- Thermal decomposition of potassium metaperiodate doped with trivalent ions
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The kinetics of isothermal decomposition of potassium metaperiodate (KIO4), doped with phosphate and aluminium has been studied by thermogravimetry (TG). We introduced a custom-made thermobalance that is able to record weight decrease with time under pure isothermal conditions. The decomposition proceeds mainly through two stages: an acceleratory stages up to α = 0.50 and the decay stage beyond. The decomposition data for aluminium and phosphate doped KIO4 were found to be best described by the Prout-Tompkins equation. Separate kinetic analyses of the α-t data corresponding to the acceleratory region and decay region showed that the acceleratory stage gave the best fit with Prout-Tompkins equation itself whereas the decay stage fitted better to the contracting area equation. The rate of decomposition of phosphate doped KIO4 increases approximately linearly with an increase in the dopant concentration. In the case of aluminium doped KIO4, the rate passes through a maximum with increase in the dopant concentration. The α-t data of pure and doped KIO4 were also subjected to isoconversional studies for the determination of activation energy values. Doping did not change the activation energy of the reaction. The results favour an electron-transfer mechanism for the isothermal decomposition of KIO4, agreeing well with our earlier observations.
- Muraleedharan,Kannan,Gangadevi
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- Effects of dopants on the isothermal decomposition kinetics of potassium metaperiodate
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The isothermal decomposition of potassium metaperiodate (KIO4) has been studied as a function of concentration of the dopants chloride, sulphate and barium, by thermogravimetry (TG) in the temperature range 560-580 K. The decomposition data for both pure and doped KIO4 were found to be best described by the Prout-Tompkins (PT) equation. As the dopant concentration increases, the rate of decomposition remains unaffected with chloride, increases approximately linearly with sulphate and passes through a maximum with barium. However, doping did not change the activation energy of the reaction. The results favour an electron-transfer mechanism for the decomposition. (C) 2000 Elsevier Science B.V.
- Muraleedharan,Kannan
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- Thermal Decomposition of KIO4 and NaIO4 in Relation to Solid-state Isotopic Exchange Reactions
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The thermal decomposition of KIO4 and NaIO4 has been studied.The decomposition product, KIO3 or NaIO3, suffers a very efficient exodiffusion during heating in such a way that the partly decomposed crystals consists of two parts: the outer part is a fragile layer of almost pure iodate, while the inner part is a solid crystalline lattice of almost pure periodate.The dimensions of the latter are not affected by the decomposition, so that its density decreases in proportion to the decomposed fraction.The decomposition isotherms present a saturation at long heating times which is not due to atmospheric effects, but is supressed when heating is performed with continuous removal of the outer layer.Kinetic analysis of the data shows a remarkable continuity between the exchange process, occurring at lower temperatures, and the decomposition.In paticular, the dimensionality of the reaction, n, from the Erofeev equation, ranges in KIO4 roughly from 1 to 2 with increasing temperature in the former case, then from 2 to 3 in the latter.These values are systematically higher by one unit in NaIO4, indicating that the nucleation process, which creates the driving defect, cannot be neglected as it can for KIO4.Both exchange and decomposition are dominated by the exodiffusion of some combined vacancy type defect, promoting the exodiffusion of the iodate and eventually triggering the decomposition; at sufficiently high temperature, the latter process becomes autocatalytic and develops three-dimensionally (n= 3 or 4).
- Takriti, Salaheddin,Duplatre, Gilles
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- Synthesis, thermal investigations and solubility of a new double salt K2Mg(IO3)4·2H2O
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A new double salt K2Mg(IO3)4·2H2O has been synthesized. Its thermal and calorimetric behaviors were investigated by the DTA, TG and DSC methods. A mechanism of thermal decomposition has been suggested. The ΔfH0298 was calculated from the recorded ΔH0 of the DSC curve. The data from the TG curves were processed by the methods of formal kinetics involving the calculation of the kinetic parameters E* and Z, and the type of the kinetic equation determined. The solubility of K2Mg(IO3)4·2H2O in water was investigated in the 20-50°C temperature interval. The value of ΔdissolH0298 was calculated on the basis of the solubility data, whence the value of ΔfH0298 of the double salt was calculated. The values of ΔfH0298, determined by the two methods, were compared.
- Rabadjieva,Maneva
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- A new oscillatory mechanism for the electro-oxidation of iodide involving two phase transitions and a disproportional reaction
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Oscillations have been first observed during iodide oxidation in alkaline solution on a static platinum electrode, where phase transitions at the interface of electrode/solution are essential. The film formation of solid iodine acts as a negative nonlinear feedback slowing down the iodide oxidation due to its poor conductivity, and oxygen evolution as a positive nonlinear feedback by destroying the iodine film mechanically and by promoting its dissolution through convection mainly via a disproportional reaction. Based on the results of electrochemical experiments and in situ Raman spectroscopy, a tentative mechanism is given concerning the interfacial phase transitions and the disproportional reaction.
- Chen, Shu,Huang, Wei,Niu, Zhenjiang,Li, Zelin
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- Effect of metal oxide additives on the thermal decomposition kinetics of potassium metaperiodate
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The effect of additives (CuO, MnO2 and TiO2) on the thermal decomposition kinetics of potassium metaperiodate (KIO4) to potassium iodate (KIO3) has been studied in air by thermogravimetry under isothermal conditions. Irrespective of whether p- or n-type, the metal oxides show only a little or no influence on the rate of the decomposition except for the small decrease when the oxide concentration is as high as 10 wt%. The rate law for the decomposition of KIO4 (Prout-Tompkins model) remained unaffected by the additives.
- Muraleedharan,Kannan,Gangadevi
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- New approach to electrochemical iodination of arenes exemplified by the synthesis of 4-iodopyrazoles of different structures
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The two-stage electrosynthesis of 4-iodosubstituted pyrazole derivatives was performed. At the first stage, KIO3 was obtained at the Ni anode under the undivided galvanostatic conditions of electrolysis of an aqueous alkaline solution of KI (or I2) at the Ni anode. At the second stage, pyrazole and its derivatives were iodinated in the heterophase (H2O-CHCl3 (CCl4)) medium by the KIO3-KI (or KIO3-I2) system in the presence of H2SO4. The yields of iodopyrazoles were 74-92%. The electrochemical iodination of anisole, 2-methylpyrazole, and thiophene was carried out to form 4-iodoanisole (88% yield), 4,5-diiodo-2-methylimidazole (54% yield), and a mixture of 2-iodothiophene (60% yield) and 2,5-diiodothiophene (4% yield).
- Lyalin,Petrosyan
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p. 360 - 367
(2015/02/05)
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- The lone-pair cation I5+ in a hexagonal tungsten oxide-like framework: Synthesis, structure, and second-harmonic generating properties of Cs2I4O11
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The layered iodate Cs2I4O11 has been synthesized and characterized. Its hexagonal tungsten oxide-like framework consists of six-membered rings of corner-sharing IO5 polyhedra with three lone pairs pointing inward and three lone pairs pointing outward (depicted for central ring). Capping of the layer by asymmetric IO3 polyhedra on one side results in a noncentrosymmetric material with highly efficient second-harmonic generating properties.
- Ok, Kang Min,Halasyamani, P. Shiv
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p. 5489 - 5491
(2007/10/03)
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- Structural modulation of molybdenyl iodate architectures by alkali metal cations in AMoO3(IO3) (A = K, RB, Cs): A facile route to new polar materials with large SHG responses
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Three new molybdenyl iodates, KMoO3(IO3) (1), RbMoO3(IO3) (2), and CsMoO3(IO3) (3), have been prepared through the hydrothermal reactions of MoO3 with AIO4 (A = K, Rb, or Cs) at 180°C. These compounds are isolated as nearly colorless, air-stable crystals. Single-crystal X-ray diffraction experiments reveal that 1 possesses a corrugated layered structure constructed from molybdenum oxide chains that are bridged by iodate anions. The puckering of the layers is caused by the alignment of bent molybdenyl (MoO22+) groups along one side of the molybdenum oxide chains. The K+ cations separate these layers from one another and serve to balance charge. In contrast, compounds 2 and 3, which are isostructural, form three-dimensional structures with small cavities filled with Rb+ or Cs+ cations. The differences between the structures of 1 and those of 2 and 3 are due to rotation of the molybdenyl units as translation occurs down the molybdenum oxide chains in order to accommodate the increased size of the Rb+ and Cs+ cations. This rotation allows for the iodate anions to bridge the molybdenum oxide chains in an additional dimension, creating a three-dimensional network structure. Furthermore, while 1 crystallizes in a centrosymmetric space group, 2 and 3 crystallize in polar space groups. Second-harmonic generation measurements on 2 and 3 show large responses of 400x α-quartz. Differential scanning calorimetry measurements demonstrate that 2 and 3 are thermally stable to 494 and 486°C, respectively. UV-vis diffuse reflectance spectra of these compounds show a high degree of transparency from 1 to 3 eV and a band gap of 3.1 eV.
- Sykora, Richard E.,Kang, Min Ok,Halasyamani, P. Shiv,Albrecht-Schmitt, Thomas E.
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p. 1951 - 1957
(2007/10/03)
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- OXIDATION OF ALKALI METAL IODATES IN MOLTEN ALKALI METAL NITRATES
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Alkali metal iodates MIO3 (M=Li, Na, K) were oxidized in the presence of hydroxides MOH in molten nitrates MNO3 with oxygen or ozone.The following products were precipitated at variable MOH:MIO3 rations and then separated from the melts and identified after purification with liquid ammonia: Li5IO6, Na4IO5, Na5IO6, K2IO4, K3IO5.Two of these substances, Na4IO5 and K2IO4 contain formally hexavalent iodine and were studied by X-ray powder method, IR spectroscopy and measurements of the magnetic susceptibility.Their thermodynamic stability was also investigated.Periodates Na5IO6 and K3IO5 have been pepared for the first time from a homoge neous mixture by precipitation with an oxidizing agent.
- Dratovsky, M.,Dvorakova, E.,Rytir, Z.
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p. 175 - 182
(2007/10/02)
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