摘要:

Ultrasonic measurements on liquids at very high pressures and an accurate self‐consistent ultrasonic method for the determination of the equation of state of liquids at very high pressures are described. The liquid sample is contained in a polyethylene‐lined piston and cylinder device. The method described requires only the measurement of the transit time of an ultrasonic pulse through the liquid as a function of pressure. The difficulties and errors connected with a direct volumetric determination are thus avoided and a high accuracy is achieved. A computation of the uncertainties in the determination of the bulk moduli, the density and the velocity of sound is presented. Experimental results are given for water at 22°C and pressures up to 12.6 kbar. Data for the density of water reported by P. W. Bridgman and by L. H. Adams, and for the velocity of sound reported by Holtonet al.are found to be in good agreement with the present work.

ISSN:0021-8979    

DOI:10.1063/1.1657820

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The phase velocities of acoustic shear‐wave motions in isotropic solids such as glasses can be influenced by residual or applied stresses that make the material acoustically birefringent (the acoustoelastic effect) in much the same way as residual or applied stresses make a transparent material optically birefringent (the photoelastic effect). When a uniaxial stress is applied to an isotropic solid, the acoustoelastic effect depends upon &mgr;, the shear modulus, and &ngr;3, one of the three third‐order elastic constants describing an isotropic solid. A method based on an analysis by Toupin and Bernstein is used to determine values of &ngr;3for four glasses: fused quartz and fused silica (two types of vitrous silica), Pyrex, and Bausch and Lomb T‐40 glass. The values of &ngr;3obtained for vitreous silica and Pyrex are compared with previously reported values. Although the paper includes results for Pyrex and T‐40 glass, the principal emphasis is on the results for vitreous silica and the significance of the findings regarding the acoustoelastic effect in vitreous silica for applications of this material in high‐frequency ultrasonic devices.

ISSN:0021-8979    

DOI:10.1063/1.1657821

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The elasto‐optic matrix elements for longitudinal waves in four new single crystals have been measured. Piezoelectric bismuth silicon oxide and bismuth germanium oxide, cubic point group 23, show an elasto‐optic strength of 6.0 and 6.6, respectively, relative to fused silica based on an equal acoustic power criterion discussed below. Ferroelectric crystals from the strontium barium niobate system, tetragonal point group 4mm, were also studied. One with a Sr to Ba ratio of 3:1 showed an elasto‐optic strength of 26; another with a ratio of 1:1 had a strength of 5.8.

ISSN:0021-8979    

DOI:10.1063/1.1657822

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Measurement results on CdS ultrasonic amplifiers which were operated with continuous drift fields at room temperature are presented. A material gain of 26 dB was obtained for a 200‐MHz transverse‐wave signal. Comparisons are made with pulsed‐field data obtained from the same samples. The presence of saturation‐level ultrasonic flux significantly reduces the maximum gain obtainable under continuous operation.

ISSN:0021-8979    

DOI:10.1063/1.1657823

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The solution of a Boltzmann equation for electron transport is discussed with emphasis on its application to x‐ray production and electron scattering in electron‐probe microanalysis. Particular attention is given to the assumptions involved in associating an energy, a cross section for scattering, and a cross section for ionization with each position along the electron path. The Spencer‐Fano theory of electron stopping power is applied. The treatment of electron scattering of Brown and Ogilvie is refined using (1) a single scattering equation for short path lengths, (2) a transport equation for intermediate path lengths, and (3) a diffusion equation for long path lengths. The predictions of this Transport Equation Program are compared with experimental data for (1) the energy distribution of backscattered electrons, (2) the depth distribution of x‐ray production, and (3) x‐ray intensity ratio as a function of alloy composition. The x‐ray intensity ratios are corrected for fluorescence due to the continuum, and it is indicated that this correction may be significant.

ISSN:0021-8979    

DOI:10.1063/1.1657824

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The mechanism of alkali ion movement in glasses during electron‐probe analysis must include a dependence on the temperature of the volume irradiated. Experimental results of the composition changes of binary oxide glasses of Na2O and K2O with SiO2during electron bombardment indicate that there is a critical temperature for alkali ions in the diffusion process. Dependence of the critical temperature on composition and a comparison of these temperatures to the equilibrium temperature that can be produced from heat flow consideration indicates that for small beam diameters the actual temperature may be lower than that predicted. The rate of change of temperature may be more important to a probe operator than the equilibrium temperature.

ISSN:0021-8979    

DOI:10.1063/1.1657825

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Internal growth defects of high‐quality garnet crystals were studied by selective etchants and Lang x‐ray transmission topography. Terminal growth sections contained the fewest defects and dislocation densities were 102−104/cm2. Internal sections revealed both randomly dispersed etch pits and linear arrays. The latter were frequently found in the form of parallel grids. Results indicated that {100}, {111}, {411}, and {105} were the defective planes. X‐ray topographs verified that parallel linear faults are present in crystals on these same planes. The faults are not dislocation lines but tubular structural deviations caused by flux precipitation or other compositional changes. The origin and arrangement of the internal faults are related to fluctuations of the crystal growth rate. The rate changes can be initiated by small thermal gradients in the solution.

ISSN:0021-8979    

DOI:10.1063/1.1657826

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The wavelengths of sinusoidal perturbations in the shape of single‐crystal ice cylinders growing in supercooled water have been measured as a function of the experimental variables, primarily bath supercooling. The experimental results are in good agreement with theory.

ISSN:0021-8979    

DOI:10.1063/1.1657827

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A simple analysis assuming hard‐sphere atomic behavior and considering surface and volume energies has been applied to estimate the stability of very small fcc crystals having different external shapes. Such crystals or particles are commonly produced by vacuum evaporation, or evaporation in a reduced pressure inert gas atmosphere. The analysis has been extended to small crystals (or nuclei) of fcc metals condensed on substrates by assuming that the metal‐substrate interfacial energy is comparable to that of a large angle metallic grain boundary. Icosahedral, pentagonal decahedral, tetrahedral, octahedral, and pyramidal particles were considered, and the relative stability predictions are generally in accord with observations.

ISSN:0021-8979    

DOI:10.1063/1.1657828

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

By means of a preferential etch technique in conjunction with transmission electron microscopy, a stress‐annealed pyrolytic graphite has been shown to be a compact of crystallites withLavalues typically lying in the range 1–40 &mgr;. The boundaries defining these crystallites varied from the low‐angle tilt boundaries &thgr;∼1′, found in Ticonderoga crystals, to high‐angle boundaries denoting misorientations of up to 30°. In contrast to the low over‐all boron concentration of the material, 1–2 ppm wt/wt, the concentration of this element residing in the intercrystallite boundaries was calculated at ∼103ppm wt/wt. This provides confirmation of the premise that the lattice disorder existing across a boundary trace supports a vacancy concentration far in excess of that pertaining to more perfect regions of the graphite. It is postulated that at temperatures >2100°C this enhanced vacancy concentration will allow a dynamic interchange mechanism for crystallite growth, having an activation energy given byE*= ½(Efv+Efi) +Emai. Nonbasal screws have a deleterious effect on the rate of graphitization for two principal reasons. First, the nonbasal screws residing in intercrystallite boundaries effectively stabilize the excessive vacancy concentration at the latter sites. Second, if the distance of closest approach of these dislocations becomes less than some critical value, they may be responsible for creating new boundaries. As it appears unlikely that many formal boundaries, which can be described in terms of lattice defects, will exist between neighboring crystallites in pyrolytic graphite, the initial stages of graphitization must occur by an alternative mechanism. The recent work of Murty would seem to imply that the latter is in fact an interstitial mechanism, having an activation energy of 9.8±0.7 eV as compared to the value of 8.3±0.3 eV predicted for the dynamic interchange mechanism.

ISSN:0021-8979    

DOI:10.1063/1.1657829

出版商:AIP    

年代:1969

数据来源: AIP