Negative Dilatation Research Articles

Crystallization of glassforming melts under hydrostatic pressure and shear stress: Part I Crystallization catalysis under hydrostatic pressure: possibilities and limitations

This is the first part of a thorough study of the kinetics of melt crystallization under applied static pressure, P, and under shear stress. The thermodynamic and kinetic consequences of increased external pressure on nucleation rate, non-steady-state time lag, rate of crystal growth and overall crystallization kinetics in undercooled melts are analysed. Two types of undercooled liquids (with either positive or negative volume dilatation upon crystallization) are considered. Particular attention is given to the effect of pressure on the specific interface energy, σ, at the crystal/melt phase boundary. Using an appropriate thermodynamic model it is shown that for one-component systems, (∂σ/∂p)<0 is to be expected as a rule. Thus an additional decrease of the thermodynamic barrier of nucleation in pressurized melts is to be expected. However, it is also shown that the increase of melt viscosity with pressure in most cases reduces the effect of this decrease. Thus increased pressure has a limited effect as a nucleation catalyst. The possibilities in this respect are analysed and conditions under which static pressure may lead to enhanced crystallization are outlined.

Numerical Study of a Turbulent Flow Compressed by a Weak Shock Wave

Modification of a two-dimensional isotropic trbulent flow by passage of a weak shock wave was numerically studied by the explicit spectral collocation method with the fourier series in the ranges of M1 = 0.14−0.21 and Ms = 1.06−1.14. The density 1 trbulent kinetic energy increased by 10 to 19 % and density fluctuation increased by 14 to 50 % in proportion to the shock wave mach number. The amplification of turbulent kinetic energy did not change by increase of the turbulent Mach number, while that of density fluctuation decreased from1.35 to 1.15%. The argumentation of turbulent kinetic energy appeared at moderate and high wave numbers of energy spectra and resulted in a reduction of the integral scale by3.33 to 5.4%. Modifications mechanisms of turbulent kinetic energy, density fluctuation and vorticity were verified by the transport equations It was shown that the decreased amplification of the density fluctuation In the increased trbulent Mach number attributed to the unchanged production terms and the negative dilatation correlation behind the shock wave.the vorticity-dilatation term was responsible for more than 80 % of the total vorticity production at the shock front.

The structural properties of Tb 3Fe 5O 12 and growth induced anisotropy

In order to define the role of growth induced anisotropy in Terbium Iron Garnet (TbIG), the temperature dependences of both lattice constants and rhombohedral distortion angles were studied on a flux “as grown” single crystal and compared with the properties of a single crystal originated from the same melt and then submitted to a thermal treatment (1273 K during 96 h). In the 20–300 K temperature range where the X-ray diffraction experiments were performed, large difference between the two samples behaviours were found; at low temperatures, the growth induced anistropy (if it is not cancelled) is the dominant contribution to the crystal anisotropy. In the 45–80 K temperature range, where both samples present strong anomalies, a negative dilatation is observed for the sample with thermal treatment. The λ 111 and λ 100 magnetostriction constants are deduced and compared with the literature data.

Thermoluminescence and radiation‐induced volume changes in CaF2 (Mn, RE) materials

AbstractThe thermoluminescence properties of various CaF2 materials (natural fluorite, CaF2‐glass ceramics and enamels) doped with RE oxides and Mn are investigated in details. Volumetric measurements show that γ‐irradiation leads to a change in the volume density of powder samples of these materials. Depending on the character of the sample, positive (increased volume) or negative dilatation (decreased volume) can be observed during irradiation with doses within the range 1 C/kg–9 C/kg. As time elapses, the radiation‐induced alteration of the sample volume is relaxed and after 2–3 months reaches again the initial volume density of the sample. The unexpected result of radiation‐induced volume changes are discussed in details accounting for supplementary X‐ray, electron microscopy and EPR studies.

Source parameters of the October 1, 1987 Whittier Narrows Earthquake from crustal deformation data

Offsets in the regional strain field, generated by the October 1, 1987, Whittier Narrows earthquake, were recorded with large amplitudes on two deep‐borehole dilational strainmeters at distances of 46.7 and 65.5 km from the hypocenter and marginally on instruments at greater distances in the Parkfield area and at Pinon Flat, where laser extensometers also recorded small offsets. These data are insufficient to solve for the location and physical parameters of the earthquake, but by also using the measured elevation changes in the epicentral area, we are able to invert for source models consistent with all available observations of crustal deformation. The source models obtained indicate that slip extends to a depth of about 30 km, well below the recorded aftershock zone. The requirement for deeper (and presumably aseismic) slip derives from the large negative dilatation experienced by the nearest strainmeter (PUBS), but high‐frequency data from the same site exclude any significant slow component of moment release. By ignoring PUBS we obtain a moment of about 0.7 × 1018 N m on a fault that has a strike and dip of about N60°W and 40° down to the north, respectively, and extends to a depth of about 16 km. The most likely reason for the anomalous offset at PUBS appears to be sympathetic slip triggered on a nearby fault by the main shock. Precursive strain during the month prior to the earthquake is not apparent at the nanostrain level in the data from the closest instrument, but the event was accompanied by a change in strain rate at the two nearer sites.

Structural Analysis of Shear Zones in Basement Granite and their Relationship with Folding, Shearing and Faulting in the Cover Sediments Near Hirapur, District Sagar, Central India

Abstract The morphology of ductile shear zones in the granitic basement of Bijawar rocks is described. The dextral shear zones are more ubiquitous than their sinistral counterparts and the obtuse angle between the two sets faces the direction of maximum shortening in rocks, the exact value of the angle presumably controlled by the mean stress. The maximum displacement vector of shear zones is generally subhorizontal. The negative dilatation in some shear zones has caused the overall defoi marion in them to be of the flattening type. The orientations of the principal stresses are calculated. The cleavage trajectories do not sometimes exactly bisect the acute angle between the conjugate zones, presumably due to rotation of principal strains with progressive shear or to the more accentuated development of one set of zones. The sinusoidal and conjugate folds of monochnic or triclinic symmetry (D-1) in the Bijawar rocks are shown to be related genetically and from the point of view of orientation of principal compressive stresses to the ductile shear zone development in basement granite. The brittle-ductile shear zones in the basal carbonate unit associated at places with pressure solution or tectonic stylolitic structures whose formation was accompanied by about 14 to 24 per cent volume reduction formed at the same time. There was a renewed activity during post-Vindhyan time along pre-existing shear zones in the older rocks but in the opposite sense under very Jow P-T conditions which produced ductile D-2 structures in Bijawar rocks, culminating in small or moderate scale strike-slip faults. The youngest movements along these faults were, however, with a vertical component under a subvertically oriented maximum principal compression. It appears that most shear zones have an minal period of strain softening, followed by rather sudden strain hardening or loss of material contmuity which causes either the termination of such zones or their passing into model ate scale wrench faults.

Calibration of the sound attenuation equation

An alternative development for sound attenuation and dispersion equations based upon a component of pressure rather than total pressure suggests that the traditional equation for sound attenuation may be erroneously calibrated over unit lengths instead of wave lengths. The component is named “aberrant” pressure and represents the differences between instantaneous pressure and equilibrium pressure in a mechanically disturbed fluid. This aberrant component of pressure is further broken into components, one of which is in phase with condensation (negative dilatation) and the other in phase with density. The component in phase with condensation represents attenuation and the component in phase with density represents dispersion. The new equation for attenuation differs from the traditional equation by a factor of π.

Nuclear magnetic resonance brain imaging in chronic schizophrenia.

Patients with chronic schizophrenia were examined by nuclear magnetic resonance imaging of the brain. Subgroups of the syndrome with high positive or high negative symptom scores and ventricular dilatation were compared with each other and with normal controls in respect of regional spin lattice relaxation time (T1) changes. Significant differences were not observed between the schizophrenic subgroups and controls but there were significant differences between the subgroups themselves. The presence of tardive dyskinesia was associated with increased T1 of the basal ganglia. The significance of these results is discussed in relation to findings using other techniques.

Stress relaxation in electron bombarded silicate glasses

In contrast to the behavior of vitreous silica which has developed internal stresses consequent upon nonuniform irradiation with ions (e.g., protons, deuterons, helium ions), the electron-bombarded vitreous silica does not show a post-irradiation stress relaxation. The complex silicate glasses which have been irradiated nonuniformly with electrons display large post-irradiation internal stress changes, which may be increases or decreases. It is evident that in them both positive and negative dilatation centers were formed and that they possess different annealing properties. It is not clear to what extent the internal stress changes found in these irradiated glasses are caused by annealing or by stress relaxation. Since plates which had been irradiated until they fractured did not appear to behave differently from unfractured samples, it is concluded that the stress changes are a microscopic rather than a macroscopic phenomenon. The reduced power dependence of the ionization compaction of vitreous silica on dose is discussed.

Geodetic analysis of reservoir depletion at the Geysers Steam Field in northern California

Reservoir depletion at the Geysers from 1974 to 1977 is evident in measured changes in gravity, surface strain, and pore pressure drainage. The drainage area increased about 20%, the maximum gravity decrease was about −120 μGal, and the maximum elevation change was about 6 cm during this period. Since the net mass withdrawal is known, it may be combined with the gravity change to estimate a drainage volume. The maximum drainage volume is 25 km3. Because the depth of the caprock and extent of the pore pressure drainage is known, this volume limit implies that no significant mass withdrawal occurs below a depth of 4 km. The ratios of surface elevation changes to horizontal contraction coinciding with the drainage area imply an equant drainage geometry, assuming that fluid production produces negative dilatation. Using the same cylindrical geometry used to model the gravity, negative dilatational strain rates of 4 to 5 × 10−5/yr were found to produce the observed surface displacements. The likelihood of boiling in the system to produce steam combined with apparent large bulk moduli (from seismic velocities) and small pore pressure declines suggest that most of the reservoir contraction is due to cooling.

Strain accumulation rates in the western United States between 1970 and 1978

The rate of dilatation and the rate and direction of shear have been determined from trilateration data for 23 Geodolite networks in the western United States. Sixteen nets are located along the San Andreas fault system between Point Reyes, California, and the United States‐Mexico border. Other locations are across the Garlock fault in California; across Puget Sound near Seattle, Washington; near Hanford in eastern Washington; near Hebgen Lake in Montana; across the Wasatch fault at Ogden, Utah; across the Rio Grande rift at Socorro, New Mexico; and Dixie Valley in Nevada; and at the northern end of Owens Valley on the California‐Nevada border. Implicit in the treatment are the assumptions that the strain was accumulating at a constant rate over the time period (within the interval 1970–1978) and over the local area (usually about 50‐km diameter) covered by the surveys. Of the nets located away from the San Andreas fault, only Ogden and Hebgen show significant strain accumulation. At Ogden the deformation is principally an east‐west compression of 0.23±0.05 μstrain/yr and at Hebgen Lake a northeast‐southwest extension of 0.17±0.03 μstrain/yr. Along the San Andreas fault system the rate of shear is 0.2 to 0.4μ/yr. The direction of shear agrees very well with the surface strike of nearby faults. This agreement is maintained even in regions like the ‘big bend,’ where both the fault strike and the observed shear direction are more westerly than they are elsewhere. Shear strain in northern California appears to be concentrated more closely on the faults, whereas in southern California the strain is a broader, smoother feature. In the San Francisco Bay area the strain data indicate slip at depth on both the San Andreas and the Calaveras faults. In addition to the observed shear the nets in California indicate a negative dilatation (areal decrease) of about 0.2 μstrain/yr. This dilatation is unexplained, but the following sources appear unlikely: (1) systematic survey error, (2) an association with the southern California uplift, (3) an association with the big bend in the San Andreas fault in Southern California, or (4) the result of the superposition of a uniaxial strain on the Pacific‐North American plate boundary shear.

On Zero or Negative Thermal Dilatation of the Quenched Irreversible Fe–Ni Invar Alloys

The effect of quenching on the thermal dilatation of the Fe–Ni Invar alloys has been studied by absolute thermal dilatation measurements. It is well known that the reversible alloy with 36%Ni possesses the lowest coefficient of dilatation. The present study shows that the quenched irreversible alloy with 34%Ni also indicates zero or negative thermal dilatation. And apparent two A s -points are detected in the irreversible Invar alloys. These observations suggest that a stable state in the γ-phase region is not the perfect γ-phase. The measurements of magnetic susceptibility in the para-process and X-ray analyses indicate that the states produced by quenching have some similarities to those by cold-working, which can be ascribed to a transitional structure far from the perfect f.c.c. lattice.

Dependence of the compaction of vitreous silica on the ionization dose

Earlier data for the relationship of negative dilatation of vitreous silica to the ionization dose of 0.3 and 0.6-MeV electrons are clarified and corrected. Values are given for the maximum and the mean dilatations along the electron path in the material.

On Zero or Negative Thermal Dilatation and Phase Transformations in Cold-Worked Fe–Ni Invar Alloys

The effect of cold-swaging on the low thermal dilatation in the Fe–Ni Invar alloys, especially the negative dilatation of the 36%Ni alloy, was investigated by the X-ray and magnetic measurements as well as the thermal expansion measurements in the directions perpendicular and parallel to the swaging direction. Anomalies of the α→γ transformation were found in the irreversible alloy, which behaves as including higher A f -points or lower nickel contents. The γ-phase alloy after this transformation includes presumably lower Curie points. For the 36%Ni alloy, a swelling portion was found in the magnetic susceptibility in the para-process versus temperature curve in a lower temperature range, which is in agreement with the range of the negative dilatation. To explain such a state, a shear mechanism was discussed.

Electron irradiation dilatation in SiO2

Negative dilatation (shrinkage) induced by 10-keV electron bombardment of SiO2 films thermally grown on Si has been studied. Measured deflection changes in continuous SiO2 bridges etched following irradiation showed a maximum shrinkage of [inverted lazy s] 0.8%, which occurred at 0.2 C/cm2, followed by a slight expansion, and subsequent saturation at higher exposures. Exposures up to 3 C/cm2 were utilized. Isochronal annealing studies show the activation energy for recovery to be approximately 1 eV with 2% recovery occurring in 1 h at 400°C.

Phonon Scattering by Cottrell Atmospheres Surrounding Dislocations

Cottrell atmospheres modulate the solute concentration of alloys and lead to fluctuations in phonon velocity essentially proportional to the dislocation strain field. Normally one regards point defects as ineffective in scattering phonons at the very low temperatures when the thermal resistance due to dislocations is important. However, the modulation of the impurity concentration about the dislocations increases the phonon scattering by dislocations if heavy impurities are associated with positive dilatation, or light impurities with negative dilatation, and decreases phonon scattering for the opposite combinations. Cottrell atmospheres may thus account for an apparent dependence of phonon scattering by dislocations on the solute content of alloys, as well as changes in the lattice thermal conductivity with aging.

Intersecting stacking faults in face-centered cubic lattices

The geometry of intersecting intrinsic stacking faults has been examined. Depending on the stacking fault displacement vectors, a region of positive or negative dilatation is created along the intersection. The energies required to produce these intersections have been estimated from the magnitudes of the dilatations. The dilatation is removed by completion of slip on the intersected plane, and increased by completion of slip on the intersecting plane.

Sur la théorie moléculaire de l'hélium liquide II — le coefficient de dilatation thermique de l'hélium liquide

Synopsis The cell model applied to liquid helium by the authors in their first communication is slightly extended. The volume per cell and the total number of cells are obtained by the condition of minimum free energy. In this model the number of cells wich accomodate two particles is no more equal to the number of cells with zero particles. The results obtained in the first paper are not appreciably changed but the present model permits not only to explain the anomalous specific heat and increase of entropy, but also the negative thermic dilatation of liquid helium at temperatures below the λ-point.