Resource-saving processing of technological solutions and wastewater by electrochemical method (methods overview)

The paper summarizes the data on the wastewater formation from a number of plants of chemical, engineering, energy and leather industries and its processing in electrolyzers of various designs to obtain the substances that can be used in various production processes. In the ethylenediamine production, wastewater occurs at the stages of amines rectification and of ethylenediamine dihydrochloride neutralization. Recycling of effluents generated during the amine rectification in a two-chamber electrolysis cell allows the ethylenediamine and ammonia to be returned to the production process. The processing of ethylenediamine dihydrochloride solution in the membrane electrolyzers saves alkali for the neutralization process. Electrochemical processing of distilled liquid in soda production makes possible to obtain calcium hydroxide, sodium hydroxide and hydrochloric acid or chlorine, which can be used in various industrial processes. Wastewater generated during the demineralized water production contains a significant amounts of sodium sulfates and chlorides. The processing of these effluents in a membrane electrolyzer yields sulfuric acid and alkali, which are suitable for the regeneration of ion-exchange filters. After processing in an electrodialysis apparatus the wastewater generated during the chromium and nickel coatings, is concentrated to values that allow them to be used to prepare an electrolyte adjustment. The leather industry effluents contains an amount of trivalent chromium and sulphides. Electrochemical processing of these effluents leads to almost complete extraction of chromium and sulfides.

Influence of Wetting Additive Based on C12 - C14 Alkyl Ester Sulphate with Essential Oils on the Quality of Nickel Coating

The influence of wetting additive based on C12 - C14 alkyl ester sulfate with essential oils on the quality of nickel coatings is examined in the paper. The additive was tested at different concentrations added to the base electrolyte, taking the following concentrations: the concentration recommended twice lower (C1); lower recommended concentration (C2); upper recommended concentration (C3); the concentration twice higher compared to the lower recommended (C4) and the concentration twice higher compared to the upper recommended (C5). The value of the surface tension of the solution was determined, and the corrosion resistance in the salt chamber was examined. In addition, what is important in the production itself is the visual appearance of the coating, which was determined using the Hull cell test. The additive has been proven to be effective in reducing the surface solutions, which directly affects the production of nickel coatings of better quality and aesthetic appearance.

Effects of SiC particles codeposition and ultrasound agitation on the electrocrystallisation of nickel-based composite coatings

This study analysed the influence of the codeposition of SiC particles with different sizes: 50 nm, 500 nm and 5 μm, and the type of bath agitation (stirring or ultrasonic) on the electrocrystallisation of nickel coatings. The composites matrix microstructure was analysed by means of SEM, EBSD and XRD, to evaluate the grain size, crystal orientation, and internal stresses and was benchmarked against pure nickel samples electrodeposited in equivalent conditions. The codeposition of nano- and microsize particles with an approximate content of 0.8 and 4 vol.%, respectively, caused only a minor grain refinement and did not vary the dominant < 100 > crystal orientation observed in pure Ni. The internal stress was, however, increased by particles codeposition, up to 104 MPa by nanoparticles and 57 MPa by microparticles, compared to the values observed in pure nickel (41 MPa). The higher codeposition rate (11 vol.%) obtained by the addition of submicron-size particles caused a change in the grain growth from columnar to equiaxial, resulting in deposits with a fully random crystal orientation and pronounced grain refinement. The internal stress was also increased by 800% compared to pure nickel. The ultrasound (US) agitation during the deposition caused grain refinement and a selective particle inclusion prompting a decrease in the content of the particles with the larger particles. The deposits produced under US agitation showed an increase in the internal stresses, with double values compared to stirring. The increase in the deposits microhardness, from 280 HV in pure Ni to 560 HV in Ni/SiC submicron-US, was linked to the microstructural changes and particles content. Graphical abstract

Investigation of nickel coatings obtained by laser processing on the surface of bronze

The article presents the results of a comprehensive study of the modes of laser processing during the formation of a coating on nickel-aluminum bronze using nickel powders. The coating was obtained in two stages. At the first stage, a precursor coating of the powder material was applied by cold spraying, at the second stage, its surface treatment with a laser was performed. The change in the composition and properties of the coating is shown depending on the processing modes and the thickness of the precursor coating, as well as the modes of laser processing.

Hard Chrome Replacement with Cirrus Doped Electroless Nickel Coatings

The intrinsic hardness, high abrasive wear resistance, and corrosion properties of hard chrome coatings have resulted in their wide industrial application. However, chrome plating involves hazards associated with chrome 6+ which affect human health and drive the need to identify viable alternatives. This study investigated the addition of Cirrus alumina Dopant™ to a low phosphorus electroless nickel bath to evaluate the performance of the resulting nanocomposite coating as a potential replacement for hard chrome. A comprehensive comparison for the performance of coatings for alumina doped electroless nickel and a pure low electroless nickel coating were investigated. Results showed that Cirrus doped electroless nickel possessed a minimum hardness of 850HV0.1, high corrosion resistance, excellent abrasive wear resistance, and a Taber Wear Index of 2.25mg/1000 cycles. These attributes suggest Cirrus Dopant™ for electroless nickel may offer an outstanding candidate to replace hard chrome coatings in many applications.

Influence of Bath Hydrodynamics on the Micromechanical Properties of Electrodeposited Nickel-Cobalt Alloys

The influence of bath hydrodynamics on the resultant micromechanical properties of electrodeposited nickel-cobalt alloy system is investigated. The bath hydrodynamics realized by magnetic stirring is simulated using COMSOL Multiphysics and a region of minimum variation in velocity within the electrolytic cell is determined and validated experimentally. Nickel-cobalt alloy and nickel coating samples are deposited galvanostatically (50 mA/cm2) with varying bath velocity (0 to 42 cm/s). The surface morphology of samples gradually changed from granular (fractal dimension 2.97) to more planar (fractal dimension 2.15) growth type, and the according average roughness decreased from 207.5 nm to 11 nm on increasing the electrolyte velocity from 0 to 42 cm/s for nickel-cobalt alloys; a similar trend was also found in the case of nickel coatings. The calculated grain size from the X-ray diffractograms decreased from 31 nm to 12 nm and from 69 nm to 26 nm as function of increasing velocity (up to 42 cm/s) for nickel-cobalt and nickel coatings, respectively. Consecutively, the measured Vickers microhardness values increased by 43% (i.e., from 393 HV0.01 to 692 HV0.01) and by 33% (i.e., from 255 HV0.01 to 381 HV0.01) for nickel-cobalt and nickel coatings, respectively, which fits well with the Hall–Petch relation.

Study on efficiency of corrosion inhibitors based on derivatives of isothiuronic salts

Metals play a pivotal role in industry; their use constantly grows. It is virtually impossible to find an industrial field without the use of metals and their alloys. However, owing to the quality degradation of metal during the operational process, corrosion appears not only on its surface but also under a coating, which leads to its destruction. To avoid this, corrosion inhibitors are necessary. Organic compounds have been widely used as corrosion inhibitors. Many organic corrosion inhibitors have been developed nowadays. In the literature, organic compounds comprising N, O, S and P heteroatoms are described, which reduce corrosion rate. The organic compounds are adsorbed on the metal surface, forming a thin layer. Adsorption occurs either through electrostatic interaction or, in some cases, the formation of covalent bonds. The work aimed to study isothiuronic salts as corrosion inhibitors to evaluate their protective properties using the polarisation curves method. Objects of research were isothiuronic compounds containing two active centres separated by saturated and unsaturated carbon bonds (structures 1-3). In structures 4-7, one isothiuronic fragment has different propylene substituting groups. It has been previously shown that these compounds can act as effective brightening agents when applying nickel coatings. A model solution with a density of 1.12 g/cm3 was prepared to study the corrosion inhibitors. The corrosion inhibitor concentration was 400 mg/L. Studies have shown that the compounds with two isothiuronic moieties do not always exhibit improved properties for inhibiting metal degradation in a corrosive environment. In particular, they showed worsening of the inhibiting properties for samples made of steel 20 and identical properties for that made of steel 3.