Influence of chemical compositions of slag and graphite on the phenomena occurring in the graphite/slag interfacial region

Silica reduction reactions taking place in the slag/carbon interfacial region were investigated for synthetic/natural graphite in the temperature range 1500 °C to 1700 °C. Two silica-rich blast furnace slags, with low levels of iron oxide, were used in this study. Silica concentration in these slags, labeled as 1 and 2, was 30.80 pct and 36.80 pct with a respective basicity of 1.67 and 1.22. Reaction rate investigations were supplemented with wettability measurements on these systems with an aim to probe a possible interdependence between wetting characteristics and reaction rates of silica reduction. Wettability and slag/carbon reactions were studied in a horizontal tube resistance furnace in argon atmosphere, using the sessile drop approach. While the contact angles were measured by recording live images of the assembly with a charge-coupled device camera, the volumes of CO and CO₂ evolved were obtained from an analysis of off-gases with the help of a mass spectrometer. Reaction rates for silica reduction showed a wide variation for different systems. Synthetic graphite showed nonwetting behavior with both slags. Natural graphite, however, showed dynamic wetting with slag 2, resulting in low contact angles. This is attributed to the difference in the deposition of Si-based reaction products in the interfacial region, which in turn influences wettability. Temperature had a significant effect on both the wettability and silica reduction rate of the graphite/slag system. Activation energies for silica reduction in slags 1 and 2 with natural graphite were estimated to be 253 and 241 kJ/mol, respectively. Chemical composition of carbonaceous materials and slags were found to play a very important role in dictating overall reaction rates and wetting characteristics.     

Thermal Stability of Nitride-Based Diffusion Barriers for Ohmic Contacts to <Emphasis Type="Italic">n</Emphasis>-GaN

The use of TaN, TiN, and ZrN diffusion barriers for Ti/Al-based contacts on n-GaN (n ∼ 3 × 10¹⁷ cm⁻³) is reported. The annealing temperature (600–1,000°C) dependence of the Ohmic contact characteristics using a Ti/Al/X/Ti/Au metallization scheme, where X is TaN, TiN, or ZrN, deposited by sputtering was investigated by contact resistance measurements and Auger electron spectroscopy (AES). The as-deposited contacts were rectifying and transitioned to Ohmic behavior for annealing at ≥600°C. A minimum specific contact resistivity of ∼6 × 10⁻⁵ Ω-cm⁻² was obtained after annealing over a broad range of temperatures (600–900°C for 60 s), comparable to that achieved using a conventional Ti/Al/Pt/Au scheme on the same samples. The contact morphology became considerably rougher at the high end of the annealing range. The long-term reliability of the contacts at 350°C was examined; each contact structure showed an increase in contact resistance by a factor of three to four over 24 days at 350°C in air. AES profiling showed that the aging had little effect on the contact structure of the nitride stacks.     

Six-year experience with Swan neck presternal peritoneal dialysis catheter

Airway control is the initial priority in the management of the injured patient. The purpose of this investigation was to evaluate the experience of an aeromedical transport team in the utilization of rapid sequence induction (RSI) for endotracheal intubation in the prehospital setting. Records of a consecutive series of injured patients undergoing RSI between June 1988 and July 1992 by a university-based aeromedical transport team were reviewed for demographics, intubation mishaps, and pulmonary complications. The relationship between intubation mishaps and pulmonary complications was analyzed. Eighty-four patients were studied with a mean age of 30.8 +/- 15.3 years. The mean Revised Trauma Score was 11.3 +/- 2.4, and the mean Injury Severity Score (ISS) was 19.6 +/- 11.5. Intubation mishaps occurred in 15 patients (18%), and pulmonary complications developed in 22 (29%) of the 75 patients surviving longer than 24 hours. There was no relationship between intubation mishaps and pulmonary complications. Abbreviated Injury Scale (AIS) face score was significantly higher in patients with intubation mishaps, compared with patients without mishaps (1.1 +/- 1.2 and 0.5 +/- 0.9, respectively, P < .05, Wilcoxon rank-sum). ISS and AIS chest were higher in patients with pulmonary complications, compared with those without (25.7 +/- 12.6 and 17.4 +/- 10.3 and 2.2 +/- 1.8 and 1.0 +/- 1.5, ISS and AIS respectively; P < .05, Wilcoxon rank-sum). Eighty-one patients (96%) underwent successful RSI, 73 (87%) on the first attempt. Failure to intubate occurred in three patients (4%). Performed under strict protocol by appropriately trained aeromedical transport personnel, RSI is an effective means to facilitate endotracheal intubation in the injured patient requiring definitive airway control. Pulmonary complications were related to injury severity and not to intubation mishaps.     

Psychophysical estimation of speed discrimination. I. Methodology

Thresholds were assessed for a speed discrimination task with a pair of luminance-defined drifting gratings. The design and results of a series of experiments dealing in general with speed discrimination are described. Results show that for a speed discrimination task using drifting gratings, simultaneous presentation of the pair of gratings (spatially separated) was preferred over sequential presentation (temporally separated) in order to minimize the effects of eye movements and tracking. An interstimulus interval of at least 1000 ms was necessary to prevent motion aftereffects on subsequently viewed stimuli. For the two reference speeds tested of 2 and 8 deg/s using identical spatial frequency or randomizing spatial frequency for the pair of gratings did not affect speed discrimination thresholds. Implementing a staircase method of estimating thresholds was preferred over the method of constant stimuli or the method of limits. The results of these experiments were used to define the methodology for an investigation of aging and motion perception. These results will be of interest and use to psychophysicists designing and implementing speed discrimination paradigms.     

Acoustic emission as a technique to study breakaway oxidation and spalling behaviour of 2.25Cr-1 Mo steel

The onset of breakaway oxidation and cracking of the oxide scale formed on 2.25Cr-1Mo steel in air at 1173 K have been studied by the acoustic emission (AE) technique. AE parameters, i.e. events, ring-down counts, rise time, event duration and root mean square voltage show negligible increase during isothermal heating at this temperature, until a point where a sudden increase in AE activity is found. This point corresponds to the onset of breakaway oxidation. An enormous increase in AE activity after the start of cooling from the oxidation temperature has been attributed to separation of the oxide scale from the matrix. The peak amplitude distribution is measured and a derived b parameter is calculated. This has helped in distinguishing the phenomena of isothermal oxidation at 1173 K and internal cracking of oxide scale during cooling from 1173 K.     

Residual stresses and sliding wear

The residual stresses that develop during the wear of AISI-SAE 1018 and 4340 steels have been examined. The entire three-dimensional stress tensor was obtained. A normal stress perpendicular to the surface, predicted by theory, has been found, but its magnitude is too small to affect the wear rate. There are also significant shear stresses. The wear process rapidly alters any initial stress distribution produced by heat treatment or peening to such a degree that the wear rate is not affected by these stresses, unless they are initially larger than those that can be produced by the wear parameters.     

Room temperature-vulcanized silicone elastomer: Effect of curing conditions and the nature of filler on mechanical and thermal properties

Linear poly(dimethylsiloxane diol) of about 650 D.P. was synthesized by hydrolytic condensation of dimethyldichlorosilane in a saturated solution of sodium chloride. The polymer was then compounded with various fillers, Cab-O-Sil, Dicalite, and titanium dioxide, and cured at room temperature in the presence of tin salt and tri- or tetrafunctional silane. The tensile strength and elongation of the unfilled rubber were found to be 0.8 kg/cm² and 320%, respectively. However, Dicalite White (100 phr)-reinforced elastomer showed a tensile strength of 40 kg/cm². Crosslink density was determined from the swelling studies. Thermal aging at 150, 200, and 250°C was also studied.     

Contact resistance characteristics of the low cost CuNiCr thin film resistor system

In this paper an investigation of the use of copper as a contact and interconnecting material for thin film resistors and hybrid circuits is reported. The current-voltage characteristics of Nichrome thin film resistors with copper contacts and the contact resistance of $\text{Cu}\text{NiCr}$ metallizations were measured. The effect of thermal annealing on the contact characteristics was also studied.