Thermoanalytical behavior of cadmium(II) oxide—alkali persulfate binary systems

The non-isothermal behavior of two binary CdO—persulfate systems has been investigated. The molar ratios and T_i—T_f are established. The temperatures for the α- to β-Na₂SO₄ phase transition, as well as for α- to β- to γ-CdSO₄ of the CdONa₂S₂O₈ system have been fixed. No evidence for the occurrence of the β- to γ-CdSO₄ polymorphic trans-formation has been obtained from the reaction of the CdOK₂S₂O₈ system. This is because of the formation of a CdSO₄/K₂SO₄ eutectic mixture which melts at 653°C, i.e., before the β- to γ-phase change transition, which usually occurs later. No basic cadmium sulfate has been identified. The excess cadmium oxide acts as a p-type semiconductor which accelerates the thermal decomposition of pyrosulfates.     

A DSC study of benzoic acid: a suggested calibrant compound

It has been found that cobalt(II, III) oxide, Co₃O₄, lowers the thermal decomposition temperature of Na₂S₂O₈ and K₂S₂O₈ by about 25°C by catalysis, and it therefore acts as a P-type semiconductor at high temperature and atmospheric (air) pressure. Also, this oxide reacts at high temperature with sodium or potassium pyrosulfates to form thermally stable sodium cobalt disulfate, Na₂Co(SO₄)₂ and potassium cobalt trisulfate, K₂Co₂(SO₄)₃, respectively. Binary systems, consisting of a 1 : 3 mole ratio (oxide : persulfate), are established as representing the solid state stoichiometric reaction. X-Ray diffractometry is employed to identify intermediate and final reaction products in general. All calculations are based on data obtained from TG, DTG and DTA curves.     

Thermal and X-ray diffraction investigations of some lanthanum(III) and neodymium(III) oxide-alkali persulfate binary systems

Different molar ratios of La₂O₃ or Nd₂O₃:Na₂/K₂S₂O₈ have been prepared, and the results of their TG and DTA investigations, under an atmosphere of static air, are reported. The effects of either La₂O₃ or Nd₂O₃ on the thermal decomposition of the persulfates from ambient to 1050°C, using a derivatograph, have been studied. It has been found that La₂O₃ lowers the initial decomposition temperatures of these alkali persulfates through catalytic activity. Nd₂O₃ shows little or no catalytic effect and therefore it acts as an insulator. Intermediate and final products are identified by X-ray diffraction analysis. The stoichiometric molar ratios of the solid state reactions are 1:3::R₂O₃:M₂S₂O₈. (R = La or Nd. M = Na or K), which give double salts of formulae: NaLa(So₄)₂, KLa(SO₄)₂, NaNd(SO₄)₂, and KNd(SO₄)₂. No sulfates or oxysulfates of lanthanum or neodymium have been identified.     

Thermoanalytical investigation of someβ-manganese(IV)oxide-alkalimetalpersulfate systems

A TG and DTA investigation, under a static air atmosphere, of mixtures ofβ-MnO₂ and Na₂S₂O₈ or K₂S₂O₈ in different molar ratios is reported.β-MnO₂ lowers the initial decomposition temperatures of these persulfates by 25° through a catalytic effect. A mechanism is proposed for this effect. The X-ray diffractometry results in this investigation could be used to decide which type of semiconductorβ-MnO₂ should be used for the best activity.     

High temperature reactions of titanium(IV) oxide with some alkali persulfates and their decomposition products

The solid state reactions between TiO₂ and Na₂S₂O₈ or K₂S₂O₈ have been investigated using TG, DTG, DTA, IR, and X-ray diffraction studies in the range of 20 to 1000°C.It has been shown that TiO₂ reacts stoichiometrically (1 : 1) with Na₂S₂O₈ in the range of 160 and 220°C forming the complex sodium monoperoxodisulfato—titanium(IV) as characterized by IR and X-ray analysis. The new complex then decomposes into the reactants above 190°C.An exothermic reaction has been observed between TiO₂ and molten K₂S₂O₇ at mole ratio 1:2 respectively and higher, in the range of 280 and 350°C. The IR and X-ray analyses have shown the formation of a complex namely, potassium tetrasulfato titanium(IV) for which the formula and structure have been proposed. This complex decomposes at higher temperatures into K₂SO₄ and a mixed sulfate of potassium and titanium. The mixed sulfate melts at 620°C and decomposes into K₂SO₄, TiO₂, and the gaseous SO₃.On the other hand, Na₂S₂O₈ decomposes in a special mode producing a polymeric product of Na₁₀S₉O₃₂. Decomposition of this species occurs after melting at 560°C into Na₂SO₄ and sulfur oxides. The decomposition reaction has been proved to be catalysed by TiO₂ itself.     

Solid-state reactions between alkali persulfates and oxides of corundum structure

The effects of three corundum structure oxides, α-Al₂O₃, α-Cr₂O₃, and α-Fe₂O₃, 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 Na₃Al(SO₄)₃, K₃Al(SO₄)₃, Cr₂(SO₄)₃, K₃Cr(SO₄₃, and Na₃Fe(SO₄)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-Al₂O₃ acts as a promoter catalyst for the decomposition of pyrosulfate to sulfate, whereas α-Cr₂O₃ behaves as a retarder for the decomposition of persulfate. A eutectic mixture is formed between K₃Al(SO₄) and K₂SO₄ at 675°C. Also, K₃Fe(SO₄)₃ is identified as two crystalline phases.     

Stages of thermal decomposition of sodium oxo-salts of sulphur

Thermal behaviour of sodium oxo-salts of sulphur: Na₂SO₄, Na₂S₂O₇, Na₂S₂O₆, Na₂SO₃, Na₂S₂O₅, Na₂S₂O₄, Na₂S₂O₃, Na₂S₃O₆ and of sulphides Na₂S and Na₂S₂ was studied on heating up to 1000°C. The experiments were performed with anhydrous compounds obtained from commercial products by recrystallisation and dehydration. The stage mechanisms of decomposition of anionic sub-lattices of the salts have been proposed basing on the Górski’s morphological classification of simple species. The thermal stability and the stage decomposition mechanisms were correlated with the structure and the potential chemical properties of the salt anions. The thermal decomposition processes were studied by means of thermal analysis, and the decomposition products were identified by means of X-ray phase analysis.     

Thermal and X-Ray studies of reactions between scandium(III) oxide and sodium or potassium persulfates

TG, DTG, and DTA experiments were carried out to elucidate the influence of Sc₂O₃ on the thermal decomposition of Na₂S₂O₈ and K₂S₂O₈ under a static (air) atmosphere from ambient to 1050°C, using a derivatograph. X-Ray diffractometry has been employed to identify the intermediate and final decomposition products. Different Sc₂O₃ Na₂(K₂)S₂O₈ molar ratios were investigated and the 1 : 3 ratio found to be the one that gives stoichiometric reactions with either of these salts. Sc₂O₃ was found to react at 250 and 440°C with the thermally produced Na₂S₂O₇ yielding Sc₂(SO₄)₃. The scandium(III) sulfate was thermally stable up to 840°C. Similarly, the oxide reacts stoichiometrically at 420°C to produce KSc(SO₄)₂, a double salt which began to decompose at 840°. Moreover, three new crystalline phase-transformations were detected for Sc₂(SO₄)₃ at 640, 695, and 735°C.     

Na2CrO4-NaF-NaI and K2CrO4-KF-KI three-component systems

Na₂CrO₄-NaF-NaI and K₂CrO₄-KF-KI three-component systems have been studied by differential thermal analysis (DTA). The compositions and melting temperatures have been determined and the enthalpies of melting have been measured for eutectic mixtures. Phase equilibria in the title systems have been described, and phase fields have been demarcated.     

Synthesis of latex particles with surface amino groups

Monodisperse latex particles with surface amino groups were prepared by a two‐step emulsion polymerization. In the first step, the seeds were synthesized by batch emulsion polymerization of styrene; and in the second step, two different amino‐functionalized monomers [aminoethylmethacrylate hydrochloride (AEMH) and vinylbenzylamine hydrochloride (VBAH)], two different initiator systems (K₂S₂O₈ and K₂S₂O₈/Na₂S₂O₅) and mixtures of emulsifiers sodium dodecylsulfate (SDS) and Tween 21 were used to synthesize the final latexes. To characterize the final latexes, conversions were obtained gravimetrically and particle size distributions and average particle diameters were determined by transmission electron microscopy (TEM) and photon correlation spectroscopy (PCS). The amount of amino groups was determined by the SPDP (N‐succinimidyl 3‐(2‐pyridyldithio)propionate) method. The influence of the different conditions used to synthesize the latexes on the colloidal stability of the particles was evaluated by measuring the diameters of the final latexes dispersed in solutions at different pHs and ionic strengths. The most stable latexes were obtained using the smallest seed, VBAH monomer, and the K₂S₂O₈/Na₂S₂O₅ initiator system. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4230–4237, 2000     

Effects of alkali metal ions on the thermal decomposition of ammonium heptamolybdate tetrahydrate

The thermal decomposition of pure ammonium heptamolybdate tetrahydrate (AHMT), and doped with Li⁺, Na⁺ and K⁺ ions was investigated using thermogravimetry, differential thermal analysis, infrared and X-ray diffraction techniques. Results obtained revealed that the decomposition of AHMT proceeded in three decomposition stages in which both NH₃ and H₂O were released in all stages. The presence of 0.5 mol % alkali metal ions enhances the formation of the intermediateb (NH₄)₂MO₇O₂₂·2H₂O while the decomposition of this intermediate into MoO₃ is slightly affected in the presence of all dopant concentrations used. The infrared absorption spectra of the thermal products of AHMT treated with 10 mol% alkali metal ions (AMI) at 350°C indicated a reduction of some Mo⁶⁺ ions. By heating of AHMT above 500°C in presence of 5 or 10 mol % of AMI, a solid-solid interaction between alkali metal oxides and MoO₃ giving rise to well crystallized alkali metal molybdates. finally the activation energies accompanied various decomposition stages were calculated.     

Studies on the thermal decomposition of calcium carbonate in the presence of alkali salts (Na2Co3, K2CO3 and NaCl)

Mixtures of CaCO₃ and varying amounts of Na₂CO₃, K₂CO₃ and NaCl were subjected separately to thermal analysis. DTG, DTA, TG analyses indicate that the presence of alkali salts in CaCO₃ influences its decomposition behaviour. A minimum DTA peak temperature of CaCO₃ decomposition is noticed at low concentrations of alkali salts (K₂CO₃ and Na₂CO₃); an increase in concentration increases the DTA peak temperature. However, in the case of NaCl no appreciable lowering of the DTA peak temperature of CaCO₃ decomposition is observed. Similarly, the minimum temperature at which decomposition completes is found to correspond to the concentration of 1 per cent salt (K₂CO₃ and Na₂CO₃) in CaCO₃.     

Oxidation of magnesium in the systems NaClO4-Mg-Metal oxide (peroxide)

Oxidation of magnesium in mixtures NaClO₄ + Mg + metal oxide or peroxide has been investigated using differential thermal analysis (DTA). In the systems with peroxides Na₂O₂, Li₂O₂, BaO₂, CaO₂ or ZnO, magnesium oxidizes simultaneously with decomposition of NaClO₄ in the region 380–520°C, which is 100–200°C below the oxidation temperature of magnesium in air. In the ternary systems with transition-metal oxides NiO, CuO, FeO, and Fe₂O₃, magnesium transforms into oxide at above 600°C after sodium perchlorate had been decomposed completely. The low-temperature oxidation of magnesium occurs in the systems in which sodium chlorate is accumulated during the catalytic decomposition of NaClO₄.     

Evaluation of cation influence on the formation of M(II)Cr2O4 during the thermal decomposition of mixed carboxylate type precursors

This paper reports an investigation regarding the influence of the cation M(II) (M = Zn, Ni, Mg) on the formation of MCr₂O₄ by thermal decomposition of the corresponding M(II),Cr(III)-carboxylates (precursors) obtained by redox reaction between the corresponding metal nitrates and 1,3-propanediol. The decomposition products at different temperatures have been characterized by FT-IR spectroscopy and thermal analysis. Thus, we have evidenced that by thermal decomposition of the studied precursors in the range 250–300 °C, different amorphous oxidic phases mixtures form depending on the nature of metalic cation: (Cr₂O_3+x + ZnO) (Cr₂O_3+x + Ni/NiO) and (Cr₂O_3+x+MgO). In case of M = Zn, around 400 °C when the transition Cr₂O_3+x to Cr₂O₃ takes place, zinc chromite nuclei form by the interaction ZnO with Cr₂O₃. In case of M = Ni, due to the partial reduction of Ni(II) at Ni(0) during the thermal decomposition of the precursor the formation of nickel chromite by the reaction NiO + Cr₂O₃ is shifted toward 500 °C, when Ni is oxidized at NiO. The thermal evolution of the mixture (MgO + CrO₃) is different due to the formation as intermediary phase of MgCrO₄, which decomposes to MgCr₂O₄ around 560 °C. In order to investigate the chromites formation mechanism, we have studied the mechanical mixtures of single oxides obtained from the corresponding carboxylates. These mixtures (MO + Cr₂O₃) have been annealed at 400, 500, and 600 °C to study the evolution of the crystalline phases. It results in the prepared mixture behaving different from the mixtures obtained by thermal decomposition of the binary M(II),Cr(III)-carboxylates, recommending our synthesis method for obtaining binary oxides.     

The detection of potassium sulfate in excess of potassium pyrosulfate

X-Ray diffraction, infrared, and raman spectroscopic methods were investigated for the detection of K₂SO₄ in excess of K₂S₂O₇ in solid solutions.The X-ray diffraction lines of K₂SO₄ were found to be overlapped by the diffraction pattern of K₂S₂O₇ and infrared studies indicated that K₂SO₄ absorption bands corresponded to regions of strong absorption in K₂S₂O₇. The detection of sulfate could not be carried out by the X-ray diffraction and infrared methods. However, the raman method indicated that a strong and narrow K₂SO₄ band at 981 cm^?1 could unambiguously be used for the detection of sulfate in solid solutions of K₂SO₄ in K₂S₂O₇, as pyrosulfate showed no absorption around this band.     

Studies on the thermal decomposition of alkali metal thiosulphatobismuthates(III)

The thermal decomposition of thiosulphatobismuthates(III) of alkali metals was investigated. The general formulae of the thiosulphatobismuthates are M₃[Bi(S₂O₃)₃]·H₂O where M = Na, K, Rb or Cs, and M₂Na[Bi(S₂O₃)₃]·H₂O where M = K or Cs.Typical thermal curves for thiosulphatobismuthates(III) and the results obtained in thermal, X-ray, chemical and spectrophotometrical analyses of the decomposition products are shown. The results were used to determine three stages of the thermal decomposition. At the first stage, at about 200°C, hydrated compounds are dehydrated. At the second stage, above 200°C, there is a rapid decrease in mass which is caused by evolving sulphur dioxide; bismuth sulphide and an intermediate decomposition product are formed. At about 320°C the thermal decomposition products are bismuth sulphide and alkali metal sulphate.     

Stress-strain behaviour of graft copolymers of methyl methacrylate and natural wool fibres

The graft polymerization of methyl methacrylate onto wool, using LiBrK₂S₂O₈ and Na₂S₂O₃H₂O₂ redox systems as initiators, does not change dramatically the stress-strain behaviour of single fibres even for high graft yields. Variations in tensile properties are essentially due to an important radial swelling effect of the deposited polymer accompanied by a moderate increase of internal viscosity and, in the case of Na₂S₂O₃H₂O₂ initiation, to interference from oxidative processes.     

Crystal chemistry and synthesis of Ternary Silicates and Germanates containing alkali (Na+, K+) and alkaline earth (Ca2+, Sr2+, Ba2+) cations

The synthesis of new ternary silicate and germanate phases containing large alkali and alkaline-earth cations is described. They are made by solid-state reaction of mixtures of carbonates or oxalates with SiO₂ or GeO₂, or by fusion and subsequent recrystallization of the glass. Representatives of the cubic MM²⁺X₃O₉ family include Na₄CaSi₃O₉ and the isostructural compounds K₄CaGe₃O₉, K₄SrGe₃O₉ and K₄SrSi₃O₉. K₄BaSi₃O₉ is pseudocubic: the symmetry of Na₄SrSi₃O₉ is unknown. The rhombohedral MM²⁺X₁₀O₂₅ family includes K₈CaSi₁₀O₂₅, K₈SrSi₁₀O₂₅ and K₈BaSi₁₀O₂₅. Na₂CaGe₂O₆ and Na₂SrGe₂O₆ are isostructural but both are structurally unrelated to Na₂BaSi₂O₆. Na₂Ba₂Ge₂O₇ and Na₂Ba₂Si₂O₇ are structurally similar.     

Studies on the thermal decomposition of the silver group of alkali metal nitritocobaltates(III)

The thermal decomposition of nitritocobaltate(III) of the silver group of general formula M₂Ag[Co(NO₂)₆] (where M = K⁺, NH⁺₄, Rb⁺ or Cs⁺) has been investigated. Based on the thermal curves of the investigated compounds and chemical and diffractometric analysis, the mechanism of thermal decomposition has been determined. The results obtained indicate that the decomposition proceeds in three stages. As a result of decomposition in the first stage (300°C), nitrates of alkali metals, metallic silver and Co₃O₄ are formed. In the second stage (500°C), a partial decomposition of nitrates to alkali metal oxides occurs, and in the third stage the products are alkali metal oxides, silver and Co₃O₄. This paper also presents the dependence of the decomposition temperature of nitritocobaltates(III) of the silver group on the ionic radius of the outer-sphere cation.     

Mössbauer study of the thermal decomposition of alkali tris(oxalato)ferrates(III)

The thermal decomposition of alkali (Li,Na,K,Cs,NH₄) tris(oxalato)ferrates(III) has been studied at different temperatures up to 700°C using Mössbauer, infrared spectroscopy, and thermogravimetric techniques. The formation of different intermediates has been observed during thermal decomposition. The decomposition in these complexes starts at different temperatures, i.e., at 200°C in the case of lithium, cesium, and ammonium ferrate(III), 250°C in the case of sodium, and 270°C in the case of potassium tris(oxalato)ferrate(III). The intermediates, i.e., Fe¹¹C₂O₄, K₆Fe¹¹₂(ox)₅. and Cs₂Fe¹¹ (ox)₂(H₂O)₂, are formed during thermal decomposition of lithium, potassium, and cesium tris(oxalato)ferrates(III), respectively. In the case of sodium and ammonium tris(oxalato)ferrates(III), the decomposition occurs without reduction to the iron(II) state and leads directly to α-Fe₂O₃.