Etching technique for revelation of plastic deformation zone in low carbon steel

Abstract

In this study, an etching technique to detect the localised plastic deformation behaviour in a low carbon steel was developed. With this technique, etching with Fry solution under ultrasonic vibration was carried out on samples plastically deformed and then heated at 550°C for a certain period of time. The plastic zone was revealed by different degrees of etching in the plastically deformed and non-deformed regions; the plastic zone was found to be only slightly etched, whereas the other region was deeply etched. From the surface offset after etching, the deformation zone was found to be observable even at low magnification, such as 10 times. As the heating duration increased, the plastic zone became clearer. The mechanism for such an etching reaction is discussed on the basis of electrochemical analysis.     

Grain growth of zircon pigment in tile glaze

Abstract

Glazes for ceramic materials are often opacified by a zircon pigment. The increase in optical density is related to the number and size of pigment particles, which are well dispersed in the glass. Mechanical dispersion by grinding of a fine zircon powder in a raw glaze mixture results in an unoptimised pigment dispersion in the melted glassy phase at high temperature. A significant reduction in the number of particles and a simultaneous large increase in their size is observed. In this case the optical glaze density does not attain the expected value and a very large quantity of zircon must be added. In the present work it is shown that a large part of the zircon reacts with the glass phase during firing. Simultaneously, the remaining zircon grains undergo a large increase in grain size by Ostwald ripening through the liquid phase. This process is characterised by a low activation energy (79 ± 1 kJ mol^-1) and a short diffusion path for Zr through the liquid phase between neighbouring grains. The path length is shorter than the size of the larger grains. In the usual firing range, both populations of smaller and larger grains vary in size, the smaller grains favouring growth of the larger grains.     

Local path planning using a new artificial potential function composition and its analytical design guidelines

This paper presents a new framework for path planning based on artificial potential functions (APFs). In this scheme, the APFs for path planning have a multiplicative and additive composition between APFs for goal destination and APFs for obstacle avoidance, unlike conventional composition where the APF for obstacle avoidance is added to the APF for goal destination. In particular, this paper presents a set of analytical guidelines for designing potential functions to avoid local minima for a number of representative scenarios based on the proposed framework for path planning. Specifically the following cases are addressed: (i) a non-reachable goal problem (a case in which the potential of the goal is overwhelmed by the potential of an obstacle), (ii) an obstacle collision problem (a case in which the potential of the obstacle is overwhelmed by the potential of the goal) and (iii) a narrow passage problem (a case in which the potential of the goal is overwhelmed by the potential of two obstacles). The example results for each case show that the proposed scheme can effectively construct a path-planning system with the capability of reaching a goal and avoiding obstacles despite possible local minima.     

New repulsive potential functions with angle distributions for local path planning

This paper presents new repulsive potential functions (RPFs) for point robot path planning. In this scheme, the RPF for path planning has a different magnitude at each direction of a RPF based on the angle between a goal and an obstacle, unlike a conventional RPF in which the same magnitude at each direction is obtained. In doing so, the RPF attempts to overcome some of the typical problems that may arise with the conventional RPF. In particular, this paper presents a set of analyses for designing potential functions to avoid local minima for a number of representative scenarios. Specifically, the following cases are addressed: (i) a non-reachable goal problem (a case in which the potential of the goal is overwhelmed by the potential of an obstacle), (ii) an obstacle collision problem (a case in which the potential of the obstacle is overwhelmed by the potential of the goal) and (iii) a narrow passage problem (a case in which the potential of the goal is overwhelmed by the potential of two obstacles). The proposed RPF scheme eliminates the non-feasible area for the three cases by the help of an angle-varying magnitude between a goal and an obstacle. The example results show that the proposed RPF scheme can effectively construct a path-planning system with the capability of reaching a goal and avoiding obstacles despite possible local minima.     

Influence of the growth medium,suspending liquid and measurement temperature on the physico-chemical surface properties of two enterococci strains

A knowledge of the physico-chemical surface properties of a bacterium is important to predict the first step in the adhesion process of such a microorganism to biomaterials. In this work, hydrophobicity, surface free energy and surface charge of Enterococcus faecalis ATCC29212 and E. faecalis 72 bacterial strains have been analysed under the followings conditions, which were considered as criteria that could affect the thermodynamical parameters of the cell surface: culture medium was supplemented with serum and urine and the experiments were carried out in two different buffers (KPi and PBS) and at two temperatures (22 and 37 °C). MATH hydrophobicity does not seem to be affected by temperature but water contact angle increased with temperature for both strains. Serum and urine added to the culture medium made the strains more and less hydrophobic, respectively. The zeta potential was dependent on the addition to the culture medium of serum and urine, the experimental temperature and the buffer employed and it decreased with increasing ionic strength in all cases studied. The results reveal that physico-chemical surface properties of bacteria are greatly affected by the environmental conditions in which they are measured, indicating that experiments should be carried out under experimental conditions as similar as possible to the situation of clinical interest.     

Studying surface charge and suspension stability of hydroxyapatite powder in isopropyl alcohol to prepare stable suspension for electrophoretic deposition

Abstract

Suspension stability of hydroxyapatite powder in isopropyl alcohol was investigated by measuring zeta potential. In this study, isopropyl alcohol was used as a suspension media, and nitric acid, polyvinyl butyral and polyethylenimine were the dispersing agents. Fine grain particles with mean particle size and surface area of 2·54 μm and 5·8 m² g^?1 respectively, were prepared. Stable suspensions were made by mixing 40 g L^?1 milled powders in isopropyl alcohol. The zeta potential of the suspensions was measured by using zeta sizer equipment. The results showed that by adding nitric acid and polyvinyl butyral to the system, negative charge was introduced, while polyethylenimine donated positive charge to the surface of particles and induced electrostatic and steric stabilisation. It was concluded that the suspension which was stabilised with 4 g L^?1 polyethylenimine revealed the highest zeta potential and stability which is suitable for cathodic electrophoretic deposition.     

Stress Generated on Aluminum During Anodization as a Function of Current Density and pH

Anodic oxidation is accompanied by stressgeneration during the growth of the oxide. The presentstudy focuses on the stress-generation mechanism onaluminum as a function of the applied current density in acidic solutions of sulfuric acid ofdifferent strengths giving variable pH. Abeam-deflection technique was utilized for thedetermination of the magnitude and direction of stressesgenerated during the anodic oxidation process. Generally,thickness of the oxide determines whether the stress iscompressive or tensile in nature. The results have beeninterpreted in terms of the formation and annihilation of anion (O^2-) and cation(Al³⁺) vacancies. A reduction in thealuminum-ion vacancy concentration (V Al ³ ) results in a compressive stressdeflection, whereas tensile-stress deflection isintroduced by an increase in the oxygen vacancy(Vo²⁺) concentration. The mechanism isfurther elucidated by current-density jump/dropexperiments. The results show that stress in this caseis affected by the dissolution of the oxide at the oxide-electrolyteinterface.     

Influence of environmental parameters on application of standard ASTM C876-91: half cell potential measurements

Abstract

Since the potential of corrosion of any metal in contact with concrete is a function of a large number of variables related to the composition of pore solution, degree of polarisation, temperature and cover depth, no quantitative (corrosion rate) conclusion can be drawn from it. Potentials do not provide relevant information on the amount of corrosion. The validity of these interpretations has been questioned in some situations such as saturated structures, or when carbonation is the cause of the corrosion or cathodic processes are modified. Half cell potential technique (ASTM C 876) is however a useful tool widely used for in situ assessment of the corrosion state of rebars. Some applications of the ASTM C 876 standard are presented and it has been shown that this standard cannot be used under all conditions. Finally, some recommendations are provided in an attempt to optimise the application of the ASTM C 876 standard.     

Investigation of computer hardware failure due to corrosion

Abstract

Failure analysis was conducted on two failed electronic cardsfrom the Computer Center of the Kuwait Institute for Scientific Research. The results of the elemental analysis indicated that the corrosion product film found on contact pins and soldered through holes was composed of copper and sulphur compounds. Chemical analysis of the air in the computer room indicated a high level of nitrogen oxide (up to 300 ppb), whereas other gases such as H²S and SO² were below the detectahle limits (100 and 200 ppb respectively) of the analytical technique used. It was concluded that the initial high relative humidity ( ～ 75%) had synergised with the strongly oxidising nitrogen oxide and H²S and/or SO² to bring about the corrosion of copper substrate in ‘bare spots’ or gaps in the soldered contacts, causing card failure. Other factors, such as galvanic coupling of the copper substrate with nickel, silver, and gold plates, and the relatively high local temperature, may have accelerated the corrosion process. A decrease in the relative humidity to the optimum value of 45% did not obviate card failure. It was concluded that efficient air filters should be utilised in the computer environment, as electronic equipment can be damaged by levels of pollutant gases 10 times lower than those cited for human safety requirements.     

Electrochemical rehabilitation methods for reinforced concrete structures: advantages and pitfalls

Abstract

There are still many unresolved issues concerning the efficiency of electrochemical realkalisation and electrochemical chloride removal as electrochemical rehabilitation methods for corroding reinforced concrete structures. The present paper seeks to answer a number of questions which, though seemingly elementary, continue to arouse controversy in scientific, technical and economic communities, despite the vast amount of work that has been devoted to research on corrosion in concrete embedded steel, such as whether corrosion can be stopped once it has started, whether corroded reinforced concrete structures can be repassivated, and whether it is sufficient to remove the sources of corrosion in order to stop rusting. A discussion is conducted on the relationship between the prerusting grade of rebars and the possibility of their repassivation; on whether electrochemical rehabilitation methods treatments are efficient, and if so, when and on whether a simple potential measurement can determine the passive or active state of a rebar. For this purpose an analysis is made, using electrochemical, gravimetric and metallographic techniques, of the response of clean and previously corroded steel electrodes in a Ca(OH)₂ saturated solution with and without a sodium nitrite corrosion inhibitor and in cement mortar. The effectiveness of electrochemical realkalisation and electrochemical chloride removal for repassivating prerusted steel in concrete is found to depend heavily on the prerusting grade.