Some of the important results emerging from our recent investigations on liquid crystals at high pressure are presented. In particular the following topics will be discussed: i) The relation between Pm, the maximum pressure of smectic stability, and the temperature range of the nematic phase in reentrant nematogenic compounds. ii) Piezothermal studies in the vicinity of the smectic A-nematic transition in 8 OCB. iii) The effect of molecular ordering on the pressure behaviour of the nematic-isotropic transition in reentrant nematic mixtures. iv) The first observation of a multicritical point in a single component liquid crystal.

Sodium oleate is practically insoluble in water at room temperature. Yet, when heated above the critical micellization temperature (cmt), its solubility increases rapidly and an isotropic optically clear micellar solution is formed. Upon cooling below the critical coagelization temperature (cct), the micellar phase transforms to an opaque curd, the coagel phase. The structural changes and the nature of this phase transition are, however, not well characterized.

The results of several Raman studies of vibrational dephasing in polyatomic molecular liquids at high pressure are reviewed. The density and temperature effects on vibrational dephasing of isotropic Raman bands for different vibrational models are reported for the following liquids: C(CH3)4; Si(CH3)4; Ge(CH3)4; ; Sn(CH3)4 and isobutylene CH2; = C(CH3) 2.The experimental data are used to test the current theoretical models of vibrational dephasing. Selected results of our high pressure experiments on collision induced scattering in polyatomic molecular liquids demonstrate well the essential role of high pressure in studying these phenomena.

The results of a Brillouin scattering study of the room temperature phases of H2;O (liquid, ice VI and ice VII) up to 30 GPa are presented. Longitudinal elastic moduli thus obtained are compared with values of the bulk modulus obtained from density measurements [1] and with both static and molecular dynamics calculations of the bulk modulus using potentials which have been proposed in studies of the liquid state. The calculations indicate that the potentials are not capable of describing the high pressure region of ice VII.

A depolarized light scattering study of pressure supercooled Pentachlorobiphenyl is presented. Fram the analysis of propa gative depolarized shear doublets, the shear modulus G∞ at infinite frequency is measured for various temperatures. The pressure range is from atmospheric pressure to pressures whem the liquid is in a glassy state : G∞ (p) is found to vary linearly at each measured temperature.

Initial results of a novel Raman spectroscopic method for studying fluid lubricant characteristics in a simulated elastohydrodynamic contact are reported. The method uses a Raman microscope which allows spectra to be obtained from a small volume (∼ 0.1 nl) of lubricant entrapped in the elastic deformation formed when a loaded glass plate falls onto a lubricated steel ball. The work described here was undertaken to obtain direct pressure measurements from an entrapped fluid at equilibrium after the initial impact. Our results indicate that pressures in twofold excess of the maximum Hertzian pressure can be generated in ball-plate entrapments of the polyphenyl ether 5P4E. In addition 5P4E has been studied as a pure liquid and as a solution in CCl4 using a diamond anvil cell (DAC). Preliminary results on 2,4-dicyclohexyl-2-methylpentane studied using a DAC and a hydrostatic equilibrium cell are also described.

Probe molecules P placed in dilute solution and absorbing radiation Ia produce electronically excited species P* which can return to thermal equilibrium by radiative (luminescence) kR and nonradiative (heat) kNR processes. The relative probabilities of the two decay channels are determined by measuring the lifetime τ of P* and the luminescence quantum yield φ = I/Ia, where I is the luminescent intensity. The kinetic scheme and relevant relations are

In 1960 David and Ewald [1] developed a technique for photographing the absorption spectra of solutions under shock wave conditions. A photograph of the spectrum of a uranyl nitrate solution exposed to a shock wave of 75 kbar showed the absorption to extend beyond 500 nm, the long wavelength limit for uranyl solutions under ordinary conditions. A.H. Ewald (unpublished, 1963) found that at room temperature pressure up to 6 kbar had no appreciable effect on absorption. Bell and Biggers [2,3] published an analysis of the spectrum of uranyl perchlorate solutions. The longest wavelength absorption band was at 486 nm but Bell [4] later found bands at 508 and 531 nm. The intensity of these very weak bands increased when the solution was heated to 95° C, and they were interpreted as “hot bands” due to absorption from an excited ground state. This paper reports new absorption measurements made on uranyl solutions heated to 250°C at low pressure and offers an interpretation of the effect observed in the shock experiments.

The absorption and emission spectra and the phosphorescence decay time of bis-tetrabutylammonium tetrabromomanganate-(II) were measured to 440 K and 3 kbar. In addition the melting pressure of the salt and its viscosity and electrical conductivity at normal pressure were determined as functions of temperature.

As predicted by the Hubbard-Onsager continuum dielectric friction theory for ionic mobility in solution, the observed pressure coefficient of the difference ζ between the observed ionic drag coefficient and the Stokes law friction (4πηR), is negative for the small ion Li+ even at low temperatures where the water structure is highly developed. For the large ion Cs+, however, it is positive at any temperature in contrast to the theoretical prediction, its magnitude being larger at lower temperatures and pressures. The anomaly is shown also by the medium-sized ion K+ below room temperature. The passing-through-cavities (PTC) mechanism has been proposed to explain the limitations of the continuum theory.

Solid methane has been a favourite subject for the study of phase transitions ever since the discovery by Clusius [1] of the phase transition α → β at 20.4 K in CH4. The reasons for the sustained interest in solid CH4 may be attributed to the following facts. i. The CH4 molecule has an almost spherical shape with a slight TD anisotropy. As a result, CH4 crystallizes below 90.7 K into a plastic crystal, α, of cubic symmetry, exhibiting almost complete rotational freedom of the molecules. ii. The CH4 molecule is very small in size with a low moment of inertia (I × 1040 g cm2 = 5.34 in CH4 and 10.64 in CD4), leading to a large rotational kinetic energy and related quantum effects at low temperature. iii. The protons in CH4 and the deuterons in CD4 carry a nuclear spin resp. Ip = 1/2 and I. = 1, which gives rise to spin-isomerism. Thus, CH4 has three spin varieties, meta (A1, In = 2), ortho (T2, in = 1) and para (E, In = 0). The isomerism may be expected to have profound influence on the phase diagram of solid methane.

Thermodynamic properties of materials above a few hundred KBars can normally be obtained only by dynamic techniques which have the associated difficulty (from the theoretical point of view) that the high pressure states are usually also at quite high temperatures. Thus, it is important to obtain accurate estimates of the thermal contribution to the thermodynamic functions. Within the pair potential model of solids, these thermal contributions may be determined by a self-consistent phonon approximation, but this is generally a very complicated calculation. Numerous approximate methods have thus been developed to estimate the thermal contribution to the thermodynamic functions [1].

In this article, the formation of superconducting compounds through structure transition of metallic glasses at high pressure high temperature are emphasized, and investigations on structure transition of metallic glasses made of niobiun alloys and lanthanun alloys are summarized.

Discussion of the proposed extension of the ASME pressure vessel code to cover operating pressures up to 1.4 GPa (200000 lbf/in2 ) has generated the proposal that two criteria should be used, of which one would be the collapse or ballooning pressure not the bursting pressure. The present paper examines this proposal in relation to extensive data on the collapse and bursting of thick-walled vessels available to the author.

It is concluded that the collapse pressure is only readily calculable for materials which approach the behaviour of an elastic/perfectly plastic material. It also appears for materials with significant strain hardening characteristics, such as mild steel, that the collapse pressure considerably underestimates the bursting pressure, whereas for a material which behaves as an elastic/perfectly plastic material the collapse pressure is nearly coincident with the bursting pressure. Consequently if the collapse pressure was adopted and if the factor of safety against collapse was adequate for one material it might be more or less than adequate for another material, which would appear to be unacceptable.

Pressure vessels often have notches or other stress concentrations present. Considering further that pressure vessels are nearly always subjected to some cyclic loading, fatigue cracking at notches is an important problem. The objective here is to describe some fatigue life testing and analysis which was performed with notched specimens in order to determine the effects of notch overload on fatigue life of pressure vessels.

Fatigue crack growth studies have been made on C-shaped and ring specimens taken from as-received and autofrettaged 4333 M4 thick-walled tubing. The ring specimen was chosen because it enables cracks to be propagated through the same residual stress distribution as that present in the tubing. It is shown that the reduced crack growth rates measured close to the bore in autofrettaged tubing can be attributed to the presence of compressive residual stresses there and can be explained in terms of the contribution of these stresses to the stress intensity factor range applied.

ASME recently formed two committees which were given thetask of drafting a new Vessel Code and a new Piping Code for pressures ranging from approximately 70 Mpa (10,000 psi) up to 1,400 Mpa (200,000 psi). Pressure vessels and pipework operating in this pressure range are, in many cases, employed for batch-type operations or are subjected to pulsating pressures, for example in LDPE (low-density polyethylene) plants, in isostatic pressing processes, or in the production of synthetic crystals. For this reason, it is very important to design the pressure-bearing components so that they can safely tolerate the load cycles which are to be imposed on them.

The authors have previously published stress intensity (K) solutions for singly and multiply cracked thick cylinders with internal pressure and autofrettage stress fields. In this paper a method of obtaining K values for intermediate radii ratios is proposed. The method involves an approximate superposition procedure which models the removal (or addition) of cylinder material and is based on the nearest available radii ratio. The procedure is exact for very short crack lengths, and generally gives answers within 5% at crack lengths up to 20% of wall thickness (wherein most of the fatigue lifetime is expended) after removal of 20% of the wall thickness. A simple expression is given for the anticipated change in fatigue lifetime resulting from material removal.

Most of the earlier results for residual stresses are based on the assumption of elastic unloading. In this paper, the prediction of residual stresses for the case of reverse yielding including the combined Bauschinger and hardening effect will be reported for an autofrettaged thick-walled cylinder. The Bauschinger effect factor is varying as a function of overstrain. The strain-hardening effect is considered with different parameters used for loading and unloading process. The new results indicate that the influence of the combined Bauschinger and hardening effect on residual stress distribution is significant.

A finite element stress analysis has been performed on a brilliant cut high pressure diamond anvil. The analysis includes the presence of a metal gasket. A perfectly cohesive interface is assumed to exist between the diamond and metal. Different configurations of the anvil face were studied. The stress distribution resulting from various beveled angles has been analyzed. It has been found that for a flat anvil, with a center normal pressure of about 210 kbar, an octahedral shearing stress of about 90 kbar is present near the center and monotonically increases radially to about 208 kbar along the outer edge. When the anvil surface is beveled, the octahedral shearing stress at the outer corner decreases significantly. The optimum beveled angle necessary to minimize these stresses seems to lie in the neighborhood of 15 degrees. The assumptions made and other stress considerations are discussed.