B. Szczygieł

Self-healing coatings in anti-corrosion applications

Nonmetallic (based on polymers or oxides) and metallic protective coatings are used to protect metal products against the harmful action of the corrosion environment. In recent years, self-healing coatings have been the subject of increasing interest. The ability of such coatings to self-repair local damage caused by external factors is a major factor contributing to their attractiveness. Polymer layers, silica-organic layers, conversion layers, metallic layers and ceramic layers, to mention but a few, are used as self-healing coatings. This paper presents the main kinds of self-healing coatings and explains their self-healing mechanisms.

An electrochemical study on the influence of sodium molybdate on electrodeposition process and phase composition of ternary Zn–Ni–Mo alloy coatings

Ternary Zn–Ni–Mo alloy coatings were deposited from a citrate-sulphate bath at pH 5.7 containing different amounts of sodium molybdate. The content of molybdenum in the coatings (from 0.3 to 5.2 at.-%) can be easily controlled by increasing sodium molybdate concentration in the plating bath from 0.0025 to 0.05 mol dm− 3, which results also in deposition of smoother deposits. An increase in molybdate concentration leads to the shift of reduction potentials towards more negative values and to the decrease in current efficiency of deposition process. XRD analyses and anodic linear sweep voltammetry (ALSV) measurements demonstrated that at least two phases are formed in the Zn–Ni–Mo alloy: a hexagonal zinc phase or solid solution of nickel in zinc and Ni5Zn21 intermetallic compound. Furthermore, the XRD analyses revealed a third phase, which could be assigned to the oxidised species of molybdenum or other alloying metals.

Evaluation of the Growth Mechanism of Ti-Containing Conversion Coatings Using XPS

Ti-containing coatings as chromate replacement were prepared on electrogalvanized steel. Zinc coatings were deposited from a weak acid chloride bath. Cr-free conversion coatings were deposited from bath composed of: TiCl3, H2SiF6, H2O2 and oxalic acid. XPS was used to evaluate chemical composition of the coatings as a function of deposition time. Deposited coating were of conversion type. Regardless of the achieved conversion coating thickness, Zn from the substrate was always present. In the coatings were identified: Zn2SiO4 / Zn4Si2O7(OH)2, ZnTiO3, ZnO, Zn (OH)2, Zn0, SiOx and Ti-O-Si in varying proportions. The chemical composition of the outer surface of the coating depended on deposition time, e.g. in a time interval 0-300 s 30 fold increase of the Si:Ti ratio and 20 fold of the Si:Zn ratio were observed. Estimated thickness of conversion coating was 3, 14, 35, and 100 nm for the time deposition of 1, 40, 80 and 300 s respectively. It is the proposed model for distinguishing Zn (0) phase from Zn (2+) quantitatively, based on the Zn L3M45M45 spectrum. The composition of the ZnTiSi conversion coating determined its mechanical properties and corrosion resistance. Standard tests carried out showed that the coatings obtained at the time of 20-40 s had the best corrosion performance and mechanical resistance

Prospects for processing wastes into products used in agriculture.

The authors have proposed their own newly developed universal procedure for assessing waste and selecting methods of processing the waste for agricultural purposes. Increasingly more rigorous environmental legal regulations, especially pertaining to sustainability in agricultural and chemical production, were the most convincing motivation for such approach. The procedure is based on technological and environmental safety criteria. Special attention is devoted to the chemical processing of hazardous wastes into fertilizer products and the underlying reasons for such methodology. As opposed to physical and biochemical processes, in chemical processes the agents used completely change the chemical structure of the waste materials or at least that of some of their components. As a result, new phases are formed and the harmful properties of the initial material are eliminated. Prospects for the chemical processing of hazardous wastes are demonstrated using as an example the utilization of asbestos wastes. There are vast amounts of asbestos materials installed in industrial, communal, and service facilities. Landfill asbestos waste disposal is the common practice, but this does not solve properly the problem of environmental hazard. The proposed utilization concept consists in destroying asbestos with a phosphoric acid solution in a two-stage process. The obtained suspension is then filtered, and the solution of phosphates containing an excess of phosphoric acid is subsequently neutralized with lime and processed into phosphate fertilizers of TSP (triple superphosphate) or DCP (dicalcium phosphate) type. Experiments showed that the process yielded asbestos-free products which did not contain any respirable fibers. Comparative immunological tests showed that the products did not cause any degeneration of human lung cells exposed to them, as opposed to the original asbestos, which had a highly damaging effect on the cells.

EIS study of the codeposition of SiC powder with nickel in a watts bath

SUMMARY The results of impedance investigations of the nickel electrocrystallisation from the Watts baths (with additions of a wetting substance—sodium dodecyl sulphate and of brightening components—2-butyne-1, 4-diol and saccharine), containing SiC powder are presented. The suggested equivalent circuit consists of three resistance and two capacitance elements. The influence of organic additions and silicon carbide powder on the electrolyte resistance (R1), the charge transfer resistance (R3), the desorption resistance (R4), the double layer capacitance (C2) and the pseudo-capacitance (C5) of adsorbed intermediates has been established.

Machine Vision System for Corrosion Detection as an Additional Tool beside EIS for Evaluation of Protective Properties of Electrolessly Deposited Ni-P Coatings

The electroless deposition technique was used to obtain Ni-P coatings with various phosphorus content. Machine vision method was applied as a tool for the analysis and interpretation of the data provided by electrochemical impedance spectroscopy (EIS) corrosion studies. The degree of corrosion of the coating surface could be determined by this method. The combination of both methods allows a more complete evaluation of the protective properties of the obtained coatings.

Properties of Rubber Lining after Sixteen Years Operation in Different Places of FGD Plant

After over 16 years long service on the inner walls of a steel absorber and outlet channel in wet FGD system, the rubber lining was subjected to examinations. A series of impedance spectra for the pre-vulcanized soft rubber lining based on chlorobutyl rubber (CIIR) were recorded. Rubber lining samples taken from the absorber bottom, which had been in contact with the washer sump solution, exhibited properties similar to those of new rubber lining samples not exposed to the corrosive environment. Rubber lining samples taken from the absorber upper part and from the outlet channel showed significant damage, and so deterioration in their protective properties, in comparison with the new lining. Also the results of tensile strength and hardness tests carried out on rubber samples taken from various parts of the absorber and the outlet channel are presented.