Search results for "COMPOSITES"
showing 10 items of 1905 documents
The preparation and thermal evolution of polymeric gels with garnet stoichiometry in the CaOAl2O3SiO2 and CaOCr2O3SiO2 systems
1990
Abstract The synthesis of gels with garnet stoichiometry in the CaOAl 2 O 3 SiO 2 and CaOCr 2 O 3 SiO 2 systems and their evolution in thermal processing have been studied. Dried gels with the stoichiometry 3CaO.Al 2 O 3 .3SiO 2 show a homogeneous aspect without detectable crystalline phase. The thermal evolution of these gels indicates no formation of grossularite at temperatures up to 1000°C after 12 h. In the uvarovite garnet samples, 3CaO.Cr 2 O 3 .3SiO 2 , a small amount of crystalline phase was detected in the dried gels. The homogeneity of the gels was checked by scanning electron microscropy. The infrared study of these polymeric gels confirmed the presence of SiOMe (MeCr 3+ …
Influence of stoichiometry on high temperature intrinsic defects in fused silica
1992
Abstract The set of intrinsic defects, their generation, interactions and recombination reactions are discussed, including the participation of atomic and molecular oxygen, which allows one to take into account the stoichiometry of fused silica. The mathematical solution of the set of equations, which characterizes the equilibrium concentrations of intrinsic defects, gives the specific values of intrinsic defect concentrations at different temperatures and stoichiometries. The influence of such intrinsic defects frozen in at room temperature on the spectroscopic characteristics of fused silica is analyzed.
Drug release from alpha,beta-poly(N-2-hydroxyethyl)-DL-aspartamide-based microparticles.
2004
Abstract Spherical pH-sensitive microparticles have been prepared by reverse phase suspension polymerization technique. Starting polymer has been α , β -poly( N -2-hydroxyethyl)- dl -aspartamide (PHEA) partially derivatized with glycidylmethacrylate (GMA). PHEA-GMA copolymer (PHG) has been crosslinked in the presence of acrylic acid (AA) or methacrylic acid (MA) at various concentration. The obtained microparticles have been characterized by FT-IR spectrophotometry, particle size distribution analysis and scanning electron microscopy. In order to have information about water affinity of the prepared samples, swelling measurements have been carried out in aqueous media which simulate some bi…
Linear assembly of lead bromide-based nanoparticles inside lead(ii) polymers prepared by mixing the precursors of both the nanoparticle and the polym…
2019
Mixing precursors of lead(ii) polymers with those of lead bromide-based nanoparticles (CH3NH3PbBr3 perovskites or PbBr2), at room temperature and in the presence of cyclohexanemethylammonium bromide, generated colloidal nanocomposites which, when deposited on a hydrophobic surface led to long, one-dimensional, ordered and well-defined architectures. ispartof: CHEMICAL COMMUNICATIONS vol:55 issue:20 pages:2968-2971 ispartof: location:England status: published
Preparation, characterization and in vitro antimicrobial activity of ampicillin-loaded polyethylcyanoacrylate nanoparticles.
1998
In this paper, the experimental conditions for preparing ampicillin-loaded polyethylcyanoacrylate (PECA) nanoparticles are described. The effects of drug concentration and surfactant type in the polymerization medium on the particle size distribution and loading capacity were studied. The results of these studies show that only the type of surfactant has an impact on the nanoparticle dimensions. The release rate of ampicillin from PECA nanoparticles at pH 7.4 (extracellular value pH) performed either with and without esterases, show that the drug release is considerably increased in the presence of these exzymes. The results of drug release study at pH 1.1 (simulated gastric juice) are very…
A new method for generating fully isotropic laminates
2002
In this paper the authors propose some new kinds of isotropic laminates, made with identical anisotropic layers. In particular, these laminates satisfy some conditions which generalise the well-known Werren and Norris rules, in order to obtain fully isotropy, that is, isotropy of the three tensors A, B and D. To this purpose, the authors utilise some results found in a preceding research, namely the so-called quasi-trivial solutions. The way to form particular isotropic laminates that do not follow the Werren and Norris rule is also indicated. The paper ends with some numerical examples which illustrate the theoretical results found.
Investigation of absorber and heterojunction in the pure sulphide kesterite
2021
This paper aims to study the properties of the absorber layer and the heterojunction in kesterite solar cells. The Cu2ZnSnS4 (CZTS) thin films were layered on a glass substrate from a colloidal solution of metal salts and thiourea dissolved in a mixture of water and ethanol and deposited by spin coating technique. The samples were then heat treated in a furnace, in the presence of sulphur powder and under a nitrogen gas flow. The results revealed the formation of homogeneous layers of a pure kesterite phase of CZTS crystallites after heat treatment with correct stoichiometry and oxidation states. The optical transmission measurements indicate an energy band-gap of 1.4 eV and an absorption c…
Elastic properties of UV irradiated polyethylene-octene copolymer composites with functionalized multi-walled carbon nanotubes
2016
ABSTRACTPolyethylene-octene copolymer (E38) is melt compounded with carboxylated carbon nanotubes (CNT-COOH) in the presence of maleic anhydride grafted polyethylene (PEgMA). The effects of CNT-COOH in the amount of 1–10 wt. % on the mechanical properties of E38 based composite are investigated. It is revealed that addition of CNT-COOH considerably increases the stiffness and mechanical strength of the E38 based composites. The effect of UV irradiation on the structure as well as on the mechanical properties of E38/PEgMA/CNT-COOH composites is also investigated. Results of the investigation testify that UV resistance of the E38 based composites increases by increasing the content of CNT-COO…
Evolution of the bearing failure map of pinned flax composite laminates aged in marine environment
2020
Abstract Aim of the present paper is to evaluate how the bearing behavior of pinned flax composites can be influenced by their exposition to critical environment such as marine one. To this scope, flax fibers/epoxy pinned laminate was exposed up to 60 days to salt-fog environment, according to ASTM B 117 standard. In particular, samples having different hole diameter (D), laminate width (W), and hole center to laminate free edge distance (E) have been tested under single lap bearing tests at varying the aging exposition time. Following this procedure, an experimental 2D failure map clustering main failure modes was created by placing the experimental results in the plane E/D versus W/D rati…
Failure Map of Composite Laminate Mechanical Joint
2007
The aim of this research is to investigate the pin/hole contact stress of a composite laminate and failure modes when submitted to tensile bearing tests. The limit loads and failure modes are evaluated as a function of pin diameter and hole position. Analyzing the joint geometry effect on the fracture mechanisms, a failure map is obtained, identifying three regions of typical failure modes of mechanically fastened joints. A theoretical approach is proposed to identify the field of each fracture mode to obtain a simple experimental methodology to support the design of a particular joint laminate. In addition, a simplified numerical model is proposed to evaluate near the hole the stress/stra…