Influence of boric acid on the electrochemical deposition of Ni

The electrolytic deposition of Ni onto a paraffin-impregnated graphite electrode from supporting chloride electrolyte (0.5 mol dm⁻³ NaCl) adjusted to the required pH using dilute HCl is investigated. The effect of electrolyte composition on the Ni electrodeposition is studied using linear sweep voltammetry in the cathodic region. An elimination voltammetry procedure was applied to evaluate the polarization curves. The aim of this work was to deduce the mechanism of Ni reduction in the chloride bath as well as the influence of boric acid on this. Positively-charged NiCl⁺ ions were found to be the electroactive particles in the Ni reduction mechanism. The strong competition between the NiCl⁺, Cl⁻ and H⁺ ions for active sites at the electrode is discussed. Kinetically-controlled adsorption/desorption processes of various species were also confirmed using elimination voltammetry with a linear scan. The evolution of gaseous hydrogen, catalyzed by the freshly-deposited Ni, accompanies the electrodeposition process. The presence of boric acid at a sufficiently high concentration inhibits the deposition of Ni and, at the same time, improves the morphology and brightness, as well as the adhesion of the deposited Ni. Elimination voltammetry with a linear scan is an efficient way to evaluate current–potential curves that reflect the electrodeposition of one-component Ni coatings. By eliminating selected currents, additional interesting and useful information can be obtained from voltammetric data.     

Dry deposition of elemental iodine on skin,hair, and clothing from air

Hairless rats, clothes, human hair, filter paper and water were exposed to gaseous elemental iodine in a glass chamber for 60–120 minutes. The deposition of gaseous elemental iodine on skin and lung of rats, human hair, water, clothes and paper were investigated by measuring iodine content in the exposed material by epithermal neutron activation analysis (ENAA). For measurement of the iodine concentration in the chamber air, elemental iodine in the air was collected by continuously sucking air through an active charcoal column. The trapped iodine in the active charcoal was then determined by ENAA. The measured deposition velocity in the test chamber of gaseous elemental iodine on skin, clothing, hair and water ranges from 0.006 on filter paper and water to about 0.05 cm/s on skin and clothes. The variation of elemental iodine concentration in air of the glass chamber was investigated by collecting and analyzing air samples at various time intervals. The results show that the variation with time in the concentration of the iodine can be described by an exponential function.     

Interrelations between hair content,intravenous dose and retention of Cd in different rat tissues

The Cd content in induced hair decreases with time between Cd injection and hair induction. This decline in Cd deposition in newly grown hair is faster than can be attributed to its decline in the plasma. Deposition in the ventrally-induced hair is consistently higher than in the dorsal site. In spontaneously growing “normal” hair, the Cd content is low at the beginning and remains practically unchanged until the end of the experiment. The bulk of Cd is taken up by the liver right after injection. During the experiment (93 d) Cd in the whole body, liver, brain, peripheral blood cells and plasma decreases at different rates, whereas Cd in the kidney increases. The lower dose of Cd (0.125 μg per rat) is handled by the organism in the same way as the higher one (12.500 μg per rat), i.e., the amounts of Cd found in corresponding samples of the two dose groups of hair, total body, tissues and blood are proportional to the doses administered. A direct relationship between the behaviour of Cd concentrations in hair and that of the Cd content of the total body, the tissues or plasma, could not be found. This work was done under a contract with the International Atomic Energy Agency, Vienna.     

Influence of surfactants on laser-induced copper deposition from solution

The influence of surfactants on the result of laser induced copper deposition from solution on the dielectric surface was studied. The dependences of the topology of the copper structures on the hydrophilic—lipophilic balance of non-ionogenic surfactants was found. The surface tension at the gas phase—solution interface was measured. The best results of laser deposition are obtained by the use of non-ionogenic surfactants with low values of hydrophilic—lipophilic balance.     

Uniform-sized silicone oil microemulsions: preparation, investigation of stability and deposition on hair surface

Emulsions are commonly used in foods, pharmaceuticals and home-personal-care products. For emulsion based products, it is highly desirable to control the droplet size distribution to improve storage stability, appearance and in-use property. We report preparation of uniform-sized silicone oil microemulsions with different droplets diameters (1.4-40.0 μm) using SPG membrane emulsification technique. These microemulsions were then added into model shampoos and conditioners to investigate the effects of size, uniformity, and storage stability on silicone oil deposition on hair surface. We observed much improved storage stability of uniform-sized microemulsions when the droplets diameter was ≤22.7 μm. The uniform-sized microemulsion of 40.0 μm was less stable but still more stable than non-uniform sized microemulsions prepared by conventional homogenizer. The results clearly indicated that uniform-sized droplets enhanced the deposition of silicone oil on hair and deposition increased with decreasing droplet size. Hair switches washed with small uniform-sized droplets had lower values of coefficient of friction compared with those washed with larger uniform and non-uniform droplets. Moreover the addition of alginate thickener in the shampoos and conditioners further enhanced the deposition of silicone oil on hair. The good correlation between silicone oil droplets stability, deposition on hair and resultant friction of hair support that droplet size and uniformity are important factors for controlling the stability and deposition property of emulsion based products such as shampoo and conditioner.     

Influence of the deposition method, temperature and deposition time on the corrosion inhibition of lead dodecanoate coatings deposited on lead surfaces

Electrochemical impedance measurements have been used to investigate the influence of the deposition method, including time and temperature, upon the corrosion inhibition characteristics of lead dodecanoate coatings on lead electrodes. The results were analysed using multivariate statistics and show that, in general, these easily prepared coatings are very protective against corrosion. The temperature proves to be an important parameter for the quality and the corrosion inhibition efficiency of the coating. A comparison between two different electrochemically assisted deposition methods, immersion using a reduction pretreatment and cyclic voltammetry, does not show significant differences. Using the immersion technique at room temperature, the deposition time was tested as the third influencing parameter for the corrosion inhibition efficiency of the deposited lead dodecanoate coatings. A longer deposition time of the lead into the sodium dodecanoate solution provides a layer with a somewhat higher corrosion resistance.     

Influence of Anionic Layer Structure of Fe-Oxyhydroxides on the Structure of Cd Surface Complexes

The nature of crystallographic reactive sites on the lepidocrocite (gammaFeOOH) surface has been determined by atomic force microscopy (AFM) and extended X-ray absorption fine structure (EXAFS) spectroscopy and compared to the surface bonding properties of goethite. To this end, the specific surface areas of lepidocrocite particles, and of their crystal faces, were calculated from the size and shape of individual particles determined by AFM, and the structure of Cd surface complexes was determined from Cd-Fe EXAFS distances. The combined results show that Cd forms solely mononuclear surface complexes, even at 100% surface coverage, and that hydrated Cd octahedra sorb on basal {010} and lateral {hk0}, {h0l} faces of lepidocrocite platelets by sharing edges with surface Fe octahedra. The absence, or scarcity, of corner-sharing linkage between Fe and Cd octahedra on the surface of lepidocrocite is in contrast to goethite (alphaFeOOH), where this type of complex is predominant. The explanation for the observed difference of Cd sorption mechanism on these two polymorphs lies not in the shape and relative surface area of their crystallographic faces, but in their different bulk structures and, specifically, in the stacking mode of anion layers (O(2-), OH(-)) which is hexagonal in alphaFeOOH and cubic in gammaFeOOH. This study demonstrates that the stacking mode of anions in the sorbent solid is a key factor in determining the structure of surface complexes on mineral surfaces. Copyright 2000 Academic Press.     

Cloud point preconcentration and flame atomic absorption spectrometric determination of Cd and Pb in human hair

Cloud point methodology has been successfully used for the preconcentration of trace amounts of Cd and Pb as a prior step to their determination by flame atomic absorption spectrometry. O,O-Diethyldithiophosphate and Triton X-114 are used as hydrophobic ligand and non-ionic surfactant, respectively. After phase separation at 40 °C based on cloud point of the mixture, the surfactant-rich phase is diluted with methanol. The enriched analyte in the final solution is determined by flame atomic absorption spectrometry using conventional nebulization. After optimization of the complexation and extraction conditions, enhancement factors of 22 and 43 were obtained for Cd and Pb, respectively. Under the experimental conditions used, preconcentration of only 10 ml of sample in the presence of 0.05% (v/v) Triton X-114 permitted the detection of 0.62 μg l⁻¹ of Cd and 2.86 μg l⁻¹of Pb. The proposed method was applied to the determination of Cd and Pb in human hair samples.     

Influence of polymeric additives on biomimetic silica deposition on patterned microstructures

Microstructured polymer films prepared by photochemical grafting of different polymers were used as restricted reaction areas in silica deposition experiments. Linear and branched poly(alkyleneimines) and poly(allylamine hydrochloride) in pure aqueous or phosphate-containing solutions were used as additives to silica precursor solutions. The silica deposits obtained by spin-coating these solutions onto microstructured polymer films were investigated by scanning electron microscopy and atomic force microscopy. Experiments with poly(alkylene imines) in the silica precursor solution show the deposition of smooth and granular silica structures that closely mimic the natural patterns. The structure formation can be explained by physicochemical processes. Hypotheses that have been made for the natural silification processes can be evaluated on this basis.     

Influence of substrate temperature on the stability of glasses prepared by vapor deposition

Physical vapor deposition of indomethacin (IMC) was used to prepare glasses with unusual thermodynamic and kinetic stability. By varying the substrate temperature during the deposition from 190 K to the glass transition temperature (Tg=315 K), it was determined that depositions near 0.85Tg (265 K) resulted in the most stable IMC glasses regardless of substrate. Differential scanning calorimetry of samples deposited at 265 K indicated that the enthalpy was 8 J/g less than the ordinary glass prepared by cooling the liquid, corresponding to a 20 K reduction in the fictive temperature. Deposition at 265 K also resulted in the greatest kinetic stability, as indicated by the highest onset temperature. The most stable vapor-deposited IMC glasses had thermodynamic stabilities equivalent to ordinary glasses aged at 295 K for 7 months. We attribute the creation of stable IMC glasses via vapor deposition to enhanced surface mobility. At substrate temperatures near 0.6Tg, this mobility is diminished or absent, resulting in low stability, vapor-deposited glasses.     

Influence of fused deposition modeling parameters on the mechanical properties of ABS parts

This work aims to determine the influence of fused deposition modeling (FDM) printing parameters on the mechanical properties of parts fabricated on an Ultimaker2 printer with acrylonitrile butadiene styrene (ABS). The effect of several parameters such as interlayer cooling time (ILCT), nozzle diameter, infill density, raster angle and layer thickness on the ultimate tensile strength, yield strength, and elastic modulus of produced parts was evaluated. Two independent studies were conducted: a first study dedicated to the ILCT and a second study where the influence of other parameters was evaluated through a design of experiments (DoE) approach. Both studies were carried out through the execution of standard tensile tests. The statistical analysis of tensile tests results was processed with the ANOVA methodology. The obtained results indicate that a reduced ILCT improves the tensile strength of parts. It is shown that nozzle diameter and infill density are the parameters that most influence the mechanical properties of ABS, with the upper range selected values improving the studied mechanical properties. The raster angle configuration of (?45^o/45^o) benefits UTS and yield strength of ABS samples. Interactions of nozzle diameter on layer thickness were detected. It was observed that smaller layer thickness promotes a higher elastic modulus and UTS; however, for thinner layers (0.06‐0.10 mm), no significant differences were found on strength of samples due to potential high distortion levels.     

Influence of solution chemistry on the deposition and detachment kinetics of RNA on silica surfaces

The deposition kinetics of RNA extracted from both virus and bacteria on silica surfaces were examined in both monovalent (NaCl) and divalent (CaCl(2)) solutions under a wide range of environmentally relevant ionic strength and pH conditions by utilizing a quartz crystal microbalance with dissipation (QCM-D). To better understand the RNA deposition mechanisms, QCM-D data were complemented by diffusion coefficients and zeta potentials of RNA as a function of examined solution chemistry conditions. Favorable deposition of RNA on poly-l-lysine-coated (positively charged) silica surfaces was governed by the convective-diffusive transport of RNA to the surfaces. The deposition kinetics of RNA on bare silica surfaces were controlled by classic Derjaguin-Landau-Verwey-Overbeek (DLVO) interactions. The presence of divalent cations (Ca(2+)) in solutions greatly enhanced the deposition kinetics of RNA on silica surfaces. Solution pH also affected the deposition behavior of RNA on silica surfaces. Release experiments showed that detachment of RNA from silica surfaces was significant in NaCl solutions, whereas, the deposited RNA on silica surfaces in CaCl(2) solutions was more likely to be irreversible.     

The single crystal metal-non-aqueous solvent interface: Underpotential deposition of Cd on Ag (111) in propylene carbonate

The underpotential deposition of cadmium on Ag (111) in propylene carbonate using either lithium perchlorate or tetra-n-butylammonium perchlorate as supporting electrolytes has been found to yield sharp and well defined voltammetric peaks. The results obtained in aqueous LiClO₄ and tetraethylammonium perchlorate solutions for the same UPD-host metal system were, however, found to be different from those in propylene carbonate, particularly in the case of LiClO₄ for which the voltammetry was characterized by broad and ill-defined features. This novel solvent-induced effect has been attributed to differences in the extent of specific adsorption of the perchlorate anion in water and PC and/or to solvent-metal substrate interactions.     

Influence of the size of the formed cycle on the reactivity of free radicals in cyclization reactions

Numerous experimental data for the cyclization of free radicals C·H₂(CH₂)_nCH=CH₂ cyclo-[(CH₂)_n+1CH(C·H₂)], and C·H₂(CH₂)_nCH=CHR cyclo-[(CH₂)_n+1C·HCHR] were analyzed in the framework of the parabolic model. The activation energy of thermoneutral (H _e = 0) cyclization E _e0 decreases linearly with an increase in the energy of cycle strain E _rsc: E _e0(n) (kJ mol–1) = 85.5 – 0.44E _rsc(n) (n is the number of atoms in the cycle). The activation entropy of cyclization S ^# also depends on the cycle size: the larger the cycle, the lower S ^#. A linear dependence of S ^# on the difference between the entropies of formation S° of cyclic hydrocarbon and the corresponding paraffin was found: S ^# = 1.00[S°(cycle) – S°(C_nH_2n+2)]. The E _e0 values coincide for cyclization reactions with the formation of the six-membered cycle and the bimolecular addition of alkyl radicals to olefins.     

Influence of the curing cycle selection on the thermal degradation of an epoxy-diamine system

Summary Polymers have a great interest for the study and design of new materials. Among these materials are epoxy resins, that have good properties, such as low shrinkage during cure, good adhesion, high water and chemical resistance, etc. They have also fast and easy cure in a broad range of temperatures. TTT diagrams are very helpful to design new epoxy materials as they allow the search for very important final properties, such as thermal stability, conversion or glass transition temperature of a material cured through a selected curing cycle. In this work the dependence of the thermal stability on the selected curing cycle for a DGEBA/1,2 DCH system was studied.     

Influence of hydrocarbon gasses on PECVD a-C:H film deposition

Hydrogenated amorphous carbon layers (a-C:H) deposited at near room temperature by CH₄ and C₂H₂-Ar rf discharges have been studied. Discharge processes were investigated using growth kinetics and optical emission spectroscopy (OES). The role of plasma chemistry and of ion bombardment is discussed. Addition of argon, necessary to stabilize the C₂H₂ discharge, is found to enhance susbstantially gas phase processes such as dissociation, formation of atomic hydrogen and of CH, C₂, C₃ species (revealed by OES). It appears that rf plasma is very efficient for dissociation and ionization processes with threshold energies in the ten eV range. The layers' properties have been characterized by means of UV-Visible absorption, Fourier transform IR and Raman spectroscopies.     

Coke deposition on naphtha reforming catalysts: I. Influence of the hydrocarbon feed

During hydrocarbons reactions over Pt/Al₂O₃ the catalyst is covered by coke. It is accepted that coke formation occurs on metal and acid sites. During normal heptane and methylcyclopentane reforming it was found that the nature and the rate of coke deposited on the catalyst surface was not same, depending on the structure of the hydrocarbon feed.

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Influence of surfactant counterions during electrophoretic particle deposition

This study demonstrates the influence of a cationic surfactant on colloidal particle electrodeposition (migration and adhesion). Three cetyltrimethylammonium salts (CTA+) with various counterions (bromide, chloride, and hydrogenosulphate) were studied. Particle transport toward the electrode was driven by the electrophoretic force. Once particles reached the electrode, a wide variety of behaviors were observed, depending on surfactant concentration and counterions: particles would stick permanently or slide along the electrode surface, remain or detach upon potential switching, act as nuclei for aggregate growth, or produce a homogeneous particle film. The experimental results also demonstrate the specific influence of surfactant counterions on the deposited film morphology.