Ozonation of textile effluents and dye solutions under continuous operation: Influence of operating parameters

Ozonation experiments were carried out under continuous operation in a bubble column. The effect of several parameters (inlet dye concentration, applied ozone dose, pH and conductivity) in colour and TOC removal of an acid dye solution was investigated with the aim to optimize the operation conditions. The ozone consumption was measured in each experiment. Ozonation was found to be effective for decolourisation of an acid dye; however, it only has a slight effect on TOC removal. Increasing the inlet dye concentration leads to a decrease in the decolourisation efficiency and an increase in the ozone consumption. The decolourisation increases with the applied ozone dose. Colour removal efficiencies for different ozone doses were between 76 and 100%. In the pH range 5-9, the decolourisation efficiency decreases with pH only when buffered solutions were used. The presence of salt decreases the decolourisation efficiency. Several dyes of different classes were also studied and ozonation was found to be effective for decolourisation but considerably less efficient for TOC removal. Under the conditions tested, only the disperse and sulphur dyes presented a colour removal lower than 86%. Practical application of this process was validated by treating two industrial textile effluents collected after two different biological treatments.     

Impurity effects in carbon fibres

Outgassing experiments have been performed on a variety of polyacrylonitrile- and rayon-based carbon yarns. Major residual impurities, as well as those introduced from surface treatments, have been identified. Sulphur has been shown to be a major impurity of rayon-based carbon fibres, with concentrations up to 3110 ppm by weight having been determined by neutron-activation analyses. Removal of this contaminant as a volatile material commences at approximately 1300° C. Interrelationships between sulphur removal and mechanical and crystallographic properties have been considered for one rayon-based carbon yarn. Decreases in both interlayer spacing and tensile strength are associated with sulphur evolution, whereas apparent crystallite size and Young's modulus are unaffected by the outgassing.     

Photoelectrochemistry of Culn11S17

Polycrystalline samples of Culn₁₁S₁₇ have been prepared by the homogeneous precipitation technique. The electron probe microanalyses (EPMA) have shown the presence of excess sulphur with as-precipitated samples, which has been considerably reduced by subsequent annealing. From the reflectance measurements, the band gap has been determined to be 1.45eV. The photoelectrochemical behaviour of n-Culn₁₁S₁₇ has been studied in different redox electrolytes, namely, polysulphide, polyiodide, and ferro/ferricyanide, and the best photoresponse was observed with the polysulphide redox system. Photoetching in a poly-sulphide electrolyte at a strong anodic bias highly improves the photoresponse of this material. It has also been shown that our n-Culn₁₁S₁₇ photoanode in electrochemical photovoltaic cell has a good stability at working conditions in a polysulphide solution. Finally, the future perspectives of the material have been briefly discussed.     

Hot corrosion cracking of Nimonic 80A

Experimental investigations have been carried out to study the hot corrosion crack growth behaviour ofN imonic BOA in a combustion gas containing sulphur, vanadium or sodium at 600 and 700°C. The time to rupture has been found to be inversely proportional to the applied stress, and the crack growth rate, da/dt, can be described by the LEFMparameter K, the stress intensity factor. The threshold stress intensity factor, K_th , and the critical stress intensity factor, K_c, have been found to be functions oftemperature and corrodent level. In the case ofsulphur, K_th decreases continuously with increasing sulphur content in the fuel. In the case of vanadium or sodium, there appears to be a critical level ofcorrodent for the worst attack.     

Mechanism for CdS electrodeposition from fused salt

Electrodeposition of CdS on a graphite substrate from LiCl-KCl eutectic melt containing CdCl₂ and Na₂SO₃ has been examined. It has been found that the cathodic deposition of CdS onto a graphite substrate occurs in competition with the formation of CdS particles by homogeneous precipitation in the bath. We have proposed as a deposition mechanism that the underpotential deposition of cadmium occurs under the influence of some sulphur species. We have also found that crystals of solid solution of CdS-CdSe are electrodeposited by adding selenium powder in the bath.     

Kinetic behaviour and reactivity of zinc ferrites for hot gas desulphurization

Different zinc ferrite samples have been prepared with varying Fe:Zn atomic ratios and preparation procedures in order to optimize their behaviour as hot gas desulphurization agents. Kinetic studies on metal oxide sulphidation were performed in a thermobalance and sulphur removal tests were conducted in a fixed-bed reactor. Fresh and exhausted samples were characterized by several physical techniques. The results show that reaction rate is mainly controlled by mass transfer processes of the reactant through the gas film in contact with the solid and through the sulphide layer. Bulk ferrites displayed the best performance for sulphur removal. Ferrites deposited on an alumina substrate by impregnation are highly dispersed, however they exhibited a very poor efficiency for sulphur removal. Solid-state reactions of single oxides at the alumina interface, i.e. zinc and/or iron aluminate formation, instead of pore occlusion by the active ingredient seem to be responsible for a low reactivity.     

Relative importance of transformation temperatures and sulphur content on hot ductility of steels

Abstract

Low (0·3%) and high manganese (1·4%) plain C – Mn steels with varying sulphur levels have had their hot ductility determined over the temperature range 700 – 1000°C, both after 'solution treatment' at 1330°C and directly after casting. It has been established that the width, depth and position of the hot ductility curves after solution treatment is more related to the transformation behaviour than either the sulphur in solution or the sulphide volume fraction or distribution. The growth of deformation induced ferrite at the austenite boundaries seems to be mainly diffusion controlled, and the higher is the transformation temperature for the γ – α phase change, the faster is the growth. Large amounts of ferrite can then form, giving good ductility. Thus, high transformation temperatures Ae ₃ or Ar ₃ are required to produce narrow ductility troughs. It is believed that any detrimental influence of the sulphides on these 'solution treated' steels is swamped by the rapid increase in ferrite volume fraction. For the as cast state, as more sulphides are able to precipitate at the interdendritic boundaries and austenite grain boundaries than in the solution treated condition, increasing the sulphur level causes a small deterioration in ductility at the high temperature end of the trough. In the present work, only narrow troughs have been found. This is in contrast to previous work on as cast C – Mn – Nb – Al steels, which exhibited wide troughs in the ductility curves, where it was shown that higher total sulphur levels lead to considerably worse ductility and that sulphur can be as detrimental to the ductility as niobium. It is recommended that, to avoid transverse cracking during continuous casting, in addition to keeping the sulphur level low, the carbon and manganese should also be as low as possible.     

TEM study of nanopores and the embrittlement of CVD nickel foam

Abstract

Ni foam, manufactured by depositing Ni onto polyurethane foam using the carbonyl CVD process, exhibits brittleness which has been correlated with the presence of a high number-density of 'nanopores'. These nanopores, which were typically less than ~25 nm in diameter, tended to be associated with sulphur, which is present in the form of H₂S as a catalyst during the deposition process. The as deposited foam also shows significant hardening, ascribed to the high density of nanopores. This hardening may also help to reduce the ductility compared to well annealed nickel foam. High temperature annealing restores the foam to the high ductility typical of high purity nickel by coarsening the nanopores and removing the sulphur. The failure of the pores to sinter during high temperature annealing indicates the presence of stable gas molecules, the pressure from which balances the surface tension forces that drive sintering.     

Preparation and crystal growth of NiS(h)

A procedure is described for the preparation of 90 g batches of NiS. Molten NiS has been shown to exert a pressure of about 9 atm of sulphur and to be compatible with liquid B₂O₃. Near single crystals of NiS(h) have been grown by the high pressure liquid encapsulated Czochralski technique. Evidence suggests that the as-grown crystals exhibit variable stoichiometry and an annealing procedure which gives apparently homogeneous samples is described.     

Defect characterization of spray pyrolised β -In<Subscript>2</Subscript>S<Subscript>3</Subscript> thin film using Thermally Stimulated Current measurements

Thermally Stimulated Conductivity (TSC) has been used to analyse defects in the novel material -In₂S₃. These films were deposited using spray pyrolysis technique, varying In:S concentration ratio in the spraying solution. TSC measurements allowed the study of electrical property and non-radiative transitions, due to the defects present in the material. TSC spectra revealed four defects with their prominence varying with In:S concentration ratio. Samples with lower In concentration showed the presence and prominence of indium vacancy. A chemical impurity level due to the presence of chlorine was also detected. Even though sulphur vacancy existed in all the samples irrespective of the variation of In:S concentration ratio its effect decreased with the increase of sulphur concentration. Another defect level was also detected from TSC measurements at high temperature that was attributed to the replacement of sulphur by oxygen which was maximum in films prepared from a spray solution of In:S = 2:3 and minimum for 2:8. This high temperature defect level acts as a neutral center while all the other three levels were seen to be coulomb repulsive. Results from XPS analysis are found to be in good agreement with the TSC results.     

Electrical conductivity,crystallinity and glass transition in vulcanised rubber

Temperature variation of electrical conductivity has been measured for rubber vulcanised with different concentrations of sulphur. Change of amorphous character with sulphur concentration has also been measured from the amorphous halo of the Debye-Scherrer x-ray photographs of the samples. The conductivity of vulcanised rubber in glassy state shows a slow and gradual increase; but during glass transition it increases suddenly to a high value which again exhibits gradual increase in high elastic state. X-ray studies show that with increase of sulphur, the amorphous region decreases due to formation of cross-links by the chain units. The decrease of conductivity with increase of sulphur is then due to decrease of amorphous region. The fast decrease of conductivity with sulphur at low concentration in the high elastic state indicates high rate of formation of cross-links at such concentration.     

Starch‐capped sulphur nanoparticles synthesised from bulk powder sulphur and their anti‐phytopathogenic activity against Clavibacter sepedonicus

Water‐soluble, stable nanoparticles of elemental sulphur with a size of 9‐52 nm have been synthesised using the stabilising potential of starch. Sulphide anions were used as sulphur precursors that were generated earlier from the bulk powder sulphur in the base‐reduction system NaOH‐N₂H₄·H₂O followed by their oxidation with molecular oxygen to element sulphur atoms. Using a set of modern spectral and microscopic methods (XRD, optical spectroscopy, DLS, TEM), the phase state, elemental composition of the nanocomposites and their nanomorphological characteristics have been investigated. It was found that nanocomposites are formed as sulphur particles with the shape which is nearly spherical dispersed in the polysaccharide starch matrix with a pronounced tendency to cluster into ring formations. Water solubility and stability of the obtained nanoparticles is ensured by sorption of starch macromolecules on the surface of sulphur nanoparticles, with the thickness of the stabilising shell in a range of 10‐171 nm. In vitro experiments were carried out to study the anti‐microbial activity of the obtained sulphur nanocomposite (1.6% S) using the propidium iodide fluorescent dye staining method and the diffusion method. It showed that the water solution of the starch‐capped sulphur nanoparticles at the concentration of 6.25 µg/ml had a pronounced anti‐phytopathogenic activity against the potato ring rot pathogen Clavibacter michiganensis subsp. sepedonicus.     

2.15 The stoichiometry of surfaces in cadmium sulphide thin films

The sulphur to cadmium ratio in cadmium sulphide thin films has been compared to that of a clean single crystal using Auger spectroscopy. Thermally evaporated CdS films were found to be deficient in sulphur in their outer layers, but were stoichiometric after etching. Electron beam evaporated CdS films were found to be stoichiometric.It was found that baking these films at 190°C in argon or nitrogen at atmospheric pressure increased the sulphur to cadmium ratio, probably due to sulphur diffusing to the surface and being physisorbed there.From measurements of the temperature dependence of the copper sulphide layer in CdSCu₂S cells it was found that chalcocite, djurleite and diginite copper sulphide phases are present even in efficient cells. A model is proposed for the structure of the copper sulphide layer in which the copper deficient phases are the result of excess sulphur on the CdS surfaces and vary in thickness according to the degree of non-stoichiometry of the CdS surfaces.     

Cost-Minimization Model for Reducing Sulphur Dioxide Emission from Coal-Fired Generating Stations

To limit emission of sulphur dioxide, an electrical utility has several available options: (i) Burn low-sulphur coal, (ii) remove SO₂ from flue gases after combustion (Flue Gas Desulphurization or FGD), and (iii) remove sulphur from coal before combustion (Physical Coal Cleaning or PCC). Options (ii) and (iii) vary in their cleaning capabilities and scale economies. Pre-cleaning of coal followed by post-cleaning of flue gases may thus be less costly than either PCC or FGD alone to obtain a given level of sulphur removal. A mathematical programming model to determine the best combination of options is developed from empirical cost data and solved for typical conditions encountered by North American utilities. Sensitivity analyses are carried out with respect to the various operating and capital costs, as well as the maximum SO. emission level. The latter enables assessment by the regulatory authorities of proposed environmental standards. Finally, we show how the model can aid a utility in directing its R&D effort by estimating the target sulphur removal capability which should be sought for each control technique and the cost saving (ROI from R&D) if successful.     

Properties and characterization of low-temperature amorphous PECVD silicon nitride films for solar cell passivation

Deposition conditions and some structural and electrical properties of amorphous silicon nitride (Si_xN_y:H) films deposited on Si substrates have been studied for photovoltaic applications. A plasma enhanced chemical vapor deposition (PECVD) system has been used for the study. Experiments have been performed varying the flow ratios and dilution of the reactant gases. Increased hydrogen (H₂) dilution leads to reduced deposition rate and a better controllability in the growth process. The hydrogen content in the film also decreases with increasing H₂ dilution of the reactant gases. Flow ratio of the reactant gases (SiH₄/NH₃) also influences the growth rate. There is an optimal reactant gas mix to maximize the film growth rate. However, the film stoichiometry is also modified by changing the gas mix, with higher flow ratios resulting in Si-rich films. The level of interfacial recombination of minority carriers has been studied by capacitance-voltage and effective lifetime measurements. Bombardment by the energetic species in the plasma leads to plasma damage at the interface. These interfacial defects can be annealed by a post-deposition, low temperature treatment.     

Chemical/mechanical polishing of diamond films assisted by molten mixture of LiNO3 and KNO3

Chemical/mechanical polishing can be used to polish the rough surface of diamond films prepared by chemical vapor deposition (CVD). In this paper, a mixture of oxidizing agents (LiNO₃ + KNO₃) has been introduced to improve the material removal rate and the surface roughness in chemical/mechanical polishing because of its lower melting point. It had been shown that by using this mixture the surface roughness R_a (arithmetic average roughness) could be reduced from 8-17 to 0.4 μm in 3 h of polishing, and the material removal rate can reach 1.7-2.3 mg/cm²/h at the temperature of 623 K. Pure aluminium is compared with cast iron as the contact disk material in the polishing. Although the material removal rate of aluminiumdisk is lower than that of cast iron, it can eliminate the carbon contamination from the contact disk to the surface of diamond films, and facilitate the analysis of the status of diamond in the chemical/mechanical polishing. The surface character and material removal rate of diamond films under different polishing pressure and rotating speed have also been studied. Graphite and amorphous carbon were detected on the surface of polished diamond films by Raman spectroscopy. It has been found that the oxidization and graphitization combined with mechanical cracking account for the high material removal rate in chemical/mechanical polishing of diamond films.     

Carbon and sulphur on Pd(111) and Pt(111): Experimental problems during cleaning of the substrates and impact of sulphur on the redox properties of CeOx in the CeOx/Pd(111) system

The X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and CO titration has been used to detect common impurities like carbon and sulphur on Pd(111) and Pt(111) surfaces. Different experimental problems are discussed and practical tips for the cleaning of Pd(111) and Pt(111) are given. A mechanism for the carbon oxidation on closed packed platinum group metals like Pt(111) and Pd(111) is presented. The bulk carbon concentration of Pd(111) was estimated based on the Langmuir-McLean theorem. Additionally it was shown that the titration with CO and subsequent XPS measurement is a powerful yet convenient method for quantitative detection of impurities and ceria coverage determination. A CeO_x/Pd(111) inverse model system was prepared by evaporation of cerium in an oxygen atmosphere. The comparative study has shown that sulphur contamination changes the redox properties of the CeO_x in the CeO_x/Pd(111) system.     

Influence of calcium on hot ductility of steels

Abstract

The hot ductility of C–Mn–Al and C–Mn–Nb–Al steels with and without calcium additions have been examined over the temperature range 700–1000°C both after solution treating at 1330°C followed by cooling to the test temperature and directly after casting. Calcium additions invariably improved hot ductility. For hot rolled plate reheated to 1330°C and cooled to the test temperature, calcium is beneficial to hot ductility because it reduces the amount of sulphur able to redissolve and precipitate in a fine form at the new γ-grain boundaries produced on solution treating. For the C–Mn–Al steels, strain concentration occurred in the thin films of softer ferrite surrounding the γ-grains causing voiding around the sulphide inclusions that link up to cause intergranular failure. The removal of the sulphides by calcium addition therefore accounts for the improvement in hot ductility. Similar behaviour was observed for the C–Mn–Nb–Al steels, but for temperatures above the Ae₃ temperature calcium containing steels continued to give improved hot ductility over calcium free steels and this is believed to be due to the fewer sulphides present at the boundaries allowing an earlier onset of dynamic recrystallisation. For steels subjected to direct casting, interdendritic failure as well as intergranular failure by microvoid coalescence occurs. Calcium additions reduce the total amount of sulphur in the steel so that the volume fraction of sulphides precipitated at the interdendritic and γ-boundaries is low.

MST/962     

Electric-field-controlled memory effect in heterostructures for gas sensors

A capacitive gas sensor has been created on the basis of an n-SnO₂/SiO₂/p-Si heterostructure with two successive oxide layers. The presence of polar C₂H₅OH, NH₃, and H₂O gas molecules in air leads to a significant increase in the capacitance of the structure at room temperature. An important feature of the adsorption process is a memory effect, which is confined to the possibility of maintaining the capacitance value after removal of the active component from the gas mixture. The possibility of quenching the accumulated useful signal by electric-field pulses has been realized for the first time as applied to gas sensors. Pis’ma Zh. Tekh. Fiz. 25, 22–29 (June 26, 1999)     

A structural and compositional analysis of interfaces in ZnSe0.94S0.06 layers grown on to GaAs by OMCVD

High resolution transmission electron microscopy of lattice-matched ZnSe_0.94S_0.06 layers grown by organometallic chemical vapour deposition in the temperature range 275 to 350° C onto GaAs has shown that under specific growth conditions, layers of ZnS can form at the heterojunction interface. Chemical data from secondary ion mass spectrometry and energy dispersive X-ray analyses confirm the enhancement in sulphur content at the interface and also establish that gallium can diffuse into the II–VI layer from the III–V substrate. Growth conditions which eliminate the formation of the intermediate ZnS layer and the gallium diffusion have been identified.