rss_2.0Koroze a ochrana materialu FeedSciendo RSS Feed for Koroze a ochrana materialu a ochrana materialu 's Cover assisted cracking in the low pressure superheated hydrogen steam<abstract> <title style='display:none'>Abstract</title> <p>Low pressure superheated H<sub>2</sub>-steam appears to be an interesting alternative to pressurized water environments, since it is capable of performing accelerated environmentally assisted cracking (EAC) experiments for nickel base and stainless steel alloys. Constant Extension Rate Tensile (CERT) tests were performed with displacement rates of 2×10<sup>-6</sup> or 2×10<sup>-8</sup> ms<sup>-1</sup> at 350, 400, 440 and 480 °C on flat tapered specimens of Type 316L austenitic stainless steel. The tapered shape allows the determination of crack initiation over a range of stresses and strains simultaneously on one specimen and therefore the threshold stress value was obtained. The environment was 6 times more oxidizing than the dissociation pressure of NiO. The acquired mechanical properties are summarized and threshold stresses for EAC crack initiation are evaluated.</p> </abstract>ARTICLE2021-06-12T00:00:00.000+00:00Simulation of boronizing kinetics of ASTM A36 steel with the alternative kinetic model and the integral method<abstract> <title style='display:none'>Abstract</title> <p>In this study, two different mathematical models have been proposed for estimating the diffusivities of boron in the Fe<sub>2</sub>B layer on ASTM A36 steel in the range of 1173 to 1273 K with exposure times of 2 to 8 h. The boride incubation period required for the formation of such a layer was constant regardless of the boriding conditions. In both approaches, the boron diffusivity in the iron phase was considered in an unsaturated matrix. The first approach was derived from the mass balance equation at the (Fe<sub>2</sub>B/substrate) interface while the second approach employed the integral diffusion model. The calculated values of boron activation energies for ASTM A36 steel were found to be very comparable for the two approaches (161.65 and 160.96 and kJ mol<sup>-1</sup>). Afterwards, these values of activation energy were confronted with the results from the literature. Experimental validation of these two approaches has been done by comparing the experimental value of Fe<sub>2</sub>B layer thickness measured at 1123 K for 2.5 h with the simulated values. Finally, the predicted values of Fe<sub>2</sub>B layer thickness were in line with the experimental measurement.</p> </abstract>ARTICLE2021-06-12T00:00:00.000+00:00Terephthalohydrazide and isophthalo- hydrazide as new corrosion inhibitors for mild steel in hydrochloric acid: Experimental and theoretical approaches<abstract> <title style='display:none'>Abstract</title> <p>Most organic corrosion inhibitors have polar groups through which the molecule can be adsorbed strongly or specifically on the metal surface. In this investigation, terephthalo- hydrazide and isophthalohydrazide were synthesized as corrosion inhibitors, and their corrosion-inhibiting properties on mild steel were evaluated in a corrosive environment by weight loss measurements. The results of corrosion experiments revealed that terephthalohydrazide and isophthalohydrazide as inhibitors controlled or reduced corrosion through adsorption mechanism and showed inhibitive efficiencies of 96.4 % and 97.2 %, respectively, at the optimum concentration of 0.5 mM. The surface morphology of the metal was evaluated by scanning electron microscopy. The terephthalohydrazide or isophthalohydrazide molecules were adsorbed on the mild steel surface, and the process of adsorption follows chemical adsorption. Quantum chemical calculations of the tested corrosion inhibitors were consistent with the experimental observations.</p> </abstract>ARTICLE2021-06-12T00:00:00.000+00:00Investigation on the microstructure, microhardness, and tribological behavior of AA1100-hBN surface composite<abstract> <title style='display:none'>Abstract</title> <p>Aluminum alloy AA1100 has less wear resistance and mechanical properties than that of other aluminum alloys. This research work is on the fabrication of surface composites of AA1100 alloy by friction stir processing (FSP). The surface composites are fabricated by reinforcing hBN (hexagonal Boron Nitride) in AA1100 alloy to improve the mechanical and tribological properties. The influence of process parameters, rotational speed (rpm), and transverse speed (mm/min) on the microstructural evolution and properties of the fabricated surface composites is investigated.</p> </abstract>ARTICLE2021-06-12T00:00:00.000+00:00Evaluation of microstructure of the steels after exposure in supercritical CO<abstract><title style='display:none'>Abstract</title><p>The Brayton cycle with supercritical carbon dioxide is considered as an innovative technology with the potential to replace conventional steam cycles. The optimization of the supercritical CO<sub>2</sub> cycle (sCO<sub>2</sub>) is necessary and important to achieve the required thermal cycle parameters. The above optimization focuses on the setting of the energy cycle as such, the design solution of the individual components and, the last but not least, on the selection of suitable construction materials. Due to the operating conditions, namely temperatures exceeding 550 °C and pressure up to 25 MPa, material research is one of the important areas of the research and development of sCO<sub>2</sub> energy cycles. Construction materials for sCO<sub>2</sub> power cycle equipment include HR6W, T92 and Haynes HR235 alloys. This work presents results of the corrosion test, in which samples of these materials were exposed to sCO<sub>2</sub> at 550 °C and 25 MPa for 1000 hours. Corrosion after exposure was examined using a light optical microscope (LOM) and a scanning electron microscope (SEM). The significant differences in corrosion attack between the investigated materials and the formation of a protective oxide layer on the surface were observed.</p></abstract>ARTICLE2020-12-31T00:00:00.000+00:00Influence of surface treatment on corrosion resistance of steel in liquid Pb<abstract><title style='display:none'>Abstract</title><p>This work deals with behaviour of steel in liquid lead environment and possibilities of corrosion resistance improvement. Liquid metal cooled systems are under wide investigation and development and represent a good alternative. It is necessary to find materials, which would be affected by liquid lead minimally. Austenitic steel 316L without coating and coated with TiSiC was studied in flowing liquid lead. Conditions of the experiment simulated real environment of the system. Deposition of protective barrier reduced the metals dissolution and diffusion of liquid lead into the steel substrate, degradation of substrate due to high temperature and mechanical stress. Presence of Si in the layer increased the surface ability to form stabile oxide and contribute to steel´s protection.</p></abstract>ARTICLE2020-12-31T00:00:00.000+00:00Gravimetrical, theoretical, and surface morphological investigations of corrosion inhibition effect of 4-(benzoimidazole-2-yl) pyridine on mild steel in hydrochloric acid<abstract><title style='display:none'>Abstract</title><p>The corrosion inhibition efficiency of the novel pyridine namely, 4-(Benzoimidazole-2-yl)pyridine has been studied for mild steel in a 1 M hydrochloric acid environment by utilizing gravimetrical techniques. The synthesized inhibitor exhibits a significant inhibitive efficiency of 93.8% at 0.005 M. The adsorption isotherm of the investigated inhibitor on mild steel surface obeys the Langmuir isotherm. Surface morphology investigated by utilizing scanning electron microscopy (SEM) demonstrates a smooth metal surface with the addition of 4-(Benzoimidazole-2-yl)pyridine in a hydrochloric acid environment. Quantum chemical calculations using density functional theory (DFT) have been used to investigate the molecular structure and behavior of 4-(Benzoimidazole-2-yl) pyridine as a corrosion inhibitor. Different parameters have been calculated using DFT, such as energies of highest occupied molecular orbital and lowest occupied molecular orbital (EHOMO and ELUMO), energy gap (∆E), and dipole moment (μ). These parameters were important to elucidate the behavior of the investigated molecule as a corrosion inhibitor in acidic solution and also suggest the mechanism of inhibition.</p></abstract>ARTICLE2020-12-31T00:00:00.000+00:00The change in the morphology of the blasted surface after phosphating and cataphoretic coating<abstract><title style='display:none'>Abstract</title><p>The paper focuses on the quality of coatings applied by cataphoretic deposition and cataphoretic deposition technology with a phosphate layer. The quality of the coatings was evaluated by determining the roughness of the coatings, the morphology of the coatings, spectral analyses were performed detecting the presence of individual elements in the coatings. There was analysed also defect – uncoated spot.</p></abstract>ARTICLE2020-12-31T00:00:00.000+00:00EFC Activity: Highlights 2020 impact of diverse composition of historical plasters on their resistance<abstract xml:lang="cs"><title style='display:none'>Vliv rozdílného složení historických omítek na jejich odolnost</title><p>Na základě restaurátorského a technologického průzkumu omítek v kostele sv. Jiljí v Uhlířských Janovicích, který byl prováděn v roce 2010 v rámci projektu obnovy presbytáře kostela, byly zhodnoceny a zobecněny historické technologie a surovinové složení malt zde použité v přibližném časovém rozmezí 1250 - 1954. Pro volbu technologie oprav, techniky zajištění a stabilizaci omítek byl veškerý dochovaný maltovinový materiál rozřazen do několika skupin podle výchozí charakteristiky, stáří, hodnoty a stupně dochování, resp. jejich technického stavu.</p></abstract>ARTICLE2012-04-03T00:00:00.000+00:00Exfoliation of a snap-link in a karst cave environment<abstract xml:lang="cs"><title style='display:none'>Exfoliace karabiny v prostředí krasové jeskyně</title><p>V rámci práce byl studován zajímavý případ exfoliace hliníkové slitiny. Jednalo se o expresní karabinu exponovanou v prostředí krasové jeskyně. Jednotlivé části jisticí sady byly sledovány na metalografických výbrusech pomocí optického i skenovacího elektronového mikroskopu s rentgenovou energiově disperzní analýzou (SEM/EDS). Korozní produkty byly analyzovány metodou rentgenové difrakce (XRD). Příčinami selhání karabiny bylo nevhodné termomechanické zpracování a expozice v trvale vlhkém prostředí.</p></abstract>ARTICLE2012-04-03T00:00:00.000+00:00Direct measurement of a dew point in combustion equipment<abstract xml:lang="cs"><title style='display:none'>Přímé měření kyselého rosného bodu ve spalovacích zařízeních</title><p>V důsledku poklesu teploty spalin pod teplotu rosného bodu dochází u řady energetických celků k problémům s korozí vlivem zkondenzovaných kyselin. Dochází tak k značným korozním napadením a poškozením zejména na ohřívácích vzduchu, ekonomizérech, vedeních kouřovodů, ale i v samotném komíně. Ve SVÚMu byla vyvinuta a vyzkoušena sonda pro přímé měření teploty rosného bodu spalin. Pomocí této metody je možné rychle zjistit teplotu rosného bodu bez nutností složitých výpočtů, analýz spalin, náročných odběrů spalin, atd. Následnou úpravou teploty spalin je tak možné předejít značným korozním problémům.</p></abstract>ARTICLE2012-04-03T00:00:00.000+00:00The preparation of Ti-Al-Si intermedial layers for high-temperature applications by the liquid-phase siliconizing method<abstract xml:lang="cs"><title style='display:none'>Příprava intermediálních vrstev Ti-Al-Si pro vysokoteplotní aplikace metodou křemíkování z kapalné fáze</title><p>Metoda křemíkování z kapalné fáze je jednoduchá a efektivní metoda pro přípravu vrstev tvořených intermediálními fázemi Ti-Al-Si na titanu a slitinách titanu, založených na reakci vzorků ponořených do tavenin Al-Si. Tyto vrstvy mají uplatnění především při vysokoteplotních aplikacích jako ochranné vrstvy. Touto metodou lze připravit kompaktní, masivní vrstvy bez pórů a trhlin, při teplotách 650 °C po dobu 60 min lze připravit vrstvy s tloušťkou 60 μm. V tomto příspěvku jsou shrnuty důležité poznatky o vlastnostech vrstev připravených metodou křemíkování z kapalné fáze.</p></abstract>ARTICLE2012-04-03T00:00:00.000+00:00Corrosion rate of cathodically "protected" steel in carbonate environment<abstract xml:lang="cs"><title style='display:none'>Korozní rychlost katodicky "chráněné" oceli v prostředí uhličitanů</title><p>Jedním ze způsobů vysvětlení mechanizmu ochranné funkce katodické ochrany je katodická pasivace. Vlivem katodické reakce dochází v okolí úložného zařízení k alkalizaci půdy, která usnadňuje přechod železa do pasivního stavu. K zapasivování oceli však dojde pouze v případě, že vložený ochranný potenciál má kladnější hodnotu než pasivační potenciál. Cílem práce bylo určit závislost pasivačního potenciálu a korozní rychlosti na korozním potenciálu v prostředí uhličitanu s různým pH s využitím elektrochemických metod a rezistometrické techniky. Korozní rychlost železa při dlouhodobé expozici byla určena pomocí rezistometrického čidla. Hodnota pasivačního potenciálu klesá s rostoucí hodnotou pH. Ocel se v prostředí uhličitanu pasivuje při běžném ochranném potenciálu -850 mV/CSE dosažením pH 11. Pod touto hodnotou ocel koroduje v aktivním stavu, a to pro úložná zařízení nepřijatelnou korozní rychlostí (&gt; 0,01 mm/rok).</p></abstract>ARTICLE2012-04-03T00:00:00.000+00:00Testování mechanických vlastností Inconelu 713 a 738 pro pokročilé reaktory<p>Nickel superalloys Inconel 713 and 738 belong among metallic construction materials used for components of advances gas cooled reactors. The project of applied research solved by the UCT Prague and RC Řež tested mechanical properties of these alloys in the starting phase and after the exposure to helium containing trace pollutants (CO, H<sub>2</sub>, CH<sub>4</sub>, H<sub>2</sub>O) at the temperature of 900°C for a period of 1000 hours. The samples of tested alloys were made from: a) the virgin cast material, b) remanufactured material (revert 100R) and c) casting of previous materials in the ratio of 50V/50R. To identify mechanical properties of the materials after exposure, tensile tests and structural analyses by SEM were carried out. The changes of properties after the exposure of tested alloys and the same alloys made in various procedures were compared. While the yield and tensile strengths dropped insignificantly for Inconel 713, the plummeted for Inconel 738. The 50V/50R state showed better mechanical properties than the revert 100R state.</p>ARTICLE2015-12-30T00:00:00.000+00:00Corrosion behaviour of copper in wet bentonite Rokle B75<p>Materials for storing nuclear waste are a hot topic all over the globe right now. This study monitors corrosion behaviour of copper as one of the contemplated materials in the Czech bentonite Rokle B75. The tests were carried out in a thermostated cell deaerated with argon at temperatures of 90 and 40°C in the environment of bentonite pore solution, bentonite pore solution with an addition of sulphides and wet bentonite suspension. The scanning electron microscopy, X-ray diffraction, Raman spectroscopy, electrochemical impedance spectroscopy and resistometric methods of corrosion rate measurements were applied. The most compact layer is formed in the environment of bentonite pore solution. The addition of sulphides leads to a significant growth of thickness of the layer of corrosion products and its porosity. However, the porosity decreases towards the layer - metal interface. The layer formed after exposure to the wet bentonite suspension is reported to have the worst parameters. Nevertheless, considering the final temperature of 40°C in the repository, the corrosion rate will still be acceptable.</p>ARTICLE2014-07-10T00:00:00.000+00:00The impact of inorganic compounds used for protection of wood on cellulose<p>Inorganic compounds were often used to protect wood from wood-decaying fungi and insects (e.g. compounds of arsenic, copper, chromium, zinc or boron) or as a retarder of combustion (e.g. ammonium salts, boron compounds). However, their use may accelerate degradation processes, which may show up as worsening of mechanical properties. The study deals with the impact of selected inorganic compounds (sodium chloride, copper sulphate pentahydrate, boric acid and ammonium sulphate) on cellulose. The samples of cellulose impregnated with the said compounds were subject to artificial aging. The cellulose was monitored for weight changes, changes in colour, values of aqueous extract pH, an average polymerization grade, mechanical properties, elementary composition and the content of bound inorganic compounds. The study was meant to identify stability of the used inorganic compounds in the conditions of artificial aging. The results imply that copper sulphate pentahydrate and ammonium sulphate accelerated degradation of cellulose the most. The effect of boric acid lead to larger deterioration of specimens namely in the conditions of dry aging. Sodium chloride had a negligible impact on the course of degradation. Used compounds continue to be at least partly retained in the cellulose specimens even after rinsing.</p>ARTICLE2014-07-10T00:00:00.000+00:00Evaluation of protective properties of acrylate varnishes used for conservation of historical metal artefacts<p>Acrylate varnishes are due to their suitable properties frequently used in restoration and preservation on variety of historical objects and materials. Common practice of their application involves using as an adhesive agents, consolidants and protective coatings. The purpose of protective coatings especially on metal artefacts is to reduce access of pollutants to the surface of the artefact. In this paper, coatings prepared from two acrylate polymers Paraloid B72 and Paraloid B48N are compared in terms of permeability for water and level of protective properties against air pollutants. For this purpose, electrochemical impedance spectroscopy and resistometric method were chosen for analysis of the coatings. Obtained results show lower permeability for water in case of Paraloid B72. However, same coating provided lower protection against air pollutants than Paraloid B48N coating.</p>ARTICLE2017-02-23T00:00:00.000+00:00Influencing the anticorrosion efficiency of pigments based on zinc ferrite by conductive polymers<p>Generally, organic coatings which contain zinc ferrites are able to protect metal substrate, most often low-carbon steel, by inhibition mechanism. Conductive polymers are using a system of conjugated double-bonds to transfer a charge over the chain thereby providing their own electrical conductivity in the organic coatings. The charge from the chain in combination with the iron substrate generates electrons to the formation of passivation products on the surface of paint film. This paper is focused on combination of zinc ferrite with conductive polymer and using of synergic effect of these two components. The organic coatings were formulated from hematite and specularite on pigments concentration line 5, 10, 20 and 25 wt.% for better recognizing of the effectiveness of zinc ferrite component. The content of the conductive polymer was consistently set at 3 wt.% in each organic coating. A solvent-based epoxy-ester resin was used as a binder. The physico-mechanical and corrosion tests were performed for all samples. The corrosion signs were evaluated on the surface of coating and also on the surface of metal substrate. In the end, the efficiency was compared alone zinc ferrite and alone polymers and also their combinations.</p>ARTICLE2018-08-06T00:00:00.000+00:00The impact of a relaxation time on the quality of a pigment layer for a solar collector<p>Skúmal sa vplyv relaxačného času periodického reverzného prúdu na kvalitu vyfarbovania povrchu anodicky oxidovaného hliníka. Na vyfarbovanie sa použil elektrolyt bez komplexotvorného činidla a s komplexotvorným činidlom. Študoval sa aj vplyv frekvencie impulzového prúdu. Kvalita vyfarbených povrchov sa hodnotila spektrokolorimetricky a množstvo vylúčeného niklu sa určilo atómovou absorpčnou spektroskopiou. Zistilo sa, že relaxačný čas periodického reverzného prúdu významne ovplyvňuje kvalitu vyfarbených povlakov pre elektrolyty bez komplexotvorného činidla.</p>ARTICLE2012-08-02T00:00:00.000+00:00en-us-1