SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Suitability of activated alumina for removal of hexavalent chromium from electroplating wastewater has been investigated. Activated alumina exhibited good sorption capacity for hexavalent chromium and pH has no pronounced effect on the sorption capacity. Both batch and column adsorption studies have been carried out and an adsorption column design indicated reasonable depth of column for practical application.
A clinical technique is presented that allows practitioners to use adhesive bonding techniques to improve the retention and seal of gold castings. At the time of delivery of a gold casting, the preparation is treated with a self-curing enamel and dentinal bonding agent. The internal surface of the casting is sandblasted and electroplated with tin to produce a surface suitable for bonding with a resin cement, which is virtually insoluble and is adhesive to both the metal surface and the treated tooth.
This paper presents the technical background and research relevant to the electroplating technique. Electroforming is a process whereby a metallized layer is applied to an object via a chemical process referred to as electrolysis. Electrodeposition of dental elastomeric impressions enables a metallized die to be fabricated. Different die materials and techniques exist for the fabrication of dental prostheses via the indirect technique. Electrodeposition of elastomeric impressions offers many advantages, provided an understanding and application of principles is adhered to.
A method is described for analysis of nickel in urine, which involves dilution of urine with dilute nitric acid and direct quantitation of nickel by electrothermal atomic absorption spectrophotometry with Zeeman background correction. The detection limit for nickel is 0.5 micrograms per L of urine; the coefficient of variation of replicate determinations is 4 to 5 percent (within-run) and 6 percent (run-to-run). Recovery of nickel added to urine (20 micrograms per L) averages 99 +/- 5 percent (mean +/- SD). Analytical results agree closely with measurements by the International Union of Pure and Applied Chemistry (IUPAC) reference procedure (correlation coefficient = 0.99). Nickel concentrations in urine specimens from 34 non-exposed, healthy, adult persons living in Connecticut average 2.0 +/- 1.5 microgram per L (range = 0.5 to 6.0 micrograms per L). Urine nickel concentrations are directly correlated with urine creatinine concentrations and specific gravity measurements. Elevated concentrations of nickel are observed in urine specimens from nickel-exposed workers, including nickel electroplating workers (mean = 27 micrograms per L, range = 3.1 to 82 micrograms per L, N = 19) and nickel battery workers (mean = 32 micrograms per L, range = 2.8 to 103 micrograms per L, N = 7). This method is more rapid and convenient than previous techniques and is suitable for routine use in clinical and industrial laboratories.
Chromizing improves physicochemical and mechanical properties of carbon steels. In some instances, for the treatment of medical pieces made of carbon steels chromizing is advisable rather than electroplating and chemical-conversion plating as well as the use of stainless steels.
A new way to obtain in a replica vast pictures of membranes situated at the same level in the preparation is described. The tissue specimen is flattened during fixation with a given orientation. It can be fractured afterwards, either along the plane of fixation or, after rotation, perpendicular to this plane. The method utilizes standard freeze-fracture equipment and readily available materials. This approach has a large range of potential applications, especially with tissues displaying a layered organization such as epithelia, nervous system, etc. It was found very appropriate for studying pre- and postsynaptic membranes in the Torpedo electric organ, to reveal specific junctions between cells in organotypic cultures, and to examine photoreceptors and other layers of the mammalian retina. In those tissues we obtained in a fairly reproducible manner freeze fractures at the desired level and orientation. With Torpedo synapses, vast pictures of the nerve terminals were performed in a plane quasi-parallel to the membrane postsynaptic cells (electroplates). Using double or triple flatten-peeled, it has also been possible to render the whole tissue specimen thin enough to perform gold label fracture [Pinto da Silva and Kan (1984), J. Cell Biol., 99:1156-1161].
Telescopic retainers with conical ceramic abutment crowns and electroplated gold copings define a new retainer for removable dentures exhibiting favorable tribological properties that could offer clinical advantages. The objective of this study was to evaluate the clinical effects of this retainer. To do so, a novel treatment modality was developed based on intraoral bonding of the copings to the framework in order to be able to realize, in a clinical setting, the retainer function based on a precision fit. A total of 32 patients wearing 33 dentures (16 mandibular, 17 maxillary; period of risk [months]: minimum = 3; maximum = 58; mean = 27.6), supported by 147 abutments (83 natural teeth, 64 implants) with ceramic abutment crowns (IPS Empress 1, IPS Empress 2, InCeram, Procera, CerAdapt; CeraBase) were followed at 6-month intervals. The ceramic abutment crowns showed low plaque accumulation (mean PI = 17.3%). The gingival tissues around natural abutments were generally free of inflammation; so was the mucosa around the implants (mean SBI = 4.9%). Denture adhesion and occlusion did not change, and there were no rocking movements. The mobility (as determined by Periotest) of 29 teeth was reduced in a highly significant manner within 6 months (t test, p < 0.001). Osseointegration was preserved for all implants. One abutment loosened. Six Empress 1 ceramic copings failed (94.6% Kaplan-Meier survival rate), and one abutment tooth was lost (99.2% survival rate). All patients reported problem-free handling, no rocking movements, and constant adhesion. The adhesive strength of one denture was too low at insertion. 94% of the patients experienced no problems with oral hygiene. The retainer examined has relevant clinical advantages and meets geriatric requirements for removable dentures.
BACKGROUND: After exposure to mercury vapor at three consecutive 10-month intervals, an electrician in an electroplating plant had flare-ups of ulcerative colitis within 24 hr, that subsided in several days, then returned upon re-exposure 10 months later. METHODS: The patient and his workplace were both evaluated for mercury exposure. In addition to workplace inspection, both personal and area monitoring for environmental mercury was performed, using both multiple mercury diffusion badges and direct (instantaneous) readings, during maintenance of mercury-filled electrical blocks. RESULTS: Eight-hour time weighted average (TWA) mercury vapor exposure was measured at 0.41 mg/m3 (ACGIH and NIOSH recommended TWA = 0.025 mg/m3; OSHA permissible exposure limit -0.1 mg/m3) for 5 years since stopping overexposure to mercury, the patient remained symptom free in clinical remission. CONCLUSIONS: In a patient with chronic ulcerative colitis in remission, occupational exposure to mercury vapor led to episodes of disease reactivation.
A dark green, viscous liquid can be formed by mixing choline chloride with chromium(III) chloride hexahydrate and the physical properties are characteristic of an ionic liquid. The eutectic composition is found to be 1:2 choline chloride/chromium chloride. The viscosity and conductivity are measured as a function of temperature and composition and explained in terms of the ion size and liquid void volume. The electrochemical response of the ionic liquid is also characterised and it is shown that chromium can be electrodeposited efficiently to yield a crack-free deposit. This approach could circumvent the use of chromic acid for chromium electroplating, which would be a major environmental benefit. This method of using hydrated metal salts to form ionic liquids is shown to be valid for a variety of other salt mixtures with choline chloride.
For disposable microfluidic devices, easy and inexpensive fabrication is essential. Consequently, replication of microfluidic devices, using injection molding or hot embossing, from a master-mold is widely used. However, the conventional master-mold fabrication technique is unsatisfactory in terms of time and costs. In this regard, direct Ni growth (electroplating) from a back plate is promising when the photoresist is well-defined. Here, we demonstrate the use of SU-8 as a photoresist to define the Ni-growth region. We accomplish this application by focusing on the adhesion, the sidewall profile, and the removal of SU-8: the adhesion is enhanced by controlling the exposure dose, the soft-baking time, and by choosing the adhesion-promoting layer; the sidewall profile is regulated by selecting the intensity of each exposed wavelength, showing an aspect ratio of up to 20.9; and, easy removal is achieved by choosing a proper photoresist-stripper. Using the master-mold fabricated by this method, we test the mechanical stability of the features according to the aspect ratio and length; in the hot embossing process, the features are stable in the aspect ratio of up to 5.8 at a length of 200 microm. In addition, the plastic devices fabricated from this method are applied to the passive stop valves, showing a capillary pressure (-0.2 to -7.2 kPa).
The reaction between liquid mercury and Ag3Sn was studied at room temperature using a new type of specimen; i.e. bulk Ag3Sn electroplated with mercury. The surface morphology of the specimen and the phases formed on the Ag3Sn substrate were investigated by various techniques including optical microscopy, electron (scanning) microscopy, electron microprobe analysis, and electron diffraction. It was found that the mode of formation and type of crystalline phase appearing on the Ag3Sn specimen depended on the amount of mercury available. When the amount of mercury exceeded a certain quantity (about 1 mg/cm2) only the gamma1 and gamma2 phases were formed. On the other hand, when the amount of mercury was reduced below a certain low value (less than 0.3 mg/cm2), another silver-mercury phase, beta1, formed as tiny "liquid-like" drops. The experimental technique employed in the present investigation has proved to be an excellent method for studying the reaction between liquid mercury and metal specimens. This new procedure may be employed to evaluate the amalgamation ability of potential new alloy systems.
The effects of corrosion on the major phases of dental amalgam microstructure have been studied in vitro on samples prepared by electroplating mercury on Ag3Sn. Tests were made in synthetic saliva, and samples were examined in a scanning electron microscope before and after the exposure. Simple immersion had little effect on the phases. Contact of amalgam with gold increased the probability of deterioation of the gamma2 phase. By anodic polarization beyond the breakdown potential, the gamma2 phase was selectively dissolved. Under conditions simulating a crevice, the gamma2 phase was dissolved and the gamma1 phase suffered morphological changes.
The effects of crevice corrosion on the major structural phases of a high copper dental amalgam were studied in vitro. Three kinds of samples were used: (1) amalgam prepared from a high copper, single composition alloy, (2) annealed ingots of the Ag3Sn and Cu3Sn phases, and (3) high copper, single composition alloy tablets electroplated with mercury. Specimens were examined in a scanning electron microscope before and after the exposure to a corrosion environment. The Ag3Sn and Cu3Sn phases were least affected by corrosion. The Ag-Hg-Sn phase (gamma1) slowly deteriorated, but the attack was nonuniform. The Cu6Sn5 phase exhibited good corrosion resistance, better than that of gamma1 phase. Particles of a tin rich phase of uncertain origin were observed on some of the samples after long exposures.
It has been shown previously that supplementing plastic intrauterine devices (IUDs) with copper wire enhances the antifertility effect of the device. The use of copper intrauterine contraceptive devices, however, is currently limited to two to three years, mainly because of wire fragmentation, which was observed as early as after eight months of use. In the resulting search for a long-lasting device, two new systems of duplex wire, with gold and platinum cores electrolytically coated with copper, were devised and studied. Initially, duplex wires and controls were exposed to physiological solution. Copper dissolution rate and corrosion morphology were studied by weight-loss measurements and optical metallography. Similar systems were then surgically implanted in rat uteri for varying periods of up to 26 weeks. Electron microanalysis of corrosion products, in addition to weight-loss measurements and metallography, was performed. The results showed that a uniform and ductile copper coating is obtainable by electroplating on gold and platinum wires. Rate of copper dissolution is similar to that of solid copper wire. No dissolution of gold and platinum in the controls or coated wires was detected by weight loss, metallography, or atomic absorption measurements. Microanalysis of the deposits and corrosion products on the wires in the uteri environment showed sulfur, chlorine, and calcium, in addition to copper. The results of this study suggest that supplementing IUDs with copper-coated gold or platinum wires may result in significant prolongation of the life span of the device by preventing uncontrolled loss of copper caused by wire fragmentation.
The occupational hazards and respiratory problems of workers associated with the chromium related industries like mining, electroplating and tanning have received much focus. Although the cytotoxic and mutagenic effects of common chromium(VI) compounds are now established, to the best of our knowledge, this is the first report of apoptosis (programmed cell death) caused by a set of Cr(III) complexes in human lymphocyte cells. The effects of five Cr(III) complexes with differing ligand environment and structure as well as K2Cr2O7 on Phytohaemagglutinin (PHA) induced lymphocyte cell proliferation have been investigated. Two of the Cr(III) complexes and K2Cr2O7 are found to cause apoptosis of lymphocytes but not the others. A case for the importance of species specific effects rather than non specific metal oxidation state dependent processes has now been made.
Improper disposal of hazardous wastes can lead to release of potentially harmful substances through leaching such as heavy metals, which ultimately contaminate soil, sediment surface water, and groundwater through runoff. To remove these toxic metals and avoid any adverse effect on the ecosystem, a novel approach involving calcium alginate (CA) beads containing humic acid (HA) was used. For this, 10% leachates of the waste obtained from two major industrial units with electroplating processess were prepared at neutral pH and analyzed by atomic absorption spectrophotometry (AAS). Both leachates contained Cd, Cu, Cr, Ni, Mn, Fe, and Zn. The concentrations of Ni, Mn, Fe, and Zn in the waste were found to be significant. The leachates analyzed were passed through columns packed with calcium alginate beads with or without humic acid. The concentrations of various metals in beads and in different fractions collected after adsorption were measured. Data recorded indicate that calcium alginate beads containing humic acids are more efficient in removal of all metals in substantial amounts from the two leachates. Along with removal of metals, this process led to considerable detoxification of the leachates as tested by Microtox assay, indicated by earlier protection and higher EC(50). The significance of the results in relation to removal of toxic metals by beads containing humic acid is discussed.
Discharge of Cr waste from many industrial applications such as leather tanning, textile production, electroplating, metallurgy, and petroleum refinery has led to large-scale contamination of land and water. Generally, Cr exists in two stable states: Cr(III) and Cr(VI). Cr(III) is not very soluble and is immobilized by precipitation as hydroxides. Cr(VI) is toxic, soluble, and easily transported to water resources. Cr(VI) undergoes rapid reduction to Cr(III), in the presence of organic sources or other reducing compounds as electron donors, to become precipitated as hydroxides. Cr(VI)-reducing microorganisms are ubiquitous in soil and water. A wide range of microorganisms, including bacteria, yeasts; and algae, with exceptional ability to reduce Cr(VI) to Cr(III) anaerobically and/or aerobically, have been isolated from Cr-contaminated and noncontaminated soils and water. Bioremediation approaches using the Cr(VI)-reducing ability of introduced (in bioreactors) or indigenous (augmented by supplements with organic amendments) microorganisms has been more successful for remediation of Cr-contaminated water than soils. Apart from enzymatic reduction, nonenzymatic reduction of Cr(VI) can also be common and widespread in the environment. For instance, biotic-abiotic coupling reactions involving the microbially formed products, H2S (the end product of sulfate reduction), Fe(II) [formed by Fe(III) reduction], and sulfite (formed during oxidation of elemental sulfur), can mediate the dissimilatory reduction of Cr(VI). Despite the dominant occurrence of enzymatic and nonenzymatic reduction of Cr(VI), natural attenuation of Cr(VI) is not taking place at a long-term contaminated site in South Australia, even 225 years after the last disposal of tannery waste. Evidence suggests that excess moisture conditions leading to saturation or flooded conditions promote the complete removal of Cr(VI) in soil samples from this contaminated site; but Cr(VI) reappears, probably because of oxidation of the Cr(III) by Mn oxides, with a subsequent shift to drying conditions in the soil. In such environments with low natural attenuation capacity resulting from reversible oxidation of Cr(III), bioeremediation of Cr(VI) can be a challenging task.
The ability of human subjects to discriminate plane metal plates of different thickness was measured using of forced-choice paradigm. The plates, made by electroplating a thin layer of copper onto flat brass shims, were gripped between the thumb and the index finger. Subjects were presented with either 2 standard plates (0.2 mm thick), or a standard plate and a test plate that was slightly thicker, and were required in state which alternative had occurred. When the edges of the plates could not be touched, a difference in thickness of about 0.075 mm could be discriminated. Surprisingly, when the edges were included in the grip, performance did not improve. All hypotheses of strategies used by the subjects required them to sense the angles of the finger joints with a precision of about 0.1 degrees.