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Results for “Zero thermal expansion”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Composite Riflescope

Bushnell Division of Bausch & Lomb's Armor-Sight riflescope combines the company's world-renowned optics with a graphite composite (Graphlon VI) developed for space applications. The riflescope is 10 percent lighter than aluminum scopes, and, because its thermal expansion coefficient is near zero, optical distortion from heat and cold extremes is eliminated. It is fogproof and waterproof; advanced multicoated optics provide maximum light transmission to brighten target ranges. Bushnell was assisted by NIAC/USC in searching for technical information on graphic composites and in overcoming difficulties with bonding and porosity.

Source record↗
NASA NTRS1980

Anorthite - Thermal equation of state to high pressures

New shock-wave data are presented for anorthite from which a full high-temperature, high-pressure equation of state is derived. Whereas anorthite has relatively low values of thermal expansion and Grueneisen parameter at zero pressure, it is found that these attain relatively high values in the high density state corresponding to the high-pressure phase Hugoniot but decrease upon compression as expected. It is noted that higher order anharmonic contributions decrease more rapidly with pressure and that the thermal expansion therefore saturates to a high temperature value at pressures above about 100 GPa. Reduction of the Hugoniot data permits shock temperatures to be calculated; it also yields a principal adiabat for the high pressure branch of the Hugoniot. The initial bulk modulus of this adiabat is essentially identical to that of anorthite, whereas the initial density is about 3.40 Mg/cu m.

Jeanloz, R.↗
DOE OSTI2021

Modeling brittle fracture due to anisotropic thermal expansion in polycrystalline materials

Here, this work investigated brittle fracture of polycrystalline materials due to thermal stresses arising from anisotropic thermal expansion. We used phase-field fracture simulations with the properties of alpha-uranium (α-U) and assumed a linear elastic mechanical response. Three-dimensional simulations were used to predict fracture for various conditions and crystallographic textures. We found that fracture was more pronounced during cooling than during heating because the anisotropy increased with temperature. We also found that the total crack surface area increased with increasing average misorientation, while the net shape change of the material decreased with increasing misorientation. Two-dimensional simulations in which one crystallographic coefficient of thermal expansion (CTE) was set to zero indicated that the expansion behavior in the crystallographic direction with the smallest CTE was the primary cause of fracture.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Electronically driven collapse of the bulk modulus in δ -plutonium

Plutonium metal exhibits an anomalously large softening of its bulk modulus at elevated temperatures that is made all the more extraordinary by the finding that it occurs irrespective of whether the thermal expansion coefficient is positive, negative, or zero—representing an extreme departure from conventional Grüneisen scaling. We show here that the cause of this softening is the compressibility of plutonium’s thermally excited electronic configurations, which has thus far not been considered in thermodynamic models. We show that when compressible electronic configurations are thermally activated, they invariably give rise to a softening of the bulk modulus regardless of the sign of their contribution to the thermal expansion. The electronically driven softening of the bulk modulus is shown to be in good agreement with elastic moduli measurements performed on the gallium-stabilized δ phase of plutonium over a range of temperatures and compositions and is shown to grow rapidly at small concentrations of gallium and at high temperatures, where it becomes extremely sensitive to hydrostatic pressure.

36 MATERIALS SCIENCE↗
NASA NTRS1985

Properties of Low-Expansion Laminates

Laminate elastic constants and coefficients of thermal expansion calculated for near-zero-expansion graphite/aluminum and graphite/ magnesium composites. Report presents results in graphic form for these properties as function of laminate angle and fiber volume fraction for four high-modulus continuous-pitch fiber.

Kural, M.↗
DOE OSTI2021

Empty perovskites as Coulomb floppy networks: Entropic elasticity and negative thermal expansion

Floppy networks (FNs) provide valuable insight into the origin of anomalous mechanical and thermal properties in soft matter systems, from polymers, rubber, and biomolecules to glasses and granular materials. Here, we use the same FN concept to construct a quantitative microscopic theory of empty perovskites, a family of crystals with ReO 3 structure, which exhibit a number of unusual properties. One remarkable example is ScF 3 , which shows a near-zero-temperature structural instability and large negative thermal expansion (NTE). Furthermore, we trace these effects to an FN-like crystalline architecture formed by strong nearest-neighbor bonds, which is stabilized by net electrostatic repulsion that plays a role similar to osmotic pressure in polymeric gels. NTE in these crystalline solids, which we conceptualize as Coulomb floppy networks, emerges from the tension effect of Coulomb repulsion combined with the FN's entropic elasticity and has the same physical origin as in gels and rubber. Our theory provides an accurate, quantitative description of phonons, thermal expansion, compressibility, and structural phase diagram, all in excellent agreement with experiments. The entropic stabilization of critical soft modes, which play only a secondary role in NTE, explains the observed phase diagram. Significant entropic elasticity resolves the puzzle of a marked, ≈50% discrepancy between the experimentally observed bulk modulus and ab initio calculations. The Coulomb FN approach is potentially applicable to other important materials with markedly covalent bonds, from perovskite oxides to iron chalcogenides, whose anomalous vibrational and structural properties are still poorly understood.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1991

Graphite Fiber/Copper Matrix Composites for Space Power Heat Pipe Fin Applications

High specific thermal conductivity (thermal conductivity divided by density) is a major design criterion for minimizing system mass for space power systems. For nuclear source power systems, graphite fiber reinforced copper matrix (Gr/Cu) composites offer good potential as a radiator fin material operating at service temperatures above 500 K. Specific thermal conductivity in the longitudinal direction is better than beryllium and almost twice that of copper. The high specific thermal conductivity of Gr/Cu offers the potential of reducing radiator mass by as much as 30 percent. Gr/Cu composites also offer the designer a range of available properties for various missions and applications. The properties of Gr/Cu are highly anisotropic. Longitudinal elastic modulus is comparable to beryllium and about three times that of copper. Thermal expansion in the longitudinal direction is near zero, while it exceeds that of copper in the transverse direction.

McDanels, David L.↗
NASA NTRS1985

Transient Heat Transfer in Zero Gravity Environment

The objective is to provide computer codes and/or correlations for application in the design of transient heat transfer systems. The mathematical models in the computer codes are being tested by experimental data obtained in the laboratory using optical techniques. The elimination of natural convection (buoyancy) in the experimental data obtained in zero-g (KC-135) facilitates the study of thermal expansion effects which is of interest in the development and testing of the mathematical models of the transient heat transfer. Initial flight in the KC 135 (June 1983) suggested some modifications to the experimental apparatus and the data acquisition technique (high speed video will replace high speed movies for recording optical records generated during the experiments). A series of KC-135 flights with this experiment on board are scheduled for summer/fall 1984. The acquisition of the aforementioned data using interferometry and beam deflection optical techniques is anticipated. The measurements provide time dependent temperature fields above a horizontal heater surface submerged in a static fluid (Freon 13). The heater surface is electrically heated for a time interval approximately 0.100 sec. during which the data are optically recorded.

Giarratano, P. G.↗
NASA NTRS2004

Vacuum/Zero Net-Gravity Application for On-Orbit TPS Tile Repair

The Orbiter Columbia catastrophically failed during reentry February 1, 2003. All space Shuttle flights were suspended, including logistics support for the International Space Station. NASA LaRC s Structures and Materials Competency is performing characterizations of candidate materials for on-orbit repair of orbiter Thermal Protection System (TPS) tiles to support Return-to-Flight activities led by JSC. At least ten materials properties or attributes (adhesion to damage site, thermal protection, char/ash strength, thermal expansion, blistering, flaming, mixing ease, application in vacuum and zero gravity, cure time, shelf or storage life, and short-term outgassing and foaming) of candidate materials are of interest for on-orbit repair. This paper reports application in vacuum and zero net-gravity (for viscous flow repair materials). A description of the test apparatus and preliminary results of several candidate materials are presented. The filling of damage cavities is different for some candidate repair materials in combined vacuum and zero net-gravity than in either vacuum or zero net- gravity alone.

Harvey, Gale A.↗
NASA NTRS2004

Vacuum/Zero Net-Gravity Application for On-Orbit TPS Tile Repair

The Orbiter Columbia catastrophically failed during reentry February 1, 2003. All Space Shuttle flights were suspended, including logistics support for the International Space Station. NASA Langley Research Center s (LaRC) Structures and Materials Competency is performing characterizations of candidate materials for on-orbit repair of orbiter Thermal Protection System (TPS) tiles to support Return-to-Flight activities led by Johnson Space Center (JSC). At least ten materials properties or attributes (adhesion to damage site, thermal protection, char/ash strength, thermal expansion, blistering, flaming, mixing ease, application in vacuum and zero gravity, cure time, shelf or storage life, and short-term outgassing and foaming) of candidate materials are of interest for on-orbit repair. This paper reports application in vacuum and zero net-gravity (for viscous flow repair materials). A description of the test apparatus and preliminary results of several candidate materials are presented. The filling of damage cavities is different for some candidate repair materials in combined vacuum and zero net-gravity than in either vacuum or zero net-gravity alone.

Harvey, Gale A.↗
NASA NTRS2012

Method of Bonding Optical Elements with Near-Zero Displacement

The International X-ray Project seeks to build an x-ray telescope using thousands of pieces of thin and flexible glass mirror segments. Each mirror segment must be bonded into a housing in nearly perfect optical alignment without distortion. Forces greater than 0.001 Newton, or displacements greater than 0.5 m of the glass, cause unacceptable optical distortion. All known epoxies shrink as they cure. Even the epoxies with the least amount of shrinkage (<0.01%) cause unacceptable optical distortion and misalignment by pulling the mirror segments towards the housing as it cures. A related problem is that the shrinkage is not consistent or predictable so that it cannot be accounted for in the setup (i.e., if all of the bonds shrunk an equal amount, there would be no problem). A method has been developed that allows two components to be joined with epoxy in such a way that reduces the displacement caused by epoxy shrinking as it cures to less than 200 nm. The method involves using ultraviolet-cured epoxy with a displacement sensor and a nanoactuator in a control loop. The epoxy is cured by short-duration exposures to UV light. In between each exposure, the nano-actuator zeroes out the displacement caused by epoxy shrinkage and thermal expansion. After a few exposures, the epoxy has cured sufficiently to prevent further displacement of the two components. Bonding of optical elements has been done for many years, but most optics are thick and rigid elements that resist micro-Newton-level forces without causing distortion. When bonding thin glass optics such as the 0.40-mm thick IXO X-ray mirrors, forces in the micro- and milli-Newton levels cause unacceptable optical figure error. This innovation can now repeatedly and reliably bond a thin glass mirror to a metal housing with less than 0.2 m of displacement (<200 nm). This is an enabling technology that allows the installation of virtually stress-free, undistorted thin optics onto structures. This innovation is applicable to the bonding of thin optical elements, or any thin/flexible structures, that must be attached in an undistorted, consistent, and aligned way.

Robinson, David↗
DOE OSTI2025

Anharmonic phonons, thermal expansion, and nuclear quantum effects in Zn

The anharmonic behavior of phonons and thermal expansion of hexagonal zinc were studied from 15 to 690 K by inelastic neutron scattering (INS) and ab initio simulations. Phonon spectra were measured for Q-points covering the full Brillouin zone, giving the phonon density of states (DOS) and dispersions along high-symmetry directions. The dispersions were sharp at 15 K, but diffuse intensity was observed at energies above them. The dispersions broadened with temperature T and the diffuse intensity became stronger. This diffuse intensity appeared in all INS measurements and simulations, except for classical molecular dynamics at 15 K. The temperature-dependent effective potential (TDEP) method, which included the nuclear quantum effect from zero-point vibrational dynamics, was used to calculate the free energy and thermal expansion. For T < 100 K nuclear quantum effects were important for obtaining the correct negative thermal expansion, and path integral molecular dynamics (PIMD) was particularly effective for obtaining the negative thermal expansion in the basal plane. A Heisenberg-Langevin model for interacting phonons coupled to a thermal bath was able to reproduce the shape and intensity of the diffuse spectral features.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2017

Thermal Expansion from Stochastic Nonlinear Acoustic Fields

The methods of stochastic mechanics are applied to nonlinear acoustic fields generated by random acoustic radiation sources associated with oscillating lattice sites in nonlinear lattices. The assumption of stochastically independent zero-point and temperature-dependent acoustic fields leads to expressions of the thermodynamic internal and Helmholtz free energies per unit mass in terms of modal energies per unit mass that account for the nonlinearity of the propagation modes. The thermodynamic state functions canonically transform to the familiar results of a system of quantized, simple harmonic oscillators in the linear field limit. The thermal expansion coefficient, derived from the Helmholtz free energy per unit mass, is obtained as a sum of the zero-point modal nonlinearity parameters, weighted by temperature-dependent, modal heat capacities. The relationship is fully anharmonic, in contrast to commonly used quasi-harmonic models, and predicts with excellent agreement the experimentally observed null thermal expansion of vitreous silica at the ‘cross-over’ temperature corresponding to the balance between long wavelength modes that contribute negative nonlinearity parameters to the modal sum and short wavelength modes that contribute positive nonlinearity parameters.

Cantrell, John H., Jr.↗
NASA NTRS1988

Equation of state of ammonia-water liquid - Derivation and planetological applications

The present least-squares fit calculation of the equation of state for ammonia-water liquid has yielded results for the zero-100 wt pct NH3, 170-300 K temperature, and zero-10 kb pressure parameter ranges. In conjunction with solid density and thermodynamic measurements, the present calculated and measured liquid densities are used to yield estimates of density and thermal expansion at 1 bar for the solid phases of ammonia's monohydrate, dihydrate, and hemihydrate between absolute zero and their respective melting points. Attention is given to the implications for icy satellite morphologic and tectonic forms of peritectic ammonia-water liquid that is neutrally buoyant relative to the corresponding solid phases.

Croft, S. K.↗
DOE OSTI2023

Coupling of magnetism, crystal lattice, and transport in EuCuP and EuCuAs

EuCuP and EuCuAs are members of a family of materials with candidates for realizing magnetically tuned electronic topology. Here, in this work, the magnetic phase transitions and magnetoelastic coupling of EuCuP and EuCuAs have been investigated. Around the Curie temperature, the thermal expansion coefficient and specific-heat capacity of EuCuP are found to have two closely spaced features, at approximately 30 and 31.3 K, which may indicate a cascading magnetic transition or perhaps an electronic transition closely coupled to the magnetic ordering. The zero-field magnetoelastic coupling appears to be stronger in EuCuP than in EuCuAs, and field-dependent measurements suggest this is due to the dominant ferromagnetic interaction in EuCuP as opposed to antiferromagnetic order in EuCuAs below T N =13.5 K. Thermal expansion is anisotropic around T N in EuCuAs, with a maximum expansion along [001] occurring above T N prior to a stiffening of this c -axis component on cooling through T N ; the expansion of the basal plane has a lambda-like peak centered slightly above T N . Matching these behaviors, the ac susceptibility data for EuCuAs suggest the presence of strong ferromagnetic correlations above T N in the vicinity where the c-axis expansion peaks. Both compounds possess similar electrical and thermoelectric transport behaviors, with short-range magnetic order likely playing an important role above T C or T N . Transport properties suggest these are predominantly hole doped due to intrinsic defects, and narrow-gap semiconducting or semimetallic behavior may be achievable if the underlying defects can be tuned.

36 MATERIALS SCIENCE↗
NASA NTRS1984

Universal binding energy relations in metallic adhesion

Rose, Smith, and Ferrante have discovered scaling relations which map the adhesive binding energy calculated by Ferrante and Smith onto a single universal binding energy curve. These binding energies are calculated for all combinations of Al(111), Zn(0001), Mg(0001), and Na(110) in contact. The scaling involves normalizing the energy by the maximum binding energy and normalizing distances by a suitable combination of Thomas-Fermi screening lengths. Rose et al. have also found that the calculated cohesive energies of K, Ba, Cu, Mo, and Sm scale by similar simple relations, suggesting the universal relation may be more general than for the simple free electron metals for which it was derived. In addition, the scaling length was defined more generally in order to relate it to measurable physical properties. Further this universality can be extended to chemisorption. A simple and yet quite accurate prediction of a zero temperature equation of state (volume as a function of pressure for metals and alloys) is presented. Thermal expansion coefficients and melting temperatures are predicted by simple, analytic expressions, and results compare favorably with experiment for a broad range of metals.

Ferrante, J.↗
NASA NTRS1978

Atmospheric Cloud Physics Laboratory thermal control

The paper presents the development background and the present status of the Atmospheric Cloud Physics Laboratory (ACPL) thermal control capability. The ACPL, a Spacelab payload, is currently in the initial flight hardware development phase for a first flight scheduled in June 1981. The ACPL is intended as a facility for conducting a wide variety of cloud microphysics experimentation under zero gravity conditions. The cloud chambers, which are key elements of the ACPL, have stringent thermal requirements. Thus the expansion chamber inner walls must be uniform to within + or - 0.1 C during both steady-state and transient operation over a temperature range of +30 to -25 C. Design progression of the expansion chamber, from early in-house NASA-MSFC concepts (including test results of a prototype chamber) to a thermal control concept currently under development, is discussed.

Moses, J. L.↗