Showing papers on "Thermal expansion published in 1971"

Improved Hot-Pressed Electrooptic Ceramics in the (Pb,La)(Zr,Ti)O3 System

Abstract: Physical, electrical, and optical properties of selected compositions within the lead lanthanum zirconate-titanate (PLZT) system are presented, including chemically and thermally etched microstructures, examples of residual porosity defects, temperature dependence of remanent polarization and coercive field, lateral switching strains, and thermal expansion and optical transmission data. Optical-quality ceramics were produced by stringent raw material selection and improved ceramic processing and hot-pressing. Optimum results were obtained from starting oxides with higher purity (99.9%) and smaller particle size (<2 μm) than those used in previous investigations. These oxides were processed by methods developed to minimize segregation and promote chemical homogeneity and hot-pressed at temperatures (1050° to 1250°C) higher than those used previously to remove residual porosity.

Analysis of thermal elastic-plastic stress and strain during welding by finite element method

Abstract: It is well known that welding thermal stresses and resulting residual stresses influence the strength of welded construction, causing troubles such as brittle fracture, buckling and weld cracking. At the instant of welding, a limited portion of the welded joint is heated up to a very high temperature and cooled down to room temperature. In the thermal cycle which takes place, the temperature distribution changes with time and it affects the mechanical properties of the metals. In order to perform a reliable theoretical analysis, the above mentioned factors should be taken into account. The authors developed a method of theoretical analysis of this problem based on the finite element method, with consideration of the effects of changes in the modulus of elasticity, yield stress and the coefficient of linear thermal expansion of the metal with temperature. They analysed thermal transient stresses induced in a butt weld under a moving electrode and also in a fillet weld in the courses of the first and second beads and obtained various information on thermal stress history in the process of welding. Examples verifying usefulness of the method are cited.

Pressure-volume-temperature relations in liquid and solid 3 He

Abstract: Liquid and solid3He P-V-T relations were measured over 026–18 K with concentration on regions near the melting curve The method used a cell whose volume was varied with diaphragms, the positions of which determined the volume and pressure The molar volumes of liquidV lm and solidV sm along the melting curve were consistent with the directly measured volume change on melting ΔV m Below 1 K,V lm , Vsm, and ΔV m were greater than previous results Along the melting curve, the compressibility of the solid became greater than the compressibility of the liquid atT<12 K, the difference rising to 12% at 032 K The thermal expansion of the solid became negative below 030–035 K The melting curve minimum was measured at 28932±0003 atm and 0319±0003 K Starting with the minimum, the melting curve was calculated to 002 K, where it should be useful in thermometry A set of self-consistent data is presented

Equation-of-state parameters for polystyrene

Abstract: The absolute density, thermal expansion coefficient α, and thermal pressure coefficient γ have been determined for atactic polystyrene in the non-glassy liquid (or amorphous) state. Dilatometric measurements on the pure polymer furnished α over the range 100° to 230°C. Thermal pressure coefficients were determined by extrapolation from measurements on concentrated solutions of the polymer in benzene, from 24° to 100°C. No evidence was found for a second order transition above 100°C. A small change in dα/dT was observed near 170°C. This and other observations suggest a minor departure from equilibrium below this temperature.

Thermal expansion characteristics and stability of pseudobrookite-type compounds, Me3O5

Abstract: Thermal expansion measurements on various oxide compounds crystallizing with the orthorhombic pseudobrookite structure are reported. The unusual expansion anisotropy appears to be a structure-related property. It was observed for all pseudobrookites including the new phases MgTi 1.6 Zr 0.4 O 5 , MgFeNbO 5 and MgFeTaO 5 . The highest thermal expansion coincides with the direction of the double chains of strongly distorted (MeO 6 )-octahedra. This is in the direction of the c -axis where the shortest 0–0 distances are also found. The smallest, or even “negative”, expansion always occurs in the direction of the a -axis. This is the shortest axis, its length corresponds to the height of the distorted (MeO 6 )-octahedra. Isothermal heat treatment and DTA runs proved the instability of Al 2 TiO 5 , MgFeNbO 5 and, especially, Ga 2 TiO 5 . Stable compounds like Fe 2 TiO 5 and MgTi 2 O 5 are formed at much lower temperatures than the unstable compounds Al 2 TiO 5 and Ga 2 TiO 5 (strongly endothermic reactions at 1360 °–1370 °C). Ga 2 TiO 5 decomposes spontaneously and strongly exothermically into the component oxides at about 980 °C. All pseudobrookite compounds are mechanically very weak due to their strong expansion anisotropy.

Experimental Study of the Equation of State of Liquid Krypton

Abstract: The gas expansion method has been used to measure the density of liquid krypton at 11 temperatures from 120 to 220°K and at pressures up to 3680 atm. The results have been fitted to the Strobridge equation, which has been used to estimate, at regular intervals of pressure and temperature, the following properties: density, isothermal compressibility, thermal expansion coefficient, thermal pressure coefficient, configurational internal energy, and entropy relative to the saturated liquid. The equation of state results, together with estimated values of the third virial coefficient and published values of vapor pressure, second virial coefficient, and sound velocity in the liquid phase, have been used to estimate the following properties of the saturated liquid: enthalpy of vaporization, configurational internal energy, isothermal compressibility, thermal expansion coefficient, thermal pressure coefficient, adiabatic compressibility, and specific heats. The linear dependence of configurational internal energy on density, over a wide range of pressures and temperatures, suggests a relatively simple form for a hard sphere equation of state for monatomic liquids. The evaluation of constants for such an equation is briefly discussed.

Properties and structure of glasses in the system AsS

Abstract: In obtaining the glass, at first, the raw materials were mixed up and melted by using porcelain crucible, but in this case it was found by infra-red absorption method that the glass contains some oxygen impurities. Then a range of glasses was prepared by melting elementary pure As and S in definite proportions in a sealed vacuum tube. The infra-red absorption, molecular volume, molecular refraction, hardness, thermal expansion and viscosity of sample glasses with various compositions were investigated and, additionally, solubility of these glasses into CS2 was measured. The structure of glasses in the system AsS was studied by X-ray diffraction and a structural model was set up. From the measurements the following conclusions were made. The structure of As2S3 glass is a distorted form of the crystalline orpiment structure. With increasing S content above As2S3, S is likely to exist in the chain-like form, but when the S content is greater than that in As2S8–10, both chain-like and ring type forms co-exist. With decreasing S content below As2S3, S between As and As is eliminated and AsAs bonds are formed. Consequently a deformation of layer occurs and an expansion of the layer distance was observed.

Thermal Expansion Coefficient and Spontaneous Volume Magnetostriction of Fe-Ni (fcc) Alloys

Abstract: The thermal expansion coefficient α of Fe-Ni ( fcc ) alloys was measured in the range from 800°C to room temperature. Below the Curie temperature T c , the α– T curve exhibits an anomaly corresponding to the spontaneous volume magnetostriction ω s . The `paramagnetic' thermal expansion coefficient α p below T c was determined by the extrapolation of the α– T curve above T c and the value of ω s was estimated from the difference between α p and α below T c . The relation between ω s and the change of T c with pressure was discussed. The α p vs. composition curve at a fixed temperature shows a minimum around the invar alloys. This minimum corresponds to the anomaly in the elastic moduli vs. composition curves. It is thus pointed out that the lattice energy must be considered in addition to the magnetic energy in discussing the origin of the invar properties.

Hole Theory of Liquids and Glass Transition

Abstract: A recently elaborated theory of the p‐V‐T properties successfully describes the behavior of amorphous polymers above the glass temperature. The improvement over earlier results arises from the introduction of a vacancy fraction which is obtained as a function of volume and temperature by a maximization of the partition function. We now explore a possible application of this theory to the glassy state by introducing an assumption following a frequently used idea, namely, the freezing of one parameter, (or more), for example, an unoccupied volume ratio. The natural quantity to consider is the vacancy fraction and its effect on the thermal expansion coefficient at the glass temperature. Experimental data at atmospheric pressure on a series of polymers, encompassing a wide range of Tg's, are examined and compared with theoretical predictions. The computed expansivities αg at T=Tg are uniformly smaller than is observed. We suggest as the primary reason for this discrepancy the assumption of a complete freezing of the hole fraction at the glass temperature, which should be replaced by a decreased dependence on volume and temperature as compared with the liquid. Additional factors are discussed.

Thermal Expansion of Rocksalt

Abstract: The microscopic Grueneisen parameters and the temperature dependence of the thermal Grueneisen parameter of NaCl are calculated from a shell model with six parameters, five of which are taken as pressure dependent. All parameters are determined from experimental elastic, optical, and dielectric data at absolute-zero temperature. The results agree within 6-8% with experimental data. The discrepancy is primarily attributed to the experimental error of the input data that are used to determine the parameters of the model. Calculations have also been made for two versions of the rigid-ion model (RIM) which indicate that the apparent success previously attributed to the Kellermann model is mainly due to cancellation of errors arising from omitting second-nearest-neighbor interaction and electronic polarizability.

Magnetic behavior of rare-earth iron-rich intermetallic compounds

Abstract: The thermal variation of lattice parameters of rare earth-transition metal intermetallic compounds rich in Fe, Co or Ni in the temperature range of 25-900°K is studied. For the Fe compounds, negative thermal expansion is observed below their magnetic ordering temperatures regardless of the nature of substitutional ordering. For Co and Ni compounds, the thermal expansion behavior is normal. It is then concluded that for the Fe compounds, the magnetic properties are mainly determined by the Fe-Fe interatomic distances and the number of Fe nearest neighbors, whereas for Co and Ni compounds the magnetic properties are determined by the conduction electron transfer from the rare earth to the 3d band of Co or Ni, The anomalous thermal expansion of Fe compounds and the metamagnetic transition of the Lu compound is explained in terms of the distance dependence of the interaction energy as proposed by Neel.

Lattice parameters and thermal expansion coefficients of Al, Ag and Mo at low temperatures. Comparison with dilatometric data

Abstract: Lattice parameters and thermal expansion coefficients of Al, Ag and Mo were determined at temperatures between 30 and 180°K in a special X-ray camera without the use of liquid gases. The powder samples were cooled by a mechanical refrigerator, and symmetrical back-reflections patterns of the three metals were prepared. The purpose was to check the reliability of this method by comparing the lattice parameters and expansion coefficients calculated from X-ray patterns with those obtained by other well established, interferometric-dilatometric methods. The expansion coefficients were reproduced with reasonable precision, but the lack of reliable measurements of low-temperature parameters in the literature prevented a conclusion from being reached concerning the accuracy of the lattice parameters calculated. Values of the expansion coefficients and the lattice parameters are given.

Spontaneous Volume Magnetostiction of Fe65 (Ni1-xMnx)35 Alloys

Abstract: Thermal expansion measurements were made on f.c.c. Fe 65 (Ni 1- x Mn x ) 35 alloys at temperatures down to 4.2°K and the spontaneous volume magnetostriction of these alloys was evaluated from their thermal expansion curves. The results indicate that the spontaneous volume magnetostriction at 0°K is positive and decreases with increasing x in the ferromagnetic alloys ( x <0.3), and is positive and increases with increasing x in the antiferromagnetic alloys (0.3< x ). The spontaneous volume magnetostriction varies with temperature as T 2 in the temperature range below about half of the magnetic transition temperature. If a simple and reasonable density of states curve is assumed, these experimental results can be understood on the basis of the weak itinerant electron ferromagnetism or of the weak itinerant electron antiferromagnetism.

The solid state bonding of nickel to alumina

Abstract: The paper describes the effect of sintering atmosphere (argon, hydrogen and vacuum), sintering temperatures (700 to 1300° C), sintering pressure (1/2 to 6 tsi [7.7 to 92.4 MN. m−2]) and sintering time (1/2 to 24 h) on the room temperature shear bond strength developed between nickel powder compacts and alumina single crystals: bond strengths of 3 to 11×103 psi (20.7 to 75.9 MN. m−2) were developed and are satisfactory for composite strengthening. The spinel, NiAl2O4 was detected at the nickel/alumina interface. Heat treatment at 1100° C for 300 h resulted in gross chemical attack, but without degeneration of the bond strength. The variations in shear strength observed are discussed in terms of the nickel grain size and porosity and the differential thermal expansion of the two components.

Small angle x-ray scattering studies of phase transitions in polymeric and oligomeric systems

Abstract: Small angle x-ray scattering (SAXS) is a valuable method for studying structure changes which take place during phase transitions in polymeric and oligomeric systems. Measurements of the dependence of SAXS on temperature yield information on the changes in morphology or of the structure on a supermolecular level. The technique can be applied to various problems: glass transition in highly crystalline polymers, solid state phase transitions in crystalline polymers, rotational transition in n-paraffins, premelting phenomena in crystals of chain molecules, and partial melting of homoand co-polymers. The glass transition temperature of the amorphous regions in highly crystalline polymers can be measured by SAXS since the scattered intensity depends on the thermal expansion coefficient of the two phases. This technique was applied to so-called single crystals grown from solution of polybutene-1, branched and linear polyethylene. The amorphous surface layer of linear polyethylene single crystals exhibits a 7, of — 125° ± 4°C. Solid state phase transitions of polymer crystals are often accompanied by characteristic changes in morphology. As examples, the annealing behaviour of trans-1,4-polybutadiene and isotactic polybutene-1 is described. The rotationa1' transition in paraffins studied with n-tritriacontane as an example also leads to a pronounced structure change of the surface of the paraffin lamellae, speaking in favour of a transition theory which is based on the assumption of a sudden change in the concentration of kinks within the crystals. With increasing temperature an increase of the roughness and depth of the surface region of paraffin crystals is observed. This phenomenon can be described as 'surface premelting of chain molecular crystals' and SAXS yields quantities suitable for a thermodynamic explanation of that process. In homoand co-polymer crystals partial melting during heating is observed. The SAXS studies show that this effect can be due to a 'boundary premelting of polymer crystals' which manifests itself by a reversible increase of the thickness of the intercrystalline layers. This phenomenon can be observed in many polymers, it can be described quantitatively by analysis either of the scattering curves or of the correlation functions y(x) obtained from the intensity distribution.

Thermal Stress Crack Stability and Propagation in Severe Thermal Environments

Abstract: A fracture-mechanical analysis is presented for stability criteria and propagation behavior of thermal stress cracks in brittle ceramics in environments so severe that initiation cannot be avoided. It is based on a mechanical model consisting of a rigidly constrained, uniformly cooled thin flat plate with a uniform distribution of microcracks; results are qualitatively similar to those obtained for a three-dimensional body with penny-shaped cracks. High stability of thermal stress cracks is attained in materials with high values of surface fracture energy, and low values of thermal expansion and Young’s modulus. On catastrophic propagation of an initially short crack, the final crack is subcritical and has a length which is independent of material properties but depends only on the initial crack length and the crack density. It is suggested that materials with very high thermal shock resistance can be developed by synthesizing materials with high densities of microcracks.

Heat capacities and thermal behavior of alkali borate glasses

Abstract: The heat capacities of selected glasses in the five alkali borate systems have been measured over a range of high temperatures which includes the respective glass transition regions. The heat capacities per gram atom at 350°K show little variation with composition while those at the low temperature ends of the glass transition, Tg-, show some systematic variations. When compared with the respective 3R values, the heat capacities at Tg- range from about 0.75 for B2O3 to values in excess of unity for various alkali borate compositions. The present data on heat capacity have been combined with previous data on the elastic moduli, densities and thermal expansion coefficients to evaluate the Gruneisen constant, γ, for each composition for temperatures around ambient. For B2O3, γ has a low value of about 0.25. It decreases with additions of Li2O and increases with additions of the other alkali oxides.

Thermal Properties of Synthetic Fluorapatite Crystals

Abstract: Measurements of the heat capacity, thermal expansion, and thermal conductivity on synthetic crystals of undoped and neodymium‐doped fluorapatite are reported. Fitting the low‐temperature specific heat data to a Debye model yields a Debye temperature of 550°K. At 25°C the thermal expansion coefficients are 10.0×10−6 °K−1 and 9.4×10−6 °K−1, respectively, along the [0001] and [1010] directions. The thermal‐expansion measurements yield a Debye temperature of 500°K. A typical value of the thermal conductivity is 0.020 W cm−1 °K−1 at room temperature. The thermal conductivity is only feebly temperature dependent and, similar to the thermal‐expansion coefficient, shows very little crystallographic anisotropy.

X‐Ray Determinations of the Debye Temperatures and Thermal Expansions for the Pd–Ag–Au System

Abstract: X‐ray measurements of the Debye characteristic temperatures ΘM and the coefficient of thermal expansion for the Pd–Ag–Au ternary‐alloy system are presented The integrated intensities of Bragg reflections and lattice parameters were measured in the temperatures range 80–298°K For all the alloys, the predominant lattice disturbance was due to thermal vibrations No significant effect due to static displacements was found Debye temperatures were found to range from a low of 184°K for gold to a high of 290°K for palladium, with silver intermediate at 226°K The mean coefficient of thermal expansion was found to range from 98×10−6 for palladium to 179×10−6 for silver Gruneisen's relationship between the meansquare atomic‐vibration amplitude and the thermal expansion for cubic solids has been found to be valid for these alloys and the constant γZ2 was found to be 0167 The results suggest that a general weakening of the cohesive forces might be taking place as the smaller palladium atoms are replaced by

The System ThO2‐P2O5

Abstract: The existence of compounds with 1:1, 3:2, and 3:1 ThO2:P2O5 ratios in the system ThO2-P2O5 was confirmed. A 1:2 compound found by previous workers was not investigated, and their 2:1 compound was not detected; however, extensive solid solution on either side of the 3:2 compound was established. The linear thermal expansion behavior of the compounds and solid solutions was determined.

Glass-transition Temperature and Thermal Expansion Coefficient of a Two-Phase System of Polymers

Abstract: The abnormal increase of glass-transition temperature (T g) and the deviation of thermal expansion coefficient from the simple additivity relationship in a two separate phase system having different Tg, s were explained by the thermal stress originating from the difference of the thermal expansion coefficients of the two component polymers. Among the two T g, s of the blend system, the higher Tg was increased and the lower Tg was decreased compared with the original T g s of the component polymers in some cases. The spherical shell model composed of three layers was adopted to interpret such phenomena of the blend system. These three layers were numbered 0, 1, and 2 from the outer layer. The component polymer of the layer 0 was assumed to be the same as in the layer 2. In this model, vs, which is defined as the volume ratio of the sphere 2 to the sphere 1, represents the mixing state of the two component polymers. The thermal expansion coefficients of the whole system and the layers 0, 1, and 2 w...

Plasma expansion under heating by a co2 laser pulse

Abstract: This paper treats the expansion of a gas breakdown plasma produced in argon by the focused radiation from a high‐voltage transient‐pumped CO2 laser. With the long pulses attainable from such pulsed CO2 lasers, a transition is observed in the mechanism of expansion from a radiation‐driven detonation to a thermal expansion. The implications of this observation for CO2 laser heating of plasmas are discussed.