68 Matching Results

Search Results

Advanced search parameters have been applied.

Brookhaven National Laboratory's multiparticle spectrometer drift chamber system

Description: A system of drift chambers is being built to replace the present spark chambers in the Brookhaven National Laboratory's Multiparticle Spectrometer. This system will handle a beam of approx. 3 million particles per second and have a resolution of 200 ..mu..m. A summary of the status of the chambers and the custom integrated circuits is presented. The data acquisition system is described. Prototype chambers have been built and tested with results that are consistent with the expected chamber properties.
Date: January 1, 1979
Creator: Etkin, A. & Kramer, M.A.
Partner: UNT Libraries Government Documents Department

The 5- by 7-meter wind tunnel of the DVL

Description: The report contains a description of the DVL wind tunnel. According to the cones fixed, an elliptical stream with axes 5 by 7 meters and length 9 meters, or a stream 6 by 8 meters in cross section and 11 meters in length is available. The top speed with the smaller cone is 65 meters per second. The testing equipment consists of an automatic six-component balance and a test rig for propellers and engines up to 650 horsepower.
Date: March 1936
Creator: Kramer, M.
Partner: UNT Libraries Government Documents Department

Innovative approach to modeling accident response of Gravel Gerties

Description: Recent safety analyses at nuclear explosive facilities have renewed interest in the accident phenomenology associated with explosions in nuclear explosive cells, which are commonly referred to as {open_quotes}Gravel Gerties.{close_quotes} The cells are used for the assembly and disassembly of nuclear explosives and are located in the Device Assembly Facility (DAF) at the Nevada Test Site (NTS) and at the Pantex facility. The cells are designed to mitigate the release of special nuclear material to the environment in the event of a detonation of high explosive within the Gravel Gertie. Although there are some subtle differences between the cells of DAF and Pantex, their general design, geometry, and configuration are similar. The cells consist of a round room approximately 10.4 m in diameter and 5.2 m high enclosed by 0.3-m-thick concrete. Each cell has a wire-rope cantenary roof overlain with gravel. The gravel is approximately 6.9 m deep at the center of the roof and decreases toward the outer edge of the cell. The cell is connected to a corridor and subsequent rooms through an interlocking blast door. In the event of a accidental explosion involving significant amounts of high explosive, the roof structure is lifted by the force of the explosion, the supporting cables break, the gravel is lifted by the blast (resulting in rapid venting of the cell), and the gravel roof collapses, filling the cell. The lifting and subsequent collapse of the gravel, which acts much like a piston, is very challenging to model.
Date: August 1, 1997
Creator: Kramer, M.; McClure, P. & Sullivan, H.
Partner: UNT Libraries Government Documents Department

Computational and Experimental Development of Novel High Temperature Alloys

Description: The work done in this paper is based on our earlier work on developing an extended Miedema model and then using it to downselect potential alloy systems. Our approach is to closely couple the semi-empirical methodologies to more accurate ab initio methods to dentify the best candidates for ternary alloying additions. The architectural framework for our material's design is a refractory base metal with a high temperature intermetallic which provides both high temperature creep strength and a source of oxidatively stable elements. Potential refractory base metals are groups IIIA, IVA and VA. For Fossil applications, Ni-Al appears to be the best choice to provide the source of oxidatively stable elements but this system requires a 'boost' in melting temperatures to be a viable candidate in the ultra-high temperature regime (> 1200C). Some late transition metals and noble elements are known to increase the melting temperature of Ni-Al phases. Such an approach suggested that a Mo-Ni-Al system would be a good base alloy system that could be further improved upon by dding Platinum group metals (PGMs). In this paper, we demonstrate the variety of microstructures that can be synthesized for the base alloy system, its oxidation behavior as well as the oxidation behavior of the PGM substituted oxidation resistant B2 NiAl phase.
Date: June 29, 2010
Creator: Kramer, M.J.; Ray, P.K. & and Akinc, M.
Partner: UNT Libraries Government Documents Department

Computer facilities for Isabelle data handling

Description: The analysis of data produced by Isabelle experiments will need a large system of computers. Included in the array should be a substantial computer system at each Isabelle intersection in use. These systems must include enough computer power to keep experimenters aware of the status of the experiment. This will require at least one very fast sophisticated processor in the system, the size depending on the experiment. Other features of the intersection systems must be a good, high speed graphic display, ability to record data on magnetic tape at 500 to 1000 KB, and a high-speed link to a central computer. The operating system software must support multiple interactive users. A substantially larger capacity computer system, shared by the six intersection region experiments, must be available with good turnaround for experimenters while Isabelle is running. The computer mainframes should ideally be compatible members of the same family of computers. A very large computation load will be generated by the post experiment data reduction. Much of this may have to be run at lower priority. A computer support group will be required to maintain the computer system and to provide and maintain software common to all experiments. Such software support may include providing a compatible compiler. Special superfast computing hardware or special function processors constructed with microprocessor circuitry may be necessary both in the data gathering and data processing work. Thus, both the local and central processors should be chosen with the possibility of interfacing such devices in mind.
Date: January 1, 1977
Creator: Kramer, M.A.; Love, W.A.; Miller, R.J. & Zeller, M.
Partner: UNT Libraries Government Documents Department

A new spinning-test method

Description: This report contains a description of a new spinning-test arrangement wherein the otherwise customary rotation of the model about a fixed axis is abandoned in favor of a corresponding rotation of the air stream. The advantage of this method lies in the fact that the model is at rest while the spin is recorded. In this manner it is possible to secure systematic results with little loss of time while employing 3- or 6-component wind-tunnel balances. The troublesome equalization of the mass forces is eliminated and the flow phenomena are accessible to direct observation.
Date: April 1938
Creator: Kramer, M. & Kr├╝ger, K. B.
Partner: UNT Libraries Government Documents Department

Review of experiments

Description: A study was made to examine the effects which raising the ISA from 200 x 200 GeV to 400 x 400 GeV would have on the ''canonical'' experiments. These were ''canonical'' in the sense that they span the full range of foreseeable physics and have served as topics in previous Summer Studies and Workshops which resulted in quite explicit hardware designs and experimental goals. The study results indicate that all of the ''canonical'' experiments survive. Some are actually improved, some are unaffected, and some require changes which are suggested. In general, the 90/sup 0/ experiments are relatively unaffected. The single arm small angle spectrometer, the wide aperture (FATS-WASP) spectrometer and the Coulomb interference experiment have the largest number of modifications suggested. No uniqueness to these solutions are claimed, and there may be more desirable radical approaches. It is, however, felt that the 400 x 400 GeV ISA not only permits the work on conceptual experiments from previous Summer Studies to be taken over entirely, but indicates areas of improvement in many of them. Specifics of the individual experiments are discussed.
Date: August 18, 1977
Creator: Chang, C.; Yodh, G.; Cutts, D.; Lanou, R.; Engels, E.; Kramer, M. et al.
Partner: UNT Libraries Government Documents Department

Systematic airfoil tests in the large wind tunnel of the DVL

Description: The present report is a description of systematic tests at maximum lift on airfoils with and without split flap and of profile drag at low lift. In order to obtain an opinion as to the suitability of the airfoils with flaps, the maximum-lift measurements were repeated on airfoils with split flaps. The profile drag at low lift was arrived at by direct weighing and momentum measurements and, since the profiles were of unusual depth, extended to large Reynolds numbers.
Date: March 1938
Creator: Doetsch, H. & Kramer, M.
Partner: UNT Libraries Government Documents Department

The effect of Ag on the decomposition pathway of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} in air

Description: The decomposition pathway of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (Bi2212) in .21 bar O{sub 2} with 0, 2, and 10 wt.% Ag added has been determined by performing SEM/EDS and microprobe analysis on oil quenched samples. A series of quaternary phase diagrams were constructed to describe the evolution of the phase assemblage with temperature. It was found that the first decomposition products are Bi{sub 9}Sr{sub 11}Ca{sub 5}O{sub x} (9{und 11}5), (Sr{sub 1{minus}x}Ca{sub x})CuO{sub 2} (11), and liquid. The addition of Ag acted to depress the first peritectic temperature by 16--20 C and slightly modified the order in which some of the subliquidus solid phases nucleate and decompose. The effect of C on the peritectic melting temperature was examined through thermal analysis of powder samples.
Date: May 1, 1996
Creator: Margulies, L.; Dennis, K.W.; Kramer, M.J. & McCallum, R.W.
Partner: UNT Libraries Government Documents Department

Surface carbon films on Al-Cu-Fe quasicrystalline powders

Description: In order to study the unique properties of quasicrystals, it is necessary to form dense, homogeneous monoliths of these alloys. Unfortunately, Al-Cu-Fe quasicrystalline alloy ingots prepared by conventional casting techniques result in large scale chemical inhomogeneities which contain numerous cracks due to differential thermal contraction between the various phases during cooling. Thus a powder metallurgical approach using gas atomized (GA) powders is being pursued in order to form large samples of phase pure Al-Cu-Fe quasicrystal. A samples of specific compositions and sizes are hot isostatic pressed (HIPed) to form dense monoliths. The effects of surface contamination of GA powders, which may inhibit particle-to-particle sintering and may also increase second phase contamination in the HIPed piece, is being studied by scanning Auger microprobe (SAM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).
Date: December 31, 1996
Creator: Bloomer, T.E.; Flumerfelt, J. & Kramer, M.J.
Partner: UNT Libraries Government Documents Department

Numerical prediction of heat-flux to massive calorimeters engulfed in regulatory fires with the cask analysis fire environment (CAFE) model

Description: Recent observations show that the thermal boundary conditions within large-scale fires are significantly affected by the presence of thermally massive objects. These objects cool the soot and gas near their surfaces, and these effects reduce the incoming radiant heat-flux to values lower than the levels expected from simple {sigma}T{sub fire}{sup 4} models. They also affect the flow and temperature fields in the fire far from their surfaces. The Cask Analysis Fire Environment (CAFE) code has been developed at Sandia National Laboratories to provide an enhanced fire boundary condition for the design of radioactive material packages. CAFE is a set of computer subroutines that use computational fluid mechanics methods to predict convective heat transfer and mixing. It also includes models for fuel and oxygen transport, chemical reaction, and participating-media radiation heat transfer. This code uses two-dimensional computational models so that it has reasonably short turnaround times on standard workstations and is well suited for design and risk studies. In this paper, CAFE is coupled with a commercial finite-element program to model a large cylindrical calorimeter fully engulfed in a pool fire. The time-dependent heat-flux to the calorimeter and the calorimeter surface temperature are determined for several locations around the calorimeter circumference. The variation of heat-flux with location is determined for calorimeters with different diameters and wall thickness, and the observed effects discussed.
Date: May 11, 2000
Partner: UNT Libraries Government Documents Department

Effect of Ag on the peritectic decomposition of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x}

Description: During the melt processing of superconducting wires and tapes a number of partial liquid phase regions are entered, and the type and amount of second phases that exist in the melt before cooling are critical in determining the microstructure of the final material. Decomposition pathway of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x}(Bi2212) with 0, 2, and 10 wt% Ag added was examined at 1 bar PO{sub 2} by performing SAME/EDS analysis on oil quenched samples. A variety of quaternary phase diagrams were constructed to describe the evolution of the phase assemblage with temperature. At all Ag contents, Bi2212 first undergoes a peritectic reaction producing (Sr{sub 1-x}Ca{sub x}){sub 14}Cu{sub 24}O{sub 41}(14,24), Bi{sub 2}(Sr{sub 1-x}Ca{sub x}){sub 4}O{sub x}(24x), and liquid.
Date: December 31, 1995
Creator: Margulies, L.; Dennis, K.W.; Kramer, M.J. & McCallum, R.W.
Partner: UNT Libraries Government Documents Department

Microstructural evolution, oxidation and wear of Al-Cu-Fe quasicrystalline coatings

Description: Plasma arc sprayed coatings were prepared with two different size fraction starting powders having a nominal composition of Al{sub 63}Cu{sub 25}Fe{sub 12}. Powders were obtained by crushing a cast ingot and by gas atomization. Coatings were characterized by electron microscopy, X-ray diffraction and chemical analysis. Oxidation tests were performed in dry oxygen at 500 and 700 C. Finer powders produced coatings with more of the cubic phase than coatings formed with coarser powders. The as-sprayed coatings developed different phases during oxidation. Wear tests of as-sprayed coatings were performed over a range of temperatures in a pin-on-disc arrangement against aluminum oxide. The coefficient of friction increased from around 0.44 at room temperature to near 0.60 at 600 C. Differences in wear behavior of the coatings were seen as a function of temperature.
Date: October 1, 1995
Creator: Sordelet, D.J.; Kramer, M.J.; Anderson, I.E. & Besser, M.F.
Partner: UNT Libraries Government Documents Department

Oxidation resistance and compressive creep behavior of boron doped Mo{sub 5}Si{sub 3}

Description: Use of Mo{sub 5}Si{sub 3} in high temperature applications is limited by oxidation induced catastrophic failure above 800 C. Oxidation resistance of Mo{sub 5}Si{sub 3} is substantially improved from 800--1,300 C by the addition of boron. The oxidation rate at 1,200 C was decreased by five orders of magnitude with less than 2 weight percent boron addition. The improvement in oxidation resistance of B doped Mo{sub 5}Si{sub 3} is due to formation of a protective scale layer due to viscous flow. The compressive creep rate of B doped Mo{sub 5}Si{sub 3} was measured at various temperature/stress levels and found to be similar to that of the undoped material. The creep rate of B doped Mo{sub 5}Si{sub 3} was measured as 1.8 {times} 10{sup {minus}7} s{sup {minus}1} at 1,242 C and 138 MPa. Creep tests were conducted at 140--180 MPa and 1,220--1,320 C. Average creep activation energy and stress exponent in this range were found to be E{sub a} {approx} 400 kJ/mol and n = 4.3 respectively.
Date: October 1, 1995
Creator: Meyer, M.K.; Akinc, M. & Kramer, M.J.
Partner: UNT Libraries Government Documents Department

Processing and Oxidation Behavior of Nb-Si-B Intermetallics

Description: Single phase materials of {alpha}-Nb{sub 5}Si{sub 3}, Nb{sub 5}(Si,B){sub 3} (T2) and Nb{sub 5}Si{sub 3}B{sub x} (D8{sub 8}) in the Nb-Si-B system were prepared by powder metallurgy processing. T2 was almost fully dense, while {alpha}-Nb{sub 5}Si{sub 3} and D8{sub 8} were porous after sintering at 1900 C for 2 hours. The lattice parameters of T2 decreased linearly with the substitution of B for Si. Isothermal oxidation testing at 1000 C in flowing air indicated that the oxidation resistances of T2 and D8{sub 8} are much better than {alpha}-Nb{sub 5}Si{sub 3}, but still extremely poor compared to the boron-modified Mo{sub 5}Si{sub 3}. Extensive cracking in the oxide scale and matrix were observed and arose from the volume expansion associated with the formation of Nb{sub 2}O{sub 5} and boron-containing silica glass.
Date: September 30, 2004
Creator: Y.LIU; Thom, A.J.; Kramer, M.J. & Akinc, M.
Partner: UNT Libraries Government Documents Department

Novel Processing of mo-si-b Intermetallics for improved efficiency of power systems

Description: Multiphase composite alloys based on the Mo-Si-B system are candidate materials for ultra-high temperature applications. In non load-bearing applications such as thermal barrier coatings or heat exchangers in fossil fuel burners, these materials may be ideally suited. Alloys based on the Mo{sub 5}Si{sub 3}B{sub x} phase (Tl phase) possess excellent oxidation resistance to at least 1600 C in synthetic air atmospheres. However, the ability of Tl-based alloys to resist aggressive combustion environments has not yet been determined. The present work seeks to investigate the resistance of these Mo-Si-B alloys to simulated combustion atmospheres. Material was pre-alloyed by combustion synthesis, and samples for testing were prepared by classic powder metallurgical processing techniques. Precursor material synthesized by self-heating-synthesis was sintered to densities exceeding 98% in an argon atmosphere at 1800 C. The approximate phase assemblage of the material was 57% Tl, 29% MoB, 14% MoSi{sub 2} (wt%). The alloy was oxidized from 1000-1100 C in flowing air containing water vapor at 18 Torr. At 1000 C the material achieved a steady state mass loss, and at 1100 C the material undergoes a steady state mass gain. The oxidation rate of these alloys in this temperature regime was accelerated by the presence of water vapor compared to oxidation in dry air. The results of microstructural analysis of the tested alloys will be discussed. Techniques and preliminary results for fabricating near-net-shaped parts will also be presented.
Date: September 30, 2004
Creator: Kramer, M.J.; Degirmen, O.; Thom, A.J. & Akinc, M.
Partner: UNT Libraries Government Documents Department


Description: Since the early eighties, we have shared with Leon Van Hove the view that if a QGP were produced in high energy heavy ion colliders that its hadronization products would likely come from small localized in phase space bubbles of plasma. In previous papers we have discussed the case where one to at most a few separated bubbles were produced. In this paper we develop a model based on HIJING to which we added a ring of adjoining multi bubble production, which we believe is a higher cross-section process which dominates the near central rapidity region. We have performed simulations which were designed to be tested by the expected first to become available suitable test data, namely the forthcoming RHIC STAR detector data on 65Gev/n Au colliding with 65 Gev/n Au. We took into account background effects and resonance effects so that a direct comparison with the data, and detailed test of these ideas could be made in the near future. Subsequently 100 Gev/n Au on 100 Gev/n Au forthcoming data can be tested, and of course these techniques, suitably modified by experience can be applied to it and eventually to LHC. We concluded that two charged particle correlations versus the azimuthal angle {Delta}{phi}; vs the opening angle, and vs psuedorapidity {eta}, can detect important bubble signals in the expected background, with statistical significances of 5 - 20{sigma}, provided the reasonably conservative assumptions we have made for bubble production occur. We also predicted charge fluctuation suppressions which increase with the bubble signal, and range from {approx} 5% to 27% in the simulations performed. We demonstrated reasonably that in our model, these charge suppression effects would not significantly be affected by resonances.
Date: March 1, 2003
Partner: UNT Libraries Government Documents Department

Numerical prediction of subsidence with coupled geomechanical-hydrological modeling

Description: A coupled finite element geomechanical-hydrology code is currently under development for application to the problem of predicting groundwater disturbances associated with mine subsidence. The structural-fluid coupling is addressed by calculating the subsided mine geometry, with emphasis placed on determining the strata disturbance and locating damaged regions, for input into a hydrology code, which determines localized volume flow rates and aquifer fluctuations. Benefits from coupling will be best realized when field measurements, an additional aspect of the study concurrent with analytical investigations, indicating the relationship between increasing rock strain and increasing permeability are incorporated into hydraulic material descriptions. Hydrologic and structural calculations are presented to demonstrate computational capabilities applicable to mine subsidence.
Date: January 1, 1981
Creator: Girrens, S.P.; Anderson, C.A.; Bennett, J.G. & Kramer, M.
Partner: UNT Libraries Government Documents Department

Organic C and N stabilization in a forest soil: evidence from sequential density fractionation

Description: In mineral soil, organic matter (OM) accumulates mainly on and around surfaces of silt- and clay-size particles. When fractionated according to particle density, C and N concentration (per g fraction) and C/N of these soil organo-mineral particles decrease with increasing particle density across soils of widely divergent texture, mineralogy, location, and management. The variation in particle density is explained potentially by two factors: (1) a decrease in the mass ratio of organic to mineral phase of these particles, and (2) variations in density of the mineral phase. The first explanation implies that the thickness of the organic accumulations decreases with increasing particle density. The decrease in C/N can be explained at least partially by especially stable sorption of cationic peptidic compounds (amine, amide, and pyrrole) directly to mineral surfaces, a phenomenon well documented both empirically and theoretically. These peptidic compounds, along with ligand-exchanged carboxylic compounds, could then form a stable inner organic layer onto which less polar organics could sorb more readily than onto the highly charged mineral surfaces (''onion'' layering model). To explore mechanisms underlying this trend in C concentration and C/N with particle density, we sequentially density fractionated an Oregon andic soil at 1.65, 1.85, 2.00, 2.28, and 2.55 g cm{sup -3} and analyzed the six fractions for measures of organic matter and mineral phase properties. All measures of OM composition showed either: (1) a monotonic change with density, or (2) a monotonic change across the lightest fractions, then little change over the heaviest fractions. Total C, N, and lignin phenol concentration all decreased monotonically with increasing density, and {sup 14}C mean residence time (MRT) increased with particle density from ca. 150 y to >980 y in the four organo-mineral fractions. In contrast, C/N, {sup 13}C and {sup 15}N concentration all showed the second pattern. All these data ...
Date: July 15, 2005
Creator: Sollins, P; Swanston, C; Kleber, M; Filley, T; Kramer, M; Crow, S et al.
Partner: UNT Libraries Government Documents Department

Old and stable soil organic matter is not necessarily chemically recalcitrant: Implications for modeling concepts and temperature sensitivity

Description: Soil carbon turnover models generally divide soil carbon into pools with varying intrinsic decomposition rates. Although these decomposition rates are modified by factors such as temperature, texture, and moisture, they are rationalized by assuming chemical structure is a primary controller of decomposition. In the current work, we use near edge X-ray absorption fine structure (NEXAFS) spectroscopy in combination with differential scanning calorimetry (DSC) and alkaline cupric oxide (CuO) oxidation to explore this assumption. Specifically, we examined material from the 2.3-2.6 kg L{sup -1} density fraction of three soils of different type (Oxisol, Alfisol, Inceptisol). The density fraction with the youngest {sup 14}C age (Oxisol, 107 years) showed the highest relative abundance of aromatic groups and the lowest O-alkyl C/aromatic C ratio as determined by NEXAFS. Conversely, the fraction with the oldest C (Inceptisol, 680 years) had the lowest relative abundance of aromatic groups and highest O-alkyl C/aromatic C ratio. This sample also had the highest proportion of thermally labile materials as measured by DSC, and the highest ratio of substituted fatty acids to lignin phenols as indicated by CuO oxidation. Therefore, the organic matter of the Inceptisol sample, with a {sup 14}C age associated with 'passive' pools of carbon (680 years), had the largest proportion of easily metabolizable organic molecules with low thermodynamic stability, whereas the organic matter of the much younger Oxisol sample (107 years) had the highest proportion of supposedly stable organic structures considered more difficult to metabolize. Our results demonstrate that C age is not necessarily related to molecular structure or thermodynamic stability, and we suggest that soil carbon models would benefit from viewing turnover rate as codetermined by the interaction between substrates, microbial actors, and abiotic driving variables. Furthermore, assuming that old carbon is composed of complex or 'recalcitrant' compounds will erroneously attribute a greater temperature ...
Date: March 1, 2010
Creator: Kleber, M.; Nico, P.S.; Plante, A.; Filley, T.; Kramer, M.; Swanston, C. et al.
Partner: UNT Libraries Government Documents Department

A metallurgical approach toward alloying in rare earth permanent magnet systems

Description: TiC is added as an alloying agent to Nd{sub 2}Fe{sub l4}B (2-14-1) system to both alter the solidification behavior of the melt and to act as pinning sites to control grain growth. The addition of TIC to 2-14-1 results in a factor of three reduction of the quench rate required to produce amorphous material. In addition, the crystallization temperature of the glass is enhanced leading to enhanced nucleation and finer grain size during crystallization. TIC additions to the stochiometric melt affect the range of primary solidification of the 2-14-1 phase. When TIC is added to the limit of its liquid solubility, the primary solidification range is move further from the stochiometric composition to the Nd rich region.
Date: December 31, 1995
Creator: McCallum, R.W.; Willard, M.A.; Dennis, K.W.; Branagan, D.J. & Kramer, M.J.
Partner: UNT Libraries Government Documents Department


Description: Insight into the solidification behavior of Nd{sub 2}Fe{sub 14}B-based materials processed by rapid solidification techniques has been obtained by a systematic experimental study of the Curie temperatures of selected phases found in these materials. Nd{sub 2}Fe{sub 14}B-based materials fabricated by two disparate rapid solidification techniques, inert gas atomization (IGA) and melt-spinning, has been studied. The compositions of the starting materials have been altered with additions of the refractory elements Ti and C which are known to alter the solidification behavior of these materials. Special emphasis has been placed on trying to understand the effect of alloying additions upon the nature of the quenched glass, the distribution of the elemental additions within the Nd{sub 2}Fe{sub 14}B lattice and the evolution of the elemental partitioning with quench rate and annealing condition. The experimental Curie temperature data obtained using thermal analysis methods from the particles produced by gas-atomization is consistent with both an ejection of quenched-in refractory species from the crystalline Nd{sub 2}Fe{sub 14}B lattice and with increased crystallographic order as particle size, and hence grain size, increases. Magnetic ac susceptibility measurements performed on nominally-amorphous Nd{sub 2}Fe{sub 14}B ribbons produced by melt-spinning indicate a decrease of the Curie temperature with increasing quench rate, a result that may be attributed either to the degree of Ti/C retention in the glass or to the degree of disorder in the glass, independent of Ti/C retention.
Date: November 2, 1999
Partner: UNT Libraries Government Documents Department

Effects of Wet Air and Synthetic Combustion Gas Atmospheres on the Oxidation Behavior of Mo-Si-B Alloys

Description: Continuing our work on understanding the oxidation behavior of multiphase composite alloys based on the Mo-Si-B system, we investigated three alloys in the Mo-Si-B system, designated as A1, A2, and A3. The nominal phase assemblages of these alloys are: A1 = Mo{sub 5}Si{sub 3}B{sub x} (T1)-MoSi{sub 2}-MoB, A2 = T1-Mo{sub 5}SiB{sub 2} (T2)-Mo{sub 3}Si, and A3 = Mo-T2-Mo{sub 3}Si. Our previous work showed that for exposures to 1100 C, all alloys formed a protective oxide scale in dry air. Exposures to wet air containing about 150 Torr water promoted the formation of a multiphase layer near the scale/alloy interface composed of Mo and MoO{sub 2}. Interrupted mass loss measurements indicated a near zero mass change. In the present study, isothermal mass measurements were conducted in order to quantitatively determine the oxidation rate constants at 1000 C in both dry and wet air. These measurements are critical for understanding the nature of scale development during the initial exposure, as well as the nature of scale stability during the long-term exposure. Isothermal measurements were also conducted at 1600 C in dry air to make an initial determination of alloy stability with respect to Vision 21 goals. We also conducted alloy oxidation testing in a synthetic oxidizing combustion atmosphere. Alloys were exposed up to 300 hours at 1100 C to a gas mixture having an approximate gas composition of N{sub 2} - 13 CO{sub 2} - 10 H{sub 2}O - 4 O{sub 2}. This gas composition simulates oxidizing flue gas, but does not contain a sulfidizing agent that would also be present in flue gas. The oxidized samples were carefully analyzed by SEM/EDS. This analysis will be discussed to provide an understanding of the role of water vapor and the synthetic combustion atmosphere on the oxidative stability of Mo-Si-B alloys.
Date: April 24, 2003
Creator: Kramer, M.J.; Thom, A.J.; Mandal, P.; Behrani, V. & Akinc, M.
Partner: UNT Libraries Government Documents Department