Volume 59 (2015): Edizione 4 (December 2015)

The oxidation kinetics of zirconium alloys corrosion can be divided in two phases that are detached by a transient state. The occurrence of the transient state is crucial from the corrosion perspective, since it accelerates the oxidation rate. This work employs in-situ electrochemical impedance spectroscopy to study Zr-Nb and Zr-Sn alloys at the temperature of 340° and the pressure of 15 MPa in the environment simulating the cooling agent of PWR reactor. The goal of long-term experiments (up to 9000 hours) was to characterise oxidation kinetics, depending on the exposure time and the type of zirconium alloy. The results showed that the transient state is achieved sooner for the Zr-Sn alloy.

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, H₂, CH₄, H₂O) 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.

A contact between the primary medium containing boric acid and construction metallic materials cannot be avoided in production conditions of the primary circuit of nuclear power plants. The goal of this experimental project was to simulate selected exposures of construction materials to the primary medium and quantify its corrosion impacts. The basic factors affecting corrosion include the temperature of the material surface, acid concentration and the possibility of steam suction from the surface. The steam layer forms at a high temperature and protects the surface from the contact with boric acid and prevents corrosion. Evaporation of boric acid also depends on the quantity of water (boric acid concentration). The excess of water enables distillation of boric acid and the excess of boric acid results in formation of a harmless glasslike layer from the boric acid melt.

Under certain circumstances, timber protective coatings may accelerate corrosion of metallic fasteners. The phenomenon of metal corrosion in wood chemically modified with silicones is a crucial factor for definition of appropriate rules for application of these materials on timber. The study presents results of the impact of modified spruce (Picea Abies L.), oak (Quercus SPP.) and larch (Larix decidua Mill.) timber and standard steel, copper and galvanised steel nails. Samples of timber with driven nails were exposed to the environment of 30°C temperature and 100% atmospheric humidity for a period of 6 weeks, when humidity of wood approximated the point of fibre saturation. After the exposure, the surface of steel nails removed from the timber was visually evaluated; corrosion products from selected samples were analysed using infrared spectroscopy. Based on the analyses results, the hypothesis of material compatibility between modified spruce (Picea Abies L.) timber and steel fixtures in the environment with high atmospheric humidity was formulated. After the exposure period, the extent of the surface corrosion of steel nail was lower than in untreated reference timber (without the protective coating).

Unsuitable storage conditions and use of materials which may be a source of pollutants in indoor environments are major threats to the long-term preservation of historic metal objects. Materials proposed for use in protecting and storage of museum or archive collections need to be sufficiently verified in terms of safety for the protected objects before these materials can be safely recommended. One of the basic techniques used for the purpose of testing of new materials (and verifying of those that are already in use) is the Oddy test whose advantages lies in its simple requirements for the experimental equipment and a possibility to modify this method for a particular use. In this work, a variant of the Oddy test was applied with a modification for a specific case – evaluation of materials used for recasing of daguerreotypes. Besides the commonly used visual assessment, electrochemical reduction of corrosion products on the exposed samples was used to compare the Oddy test results. The results indicate that the influence of the test materials is minor compared to the influence of the state of the daguerreotypes surface. This conclusion is consistent with expectations about safety of the tested materials that are used in conservation practice for the protection of archival and historical photographic collections.