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31.
In this work, an experimental study on the chemical etching reaction of polycrystalline p-type 6H-SiC was carried out in HF/Na2O2 solutions. The morphology of the etched surface was examined with varying Na2O2 concentration, etching time, agitation speed and temperature. The surfaces of the etched samples were analyzed using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) Fourier transform infrared spectroscopy (FT-IR) and photoluminescence. The surface morphology of samples etched in HF/Na2O2 is shown to depend on the solution composition and bath temperature. The investigation of the HF/Na2O2 solutions on 6H-SiC surface shows that as Na2O2 concentration increases, the etch rate increases to reach a maximum value at about 0.5 M and then decreases. A similar behaviour has been observed when temperature of the solution is increased. The maximum etch rate is found for 80 °C. In addition, a new polishing etching solution of 6H-SiC has been developed. This result is very interesting since to date no chemical polishing solution has been developed on the material. 相似文献
32.
Walid Rekik Houcine Naïli Tahar Mhiri 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(4):i50-i52
Potassium gadolinium polyphosphate, KGd(PO3)4, was synthesized using the flux method. The atomic arrangement consists of an infinite long‐chain polyphosphate organization. Two types of chains, with a period of eight PO4 tetrahedra, run along the [101] direction. The Gd atoms have an eightfold coordination, while the K atoms have nine O‐atom neighbours. 相似文献
33.
A New Higher Order Shear Deformation Model for Static Behavior of Functionally Graded Plates
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Tahar Hassaine Daouadji Abdelouahed Tounsi & El Abbes Adda Bedia 《advances in applied mathematics and mechanics.》2013,5(3):351-364
In this paper, a new displacement based high-order shear deformation theory is introduced
for the static response of functionally graded plate. Unlike any other theory, the number
of unknown functions involved is only four, as against five in case of other shear deformation
theories. The theory presented is variationally consistent, has strong similarity with
classical plate theory in many aspects, does not require shear correction factor, and
gives rise to transverse shear stress variation such that the transverse shear stresses
vary parabolically across the thickness satisfying shear stress free surface conditions.
The mechanical properties of the plate are assumed to vary continuously in the thickness
direction by a simple power-law distribution in terms of the volume fractions of the
constituents. Numerical illustrations concerned flexural behavior of FG plates with
Metal-Ceramic composition. Parametric studies are performed for varying ceramic volume
fraction, volume fraction profiles, aspect ratios and length to thickness ratios. The
validity of the present theory is investigated by comparing some of the present results
with those of the classical, the first-order and the other higher-order theories. It
can be concluded that the proposed theory is accurate and simple in solving the static
behavior of functionally graded plates. 相似文献
34.
Ahmed El Kharroubi Abdelhak Yaacoubi Abdelghani Ben Tahar Kawtar Bichard 《Queueing Systems》2012,70(4):299-337
In this paper we consider the variational problem in the non-negative orthant of ℝ3. The solution of this problem gives the large deviation rate function for the stationary distribution of an SRBM (Semimartingal
Reflecting Brownian Motion). Avram, Dai and Hasenbein (Queueing Syst. 37, 259–289, 2001) provided an explicit solution of this problem in the non-negative quadrant. Building on this work, we characterize reflective
faces of the non-negative orthant of ℝ
d
, we construct boundary influence cones and we provide an explicit solution of several constrained variational problems in ℝ3. Moreover, we give conditions under which certain spiraling paths to a point on an axis have a cost which is strictly less
than the cost of every direct path and path with two pieces. 相似文献
35.
Ikram Dhouib Zakaria Elaoud Tahar Mhiri Abdelaziz Daoud 《Journal of chemical crystallography》2012,42(5):513-518
Abstract
The salt bis benzyl ammonium monohydrogentetraoxoarsenate(V) monohydrate [C6H5CH2NH3 +]2HAsO4 2−·H2O, M = 373.92, Triclinic, P−1. a = 6.514(1), b = 8.910(2), c = 15.061(3) ?, α = 99.26(2), β = 93.93(1), γ = 97.64(1)°, V = 851.5(3), Z = 2, D x = 1.460, λ (MoKα) = 0.71073 ?, μ = 0.99 mm−1, F(000) = 126, T = 20(2) °C, final R = 0.673 for 5488 unique reflections. Planes of HAsO4 2− alternate with planes of C6H5CH2NH3 + groups. The structure consists of infinite parallel two-dimensional planes built of mutually connected ions and water molecules by strong O–H···O and N–H···O hydrogen bonding. There are no contacts other than van der Waals interactions between the layers. Differential scanning calorimetry study on bis benzyl ammonium monohydrogentetraoxoarsenate(V) monohydrate was carried out. The infrared of polycrystalline samples of this compound have been recorded at room temperature. 相似文献36.
This work reports the synthesis of novel 1,4,3,5-oxathiadiazepanes 4,4-dioxides from the reaction of N'-benzyl-N-(2-hydroxyethyl)-sarcosine or proline sulfamide with aromatic aldehydes under acid catalysis. To prepare the starting materials N-Boc-sulfamide derivatives of sarcosine or proline were alkylated with benzyl alcohol under Mitsunobu reaction conditions, the Boc group was removed chemoselectively by acidolysis, and the resulting product reduced to the corresponding alcohol in good yields. 相似文献
37.
Nasreddine Ennaceur Khaled Jarraya Anu Singh Isabelle Ledoux-Rak Tahar Mhiri 《Journal of Physics and Chemistry of Solids》2012,73(3):418-422
Aiming at the development of new proton conducting solids, recent studies of the NaH2PO4·H2O–NaH2AsO4·H2O system have lead to the synthesis of a new compound NaH2(PO4)0.48(AsO4)0.52·H2O (NDAP). Calorimetric studies have confirmed the presence of four reversible phase transitions (abbreviated by PhT), at 257/270 (PhT, IV), 261/290 (PhT, III), 267/301 (PhT, II) and 317/317.5 K (PhT, I) (for cooling/heating processes, respectively). It is shown that the III and IV phase transitions are of a first order type, with a “order-disorder and displacive” character, accompanied by specific dielectric anomalies. The behavior of the dielectric constant ε′r and of tan δ shows that, at 272 K, the (PhT, IV) could be ferroelectric–paraelectric. As for the (PhT, III) at 296 K, it leads to a superionic–protonic phase; a jump in the conductivity is associated to this transition with an unusual high value of conductivity 1.07×10?4 Ω?1 cm?1 and a low activation energy 0.39 eV (Kh. Jarraya et al.). Quandratic nonlinear (NLO) properties of NDAP powder was confirmed efficiency of the grown crystal by the Kurtz and Perry second harmonic generation (SHG) technique. 相似文献
38.
Benkhedda Mohammed Boufendi Toufik Tayebi Tahar Chamkha Ali J. 《Journal of Thermal Analysis and Calorimetry》2020,139(1):411-426
Journal of Thermal Analysis and Calorimetry - In the present paper, the first and second laws of thermodynamics are utilized to select the optimized position of porous insert to achieve maximum... 相似文献
39.
40.
Adib Ghaleb Aouidate Adnane Lakhlifi Tahar Bouachrine Mohammed Maghat Hamid Sbai Abdelouahid 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2018,92(12):2464-2471
Russian Journal of Physical Chemistry A - Copper-catalyzed azide–alkyne cycloaddition (CuAAC) is a straightforward way for making covalent connections between building blocks containing... 相似文献