Influences of temperature and atmosphere on thermal stability of BaCrO4

In this article, the influences of temperature and atmosphere on thermal stability of BaCrO₄ were investigated. BaCrO₄ powders with an orthorhombic structure were synthesized by a facile aqueous solution route. The synthesized BaCrO₄ products were then heat treated at different atmospheres to evaluate their thermal stability by differential thermal analysis–thermogravimetry (DTA–TG), X-ray photoelectron spectroscopy and X-ray diffraction. BaCrO₄ has a good thermal stability and does not decompose in air up to 1,400 °C. However, the decomposition of BaCrO₄ in vacuum depends mainly upon a two-stage chemical reaction. BaCrO₄ is finally decomposed into BaCr₂O₄ with trivalent Cr³⁺ cations and Ba₃(Cr⁶⁺ Cr⁵⁺)₂O_9?x with both pentavalent Cr⁵⁺ and hexavalent Cr⁶⁺ cations after heat treatments in vacuum.     

铬酸铵钠复盐结晶的热分解

采用TG-DTG、DTA和XRD对铬酸铵钠复盐结晶(NaNH4CrO4•2H2O)的热分解过程进行研究,结果表明NaNH4CrO4•2H2O的热分解过程分为三步进行,第一步是在50～95 ℃温度范围结晶水的脱除,第二步是在100～180 ℃的温度范围铵的初步热分解,产物为铬酸钠和重铬酸铵,第三步是215～385 ℃进行的铵的完全分解.存在生成重铬酸钠与生成三氧化二铬的竞争反应.在氨不易扩散的条件下,最终分解产物为三氧化二铬、重铬酸钠和铬酸钠的混合物;在流动气氛中,400～790 ℃温度范围,NaNH4CrO4•2H2O热分解产物为重铬酸钠.与传统的铬酸钠硫酸酸化生产重铬酸钠工艺相比,该方法无副产物产生,是一清洁工艺.     

Thermoanalytical studies on lobster shell

Chromium(III) oxide reverses the sequence of dehydration of barium perchlorate trihydrate (BP). Between 223 and 310? the oxide reacts with anhydrous BP in a 1∶1 molar ratio to give the yellow barium dichromite BaCr₂O₄. Between 350 and 430? this material reacts in 1∶1 stoichiometry with BP, to give barium chromate BaCrO₄. The products have been identified by X-ray diffraction analysis. The formation of an unkown phase is also reported.     

Decomposition mechanism of copper ammonium chromate: A basic material for copper chromite catalyst

The mechanism of thermal decomposition of basic copper ammonium chromate has been investigated using TG/DTG/DSC and X-ray studies. The decomposition is a three-step process. Calcination at lower temperatures can be achieved by taking advantage of the exothermicity of the decomposition process.     

Electrical conductivity measurements during the thermal decomposition reaction of ammonium metavanadate

Electrical conductivity vs. temperature curve shows all characteristic peaks due to individual stages of the thermal decomposition reaction of NH₄VO₃, including the stage of formation of the anhydrous ammonium divanadate at ～150°, obtainable only under special experimental conditions on TG, DTG, and DTA curves. It is suggested that such measurements can be used for detecting and/or confirming the existence of intermediate solid products of decomposition in case they are difficult to be identified.     

Thermal decomposition kinetics of diethyl dithiocarbamate complexes of copper(II) and nickel(II)

Thermogravimetric (TG), derivative thermogravimetric (DTG) and differential thermal analysis (DTA) curves of CuL₂ and NiL₂ (L^?=diethyl dithiocarbamate anion) in air are studied. The main decomposition temperature ranges are: For CuL₂, DTG 250–350°, DTA 300–320° and for NiL₂, DTG 290–390°, DTA 360–400°. Mass loss considerations at the main decomposition stages indicate conversion of the complex to sulphides. Mathematical analysis of TG data shows that first order kinetics are applicable in both cases. Kinetic parameters (energy and entropy of activation and preexponential factor) are reported.

     

Thermal Decomposition of Barium Dioxodiaquaperoxyoxalato Uranate(VI) Hydrate

Barium dioxodiaquaperoxyoxalatouranate was obtained by reaction of uranyl nitrate with oxalic acid and then hydrogen peroxide in the presence of barium ion. The complex was subjected to chemical analysis. The thermal decomposition behaviour of the complex was studied using TG, DTG and DTA techniques. The solid complex salt and the intermediate product of its thermal decomposition were characterized using IR absorption and X-ray diffraction spectra. Based on data from these physico-chemical investigations the structural formula of the complex was proposed as Ba[UO₂(O₂)(C₂O₄)(H₂O)₂]⋅H₂O. This revised version was published online in August 2006 with corrections to the Cover Date.     

Some studies on thallium oxalates. II. Thermal decomposition of potassium bisoxalato diaquothallate(III) dihydrate

Potassium bisoxalato diaquothallate(III) dihydrate is obtained by precipitating thallium(III) with oxalic acid from slightly acidic (HNO₃ or H₂SO₄) solutions in the presence of potassium ions. The thermal decomposition behaviour of the complex is studied using the techniques of TG, DTA and DTG. The solid complex salt and the intermediate products of its thermal decomposition are characterised using IR absorption spectra, microscopic observations, electrical conductivity measurements and X-ray diffraction data.     

Thermal analysis of quinolinium tetrachloroferrate(III)

Thermal decomposition of a compound consisting of a tetrachloroferrate(III) anion and a quinolinium cation, of general formula [QH][FeCl₄], has been studied using TG-FTIR, TG-MS, DTA and DTG techniques. The measurements were carried out in an argon atmosphere over the temperature range 20-800 °C. The solid products of the thermal decomposition were identified by IR, FIR and Mössbauer spectroscopy.     

Effect of nanoclay and barium sulfate nanoparticles on the thermal and morphological properties of polyvinylidene fluoride nanocomposites

The thermal, morphological and optical studies of BaSO₄ and MMT (nanoclay) embedded in PVDF were investigated. Nanocomposites samples of PVDF–BaSO₄–MMT were prepared by varying the loadings (1–4 mass%) in case of BaSO₄ and MMT nanomaterials, respectively. Polyvinylidene fluoride–barium sulfate-montmorillonite (PVDF–BaSO₄–MMT) nanocomposites were prepared by solvent-mixing technique. Nanoparticles were synthesized by in situ deposition technique with the help of nonionic polymeric surfactant, and the particle size of nanoparticles was recognized by scanning electron microscopy (SEM) analysis which confirms that the particle has diameter of 80–90 nm. As prepared, nanocomposites films (thickness, 25 μm) were characterized by Fourier transform infrared microscopy (FTIR), SEM and electron diffraction spectroscopy (EDS). FTIR shows that all the chemical constituents were present in the nanocomposites, whereas SEM analysis suggested that the nanofillers dispersed well in polymer matrix and EDS showed the elemental composition of nanocomposite samples. Thermal properties of nanocomposites were studied by using TG/DTA/DTG. TG/DTA studies showed decomposition temperature of pure PVDF is 473.5 °C. The decomposition temperature (T _d) of nanocomposites was increased by 93 °C in case of nanocomposites with addition of both BaSO₄ and MMT nanomaterials. The difference in the thermal degradation temperature was found to be 1.2% higher in case of addition of BaSO₄ nanoparticle as compared to nanoclay. The obtained transparent nanocomposite films were characterized by using UV–Vis spectrophotometer which shows that transparencies of nanocomposites are maintained in visible region, the intensity of absorption band in UV region is increased with the addition of BaSO₄ nanoparticles, while in case of addition of nanoclay the UV region does not show drastic changes. Addition of both nanoparticle and nanoclay shows higher absorption in comparison with the individual samples. But further, doubling the amount of nanoparticle and nanoclay shows decrease in UV absorption. Overall, the results of thermal studies show that the incorporation of BaSO₄ and MMT could significantly improve the thermal properties of nanocomposites.     

Thermal analysis of copper(Ii) complexes of general formula [Et<Subscript>4</Subscript>N]<Subscript>2</Subscript>[CuBr<Subscript>n</Subscript>Cl<Subscript>4-n</Subscript>]

Thermal decomposition of compounds consisting of tetrahalogenocuprate(II), [CuBr_nCl_4−n]²⁻ (n=0–4) anions and a tetraethylammonium cation has been studied using TG-FTIR, TG-MS, DTA and DTG techniques. The measurements were carried out in an argon and air atmospheres over the temperature range 293-1073 K. The products of the thermal decomposition were identified by IR and Far Infrared (FIR) spectroscopy as well as X-ray powder diffractometry.     

Thermal Studies on Ammonium Uranates

Ammonium uranates are important intermediates in the preparation of nuclear fuel UO₂. These can generally be prepared through two different routes: heterogeneous (conventional) and homogeneous methods of precipitation. In the conventional method, ammonium hydroxide, gaseous ammonia and ammonium carbonate are the precipitating agents. In the homogeneous method, urea hydrolysis is used to generate in situ ammonia needed for precipitation. For the present studies, ammonium hydroxide is used for the conventional and urea for the homogeneous methods of precipitation. The uranates, thusprepared, are characterized by thermogravimetry (TG), differential thermogravimetry (DTG)and differential thermal analysis (DTA). Thermally the numbers of decomposition steps are identical for both uranates but the temperatures of the decomposition and mass losses vary. The intermediate and final oxides are identified by X-ray diffractometry (XRD). This revised version was published online in July 2006 with corrections to the Cover Date.     

Studies on thermal decomposition of electrochemically oxidized glass-like carbon

Glass-like carbon (GC) tiles were electrochemically oxidized in 1 mol·dm^?3 H₂SO₄ solution at a potential of 2.3 V/SCE. The surfaces of the oxidized samples were examined by scanning electron microscopy (SEM). The solid oxidation products were studied by derivatographic (TG, DTG and DTA) and elemental analyses. The solid products of electrochemical oxidation of GC, with the general formula C₈O_4.2H_2.3 were thermolabile and revealed properties similar to those of graphite oxide. They are hydrophylic and their thermal decomposition proceeds in three steps: (i) evaporation of-chemisorbed water (320–400 K), (ii) exothermic decomposition of graphite oxide (370–430 K), and (iii) gradual decomposition of the oxidation products (>430 K).     

Sol–gel combustion synthesis and characterization of nanostructure copper chromite spinel

Nanocomposite copper chromite spinel was fabricated by sol–gel process using copper nitrate trihydrate, chromium nitrate nonahydrate, ethylene glycol, diethyl ether, and citric acid. The thermoanalytical measurements (TG–DTG), X-ray powder diffractometry (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray analysis were used to characterize the structural and the chemical features of the nanocomposites. TG–DTG results showed that the major mass loss for copper(II) nitrate, chromium(III) nitrate as precursors occur at 258 and 140 °C, respectively. The major mass loss for dried gel of copper chromite occurs at 310 °C. XRD data revealed the formation of pure copper chromite after thermal decomposition at 1,000 °C for 2 h. The observation of XRD patterns reveals the presence of single-phase tetragonal spinel CuCr₂O₄. FESEM analysis of calcined composite was found to be in the range of 20–30 nm.     

Synthesis, spectroscopic and thermal studies of the copper(II) aspartame chloride complex

Aspartame adduct of copper(II) chloride Cu(Asp)₂Cl₂·2H₂O (Asp=aspartame) is synthesized and characterized by elemental analysis, FT IR, UV/vis, ESR spectroscopies, TG, DTG, DTA measurements and molecular mechanics calculations. Aqueous solution of the green solid absorbs strongly at 774 and 367 nm. According to the FT IR spectra, the aspartame moiety coordinates to the copper(II) ion via its carboxylate ends, whereas the ammonium terminal groups give rise to hydrogen bonding network with the water, the chloride ions or neighboring carboxylate groups. The results suggest tetragonally distorted octahedral environment of the copper ions.     

Investigation of thermal decomposition of rice husk

Studies on the thermal decomposition of untreated rice husk and that treated with HCl and H₂SO₄ of various concentrations were carried out by TG, DTG and DTA. The mass loss occurred in three distinct stages, namely, removal of moisture, release of volatile matter and burning of combustible material. The corresponding temperature ranges for untreated husk were 40–150, 215–350 and 350–690°C. The final temperature of combustion decreased with acid-treatment of the husk. The thermal decomposition of the husk was found to be an exothermic process.     

New view on the oxidation mechanisms of crude oil through combined thermal analysis methods

In the previous study, the oxidation behavior of four Chinese crude oils (Oil 1 to 4) in the presence and absence of rock cuttings was investigated by thermogravimetry/derivative thermogravimetry (TG/DTG) techniques and oxidation tube experiments. The present work investigates the thermal behavior of these oils by combining DTG–DTA method. First, we conducted comparative analysis about mass loss rate from DTG curves and endothermic/exothermic phenomenon from DTA curves attempting to clarify the endothermic or exothermic mechanism in crude oil low-temperature oxidation. Finally, we combined the thermal analysis method with low-temperature oil oxidation tube experiment in porous media to ascertain, whether the two methods are consistent in the aspect of low-temperature oxidation mechanism of crude oil by O₂ consumption rate and CO₂ generating rate (carbon bond stripping reaction rate). Results show that crude oils undergo an endothermic oxidation behavior during low-temperature oxidation stage, suggesting the decomposition of hydrocarbon components. Clay can play a catalytic effect on low-temperature oil oxidation. The results of DTG–DTA tests can also better reflect oil oxidation mechanism under real conditions.     

Pure CuCr2O4 nanoparticles: Synthesis,characterization and their morphological and size effects on the catalytic thermal decomposition of ammonium perchlorate

In the present paper a pure phase of the copper chromite spinel nanoparticles (CuCr₂O₄ SNPs) were synthesized via the sol–gel route using citric acid as a complexing agent. Then, the CuCr₂O₄ SNPs has been characterized by field emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). In the next step, with the addition of Cu–Cr–O nanoparticles (NPs), the effects of different parameters such as Cu–Cr–O particle size and the Cu/Cr molar ratios on the thermal behavior of Cu–Cr–O NPs + AP (ammonium perchlorate) mixtures were investigated. As such, the catalytic effect of the Cu–Cr–O NPs for thermal decomposition of AP was evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). TGA/DSC results showed that the samples with different morphologies exhibited different catalytic activity in different stages of thermal decomposition of AP. Also, in the presence of Cu–Cr–O nanocatalysts, all of the exothermic peaks of AP shifted to a lower temperature, indicating the thermal decomposition of AP was enhanced. Moreover, the heat released (ΔH) in the presence of Cu–Cr–O nanocatalysts was increased to 1490 J g⁻¹.     

The non-isothermal decomposition of cobalt acetate tetrahydrate

The non-isothermal decomposition of cobalt acetate tetrahydrate was studied up to 500°C by means of TG, DTG, DTA and DSC techniques in different atmospheres of N₂, H₂ and in air. The complete course of the decomposition is described on the basis of six thermal events. Two intermediate compounds (i.e. acetyl cobalt acetate and cobalt acetate hydroxide) were found to participate in the decomposition reaction. IR spectroscopy, mass spectrometry and X-ray diffraction analysis were used to identify the solid products of calcination at different temperatures and in different atmospheres. CoO was identified as the final solid product in N₂, and Co₃O₄ was produced in air. A hydrogen atmosphere, on the other hand, produces cobalt metal. Scanning electron microscopy was used to investigate the solid decomposition products at different stages of the reaction. Identification of the volatile gaseous products (in nitrogen and in oxygen) was performed using gas chromatography. The main products were: acetone, acetic acid, CO₂ and acetaldehyde. The proportions of these products varied with the decomposition temperature and the prevailing atmosphere. Kinetic parameters (e.g.E and lnA) together with thermodynamic functions (e.g. °H, C _p and °S) were calculated for the different decomposition steps. In celebration of the 60^th birthday of Dr. Andrew K. Galwey     

Preparation of aluminas

Aluminium hydroxide was prepared by precipitation from aluminium nitrate solution with ammonia solution. Thermal decomposition of the solid hydroxide was studied by means of TG, DTG and DTA. The sample was thermally treated in the temperature interval between 200 °C and 1000 °C. X-ray phase analysis was used to study the phase compositions of the resulting products, and their surface areas were compared.