Showing papers on "Thermal expansion published in 1976"

Effects of temperature and pressure on the crystal structure of forsterite

Abstract: The crystal structure of synthetic forsterite has been studied as a function of temperature and pressure. Crystal structures have been refined from three-dimensiona l diffraction data collected at temperatures from -196°C to 1020°C and at pressures to 50 kbar. Volume compressibility and thermal expansion of individual magnesium octahedra are comparable to those of bulk foresterite. However, the silicon tetrahedron neither expands nor compresses within the range of conditions investigated. Thus, changes in Mg-0 bond distances account for virtually all of forsterite's volume response to changes in temperature and pressure. Short Mg-0 bonds vary significantly less with temperature and pressure than do long bonds, implying that shorter bonds are stronger. Octahedral distortions increase with temperature, but show no strong trends with increasing pressure.

The thermal expansion of 2H-MoS2, 2H-MoSe2 and 2H-WSe2 between 20 and 800°C

Abstract: The hexagonal cell dimensions a and c of 2H-MoS2, 2H-MoSe2 and 2H-WSe2 have been measured over the temperature range 20 to 800 °C. In all three compounds a and c increased non-linearly with temperature, the linear thermal expansion coefficient of c being greater than that of a. Above 500°C the compounds begin to decompose in vacuum.

Binary Titania-Silica Glasses Containing 10 to 20 Wt% TiO2

Abstract: A series of glasses in the TiO2-SiO2 system was prepared by the flame hydrolysis boule process. Clear glasses containing as much as 16.5 wt% TiO2 were obtained. More TiO2 caused opacity due to phase separation and anatase/rutile crystallization during glass boule formation. Glasses in the 12 to ∼17 wt% TiO2 range were metastable and showed structural rearrangements on heat treatment at temperatures as low as 750CEC (∼200° below the annealing point). These changes were accompanied by large changes in thermal expansion. Thermal treatment can be designed to produce almost any desired expansion between α-200+700=−5 × 10-7/°C and +10 × 10-7/°C. Zero expansion between 0 and 550°C was obtained. Evidence that these changes are due to phase separation and anatase formation is presented. Viscosity data in the glass transition range, refractive index, and density are also presented.

Residual stress in silicon nitride films

Abstract: The mechanical stress caused by Si3N4 films on (111) oriented Si wafers was studied as a function of the Si3N4 film thickness, deposition rate, deposition temperature and film composition. The Si3N4 films were prepared by the reaction of gaseous SiH4 and NH3 in the temperature range 700–1000°C. The curvature of the Si substrates caused by the Si3N4. films is related to the film stress; the substrate curvature was measured by an optical interference technique. The measured Si3N4. film stress was found to be highly tensile with a magnitude of about 1010 dynes/cm2. For the thickness range of 2000–5000A, there was no change in the measured stress. The total film stress was observed to decrease for decreasing deposition rate and increasing deposition temperature. A large change in film stress was observed for films containing excess Si; the stress decreased with increasing Si content. Based on published values for the thermal expansion coefficients for Si and Si3N4, a published value for Young’s Modulus for Si3N4, and the measured total stress values, a consistent argument is developed in which the total stress consists of a compressive component due to thermal expansion coefficient mismatch and a larger tensile intrinsic stress component. Both the thermal and intrinsic stress components vary with film deposition temperature in directions which decrease the total room temperature stress for higher deposition temperatures.

Magnetization, Thermal Expansion and Low Temperature Specific Heat of Fe 72 Pt 28 Invar Alloy

Abstract: In order to clarify the effect of concentration fluctuation on the Invar effect, the temperature dependences of magnetization and thermal expansion and the low temperature specific heat of the Fe 72 Pt 28 alloy were measured in both the ordered and disordered states. The thermal expansion anomaly, which is the most essential Invar effect, was observed in both states of the alloy. This anomaly is more remarkable in the disordered state than in the ordered state, particularly around T C . This different behavior can be attributable to the difference in the magnetization versus temperature curve; the magnetization of the disordered alloy decreases more rapidly around T C . The spontaneous volume magnetostriction at 0 K were estimated for the ordered and disordered states as 1.4×10 -2 and 1.6×10 -2 , respectively. These phenomena can not be explained by the proposed models for the Invar effect based on the inhomogeneity or the fluctuation of composition.

Change with Temperature in Crystal Structures of Nylons 6, 66 and 610

Abstract: It is verified from the results of infrared absorption and X-ray analyses that the hydrogen bonds between the adjacent amide groups in crystalline regions of nylons 6, 66 and 610 are not broken but the motion of amide groups in a molecule is rather restricted in the whole temperature range below respective melting points. All lattice parameters of three polyamides are determined at about 20, 80, 120, 160, 200 and 240°C. It is deduced that the length of a-axis or hydrogen bond varies little, but the large thermal expansion along b-axis causes inversion of (100) and (010) spacings for nylons 66 and 610. The difference in the melting point and in the behavior of the structure change between even polyamide and even-even one is attributed to the degree of ease with which the CH2-segment is rotated.

Ultraprecise thermal expansion measurements of seven low expansion materials

Abstract: We summarize a large number of ultraprecise thermal expansion measurements made on seven different low expansivity materials. Expansion coefficients in the -150-300 C temperature range are shown for Owens-Illinois Cer-Vit C-101, Corning ULE 7971 (titanium silicate) and fused silica 7940, Heraeus-Schott Zerodur low-expansion material and Homosil fused silica, Universal Cyclops Invar LR-35, and Simonds Saw and Steel Super Invar.

Some physical properties of GeAsSe infrared optical glasses

Abstract: This paper presents measured data on glass transition temperature, thermal expansion, density, hardness, refractive index and electron microscopy of GeAsSe glasses and bring together some literature data on viscosity and mechanical properties Interpretation of this information to identify suitable compositions for bulk synthesis is discussed

Sound-suppressing structure with thermal relief

Abstract: Sound-suppressing structure comprising stacked acoustic panels wherein the inner high frequency panel is mounted for thermal expansion with respect to the outer low frequency panel Slip joints eliminate the potential for thermal stresses, and a thermal expansion gap between the panels provides for additional relative thermal growth while reducing heat convection into the low frequency panel

Thermal expansion of isobutyric acid+water near the upper critical solution temperature

Abstract: We report the precise measurement of volume changes as a function of temperature near the critical solution point of isobutyric acid–water. We find not only evidence of a critical anomaly in the thermal expansion but also a small range of temperature in which it is negative, a requirement for thermodynamic consistency. Although the uncertainty in α, the critical exponent determined from these measurements, is on the same order as α itself, we find that α is consistently in the range 0.08–0.14; that is comparable to the Ising value of 1/8.

Glass-ceramics with random and oriented microstructures

Abstract: The variation of a number of physical properties of a glass-ceramic composition as a function of the crystallization heat-treatment temperature are reported. The properties studied include mechanical strength, modulus of elasticity, electrical properties and linear coefficient of thermal expansion. It is shown that several of the properties are dependent on microstructural effects. This dependence is especially marked for modulus of rupture and is also apparent for electrical properties such as conductivity and loss tangent. For the latter, however, compositional changes in the residual glass phase also exert a significant influence. For other properties, such as indentation hardness, the microstructural dependence is less well defined.

Electrical temperature measuring resistor structure, particularly for resistance thermometers

Abstract: A substrate carrier of electrically non-conductive material has a strip of resistance platinum applied thereto; in order to avoid the use of an intermediate temperature coefficient of expansion matching layer, the substrate carrier, for example of aluminum oxide, beryllium oxide, or a magnesium silicate, has less than thirty parts per million (ppm) Fe, less than 15 ppm Cr, less than 45 ppm Pb and less than 70 ppm Si in a form capable of reacting with platinum, the sum of the impurities by these metals, if all, or more than one are present, not exceeding 20 ppm; the average thermal coefficient of expansion of the substrate does not deviate from the mean thermal coefficient of expansion of the thermometer grade platinum by more than ± 30%; the platinum layer has a thickness of from 0.1 to 10 μm, and is applied at a temperature in the range of between about 1000° C to 1400° C during 60 minutes in an atmosphere containing oxygen, for example free air.

Dimensional Stability of Fused Silica, Invar, and Several Ultralow Thermal Expansion Materials

Abstract: A method is developed for testing the long-term dimensional stability of an iodine-stabilized He-Ne laser, using a technique whereby thermal expansion coefficients are measured by forming a Fabry-Perot etalon from the sample and monitoring the optical resonant frequencies with tunable sidebands impressed on a laser beam from a frequency-stabilized He-Ne laser. A change of 1 ppm over a 3-yr period on the part of fused silica dimensions and the differential thermal expansion of Invar LR-35 and Super Invar materials are noted. The method is of interest for the metrology of extremely stable structures such as telescopes and optical resonators.

The anomalous thermal properties of glasses at low temperatures

Abstract: While experimentally there is great regularity below 1 deg K in the behavior of a particular thermal property for all amorphous dielectrics it is not understood why these properties should differ from those of crystalline dielectrics, since it would seem that at low temperatures long-wavelength elastic waves, similar in both cases, would determine the thermal properties. A model involving systems having very few levels is used in the present study, although the relation between the model's systems and the nature of the glassy state is not known. It is shown, among other effects, that: specific heat measurements above 0.1 K indicate a distribution of local modes independent of energy; ultrasonic velocity measurements give information about phonon-local mode coupling parameters; and thermal expansion and far infrared experiments indicate a phonon-assisted tunneling model.

Hydrogen softening in some palladium-rare earth solid-solution alloys

Abstract: Microhardness measurements have been made on a series of palladiumrare earth solid-solution alloys (namely, PdY, PdGd, PdEu and PdCe) both in the non- and in the hydrogenated conditions. In the former condition, the variations of hardness with increasing solute content are characterised by a plateau region or inflection in the curve, around the middle of the solid solution range, i. e., around 6 at.% solute. The hardnesses of the alloys have been correlated with the lattice expansion measured by X-ray diffraction, and with the electron concentration. The palladium-cerium alloys do not agree with the general trend of hardness with lattice expansion exhibited by the other rare-earth solid solution alloys and this has been attributed to the unstable nature of the 4ƒ-states on the cerium atoms in a solid-solution environment. Transmission electron microscopy, resistivity and thermal expansion measurements have indicated the presence of short-range-order (S.R.O.) in the PdCe alloys, and this is thought to be a general characteristic of all the palladium-rare earth solid solutions. It is proposed that the shapes of the hardness/composition curves can be explained by the presence of S.R.O. in these alloys. The microhardness measurements on the alloys in the hydrogenated condition indicate that, apart from palladium and very dilute solutions, a pronounced softening occurs. For the composition range from 0 to about 5 at.% solute, hardness values are practically invariant with composition and independent of the particular solute element. Differences are observed for the higher concentrations and the rate of increase of hardness with composition is similar to that observed in the non-hydrogenated condition. The behaviour of the alloys on hydrogenation can be interpreted in terms of a transformation hardening effect for the dilute solutions, and an overall softening due to a reduction in both the shear modulus and the atomic mismatch factor as a consequence of the filling of the 4d-states.

Annealing characteristics of ultraoriented high‐density polyethylene

Abstract: The annealing characteristics of ultraoriented high‐density polyethylene fibers have been studied using differential scanning calorimetry, thermomechanical analysis, and tensile testing. The melting point of unannealed fibers was estimated to be 130 °C using a 10 °C min −1 heating rate. Fiber annealing between 126 and 132 °C split the melting endotherm into two peak melting at 132 and 139 °C. The weight fraction of fiber which had reorganized to the lower melting point increased with annealing time, finally attaining a constant value. However, annealing of laterally constrained fibers below 136 °C did not result in structural changes as detected by calorimetry. Melting‐point variations with heating rates≳0.625 °C min−1 indicated the equilibrium melting point of the unconstrained fiber at zero heating rate as 138 °C, while a similarly extrapolated value using heating rates <0.625 °C was ∼132 °C. The linear expansion coefficients rapidly increased near 132 °C and were attributed to the structural reorganization detected by calorimetry. Fiber annealing markedly decreased the tensile modulus from 50 GPa towards the 1 GPa observed for the unoriented polyethylene. The annealing behavior was consistent with the thermal instability associated with the anisotropy of the surface free energies of the ultraoriented crystalline fibers as well as sources of melting‐point reduction such as defects.

Effects of temperature and pressure on the crystal structure of forsterite

Abstract: The crystal structure of synthetic forsterite has been studied as a function of temperature and pressure. Crystal structures have been refined from three-dimensional diffraction data collected at temperatures from -196'C to 1020'C and at pressures to 50 kbar. Volume compressibility and thermal expansion of individual magnesium octahedra are comparable to those of bulk foresterite. However, the silicon tetrahedron neither expands nor compresses within the range of conditions investigated. Thus, changes in Mg-O bond distances account for virtually all of forsterite's volume response to changes in temperature and pressure. Short Mg-O bonds vary significantly less with temperature and pressure than do long bonds, implying that shorter bonds are stronger. Octahedral distortions increase with temperature, but show no strong trends with increasing pressure.

High pressure calorimetry as applied to piezothermal analysis

Abstract: This paper describes an apparatus which can be used to determine bulk thermal expansion coefficients of liquids as a function of temperature and pressure up to 10 kilobar in a temperature range from −20° to 100 °C. The principle of the method consists in measuring the heat of compression by a step by step procedure. The apparatus is a Joule twin calorimeter which is composed of a high pressure vessel and a reference cylinder. Temperature differences between these two components can be detected at better than 10−5 K by means of a gas thermometer, thus providing high sensitivity. Results are given for liquid n‐hexane and ethyl alcohol.

Copper-carbon fiber composites and process for preparation thereof

Abstract: Copper powder, carbon fibers arranged in random directions and a metal capable of reacting with carbon fibers are homogeneously mixed together, and the mixture is heated and molded under high pressure to form an integral composite. The so formed carbon fiber-copper matrix composite has no directional characteristic in mechanical properties, and the linear thermal expansion coefficient of the composite is low and the thermal stability of the composite is so high that when it is exposed to high temperature, no damage by thermal deformation is caused.

Calculation of thermal expansion coefficient of glasses

Abstract: Thermal expansion of oxide glasses has been theoretically studied to derive an equation for the calculation of the thermal expansion coefficient of glass from chemical composition. Gruneisen's constant may be correlated with packing density and a ratio of cation-to-anion radius and, considering the packing density and dissociation energy per unit volume, a semi emprical equation was derived. The agreement between observed and calculated values was satisfactory over 150 glasses of the binary, ternary and quarternary systems.

Thermally compensated microwave resonator

Abstract: Thermal compensation for frequency control of microwave resonators through utilization of bimetallic boundary motion type phenomena is described, the resonator being rectangular and preferably having composite broad walls of integral layers, one of which having a relatively lower thermal expansion coefficient than another of the layers and each having an initial deformation in a stabilized curvature condition to render these walls frequency sensitive.

Dynamic mechanical behavior of poly(2-hydroxyethyl methacrylate)–glass beads composites

Abstract: The dynamic relaxation behavior of a model two-phase system, poly(2-hydroxyethyl methacrylate)–glass beads, was studied by means of a freely oscillating torsional pendulum. The effect of the filler content on the storage and loss moduli of the composites could be described in terms of the modified Kerner equation in complex form. At temperatures below the glass transition temperature of the matrix, the agreement between experimental and theoretical data was satisfactory after correction for thermally induced stress due to different thermal expansion coefficients of matrix and filler. In the presence of filler, the capacity of the matrix to store and dissipate energy increases, but the character of molecular motions underlying the dispersions observed is preserved because the temperature of the dispersions remains unchanged. The effect of water on the dynamic relaxation behavior of composites is primarily reflected in changes in the shape of the temperature dependence of the dissipating capacity of the matrix. The data allow the conclusion to be drawn that the chain mobility at the interphase boundary does not decrease and that no additional frictional mechanisms appear.