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1.
Pure cobaltic oxide, prepared by thermal decomposition of pure basic cobalt carbonate in air at 500°C, was subjected to different doses of γ-radiation varying between 5 and 50 M rad. The influence of γ-radiation on the thermal decomposition of cobaltic oxide to cobaltous oxide and the re-oxidation of CoO to Co 3O 4 was studied using DTA, with a controlled rate of heating and cooling. The effects of γ-radiation on the specific surface area ( SBET) and oxidation character of Co 3O 4 were also investigated.The DTA investigation revealed that γ-radiation effectively decreased the thermal stability of cobaltic oxide to an extent proportional to the dose employed. The maximum decrease in the thermal stability of 60% was attained by exposing Co 3O 4 solid to 30 M rad. γ-Irradiation, however, exerted no detectable effect on the re-oxidation of CoO by O 2 to Co 3O 4.The SBET measurements showed that the small dose (5 M rad) of γ-radiation effected a decrease of 15% in the surface area of Co 3O 4, the higher doses (10–50 M rad) caused a further slight decrease of 18% in its surface area.γ-Irradiation was found to decrease the oxidation character of Co 3O 4 to an extent proportional to the dose employed.The decrease in the thermal stability of Co 3O 4 due to radiation is explained in terms of the decrease in the oxidation character of cobaltic oxide observed after subjecting the solid to γ-radiation. 相似文献
2.
The effects of doping cobalt oxides with different amounts of ZrO 2 and ThO 2 (1.5–9 mol%) on the thermal stability of Co 3O 4 and the re-oxidation of CoO by O 2 to Co 3O 4 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 Th 4+ and Zr 4+ (up to 6 mol%) exerted no appreciable effect on the thermal stability of Co 3O 4. Increasing the amount of the dopant ions to 9% resulted in no further change in the thermal stability of Co 3O 4 in the case of Th 4+, and an increase of 16% in case of Zr 4+-doping. However, ThO 2-doping of cobalt oxide was accompanied by an enhancement in the reactivity of CoO towards re-oxidation by O 2 to Co 3O 4 to an extent proportional to the amount of dopant oxide.The X-ray investigation of ZrO 2-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
3.
The results obtained showed that the addition of small amounts of LiNO 3 to the reacting mixed solids, consisting of equimolar proportion of Fe 2O 3 and basic MgCO 3 much enhanced the thermal decomposition of magnesium carbonate. The addition of 12 mol% LiNO 3 (6 mol% Li 2O) decreased the decomposition temperature of MgCO 3 from 525.5 to362°C. MgO underwent solid–solid interaction with Fe2O3 at temperatures starting from800°C yielding MgFe 2O 4. The amount of ferrite produced increased by increasing the precalcination temperature of the mixed solids. However, the
completion of this reaction required prolonged heating at elevated temperature above 1100°C. Doping with Li 2O much enhanced the solid–solid interaction between the mixed oxides leading to the formation of MgFe 2O 4 phase at temperatures starting from 700°C. The addition of 6 mol% Li 2O to the mixed solids followed by precalcination at 1050°C for 4 h resulted in complete conversion of the reacting oxides
into magnesium ferrite. The heat treatment of pure and doped solids at 900–1050°C effected the disappearance of most of IR
transmission bands of the free oxides with subsequent appearance of new bands characteristic for MgFe 2O 4 structure. The promotion effect of Li2O towards the ferrite formation was attributed to an effective increase in the mobility
of the various reacting cations. The activation energy of formation (Δ E) of magnesium ferrite was determined for pure and variously doped solids and the values obtained were 203, 126, 95 and 61
kJ mol −1 for pure mixed solids and those treated with 1.5, 3.0 and 6.0 mol% Li 2O, respectively.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
The paper describes the synthesis and characterization of cobalt(II) bis (tartrato) cobaltate(II) trihydrate Co[Co[C 4O 6H 4) 2]·3H 2O. The complex was characterized on the basis of elemental analysis, infrared, electronic, e.s.r. spectra and X-ray powder
diffraction studies. The thermal decomposition of the complex led to a mixture of Co 2O 3and Co 3O 4in air at about 400°C, whereas in nitrogen it was decomposed to a mixture of CoO and C at about 384°C. A tentative reaction
mechanism is suggested for the thermal decomposition of the complex in air and nitrogen.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
Thermodynamic instability of positive electrodes (cathodes) in Li-ion batteries in humid air and battery solutions results in capacity fading and batteries degradation, especially at elevated temperatures. In this work, we studied thermal interactions between cathode materials Li 2MnO 3, xLi 2MnO 3 .(1??? x)Li(MnNiCo)O 2,LiNi 0.33Mn 0.33Co 0.33O 2, LiNi 0.4Mn 0.4Co 0.2O 2, LiNi 0.8Co 0.15Al 0.05O 2 LiMn 1.5Ni 0.5O 4, LiMn(or Fe)PO 4, and battery solutions containing ethylene carbonate (EC) or propylene carbonate (PC), dimethyl carbonate (DMC) or ethylmethyl carbonate (EMC) and LiPF 6 salt in the temperature range of 40–400 °C. It was found that these materials are stable chemically and well performing in LiPF 6-based solutions up to 60 °C. The thermal decomposition of the electrolyte solutions starts >180 °C. The macro-structural transformations of cathode materials upon exothermic reactions were studied by transmission electron microscopy (TEM), X-ray difraction (XRD) and Raman spectroscopy. Differential scanning calorimetry (DSC) studies have shown that the exothermic reactions in the temperature range of 60–140 °C lead to partial decomposition of both the cathode material and electrolyte solution. The systems thus formed consisted of partially decomposed solutions and partially chemically delithiated cathode materials covered by reactions products. Thermal reactions terminate and this system reaches equilibrium at about 120 °C. It remains stable up to the beginning of the solution decomposition at about 180 °C. The increased content of surface Li 2CO 3 is found to significantly affect the thermal processes at high temperature range due to extensive exothermic decomposition at low temperatures. 相似文献
6.
The homopolynuclear coordination compound [CoL · 2.5H 2O] n with L=C 2O 4
2− was synthesized by a new unconventional method. It consist in the redox reaction between 1,2-ethanediol and cobalt nitrate
in presence of nitric acid. The coordination compound was characterized by chemical analysis, electronic and vibrational spectra
respectively, thermal analysis. In the coordination compound the Co(II) ion exists in a high spin octahedral configuration
and oxalate anion acts as double-bridge ligand, tetradentate, similar as in CoC 2O 4 · 2H 2O obtained by the classical method. Nonstoichiometric oxide, Co 3O 4+0.25 with deficit in cobalt and normal spinel Co 3O 4 where identified as thermal decomposition intermediates. As final product of decomposition, the oxide CoO was obtained. 相似文献
7.
This study investigated the catalytic effect of NiO, Co 3O 4 and Fe 3O 4 nanoparticles toward asphaltene thermal decomposition (pyrolysis) under inert conditions. Asphaltene adsorbed onto the selected nanoparticles were subjected to thermal decomposition up to 800?°C in a thermogravimetric analyzer. The presence of nanoparticles caused a significant decrease in the asphaltene decomposition temperature and activation energy. Activation energies for the process were calculated using the Ozawa?CFlynn?CWall method. All the selected metal oxide nanoparticles showed high catalytic activity toward asphaltene decomposition in the following order NiO?>?Co 3O 4?>?Fe 3O 4. This study confirms that metal oxide nanoparticles can significantly enhance the thermal decomposition of heavy hydrocarbons, like asphaltenes. 相似文献
8.
The role of Na 2O- and Li 2O-doping on the thermal decomposition of Co 3O 4 to CoO and the re-oxidation of cobaltous to cobaltic oxide has been investigated using DTA, with controlled rates of heating and cooling, IR and X-ray diffraction spectrometry techniques. The DTA investigation revealed that both Li2O and Na2O increased the thermal stability of Co3O4. However, the effect was much more pronounced in the case of lithium oxide. Doping Co3O4 with 1.5 mole% Li2O was found to prevent any thermal decomposition of cobaltic oxide even by heating at 1100°C. The maximum thermal stabilization effect induced by doping with sodium oxide (4.5 mole%) was 30%. The sodium oxide- and lithium oxide-doping enhanced the reactivity of the produced CoO towards the re-oxidation by O2 yielding Co3O4. The X-ray diffraction and IR spectrometric investigations showed that part of Li2O and Na2O was effectively incorporated in the Co3O4 lattice, affecting the thermal stabilization of the solid, and another part of the dopant oxide interacted with the produced CoO and also with Co3O4 giving a new sodium cobalt compound, and with Co3O4 producing, also, a new lithium cobalt oxide phase. However, the amount of Li2O dissolved in the Co3O4 lattice was greater than that of Na2O. The sudden cooling of doped solids, from 1000°C to room temperature, favoured the formation of the new sodium cobalt oxide compound, and exerted no effect on the production of the new lithium cobalt oxide phase. The characteristic d spacings and IR absorption bands of these new compounds have been determined. The possible mechanisms of dissolution of Li2O and Na2O in cobaltic oxide lattice are discussed. 相似文献
9.
The CO adsorption species on Co 3O 4 and (0.5-15%)CoO/CeO 2 catalysts have been investigated by temperature-programmed desorption and IR spectroscopy. At 20°C, the largest amount of CO is adsorbed on the 5%CoO/CeO 2 sample to form, on Co m2+O n2+ clusters, hydrogen-containing, bidentate, and monodentate carbonate complexes, whose decomposition is accompanied by CO 2 desorption at 300 and 450°C (1.1 × 10 20 g –1). The formation of the carbonates is accompanied by the formation of Co + cations and Co 0, on which carbonyls form. The latter decompose at 20, 90, and 170°C to release CO (2.7 × 10 19 g –1). Part of the carbonyls oxidizes to CO 2 upon oxygen adsorption, and the CO 2 undergoes desorption at 20°C. Adsorbed oxygen decreases the decomposition temperature of the H-containing and bidentate carbonates from 300 to 100-170°C and maintains the sample in the oxidized state, which is active in subsequent CO adsorption and oxidation. CO oxidation by oxygen of the catalyst diminishes the activity of the sample in these processes and increases the decomposition temperature of the carbonate complexes. Taking into account the properties of the adsorption complexes, we concluded that the H-containing and bidentate carbonates are involved in CO oxidation by oxygen of the catalyst at ~170°C under isothermal conditions. The rate limiting step is the decomposition of the carbonates, a process whose activation energy is 65-74 kJ/mol. 相似文献
10.
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 CaC 2O 4 and Co 3O 4 at 340 °C, and a mixture of CaCO 3 and Co 3O 4 identified at 510 °C. A mixture of CaCO 3 and Ca 3Co 2O 6 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, SrC 2O 4, CoC 2O 4 and Co 3O 4 were generated at 255 °C in case of SOC in air, which ultimately changed to CoSrO 3, SrCO 3 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 BaCoO 2, 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, Δ H and Δ S 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. 相似文献
11.
New Oxoterbates(IV) with Lithium: On Rb 2Li 14[Tb 3O 14] and Li 6Tb 2O 7 For the first time we prepared Rb 2Li 14[Tb 3O 14] as yellow single crystals from Li 8TbO 6 and Rb 2O (Tb:Rb = 1:2) [Ag-cylinder, 500°C, 30 d, then Au-tube, 700°C, 27 d]. The structure refinement [652 I 0 (h kl), four circle diffractometer Philips PW 1100, ω-scan, MoKα, R = 4.69%, R w = 3.24%, absorption considered, Immm with a = 1 283.07(10), b = 790.87(7), c = 736.87(7)pm, Z = 2, d x = 4.30 g · cm ?3] confirms that it is isotypic with K 2Li 14[Pb 3O 14]. Furthermore we got for the first time Li 6Tb 2O 7 as a bright yellow compound from Li 2O 2 and “Tb 4O 7*” [(Li:Tb = 3.4:1), Au-ube, 750°C, 13 d (powder), 850°C 22 d (single crystals)] and by thermal decomposition of Rb 2Li 14[Tb 3O 14] (Au-tube, 850°C, 25 d). Powder and single crystal data [1 327 I 0 (h kl), four circle diffractometer PW 1100, ω-scan, AgKα, R = 9.38%, R w = 5.23%, absorption not considered, P2 1/a, a = 1 056.30(10), b = 613.50(4), c = 546.56(5) pm, β = 109.668(7)°, Z = 2, d x = 4.67 g · cm ?3 d pyc = 4.53 g · cm ?3] reveal a new type of structure that may be deduced by the NaCl-type of structure. The Madelung Part of Lattice Energy, MAPLE, Effective Coordination Numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, are calculated and discussed. 相似文献
12.
Joint thermolysis of the dinuclear pivalate complexes M 2(μ-H 2O)(μ-Piv) 2(Piv) 2(HPiv) 4 (M = Co (1) and Ni (2), Piv - is the pivalate anion), in decane at 174 °C at the reactant ratio 1: 1 followed by treatment of the dry thermolysis product
with methanol afforded crystals of a new cocrystallization product of the molecules containing the heterometallic cubane-like
core M 4(Co,Ni)O 4. According to the X-ray diffraction data and the results of magnetic measurements, inductively coupled plasma atomic emission
spectrometry (ICP-AES), and investigations of the solid-state thermal decomposition products, the isolated cocrystallization
product has the general formula [Co 1.6Ni 2.4(μ 3-OMe) 4(μ 2-Piv) 2(pg 2 -Piv) 2(MeOH) 4] ·4MeOH (3·4MeOH). Thermolysis of the crystals of the solvate 3·4MeOH is a destructive process accompanied by the intramolecular
redox reaction. A mixture of metallic Ni and cobalt oxide (CoO) are the final solid decomposition products of 3 · 4MeOH in
an argon atmosphere, whereas a mixture of the phases NiO, Co 3O 4, and NiCo 2O 4 is formed in air. 相似文献
13.
Oxidation of magnesium in mixtures NaClO 4 + Mg + metal oxide or peroxide has been investigated using differential thermal analysis (DTA). In the systems with peroxides Na 2O 2, Li 2O 2, BaO 2, CaO 2 or ZnO, magnesium oxidizes simultaneously with decomposition of NaClO 4 in the region 380–520°C, which is 100–200°C below the oxidation temperature of magnesium in air. In the ternary systems with transition-metal oxides NiO, CuO, FeO, and Fe 2O 3, magnesium transforms into oxide at above 600°C after sodium perchlorate had been decomposed completely. The low-temperature oxidation of magnesium occurs in the systems in which sodium chlorate is accumulated during the catalytic decomposition of NaClO 4. 相似文献
14.
The thermal decomposition of a chloride and water-containing basic cobalt carbonate was studied. As a first step, crystal water is lost without change of structure. The following decomposition steps overlap and proceed in different ways, depending on the atmosphere over the sample: under nitrogen, chloride volatilizes as HCl and CoCl 2; in air, oxidation occurs. CoO and Co 3O 4, respectively, are the final solid products at 700–800°. 相似文献
15.
Kinetics of thermal decomposition in vacuum of Co 3O 4 powder as well as single crystals has been investigated. Discrepancies with the results of previous authors have been discussed. Decomposition of Co 3O 4 proceeds through formation of a compact layer of CoO and hence diffusion is the rate-limiting factor. The experimental curves α( t) be described for 0.05 < α < 0.85 using a modified Ginstling-Brounshtein equation: 1 ? 2α/3 ? (1 ? α) 2/3 = ktn where the activation energy varies with the degree of decomposition. 相似文献
16.
The thermal decomposition of nitritocobaltate(III) of the silver group of general formula M 2Ag[Co(NO 2) 6] (where M = K +, NH +4, Rb + or Cs +) has been investigated. Based on the thermal curves of the investigated compounds and chemical and diffractometric analysis, the mechanism of thermal decomposition has been determined. The results obtained indicate that the decomposition proceeds in three stages. As a result of decomposition in the first stage (300°C), nitrates of alkali metals, metallic silver and Co 3O 4 are formed. In the second stage (500°C), a partial decomposition of nitrates to alkali metal oxides occurs, and in the third stage the products are alkali metal oxides, silver and Co 3O 4. This paper also presents the dependence of the decomposition temperature of nitritocobaltates(III) of the silver group on the ionic radius of the outer-sphere cation. 相似文献
17.
Various nickel aluminium mixed hydroxide samples of different compositions were prepared by co-precipitation from their nitrate solutions using dilute NH 4OH. Additional samples were prepared by impregnation of hydrated Al 2O 3, preheated at 600 and 900°C, with nickel nitrate solution in an equimolar ratio. The thermal decomposition of different mixed solids was studied using DTA. The X-ray investigation of thermal products of the mixed solids was also studied.The results obtained revealed that the presence of NiO up to 33.3 mole % with aluminium oxide much enhanced the degree of crystallinity of the γ-Al 2O 3 phase. In contrast, the presence of Al 2O 3 much retarded the crystallization process of the NiO phase. With the exception of samples containing 20 mole% NiO, all the mixed hydroxide samples, when heated in air at 900°C, led to the formation of well-crystalline Ni Al 2O 4 spinel, alone, or together with either NiO or γ-Al 2O 3, depending on the composition of the mixed oxide samples. The solid containing 20% NiO and heated at 900°C was constituted of amorphous NiO dispersed in γ-Al 2O 3. Heating the nickel nitrate-impregnated Al 2O 3 in air at 800–1000°C led to the formation of Ni Al 2O 4 together with non-reacted NiO and γ-Al 2O 3. The degree of crystallinity of the spinel was found to increase by increasing the calcination temperature of the impregnated solids from 800 to 1000°C and by increasing the preheating temperature of the hydrated Al 2O 3 employed from 600 to 900°C. 相似文献
18.
The effect of ferric and manganese oxides dopants on thermal and physicochemical properties of Mn-oxide/Al 2O 3 and Fe 2O 3/Al 2O 3 systems has been studied separately. The pure and doped mixed solids were thermally treated at 400–1000°C. Pyrolysis of pure
and doped mixed solids was investigated via thermal analysis (TG-DTG) techniques. The thermal products were characterized
using XRD-analysis. The results revealed that pure ferric nitrate decomposes into Fe 2O 3 at 350°C and shows thermal stability up to1000°C. Crystalline Fe 3O 4 and Mn 3O 4phases were detected for some doped solids precalcined at 1000°C. Crystalline γ-Al 2O 3 phase was detected for all solids preheated up to 800°C. Ferric and manganese oxides enhanced the formation of α-Al 2O 3 phase at1000°C. Crystalline MnAl 2O 4 and MnFe 2O 4 phases were formed at 1000°C as a result of solid–solid interaction processes. The catalytic behavior of the thermal products
was tested using the decomposition of H 2O 2 reaction.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
19.
ZnO/Co 3O 4 porous nanocomposites were successfully fabricated by the thermal decomposition of Prussian Blue analogue (PBA) Zn 3[Co(CN) 6] 2 nanospheres obtained at room temperature. Interestingly, ZnO/Co 3O 4 porous nanocomposites exhibit room‐temperature ferromagnetism. Moreover, the ZnO/Co 3O 4 porous nanocomposites show good catalytic activity for CO oxidation, and the CO conversion rate reaches 100 % at 250 °C. It is suggested that the synergistic effect of each component, relative high surface area (32 m 2 g ?1) and porous structure lead to the promising catalytic properties. 相似文献
20.
The present study deals with preparation and characterization of spinel mixed oxide systems NiM 2 III O 4, where M III?=?Fe III, Cr III. In order to obtain 50% NiFe 2O 4/50% SiO 2 and 50% NiCr 2O 4/50% SiO 2 nanocomposite, we have used a versatile route based on the thermal decomposition inside the SiO 2 matrix, of some particular precursors, coordination compounds of the involved M II and M III cations with dicarboxylate ligands. The ligands form in the redox reaction between metal nitrates mixture and 1,3-propanediol at the heating around 140?°C of the gels (tetraethylorthosilicate?Cmetal nitrates?C1,3-propanediol?Cwater). The as-obtained precursors, embedded in silica gels, have been characterized by FT-IR spectrometry and thermal analysis. Both precursors thermally decompose up to 350?°C leading to the formation of the corresponding metal oxides inside the silica matrix. X-ray diffraction of the annealed powders have evidenced the formation of NiFe 2O 4 starting with 600?°C, and NiCr 2O 4 starting with 400?°C. This behavior can be explained by the fact that, by thermal decomposition of the Fe(III) carboxylate at 300?°C, the spinelic phase ??-Fe 2O 3 is formed, which interacts with the NiO, forming the ferrite nuclei. By thermal decomposition of chromium carboxylate, a nonstoichiometric chromium oxide (Cr 2O 3+x ) is formed. In the range 380?C400?°C, Cr 2O 3+x turns into Cr 2O 3 which immediately interacts with NiO leading to the formation of nickel chromites nuclei inside the pores of silica matrix. Both spinels have been obtained as nanocrystalites homogenously dispersed as resulted from XRD and TEM data. 相似文献
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