Showing papers on "Thermal expansion published in 1975"

Thermal expansion of some diamondlike crystals

Abstract: The thermal expansion of AlN, cubic BN, and BP has been measured from 77 to 1300 K by x−ray techniques The derived thermal expansion coefficients are compared with those of diamond, Si, Ge, SiC, GaP, and BeO using the Debye temperature as a scaling parameter It is apparent that the thermal expansion of Si is the smallest, SiC is intermediate, and all of the others are larger The thermal expansion of Mo and W is also reviewed in order to determine how well these metals match the thermal expansion of the adamantine or diamondlike crystals

Thermal Expansion: Metallic Elements and Alloys

Abstract: The introductory sections of the work are devoted to the theory of thermal expansion of solids and to methods for the measurement of the linear thermal expansion of solids (X-ray methods, high speed methods, interferometry, push-rod dilatometry, etc.). The bulk of the work is devoted to numerical data on the thermal linear expansion of all the metallic elements, a large number of intermetallics, and a large number of binary alloy systems and multiple alloy systems. A comprehensive bibliography is provided along with an index to the materials examined.

Thermal Expansion of Periclase and Olivine, and their Anharmonic Properties

Abstract: Thermal expansions of single-crystal periclase and olivine were measured by a dilatometric method in a temperature range from room-leve1 to 1000°C. The calculated thermal expansion coefficients of periclase and olivine are given in a range of temperature from -250 to 1500°C based on the Gruneisen's theory of thermal expansion. This theory involves several harmonic and anharmonic parameters. The parameters determined in this study are well related to acoustic wave velocities, pressure and temperature derivatives of bulk modulus, Gruneisen's parameter, which have been determined by other means. It is shown that the accurate thermal expansion data provide a good estimation of elastic wave velocities and other physical constants, which are important in the study of the equation of state of the deep interior of the earth.

Positron trapping in solid and liquid metals

Abstract: Measurements of the peak counting rate in the angular correlation curve of positron annihilation radiation have been performed in the solid and liquid phase of indium, lead, and aluminum, and in the solid phase of magnesium, as a function of temperature. In the solid phase In, Pb, and Al show at low temperatures the thermal-expansion effect and at higher temperatures in addition the positron-trapping effect. At the melting point the peak counting rate increases abruptly and stays then constant with temperature. This behavior in the liquid phase is interpreted as "saturation trapping," i.e., all positrons annihilate from a trapping site and the thermal expansion of the lattice is not effective for these positrons. Trapped positrons are effectively "shielded" from the thermal expansion of the lattice. Therefore, it is possible to separate the thermal-expansion effect from the vacancy-trapping effect and very accurate values for the monovacancy formation energy can be obtained. A difference was found in the nature of trapping sites in solid and liquid aluminum. Magnesium shows only the thermal-expansion effect and no vacancy-trapping effect.

The low-temperature thermal expansion and Gruneisen parameters of some tetrahedrally bonded solids

Abstract: The results of thermal expansion measurements using a three-terminal capacitance dilatometer on Ge, GaAs, ZnS, ZnSe and CdTe below 30K and on ZnSe and CdTe between 57 and 90K are reported. Respective values of 0.49, 0.32, -0.14, 0.0 and -0.85 derived for gamma 0th, the zero temperature limit of the Gruneisen parameter gamma =3 alpha VBs/Cp are given. These are in good agreement with the values of gamma 0el calculated from the pressure dependence of the elastic constants. gamma (T) as a function of reduced temperature, T/ theta 0, where theta 0 is the Debye temperature determined at the zero temperature limit, is found to have an essentially universal form and passes through a negative minimum at T approximately 0.06 theta 0. The implications of this observation and the importance of the degree of ionicity in dictating gamma 0 are discussed.

Elastic modulus, thermal expansion, and specific heat at a phase transition

Abstract: The interrelation of the elastic modulus, thermal-expansion coefficient, and specific heat of a transformed phase relative to the untransformed phase is calculated assuming a particular but useful form of the thermodynamic potential. For second-order phase transitions where this potential applies, measurements of modulus, expansion, and specific heat can yield the general (longitudinal as well as shear) first- and second-order stress (or strain) dependences of the transition temperature and of the order parameter at absolute zero. An exemplary application to one type of phase transition is given. (AIP)

Comparison of observed and predicted structural parameters of mica at high temperature

Abstract: A geometrical model structure for trioctahedral micas has been applied to predict the structural changes of a synthetic fluorphlogopite, KMg3(Si3AI)OIoF2, as a function of temperature and these are compared with observed structural parameters determined at 700°C. The model employs the cell dimensions measured as a function of temperature, the bond lengths determined at room temperature and thermal expansion coefficients of the bond lengths determined in previous studies. The predicted tetrahedral rotation angle, c~, suggests that the silica oxygen ring about the potassium becomes more nearly hexagonal at higher temperatures. The mode of expansion of the Mg octahedron changes at about 400°C, whereafter the octahedron tends to become elongated along the normal to the layer formed by the octahedra. This change in the mode of expansion corresponds to the observed kink in the linear expansivities of the cell dimensions. The predicted parameters have been confirmed by a structure refinement on data collected at 700°C. The observed ~ (3 ~) and octahedral flattening angles for magnesium (58.0 °) and for potassium (56.5 °) at 700 °C agree with the predicted values. The very large expansion coefficient of the K-O bond length accounts for large linear expansivity along c.

The anisotropic thermal expansion of boron nitride

Abstract: Interferometric measurements of the linear thermal expansion coefficients αc and αa in the c and a axial directions of well-orientated hexagonal pyrolytic boron nitride are reported for temperatures between approximately 80 and 780 K. The primary data for the direction parallel to the c-crystallographic axis yield smoothed results which are believed to be accurate in an absolute sense to within 3% at 780 K, falling to 5% at 80 K. The corresponding figures for the direction perpendicular to the c-crystallographic axis are 9% at 780 K, passing smoothly through 3% at 230 K to 6% at 80 K. In association with earlier specific heat capacity results and provisional values for the elastic constants c 13 and c 33, a Gruneisen parameter corresponding to the direction parallel to the c-crystallographic axis has been calculated as a function of temperature. This parameter has been applied to the determination of the temperature dependence of averaged reduced vibrational frequencies associated with this axial...

Boron Nitride Composites By Chemical Vapor Deposition

Abstract: Composites of boron nitride (BN) have been made by the chemical vapor deposition (CVD) of a BN matrix on a BN felt fiber substrate. Reactant gases were boron trifluoride and ammonia. The composites have a relatively high density (1.70 g/cm3), a crystallite size LC = 150 A and an interlayer spacing d002 = 3.35 A. Measurements of elastic modulus and thermal conductivity and expansion showed some anisotropy as a result of the preferred fiber orientation of the substrate.

Thrust chamber life prediction. Volume 1: Mechanical and physical properties of high performance rocket nozzle materials

Abstract: Pertinent mechanical and physical properties of six high conductivity metals were determined. The metals included Amzirc, NARloy Z, oxygen free pure copper, electroformed copper, fine silver, and electroformed nickel. Selection of these materials was based on their possible use in high performance reusable rocket nozzles. The typical room temperature properties determined for each material included tensile ultimate strength, tensile yield strength, elongation, reduction of area, modulus of elasticity, Poisson's ratio, density, specific heat, thermal conductivity, and coefficient of thermal expansion. Typical static tensile stress-strain curves, cyclic stress-strain curves, and low-cycle fatigue life curves are shown. Properties versus temperature are presented in graphical form for temperatures from 27.6K (-410 F) to 810.9K (1000 F).

Ceramic mounting and heat sink device

Abstract: This relates to a multi-layer composite metallic sheet having a predetermined coefficient of thermal expansion for use as a heat sink and mounting arrangement when bonded to a ceramic substrate. Since copper has a coefficient of thermal expansion greater than that of ceramic and molybdenum has a coefficient of thermal expansion less than that of ceramic, layers of copper and molybdenum can be combined to provide a composite having a coefficient of thermal expansion equal to that of ceramic. To avoid a bimetallic effect, a core layer of a fused metal is sandwiched between two outer layers of the second metal.

The thermal expansion and high temperature transformation of GeSe

Abstract: The thermal expansion of GeSe has been studied above room temperature up to the melting point of 670 plus or minus 5 C by X-ray diffraction techniques using a 190 mm Unicam high temperature camera. The thermal expansion of the crystallographic axes is linear with a distinct change in the expansion coefficients for all axes above 400 C. The relative changes in the axes indicate a rearrangement of the structure towards cubic symmetry with increasing temperature. The transformation of GeSe from the orthorhombic to a normal NaCl-type structure is observed at 651 plus or minus 5 C. The lattice parameter of the cubic form of GeSe is a 0 ? 5.730 plus or minus 0.003 A at 656 C. The GeSe lattice remains cubic up to the melting point.

Lattice parameter of niobium between 4.2 and 300 K

Abstract: The results of lattice parameter measurements and the linear thermal expansion coefficient of niobium are reported from liquid helium temperature to room temperature, using a commercially available cryostat. 2 references.

Carbon-Felt, Carbon-Matrix Composites: Dependence of Thermal and Mechanical Properties on Fiber Precursor and Matrix Structure

Abstract: Properties of carbon-felt, pyrolytic carbon-matrix composites have been measured as a function of fiber precursor [rayon and polyacrylonitrile (PAN)] and matrix microstructure (smooth laminar, rough laminar, and isotropic). The primary matrix effect is caused by the graphitic nature of the heat-treated rough laminar matrix which yields a high composite thermal conductivity. The increased modulus of the PAN-based fibers results in increased composite strength and modulus and a significantly reduced thermal expansion. A heat-treated, PAN-based carbon felt, rough laminar carbon matrix composite has a superior thermal shock figure-of-merit based on these results.

Thermal expansion near a critical solution point

Abstract: We report precise measurements of the density as a function of temperature in the one‐phase region near the consolute point in nitroethane + 3‐methylpentane. We find evidence of the critical anomaly in the thermal expansion, but are not able to determine a unique value for the critical exponent α. We have performed computer experiments to determine under what conditions α could be extracted from thermal expansion data.

X‐ray powder diffraction at low temperature applied to the determination of magnetoelastic properties in terbium iron garnet

Abstract: An x‐ray powder diffraction apparatus has been built to perform experiments between 2.6 and 350 K. The experimental procedure and the data analysis allow the measurement of small lattice distortions and very small parameter variations with a good accuracy. Relative variations of the crystal parameters of terbium iron garnet, with an accuracy up to 10−5, have been observed at low temperature. A very small lattice distortion has been determined: TbIG becomes rhombohedral below 100 K; at 4.2 K the rhombohedral angle of the distorted cell is αR=89°52′30″, while the cell side is slightly contracted. A noncollinear spin arrangement, an anomalous thermal expansion (Δa=28×10−4 at 4.2 K), and a rhombohedral distortion (β=90°−αR=7′30″ at 4.2 K) appear simultaneously at about 45 K. These phenomena are to be connected with a very large magnetostriction (λIII=2400×10−6 at 4.2 K).

X-ray investigation of copper selenides Cu2−xSe (2.00≥2-x≥1.72)

Abstract: The lattice parameters and the linear coefficient of the lattice thermal expansion of f.c.c. β-Cu2−xSe (1.86 ≥ 2−x ≥ 1.72) were determined by means of the Debye–Scherrer X-ray diffraction technique in the temperature range 25–336°C. The concentration and temperature dependence of the coefficient of thermal expansion are discussed. In addition the equilibrium phase diagram of the Cu–Se system in the region of a non-stoichiometric Cu2−xSe compound (2.00 ≥2−x ≥1.72) was redetermined, with special consideration of the homogeneity range of the f.c.c. β-Cu2−xSe, and compared with previously published results.

Study of Thermal Expansion of NaNO 2 with Special Emphasis on the Vicinity of the Transition Points

Abstract: By use of a capacitance method, the thermal expansions of NaNO 2 ( T C =163.9°C, T N =165.2°C) along the a -, b - and c -axes were measured from -180°C to 240°C with the accuracy of 1×10 -6 cm in Δ l . Anomalies associated with the phase transitions were observed over the wide temperature range 100 to 200°C. The thermal expansion showed a distinct jump at T C , and the thermal expansion coefficient exhibited a divergent character near T N . The critical exponents were found to be 0.34∼0.36 for T > T N and 0.09∼0.20 for T < T N . These agree very well with those of the specific heat. It was revealed that the Neel temperature determined by the analysis of the thermal expansion data lies 0.1∼0.2 deg below the peak position of the dielectric constant. The pressure dependences of the transition points deduced from the Clausius-Clapeyron equation and the Pippard equation were found to agree with the result of the hydrostatic pressure experiment.

Warp-resistant heat sink

Abstract: A warp-resistant heat sink suitable for soldering to one side of a relatively fragile, ceramic semiconductor substrate comprises a plate of heat-conducting material having a plurality of slits along two sides thereof, and a plurality of U-shaped heat-conducting members each of which extends through a respective one of the slits in the plate. The U-shaped heat-conducting members are soldered to the same side of the plate, the members along one edge of the plate being off-set with respect to the members along the opposite side of the plate in order to increase the heat transfer efficiency when air is forced through the heat sink. The plate material is selected so as to have a substantially identical thermal coefficient of expansion as that of the substrate material. When the heat sink plate is soldered to the substrate surface, a laminate is thereby formed comprising two outer layers of material having substantially identical thermal coefficients of expansion and an inner layer having a different thermal coefficient of expansion. Relatively large heat sinks can thus be fabricated which have a high resistance to the warpage which would otherwise result from the dissimilar thermal expansion and contraction of the ceramic substrate and the heat-conducting members.

Determining absolute thermal expansion of titania-silica glasses: a refined ultrasonic method.

Abstract: Specific test conditions for determining ultrasonic velocities in titania-silica glasses are shown to improve the experimentally established linear correlation between velocity and thermal expansion. Finer surface finish, normalized thermal history (annealing), and controlled temperature for the test specimen improve the relationship. A statistical analysis shows that 5–35°C average expansion coefficients can be accurately predicted from ultrasonic velocities with a standard deviation of 1 ppb/°C. Excellent agreement is established between the ultrasonic predicted expansion and test results supplied by the University of Arizona Optical Sciences Center.