Barium oxalate, decomposition

Barium acetate converts to barium carbonate when heated in air at elevated temperatures. Reaction with sulfuric acid gives harium sulfate with hydrochloric acid and nitric acid, the chloride and nitrate salts are obtained after evaporation of the solutions. It undergoes double decomposition reactions with salts of several metals. For example, it forms ferrous acetate when treated with ferrous sulfate solution and mercurous acetate when mixed with mercurous nitrate solution acidified with nitric acid. It reacts with oxahc acid forming barium oxalate. 

Kabanov and Skrobot have shown [67] that magnetic fields (200 to 500 oersteds) caused a slight diminution in the rate of KMn04 decomposition. Relatively few studies of this type have been made but these workers mention that magnetic fields increase the rate of barium azide decomposition, decrease the rate of decomposition of silver oxalate and do not change the rate of decomposition of silver azide. 

After the loss of the water of hydration, the curve exhibited a horizontal mass level from 250-360°C, which corresponded to the composition for anhydrous metal oxalates. Decomposition of the three oxalates then took place simultaneously, the process being completed al about 500°G The anhydrous metal carbonates were then stable from about SOO-eKTG followed by strontium carbonate, which also began to decompose in this range and was completely decomposed at 1100°C, at which temperature barium carbonate began to decompose. 

It may be seen that a change in atmosphere often causes a change in shape of decomposition curve. Calcium, strontium and barium oxalates, however, behave somewhat differently. Their carbonates are all more stable than their oxalates. For this reason their oxalates decompose to carbonate first and to oxide at a higher temperature. This is shown for calcium oxalate in Figure 6 and discussed above. 

Fig. 5.16 Temperature dependence of transformation percentage, weight loss rate and thermal effects during barium titanyl-oxalate decomposition with heating rate of 480 °C/h [291]...

The summary of barium titanyl oxalate decomposition for different heating rates can be represented by the equations of mass balance (as in Fig. 5.17), which show the increasing role of oxygen with increasing heating rate (Table 5.9). 

Table 5.9 Analysis of gas release on barium titanyl oxalate decomposition...

Fig. 5.19). The input barium titanyl oxalate powder has specific surface area 1 m /g. Therefore, the coefficient of refining rox/rut reaches 10 0 times on oxalate decomposition. Using more dispersed oxalate, however, is not reasonable due to the small particles coalescence on heating, and therefore, the oxalate grinding has almost no effect on the end of the BaTiOs synthesis. The morphology of nanoparticles depends on the gas release rate during the decay of oxalate, and hence the heating rate determines density of nucleation and nuclei coalescence probability. In addition, the increase in heating rate leads to a change in the mechanism of oxalate oxidation as described above. Structurally barium titanyl oxalate crystal transforms to the microreactor - particles of resin-like phase, size and activity of which can be flexibly controlled by the heating rate. The general view of the reactor is shown in Fig. 5.20.

Kabanov, A. A. etal., Russ. Chem. Rev., 1975, 44, 538-551 Application of electric fields to various explosive heavy metal derivatives (silver oxalate, barium, copper, lead, silver or thallium azides, or silver acetylide) accelerates the rate of thermal decomposition. Possible mechanisms are discussed. 

Reactions in aqueous phase are similar to those of barium chloride. When treated with sulfuric acid, hydrofluoric acid, phosphoric acid or oxalic acid, the insoluble barium salts of these anions are formed. Similarly, many insoluble barium salts may form by double decomposition reactions when treated with soluble salts of other metals. 

In an atmosphere of nitric oxide, thermal decomposition produces barium nitrite, Ba(N02)2. Reactions with soluble metal sulfates or sulfuric acid yield barium sulfate. Many insoluble barium salts, such as the carbonate, oxalate and phosphate of the metal, are precipitated by similar double decomposition reactions. Ba(N03)2 is an oxidizer and reacts vigorously with common reducing agents. The solid powder, when mixed with many other metals such as aluminum or zinc in their finely divided form, or combined with alloys such as... 

K. G. Thurnlackh and K. F. von Hayn prepared a mixed soln. of potassium chlorate and chlorite by the action of potassium hydroxide free from chlorine on a soln. of chlorine dioxide. Light was carefully excluded, and the soln. was evaporated in vacuo at 45°-50°—potassium chlorate separated out first, and after further evaporation, alcohol was added, and the clear alcoholic soln. evaporated. Needle-like crystals of potassium chlorite, KC102, were obtained which deliquesced on exposure to air. As already indicated in connection with the preparation of the acid, G. Bruni and G. Levi made the potassium chlorite by reducing a soln. of potassium chlorate with oxalic acid and A. Reychler, sodium chlorite, by the action of chlorine dioxide on a soln. of sodium peroxide. Sodium chlorite, NaClQ2, can be also made by double decomposition by treating a soln. of barium chlorite with sodium sulphate and evaporating the clear soln. in vacuo. 

The product of nitration of dimethyloxamide is soluble in nitric acid and is separated by pouring the solution into water. It decomposes on treatment with concentrated sulphuric acid or on boiling with aqueous ammonia or barium hydroxide solution, forming the corresponding methylnitramine salt. Similarly, long-continued boiling in water results in complete decomposition, with the formation of oxalic acid and methylnitramine. 

Tompkins [80] investigated the thermal decomposition of silver oxalate at 110— 130°C. Its decomposition, in his opinion, is similar to that of barium azide. 

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 barium titanyl oxalate tetrahydrate, BaTi0(C204)2.4H20, occurs in three stages [105] (i) dehydration, (ii) decomposition of the anhydrous oxalate to the carbonate, and (iii) decomposition of the carbonate forming barium titanate. Isothermal ar-time curves for stage (ii), 509 to 599 K in vacuum, derived from separate measurements of pressures of evolved CO and COj, were deceleratory and superimposable up to ar= 0.3. CO evolution was slower beyond ar= 0.3 and a diffusion mechanism was proposed, , = 189 kJ mol . 

Many studies have been intentionally concerned with relatively simple rate processes to minimize stoichiometric problems. However, even relatively simple reactions do not always give a single product, for example barium azide has been reported to give about 70% BajNj together with the metal [26]. The extensively studied decompositions of oxalates require that the identity of the residual solid be identified, for each constituent cation, as either carbonate, oxide or metal, together with any change of cation valency. The chemistry of oxalate breakdown can, however, be much more complicate as has been shown for the Y, Eu and Yb salts [27]. 

Tests for Oxalic Acid and Oxalates (SECTIONS 134, 136).— (a) Oxalic acid and sulphuric acid.—Heat about 2 grams of oxalic acid with about 5 cc. of concentrated sulphuric acid. (Eq.) Pour some of the gas formed into a test-tube containing a solution of barium hydroxide, and shake. Ignite the gas which is produced in the reaction. How could you prepare carbon monoxide free from carbon dioxide by making use of this decomposition What other acid yields carbon monoxide when heated with sulphuric acid ... 

From the mass-loss curve, then, the following data are obtained D, mass of dry precipitate at 100°C , mass of water of hydration F, mass of carbon monoxide formed by the decomposition of the anhydrous metal oxalates G, mass of carbon dioxide formed by the decomposition of calcium carbonate and L, the mass of carbon dioxide formed by the decomposition of strontium carbonate. From these data, the amounts of calcium, C, strontium, S, and barium, By can be calculated from... 

Erdey and Paulik (100), in a simultaneous DTA-TG study, investigated the thermal decomposition of barium, strontium, manganese(II), calcium, magnesium, and zinc oxalates in air and nitrogen atmospheres. It was found that the evolved carbon dioxide formed in the reaction played an important part in that it may inhibit the progress of the reaction and shift the peak temperatures to higher values. 

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