Gold Powder Research Articles

Heats of interaction of hydrogen with gold and platinum powders and its effect on the subsequent adsorptions of oxygen and noble gases

Exposure of pure gold powders to hydrogen flow at 125 °C and atmospheric pressure causes heat evolution accompanied by hydrogen adsorption. The exposure takes place in a flow-through microcalorimeter, in which the metal powders are purged by nitrogen flow used as an inert carrier gas. The adsorbed hydrogen is slowly desorbed by nitrogen flow. The heats of hydrogen adsorption and its uptake by the gold powder are greatly increased by its sequential treatments with micromole quantities of oxygen and noble gases, such as helium and argon. This increase does not take place if the gold treatment is confined only to oxygen, or only to pure noble gases. The radically increased hydrogen adsorption by gold is caused by a combination of its treatments with oxygen and the noble gases. Similar results were obtained with pure platinum powder exposed to hydrogen at room temperatures. Gold powder containing adsorbed hydrogen reacts very strongly with molecular oxygen/argon mixtures, generating heats of adsorption several times higher than the heat of formation of water. The heat evolution is very rapid and is not accompanied by the formation of water. These intense interactions are not observed after complete desorption of hydrogen from the gold surfaces.

Evaluation of the radiopacity of calcium silicate cements containing different radiopacifiers

To identify the suitable ratio of alternative radiopacifiers to impart the necessary radiopacity to calcium silicate cements (CSC) and assess the purity of the radiopacifying agents. Alternative radiopacifying materials for incorporation into CSC included barium sulphate, titanium oxide, zinc oxide, gold powder and silver/tin alloy. The chemical composition of the alternative radipacifying materials and bismuth oxide, which is used in mineral trioxide aggregate (MTA), was determined using energy dispersive X-ray analysis. In addition, using an aluminium step-wedge and densitometer, the radiopacity of each material was evaluated as recommended by international standards. The optical density was compared with the relevant thickness of aluminium (Al). A commercial MTA and CSC were used as controls. Statistical analysis comparing the radiodensity of the different cements to MTA was performed using anova with P = 0.05 and post hoc Tukey test. All percentage replacements of bismuth oxide, gold and silver-tin alloy powder, and the 25% and 30% replacements with barium sulphate and zinc oxide had radiopacities greater than 3 mm thickness of aluminium (Al) recommended by ISO 6876 (2002). The 25% replacement of cement with gold powder and 20% replacement of cement with silver/tin alloy powder exhibited radiopacity values of 8.04 mm Al and 7.52 mm Al, respectively, similar to MTA (P > 0.05). The cement replaced with 20% bismuth oxide showed a radiopacity of 6.83 mm Al, lower than MTA (P = 0.003). Silver/tin alloy and gold powder imparted the necessary radiopacity to a calcium silicate-based cement. Barium sulphate was also a suitable radiopacifier together with a lower concentration of silver/tin alloy and gold powder that achieved the radiodensity recommended by ISO 6876. Further research is required to investigate the broader properties of the calcium silicate-based cement with the different radiopacifiers.

Catalytic Reactions of Carbene Precursors on Bulk Gold Metal

Bulk gold metal powder, consisting of particles (5-50 microm) much larger than nanoparticles, catalyzes the coupling of carbenes generated from diazoalkanes (R(2)C=N(2)) and 3,3-diphenylcyclopropene (DPCP) to form olefins. It also catalyzes cyclopropanation reactions of these carbene precursors with styrenes. The catalytic activity of the gold powder depends on the nature of the gold particles, as determined by TEM and SEM studies. The reactions can be understood in terms of mechanisms that involve the generation of carbene R(2)C: intermediates adsorbed on the gold surface.

Aerobic oxidation of amines to imines catalyzed by bulk gold powder and by alumina-supported gold

Both bulk gold powder (∼50 μm particle size) and alumina-supported gold (50–150 nm) are highly active catalysts for the aerobic oxidative dehydrogenation of amines (CH–NH) to imines (CN) under the mild conditions of 1 atm O2 and 100 °C. Reactions using the 5% Au/Al2O3 catalyst make efficient use of the gold metal and offer a practical synthesis of imines from amines. These studies add to the growing list of reactions that are catalyzed by bulk gold metal.

Gold and Gold Alloy foams

The possibilities to manufacture gold-based foams are explored. Gold powder and various powdered alloying elements are mixed with a small volume fraction of a gas-releasing blowing agent. The blend is compacted to a dense precursor, which is then melted in a further step in order to trigger foam formation. We find that gold-silicon alloys containing 2–3 wt.% of silicon or around 8 wt.% of germanium can be foamed using TiH2 or ZrH2 as a blowing agent. Foams with about 85% porosity are obtained.

Stripping of Au(I) from a Loaded Cetyltrimethylammonium Bromide/Tributyl Phosphate Organic Solution: Conversion and Reduction

The recovery of Au(I) from cyanide leaching solutions by solvent extraction techniques has attracted wide interest in the past decades. However, no substantial progress in industries has been reported yet, because of the difficulties concerning gold stripping from loaded organic phases, such as the quaternary amines extraction systems. In this work, a new technique for the recovery of Au(CN)2 − from the loaded cetyltrimethylammonium bromide / tributyl phosphate organic solution by a two‐step stripping procedure is suggested first by Au(CN)2 − conversion by HCl into corresponding chloride complex ions, and then by chemical reduction of auro‐chloride complex ions in TBP organic phases to give metal gold powder. The influences of HCl concentrations, reaction time, and various reducing agents used on the percent gold conversion and reduction were investigated. About 33% of Au(CN)2 − in the initial TBP organic phase could be precipitated as metal gold powder in the conversion step, while 67% was converted into AuCl2 − or AuCl4 − and held in the organic phase. Subsequently, the loaded organic phase after conversion was contacted with reducing agents such as sodium sulfite, ammonium oxalate, or hydrazine hydrate. Most (>98%) of the auro‐chloride complex ions could be effectively reduced as metal gold. As a result, the total gold recovery from the initial TBP organic phases after the two stripping procedures achieved more than 98%. The 198Au radioactive tracer was employed to determine the concentration and distribution behavior of gold in both organic and aqueous solutions. In addition, the experiment on the reuse of the organic phase after gold stripping showed that there was no obvious loss in percent gold(I) recovery after one cycle of the extraction‐ stripping‐ regeneration process no matter what reducing agent was used.

Processing of high purity gold from scraps using diethylene glycol di- N-butyl ether (dibutyl carbitol)

An improved process was developed to produce gold with purity > 99.9998% (> 5 N) from gold scraps using dibutyl carbitol (DBC) as an extractant. The extraction of gold into DBC was optimised, which showed that gold could be effectively loaded into DBC up to 190 g/L Au. Only small amounts of other minor elements and impurities, such as Pt, Pd, Ag, Cu and Zn, were extracted into the DBC phase. Fe on the other hand has to be removed by pH adjustment to pH3, prior to solvent extraction. The novel stripping step recovered solid fulminating gold Au 2O 3×3NH 3, which was formed by contacting the gold-loaded DBC with concentrated ammonia. This intermediate product was then further reduced to gold powder by hydrazine. Further washing of this gold powder with nitric acid yielded > 5 N gold.

H 2-induced promotion of CO oxidation over unsupported gold

The kinetics and mechanism of the preferential oxidation of carbon monoxide in the presence of hydrogen (PrOx) over an unsupported gold powder (mean particle size ∼20 nm and free of silver) have been investigated using flow fixed bed catalytic testing and diffuse reflectance infrared Fourier transform spectroscopy coupled to mass spectrometry ( operando DRIFTS or DRIFTS-MS). It is shown that the presence of H 2 has a favourable effect on the oxidation of CO, either by strongly accelerating the reaction or by preventing the catalyst deactivation, depending on the conditions used. Variation of the hydrogen partial pressure has allowed us to determine partial reaction orders for both CO oxidation and H 2 oxidation under PrOx conditions. An infrared band at ∼2113 cm −1, corresponding to on-top CO adsorption on metallic gold, has been observed below 150 °C. In addition, adsorbed hydroxyl groups gradually develop simultaneously to gas-phase water in the course of the reaction at increasing temperatures. The promotional effect of hydrogen is ascribed to highly oxidative H x O y intermediates formed from the interaction between H 2 and O 2 on the gold surface.

Degradation of gold and false golds used as gildings in the cultural heritage of Andalusia, Spain

Abstract The causes and degree of alteration of metals such as gold, tin, silver and bronze powders from ornamental implements of Andalusia Cultural Heritage have been studied. The unaltered gold is lost due to the alteration of the material used to adhere the leaf gold on the ceramic. Tin is transformed to romarchite and is lost due to a similar alteration as with the gold leaf adhesive. Silver is altered to Ag 2 S due to environmental contamination. Part of the bronze powders and silver used in Huercal-Overa altarpiece are altered to atacamite and AgCl, respectively, due to an unsuitable cleaning process.

Development of Traditional Cultural Products Using Persimmon Dyeing

This study purposed to restructure representative traditional patterns formatively, manufacture actual cultural products with traditional dyeing technique using persimmon, and commercialize the results of the research. Traditionally in Korea, the dying of natural fiber such as cotton, flax and silk with persimmon was called Galmul dyeing, and clothes made through Galmul dyeing were called Galot. Galot was very useful because it is strong, does not pick up dirt easily, dries easily, and is cool in summer. In addition, cloth dyed with persimmon becomes stiff, so it does not need to be starched or ironed after washing. Moreover, it does not transmit heat under direct rays and is highly air-permeable, so it is cool and useful for standing the heat. In this study, we used traditional persimmon dyeing technique, printing traditional patterns fit for contemporary people's aesthetic sense not through dip-dying but through printing. When persimmon dyeing is used in expressing patterns, it produces not only visual effect but also embossing effect due to the characteristic of persimmon that makes printed patterns stiff, so we can obtain unique texture distinguished from other printing methods. We chose seven motive patterns, which were lotus pattern symbolizing eternal life, peony pattern symbolizing wealth and rank and prosperity, character Su(壽) pattern widely used as a symbol of health, bird and cloud pattern in the Goryeo Dynasty, Sahapyeoeuisohwa(四合如意小花) pattern printed on brocade in the Goryeo Dynasty, lattice pattern, cloth pattern on wall paintings from the Period of the Three Kingdoms. From each pattern chosen as a motive was extracted unit patterns and the original pattern was restored using Adobe Illustrator. Restored patterns were restructured to be applied to cultural products fit for contemporary formative sense. Fabrics used in dyeing were cotton, linen, ramie, silk, and polyester. Although the same persimmon dyeing was applied, we produced different feelings of patterns using various fabrics and in some cases gold and silver powder was added for the effect of gloss in addition to the embossing of patterns. Using printed fabrics we manufactured tea pads, place mats, cushions, wrapping cloth for gifts, wallet, lampshades.

Organometallic chemistry and catalysis on gold metal surfaces

As in transition metal complexes, C N–R ligands adsorbed on powdered gold undergo attack by amines to give putative diaminocarbene groups on the gold surface. This reaction forms the basis for the discovery of a gold metal-catalyzed reaction of C N–R, primary amines (R′NH 2) and O 2 to give carbodiimides (R′–N C N–R). An analogous reaction of C O, RNH 2, and O 2 gives isocyanates (R–N C O), which react with additional amine to give urea (RNH) 2C O products. The gold-catalyzed reaction of C N–R with secondary amines (HNR′ 2) and O 2 gives mixed ureas RNH(C O)NR′ 2. In another type of gold-catalyzed reaction, secondary amines HN(CH 2R) 2 react with O 2 to undergo dehydrogenation to the imine product, RCH N(CH 2R). Of special interest is the high catalytic activity of gold powder, which is otherwise well-known for its poor catalytic properties.

Effect of Metal Powder Packing on the Conductivity of Nanometal Ink

The power of nanotechnology is realized in its application in numerous areas. One such area is undoubtedly the use of metallic nanoparticles as a direct write application. An effort in this area has resulted in a conductive ink whose conductivity approaches 60-70% that of the bulk copper. Such an ink has been developed by reducing silver, gold, and copper nano-sized powders by a wet method and followed by a heat treatment at less than 400 degrees C. The conductivity of the resulting ink product was found to be very much affected by how various sizes of metal powders are packed when particles were dried and packed on various substrates. The effect of packing and various kinds of metal powders on the eventual conductivity of the final product of the ink has been described and discussed in this paper.

Ethanol sensor based on ZnO and Au-doped ZnO nanowires

ZnO nanowires and Au-doped ZnO nanowires were prepared by oxidation reaction. The oxidation was performed by heating zinc powder and a mixture of zinc and 1 wt% gold powder which was pressed into a tube shape at 600 °C for 24 h. The ethanol sensors based on ZnO nanowires were simply fabricated by applying silver electrode at each end of the tube and inserting a coil heater into the tube. The ethanol sensing properties of ZnO nanowires were observed from the resistance change under ethanol vapor atmosphere. By considering the sensitivity and response time, the optimum operating temperature of the ethanol sensor was found to be 240 °C. Also, it was found that the sensitivity of the sensor based on Au-doped ZnO nanowires exhibits higher value than that of the sensor based on undoped ZnO nanowires.

Synthesis and crystal structure of [Co(NH3)6][AuX4]X2 (X = Cl−, Br−)

[Co(NH3)6][AuX4]X2 binary complex salts, where X = Cl− (I) and Br− (II), have been obtained and defined by element, X-ray diffraction, and thermal analyses and by IR, Raman, and electron spectroscopy. The compounds are isostructural. Their structural units are the [Co(NH3)6]3+ complex cations, the [AuX4]− complex anions, and the X− anions. The plane square environment of the gold atom is completed to an elongated bipyramid by two halide ions lying at distances Au...Cl 3.245 A for I and Au...Br 3.362 A for II. The thermolysis products of I and II are pure gold and cobalt metal powders when thermolysis is performed under hydrogen and a mixture of metallic gold with cobalt halide in a reaction under an inert atmosphere.

Non-nanogold Catalysis of Reactions of Isocyanides, Secondary Amines, and Oxygen to Give Ureas

Although numerous studies show that supported nanogold particles (<5 nm) catalyze a variety of reactions, the results presented in this paper show that unsupported bulk gold powder (∼1000 nm particle size), which is generally known to be a poor catalyst, catalyzes the reactions of isocyanides (R−N⋮C), secondary amines (HNR‘2), and O2 to give ureas OC(NHR)(NR‘2) under mild conditions (60 °C, 1 atm O2). Kinetic studies are consistent with a proposed mechanism.

Non-nanogold catalyzed aerobic oxidation of secondary amines to imines

Bulk gold powder (approximately 10(3) nm particle size) is a highly active catalyst for the oxidative dehydrogenation of secondary amines to imines under the mild conditions of 1 atm O2 and 60-100 degrees C.

Bindi dermatitis to ‘chandan’ bindi

Bindi (meaning dot in Sanskrit) is a mark worn by most Indian women on their forehead for religious and social purposes. Traditionally it was worn by only Hindu women to signify their marital status. Nowadays, it is a huge fashion accessory, being worn in different sizes, shapes, designs and colours. The variety includes sequined designs, motifs dusted with gold and silver powder, studded with beads, or even surrounded by glittering gems. Stick-on and liquid ranges are both equally in demand. We report a case of bindi dermatitis with 'chandan' (sandalwood) bindi. To our knowledge this is the first report of contact allergic dermatitis to 'chandan' (sandalwood) bindi.

Nonhydrostatic compression of gold powder to 60 GPa in a diamond anvil cell: estimationof compressive strength from x-ray diffraction data

Two gold powder samples, one with average crystallite size of≈30 nm (n-Au) andanother with ≈120 nm (c-Au), were compressed under nonhydrostatic conditions in a diamond anvil cell to different pressuresup to ≈60 GPa and the x-ray diffraction patterns recorded. The difference between the axial andradial stress components (a measure of the compressive strength) was estimated from theshifts of the diffraction lines. The maximum micro-stress in the crystallites (anothermeasure of the compressive strength) and grain size (crystallite size) were obtained fromanalysis of the line-width data. The strengths obtained by the two methods agreed well andincreased with increasing pressure. Over the entire pressure range, the strength of n-Au wasfound to be significantly higher than that of c-Au. The grain sizes of both n-Au and c-Audecreased under pressure. This decrease was much larger than expected from thecompressibility effect and was found to be reversible. An equation derived from thedislocation theory that predicts the dependence of strength on the grain size and theshear modulus was used to interpret the strength data. The strength derivedfrom the published grain size versus hardness data agreed well with the presentresults.

Dissolution kinetic model for metal powders — a case of varying surface area

A kinetic model for leaching particulate metals in a batch system was developed. The leaching mechanism was analyzed by solving a series of ordinary differential equations relating heterogeneous reaction kinetics at the solid/liquid interface to mass transfer of reactant and products. Special emphasis was given to the effects of substrate surface area changes and initial particle distribution on the overall leaching rate. The dissolution of gold powders in acidic solution with bromine as an oxidant was used as a model system. The effects of particle size. particle distribution, chemical reaction order, rate constant and mass transfer coefficient on the overall metal powder dissolution rate are analyzed and discussed.

3958 サブミクロン金粒子低温焼結体の引張特性評価におけるモデル化の検討(S21-4 微細構造体の設計と解析,S21 ナノ・マイクロ構造体の強度物性と信頼性)

3958 サブミクロン金粒子低温焼結体の引張特性評価におけるモデル化の検討(S21-4 微細構造体の設計と解析,S21 ナノ・マイクロ構造体の強度物性と信頼性)