Oxidation Behavior of β-Sialon Ultrafine Powders Prepared by the Combined Sol-Gel and Microwave Carbothermal Reduction Nitridation Method

2018 ◽  
Vol 281 ◽  
pp. 34-39
Author(s):  
Fa Liang Li ◽  
Fang Fu ◽  
Li Lin Lu ◽  
Hai Jun Zhang ◽  
Shao Wei Zhang
Keyword(s):  
Activation Energy ◽  
Carbothermal Reduction ◽  
Oxidation Behavior ◽  
Oxidation Process ◽  
Sol Gel ◽  
Probable Mechanism ◽  
Ultrafine Powders ◽  
Isothermal Thermogravimetry ◽  
Temperature Range ◽  
Mechanism Function

Ultrafine powders of β-Sialon were prepared by the combined sol-gel and microwave carbothermal reduction nitridation method, and their oxidation process was studied by a non-isothermal thermogravimetry method. The results indicated that two different mechanism functions respectively corresponded to the initial and final oxidation stages. The reverse Jander equation with activation energy of 240.5 kJ/mol and the Avrami-Erofeev equation with activation energy of 410.7 kJ/mol were respectively identified as the most probable mechanism function for the initial and final oxidation stages in the temperature range of 1423-1623 K.

Thermoreactivity of Sol-Gel Precursor for ZnO-Based Thin Films

2006 ◽  
Vol 514-516 ◽  
pp. 73-77 ◽  
Author(s):  
Viorica Muşat ◽  
Paula M. Vilarinho ◽  
Regina da Conceição Corredeira Monteiro ◽  
Elvira Fortunato ◽  
E. Segal
Keyword(s):  
Differential Equation ◽  
Thin Films ◽  
Activation Energy ◽  
Thermal Decomposition ◽  
Organic Compounds ◽  
Sol Gel ◽  
Hexagonal Lattice ◽  
Kinetic Investigation ◽  
Temperature Range ◽  
Carbonate Hydroxide

The thermoreactivity of a zinc acetate non-alkoxide solution used for the preparation of ZnO-based thin films was investigated in the temperature range 20-600°C by TG-DTA, XRD and SEM data. We found that the formation in air of ZnO crystallites from the sol-gel precursor occurs above 150°C simultaneously with the decomposition of an intermediary compound, most probably carbonate hydroxide (sclarite and/or hydrozincite). At 200 °C, the crystalline structure is well defined in terms of ZnO hexagonal lattice parameters, although residual organic compounds and water were not yet fully removed and an amorphous phase coexists. A kinetic investigation on the thermal decomposition of sol-gel precursor from DTA data using Kissinger differential equation is also presented. Apparent activation energy values of about. 100 kJ mol-1 corresponding to the nonisothermal decomposition of solid precursors in the temperature range 170-250oC have been found.

scholarly journals Oxidation Activation Energy of Titanium Alloy Based on TiAl(γ) Intermetalic Phase

2018 ◽  
Vol 18 (2) ◽  
pp. 5-14 ◽  
Author(s):  
J. Małecka
Keyword(s):  
Activation Energy ◽  
Titanium Alloy ◽  
Oxidation Process ◽  
Temperature Range ◽  
Air Atmosphere ◽  
Hot Air

AbstractThe present paper deals with the analysis of the course of oxidation of the cyclic Ti-46Al-7Nb-0.7Cr-0.1Si-0.2Ni alloy in a hot air atmosphere in the temperature range of 875-975°C. The constant rates of the oxidation were determined (separately for the first and second stages of oxidation) and the energy of oxidation activation of the tested alloy was established. It was discovered that the oxidation process of the Ti-46Al-7Nb-0,7Cr-0.1Si-0.2Ni alloy develops according to the parabolic correlation, and it is only possible to determine the apparent energy of oxidation activation.

scholarly journals Kinetics of Dehydroxylation and Decarburization of Coal Series Kaolinite during Calcination: A Novel Kinetic Method Based on Gaseous Products

Materials ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1493
Author(s):  
Simeng Cheng ◽  
Shaowu Jiu ◽  
Hui Li
Keyword(s):  
Activation Energy ◽  
Kinetic Method ◽  
Kinetic Equations ◽  
Second Step ◽  
Traditional Methods ◽  
Temperature Range ◽  
Gaseous Products ◽  
Mechanism Function ◽  
Kinetics Of

The analysis of gaseous products reveals the characteristics, mechanisms, and kinetic equations describing the dehydroxylation and decarburization in coal series kaolinite. The results show that the dehydroxylation of coal series kaolinite arises from the calcination of kaolinite and boehmite within the temperature range of 350–850 °C. The activation energy for dehydroxylation is 182.71 kJ·mol−1, and the mechanism conforms to the A2/3 model. Decarburization is a two-step reaction, occurring as a result of the combustion of carbon and the decomposition of a small amount of calcite. The temperature range in the first step is 350–550 °C, and in the second is 580–830 °C. The first step decarburization reaction conforms to the A2/3 mechanism function, and the activation energy is 160.94 kJ·mol−1. The second step decarburization reaction follows the B3 mechanism function, wherein the activation energy is 215.47 kJ·mol−1. A comparison with the traditional methods proves that the kinetics method utilizing TG-FTIR-MS is feasible.

The kinetics of dehydroxylation of kaolinite

Clay Minerals ◽  
1987 ◽  
Vol 22 (4) ◽  
pp. 447-456 ◽  
Author(s):  
S. A. T. Redfern
Keyword(s):  
Activation Energy ◽  
Reaction Mechanism ◽  
Kinetic Analysis ◽  
Rate Constants ◽  
Avrami Equation ◽  
Isothermal Thermogravimetry ◽  
Temperature Range ◽  
Homogeneous Models ◽  
Kinetics Of ◽  
Fraction Method

AbstractThe dehydroxylation of kaolinite has been investigated by isothermal thermogravimetry. Kinetic analysis using the Avrami equation shows that a combination of atomic mechanisms operates throughout the temperature range 734 K to 890 K. An empirical activation energy of 222 kJ mol-1 was calculated from the Arrhenius relationship using rate constants based on diffusion and homogeneous models. The activation energy (Ea) was calculated for a series of degrees of dehydroxylation by the time to a given fraction method, showing an increase in Ea during the early stages of the reaction. The isothermal plots indicate that OH is retained in the final stages of the reaction. The observations are explained in terms of a reaction mechanism in which kaolinite grains dehydroxylate from the edges inwards, parallel to (001).

Thermal Decomposition of Hydroxylamine Nitrate Studied by Differential Scanning Calorimetry Analysis and Density Functional Theory Calculations

2017 ◽  
Vol 42 (4) ◽  
pp. 334-343
Author(s):  
Jianguo Liu ◽  
Zhentao An ◽  
Qian Zhang ◽  
Chaoyang Wang
Keyword(s):  
Activation Energy ◽  
Density Functional Theory ◽  
Differential Scanning Calorimetry ◽  
Thermal Decomposition ◽  
Density Functional ◽  
Probable Mechanism ◽  
Thermal Decomposition Mechanism ◽  
Scanning Calorimetry ◽  
Functional Theory ◽  
Mechanism Function

The thermal stability and kinetics of hydroxylamine nitrate (HAN) decomposition were studied by differential scanning calorimetry (DSC) and the thermal decomposition reaction mechanism was determined by density functional theory (DFT). With the help of parameter values from the non-isothermal DSC curves of HAN, the thermal decomposition activation energy and pre-exponential constant were obtained by the Kissinger and Ozawa methods. Then, the most probable mechanism function was calculated by the Šatava–Šesták method. Seven different paths for the thermal decomposition mechanism of HAN were formulated and DFT at the B3LYP/6-311++G(d,p) level was used to carry out the dynamics analysis. The calculated results show that the values of the activation energy calculated by the Kissinger and Ozawa methods are 67.892 and 70.412 kJ mol−1 respectively. The most probable mechanism function calculated by the Šatava–Šesták method is [Formula: see text]. The path being favoured energetically in the dynamics is in the order: Path6 > Path5 > Path4 > Path1 > Path2 > Path7 > Path3.

scholarly journals High-Temperature Deformation of Naturally Aged 7010 Aluminum Alloy

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 581
Author(s):  
Abdulhakim A. Almajid
Keyword(s):  
Activation Energy ◽  
Aluminum Alloy ◽  
High Temperature ◽  
Threshold Stress ◽  
Activation Energies ◽  
Temperature Deformation ◽  
High Temperature Range ◽  
Temperature Range ◽  
True Activation Energy ◽  
Two Temperatures

This study is focused on the deformation mechanism and behavior of naturally aged 7010 aluminum alloy at elevated temperatures. The specimens were naturally aged for 60 days to reach a saturated hardness state. High-temperature tensile tests for the naturally aged sample were conducted at different temperatures of 573, 623, 673, and 723 K at various strain rates ranging from 5 × 10−5 to 10−2 s−1. The dependency of stress on the strain rate showed a stress exponent, n, of ~6.5 for the low two temperatures and ~4.5 for the high two temperatures. The apparent activation energies of 290 and 165 kJ/mol are observed at the low, and high-temperature range, respectively. These values of activation energies are greater than those of solute/solvent self-diffusion. The stress exponents, n, and activation energy observed are rather high and this indicates the presence of threshold stress. This behavior occurred as a result of the dislocation interaction with the second phase particles that are existed in the alloy at the testing temperatures. The threshold stress decreases in an exponential manner as temperature increases. The true activation energy was computed by incorporating the threshold stress in the power-law relation between the stress and the strain. The magnitude of the true activation energy, Qt dropped to 234 and 102 kJ/mol at the low and high-temperature range, respectively. These values are close to that of diffusion of Zinc in Aluminum and diffusion of Magnesium in Aluminum, respectively. The Zener–Hollomon parameter for the alloy was developed as a function of effective stress. The data in each region (low and high-temperature region) coalescence in a segment line in each region.

A NEW ORGANIC/INORGANIC HYBRID WITH HIGH ELECTRORHEOLOGICAL ACTIVITY

2002 ◽  
Vol 16 (17n18) ◽  
pp. 2454-2460 ◽  
Author(s):  
X. P. ZHAO ◽  
X. DUAN
Keyword(s):  
Activation Energy ◽  
Shear Stress ◽  
Necessary Conditions ◽  
Sol Gel ◽  
Root Temperature ◽  
Sedimentation Stability ◽  
Inorganic Hybrid ◽  
Active Particles ◽  
Static Shear

In-situ sol-gel method to prepare colloidal hybrids of surfactant modified polysucchride and titanium oxide has been presented, and experiments indicated these highly ER active particles exhibited a remarkable ER effect. The static shear stress can be up to 37 k Pa (shear rate 5 S -1) under DC field of 4 kV/mm at root temperature, well above that of simple blends of starch and TiO 2. In the meanwhile, temperature dependence and sedimentation stability were also greatly improved. Based on recent experimental facts, we find that dielectric properties and surface (interface) activity are two necessary conditions fulfilling the requirement of high ER activity. Adequate grinding of particles with oil can effectively enhance the shear stress, which may be owed to the decline of the activation energy needed for restructuring. It has provided us a new horizon for preparation of excellent ER materials and further studies should be continued to make.

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