ساختار و استحکام کامپوزیت کربن- تقویت شده با کربن

Strength and structure of carbon–carbon reinforced composite

ساختار و استحکام کامپوزیت کربن- تقویت شده با کربن

ABSTRACT

The atomistic simulations of carbon nanotube (CNT) – carbon reinforced composite material are reported. The studied composite samples are obtained by impregnating certain amounts of CNTs (3,3) and (6,6) into a pristine graphite matrix. The addition of CNTs is found to be of significant usefulness for the CNT–reinforced composites, since it allows to achieve extreme lightness and strength. Being impregnated into graphite matrix, CNTs are able to increase the critical component of its initially highly anisotropic Young modulus by 2–8 times. The linear thermal expansion coefficients do not exceed 10−6 to 10−5 K−1, making this material applicable for novel aviation and space vehicles. The degree of dispersion of CNTs within graphite matrix is found to drastically influence composite properties.

 

مقاومت به فرسایش و اکسیداسیون پوشش SiC برای کامپوزیت های کربن- کربن

Oxidation and ablation resistance of ZrB2–SiC–Si/B-modified

SiC coating for carbon/carbon composites

مقاومت به فرسایش و اکسیداسیون پوشش SiC اصلاح شده با ZrB2-SiC-Si/B

برای کامپوزیت های کربن/ کربن

ABSTRACT

ZrB2–SiC–Si/B-modified SiC coating was prepared on the surface of carbon/carbon (C/C) composites by two-step pack cementation. The coating could efficiently provide protection for C/C composites from oxidation and ablation. The improvement of oxidation resistance was attributed to the self-sealing property of the multilayer coating. A dense glassy oxide layer could afford the high temperature up to 2573 K and efficiently protect C/C composites from ablation.

اثر توزیع ZrB2 و SiC روی فرسایش کامپوزیت های کربن/کربن اصلاح شده

Effect of ZrB2 and SiC distributions on the ablation of

modified carbon/carbon composites

اثر توزیع ZrB2 و SiC روی فرسایش کامپوزیت های کربن/کربن اصلاح شده

ABSTRACT

To understand the effect of introduced phases’ distribution on the ablation of carbon/carbon (C/C) composites, C/C–ZrB2–SiC composites containing isolated (SZ-1) and coupled (SZ-2) ZrB2–SiC particles were prepared via controllable precursor infiltrations and pyrolysis, respectively. Ablation under oxyacetylene torch at both Z and XY directions showed that SZ-1 had better ablation resistance than SZ-2, while the surface temperature rose up to about 2400 °C. The ablated surface morphologies showed that a relative integrate layer of ablation products was formed on SZ-1, whereas the layer on SZ-2 was defective. It was believed that the dissimilar distributions of ZrB2–SiC particles in composites resulted in distinct structures of ablation products on the surfaces and consequently their different ablation behavior.

چاپ سه بعدی کامپوزیت کربن/کربن توسط زینتر لیزر انتخابی

Three dimensional printing of carbon/carbon composites

by selective laser sintering

چاپ سه بعدی کامپوزیت کربن/کربن توسط زینتر لیزر انتخابی

ABSTRACT

A novel three dimensional (3D) printing method is developed to fabricate complex carbon/carbon (C/C) composite components. The C/C composites with the high mechanical performance are achieved by combining the selective laser sintering and the chemical vapor infiltration-thermal treatment process. The C/C composites with a maximum density of 1.5 g/cm3 and bending strength of 100 MPa are obtained. Complex C/C composite parts with the minimum thickness of 0.5 mm are accurately fabricated with the computer-aided design technique. This developed 3D printing method can be well applied to the production of complex C/C composite parts with high precision and good mechanical performance.

 

رسوب دهی لیزر پالسی لایه های نازک CdTe و اثر دمای زیرلایه

CdTe thin films grown by pulsed laser deposition

using powder as target: Effect of substrate temperature

لایه های نازک CdTe رشد کرده به روش رسوب دهی لیزر پالسی و با استفاده از

پودر به عنوان ماده هدف : اثر دمای زیرلایه

ABSTRACT

CdTe thin films were deposited by pulsed laser deposition on Corning glass slides using CdTe powder as target. Films were grown at substrate temperatures ranging from room temperature (~25 °C) to 300 °C. The structural, compositional and optical properties were analyzed as a function of substrate temperature. X-ray diffraction shows that CdTe films grown at room temperature have hexagonal phase, while for higher temperatures the films have cubic phase. Raman and EDS indicate that films grew with Te excess, which suggests that CdTe films have p-type conductivity.

 

رسوب نشانی الکتروشیمیایی کادمیوم تلوریم نانوکریستال

Synthesis and characterization of electrochemically

deposited nanocrystalline CdTe thin films

شناسایی و سنتز لایه های نازک نانوکریستال CdTe

به روش رسوب نشانی الکتروشیمیایی

ABSTRACT

Electrodeposition is emerging as a method for the synthesis of semiconductor thin films and nanostructures. In this work we prepared the nanocrystalline CdTe thin films on indium tin oxide coated glass substrate from aqueous acidic bath at the deposition temperature 50 ± 1 °C. The films were grown potentiostatically from −0.60 V to −0.82 V with respect to saturated calomel reference electrode. The structural, compositional, morphological and optical properties were investigated using X-ray diffraction (XRD), energy dispersive analysis by X-rays (EDAX), atomic force microscopy (AFM), and UV–vis spectroscopy respectively and cyclic voltammetery. The structural and optical studies revealed that films are nanocrystalline in nature and possess cubic phase, also the films are preferentially oriented along the cubic (1 1 1) plane. The effect of cadmium composition on the deposited morphology was also investigated. The size dependent blue shift in the experimentally determined absorption edge has been compared with the theoretical predictions based on the effective mass approximation and tight binding approximation. It is shown that the experimentally determined absorption edges depart from the theoretically calculated values.

 

خواص لایه های رسوب نشانی شده CdTe به روش تبخیر باریکه الکترونی

Properties of CdTe films deposited by

electron beam evaporation

خواص لایه های رسوب نشانی شده  CdTe به روش تبخیر باریکه الکترونی 

ABSTRACT

Cadmium telluride thin films were prepared by electron beam evaporation on glass substrates kept at different temperatures in the range 30 - 300 °C. The films were characterized by X-ray diffraction, scanning electron microscopy and optical absorption measurements. The conductivity of the films was measured in the temperature range 100 - 300 K. While the low temperature data (100 - 200 K) could be explained by the variable range hopping process, the high temperature data (200 - 300 K) could be explained on the basis of Seto's model for thermionic emission of the carriers over the grain boundaries. Transmission spectra have indicated a direct band gap around 1.55 eV.

 

سنتز شیمیایی لایه های نازک نانوکریستال کادمیوم تلوریم

Structural and optical properties of CdTe-nanocrystals

thin films grown by chemical synthesis

خواص نوری و ساختار لایه های نازک نانوکریستال CdTe رشد کرده به روش سنتز شیمیایی

ABSTRACT

By mans of a chemical synthesis technique stoichiometric CdTe-nanocrystals thin films were prepared on glass substrates at 70 °C. First, Cd(OH)2 films were deposited on glass substrates, then these films were immersed in a growing solution prepared by dissolution of Te in hydroxymethane sulfinic acid to obtain CdTe. The structural analysis indicates that CdTe thin films have a zinc-blende structure. The average nanocrystal size was 19.4 nm and the thickness of the films 170 nm. The Raman characterization shows the presence of the longitudinal optical mode and their second order mode, which indicates a good crystalline quality. The optical transmittance was less than 5% in the visible region (400–700 nm). The compositional characterization indicates that CdTe films grew with Te excess.

 

شناسایی و سنتز نانوکریستال های CdTe شفاف فوتولومینسنت

Synthesis and characterization of

brightly photoluminescent CdTe nanocrystals

شناسایی و سنتز نانوکریستال های CdTe شفاف فوتولومینسنت

ABSTRACT

A new synthesis procedure for the preparation of spherical shaped CdTe nanocrystals (NCs) is presented, exhibiting bright luminescence with exceptionally high quantum efficiency (up to 85%). The growth of these NCs occurs in a non-coordinating solvent, octadecene, with the addition of oleic acid/tri-octylphosphine stabilizers, CdO as a precursor for the Cd monomers and additional Cd metal particles as a supplementary Cd reservoir source. The dependence of the crystalline quality and the optical properties of the CdTe NCs, on the initial Cd:Te precursors’ molar ratio, and the reaction duration were investigated. It was demonstrated that the NCs’ properties improved significantly as the initial Cd:Te molar ratios are increased. The obtained NCs’ properties were correlated with measurements of the Cd0 concentration in Cd metal particles, CdTe NCs and in Cd monomer solutions.

 

شناسایی کوآنتوم دات های CdTe در نانوذرات ژلاتینی

Synthesis and characterization of CdTe quantum dots

embedded gelatin nanoparticles 

شناسایی و سنتز کوآنتوم دات های CdTe محاط در نانوذرات ژلاتینی

ABSTRACT

Novel CdTe quantum dots (QDs) embedded gelatin nanoparticles (CdTe/gelatin nanoparticles) were synthesized via a two-step desolvation method. The morphology and size distribution of the nanoparticles were characterized by transmission electron microscope (TEM) and laser particle size analyzer. They are presented spherically and relatively uniform with a diameter of 150 nm. The luminescent properties of the nanoparticles were investigated by using fluorescence spectrophotometry and fluorescence microscopy. The fluorescence stability of nanoparticles was tested in vitro. It was found that the nanoparticles were stable in water and phosphate-buffered saline (PBS) solution (pH 7.4) for at least 15 days. A possible formation mechanism of the CdTe/gelatin nanoparticles was also proposed. The inherent stability and biocompatibility indicate that the nanoparticles are expected to be promising candidates for in vivo biological imaging studies.