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1.
Thermal decomposition of Ln 2(C 2O 4) 3 · 9H 2O concentrate (Ln = La, Ce, Pr, Nd) in the presence of CaC 2O 4 · H 2O was studied by X-ray diffraction, thermogravimetry, and chemical analysis. Annealing at temperatures above 374°C in the absence of calcium oxalate gives rise to the solid solution of CeO 2-based rare-earth oxides. Calcite CaCO 3 is formed in the presence of calcium oxalate at annealing temperatures above 442°C, which impedes the formation of lanthanide oxide solid solution and favors crystallization of oxides as individual La 2O 3, CeO 2, Pr 6O 11, and Nd 2O 3 phases. An increase in temperature above 736°C is accompanied by decomposition of calcium carbonate to give rise to an individual CaO phase and an individual phase of CeO 2-based lanthanide oxide solid solution. 相似文献
2.
The multistep decomposition of CaC 2O 4·H 2O in the gaseous phase was explored at the MP2/cc-pVDZ level of theory. As a result, the structure and energy of the entities occurring at stationary points along the reaction pathway were determined. Statistical thermodynamics routines were used to obtain thermal energies/enthalpies and entropies. The results demonstrated the consecutive release of H 2O, CO and CO 2 from the substrate with increasing temperature. Moreover, the application of thermodynamic and kinetic characteristics to relevant phenomenological relationships enabled the decomposition pattern in equilibrium and non-equilibrium conditions to be predicted. The forecast patterns qualitatively match the experimental thermal gravimetry data. This study supplies much important information on the molecular changes taking place in a stoichiometric unit of calcium oxalate monohydrate during continuous heating 相似文献
3.
0IntroductionTherearemanykindsofhydratedcalciumbo-rates,bothnaturalandsynthetic.Someofthemarematerialsusedinglass,potteryandporcelainenamelindustry,especiallyinunalkaliglassindustry.4CaO·5B2O3·7H2O,calledpriceite,isacalciumboratemin-eral,notfoundinCaO-B… 相似文献
4.
2CaO·3B 2O 3·H 2O which has non-linear optical (NLO) property was synthesized under hydrothermal condition and identified by XRD, FTIR and
TG as well as by chemical analysis. The molar enthalpy of solution of 2CaO·3B 2O 3·H 2O in HCl·54.572H 2O was determined. From a combination of this result with measured enthalpies of solution of H 3BO 3 in HCl·54.501H 2O and of CaO in (HCl+H 3BO 3) solution, together with the standard molar enthalpies of formation of CaO(s), H 3BO 3(s), and H 2O(l), the standard molar enthalpy of formation of −(5733.7±5.2) kJ mol −1 of 2CaO·3B 2O 3·H 2O was obtained. Thermodynamic properties of this compound were also calculated by a group contribution method. 相似文献
5.
Different hydrates of calcium oxalate have been electrodeposited by electrogeneration of acid at the anode from an EDTA-stabilized calcium nitrate bath containing dissolved oxalate ions. The deposition is controlled by varying the bath pH, temperature, and current density. Formation of metastable CaC 2O 4·2H 2O is favored at high current densities at ambient temperature, whereas the thermodynamically stable CaC 2O 4·H 2O is formed at elevated bath temperatures. Both the polymorphs show oriented growth with respect to the substrate normal under different deposition conditions. 相似文献
6.
On the Coordination of Al in the Calcium Aluminate Hydrates 2 CaO · Al 2O 3 · 8 H 2O and CaO · Al 2O 3 · 10 H 2O By investigations with high-resolution 27Al-NMR in solids it is shown that in the compound 2 CaO · Al 2O 3 · 8 H 2O the Al merely exist in octahedral coordination. According to this and considering its structural relationship with 4 CaO · Al 2O 3 · 19 H 2O the dicalcium aluminate hydrate is proposed to be formulated as [Ca 2Al(OH) 6][Al(OH) 3 (H 2O) 3]OH. Likewise for the compound CaO · Al 2O 3 · 10 H 2O the octahedral coordination of the Al is proved by 27Al-NMR. This result corresponds with literature according to which a constitution as cyclohexaaluminate Ca 3[Al 6(OH) 24] · 18 H 2O is proposed. 相似文献
7.
The mineral and microelement compositions of urinary stones from patients in various districts of the Novosibirsk region are analyzed. The mineral composition is determined using X-ray powder diffraction and vibrational spectroscopy. The microelement composition is identified using synchrotron radiation X-ray fluorescence analysis. Calcium oxalates (whewellite CaC 2O 4 · H 2O and weddellite CaC 2O 4 · 2H 2O) are the most frequent components of the urinary stones. Oxalate uroliths contain a variety of microelements in significant amounts. Phosphate uroliths, represented by hydroxylapatite Ca 5(PO 4) 3(OH) and struvite MgNH 4PO 4 · 6H 2O, account for about one-fifth of the collection. Apatite urinary stones contain maximal strontium amounts. The struvite uroliths have higher rubidium levels. Uric acid uroliths (C 5H 4N 4O 3) account for about 11% of the collection. Their strontium concentrations are minimal. The element composition of the urinary stones is a function of their mineral constituents, the environmental surroundings, and the metabolism specifics of the patient. 相似文献
8.
Thermal decomposition and structural characterization of three human kidney stones (KS1–KS3) extracted from patients of Eastern
Bohemia have been carried out using X-ray powder diffraction systems (XRD), scanning electron microscope with energy dispersive
X-ray micro analyser (SEM-EDX) and differential thermal analysis (DTA). The samples KS1 and KS2 solely consisted of calcium
oxalate monohydrate (a.k.a. whewellite, CaC 2O 4·H 2O). The third sample, KS3, was formed from calcium oxalate dihydrate (weddellite, CaC 2O 4·2H 2O), calcium oxalate monohydrate, and hydroxyapatite (HA, Ca 10(PO 4) 6(OH) 2). Thermal measurements were carried out in the range between room temperature and 1,230 °C. XRD analysis was utilized to
investigate the change of phases at 800 and 1,230 °C. 相似文献
9.
The standard molar enthalpies of formation of H 4SiW 12O 40·6H 2O (I), H 4SiW 12O 40·6DMF·H 2O (II), H 4SiW 12O 40·8DMSO·H 2O (III) have been determined. Thermodynamic cycles were designed, and the heat of reactions in the thermodynamic cycles were measured calorimetrically. The infrared spectra were compared with those of the heteropoly anion α-H 4SiW 12O 40 [1] and of the ligands DMF and DMSO. The evolved gas from the adducts was monitored by a quadrupole mass spectrometer at a heating rate of 16 deg·min ?1. 相似文献
10.
IntroductionTherearemanykindsofmagnesiumborates ,bothnaturalandsynthetic .Aboratedoublesalt (2MgO·2B2 O3 ·MgCl2 · 14H2 O)namedchloropinnoitewasob tainedfromthenaturalconcentratedsaltlakebrine .1Inordertofindtheformingrelationbetweenthedoublesaltandmagnesium bora… 相似文献
11.
A pure mixed alkali–alkaline earth metal borate of Li 2Sr 4B 12O 23 with microporous structure has been synthesized by high-temperature solid state reaction, and characterized by XRD, FT-IR, TG techniques, and chemical analysis. The molar enthalpies of solution of Li 2Sr 4B 12O 23 in 1 mol L ?1 HCl(aq), and of SrCl 2·H 2O(s) in [1 mol L ?1 HCl + H 3BO 3 + LiCl·H 2O](aq) have been determined by microcalorimeter at 298.15 K, respectively. From these data and with the incorporation of the previously determined enthalpies of solution of H 3BO 3(s) in 1 mol L ?1 HCl(aq), and of LiCl·H 2O(s) in [1 mol L ?1HCl + H 3BO 3](aq), together with the use of the standard molar enthalpies of formation for SrCl 2·6H 2O(s), LiCl·H 2O(s), H 3BO 3(s), HCl(aq), and H 2O(l), the standard molar enthalpy of formation of ?(11,534.0 ± 10.0) kJ mol ?1 for Li 2Sr 4B 12O 23 was obtained on the basis of the appropriate thermochemical cycle. 相似文献
12.
The goal of this study is twofold: to take a fresh look at the decomposition of calcium oxalate and to warn users of thermogravimetric analysis against the hasty interpretation of results obtained. Since the pioneer work of Duval 70 years ago, the scientific community has agreed unanimously as to the decomposition of anhydrous calcium oxalate (CaC2O4) into calcium carbonate (CaCO3) and CO gas, and that of the calcium carbonate into calcium oxide (CaO), and CO2 gas. We will demonstrate how these reactions, simple in appearance, in fact result from a succession of reactive phenomena involving numerous constituents both solid (CaCO3, free carbon) and gaseous (CO2 and CO) produced by intermediary reactions. The mass losses evaluated in the two distinct domains correspond closely to the molar masses of CO and CO2, respectively. The simple mathematical calculation of that mass loss has simply concealed the existence of other reactions, and, most particularly the Boudouard reaction and that of solid phases between CaCO3 and C. It just goes to show that appearances can be deceiving. 相似文献
13.
In this study, the synthesis of bis-(2-ethylhexyl) terephthalate, via the transesterification reaction of dimethyl terephthalate (DMT) by 2-ethylhexanol in the presence of different heterogeneous catalysts, such as Pb(OAc)2·3H2O, Cd(OAc)2·2H2O, Zn(OAc)2·2H2O, Hg(OAc)2·Ca(OAc)2·H2O, Cu(OAc)2·H2O, NaOAc, CaCO3, CaO, ZnSO4·7H2O, and sulfated zirconia, has been investigated. The reactivity of the catalysts in the reaction progress has been studied and compared. It was found that, hydrated cadmium acetate and sulfated zirconia were reactive catalysts to this reaction. The extent of transesterification of methyl ester groups reached up to 93% and 85.6% using these catalysts, respectively. 相似文献
14.
Differential scanning calorimetry (DSC) was used to determine the molar enthalpies of dehydration and decomposition of CoC 2O 4·2H 2O, Co(HCOO) 2·2H 2O and [Co(NH 3) 6] 2(C 2O 4) 3·4H 2O. The first stage of dissociation of each compound is a single-step dehydration both in air and argon atmospheres. The next
stages are decomposition processes influenced by experimental parameters. The enthalpies of dehydration and decomposition
vary from compound to compound in each atmosphere. The obtained data have been related to the macromechanisms proposed for
the thermal decomposition and the parallel-consecutive decomposition-oxidation processes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
The reactions of Li 2C 2O 4, Na 2C 2O 4, K 2C 2·H 2O, CaC 2·H 2O, ZnC 2O 4, La 2(C 2O 4) 3 and K 2TiO(C 2O 4) 2· 2H 2O with K 2S 2O 7 were investigated using thermal methods of analysis. Reaction products were analysed by various techniques. It was found that anhydrous oxalates reacted with K 2S 2O 7, evolving a mixture of CO 2 and CO with the formation of K 2SO 4 and the corresponding metal sulfates, which, in the reactions of ZnC 2O 4 and K 2TiO(C 2O 4) 2 2H 2O, probably existed as K 2[Zn(SO 4) 2] and K 4[Ti(SO 4) 4], respectively. Water was found to be an additional product in the hydrated metal oxalate reactions. The stoichiometries of these reactions have been established from the thermogravimetric and acidimetric results. 相似文献
16.
Introduction 2MgO·B2 O3(Mg2 B2 O5)and 2MgO·B2 O3·H2 Omightbepreparedaswhiskermaterials .12MgO·B2 O3·H2 OnamedszaibelyiteisamagnesiumboratemineralwithastructuralformulaofMg2 [B2 O4 (OH) 2 ].2 Itisdifficulttosynthesizethiscompoundinthelaboratory .Recently ,weobtainedasimilarcompound 2MgO·B2 O3·1 5H2 Owhenwetriedtopreparewhiskerof 2MgO·B2 O3·H2 Obythephasetransformationof 2MgO·2B2 O3·MgCl2 ·14H2 OinH3BO3solutionunderhydrothermalcondition .Itishope fultopreparewh… 相似文献
17.
New Compounds in the System CaO/SiO 2/CaCl 2/H 2O The hydrothermal formation of novel calcium silicate hydrates of compositions 5 CaO · 2 SiO 2 · CaCl 2 · 4 H 2O, 5 CaO · 2 SiO 2 · CaCl 2 · 2 H 2O and 4 CaO · 2 SiO 2 · CaCl 2 · H 2O from Ca 3SiO 5 and mixtures of CaO and SiO 2, respectively, in presence of calciumchloride at 200°–350 °C is described. From molybdate-reaction, 29Si MAS NMR, DTA and TG measurements it is concluded that these compounds are based on disilicate anions and are to be interpreted as calcium hydroxide disilicate chlorides. 相似文献
18.
The direct measurements of differential enthalpies of solution Δ sol H 2, of LiCl·H 2O, NaCl, KCl, MgCl 2·6H 2O, CaCl 2·6H 2O and BaCl 2·2H 2O, as the function of molality, m, in the region of concentrated solutions were performed. On this basis the enthalpies of crystallization, Δ cryst H m, were calculated and compared to the appropriate literature data. 相似文献
19.
On the Chemistry of Bauxite Extraction. II. Studies in the System Na 2O? CaO? Al 2O 3? TiO 2? H 2O between 100 and 275°C The formation of crystalline compounds in the system Na 2O? CaO? Al 2O 3? TiO 2? H 2O was studied between 100 and 275°C. With caustic alkali concentrations up to 300 g Na 2O/l the calcium aluminate 3 CaO · Al 2O 3 · 6 H 2O is formed. With rising temperatures two different calcium titanates, among them perovskite, CaTiO 3, are identified. Above 200°C perovskite is formed at all concentrations investigated. 相似文献
20.
Abstract On obtaining defluorinated feeding phosphates from Kovdor apatite the system of Ca 10(PO 4) 6(OH) 1,4F 0,6-CaCO 3-(Ca,Mg)CO 3-Mg 2SiO 4-Ca(H 2PO 4) 2·H 2O-Mg(H 2PO 4) 2·xH 2O with mole correlation (CaO+MgO)/P 2O 5V3 is subjected to thermal treatment. On heating up to 500°C calcium and magnesium hydrophosphates turn into polyphosphates M(PO 3) 2 which in accordance with the increase of the temperature react with other components of the system. To establish the mechanism and conditions for reactions, thermal interactions in the mixtures of Ca(PO 3)2 and Ca 2P 2O 7 with apatite, phorsterite, dolomite and calcite when (CaO+MgO)/P 2O 5=3 have been investigated. Methods of chemical, thermal, chromatographic, X-ray and IR-spectroscopy analysis were used. 相似文献
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