Silver sulfide

Hagege et al. [281] used a similar silver sulfide insertion technique in the study of aramid fibers. The fibers were treated according to the method described above and also by a method [179] using isoprene but excluding the staining. Sections examined in the TEM showed details of the void microstructure. The Leeds group (e.g., [282,283]) used the silver sulfide method to prepare new aramid fibers for TEM in order to evaluate the natiure of the microvoids and to determine their influence on the tensile and compressive behavior of the fibers  

Polymers that may be stained include esters and aromatic polyamides. 

Treat the specimen with gaseous hydrogen sulfide at a pressure of 1,380kPa at 20°C for 16 h wash in alcohol (see suppliers for safe handling methods). 

Embed the specimen in a low viscosity resin (e.g.. Spun- resin). 

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Motte L and Pileni M P 1998 Influenoe of length of alkyl ohain used to passivate silver sulfide nanopartioles on two-and three-dimensional self-organization J. Phys. Chem. B 102 4104... 

Acanthite, see Silver sulfide Alabandite, see Manganese sulfide Alamosite, see Lead(II) silicate(2—)... 

V. a term used to describe a voltage difference between one electrode and another VCDT. Vienna canyon diabolo troilite (actually silver sulfide used as a replacement standard for CDT [sulfur isotopes])... 

When heated to 100°C, silver oxide decomposes into its elements, and is completely decomposed above 300°C. Silver oxide and sulfur form silver sulfide. Silver oxide absorbs carbon dioxide from the air, forming silver carbonate. 

Silver Sulfide. Silver sulfide, Ag2S, forms as a finely divided black precipitate when solutions or suspensions of most silver salts are treated with an alkaline sulfide solution or hydrogen sulfide. Silver sulfide has a dimorphic crystal stmcture. Transition from the rhombic (acanthite) to the cubic (argentite) form occurs at 175°C. Both crystal stmctures are found in nature. 

Silver sulfide is one of the most insoluble salts known. It is not solubilized by nonoxidizing mineral acids, but it is soluble in concentrated nitric acid, concentrated sulfuric acid, and alkaline cyanide solutions. 

Silver and sulfur combine even in the cold to form silver sulfide. The tendency of silver to tarnish is an example of the ease with which silver and sulfur compounds react. PoHshes that contain silver complexing agents, such as chloride ion or thiourea, are used to remove silver tarnish. 

Silver sulfide is exceptionally stable in air and sunlight, but decomposes when heated to 810°C. Moss silver (filiform silver), consisting of long hair-like growths of pure silver, is formed when silver sulfide is heated for a prolonged period at elevated temperatures below 810°C. 

Silver Thiosulfate. Silver thiosulfate [23149-52-2], Ag 2 y is an insoluble precipitate formed when a soluble thiosulfate reacts with an excess of silver nitrate. In order to minimize the formation of silver sulfide, the silver ion can be complexed by haUdes before the addition of the thiosulfate solution. In the presence of excess thiosulfate, the very soluble Ag2(S203) 3 and Ag2(S203) 3 complexes form. These soluble thiosulfate complexes, which are very stable, are the basis of photographic fixers. Silver thiosulfate complexes are oxidized to form silver sulfide, sulfate, and elemental sulfur (see Thiosulfates). 

Cyanide Complexes. Insoluble silver cyanide, AgCN, is readily dissolved in an excess of alkah cyanide. The predominant silver species present in such solutions is Ag(CN) 2) with some Ag(CN) 3 and Ag(CN) 4. Virtually all silver salts, including the insoluble silver sulfide, dissolve in the presence of excess cyanide because the dissociation constant for the Ag(CN) 2 complex is only 4 x 10 (see Cyanides). 

Sulfur Complexes. Silver compounds other than sulfide dissolve in excess thiosulfate. Stable silver complexes are also formed with thiourea. Except for the cyanide complexes, these sulfur complexes of silver are the most stable. In photography, solutions of sodium or ammonium thiosulfate fixers are used to solubilize silver hahdes present in processed photographic emulsions. When insoluble silver thiosulfate is dissolved in excess thiosulfate, various silver complexes form. At low thiosulfate concentrations, the principal silver species is Ag2(S203) 2j high thiosulfate concentrations, species such as Ag2(S203) 3 are present. Silver sulfide dissolves in alkaline sulfide solutions to form complex ions such as Ag(S 2 Ag(HS) 4. These ions are... 

Silver compounds having anions that are inherently toxic, eg, silver arsenate and silver cyanide, can cause adverse health effects. The reported rat oral LD values for silver nitrate, silver arsenate [13510-44-6] and silver cyanide are 500—800 (29), 200—400 (29), and 123 mg/kg (30), respectively. Silver compounds or complexes ia which the silver ion is not biologically available, eg, silver sulfide and silver thiosulfate complexes, are considered to be without adverse health effects and essentially nontoxic. 

The impact that a silver compound has in water is a function of the free or weaMy complexed silver ion concentration generated by that compound, not the total silver concentration (3—5,27,40—42). In a standardized, acute aquatic bioassay, fathead minnows were exposed to various concentrations of silver compounds for a 96-h period and the concentration of total silver lethal to half of the exposed population (96-h LC q) deterrnined. For silver nitrate, the value obtained was 16 )-lg/L. For silver sulfide and silver thiosulfate complexes, the values were >240 and >280 mg/L, respectively, the highest concentrations tested (27). 

The chronic aquatic effects which relate silver speciation to adverse environmental effects were studied on rainbow trout eggs and fry. The maximum acceptable toxicant concentration (MATC) for silver nitrate, as total silver, was reported to be 90—170 ng/L (43). Using fathead minnow eggs and fry, the MATC, as total silver, for silver thiosulfate complexes was reported as 21—44 mg/L, and for silver sulfide as 11 mg/L, the maximum concentration tested (27). 

In secondary wastewater treatment plants receiving silver thiosulfate complexes, microorganisms convert this complex predominately to silver sulfide and some metallic silver (see Wastes, INDUSTRIAL). These silver species are substantially removed from the treatment plant effluent at the settling step (47,48). Any silver entering municipal secondary treatment plants tends to bind quickly to sulfide ions present in the system and precipitate into the treatment plant sludge (49). Thus, silver discharged to secondary wastewater treatment plants or into natural waters is not present as the free silver ion but rather as a complexed or insoluble species. 

Silver sulfide, when pure, conducts electricity like a metal of high specific resistance, yet it has a zero temperature coefficient. This metallic conduction is beheved to result from a few silver ions existing in the divalent state, and thus providing free electrons to transport current. The use of silver sulfide as a soHd electrolyte in batteries has been described (57). 

Other useful solid-state electrodes are based on silver compounds (particularly silver sulfide). Silver sulfide is an ionic conductor, in which silver ions are the mobile ions. Mixed pellets containing Ag2S-AgX (where X = Cl, Br, I, SCN) have been successfiilly used for the determination of one of these particular anions. The behavior of these electrodes is determined primarily by the solubility products involved. The relative solubility products of various ions with Ag+ thus dictate the selectivity (i.e., kt] = KSp(Agf)/KSP(Aw)). Consequently, the iodide electrode (membrane of Ag2S/AgI) displays high selectivity over Br- and Cl-. In contrast, die chloride electrode suffers from severe interference from Br- and I-. Similarly, mixtures of silver sulfide with CdS, CuS, or PbS provide membranes that are responsive to Cd2+, Cu2+, or Pb2+, respectively. A limitation of these mixed-salt electrodes is tiiat the solubility of die second salt must be much larger than that of silver sulfide. A silver sulfide membrane by itself responds to either S2- or Ag+ ions, down to die 10-8M level. 

Under deposition of cobalt nanocrystals, self-assemblies of particles are observed and the nanocrystals are organized in a hexagonal network (Fig. 2). However, it can be seen that the grid is not totally covered. We do not have a simple explanation for such behavior. In fact, the size distribution, which is one of the major parameters in controlling monolayer formation, is similar to that observed with the other nanocrystals, such as silver and silver sulfide. One of the reasons could be that the nanocrystals have magnetic properties, but there is at present no evidence for such an assumption. 

AOTF w/c RMs bearing the silver, silver iodide and silver sulfide nanoparticles were depressurized slowly and the nanoparticles in the cell were collected and re-dispersed in ethanol. Finally, the sample grids for the TEM (FEl TECNAl G ) measurements were prepared by placing a drop of ethanolic dispersion of nanoparticles on the copper grid. The morphology and size distribution of the silver, silver iodide, and silver sulfide nanoparticles were determined by TEM at an operation voltage of 200kV. The crystallinity of the silver, silver iodide, and silver sulfide nanoparticles was studied by electron diffraction techniques. 

The effect of complex formation on the solubility of a solid can be observed in the home. Silver dinnerware eventually becomes discolored by an unsightly black tarnish of Ag2 S, formed from the reaction of the silver surface with small amounts of H2 S present in the atmosphere. Silver sulfide is highly insoluble in water. Commercial silver polishes contain ligands that form strong soluble complexes with Ag ions. If a tarnished serving pan is rubbed with a polish, the black tarnish dissolves, returning the silver to its brilliant shine. 

C19-0012. The tarnish that collects on objects made of silver is silver sulfide, a black solid. Tarnish can be removed by heating the tarnished object in an aluminum pan containing mildly basic water. Balance this equation Al( ) + Ag2 S( ) Ag( ) + A1 (0H)3 (s) + H2 S(g)... 

The kinetics and mechanism of the growth of anodic silver sulfide films on silver metal in aqueous sulfide solutions has been studied under potentiodynamic conditions [162], The Ag2S film formation was presumed to proceed as... 

Birss VI, Wright GA (1982) The potentiodynamic formation and reduction of a silver sulfide monolayer on a silver electrode in aqueous sulfide solutions. Electrochim Acta 27 1-7... 

Reber JF, Rusek M (1986) Photochemical hydrogen production with platinized suspensions of cadmium sulfide and cadmium zinc sulfide modified by silver sulfide. J Phys Chem 90 824-834... 

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