Inhibition of atmospheric corrosion of mild steel by sodium benzoate treatment

The objective of this study was to evaluate the effectiveness of sodium benzoate as an inhibitor to slow down or prevent atmospheric corrosion/discoloration of the local mild steel during storage in the Arabian Gulf region. Test specimens were prepared from locally produced reinforcing steel products. The inhibitor solution was applied on steel specimens at a concentration of 100 mM for 1 day at room temperature. Wooden exposure racks were used to hold as-received and inhibitor-treated specimens during atmospheric exposure for different periods. Corrosion was evaluated through weight loss determination and electrochemical technique. As expected, the Arabian Gulf atmosphere was corrosive on the as-received local mild steel. On the other hand, treatment of steel with sodium benzoate lowered its corrosion rate during initial days of its exposure to atmosphere. However, atmospheric corrosion inhibition performance of sodium benzoate deteriorated with exposure time after 30 or more days of atmospheric exposure, and the corrosion rates of sodium benzoate-treated specimens reached that of the unprotected specimens at the end of 90 days of atmospheric exposure.     

HiSQL: A Front-end Query System for Historical Relational Databases

The paper describes a prototype system called HiSQL (Historical SQL) which extends the functionality of SQL in manipulating historical data, by providing functions for spatial and temporal processing. Conceptually the paper is divided into three parts: the first part deals with the design and architecture of the system; the second part introduces a case study (the defters); and the third part describes specific functions for spatial and temporal processing of serial documents. The paper concludes with a comparison between HiSQL and SQL and suggestions for further work. This revised version was published online in August 2006 with corrections to the Cover Date.     

Exact solution of elasto-plastic stresses in a metal-matrix composite beam of arbitrary orientation subjected to transverse loads

An analytical elasto-plastic stress analysis is presented for a metal-matrix composite beam of arbitrary orientation subjected to a single transverse force applied to the free end of the beam and a uniformly distributed load. The material is assumed to be perfectly plastic in the elasto-plastic solution. A composite consisting of stainless-steel-reinforced aluminum was produced for this work. Sample problems are given for various orientation angles. Elastic, elastoplastic and residual normal and shear stresses are calculated. The location of the elasto-plastic boundary of the beam is obtained according to the x coordinates of the beam.     

Wear Mechanisms of Glass-Infiltrated Alumina Sliding Against Alumina in Water

Glass-infiltrated alumina is now commonly used as a core material in dental restorations. If the veneer layer, which covers the core, is broken or damaged through use, a direct contact between the core and the opposing restorative material or human enamel can occur. The wear behavior in simulated contacts with human enamel has already been studied. In the present work, we have investigated the wear mechanisms of glass-infiltrated alumina in contact with a high-purity alumina as an opposing ceramic restoration. Wear tests were performed in a pin-on-disk tribometer under conditions that roughly resemble those in the oral environment. The wear rates of the alumina balls and the glass-infiltrated disks sliding in water increased linearly with load. No wear transition (i.e., a sudden increase in wear) was observed as either the load or the sliding distance was increased. Examination of the wear debris in the SEM suggested the presence of wear particles that are often attributed to the formation of hydrated aluminum oxide through tribochemical reactions between water and alumina. While tribochemical wear was the dominating wear mechanism for the alumina balls, microfracture and delamination governed the wear behavior of the glass-infiltrated alumina disks. Examination of the surface layers formed on the disk wear tracks confirmed the presence of amorphous hydrated alumina on the wear track. It is suggested that these reaction products smear on the wear track filling the pores produced by microfracture and delamination. The high wear resistance of glass-infiltrated alumina is attributed to the presence of hydrated alumina in the third body layer that accommodates the interfacial shear stresses and the high strength due to strong bonding between the glass phase and alumina grains. Based on the observed wear resistance of glass-infiltrated alumina in the present study, this material should be evaluated for applications in addition to dental restorations.     

Maximization of total surface area of Pt-SnO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst by the Taguchi method

The maximization of the total surface area of Pt-SnO₂/Al₂O₃ catalyst was studied by using the Taguchi method of experimental design. The catalysts were prepared by sol-gel method. The effects of HNO₃, H₂O and aluminum nitrate concentrations and the stirring rate on the total surface area were studied at three levels of each. L₉ orthogonal array leading nine experiments was used in the experimental design. The parameter levels that give maximum total surface area were determined and experimentally verified. In the range of conditions studied it was found that, medium levels of HNO₃ and H₂O concentration and lower levels of aluminum nitrate concentration and stirring rate maximize the total surface area.     

Formation of Helium Porosity in Different Materials during Post-Radiation Annealing

The characterisitics of the development of helium porosity in bcc and fcc alloys and structural steel after irradiation with 40-keV He⁺ up to dose 5⋅10²⁰ m⁻² at 20°C and subsequent annealing at 650°C for 1 h and 5 h are studied by transmission electron microscopy. It it found that under these conditions smaller bubbles with high density are formed in bcc than in fcc materials. It is shown that for an annealing time of 5 h higher porosity is formed in all materials, except nickel, than with 1 h annealing. This is due to the inflow of thermal vacancies from the free surface. The data obtained are discussed from the standpoint of the formation of various helium-containing complexes, their thermal stability, and the diffusion mobility of the matrix atoms. __________ Translated from Atomnaya Energiya, Vol. 99, No. 2, pp. 115–120, August 2005.     

Experiments on the transition from the steady to the oscillatory marangoni convection of a floating-zone under various cold wall temperatures and various ambient air temperature effects

The transition from the steady to the oscillatory Marangoni convection of a floating-zone under various cold wall temperatures and various ambient air temperature effects have been investigated experimentally by heating the sample from above (opposite direction of Marangoni convection and buoyant forces). The heat transfer takes place mainly through conduction as well as the natural convection of the air around the cylindrical liquid bridge. The ambient airflow in the present work is varied by varying the cold wall temperature and ambient air temperature. In this study, the transition from the steady to the oscillatory Marangoni convection flow of a high Prandtl number fluid in a floating half-zone is visualized by means of the already proven method of the “light-cut-technique”. The test fluid zone is held in ambient air at +4 °C, +10 °C, +16 °C, +23 °C, and +28 °C. The onset of oscillations, the oscillation level, and oscillation pattern are investigated under various conditions. It is found that the critical temperature difference (ΔT_Cr) varies substantially when the cold wall temperature and the ambient air temperature are varied.     

The tribological performance of DLC coatings under oil-lubricated fretting conditions

Whether or not the process of fretting occurs is to a large extent dependent on the coefficient of friction, because the coefficient of friction directly affects the amount of shear stress. As a result, the key factor when it comes to reducing the amount of fretting damage is to reduce the coefficient of friction. Various surface coatings, and especially hard, diamond-like carbon (DLC) coatings, are known to be able to produce surfaces with a low level of friction. Despite some such attempts in the past, which did not result in major improvements, the developments and improvements in DLC coatings in recent years suggest the need for a re-evaluation of these coatings for fretting applications. Another way to reduce the amount of friction in mechanical components is to apply lubricants, and recent studies on the lubrication of DLC coatings suggest that this combination could be very successful in preventing failures under boundary-lubrication conditions. Therefore, in this work we present the results of friction and wear measurements from three types of fretting contacts: steel/steel, steel/DLC and DLC/DLC. Boundary oil-lubrication conditions were investigated and a wide range of displacement amplitudes, i.e., from 25 to 500 μm, were selected to assess the fretting and sliding behaviours. The results show a significant difference between the fretting and sliding regimes. In the fretting regime, the DLC-containing contacts, and especially the self-mated DLC/DLC contacts, performed much better than the steel/steel contacts, and significantly reduced both the wear (a 3–10 times reduction with steel/DLC and DLC/DLC) and the friction (a more-than-two-times reduction with DLC/DLC). In the sliding regime, the lubrication effects governed the tribological performance, making the results for all three material combinations very similar.