Producing graphite with desired properties

Isotropic or anisotropic graphite is synthesized with precise control of particle size, distribution, and shape. The isotropic graphites are nearly perfectly isotropic, with thermal expansion coefficients two or three times those of ordinary graphites. The anisotropic graphites approach the anisotropy of pyrolytic graphite

Carbide coated fibers in graphite-aluminum composites

The study of protective-coupling layers of refractory metal carbides on the graphite fibers prior to their incorporation into composites is presented. Such layers should be directly wettable by liquid aluminum and should act as diffusion barriers to prevent the formation of aluminum carbide. Chemical vapor deposition was used to uniformly deposit thin, smooth, continuous coats of ZrC on the carbon fibers of tows derived from both rayon and polyacrylonitrile. A wet chemical coating of the fibers, followed by high-temperature treatment, was used, and showed promise as an alternative coating method. Experiments were performed to demonstrate the ability of aluminum alloys to wet carbide surfaces. Titanium carbide, zirconium carbide and carbide-coated graphite surfaces were successfully wetted. Results indicate that initial attempts to wet surfaces of ZrC-coated carbon fibers appear successful

Carbide coated fibers in graphites-aluminum composites

Research activities are described for a NASA-supported program at the Los Alamos Scientific Laboratory to develop graphite fiber-aluminum matrix composites. A chemical vapor deposition apparatus was constructed for continuously coating graphite fibers with TiC. As much as 150 meters of continuously coated fibers were produced. Deposition temperatures were varied from 1365 K to about 1750 K, and deposition time from 6 to 150 seconds. The 6 sec deposition time corresponded to a fiber feed rate of 2.54 m/min through the coater. Thin, uniform, adherent TiC coats, with thicknesses up to approximately 0.1 micrometer were produced on the individual fibers of Thornel 50 graphite yarns without affecting fiber strength. Although coat properties were fairly uniform throughout a given batch, more work is needed to improve the batch-to-batch reproducibility. Samples of TiC-coated Thornel 50 fibers were infiltrated with an aluminum alloy and hot-pressed in vacuum to produce small composite bars for flexure testing. Strengths as high as 90% of the rule-of-mixtures strength were achieved. Results of the examination of the fracture surfaces indicate that the bonding between the aluminum and the TiC-coated fibers is better than that achieved in a similar, commercially infiltrated material made with fibers having no observable surface coats. Several samples of Al-infiltrated, TiC-coated Thornel 50 graphite yarns, together with samples of the commercially infiltrated, uncoated fibers, were heated for 100 hours at temperatures near the alloy solidus. The TiC-coated samples appear to undergo less reaction than do the uncoated samples. Photomicrographs are shown

Carbide coated fibers in graphite-aluminum composites

The NASA-supported program at the Los Alamos Scientific Laboratory (LASL) to develop carbon fiber-aluminum matrix composites is described. Chemical vapor deposition (CVD) was used to uniformly deposit thin, smooth, continuous coats of TiC on the fibers of graphite tows. Wet chemical coating of fibers, followed by high-temperature treatment, was also used, but showed little promise as an alternative coating method. Strength measurements on CVD coated fiber tows showed that thin carbide coats can add to fiber strength. The ability of aluminum alloys to wet TiC was successfully demonstrated using TiC-coated graphite surfaces. Pressure-infiltration of TiC- and ZrC-coated fiber tows with aluminum alloys was only partially successful. Experiments were performed to evaluate the effectiveness of carbide coats on carbon as barriers to prevent reaction between alluminum alloys and carbon. Initial results indicate that composites of aluminum and carbide-coated graphite are stable for long periods of time at temperatures near the alloy solidus

A Few Problems on the Steiner Distance and Crossing Number of Graphs

We provide a brief overview of the Steiner ratio problem in its original Euclidean context and briefly discuss the problem in other metric spaces. We then review literature in Steiner distance problems in general graphs as well as in trees. Given a connected graph G we examine the relationship between the Steiner k-diameter, sdiamk(G), and the Steiner k-radius, sradk(G). In 1990, Henning, Oellermann and Swart [Ars Combinatoria 12 13-19, (1990)] showed that for any connected graph G, sdiam3(G) ≤(8/5)srad3(G) and conjectured that for all k ≥ 2 and a connected graph G, sdiamk(G) ≤ (2(k+1))/(2k−1)sradk(G). The paper also included an incorrect proof that sdiam4(G) ≤ (10/7)srad4(G). We provide a correct proof that sdiam4(G) ≤ (10/7)srad4(G) and show that for k ≥ 5, sdiamk(G) ≤ (k+3)/(k+1)sradk(G). By construction, we also show that the latter of these bounds is tight for each k ≥ 5. We then examine the Steiner distance of large sets in hypercubes. In particular, we show that for k = O(2n/n), the Steiner k-diameter of the n-cube is k + Θ((2n)/√n) using a recent result of Griggs. This section is a joint work with Éva Czabarka and László Székely. Finally, we move to structural properties of graphs in the context of crossing numbers. For positive integers n and e, let κ(n, e) be the minimum number of crossings among all graphs with n vertices and at least e edges. Under the condition that n \u3c\u3c e \u3c\u3c n2, Pach, Spencer, and Tóth [Discrete and Computational Geometry 24 623-644, (2000)] showed that κ(n, e)(n2)/(e3) tends towards a positive constant (called the midrange crossing constant) as n → ∞. We extend their proof to show that the midrange crossing constant exists for graph classes that satisfy a certain set of graph properties. As a corollary, we show that the the midrange crossing constant exists for the family of bipartite graphs. This section is a joint work with Éva Czabarka, László Székely, and Zhiyu Wang

Palynological Differences Between the Chuckanut and Huntingdon Formations, Northwestern Washington

Pollen and spore assemblages from the Tertiary coal-bearing Chuckanut and Huntingdon Formations were studied to determine the existence and location of the southern boundary of the Bellingham Basin. Ages of deposition were determined for each formation based on the flora recovered. The age of the Chuckanut Formation ranges from Middle Paleocene at its base to Late Eocene at its top. The age of the Huntingdon in northwestern Washington is Late Eocene to perhaps Earliest Oligocene. From the evidence of palynomorph ranges, no definite age breaks were found within the Chuckanut Formation, or between the Chuckanut and Huntingdon Formations. The structure of Squalicum Mountain, located near the southern boundary of the Bellingham Basin, was determined by taking numerous strikes and dips (Pevear and Reinink-Smith, unpublished data, 1980; Patrick, unpublished data, 1981). These data suggest that there is not a major angular unconformity at the southern boundary of the Bellingham Basin as previously reported. The data obtained also show that structurally, palynologically, and lithologically the Huntingdon Formation south of the Nooksack River is indistinguishable from the top of the Chuckanut Formation; therefore all of the rocks formerly mapped as Huntingdon Formation in this area should be included in the Chuckanut Formation