Joseph J. Ratto

Low level mobile liquid droplet mechanism allowing development of large platelets of high-Tc “Bi-2223” phase within a ceramic

Abstract A VLS-like mechanism is illustrated of how 3-Cu-layer Bi-HTSC (high temperature superconductor) is slowly formed from precursors by small, Bi/Pb rich, liquid droplets migrating over growing platelets, depositing ledges (steps) of product in their wakes. The difficulty of obtaining a pure 3-layer, i.e. without syntactic intergrowths, is explained.

Hydrogen incorporation during coal liquefaction

Coal hydrogenation reactions have been investigated using a deuterium tracer method which makes it possible to determine which structural positions in the coal react with hydrogen gas or donor solvent during liquefaction. 2H2 and/or tetralin-d12 were reacted with a Pittsburgh Seam coal at 13.8 to 22.1 MPa and 360 to 425 °C for 0.25 to 1.0 h. Hydrogenation and exchange indices were formulated to indicate the relative contribution of each type of reaction to the total H incorporation. In the coal-deuterium gas system, deuterium incorporation in the solvent-separated products increases in the order oil < asphaltene < preasphaltene < residue. However, in the coal-tetralin-d12-deuterium gas system, deuterium incorporation is similar in each of these four fractions. In both systems, 2H incorporation varies with structural position, with the α-aliphatic positions exhibiting the greatest extent of incorporation. The α-tetralyl radical appears to be an important intermediate in hydrogen transfer to and exchange with the coal. The results indicate that in the donor system the abstraction of hydrogen from the solvent by coal-derived radicals is involved in the rate-determining step of the formation of the soluble products. Evidence indicates that considerable direct interaction of the gas-phase hydrogen with the coal also occurs in the donor solvent system.

Flux penetration in high-Tc superconductors: implications for magnetic suspension and shielding

Two new effects associated with flux penetration and pinning in superconducting YBa2Cu3Ox are demonstrated. One of these is focussing of magnetic field lines by the superconductor and the other is magnetic suspension. The existence of stable equilibrium in suspension is shown to be related directly to hysteresis observed in the force-separation relation for a magnet and the superconductor. We also observe that the levitation height of a magnet increases with the magnet volume, contrary to results in the literature.

Magnetic forces in thallium- and bismuth-based superconductors

Hysteretic force-separation relations for Tl, Bi and Y based superconductors and a magnet are compared. The magnitudes of the forces, the hysteresis, and the magnetic stiffness were all largest in the three-layer Tl2Ba2Ca2Cu3Ox compound, indicating strong flux pinning. The hysteresis in both two and three layer thallium compounds was sufficient to generate attractive forces as the superconductor and magnet were moved apart. The use of remanent fields to improve stability of levitated and suspended magnets is described.

Investigation of Coal Hydrogenation Using Deuterium as an Isotopic Tracer

Mechanisms of coal hydrogenation were investigated by using a deuterium tracer method. This method makes it possible to determine which structural positions in the coal react with hydrogen during liquefaction. A hydrogenation index (HI) and exchange index (EI) were formulated to measure the amount of deuterium incorporated due to hydrogenation and exchange reactions, respectively. In the coal-deuterium system, deuterium incorporation was found to vary both with product fraction and with structural position. In contrast, the deuterium contents of the fractions from donor solvent experiments were essentially uniform. The donor solvent experiments did, however, show preferential deuterium incorporation with respect to structural position. Important information with regard to the reaction mechanisms in the donor solvent system was obtained by analyzing the spent solvent mixture that was recovered from the reaction products. The results indicate that not only hydrogen donation but also hydrogen exchange involving the α-positions of tetralin can have a significant role in stabilizing the fragments that form during the thermal decomposition of the coal. In addition, evidence was obtained that there is also a direct route for deuterium incorporation into the coal products from the gas phase without the participation of tetralin.

Ceramic Problems/Challenges in High Temperature Oxide Superconductors; Hysteretic Force Measurements As a New Analysis Tool

Increasing realism that high temperature oxide superconductors have many unusual and difficult aspects is setting in. It is becoming apparent that many of the problems/challenges are directly dependent upon the ceramic-like properties of these materials, when in polycrystalline form, and that many of these have been encountered before in other ceramic guises. We originally guessed, without making hundreds of specimens, that the peculiar R/T double step (with one drop at ~ 100K, and a second drop at ~ 85K) in the Bi HTSC and the inability initially to get R = 0 at > 100K came about through syntactic (coherent) intergrowths [1,2] which are so well known in minerals [2]. We therefore disagree with many ideas that have been put forward to explain this phenomenon [3–12]. We will show that problems with the Bi containing superconductors are extreme to the point where our personal decision is to abandon work on their polycrystalline forms in favor of Tl materials, at least for the time being. We prefer to make bad ceramics of a 125K material than of a 90K variety for obvious reasons. Space applications, where passive cooling, with attendant weight saving and increased robustness, are our major incentive.

Liquid Crystals II. Liquid Crystalline Properties of Transcinnamic Acid Esters

Research interest in room temperature liquid crystals has grown in recent years due to their increased applications in display devices. A current emphasis in the area has “been to obtain nematic materials that are colorless as well as stahle to atmospheric contaminants. Several low melting compounds and mixtures from the Schiff-base,2,3 azo and azoxy benzenes,4,5 chlorostilbenes,6 and benzoyloxybenzoate7,8 series have been investigated for these purposes. Many of these compounds exhibit properties that are undesirable for display applications such as instabilities toward moisture and u.v. radiation in addition to some yellow colorations.