Cr6+-containing phases in the system CaO−Al2O3−CrO42−−H2O at 23 °C

Synthesis and investigation of lamellar calcium aluminium hydroxy salts was performed to study the incorporation of chromate ions in the interlayer of lamellar calcium aluminium hydroxy salts. Different AFm-phases (calcium aluminate hydrate with alumina, ferric oxide, mono-anion phase) containing chromate were synthesized. These AFm-phases belong to the group of layered double hydroxides (LDHs).3CaO·Al₂O₃·CaCrO₄·nH₂O and C₃A·1/2Ca(OH)₂·1/2CaCrO₄·12H₂O were obtained as pure phases and their different distinct interlayer water contents and properties determined. Solid solution of chromate-containing phases and tetracalcium-aluminate-hydrate (TCAH) were studied. The uptake of chromate into TCAH from solutions was proven. Chromate contents in solution decrease to <0.2 mg/l.     

Thermal decomposition of hydrotalcites with variable cationic ratios

Thermal analysis complimented with evolved gas mass spectrometry has been applied to hydrotalcites containing carbonate prepared by coprecipitation and with varying divalent/trivalent cation ratios. The resulting materials were characterised by XRD, and TG/DTG to determine the stability of the hydrotalcites synthesised. Hydrotalcites of formula Mg₄(Fe,Al)₂(OH)₁₂(CO₃)·4H₂O, Mg₆(Fe,Al)₂(OH)₁₆(CO₃)·5H₂O, and Mg₈(Fe,Al)₂(OH)₂₀(CO₃)·8H₂O were formed by intercalation with the carbonate anion as a function of the divalent/trivalent cationic ratio. XRD showed slight variations in the d-spacing between the hydrotalcites. The thermal decomposition of carbonate hydrotalcites consists of two decomposition steps between 300 and 400°C, attributed to the simultaneous dehydroxylation and decarbonation of the hydrotalcite lattice. Water loss ascribed to dehydroxylation occurs in two decomposition steps, where the first step is due to the partial dehydroxylation of the lattice, while the second step is due to the loss of water interacting with the interlayer anions. Dehydroxylation results in the collapse of the hydrotalcite structure to that of its corresponding metal oxides and spinels, including MgO, MgAl₂O₄, and MgFeAlO₄.     

CoC2O4·2H2O在空气中的热分解动力学研究

纳米Co3O4具有尖晶石结构,Co3 占据八面体位,具有较高的晶体场稳定化能,在空气中低于800℃时十分稳定,是优良的催化材料[1]。Co3O4还可以作为高比能锂离子电池负极材料具有非常好的电化学活性,充放电容量高达960m A h·g-1。纳米Co3O4在紫外、可见及近红外区域都有良好的吸收效果,因此,在隐身技术、保温节能技术等领域具有潜在的应用前景。所以,Co3O4超细粉体的制备和应用研究具有十分重要的意义。我们合成了草酸盐先驱物制备纳米Co3O4用作隐身材料,因此对先驱物的热分解过程研究是十分必要的。热分析方法在了解先驱物热分解反应的物理…     

Thermal behavior of Cu(II)-, Cd(II)-, and Hg(II)-exchanged montmorillonite complexedwith cysteine

The thermal behavior of montmorillonite and organically modified montmorillonite, both treated with heavy metal cations [Cu(II), Cd(II) and Hg(II)], was characterized via thermal analyses (TG, DTG and DTA) combined with evolved species gas mass spectrometry (MS-EGA), and X-ray diffraction at in situ controlled temperature (HTXRD). The reactions involving Cu(II)- and Cd(II)-montmorillonite samples are mostly related to H₂O and OH loss, unlike Hg(II)-montmorillonite, where effects associated to Hg(II) loss are also present. Finally reactions related to dehydration, dehydroxylation and to organic matter decomposition can be observed in montmorillonite samples treated with cysteine.     

Thermal decomposition of natural iowaite

The thermal decomposition of natural iowaite of formula Mg₆Fe₂(Cl,(CO₃)_0.5)(OH)₁₆·4H₂O was studied by using a combination of thermogravimetry and evolved gas mass spectrometry. Thermal decomposition occurs over a number of mass loss steps at 60°C attributed to dehydration, 266 and 308°C assigned to dehydroxylation of ferric ions, at 551°C attributed to decarbonation and dehydroxylation, and 644, 703 and 761°C attributed to further dehydroxylation. The mass spectrum of carbon dioxide exhibits a maximum at 523°C. The use of TG coupled to MS shows the complexity of the thermal decomposition of iowaite. This revised version was published online in July 2006 with corrections to the Cover Date.     

Study of the alkaline earth metals with 8-hydroxyquinolinate derivatives

Metal complexes of calcium with 5,7-dibromo, 7-iodo and 5-chloro-7-iodo-8-hydroxyquinolate were precipitated in aqueous ammonia and acetone medium, except for the solid state compound with 5,7-dichloro-8-hydroxyquinoline which hasn"t been obtained under these conditions. The complexes obtained through the mentioned precipitation are Ca[(C₉H₄ONBr₂)₂]₃·H₂O, Ca[(C₉H₅ONI)₂]·2H₂O and Ca[(C₉H₄ONICl)₂]·2.5H₂O. Their intermediate from the thermal decomposition found through TG/DTA curves in air indicated the presence of different kinds of calcium carbonates related to the reversibility and crystalline structure, depending on the original compounds. The initial compounds and the intermediate from the thermal decomposition were also characterized through IR spectra and X-ray diffraction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal Decomposition and Dehydration Kinetics of Tetra(piperidinium) Octamolybdate Tetrahydrate in Air

Thermal decomposition of tetra(piperidinium) octamolybdate tetrahydrate, [C₅H₁₀NH₂]₄[Mo₈O₂₆]·4H₂O, was investigated in air by means of TG‐DTG/DTA, DSC, TG‐IR and SEM. TG‐DTG/DTA curves showed that the decomposition proceeded through three well‐defined steps with DTA peaks closely corresponding to mass loss obtained. Kinetics analysis of its dehydration step was performed under non‐isothermal conditions. The dehydration activation energy was calculated through Friedman and Flynn‐Wall‐Ozawa (FWO) methods, and the best‐fit dehydration kinetic model function was estimated through the multiple linear regression method. The activation energy for the dehydration step of [C₅H₁₀NH₂]₄[Mo₈O₂₆]·4H₂O was 139.7 kJ/mol. The solid particles became smaller accompanied by the thermal decomposition of the title compound.     

Thermal decomposition of cadmium peroxotitanate to CdTiO3

TG, DTA and DSC curves of Cd₂[Ti₂(O₂)₂O(OH)₆]·H₂O were recorded and used to determine the isothermal conditions suitable for obtaining the intermediate samples corresponding to the phases observed during the thermal decomposition. The samples were identified by quantitative analysis, IR spectroscopy and X-ray analysis. The experimental results were used to propose a mechanism of thermal decomposition of the investigated compound to CdTiO₃. The optimum conditions were also determined for obtaining CdTiO₃ with well-defined crystallinity.     

Ein anionischer Oxohydroxo‐Komplex mit Bismut(III): Na6[Bi2O2(OH)6](OH)2 · 4H2O

An Anionic Oxohydroxo Complex with Bismuth(III): Na₆[Bi₂O₂(OH)₆](OH)₂ · 4H₂O Colourless, plate‐like, air sensitive crystals of Na₆[Bi₂O₂(OH)₆](OH)₂ · 4H₂O are obtained by reaction of Bi₂O₃ or Bi(NO₃)₃ · 5H₂O in conc. NaOH (58 wt %) at 200 °C followed by slow cooling to room temperature. The crystal structure (triclinic, P 1¯, a = 684.0(2), b = 759.8(2), c = 822.7(2) pm, α = 92.45(3)°, ß = 90.40(3)°, γ = 115.60(2)°, Z = 1, R1, wR2 (all data), 0, 042, 0, 076) contains dimeric, anionic complexes [Bi₂O₂(OH)₆]^4— with bismuth in an ψ¹‐octahedral coordination of two oxo‐ and three hydroxo‐ligands. The thermal decomposition was investigated by DSC/TG or DTA/TG and high temperature X‐ray powder diffraction measurements. In the final of three steps the decomposition product is Na₃BiO₃.     

Thermal and structural behavior of Buriti oil/poly(methyl methacrylate) and Buriti oil/polystyrene materials

Melting processes and thermal decompositions of [Ca(H₂O)₄](ClO₄)₂ and [Ca(NH₃)₆](ClO₄)₂ were studied by thermogravimetry analysis (TG) and differential scanning calorimetry (DSC). The gaseous products of the decomposition were on-line identified by a quadruple mass spectrometry (QMS). In both compounds the processes of loss of the ligands start at ca. 340–350 K and continue up to ca. 600 K. Tetraaquacalcium perchlorate dissolves in own coordination water (melts) at T _m=350 K. The decomposition of the sample proceeds in three main stages. In stage I (351–602 K) dehydration of [Ca(H₂O)₄](ClO₄)₂ to anhydrous Ca(ClO₄)₂ undergoes in two steps, in which consecutively 2/4 and 2/4 of all H₂O molecules are liberated. In stage II (602–701 K) anhydrous Ca(ClO₄)₂ has one solid-solid phase transition at T _c=619 K and then melts at T _m=689 K. Stage III (above 700 K) is connected with decomposition of melted Ca(ClO₄)₂ to oxygen and solid CaCl₂. The decomposition of the [Ca(NH₃)₆](ClO₄)₂ proceeds also in three main stages. In stage I (341–601 K) deamination of [Ca(NH₃)₆](ClO₄)₂ to Ca(ClO₄)₂ undergoes in two steps, in which consecutively 3/6 and 3/6 of all NH₃ molecules are liberated. Stages II and III (601–868 K) are exactly the same as they were observed for [Ca(H₂O)₄](ClO₄)₂.     

CaNa[Cr(OH)6] – A Layered Hydroxochromate(III) with Ordered Brucite Structure and its Thermal Decomposition

Green single-crystals of the hydroxochromate(III) CaNa[Cr(OH)₆] were grown under highly alkaline hydrothermal conditions at about 200 °C. The starting materials Ca(NO₃)₂ · 6H₂O and Cr(NO₃)₃ · 9H₂O were reacted in a mixture of water and sodium hydroxide with the molar ratio of 2.8:1. CaNa[Cr(OH)₆] crystallizes in the non-centrosymmetric trigonal space group R3 with the lattice parameters a = 583.86(2) pm and c = 1428.73(6) pm [T = 100(1) K]. Characteristically, the crystals are reverse-obverse as well as inversion twins. The crystal structure is a stack of uncharged metal hydroxide layers, which can be regarded as a cation-ordered rhombohedral variant of the Mg(OH)₂ (brucite) structure type. The oxidation state of chromium(III) and its coordination by hydroxide groups was confirmed by UV/Vis and IR spectroscopy, respectively. Temperature-dependent magnetic measurements revealed paramagnetic behavior with an effective moment of 3.82 μ_B per chromium atom. The thermal decomposition of CaNa[Cr(OH)₆] takes place at about 225 °C, where the fast elimination of 1.5 equivalents of water is followed by the oxidation of chromium(III) to chromium(VI). Upon further heating to 1000 °C and 1200 °C, the intermediate decomposition products CaCrO₄ and Na₂CrO₄ transform into the oxochromates(V) Ca₅(CrO₄)₃O_0.5 and Ca₃(CrO₄)₂, respectively.     

Thermal decomposition of cadmium succinate dihydrate

Thermal decomposition of cadmium succinate dihydrate, CdC₄H₄O₄·2H₂O, was studied in dynamic helium and air atmospheres by means of simultaneous TG, DTA and MS analysis. It was found that dehydration of CdC₄H₄O₄·2H₂O takes place in the temperature range 80–165°C and at low heating rates formation of monohydrate was stated. The anhydrous cadmium succinate decomposes at about 350°C to metallic cadmium. The gaseous products of cadmium succinate decomposition are CO₂ and H₂O. Formation of small amounts of 3-phenylpropanal and 1,7-octadiene during decomposition in helium was revealed. In helium cadmium evaporates at the temperature of decomposition and the residue consists of small amount of elementary carbon formed in result of pyrolysis of succinate groups. In air cadmium oxidizes and the final solid product of decomposition is CdO.     

Kinetics of decomposition of different acid calcium phosphates

The kinetics of thermal decomposition of Ca(H₂PO₄)₂·H₂O under non-isothermal conditions was studied. The TG/DTG curves were obtained at five heating rates: 5, 7, 10, 12 and 20 K min^–1. The kinetic analysis was performed by means of three methods: Friedman, Budrugeac–Segal and NPK by Sempere and Nomen. An important dependence of the activation energy vs. the conversion degree was observed and also a compensation effect. The decomposition consists of water loss and is due to the elimination of crystallization water and an intermolecular condensation, respectively.     

Thermal analysis of β-Co2(OH)3Cl and Zn5(OH)5Cl2 · H2O

Samples of β-Co₂(OH)₃Cl and Zn₅(OH)₈Cl₂ · H₂O have been prepared and their thermal decomposition studied in air and N₂ by DTA and TG up to 1000°C. X-Ray diffraction analysis of the thermal treatment products in air at various temperatures from 100 to 100°C was also carried out. The results obtained made it possible to establish the steps through which the pyrolysis of both compounds proceeds.     

Monitoring of thermal behavior and decomposition products of soybean oil

The thermal degradation and corresponding decomposition products of fresh and heat-treated soybean oil were investigated by synchronous thermal analyzer combined with Fourier transform infrared spectrometry and quadrupole mass spectrometry (STA–FTIR–QMS). Two longtime heat-treated soybean oil samples were aforehand prepared by consistently heating the fresh soybean oil for 50 and 100 h, respectively. N₂ and simulative air (N₂/O₂ = 4:1, volume) were used as the thermal reaction gas atmosphere. The results showed that one stage of mass loss appeared in analysis of the all oil samples under N₂ atmosphere condition and longtime heat pre-treatment had no effect on the thermal behavior of the soybean oil under N₂ atmosphere condition. However, four stages occurred in analysis of both untreated and heat-treated oil samples under the simulative air atmosphere condition. Longtime heat pre-treatment influenced the thermal behavior of the soybean oil in certain extent, which was reflected in the different mass loss values of the four stages. According to the infrared absorption profiles and MS spectra of the released compounds in vapor phase, H₂O, CO, CO₂, hydrocarbons (such as CH₄), and hydroxyl, carbonyl, and carboxyl-contained compounds have been confirmed. Therefore, STA–FTIR–QMS can be suggested as a promising technique for investigating of thermal degradation and monitoring the decomposition products of the evolving substances in edible oils.     

Thermoanalytical investigations of decomposition course of copper oxysalts

The thermal decomposition of basic copper carbonate (malachite; CuCO₃·Cu(OH)₂) in a dynamic atmosphere of air or nitrogen was studied via TG, DTA and DSC at different heating rates. The non-isothermal kinetic and thermodynamic parameters were estimated. The decomposition course was thoroughly followed by examining the structural and morphological consequences of calcining the material at elevated temperatures by IR, XRD and SEM. The results obtained showed that in air CuCO₃·Cu(OH)₂ released 0.5 H₂O at 195°C, transforming into the azurite structure 2CuCO₃·Cu(OH)₂. Decomposition then commenced, through two endothermic steps maximized at 325 and 430°C. The resultant product maintained the water released from the decomposition process up to 650–750°C. A schematic decomposition pathway has been proposed in terms of the thermal and physicoanalytical results.     

Synthesis and thermal decomposition of bismuth peroxotitanate to Bi2Ti2O7

Bi-peroxotitanate was synthesized by a peroxo method and after thermal decomposition Bi₂Ti₂O₇ was obtained. DTA, TG and DSC curves of Bi₂[Ti₂(O₂)₄(OH)₆]5H₂O were recorded and used to determine isothermal conditions suitable for obtaining the intermediate samples corresponding to the phases observed during the thermal decomposition. The samples were identified by quantitative analysis, IR spectroscopy and X-ray analysis. The experimental results were used to propose a mechanism of thermal decomposition of the investigated compound to a nanosized Bi₂Ti₂O₇. The optimum conditions were also determined for obtaining Bi₂Ti₂O₇, which is applicable for piezosensors.     

Thermal behaviour of the homopolynuclear glyoxylate complex combinations with Cu(II) and Cr(III)

Homopolynuclear complexes of Cu(II) respectively Cr(III) with the glyoxylate dianion, C₂H₂O₄ ^2-, have been studied in non-isothermal regime in air and nitrogen. The results of the non-isothermal analysis performed for the synthesised complexes, Cu(C₂H₂O₄)·0.5H₂O, respectively [Cr₂(OH)₂(C₂H₂O₄)₂(OH₂)₄]·2H₂O, correlated with the results of the IR and TG analysis of the compounds obtained by thermal treatment from the initial complexes and the results of the GLC and XR analysis have led to the establishment of the thermal decomposition mechanisms for the two studied complexes. The decomposition mechanisms confirm the stoichiometric and structural formulae proposed for the two synthesised homopolynuclear complexes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis of the mixed oxide catalysts based upon the nickel-copper hydrotalcites of the type Ni<Subscript>x</Subscript>Cu<Subscript>6-x</Subscript>Cr<Subscript>2</Subscript>(OH)<Subscript>16</Subscript>(CO<Subscript>3</Subscript>)×4H<Subscript>2</Subscript>O

Summary High resolution TG coupled to a gas evolution mass spectrometer has been used to study the thermal properties of a chromium based series of Ni/Cu hydrotalcites of formulae Ni_xCu_6-xCr₂(OH)₁₆(CO₃)×4H₂O where x varied from 6 to 0. The effect of increased Cu composition results in the increase of the endotherms and mass loss steps to higher temperatures. Evolved gas mass spectrometry shows that water is lost in a number of steps and that the interlayer carbonate anion is lost simultaneously with hydroxyl units. Differential scanning calorimetry was used to determine the heat flow steps for the thermal decomposition of the synthetic hydrotalcites. Hydrotalcites in which M²⁺ consist of Cu, Ni or Co form important precursors for mixed metal-oxide catalysts. The application of these mixed metal oxides is in the wet catalytic oxidation of low concentrations of retractable organics in water. Therefore, the thermal behaviour of synthetic hydrotalcites, Ni_xCu_6-xCr₂(OH)₁₆CO₃×nH₂O was studied by thermal analysis techniques in order to determine the correct temperatures for the synthesis of the mixed metal oxides.     

The role of anhydrous zinc nitrate in the thermal decomposition of the zinc hydroxy nitrates Zn5(OH)8(NO3)2·2H2O and ZnOHNO3·H2O

The steps associated with the thermal decomposition of Zn₅(OH)₈(NO₃)₂·2H₂O and ZnOHNO₃·H₂O are re-examined. Previous reports have suggested that Zn₅(OH)₈(NO₃)₂·2H₂O decomposes to ZnO via two intermediates, Zn₅(OH)₈(NO₃)₂ and Zn₃(OH)₄(NO₃)₂ whereas ZnOHNO₃·H₂O has been reported to decompose to ZnO via a Zn₃(OH)₄(NO₃)₂ intermediate. In this study, we demonstrate using TG, mass spectral analysis of evolved gases and in situ variable temperature powder X-ray diffraction analysis that, in fact, in the decomposition of Zn₅(OH)₈(NO₃)₂·2H₂O an anhydrous zinc nitrate intermediate is also involved. We, additionally, show that the decomposition of ZnOHNO₃·H₂O to ZnO also involves the formation of an anhydrous zinc nitrate intermediate. The anhydrous zinc nitrate formed in both cases is poorly crystallised and this observation may explain why this phase could not be observed by PXRD analysis in the previous studies.