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1.
The kinetics, mechanism, and activation energy of the isothermal decomposition of CuCrO4 was studied using an isothermal TG method and an X-ray high-temperature diffraction technique in either air or a flowing atmosphere of N2. The enthalpy change ΔH of the decomposition reaction
2CuCrO4CuO+CuO+CuCr2O4+32O2
was determined by DSC analysis. The mechanism of the thermal decomposition of CuCrO4 is well represented by the standard Avrami-Erofeev kinetic equation [?ln(1 ? α)]12 = kt. According to this mechanism, the reaction rate is controlled by the formation and growth of nuclei on the surface of the reactant. The activation energy EA of the process in air is EA = (248 ± 8) kJ mole?1, in flowing atmosphere of nitrogen EA = (229 ± 8) kJ mole?1. ΔH in air is 110 kJ mole?1, in flowing nitrogen 67 kJ mole?1. The lower values of ΔH and EA in the flowing atmosphere of nitrogen are due to the fast elimination of O2 from the reaction interface. However, the decay of the crystalline portion of CuCrO4 during its thermal decomposition, studied by the X-ray diffraction, is controlled by a different reaction mechanism (first-order kinetics). The reaction mechanism is discussed in the relation to the crystal structure of the reactants.  相似文献   

2.
If in a potentiometric titration each addition of reagent equals Δv and if the observed potential steps are, in decreasing order, ΔEm, ΔE1 and ΔE2, the ratio ρα = ΔE2E1is formed; ραΔv is the difference between the equivalence point and the known volume of reagent next to it. Both an extraordinary increase in the precision and a valuable simplification of the analysis are obtained. For Q = ΔEmΔE1 < 2.5 or ρα < 0.25 this value is approximated; but in this case a new series with doubled intervals may be formed from the potential steps observed in which ρα is very near to 0.5, found hence absolutely accurate.  相似文献   

3.
Geometric constraints present in A2BO4 compounds with the tetragonal-T structure of K2NiF4 impose a strong pressure on the BOIIB bonds and a stretching of the AOIA bonds in the basal planes if the tolerance factor is t ? RAO√2 RBO < 1, where RAO and RBO are the sums of the AO and BO ionic radii. The tetragonal-T phase of La2NiO4 becomes monoclinic for Pr2NiO4, orthorhombic for La2CuO4, and tetragonal-T′ for Pr2CuO4. The atomic displacements in these distorted phases are discussed and rationalized in terms of the chemistry of the various compounds. The strong pressure on the BOIIB bonds produces itinerant σ1x2?y2 bands and a relative stabilization of localized dz2 orbitals. Magnetic susceptibility and transport data reveal an intersection of the Fermi energy with the d2z2 levels for half the copper ions in La2CuO4; this intersection is responsible for an intrinsic localized moment associated with a configuration fluctuation; below 200 K the localized moment smoothly vanishes with decreasing temperature as the d2z2 level becomes filled. In La2NiO4, the localized moments for half-filled dz2 orbitals induce strong correlations among the σ1x2?y2 electrons above Td ? 200 K; at lower temperatures the σ1x2?y2 electrons appear to contribute nothing to the magnetic susceptibility, which obeys a Curie-Weiss law giving a μeff corresponding to S = 12, but shows no magnetic order to lowest temperatures. These surprising results are verified by comparison with the mixed systems La2Ni1?xCuxO4 and La2?2xSr2xNi1?xTixO4. The onset of a charge-density wave below 200 K is proposed for both La2CuO4 and La2NiO4, but the atomic displacements would be short-range cooperative in mixed systems. The semiconductor-metallic transitions observed in several systems are found in many cases to obey the relation Ea ? kTmin, where ? = ?0exp(?EakT) and Tmin is the temperature of minimum resistivity ?. This relation is interpreted in terms of a diffusive charge-carrier mobility with Ea ? ΔHm ? kT at T = Tmin.  相似文献   

4.
Spectrophotometric studies have been carried out on the kinetics of the ligand-substitution reaction of the Zinc(II)-4-(4′-methyl-2′-thiazolylazo)-2-methylresorcinol complex with 1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid, in the pH range 8.4–9.4 at μ = 0.25 and 25 °C. The reaction rate constant was established to be ?(d[ZnR2]dt) = K[ZnR2][H+][Y′]/[HR?], and K = 6.88 × 104liter · mol?1 · sec?1 was obtained.  相似文献   

5.
Results on the rate of polymerization of acrylic acid by S2O2?8 ion in alkaline and acid conditions are presented. Rp depended upon [S2O2?8]12 and [monomer]32 both in acid and alkaline solutions. The influence of ionic strength, the effect of pH on Rp and the catalytic effect of Ag+ and Cu2+ on the system have been discussed. Suitable mechanisms are proposed.  相似文献   

6.
Proton NMR relaxation times (T2T1, and T1?) and absorption spectra are reported for the compounds H1.71MoO3 (red monoclinic) and H0.36MoO3 (blue orthorhombic) in the temperature range 77 K < T < 450 K. Rigid lattice dipolar spectra show that both compounds contain proton pairs, as OH2 groups coordinated to Mo atoms in H1.71MoO3 and as pairs of OH groups in H0.36MoO3. The room temperature lineshape for H1.71MoO3 shows that the average chemical shielding tensor has a total anisotropy of 20.1 ppm. The relaxation measurements confirm that hydrogen diffusion occurs and give EA = 22 kJ mole?1 and τ0C ? 10?13sec for H1.71MoO3 and EA = 11 kJ mole?1 and τ0C ? 3 × 10?8sec for H0.36MoO3.  相似文献   

7.
The paper refers to the synthesis and properties of some bifunctional initiators, viz. 4.4′-azo-bis(4-cyanovaleryl)bisbenzoyl diperoxide (I) and 4,4′-azobis(4-cyanovaleryl)bisacetyl diperoxide (II), obtained from the acid chloride of cyanovaleric acid and condensed with perbenzoic acid or peracetic acid. The structures of the products were established by i.r. and NMR spectroscopy, as well as by elemental analysis. Kinetic studies on the thermolyses of the two initiators led to the following results: for I. t12azo, 360°K = 129 min, t12peroxy, 360°K = 245 min, Eazo = 174.2 kJ/mol, Eperoxy = 206.5 kJ/mol; for II, t12azo, 357°K = 152 min, t12peroxy, 357°K = 208 min, Eazo = 155.4 kJ/mol, Eperoxy = 188.5 kJ/mol.  相似文献   

8.
9.
The reaction of 4-chloro- and 4-chloro-7-deuteriobenzofurazan with MeS-, isopropyl-S-, and t-Butyl-S- in different alcohols as solvents has been investigated. In going from methanol through isopropanol to t-butanol, a progressive decrease of the contribution of the cine-substitution as compared with the normal substitution pathway has been found. By proceeding in the same order, a decrease of the ratio kMeS?kisopropylS? and kMeS?kt-ButylS? has also been observed.  相似文献   

10.
The mechanism of the following solid-state reactions between bismuth(III) oxide and molybdenum(VI) oxide was investigated within the temperature range 400–650°C.
(i)Bi2O3 + MoO3 → Bi2MoO6, (ii)Bi2O3 + 2MoO3 → Bi2MO2O9, (iii)Bi2O3 + 3MoO3 → Bi2(MOO4)3, (iv)Bi2MoO6 + MoO3 → Bi2MO2O9, (v)Bi2Mo2O9 + MoO3 → Bi2(MoO2)3.
Two types of experiments, capillary and particle size, were performed to ascertain whether MoO3 diffuses into Bi2O3 or vice versa. These show that molybdenum trioxide diffuses into bismuth oxide grains. If α is the fraction of molybdenum trioxide reacted, the kinetics in all five cases are found to be governed by the equation αn = kt throughout the temperature range, where n and k are constants at a given temperature and t is the time. Both n and k are temperature dependent. The characteristic feature of these reactions is that they proceed to completion. Results are also fitted by the relation α = k2t12 ? k3t, where k2 and k3 are constants, which shows that the reactions occur by bulk diffusion through grain boundary contacts. The number of grain boundary contact points decreases with time in the course of reaction.  相似文献   

11.
In order to elucidate the defect structure of the perovskite-type oxide solid solution La1?xSrxFeO3?δ (x = 0.0, 0.1, 0.25, 0.4, and 0.6), the nonstoichiometry, δ, was measured as a function of oxygen partial pressure, PO2, at temperatures up to 1200°C by means of the thermogravimetric method. Below 200°C and in an atmosphere of PO2 ≥ 0.13 atm, δ in La1?xSrxFeO3?δ was found to be close to 0. With decreasing log PO2, δ increased and asymptotically reached x2. The log(PO2atm) value corresponding to δ = x2 was about ?10 at 1000°C. With further decrease in log PO2, δ slightly increased. For LaFeO3?δ, the observed δ values were as small as <0.015. It was found that the relation between δ and log PO2 is interpreted on the basis of the defect equilibrium among Sr′La (or V?La for the case of LaFeO3?δ), V··O, Fe′Fe, and Fe·Fe. Calculations were made for the equilibrium constants Kox of the reaction
12O2(g) + V··o + 2FexFe = Oxo + 2Fe·Fe
and Ki for the reaction
2FexFe = FeFe + Fe·Fe·
Using these constants, the defect concentrations were calculated as functions of PO2, temperature, and composition x. The present results are discussed with respect to previously reported results of conductivity measurements.  相似文献   

12.
Binary systems consisting of dimethylaniline-N-oxide (DMOA) and some α-halo-carbonyl compounds, such as phenacyl halide and α-halo-acetic acid ester, were found to induce radical polymerization of vinyl monomers. Bromo-derivatives showed higher initiating activities than chloroderivatives. The polymerization of methyl methacrylate (MMA) with DMAO and phenacyl bromide (PBr) was investigated kinetically. The polymerization rate (Rp) was expressed as follows; Rp = k[DMAO]12[PBr]12[MMA].The overall activation energy of the polymerization was calculated to be 42.7 kJ mol?1. No noticeable chain-transfer from the polymer radical to DMAO or PBr was observed. The benzoyl radical was trapped by 2-nitroso-2-methylpropane, a spin trapping reagent, in the reaction of DMAO and PBr. The u.v. spectrum of poly (MMA) obtained suggests that the polymer contains end-groups similar to acetophenone and DMA. From the results, an initiation mechanism for the polymerization has been proposed and discussed.  相似文献   

13.
14.
The solid-, cholesteric- and liquid-state polymerizations of cholesteryl-vinyl-succinate (CVS) are studied. Only one of the three polymorphic modifications of CVS oligomerizes in the solid state into oligomers of degree P = 2 to 6 in a homogeneous topochemical reaction. The rate of polymerization in the cholesteric state is lower than that in the liquid state at the same temperature. Kinetic constants were measured at 85° using benzoyl peroxide as initiator and the Banfield radical, giving Eoverall = 15.4, 36.4 kcal/mole?1; f = 0.52, 0.19; kp/kt12 = 0.0167, 0.0192, (1/mole sec)12, (Ep ? 12Et) = 0.40, 21.4 kcal mole?1. The values refer to the liquid- and the cholesteric-state reactions, respectively. The average degree of polymerization is low in both cases (P = 20 and 22). It was concluded that the molecular weights are controlled by chain transfer and that the initiation reaction is mostly dependent on the phase where the reaction takes place.  相似文献   

15.
Polymerization experiments with styrene in benzene at 60°, initiated by benzoyl peroxide, covering a wide range of concentration of both monomer and initiator are reported; the results cannot be explained in terms of the classical rate relationship with Rp ∝ [I]12 [M]. Deviations were reflected in unexpected orders of monomer up to [M]1·4 and of initiator down to [I]0·42 when the initiator concentration is increased and monomer concentration is decreased. Based on the concept of primary radical termination, an equation, viz.
lnRp2[I][M]2=ln2fkkdkp2kt?2kprtkikp×Rp[M]2
is proposed. Semi-log plots of Rp2/[I] [M]2 vs Rp/[M]2 show a wide range of linearity; the characteristic constant kprt/kikp and also fk can be obtained from the slope and intercept, respectively, kprt, ki and kp are, respectively, the rate constants of primary radical termination, initiation and propagation and fk is the efficiency of initiation, defined as the fraction of radicals which come out of the solvent cage and take part in initiation, primary radical termination and primary radical recombination. The definition of fk is thus differentiated from the conventional efficiency of initiation. Finally, we have derived an equation which allows determination of the classical efficiency of initiation as a function of [I]/[M]2 and also allows a correction of Rp in handling the above equation by taking into account the small amount of monomer consumed in initiation.  相似文献   

16.
The new phosphine, PBut2Bui (L), was prepared from But2PCl and LiBui. PPh2Bui (L′) was prepared from Ph2PCl and LiBui. Treatment of [PtCl2(NCBut)2] with L′ gives [PtCl2L′2] which does not cyclometallate even on prolonged boiling in 2-methoxyethanol. In contrast, [PtCl2(NCBut)2] reacts with PBut2Bui in boiling 2-methoxyethanol to give the cyclometallated complex [Pt2Cl2(PBut2CH2-CHMeCH2)2] (II, X = Cl). The corresponding bromide, iodide and acetylacetonate were prepared. With PPh3 II (X = Cl) gives [PtCl(PBut2CH2CHMeCH2)(PPh3)] which with NaBH4 gives [PtH(PBut2CH2CHMeCH2)(PPh3)]. Na2PdCl4 with L (2 mol equivalents) gave trans-[PdCl2L2], which was converted into trans-[Pd(NCS)2-L2] by metathesis with KSCN. Treatment of Na2PdCl4 with L (1 mol equivalent) gave [Pd2Cl4L2], which on heating in 2-methoxyethanol gave [Pd2Cl2(PBut2CH2-CHMeCH2)2], as a mixture of syn- and anti-isomers. The complexes trans-[PdCl2-L′2] and [Pd2Cl4L′2] were also prepared. 1H- and 31P NMR data are given.  相似文献   

17.
The reduction of permanganate by oxalate in the presence of manganese(II) ion in acidic media is described. All reactions were run at 525 nm and constant ionic strength 1.0 M. The reaction was found to obey the rate expression —d[MnO4-]dt = k [Mn2+] [C2O42-]2 [MnO4-] [H+]-2 = k' [MnC2O4] [MnO4-]. The values of k and k' were shown to be 5.4 × 104 M-1 s-1 and 8.2 × 104 M-1 s-1, respectively. Reaction rate methods for the determination of manganese(II) and oxalic acid are reported. The rate of disappearance of permanganate was monitored automatically and related directly to manganese-(II) and oxalic acid concentrations. Manganese(II) in the ranges 1–10 × 10-4 M and 1–10 × 10-3 M and oxalic acid in the range 0–20 μg ml-1 can be determined very rapidly with a precision of 1–2%.  相似文献   

18.
The extraction of Co(II) with mixtures of 1-phenyl-3-methyl-4-benzoyl-pyrazol-5-one ((H)PMBP) and tri-n-octylamine (TOA) is investigated in order to explore the influence of diluents and inorganic anions with synergistic acidic extractant + liquid anion exchanger systems. Although it is proved that the same species [HTOA]+ [Co(PMBP)3]? is extracted from various inorganic media, with toluene as the diluent, the presence of ClO4? SO42? or Cl? anion modifies the distribution of the anions which are associated to (HTOA)+ in the organic phase, leading to different synergistic equilibria; with Cl? or SO42?: CO(PMBP)2 + (HTOA+,PMBP?) ?(HTOA+,Co(PMBP)3? (log K = 6.10) and with ClO4? : Co(PMBP)2 + HPMBP + (HTOA+,ClO4? ? (HTOA+,Co(PMBP)3? + H+ + ClO4? (log K = 2.34) The same synergistic equilibrium is observed for the extraction of Ni(II) from ClO4? medium, with a comparable value of the constant (log K = 2.45). The synergistic effect is cancelled in n-octanol.  相似文献   

19.
The kinetics of the aminolysis of different nitrophenylacetates were investigated with n-butylamine in dioxane at 20°C. The reaction rate can be described up to high concentrations of amine (~1 mole dm?3) by the equation v=k2[ester][amine]+k3[ester][amine]2. The ratio k3k2 is larger for p-nitrophenylacetates than for o-nitrophenylacetates, while for 2,4-dinitrophenylacetates a third order term is not observed.  相似文献   

20.
A series of titanates which have perovskite-like arrangements and are isostructural with [CaCu3](Mn4)O12 have been synthesized. The total charge of the A sites can be modified (1) by substituting the Ca2+ cations with monovalent ones and the tetravalent manganese cations of the B sites by a mixture of (Ti4+ + M5+) in which M = Ta, Nb, Sb, or (2) by substituting the Ca2+ cations by a combination of cations plus vacancies. In this case, if the total charge of the A sites is 2, one obtains compounds such as [Th4+1212Cu3](Ti4)O12 and [T3+2313Cu3](Ti4O12 (T = rare earth); on the contrary, if the charge is less than 2, then one has to compensate it by changing that of the B sites. This leads to compounds such as [□Cu3](Ti2M2)O12 (M = Ta, Nb, Sb).  相似文献   

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