Influence Of Preferred Orientation Research Articles

Influence of preferred orientation on the bioactivity of hydroxyapatite: a potential tooth repair and implant surface coating material

Abstract Bioactive hydroxyapatite (HAp) material was synthesized using a simple wet chemical precipitation and heat-treatment method from snail (Achatina achatina) shells and a phosphate-containing solution. According to X-ray diffraction patterns obtained, the heat-treatment caused a crystallographic preferred orientation along the HAp c-axis and thus, affected the material mineralization and bioactivity modeled in vitro using simulated body fluid (SBF) for 7 and 21 days. After 21 days of immersion, calcium and phosphate mineral concentrations in SBF decreased by 66% and 83%, respectively. This corresponded to a transformation from a poor calcium amorphous apatite phase (calcium phosphate) to a resorbing crystalline calcium apatite indicated by scanning electron microscopy micrographs. The material crystallite size (~15 nm), lattice parameters, physicochemical properties, and morphological characteristics were all typical of the human enamel apatite and, therefore, could be considered ideal for use in tooth repairs and implant surface coatings.

The influence of preferred orientation and poling temperature on the polarization switching current in PZT thin films

In this paper, Pb(Zr0.52Ti0.48)O3 (PZT) thin films with different preferred orientation were prepared on platinized silicon substrates by a modified sol–gel method. Our results indicate that the polarization switching current in PZT thin films is dependent on preferred orientation and poling temperature. In our measurements, (111)-oriented PZT has a larger polarization switching current than randomly oriented PZT, and with the increase of the degree of (111) preferred orientation and the poling temperature, the polarization switching current gradually increase. Considering the contact of PZT thin film with electrodes, the space-charged limited conduction (SCLC) combined with domain switching mechanism may be responsible for such phenomena. By analyzing the conduction data, we found the interface-limited Schottky emission (ES) and bulk-limited Poole–Frenkel hopping (PF) are not suitable for our samples.

Influence of preferred orientation on the electrical conductivity of fluorine-doped tin oxide films.

Current development of high-performance transparent conductive oxide (TCO) films is limited with tradeoff between carrier mobility and concentration since none of them can be improved without sacrificing the other. In this study, we prepare fluorine doped tin oxide (FTO) films by chemical vapor deposition with inclusions of different additives and report that the mobility can be varied from 0.65 to 28.5 cm2 V−1 s−1 without reducing the achieved high carrier concentration of 4 × 1020 cm−3. Such an increase in mobility is shown to be clearly associated with the development of (200) preferred orientation (PO) but concurrent degradation of (110) PO in films. Thus, at a constant high carrier concentration, the electrical conductivity can be improved via carrier mobility simply by PO control. Such a one-step approach avoiding conventional post-deposition treatment is suggested for developing next-generation FTO as well as other TCO films with better than ever conductivities.

Effects of morphology and geometry of inclusions on two-point correlation statistics in two phase composites

A spectral form of the two-point correlation functions for two-phase composites is presented and the effects of secondary phase morphology, geometry and volume fraction on the coefficients of the corresponding series are studied. Initially, a principal component analysis is performed on the coefficients of the series and then, the effects of different morphological and geometrical parameters of the second phase inclusions on two-point correlation functions are examined. A direct linkage between the principal components of the coefficients with the morphological features (inclusion shape, aspect ratio and size) is established and the influence of preferred orientation of the anisotropic inclusions is also investigated. Finally a composite hull is constructed using the principal components of the coefficients in a three-dimensional space, which helps in determining the interrelation of properties and microstructures of any composite containing these types of inclusions.

Two-dimensional time-resolved x-ray diffraction study of dual phase rapid solidification in steels

The high intensity heat source used for fusion welding creates steep thermal gradients of 100 °C/s from 1800 °C. Further, the influence of preferred orientation is important for the observation of a directional solidification that follows the dendrite growth along the ⟨100⟩ direction toward the moving heat source. In the present study, we observed the rapid solidification of weld metal at a time resolution of 0.01–0.1 s by a two-dimensional time-resolved x-ray diffraction (2DTRXRD) system for real welding. The diffraction rings were dynamically observed by 2DTRXRD with synchrotron energy of 18 keV while the arc passes over the irradiation area of the x-rays. The arc power output was 10 V-150 A, and the scan speed of the arc was 1.0 mm/s. The temperature rise in instruments was suppressed by a water-cooled copper plate under the specimen. Further, the temperature distribution of the weld metal was measured by a thermocouple and correlated with the diffraction patterns. Consequently, solidification and solid phase transformation of low carbon steels and stainless steels were observed during rapid cooling by 2DTRXRD. In the low carbon steel, the microstructure is formed in a two step process, (i) formation of crystallites and (ii) increase of crystallinity. In stainless steel, the irregular interface layer of δ/γ in the quenched metal after solidification is expected to show the easy movement of dendrites at a lower temperature. In carbide precipitation stainless steel, it is easy for NbC to grow on δ phase with a little undercooling. Further, a mistlike pattern, which differs from the halo pattern, in the fusion zone gave some indication of the possibilities to observe the nucleation and the early solidification by 2DTRXRD.

On Coincidence Site Lattice Modelling of Twins in the Sphalerite and Chalcopyrite Structures

AbstractCoincidence site lattice (CSL) modelling has been applied to determine the orientations and atomic structures of first order twin boundaries in the chalcopyrite structure. A rotation of 250°32' about [110] generated a CSL similar to that for the Ó = 3 sphalerite boundary, but with one in two cation columns being metal-metal anti-sites. The models predict one coherent boundary type i.e. (112)M-(112)T, and four lateral types, (110)M-(118)T, (1110)M-(112)T, (114)M-(114)T, (001)M-(114)T. Un-relaxed atomic models for the boundaries have been constructed. The coherent boundary is shown to differ from that in sphalerite by the inclusion of one in two Se columns having alternate atoms with either three Cu and one In nearest neighbours or vice versa. All of the [110] tilt boundaries in chalcopyrite are expected to be electrically active. A tentative list of the boundaries ranked by energy, electrical and chemical activity is given, along with comments on the influence of preferred orientation in polycrystalline films in the context of solar cells.

Preferred-Orientation Correction and Normalization Procedure forAb InitioStructure Determination from Powder Data

A preferred-orientation analysis for powder diffraction data is proposed, based upon an extension of the Wilson-plot intensity analysis, in order to correct the integrated intensities before the structure determination is started. The technique is based on an empirical exponential model for preferred orientation proposed earlier in the literature, of which a formal derivation is now given. Prerequisites are disc-shaped behaviour of the crystallites and spinning of the specimen. Furthermore, the indexed powder pattern and the unit-cell contents are required, but neither a structural model nor pole-figure observations are necessary. The influence of preferred orientation on the statistics of the normalized structure factor are assessed. It is shown that preferred orientation diminishes the quality of the triplet-phase-sum statistics. Improvements of the normalization procedure for powder diffraction intensities are proposed. Finally, it is shown by means of simulated powder data under which conditions the (most likely) preferred-orientation direction and corresponding strength can be established. Test results indicate that a reconstruction of the preferred-orientation model imposed is feasible provided the maximum individual intensity enhancement (or decrease) as a result of imposed preferred orientation is at least 70%, when compared with data in which preferred orientation is absent.

Simulation of the percolation behavior of quasi- and transversely isotropic short-fiber composites with a continuum model

This study uses a continuum model to predict the percolation threshold of composites consisting of electrically conducting fibers in an insulating matrix. The influence of preferred orientations (resulting from differences in processing conditions) on the threshold volume fractions is discussed. The model consists of an impenetrable cylindrical core surrounded by a fully penetrable soft shell. The hard core represents a physical fiber whereas the soft shell represents an effective range for electrical conduction in the otherwise insulating matrix. The simulation procedure consists of the addition of fibers to a control volume to probe the formation of a 3-D interconnected network. Finite size scaling (FSS) theory is used to predict the threshold volume fractions for infinite systems. The correlation length exponent was found to be 0·89, in agreement with values reported in our earlier study for particulate composites as well as in other literature studies. For transversely isotropic composites, the threshold values were found to be anisotropic for finite systems. However, the anisotropy vanishes as the system size becomes infinitely large. The correlation length exponent for these transversely isotropic composites was also found to be 0·89. The effect of shell thickness on the threshold volume fractions is investigated. The influence of fiber aspect ratio on percolation behavior is discussed, and the simulation results are compared with experimental results reported in the literature.

The influence of texture on superplasticity of the titanium alloy VT 6

This paper describes a specific influence of crystailographic texture on tensile properties of the titanium alloy VT6 under superplastic flow conditions. The texture effect has been examined on alloy states with identical microstructures but with different preferred grain orientations. Tests over wide temperature and strain-rate intervals have shown that the formation of a strong texture as a result of pretreatment of a titanium alloy leads to a decrease in flow stress, an increase in plasticity and a shift of the optimum strain-rate region to higher rates. Data on the effect of texture on the anisotropy of properties of the VT6 alloy are also presented. The present results suggest that the influence of preferred orientation on the characteristics of superplastic flow is a general phenomenon for finegrained superplastic materials.

The influence of texture on superplasticity of the Zn-22% Al alloy

The influence of preferred orientation on tensile properties of Zn-22 %Al has been examined on the specimens of similar microstructure but with different textures. Tests over wide temperature and strain-rate intervals have shown that the formation of a favourable texture leads to a decrease in flow stress, an increase in plasticity and a shift of the optimum rate region to higher strain rates. The influence of preferred grain orientation on the superplastic flow of the alloy rises with an increase in strain rate and decrease in the deformation temperature. The results of the structural study of the deformed alloy allow one to suppose that the influence of texture is connected with a change in grain-boundary structure.

The Effect of Anisotropy on the Creep of Polycrystalline Ice

AbstractQuantitative effects of crystallographic orientation fabrics are incorporated into the flow law for isotropic polycrystalline ice by the introduction of an enhancement factor applied to the isotropic fluidity. An aggregate is viewed to a first approximation as a collection of grains deforming independently by basal glide. The influence of preferred orientations on the mean intragranular rate of strain is treated in terms of a redistribution of the magnitude and orientation of resolved basal shear stress. A quantitative measure of this effect on the fluidity of the aggregate is provided through the development of a geometric tensor and a stress configuration parameter. Intergranular interference is then considered as a dissipative process modifying the fluidity of the aggregate.Empirical justification for the model at low octahedral shear stresses is provided by several laboratory creep tests on naturally anisotropic bore-hole specimens under both in situ and anomalous stress situations. Predicted enhancement factors ranged from approximately 0.2 to 2.8 and agree well with measured values. The tests were carried out in uniaxial compression and simple shear.

The Effect of Anisotropy on the Creep of Polycrystalline Ice

Abstract Quantitative effects of crystallographic orientation fabrics are incorporated into the flow law for isotropic polycrystalline ice by the introduction of an enhancement factor applied to the isotropic fluidity. An aggregate is viewed to a first approximation as a collection of grains deforming independently by basal glide. The influence of preferred orientations on the mean intragranular rate of strain is treated in terms of a redistribution of the magnitude and orientation of resolved basal shear stress. A quantitative measure of this effect on the fluidity of the aggregate is provided through the development of a geometric tensor and a stress configuration parameter. Intergranular interference is then considered as a dissipative process modifying the fluidity of the aggregate. Empirical justification for the model at low octahedral shear stresses is provided by several laboratory creep tests on naturally anisotropic bore-hole specimens under both in situ and anomalous stress situations. Predicted enhancement factors ranged from approximately 0.2 to 2.8 and agree well with measured values. The tests were carried out in uniaxial compression and simple shear.

Influence of preferred orientation on the powder pattern of deerite

Attention is drawn to the differences in the relative intensities of the reflections of deerite measured on a Guinier photograph and those obtained from diffractometer data (Langer et al., 1977), which were probably collected without taking adequate precautions to reduce the orientation effect. Powder data for deerite, which are in conformity with the structure, are presented.

A Study of Preferred Orientation by Energy‐Dispersive X‐Ray Diffraction

The influence of preferred orientation on integrated x‐ray intensities in powder specimen using energy‐dispersive diffraction method is investigated. The theory used is based upon examination of the polar axis density distribution. The measurements were carried out using the Schulz technique added with defocusing correction. Experimental results are given for three aluminium powder specimens.

The influence of preferred orientation on the line width of (hk) interferences

The influence of preferred orientation on the line width of (hk) interferences

Temperature Dependence, Orientation Correlation, and Molecular Fields in Second-Harmonic Light Scattering from Liquids and Gases

The properties of second-harmonic light scattering in fluids are derived in terms of the molecular polarizabilities, orientation correlation among molecules, and the molecular field Fα. Measurements of scattering intensity in CCl4 and water, from about 10° to 60°C, are reported. The variations with temperature, and therefore apparently the effects of changes of orientation correlation, are slight. The influence of preferred orientation in CCl4, of the type deduced from x-ray diffraction, is calculated. The third-rank molecular polarizability tensor consists of a fourth-rank tensor contracted with Fα, in addition to the term previously known, which is independent of Fα. With Fα arising from molecular multipole moments, the new term explains some measured depolarizations in liquids, and accounts for the spectral line, but not the background, observed in methane gas. In the case of molecular dipole moments, the new term can cause spectral narrowing.