Total concentration of main components in solutions for metal electroplating as a criterion for classifying and choosing resource-saving compositions of solutions

A comparative analysis is performed of the variations in the total concentration of the main components $\left( {\sum\limits_i {c_i } } \right)$ , in the solutions proposed and used in different years for electroplating individual metals (Cr, Cu, Ni, Zn, Sn, Cd, Pb, and Fe). A quantitative concentration criterion is determined for classifying solutions into resource-saving ( $\left( {\sum\limits_i {c_i \leqslant 2.32} } \right)$ mol-equiv/L) and resourceintensive ( $\left( {\sum\limits_i {c_i \geqslant 2.78} } \right)$ mol-equiv/L) compositions. In addition to scientific interest, this material can be useful for developing studies aimed at reducing the negative environmental impact of electroplating shops or sections.     

Simultaneous recovery of copper and surfactant by an electrolytic process from synthetic solution prepared to simulate a concentrate waste stream of a micellar-enhanced ultrafiltration process

Electroplating method was employed to recover copper and surfactant simultaneously from synthetic solutions prepared to simulate concentrated waste stream generated from micellar-enhanced ultrafiltration. Effects of surfactant and copper (II) concentrations, surfactant to copper (II) molar ratio (S/M), electroplating voltage and time, solution pH, and ionic strength on metal recovery and electrical current efficiency were investigated. Results show that at a fixed S/M ratio of 5, the first-order kinetic constant for Cu (II) removal by electroplating increases with decreasing SDS concentration. At fixed SDS concentration of 8.5 mM, increasing initial Cu (II) concentration increases both Cu (II) recovery and current efficiency. Electrolyte pH has profound effects on the metal recovery and current efficiency due to the difference in solution conductivity after pH adjustment and the extent of Cu (II) adsorption onto SDS at different pHs.     

Electrochemical kinetic parameters for the cathodic deposition of copper from dilute aqueous acid sulfate solutions

The use of linear-sweep voltammetry and chronopotentiometry for the determination of kinetic parameters for the electrolytic recovery of copper from a simulated acid-copper electroplating waste solution was demonstrated. For the electrodeposition of copper from solutions of 0.007?0.008 mol/L CuSO₄ + 0.5 mol/L H2SO₄ at 25°, the recommended values of the transfer coefficient (α) and exchange current density (i₀) are α = 0.46±0.06 (95% confidence interval) and i₀ = 11±4 A/m². The close agreement between these values and the available literature values indicates the reliabilaity of the voltammetric and chronopotentiometric methods.     

Concentration dependence of static and hydrodynamic screening lengths for three different polymers in a variety of solvents

We have used small angle neutron scattering and dynamic light scattering to measure the static and hydrodynamic screening lengths of polystyrene, polymethylmethacrylate and polydimethylsiloxane solutions ranging from marginal to good solvent quality. A universal plot is found for the scaled static screening length when the concentration is scaled using the second virial coefficient in the way suggested by renormalization group theories. The same concentration units do not produce a universal plot for the hydrodynamic screening length at the molecular weights that we have studied (all around 1-2×10⁵ g/mol). However, when the concentration is expressed in terms of k_Dc, where k_D is the virial expansion coefficient for the cooperative diffusion coefficient and c is the concentration, most of the variation between different polymer-solvent combinations is eliminated. The ratio of hydrodynamic screening length to static screening length increases with concentration for all of the polymer solvent pairs studied, and its value differs for different polymer solvent pairs.     

Electrospinning of linear homopolymers of poly(methyl methacrylate): exploring relationships between fiber formation, viscosity, molecular weight and concentration in a good solvent

A series of seven linear homopolymers of poly(methylmethacrylate) ranging from 12,470 to 365,700 g/mol M_w, were utilized to further explore scaling relationships between viscosity and concentration in a good solvent at 25 °C and to investigate the impact of these relationships on fiber formation during electrospinning. For each of the polymers investigated, chain dimensions (hydrodynamic radius and radius of gyration) were measured by dynamic light scattering to determine the critical chain overlap concentration, c^*. The experimentally determined c^*, was found to be in good agreement with the theoretically determined value that was calculated by the criteria c^*∼1/[η], where the intrinsic viscosity was estimated from the Mark-Houwink parameters, K and a (at 25 °C in dimethyl formamide) obtained from the literature. The plot of the zero shear viscosity vs. c/c^* distinctly separated into different solution regimes, viz. dilute (c/c^*<1), semidilute unentangled (1<c/c^*<3) and semidilute entangled (c/c^*>3). The crossover between semidilute unentangled and semidilute entangled regimes in the present investigation occurred at c/c^*∼3, which, therefore, marked the onset of the critical chain entanglement concentration, c_e, according to the procedure utilized by Colby and co-workers [Colby RH, Rubinstein M, Daoud M. J de Phys II 1994;4(8):1299-310. [52]]. Electrospinning of all solutions was carried out at identical conditions to ascertain the effects of solution concentration, molecular weight, molecular weight distribution and viscosity on fiber formation and morphological features of the electrospun material. Only polymer droplets were observed to form from electrospinning of solutions in the dilute concentration regime due to insufficient chain overlap. As the concentration was increased, droplets and beaded fibers were observed in the semidilute unentangled regime; and beaded as well as uniform fibers were observed in the semidilute entangled regime. Uniform fiber formation was observed at c/c^*∼6 for all the narrow MWD polymers (M_w of 12,470-205,800 g/mol) but for the relatively broad MWD polymers (M_w of 34,070 and 95,800 g/mol), uniform fibers were not formed until higher concentrations, c/c^*∼10, were utilized. Dependence of fiber diameter on concentration and viscosity was also determined, viz. fiber dia∼(c/c^*)^3.1 and respectively. These scaling relationships were in general agreement with that observed by Mckee et al. [McKee MG, Wilkes GL, Colby RH, Long TE. Macromolecules 2004;37(5):1760-67. [33]].     

Kinetics of Sn electrodeposition from Sn(II)–citrate solutions

The influence of solution chemistry on the electrodeposition of Sn from Sn(II)–citrate solutions is studied. The distribution of various Sn(II)–citrate complexes and citrate ligands is calculated and the results presented as speciation diagrams. At a SnCl₂·H₂O concentration of 0.22 mol/L and citrate concentration from 0.30 mol/L to 0.66 mol/L, SnH₃L⁺ (where L represents the tetravalent citrate ligand) is the main species at pH below about 1.2 and SnHL⁻ is the main species at pH above about 4. Polarization studies and reduction potential calculations show that the Sn(II)–citrate complexes have similar reduction potentials at a given solution composition and pH. However, the Sn(II)–citrate complexes become more difficult to reduce with higher total citrate concentration and higher solution pH. Nevertheless, SnHL⁻ which forms at higher pH is a favored Sn(II)–citrate complex for Sn electrodeposition due to better plated film morphology, likely as a result of its slower electroplating kinetics. Precipitates are formed from the Sn(II)–citrate solutions after adding hydrochloric acid (to lower the pH). Compositional and structural analyses indicate that the precipitates may have the formula Sn₂L.     

Optimization of zinc‐nickel film electrodeposition for better corrosion resistant characteristics

Corrosion is one of the main causes of structural deterioration in offshore and marine structures. One way to mitigate the effect of corrosion is with Zn‐Ni electroplated coatings. An experimental design and optimization procedures for Zn‐Ni alloy electroplating was an explored. This study analyzed a five‐variable experimental plan comprised of four steps: (1) a two‐level fractional factorial design (FFD); (2) a response surface design the steepest ascent analysis; (3) a central composite design (CCD); and (4) a corrosion behaviour test to optimize the factors in Zn‐Ni deposition. The critical plating variables in step 1 were zinc/nickel molar concentration ratio, current density, citrate concentrations, plating temperature, and plating time, used to determine their influence on the polarization resistance and corrosion resistance. In steps 2 and 3 the significant variables were studied using the steepest ascent method and the central composite design (CCD) to find the most optimal conditions for zinc‐nickel electroplating. These conditions were found to be a Zn/Ni molar concentration ratio of 0.66, a plating temperature of 28 °C, an electroplating current density of 60 mA/cm², an electroplating time of 13 min, and a citrate concentration of 0.062 mol/L. The corrosion behaviour test of step 4 showed that the films with a higher intensity of the γ‐NiZn₃, γ‐Ni₂Zn₁₁, and γ‐Ni₃Zn₂₂ phases exhibited better corrosion resistance.     

Sulfate attack on cementitious materials containing limestone filler — A review

This review summarizes the results of sulfate performance in laboratory and field tests where limestone is used as a constituent of cement (PLC) or as a sand replacement where it is particularly beneficial to the properties of self compacting concretes (SCC).Laboratory studies on paste, mortar or concrete specimens exposed to Na₂SO₄ and MgSO₄ solutions in a wide range of concentrations at different temperatures as well as mixtures with different compositions, cement compositions and limestone proportions are considered in a conceptual analysis as for the resistance to external sulfate attack and, especially, thaumasite sulfate attack.A detailed analysis of environmental aggressiveness (concentration, temperature and pH), mixture composition and cement composition used in each study are presented for PLC and SCC. Reported field studies are also shown, only a few cases have used limestone filler in their composition. A conceptual graphical analysis is then proposed to relate the degree of surface deterioration and mineralogical composition of attacked surface to the main variables of external sulfate attack: water/cementitious material ratio, limestone content and C₃A content of the cement. Observation of graphical analysis clearly shows that deterioration by ESA is mainly governed by effective w/c ratio and C₃A content of the cement. Surface damage is controlled when low effective w/c ratio and low C₃A are used. In MgSO₄ solution, low temperatures increase the degree of deterioration. Thaumasite is the last attack stage in the different sulfate environments.     

Isothermal crystallization study on aqueous solution of poly(vinyl methyl ether) by DSC method

A study on the isothermal crystallization of water in aqueous solutions of poly(vinyl methyl ether) (PVME) was carried out by the differential scanning calorimetry (DSC). The influence of PVME concentration (49.5, 44.5 and 39.5 v%) and the crystallization temperature (T_c) on crystallization rate G, crystallization enthalpy (ΔH_c) and melting enthalpy (ΔH_m) was investigated. Avrami equation cannot be used to describe the crystallization process of water in aqueous PVME solution. Within the measured temperature range, the crystallization rate G increases with the crystallization temperature T_c and with the decreasing PVME content. The crystallization enthalpy ΔH_c linearly increases with the degree of supercooling. The influence of T_c on the ΔH_c becomes more marked with increasing PVME concentration. For 49.5 and 44.5 v% PVME solutions, the amount of water arrested in solution during the isothermal crystallization and the final concentration of PVME-rich phase increase linearly with the T_c, whereas for 39.5 v% PVME solution, these two values almost do not change with T_c. The amount of frozen water in the subsequent cold crystallization is approximately proportional to the initial T_c. The approximately constant ΔH_m for a given concentration at the different initial isothermal crystallization temperatures suggests that the total amount of ice from the first isothermal crystallization and the second cold crystallization is same. The quantitative relation of the amount of frozen water in the cold crystallization and the initial T_c demonstrates that PVME/water complexes are thermodynamically unstable.     

Solution behavior and associating structures of a salt-tolerant tetra-polymer containing an allyl-capped macromonomer

A novel salt-tolerant macromonomer, allyl-capped octylphenoxy poly(ethylene oxide) (AOP) with the degree of polymerization equal to 20, was synthesized, and then a novel acrylamide(AM)-based tetra-polymer (PSAA) containing sodium 2-acrylamido-2-methylpropane sulphonate (NaAMPS), AOP, and vinyl biphenyl (VP) was synthesized by aqueous free-radical copolymerization. Static light scattering measurement shows that the weight-average molecular weight of PSAA is only 6.75?×?10⁶ g/mol, but the z-average radius of gyration in 30 g/L NaCl is up to 189 nm. The apparent viscosities of aqueous PSAA solutions are very low at all polymer concentrations. However, for PSAA in 70 g/L NaCl, the critical association concentration (C _p *) decreases from 0.4 g/L in water to 0.3 g/L, and the apparent viscosity increases sharply with an increase in polymer concentration and is higher surprisingly than that in water above C _p *. The influences of NaCl and CaCl₂ concentrations on solution viscosities of PSAA were measured, and the brine solutions display the strong salt-thickening effect in a wide range of salt concentration. This is different from hydrophobically associating polymers reported in the literature. Moreover, the thickening mechanisms of PSAA in water and brine solutions were investigated by a fluorescent probe and atomic force microscope (AFM).     

Static and dynamic light scattering study of strong intermolecular interactions in aqueous solutions of PVP/C60 complexes

The investigations of the dilute aqueous solutions of polyvinylpyrrolidone/fullerene (PVP/C₆₀) complexes by static (SLS) and dynamic (DLS) light scattering showed that strong intermolecular interactions, effective on the distances of about 45-50 nm, take place in the solutions. Two concentration ranges are well distinguished in these solutions. Above a critical concentration (c_cr) the fluctuations in the solutions are hindered and only one, diffusive, mode is observed in DLS experiments. Upon dilution (c<c_cr) this unified structure divides into large fragments (domains) and the slow mode attributed to long-range concentration fluctuations, gradually appears. The angular and concentration dependencies of the diffusion coefficient of the slow mode indicate the existence of strong intermolecular interactions.     

Thermo- and pH-sensitivity of aqueous poly(N-vinylpyrrolidone) solutions in the presence of organic acids

The phase transition in poly(N-vinylpyrrolidone) (PVP) aqueous solutions is shown to occur at heating upon addition of organic acids such as isobutyric, isovaleric, and, especially, trichloroacetic (TCA) ones. The cloud point temperature (T_c) of PVP solutions drops from 70 to 6 °C when the TCA concentration rises from 0.2 to 0.3 mol/l. A decrease in T_c is even more drastic when HCl is also added though HCl addition to the system without TCA does not result in phase separation. These phenomena are explained by the reversible coordination between the non-ionized form of TCA and PVP units via hydrogen bonding. An increase in the medium acidity depresses TCA dissociation, resulting in an increase in PVP-TCA associate concentration. Calculations based on the pK_a values of TCA confirm this suggestion. The similar behavior is observed with poly(N-vinylcaprolactam) systems. The amount of TCA bound to PVP has been determined by means of separation of the precipitate by centrifugation at temperatures above T_c and subsequent titration of TCA in the polymer with NaOH. It is shown that the precipitate contains one TCA molecule per 3-6 VP units, this value decreasing down to 1.25-2 upon HCl addition to the system.     

Thermosensitive and ampholytic hydrogels for salt solution

A series of N‐isopropylacrylamide/[[3‐(methacryloylamino)propyl]dimethy(3‐sulfopropyl)ammonium hydroxide] (NIPAAm/MPSA) copolymer hydrogels were prepared with various compositions. Swelling of the hydrogels in water, aqueous NaCl, KCl, CaCl₂, and MgCl₂ solutions was studied. NIPAAm/MPSA hydrogels have a higher degree of swelling in water and salt solutions than that of poly(N‐isopropylacrylamide) (PNIPAAm). Also, NIPAAm/MPSA hydrogels are more salt resistant when deswelling in salt solutions. For <7 mol % MPSA, the formed hydrogels retain both temperature reversibility and high swelling. A higher content of MPSA (>11 mol %) leads to better salt resistance but a decrease in thermosensitivity. The swelling of NIPAAm/MPSA hydrogel in 0.05M NaCl is non‐Fickian. In NaCl and KCl aqueous solutions, the zwitterionic hydrogels do not show obvious antipolyelectrolyte swelling behavior, whereas in divalent salt CaCl₂ and MgCl₂ solutions, the swelling ability of NIPAAm/MPSA hydrogels is enhanced at low salt concentration, then decreases with further increase in salt concentration. The lower critical solution temperatures of NIPAAm/MPSA hydrogels are also affected by concentrated salt solution. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2032–2037, 2003     

Effect of Bis-(2-ethylhexyl)Phosphoric Acid on Sodium Bis-(2-ethylhexyl)Phosphate Microemulsion for Selective Extraction of Non-Ferrous Metals

The effect of bis-(2-ethylhexyl)phosphoric acid (DEHPA) on the region of existence, conductivity and structure of sodium bis-(2-ethylhexyl)phosphate (NaDEHP) microemulsion has a dual nature and depends on DEHPA concentration. In the system NaDEHP–DEHPA–kerosene–water, the narrowing of the microemulsion region is observed with DEHPA concentration in the organic phase growth from 0.1 to 0.5 mol/L. The increase of DEHPA concentration in the organic phase from 0.1 to 0.4 mol/L leads to the reduction of electrical conductivity of the microemulsions. Based on the conductivity and viscosity measurements, we suppose the transition from reverse microemulsion with isolated droplets to percolate microemulsion at volume fraction of water 0.18 ( \(W = C_{{H_{2} O}} /C_{\text{NaDEHP}}\)  = 8). Droplet size of the microemulsions increases linearly with W growth. The rise of DEHPA concentration in the organic phase from 0.1 to 0.3 mol/L causes the growth of the coefficient at W in the equation d = kW + b from 0.038 to 0.249, i.e., it increases the slope of the lines. In contrast, DEHPA introduction at the concentration 0.1 mol/L (in the organic phase) leads to the expansion of the microemulsion region, does not affect the conductivity and decreases the coefficient at W. The rate of copper recovery into the microemulsion increases considerably with the rise of DEHPA concentration from 0.0 to 0.3 mol/L; no dual effect is observed. The following composition of the microemulsion for non-ferrous metals leaching is recommended: C _NaDEHP = 1.6 mol/L, C _DEHPA = 0.3 mol/L (in the organic phase); W = 8–32.     

Conductivity of highly concentrated aqueous electrolyte solutions III: H2O+NH4NO3+RbNO3 system

Conductivity of H₂O+NH₄NO₃+RbNO₃ system containing up to 5.15 stoichiometric mol percent of RbNO₃ and water/ammonium nitrate mol ratio varying between 1 and 6 have been measured at temperatures ranging between 275–345 K. At all compositions, variation of conductivity with temperature deviated slightly from Arrhenius behaviour. Conductivity-composition isotherms pass through a maximum at c0.18 mol fraction of electrolyte concentration; these have been discussed using the free volume model, cooperative rearrangement theory and environmental relaxation model of liquid transport.     

The effect of morphotropic phase boundary on dielectric properties of Bi0.5Na0.5Ti1−xZrxO3 solid solutions

Lead-free bismuth sodium titanate zirconate (Bi_0.5Na_0.5Ti_1?xZr_xO₃ or BNTZ) solid solutions with varied composition of x=0.50, 0.55, 0.58, 0.60, 0.63, 0.65, 0.68, 0.70, 0.73, 0.75 and 0.78 mol fraction were obtained using a conventional mixed-oxide method. XRD analysis indicated that the increase in concentration of Zr led to compositions across morphotropic phase boundary region. A quantitative structural investigation was carried out using the X-ray powder diffraction data. The rhombohedral phase was found to dominate for x<0.68 with space group R3c. In the morphotropic phase boundary (MPB) region i.e. 0.68≤x≤0.75, it was demonstrated that coexistence of rhombohedral and orthorhombic phase was observed. For x=0.78, the phase was completely orthorhombic with space group Pmna. Furthermore, the dielectric properties showed some enhanced activity of dipole movement at MPB boundaries which supported the presence of MPB region in this material system.     

Direct electrochemistry of Cytochrome c on natural nano-attapulgite clay modified electrode and its electrocatalytic reduction for H2O2

Natural nano-structural attapulgite clay was purified by mechanical stirring with the aid of ultrasonic wave and its structure and morphology was investigated by XRD and transmission electron microscopy (TEM). Cytochrome c was immobilized on attapulgite modified glassy carbon electrode. The interaction between Cytochrome c and attapulgite clay was examined by using UV-vis spectroscopy and electrochemical methods. The direct electron transfer of the immobilized Cytochrome c exhibited a pair of redox peaks with formal potential (E0′) of about 17 mV (versus SCE) in 0.1 mol/L, pH 7.0, PBS. The electrode reaction showed a surface-controlled process with the apparent heterogeneous electron transfer rate constant (k_s) of 7.05 s⁻¹ and charge-transfer coefficient (α) of 0.49. Cytochrome c immobilized on the attapulgite modified electrode exhibits a remarkable electrocatalytic activity for the reduction of hydrogen peroxide (H₂O₂). The calculated apparent Michaelis-Menten constant was 470 μmol/L, indicating a high catalytic activity of Cytochrome c immobilized on attapulgite modified electrode to the reduction of H₂O₂. Based on these, a third generation of reagentless biosensor can be constructed for the determination of H₂O₂.     

Rheological studies of hyaluronan solutions based on the scaling law and constitutive models

We have investigated the scaling relationship between rheological behavior and concentration for both salt-free and saline solutions of hyaluronan (HA), and adopted three viscoelastic constitutive models to predict the linear/non-linear viscoelastic behavior of these aqueous solutions of HA with different molecular weights at different concentrations up to 20 mg/ml. A series of concentration equations are obtained to describe the influence of HA concentration on solution viscosity. Corresponding to dilute and semi-dilute concentration region, salt-free HA solutions have scaling relationship between specific viscosity and HA concentration as η_sp ∼ c^1.0 and η_sp ∼ c^3.5, respectively, while for 0.15 M NaCl HA solutions, the scaling exponents are 1.5 and 4.2, respectively. Simulation results indicate that these constitutive models have good applicability to describe quantitatively the rheological properties of HA entangled solutions under either dynamic or steady shear flow. In addition, the plateau modulus scaling of HA solutions can be well described by the concentration-dependent length scale.     

The use of organic acids as precipitants for metal recovery from galvanic solutions

The abundance of metal ions in galvanic waste solutions enables these solutions to be used for recovery of metals as well as complexing agents such as citrate and tartrate. The addition of oxalic acid to solutions containing complexing agents precipitates pure metal oxalate or mixtures of metal oxalate and tartrate or citrate, the product depending on pH and concentration of components. The addition of oxalic acid to the rinsing bath after electroplating precipitates the most of the metals such as Cu(II), Zn(II) and Pb(II). ©1997 SCI     

Piezoelectric and mechanical properties of CaO reinforced porous PZT ceramics with one-dimensional pore channels

The formation of capillaries in sodium alginate gels is a dissipative process driven by unidirectional diffusion of divalent cations into sodium alginate sols. In the present work, we have prepared 3-1 type porous lead zirconate titanate (PZT) ceramics with oxides (CaO) being doped on a molecular level from the dissipative process by incorporating PZT particles into the sodium alginate gel matrix. By varying the concentration of cation solutions (CaCl₂) from 0.5 mol/L to 2.5 mol/L, both the microstructure, doping amount of oxides (CaO) and crystalline phase of the porous PZT ceramics were tailored. Accordingly, increase in the concentration of Ca²⁺ has led to a reduction in the relative permittivity (ε_r) first, and then an increase, while the piezoelectric coefficient (d₃₃ and d₃₁) demonstrated an opposite variation tendency. The prepared samples possessed a maximal HFOM value of 4755×10^–15 Pa⁻¹ when the concentration of Ca²⁺ was 1.0 mol/L. Addition of CaO was found to improve the compressive strength of porous PZT ceramics, which was preferential to promoting the stability and reliability for application.