Decomposition of silver carbonate

In a DTA study [1193] of decomposition reactions in Ag2C03 + CaC03 mixtures, the presence of a response peak, absent on heating the silver salt alone, resulted in the identification of the double salt Ag2C03 2 CaC03, stable at 420 K. One important general consideration which arises from this observation is that the formation of a new phase, by direct interaction between the components of a powder mixture, could easily be overlooked and, in the absence of such information, serious errors could be introduced into attempts to formulate a reaction mechanism from observed kinetic characteristics. Due allowance for this possibility must be included in the interpretation of experimental data. 

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The last example in Fig. 7.12 represents the thermal decomposition of silver carbonate, Ag2C03, in helium. A mass of 100 mg of the sample was heated at 4 K/min. At about 400 -550 K the carbonate loses carbon dioxide and changes into the oxide Ag20. A second, smaller mass loss begins at a temperature of 675 K. Both mass losses are endothermic, meaning that the reactions are entropy driven. The final product in the decomposition is metallic silver. 

The studies of the influence of foreign gases are very few however, frequently, a catalytic effect of the water vapor that seems to accelerate the reaction was noted. In the case of the decomposition of silver carbonate, the curve in Figure 13.5a shows this acceleration. The other gases often have, on the contrary, a reducer effect on the speed however, Bardel announces the presence of a minimum in the influence of the oxygen pressure on the rate of decomposition of silver carbonate [BAR 78] (Figure 13.5b). 

Figure 13.5. Influence of a foreign gas in the decomposition of silver carbonate...

In the decomposition of silver carbonate to form metallic silver, carbon dioxide gas, and oxygen gas, (a) one mol of oxygen gas is formed for every 2 mol of carbon dioxide gas (b) 2 mol of silver metal is formed for every 1 mol of oxygen gas (c) equal numbers of moles of carbon dioxide and oxygen gases are produced (d) the same number of moles of silver metal are formed as of the silver carbonate decomposed. 

Preliminary experiments on the coupling of the chloride (lb) with digitoxigenin (3/ ,14,/ -dihydroxy-5/ -card-20(22)-enolide) in the presence of silver carbonate, led to gross decomposition of the halide, and it was suspected that, under the conditions of the experiments, the silver carbonate was causing elimination of hydrogen chloride. When, however, digitoxigenin was treated with an excess of lb in a small volume of... 

Potassium nitrite, KN02.—The nitrite is made by the reduction of potassium nitrate by heating it alone, or with metals such as lead and iron, or with substances containing sulphur or carbon. It is also formed from potassium nitrate by electrolysis with a silver cathode and a copper anode, the yield being almost quantitative.8 The pure salt can be obtained by precipitating the aqueous solution with methyl alcohol.9 Another method for the production of the nitrite depends on the double decomposition of silver nitrite and lithium chloride.10... 

McCowan [38] used electron microscopic and X-ray measurements to study the thermal decomposition of silver acetylide. Although detailed or-time relationships could not be established, the value of was estimated to be 170 kJ mol in the interval 388 to 408 K. The rate-limiting step was identified as the production of an electron and an acetylide radical that react fiirther to yield amorphous carbon. Decomposition is catalyzed by the product, probably metallic silver, and explosion was ascribed to the accumulation of catalyst rather than heat. 

Many kinetic studies of the thermal decomposition of silver oxalate have been reported. Some ar-time data have been satisfactorily described by the cube law during the acceleratory period ascribed to the three-dimensional growth of nuclei. Other results were fitted by the exponential law which was taken as evidence of a chain-branching reaction. Results of both types are mentioned in a report [64] which attempted to resolve some of the differences through consideration of the ionic and photoconductivities of silver oxalate. Conductivity measurements ruled out the growth of discrete silver nuclei by a cationic transport mechanism and this was accepted as evidence that the interface reaction is the more probable. A mobile exciton in the crystal is trapped at an anion vacancy (see barium azide. Chapter 11) and if this is further excited by light absorption before decay, then decomposition yields two molecules of carbon dioxide ... 

The thermal decomposition of silver acetyhde, (Ag+)2 C=C, is unusual in that it is a potentially explosive reaction in which no gases are evolved18. The material explodes when dropped on to a surface at 195-200 °C but the reaction may be carried out in a controlled way by heating the solid at 115-135 °C to give silver and carbon, and there has been some interest in the microcrystalline structure of the silver formed in this way19. 

The thermal decomposition kinetics of silver carbonate using the disk technique was reported by Wvdenen and Leban (59). Continuous, in siru quantitative analysis of infrared active reactants and products of the decomposition reactions was made possible by use of a heated cell. The cell was constructed of stainless steel and could be heated to 500 C with the KRS-5 cell windows maintained at room temperature by cooling water. A similar approach was used by Wendlandt (60). 

The capillarity of carbon nanotubes offers two key properties, low chemical reactivity and superior burst strength. The hollow core of a carbon nanotube has been known to suck in water despite the hydrophobic nature of graphite, or molten metal such as lead [17] [52] and it has recently been filled, also by capillary forces, with molten silver nitrate [53]. Only nanotubes with a minimum capillary diameter of 4 nm were required, and found to be chemically less reactive than graphite. This property has been illustrated by monitoring the decomposition of silver nitrate within nanotubes in-situ in an electron microscope. In the nanospace available, chains of silver nanobeads were produced, separated by gas pockets developing gas pressures of up to 1300 bar at room temperature. 

Dentzer et al. examined the adsorption and decomposition of silver diamine complexes from ammonical solution on a graphitic carbon black activated to different degrees of bum-off and observed that the amount of silver adsorbed increased with increase in the degree of bum-off. A linear relationship was observed between the amount of silver adsorbed and the ASA as determined by the Walker method. This was attributed to specific reductive interaction of silver diamine with the carbon active sites producing metallic silver, which was chemisorbed on the active sites. 

Bromocyclopropane has been prepared by the Hunsdiecker reaction by adding silver cyclopropanecarboxylate to bromine in dichlorodifluoromethane at —29° (53% yield) or in tetrachloro-ethane at —20° to —25° (15-20% yield).3 Decomposition of the peroxide of cyclopropanecarboxylic acid in the presence of carbon tetrabromide gave bromocyclopropane in 43% yield.4 An attempt to prepare the bromide via the von Braun reaction was unsuccessful.3... 

Above 140°C its exothermic decomposition to metal and carbon dioxide readily becomes explosive [1], A 1 kg batch which had been thoroughly dried at 50°C exploded violently when mechanical grinding in an end-runner mill was attempted [2], Explosions have been experienced when drying the oxalate as low as 80°C [6], It is a compound of zero oxygen balance. The explosion temperature of the pure oxalate is lowered appreciably (from 143 to 122°C) by application of an electric field [3], The salt prepared from silver nitrate with excess of sodium oxalate is much less stable than that from excess nitrate [4], Decomposition at 125°C in glycerol prevents explosion in the preparation of silver powder [5],... 

Decomposition of the salt at 375°C under nitrogen, with subsequent cooling under hydrogen, gives a black carbon-like polymer containing metallic silver which ignites at 25°C on exposure to air. 

The competitive decomposition of phenyl silver and p-tolyl silver in pyridine solution45 gives (C6H5)2, (C6H4CH3)2 and (C6H5C6H4CH3) in yields consistent with simple metal-carbon bond rupture. Kinetic data is not available. 

An extremely mild method for the synthesis of nitrate esters from easily oxidized or acid-sensitive alcohols involves the decomposition of a nitratocarbonate (29). The nitratocar-bonate is prepared in situ from metathesis between a chloroformate (reaction between phosgene and an alcohol) and silver nitrate in acetonitrile in the presence of pyridine at room temperature. Under these conditions the nitratocarbonate readily decomposes to yield the corresponding nitrate ester and carbon dioxide. Few examples of these reactions are available in the literature and they are limited to a laboratory scale. 

Thermal decomposition of [Fe(CO)5] can produce at relatively low temperatures, when compared to oxide supports, clean iron deposits when the support is copper or silver [78, 79], Thus, at 80 K under UHV, [Fe(CO)5] has been adsorbed on a Cu(lll) substrate. Decomposition of the iron precursor begins at 233 K and produces mainly adsorbed Fe(CO)4 species. A moderate heating to 323 K allows an iron film to be formed through decarbonylation of [Fe(CO)4]ads. No carbon contamination of the deposit has been detected [78]. A similar effect has been observed... 

Chloro-pentammino-iridium Hydroxide, [Ir(NH3)5Cl](OH)2, may be obtained by decomposition of the chloride with freshly precipitated silver oxide, or by warming the chloride with sodium hydroxide on a water-batli. The base is stable, absorbs carbon dioxide from the air, and only slowly decomposes on boiling with water. 

A mixture of 150 parts of oxalic acid, 40 of potassium chlorate, and 20 of water is heated to 60°, and the soln. cone, in vacuo at 50° until it begins to crystallize. The cold liquid i3 then treated with 3 volumes of absolute alcohol, when potassium carbonate is precipitated. Fine deliquescent needles of potassium chlorite can be obtained by fractional crystallization in vacuo. The residue gives a further crop of crystals of the chlorite by treatment with 95 per cent, alcohol. Small yellow crystals of silver or lead chlorites can be obtained by double decomposition. 

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