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This is an overview of the early investigations into the mechanism of solid decompositions since the fundamental studies by Ostwald on catalysis during 1890–1902 and the first experimental study of the autocatalytic decomposition of Ag2O by Lewis in 1905. In order to explain the formation mechanism of the solid product, Volmer suggested in 1929 that the decomposition of Ag2O includes two sequential stages: first, a thermal decomposition of the oxide into gaseous silver atoms and oxygen molecules and second, the condensation of the supersaturated silver vapor. This revolutionary idea was immediately used by Schwab to explain the autocatalytic peculiarity of solid-state decomposition reactions. However, this mechanism did not receive the acceptance of the scientific community. On the contrary, as can be seen from the results presented at the conference “Chemical reactions involving solids” in Bristol in 1938, this model was dismissed as unrealistic and, as a result, was since forgotten. Instead, considerable attention at this conference was devoted to the disorder theory proposed earlier by Wagner and Schottky, and to the mechanism of ion transport in the solid crystals. During the subsequent 70 years, decomposition mechanisms have been interpreted, without visible progress, on the latter basis. The mechanism of congruent dissociative vaporization proposed independently in 1990 turned out to be in complete agreement with the Volmer–Schwab model. It has been treated with the same distrust. These historical events, in the author’s opinion, are responsible for the prolonged stagnation in the development of solid-state decomposition theory.

Quartz solubility in H 2 O-CO 2 fluids was measured at 800 °C and 10 kbar. Mixed fluids were generated from hydrous oxalic acid, silver oxalate, silver carbonate, and liquid H 2 O; solubility was determined by weight changes of the quartz crystals. Stringent blank tests and weighing procedures were used to establish the CO 2 and H 2 O contents of experimental fluids. Using experimentally constrained models of H 2 O activity and mixing of silica monomers and dimers, a logarithmic plot of monomer activity vs. H 2 O activity yields a linear data array of constant slope n insignificantly different from 4 ( n = 4.024, R 2 = 0.997), where n is the total monomer hydration number. Moreover, all high-quality quartz solubility data in H 2 O-CO 2 fluids at lower temperature and pressure fall on the same line when SiO 2 and H 2 O activities are calculated with this formulation. The same analysis for the dimer yields slope n of 7 ( n = 7.049, R 2 = 0.996). Our results show that neutral silica monomers and dimers have fixed stoichiometry of Si(OH) 4 ·2H 2 O and Si 2 O(OH) 6 ·4H 2 O (i.e., two solvating H 2 O molecules per Si) in H 2 O-CO 2 fluids for a large range of crustal metasomatic processes. This provides a simple basis for modeling H 2 O-CO 2 -SiO 2 fluids over a range of pressure, temperature, CO 2 , and SiO 2 activity.

Detailed analysis of the results of full potential linearized augmented plane wave (FP LAPW) ab initio calculations for anhydrous silver and cadmium oxalates, reported in first part of this paper [1] has been presented. Additional calculations of Bader’s AIM (Atoms in Molecules) topological properties of the electron density, bond orders (Pauling, Bader, Cioslowski and Mixon) and bond valences according to bond valence model have been done. The obtained results show the similarities in electronic structure of both compounds and support the conclusion, that during the thermal decomposition process, these compounds should most probably decompose to metal and carbon dioxide, in agreement with the experiment.

In this study, an orthogonal array design (OAD), OA9, was employed as a statistical experimental method for the controllable, simple and fast synthesis of silver oxalate nanorods. Ultrafine silver oxalate rods were synthesized by a precipitation method involving the addition of silver ion solution to the oxalate reagent. The effects of reaction conditions, i.e., silver and oxalate concentrations, flow rate of reagent addition and temperature, on the diameter of the synthesized silver oxalate rods were investigated. The effects of these factors on the width of the silver oxalate rods were quantitatively evaluated by the analysis of variance (ANOVA). The results showed that silver oxalate nanorods can be synthesized by controlling the silver concentration, flow rate and temperature. Finally, the optimum conditions for the synthesis of silver oxalate nanorods by this simple and fast method were proposed. The results of ANOVA showed that 0.001 mol/L silver ion concentration, 40 mL/min flow rate for the addition of the silver reagent to the oxalate solution and 0 °C temperature are the optimum conditions for producing silver oxalate nanorods with 107 ± 45 nm width.

Silver oxalate, one of the coordination polymer crystals, is a promising synthetic precursor for transformation into Ag nanoparticles without any reducing chemicals via thermal decomposition of the oxalate ions. However, its insoluble nature in solvents has been a great disadvantage, especially for systematic control of crystal growth of the Ag nanoparticles, while such control of inorganic nanoparticles has been generally performed using soluble precursors in homogeneous solutions. In this paper, we document our discovery of water-soluble species from the reaction between the insoluble silver oxalate and N,N-dimethyl-1,3-diaminopropane. The water-soluble species underwent low-temperature thermal decomposition of the oxalate ions at 30 °C with evolution of CO2 to reduce Ag+ to Ag0. Water-dispersible Ag nanoparticles have been successfully synthesized from the water-soluble species in the presence of gelatin via similar thermal decomposition at 100 °C. The gelatin-protected and water-dispersible Ag nanoparticles with a mean diameter of 25.1 nm appeared. In addition, antibacterial activity of the prepared water-dispersible Ag nanoparticles has been preliminarily investigated.

The pressure-temperature equilibrium curve of the reaction siderite + hematite = magnetite + CO 2 was determined in the range 5–12 kbar and 480–650°C by piston-cylinder experiments, with NaCl as a pressure medium. Silver oxalate was used as a CO 2 source and samples were buffered at hematite-magnetite oxygen fugacity. Reaction progress was monitored by extent of CO 2 gas loss and by X-ray diffraction (XRD) analysis. The data define a univariant curve, which is described by P = −14.599 + 0.025 T + 0.000027 T 2 with P in kbar and T in°C. Calculations based on these data give Δ H f 0 (298K) siderite = −760.6 ± 0.9 kJ (kilojoules) from the oxides. The formation of siderite requires a specific range of ambient oxygen and carbon dioxide fugacities, dependent upon temperature and pressure. The stable assemblage of siderite and magnetite, at a given temperature and pressure, implies more restrictive ranges of oxygen and carbon dioxide fugacities, defined by reactions among siderite, magnetite, graphite, and hematite. Experimental and thermodynamic investigation of the Fe-C-O system indicates that the formation of magnetite along with Ca-Fe-Mg carbonate globules by inorganic processes is possible and may be relevant to Martian meteorite ALH84001. Decarbonation of the siderite component of the carbonate, either by a transient heating event or by a change in oxygen fugacity of a coexisting fluid, may have formed the observed grains, although this study does not address the size or morphology of magnetite grains formed by this mechanism.

This is a review of the studies of the thermal decomposition of silver oxalate from 1950s through the 1990s. The role of various factors, which have influence on the thermal decomposition rate, is discussed. A detailed mechanism of the reaction is proposed, unsolved problems are summarised.

Currently, for the industrial ethylene epoxidation α-alumina supported silver catalysts are the only catalyst of choice. We demonstrate a novel method to produce these catalysts with different silver particle sizes, but without changing other key parameters that may affect the catalytic performance such as support specific surface area or metal precursor. α-Alumina was impregnated with a silver oxalate solution, and was subsequently dried and treated in different gas atmospheres and at different temperatures to tune the silver particle sizes in the range of 20–500 nm. Particles of 20 nm exhibited a lower turnover frequency than particles of 70 nm and larger, which exhibit a constant turnover frequency, in accordance with results in literature. However, the selectivity, when measured at constant conversion, was particle size independent. This is the first time that the effect of the particle size on the selectivity of ethylene epoxidation is reported at constant conversion. This was made possible by a new method of producing supported silver catalysts, which we expect that is also applicable for silver catalysts with other supports and for the preparation of other supported metal catalysts.

A newly developed silver nanoparticle ink for gravure offset printing has been prepared through the thermal decomposition reaction of silver oxalate. The resistivity of silver thin films made of the ink was estimated to be 3.1 µΩ cm by sintering at 250 °C, which is comparable to that of bulk silver. In addition, we achieved the patterning of fine lines with a width of 20 µm using the combination of the ink and gravure offset printing. The prepared ink could be used to fabricate various printed electronic circuits in the near future.

Crystallization of diamond was studied in the CO2–C, CO2–H2O–C, H2O–C, and CH4–H2–C systems at 5.7 GPa and 1200–1420°C. Thermodynamic calculations show generation of CO2, CO2–H2O, H2O and CH4–H2 fluids in experiments with graphite and silver oxalate (Ag2C2O4), oxalic acid dihydrate (H2C2O4·2H2O), water (H2O), and anthracene (C14H10), respectively. Diamond nucleation and growth has been found in the CO2–C, CO2–H2O–C, and H2O–C systems at 1300–1420°C. At a temperature as low as 1200°C for 136 h there was spontaneous crystallization of diamond in the CO2–H2O–C system. For the CH4–H2–C system, at 1300–1420°C no diamond synthesis has been established, only insignificant growth on seeds was observed. Diamond octahedra form from the C–O–H fluids at all temperature ranges under investigation. Diamond formation from the fluids at 5.7 GPa and 1200–1420°C was accompanied with the active recrystallization of metastable graphite.

Experiments to determine the distribution of H2O and CO2 between synthetic peraluminous granitic melt and natural Fe–Mg cordierite have been conducted at 5 kbar and 900 °C under fluid-saturated conditions. Up to seven charges, saturated with a range of H2O–CO2 fluid compositions, were run simultaneously. The H2O and CO2 contents of the cordierites and the H2O contents of the melts were determined using secondary ion mass spectrometry. As the CO2 content of the fluid increases, the H2O content of both the cordierite and the melt decrease in a similar manner to fluid-undersaturated experiments in the H2O only system. The cordierite H2O contents in the experiments range from 0.5 to 1.7 wt% H2O. The distribution coefficients (Dw=wt% H2O(melt)/wt% H2O(cordierite)) are in the range 3.5–5.9 and agree with the model of Harley and Carrington for 5 kbar and 900 °C. The CO2 content of the cordierite increases from 0 to 1 wt% CO2 in the most CO2-rich experiment as the cordierite and melt H2O contents decrease. Our H2O–CO2 cordierite data allow us to model and predict the maximum CO2 content in cordierite to be 0.16±0.01 molecules per formula unit (i.e. 1.16 wt% CO2) at 5 kbar and 900 °C. This value, and the channel CO2 contents of cordierite in equilibrium with H2O–CO2 fluids at high XCO2, are significantly lower than predicted using previous models. On the basis of these experiments cordierites that are saturated in H2O + CO2 and have channel XCO2>0.25 require aCO2 of over 0.75.

Fluid inclusions were synthesized in quartz from silver oxalate (Ag2C2O4) and a 6-wt.% NaCl aqueous solution to produce a CO2–H2O–NaCl fluid, following the method of previous workers. Synthesis conditions of 500–650°C and 1500–4500 bar were chosen with the intention of trapping a homogeneous, ternary fluid. The resulting inclusions were analyzed by microthermometry and by Raman spectroscopy. Solid residues in the experimental capsules were analyzed after the syntheses by XRD and SEM-EDS. Several properties of the synthetic inclusions were unexpected: TmCla and Thtot vary over significant ranges and they correlate negatively; the calculated total molar volumes deviate significantly from data on the same bulk composition derived by Gehrig [Gehrig, M., 1980. Phasengleichgewichte und pVT-Daten ternarer Mischungen aus Wasser, Kohlendioxid und Natriumchlorid bis 3 kbar und 500°C. Hochschul Sammlung Naturwissenschaft, Chemie, Band 1. Hochschul Verlag, Freiburg] in an optical cell, and from data derived from our fluid inclusions synthesized for comparison using the gas-loading technique of Frantz et al. [Frantz, J.D., Zhang, Y.-G., Hickmott, D.D., Hoering, T.C., 1989. Hydrothermal reactions involving equilibrium between minerals and mixed volatiles: 1. Techniques for experimentally loading and analyzing gases and their application to synthetic fluid inclusions. Chem. Geol. 76, 57–70]; all fluid inclusions contain a chlorargyrite (AgCl) daughter crystal; and HCO3− was detected in the aqueous phase of the inclusions by Raman spectroscopy, presumably reflecting high concentrations of NaHCO3(aq). All these anomalous features can be traced back to effects caused by precipitation of insoluble AgCl and simultaneous formation of sodium oxalate upon loading the experimental capsules with silver oxalate and NaCl solution. Reconstruction of the chemical reactions that occurred during the hydrothermal syntheses suggests that incomplete redissolution of the AgCl during progressive quartz precipitation and fluid trapping yields inclusions with variable bulk properties. Nevertheless, quite accurate total homogenisation temperatures can be recovered by regressing the Thtot–TmCla correlations, but considerable effort is required. We conclude that silver oxalate should be used in combination with chloride solutions only with extreme caution, whereas the gas-loading technique provides an excellent alternative for the synthesis of CO2–H2O–NaCl fluid inclusions.

A brief search in Sci Finder for oxalic acid and oxalates will reward the researcher with a staggering 129,280 hits. However, the generation of alkali metal and silver anions via collision-induced dissociation of the metal oxalate anion has not been previously been reported, though Tian and coworkers recently investigated the dissociation of lithium oxalate [18]. The exothermic decomposition of alkali metal oxalate anion to carbon dioxide in the collision cell of a triple quadrupole mass spectrometer leaves no place for the electron to reside, resulting in a double electron-transfer reaction to produce an alkali metal anion. This reaction is facilitated by the negative electron affinity of carbon dioxide and, as such, the authors believe that metal oxalates are potentially unique in this respect. The observed dissociation reactions for collision with argon gas (1.7–1.8 × 10−3 mbar) for oxalic acid and various alkali metal oxalates are discussed and summarized. Silver oxalate is also included to demonstrate the propensity of this system to generate transition-metal anions, as well.

Activity-composition relations in CO 2 -H 2 O solutions were determined at 6, 10, and 14 kbar over broad temperature-fluid composition ranges from 70 reversed determinations of three simple-system decarbonation and dehydration reactions: CaCO 3 (calcite) + SiO 2 (quartz) = CaSiO 3 + CO 2 (WQC)(wollastonite); MgCO 3 (magnesite) + MgSiO 3 (enstatite) = Mg 2 SiO 4 (forsterite) + CO 2 (FEM); Mg 3 Si 4 O 10 (OH)2(talc) = 3 MgSiO 3 (enstatite) + SiO 2 (quartz) + H 2 O (TEQ). Brackets of WQC and FEM were achieved by reversing, at constant T and P, the fluid composition coexisting with the assemblages of either reaction, starting with fine-grained mixtures of reactants and products in nearly equimolar amounts and liquid water, oxalic acid, and silver oxalate as fluid sources. Brackets of TEQ were secured by reversing the reaction over narrow temperature intervals at constant P and fluid composition. All experiments were made in the piston-cylinder apparatus with NaCl or NaCl-soft glass pressure media, and all experiments with two-component fluids were buffered at hematite-magnetite. Closure intervals of reversed fluid composition averaged less than 2 mol% CO 2 . Activity values of H 2 O (1) and CO 2 (2) were retrieved based on the THERMOCALC 2.3 thermodynamic data set of Holland and Powell (1994), which includes equations of state of H 2 O and CO 2 , supplemented by several tight reversals of the end-member equilibria. A simple van Laar-type expression reproduces our composition determinations with a standard deviation of only 1.2 mol% CO 2 : RT 1ngamma 1 = (X 2 ) 2 W {V 0 1 V 02 2 /[V 0 1 +V 0 2 )(X 1 V 1 0 +X 2 V 2 0 ) 2 ]} RT 1ngamma 2 = (X 1 ) 2 W {V 0 1 V 02 2 /[V 0 1 +V 0 2 )(X 1 V 1 0 +X 2 V 2 0 ) 2 ]} where V 0 1 and V 0 2 are, respectively, the specific volumes of pure H 2 O and CO 2 at a given (P,T), the X9s are the mole fractions, the gamma 9s the activity coefficients and W is analogous to a regular solution parameter: W = (A+BT)[1-exp(-20P)]+CPT, with T in K and P in kbar. The best-fit values of the constants are: A = 12893 J, B =-6.501 J/K, C = 1.0112 J/(K.kbar). With these formulas, the activity-concentration relations of CO 2 -H 2 O solutions may be reconstructed in a broad P-T-X range using any reasonably accurate equations of state of pure CO 2 and H 2 O. The activity-concentration relations are closely similar to the modified Redlich-Kwong (MRK) reconstruction of Kerrick and Jacobs (1981) to pressures of 6 kbar, but the binary fluids have marginally greater positive non-ideality than the MRK predictions at 10 kbar and significantly greater non-ideality at 14 kbar. The present results can serve as a basis for reliable calculations of mineral-fluid equilibria in metamorphism of the deep crust and upper mantle.

The reaction of the dimeric rhodium-complexes [CpxRhCl2]2 (Cpx=C5Me5, C5 tBu2H3) with silver oxalate Ag2C2O4 leads to polymeric species with the formula [CpxRh(C2O4)]n in high yields. These compounds react with Lewis-bases L [L=DMSO, P(OMe)3, PPh3, P(C8H17)3] under depolymerisation to addition products of the type CpxRh(C2O4)L. The solubility of these compounds depends on the ligand L. While Cp*Rh(C2O4)P(OMe)3 is only soluble in polar organic solvents, Cp*Rh(C2O4)P(C8H17)3 can be dissolved in unpolar solvents like alkanes. All these compounds are resistant against air and moisture. The structure of Cp*Rh(C2O4)P(OMe)3 has been solved by X-ray analysis. UV-irradiation of Cp*Rh(C2O4)L (L=P(OMe)3, PPh3) in CHX3 (X=Cl, Br) results in the elimination of CO2 and in the formation of the substitution products Cp*RhX2L.

The P-T equilibrium curve of the reaction of magnesite 1 enstatite 5 forsterite and CO2 was determined in the ranges 6‐25 kbar and 700‐1100 8C by 53 reversed experiments carried out in 1.91 cm diameter piston-cylinder apparatus with NaCl pressure medium. Silver oxalate was used as a CO2 source and charges were buffered at hematite-magnetite oxygen fugacity. Reaction progress was monitored by weight changes upon puncturing of CO2-inflated quenched charge capsules and was confirmed by comparing X-ray diffractograms of charges made before and after the experiments. The data satisfy the relation: PEQ 52 3.215 2 4.784 3 10 23 T 1 2.542 3 10 25 T 2 with P in kbar and T in 8C. A P-T curve calculated with the 1994 version 2.3 THERMOCALC program agrees well with our results except in the highest pressure range. Our data, together with three existing tight experimental brackets on the decarbonation reaction of magnesite to periclase and CO2, give DH (298 K) (forsterite) 52 61.20 6 0.87 kJ/mol from the oxides. This value is in 0 f agreement with the value adopted by Berman (1988). An analysis of various proposed

The results of a single-crystal structure solution and refinement for silver oxalate are reported. Possible anion-anion, cation-cation and anion-cation interactions in the crystal and their role in the solid-state decomposition are discussed on the basis of (i) a detailed analysis of the Ag 2 C 2 O 4 crystal structure, (ii) a statistical analysis of data from Cambridge Structural Database and (iii) ab initio calculations. The role of interstitial silver cations in the decomposition of silver oxalate is also considered from a structural point of view.

The carbon solubility in a Mid-Ocean Ridge Basaltic (MORB) melt was determined by equilibrating natural glass with CO2 produced by decomposition of silver oxalate. These experiments were performed in closed platinum capsules in an internally heated pressure vessel at 1200 and 1300°C, at oxygen fugacity close to the QFM buffer and at pressures between 250 and 1950 bar. Carbon was extracted by incremental heating to fusion and determined by manometry after oxidation to CO2. This method separates small contributions from bubbles trapped in the experimental melts and extracts all the dissolved carbon regardless of its chemical form. Linear correlation between total dissolved C and the total pressure was observed, confirming that carbon solubility obeys Henry's law in the range 0–2000 bar. This yields a best fit minimum solubility of 0.137 ± 0.004 ppm C/bar which can be applied to MORB at crustal pressures. These experimental glasses, measured by FTIR for carbonate ion absorptions, provide a new determination of the CO32− molar absorption coefficient (e = 398 ± 10 l mol−1 cm−1) in perfect agreement with an independent natural sample calibration (e = 397 ± 7 l mol−1 cm−1). Comparison to results from literature dissolved C contents of MORB glasses confirms that many are supersaturated at eruption as a result of slow kinetics of degassing, while a few others are undersaturated because of either C loss during degassing of water-rich melts or generation from carbon-poor sources.

Near-infrared surface-enhanced Raman scattering (NIR SERS) spectra were obtained for 2,2-bipyridine, 5,6-benzoquinoline, pyrene, anthracene, and fluoranthene on SERS pre-activated thin-layer chromatography (TLC) plates by Fourier transform (FT) Raman spectroscopy. The pre-activation of TLC plates was based on a procedure of dipping the plates into a solution of silver oxalate and the subsequent pyrolysis of adsorbed silver oxalate forming silver particles on the plates. The effects of the type of TLC plates, the time of immersion in the silver oxalate solution, and the time of pyrolysis are discussed with respect to the SERS activity of the systems formed.

International audience; Micrometric oxalate powders can be decomposed starting from temperatures as low as 90°C, leading to the formation of temporary nanometric grains of metallic silver with a high propensity for sintering. The decomposition being highly exothermic, this additional energy favours the sintering, i.e. the soldering, process. Solders processed at 300°C and very low pressure (

The effects of packing materials on H infiltration into sample capsules during pistoncylinder experiments has been examined using samples of oxalic acid dihydrate, silver oxalate, and pure carbon dioxide. Mass scans revealed that as much as several mole percent carbon monoxide, accompanied by H20, can result from a reaction between H and carbon dioxide in experiments using all three reactants. A measurable 0 isotopic shift was detected in carbon dioxide samples where carbon monoxide was detected. Traditional means for measuring C-O-H volatile composition at the end of piston-cylinder experi~ents will not ident~fYthis chemical change in the volatile composition and may result m erroneous determmation of fluid composition. Glass and witherite packing materials effectively maintaineda lowfH2 around the samples.

A new high pressure-temperature (P -T Neutron Reflectometry (NR) cell developed at Los Alamos National Laboratory (LANL) is described that significantly extends the capabilities of solid/fluid interface investigations up to 200MPa ( \(\ensuremath \sim 30000\) psi) and 200 ° C. The cell's simple aluminum construction makes it light and easy to operate while thinned neutron windows allow up to 74% neutron transmission. The wide-open neutron window geometry provides a maximum theoretical \(\ensuremath Q_{{\rm z}}\) range of 0.31A-1. Accurate T and P controls are integrated on the cell's control panel. Built-in powder wells provide the ability to saturate fluids with reactive solids, producing aqueous species and/or decomposing into gaseous phases. The cell is designed for samples up to 50.8mm in diameter and 10.0mm in thickness. An experiment investigating the high P -T corrosion behavior of aluminum on LANL's Surface ProfilE Analysis Reflectometer (SPEAR) is presented, demonstrating the functioning and capability of the cell. Finally, outlooks on high P -T NR applications and perspectives on future research are discussed.

The crystal structure of Ag2C2O4 was determined; space group P21/c, a=3.4603(5), b=6.1972(9), c=9.548(2) A, β=103.47(1)0, V=199.12(6) A3, Z=2, dcalc=5.066 g/cm3 (Syntex P21 automatic diffractometer, CuKα radiation, ф/2ф scan mode with a rate of 1.98–14.5 deg/min to 2θmax=115°, 548 measured and 274 independent Ihkl, R(F)=0.259). The structure is channel type ionic, with single-layer packing of anions in the (100) plane according to the hexagonal law. In the channels stretched along [100], there are silver dimers with the Ag−Ag distance of 2.945 A. The C2O 4 2− anion has $$\bar 1$$ symmetry; the C−C bond lengths are 1.60(1) and C−O are 1.23(1) and 1.24(1) A. The observation and X-ray diffration monitoring of the initial stage of photolysis allowed us to conclude that it proceeds in a thin surface layer and has no effect on the crystal struture. The obtained results are discussed in the light of the literature data on the photolysis and thermolysis mechanisms of Ag2C2O4. The results of previous structural studies are analyzed.

The solubility of carbon dioxide in a Ca-rich leucitite has been investigated as a function of pressure (0.1–2.0 GPa), temperature (1200–1600°C), and oxygen fugacity. The experiments were done in a rapid-quench internally-heated pressure vessel (0.1 GPa) and a piston cylinder (0.5–2.0 GPa). The leucitite glass, previously equilibrated at NNO, and silver oxalate were loaded in Fe-doped Pt capsules (oxidized conditions) and graphitelined Pt capsules (reduced conditions). Secondary Ion Mass Spectrometry and bulk carbon analyses were used to determine the amount of dissolved carbon. Speciation of carbon was characterized by Fourier transform microinfrared spectroscopy. At oxidized conditions, only CO3 2- is observed as a dissolved species. The solubility is high with CO2 contents in the melt attaining 6.2 wt% at 2.0 GPa and 1350°C. The solubility increases with pressure and shows a significant negative temperature dependence. An excellent correlation is obtained when the data are fit to a model, based on the simplified solubility reaction CO2 (vapor)+O2-(melt)⇒CO3 2-(melt), which describes the solubility of CO2 as a function of pressure, temperature and fCO2. At reduced conditions, the amount of carbon dissolved is significantly lower, and CO3 2- is still the only species present in the melt. If the solubility model established at oxidized conditions is applied, the carbon dissolved appears to be essentially a function of fCO2 alone although divergence increases in a consistent manner with pressure and temperature. This could suggest a low but significant solubility of CO with a positive temperature dependence or a departure of the calculated fluid compositions determined by the equation of state from the actual ones. The strong preferential solubility of carbon in its oxidized C4+ form, even at reduced conditions, implies that ascending melts with high CO2 solubility can experience significant oxidation through degassing. This could reconcile the oxidized nature of some Ca-rich alkaline magmas with more reduced mantle source regions.

Anisotropic silver nanoparticles (NPs) have been synthesized rapidly using microwave irradiation by the decomposition of silver oxalate in a glycol medium using polyvinyl pyrolidone (PVP) as the capping agent. The obtained Ag nanoparticles have been characterized by UV-visible spectroscopy, powder x-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) studies. Anisotropic Ag nanoparticles of average size around 30 nm have been observed in the case of microwave irradiation for 75 s whereas spherical particles of a size around 5-6 nm are formed for 60 s of irradiation. The texture coefficient and particle size calculated from XRD patterns of anisotropic nanoparticles reveal the preferential orientation of (111) facets in the Ag sample. Ethylene glycol is found to be a more suitable medium than diethylene glycol. A plausible mechanism has been proposed for the formation of anisotropic Ag nanoparticles from silver oxalate. � IOP Publishing Ltd.

Triphenyltin chloride reacts with equimolar amounts of tetramethylammonium chloride and of silver oxalate to yield tetramethylammonium bisoxalatotris(triphenylstannate). A crystal structural study has shown the trinuclear stannate to be composed of helical [Ph 3 Snox · (Ph 3 Sn) 2 ox] n n − chains that run parallel to the b -axis; the cations fill up the space between the chains. The structure is an unusual example of a triorganotin compound having within the same molecule five-coordinate tin sites in distinct cis - and trans -trigonal bipyramidal geometries.

Oxidation of diphenylantimony fluoride and thiocyanate with t-butyl hydroperoxide leads to tetrameric products containing a four-membered Sb2O2 ring with a further antimony atom, carrying respectively either two fluorine or two thiocyanate substituents, attached via a single oxygen bridge to each of the ring antimony atoms. This is in contrast to the formation of simple four-membered ring compounds when the corresponding bromide and chloride are oxidised. The reaction between [Ph2SbOBr]2 and silver oxalate is not a simple substitution and the product is a complex salt whose cation contains a planar twelve-membered Sb6O6 ring.

The kinetics and thermal stability of copper oxalate prepared under stoichiometric and non-stoichiometric conditions have been studied by isothermal and rising temperature experiments in nitrogen and in air. In addition, a mechanism-independent method and a computer program were used to interpret the isothermal data to give additional information on the stability of the systems. In nitrogen, the presence of excess copper chloride stabilizes the salt whilst the presence of excess oxalic acid reduces the stability. This trend is also observed for silver oxalate. The interpretations of the stability of the salts based solely on the activation energy were misleading. The use of a computer program shows that a more accurate evaluation requires the consideration of the pre-exponential factor and the reaction mechanism in addition to the activation energy.

Worm-like nanorods and nanospheres of silver have been synthesized by photochemical decomposition of silver oxalate in water by UV irradiation in the presence of CTAB and PVP, respectively. No external seeds have been employed for the synthesis of Ag nanorods. The synthesized Ag colloids have been characterized by UV-visible spectra, powder XRD, HRTEM, and selected area electron diffraction (SAED). Ag nanospheres of average size around 2 nm have been obtained in the presence of PVP. XRD and TEM analyses revealed that top and basal planes of nanorods are bound with {111} facets. Williamson–Hall plot has revealed the presence of defects in the Ag nanospheres and nanorods. Formation of defective Ag nanocrystals is attributed to the heating effect of UV-visible irradiation.

The solubility of carbon dioxide in tholeiitic melt (1921 Kilauea basalt ) was determined under experimental conditions of 1 kbar, 1200°C; 10 and 15 kbar and 1300–1600°C. We examined the solubility at pressure and temperature conditions intermediate to those reported in previous studies, and, in particular, we addressed the effect of temperature on carbon dioxide solubility. Two different carbon sources were used in the experiments, silver oxalate and a mixture of carbonate minerals, to examine the effects of dissolved silver on carbon dioxide solubility. Three analytical methods were employed to measure accurately and precisely the dissolved carbon in the run products: ( 1 ) Fourier transform micro-infrared spectroscopy, ( 2 ) secondary ion mass spectrometry, and ( 3 ) bulk carbon analysis with a Perkin Elmer Elemental Analyzer. The first two methods are micro-beam techniques which allowed for assessment of sample homogeneity. Consistent with previous solubility studies, infrared analyses showed that carbon is dissolved in basaltic melt in the form of carbonate. However, our experimental results differ from the previous solubility study in that we demonstrate carbon dioxide solubility is temperature independent. At 1 kbar and 1200°C, carbon dioxide solubility is 543 ppm; at 10 kbar and 1300, 1400, and 1500°C, carbon dioxide solubility is approximately 0.77 ± .07 wt%; and at 15 kbar and 1400, 1450, 1500, 1550, and 1600°C, the solubility is approximately 1.21 ± .13 wt%. Dissolved silver does not appear to affect the solubility. These results invalidate previous models for carbon dioxide solubility. We have developed a new model which describes the pressure and temperature dependence of carbon dioxide solubility for tholeiitic basalts. Regression of the solubility data for the reaction CO2vapor + O2−melt = CO32−melt gives a heat of solution (ΔH0 at 1 kbar and 1473 K) of 5.20 ± 4.30 kJ/mol and the change in partial molar volume ΔV0[CO32−melt− O2−melt of 23.14 ± 1.03 cm3/mol. Application of this model suggests that fluid-saturated partial melting of the MORB source region cannot be supported.

The thermal decomposition of silver oxalate has been studied using mechanism-dependent and mechanism-independent isothermal kinetics, conventional rising temperature thermogravimetry (TG) and a TG computer program. Studies were carried out on four different preparations of the sample which involved precipitation from stoichiometric and non-stoichiometric conditions. Each sample was studied under atmospheres of nitrogen, air, oxygen, and carbon dioxide as well as under vacuum. The assignment of stability information based on the magnitude of the Arrhenius parameters is shown to be deceptive. Applying the computer program and the limiting kinetic condition of α → 0 allows the relative stability of various preparations and the retarding influence of oxygen and carbon dioxide, to be quantitatively evaluated.

The thermal decomposition of silver oxalate has been carried out under isothermal conditions using atmospheres of nitrogen, air, oxygen and carbon dioxide, as well as under vacuum. The decomposition results obtained are treated by conventional methods to obtain the reaction mechanisms, φ(α), and by the integral method to obtain the rate constants and hence the Arrhenius parameters. Differential scanning calorimetry (DSC) has been used to follow the energy profile of the decomposition and in each case the decomposition has been found to be exothermic and the final product to be silver metal. The exothermic nature can be explained on the basis of conventional thermodynamics, although a release of the strain set up in the solid during the decomposition is proposed to account for the unsymmetrical energy profiles obtained.

The early data of Griffith (J. Chem. Phys. (1943), pp. 499-505] and of Kolesnikov & Baumer (Vestn. Khar'k. Univ. Ser. Khim. (1975), 127, 38-41] on the structure of silver oxalate, 2Ag + .C 2 O 4 2− , are revised and refined. In the structure, the oxalate anions form a framework with channels extended along [100] and Ag + cations are located in these channels, forming dimers with an Ag-Ag bond distance of 2.945 (1) A (close to that in metallic Ag). A noticeable elongation of C-C bond is observed

The crystal structure of trimethylsulfonium oxalatotriphenylstannate, C23H24O4SSn, synthesized from the metathetical reaction of trimethylsulfonium iodide, silver Oxalate and triphenyltin chloride in methanol, consists of [(CH3)3S]+ ions interspersed among the linear [(C6H5)3SnO2CCO2] n n− chains that are constructed from [O2CCO2]2− dianions bonded axially to planar [(C6H5)3Sn]+ (Sn–O = 2.220(3) Å, ΣC–Sn–C = 360.0(4)°) cations.

In this paper, silver colloidal solutions have been synthesized rapidly in green conditions by using microwave irradiation and non-toxic chemistry substances (acid oxalic, silver nitrate, polyvinyl pyrolidone (PVP; Mw = 55 000)). The particle size and morphology of these solutions can be controlled by altering several factors like the time, the power of microwave exposure, and the ratio of silver oxalate and PVP etc. The silver nanoparticles were fabricated by thermal decomposition of silver oxalate. The synthesized silver colloidal solutions and silver nanoparticles were characterized by several analytical techniques like UV- VIS, XRD, TEM, FESEM/EDS and ICP-AAS studies. Finally, we used the synthesized silver colloidal solutions for antibacterial purpose. The obtained results showed that the synthesized silver colloidal solutions, even at very low concentrations, have highly efficient anti-bacterial property.

Well crystallized silver chalcogenides were synthesized by a solvothermal reaction of silver oxalate Ag2C2O4 with chalcogens in organic solvents at relatively low temperature (140 °C-180 °C). It was found that both solvents and temperature have significant influence on the synthesis of silver chalcogenides.

The course of the reaction between triphenylantimony dichloride and silver oxalate depends on both the solvent and temperature at which the reaction is carried out. No reaction occurs in toluene at room temperature, but on refluxing the solution, crystals of [SbPh4][SbPh2(ox)2]1[ox = oxalate(2–)], an ionic form of SbPh3(ox), are obtained. Covalent SbPh3(ox), on the other hand, is probably the initial product of reaction in methanol at room temperature, but on recrystallisation from hot methanol, crystals of a methoxy derivative, [SbPh3(OMe)]2ox 2, are obtained. Structures have been determined for both compounds. Compound 1 consists of tetrahedral [SbPh4]+ cations and octahedral [SbPh2(ox)2]– anions containing two chelating oxalate groups and phenyl groups in cis positions. The methoxy derivative 2 is centrosymmetric, with a quadridentate oxalate group and each antimony octahedrally co-ordinated to three phenyl groups, one methoxy group and two oxygens from the oxalate group. A quadridentate oxalate group is also present in (SbPh4)2ox 3, obtained from [SbPh4]Br and silver oxalate. The structure contains two essentially identical, independent, centrosymmetric molecules with antimony again in distorted-octahedral co-ordination.

Treatment of diphenylantimony bromide oxide, (Ph2SbBrO)2, with silver oxalate leads to a novel ionic product, containing a planar twelve-membered cyclic antimony–oxygen dication in which two pairs of adjacent antimony atoms are further linked by hydroxy bridges to give Sb2O2 rings and a quadridentate oxalate is coordinated between the two remaining antimony atoms of the ring; the counter ions are two cis-dioxalatodiphenylantimony anions.

Sowohl durch mechanische Bearbeitung als auch durch Bestrahlung von Silberoxalat wird die Konzentration an Frenkel-Defekten im Kristallgitter stark erhoht. Hierdurch werden der mit einem Elektronenubergang verbundene Zerfallsprozes erleichtert und die Ag-Keimbildung beschleunigt. Bei langerer Bearbeitungsdauer wird die Reaktionshemmung durch Keimbildung nahezu vollstandig aufgehoben. Das Keimwachstum an bestrahlten Proben vollzieht sich zu Beginn der Zersetzung dreidimensional, in einem spateren Zersetzungsstadium dagegen eindimensional. Durch Oberflachenvergroserung ist bei der mechanischen Bearbeitung das Gebiet des dreidimensionalen Wachstums starker ausgedehnt. Bei der mechanischen Bearbeitung von unterschiedlich Cu2+-dotiertem Silberoxalat kommt es zu einer uberlagerung von zwei entgegengesetzt auf die thermische Stabilitat des Gitters einwirkenden Effekte. On the Thermal Decomposition of Mechanically Activated and γ-Radiation-treated, Pure and Doped Silver Oxalate Both on mechanical activating and on γ-radiation treating of silver oxalate, the concentration of Frenkel defects in the crystal lattice is strongly increased, leading to a facilitation of the electron transfer decomposition process and to an acceleration of the Ag° nucleation. At longer treating the reaction inhibition is almost completely compensated by nuclei formation. In the beginning of the decomposition, the nuclei grow 3-dimensionally, at a later stage, however, 1-dimensionally. Due to an increase of the surface in the case of mechanical treatment the range of 3-dimensional growth is more extended. On mechanical treating of variously Cu2+ doped silver oxalate two overlapping effects, acting contrarily on the thermal lattice stability, result.

The effect of mechanical pretreatment on the thermal decomposition of silver oxalate was investigated using mass-spectrometric thermoanalysis. Starting at different levels of predecomposition, kinetic data were obtained by analysis of the kinetics at the initial rise of decomposition. The observed mechanically induced increase in reactivity of the silver oxalate used is due to three effects: (i) A thermally more stable “phase” at the surface of the grains is rendered ineffective by the creation of new surfaces. (ii) Disintegration processes increase the specific surface by several orders of magnitude. (iii) The number of potential nuclei in the surface is considerably increased by the generation of lattice defects.

Silver oxalate films have been formed on silver electrodes by polarizing them slightly cathodically in dilute aqueous solutions containing Ag+ ions and dimethyl oxalate. The solutions were supersaturated with silver oxalate which was produced as a result of the hydrolysis of dimethyl oxalate and was sparingly soluble. The supersaturation was maintained during the film formation.The potential of the silver electrode with silver oxalate formed at a very low current density, showed a linear response to the oxalate ion concentration between 10-4 and 10-1 M.

The thermal decompositions of the even silver dicarboxylates from silver oxalate to silver sebacate were studied. In vacuum, the dicarboxylates decomposed to give metallic silver, CO2 and organic diradicals as primary products, and polymers as secondary products. The higher silver dicarboxylates were much more stable to thermal treatment than silver oxalate, probably due to the initiation of decomposition of all carboxylates except silver oxalate by the rupture of a Ag-O and not a C-C bond.

A little-known staining technique has been applied to a variety of nervous tissues, and variants have been devised for paraffin and cryostat sections.

Conditions of generation and removal are considered for one type of paramagnetic center produced in polycrystalline silver oxalate by X-rays, γ-rays, and UV light. The ESR spectra show that these are C2O 4 − ions trapped at cation vacancies. The mechanisms of photolysis and radiolysis are discussed.