Pore morphology in pressurized lignite coal: A small angle x-ray scattering investigation

The morphological changes in lignite coal at two different pressures, using small angle x-ray scattering, have been investigated. All the scattering profiles are interpreted in terms of surface fractal morphology. It is observed that the surface fractal dimension does not change appreciably under the experimental pressure range, while the volume of micro-cracks and inter-particle pore space is reduced with increasing pressure. By and large, the constant value of the surface fractal dimension of all the specimens, as calculated from the scattering profiles, indicates that the roughness on the pore coal interface remains almost unaffected under the experimental pressure range. The validity of single scattering approximation for this experiment has also been confirmed by the observation of the identical nature of the small angle scattering profiles with respect to change of wave lengths, namely, 0.154 nm. (Cu K) and 0.072 nm (Mo K), of the probing radiation.     

Gloss and Texture Control of Powder Coated Films

The desired appearance of powder coated film depends upon the specific industrial application. While a glossy, mirror-like finish with a high distinctiveness of image (DOI) is required for automotive clear coat applications, much outdoor equipment and many household appliances require smoothly textured finishes that hide surface irregularities, fingerprints, and surface markings. This textured finish of powder coated film, often termed orange peel appearance, can be controlled by adjusting the chemical formulation and the physical properties of the powder and by optimizing the electrostatic application process. These adjustments allow a wide-ranging control of gloss and orange peel texture. The chemical formulation of the powder is often determined by the functional needs of the coatings: providing protection against corrosion, heat, UV radiation, and physical impact. In many cases where the formulation cannot be changed, the electrostatic spraying process for the powder can be adjusted to achieve the desired gloss and texture.

In electrostatic powder coating, back corona on the deposited powder layer often causes defects in the film. However, if the electrical field intensity inside the powder layer is below the breakdown level, the adverse effect of back corona can be avoided, thus improving the uniformity of the deposited powder layer. In the absence of back corona, increasing the high voltage applied to the corona gun improves both the smoothness and the glossiness of cured films. Back corona can be reduced by increasing the surface conductivity of the powder. Increasing the relative humidity during spraying also decreases the roughness, since the augmented surface conductivity allows the powder layer charge to decay faster. The optimal relative humidity value for applying powder for uniform film thickness was found to be 60%; increasing humidity beyond that point led to surface degradation, possibly due to excess moisture trapped in the powder layer. While the surface smoothness increased, the glossiness did not vary significantly with the change in relative humidity. Another factor for film surface properties is the "hiding power" of the unevenness of the substrate surface. A rough substrate can be responsible for a rough film surface when film thickness is less than 25 µm. It was found that films 40 to 50 µm thick can successfully cover scratches of about 20 µm depth on the substrate. Typical values of film waviness varied from 1.5 to 3 µm, and film roughness varied from 0.2 to 0.4 µm for epoxy film with 60 to 65 µm thickness.     

Taylor diffusion for a natural convective flow through a vertical channel

Dispersion of a solute in natural convective laminar flow through a vertical channel is investigated when there is a uniform axial temperature variation along the walls. It is observed that the effective Taylor diffusion coefficient is oscillatory in nature for small and moderate values of Rayleigh number r and it increases gradually with increase in Rayleigh number (r > 3.0).     

Interface study and boundary smoothing on designed composite material microstructures for manufacturing purposes

The manufacturability of composite material microstructures designed by the homogenized topology optimization method has to be considered when bringing the design into reality. In this paper, numerical studies are conducted on multiphase material microstructures that have negative coefficients of thermal expansion, for the purpose of improving manufacturability. Realistic manufacturing factors are considered, including the diffusion interface between two constituent phases and vectorized toolpath design. The effect of the mixture interface between two solid phases is examined by homogenization analysis. An image-processing program is developed to smooth out the boundaries of the topological structure to facilitate toolpath design. Numerical results show that the diffusion interface between two solid material phases reduces the effective negative thermal expansion property of the whole microstructure. The designed material properties are retained and converge after boundary smoothing .     

Hall effects on combined free and forced convective hydromagnetic flow through a channel

Hydromagnetic free and forced convection in a parallel plate channel permeated by a transverse magnetic field has been considered taking Hall effects into account. When there is a uniform axial temperature variation along the walls, the primary flow shows incipient flow reversal at the upper plate for an increase in temperature along that plate. Similarly flow reversal at the lower plate occurs for a decrease in temperature along that plate. Hall currents are found to exert a destabilizing influence on the flow. The skin-friction for the cross-flow increases with the Hall parameter. The induced magnetic field and the heat transfer characteristics in the flow are also determined.     

A model of convection-induced oscillatory structure formation in peritectic alloys

In the two-phase region of a peritectic system, experimental studies have shown that the primary phase (α) often forms a large treelike structure that is surrounded by peritectic phase (β). The formation of this novel structure has been attributed to the presence of convection in the liquid. Here, specific physical mechanisms of convection-induced treelike structure formation are proposed. A mathematical model based on advection-diffusion of solute, with prototype flows for advection, is presented and solved numerically to show that an oscillating fluid motion can give rise to a complex oscillatory, treelike structure. Three different regimes are established: diffusive, steady convective, and unsteady convective regimes. In the diffusive regime, a banded structure is predicted within a narrow composition range, and the spacing of the bands is dictated by the nucleation undercoolings of the two phases. Under steady convection, the primary phase transforms into the peritectic phase with a curved α:β interface. Finally, in the presence of oscillating convection, a treelike shape of the primary phase is predicted, as observed experimentally.     

Direct materials deposition: designed macro and microstructure

Solid freeform fabrication of engineering materials is now possible using the Direct Metal Deposition (DMD) technique. Closed loop optical feedback system for DMD makes realistic components with dimensional accuracy of 0.01 inch. On the other hand, close control of the process parameter can provide microstructure of choice. Such continued capability to control macro and microstructure is creating considerable interest. H13 tool steel is one of the difficult alloys for deposition due to residual stress accumulation from martensitic transformation. However, it is the material of choice for the die and tool industry. DMD offers Copper chill blocks and water cooling channels as the integral part of the tool. On the other hand ZrO₂ was co-deposited with nickel superalloys using DMD. This process thus is amenable to produce both macro and microstructure to a designed specification. This paper briefly reviews the state of the art of DMD and describes the microstructure and mechanical properties of selected engineering alloy systems deposited by DMD. Received: 5 April 1999 / Reviewed and accepted: 19 July 1999     

Electrostatic Microencapsulation Technique for Producing Composite Particles

The electrostatic microencapsulation process and the various means of achieving such encapsulation for developing composite particles with two or more powders is briefly reviewed, with a particular focus on the dual-function sorbent/scintillation particles for use in radionuclide selective sensing. In preparing the composite particles, two different types of particles, an ion-exchange resin and scintillating microbeads, were used. The sorbent particles capture and preconcentrate the radionuclide of interest (e.g., 99 Tc) from solution. The scintillating microbeads are used to convert the energy of radioactive decay into that detectable light that can be deducted by a photomultiplier tube arrangement. To simulate the electrostatic microencapsulation of resin and scintillators, several surrogate materials such as acrylic powder (mean particle diameter, d 50 =23 µm), red toner (d 50 =16 µm), resin (d 50 =134 µm), and fluorescent latex spheres (d 50 =2 µm) were used. A microencapsulation tower was constructed to use corona guns operating at high voltages of opposite polarity to charge the "host" and "guest" particles. Experimental arrangements and test results are presented. The results show that if polymer particles are used and if one of the two powders is smaller than 10 µm in diameter, the electrostatic and van der Waals forces provide enough interparticle adhesion to bond the guest and host particles through plastic deformation. Interparticles adhesion between resin (d 50 =133 µm) and toner (d 50 =15 µm) showed that the composite particles were stable in water suspension. For larger particles, such as resin and scintillators, the use of a binding agent is necessary to form stable composite particles.

electrostatic microencapsulation particle coating groundwater monitoring composite particles radionuclide detection     

The effect of convection on disorder in primary cellular and dendritic arrays

Directional solidification studies have been carried out to characterize the spatial disorder in the arrays of cells and dendrites. Different factors that cause array disorder are investigated experimentally and analyzed numerically. In addition to the disorder resulting from the fundamental selection of a range of primary spacings under given experimental conditions, a significant variation in primary spacings is shown to occur in bulk samples due to convection effects, especially at low growth velocities. The effect of convection on array disorder is examined through directional solidification studies in two different alloy systems, Pb-Sn and Al-Cu. A detailed analysis of the spacing distribution is carried out, which shows that the disorder in the spacing distribution is greater in the Al-Cu system than in Pb-Sn system. Numerical models are developed which show that fluid motion can occur in both these systems due to the negative axial density gradient or due the radial temperature gradient which is always present in Bridgman growth. The modes of convection have been found to be significantly different in these systems, due to the solute being heavier than the solvent in the Al-Cu system and lighter than it in the Pb-Sn system. The results of the model have been shown to explain experimental observations of higher disorder and greater solute segregation in a weakly convective Al-Cu system than those in a highly convective Pb-Sn system.     

An efficient built-in self testing for random-access memory

The authors propose a test algorithm for pattern-sensitive faults in large-size RAM with high circuit density. The algorithm tests an n-bit RAM in 195√n time to detect both static and dynamic pattern-sensitive faults over the 9-neighbourhood of every memory cell. A 4 Mb RAM can be tested by the proposed algorithm several thousand times faster than the conventional sequential algorithms for detecting pattern-sensitive faults. The test speedup has been achieved by writing a test data simultaneously over many cells, and the stored data are tested simultaneously by a parallel comparator and error detector in a read operation. The existing RAM architecture has been modified very little so that the proposed technique can be implemented very easily even in switched-capacitor DRAM (dynamic random-access memory) with low intercell pitch width. The test procedure has also been applied to built-in self-testing (BIST) and is compared with other BIST implementations