Sarbajit Ghosal

Particle size-density relation and cenosphere content of coal fly ash

The results are reported of detailed physical characterization of six ashes from coals representative of those burned in US power plants. Centrifugal separation was used to classify the ashes into six density categories in the range 3.2 g cm−3. The size distributions of all density classes were determined in the range 1–200 μm. For most of the density classes, log-normal functions, truncated outside the measurement limits, described the size distributions quite well. For all six ashes, the median diameter initially decreased and then increased with increasing particle density. The influence of particle structure on this large variation (up to sixfold) in size is discussed. Centrifugal separation using a liquid of density 2.2 g cm−3 was used to estimate the mass fraction of cenospheres (i.e. particles with trapped interior ‘bubbles’) in the ashes. This fraction varied from 95 wt%. The cenosphere content was apparently uncorrelated with coal rank but was positively correlated with the total mineral content of the coal. The median diameters of the cenospheric fractions were found to be two to three times those of the non-cenospheric (solid) fractions. The density-size data were used to determine the Fe2O3 distribution in the ashes.

Chemical composition and size distributions for fly ashes

Abstract Inter-particle variations in particle diameter and chemical composition in coal fly ashes are significant, and can be quantitatively studied using currently available microanalytical techniques. One such technique, computer controlled scanning electron microscopy (CCSEM), is now routinely used to determine chemical compositions and diameters of individual fly ash particles, using statistically significant sample sizes. This paper proposes simple mathematical formulae for expressing the inter-particle variations. Additionally, these formulae can be used for economically storing the large amount of data generated by CCSEM. Two apparent limitations of the CCSEM technique are discussed — one relating to the measurement of size distribution, and the other to determining the iron oxide distribution in the ash. These limitations are imposed by statistical considerations, and by artifacts of sample preparation techniques.

Growth of giant magnetoresistance multilayers: Effects of processing conditions during radio-frequency diode deposition

The magnetotransport properties of giant magnetoresistance multilayers are significantly effected by the atomic-scale structure of the interfaces between the nonferromagnetic conducting and ferromagnetic (FM) metal layers. The interfacial roughness and the extent of intermixing at these interfaces are both known to be important. A combination of experimental and multiscale modeling studies have been used to investigate control of interface structure during multilayer growth by rf diode deposition and the consequences of such control for magnetotransport. Experiments were conducted to evaluate the dependence of the magnetotransport properties of NiFeCo/CoFe/CuAgAu multilayers upon the growth conditions (background pressure, input power), and to link the roughness of vapor-deposited copper layers to the same process parameters. These experimental studies reveal the existence of intermediate background pressure (20 mTorr) and plasma power (175 W) that resulted in the highest magnetoresistance and a strong se...

Real-time model-based control system design and automation for gelcast drying process

Gelcasting is a new method for manufacturing advanced structural ceramics for use, for example, in the aerospace industry. The process involves a drying stage, where moisture, which constitutes approximately a quarter of the mass of the part, is removed in a commercial dryer. The control system design for the gelcast ceramic drying process is complicated by the requirement of minimizing the drying time while avoiding cracking during shrinkage of the part. The paper describes the application of Lyapunov theory for finding an exponentially stablizing controller for the nonlinear drying model. A RealSim/sup (T/)Rapid Prototyping model and the MATRIXx/sup (T)/ design automation environment are used for real time control, as well as feedback system implementation. It is shown that the proposed design and testing automation process with a user friendly interactive animation (IA) graphical user interface (GUI) provides an effective and efficient environment for real time control of the gelcast drying process.

The infrared refractive indices of CHBr3, CCl4 and CS2

Abstract Spectrally resolved data for the real part, n(λ) of the complex refractive index, n = n + i k , of bromoform (tribromomethane, CHBr3) at room temperature (298 K) in the wavelength range 1–13 μm are presented. The measurements were made using the near-normal reflectance technique. The accuracy of the method was confirmed by comparing measured values of n(λ) of water with available data in the literature. For bromoform, n(λ) is found to decrease gradually from 1.58 to 1.51 over this wavelength range, except in the region of anomalous dispersion near absorption bands at 3.3 and 8.7 μm. A complete infrared window for extinction measurements on suspended particulates can be obtained using CCl4 in the spectral range 1–6 μm, CHBr3 in the ranges 6.0–7.4 μm and 11–13 μm, and CS2 in the range 7.4–11.0 μm. The data for n(λ) of CCl4 in the range 1–9 μm, and those for CS2 in the range 7.4–11.0 μm, obtained from reflectance measurements, compare favorably with data available in the literature.

An Integrated Tool for Estimation of Material Model Parameters

In this paper, we present results on estimating material model parameters from inverse analysis of full-field deformation data that was obtained with a prototype of a novel integrated tool consisting of a digital image correlation system and software for data analysis and parameter estimation. Such a tool is needed for characterizing the properties of new materials, and for calibrating and validating material models. The stereo microscope-based image analysis system may be used for measurements at temperatures up to 75°C, and field sizes of approximately 1 mm. The Graphical User Interface (GUI)-based parameter estimation tool integrates modules for image data analysis and inverse analysis, and incorporates features for interfacing the tool with commercial finite element (FEM) packages. The GUI, together with a micrograph of the sample, is used to select a subset of the imaged region for analysis, and for specifying sample grain boundaries needed for developing the FEM model. Data analysis includes data averaging to reduce measurement noise, and filtering to correct for rigid body translations and rotations. The inverse analysis module runs the FEM model under experimental loading conditions within its iterative loop, using the downhill simplex method for parameter estimation. The methodology was successfully validated from measurements on a superalloy sample.

IDENTIFICATION OF MECHANICAL PROPERTIES OF MATERIALS FROM FULL-FIELD DEFORMATION MEASUREMENTS

Abstract For small errors in grain angle measurements, we show that estimating elastic material properties from deformation measurements of a sample under load can be done efficiently by iterating between elasticity parameter and grain angle estimation. The efficiency is obtained because estimating the elasticity parameters is in general a convex optimization problem.