共查询到20条相似文献,搜索用时 15 毫秒
1.
The peculiarities of the effects of upd thallium, lead, bismuth, and mercury on the dissolution rates of gold and silver in cyanide electrolytes are compared. In general, they feature the abrupt acceleration of the dissolution of gold and, to a lesser extend, silver in the chemisorption range of mentioned ions. As the potential increases, the gold dissolution rates passes through a maximum the height of which is comparable with the limiting current of this process associated with limitations in the delivery of cyanide ions to the electrode surface. The current decay after the maximum is due to desorption of catalytically active adatoms. The chemisorption rate of thallium, lead, and bismuth ions at potentials more negative than the current peak is controlled by their diffusion to the gold surface, whereas the chemisorption rate of mercury is controlled by the adsorption kinetics. With the increase in the surface coverage with adatoms θ, the catalytic activity of all considered adatoms passes through a maximum. The sharp increase in the effective transfer coefficient in the presence of these adatoms makes the main contribution into the acceleration of the gold dissolution, while the increase in the exchange current has a smaller effect. The chemisorption of mentioned atoms on gold not only accelerates the dissolution but also changes its mechanism. For gold dissolution, the catalytic activity of upd thallium, lead, and bismuth increases in the following sequence: Tl ? Pb < Bi and the effect is additive in their simultaneous presence. For silver, the increase in the exchange current makes the main contribution into the acceleration of dissolution, whereas the transfer coefficient and the reaction order with respect to the ligand change insignificantly. Explanation of the observed peculiarities is given. 相似文献
2.
Submicrogram amounts of silver have been determined in lead by neutron-activation analysis. The activity of the 110Ag isotope was measured by following the decay of the 0·66-MeV gamma ray. Reproducibility was generally better than 10%. The smallest amount of silver determined was approximately 0·02 μg. The analyses were completed within 15 min. 相似文献
3.
Tertiary alcohols with a λ-silyl group (3) generally undergo a simple carbonium ion rearrangement in acid giving a single alkene product (4) with loss of the silyl group. 相似文献
4.
A new type of silver composite electrode was examined, prepared from silver, graphite powder, and methacrylate resin. The effects of the presence of various cations (cadmium, copper, bismuth, thallium), anions (chlorides), surface-active substances (Triton X-100), and oxygen on the anodic-stripping voltammetric determination of lead were studied. It was found that the effect of underpotential deposition at the composite electrode differs from that produced at a metallic silver electrode, mainly at low concentrations of the deposited metal. The use of this type of silver composite electrode in differential pulse anodic-stripping voltammetry enables direct determination of lead in natural water samples without elimination of surface-active substances (LOD about 3 g L–1). 相似文献
5.
Alina Sionkowska Alina Kami
ska 《Journal of photochemistry and photobiology. A, Chemistry》1999,120(3):448-210
The influence of UV radiation (253.7 nm) on collagen fluorescence in the absence, and presence, of β-carotene was investigated. It was found that UV radiation of 253.7 nm causes irreversible destruction of tyrosyl and phenylalanyl residues. The fluorescence of collagen (excitation at 275 nm, emission at 305 nm) decreased rapidly during irradiation and a new fluorescence large band at 400–500 nm formed under UV radiation. Smaller changes in the fluorescence of collagen in the presence of β-carotene suggest that it makes collagen less sensitive to the action of UV radiation. 相似文献
6.
Nadesalingam MP Mukherjee S Somasundaram S Chenthamarakshan CR de Tacconi NR Rajeshwar K Weiss AH 《Langmuir : the ACS journal of surfaces and colloids》2007,23(4):1830-1834
Vacuum anneal induced changes in the surface layers of electrodeposited copper(I) oxide (Cu2O) were probed by time-of-flight positron annihilation induced Auger electron spectroscopy (TOF-PAES) and by electron induced Auger electron spectroscopy (EAES). Large changes in the intensity of the Cu PAES intensity resulting from isochronal in situ vacuum anneals made at increasing temperatures indicated that, before thermal treatment, the surface was completely covered by a carbonaceous overlayer and that this layer was removed, starting at a temperature between 100 and 200 degrees C, to expose an increasing amount of Cu in the top layer as the anneal temperature was increased. The thickness of this overlayer was estimated to be approximately 4 A based on analysis of the EAES data, and its variation with the thermal anneal temperature was mapped. This study demonstrated the order-of-magnitude enhancement in the sensitivity of PAES to the topmost surface layer in Cu2O relative to the EAES counterpart; factors underlying this contrast are discussed. Finally, the implications of ultrathin carbon layers on semiconductor surfaces are discussed. 相似文献
7.
R. Inguanta E. Rinaldo S. Piazza C. Sunseri 《Journal of Solid State Electrochemistry》2012,16(12):3939-3946
Metallic lead was deposited, both in form of bulk films and nanowire array within pores of anodic alumina membranes, following a new two-step procedure, consisting in anodic electrodeposition of α-PbO2, followed by its reduction to metallic lead. This method allows to overcome drawbacks of the “direct” electrodeposition of lead from aqueous solution, consisting, essentially, in the formation of dendritic deposits. Here, we report the comparison between results obtained in the two cases and discuss the kinetic of oxide reduction both for films and nanowires. Deposit morphology and structure are also discussed. We have found that reduction of α-PbO2 films proceeds always at high speed and unitary efficiency, with the formation of polycrystalline compact films. Unfortunately, these films present cracks due to the volume shrinkage accompanying the conversion of α-PbO2 into Pb metal. In addition, α-PbO2 nanowires reduction proceeds up to a complete conversion to metallic Pb, which present a characteristic “sausage-like” shape caused by the lower molar volume of metal with respect to oxide. 相似文献
8.
Carmen Racles Alexandra Nistor Maria Cazacu 《Central European Journal of Chemistry》2013,11(10):1689-1698
Silver nanoparticles (AgNPs) were obtained by a redox reaction, using a glucose-containing cyclosiloxane as a reduction agent and stabilizer. Then the AgNPs aqueous solution was used as the reaction medium for the sol-gel process, starting from tetraethylorthosilicate (TEOS) as silica precursor. The nanocomposite material resulted (SilAg) after solvent removal, aging and calcination and was investigated by infrared spectroscopy (FT-IR), atomic force microscopy (AFM), scanning electron microscopy coupled with energy dispersive X-ray system (SEM/EDX), transmission electron microscopy (TEM), energy-dispersive X-ray fluorescence spectroscopy (EDXRF), X-ray diffraction (XRD) and dynamic vapor sorption (DVS). The results were compared to model silicas obtained without silver. A higher condensation degree in SilAg was obtained due to the basic medium used in the first step and was confirmed by a sorption capacity lower than for the model silicas. The solid surface area calculated with GAB analysis using DVS data for the water vapors is 210 m2 g?1. The nanocomposite showed good catalytic activity for hydrogen peroxide decomposition. 相似文献
9.
Preparation of silver nanocrystals in the presence of aniline 总被引:7,自引:0,他引:7
The preparation and characterization of silver nanocrystals by chemical reduction of silver ions in the presence of aniline using hydrazine monohydrate (N(2)H(4).H(2)O) or sodium citrate as the reducing agent are described. A high yield of aniline-derivatized hexagonal silver nanoparticles is obtained by the reduction of Ag(2)SO(4) with N(2)H(4).H(2)O. An alternative strategy is the reduction of Ag(+) by citrate in the presence of aniline, by which the size and morphology of the Ag nanocrystals can be controlled to a certain degree by changing the concentration ratio of aniline to Ag(+). It is believed that the amount of aniline added in the starting solutions for the preparation influences the morphology of the Ag nanoparticles. In addition, the long Ag nanorods with a high mean aspect ratio are prepared in the presence of aniline at a low concentration or o-anisidine. 相似文献
10.
采用氟化铵-盐酸-硝酸-高氯酸溶解样品,加入氢溴酸除去样品中的砷、锑、锡等共存元素,加入硫酸将样品中的铅转化为硫酸铅沉淀,通过过滤与其它元素分离,滴定前加入巯基乙酸掩蔽铋,在乙酸-乙酸钠缓冲体系下,以二甲酚橙为指示剂,建立了采用EDTA络合滴定法测定分银渣中铅含量的方法。实验方法用于测定分银渣中的铅含量,测定结果的相对标准偏差(RSD,n=11)为0.32%~0.90%,加标回收率为100%~102%。能够满足日常测定需求。 相似文献
11.
12.
Claisen rearrangements of glycine crotyl ester enolates in the presence of chelating metal salts and chiral ligands provide ,-unsaturated amino acids in a highly stereoselective fashion. Best results are obtained with electron withdrawing protecting groups, isopropylates of aluminum and magnesium, and the cinchona alkaloids as chiral ligands. While the use of quinine gives rise to the (2R)-configured amino acids, quinidine provides the opposite enantiomer. The different enantiomers can also be obtained by using only one of the chiral ligands by simply changing the reaction conditions. A mechanistic rational for the stereochemical outcome of the reaction is given, which is supported by several experiments. 相似文献
13.
R. Yu. Bek 《Russian Journal of Electrochemistry》2008,44(9):1078-1082
Catalytic activity of thallium and lead adatoms is compared in electrode processes involving gold in cyanide solutions. It is shown that in the presence of considered atoms on the interface, the gold dissolution is accelerated to the greater extent than its electrodeposition. Lead adatoms are shown to exert a substantially stronger effect on the anodic dissolution rate as compared with thallium adatoms, whereas the opposite trend is observed in the cathodic deposition. An explanation for the fact is proposed. 相似文献
14.
15.
A series of arylated vinyltrimethylsilanes have been prepared by means of Heck Arylation in the presence of silver nitrate, which serves to suppress the elimination of the silicon group and enhance the reaction rate. 相似文献
16.
P. A. Moryganov V. N. Galashina A. E. Zavadskii 《Russian Journal of Applied Chemistry》2010,83(9):1615-1621
Biodegradation of flax fibers differing in the chemical composition, structure of cellulose, and content of concomitant natural
impurities (pectin compounds, lignin, hemicellulose) was studied. The effect exerted on the biodegradation by silver nanoparticles
immobilized in the fiber was evaluated. 相似文献
17.
Masao Hisatome Yoshiki Kawajiri Jun Watanabe Masahiro Yoshioka Koji Yamakawa 《Journal of organometallic chemistry》1984,266(2):147-157
Two bridge-rearrangement reactions with AlCl3 have been found in the cyclization of [4](1,1′)[3](2,2′)[4](4,4′)ferrocenophanebutanoic acids (XIb and XIIb) and in the Friedel-Crafts acylation of [4](1,1′)-α-oxo[3](2,2′)[4](4,4′)ferrocenophane(I). The cyclization of XIb and XIIb with ClCO2Et/NEt3/AlCl3 gives no tetrabridged ferrocenophane but three dibridged ferrocenophanes (XVII, XVIII and XIX) each containing two six-membered condensed-rings which are formed via homoannular cyclization of the side chains followed by rearrangement of the existing tetramethylene bridges. Various multibridged ferrocenophanes were treated with AlCl3 to account for the reaction mode in the rearrangement of I, and evidence for selective acyl migration of the oxotrimethylene bridge to the other cyclopentadienyl ring has been obtained. 相似文献
18.
19.
Controlled thermolysis of silver alkylcarboxylates with primary alkylamines was investigated as a facile synthetic method of silver nanoparticles. A series of silver alkylcarboxylates, C(7)H(15)COOAg, C(13)H(27)COOAg, and C(17)H(35)COOAg, have been prepared and the thermolysis of those silver alkylcarboxylates in the presence of various alkylamines, C(8)H(17)NH(2), C(12)H(25)NH(2), and C(18)H(37)NH(2), with no use of solvent was conducted at 120 or 180 degrees C for 5 h, providing spherical silver nanoparticles stabilized by alkylcarboxylates and alkylamines. The size and dispersibility of nanoparticles depend on the alkyl chain length of the precursors, alkylcarboxylates and alkylamines. 相似文献
20.
The energy dispersive X-ray fluorescence method of Pb and Ag determination in metallic copper is described. Radioisotopic
sources of57Co and241Am/target have been used for excitation and Si(Li) and hyperpure Ge spectrometers for spectra analysis. The standard deviation
of Pb and Ag determination for a single measurement is 0.015 and 0.012%, respectively. 相似文献