Zinc Disc Research Articles

Microbially influenced corrosion of galvanized steel pipes in aerobic water systems

To investigate the role of heterotrophic bacteria in the corrosion of galvanized steel in the presence of water. Samples were taken from corroding galvanized steel pipes conveying water for specialist applications, and heterotrophic bacteria were isolated and cultured. The majority of bacteria were Gram-negative aerobes and included Pseudomonas sp., Bacillus pumilus, Afipia spp. and Blastobacter denitrificans/Bradyrhizobium japonicum. Zinc tolerance was assessed through growth and zinc disc diffusion experiments. In general, zinc negatively influenced growth rates. An unidentified yeast also isolated from the system demonstrated a high tolerance to zinc at concentrations up to 4 g l(-1) . Coupon experiments were performed to assess corrosion by the bacteria on galvanized steel and steel coupons. The majority of isolates as pure culture biofilms (69%) accelerated corrosion of galvanized coupons, assessed as zinc release, relative to sterile control coupons (P < 0·05). Pure culture biofilms did not increase the corrosion of steel, with four isolates demonstrating protective effects. Pure culture biofilms of heterotrophic bacteria isolated from a corroding galvanized pipe system were found to accelerate the corrosion of galvanized steel coupons. Microbially influenced corrosion is a potential contributor to sporadically occurring failures in galvanized steel systems containing water. Management strategies should consider microbial control as a means for corrosion prevention in these systems.

Intensification of the rate of heavy metal removal from wastewater by cementation in a jet reactor

Removal of copper by cementation on zinc disc from dilute copper sulfate solution in a recirculating batch reactor which consisted of a horizontal zinc disc impinged by an axial turbulent submerged jet was studied. The effect of different parameters such as, initial copper ion concentration, solution flow rate and the axial distance between the zinc disk and submerged jet on the rate of copper ion removal were investigated. The rate of cementation was found to increase with increasing solution flow rate, decreasing the axial distance between jet and zinc disc, and by increasing copper ion concentration. The rate of diffusion controlled cementation of copper ion was expressed in terms of the mass transfer coefficient, the data were correlated with the following dimensionless correlation: Sh = 0.306 S c 0.33 Re 0.997 ( d n / l ) 0.0337 . The high rate of mass transfer of the jet reactor, qualifies the reactor for diffusion controlled heavy metals removal from wastewater.

Antiurolithiatic activity of aqueous extract of bark of moringa oleifera (lam.) in rats

In the present study, aqueous extract of bark of Moringa oleifera administered orally, was eva- luated for its antiurolithiatic potential in albino rats of Wistar strains. The stones were produced in this study by zinc disc foreign body insertion in the bladder supplemented with 1% ethylene glycol in drinking water. The reduction in weight of the stones was used as criteria for assessing the preventive or curative antiurolithiatic effect of the bark of this plant. Two doses of extract for prophylactic and curative groups were used. In both groups the oral administration of the extract of bark of Moringa oleifera has resulted in significant reduction in the weight of bladder stones compared to the control group.

Are New-Generation Bisphosphonates Effective for the Inhibition of Calcium Oxalate Stone Formation in a Rat Model?

Background: The effects of bisphosphonates on prophylaxis of stone formation are unclear. We evaluated the outcome of two new-generation bisphosphonates in a lithogenic rat model. Methods: 36 male rats were divided into three groups of 12 animals each. Both calcium and creatinine levels of plasma and urine were measured. Zinc discs of about 40 mg each were surgically placed into the bladder. The first group received no treatment and the second and third groups were treated with an intraperitoneal injection of weekly clodronate (20 mg/kg) and zoledronic acid (7.5 µg/kg), respectively. At the end of the 8th week, the weight increase in discs and biochemical changes were analyzed comparatively. Results: The mean weight of discs in the control, clodronate and zoledronic acid groups was 109.65 ± 80.97, 79.82 ± 17.99 and 72.91 ± 19.29 mg, respectively (p > 0.05). The percentage increase in weight of discs was 164% for control, 90% for clodronate and 71% for the zoledronic acid group. The increase of urinary calcium level in the zoledronic acid group was lower than the others (p < 0.05). Conclusions:When considering the percentage increase in weight of discs, the difference between control and bisphosphonate groups support the idea that these drugs may have a preventive role in stone formation.

Effects of low-molecular-weight polyguluronate sulfate on experimental urolithiasis in rats

Urinary macromolecules, especially glycosaminoglycans (GAGs), have attracted great interest as promising inhibitors of urinary stone formation. As an analogue of GAGs, low-molecular-weight polyguluronate sulfate (LPGS) with strong polyanionic nature was prepared by chemical modification of brown algae extract. The effects of LPGS both on ethylene glycol-induced nephrolithiasis and Zinc disc implant-induced urinary bladder stone formation in Wistar rats were evaluated, and its acute toxicity in Kunming mice and Wistar rats were also investigated. The contents of renal oxalate and calcium in ethylene glycol-induced nephrolithiasic rats were decreased significantly from 5.01 +/- 0.96 to 3.26 +/- 1.31 mumol/g kidney (P < 0.01) and 20.11 +/- 4.60 to 11.83 +/- 3.54 mumol/g kidney (P < 0.01), respectively, after oral administration of LPGS at dose-level of 100 mg/kg. The renal crystal depositions and histopathological changes were reduced also. The formation of zinc disc implant-induced urinary bladder stones in rats was inhibited considerably after oral administration of LPGS at dose-levels of 50 mg/kg (P < 0.05) and 100 mg/kg (P < 0.01). The intravenous LD(50) and the oral maximum tolerance value of LPGS in mice are 6.29 and 25 g/kg, and in rats are 2.25 and 10 g/kg, respectively. These data show that LPGS has significant prevention effects both on nephrolithiasis and urinary bladder stone formation in rats, and negligible oral toxicity both in mice and rats. LPGS is a safe and promising drug candidate for the prevention of urolithiasis.

The acid–base properties of the surface of native zinc oxide layers: An XPS study of adsorption of 1,2-diaminoethane

The acid–base properties of native zinc oxide surfaces have been studied using X-ray photoelectron spectroscopy (XPS). The native layers of zinc oxide have been obtained by ageing mechanically polished pure zinc disks in a glass dryer for 1 month. Such a treatment lead to the formation of an unstable oxide layer and dehydroxylation has been observed during storage in vacuum. By following adsorption in ultrahigh vacuum of 1,2-diaminoethane (DAE) several types of active sites have been evidenced. Zinc cations react with the probe molecule following a Lewis acid/base interaction, while the hydroxyl and the carbonate-like species react following a Brønsted acid/base reaction. Although initial interaction via the Brønsted-like mechanisms is favoured, it has been shown that the resulting complexes are not stable. Under vacuum conditions, the adsorbed DAE molecules either partly desorb or modify their interaction mode with the surface to form additional Lewis-like bonded stable complexes. In addition, a cleaning effect of the molecule has been observed which lead to partial removal of the carbonate-like contamination.

Mass transfer correlation of removal of nickel by cementation onto rotating zinc disc in industrial zinc sulfate solutions

A rotating zinc disc was used to study the cementation of nickel from an industrial acidic solution of zinc sulfate. The reduction of nickel was evaluated for a wide concentration range of initial nickel concentration, electrode rotation speed and temperature. The rate of cementation giving the product ka e of the local mass transfer coefficient k and the effective surface area a e was analyzed and expressed in terms of the rate of mass transfer versus the apparent mass transfer coefficient and correlated by a controlling numbers relationship. An estimation, by two methods, of the surface roughness variation caused by the nickel deposit was presented.

Fabrication and characteristics of the low-resistive p-type ZnO thin films by DC reactive magnetron sputtering

ZnO thin films were deposited onto glass substrates by DC reactive magnetron sputtering using pure zinc disk as sputtering target and Ar–N2–O2 mixture as sputtering gas. The influence of N2-to-O2 ratio as well as annealing treatment on the structural and electrical characteristics of the films was studied. By optimizing the N2-to-O2 ratio, low-resistive p-type ZnO thin films were obtained. The film prepared at N2-to-O2 ratio of 20:10 and annealed at 450 °C for 3 h has the lowest resistivity (8.34 Ω cm) and the highest hole concentration (7.47×1018 cm−3).

Fundamental considerations on the mechanisms of silver cementation onto zinc particles in the Merril–Crowe process

Studies on the Merrill–Crowe process as applied to silver recovery have shown that one half of the used zinc powder is wasted in water reduction at high cyanide concentrations, while the other half reduces silver ions from the cyanide solution. However, the cementation mechanisms as an electrochemical process taking place on the zinc surface do not explain the split of the electric current resulting from the anodic dissolution of zinc into two equal values. This study demonstrates that the mechanism for silver precipitation at high and low cyanide concentrations differs considerably. At low cyanide concentrations cementation is essentially an electrochemically-controlled process following a shrinking-core behavior. At high cyanide concentrations, the process seems not to be electrochemically controlled. The areas for zinc dissolution and silver deposition are not connected by an electrical-conducting medium and reduction of silver–cyano complex ions takes place by hydrogen adsorbed onto silver growing outward from the cementing zinc particles. The results are based on scanning electron microscopy of solids recovered from cementations in stirred reactors and in situ observations by optical microscopy of the cementation process on the edge of thin zinc disks in cyanide solutions.

Recovery of copper from industrial waste solution by cementation on reciprocating horizontal perforated zinc disc

Rates of Cu ++ removal from waste solutions by cementation on a perforated reciprocating zinc disc were studied under different conditions of frequency and amplitude of oscillation. Disc pulsation was found to increase the rate of cementation by a factor ranging from 2.8 to 5.5 compared to cementation on stagnant disc, initial Cu ++ concentration, temperature, disc diameter and hole diameter. The effect of temperature was found to fit Arrhenius equation with an activation energy of 2.95 kcal/mole which confirms the diffusion controlled nature of the reaction. Mass transfer study of the process has revealed that the data fit the dimensionless equation Sh = 89 Sc 0.33.Re 0.537(d/d h ) −O.496. The importance of using the above equation in the design and operation of high productivity cementation reactor was pointed out.

The spatial distribution of Zn 2+ during galvanic corrosion of a Zn/steel couple

The spatial distribution of Zn 2+ during galvanic corrosion of a model Zn/steel couple in 0.01 M NaCl was investigated using a scanning zinc disk electrode. The couple had a coplanar arrangement of a steel substrate with an electroplated zinc layer at the center. During galvanic corrosion, the marked changes in the Zn 2+ concentration were confined to a thin solution layer ca. 1.0 mm thick above the couple surface. In this thin solution layer above the zinc layer, a higher concentration region of Zn 2+ in the range of 5–18 mM extended around the zinc layer in the solution during galvanic corrosion. Conversely, above the steel surface distant from the zinc layer, the surface concentration of Zn 2+ was almost zero during galvanic corrosion. On this surface, the precipitation of zinc corrosion products due to the hydrolysis reaction of Zn 2+ was observed. The distribution of the Zn 2+ concentration supported that Zn 2+ acted as a buffer that suppressed the increased pH due to the cathodic reaction on the steel surface near the zinc layer and almost no corrosion products formed there. The spatial distribution of Zn 2+ is discussed in relation to the distributions of potential and pH and the surface morphology of the galvanic couple.

P-Type ZnO thin films prepared by oxidation of Zn 3N 2 thin films deposited by DC magnetron sputtering

p-Type ZnO thin films were prepared by oxidation of Zn 3N 2 thin films. The Zn 3N 2 thin films were deposited by reactive DC magnetron sputtering using pure zinc disk as target and Ar–N 2 mixture as working gas. For oxidation temperature between 350°C and 500°C, p-type ZnO thin films were obtained, with a hole concentration as high as 5.78×10 17 cm −3 at 500°C, but for oxidation temperature at 550°C, n-type ZnO film was obtained.

Antiurolithiatic Activity of Salix taxifolia Aqueous Extract

The aqueous extract of the bark of Salix taxifolia was tested for antilithiatic and diuretic activities. Urolithiasis was experimentally induced by implantation of a zinc disc in the urinary bladder of rats. A significant decrease in the weight of the stones was observed after treatment in animals with the aqueous extract. This extract caused an increase in the 24h urine volume.

Antiurolithiatic Activity of 7-Hydroxy-2′,4′,5′- Trimethoxyisoflavone and 7-Hydroxy-4′ -Methoxyisoflavone from Eysenhardtia polystachya

ABSTRACT The antilithiatic and diuretic activity of 7-hydroxy-2′,4′,5′-trimethoxyisoflavone and 7-hydroxy-4′-methoxyisoflavone, isolated in aqueous extracts of the heartwood of Eysenhardtia polystachya, was tested in rats by observing calculus formation (experimentally induced by implantation of a zinc disc in the urinary bladder) and urine production. A significant decrease in urinary stone size was observed in animals treated with the compounds as compared with animals in control groups. The compounds also increased 24 h urine volume in rats as compared with the control animals not receiving the test compounds.

The influence of tartrate on cobalt cementation on a rotating zinc disc in zinc sulphate

Basic cobalt salts redissolve more easily than Co alloys; this is the major reason for cobalt redissolution during the technical purification of the zinc sulphate electrolyte before zinc electrolysis. The electrolysis is performed using a very pure zinc sulphate solution. Co 2+ is a harmful impurity in the electrolyte, and is therefore usually removed by cementation. This cementation process is very slow. Cu 2+ and Sb 3+, which are used as cementation aids, are added as CuSO 4 and potassium–antimony–tartrate, KSbC 4O 6H 2·1.5H 2O, respectively. Laboratory scale experiments show that large amounts of tartrate in the solution reduce the cementation rate of Co 2+ significantly. Accumulation of tartrate may cause operational problems in a zinc plant.

Antiurolithiatic activity of Raphanus sativus aqueous extract on rats

The aqueous extract of the bark of Raphanus sativus was tested for its antiurolithiatic and diuretic activity. The urolithiasis was experimentally induced by implantation of zinc disc in the urinary bladder of rats. Significant decrease in the weight of stones was observed after treatment in animals which received aqueous extract in comparison with control groups. This extract showed an increase in the 24 h urine volume as compared to the control.

Evaluation of the antiurolithiatic activity of the extract of Costus spiralis Roscoe in rats

The antiurolithiatic activity of the water extract of Costus spiralis Roscoe was tested on formation of calculi on implants of calcium oxalate crystals or zinc disc in the urinary bladder of rats. The plant is a species from the family Zingiberaceae used in Brazilian folk medicine in urinary affections and for expelling urinary stones. Implantation of the foreign body in the urinary bladder of adult rats induced formation of urinary stones and hypertrophy of the smooth musculature. Oral treatment with the extract of Costus spiralis Roscoe (0.25 and 0.5 g/kg per day) after 4 weeks surgery reduced the growth of calculi, but it did not prevent hypertrophy of the organ smooth musculature. The contractile responses of isolated urinary bladder preparations to the muscarinic agonist bethanecol, in the presence and absence of the extract (0.3–3 mg/ml) or atropine (0.3–3 nM) did not differ among the experimental groups. The results indicate that the extract of Costus spiralis Roscoe is endowed with antiurolithiatic activity confirming thus folk information. The effect, however, was unrelated to increased diuresis or to a change of the muscarinic receptor affinity of the bladder smooth musculature to cholinergic ligands.

Isobutanol effect on the production rates of copper powder on rotating zinc disc

The rates of copper/zinc cementation reaction in isobutanol‐water mixture was measured at different temperatures using an atomic absorption spectrophotometer. The rate of cementation decreases with increasing the percentage composition of alcohol, and increases by increasing temperature and the rate of rotation. Thermodynamic parameters ΔH*, ΔG* and ΔS* were calculated.

Electrochemical study on copper cementation from cyanide liquors using zinc

A rotating-disc electrode system was used to study the half-cell reactions involved in the cementation of copper from cyanide liquors onto zinc. Using scanning voltammetry, the reduction of copper cyanide onto glassy carbon and copper discs and the oxidation of zinc from a zinc disc were evaluated at different conditions of solution pH, temperature and free cyanide concentration. Evans diagrams were constructed yielding mechanistic information and rate of the cementation process. Thermodynamic modelling of the copper cyanide system also predicts the electrochemical active species responsible for the reduction of copper cyanide as Cu(CN) 2 −. The study allows optimised conditions to be chosen for the selective recovery of gold from copper–gold cyanide mixture using zinc powder cementation.

Cementation of Ni2+ ions from acidic sulfate solutions onto a rotating zinc disc

During cementation of Ni 2+ ions onto a zinc electrode, the time-dependence of the concentration of Ni 2+ ions was studied by atomic absorption spectroscopy. The electrode surface was analyzed by S.E.M. and the surface area was measured by electrochemical impedance spectroscopy. The cementation is shown to be a first-order reaction which is diffusion-controlled. The reaction rate is strongly affected by the increase in the electrode surface area with increasing cementation time.