George C. Kennedy

Effect of Pressure on the emf of Chromel‐Alumel and Platinum‐Platinum 10% Rhodium Thermocouples

A differential technique has been used to measure the absolute effect of pressure on the emf of Chromel‐Alumel and Pt‐Pt10Rh thermocouples. The experiments were conducted in a solid pressure medium piston‐cylinder apparatus to 35 kbar and 1000°C. Extrapolation of these data shows Chromel‐Alumel to read as much as 28°C high at 50 kbar and 1200°C and Pt‐Pt10Rh as much as 28°C low at 50 kbar and 2000°C. Graphs are presented which show correction voltage versus temperature for various pressures.

Compressibility of 27 halides to 45 kbar

Abstract New compressibility data on 27 halides are reported. Compressibilities were determined by observations of piston displacement in the static high pressure apparatus to 45 kbar. We report measurements on a number of halides for the first time. Our results are in fair agreement with prior measurements by Bridgman on some of the halides where our data overlap. Our agreement with reductions of shock data is in many cases extremely poor because the reductions of the shock data did not take into account the phase transitions found in the halides.

The energetics of natural garnet solid solution - I. Mixing of the aluminosilicate end-members

Approximate mixing properties of the dominant calcium silicate end-member components of natural garnets, namely grossularite, andradite and uvarovite, have been derived through theoretical thermodynamic and crystal chemical analysis, and appropriate reduction of the available experimental data. The stability of the solid solution with respect to phase separation in the ternary system has been analyzed. Finally, a general model is presented as to the approximate mixing properties of multicomponent natural garnet solid solution involving substitutions in both eight and six coordinated sites.

Equation of state of sodium chloride up to 32 kbar and 500°C†

Abstract The length change of a 25mm long single crystal of NaCl has been determined as a function of hydrostatic pressure up to 32 kbar and temperatures up to 500°C using an electrical contact piezometer with tungsten carbide as a standard. The measurements were carried out in an end loaded piston cylinder apparatus. The length change of the tungsten carbide standard is small compared to that of NaCl and therefore reliable data are obtained. Compression data by Bridgman[1] and thermal expansion data by Kennametal Inc. were used for the equation of state of tungsten carbide. We estimated an absolute uncertainty in the length change measurement of NaCl of ±0.7%. The temperature was accurate within 0.3°C. The uncertainty in pressure is ±0.4%. The results are compared with Deckers [2] equation of state which is frequently used when NaCl is taken as a standard in high pressure work. At room temperature we find a smaller compression of NaCl than Decker and find excellent agreement with Bridgmans[3] data. At higher temperatures we find very good agreement between our data and Deckers equation of state.

Melting and phase relations in the plane tholeiite-lherzolite-nepheline basanite to 40 kilobars with geological implications

Six crystalline mixtures, picrite, olivine-rich tholeiite, nepheline basanite, alkali picrite, olivine-rich basanite, and olivine-rich alkali basalt were recrystallized at pressures to 40 kb, and the phase equilibria and sequences of phases in natural basaltic and peridotitic rocks were investigated.The picrite was recrystallized along the solidus to the assemblages (1) olivine+orthopyroxene+ clinopyroxene +plagioclase+spinel below 13 kb, (2) olivine+orthopyroxene+clinopyroxene+spinel between 13 kb and 18 kb, (3) olivine+orthopyroxene+clinopyroxene+ garnet+spinel between 18 kb and 26 kb, and (4) olivine+clinopyroxene+garnet above 26 kb. The solidus temperature at 1 atm is slightly below 1,100° and rises to 1,320° at 20 kb and 1,570° at 40 kb. Olivine is the primary phase crystallizing from the melt at all pressures to 40 kb.The olivine-rich tholeiite was recrystallized along the solidus into the assemblages (1) olivine+ clinopyroxene+plagioclase+spinel below 13 kb, (2) clinopyroxene+orthopyroxene+ spinel between 13 kb and 18 kb, (3) clinopyroxene+garnet+spinel above 18 kb. The solidus temperature is slightly below 1,100° at 1 atm, 1,370° at 20 kb, and 1,590° at 40 kb. The primary phase is olivine below 20 kb but is orthopyroxene at 40 kb.In the nepheline basanite, olivine is the primary phase below 14 kb, but clinopyroxene is the first phase to appear above 14 kb. In the alkali-picrite the primary phase is olivine to 40 kb. In the olivine-rich basanite, olivine is the primary phase below 35 kb and garnet is the primary phase above 35 kb. In the olivine-rich alkali basalt the primary phase is olivine below 20 kb and is garnet at 40 kb.Mineral assemblages in a granite-basalt-peridotite join are summarized according to reported experimental data on natural rocks. The solidus of mafic rock is approximately given by T=12.5 PKb+1,050°. With increasing pressure along the solidus, olivine disappears by reaction with plagioclase at 9 kb in mafic rocks and plagioclase disappears by reaction with olivine at 13 kb in ultramafic rocks. Plagioclase disappears at around 22 kb in mafic rocks, but it persists to higher pressure in acidic rocks. Garnet appears at somewhat above 18 kb in acidic rocks, at 17 kb in mafic rocks, and at 22 kb in ultramafic rocks.The subsolidus equilibrium curves of the reactions are extrapolated according to equilibrium curves of related reactions in simple systems. The pyroxene-hornfels and sanidinite facies is the lowest pressure mineral facies. The pyroxene-granulite facies is an intermediate low pressure mineral facies in which olivine and plagioclase are incompatible and garnet is absent in mafic rocks. The low pressure boundary is at 7.5 kb at 750° C and at 9.5 kb at 1,150° C. The high pressure boundary is 8.0 kb at 750° C and 15.0 kb at 1,150° C. The garnet-granulite facies is an intermediate high pressure facies and is characterized by coexisting garnet and plagioclase in mafic rocks. The upper boundary is at 10.3 kb at 750° C and 18.0 kb at 1,150° C. The eclogite facies is the highest pressure mineral facies, in which jadeite-rich clinopyroxene is stable.Compositions of minerals in natural rocks of the granulite facies and the eclogite facies are considered. Clinopyroxenes in the granulite-facies rocks have smaller jadeite-Tschermaks molecule ratios and higher amounts of Tschermaks molecule than clinopyroxenes in the eclogite-facies rocks. The distribution coefficients of Mg between orthopyroxene and clinopyroxene are normally in the range of 0.5–0.6 in metamorphic rocks in the granulite facies. The distribution coefficients of Mg between garnet and clinopyroxene suggest increasing crystallization temperature of the rocks in the following order: eclogite in glaucophane schist, eclogite and granulite in gneissic terrain, garnet peridotite, and peridotite nodules in kimberlite.Temperatures near the bottom of the crust in orogenic zones characterized by kyanitesillimanite metamorpbism are estimated from the mineral assemblages of metamorphic rocks in Precambrian shields to be about 700° C at 7 kb and 800° C at 9 kb, although heat-flow data suggest that the bottom of Precambrian shield areas is about 400° C and the eclogite facies is stable.The composition of liquid which is in equilibrium with peridotite is estimated to be close to tholeiite basalt at the surface pressure and to be picrite at around 30 kb. The liquid composition becomes poorer in normative olivine with decreasing pressure and temperature.During crystallization at high pressure, olivine and orthopyroxene react with liquid to form clinopyroxene, and a discontinuous reaction series, olivine → orthopyroxene → clinopyroxene is suggested. By fractional crystallization of pyroxenes the liquid will become poorer in SiO2. Therefore, if liquid formed by partial melting of peridotite in the mantle slowly rises maintaining equilibrium with the surrounding peridotite, the liquid will become poorer in MgO by crystallization of olivine, and tholeiite basalt magma will arrive at the surface. On the other hand, if the liquid undergoes fractional crystallization in the mantle, the liquid may change in composition to alkali-basalt magma and alkali-basalt volcanism may be seen at a late stage of volcanic activity.

Compressibility of 18 Molecular Organic Solids to 45 kbar

New compressibility data on 18 organic solids are reported. Measurements on a number of these solids have been made for the first time. Compressibilities up to 45 kbar were determined by observing piston displacement in a static high‐pressure apparatus. Related compounds show a progressive decrease in compressibility with increase in molecular volume.

Compressibility of 22 elemental solids to 45 KB

Abstract The compressibility of 22 elemental solids has been measured by static methods in a piston cylinder apparatus to 45 kb. In most cases agreement with the data derived by reduction of shock wave data is extremely good. In a few cases, low pressure phase changes makes the agreement less good. In general, our new measurements of compressibility are in closer agreement with the results from shock data than they are with Bridgmans earlier results. The bulk moduli and some pressure derivatives have been estimated by fitting a Murnaghan equation and a modified Murnaghan equation to our data points, and these results are intercompared with the results from ultrasonic measurements, from shock measurements and from prior results of Bridgman.

Grüneisen parameter of NaCl at high compressions

A new method of determining the pressure dependence of the Gruneisen parameter is described. The measurements were carried out on NaCl to 33 kbar at room temperature using an end-loaded piston-cylinder apparatus. A fluid cell arrangement with Bridgman unsupported area seals was used. Changes of sample temperature associated with small adiabatic pressure changes were measured and the Gruneisen parameter could be calculated from the thermodynamic relationship γ = (KsT)(∂T∂P)s where Ks is the adiabatic bulk modulus. Our results are in excellent agreement with those reported by Roberts and Ruppin [1] who calculated the pressure dependence of γ from thermodynamic and ultrasonic data and in excellent agreement with those reported by Hardy and Karo [2] who carried out a lattice-dynamical calculation.

Uniaxial stress component in tungsten carbide anvil high‐pressure x‐ray cameras

A method is proposed to detect the presence of a uniaxial stress component in samples belonging to the cubic system, pressed in a tungsten carbide anvil x‐ray camera unit. The method is based on fitting the experimental data to an expression of the form ew(hkl)=ewp−m t(C11+4C12−2C44)/2 (C11+2C12)(C11−C12+3C44)+n t [S12+(S11−S12−S44/2) Γ(hkl)], where ew(hkl) is the strain calculated from the shift of the diffraction line (hkl) at a load w applied between the anvils, ewp is the strain arising from the hydrostatic component of the stress p, t is the uniaxial stress component, and Γ(hkl)=(h2k2+k2l2+l2h2)/ (h2+k2+l2)2. If the state of stress continuity in the crystallites is assumed, then m =0 and n =1; and m =1 and n =0 if the state of strain continuity in the crystallites is assumed. The experimental data for Si at w = 1400 kg and for NaCl at w = 510 kg indicate a linear dependence of ew(hkl) on Γ(hkl) as is expected for n ≠0. The slope of the ew(hkl) versus Γ(hkl) plot is negative for Si and positive for Na...

The Composition of Liquids Formed by Partial Melting of Eclogites at High Temperatures and Pressures

We have examined the composition of the liquids formed by partial melting of an eclogite nodule from the Roberts Victor kimberlite pipe. We show that at high pressures and low degrees of partial melting, a nepheline normative liquid is formed. Hypersthene normative melts are formed with greater degrees of partial melting or partial melting at lower pressures. Nonetheless, the demonstration of the possibility of the formation of nepheline normative magmas by partial melting of an eclogite does not mean that this is the only possible origin. Although alkaline rock may be formed by partial melting at great depths, abundant field data suggest that many alkaline rocks are formed at shallow depths in a volcanic edifice. Volatiles also apparently play an important role in the genesis of the melts. It seems quite possible to one of us (GCK) that a large number of alkaline magmas are formed by access of sea water to basaltic magma chambers at shallow depths.