Cool-down Rates Research Articles

Local Structure Study About Co in a-Axis Films of YBa2(Cu0.93Co0.07)3O7-δUsing Polarized XAFS

We present polarized XAFS data for quenched and slow cooled a-axis thin films of YBCO. The oxygen peak is the same for both the a and b axes and does not change with cool-down rate. This suggests that Co acts as an oxygen getter in the YBCO film.

Particle size control of 1,3,5-triamino-2,4,6-trinitrobenzene by recrystallization from DMSO

Batches of up to 46g of the insensitive explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) have been recrystallized from DMSO in an effort to prepare larger particle-size material for recycling previously-used TATB and also for use in special formulations. The first part of the study investigated the conditions required to shift the particle-size distribution maximum from ∼50–70 μm to several hundred micrometres in diameter. Distributions peaking at ∼200–246 μm were successfully produced by varying the cooldown rate and degree of agitation during cooling. The second part of the study emphasized regeneration of the standard ∼50–70 μm distribution from submicron size (“ultrafine” TATB) particles. The distributions peaking at ∼76–88 μm, ∼27–31 μm, and ∼15–17 μm, successfully bracketed the target particle sizes, were grown by changing the degree of solution saturation. The choice of saturation temperature for the TATB/DMSO solution was based on earlier small-scale recrystallization and solubility work.

Cure Cycle Optimization for the Reduction of Processing-Induced Residual Stresses in Composite Materials

The control and reduction of processing-induced residual stresses has been investigated by modifying processing conditions for a graphite/BMI composite material. The effects of dwell temperature, dwell time, cool-down rate, cool-down pres sure, and postcure on residual stresses were investigated using unsymmetric cross-ply laminates. The effects on transverse mechanical properties were also measured. Experi mental results have shown that residual stresses can be reduced by as much as 25-30% while retaining or enhancing transverse mechanical properties by curing at lower tempera tures for longer times or utilizing an intermediate low-temperature dwell in three-step cure cycles. Overall process cycle times are not lengthened for three-step curing.

The effect of homogenization and precipitation treatments on the extrudability and ambient-temperature mechanical properties of aluminum alloy AA2024

Abstract This study determined the independent effects of various homogenization cycles and precipitation treatments on the elevated temperature workability and the final ambient temperature mechanical properties of aluminum alloy AA2024. The elevated-temperature tensile and extrusion tests indicate that the workability of AA2024 improves with elevated-temperature precipitation treatments as suggested by earlier investigations. The precipitation treatments do not appear to degrade the ambient-temperature T3 and T8 tensile properties. The time at the precipitation temperature appears to affect the T3 and T8 tensile properties in homogenized ingot, longer times especially providing both relatively high ambient-temperature strength and ductility. The time at the standard homogenization temperature and the heat-up and cool-down rates do not dramatically affect the T3 tensile properties of homogenized ingot. However, long soak times (24 h) at the homogenization temperature and more rapid cooling rates (120 °C h−1) may improve the properties somewhat.

Effect of thermal history on the transport properties and the location of Fe in YBa2Cu3O7 thin films

Epitaxial Fe-substituted YBa2Cu3O7 films on LaAlO3 substrates prepared by pulsed-laser deposition exhibit a large variation in Tc with changes in the cooldown rate of the films in an O2 environment immediately after deposition. A rapid cooldown rate (200 °C/min) yields surprisingly high-Tc films with Tc≳75 K for 13% of the Cu replaced by Fe, while a slow cooldown of 10 °C/min results in low-Tc films with Tc→0 at 11% Fe, a greater suppression than reported for bulk materials. In addition, post-deposition anneals in O2 affect Tc significantly, even for anneal temperatures as low as 370 °C. These results are interpreted in terms of isolated- and clustered-Fe atoms substituted on the Cu chains sites.

Extreme Sensitivity of Tc to Cool-Down Rate and Substrate Temperature for Epitaxial Fe-DOPED Ybco Films

ABSTRACTEpitaxial Fe-substituted YBCO films on LaAIO3 substrates prepared by pulsed laser deposition exhibit a large variation in Tc with the substrate temperature and the cool-down rate of the films in an O2 environment, immediately after deposition. For 9% Fe films deposited at 700°C, a rapid cool-down yields a Tc of 60 K while a slow cool-down of 10°C/minute gives 18 K; Tc goes to 0 at 11% Fe for the slow cool-down films. For 9% Fe films deposited at 770°C, Tc > 80K and is much less sensitive to the cool-down rate or additional anneals.

A Computerized System for Continuous Monitoring of the Core Cooling Margin

A computerized system that assists pressurized water reactor (PWR) nuclear plant operators in controlling the saturation margin is described. This system continuously calculates and provides the temperature or pressure margin from saturation, and indicates the temperature and pressure values used for its calculation. The reactor core heatup and cooldown rates are also continuously provided by this computer-based system. The saturation curve is represented by a polynomial approximation as a function of temperature or pressure. Twenty-one analog signals of a PWR power plant are acquired by the system for calculating the margin and temperature variation rates. The man/machine interface is done through the visualization panel, which displays the above-mentioned values. Compared to the temperature and pressure values displayed in the visualization panel, the error of margin is always <0.5%.

Recent experience in pressure vessel materials irradiation

The reactor pressure vessel has been repeatedly cited as a primary concern in assessment of pressure boundary structural integrity and in planning for plant life extension programs. The life of the reactor pressure vessel will be limited by radiation-induced embrittlement; this is monitored in Westinghouse designed nuclear steam supply systems by testing samples of base metal, heat-effect-zone and weld metal in the form of Charpy V-notch, tensile, and fracture mechanics specimens which have been irradiated in surveillance capsules adjacent to the wall. The earliest reactor vessel material radiation surveillance program was the Yankee Rowe program which started in 1961. As data became available from power reactor surveillance and test reactor programs, estimates of radiation-induced changes in mechanical properties were predicted in the form of radiation damage trend curves which provide methods for calculating numerical estimates of changes in mechanical properties as a function of chemistry and fluence. For example, the proposed Revision 2 to Regulatory Guide 1.99 provides estimates of shifts in transition temperature as a function of copper and nickel content and fluence. Slight variations in chemical analyses for copper and/or nickel can result in limitation on heat-up and cool-down rates or compliance with regulatory rules, such as the PTS screening criteria. Automatic submerged arc welding was employed in the fabrication of reactor vessels in Westinghouse designed nuclear steam supply systems. The type of flux material utilized in the welding process is important because mechanical properties can differ depending upon what flux is used. This paper correlates the results from over 50 surveillance capsules with the welding practice and concludes that radiation damage trend curves can be developed for welding practice. By using trend curves based on welding practices, discrepancies in chemical analyses are eliminated and credibility is restored to structural integrity assessments.

The Effects of Cure Temperature and Time on the Bulk Fracture Properties of a Structural Adhesive

Abstract The effects of cure time and temperature as well as cool-down rate on the adhesive tensile properties, yield stress ([sgrave]y) and elastic modulus (E), were determined experimentally. Commercially available, solid film Metlbond 1113 (with carrier cloth) and 1113-2 (without carrier cloth) adhesives were used as model adhesives. The experimentally determined tensile properties were used to calculate theoretically the critical stain energy release rate (GIC) based on the radius of the crack tip deformation zone reported by Bascom. The calculated GIC values were then compared with the measured values which are available in the literature. The comparison revealed good agreement between the calculated and measured GIC values.

Oxide Growth Using the Water-Wall Arc Lamp

ABSTRACTThe uses of Rapid Thermal Annealing or Rapid Thermal Processing (RTP) have been expanding beyond the original post implant annealing. RTP has been used to reflow low temperature oxides (PSG or BPSG), anneal silicides and to sinter contacts. One application of RTP which is beginning to receive attention is the growth of oxides or nitrides of silicon.This paper will examine the use of a commercial rapid thermal processing system based on a very high power water-wall DC arc lamp to grow oxides on silicon wafers. The work includes a study of the growth rates of oxides at different temperatures. Direct feedback control of wafer temperature and high ramp-up and cool-down rates are used to minimize the effects of temperature errors or “tails” in the temperature/time profiles. Ellipsometry is used as the primary measurement tool to characterize the oxide films.In addition to using a pure, dry oxygen atmosphere, several oxygen-argon mixtures are used. The effects of atmosphere on the growth rate of the oxide film are reported.In order to become a practical application of RTP, oxide growth must be accomplished uniformly and reproducibly. These characteristics are machine-dependent. The uniformity of films grown in this system are discussed. The growth of oxide films and the uniformity measurements are used as an indirect technique to characterize the uniformity of the system. The reproducibility of film thickness is also examined.

The Effects of Cure Temperature and Time on the Bulk Tensile Properties of a Structural Adhesive

Abstract The effects of cure time and temperature as well as cool-down rate on the adhesive tensile properties, yield stress ([sgrave]y) and elastic modulus (E), were determined experimentally. Commercially available, solid film Metlbond 1113 (with carrier cloth) and 1113-2 (without carrier cloth) adhesives were used as model adhesives. The experimentally determined tensile properties were used to calculate theoretically the critical stain energy release rate (GIC) based on the radius of the crack tip deformation zone reported by Bascom. The calculated GIC values were then compared with the measured values which are available in the literature. The comparison revealed good agreement between the calculated and measured GIC values.

Evaluation of Acid-Gelling Agents for Use in Well Stimulation

Abstract Various polymers and other thickening agents have been evaluated as gelling agents for hydrochloric acid (HCl). These materials were compared on the basis of thickening efficiency, acid stability, and residue formation upon spending of the acid. Thickeners tested include xanthan polymers (XP), guar gum (GG), hydroxyethyl cellulose (HEC), carboxymethylhydroxyethyl cellulose (CMHEC), polyacrylamide (PAM), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), acrylamide/sodium-2-acryl-amido-2-methylpropane sulfonate copolymer (PAM/AMPS), and a cationic surfactant that thickens acid when used at high concentrations. Of the thickening agents tested, XP showed the greatest overall potential for use as an acid gelling agent. This polymer is an efficient viscosity builder and has good stability in 15% HCl at temperatures up to 150°F. Computer model studies, which take into consideration cool-down and gel degradation rate at various stages of acid spending, indicate viscosity is maintained when treating wells that have bottomhole temperatures (BHT's) up to 220°F. Since the gelled acid retains its viscosity during spending, both reaction rate and fluid leakoff are retarded. Laboratory studies simulating downhole spending conditions yield a 3.6-fold increase in spending time for gelled 15% HCl (22-cp) compared with ungelled acid. Well test results are presented that demonstrate the effectiveness of acid fracturing treatments using HCl with XP.

Operating Experience with the Cryogenic Systems for a Superconducting Cyclotron

The successful operation of the superconducting cyclotron cryogenic system has been primarily dependent on understanding and improving its performance. In particular, operating experience with a superconducting magnet coil, a vacuum cryopanel, and a cryogenic distribution system has been gained during the past three years. The coil cryostat cooldown, boiloff rate, warmup, eddy current pulse, median plane heat leak, and helium leakage into the cryostat vacuum jacket have been measured. The vacuum cryopanel cooldown rate, heat load, pumping speed and long term gas storage have been determined. The present measurements have been conducted with simple independent transfer lines. A subcooled cryogenic distribution system, with parallel branches, has been designed and is presently under construction.

Warping of Unsymmetric Cross-Ply Graphite/Epoxy Laminates

Warping in unsymmetric graphite/epoxy laminates was studied with particular attention given to the change of residual stresses resulting from long term environmental exposure. Square, cured prepreg sheets were measured for edge deflection with a cathetometer, then quartered and remeasured. Two postcuring durations were then used, 7.5 and one hr at 177 C; varying cooldown rates after curing were used for other samples, and one set was stored in vacuum at 75 C. Maximum deflections and weight changes were measured periodically at room temperature. Average curvatures, the effect of postcure, and the effect of long-term exposure were determined. Larger panels exhibited cylindrical warping and smaller panels underwent anticlastic warping. The deflections were related to weight changes, i.e. moisture absorption, and the lower the moisture content, the higher the deflection. Relaxation of residual stresses at 75 C was neglibible after 220 days.

Transient Response of the Miniature, Reversed Stirling-Cycle, Cryogenic Cooling Machine—An Empirical Approach

By regarding the ideal thermodynamic cycle as being artificially separated from the hardware, and by treating the former as a simple energy flux path, an energy-rate balance is set up for the miniature, reversed-cycle, Stirling cooling machine. Account is taken of thermal energy storage and release rates corresponding to the rates of change of temperature of regenerator and cylinder walls. There results a first-order, linear differential equation. Solutions are obtained numerically using the parameters of a tentative cooler design. The solutions are presented in the form of curves of temperature ratio, τ (=Tc/Te), against time, t, at uniform angular speed. Regenerator inefficiency, Ie, emerges as the parameter that is most critical in the achievement of desired heat-lifting capacity at cryogenic temperatures. For a machine of given thermal mass, both Ie and ηc (cycle efficiency relative to corresponding Carnot efficiency) strongly influence the cool-down rate. The treatment is capable of application to Stirling machines operating as prime movers.

A Proposed Method for Specifying the Temperature History of Cells During the Rapid Cool-down of Plant Specimens

Existing methods for defining cool-down rates of plant specimens quenched in cryogenic liquids are considered unsatisfactory. An analytical method is proposed for specifying the temperature history and cool-down rates at particular cell locations within a plant specimen. This method should provide realistic peak cool-down rates when examining cell structures and the survival rate of cell systems.