CONTROL OF COKE FORMATION FROM HYDROCRACKED ATHABASCA BITUMEN

The mechanism of formation of carbonaceous deposits from hydrocracked Athabaca bitumen is shown to result in both isotropic and anisotropic solids. The formation of mesophase spheres present as a separate liquid phase has been observed in the laboratory High severity results in the formation of an increased amount of anisotropic solid which is observed in both laboratory and commercial samples. The formation of these deposits in the downstream separators of a commercial plant has occurred and is a hindrance to reliable operation. A strategy to reduce the formation of these deposits in a commercial plant was evaluated in a series of laboratory experiments. The use of process-derived gas oils can be used as quench oil to lower the temperature of the commercial separators. There was no increase in the rate of toluene insoluble formation as a result of the use of quench oils, which allowed the full advantage of the temperature decrease to be achieved. A qualitative comparison of the build-up of deposits in the commercial separators is provided from separator vessel monitoring.     

Oxygen-enrichment of YBa2Cu3 YBa2Cu3O7-δ using the fluidization techniqueusing the fluidization technique

The oxygen-deficient phase of the highT _c superconductor, YBa₂Cu₃O₇, was oxygen-enriched using the fluidization technique to give good superconducting properties. The normal method of oxygen treatment at 900°C for 24 h and at 600°C for 24 h has been reduced to just one treatment at 600°C for 12 h by the fluidization technique to achieve almost the same strength of superconducting signal for the YBa₂Cu₃O₇ powder, which establishes the attractiveness of the latter route for the large-scale preparation of superconducting material. The particle sizes were in the range 0–90, 90–180 and 180–420 μm. The fluidized particles were crystalline with orthorhombic distortion.T _c ^onset , estimated using the a.c. magnetic susceptibility method, was 91·3 K. The volume fraction of superconducting material in the product was 83·7–85·3%, one of the highest values reported so far for YBa₂Cu₃O₇.     

Phase diagram modeling for titanium alloys with light element impurities

It is well known that low levels of light element impurities, such as oxygen and nitrogen, can significantly modify phase equilibria in conventional titanium alloys. However, although the role of nitrogen and oxygen as alpha stabilizers is well established, little quantitative work exists in ternary and higher order systems. Moreover the effect of such elements on equilibria with phases other than cx-and P-Ti is often unknown. The problems in measuring light elements at the microscopic level adds to the difficulty of establishing partitioning, and old axioms are often transferred to new alloys with little evidence that they are applicable. As part of a current program on titanium alloys, phase diagram modeling has been performed for a variety of titanium alloys with additions of oxygen and nitrogen. This paper presents results for the system Ti-Al-V-O-(N,C) with particular reference to the O additions to the commercially important alloy Ti-6A1-4V. This paper was presented at the International Phase Diagram Prediction Symposium sponsored by the ASM/MSD Thermodynamics and Phase Equilibria Committee at Materials Week, October 21–23,1991, in Cincinnati, OH. The symposium was organized by John Morral, University of Connecticut, and Philip Nash, Illinois Institute of Technology.     

Preparation of TEM foils from Nb-10 a/o Si.

Ductile phase toughened composites contain phases with significantly different physical properties. Consequently, these phases thin at different rates depending on the sample preparation procedure. A new TEM foil preparation method for the ductile phase toughened Nb-10 a/o Si material has been developed. The method involves chemical thinning in a 70% nitric acid/30% hydrofluoric acid solution followed by electropolishing in a 12.5% sulfuric acid/87.5% methanol electrolyte at -40 degrees C. This procedure for making TEM foils results in large thin areas with the minimum of artifacts. Mechanical grinding of a sample followed by either ion milling, dimpling, or electropolishing produced foils with large electron transparent areas, but with uncharacteristic features of the original Nb-10 a/o Si alloy microstructure. These artifacts were identified as dislocations, surface mottling, and antiphase domains.     

Characterization of surface micromachined metallic microneedles

The purpose of the paper is to provide quantitative characterization of metallic microneedles. Mechanical and fluid flow experiments were performed to evaluate the buckling force, the penetration force, and the pressure versus flow rate characteristics of the microneedles. The microneedle design variations characterized included varying the shaft lengths, varying the tip taper angles/geometries, and the inclusion of micromechanical barbs. The penetration force was found to range from 7.8 gF for a microneedle of shaft length 500 /spl mu/m, to 9.4 gF for a length of 1500 /spl mu/m, both with a tip taper angle of 30/spl deg/. Microneedles with a linear tip taper angle of 30/spl deg/ penetrated 95 +% of the time without failure. The microneedles with a 15/spl deg/ and 20/spl deg/ linear tip taper penetrated 10% and 25% of the time, respectively. The buckling force was found to be 98.4 gF for a 500 /spl mu/m long microneedle shaft, 72.3 gF for a needle of shaft length 1000 /spl mu/m, and 51.6 gF for a 1500 /spl mu/m long shaft. The results demonstrate that the penetration force was 7.9% of the buckling force for 500 /spl mu/m long shafts, 11.6% for a 1000 /spl mu/m long shaft, and 18.2% for a 1500 /spl mu/m long microneedle shafts. The microneedle fluid flow characteristics were studied. An inlet pressure of 49.0 Pa was required for a flow rate of 1000 /spl mu/L/h and 243.0 Pa for a flow rate of 4000 /spl mu/L/h using air as the fluid medium. For water, an average pressure of 30.0 kPa was required for a flow rate of 1000 /spl mu/L/h and 106.0 kPa for a flow rate of 4000 /spl mu/L/h.     

The 3DP: a processor architecture for three-dimensionalapplications

The 3DP (3-Dimensional Processor), a parallel-computing architecture that targets problems that have a 3-D numerical structure and require numerous calculations on 3-D vectors, is described. The 3DP architecture differs from traditional scalar architectures in that it operates directly on vectors. It differs from general parallel architectures in that it can solve problems that predict the behavior of highly coupled systems, and it differs from vector architectures in that it runs efficiently on length-3 vectors. Object-oriented programming on the 3DP and programming the 3DP in C++ are discussed. 3DP performance is reviewed, and the current implementation of the 3DP architecture, as an attached processor that plugs directly into Sun host VMEbus, is described     

Sliding wear behavior of salt bath nitrocarburized medium carbon steel

Salt bath nitrocarburizing is a well-known thermochemical diffusion process for enhancing the tribological and corrosion properties of ferrous components. The current work describes the role of a compound layer developed during nitrocarburizing, both in the ferritic and austenitic regimes of Fe-N-C system, on the sliding wear behavior of a medium carbon steel. The wear behavior of the nitrocarburized steel discs was assessed by the pin-on-disc tests (ASTM G 99-99) under different normal loads running against a hardened SAE52100 pin. It was observed that the compound layer on the surface not only controlled the wear rate but also resisted the adhesive wear/transfer of material from pin to disc, aside from providing low-friction coefficients.     

Diurnal and environmental characterization of solar photovoltaic panels using a PC-AT add on plug in card

This article describes the development of an instrumentation system for characterizing photovoltaic panels. It uses an add on card (which contains DAC, ADC and digital input/output ports) in conjunction with a PC-AT. The panels in a field are selected in succession through a set of relays actuated by the digital output port. The selected panel is loaded in discreet steps by a transistor loading circuit which is activated by the digital to analog convertor to trace the most significant portion of the I-V curve. The data shows that the power output is invariably lower than that specified by the manufacturer. The reasons for drop in output have been analyzed. It is shown that these effects can be represented by the curvature of I-V characteristic at the maximum power point (OP). The loss of power due to accumulation of dust and the increase in temperature of the panels can be significant.     

Hardness-stress-strain correlation in aluminium—A simpler alternative to visioplasticity in metal forming

Local stress and strain variations in the deformation zone can be ascertained by measuring hardness. Hardness is correlated with strain and stress. The expressions discussed later are useful in determining the local variations in stress and strain from hardness measurement. It is a simple method compared to visioplasticity. One can estimate the forces required for a forming process. It helps in the choice of equipment, design of tooling and selection of lubricant for the particular process.