Selective self-assembly synthesis of MnV2O6·4H2O with controlled morphologies and study on its thermal decomposition

The MnV₂O₆·4H₂O with rod-like morphologies was synthesized by solid-state reaction at low heat using MnSO₄·H₂O and NH₄VO₃ as raw materials. XRD analysis showed that MnV₂O₆·4H₂O was a compound with monoclinic structure. Magnetic characterization indicated that MnV₂O₆·4H₂O and its calcined products behaved weak magnetic properties. The thermal process of MnV₂O₆·4H₂O experienced three steps, which involves the dehydration of the two waters of crystallization at first, and then dehydration of other two waters of crystallization, and at last melting of MnV₂O₆. In the DSC curve, the three endothermic peaks were corresponding to the two steps thermal decomposition of MnV₂O₆·4H₂O and melting of MnV₂O₆, respectively. Based on the Kissinger equation, the average values of the activation energies associated with the thermal decomposition of MnV₂O₆·4H₂O were determined to be 55.27 and 98.30?kJ?mol^?1 for the first and second dehydration steps, respectively. Besides, the thermodynamic function of transition state complexes (??H ^??, ??G ^?? , and ??S ^?? ) of the decomposition reaction of MnV₂O₆·4H₂O were determined.     

Studies on the non-isothermal kinetics of the thermal decomposition of [Cu(NBOCTB)][Cu(NO3)4]· H2O

The thermal decomposition process of the complex [Cu(NBOCTB)][Cu(NO₃)₄] H₂O has been studied by TG and DTG technique, and possible intermediates of the thermal decomposition have also been conjectured from the TG and DTG curves. The results suggest that the decomposition of the complex involves five steps: The non-isothermal kinetics of steps 1, 2 and 3 have been studied by means of the Achar and Coats-Redfern method based on TG and DTG curves. Step 1 is a Coring and Growth mechanism (n= 1), its kinetic equation may be expressed as: d/dt=Ae^–E/RT(1–). Steps 2 and 3 are both two order chemical reaction mechanisms, their kinetic equations can be expressed as: d/dt=Ae^–E/RT(1–)².This project was supported by the National Natural Science Youth Fundation of China.     

Preparation of 2CaO·3B2O3·H2O nanomaterials and evaluation of their flame retardant properties by a thermal analysis method

Different morphologies of calcium borate 2CaO·3B₂O₃·H₂O, nanoribbon, bundle-like nanostructure and fan-shaped non-nanostructure, have been prepared under hydrothermal conditions, which were characterized by XRD, FT-IR, TGA and SEM. Their flame retardant properties to the polypropylene were investigated by thermal analysis method (including TG, DSC and non-isothermal decomposition kinetics) and oxygen index method. With the decrease in TG mass loss, the increase in heat absorption for DSC in N₂ atmosphere, the increase in LOI values, and the increase in apparent activation energy E_a, the flame retardant properties of prepared 2CaO·3B₂O₃·H₂O samples increased gradually from non-nanostructure to bundle-like nanostructure and then to nanoribbon. This trend may be ascribed to their sizes being decreased accordingly. The flame retarding mechanism has been proposed. The mechanical property of polypropylene/2CaO·3B₂O₃·H₂O composite material has also been evaluated. It can be predicted that 2CaO·3B₂O₃·H₂O nanoribbon could serve as an excellent flame retardant.

     

The thermal dehydration and decomposition of Ba[Cu(C2O4)2(H2O)]·5H2O

The thermal behaviour of Ba[Cu(C₂O₄)₂(H₂O)]·5H₂O in N₂ and in O₂ has been examined using thermogravimetry (TG) and differential scanning calorimetry (DSC). The dehydration starts at relatively low temperatures (about 80°C), but continues until the onset of the decomposition (about 280°C). The decomposition takes place in two major stages (onsets 280 and 390°C). The mass of the intermediate after the first stage corresponded to the formation of barium oxalate and copper metal and, after the second stage, to the formation of barium carbonate and copper metal. The enthalpy for the dehydration was found to be 311±30 kJ mol^–1 (or 52±5 kJ (mol of H₂O)^–1). The overall enthalpy change for the decomposition of Ba[Cu(C₂O₄)₂] in N₂ was estimated from the combined area of the peaks of the DSC curve as –347 kJ mol^–1. The kinetics of the thermal dehydration and decomposition were studied using isothermal TG. The dehydration was strongly deceleratory and the -time curves could be described by the three dimensional diffusion (D3) model. The values of the activation energy and the pre-exponential factor for the dehydration were 125±4 kJ mol^–1 and (1.38±0.08)×10¹⁵ min^–1, respectively. The decomposition was complex, consisting of at least two concurrent processes. The decomposition was analysed in terms of two overlapping deceleratory processes. One process was fast and could be described by the contracting-geometry model withn=5. The other process was slow and could also be described by the contracting-geometry model, but withn=2.The values ofE _a andA were 206±23 kJ mol^–1 and (2.2±0.5)×10¹⁹ min^–1, respectively, for the fast process, and 259±37 kJ mol^–1 and (6.3±1.8)×10²³ min^–1, respectively, for the slow process.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthday     

Thermal decomposition kinetics and reversible hydration study of the Li2Zn(HPO4)2·H2O

The dilithium zinc hydrogen phosphate monohydrate (Li₂Zn(HPO₄)₂·H₂O) was synthesized at the ambient temperature by using zinc acetyl acetonate monohydrate, phosphoric acid and lithium hydroxide monohydrate. The thermal stability of the Li₂Zn(HPO₄)₂·H₂O was studied by non-isothermal kinetic method (Ozawa and Kissinger) from the differential scanning calorimetric (DSC) data. The studied hydrate undergoes two endothermic thermal transformations, which the first transformation is due to the release of water molecule of crystallization and the second one is due to the release of water of constituent from HPO₄^2? anions and transforms to P₂O₇^4?. The activation energies (E_a) calculated for the dehydration step and decomposition step of the Li₂Zn(HPO₄)₂·H₂O from different methods were found to be consistent. The dehydration and rehydration processes of the synthesized compound were investigated and found that the water of crystallization can be removed and rehydrated without the disrupting the structure of the material, provided it is not heated beyond 200 °C. The dehydration and rehydration processes of the synthesized Li₂Zn(HPO₄)₂·H₂O exhibits similar property to the zeolite.     

Analysis of (NH4)6Mo7O24·4H2O thermal decomposition in argon

Nanometric carbides of transition metals and silicon are obtained by using precursors. Control of the course of these processes require data concerning transformations of single precursor, transformations of precursor in the presence of reducing agent and synthesis of the carbide. In this work, the way of investigating such processes is described on the example of thermal decomposition of (NH₄)₆Mo₇O₂₄·4H₂O (precursor) in argon. The measurements were carried out by TG–DSC method. The solid products were identified by XRD method, and the gaseous products were determined by mass spectrometry method. There was demonstrated that the investigated process proceeded in five stages. Kinetic models (forms of f(α) and g(α) function) most consistent with experimental data and coefficients of Arrhenius equation A and E were determined for the stages. The Kissinger method and the Coats–Redfern equation were applied. In case of the Coats–Redfern equation, the calculations were performed by analogue method. In this way good consistency between the calculated and determined conversion degrees α(T) at practically constant values of A and E were obtained for distinguished stages and different sample heating rates.     

Kinetics of thermal decomposition of a synthetic K–H3O jarosite analog

The thermal decomposition kinetics of a synthetic K–H₃O jarosite analog was determined from thermogravimetric analysis at various heating rates in air. A thermal decomposition mechanism was proposed based on X-ray analysis of partially decomposed material and distinct features observed during thermal decomposition analysis. The decomposition path is complex. The material was treated as a composite of K-jarosite, H₃O-jarosite, and a “vacancy component”. The evolution of (OH)^? and SO₃ from these individual components was modeled. The decomposition is broken into subreactions according to distinct features in the thermoanalytical measurements. The subreactions are arranged sequentially and in parallel according to the evolution of the participating phases. A set of associated apparent activation energies was determined using isoconversion analysis. Kinetic triplets were assigned to each subreaction. A reasonable match with the observed decomposition was achieved by varying pre-exponential factors.     

Thermal decomposition and kinetic data of Cd(BF4)2·6H2O

The thermal dehydration and decomposition of Cd(BF₄)₂·6H₂O were studied by means of DTA, TG, DSC and X-ray diffraction methods and the end products of the thermal decomposition were identified. The results of thermal analysis show that the compound is fused first, then it is dehydrated until Cd(BF₄)₂·3H₂O is obtained, which has not been described in the literature so far. The enthalpy of phase transition is H _ph.tr.=115.6 kJ mol^–1 Separation of the compound is difficult since it is highly hygroscopic. Then, dehydration and decomposition take place simultaneously until CdF₂ is obtained which is proved by X-ray diffraction. On further increasing the temperature, CdF₂ is oxidized to CdO and the characteristic curve assumes a linear character.Based on TG data, kinetic analyses were carried out separately for both parts of the curve: first until formation of the trihydrate and then — until formation of CdF₂. The formal kinetic parameters are as follows:for the first phase:E ^*=45.3 kJ mol^–1; rate equationF=^2/3; correlation coefficient 0.9858 for the second phase:E ^*=230.1 kJ mol^–1; rate equationF=(1–)^2/3[1-(1–)^1/3]^–1; correlation coefficient 0.9982.     

The solid-state thermal decomposition of Sr3[La(C2O4)3(H2O)2]2·11H2O

Strontium(II)diaquatris(oxalato)lanthanate(III)unidecahydrate, Sr₃[La(C₂O₄)₃(H₂O)₂]₂·11H₂O, has been synthesized and characterized by elemental, IR and electronic spectral studies. Thermal studies (TG, DTG and DTA) in air showed that all the crystal and coordinated water molecules are removed at ca. 225 °C. The final end product at 1,000 °C was shown to be a mixture of mainly SrCO₃, Sr₃La₄O₉ and La₂Sr₂O₅ along with oxides and carbides of both the metal, through the formation of an intermediate mixture of likely SrC₂O₄ and La₂(C₂O₄)_2.8 at 282 °C, and SrCO₃ and La₂O(CO₃)₂ at 540 °C. The multi-step dehydration and decomposition of the compound has been explored from the DSC study in nitrogen up to 670 °C, and the evaluated kinetic parameters are discussed.     

Synthesis, characterization, infrared studies, and thermal analysis of Mn0.6Zn0.4Fe2(C4H2O4)3·6N2H4 and its decomposition product Mn0.6Zn0.4Fe2O4

Manganese zinc ferrous fumarato–hydrazinate precursor, Mn_0.6Zn_0.4Fe₂(C₄H₂O₄)₃·6N₂H₄ was synthesized for the first time and characterized by chemical analysis, infrared spectral studies, and thermal analysis. Infrared studies show band at 977 cm^?1 indicating bidentate bridging nature of the hydrazine in the complex. Thermogravimetric (TG) studies show two steps dehydrazination followed by two steps total decarboxylation. The precursor on touching with burning splinter undergoes self propagating autocatalytic decomposition yielding ultrafine Mn_0.6Zn_0.4Fe₂O₄. XRD studies confirms single phase formation as well as nanosize nature of “as prepared” Mn_0.6Zn_0.4Fe₂O₄. The saturation magnetization of the “as prepared” Mn_0.6Zn_0.4Fe₂O₄ was found to be 31.46 emu gm^?1, which is lower than the reported, confirms the ultrafine nature of the oxide.     

Thermal magnetic investigation of the decomposition of NixMn1−xC2O4·2H2O

The systems Ni_xMn_1?xC₂O₄·2H₂O (x = 0.11, 0.34) are characterized by XRD, SEM, TG/DTA, EGA-MS and magnetic measurements. The last confirmed that the studied samples are real solid solutions. The SEM reveals that the morphology depends on both the excess of C₂O₄^2? and the initial ratio Ni/Mn. The thermal magnetic investigations (in situ) show that: (i) the presence of Ni in Ni_xMn_1?xC₂O₄·2H₂O leads to decreasing in the decomposition temperature in regard to that of the manganese oxalate; (ii) upon increasing the Ni content the temperature of decomposition (in air) is growing up; (iii) the presence of Ni stabilizes the manganese with respect to oxidation, in spite of the occurring process of decomposition.     

New crystalline forms of thorium arsenate: Preparation and characterisation of Th(HAsO4)2·4H2O and Th(HAsO4)2·2.5H2O

Two new forms of microcrystalline thorium arsenate have been synthesised. They have been characterised as Th(HAsO₄)₂·4H₂O and Th(HAsO₄)·2.5H₂O by chemical analysis and thermal, X-ray, IR and ion exchange studies. The interlayer distances are: Th(HAsO₄)₂·4H₂O: 8.23 Å and Th(HAsO₄)₂·2.5H₂O: 8.59 Å. However, thermally and chemically, both these exchangers are less stable than Th(HAsO₄)₂·H₂O; Th(HAsO₄)₂·2.5H₂O being more stable than Th(HAsO₄)·4H₂O. The maximum lithium ion uptake and the corresponding arsenate released, respectively are: 1.75 and 1.20 mmol/g for Th(HAsO₄)₂·4H₂O at pH 9.0 and 3.42 and 0.28 mmol/g for Th(HAsO₄)₂·2.5H₂O at pH 11.8. For both exchangers, the loss of zeolitic water as well as that released on formation of thorium pyroarsenate takes place in one step between 383 and 773 K.     

Chemical preparation and thermal behaviour of neodymium cyclotriphosphate tetrahydrate NdP3O9·4H2O

A new neodymium cyclotriphosphate tetrahydrate NdP₃O₉·4H₂O has been prepared using a classical method of aqueous chemistry and characterized by X-ray diffraction (XRD), thermogravimetric analysis (TG) and infrared spectroscopy which shows the characteristic bands of cyclotriphosphates as the triplet in the 1340–1260 cm⁻¹ area. The results of differential thermal analysis, X-ray powder diffraction and IR spectrum of the compound heated at different temperatures showed that, after dehydration, NdP₃O₉·4H₂O decomposes into an amorphous compound with a dehydration energy equals to 0.162 kJ g⁻¹, then it crystallises at 925 K in order to give the polyphosphate Nd(PO₃)₃.     

Microstructure and electrical properties of IrO2 prepared by thermal decomposition of IrCl3·x H2O: Role played by the conditions of thermal treatment

Some features of the thermal decomposition of IrCl₃·3 H₂O in an oxygen atmosphere are presented. The formation of IrO₂ phases has been followed by X-ray diffractometry, and the onset of definite reflections has been documented for samples pyrolyzed at 350° C, although moderate weight losses are observed by thermogravimetry at this temperature. The effect of the thermal history of iridium oxide coatings on their structure has been studied by means of electrical resistance measurements. An explanation of the results has been attempted in terms of impurity segregation to the oxide grain boundaries.     

Crystal Structure and Properties of Rb4H2I2O10 · 4H2O

Single crystals of the Rb₄H₂I₂O₁₀· 4H₂O were synthesized for the first time and studied by X-ray diffraction analysis. The crystals are monoclinic, a = 7.321(6) Å, b = 12.599(8) Å, c = 8.198(8) Å, = 96.30(7)°, Z = 2, space group P2₁/c. The H₂I₂O₁₀ ^4– anion is formed by the edge-sharing IO₆ octahedra. The anions are united by hydrogen bonds into a chain running along the x axis. The chains are combined by water molecules into a three-dimensional structure through hydrogen bonds. The compound is a proton conductor. The conductivity values measured at 20–60°C vary within 10^–6 to 10^–4 ohm^–1 cm^–1.     

Preparation and characterization of magnetic TiO2/ZnFe2O4 photocatalysts by a sol–gel method

A magnetic TiO₂/ZnFe₂O₄ photocatalyst was prepared by a sol-gel method, and X-ray diffraction (XRD), magnetic and photocatalytic properties analysis were employed to characterize this photocatalyst. The XRD results show that ZnFe₂O₄ can prevent the transformation of titania from anatase to rutile. The magnetic properties analysis indicates that TiO₂/ZnFe₂O₄ is of large saturation magnetization value and low coercivity. The photocatalytic experimental results show that TiO₂/ZnFe₂O₄=3 and 4 are superior in photocatalytic reactivity to other proportions. TEM shows that TiO₂/ZnFe₂O₄ has a fine core-shell fabric. After being used for four times during the photocatalytic reaction, the TiO₂/ZnFe₂O₄ nanoparticles have good photocatalytic stability.     

The layer crystal structure of [In2(C2O4)3(H2O)3]·7H2O and microstructure of nanocrystalline In2O3 obtained from thermal decomposition

A new indium oxalate, [In₂(C₂O₄)₃(H₂O)₃]·7H₂O, with a layered structure has been synthesised from precipitation methods at room temperature. It crystallises with a monoclinic symmetry, space group P2₁/c (No. 14), a=8.7456(1) Å, b=11.1479(2) Å, c=21.9376(4) Å, β=112.1(1)°, V=1979.98(6) ų and Z=4. The structure is built from neutral [In₂(C₂O₄)₃(H₂O)₃] corrugated layers, between which water molecules are intercalated. The layers are built from chains with two different sequences of indium atoms and bichelating oxalate groups. Two independent indium atoms are present in the structure with two coordination polyhedra, i.e., InO₈ as a distorted square-based antiprism and InO₇ as a nearly regular pentagonal-based bipyramid. The thermal decomposition has been studied in situ by temperature dependent X-ray diffraction and thermogravimety. The final product is nanocrystalline indium oxide. The microstructure of the oxide has been characterised with both the Voigt/Langford method based on the integral breadth and the whole pattern fitting approach. The size of the isotropic crystallites increases from 322 to 924 Å, while microstrains decrease, in the annealing temperature range 500–750 °C.     

Synthesis of novel ZnAl2O4/Al2O3 nanocomposite by sol–gel method and its application as adsorbent

Journal of Sol-Gel Science and Technology - In this research, ZnAl2O4/Al2O3 nanocomposites with different ZnAl2O4 (30, 50, and 70?wt.%) were successfully prepared in one step by sol–gel...     

Thermal decomposition reaction kinetics of complexes of [Sm(o-MOBA)3bipy]2·H2O and [Sm(m-MOBA)3bipy]2·H2O

The complexes of [Sm(o-MOBA)₃bipy]₂·H₂O and [Sm(m-MOBA)₃bipy]₂·H₂O (o(m)-MOBA = o(m)-methoxybenzoic acid, bipy-2,2′-bipyridine) have been synthesized and characterized by elemental analysis, IR, UV, XRD and molar conductance, respectively. The thermal decomposition processes of the two complexes were studied by means of TG–DTG and IR techniques. The thermal decomposition kinetics of them were investigated from analysis of the TG and DTG curves by jointly using advanced double equal-double steps method and Starink method. The kinetic parameters (activation energy E and pre-exponential factor A) and thermodynamic parameters (ΔH ^≠ , ΔG ^≠ and ΔS ^≠) of the second-step decomposition process for the two complexes were obtained, respectively.     

Mössbauer spectroscopic studies of Fe2F5·7H2O related compounds and their thermal decomposition products

The structures of Fe(III)M(II)F₅·7H₂O (where MZn, Co and Fe) were studied from room temperature to 78°K using Mössbauer resonance spectroscopy and they were confirmed to be isostructural. Similar measurements on the dihydrates formed by heating the samples to temperatures in the range of 75–115°C show these also to be isostructural. The compound AlFe(II)F₅·7H₂O behaves similarly. The temperature dependence of the quadrupole-splitting is interpreted as a change from discrete, octahedrally coordinated metal ions in the heptahydrate to face-shared octahedrally coordinated ions in the dihydrate.