Showing papers on "Thermal expansion published in 1980"

Thermal expansion of solids at low temperatures

Abstract: Studies of the thermal expansion of solids in the temperature range 1–100 K are reviewed. Effects due to thermal vibrations of the lattice, electrons, magnetic interactions and defects are fully discussed. The survey of experimental data is intended to be comprehensive. From the large volume of theoretical work in recent years the authors have aimed to select for discussion the most significant contributions.

The effect of particle shape on the mechanical properties of filled polymers

Abstract: The existing models for predicting the elastic moduli of polymers dispersed with particles of shape other than spheres and continuous fibres are reviewed. The applicability and limitation of these equations are discussed. The emphasis of the review is to seek a unified understanding and approach to the effect of particle shape at finite concentration on the elastic moduli, thermal expansion coefficient, stress concentration factor, viscoelastic relaxation modulus and creep compliance of filled polymers. The effects of anisotropic particle shape on mechanical properties of polymeric composites are clearly illustrated. Attention is also drawn to the relationship between elastic moduli, thermal expansion, creep elongation and stress relaxation moduli.

Thermal expansion of Portland cement paste, mortar and concrete at high temperatures

Abstract: Results of measurements of thermal expansion of Portland cement paste, mortar, concrete and a dolomitic rock aggregate are presented. Test temperatures ranged from 27 to 871°C. Cement paste contracted when subjected to temperatures from 204 to 871°C. Thermal expansion of mortar and concrete was dominated by thermal expansion characteristics of the mineral aggregate. However, expansion was moderated by contraction of the cement paste matrix at elevated temperatures. Average coefficients of expansion, over specific temperature ranges, are given for the materials tested. Equipment developed to control automatically the rate of heating and record strain vs. temperature relationships is described.

Effect of radiation on the physical properties of borosilicate glasses

Abstract: The effect of gamma ray irradiation on the density, refractive index, thermal expansion, and helium permeability of a variety of commercial borosilicate glasses has been measured for doses between 108 and 1011 rad. The radiation‐induced densification of these glasses for a constant dose can vary by as much as factor of 30 and appears to increase with increasing boron content of the glass. The refractive index also increases with dose and appears to be related to the change in density via the Lorentz‐Lorenz equation. The thermal expansion coefficient decreases with increasing dose for any given glass, and appears to vary inversely with the density change on a universal plot of change in thermal expansion coefficient versus change in density. Although the helium permeability was only measured for a few of the glasses, it appears that it is unaffected by radiation‐induced compaction of the glass. These effects are believed to result from the phase‐separated morphology of these glasses and from the less rigid...

Invar characteristics of amorphous (Fe,Co and Ni)-Zr alloys

Abstract: A detailed investigation on the thermal expansion, magnetic properties and electrical resistance of rapidly quenched amorphous (Fe,Co,Ni)-Zr alloys has been undertaken. Magnetic properties of these alloys are reported separately in this conference. The thermal expansion curves exhibit typical invar characteristics below the Curie temperature due to positive spontaneous volume magnetostriction us similar to those for Fe-Ni crystalline invar alloys. The reduced magnetization decreases strongly with increasing temperature being analogous to the case of other amorphous invar alloys. Moreover, w s at 0 K and electrical resistance at room temperature and Liq. N 2 temperature increase in the invar region. Amorphous ternary alloys of (Fe,Co, Ni) 90 Zr 10 with about 72 at% Fe have the invar characteristics in a wide temperature range and in this composition range, the volume magnetostriction and electrical resistance show maximum values of about 1.5 × 10-2and 160 μΩcm respectively.

Thermal expansion of dental alloys and porcelains.

Abstract: The effect of thermal coefficient of expansion (alpha) mismatch on porcelain-metal bonding is frequently referred to in the dental literature. Thermally induced stresses may develop at metal-porcelain system interfaces due to differences in the coefficients of thermal expansion of the porcelains, metals, and metal oxides. The objective of this research is to characterize alloy and porcelain expansion behavior as a first step in developing a more specific definition of thermal compatibility. It is clear from comparisons of porcelain data and alloy data that the porcelain has expansion characteristics which are quite different from those of the alloys. The overall differences in values between these alloys and porcelains constitute a mismatch. First run dilatometric heating measurements for porcelain yield large differences between delta L/L and alpha values as compared to cooling measurements. For a comparison of alloy and porcelain expansion characteristics, data should be obtained at several temperatures up to the glass transition temperature (Tg) of the porcelain.

THERMAL EXPANSION OF MODIFIED SPINEL, β-Mg2SiO4

Abstract: Thermal expansion of β-Mg2SiO4 (modified spinel; orthorhombic symmetry) was measured by the X-ray powder diffraction method in the temperature range between 20°C and 800°C. Gruneisen's theory of thermal expansion was applied to the linear and volume expansion data, and thermal expansion coefficients were obtained to be αa=9.14, αb=5.46, αc=5.92, and αv=20.6 in unit of 10-6/K, at 293K. Gruneisen's parameter γG=1.26 was obtained by assuming the Debye temperature to be 952K. The magnitude of volume expansion coefficient of β-Mg2SiO4 is located between those of γ- and α-phases. β-Mg2SiO4 is found to be a significantly anisotropic material both in thermal expansion and elasticity.

Thermal expansion in insulating materials

Abstract: A model of thermal expansion in terms of the Morse potential which was developed earlier for low temperatures is extended to high temperatures and applied to a semiempirical calculation of thermal expansion in insulating materials. In this model, the localized quantum mechanical solutions of the Morse potential are combined with the Debye model to give a localized-continuum description of thermal expansion. A set of empirical rules is developed for characterizing the interatomic potential in terms of the Morse potential. These are then applied to the quantitative calculation of thermal expansion in the alkali halide crystals and a group of binary high temperature materials with the aid of the known crystal structures, compressibilities, and Debye temperatures of these materials. Good agreement between calculated and experimental values is obtained for temperatures ranging between 0 K to values near the melting points. A discussion of the underlying basis of the empirical rules is given as well as their likely applicability to a wide range of insulating materials.

Low-expansion ceramics and method of producing the same

Abstract: The present invention relates to low-expansion ceramics essentially consisting of 1.5 to 20% by weight of magnesia (MgO), 8 to 68% by weight of alumina (Al2 O3), 24 to 80% by weight of titanium in terms of titanium oxide (TiO2), and 0.5 to 20% by weight of iron in terms of ferric oxide (Fe2 O3), that major component of crystalline phase thereof is a solid solution of magnesium oxide-aluminum oxide-titanium dioxide-iron oxide, and that the ceramics has a coefficient of thermal expansion of not more than 20×10-7 (1/° C.) in a temperature range of 25° C. to 800° C. and a melting point of not lower than 1,500° C., said coefficient of thermal expansion being maintained even after exposure 1,100° C. for 1,000 hours, and a method of producing low-expansion ceramics comprising steps of preparing a batch of compounds so as to provide a chemical composition of 1.5 to 20% by weight of magnesia (MgO), 8 to 68% by weight of alumina (Al2 O3), 24 to 80% by weight of titanium in terms of titanium oxide, and 0.5 to 20% by weight of iron in terms of ferric oxide (Fe2 O3); plasticizing the batch if necessary and shaping the batch; drying the body thus formed and firing the formed body at 1,300° C. to 1,700° C. for 0.5 to 48 hours, thereby having a coefficient of thermal expansion of less than 20×10-7 (1/° C.) in a temperature range of 25° C. to 800° C. and a melting point of not lower than 1,500° C., said coefficient of thermal expansion being maintained even after exposure at 1,100° C. for 1,000 hours, wherein the shape of ceramics is a honeycomb structure.

Anorthite - Thermal equation of state to high pressures

Abstract: The shock wave (Hugoniot) data on single crystal and porous anorthite (CaAl2Si208) to pressures of 120 GPa are presented. These data are inverted to yield high pressure values of the Grueneisen parameter, adiabatic bulk modulus, and coefficient of thermal expansion over a broad range of pressures and temperatures which in turn are used to reduce the raw Hugoniot data and construct an experimentally based, high pressure thermal equation of state for anorthite. The hypothesis that higher order anharmonic contributions to the thermal properties decrease more rapidly upon compression than the lowest order anharmonicities is supported. The properties of anorthite corrected to lower mantle conditions show that although the density of anorthite is comparable to that of the lower most mantle, its bulk modulus is considerably less, hence making enrichment in the mantle implausible except perhaps near its base.

Elastic stiffness and thermal expansion coefficient of BN films

Abstract: Room temperature stresses were found to be tensile for chemical vapor deposition films of the composition B2N and compressive for BN, with all films becoming more tensile with heating. Analyses of the stress‐temperature curves of identical films of BN deposited on two different substrate materials yield values of 1.3×1012 dynes/cm2 for the elastic stiffness parameter E/(1−ν) and 1.0 ppm/°C for the thermal expansion coefficient. This technique is of general applicability to thin films and it is believed to be the first practical (nondestructive) means of determining both the elastic stiffness parameter and thermal expansion coefficient of a film.

Thermal characteristics of phase shift in jacketed optical fibers

Abstract: Frequency and pulse methods are applied to measure thermal characteristics of phase shift in bare and jacketed optical fibers. The thermal coefficient of phase shift in bare fibers is found to be 7 x 10(-6)/deg, which is in good agreement with the value predicted theoretically. It is also found that the coefficient is increased by four times after nylon jacketing due to the increase of the coefficient of linear expansion.

Physical properties of first-row transition metal dichalcogenides and their intercalates

Abstract: This paper consists of three parts. In the first section a review is given of the structures and some properties of the dichalcogenides of titanium, vanadium and chromium. The second section deals with the results of thermal expansion studies of these dichalcogenides. A thermodynamic discussion of the thermal expansion in uniaxial crystals is given. The thermal expansion of these compounds, except TiS 2 , is anomalous, the expansion in the plane perpendicular to the unique axis is larger than along the unique axis. This anomalous behaviour is ascribed to the strong repulsion between the 3d electrons. In section 3 the structures and physical properties of the intercalates of the 3d transition metal dichalcogenides are discussed. New results are given for nonstoichiometric chromium intercalates. These compounds show semiconducting behaviour and have localized magnetic moments. The localization of the d electrons in the alkali metal intercalates increases in the series Ti, V, Cr. Chromium compounds always show localized behaviour while the vanadium compounds occur in two forms with resp. localized behaviour for the stoichiometric compounds and delocalized behaviour for the alkali-metal poor compounds.

Effect of Thermal Expansion Mismatch on the Thermal Diffusivity of Glass‐Ni Composites

Abstract: The effect of interfacial decohesion, due to the thermal expansion mismatch, on the thermal diffusivity of a hot-pressed glass matrix with a dispersed phase of nickel was investigated by the laser-flash technique at 25° to 600°C. The interfacial gap formed on cooling acts as a barrier to heat flow and lowers the thermal diffusivity to values below those predicted from composite theory and also creates a strongly positive temperature dependence of the thermdl diffusivity. Preoxidation of the Ni spheres promotes interfacial bonding and yields values of thermal diffusivity higher than those for nonoxidized spheres and a thermal diffusivity which is relatively temperature-independent. The results of the present study also confirm the criteria for the effective thermal diffusivity of composites established by Lee and Taylor.

Dynamic mechanical analysis of fiber reinforced composites

Abstract: Dynamic mechanical and thermal properties were determined for unidirectional epoxy/glass composites at various fiber orientation angles. Resonant frequency and relative logarithmic decrement were measured as functions of temperature. In low angle and longitudinal specimens a transition was observed above the resin glass transition temperature which was manifested mechanically as an additional damping peak and thermally as a change in the coefficient of thermal expansion. The new transition was attributed to a heterogeneous resin matrix induced by the fiber. The temperature span of the glass-rubber relaxation was found to broaden with decreasing orientation angle, reflecting the growth of fiber contribution and exhibiting behavior similar to that of Young's modulus. The change in resonant frequency through the glass transition was greatest for samples of intermediate fiber angle, demonstrating behavior similar to that of the longitudinal shear modulus.

Multicellular monolithic ceramic body and preparation thereof

Abstract: A multicellular monolithic ceramic body having many gas passages partitioned by thin walls is made of aluminum titanate as a major cnstituent and has less than 0.15% of a thermal expansion coefficient at 1000° C. and higher than 350 kg./cm2 of a compressive strength as zero of an open frontal area as the properties in the direction along the gas passages and more than 35% of a porosity.

Trends in the thermal expansion coefficients of the AIBIIIC2VI and AIIBIVC2V chalcopyrite compounds

Abstract: Empirical relations are derived for the average linear thermal expansion coefficient αL and the linear thermal expansion coefficients αa and αc of the lattice parameters a and c, respectively, of the AIBIIIC2IV and AIIBIVC2V compounds. It is shown that the thermal expansion coefficients of all tetrahedrally coordinated compounds can be described within the same model. The anisotropy of the thermal expansion coefficients depends essentially on the lattice constant ratio c/a. There exists a critical c/a value below of which αc becomes negative. Es werden empirische Beziehungen fur den mittleren linearen thermischen Ausdehnungs-koeffizienten αL und die linearen thermischen Ausdehnungskoeffizienten αa and αc der Gitterparameter a bzw. c fur die AIBIIIC2VI- und AIIBIVC2V-Verbindungen hergeleitet. Es wird gezeigt, das die thermischen Ausdehnungskoeffizienten aller tetraedrisch koordinierten Verbindungen im Rahmen des gleichen Modells beschrieben werden konnen. Die Anisotropie der thermischen Ausdehnungskoeffizienten hangt wesentlich vom Gitterkonstantenverhaltnis c/a ab. Es gibt kritische c/a-Werte, unterhalb derer αc negativ wird.

Anomalous thermal expansion in spinel MgAl2O4

Abstract: The accurate measurement of thermal expansion in spinel MgAl2O4 over a temperature range between 30° C and 900° C has revealed an anomalous behaviour indicating a possible presence of a second order phase transition at 660° C.

Thermal expansion and lattice anharmonicity of Pd-H and Pd-D alloys

Abstract: The authors have made thermal expansion measurements on Pd-H and Pd-D alloys. The measurements were performed between 9 and 270K, and with H(D) concentrations ranging from 0.69 to 0.82 H(D)/Pd atom ratios. Above 80K (in pure beta phase), the thermal expansion of Pd-H and Pd-D is increased compared with that of pure Pd, for comparable concentrations, D-doped samples have a larger expansion than those doped with H. For PdH0.7(PdD0.7), the authors find an essentially isotope-independent Gruneisen constant gamma H=3.0+or-0.7 for the optical phonons and a Gruneisen constant gamma ac=3.0+or-0.5 for the acoustic phonons.

Analysis of the resistance of high-E, low-E brittle composites to failure by thermal shock

Abstract: By means of the inclusion of a dispersed phase with low Young's modulus, the generally low thermal stress resistance of brittle materials for high-temperature structures can be improved significantly. An analysis of this improvement on the basis of continuum and micromechanical theory is presented in this paper. The low-E phase is shown to cause a significant decrease in Young's modulus, with a negligible effect in the coefficient of thermal expansion. The relative change in thermal conductivity is a function of the thermal conductivity of the dispersed phase. The tensile fracture stress is reduced significantly, primarily due to the mismatch in elastic properties, with smaller effects due to the mismatches in the coefficient of thermal expansion and thermal conductivity. The relative changes in Young's modulus and tensile fracture stress are such as to result in an increase in the strain-at-fracture and a simultaneous decrease in the elastic energy at fracture, the driving force for catastrophic crack propagation. The accompanying increase in fracture energy also contributes to the improvement of thermal shock resistance. By changing the size of the low-E inclusion, tradeoffs can be made between strain-at-fracture and elastic energy at fracture.

Elastic Properties of Stabilized HfO2 Compositions

Abstract: Elastic moduli of several stabilized HfO/sub 2/ compositions were studied as functions of porosity and temperature. Thermal expansion was also measured for one of the compositions. The modulus vs porosity and thermal-expansion measurements yielded typical relations. The modulus vs temperature measurements revealed an anomalous nonlinear relation between room temperature and 500/sup 0/C. Varying microstructural and testing conditions had no effect on the nonlinearity. Only the percent of stabilizer additive caused any change in this behavior. It is proposed that oxygen-vacancy motion is the probable cause of this behavior.