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This paper aims to study the oxidation kinetics of the nanocrystalline Al ultrathin films. The influence of structure and composition evolution during thermal oxidation will be observed. The reason for the change in the oxidation activation energy on increasing the oxidation temperature will be discussed.

Al thin films are deposited on the silicon wafers as substrates by vacuumed thermal evaporation under the base pressure of 2 × 10⁻⁴ Pa, where the substrates are not heated. A crystalline quartz sensor is used to monitor the film thickness. The film thickness varies in the range from 30 to 100 nm. To keep the silicon substrate from oxidation during thermal oxidation of the Al film, a 50-nm gold film was deposited on the back side of silicon substrate. Isothermal oxidation studies of the Al film were carried out in air to assess the oxidation kinetics at 400-600°C.

The activation energy is positive and low for the low temperature oxidation, but it becomes apparently negative at higher temperatures. The oxide grains are nano-sized, and γ-Al₂O₃ crystals are formed at above 500°C. In light of the model by Davies, the grain boundary diffusion is believed to be the reason for the logarithmic oxidation rate rule. The negative activation energy at higher temperatures is apparent, which comes from the decline of diffusion paths due to the formation of the γ-Al₂O₃ crystals.

It is found that the oxidation kinetics of nanocrystalline Al thin films in air at 400-600°C follows the logarithmic law, and this logarithmic oxidation rate law is related to the grain boundary diffusion. The negative activation energies in the higher temperature range can be attributed to the formation of γ-Al₂O₃ crystal.

Continuing the summaries of papers presented at the recent Dechema Corrosion Congress, the following are all concerned with electro‐chemical mechanisms. Next month our report of the congress will end with summaries of some of the papers dealing with corrosion prevention.

The subject of this paper is high temperature corrosion in chlorine and hydrogen chloride gaseous environments. The discussion will be limited to metals and alloys such as iron and carbon steel, iron‐chromium alloys and stainless steels, nickel and nickel alloys which are of interest in the petroleum industry.

The examination of products of aqueous and non aqueous corrosion is carried out to obtain information about one of a combination of aspects such as composition, hardness, stress level, adhesion to basis metal and other mechanical properties (figure 1). A number of techniques are avialable to investigate corrosion products and some of these techniques have found greater application with products of aqueous corrosion and some with products of gaseous corrosion. This paper presents the technqiues available for obtaining information about the various aspects mentioned above and discusses the main characteristics, nature of data obtainable, advantages and limitations of some of the less know techniques.

Sulphuric corrosion of refinery equipment. Characteristics of sulphuric acid solutions encountered in refineries, the types and kinds of containers, piping, valves, heaters and other equipment used to handle it are considered by the authors with respect to their corrosion resistance and certain other related qualities. Materials of construction for construction, fabrication and design details of the various vessels and equipment are discussed with relation to the several concentrations, temperatures, pressures, velocities and other peculiarities of the sulphuric acid solutions encountered in petroleum refineries.

The development of high‐temperature, oxidation‐resistant coatings needs to be thoroughly studied owing to the metal loss incurred from short‐ or long‐term exposure to high temperatures before final processing. Particularly, short‐term exposure (intermittent heating or soaking or other heat treatment schedules) always produces often unwanted scales, which cause problems in subsequent metal working, loss of metal or further necessary pickling, etc. Studies the performance of some slurry‐based coatings with regard to the protection of metals during short‐term exposure to high temperatures.

This paper aims to analyse the surface evolution of pure recycled titanium subjected to isothermal and cyclic oxidation conditions using dry air as oxidant gas. It is important to mention that the cyclic oxidation behaviour of pure titanium is a process that has been barely studied.

An isothermal and cyclic oxidation reactor was built for these purposes. This installation allows the oxidation of material under the action of any atmosphere and for temperatures up to 1,200°C. For this study, the oxidation behaviour of the material was studied at 850°C and 950°C.

Oxide growth under isothermal oxidation conditions in air follows a parabolic behaviour with an activation energy of 118 kJ/mol, and the oxide phase formed on the surface of the metal was rutile. The cyclic oxidation of the material indicates that oxide is spalled from the surface following linear behaviours; this phenomenon is controlled by the thermal stresses experienced by the samples during heating and cooling cycles.

The material is obtained from the production of electrolytic copper, and during its reprocessing practices at high temperature, it was thought that it could experience some abnormal oxidation. In addition, given that pure titanium is currently used for biomedical application, some surface degree can be given by means of oxidation and subsequent spallation process situation that is found during the cyclic oxidation experiments, which could be a low-cost method to engineer a surface for these purposes.

Climate analogues have been extensively used in ecological studies to assess the shift of ecoregions due to climate change and the associated impacts on species survival and displacement, but they have hardly been applied to urban areas and their climate shift. This paper aims to use climate analogues to characterize the climate shift of cities and to explore its implications as well as potential applications of this approach.

The authors propose a methodology to match the current climate of cities with the future climate of other locations and to characterize cities’ climate shift velocity. Employing a sample of 90 European cities, the authors demonstrate the applicability of this method and characterize their climate shift from 1951 to 2100.

Results show that cities’ climate shift follows rather strictly north-to-south transects over the European continent and that the average southward velocity is expected to double throughout the twenty-first century. These rapid shifts will have direct implications for urban infrastructure, risk management and public health services.

These findings appear to be potentially useful for raising awareness of stakeholders and urban dwellers about the pace, magnitude and dynamics of climate change, supporting identification of the future climate impacts and vulnerabilities and implementation of readily available adaptation options, and strengthening cities’ cooperation within climate-related networks.

The Orange River is one of the largest river basins in southern Africa. Since it plays a crucial role in the region's ecology and economy, it is important to estimate future developments in its hydrology. A necessary means to this end are climate projections. This paper seeks to address this issue.

In this work the authors present projections obtained by two complementary methods; they use a Statistical Analogue Re‐sampling Scheme (STARS) and a dynamical regional climate model (CCLM – COSMO in Climate Mode). In order to determine the viability of these methods, the authors perform cross‐validations for the years 1976‐2000.

CCLM shows good performance regarding the 2 m temperature but the reproduction of precipitation is rather poor. STARS, on the other hand, produces very good results for both variables. The climate projections of both models show a considerable temperature increase for the future (2036‐2060, SRES A1B scenario), especially in the inland of the simulation area. However, while CCLM projects a general decrease in precipitation, STARS indicates a strong precipitation decrease in the already dry western part of the region and a moderate decrease resp. no change in the east during the rain season.

For the first time the statistical approach used gridded data as its input. Therefore, it was possible to apply complementary methods in order to generate the climate projections and to compare them.

Investigations were aimed at the evaluation of degradation mechanisms in ultrasonically welded joints of AlSi1 per cent wire (25 μm in diameter) and Au substrate (100 μm thick), relatively thick elements, exposed to high temperature of 300°C up to 100 h. Thermally activated Al diffusion into Au generates the formation of intermetallic compounds in the area of the bond interface. With the longer thermal exposure the expansion and transformation of intermetallic compounds is observed. The characteristic “intermetallic compounds core” is formed, which from one side penetrates into the wire material and from another spreads deeply into the Au substrate up to enhancing band of Kirkendall voids.