Reaktionen im festen Zustande bei höheren Temperaturen. Reaktionsgeschwindigkeiten endotherm verlaufender Umsetzungen

Jander, Wilhelm

doi:10.1002/zaac.19271630102

Cited by 707 publications

(106 citation statements)

References 15 publications

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“…It can be clearly observed that the change in XRD patterns gradually starts from 673K towards the formation of crystalline oxides, ZnO and CuO, and is accompanied by an exothermic effect corresponding to DTG peak #4 as expected for the crystallization event. Based on the kinetic data from Table 3, this step is characterized by a high value of Ea/R and fits well with Jander's diffusion equation [27]. Upon decomposition of the carbonate-modified oxide phase, ZnO starts to crystallize.…”

Section: Thermokinetic Analysissupporting

confidence: 64%

“…A very high activation barrier features this stage (Table 2). According to Jander's original work [27], this stage of decomposition describes reactions limited by diffusion in the solid state. A likely interpretation is that, upon decomposition of hightemperature carbonate, the zinc atoms leave the shared positions in the lattice and diffuse through the solid to form zinc oxide.…”

Section: Thermokinetic Analysismentioning

confidence: 99%

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Thermokinetic investigation of binary Cu/Zn hydroxycarbonates as precursors for Cu/ZnO catalysts

et al. 2014

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A combination of thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) coupled to mass spectrometry has been applied to study the thermal decomposition of Cu/Zn hydroxycarbonates, which are used as a precursor for the active methanol synthesis catalyst. Original TG and DSC profiles and results of a formal kinetic analysis of the calcination process are compared with transformations occurring in the solid phase, which has been studied by means of in-situ XRD. A series of hydroxycarbonate precursors with different Cu/Zn molar ratios (40/60, 60/40, 80/20) was synthesized under conditions reported as optimum for catalytic performance. The samples contain primarily two crystalline phases, aurichalcite (Cu,Zn) 5 (CO 3 ) 2 (OH) 6 and zincian malachite (Cu,Zn) 2 CO 3 (OH) 2 . At least four formal decomposition stages of CO 2 and H 2 O evolution cause the major mass loss in the TG experiments. The best-fit quality for the all studied samples was obtained for a four-step competitive reaction model. The experimental TG dependences are adequately described by the n-th order equation and 3D Jander diffusion equation. The effects of the gas flow, sample mass, and water transfer conditions on the reaction pathway were studied. The presence of H 2 O vapor in the reaction feed accelerates the decomposition and dramatically changes the reaction TG profile. The decomposition enthalpy of mixed Cu/Zn (80/20) hydroxycarbonate was determined, and the formation enthalpy of the decomposition intermediate, a carbonate-modified oxide, was calculated to be ΔH f 0 =-633.7±5.6 kJ/mol.

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Section: Thermokinetic Analysissupporting

confidence: 64%

Section: Thermokinetic Analysismentioning

confidence: 99%

Thermokinetic investigation of binary Cu/Zn hydroxycarbonates as precursors for Cu/ZnO catalysts

et al. 2014

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“…Typical plots for testing the models are shown in Figures 6 and 7. Accordingly, it is found that Jander's model [2] is most suitable for describing the mechanism of reaction between reactants which is also in agreement with that reported in literature. [64] Jander's model [2] is given by the equation shown below.…”

Section: Modeling Of Solid-solid Reactionssupporting

confidence: 89%

Solid–solid reaction in a fluidized bed

Murthy

Reddy

Sankarshana

2011

Asia-Pacific J Chem Eng

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Solid-solid reactions, although of considerable industrial importance, have not received significant attention in the chemical engineering literature. In conventional method of manufacturing products using reactants in solid phase, the rate of heat transfer and rate of diffusion are very slow. In order to overcome these problems, an attempt is made to investigate these reactions employing a stirred fluidized bed. The addition reaction of phthalic anhydride and p-nitro aniline system that takes place between 80 and 120• C, forming phthaloyl derivative of p-nitro aniline is selected for the investigations. The reaction is conducted in a stainless steel column of 0.1 m diameter and 1-m height. The variables considered are reaction temperature, stirrer speed, flow rate of fluidizing medium, and static bed height. Experiments are performed using statistically designed factorial experiments. Data are used to find the model suitable to the mechanism of the reaction. Mathematical equations relating reaction parameters viz., steady state conversion, time for steady state conversion, reaction rate constant, and activation energy with operating variables are developed and activation energy is reduced from 14 kcal/mol reported in literature to less than 5.3 kcal/mol depending on operating conditions. The concept could be adopted for the manufacture of cement, and other materials with required modifications of experimental setup. 

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“…The vastly used Jander Fig. 8 Intensity of evolution of selected volatile products formed during the thermal degradation of POM and POM/HAp nanocomposites model (D3) of three-dimensional diffusion assumes that solid particles are of spherical shape [34] and parabolic law was applied to describe solid-state reactions. D4 three-dimensional model was proposed by Ginstling and Brounshtein [35] who replaced parabolic law by a dependence relating the growth of the product layer to the particle surface area [25,30].…”

Section: Resultsmentioning

confidence: 99%

The influence of polyoxymethylene molar mass on the oxidative thermal degradation of its nanocomposites with hydroxyapatite

Pielichowska

2015

J Therm Anal Calorim

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In this paper, the influence of mass-average molar mass (M w ) of polyoxymethylene (POM) copolymer on the thermooxidative degradation behavior of its nanocomposites with hydroxyapatite (HAp) is reported. POM copolymers' thermal stability slightly decreases with a decrease in mass-average molar mass. Thermal stability of POM/HAp nanocomposites is lower in comparison with pure POM, and it gets lower with a decrease in massaverage molar mass of POM copolymer. For POM copolymer with the highest molar mass, thermal stability of POM/HAp nanocomposite was ca. 30°C lower than for pure POM. To get a more in-depth insight into the decomposition process, kinetic analysis of POM/HAp nanocomposite thermal degradation process was performed using Friedman, Ozawa-Flynn-Wall and multiple nonlinear regression methods. The best fit for pristine T2, T3 and T4 copolymers with different molar mass of 100768, 74727 and 68377 g mol -1 , respectively, was obtained for onestage degradation mechanism with autocatalysis, while for T2/10 % HAp and T3/10 % it was parallel reaction model with autocatalysis (Bna) and phase-boundary reaction models (R3). For T4/10 % HAp, the best approximation was found for R2-Bna-D3 reaction model. From hyphenated TG-MS and TG-FTIR thermoanalytical studies, it was found that the main degradation product for POM/HAp nanocomposites is formaldehyde and the amount of other degradation products is lower in comparison with nonmodified POM copolymers.

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Reaktionen im festen Zustande bei höheren Temperaturen. Reaktionsgeschwindigkeiten endotherm verlaufender Umsetzungen

Cited by 707 publications

References 15 publications

Thermokinetic investigation of binary Cu/Zn hydroxycarbonates as precursors for Cu/ZnO catalysts

Thermokinetic investigation of binary Cu/Zn hydroxycarbonates as precursors for Cu/ZnO catalysts

Solid–solid reaction in a fluidized bed

The influence of polyoxymethylene molar mass on the oxidative thermal degradation of its nanocomposites with hydroxyapatite

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