Change In Orientation Of Crystallites Research Articles

Enhancing the corrosion resistance of mild steel coated zinc studies

In the presence of a newly created brightener, the zinc metal is coated on steel using the electro deposition process. Experiments using hull cells are used to optimize the settings and components of plating baths. Tafel Polarization and EIS techniques were used to conduct corrosion experiments, which made it possible to investigate the brilliant zinc coating's effective corrosion resistance. SEM and Reflectance spectroscopy both confirm that the bright zinc coating has modified surface morphology. XRD analysis is used to study and validate changes in crystallite orientation and phase structure. Electrochemical methods and theoretical molecular dynamic (MD) simulations were used to examine the interaction between Zn and the metal surface. FTIR spectroscopy has been used in blend investigations which impacts on the physical characteristics of polymer blends. The results of these research showed how novel brighteners can improve zinc deposits' brightness and corrosion resistance when applied to mild steel substrates.

Fluorination of Donor-Acceptor Copolymer Active Layers Enhances Charge Mobilities in Thin-Film Transistors.

Several recent reports have demonstrated that fluorinated analogues of donor/acceptor copolymers surpass nonfluorinated counterparts in terms of performance in electronic devices. Using a copolymer series consisting of fluorinated, partially fluorinated, and nonfluorinated benzotriazole, we confirm that the addition of fluorine substituents beneficially impacts charge transport in polymer semiconductors. Transistor measurements demonstrated a factor of 5 increase in carrier mobilities with the degree of fluorination of the backbone. Furthermore, grazing-incidence X-ray diffraction data indicates progressively closer packing between the conjugated cores and an overall greater amount of π-stacking in the fluorinated materials. It is likely that attractive interactions between the electron-rich donor and fluorinated electron-deficient acceptor units induce very tightly stacking crystallites, which reduce the energetic barrier for charge hopping. In addition, a change in crystallite orientation was observed from primarily edge-on without fluorine substituents to mostly face-on with fluorinated benzotriazole.

Spatial Variation in Structural, Morphological and Optical Properties of Aluminum-Doped ZnO Thin Films Grown by 30°-Incident Radio Frequency Magnetron Sputtering

The effect of discharge power and spatial variation, across a distance of , in structural, morphological, optical, and electrical properties of aluminum-doped ZnO thin films grown by 30°-incident radio frequency (rf)-magnetron sputtering were investigated. A significant change in orientation of crystallites of films corresponding to central and near-edge regions of the samples was observed. With increase in rf power, films of both central and near-edge regions of the sample exhibited decrease of c-axis orientation perpendicular to substrate surface and the deterioration was relatively severe for the central regions. For all films, visible transmittance was more than 80%, and remained uniform spatially. The optical bandgap of the central portions was found to be higher than that of the near-edge regions of films except the film for which both portions had the same bandgap. Dark resistivity at the center of the sample was always lower than that at the edge, away from the center. The observed variation in the film properties are discussed in terms of tilt of the substrates and bombardment of the growing films by energetic particles.

Electrical and optical properties of Sn doped CuInO2 thin films: Conducting atomic force microscopy and spectroscopic ellipsometry studies

Tin doped CuInO2 thin films deposited by rf magnetron sputtering technique show columnar structure with (006) preferred orientation. Conducting atomic force microscopy measurements show the presence of nanoconductivity regions when the current flow direction is along the in-plane InO6 layer and absence of conducting regions when the current direction is along O–Cu–O layers perpendicular to the film surface. The strong anisotropy observed in the electrical properties of tin doped samples is due to the preferred crystallite orientation and highly anisotropic delafossite structure. A large change in the electrical conductivity value and activation energy value in undoped films and tin doped samples has also been explained in terms of change in crystallite orientation on doping. Spectroscopic ellipsometry measurements have been used to determine the optical constant and dielectric function of CuInO2 and CuInO2:Sn films and show a band gap value of 4.5 eV in tin doped samples due to removal of structural defects.

Crystallite orientation during melting of oriented ultra-high-molecular-weight polyethylene

The changes in crystallite orientation during melting of oriented ultra-high-molecular-weight polyethylene (UHMW PE) were investigated by means of wide-angle X-ray scattering. The orientation distribution of crystallites in drawn UHMW PE is composed of two components differing in width. The narrow and broad components revealed in this study indicate the existence of two classes of crystallites with different orientability. Some of the crystallites are oriented almost perfectly even at low-draw ratios, while the others do not orient so effectively. The analysis of melting behaviour of such a texture composed of orthorhombic crystals indicates that highly oriented crystallites are formed by taut molecules and transform first to the hexagonal phase, while the molecules constituting low-oriented crystallites melt directly to the typical amorphous phase. The increase in orientation of highly oriented crystallites during their partial melting, observed in the samples kept at constant length and even those allowed to shrink under constant load, can be explained by the kinetic factor proposed by Ziabicki.

Non-hookean stress-strain response and changes in crystallite orientation of carbon fibres

The non-hookean stress-strain response of carbon fibres was investigated in relation to changes in crystallite orientation with tensile stress. Various one-dimensional array models and a mosaic model were examined. Amongst these models, only the mosaic model in which the stress of the crystallites can be transmitted in both the transverse and the axial directions showed any quantitative agreement with the measured increases in the tensile modulus and the crystallite orientation with tensile stress. This suggests that deformation of the crystallites is constrained with increasing tensile stress. It was also found that the ratio of the tensile stress of the fibre to that of the crystallites is close to the crystallite volume fraction rather than the ratio of the fibre density to the crystallite density.

Studies on swelling of cotton fibers in alkali metal hydroxides. IV. Influence of initial fiber properties and variations in fine structure on tensile behavior

AbstractNineteen varieties of cotton, covering a wide range of fiber properties like maturity, fineness, and strength uniformity ratio were swollen in 5N KOH and NaOH at room temperature (30 ± 1°C). Tensile and fine structural properties of the resultant samples were measured and their relationship with initial fiber properties was examined. A comparative evaluation of fiber properties of KOH swollen fibers with those swollen in NaOH revealed that, irrespective of variety, fibers swollen in the former reagent retain higher tenacity. It was further noted that fine structural parameters like crystallite orientation and amorphous content which influence tensile properties become modified differently while swelling in the two reagents. While changes in crystallite orientation were found to be less drastic during KOH swelling, unlike in NaOH, the reverse was found to be true with crystalline content. These changes in fine structure could more or less explain the variation in tensile properties of fibers swollen in these two reagents. © 1995 John Wiley & Sons, Inc.

Effects of the presence/absence of HCl during gate oxidation on the electrical and structural properties of polycrystalline silicon thin-film transistors

The influence of the presence or absence of HCl during gate oxidation at 1100 and 1150 °C on the electrical and structural properties of polycrystalline silicon thin-film transistors was investigated. Devices processed without HCl exhibited a lower leakage current, a larger current switching ratio, a 25%–55% increase in carrier mobility, and a 21%–30% lower grain-boundary trap density. Materials investigation showed that the improvement was not primarily due to an increase in grain size, which was about 1000 Å irrespective of processing conditions, but to a change in crystallite orientation. X-ray diffraction measurements showed an increased {110} texture in devices processed without HCl. In addition, in the latter devices, dopant diffusion under the gate from the source and drain contacts was reduced by 7.6% to 12%. A linear relationship was observed between the average grain-boundary trap density and the average lateral dopant diffusion length. These findings are explained by considering the point defect chemistry and its relationship to grain-boundary mobility. Removal of HCl from the oxidation ambient increases the concentration of silicon self-interstitials. The increased migration of these point defects to grain boundaries enhances their nonconservative motion and therefore increases grain-boundary mobility. This in turn, allows the boundary to more completely acquire a lower-energy configuration. This lower-energy configuration of the boundary contains a minimum of broken bonds and therefore minimizes both the grain-boundary electrical activity and the diffusion along grain boundaries.

Microstructural rearrangement during heat treatment of drawn nylon 66 fiber

AbstractMelt‐spun nylon 66 fibers were drawn and subsequently heat treated isothermally and quenched. The heat‐treated fibers were then examined by wide‐and small‐angle x‐ray scattering (WAXS and SAXS), by differential scanning calorimetry (DSC), and by static mechanical testing. These measurements allow one to follow microstructural changes taking place during the course of the heat treatment. WAXS results show that as the treatment progresses, the crystallites become both more perfect and more disoriented with respect to the fiber axis. SAXS results show crystallite thickening. DSC results show that the melting point increases, goes through a maximum, and then decreases as the heat treatment progresses. The tensile modulus decreases with time to an asymptotic level. The changes in crystallite perfection and thickness occur more rapidly than do the changes in crystallite orientation, modulus, and melting point. A model is proposed whereby the two time frames are related to intracrystalline and intercrystalline processes, respectively.

THE EFFECTS OF TENSION IN HEAT SETTING OF NYLON 6 FIBERS

The effects of the tension in heat setting on the fine structure were studied for nylon 6 fiber. The fine structure is much affected by tension, especially the degree of molecular orientation of amorphous region. The following facts were observed.The tension in heat setting of nylon 6 fibers has no considerable effect on the degree of crystallinity, whereas it exerts influence on the amorphous region.Wide angle X-ray diffraction shows a little change in crystallite orientation after heat setting even though much shrinkage occurs.In the phenol solution of equal concentration, the fibers which the shrink during heat seting swell along fiber axis, though the extended fibers shrink. By this swelling properties, it suggested that some of the molecules in the amorphous region change from the elongated to the folded conformation when the heat is set under zero tension.The diffusion velocity of dye in fiber becomes very low by tension in heat setting, though the saturated amount of dye at equilibrium does not change greatly. The orientation of molecule in amorphous region is increased remarkably by the tension in the heat set. And the diffusion coefficient of dye in fiber has linear relation to the orientation factor of molecule in the amorphous region.The tension given in heat setting has very important bearing upon the dye-ability. These results indicate that it is very important to keep tensile condition exact for heat setting process of nylon 6 fiber.

Chain folding in oriented nylon 66 fibers

AbstractWhen heated to high temperatures under zero tension, some of the molecules in oriented nylon 66 filters change from the elongated to the folded conformation, with no change in crystal orientation. This transformation is shown by a combination of structural and physical property measurements: wide and small angle x‐ray diffraction, broad and narrow line nuclear magnetic resonance, sonic modulus, density, shrinkage, and tensile properties. A fortyfold increase of the intensity of the discrete small angle x‐ray diffraction is obtained for treatments between 160‐and 255°C. as well as an increase of the length of the long period and a change from a smeared four‐point to a sharp two‐point diagram. Wide angle x‐ray measurements show little change in crystallite orientation for treatments up to 250°C. even though much shrinkage occurs. Disruption of some type is observed by sonic measurements, as would be expected if new folds occurred. An increase of density and x‐ray crystallinity confirms that heating causes much additional crystallization. The high temperature NMR spectra for these more crystalline yarns show a much larger proportion of fluidlike segments. Shrinkage of the yarns during the heating appears to be governed by the number of folds which are introduced. Tensile strength is reduced by this introduction of folded chains.

Gas permeability of highly oriented dibutyl maleate–ethylene copolymer films

AbstractThe effects of extreme uniaxial orientation on gas permeation through dibutyl maleate–thylene copolymer films have been examined. Gases employed were helium, argon, and methane. Permeability constants were measured as functions of temperature between 25 and 55°C., in unstretched film and in films stretched to elongations of 490, 512, 540, and 608% (breaking point). Uniaxial cold drawing of dibutyl maleate–ethylene copolymer films into the stable necking region (elongation ca. 490%) causes only a small (30%) decrease in permeability and virtually no change in apparent activation energy of permeation; when the necked films are further stretched to elongations approaching the breaking point (ca. 600%), a significant decrease in permeability and increase in activation energy is observed. It is deduced that the major changes in crystalline texture and arrangement which this polymer undergoes in the necking process have only a minor effect upon total level of crystallinity, amorphous‐phase properties, and diffusional impedance offered by the crystallites, suggesting that changes in crystallite orientation, perfection, and shape throughout the drawing process are compensatory. When necked polymer is further stretched, however, severe restraints are imposed upon the mobility of oriented chain segments in the amorphous regions, which are primarily responsible for the observed large changes in permeabilities and permeation activation energies.

Changes in orientation of crystallites during stretching and relaxation of polyethylene films

AbstractA microbeam camera has been used in x‐ray diffraction studies of the changes which occur in orientation of crystallites in polyethylene film when the film is stretched and later relaxed. The collimator of the microbeam camera, 100 μ in diameter, allows one to follow the orientation changes very closely in the necked‐down region of a stretched sample. The stretching of polyethylene proceeds by alignment of the a‐axes of the crystallites perpendicular to the stretching direction with the planes containing b‐ and c‐axes perpendicular to the a‐axis but randomly oriented, followed by a gradual change to a state in which the c‐axes become more nearly aligned in the stretching direction although perfect alignment is not achieved. On relaxation, either the orientation of the c‐axis parallel to the original stretching direction becomes less perfect, or folding of the oriented crystallites about the b‐axis takes place. In the latter case the preferred crystallographic directions parallel to the stretching direction have indices such as [u0w]. These orientation changes during stretching and relaxation of the stretched samples suggest that crystallites in polyethylene films consist of parallel arrangements of platelets containing b‐ and c‐axes. The distinction between directions in the reciprocal lattice and the crystal lattice is clarified. A number of x‐ray diffraction patterns and charts of dimensional changes illustrate the paper.