Temperature Dependence Of Ultrasonic Velocity Research Articles

Relaxation behavior of ultrasonic attenuation in YBa/sub 2/Cu/sub 3/O/sub 7/

It is shown that temperature-dependence ultrasonic attenuation data of YBa/sub 2/Cu/sub 3/O/sub 7/ at various frequencies exhibit anomalies at temperatures close to T/sub c/. These attenuation maxima are found to be the result of a relaxation mechanism added on top of an unusual attenuation background. It is proposed that the grain boundary motions induced by the structural distortion and the propagation of sound waves enhances the energy dissipation around T/sub c/. Whether this structural distortion is the consequence of the onset of a superconducting state remains undetermined. It is also possible that either a tunneling effect of the acoustoelectric effect contributes to sound energy dissipation. The temperature dependence of ultrasonic velocity shows a softening around T/sub c/ which may be an intrinsic property of high-temperature superconductors. >

Velocity Measurements of Laser-Generated Ultrasound at High Temperatures

The temperature dependence of ultrasonic velocities is determined by a laser-ultrasound technique in a non-contact manner for several kinds of materials. A pulsed Nd:YAG laser is used to generate ultrasound on the surface of a specimen while a He-Ne laser interferometer detects the subsequent displacement on the directly opposite surface. The results are favorably compared with those obtained with a conventional contact ultrasonic technique. The longitudinal velocities of both methods agreed within 0.4% or less in the range from room temperature to 800°C.

Intermolecular Interactions in 4,4′-di-n-propoxy-azoxybenzene. Part II—Experimental

Abstract Temperature dependence of Ultrasonic velocity and specific volume have been studied in the case of 4,4′-di-n-propoxy-azoxybenzene dissolved in a non-interacting and non-mesogenic solvent, benzene, at different concentrations. The concentration of the liquid crystal molecules was chosen such that the intermolecular separation lies in the range of 8.5 A to 13.5 A. It was observed that the solutions of liquid crystalline substances exhibit interesting variations in the physical parameters as a function of temperatures. Physical quantities like adiabatic compressibility, molar sound velocity, molar compressibility and intermolecular freelength have also been calculated. Present study offers an experimental support to the probability distribution picture obtained with the help of our theoretical investigations.

Ultrasonic velocity anisotropy of magnetic fluids

Frequency dispersion and temperature dependence of ultrasonic velocity in magnetic fluids induced by externally applied magnetic fields are determined. Observed effects are analyzed in light of the existing theories of magnetic fluids.

Ultrasonic investigations of incommensurate Rb2Zncl4

Abstract Elastic properties of Rb2Zncl4 were investigated by measuring the velocity and attenuation of both, transversal and longitudinal ultrasonic waves propagating along the crystallographic axes. At the lock-in phase transition temperature only v44 shows a remarkable anomaly. This anomaly has been found to be asymmetric with respect to the interchange of oscillation and propagation direction of the transverse ultrasonic wave. The anomaly of v44 at Tc is proportional to the contents of commensurate regions in the IC structure. From the temperature dependence of ultrasonic velocities at the phase transition from paraelectric to IC phase the critical behaviour of the order parameter should correspond rather to the (n = 2)-Heisenberg-model than to the Ising model.

The Sound Velocity near the Pressure Induced Tricritical Point of TGSe

The temperature dependence of ultrasonic velocities of TGSe single crystal was studied at several hydrostatic pressures. Particularly, the sound velocities near tricritical point ( T tri =40.6°C, p tri =5 kbar) were measured minutely. At atmospheric pressure, there is a difference between the transition temperature and the temperature at which the anomalous part of the sound velocity takes maximum. On approaching tricritical point, this temperature difference becomes small and disappears ultimately in the first order phase transition region. The pressure dependence of the magnitude of anomalous part of the sound velocity along the a * axis is examined. It is found that these pressure dependences are due to tricritical nature if the polarization relaxation is taken into account.

Measurement of Residual Stress Using the Temperature Dependence of Ultrasonic Velocity

Measurement of Residual Stress Using the Temperature Dependence of Ultrasonic Velocity

The effect of stress on the temperature dependence of ultrasonic velocity

The effects of applied elastic stress on the temperature dependence of ultrasonic velocity has been investigated in commercial aluminum and copper. Velocities of 10-MHz longitudinal and shear waves as a function of temperature were measured when specimens of these metals were subjected to external compressive stresses applied in a plane perpendicular to the direction of propagation. In all measurements, the velocity increased linearly as the temperature was lowered in the range between 280 and 200 K. The slopes of the linear relationships of the longitudinal velocities were found to decrease linearly as the amount of stress was increased within the elastic limit of the specimen. The maximum decrease in the temperature dependences of the longitudinal velocities of aluminum and copper were, respectively, 23 and 6%. These occurred at applied stresses of 96 and 180 MPa. The temperature dependence of the shear velocity in aluminum, however, remained unchanged with the application of stress.

Localized low-energy excitations in two amorphous polymers

The low-temperature specific heat, the thermal conductivity, and the temperature dependences of ultrasonic velocities have been measured for two epoxies differing primarily in crosslink density. The difference between the two epoxies is explained by a factor of \ensuremath{\approx} 1.5 difference in density of localized excitations. Below \ensuremath{\approx} 1 K all data are accounted for quantitatively by the tunneling-states model. Above \ensuremath{\approx} 1 K, however, the model does not explain both the "plateau" in the thermal conductivities and the temperature dependences of the ultrasonic velocities without additional assumptions.

Effect of neutron irradiation on the density of low-energy excitations in vitreous silica

Neutron irradiation of vitreous silica produces changes of the same relative magnitude in the low-temperature excess specific heat ${C}_{\mathrm{ex}}$, the anomalous thermal conductivity $\ensuremath{\kappa}$, and the anomalous temperature dependence of ultrasonic velocity, $\frac{\ensuremath{\Delta}v}{v}$. It is therefore likely that $\ensuremath{\kappa}$ and $\frac{\ensuremath{\Delta}v}{v}$ are dominated by the localized excitations responsible for the excess specific heat of vitreous silica. The tunneling-states model with a single energy-dependent density of states adequately accounts for the measured ${C}_{\mathrm{ex}}$, $\ensuremath{\kappa}$, and $\frac{\ensuremath{\Delta}v}{v}$ of unirradiated vitreous silica. Changes in these properties with neutron irradiation can be explained using this model by altering only the density of tunneling states.

Phonon propagation in glassy metals

The phonon thermal conductivities and the temperature dependence of ultrasonic velocities in glassy Pd-Si and Co-P at low temperature are not in accord with the tunneling-states model of amorphous systems.

A new resonant thermometer for nuclear reactor applications

An ultrasonic thermometer using the temperature dependence of ultrasonic velocity as the transducing mechanism has been developed for high temperature measurement. Essentially it is a long, thin probe consisting of a magnetostrictive launcher producing longitudinal vibrations in an acoustic line. A resonator which terminates the line constitutes the sensor. By measuring its natural resonant frequency as a function of temperature a calibration of the probe is obtained. A pulse excitation technique is used to drive the resonator after which the oscillations decay exponentially (the decrement) at the natural frequency of the resonator. The control compares this frequency with that of a signal generator to produce an error signal. This is used to make the signal frequency track that of the sensor. Digital aperiodic techniques are used throughout giving a smooth operation over the full range of the instrument. The setting-up procedure for changing a probe is minimal.

Low-temperature specific heat, thermal conductivity, and ultrasonic velocity of glassy carbons

We have measured the specific heat (0.1<T < 1 K) and thermal conductivity (0.07 <T<300 K) of two glassy carbons, one pyrolysed at 1000‡C, the other at 2500‡ C. The temperature dependence of ultrasonic velocity (0.2–300K) was also measured on the 2500‡C material. The above properties are remarkably similar to those of amorphous materials, yet it appears that these features arise from origins other than the localized excitations responsible for the low-temperature behavior of amorphous materials.

Search for Anomalies in the Temperature Dependence of Ultrasonic Velocity in Water

High-resolution measurements of the velocity of 9.9-MHz ultrasonic waves in pure distilled water have been made at about 2300 temperatures between 6° and 81°C. The results can be fitted to an 8th-order polynomial in temperature with scatter of approximately ± 30 ppm and standard deviation 10 ppm. A plot of the deviations of the experimental points from such a polynomial discloses no significant discontinuities or other anomalous behavior. A comparison with previous measurements is made.

Temperature Dependence of Ultrasonic Velocity in Some Relatively Simple Unassociated Liquids

Measurements of the ultrasonic velocity in a liquid have generally exhibited a linear dependence on temperature, with certain exceptions (temperatures close to the freezing, boiling, or critical points), unless the liquid is associated (hydrogen-bonded). Deviation from linearity has, in fact, been used as a measure of association. We have measured the velocity in cyclopentane, methyl cyclopentane, and methyl cyclohexane over the extensive range of temperature for which they are liquid at atmospheric pressure. There can be no question of association in a saturated hydrocarbon, yet the velocity versus temperature plot, in each case, is plainly curved; the variation of velocity with temperature in methyl cyclohexane, for example, is −7.0 m/sec/°C below −70°C and −3.8 m/sec/°C above 30°C. The connection between the dependence of the velocity on temperature (Rao's relation) and molecular rotation in the liquid state is discussed.

Ultrasonic Velocity and Absorption of Aqueous Solutions of Polyvinyl Alcohol

An ultrasonic pulse technique was applied to the rheological study of aqueous solutions of polyvinyl alcohol in the ultrasonic frequency region.Two samples of polyvinyl alcohol were used. The average degree of polymerization of sample A and sample B was 1800 and about 2000, respectively. The content of residual acetyl groups was smaller than 0.7% by mole for sample A and was 12.2% by mole for sample B. The molecular weight distribution curve of sample A was obtained by the successive precipitation method proposed by Spencer.Ultrasonic velocity and absorption were measured over the temperature range of 3∼70°C for the solutions in the concentration range of 5∼15% by weight. The frequency of ultrasound was 1.42Mc/s throughout the experiment.The following results were obtained:In sample A, the temperature dependence of ultrasonic velocity has similar characteristics on the whole to that observed in pure water, and the ultrasonic velocity increases with the increase of concentration. In sample B which contains acetyl groups by 12.2% by mole, however, the behavior is fairly different. In the low temperature region no remarkable difference between A and B is found, but above 40°C it is clearly seen that sound velocity is smaller than that for the solutions of sample A which have the same concentration. The tendency of smaller sound velocity becomes more evident in high temperature region, and the velocity decreases with increase of polymer concentration in sharp contrast to the case of sample A. The velocity-temperature curve of solutions of sample B has a broader peak than in pure water, and the peak becomes lower, and the peak temperature shifts to lower temperature side. For example, in the case of the 10wt.% solution of sample B the peak temperature is about 50°C, whereas the value for pure water is 74°C.The average absorption coefficient in the temperature range of the present experiment increases with increase of concentration in both samples. The data for solutions of sample B are seen to be larger than those for solutions of sample A of the same concentration.The longitudinal elastic modulus M1 and the longitudinal loss modulus divided by angular frequency M2/ω are obtained from the data of sound velocity and absorption.

Temperature dependence of ultrasonic velocity in plastics

Temperature coefficient of ultrasonic velocity as well as the expansion coefficient in polymeric materials such as mouldrite, perspex, polystyrene and styron have been determined. The transition temperature in both the cases are nearly the same. The ratio of the values of the expansion coefficient and the ratio of the slopes of the velocity-temperature curves taken above and below the transition temperature are almost same.

Temperature Dependence of Ultrasonic Velocity in Plastics

The composite piezoelectric oscillator method has been employed to study the temperature dependence of the velocity of ultrasonic waves in Perspex and polystyrene plastics. While confirming a previously reported transition in Perspex at 60°C, the results show the existence of a transition in polystyrene also at 70°C for the first time.

Temperature dependence of ultrasonic velocity in liquid mixtures

Temperature dependence of ultrasonic velocity in liquid mixtures

Temperature dependence of ultrasonic velocity in alcohols

Temperature dependence of ultrasonic velocity in alcohols