首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 78 毫秒
1.
Thermal decomposition of U(C2O4)2·6H2O was studied using TG method in nitrogen, air, and oxygen atmospheres. The decomposition proceeded in five stages. The first three stages were dehydration reactions and corresponded to removal of four, one, and one mole water, respectively. Anhydrous salt decomposed to oxide products in two stages. The decomposition products in nitrogen atmosphere were different from those in air and oxygen atmospheres. In nitrogen atmosphere UO1.5(CO3)0.5 was the first product and U2O5 was the second product, while these in air and oxygen atmospheres were UO(CO3) and UO3, respectively. The second decomposition products were not stable and converted to stable oxides (nitrogen: UO2, air–oxygen: U3O8). The kinetics of each reaction was investigated with using Kissinger–Akahira–Sunose and Flynn–Wall–Ozawa methods. These methods were combined with modeling equations for thermodynamic functions, the effective models were investigated and thermodynamic values were calculated.  相似文献   

2.
On the Mechanism of the Formations of Chromium(IV)oxide from Chromyl Chloride The decomposition of chromyl chloride in the temperature range from 380 to 400°C leads with increasing oxygen pressure to chromium oxides containing up to nearly 90% of CrO2. The interaction with the chlorine prevents a quantitative formation of CrO2. Up to 315°C during the decomposition of chromyl chloride chromium oxides of higher valencies are formed separating chlorine and taking up oxygen simultaneously. By working in flowing oxygen it could be proved that the decomposition goes at lower temperatures via the nondetectable CrO3. By heating gradually and by removing the chlorine as far as possible stoichiometric CrO2 at oxygen pressures above 60 atm could be obtained.  相似文献   

3.
The chromium oxides, obtained by the thermal decomposition of chromium trioxide, presented a bewildering array of possible mixed valency compounds. The IR absorption measurements in the range 400–5000 cm?1 revealed the presence of the valencies +6, +5, +4, +3 in the samples between CrO3 and Cr2O3.  相似文献   

4.
Ultra-high purity CrO2 was prepared by decomposing CrO3 in O2 with gas pressures up to 40 MPa, which were maintained throughout the decomposition process of CrO3 to prevent the formation of any other phases of chromium oxides. Our method is different from the traditional methods that start from or under ambient pressures. The high oxygen pressure makes the meta-stable CrO2 stable from the initial stage of preparation. As a result, the purity of the as-prepared CrO2 is improved, and this has been further proved by the highest magnetization of the samples. The as-prepared CrO2 particles show very large grains with flat surfaces, octagonal cross-section, and straight edges, owing to the high mobility of Cr ions in CrO2 at temperatures above its melting point. The lattice parameters of CrO2 are a = 4.4176 Å and c = 2.9144 Å. The maximum value of the magnetic entropy change of the high purity CrO2 particles is ∼2.83 J/kg·K for an applied field of 1.5 T. The preparation of pure CrO2 is important for studying its intrinsic properties and for applications in spintronic devices.  相似文献   

5.
The thermal decomposition of the malonates of bivalent transition metals (Mn, Fe, Co, Ni, Cu and Zn) was investigated by mainly TG-DTA, X-ray diffraction analysis and evolved gas analysis in atmospheres of N2, CO2 and O2 and in the air. It was shown that CO2 has an inhibiting effect on the decomposition whereas O2 and air have the accelerating effects on the basis of N2. The decomposition of the salts investigated can be classified into three groups from solid decomposition products: Mn and Zn malonates gave the metal oxides including 1–1.5 moles of elementary carbon, while Cu and Ni malonates gave the metals with 1–1.5 moles of the carbon. Fe and Co malonates in the last group gave once the metal oxides with 1-0.5 moles of the carbon and the oxides produced were subsequently reduced to the metals by the carbon. A possible reaction mechanism for the malonates was discussed and compared with those of the corresponding oxalates and succinates.  相似文献   

6.
The chemical compatibility of perovskite-type Ba0.5Sr0.5Co0.8Fe0.2O3?δ (BSCF) oxides with Cr2O3 has been examined between room temperature and 1,100 °C. Differential thermal analysis and thermogravimetric analysis were used to analyze the thermal behavior of BSCF–Cr2O3 binary mixtures in all composition ranges (0–100 mass% BSCF). The reaction products were identified by X-ray analysis after heating at 700–1,100 °C. As we expected, it was found that perovskite-type BSCF oxide had a poor chemical compatibility with the Cr2O3 oxide. In particular, the decomposition process of the BSCF–Cr2O3 binary mixture is quite complex and it starts at about 700–750 °C. The mixtures of BSCF and Cr2O3 oxides reacted forming mixed complex oxides based on (Ba/Sr)FeO3, (Co/Fe)CrO4, and (Ba/Sr)CrO4 mixtures.  相似文献   

7.
The thermal decomposition kinetics of UO2C2O4·3H2O were studied by TG method in a flowing nitrogen, air, and oxygen atmospheres. It is found that UO2C2O4·3H2O decomposes to uranium oxides in four stages in all atmosphere. The first two stages are the same in the whole atmosphere that correspond to dehydration reactions. The last two stages correspond to decomposition reactions. Final decomposition products are determined with X-Ray powder diffraction method. Decomposition mechanisms are different in nitrogen atmosphere from air and oxygen atmosphere. The activation energies of all reactions were calculated by model-free (KAS and FWO) methods. For investigation of reaction models, 13 kinetic model equations were tested and correct models, giving the highest linear regression, lowest standard deviation, and agreement of activation energy value to those obtained from KAS and FWO equations were found. The optimized value of activation energy and Arrhenius factor were calculated with the best model equation. Using these values, thermodynamic functions (??H *, ??S *, and ??G *) were calculated.  相似文献   

8.
This work is focused on the role of gold and Al3CrO6 support for physicochemical properties, and catalytic activity of supported nickel catalysts in partial oxidation of methane (POM). Catalysts, containing 5% Ni and 5% Ni-2% Au active phases dispersed on mono- (Al2O3, Cr2O3) and bi-oxide Al3CrO6 support, were investigated by TPR, BET and XRD methods, and the activity tests in POM reaction were carried out. Bimetallic Ni-Au catalysts dispersed on Al3CrO6 support remained highly stable and active. The amorphous binary oxide Al3CrO6 can stabilize considerable amount of Cr4+, Cr5+, and Cr6+ species in Ni-Au/Al3CrO6 catalyst network during its calcination in the air. Nickel supported on binary oxide Ni/Al3CrO6 can form Ni(III)CrO3 bi-oxide phase in reductive conditions. During TPR H2 reduction of Ni-Au/Al3CrO6 catalyst chromium(II) oxide Cr(II)O phase is observed. After POM reaction the existence of bimetallic Au-Ni alloy was experimentally confirmed on mono-oxide Al2O3 support surface, but its formation was not identified on bioxide Al3CrO6 support. Published in Russian in Kinetika i Kataliz, 2009, Vol. 50, No. 1, pp. 149–156. The article is published in the original. Based on a report at the VII Russ. Conf. on Mechanisms of Catalytic Reactions (with international participation), St. Petersburg, July 2–8, 2006.  相似文献   

9.
本文制备了均匀棒状过氧化氢合碳酸钠,化学分析确定其组成为Na2CO3·1.5H2O2,用DTA-TG-DTG技术并辅以X-ray分析研究了它在静态空气、流动氧气和流动氮气气氛中的非等温热分解过程及动力学。  相似文献   

10.
The thermal behaviour of CrO3 on heating up to 600°C in dynamic atmospheres of air, N2 and H2 was examined by thermogravimetry (TG), differential thermal analysis (DTA), IR spectroscopy and diffuse reflectance spectroscopy (DRS). The results revealed three major thermal events, depending to different extents on the surrounding atmosphere: (i) melting of CrO3 near 215°C (independent of the atmosphere), (ii) decomposition into Cr2(CrO4)3 at 340–360°C (insignificantly dependent), and (iii) decomposition of the chromate into Cr2O3 at 415–490°C (significantly dependent). The decomposition CrO3 → Cr2(CrO4)3 is largely thermal and involves exothermic deoxygenation and polymerization reactions, whereas the decomposition Cr2(CrO4)3 → Cr2O3 involves endothermic reductive deoxygenation reactions in air (or N2) which are greatly accelerated and rendered exothermic in the presence of H2. TG measurements as a function of heating rate (2–50°C min−1) demonstrated the acceleratory role of H2, which extended to the formation of Cr(II) species. This could sustain a mechanism whereby H2 molecules are considered to chemisorb dissociatively, and then spillover to induce the reduction. DTA measurements as a function of the heating rate (2–50°C min−1) helped in the derivation of non-isothermal kinetic parameters strongly supportive of the mechanism envisaged. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

11.
The thermal decomposition course of copper acetate monohydrate (CuAc) was examined on heating up to 600°C at various rates, by TG, DTA and DSC. Non-isothermal kinetic and thermodynamic parameters were determined in air or nitrogen. SEM was used to describe the decomposition course and the solid products were identified by IR and XRD analysis. The results indicated that CuAc was dehydrated at 190°C and then partially decomposed at 220°C, giving rise to CuO in addition to a minor portion of Cu2O and Cu4O3. The last two oxides seemed to facilitate the decomposition of the rest of the anhydrous acetate. Cu2O and Cu4O3 were oxidized in air at >400°C, in a process that did not occur in nitrogen.It is a pleasure to thank the Queen's University of Belfast, particularly the staff of the Electron Microscope Unit for assistance in obtaining the electron micrographs. Thanks are also due to the Egyptian Government for the granted fellowship.  相似文献   

12.
The reaction of MoO3 with various oxides of manganese (MnO, Mn2O3, Mn3O4 and MnO2) and with MnCO3 has been studied in air and nitrogen atmospheres employing DTA, TG and X-ray diffraction methods, with a view to elucidating the conditions for the formation of MnMoO4. Thermal decomposition of MnCO3 has also been studied in air and nitrogen atmospheres to help understand the mechanism of the reaction between MnCO3 and MoO3. The studies reveal that, whereas MnO, Mn2O3 and MnO2 react smoothly with MoO3 to form MnMoO4, Mn3O4 does not react with MoO3 in the temperature range investigated (48O–6OO°C). An equimolar mixture of MnCO3 and MoO3 reacts in air to yield MnMoO4, while only a mixture of Mn3O4 and MoO3 remains as final product when the same reaction is carried out in nitrogen. Marker studies reveal that manganese ions are the main diffusing species in the reaction between MoO3 and manganese oxides that result in MnMoO4.  相似文献   

13.
The complexes M[La(C2O4)3]⋅xH2O (x=10 for M=Cr(III) and x=7 forM=Co(III)) have been synthesized and their thermal stability was investigated. The complexes were characterized by elemental analysis, IR, reflectance and powder X-ray diffraction (XRD) studies. Thermal investigations using TG, DTG and DTA techniques in air of chromium(III)tris(oxalato)lanthanum(III)decahydrate, Cr[La(C2O4)3]⋅10H2O showed the complex decomposition pattern in air. The compound released all the ten molecules of water within ∼170°C, followed by decomposition to a mixture of oxides and carbides of chromium and lanthanum, i.e. CrO2, Cr2O3, Cr3O4, Cr3C2, La2O3, La2C3, LaCO, LaCrOx (2<x<3) and C at ∼1000°C through the intermediate formation of several compounds of chromium and lanthanum at ∼374, ∼430 and ∼550°C. Thecobalt(III)tris(oxalato)lanthanum(III)heptahydrate, Co[La(C2O4)3]⋅7H2O becomes anhydrous around 225°C, followed by decomposition to Co3O4, La2(CO3)3 and C at ∼340°C and several other mixture species of cobalt and lanthanum at∼485°C. The end products were identified to be LaCoO3, Co3O4, La2O3, La2C3, Co3C, LaCO and C at ∼ 2>1000°C. DSC studies in nitrogen of both the compounds showed several distinct steps of decomposition along with ΔH and ΔSvalues. IR and powder XRD studies have identified some of the intermediate species. The tentative mechanisms for the decomposition in air are proposed. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

14.
The effects of doping cobalt oxides with different amounts of ZrO2 and ThO2 (1.5–9 mol%) on the thermal stability of Co3O4 and the re-oxidation of CoO by O2 to Co3O4 were investigated. The techniques employed were DTA, with a controlled rate of heating and cooling, X-ray diffraction, and IR spectrometry.The results obtained by DTA revealed that the addition of both Th4+ and Zr4+ (up to 6 mol%) exerted no appreciable effect on the thermal stability of Co3O4. Increasing the amount of the dopant ions to 9% resulted in no further change in the thermal stability of Co3O4 in the case of Th4+, and an increase of 16% in case of Zr4+-doping. However, ThO2-doping of cobalt oxide was accompanied by an enhancement in the reactivity of CoO towards re-oxidation by O2 to Co3O4 to an extent proportional to the amount of dopant oxide.The X-ray investigation of ZrO2-doped cobalt oxides calcined in air at 1000°C revealed the presence of highly crystalline and stable zirconia in the cubic form. Such a stable phase could not be obtained at temperatures below 2370°C in the absence of stabilizing agents.X-ray and IR investigations of different solids showed the presence of free thoria and zirconia together with new thorium—cobalt and zirconium—cobalt compounds. However, the slow cooling of Zr-treated cobalt oxides from 1000°C to room temperature led to the decomposition of the newly formed compound. The d-spacings and absorption bands of the newly formed compounds were determined.  相似文献   

15.
The conditions of thermal decomposition of scandium(III) hemimellitate, trimellitate and trimezinate in air and nitrogen atmospheres have been studied. On heating, the benzene-tricarboxylates of Sc(III) decompose in two stages. First, the hydrated complexes lose crystallization water; heating in air finally yields Sc2O3, and heating in a nitrogen atmosphere Sc2O3 and C. The dehydration of the complexes is associated with strong endothermic effects. The decomposition of benzenetricarboxylates in air is accompanied by an exothermic effect and in nitrogen by an endothermic effect. The activation energies of the dehydration and decomposition reactions have been calculated for the Sc(III) benzenetricarboxylates.  相似文献   

16.
The solid-state reactions in MgO-Cr2O3 and ZnO-Cr2O3 systems under atmospheres of oxygen, air and nitrogen were investigated by means of DTA and isothermal kinetic techniques. It was shown that the application of DTA to the solid-state reactions affords useful information with respect to the initial reaction stage: oxidation of Cr2O3 to CrO3 in the presence of MgO or ZnO, followed by the formation of a thin layer of spinel, which consisted of an imperfect lattice, on the surface of the MgO or ZnO grains.  相似文献   

17.
Cement-containing catalysts of ozone decomposition were synthesized on the basis of iron oxides obtained by ozonation of iron-containing aqueous solutions. X-ray diffraction analysis and Mössbauer spectroscopy showed that α-Fe2O3 occurs in the catalyst as highly dispersed nanoparticles. The catalysts obtained are efficient in the reaction of ozone decomposition and are as active as the best representatives of cement-containing catalysts of the GTT type.  相似文献   

18.
This paper reports an investigation regarding the influence of the cation M(II) (M = Zn, Ni, Mg) on the formation of MCr2O4 by thermal decomposition of the corresponding M(II),Cr(III)-carboxylates (precursors) obtained by redox reaction between the corresponding metal nitrates and 1,3-propanediol. The decomposition products at different temperatures have been characterized by FT-IR spectroscopy and thermal analysis. Thus, we have evidenced that by thermal decomposition of the studied precursors in the range 250–300 °C, different amorphous oxidic phases mixtures form depending on the nature of metalic cation: (Cr2O3+x + ZnO) (Cr2O3+x + Ni/NiO) and (Cr2O3+x+MgO). In case of M = Zn, around 400 °C when the transition Cr2O3+x to Cr2O3 takes place, zinc chromite nuclei form by the interaction ZnO with Cr2O3. In case of M = Ni, due to the partial reduction of Ni(II) at Ni(0) during the thermal decomposition of the precursor the formation of nickel chromite by the reaction NiO + Cr2O3 is shifted toward 500 °C, when Ni is oxidized at NiO. The thermal evolution of the mixture (MgO + CrO3) is different due to the formation as intermediary phase of MgCrO4, which decomposes to MgCr2O4 around 560 °C. In order to investigate the chromites formation mechanism, we have studied the mechanical mixtures of single oxides obtained from the corresponding carboxylates. These mixtures (MO + Cr2O3) have been annealed at 400, 500, and 600 °C to study the evolution of the crystalline phases. It results in the prepared mixture behaving different from the mixtures obtained by thermal decomposition of the binary M(II),Cr(III)-carboxylates, recommending our synthesis method for obtaining binary oxides.  相似文献   

19.
Thermal decomposition and creation of reactive solid surfaces   总被引:1,自引:0,他引:1  
Three chromia precursors, namely CrO3, (NH4)2Cr2O7 and chromia gel, were subjected to thorough thermal analysis by means of TG and DTA. The thermal decomposition products obtained by calcination of these precursors at various temperatures (150–500°) for 5 h were investigated by infrared and X-ray techniques. The results obtained allowed a thorough physicochemical characterization of the intermediate steps and products throughout the thermal decomposition.  相似文献   

20.
Results of TG and DTA studies as well as an analysis of the liberated gas products have led us to recognize differences in the mechanisms of transformations taking place in the systems NH4ReO4/Al2O3-SiO2 (25 wt% SiO2 and NH4ReO4/Al2O3 containing 1.1, 3.3 and 3.3, 9.9, 17.8 wt% NH4ReO4. Thermal decomposition of NH4ReO4 on the supports used begins with release of ammonia, which is strongly bound with the surface in the system of 3.3 wt% NH4ReO4/Al2O3, and undergoes oxidation to nitrogen oxides in the air atmosphere. In the other systems studied, the process of ammonia release starts already at 473 K and ammonia does not get oxidized. Moreover, it has been established that ammonia perrhenate supported on the surface of Al2O3-SiO2 in the amount of 1.1 or 3.3 wt% undergoes partial thermal decomposition to ReO2 which is further oxidized in the air atmosphere. As follows from the thermal studies as well as the measurements of activity in a reaction of 1-hexene metathesis, the active centres of the reaction of olefin metathesis are formed on the surface of the studied systems after their calcination at 473 K.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号