Anodic behaviour of copper during electrorefining using a rotating ring-disc electrode

The anodic dissolution of copper during electrorefining has been studied by a rotating ring-disc electrode technique. The influence of temperature, some additives (Cl^– ions and polyethylene glycol) and the anode-alloying element (phosphorus) on the polarization curves was examined. It was shown that at certain conditions the concentration of Cu⁺ ions on the ring electrode decreased. As a result, a reduction of powdered copper in the electrolyte due to the disproportionation of cuprous ions may be expected.     

A Novel Magnetic Hardening Mechanism for Nd-Fe-B Permanent Magnets Based on Solid-State Phase Transformation

Permanent magnets based on neodymium-iron-boron (Nd-Fe-B) alloys provide the highest performance and energy density, finding usage in many high-tech applications. Their magnetic performance relies on the intrinsic properties of the hard-magnetic Nd₂Fe₁₄B phase combined with control over the microstructure during production. In this study, a novel magnetic hardening mechanism is described in such materials based on a solid-state phase transformation. Using modified Nd-Fe-B alloys of the type Nd₁₆Fe_bal-x-y-zCo_xMo_yCu_zB₇ for the first time it is revealed how the microstructural transformation from the metastable Nd₂Fe₁₇B_x phase to the hard-magnetic Nd₂Fe₁₄B phase can be thermally controlled, leading to an astonishing increase in coercivity from ≈200 kAm⁻¹ to almost 700 kAm⁻¹. Furthermore, after thermally treating a quenched sample of Nd₁₆Fe₅₆Co₂₀Mo₂Cu₂B₇, the presence of Mo leads to the formation of fine FeMo₂B₂ precipitates, in the range from micrometers down to a few nanometers. These precipitates are responsible for the refinement of the Nd₂Fe₁₄B grains and so for the high coercivity. This mechanism can be incorporated into existing manufacturing processes and can prove to be applicable to novel fabrication routes for Nd-Fe-B magnets, such as additive manufacturing.     

Nanocrystalline Nd–Fe–B Anisotropic Magnets by Flash Spark Plasma Sintering

Flash spark plasma sintering (flash SPS) is an attractive method to obtain Nd–Fe–B magnets with anisotropic magnetic properties when starting from melt-spun powders. Compared to the benchmark processing route via hot pressing with subsequent die upsetting, flash SPS promises electroplasticity as an additional deformation mechanism and reduced tool wear, while maximizing magnetic properties by tailoring the microstructure—fully dense and high texture. A detailed parameter study is conducted to understand the influence of Flash SPS parameters on the densification and magnetic properties of commercial MQU-F powder. It is revealed that the presintering conditions and preheating temperature before applying the power pulse play a major role for tailoring grain size and texture in the case of hot deformation via Flash SPS. Detailed microstructure and magnetic domain evaluation disclose the texture enhancement with increasing flash SPS temperature at the expense of coercivity. The best compromise between remanence and coercivity (1.37 T and 1195 kA m⁻¹, respectively) is achieved through a combination of presintering at 500 °C for 120 s and preheating temperature of 600 °C, resulting in a magnet with energy product (BH)_max of 350 kJm⁻³. These findings show the potential of flash SPS to obtain fully dense anisotropic nanocrystalline magnets with high magnetic performance.     

Selective Binding of Cyclodextrins with Leflunomide and Its Pharmacologically Active Metabolite Teriflunomide

The selectivity of encapsulation of leflunomide and teriflunomide by native α-, β- and γ-cyclodextrins was investigated through ¹H NMR and molecular modeling. Thermodynamic analysis revealed the main driving forces involved in the binding. For α-cyclodextrin, the partial encapsulation was obtained while deep penetration was characterized for the other two cyclodextrins, where the remaining polar fragment of the molecule is located outside the macrocyclic cavity. The interactions via hydrogen bonding are responsible for high negative enthalpy and entropy changes accompanying the complexation of cyclodextrins with teriflunomide. These results were in agreement with the molecular modeling calculations, which provide a clearer picture of the involved interactions at the atomic level.     

Effects of nickel foam dimensions on catalytic activity of supported Co–Mn–B nanocomposites for hydrogen generation from stabilized borohydride solutions

In the present work, the catalytic activity of electrodeposited Co–Mn–B nanocomposites towards controllable hydrolysis of sodium borohydride was studied. Deposition was performed on two types of Ni-foam (RECEMAT Int.) with different pore size, specific surface area and thickness. Higher deposit loading, as well as bigger real surface area, was obtained with foam samples possessing bigger pore size. The catalyst deposited on bigger pore foam promoted hydrogen generation with higher rates than the other one when contacted with a base-stabilized NaBH₄ solution. The same activation energy value, however, was determined for both supported catalysts. On the base of the obtained results, it may be concluded that the geometric factor plays predominant role for the catalytic activity of studied catalysts.     

Effect of brighteners on hydrogen evolution during zinc electroplating from zincate electrolytes

Hydrogen evolution during zinc electrodeposition on a steel substrate from zincate electrolytes containing different additives was studied using various experimental techniques.The hydrogen evolution reaction is limited by the electron transfer step. Hydrogen evolution is most intensive during the first seconds from the beginning of electrodeposition due to the lower overpotential of hydrogen on steel as compared with that on zinc. The evolved hydrogen is dissipated in three ways. Most is dissipated to the atmosphere via gas bubbles at a constant rate. Some is dispersed in the electrolyte some diffuses into the steel substrate, predominantly at the commencement of deposition. The additives affect both the total amount of evolved hydrogen and its distribution. The highest amount of hydrogen is evolved in the presence of the anisaldehyde bisulphite containing composite additive. The highest amount of hydrogen included in the substrate and remaining in the electrolyte corresponds to the use of the Na–N-benzylnicotinate containing additive. In this case blistering is observed.     

Poly(3-hydroxybutyrate)-based hybrid materials with photocatalytic and magnetic properties prepared by electrospinning and electrospraying

Several types of nanostructured hybrid fibrous materials containing poly(3-hydroxybutyrate), nanoparticles from iron oxide (Fe₃O₄) and titanium dioxide (TiO₂), and chitosan or chitosan oligosaccharides (COS) were prepared. The design of the surface of the materials and their magnetic properties were tailored purposefully by conjunction of electrospinning and electrospraying. The surface and bulk morphologies of the obtained nanostructured materials were examined by SEM. Further, the distribution of Fe₃O₄ and TiO₂ nanoparticles was estimated by TEM analyses, as well as their surface chemical composition was determined by XPS. It was found that the simultaneous electrospinning and electrospraying of Fe₃O₄/chitosan or TiO₂/COS dispersions resulted in uniform distribution of the nanoparticles along the length of the fibers, while electrospraying of the mixed Fe₃O₄/TiO₂/chitosan dispersion led to agglomerate formation. Furthermore, the nanostructured hybrid materials preserved the magnetic properties of Fe₃O₄ embedded therein. It was demonstrated that the hybrid materials of different designs displayed excellent photocatalytic activity under UV light irradiation against a model organic contaminant—methylene blue, even after threefold use of the materials.     

Separation and characterization of ɛ-caprolactone oligomers by gel permeation chromatography

Summary It is shown that the combined use of gel permeation chromatography and the isocyanate method of determination of hydroxyl end groups extends the possibilities for studying complex oligomer mixtures of -caprolactone. Oligomer mixtures of -caprolactone obtained by (C₆H₅)₃CSbCl₆ and by (C₆H₅)₃CK are investigated. At initiation by both the initiators — the cationic and the anionic one — a covalent bond between the initiator and the polymer chain is formed. In the case of the initiation by (C₆H₅)₃CK intramolecular transesterification proceeds which results in cyclic oligomers. At initiation by (C₆H₅)₃CSbCl₆ linear oligomers are formed. It is assumed that the -caprolactone polymerization by (C₆H₅)₃CSbCl₆ proceeds by alkyl-oxygen bond scission.     

Investigation of the processes of obtaining plastic treatment and electrochemical behaviour of lead alloys in their capacity as anodes during the electroextraction of zinc I. Behaviour of PbAg, PbCa and PBAgCa alloys

The influence of the mode of obtaining and plastic treatment of binary PbAg and PbCa, and ternary PbAgCa alloys (used as anodes in Zn electro-extraction from sulphate electrolytes) on their electrochemical behaviour and corrosion resistance is studied.It has been established that the rolled PbAg alloys possess a higher corrosion resistance and lower anodic polarization compared to the cast lead-silver ones due to the structural fineness and homogeneity of the plastic deformed anodes. The plastic deformation of the ternary alloys with calcium content of 0.06% causes Pb₃Ca precipitation in the solid solution. The hot-rolled alloys form an solid solution of Pb₃Ca with fine-grained structure, deformed through the rolling direction. The cold-rolled alloys possess clearly expressed oriented structures also through the rolling direction.Cast and plastically deformed PbCa anodes possess better electrochemical and corrosion characteristics than pure Pb but a considerably higher anodic polarization and lower corrosion resistance than PbAg alloys. Both PbCa systems, with a calcium content of 0.08 and 0.11 % are very appropriate for the preparation of ternary PbAgCa alloys. These alloys (PbAg 0.5 %-Ca 0.11 %) possess better electrochemical and corrosion characteristics than binary PbCa ones. Only ternary rolled alloys have equal corrosion and electrochemical properties to those of the alloy PbAg (0.75%–1.0%) used in practice.     

Processes during the electrorefining and electrowinning of lead

The anodic and cathodic processes in the fluorosilicate electrolytes during galvanostatic deposition under (DC) and polarity reversal current (PRC) regimes were investigated. It was established that, during the process of lead electrorefining from concentrated electrolyte without applying PRC, at c.d. i = 300 A/m² (3 A/dm²), after 60–80 h of the 95 h operation cycle, a limiting anodic polarization barrier value (Δ?_Acr = 200 mV) is attained. In this case bismuth and antimony start to dissolve actively from the anodes and are deposited onto the cathode, while under PRC conditions Δ?_Acr is not reached even after 95 h. The cathodic deposits are rounded crystal grains and display pronounced epitaxial growth. Spectral analysis shows that Sb is the main impurity of cathodic lead instead of Bi.During the electrowinning of the lead, without using H₃PO₄ as an inhibitor of β-PbO₂ parasitic deposition onto the inert graphite anodes, it was established that a critical value of the anodic potential ?_Acr = 1430–1500 mV/SCE) exists, under which β-PbO₂ is not deposited. If H₃PO₄ is present, β-PbO₂ is not deposited onto the graphite anodes at any values of the anodic potential.