Photo‐oxidation of cyanide in aqueous solution by the UV/H2O2 process

Photo‐oxidation of cyanide was studied in aqueous solution using a low‐pressure ultra‐violet (UV) lamp along with H₂O₂ as an oxidant. It was observed that by UV alone, cyanide degradation was slow but when H₂O₂ was used with UV, the degradation rate became faster and complete degradation occurred in 40 min. The rate of degradation increased as the lamp wattage was increased. It was also observed that cyanide oxidation is dependent on initial H₂O₂ concentration and the optimum dose of H₂O₂ was found to be 35.3 mmol dm^?3. Photo‐oxidation reactions were carried out at alkaline pH values (10–11) as at acidic pH values, cyanide ions form highly toxic HCN gas which is volatile and difficult to oxidise. By the UV/H₂O₂ process, using a 25 W low‐pressure UV lamp and at alkaline pH of 10.5 with an H₂O₂ dose of 35.3 mmol dm^?3, cyanide (100 mg dm^?3) was completely degraded in 40 min when air was bubbled through the reactor, but when pure oxygen was bubbled the time reduced to 25 min. The cyanide degradation reaction pathway has been established. It was found that cyanide was first oxidised to cyanate and later the cyanate was oxidised to carbon dioxide and nitrogen. The kinetics of cyanide oxidation were found to be pseudo‐first order and the rate constant estimated to be 9.9 × 10^?2min^?1 at 40 °C. The power required for complete degradation of 1 kg of cyanide was found to be 167 kWh (kilowatt hour). Copyright © 2004 Society of Chemical Industry     

Dry sliding friction and wear in plain carbon dual phase steel

In view of the potential of plain carbon dual phase (DP) steel as wear resistant material, the wear and friction characteristics of this steel, which consists of hard martensite islands embedded in a ductile ferrite matrix, have been investigated and compared with those observed in plain carbon normalized (N) steel that has the same composition of 0.14 wt pct carbon. Dry sliding wear tests have been carried out using a pin-on-disk wear testing machine at normal loads of 14.7, 24.5, and 34.3 N and at a constant sliding velocity of 1.15 m/s. Weight loss in the samples has been measured over time on the same specimen, and the variation of cumulative wear loss with sliding distance has been described by two linear segments, for both the DP and the N steel. At these loads, the mechanism of wear is primarily oxidative, although subsurface cracking and delamination wear could also be observed in a few places. The second linear segment could result from a dynamic steady state wear of the transfer layer of compacted oxide wear debris on the sliding surfaces. The wear rate calculated on the basis of the first linear segment varies linearly with normal load, which is indicative of Archard’s law, and it is significantly lower for the DP steel than for the N steel. The wear rate calculated on the basis of the second linear segment, however, varies with load linearly for the DP steel but nonlinearly in the N steel. In the first linear segment, the wear coefficient is about 0.39 × 10⁻⁴ for the DP steel and is 0.40 × 10⁻⁴ for the N steel. Higher hardness and, consequently, a lower real area of contact in the DP steel at all the loads have compensated for the lower wear rates, and have resulted in a wear coefficient similar to that in the N steel. The steady state wear coefficient from the second linear segment is 0.29 × 10⁻⁴ for the DP steel at all loads; for the N steel, these are 0.21 × 10⁻⁴ and 0.64 × 10⁻⁴, respectively, for lower and higher loads.     

Comparative study of dewatering characteristics of metal precipitates generated during treatment of monometallic solutions

The sludge dewatering properties (settling, filtration and centrifugation) of metal precipitates generated during treatment of monometallic solutions (0.020 mol/L) have been evaluated in this research. The precipitation tests carried out on 15 different metals gave metal removal yields generally similar to those predicted by MINEQL+ software, with the exception that kinetic aspects should be considered during precipitation of metal sulphides and phosphates. Hydroxides precipitation at pH 10.0 was the most efficient technique for the removal of eight metallic ions (Al³⁺, Cd²⁺, Co²⁺, Fe²⁺, Fe³⁺, Mg²⁺, Mn²⁺, Ni²⁺), whereas phosphates precipitation (at pH 6.0 with an addition of 0.0133 mol PO₄^3?/L) gave highest removal yields for Ba²⁺, Ca²⁺, Cr³⁺. Sulphides precipitation (at pH 7.0 and using, 0.020 mol S^2?/L) has been found the most efficient technique only for Cu²⁺ and Sn²⁺ precipitation, whereas carbonates precipitation (at pH 8.0 and using 0.020 mol CO₃^2?/L) gave better removal yield only for Pb²⁺. Results have also shown that metal phosphates have generally better dewatering characteristics (SVI, filtration capacity, SRF, sludge solids content) than metal carbonates, sulphides and hydroxides. In fact, considering only the sludge dewatering characteristics, phosphates precipitation appears the most appropriate technique for the precipitation of many metals (Al³⁺, Ba²⁺, Cd²⁺, Co²⁺, Cr³⁺, Fe²⁺, Fe³⁺, Ni²⁺ and Zn²⁺). Metal hydroxides formation constitutes the best option for Ca²⁺, Cu²⁺, Mg²⁺ and Sn²⁺ removal, whereas precipitation of metal carbonates is particularly interesting for treatment of Mn²⁺ and Pb²⁺ containing solutions.     

Effect of Flash Temperature on Tribological Properties of Bulk Metallic Glasses

The tribological properties of Cu-based and Zr-based bulk metallic glasses (BMGs) sliding against Si₃N₄ under dry and water lubrication were studied on a pin-on-disc tribometer. The wear mechanisms of bulk metallic glasses were investigated based on the calculated flash temperature. The friction coefficients if fully amorphous alloy are about 0.7, while those of BMGs with nanocrytalline are a little higher. The wear rates of Cu-based BMG (V101) are about one order of magnitude lower than those of Zr-based BMG (Vit1) under dry friction, even two orders of magnitude lower under water lubrication. The wear resistance of bulk metallic glasses was influenced by the flash temperature. The calculated flash temperature (3,337 K) on the friction surface of Zr-based amorphous alloy exceeds its glass transition temperature, even its melting temperature. The high flash temperature leads to glass transition accompanied with viscous flow and material transfer, which is responsible for the poor wear resistance of Zr-based BMGs.     

Magnetically tunable microstrip resonator based on polycrystallineferrite

A conventional microstrip ring resonator consisting of a polycrystalline ferrite substrate is demonstrated. This resonator produces improved tunability compared with other available versions. Resonators with tunability approaching 31% at a minimum insertion loss of 11.17 dB in a magnetic field of 3 kG applied longitudinally along wave propagation have been demonstrated using LiZiTi ferrite composition. Tunability of 31% is the best reported for any tunable structure     

Thermal cycle testing of calcium chloride hexahydrate as a possible PCM for latent heat storage

In order to study the changes in latent heat of fusion and melting temperature of calcium chloride hexahydrate (CaCl₂·6H₂O) inorganic salt as a latent heat storage material, a thousand accelerated thermal cycle tests have been conducted. The effect of thermal cycling and the reliability in terms of the changing of the melting temperature using a differential scanning calorimeter (DSC) is determined. It has been noticed that the CaCl₂·6H₂O melts between a stable range of temperature and has shown small variations in the latent heat of fusion during the thermal cycling process. Thus, it can be a promising phase change material (PCM) for heating and cooling applications for various building/storage systems.     

Natural and synthetic hormone removal using the horseradish peroxidase enzyme: temperature and pH effects

The primary objective of our research was to establish the technical feasibility of using the horseradish peroxidase (HRP) enzyme for natural and synthetic estrogens-estrone (E1), 17beta-estradiol (E2), estriol (E3), and 17alpha-ethinylestradiol (EE2)-removal. The effects of temperature and pH on enzymatic treatment kinetics were investigated. Residual estrogen concentrations were quantified by liquid chromatography, coupled with mass spectrometry analysis. In a synthetic solution at pH 7 and 25+/-1 degrees C, the HRP enzyme-catalyzed process was capable of achieving 92-100% removal of E1, E2, E3, and EE2 within 1h of treatment with an HRP activity of 0.017 U/ml. The influence of the pH (5-9) and temperature (5-35 degrees C) on estrogen removal was observed to be significant, with the optimum pH near neutral conditions. The results also showed that wastewater constituents significantly impact the HRP-catalyzed estrogen removal. The experimental research proved that the HRP-catalyzed system is technically feasible for the removal of the main estrogens present in the environment at low concentrations.     

Anti wear and anti friction characteristics of tribochemical films of alkyl octa‐decenoates and their derivatives

The wear, friction and film forming characteristic of ethyl octadecenoate and methyl 12‐hydroxy ocatadecenoates, their thio and thiopyrophosphoro derivatives have been studied on HFRR friction and wear machine. The structural characteristics of chemisorbed films formed on the iron surfaces by these derivatives have been investigated using various analytical techniques such FT‐IR, Microreflectance Absorption and Proton Magnetic Resonance. It has been inferred that these films are primarily organic in nature. The constituents of these films are hydroxy alkyl and aryl ethers, unsaturated and condensed ring hydroxy ketones, aromatic hydroxy quinones and highly condensed aromatic structures chemically linked to iron sufaces through hydroxy, oxy, thia, oxyphosphoro and thiophosphoro moieties forming chelated and coordinated complexes. The antiwear and antifriction characteristic of alkyl octadecenoates increase with increasing polar linkages in the alkyl ocatadecenoate backbone. This is primarily due to the increase in number of sites amenable to chemisorption on the surfaces and consequently their reactivity. The antiwear and antifriction characteristic of derivatives of ethyl octadecenoates are inferior to the corresponding 12‐hydroxy methyl octadecenoates derivatives. This can be attributed to increased reactivity of 12‐hydroxy methyl octadecenoates derivatives at the surfaces due to an additional hydroxyl moiety. The films formed are highly condensed ring aromatic layered structures coordinating to iron atoms of the surface particularly in case of thiopyrophosphoro derivatives of methyl 12‐hydroxy octadecenoates. These films, as a consequence, provide lower wear and friction characteristics as compared to other types of organic films. These studies have led to much clear evidence of the intimate relationship between the chemical structure of the additives and their film forming characteristics. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis of nanocrystalline mixed metal fluorides in nonaqueous medium

Synthesis of mixed metal fluorides of the general formula, KMF₃ (M = Mg, Mn, Co, Ni, Cu and Zn), possessing perovskite structure was investigated in non-aqueous medium. The fluorides were characterized by powder X-ray diffraction, FT-IR spectroscopy, thermal analysis, SEM and TEM. Monophasic cubic phases were obtained for the central metal ions such as Mg, Mn, Co, Ni, and Zn and a tetragonally distorted phase was observed for Cu. The usage of non-aqueous medium is advantageous for the bulk synthesis of these fluorides, since it eliminated the generation and handling of the hazardous HF that has usually been encountered during aqueous preparations. The average crystallite size of the fluorides obtained by this approach was estimated to be in the range of 9–30 nm. SEM micrographs of KZnF₃ showed cubic morphology of perovskite phases. TEM studies on KCuF₃ confirmed the presence of tetragonal distortion. The fluoride content was determined by titrimetry and found to be nearly stoichiometric. Some of these fluorides were found to be thermally stable up to 225°C in air. These fluorides were employed as fluorinating agents in organic fluorination reactions, thereby suggesting their possible utilization for selective fluorination of aliphatic and aromatic hydrofluorocarbons (HFCs) that are industrially relevant.     

Keyhole depth instability in case of CW CO<Subscript>2</Subscript> laser beam welding of mild steel

The study of keyhole (KH) instability in deep penetration laser beam welding (LBW) is essential to understand welding process and appearance of weld seam defects. The main cause of keyhole collapse is the instability in KH dynamics during the LBW process. This is mainly due to the surface tension forces associated with the KH collapse and the stabilizing action of vapour pressure. A deep penetration high power CW CO₂ laser was used to generate KH in mild steel (MS) in two different welding conditions i.e. ambient atmospheric welding (AAW) and under water welding (UWW). KH, formed in case of under water welding, was deeper and narrower than keyhole formed in ambient and atmospheric condition. The number and dimensions of irregular humps increased in case of ambient and under water condition due to larger and rapid keyhole collapse also studied. The thermocapillary convection is considered to explain KH instability, which in turn gives rise to irregular humps.