology/approach
Anticorrosion pigments were synthesised from oxides or carbonates at high temperature. The following pigments were synthesised: TiO2 · ZnO, 2TiO2 · ZnO, TiO2 · 2ZnO, TiO2 · MgO, TiO2 · CaO, TiO2 · ZnO · MgO, and TiO2 · ZnO · SrO. The pigments obtained were characterised by means of X‐ray diffraction analysis, measurement of particle sizes and scanning electron microscopy. The anticorrosion pigments synthesised were used to produce epoxy coatings with PVC = 10 per cent for each synthesised pigment. The coatings were tested for physical‐mechanical properties and in corrosion atmospheres. The corrosion test results were compared with those of alumino zinc phosphomolybdate.
Findings
A spinel or perovskite structure was found in the pigments synthesised. High anticorrosion efficiency was identified in all the synthesised pigments, the highest efficiency being demonstrated in the TiO2 · ZnO pigment of spinel structure and in the TiO2 · CaO pigment of perovskite structure.
Practical implications
The pigments synthesised can be conveniently used to protect metal bases from corrosion.
Originality/value
The use of pigments synthesised in anticorrosion coatings for metal protection presents a new approach. Its benefits are the use and the method of synthesising the anticorrosion pigments that do not contain heavy metals and that are acceptable for the environment.
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To synthesise anticorrosion pigments of a lamellar and core‐shell type based on Zn, Ca and Mg ferrites for metal protecting paints.
Abstract
Purpose
To synthesise anticorrosion pigments of a lamellar and core‐shell type based on Zn, Ca and Mg ferrites for metal protecting paints.
Design/methodology/approach
The anticorrosion pigments were synthesised from oxides or carbonates at high temperature. The pigments synthesised had particles with a pronounced lamellar‐tubular shape consisting of MgFe2O4; Mg0.8Zn0.2Fe2O4; Mg0.6Zn0.4Fe2O4; Mg0.4Zn0.6Fe2O4; Mg0.2Zn0.8Fe2O4; ZnFe2O4; Ca0.2Zn0.8Fe2O4; and CaFe2O4. The other type of synthesised ferrite pigments were core‐shell anticorrosion pigments where a layer corresponding to the compositions including MgFe2O4/KAl3Si3O11; Mg0.8Zn0.2Fe2O4/KAl3Si3O11; Mg0.6Zn0.4Fe2O4/KAl3Si3O11; Mg0.4Zn0.6Fe2O4/KAl3Si3O11; Mg0.2Zn0.8Fe2O4/KAl3Si3O11; ZnFe2O4/KAl3Si3O11; Ca0.2Zn0.8Fe2O4/KAl3Si3O11; and CaFe2O4/KAl3Si3O11 was applied onto the core – white mica – by a chemical reaction. The pigments prepared were characterised by means of X‐ray diffraction analysis, particle size distribution measurement, and scanning electron microscopy. The anticorrosion pigments synthesised were used to formulate alkyd paints that were tested in corrosion atmospheres.
Findings
Lamellar particles were detected in the pigments prepared, whereas quality coverage of the core was identified in the core‐shell ferrites. Good anticorrosion efficiency was detected in all of the pigments synthesised.
Practical implications
The pigments synthesised can be conveniently utilised in paints to protect metal bases from corrosion.
Originality/value
The method of using the ferrites synthesised as metal protecting anticorrosion paints is new. Of great benefit are the application and the method of synthesising the anticorrosion pigments that do not contain any heavy metals and are environmentally friendly.
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R. Otáhal, D. Veselý, J. Násadová, V. Zíma, P. Němec and P. Kalenda
The purpose of this paper is to study properties of intumescent coatings based on a silicone‐epoxy hybrid resin (with an aminosilane as hardener). In the first part of this study…
Abstract
Purpose
The purpose of this paper is to study properties of intumescent coatings based on a silicone‐epoxy hybrid resin (with an aminosilane as hardener). In the first part of this study, fire‐resistance behaviour of the intumescent coating based on silicone‐epoxy resin containing intumescent additives is evaluated. The second part assesses the effect of mineral fibres on fire‐resistant properties of intumescent coatings based on the silicone‐epoxy resin.
Design/methodology/approach
Thermal degradation and char formation of coatings were investigated by Thermogravimetric analyses, X‐ray diffraction and X‐ray fluorescence and infrared spectroscopy (FTIR). The salt spray corrosion test was applied to study the resistance of intumescent coatings. Anticorrosion and fire‐resistant properties after one, three and seven days of exposure were evaluated.
Findings
It was shown that a silicone‐epoxy hybrid resin is suitable for applications in the field of intumescent coatings. Intumescent coatings based on this resin form a thermally stable thin ceramic‐like layer, which improves the thermal insulation properties of the char. Mineral fibres reinforced the char structure and thus improved fire‐resistant properties of intumescent coating before as well as after the salt spray test. Mineral fibres also improved anticorrosion properties.
Research limitations/implications
This paper discusses only the effect of mineral fibres on properties of intumescent coatings.
Originality/value
A silicone‐epoxy hybrid resin has not previously been used in intumescent coatings. This type of intumescent coating can be used as an effective passive fire protection system for steel constructions.
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Petr Veselý, Eva Horynová, Jiří Starý, David Bušek, Karel Dušek, Vít Zahradník, Martin Plaček, Pavel Mach, Martin Kučírek, Vladimír Ježek and Milan Dosedla
The purpose of this paper is to increase the reliability of manufactured electronics and to reveal reliability significant factors. The experiments were focused especially on the…
Abstract
Purpose
The purpose of this paper is to increase the reliability of manufactured electronics and to reveal reliability significant factors. The experiments were focused especially on the influence of the reflow oven parameters presented by a heating factor.
Design/methodology/approach
The shear strength of the surface mount device (SMD) resistors and their joint resistance were analyzed. The resistors were assembled with two Sn/Ag/Cu-based and one Bi-based solder pastes, and the analysis was done for several values of the heating factor and before and after isothermal aging. The measurement of thickness of intermetallic compounds was conducted on the micro-sections of the solder joints.
Findings
The shear strength of solder joints based on the Sn/Ag/Cu-based solder alloy started to decline after the heating factor reached the value of 500 s · K, whereas the shear strength of the solder alloy based on the Bi alloy (in the measured range) always increased with an increase in the heating factor. Also, the Bi-based solder joints showed shear strength increase after isothermal aging in contrast to Sn/Ag/Cu-based solder joints, which showed shear strength decrease.
Originality/value
The interpretation of the results of such a comprehensive measurement leads to a better understanding of the mutual relation between reliability and other technological parameters such as solder alloy type, surface finish and parameters of the soldering process.
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Lawton Robert Burns, Jeff C. Goldsmith and Aditi Sen
Researchers recommend a reorganization of the medical profession into larger groups with a multispecialty mix. We analyze whether there is evidence for the superiority of these…
Abstract
Purpose
Researchers recommend a reorganization of the medical profession into larger groups with a multispecialty mix. We analyze whether there is evidence for the superiority of these models and if this organizational transformation is underway.
Design/Methodology Approach
We summarize the evidence on scale and scope economies in physician group practice, and then review the trends in physician group size and specialty mix to conduct survivorship tests of the most efficient models.
Findings
The distribution of physician groups exhibits two interesting tails. In the lower tail, a large percentage of physicians continue to practice in small, physician-owned practices. In the upper tail, there is a small but rapidly growing percentage of large groups that have been organized primarily by non-physician owners.
Research Limitations
While our analysis includes no original data, it does collate all known surveys of physician practice characteristics and group practice formation to provide a consistent picture of physician organization.
Research Implications
Our review suggests that scale and scope economies in physician practice are limited. This may explain why most physicians have retained their small practices.
Practical Implications
Larger, multispecialty groups have been primarily organized by non-physician owners in vertically integrated arrangements. There is little evidence supporting the efficiencies of such models and some concern they may pose anticompetitive threats.
Originality/Value
This is the first comprehensive review of the scale and scope economies of physician practice in nearly two decades. The research results do not appear to have changed much; nor has much changed in physician practice organization.
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Nivin M Ahmed, Walaa M. Abd El-Gawad and Eglal R. Souaya
The purpose of this study is to prepare core-shell ferrites/kaolin pigments and compare their efficiency in protecting metal substrates to original ferrites. The new pigments are…
Abstract
Purpose
The purpose of this study is to prepare core-shell ferrites/kaolin pigments and compare their efficiency in protecting metal substrates to original ferrites. The new pigments are based on precipitating a shell of different ferrites that comprise only 10-20 per cent of the whole pigment on kaolin (core), which is a cheap and abundant ore comprising 80-90 per cent of the prepared pigment. These new pigments combine the properties of both its core and shell counter-parts, exhibiting improved corrosion protection properties. Furthermore, the pigments are represented as efficient, economically feasible and eco-friendly with comparable efficiency to that of original ferrites in protecting steel substrates.
Design/methodology/approach
The new pigments were characterized using different analytical and spectrophotometric techniques, e.g. transmission electron microscopy, energy-dispersive X-ray analysis and X-ray fluorescence. The pigments were then incorporated in epoxy-based paint formulations. The physico-mechanical properties of dry films and their corrosion properties were tested using accelerated laboratory tests in 3.5 per cent NaCl for 28 days.
Findings
The results of this study revealed that ferrite/kaolin core-shell pigments performance was almost close to that of the ferrite pigments in the protection of steel, and, at the same time, they confirmed good physico-mechanical properties.
Practical implications
These pigments can be applied in other polymer composites, e.g. rubber and plastics, as fillers and reinforcing agents.
Originality/value
Ferrite and ferrite/kaolin are environmentally friendly pigments, and they can impart high anticorrosive behavior to paint films with concomitant cost savings.