Papers by Keyword: Cavities

Abstract: The extraction process is a crucial part of the synthesis of Molecularly Imprinted Polymers (MIP). The process will have a significant impact on the number of its cavities that affects the polymers’ ability to recognize targets with the same physical and chemical properties as the analytes. Caffeine polymers have been prepared by the cooling-heating method using methacrylic acid (MAA) as a monomer, ethylene glycol dimethacrylate (EDMA) as a crosslinker, benzoyl peroxide (BPO) as an initiator, and chloroform as a solvent. The resulting caffeine polymer powder was extracted using chloroform, methanol / acetic acid (1:20), and methanol, respectively. Finally, the polymer powder is washed using the aquabidest, which is heated at 60°C. The results of FTIR, XRD, and SEM characterization showed that caffeine concentration was significantly reduced. The number of cavities obtained from caffeine MIP is 604 more than before extracted, which is 132 pieces.

Abstract: This study deals with cavities under square footing which resulted from gypsum dissolving due to water flow in gypseous soil. This process leads to collapse of soil structure and progressive compression. A model was developed for governing the mass-transport to assess the variation of gypsum content of the soil during dissolution by ground water flow then cavity formation was adopted. A general three-dimensional finite element program (PLAXIS 3D) was selected for numerical analysis method to generate the solution. The study included a number of variables and their effect on bearing capacity of gypseous soil such as (gypsum content, cavity volume and location). The cavity was represented as axis and plane cavity which has square section. The results show that the most dangerous case is found when the cavity locates at the center of footing base (Z/B = 0), where the bearing capacity decreased by (14, 37, and 69%) for (20, 30, and 40%) gypsum dissolving ratio respectively. Also, the bearing capacity decreased when the cavity volume increases due to increasing dissolution ratio. The effect of cavity became disappear after (Z/B = 4). While, when using plane cavity, there was no cavity at center of footing base (Z/B = 0) because it considered as a hole not cavity. When using plane cavity, the bearing capacity decreased by (28, 43, and 53%) for (20, 30, and 40%) dissolving ratio respectively when (Z/B=1). The effect of cavity on the bearing capacity would be disappear as the distance from footing center increase until it became disappear at (Z/B = 6 m). The plane cavity is more dangerous than axis cavity.

Abstract: This study concerns the ground soils of the second runway of the Es-Sénia airport in Oran (Algeria). This airport was built on a very complex hydro geotechnical site when underground cavities, following the dissolution of gypsum soil, were found during the before-construction geologic studies. Several, techniques are used in laboratory (Permeability, triaxial compression tests at various confining pressure, and hydric tests in saturated and unsaturated conditions) and for in situ it’s used the results of SPT and pressure-meter tests. A comparison of parameters of two soils identified in saturated and partially saturated conditions by in situ and laboratory tests was performed in order to respond to questions of the similarity of hydro mechanical properties of two soils as well as their statistical representativeness of the in-situ reality. It is found that, in respect to the studied parameters, laboratory results are statistically significant and reconstituted soils is statistically representative of natural soil reconstitution.

Abstract: The study investigates alterations in surface morphology of microcrystalline diamond (MCD) film under reciprocating sliding test conditions. The MCD film was grown by microwave plasma enhanced chemical vapor deposition (MW-PECVD) on (100)-oriented Si wafer. The surface morphology was characterized by optical microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) and mechanical profilometry. The formation of ripples on the wear scar surfaces was observed. The normalized wear rate (mm³/mN) of diamond film was evaluated using different approaches in order to understand the influence of diamond film deflection to wear.

Abstract: Ion implantation into 4H-SiC induces a local gradient of strain which increases with the nuclear energy losses. With the increase of temperature the strain tends to become uniform in the whole implanted area requiring the migration of particles. In case of helium implantation, defects are more stabilized and their evolutions observed post thermal annealing are concomitant with the surface swelling. The local modifications imputed to the ion process lead to the formation and the pile-up of stacking faults in the highly damaged region.

Abstract: Amorphous silicon dioxide layers were implanted with 100 keV Ar ions to a relatively high fluence in a tentative to generate cavities in the oxide. Different oxide layers were used, obtained either by thermally growth or by chemical vapor deposition (CVD) on Si substrate. In all SiO₂ layers, cavities are not formed in the as-implanted state. However, in the transmission electron microscope, under electron beam, the combined effect of irradiation induced defects and implanted rare gas leads to the formation of cavity bands giving the unique opportunity to observed in-situ cavity growth. The cavity morphology and their distribution are found to be dependent on the silicon dioxide growth process. For thermally grown SiO₂ layer, a homogeneous cavity band is formed, centered at the mean ion path, with an average cavity size of 20 nm. For CVD SiO₂ layer, slightly smaller cavities are formed in two distinct bands. The formation of cavities is discussed in light of gas and defects interaction and field-induced migration whereas the cavity distribution is discussed in terms of self-organization.

Abstract: Technology of plasma nitriding is widely used to increase the surface hardness, fatigue strength, wear and corrosion resistance of steels [1, 2]. In this study, the properties of plasma nitrided steel of various diameters at various pressures are investigated. There was obtained new information about possibilities of plasma nitriding technology and its applications to the cavities with diameters of 6, 8 and 10 mm and a penetration depth of 400 mm.

Abstract: Defects of pieces rolled by cross wedge rolling (CWR) have great effect on its practical applications. With reference to the center-pressure method used often in the forging, the effects of non-uniform temperature field on defects were studied by using the three-roll CWR tests under different cooling conditions and the coupled thermo-mechanical finite element models. The porous can be reduced or even eliminated when the billets were rolled with a controlled non-uniform temperature filed. The optimal temperature gradient was determined by FEM, which can be used in practical applications.

Abstract: SIMOX (Separation-by-Implantation-of-Oxygen) is an established technique to fabricate silicon-on-insulator (SOI) structures by oxygen ion implantation into silicon. The main problem of SIMOX is the very high oxygen ion fluence and the related defects. It is demonstrated that vacancy defects promote and localize the oxide growth. The crucial point is to control the distribution of vacancies. Oxygen implantation generates excess vacancies around RP/2 which act as trapping sites for oxide growth outside the region at the maximum concentration of oxygen at RP. The introduction of a narrow cavity layer by He implantation and subsequent annealing is shown to be a promising technique of defect engineering. The additional He implant does not initiate oxide growth in the top-Si layer of SOI.

Abstract: The grain boundary sliding and the formation of slipped bands and cavitations during biaxial tensile deformation were examined in fine grained Al-Mg alloy. Biaxial tensile testing was conducted with cruciform specimens at initial strain rates of 10-4 to 101s-1. It was found that at the same equivalent strain conditions, the number of cavities under biaxial tension is significantly greater than that under uniaxial tension. A greater prevalence of slipped bands and grain separations were clearly observed under biaxial stress than under uniaxial stress. It was suggested that development of slipped bands resulted from the formation of elongated cavities and multiple deformed bands under biaxial stress. Additionally, the m-value under biaxial stress remained at about 0.3 over a wide range of strain rates. The effects of grain separation and formation of cavities were related to the motion of grain boundary sliding, grain size and loading conditions.