Robert Engelken

Chromium-based regulations and greening in metal finishing industries in the USA

Abstract This paper reviews the regulations pertaining to chromium emissions from metal finishing industries in the USA and technical options for compliance, and assesses the influence of regulations on the reduction of chromium emissions. Based upon the literature analysis, the paper argues that there has been discernible impact of the regulations on chromium emissions control by metal finishing industries. Chromium emission reduction by metal finishing industries has occurred mainly in response to the need to comply with chromium regulations. To meet the regulatory requirements, the industries have either installed chromium emission control equipment or moved to pollution prevention by minimizing waste generation and implementing process and product modifications. Over time, metal finishing industries have learned that pollution prevention does pay and environmental protection and pollution prevention are compatible businesses. With innovative public policy like EPA’s Common Sense Initiative (CSI) now in place, the prospects for chromium emission reduction and compliance to regulations looks better than ever. A number of metal finishing industries, mainly large businesses, have adopted “greening” as the principal philosophy of business management. However, greening is occurring slowly because of lack of personnel and capital resources, awareness, and technical competence, as well as organizational resistance, high costs of production, uncertainty about future regulatory activity, and substantial marketplace constraints.

Electrodeposition and Characterization of SnS Thin Films

A new room‐temperature electrodeposition technique was devised to synthesize thin films on indium tin oxidecoated glass slides. This technique is based on a nonaqueous ethylene glycol bath containing anhydrous and elemental sulfur. Three types of electrosyntheses, namely, potentiostatic, galvanostatic, and pulse modes, are discussed and their relative merits compared. A wide variety of characterization techniques were employed to develop a self‐consistent and complementary picture of the morphology, composition, and photoactivity of the thin films. These included scanning electron microscopy, x‐ray diffractometry, electron probe microanalyses, Auger electron spectroscopy, x‐ray photoelectron spectroscopy, optical analyses, and voltammetry. The photoactivity of these films was evaluated using photoelectrochemical techniques. Finally, the dark and photocorrosion behavior of these films are discussed with the aid of Pourbaix diagrams.

High optical absorption of indium sulfide nanorod arrays formed by glancing angle deposition.

Indium(III) sulfide has recently attracted much attention due to its potential in optical sensors as a photoconducting material and in photovoltaic applications as a wide band gap material. On the other hand, optical absorption properties are key parameters in developing photosensitive photodetectors and efficient solar cells. In this work, we show that indium sulfide nanorod arrays produced by the glancing angle deposition technique have superior absorption and low reflectance properties compared to conventional flat thin film counterparts. We observed an optical absorption value of approximately 96% for nanorods at wavelengths <500 nm in contrast to 79% for conventional thin films of indium sulfide. A superior photoconductivity (PC) response as high as about 40% (change in resistance upon illumination) was also observed in nanorod samples. This is mainly believed to be due to their high optical absorption, whereas only less than 1% PC change was detected in conventional thin films. We give a preliminary description of the enhanced light absorption properties of the nanorods by using the Shirley-George model, which predicts diffusion of light as a function of the roughness of the surface.

Modeling, Optimization, and Comparative Analysis of Trivalent Chromium Electrodeposition from Aqueous Glycine and Formic Acid Baths

Trivalent chromium electrodeposition has been studied as an alternative to hazardous hexavalent chromium electroplating. Although limited by inability to deposit thick coatings with acceptable quality, it is useful for decorative chromium electroplating. In the present work, we illustrate the application of statistical design of experiments (DOE) in empirical modeling and optimization of electrodeposition of trivalent chromium from baths of chromium complexed with glycine. DOE shows that variations in current efficiency with glycine and chromium chloride concentrations can be explained by a quadratic model. The composition of the bath was optimized with respect to current efficiency to obtain faster deposition. We compare the effects of process parameters (pH, temperature, current density, and pulsed current) on current efficiency and deposit characteristics for both glycine and formic acid-containing baths. Experiments reveal that whether pulsed current increases or decreases current efficiency is determined by how current density influences current efficiency, and the range of lower and upper current density levels.

Study and development of a generic electrochemical ion-exchange process to form MxS optoelectronic materials from ZnS precursor films formed by chemical-precipitation solution deposition

We have investigated the formation of a wide variety of metal sulfide films such as SnS and CdS by an electrochemical ion-exchange process where the metal cation of the desired product film exchanges with the Zn(II) in a ZnS film deposited on non-conductive substrates by chemical-precipitation solution techniques. The process works for most metals that can be electroplated from aqueous baths (i.e. more electrochemically noble than Zn) and yields nearly-stoichiometric, polycrystalline, and often photoconductive MxS films. Key advantages of the process include the very low hazard/toxicity and cost of the chemicals used in the process and the avoidance of secondary sulfide (PbS, CdS, In2S3, Sb2S3, etc.) sludges, colloids, precipitates, etc., of toxic and/or expensive metals. In particular, its outstanding photosensitivity and low toxicity point toward the utility of SnS farmed by our method for photodetector applications.

Optimization of the electrodeposition parameters to improve the stoichiometry of In 2 S 3 films for solar applications using the taguchi method

Properties of electrodeposited semiconductor thin films are dependent upon the electrolyte composition, plating time, and temperature as well as the current density and the nature of the substrate. In this study, the influence of the electrodeposition parameters such as deposition voltage, deposition time, composition of solution, and deposition temperature upon the properties of In2S3 films was analyzed by the Taguchi Method. According to Taguchi analysis, the interaction between deposition voltage and deposition time was significant. Deposition voltage had the largest impact upon the stoichiometry of In2S3 films and deposition temperature had the least impact. The stoichiometric ratios between sulfur and indium (S/In: 3/2) obtained from experiments performed with optimized electrodeposition parameters were in agreement with predicted values from the Taguchi Method. The experiments were carried out according to Taguchi orthogonal array L27 (34) design of experiments (DOE). Approximately 600 nm thick In2S3 films were electrodeposited from an organic bath (ethylene glycol-based) containing indium chloride (InCl3), sodium chloride (NaCl), and sodium thiosulfate (Na2S2O3·5H2O), the latter used as an additional sulfur source along with elemental sulfur (S). An X-ray diffractometer (XRD), energy dispersive X-ray spectroscopy (EDS) unit, and scanning electron microscope (SEM) were, respectively, used to analyze the phases, elemental composition, and morphology of the electrodeposited In2S3 films.

Elemental sulfur-based electrodeposition of indium sulfide films

We report research on electrodeposition of indium sulfide films, with In2S3 a less hazardous alternative to CdS buffer layers in solar cells. Numerous organic and aqueous/organic electrolytes of InCl3, NaCl, and elemental sulfur were investigated, including several glycols and amides. Temperatures ranged from 80–170 °C, and deposition voltages from −0.6 to −1.2 V (Ag/AgCl with organic filling solution). Substrates included indium tin oxide-on-glass, molybdenum, and titanium, with indium or graphite anodes. Rapid stirring was used. Deposition was sluggish in all baths. Uniformity and adherence were only moderate, with irregular coverage and cracking-and-flaking sometimes evident. The best baths were ethylene glycol or 1, 2-propanediol-based, with golden-yellow films, nominally In2S3−xOx, depositing typically heavier around the substrate edges. With low temperatures and/or large currents, brown films more rich in indium sometimes formed. Cyclic voltammetry elucidated onset potentials, secondary reactions, and photoactivity, with the greatest anodic photocurrents arising from In2S3s n-type conductivity occurring with mixed ethylene glycol/propionic acid/water baths. Scanning electron microscope photographs indicated a compact small grain microstructure for yellow films. Energy dispersive X-ray analysis and photoelectron spectroscopy data indicate up

Morphological and compositional analysis of electrodeposited indium (III) sulfide (In 2 S 3 ) films

In the last few years, notable progress in understanding the growth mechanism of thin solar films deposited by numerous techniques have been made. Electrodeposition continues to be a complex deposition technique that can lead to low-quality material regions (crack) in the semiconductor material. Such cracks form porous zones on the substrate and diminish the heterojunction interface quality of a photovoltaic (PV) cell. In this paper, electrodeposition of In 2 S 3 films was systematically and quantitatively investigated by varying the electrodeposition parameters including bath composition, current density, deposition time, and deposition temperature. Their effects upon the film growth mechanism, composition, and morphology were studied with the help of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and fracture and buckling software (digital image analysis). In addition, the effect of different glass-substrates (Mo, ITO, and FTO) and annealing treatments upon the performance of the electrodeposited In 2 S 3 film was analyzed. Furthermore, the Taguchi Method was used to determine the optimal electrodeposition parameters and study their influence upon the morphological and compositional properties of In 2 S 3 films.

Stoichiometric control via periods of open-circuit during electrodeposition

Electrodeposition can enable stoichiometric control of deposited samples through variation of electroplating potential. We demonstrate an in-situ technique for deposit analysis and stoichiometric control by interspersing periods of open-circuit during deposition. Opening the circuit in an organic Cu-In-S plating bath allows greater incorporation of Cu, In, and/or S into deposited films, based upon the open-circuit voltage the film/electrolyte interface is allowed to achieve. With the same deposition potential, samples can be made to vary from highly Cu-rich to highly In-rich through selection of an appropriate open-circuit voltage limit.

Photoelectrochemical characterization of titania photoanodes fabricated using varying anodization parameters

Titanium dioxide (TiO2) has long been considered a model photoanode material for electrolysis of water using solar energy. A number of studies have looked into the synthesis methods to optimize physical as well as chemical properties of titania photoanodes. Electric field assisted anodic oxidation of titanium (Ti) for fabrication of titania photoanodes is a relatively new synthesis technique. This paper presents a systematic study of this technique by varying anodization parameters. The current-time behavior of Ti anodization was also studied. The current-voltage (I-V) characteristic of these samples was measured under dark and illumination conditions. The electrode fabricated using 20 Volts for 20 minutes demonstrated the best performance among all the samples tested. The photocurrent density obtained under visible radiation was 0.528 mA/cm2. This study will assist in design and fabrication of new electrodes for photoelectrolysis using a material that is photoactive, stable, corrosion resistant, and cost effective.