Highlights from Recent Literature
A more comprehensive list of literature and patents, updated quarterly, will be found in the searchable Technical Database on the World Gold
Council website, www.gold.org under science and Industry domain.
with gold concentrations ranging between 50 and 100% were used as calibration set for carrying out the partial leastsquares regression (PLS). Ninety alloys, with known gold concentrations, were used to evaluate the method’s accuracy. Finally, the minimum guaranteed value of the gold content was analyzed, taking into account the values for gold hallmark in Spanish regulations.
Voltammetric and in Situ FTIRS Study on Cnand Au(Cn)X- Complexes at the Polycrystalline Gold Surface in Citrate Medium The adsorption and reactivity of citrate anions, cyanide anions, and the Au(I) and Au(III) cyano complexes (KAu(CN)2 and KAu(CN)4, respectively) on gold polycrystalline electrodes were studied by cyclic voltammetry and in situ FTIR spectroscopy in pH 7 Na citrate medium. F. Huerta, C. Mele, B. Bozzini and E. Morallon from the Departamento de Ingenieria Textil y Papelera, Universidad Politecnica de Valencia, Spain, Journal of Electroanalytical Chemistry 2004, 569(1), 53. Citrate anion adsorbs reversibly through the carboxylate groups from 0.4 V (RHE) on bare gold surfaces. However, the onset of this adsorption process is shifted by 600 mV in the pos. direction when adsorbed cyanide species are present at the electrode surface. The Au(I) cyano complex produces a film on the gold electrode that inhibits the oxidation of both citrate anions and the gold surface. The reduction of the Au(III) cyano complex gives the Au(I) cyano complex at potentials less negative than those required for gold deposition. Upon reduction, both cyano complexes release adsorbed cyanide on the gold electrode, which can be subsequently oxidized to cyanate at higher potentials. 1.2 Minimum Value Assured by a Method to Determine Gold in Alloys by Using LaserInduced Breakdown Spectroscopy and Partial Least-Squares Calibration Model A procedure for establishing the minimum value assured by an analytical method was developed. M. C. Ortiz, L. Sarabia, A. Jurado-Lopez and M. D. Luque de Castro from the Department of Chemistry, Faculty of Sciences, University of Burgos, Spain, Analytica Chimica Acta 2004, 515(1), 151 It is applied to the detection of gold in jewelry alloys by a recently proposed spectroscopy technique. The laserinduced breakdown spectroscopic data of 17 gold alloys,
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Gold-Colloid-Modified AgCl Photocatalyst for Water Oxidation to O2 The effect of gold colloids on the photocatalytic oxidation of water to dioxygen with silver chloride as the photocatalyst was studied by A. Currao, V. Reddy and G. Calzaferri from the Department of Chemistry and Biochemistry, University of Bern, Switzerland, Chem Phys Chem 2004, 5(5), 720 The nanostructured silver chloride layer acts as a photocatalyst in the presence of a small excess of silver ions in solution with a maximum evolution rate between pH 4 and 6. The photoactivity of AgCl extends from the UV into the visible-light region due to self-sensitization, caused by the formation of silver species during the photoreaction. Gold colloids were sedimented on the AgCl layer by dipping it overnight in a solution containing gold colloids. It is also conceivable to incorporate gold colloids on the AgCl layer during the electrochemical oxidation process of silver to AgCl, by adding colloidal solution to the electrolyte used. AgCl layers that were modified with gold colloids show a considerably higher photoactivity with a very stable oxygen production and photocurrent, as experiments made over a period of several days have shown. The authors thought the results very encouraging and will be using them for the development of a photo-electrochemical water-splitting device. 2.2 The Potential for Use of Gold in Automotive Pollution Control Technologies: A Short Review A review by G. Pattrick, E. Van Der Lingen, C.W. Corti, R.J. Holliday, D.T. Thompson from Mintek, Randburg, S. Africa and World Gold Council, Topics in Catalysis 2004, 30/31(1-4), 273, summarized the recent studies relevant to the future use of gold catalysts in the automotive industry. Gold catalysts have been examined for their potential in low temperature activity to combat cold-start emission problems and removal of NOx from lean-burn gasoline and diesel engines. The justification for developing gold catalyst technologies is based both on their promising technical performance and the relatively stable price and greater availability of gold compared with the platinum group metals (PGMs). Use of gold catalysts under mild conditions could
also produce lower proportions of CO in the hydrogen streams used for automotive fuel cells and they could be used for the selective oxidation of carbon monoxide in these hydrogen streams in order to increase the efficiency of these fuel cells. Technical barriers are indicated which still remain to be overcome before application of gold catalysts is successful in the automotive industry. Formation of Gold Clusters on TiO2 from Adsorbed Au(CH3)2(C5H7O2). Characterization by X-ray Absorption Spectroscopy Gold nanoclusters on TiO2 powder were prepared from adsorbed Au(III)(CH3)2(C5H7O2) (di-Me acetylacetonate gold(III)) and characterized by extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopies. J. Guzman, S. Kuba, J.C. FierroGonzalez and B. Gates from the Department of Chemical Engineering and Materials Science, University of California, USA, Catalysis Letters 2004, 95(1-2), 77. The samples were tested as catalysts for CO oxidation at 298 K and atmospheric pressure and characterized by EXAFS and XANES with the catalysts in the working state. The XANES results identify Au(III) in the initially prepared sample, and the EXAFS data indicate mononuclear gold complexes as the predominant surface gold species in this sample, consistent with the lack of Au-Au contributions in the EXAFS spectrum. The mononuclear gold complex is bonded to two oxygen atoms of the TiO2 surface at an Au-O distance of 2.16 .ANG. Treatment of this complex in He or in H2 at increasing temperatures led to formation of metallic gold clusters of increasing size, ultimately those with an average diameter of about 15 .ANG. The data demonstrate the presence of metallic gold clusters in the working catalysts and also show these clusters alone are not responsible for the catalytic activity. Oxidation of CO and C3 Hydrocarbons on Gold Dispersed on Oxide Supports Catalysts containing gold nanoparticles (1 wt.%Au) dispersed on oxides of main group elements, MGO (Mg, Si, Sn) and on transition metal oxides, TMO (Fe, Ti, Ce) were obtained by deposition-precipitation method, characterized by TPR, TEM, XPS and tested in oxidation of CO, C3H8 and C3H6. M. Gasior, B. Grzybowska, K. Samson, M. Ruszel and J. Haber from the Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Krakow, Poland, Catalysis Today 2004, 91. The catalysts with TMO as supports were considerably more active in the CO oxidation than those with MGO supports. The propane oxidation occurred at temperatures >250°C, yielding only carbon oxides. In propene oxidation in the presence of H2, the Au/MGO catalyst were active at temps. >200°C, giving mainly selective oxidation products
(propanal, ethanal, acrolein), whereas total combustion was the main reaction in these conditions for Au/TMO catalysts. High selectivities to propene oxide (.apprx.70%) were observed only for catalysts containing Ti in the support oxide at temps. 100-150°C. No clear correlations have been observed between the activity of the catalysts in the oxidation reactions and reducibility of the catalysts studied by H2TPR, nor the dominating gold particle size.
Product Class 6: Organometallic Complexes of Gold A review by H. Schmidbaur and A. Schier from the Lehrstuhl fuer Anorg. u. Analytische Chemie der Techn. Universitat Muenchen, Garching, Germany, Science of Synthesis 2004, 3, 691. Methods for preparing organometallic gold complexes are reviewed including those of alkanyl, alkenyl, alkynyl, aryl and heterocyclic ligands and gold carbon cluster complexes. Gold Distribution in Pyrrhotite Crystals Grown under Hydrothermal Conditions The distribution of gold between pyrrhotite and greenockite was studied by the method of hydrothermal thermalgradient co-crystallisation of the components at a temperature of 450.degrees, a pressure of 1 kbar, and different activities of S in the presence of As and Se impurities. N.V. Smagunov, V.L. Tauson and O.V. Ovchinnikova, from the Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, Russia, Crystallography Reports (Translation of Kristallografiya) 2004, 49(2), 299. The structural component of gold impurity in these minerals was selected by studying statistical samplings of the analytical data for single crystals. Ferrous greenockite incorporates a max. of 10 .+-. 2 ppm gold in solid solution. The incorporation limit of gold in stoichiometric pyrrhotite is 25 .+-. 9 ppm; for nonstoichiometric pyrrhotites, it is lower. The As and Se impurities barely affect the concentration of structural gold in the minerals. Constitutional vacancies in pyrrhotite do not capture gold impurity. The observed phenomenon may be the growth effect related to the surface properties of nonstoichiometric pyrrhotite crystals grown under hydrothermal conditions. Differences in the surface structure of pyrrhotites of different composition and the products of their sorption of gold were revealed by XPS. 3.2
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Electrochemical and Electrogravimetric Investigations of Prussian Blue on the Gold Electrode in the Presence Of Thallium(I) Ions Electrode processes of Prussian Blue (PB), deposited on the gold electrode, have been investigated in potassium and thallium salts solutions, using electrogravimetric and cyclic voltammetric methods. I.A. Rutkowska, J. Stroka, P.K. Wrona and Z. Galus from the Department of Chemistry, University of Warsaw, Poland, Polish Journal of Chemistry 2004, 78(5), 711. It was shown, that both electrode processes of PB (reduction of PB to Everitt’s salt and its oxidation to Berlin Yellow) undergo changes, when potassium ions were replaced by thallium(I) ones. In the presence of thallium, the formation of new redox system was observed, and T1(I) acted as a counterion. The equilibrium constant of the reaction: K(I)PB + T1(I) = T1(I)PB + K(I) was established to be equal to K = (1.7.+.0.6).times.104. At the same time almost 50% of the PB layer lost its electrochemical activity, whereas the remaining PB phase was electrochemical active. After transfer of the electrode to KNO3 solution majority of inactivated layer recovered its previous activity. These findings were tentatively interpreted, by the authors, as a result of formation of two phases of PB with T1(I): electrochemical active and inactive. Both phases were in equilibrium and thallium ions could be replaced by potassium one. In the case of the Fe(CN)63-/4electrode process (at more pos. potentials), in the presence of T1(I) irreversible deactivation occurs, since in KNO3 solution, no reactivation of the electrode process was observed. 4.2 Preparation of 2-Quinolinethiol-Capped Gold Nanoparticles and its Electrochemical Properties 2-Quinolinethiol was employed as one stabilizer to produce 8-10 nm gold nanoparticles. UV-Vis spectrum confirmed the surface plasmon absorbance and in comparison with alkanethiolate-gold nanoparticles with the same size, the blue shift in absorbance peak was interpreted as the free electron transferred from N to gold core. D. Li and J-H. Li from the State Key Lab Electroanalytical Chemistry, Changchun Inst. Appl. Chem., Chinese Acad. Sci., Changchun, Peoples Republic of China, aodeng Xuexiao Huaxue Xuebao 2004, 25(3), 553. Cyclic voltammograms proved that the reduction potential of 2-quinolinethiol was not altered as it assembled onto gold nanoparticles, however there appeared an obvious hysteresis in oxidation current, which was attributed to the oxidation ability of quinoline reduction product.
Multichannel Electrochemiluminescence of Luminol In Neutral and Alkaline Aqueous Solutions on a Gold Nanoparticle SelfAssembled Electrode The electrochemiluminescence (ECL) behaviour of luminol on a gold nanoparticle self-assembled electrode in neutral and alkaline pH conditions was studied under conventional cyclic voltammetry (CV) by H. Cui, Y. Xu and Z-F. Zhang from the Department of Chemistry, University of Science and Technology of China, Hefei, 230026, Peoples Republic of China, Analytical Chemistry 2004, 76(14), 4002. The gold nanoparticle self-assembled electrode exhibited excellent electrocatalytic property and redox reactivity to the luminol ECL system. In neutral solution, 4 ECL peaks were observed at 0.69, 1.03, -0.45, and -1.22 V (vs. SCE) on the curve of ECL intensity vs. potential. Compared with a bulk gold electrode, two anodic and one cathodic ECL peaks were greatly enhanced, and one new cathodic ECL peak appeared. In alkaline solution, two anodic ECL peaks were obtained at 0.69 and 1.03 V, which were much stronger than those on a bulk gold electrode. These ECL peaks depend on gold nanoparticles on the surface of the electrode, potential scan direction and range, the presence of O2 or N2, the pH and concn. of luminol solution, NaBr concentration, and scan rate. The emitter of all ECL peaks was identified as 3aminophthalate by analyzing the ECL spectra. The spatial distribution of the luminol ECL peaks on the gold nanoparticle self-assembled electrode was studied by CCD. The surface state of the gold nanoparticle self-assembled electrode was characterized by SEM and UV-visible reflection spectra. The mechanism for the formation of these ECL peaks is proposed. The gold nanoparticle self-assembled electrode could lead to novel ECL properties, and strong luminol ECL in neutral and alkaline solutions could be obtained on such an electrode, which is of great analytical potential. The Oxidation of Trivalent Chromium at Polycrystalline Gold Electrodes The electrochemical oxidation of Cr(III) to Cr(VI) species was examined in aqueous solution by C.M. Welch, M.E. Hyde, O. Nekrassova and R.G. Compton from the Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford, Physical Chemistry Chemical Physics 2004, 6(12), 3153. The responses of B doped diamond, glassy C and gold electrodes were probed towards the oxidation of trivalent Cr over a wide pH range (1.0-13.0). High quality voltammetric profiles appear only at a gold electrode and in solns. of pH >12. The oxidation reaction proceeds via a multi-step mechanism, where the 1st electron transfer is electrochemically irreversible and rate-determining, followed by 2 fast electron transfers. DIGISIM was successfully used to model the experimentally obtained data. The oxidation was
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additionally found to involve OH-ions, at potentials where these are adsorbed at the gold electrode surface. AFM measurements were carried out to complement these findings. 4.5 Electrochemical Control Of CO/NO Ligand Exchange in a Triruthenium Cluster Monolayer Assembled on a Gold Electrode Surface A highly selective ligand exchange reaction is realized in the self-assembled monolayer (SAM) of a triruthenium cluster on a gold electrode surface under precise electrochemical potential control. S. Ye, W. Zhou, M. Abe, T. Nishida, L. Cui, K. Uosaki, M. Osawa and Y. Sasaki from the Catalysis Research Center, Hokkaido University, Japan, Journal of the American Chemical Society 2004, 126(24), 7434. CO as well as NO molecules, which are known to play key roles in many chemical, biological, and environmental systems, can be efficiently introduced into the SAM by electrochemical tuning the electronic state of the Ru site. These unique surface reactions are more convenient and efficient than conventional ligand exchange reactions in solution and could be used for the elucidation of the electron-transfer mechanism in a biol. system as well as in the development of molecular sensors and devices. Self-Assembly of Metalloporphyrin-L-Cysteine Modified Gold Electrode A novel composite film containing metalloporphyrins was fabricated by in situ electrochemical scanning on an Lcysteine self-assembled monolayer modified gold electrode. SEM and ATR-FTIR were used to characterize the structure of the film. S. Wang, D. Du and X. Xu from the Faculty of Chemistry and Material Science, Hubei University, Wuhan, Peoples Republic of China, Journal of Applied Electrochemistry 2004, 34(5), 495. The electrochemical properties were investigated through techniques such as a.c. impedance, cyclic voltammetry and chronocoulometry. The porphyrin-L-cysteine film showed no peak in the first cycle, while each of the composite films derived from three different metalloporphyrin-L-cysteine presented a pair of reversible redox peaks in 1.0 mol L-1 H2SO4. These peaks correspond to the rapid redox process of the metal. The supporting electrolyte and its pH value influenced the stability and sensitivity of the composite film. Cupricporphyrin-L-cysteine film showed good catalytic activity for the reduction of H2O2. The catalytic current was linear to H2O2 concentration in the range 1.0 .times. 10-6 to 3.0 .times. 10-5 mol L-1, with a correlation coeff. of 0.9995. The detection limit was 1.0 .times. 10-7 mol L-1 at a signal to noise ratio of 3. The relative standard deviation was calculated as 2.4% for solutions containing 1.0 .times. 10-5 mol L-1 H2O2 (n = 11).
Electronics and Sensors
Formation of Gold Nanoparticles/ Oligothiophene Dithiols Composite Thin Films Between Microgapped Gold Electrodes and their Electronic Properties The authors studied the construction and electronic characteristics of a series of devices made from gold microgap electrodes, gold nanoparticles and conjugated oligothiophene dithiols. S. Maeda and T. Ogawa, from the Department of Chemistry, Faculty of Science, Ehime University, Matsuyama, Japan, International Journal of Nanoscience 2002, 1(5 & 6), 557. The formations of gold nanoparticle/oligothiophene dithiol composites on gold surface were monitored by quartz crystal microbalance (QCM) using gold electrode coated crystal oscillator. The formation speed was the fastest for terthiophene dithiol followed by hexathiophene and nanothiophene dithiols, the latter two showed almost the same formation speed. The current-voltage (I/V) curves of these devices were measured at various temperatures to show that at high temp. (>200 K) they were almost straight line; at lower temperature they became parabolic, and at 4 K a completely blocked region appeared between -12 to +12 V. The authors attributed the parabolic I/V curve to a tunneling mechanism and the blocked region to the Coulomb blockade phenomena. 5.2 Ab-Initio Study of The Electric Transport in Gold Nanocontacts By employing a real-space formulation of the KuboGreenwood equation based on a Green’s function embedding technique combined with the fully relativistic spin-polarized Korringa-Kohn-Rostoker method a detailed investigation of the elec. transport through atomic-scaled contacts between two Au(001) semi-infinite systems is presented. K. Palotas, B. Lazarovits, L. Szunvogh and P. Weinberger from the Center for Computational Materials Science, Vienna University of Technology, Vienna, Austria , Los Alamos National Laboratory, Preprint Archive, Condensed Matter 2004 1-14, arXiv:cond-mat/0403282. Following a careful numerical test of the method the conductance of gold nanocontacts with different geometries is calculated. In particular, for a contact formed by a linear chain of gold atoms a conductance near 1 G0 is obtained. The influence of transition metal impurities (Pd, Fe and Co) placed on various positions near the center of a particular contact is also studied. The authors found that the conductance is very sensitive to the position of the magnetic impurities and that the mechanism for the occurring relative changes can mainly be attributed to the impurities’ minority d-band inducing resonant line-shapes in the s-like DOS at the center of the contact.
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Medical and Dental
The Immobilization of Hepatocytes on 24 NmSized Gold Colloid for Enhanced Hepatocytes Proliferation Bioartificial liver and hepatocyte transplantation is anticipated to supply a temporary metabolic support for candidates of liver transplantation or for patients with fulminant liver failure. An essential restriction of this form is the inability to acquire enough of an amount of hepatocytes. Enhancement of the proliferation and differentiated function of hepatocytes is becoming a pursued target. In this work, HY. Gu; Z. Chen, R-X Sa, S-S. Yuan, H-Y. Chen, Y-T. Ding and AM. Yu, from the Institute of Analytical Science, Department of Chemistry, Nanjing University, Peoples Republic of China, Biomaterials 2004, 25(17), 3445, porcine hepatocytes were successfully immobilized on nano-sized gold colloid particles to construct a hepatocyte/gold colloid interface at which hepatocytes can be quickly proliferated. The properties of this resulting interface were characterized and confirmed by SEM and atomic force microscopy. The proliferative mechanism of hepatocytes was also discussed. The proliferated hepatocytes could be applied to the clinic based on their excellent functions for the synthesis of protein, glucose and urea as well as lower lactate dehydrogenase release. Inflammatory Responses and Cell Adhesion to Self-Assembled Monolayers of Alkanethiolates on Gold The acute inflammatory response and the adhesion of cells to self-assembled monolayers (SAMs) of well-defined surface chem. was studied in vivo using a rodent air-pouch model of inflammation. SAMs with three different terminal functional groups (OH, COOH and CH3) were implanted in s.c. air pouches induced in BALB/c mice. J.N. Barbosa, M.A. Barbosa and A.P. Aguas from the Laboratorio de Biomaterials (INEB), Instituto de Engenharia Biomedica, Oporto, Portugal, Biomaterials 2004, 25(13), 2557. After 24 h, inflammatory cells were recovered from the air pouches and the implants were removed and prepd. for observation by SEM (SEM). The implants coated with OH and CH3, were found to cause the highest recruitment of inflammatory cells into the s.c. pouches. Polymorphonuclear neutrophils (PMNs) leukocytes predominated over mononuclear cells in inflammatory exudates of SAMs-coated implants, the opposite being found in uncoated implants (controls). CH3-coated implants induced the highest no. of inflammatory cells and also the largest percentage of PMNs seen in the s.c. pouches. Control and OH-covered implants presented the higher densities of attached inflammatory cells detected by SEM. In contrast, the CH3-coated implants showed a very low d. of cells adherent to the implant surface. We conclude that the chem. nature
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and the degree of hydrophobicity of the surface of implants modulate both the local acute inflammatory reaction and the adhesion of leukocytes.
Metallurgy, Materials and Coatings
Large Solvent and Potential Effects on the Collective Surface Plasmon Band of Gold Nanoparticle Films Alkyl thiolate-covered gold nanoparticle films with various core diameters were fabricated using an electrooxidative process that introduces biferrocene units onto the particle surface. M. Yamada and H. Nishihara from the Department of Physical Materials Science, School of Materials Science, Japan Advanced Institute of Science and Technology (JAIST), Ishikawa, Japan, Chem Phys Chem 2004, 5(4), 555. The prepared films exhibit specific spectroscopic characteristics derived from dipole-dipole interactions among adjacent particles densely fixed in the film. These characteristics cannot be explained by the behavior of single gold particles. These spectroscopic features give a promising possibility for advanced application such as high-sensitive chemical sensors and nonlinear optical device. Effect of Glass Substrates on the Formation of Gold-Silver Colloids in Nanocomposite Thin Films A sol-gel route to synthesize nanocomposite thin films containing phase separated metal colloids of gold (Au) and silver (Ag) was developed. G. Suyal, M. Mennig and H. Schmidt from the Institut fuer Neue Materialien, Saarbruecken, Germany, Journal of Sol-Gel Science and Technology, 2004, 29(1), 11. Silver-Gold colloids were prepared in silica films using dip coating technique. The annealing of the samples in air results in the formation of phase separated. Silver and gold colloids in SiO2 thin films, showing the surface plasmon peaks at 410 nm and 528 nm. For the synthesis of phase separated. Silver and gold colloids on float glass substrates, formation of the silver colloids was found strongly dependent on the surface of the float glass. On the tin rich surface formation of both gold and silver colloids took place, whereas, on the tin poor surface the formation of only gold colloids was observed. The surface dependence of the formation of silver colloids was attributed to the presence of tin as Sn2+ state on the glass surface, which oxidizes into Sn4+ during heat treatment, reducing Ag+ into silver colloids. 7.2
Decorative Gold Plating Process of Si-Al Alloy Casting Artware The strike Zn alloy plating process on artware of Al alloy die casting was studied by Z. Yang, L. Zhongdong, L. Changye and Y. Wang, from the School of Material and Metallurgy, Northeastern University, Shenyang, Peoples Republic of China, Diandu Yu Tushi 2003, 22(3), 4. The strike plating solution was mainly composed of the compounds of Zn, Ni, and Fe, and cyanide-free organic complexant. Strike plating film obtained consisted of Zn-Ni-Fe alloy with smooth, fine appearance, and semi-bright cream-colour. Consequently neutral Ni, bright Cu, bright Ni, and decorative gold plating were applied. Test of adhesion and corrosion resistance showed good results. The key points in each step were introduced, preferably in pre-plating. 7.4 Innovation in electroplating of gold and gold alloys A review with references concerning electroplating of gold and gold alloys is presented by A. Vicenzo, P. Cavallotti from the Dip. Chimica, Materiali Ingegneria Chimica “G. Natta”, Politecnico di Milano, Italy, Galvanotecnica e Nuove Finiture 2003, 13(4), 208-210, 212-213. Innovation in surface finishing and electrochemical processes for jewelery manufacture will be an important issue in the future for technology development and economic growth, as market competition becomes more and more intense. Since process innovation, especially when speaking of a product category where invention and design are of the utmost importance, has a strong fertile relationship with new ideas in design and new concepts in manufacturing. Starting from the fifties, gold plating came out from the “small” business of artisan and jewelery makers for making a long ride through the connectors and switches industry towards the leading technology of microelectronics and the ultimate border of micro and nanotechnology Since then, the available gold plating processes have changed thoroughly, at first with the introduction of acidic cyanide baths, afterwards also of alternative bath chem., among which the only com. successful was the gold sulfite bath, even though its fortune is mainly confined to engineering applications. Cyanide based baths for gold and gold alloy plating are by far the most used and reliable processes; however, they suffer from many drawbacks which still call for improvements, such as hydrogen evolution during plating, possible incorporation of gold cyanide in the coatings, and relatively high tensile residual stress; finally, cyanide is an hazardous chemical, demanding special care and compliance with strict regulations. In this paper non-cyanide processes for gold and gold alloy electrodeposition, such as sulphite, mixed sulphite-thiosulfate and thiourea baths, are briefly discussed and considered in view of their potential for new engineering and jewelery applications.
Investigation of the Properties of Gold Nanoparticles in Aqueous Solution at Extremely High Lattice Temperatures Transient absorption data for gold nanoparticles in aqueous solution obtained using a double pump-pulse configuration are presented by M. Hu, H. Petrova and G.V. Hartland from the Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN, USA, Chemical Physics Letters 2004, 391(4-6), 220. The first pulse heats the particles, and the second pulse interrogates the symmetric breathing mode. The experiments were performed as a function of the intensity of the first pulse, and the relative delay between pulses. Analysis of lattice temperatures of approximately 1000 K are achieved at high intensity. This significantly perturbs the surrounding solvent, possibly causing explosive boiling at temps. >550 .+-. 50 K. This threshold is consistent with studies of superheated liquids. Novel One-Step Synthesis of Amine-Stabilized Aqueous Colloidal Gold Nanoparticles The authors, M. Aslam, L. Fu, M. Su, K. Vijayamohanan and V. Dravid from the Department of Materials Science and Engineering, Institute for Nanotechnology, Northwestern University, Evanston, USA, Journal of Materials Chemistry 2004, 14(12), 1795, demonstrate a simple 1-step process for the synthesis of H2O-dispersed spherical gold nanoparticles using the multifunctional molecule oleyl amine (OLA) that electrostatically complexes with aqueous chloroaurate ions, reduces them, and subsequently caps the nanoparticles thus formed. The gold particles thus formed were of the fcc. phase and were fairly monodisperse with particular concentrations of capping molecules. Simple Large-Scale Synthesis of Nearly Monodisperse Gold and Silver Nanoparticles with Adjustable Sizes and with Exchangeable Surfactants H. Hiramatsu and F.E. Osterloh from the Department of Chemistry, University of California, Davis, USA, Chemistry of Materials, 2004, 16(13), 2509, report an inexpensive, versatile, and very reproducible method for the large-scale synthesis of organoamine-protected gold and silver nanoparticles in the 6-21 nm (Au) and 8-32 nm (Ag) size ranges and with polydispersities as low as 6.9%. 8.4 Controlled Growth of Gold Nanowhiskers via a Soft Chemistry Method Synthesis of gold nanowhiskers with uniform lateral dimension (.apprx.100 nm) and lengths up to approximately10 .mu.m was achieved by a seed-mediated growth process involving use of silver nanoparticles as seeds
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and subsequent polymer-controlled growth in a refluxing system heated to .apprx.180.degree.. Q. Zhao, L. Hou, R. Huang and S. Li from the Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Peoples Republic of China, Materials Chemistry and Physics 2004, 85(1), 180. Glycol was used as both solvent and reducing agent to produce silver nanoparticles, while poly(diallyldimethylammonium chloride) (PDDA) was used as a shape-inducing additive to guide the growth of nanostructures into nanowhiskers. The obtained gold nanowhiskers were characterized by XRD, TEM, energy dispersive spectroscopy (EDS), and UV-visible spectroscopy. Characterization of Gold Nanoparticles Synthesized Using Sucrose by Seeding Formation in the Solid Phase and Seeding Growth in Aqueous Solution A simple method for safely preparing Au nanoparticles of a few to 20 nm in diameter was developed on the basis of chemical reduction of HAuCl4 with glucose and fructose produced by the acidic hydrolysis of sucrose. Z. Qi, H. Zhou, N. Matsuda, I. Honma, K. Shimada, A. Takatsu and K. Kato from the Energy Electronics Institute Nanoarchitectonics Research Center, and National Metrological Laboratory of Japan, National Institute of Advanced Industrial Science & Technology (AIST), Tsukuba, Japan, Journal of Physical Chemistry B 2004, 108(22), 7006. The method includes seeding formation in the solid mixture of HAuCl4 and sucrose via heat treatment at 70-100.degree. and seeding growth after dissolving the heated mixture in water at room temperature. The x-ray photoelectron spectroscopic analyses of the HAuCl4-sucrose mixt. heated at 80.degree. for 15 min confirmed the presence of Au(0) and Au(I) in the sample. Both the x-ray diffraction and UV-vis spectroscopic measurements of the heated mixture suggest the small sizes of gold clusters in the sample. The particle growth in the aqueous solution was followed by in-situ monitoring of the surface plasmon band with a time-resolved UV-vis spectrometer. The size and size distribution of the resulting nanoparticles were measured by both dynamic light scattering and TEM. Electrophoresis combined with visible spectroscopy confirmed that gold nanoparticles in the aqueous solution carried negative charges that resulted from carboxylic acid groups bound to the particles, based on the IR spectroscopic measurement. 8.5
Recovery of Gold from Cyanide Solutions using Commercial Ion Exchangers The results obtained by using some commercial anions and selective exchange resins for gold and silver recovery from hydrometallurgical cyanide solutions are presented by M. Pavel and D. Axente from the Institute de Cercetare Dezvoltare si Proiectare Miniera, S.C. CEPROMIN S.A., Romania, Revista de Chimie (Bucharest, Romania) 2004, 55(2), 86. Selective, intermediate base and strong base commercial resins were investigated. Sorption of precious metals took place from real and synthetic cyanide solutions having different pH values. Acidic thiourea solutions have been used in the gold and silver elution tests. Depending on the operating flow rate through the strong base anion resin bed, recoveries of 57.9-91.2% for gold and of 50.64-81.1% for silver have been obtained from alkaline leach solutions. From cyanide solutions with modified pH (pH < 6), gold has been absorbed with efficiencies ranged from 17 to 95% depending on the resin type. 9.2 Experimental Study on Bacterial Oxidation of Carbon-Bearing High Arsenic Refractory Gold Concentrate By conventional cyanide leaching of the carbon-bearing high arsenic refractory gold concentration from a certain place of Guangdong Province, the gold leaching rate was only 15.02%. Through the use of bacterial oxidation, the gold wrapped by sulfide were liberated or exposed, and the organic carbon which adsorbed gold were passivated and the gold leaching rate came to 94.41. F. Yang, X. Xu, J. Zhao and Z. Liang from the Changchun Gold Research Institute, Changchun, Jilin Province, 130012, Peoples Republic of China, Huangjin 2003, 24(4), 37. Study of Gold Recovery from a Barite-Ore Concentrate The gold recovery from a complex barite (BaSO4) ore concentrate is considered for the industrial product received from the beneficiation of gold-containing ore from the Muzhiev deposit in Ukraine. A.I. Samsonov, O.V. Chernyuk, G.Z. Fomin and I.L. Fomina from DonNIPITsM, Ukraine, Metallurgicheskaya i Gornorudnaya Promyshlennost 2003, (6), 66. Comparative processing was investigated for the hydrometallurgical leaching, pyrometallurgical (with Cu collector) melting, and alkali smelting with Pb collector. The alkali (NaOH) smelting with Pb collector was feasible for the gold recovery at 94-97%, vs. lower recovery with higher losses in the other two methods. 9.3
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9.4 Study on the Technology for Gold Recovery In the process of cyanide leaching at concentrator No 1 in Yindongpo Gold Mine, there are some difficult problems including low gold leaching rate, froth overflow which causes gold loss and high slime content of cyanide residue which affects seriously the comprehensive recovery of useful metals in the residue. With a new proposed process of combining grinding fineness with reagent rate, these problems have been solved. H. Wang, Z. He and M. Zhao from the Yindongpo Gold Mine Co. Ltd., Tongbai County, Henan, Peoples Republic of China, Kuangye Beijing, China 2003, 12(4), 27. The results show that the gold concentration grade is increased from 39.43% to 53.19% and overall recovery of gold flotation-cyanide leaching from 80.92% to 90.54%. Gold Extraction from Thiosulfate Solution using Trioctylmethylammonium Chloride Alkyl phosphorus esters, alkyl amines, amine oxides and their mixtures with amines were used to extract gold from thiosulfate solution. K. Liu, W. Yen, A. Shibayama, T. Miyazaki and T. Fujita from the Faculty of Engineering and Resource Science, Akita University, Japan, Hydrometallurgy 2004, 73(1-2), 41. A re-adjustment of pH was required and extraction efficiency was poor in the alkaline pH range. Therefore, trioctylmethylammonium chloride was used to ext. gold from thiosulfate leaching solns. without pH and other adjustments. The effects of gold concentration, pH, ammonia, thiosulfate and cupric ion concentrations, extractant concentration, diluent and retention time on the gold extraction were investigated. The 0.18 mol/L extractant dild. with n-octane and 1-hexanol at an organic phase/aqueous phase ratio of 1:1 could ext. >99% of the gold from the thiosulfate solution under standard leaching condition of 1.0 mol/L S2O32-, 0.03 mol/L Cu2+ and 3.0 mol/L NH3/NH4+ at pH 10.2 in 0.6 ks. The loading capacity and selectivity of the gold extractant were also studied. 9.5
biostability was tested in a rat s.c. model. After 19 days of implantation, the PU containing gold showed less surface degradation as well as much reduced tissue reaction. Powder Nanotechnology. Nanoparticle for practical use. Paints containing Gold and Silver Nano Particles A review by T. Kobayashi, from the Creat. Technol. Res. Lab., Nippon Paint Co., Ltd., Neyagawa, Japan, Funtai Kogaku Kaishi 2004, 41(6), 473. A special comb-shaped block copolymer functions as a protective colloid and effectively prevents coagulation of nanoparticle of noble metals such as gold and silver. Combined with a simple reduction process using an aliphatic tertiary amine, a high concentration. Gold and silver nanoparticles paste has been achieved. Its process, characteristics of nanoparticle pastes, and application to paints are described. 10.3 In Situ Precipitation of Gold Nanoparticles onto Glass for Potential Architectural Applications The optical properties of in situ deposited gold nanoparticle coatings are investigated for potential application in architectural glass. X. Xu, M. Stevens, M. B. Cortie from the Institute for Nanoscale Technology and Department of Chemistry, Materials and Forensic Science, University of Technology Sydney, Australia, Chemistry of Materials 2004, 16(11), 2259. It is found that the optical properties of the coating can be controlled by the pH of the deposition solution. At a pH of 5.1, the colour of the coatings develops from pink, through violet, to blue in transmission. This is due to a plasmon resonance peak at 520 nm from isolated particles, and one at about 700 nm due to near-field dipole interactions, with an intermediate zone of the coexistence of the two, which produces the violet colour. However, the two peaks do not coexist in the spectra of coatings produced at pH 8.0 or 10.0, with the peak due to the 520 nm resonance being swamped by the development of the resonance due to particle-particle interactions. In all cases the 700 nm peak could be broadened and re-shifted by increasing the deposition time. The reasons for these differences are explored and are shown to be attributable to the smaller, more aggregated morphol. of nanoparticles precipitated at the higher pHs. The wavelength of maximum plasmon resonance is examined as a function of the volume fraction of nanoparticles. Significant deviations from the well-known Genzel-Martin anal. model are observed The reasons for deviation of the model are discussed. Finally, it is shown how coatings that are blue or blue-gray in transmission can be obtained by exploiting this deviation. Such coatings may be more suitable for architectural application than the conventional pink-hued coatings obtained with colloidal gold nanoparticles.
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Enhanced Biostability of Polyurethane Containing Gold Nanoparticles S-H. Hsu and C-W. Chou from the Department of Chemical Engineering, National Chung Hsing University, Taiwan, Peoples Republic of China, Polymer Degradation and Stability (2004), 85(1), 675, prepared a polyether-type polyurethane (PU) containing 0.043% gold nanoparticles (approximately.5 nm) by mixing the waterborne PU with gold suspension, casting and drying at 60°C. The gold nanoparticles were found to be well dispersed in PU. A significant increase in the pyrolysis temperature and the glass transition temperature was demonstrated in the nano-composite PU films. The
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