Rapid Synthesis of ZnO Micro and Nanostructures

This paper focuses on the newer chemical synthesis of zinc oxide powders and the effects of reaction temperature and possible mechanism of ZnO formation. The study of the reaction mechanism at different temperatures has resulted in establishing the optimum condition for the hydrothermal process

Experimental Researches Concerning the Influence of the Oxynitrocarburizing Thermochemical Treatment over the Structure and Corrosion Resistance of C40 Steel

The aim of the paper is to present the results of the experimental researches regarding the corrosion behaviour of C40 steel, thermochemical treated by oxidant nitrocarburizing at 570 °C. The thermochemical treatment was realized using an installation of oxidant nitrocarburizing. The characterization of the samples was done using laboratory equipments, in the following way: the composition of surface was determined using a RF GDS spectrometer (Jobin Yvon type), the structural analyses by X-ray diffraction (Rigaku Ultima IV) and scanning electron microscopy (MEB FEI). The evaluation of the corrosion resistance, which is the goal of this work, was done using the test method in salt fog, in the Laboratory of the Materials Engineering Department, Dacia plant

Effect of the over-ageing treatment on the mechanical properties of AA2024 aluminum alloy.

The evolution of the hardness of the over-ageing AA2024 alloy scale was followed by measurements of Vickers hardness. The nanoindentation is adapted to the determination of elastoplastic properties (hardness and Young’s modulus) of the matrix and also of coarse intermetallic precipitates. Influence of the artificial over-ageing time to hardness and to mechanical properties as the local scale was investigated

Utilisation of Electrochemical Methods for Characterization of same Corrosion Inhibitors for Steel and Copper

The effect of chromate and molybdate on the corrosion inhibition of copper and steel has been investigated in two eutectics solution at room temperature. We used stationary electrochemical methods and optical microscopy for the characterization of these materials. For steel, the molybdate inhibitor appears less efficient than the chromate one; for copper the polarization curves present an anodic passivation domain only in the chromate inhibited medium. The possibilities of galvanic coupling between them were simulated. This simulation has shown that, between copper and steel, the risk is more important in chromate medium than in molybdate one

Study of the influence of the artificial ageing temperature on the AA2024 alloy microstructure

For the last 30 years, AA2024 aluminum alloy was very used as structural material in the aerospace industry due to its low density and good mechanical strength. The phenomenon of precipitation hardening in aluminum alloys takes place at relatively low temperature and induces the precipitation of intermetallic particles composed of the main alloying elements i.e., copper and magnesium. The fundamental stage of the age-hardening process consists in the acceleration of the decomposition phenomenon of the supersaturated solid solution, resulting in the coarse intermetallic particle precipitation; stage where the mechanical properties reaches the maximum values, but at the cost of a low corrosion resistance. In this paper, the AA2024 alloy microstructure was studied during the over-ageing process. The over-ageing treatment (T7) is supposed to stabilize the microstructure and the mechanical properties to improve the corrosion resistance. The over-ageing treatment consists in a solution treatment at 495±5°C for 1 hour, quenched into cold water and artificial aged. Three different artificial ageing temperatures were studied: 150°C, 175°C and 190°C. The mechanical properties modifications were followed by Vickers macrohardness measurements. The treatment duration for each temperature (36 days for 150°C, 50 hrs for 175°C and 24 hrs for 190°C) was determined by a given macrohardness reduction. To characterize the over-aged AA2024 alloy microstructure, a statistical analysis of the surface fraction and surface density of intermetallic particles was made. The intermetallic particle dimension distribution, depending on the over-ageing temperature, was also observed. To do so, scanning electron microscope observations were carried out and image analyses were performed from backscattered electron images

Application of Kelvin probe Force Microscopy (KFM) to evidence localized corrosion of over-aged aeronautical 2024 aluminum alloy

The 2xxx serie aluminum alloys are characterized by good mechanical performances and low density, however they are susceptible to different forms of localized corrosion: pitting corrosion, intergranular corrosion and stress corrosion cracking. The 2024-T351 aluminum alloy is used in the aircraft industry for numerous applications such as fuselage and door skin. Corrosion damage of the material is also very detrimental for the structural integrity of the aircraft. The presence of coarse intermetallic particles, with a heterogeneous size distribution was found to be responsible for the 2024 susceptibility to localized corrosion. These particles are generally the cause of initiation sites. Presence of micro-defects in the oxide film upon coarse intermetallic particles and the galvanic coupling with the matrix contribute to the development of pitting corrosion. The over-ageing treatment (T7) is supposed to stabilize the microstructure and the mechanical properties to improve the corrosion resistance. The 2024 alloy microstructure after the T7 heat treatment remains very complex. The 2024 alloy corrosion behavior was studied in the over-ageing state for three different temperatures (150, 175 and 190 °C). During the corrosion tests in chloride-containing environment, the behavior of coarse intermetallic particles was found to be different. Thus, the 2024 samples suffer a gradual attack upon S-Al2CuMg particles and finally Al(Cu,Mn,Fe,Si) particles. The corrosion damage was studied by Atomic Force Microscopy (AFM) and Kelvin probe Force Microscopy (KFM). This technique allows simultaneous topographical and electric potential mapping to be obtained. This latest potential was shown to be correlated to the corrosion potential of the 2024 alloy. This study focuses on the variation of the KFM potential of the coarse intermetallic particles and the matrix for the over-ageing conditions (T7). Observations using optical microscope and AFM were also performed to obtain the corrosion rate for each condition. The corrosion rate was correlated to the chemical composition variation of the particles obtained by scanning electron microscope observations and EDS analyses

Fuel Pellets Phase Composition Evolution During Steam or Air Oxidation

In this paper the results of laboratory tests on oxidation behavior of non-irradiated UO Studies of the physico-chemical phenomena concerning severe accidents in nuclear power stations are very challanging since in this area is not possible to conduct experiments on a real-world scale and only laboratory tests can be used. This type of tests permits each phenomenon to be considered separately The oxidation reactions that may occur on the zircaloy claddings and on fuel pellets in case of a severe nuclear accident lead to a decrease in the fuel mechanical stability and to an encrease in fission products volatility Also, in order to define proper conditions for secure storage of spent fuel it is important to understand the oxidation behaviour of UO 2 fuel pellets at low temperatures The aim of this paper is to obtain experimental data neccessary to the modelling of fuel pellets behaviour in the case of a severe nuclear accident in CANDU reactors. The paper describes the oxidation tests of UO 2 fuel pellets in a SETSYS Evolution SETARAM Thermoanalyzer in air and steam atmosphere in the temperature range 400-1200 0 C. Experimental part Two sets of oxidation experiments of UO 2 pellets in 0% and 95% steam in air atmosphere were performed in a SETARAM SETSYS Evolution Thermoanalyser. The temperature range was 400÷1200 0 C. The time duration of experiments was 4 h , except the D6 experiment where the duration was 2.5 h. The oxidation tests conditions are presented in table 1. The gas flow rate used in tests was 50 mLmin -1 . The samples were non-irradiated UO 2 sintered fuel pellets, manufactured by pressing and then sintering the green pellets for 4h at 1700 0 C in a Degussa VSL 10/18 furnace using natural UO 2 powder. The diameter of pellets was approximately 3mm with 2÷2.5mm thickness, to fit to the100 μL thermo analyzer crucible. The mass of each fuel pellets was about 0.2g UO 2 . The samples were weighed and placed in an Al 2 O 3 crucible. Then the crucible was introduced in the Setsys Evolution Thermoanalyzer furnace. The samples were * email: [email protected] heated up to working temperature in an inert atmosphere (argon). During the tests various data (temperature, gas flow rate and atmosphere composition) were recorded continnously. The weight change of samples was measured and the TG curves were obtained. The humid atmosphere was created with the WETSYS controlled humidity generator. The samples were dimensionally, morphologically and cristallografically investigated after oxidation using the Horiba Particle Size Analyser, the TESCAN VEGA LMU scanning electron microscope and the X'Pert Pro MPD_PanAlytical diffractometer, respectively. Results and discussions To study the temperature effect on oxidation the samples were exposed in air-steam mixture with a steam content of 0% and 95% at temperature in the range 400÷1200 0 C

Élaboration des revêtements de phosphates de zinc sur armature à béton (étude de leur comportement à la corrosion en milieu neutre et alcalin)

Dans le génie civil, la durabilité des infrastructures en béton armé est principalement liée à la corrosion des armatures avant ou après leur enrobage de béton. La protection de ces armatures constitue donc un enjeu économique, environnementale et sécuritaire. Dans ce but, cette étude a porté d une part, sur l élaboration et la caractérisation de revêtements protecteurs de phosphates de zinc par deux méthodes : conversion chimique (CC) et traitement électrochimique cathodique (TEC) et d autre part, sur l étude de leurs comportements à la corrosion dans divers milieux : neutre, alcalin et cimentaire chloruré ou carbonaté. Nos investigations ont permis de : - mettre au point la formulation d un bain de phosphatation et de réaliser des revêtements ni toxique ni onéreux constitués d hopeite, de phosphophylite et de zinc. - préciser, en faisant appel aux techniques électrochimiques stationnaires et transitoires, le comportement à la corrosion de l acier revêtu et l effet protecteur du revêtement en milieu neutre chloruré ou carbonaté, alcalin (pH =12,6) et très alcalin (pH=13,2) contaminé ou non par des chlorures. - caractériser la réactivité de ces revêtements ainsi que leurs interactions avec le milieu cimentaire vis-à-vis des espèces actives (Cl-) présentes en solution, responsables de l amorçage et de la propagation de la corrosion des armatures. - montrer que l application des revêtements de phosphate de zinc est l un des moyens de protection contre la corrosion du béton arméIn the civil engineering, the durability of reinforced concrete structure is mainly due to the rebar corrosion before or after their immersion in concrete. Therefore, the rebar protection is an economic, environmental and security challenge. To this end, this study focused firstly, on the elaboration and the characterization of protective zinc phosphate coatings by two methods: chemical conversion (CC) and cathodic electrochemical treatment (TEC) and secondly, on theirs behaviours to corrosion in neutral and alkaline medium. Our investigations have allowed us: - to develop the phosphate bath and to obtain no toxic and no expensive phosphate coatings consisting in hopeite, phosphophylite and zinc. - to specify, using stationary and transitory electrochemical techniques, the corrosion behaviour of steel coated and the protective coating in a neutral, alkaline (pH = 12.6) and high alkaline (pH = 13.2) solutions contaminated or not by chlorides. - to characterize the reactivity of these coatings as well as theirs interactions with the concrete pore solution, in particular with the active species (Cl-) responsibles for the initiation and the propagation of reinforcement corrosion. - to show that the use of zinc phosphate coatings is a reliable method to protection against reinforced concrete corrosion.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocSudocFranceF

Electrochemical studies on stress corrosion cracking of incoloy-800 in caustic solution. Part II: Precracking samples

Stress corrosion cracking (SCC) in a caustic medium may affect the secondary circuit tubing of a CANDU NPP cooled with river water, due to an accidental formation of a concentrated alkaline environment in the areas with restricted circulation, as a result of a leakage of cooling water from the condenser. To evaluate the susceptibility of Incoloy-800 (used to manufacture steam generator tubes for CANDU NPP) to SCC, some accelerated corrosion tests were conducted in an alkaline solution (10% NaOH, pH = 13). These experiments were performed at ambient temperature and 85 °C. We used the potentiodynamic method and the potentiostatic method, simultaneously monitoring the variation of the open circuit potential during a time period (E corr/time curve). The C-ring method was used to stress the samples. In order to create stress concentrations, mechanical precracks with a depth of 100 or 250 μm were made on the outer side of the C-rings. Experimental results showed that the stressed samples were more susceptible to SCC than the unstressed samples whereas the increase in temperature and crack depth lead to an increase in SCC susceptibility. Incipient micro cracks of a depth of 30 μm were detected in the area of the highest peak of the mechanical precrack

Comportement à la corrosion des alliages d'aluminium utilisés dans l'industrie automobile pour la fabrication de radiateur de chauffage

La protection contre la corrosion du matériau constituant le radiateur de chauffage dans les moteurs automobiles est habituellement assurée par une formulation adaptée du liquide de refroidissement. Les mécanismes de corrosion et de protection sont complexes. Ils dépendent des conditions physico-chimiques de service (nature de l'inhibiteur, température de fonctionnement, cyclages thermiques, agitation du milieu) et des caractéristiques du matériau (nature de l'alliage, état de surface). Ces dernières années, l'entreprise automobile roumaine (Dacia Renault) a connu de sérieux problèmes de corrosion interne lors du remplacement de l'acier par l'alliage d'aluminium AlMn1. L'étude entreprise a consisté en une caractérisation physico-chimique, par méthodes électrochimiques stationnaires et non stationnaires et par métallographie, de l'efficacité protectrice de deux types de liquides de refroidissement se différenciant principalement par la nature de l'inhibiteur. L'influence de la température et des cyclages thermiques (simulant les périodes de fonctionnement et d'arrêt) a été déterminée, ainsi que celle des conditions de dilution (eau permutée ou eau de distribution) du produit commercial concentré. Le mode de corrosion (par piqûres) et les zones d'amorçage ont été identifiés. Le mécanisme d'interaction de ces inhibiteurs a été déterminé par Spectroscopie d'Impédance Electrochimique et les circuits électriques équivalents au comportement des interfaces métal milieu ont été proposés. Cette modélisation a permis de déterminer les paramètres principaux relatifs aux couches passives formées par l'action de ces inhibiteurs filmogènes. L'intérêt du manganèse comme élément d'addition a été confirmé par des essais conduits avec de l'aluminium pur.The radiators associated to car engines are usually protected against corrosion by well adapted cooling liquids. Corrosion and protection mechanisms are complex, and linked to the physico-chemical conditions (nature of the inhibitor, temperature, thermal cyclings, stirring conditions ), as well as to the characteristics of the material (its nature and surface state). Several years ago, the Romanian car manufacturer Dacia Renault has encountered some severe problems of corrosion, when it has been decided to replace iron by the AlMn1 alloy. The present work consists in characterising, by stationary and transitory electrochemical methods coupled with metallography, the protective efficiency of two cooling liquids, differentiated by the nature of their inhibitor. Influence of temperature, thermal cycling (simulating the actual operating of the radiator), and inhibitor's concentration has been determined. The type of attack has been also characterized (pitting especially) and the initiation sites have been identified. A model of interaction between the metallic surface and the inhibitor has been proposed, by considering the impedance results. This model allows then to discriminate the key-parameters linked to the formed passive protective film. The beneficial effect of manganese additions has been moreover confirmed by measurements carried out with pure aluminium.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocSudocFranceRomaniaFRR