Solid-state reactions between alkali persulfates and oxides of corundum structure
TL;DR: In this paper, the effects of three corundum structure oxides, α-Al 2 O 3, α-Cr 2O 3, and α-Fe 2 O3, on the thermal decomposition of sodium and potassium peroxodisulfates (persulfates) under non-isothermal static air conditions and using various oxide/persulfate molar ratios, have been thermoanalytically investigated.
Abstract: The effects of three corundum structure oxides, α-Al 2 O 3 , α-Cr 2 O 3 , and α-Fe 2 O 3 , on the thermal decomposition of sodium and potassium peroxodisulfates (persulfates) under non-isothermal static air conditions and using various oxide/persulfate molar ratios, have been thermoanalytically investigated Compounds such as Na 3 Al(SO 4 ) 3 , K 3 Al(SO 4 ) 3 , Cr 2 (SO 4 ) 3 , K 3 Cr(SO 4 3 , and Na 3 Fe(SO 4 ) 3 are identified by X-ray diffractometry and conventional chemical analysis The molar ratios as well as temperatures of the stoichiometric formation for these compounds have been established At higher temperatures, α-Al 2 O 3 acts as a promoter catalyst for the decomposition of pyrosulfate to sulfate, whereas α-Cr 2 O 3 behaves as a retarder for the decomposition of persulfate A eutectic mixture is formed between K 3 Al(SO 4 ) and K 2 SO 4 at 675°C Also, K 3 Fe(SO 4 ) 3 is identified as two crystalline phases
Citations
More filters
40 citations
TL;DR: In this article, the authors explored potassium pyrosulphate reactivity with iron, chromium and nickel oxides as simulation of the corrosion risk caused by alkaline deposits in the oxy-fuel co-firing of coal with high KCl biomass.
Abstract: This work explores potassium pyrosulphate (K2S2O7) reactivity with iron, chromium and nickel oxides as simulation of the corrosion risk caused by alkaline deposits in the oxy-fuel co-firing of coal with high KCl biomass. TGA studies confirm the formation of metallic trisulphates (K3Fe(SO4)3, K3Cr(SO4)3 and K2Ni2(SO4)3) at 500 °C and 560 °C. Selected steels and alloys (P91, 409, 304, 347, 310, I800HT and I617) were pre-oxidised in 5% O2/CO2 for 200 h and the oxidation scales were treated with K2S2O7 to study the mechanism of oxide dissolution by Fe, Cr and Ni trisulphates, and inner sulphidation.
8 citations
TL;DR: In this paper, the course of reactions of potassium disul- phate(VI) with manganese oxides: MnO, Mn2O3 and MnO2 was studied in solid phase.
Abstract: The course of reactions of potassium disul- phate(VI) with manganese oxides: MnO, Mn2O3 and MnO2 was studied in solid phase. In the reactions all the man- ganese oxides were reduced to Mn 2? which then became a component of one of the reaction products namely K2Mn2(SO4)3. A classification scheme of the reaction path has been proposed.
4 citations
Cites background from "Solid-state reactions between alkal..."
...The effects conform to literature data [ 3 , 4]. After being melted K2S2O7 undergoes a slow decomposition in a wide temperature range, with a maximum rate at 690 � C, according to the following balance equation:...
[...]
...The reaction is more difficult with ZnO, CdO, CuO and aluminium, iron, chromium or vanadium sesquioxides of stoichiometry M2O3 [2, 3 ]. There are also cases in which a reaction of an oxide with disulphate(VI) is accompanied by reduction, as in reaction with Pb3O4 where only PbSO4 is formed [1]....
[...]
TL;DR: In this paper, the non-isothermal solid-state derivatographic behavior of HfO 2 and ZrO 2 was investigated in a static air atmosphere from ambient temperature to 1050°C.
Abstract: The non-isothermal solid-state derivatographic behaviour of HfO 2 and ZrO 2 and four systems of HfO 2 and ZrO 2 Na 2 /K 2 /S 2 O 8 of various molar ratios have been investigated in a static air atmosphere from ambient temperature to 1050°C. HfO 2 gradually loses oxygen at higher temperatures yielding Hf(II)O which reoxidises to HfO 2 on cooling. No weight loss or change of valence state was observed in the case of ZrO 2 . The 1:1 ::HfO 2 (ZrO 2 ):Na 2 /K 2 /S 2 O 8 ratios were found to be stoichiometric. Accordingly, four different thermally stable basic double salts have been identified, namely, Na 2 HfO(SO 4 ) 2 , K 2 HfO(SO 4 ) 2 , Na 2 ZrO(SO 4 ) 2 and K 2 ZrO(SO 4 ) 2 . Based on the DTA curves, a mechanism for the thermal degradation of these basic salts has been proposed which shows the liability of Hf(IV) to form unstable Hf(II) at higher temperatures. All systems tend to form melting eutectic mixtures. X-ray diffractometery has been employed to identify intermediate and final products.
3 citations
TL;DR: In the presence of moisture PdO reacts with Na 2 S 2 O 8 at about 80°C to form brittle masses whose formula can be tentatively written as Na 4 [PdO(SO 4 )] 2 which is stable up to 155°C as mentioned in this paper.
Abstract: TG, DTG and DTA investigations for PdO alone and binary PdONa 2 /K 2 /S 2 O 8 mixtures of various molar ratios have been carried out derivatographically; the stoichiometric ratios have been found to be 1:1. PdO has catalytically lowered T i values of decomposition of either Na 2 S 2 O 8 or K 2 S 2 O 8 by about 20°C. In the absence of moisture PdO reacts with Na 2 S 2 O 8 at about 80°C to form brittle masses whose formula can be tentatively written as Na 4 [PdO(SO 4 )] 2 which is stable up to 155°C. Such a complex has not been detected with the PdOK 2 /S 2 O 8 system. At elevated temperatures, pyrosulfates of sodium and potassium react with PdO in the solid state yielding PdSO 4 (thermal stability 490–540°C) which subsequently decomposes into PdO and SO 3 . The eutectics (PdSO 4 + K 2 S 2 O 7 ) and (PdSO 4 + Na 2 S 2 O 7 ) have been identified. In the presence of excess Pd, partial decomposition of melting of Na 2 SO 4 occurs with the formation of Na 2 PdO 2 and SO 2 . X-ray diffractometry and IR spectrophotometry have been employed to identify intermediate and final products.
2 citations
References
More filters
83 citations
TL;DR: In this paper, the effects of α-Fe2O3 and α-Al 2O3 additives on the thermal decomposition of perchlorates, oxalates and hydroxides were investigated by means of DTA, TG and X-ray techniques.
Abstract: The effects of α-Fe2O3 and α-Al2O3 additives on the thermal decomposition of perchlorates, oxalates and hydroxides were investigated by means of DTA, TG and X-ray techniques. It was found that the oxide additives catalytically promoted the decomposition of perchlorates (NaClO4, KClO4 and Mg(ClO4)2) and resulted in a lowering of the initial decomposition temperature (Ti). On the other hand, the oxides showed no significant effect on the decomposition of oxalates (FeC2O4 and CuC2O4) and hydroxides (Mg(OH)2 and Al(OH)3).
The thermal decomposition of KClO4 was chosen to compare the catalytic effect of twelve metal oxides. The results indicated that the transition metal oxides such as Cr2O3, α-Fe2O3 and CuO markedly accelerated the decomposition; these oxides resulted in a solid-phase decomposition before fusion of KClO4, and the initial decomposition temperature (Ti) of KClO4 with oxides was about 100–200°C lower than that without catalyst. The oxides such as α-Al2O3 and MgO resulted in a slight lowering of the temperature of the fusion and promoted the molten-phase decomposition of KClO4, but their effects were not so remarkable as those of the transition metal oxides. The modified catalytic mechanisms of transition metal oxides were proposed by considering the electron transfer and the oxygen-abstraction models.
37 citations
TL;DR: In this article, the catalytic decomposition of KClO4 by Fe2O3, obtained by calcination of Fe(II) salts at different temperatures, was investigated by DTA, TG, X-ray and IR.
Abstract: The catalytic decomposition of KClO4 by Fe2O3, obtained by calcination of Fe(II) salts at different temperatures, was investigated by DTA, TG, X-ray and IR. A sample without catalyst was found to begin fusion and decomposition simultaneously, and to form an intermediate, KClO3. Addition of catalysts resulted in solid-phase decomposition before fusion of KClO4, and in a small amount of KClO3. The difference in catalytic effect observed for different catalysts was less in the molten-phase decomposition than in the solid phase. The initial decomposition temperature (T
i) increased with the temperature of preparation of the catalyst and showed a definitive relationship with the crystallite size of the catalyst. The change ofT
i is discussed on the basis of then-type semiconductive properties of the catalyst.
32 citations
23 citations
TL;DR: In this paper, die Salze verlieren das letzte Wassermolekul in breiterem Temperaturgebiet als die vorhergehenden.
Abstract: Bei der Abspaltung des Kristallwassers aus Sulfaten werden auf ein Mol des Salzes manchmal nur 1/4, 1/2 sogar auch 3/4 Wassermolekule verfluchtigt. Diese werden in einer Stufe entfernt. Man darf annehmen, da\ dabei Verbindungen wie das Cadmiumsulfat — 3CdSO4 · 8H2O — gebildet werden. Im allgemeinen erhalt man aber die ublichen Stoffe, bei denen ein Molekul Salz ein oder mehr Wassermolekule enthalt. Die Salze verlieren das letzte Wassermolekul in breiterem Temperaturgebiet als die vorhergehenden. In einigen dieser Falle geht die letzte Wasserabspaltung schon mit der Desulfatierung einher. Diese kann in folgenden Richtungen laufen: 1. uber basische Sulfate zu Oxiden; 2. uber Sulfite zu Oxiden; 3. uber basische Sulfite zu Oxiden; 4. uber Doppelsalze (Sulfat-Sulfit) zu Oxiden. In Fallen, wo die Oxide mehreren Oxydationsstufen entsprechen konnen, ist das Endprodukt der Zersetzung eine Funktion der benutzten Temperatur, der Aufheizungsgeschwindigkeit und der Menge des eingewogenen Stoffes.
22 citations