排序方式: 共有65条查询结果,搜索用时 203 毫秒
1.
The aim of this study is to shed more light on the formation of mullite and the kinetics of mullitization from sol-gel synthesized precursors. Tetraethylorthosilicate (TEOS) and aluminum nitrate nonahydrate (ANN) were used, as a source of silica and alumina, respectively, for the synthesis of homogenous mullite precursor powder. The mullitization process was characterized by thermogravimetry (TG), differential thermal analysis (DTA), thermodilatometric analysis (TDA), and x-ray powder diffraction (XRD) techniques. It was found that mullite started to crystalize at temperatures of 1050, 1200, and 1241 °C as determined by XRD, DTA, and TDA, respectively?. Mullite crystallization kinetics was thoroughly investigated under isothermal and non-isothermal conditions using DTA. The activation energy for mullite formation was calculated, for different crystallization fractions, following the Freidman, Kissinger, Boswell, and Ozawa methods. The average values were found to be 1282.92, 1324.30, 1336.93, and 1283.09 kJ/mol, respectively. The kinetic parameters and the crystallization mechanism were determined and the results were compared with those available in the literature. The Sestak Berggren SB(m,n) model was found to be the most suitable for the determination of mullite crystallization mechanism. The calculated average values of the Gibbs free energy (ΔG#), enthalpy (ΔH#), and entropy (ΔS#) for mullite formation, at different heating rates, were 433.98 kJ/mol, 1294.20 kJ/mol, and 566.23 J/mol.K, respectively. 相似文献
2.
Aliakbar Dehno Khalaji Mahsa Nikookar Catherine Charles Smail Triki Franck Thetiot Debasis Das 《Journal of Cluster Science》2014,25(2):605-615
A novel bidentate Schiff base ligand L (L = N-(4-amino-2-chloro-phenyl)-2-hydroxybenzaldehyde) and the subsequent octahedral manganese(III) Schiff base complex MnL 3 have been synthesized and characterized by, FT-IR spectroscopy and elemental analyses (CHN). Additionally, Schiff base ligand has been characterized by 1H NMR spectroscopy. Thermogravimetric analysis of the ligand and its metal complexes reveals their thermal stability and decomposition pattern. Thus, the MnL 3 complex has been investigated as a novel precursor for the facile preparation of Mn3O4 nanoparticles via solid-state thermal decomposition under aerobic conditions, at a temperature of ca. 450 °C The resulting Mn3O4 nanocrystals were characterized by FT-IR spectroscopy, X-ray powder diffraction (XRPD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The XRPD studies reveal the characteristic diffraction peaks indexed to the Mn3O4 hausmanite structure, while the absence of additional peaks tends to clearly indicate the high purity of the sample. In addition, the TEM/SEM investigations displayed the nanoplate shape of the rather monodisperse crystalline Mn3O4 nanoparticles, with an average diameter of ca. 10 nm. The statistical distribution of the nanoparticles size has to be provided with an histogram graphic. 相似文献
3.
4.
5.
This work is concerned with the existence of unbounded positive solutions for a second-order nonlinear three-point boundary
value problem on the positive half-line. The interesting points of the results are that the nonlinearity depends on the solution
and its derivative and may change sign. Moreover, it satisfies general polynomial growth conditions. New existence results
of nontrivial single and multiple positive solutions are proved using recent fixed point theorems on cones in a special Banach
space. 相似文献
6.
Smail Djebali 《International Journal of Mathematical Education in Science & Technology》2013,44(5):677-689
The purpose of this paper is to understand whether there exists any link between the uniform continuity of a real function defined on an unbounded interval and its growth at infinity. The primary objective is to present some results from teaching experience which help in the comprehension of this notion and yield some classroom techniques. It is well known that a uniformly continuous function has a monomial growth; it will be proved that there does not exist another growth of positive order. After introducing three kinds of growth, some results are recalled in connection with the behaviour near infinity of a uniformly continuous function. Using a series of counterexamples, it is shown that the uniform continuity of a function cannot be described by its asymptotic behaviour near infinity. Finally, some useful properties of the averaging convergence are reviewed, and how this is related to uniform continuity is investigated. 相似文献
7.
Melouki Azzedine Terchi Smail Ouali Dehimi Bounab Abdelhakim 《Journal of Thermal Analysis and Calorimetry》2022,147(10):5637-5648
Journal of Thermal Analysis and Calorimetry - Polystyrene/organo-Algerian montmorillonite hybrid material was prepared by radical copolymerization of styrene monomer in the presence of the double... 相似文献
8.
Vytria Piscitelli Cavalcanti Smail Aazza Suzan Kelly Vilela Bertolucci Joo Pedro Miranda Rocha Adriane Duarte Coelho Altino Júnior Mendes Oliveira Laís Campelo Mendes Maysa Mathias Alves Pereira Ludmila Caproni Morais Moacir Rossi Forim Moacir Pasqual Joyce Dria 《Molecules (Basel, Switzerland)》2021,26(19)
Garlic is a health promoter that has important bioactive compounds. The bioactive extraction is an important step in the analysis of constituents present in plant preparations. The purpose of this study is to optimize the extraction with the best proportion of solvents to obtain total phenolic compounds (TPC) and thiosulfinates (TS) from dried garlic powder, and evaluate the antioxidant activities of the optimized extracts. A statistical mixture simplex axial design was used to evaluate the effect of solvents (water, ethanol, and acetone), as well as mixtures of these solvents, after two ultrasound extraction cycles of 15 min. Results showed that solvent mixtures with a high portion of water and pure water were efficient for TPC and TS recovery through this extraction procedure. According to the regression model computed, the most significant solvent mixtures to obtain high TPC and TS recovery from dried garlic powder are, respectively, the binary mixture with 75% water and 25% acetone and pure water. These optimized extracts presented oxygen radical absorbance capacity. Pure water was better for total antioxidant capacity, and the binary mixture of water–acetone (75:25) was better for DPPH scavenging activity. These optimized extracts can be used for industrial and research applications. 相似文献
9.
Smaïl Djebali 《Journal of Mathematical Analysis and Applications》2009,353(1):215-672
This paper is devoted to the existence and properties of solutions of the following class of nonlinear elliptic differential equations Δu(x)+f(x,u(x))+g(‖x‖)x⋅∇u(x)=0, x∈Rn, ‖x‖>R. We prove existence of positive solutions vanishing at positive infinity. Our approach is based on the subsolution and supersolution method. The nonlinearity f covers both sublinear and superlinear cases and does not necessarily satisfy f(x,0)≡0. The asymptotic behavior of solutions is also described. 相似文献
10.
In this work, we develop a general framework in which Noncommutative Quantum Mechanics (NCQM), characterized by a space noncommutativity matrix parameter θ=εijk
θk and a momentum noncommutativity matrix parameter
β=εijk
βk, is shown to be equivalent to Quantum Mechanics (QM) on a suitable transformed Quantum Phase Space (QPS). Imposing some constraints
on this particular transformation, we firstly find that the product of the two parameters θ and β possesses a
lower bound in direct relation with Heisenberg incertitude relations, and secondly that the two parameters are equivalent but with opposite sign, up to a dimension factor depending on the
physical system under study. This means that noncommutativity is represented by a unique parameter which may play the role of a fundamental constant
characterizing the whole NCQPS. Within our framework, we treat some physical systems on NCQPS : free particle, harmonic oscillator, system of two-charged particles, Hydrogen atom. Among
the obtained results, we discover a new phenomenon which consists of a free particle on NCQPS viewed as equivalent to a harmonic oscillator with Larmor frequency depending on β,
representing the same particle in presence of a magnetic field
$\vec{B}=q^{-1}\vec{\beta}$. For the other examples, additional
correction terms depending on β appear in the expression of the energy spectrum. Finally, in the two-particle system case, we emphasize the fact that for two opposite charges noncommutativity is effectively feeled with opposite sign. 相似文献