Fabrication of SiC-Whisker-Reinforced MoSi2 Composites by Tape Casting

In this paper, we describe a procedure for the processing of SiC-whisker-reinforced MoSi₂ composites via tape casting. Based on the characteristics of SiC whiskers and MoSi₂ powder in aqueous and nonaqueous solvents, a slip formulation (solvent, dispersant, binder, etc.) has been developed. The formulation developed allows for a uniform distribution of SiC whiskers in the matrix, easy separation of the tapes from the polymeric carrier, convenient control of both tape thickness and orientation of SiC whiskers, and a low binder burnout temperature. The latter is important for the prevention of the oxidation of MoSi₂ powder during the binder burnout in an oxidizing atmosphere.     

Melt characterization of ultra high molecular weight polyethylene using squeeze flow

A method for determining the melt viscosity and molecular weight of ultra high molecular weight polyethylene (UHMWPE) is described. The method, based on squeeze flow, was used to characterize seventeen UHM W-PE samples varying in molecular weight from 0.6 × 10⁶ to 5.1 × 10⁶ and in viscosity from 2.9 × 10⁶ to 3.4 × 10⁹ poise. A correlation between melt viscosity and molecular weight was demonstrated, but the reliability of a molecular weight determination decreased somewhat as molecular weight increased. As a predictor of melt processability, the method provides the speed and simplicity heretofore lacking in UHMW-PE characterization by solution viscosity while retaining high reproducibility.     

Studies of polymer–polymer solubility using a two-dimensional solubility parameter approach

The two-dimensional solubility parameter approach has been applied to the prediction of solubility of one polymer in another. The solubility parameters of a number of polymers have been calculated and the second dimension shown to improve the agreement between the calculated solubility and that measured using a ternary solution technique. The method proved most useful for predicting the effect of small structural modifications on solubility, and several examples of changing solubility, monitored by calculations and measurements, are given. Structural modifications included copolymer ratio variations and substitutions to affect polymer density or reduce polarity of functional groups. The effects of temperature and molecular weight on solubility are discussed in terms of regular solution theory, which could not account for the decrease in solubilities with increased temperature observed for several polymer–polymer systems.     

Evaluating the 1931 CIE color‐matching functions

The use of colorimetry within industry has grown extensively in the last few decades. Central to many of today's instruments is the CIE system, established in 1931. Many have questioned the validity of the assumptions made by Wright¹ and Guild,² some suggesting that the 1931 color‐matching functions are not the best representation of the human visual system's cone responses. A computational analysis was performed using metameric data to evaluate the CIE 1931 color‐matching functions as compared to with other responsivity functions. The underlying assumption was that an optimal set of responsivity functions would yield minimal color‐difference error between pairs of visually matched metamers. The difference of average color differences found in the six chosen sets of responsivity functions was small. The CIE 1931 2° color‐matching functions on average yielded the largest color difference, 4.56 ΔE. The best performance came from the CIE 1964 10° color‐matching functions, which yielded an average color difference of 4.02 ΔE. An optimization was then performed to derive a new set of color‐matching functions that were visually matched using metameric pairs of spectral data. If all pairs were to be optimized to globally minimize the average color difference, it is expected that this would produce an optimal set of responsivity functions. The optimum solution was to use a weighted combination of each set of responsivity functions. The optimized set, called the Shaw and Fairchild responsivity functions, was able to reduce the average color difference to 3.92 ΔE. In the final part of this study a computer‐based simulation of the color differences between the sets of responsivity functions was built. This simulation allowed a user to load a spectral radiance or a spectral reflectance data file and display the tristimulus match predicted by each of the seven sets of responsivity functions. © 2002 Wiley Periodicals, Inc. Col Res Appl, 27, 316–329, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10077     

Modification of Piezoelectric Characteristics of the Pb(Mg,Nb)O3-PbZrO3-PbTiO3 Ternary System by Aliovalent Additives

The effects of donor and acceptor doping on the piezoelectric properties of 18Pb(Mg_1/3Nb_2/3)O₃·39PbZrO₃·43PbTiO₃ternary solid solution have been investigated. The dopants influence in a pronounced way both the crystal structure and microstructure of the materials. The materials are transformed from the rhombohedral to the tetragonal structure, and the grain size is reduced when Nb ⁵⁺ cations are added. The crystal structures are transformed from the rhombohedral to the cubic structure, and grain growth is enhanced, when Mg ²⁺ cations are included. The values of K _P and K are maximized for 1-mol%-Nb⁵⁺-doped samples (K _P= 0.69, K = 1152); the Q _m factor and E _c are optimized for 4-mol%-Mg²⁺-doped samples ( Q _m= 1534, E _c= 0.56).     

Development of optical anisotropy in vitrains during carbonization

The purpose of this work was to examine the possible significance in the formation of metallurgical coke of the anisotropic spherical mesophase exemplified by that found during the carbonization of pitch-like materials, and to ascertain if the various types of optical anisotropy found in coke could form a basis for the characterization of cokes produced from different coals. Vitrains from a wide range of coals were carbonized at temperatures from 370 to 1000 °C and the types and amounts of optical anisotropy in the resulting semi-cokes and cokes were determined from microscopic examination, the anisotropic components being classified according to grain size of the granular mosaics and appearance. The anisotropy developed directly from the isotropic phase, appearing initially as a fine-grained mosaic. With increasing carbonization temperature, this fine-grained mosaic was transformed into progressively coarser-grained anisotropy, the extent of this transformation depending on the rank of the vitrain. It is therefore concluded that the formation, growth and coalescence of anisotropic spherical bodies, such as occurs during the carbonization of pitch, is not a necessary precursor of the mosaic anisotropy in coke. The type and amount of anisotropy developed provide a quantitative means of characterising different cokes.     

Root growth and phosphorus and potassium uptake by two corn genotypes in the field

In a field study P and K uptake by two corn (Zea mays L.) genotypes which differed in root growth was investigated. The effect of differences in root growth on P and K uptake was assessed using a mechanistic-mathematical model which describes nutrient uptake by growing plant roots in soil. Nitrogen was applied at 0 and 227 kg ha^–1 to Pioneer 3732 and B73xMo17 corn grown on Raub silt loam (fine-silty, mixed, mesic Aquic Argiudoll) and at 227 kg N ha^–1 to these two genotypes on Chalmers silt loam (finesilty, mixed, mesic, Typic Haplaquoll). Root growth and P and K uptake by the two corn genotypes was measured 31, 47, 75 and 91 d after planting on the Raub and 31, 47, 61 and 75 d after planting on the Chalmers soil.Root growth and P and K uptake by B73xMo17 was greater than that of Pioneer 3732 on N-fertilized Raub soil. On Chalmers soil the difference in root growth between the two genotypes resulted in an increase in K but not P uptake. The higher soil P level of the Chalmers appears to have offset possible differences in P uptake due to root size. There were no differences between the two genotypes in either the percentage of roots with root hairs, or the density or length of root hairs. Phosphorus and K uptake calculated with the simulation models for both corn genotypes on both soils over each of three growth periods agreed with observed P (Y = 0.68X + 1.71; r = 0.944^**) and K (Y = 0.88X + 15.52; r = 0.928^**) uptake. Differences in P and K uptake between B73xMo17 and Pioneer 3732 resulted primarily from the difference in root growth in the topsoil. A high correlation was found between root surface area and P (r = 0.893^**) and K (r = 0.928^**) uptake by both corn genotypes on both the soils.Journal paper No. 10,316 Purdue Univ. Agric. Exp. Stn., W. Lafayette, In 47906. Contribution from the Dep. of Agron. This paper was supported in part by a grant from the Tennessee Valley Authority.     

Location of steel reinforcement in concrete using ground penetrating radar and neural networks

Ground-penetrating radar is becoming increasingly popular for use as a non-destructive assessment method for investigating reinforced concrete structures. The amount of data collected however can be very large and take a significant level of subjective experience to interpret. This study focuses upon the use of a neural network approach to automate and facilitate the post-processing of ground penetrating radar results. The radar data is reduced to a simplified data set by using an edge detection routine. Signal reflections from reinforcing bars displaying a hyperbolic image format are detected using a multi-layer perceptron (MLP) network with a single hidden layer containing 8 nodes to recognise a simplified hyperbolic shape. Training and testing of the network was carried out making use of an emulsion analogue tank, simulating the properties of concrete, and using real concrete specimens. The results showed that the use of a MLP neural network approach could be quite effective in automating the identification and location of embedded steel reinforcing bars from a radar investigation. Accurate estimation of depth, or cover, requires a reliable knowledge of the dielectric properties of the concrete, and recent work using a specially-developed wideband horn antenna for direct determination of in situ properties is also outlined.