Synthesis,characterization, and thermal study of solid-state alkaline earth metal mandelates,except beryllium and radium

Characterization, thermal stability, and thermal decomposition of alkaline earth metal mandelates, M(C₆H₅CH(OH)CO₂)₂, (M = Mg(II), Ca(II), Sr(II), and Ba(II)), were investigated employing simultaneous thermogravimetry and differential thermal analysis or differential scanning calorimetry, (TG–DTA or TG–DSC), infrared spectroscopy (FTIR), complexometry, and TG–DSC coupled to FTIR. All the compounds were obtained in the anhydrous state and the thermal decomposition occurs in three steps. The final residue up to 585 °C (Mg), 720 °C (Ca), and 945 °C (Sr) is the respective oxide MgO, CaO, and SrO. For the barium compound the final residue up to 580 °C is BaCO₃, which is stable until 950 °C and above this temperature the TG curve shows the beginning of the thermal decomposition of the barium carbonate. The results also provide information concerning the thermal behavior and identification of gaseous products evolved during the thermal decomposition of these compounds.     

Thermal dehydration and decomposition of M[M(C2O4)2]·xH2O (x=3 forM=Sr(II) andx=6 forM=Hg(II))

Strontium(II) bis (oxalato) strontium(II) trihydrate, Sr[Sr(C₂O₄)₂]·3H₂O and mercury(II) bis (oxalato) mercurate(II) hexahydrate, Hg[Hg(C₂O₄)₂]·6H₂O have been synthesized and characterized by elemental analysis, reflectance and IR spectral studies. Thermal decomposition studies (TG, DTG and DTA) in air showed SrCO₃ was formed at ca. 500°C through the formation of transient intermediate of a mixture of SrCO₃ and SrC₂O₄ around 455°C. Sharp phase transition from γ-SrCO₃ to β-SrCO₃ indicated by a distinct endothermic peak at 900°C in DTA. Mercury(II) bis (oxalato) mercurate(II) hexahydrate showed an inclined slope followed by surprisingly steep slope in TG at 178°C and finally 98.66% of weight loss at 300°C. The activation energies (E ^*) of the dehydration and decomposition steps have been calculated by Freeman and Carroll and Flynn and Wall's method and compared with the values found by DSC in nitrogen. A tentative reaction mechanism for the thermal decomposition of Sr[Sr(C₂O₄)₂]·3H₂O has been proposed.     

Influence of Cu(II) in the SrSnO<Subscript>3</Subscript> crystallization

Perovskite type oxides have been intensively studied due to their interesting optical, electrical, and catalytic properties. Among perovskites the alkaline earth stannates stand out, being strontium stannates (SrSnO₃) the most important material in ceramic technology among them due to their wide application as dielectric component. SrSnO₃ has also been applied as stable capacitor and humidity sensor. In the present work, SrSnO₃:Cu was synthesized by polymeric precursor method and heat treated at 700, 800, and 900 °C for 4 h. After that, the material was characterized by thermal analysis (TG/DTA), X-ray diffraction (XRD), infrared spectroscopy, and UV–vis spectroscopy. Results indicated three thermal decomposition steps and confirmed the presence of strontium carbonate and Cu²⁺ reduction to Cu⁺ at higher dopant amounts. XRD patterns indicated that the perovskite crystallization started at 700 °C with strontiatite (SrCO₃) and cassiterite (SnO₂) as intermediate phases, disappearing at higher temperatures. The amount of secondary phase was reduced with the increase in the Cu concentration.     

Thermal investigation of strontium acetate hemihydrate in nitrogen gas

The thermal decomposition of strontium acetate hemihydrate has been studied by TG-DTA/DSC and TG coupled with Fourier transform infrared spectroscopy (FTIR) under non-isothermal conditions in nitrogen gas from ambient temperature to 600°C. The TG-DTA/DSC experiments indicate the decomposition goes mainly through two steps: the dehydration and the subsequent decomposition of anhydrous strontium acetate into strontium carbonate. TG-FTIR analysis of the evolved products from the non-oxidative thermal degradation indicates mainly the release of water, acetone and carbon dioxide. The model-free isoconversional methods are employed to calculate the E _a of both steps at different conversion α from 0.1 to 0.9 with increment of 0.05. The relative constant apparent E _a values during dehydration (0.5<α<0.9) of strontium acetate hemihydrate and decomposition of anhydrous strontium acetate (0.5<α<0.9) suggest that the simplex reactions involved in the corresponding thermal events. The most probable kinetic models during dehydration and decomposition have been estimated by means of the master plots method.     

Diaqua oxalato strontium(II) complex as a precursor for facile fabrication of Ag-NPs@SrCO3, characterization,optical properties,morphological studies and adsorption efficiency

Diaqua oxalato strontium(II) complex [Sr(C₂O₄)(H₂O)₂] was prepared via a precipitation reaction. Thermal treatment of the as-synthesized precursor at 550?°C resulted in formation of strontium carbonate (SrCO₃) nanocrystals. A new composite of silver nanoparticles decorated with strontium carbonate (Ag-NPs@SrCO₃) was fabricated by heating a mixture of silver oxalate and strontium carbonate in air at 150?°C for 2?h. The spectral, morphological and thermal properties of the materials have been studied using different physicochemical techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX), high-resolution transmission electron microscopy (HR-TEM), Fourier infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), diffrential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). From the Debye–Scherrer equation the calculated particle size of Sr(C₂O₄)(H₂O)₂], SrCO₃ and Ag-NPs@SrCO₃ are 62.1, 58.7, and 58.5?nm, respectively. The SEM and TEM images indicate tetragonal structure of [Sr(C₂O₄)(H₂O)₂] while SrCO₃ and Ag-NPs@SrCO₃ appeared as cubic structures. The calculated energy band gap of SrCO₃ and Ag-NPs@SrCO₃ using the Tauc equation are estimated at 5.9 and 4.7?eV, respectively. The adsorption capacity of the materials is tested for the adsorption of Congo red anionic dye and exhibited promising results. The adsorption capacity followed the order Ag-NPs@SrCO₃>SrCO₃>?[Sr(C₂O₄)(H₂O)₂] with efficiencies of 73.90, 67.55, and 60.50%, respectively.     

Pyrolysis of Nickel Zirconyl Oxalate

Nickel zirconyl oxalate hexahydrate (NiZrOx) is δ prepared and characterised by I.R. spectral and chemical analysis. Its thermal decomposition has been investigated by employing TG, DTG, DTA and chemical analysis. End product was identified by X-ray diffraction studies. The decomposition proceeds through four steps i) dehydration of NiZrOx in two steps, ii) partial decomposition of oxalate to give an oxalate carbonate intermediate, iii) decomposition of oxalate to give a non-stoichiometric carbonate and iv) decomposition of this non-stoichiometric carbonate to give the end product a mixture of NiO+ZrO₂. On the basis of the results obtained, a tentative scheme for the decomposition of NiZrOx is proposed.     

Synthesis of nanosized ferrites from the thermolysis of strontium and barium hexa(formato)ferrates(III)

Summary The thermal analysis of strontium and barium hexa(formato)ferrates(III), M₃[Fe(HCOO)₆]₂^. xH₂O, has been carried out from ambient temperature to 800 °C. Various physico-chemical techniques, i.e., TG, DTG, DSC, XRD, IR, M?ssbauer spectroscopy, etc., have been employed to characterize the intermediates/end products. After dehydration, the anhydrous complexes undergo decomposition to yielda-Fe₂O₃and metal oxalate in the temperature range of 275-290 °C. A subsequent oxidative decomposition of metal oxalate leads to the formation of respective alkaline earth metal carbonate in successive stages. Finally, nanosized ferrites of Sr₂Fe₂O₅and BaFe₂O₄stoichiometry have been obtained as a result of a solid-state reaction betweena-Fe₂O₃and a fraction of MCO₃. The temperature of ferrite formation is much lower than possible in the conventional ceramic method.     

Thermal analysis of monument patina containing hydrated calcium oxalates

This work describes the thermal transformation of patina samples formed on the surface of dolomitic rocks used to build the Romanesque Torme's Church (Burgos, Spain). Analyses were performed using a combination of high-temperature XRD, simultaneous TG/DTA and gas mass spectrometry. The XRD analysis revealed the presence of hydrated calcium oxalates. The following three steps were proposed for the thermal transformation of the raw material: dehydration of weddellite/whewellite to form calcium oxalate, transformation of calcium oxalate to calcium carbonate, and formation of calcium oxide produced via decomposition of the calcite. DTA/TG and mass spectrometry analyses confirmed this mechanism. In addition, a high proportion of organic compounds was detected and was possibly formed via degradation of products applied for the building's conservation by the action of microorganisms attack. Mass spectrometry analysis revealed CO (and CO₂) gas evolved during the transformation of CaC₂O₄ to CaCO₃. The CO₂ gas also appears at 765 °C due to the decomposition of calcium carbonate, and it appears over a large range of temperatures due to the decomposition of organic compounds. The TG analyses performed in a CO₂ atmosphere were used to determine the percentages of Ca and Mg contained in dolomite, and the calcium carbonate formed by oxalate decomposition. DRIFTS and mass spectrometry results revealed the presence of several aliphatic and/or aromatic compounds containing CO groups.     

Thermal decomposition of the oxo-diperoxo-molibdenum (VI)-potassium oxalate

The oxo-diperoxo-molibdenum(VI)-potassium oxalate, K₂[MoO(O₂)₂(C₂O₄)] was synthesized using an adapted version of the method suggested by Dengel. The thermal behavior of the synthesized complex was investigated by simultaneous thermal analysis TG/DTG/DTA, in air or nitrogen atmosphere, to identify and characterize the mass-loss decomposition processes. In addition, for the characterization of the observed decomposition steps, the FT-IR spectra for the initial complex, evolved gaseous compounds and isolated complex at 230 and 430/383 °C in air/nitrogen atmosphere, were recorded. On the 35–500 °C temperature range, the K₂[MoO(O₂)₂(C₂O₄)] complex presented three main decomposition steps, accompanied by mass-loss. The first degradation step is due to the elimination of one oxygen molecule, by the breaking of the peroxo groups, with the formation of an intermediary, like [MoO₃L]. The other two degradation steps can be attributed to the decomposition of the organic ligand, with the final formation of a stable metallic oxide.     

Thermogravimetric analysis of wheatleyite Na<Subscript>2</Subscript>Cu<Superscript>2+</Superscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>2</Subscript>·2H<Subscript>2</Subscript>O

Evidence for the existence of primitive life forms such as lichens and fungi can be based upon the formation of oxalates. These oxalates form as a film like deposit on rocks and other host matrices. The anhydrous oxalate mineral moolooite CuC₂O₄ as the natural copper(II) oxalate mineral is a classic example. Another example of a natural oxalate is the mineral wheatleyite Na₂Cu²⁺(C₂O₄)₂·2H₂O. High resolution thermogravimetry coupled to evolved gas mass spectrometry shows decomposition of wheatleyite at 255°C. Two higher temperature mass losses are observed at 324 and 349°C. Higher temperature mass losses are observed at 819, 833 and 857°C. These mass losses as confirmed by mass spectrometry are attributed to the decomposition of tennerite CuO. In comparison the thermal decomposition of moolooite takes place at 260°C. Evolved gas mass spectrometry for moolooite shows the gas lost at this temperature is carbon dioxide. No water evolution was observed, thus indicating the moolooite is the anhydrous copper(II) oxalate as compared to the synthetic compound which is the dihydrate.     

Infrared and thermal studies of strontium zirconyl oxalate hexahydrate

Strontium zirconyl oxalate hexahydrate (SZO) is prepared and characterized by chemical analysis and IR spectral studies. Its thermal decomposition studies have been made using thermogravimetry (TG) and differential thermal analysis (DTA). The decomposition has been found to proceed through three major steps (i) a three stage dehydration, (ii) decomposition of the oxalate and (iii) decomposition of carbonate to strontium zirconate. Carbon dioxide is found to be trapped in the solid during the decomposition of the oxalate. The identification of residues at various stages has been done by IR spectra and chemical analysis.     

Thermal decomposition of titanyl oxalates IV. Strontium and calcium titanyl oxalates

Thermal decomposition of strontium titanyl oxalate tetrahydrate and calcium titanyl oxalate hexahydrate have been studied employing TG, DTA, gas and chemical analysis. The decompositions proceed through three major steps: dehydration, decomposition of the oxalate to a carbonate and the decomposition of the carbonate to yield the final products, the metatitanates. The intermediates of the oxalate decomposition are found to be Sr₂Ti₂O_4+x(CO₃)₂-x(CO₂)_x and Ca₂Ti₂O₄(CO₃)₂, respectively. The entrapment of carbon dioxide in the former and the presence of non-equivalent carbonate groups in the latter are substantiated by their i.r. spectra. The penultimate solid residues are poorly crystalline Sr₂Ti₂O₅CO₃ and amorphous Ca₂Ti₂O₅CO₃. Decompositions of these carbonates are accompanied by growth in particle size of the products, SrTiO₃ and CaTiO₃, respectively.     

An investigation on the solid state pyrolytic decomposition of bimetallic oxalate precursors of Ca,Sr and Ba with cobalt: A mechanistic approach

The mixed metal oxalate precursors, calcium(II)bis(oxalato)cobaltate(II)hydrate (COC), strontium(II)bis(oxalato)cobaltate(II)pentahydrate (SOC) and barium(II)bis(oxalato)cobaltate(II)octahydrate (BOC) have been synthesized and their thermal stability was investigated. The complexes were characterized by elemental analysis, IR spectral and X-ray powder diffraction studies. Thermal decomposition studies (TG, DTG and DTA) in air showed that the compound COC decomposed mainly to CaC₂O₄ and Co₃O₄ at 340 °C, and a mixture of CaCO₃ and Co₃O₄ identified at 510 °C. A mixture of CaCO₃ and Ca₃Co₂O₆ along with the oxides and carbides of both the cobalt and calcium were attributed at 1000 °C as end products. DSC study in nitrogen ascertained the formation of a mixture of CaO and CoO along with a trace of carbon at 550 °C. The mixture species, SrC₂O₄, CoC₂O₄ and Co₃O₄ were generated at 255 °C in case of SOC in air, which ultimately changed to CoSrO₃, SrCO₃ and oxides of strontium and cobalt at 1000 °C. The several mixture species also generated as intermediate at 332 and 532 °C. The DSC study in nitrogen indicated the formation of CoSrO_x (0.5 < x < 1) as end product. In case of BOC in air, a mixture of BaCoO₂, BaO, CoO and carbides are identified as end product at 1000 °C through the generation of several intermediate species at 350 and 530 °C. A mixture of BaO and CoO is identified as end product in DSC study in nitrogen. The kinetic parameters have been evaluated for all the dehydration and decomposition steps of all the three compounds using four non-mechanistic equations. Using seven mechanistic equations, the kind of dominance of kinetic control mechanism of the dehydration and decomposition steps are also inferred. The kinetic parameters, ΔH and ΔS of all the steps are explored from the DSC studies. Some of the decomposition products are identified by IR and X-ray powder diffraction studies.     

Thermal treatment on tin(II/IV) oxalate,EDTA and sodium inositol-hexaphospate

The thermal behavior of tin containing oxalate, EDTA, and inositol-hexaphosphate were investigated. The end products of synthesis were identified by Mössbauer-, XRD analyses, and FTIR studies. The thermal decompose of the samples was studied by DTA-TG analysis. The simultaneously obtained DTA and TG data makes it possible to follow the thermal decomposition of the investigated samples. The tin oxalate decomposed in the temperature range of 520–625 K through tin carbonate formation and finally yielded CO₂ and SnO. The tin EDTA complex first lost its hydrate bound water till 520 K. The followed thermal events related to the pyrolysis of anhydrous salt. The intense exothermic process that exists in the temperature range of 820–915 K is due to the formation of SnO₂. The tin sodium inositol-hexaposphate lost its hydrate bound water (~10%), up to 460 K. The following sharp exothermic process, in the temperature range of 680–750 K is due to the decomposition and parallel oxidation of organic part of the molecule. At the end of this process, a mixture of phosphorous pentaoxide, sodium carbonate, and tin dioxide is obtained.     

Synthesis of lithium ferrite by precursor and combustion methods: A comparative study

The thermal decomposition of lithium hexa(carboxylato)ferrate(III) precursors, (Li₃[Fe(L)₆]·xH₂O, L = formate, acetate, propionate, butyrate), has been carried out in flowing air atmosphere from ambient temperature upto 500 °C. Various physico-chemical techniques, i.e., TG, DTG, DTA, XRD, SEM, IR, Mössbauer spectroscopy, etc., have been employed to characterize the intermediates and end products. After dehydration, the anhydrous complexes undergo decomposition to yield various intermediates, i.e., lithium oxalate/acetate/propionate/butyrate, ferrous oxalate/acetate and α-Fe₂O₃ in the temperature range of 185–240 °C. A subsequent decomposition of these intermediates leads to the formation of nanosized lithium ferrite (LiFeO₂). Ferrites have been obtained at much lower temperature (255–310 °C) as compared to conventional ceramic method. The same nano-ferrite has also been prepared by the combustion method at a comparatively lower temperature (400 °C) and in less time than that of conventional ceramic method.     

Effect of alkaline earth metal dopants on the thermal decomposition of the CaCO3-SiO2 system: Part II. Formation of dicalcium silicate

Mixtures of calcium oxide (taken as carbonate) and silica in 2:1 molar ratio containing varying amounts of MgO, SrCO₃ and BaCO₃ as dopants were subjected to thermal treatment up to 1450°C. The exothermic peaks at 1200°C and above (beyond the decomposition temperature of calcium carbonate) have been examined to elucidate the phases formed. The exothermic peak at 1210°C without dopant was found to conform to the β-dicalcium silicate phase with a significant amount of free lime and cristobalite along with small amounts of the γ-C₂S phase. MgO at 0.1–1% leads to the formation of β- and γ-dicalcium silicate phases at 1420–1430°C, while 5% MgO results in the formation of the β-C₂ S phase at 1360°C. SrCO₃, in the concentration range studied, leads to the stabilization of β-C₂S, but does not lower its temperature of formation. BaCO₃ at 0.1–1% assists in the formation of the β-dicalcium silicate phase, but 5% BaO forms a mixture of β- and α'_H-C₂S phases at a lower temperature.     

Effect of Li2O-doping on the thermal stability of cobaltic oxide

The influence of lithium oxide-doping on the thermal stability of Co₃O₄ was studied using DTA, TG, DTG and X-ray diffraction techniques. Pure and doped cobaltic oxide specimens were prepared by thermal decomposition of pure basic cobalt carbonate and the basic carbonate mixed with different proportions of LiOH, in air, at different temperatures between 500 and 1100°C.Pure Co₃O₄ was found to start partial decomposition when heated in air at 830°C yielding the CoO phase. The complete decomposition was effected by heating at 1000°C.Doping of Co₃O₄ with different proportions of Li₂O was found to much increase its thermal stability. The temperatures at which the doped oxide samples started to undergo decomposition were increased to 865, 910 and 1050°C for 0.375, 0.75 and 3% Li₂O-doped solids, respectively. The DTA revealed that the 1.5% Li₂O-doped cobaltic oxide did not undergo any thermal decomposition till 1080°C. The X-ray investigation showed that the prolonged heating of 1.5 and 3% Li₂O-doped solids at 1100°C for 36 h effected only a partial decomposition of Co₃O₄ into CoO. Heating of these solids at temperatures varying between 900 and 1100°C led also to the formation of a new lithium oxide cobaltic oxide phase, the composition of which has not yet been identified.The role of Li₂O in increasing the thermal stability of Co₃O₄ was attributed to the substitution of some of its cobalt ions by Li⁺ ions, according to Verwey and De Boer's mechanism, leading to the transformation of some of the Co²⁺ into Co³⁺ ions thus increasing the oxidation state of the cobaltic oxide lattice.     

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.     

Thermal decomposition of lead titanyl oxalate tetrahydrate

The thermal behaviour of PbTiO(C₂O₄)₂·4H₂O (PTO) has been investigated, employing TG, quantitative DTA, infrared spectroscopy and (high temperature) X-ray powder diffraction.The decomposition involves four main steps. The first is the dehydration of the tetrahydrate (30–180°C), followed by a small endothermic (270–310°C) and a large exothermic decomposition of the oxalate. The main (exothermic) oxalate decomposition (310–390°C) results in a stable oxide-carbonate PbTiO₂₅.(CO₃)_0.5. In the last step a phase transition, release of CO₂ and ordering of the crystalline cubic PbTiO₃ lattice can be detected (460–530_C).It can be argued that for thermodynamic reasons the presence of lead-oxo- carbonates in the oxide-carbonate intermediate is not possible.No differences could be found in thermal behaviour of two crystallographically different synthetic forms of PTO, of which one has an orthorhombic lattice.     

Thermal stability of synthetic aurichalcite implications for making mixed metal oxides for use as catalysts

TG combined with MS has been used to study the thermal decomposition of a synthetic aurichalcite with varying copper-zinc ratios from 0.1:0.9 to 0.5:0.5. In general, five decomposition steps are observed at 235, 280, 394, 428 and 805°C. The principal mass loss step increases in temperature from 255°C (0.1/0.9) to 300°C (0.5/0.5). MS using ion current curves show that the OH units and carbonate units decompose simultaneously and the two decomposition steps after the main decomposition are attributed to the decomposition of ZnCO₃ and CuCO₃. A higher temperature decomposition at around 805°C, based upon the ion current curves is assigned to the decomposition of CuO to Cu. The thermal decomposition of aurichalcite offers a method of preparing metal oxides mixed at the molecular level making the thermally activated aurichalcites as suitable for use as catalysts.