H. M. Strong

Diamond‐Graphite Equilibrium Line from Growth and Graphitization of Diamond

Diamond growth occurs at high temperatures and pressures in the presence of certain molten metals which serve as solvent catalysts. The zones of pressure and temperature in which diamond growth occurs have been determined for a number of metals. These zones are bounded on the low‐temperature side by the melting point of the metal‐carbon eutectic at pressure. They are bounded on the high‐temperature side by the diamond‐graphite equilibrium line. This experimentally determined equilibrium line agrees very closely with the theoretical extrapolation of the thermodynamically calculated line proposed by Berman and Simon, viz., P(kbar)=7.1+0.027T(∘K).

Crystallization of Diamond and Graphite

The key features of the complete, stable nickel—carbon phase diagram have been established at pressures up to 54 kbar, and these features have been directly related to the nucleation and growth characteristics of diamonds in this system. At pressures in excess of 52.5 kbar, a liquid+graphite+diamond eutectic is formed at approximately 0.3 at. % nickel which results in an effective displacement of the diamond—graphite equilibrium line. This displacement is shown to be of considerable importance in the nucleation and growth of diamonds in this system. Under low and moderate driving forces, the rate‐controlling mechanism in the growth on a speed diamond is the diffusion of carbon across the molten metal film surrounding the diamond. The observed diffusion coefficients at 54 kbar and 1660°

Hexagonal diamonds in meteorites: implications.

A new polymorph of carbon, hexagonal diamond, has been discovered in the Canyon Diablo and Goalpara meteorites. This phase had been synthesized recently under specific high-pressure conditions in the laboratory. Our results: provide strong evidence that diamonds found in these meteorites were produced by intense shock pressures acting on crystalline graphite inclusions present within the meteorite before impact, rather than by disintegration of larger, statically grown diamonds, as some theories propose.

Pressure Dependence of the emf of Thermocouples to 1300°C and 50 kbar

The relative and absolute effects of pressure on the emf of commonly used thermocouples were measured to 1300°C and 50 kbar. The relative temperature corrections due to the effect of pressure are presented for Pt/Pt10Rh, Pt/Pt13Rh, Chromel‐Alumel, and iron‐constantan thermocouples as a function of temperature and pressure. The accuracy of these relative temperature corrections is approximately ±1°C and their magnitudes can exceed 40°C in some cases. The absolute corrections of these thermocouples are approximately determined by: (1) correlating experimental and theoretical results on the boundary conditions for the diamond ⇄ graphite equilibrium, (2) relating experimental and calculated results for the effects of pressure on other single‐component phase transformations, and (3) evaluating theoretical and experimental results for diffusion at high pressures and high temperatures.The absolute temperature corrections for all of the thermocouples investigated are proportional to the pressure at a given temper...

Flat Panel Vacuum Thermal Insulation

Evacuated mats of glass fiber made up of fibers of proper size and orientation are capable of supporting a compressive mechanical loading of at least one atmosphere and yet maintain a thermal conductivity of less than 10 microcalories/cm°C sec. The use of such a glass fiber mat as a filler makes possible an evacuated flat‐panel thermal insulation which is comparable to a Dewar flask in insulation efficiency. The rate of heat transfer through a Dewar flask wall was reduced several‐fold at liquid nitrogen temperatures and below by adding a 2‐cm‐thick layer of orientated and evacuated glass fiber mat to the outer surface.This investigation showed that in evacuated glass fiber mats, supporting external atmospheric loading, the fiber to fiber contact area is less than 10−4 the mat area, making the contact pressure about 15 000 kg/cm2. The effective length of the thermal conduction paths along the fibers is about four times the mat thickness. The mean pore size for gas molecule motion in the mat was found to be...

Pressure Dependence of the emf of Thermocouples

Possible factors contributing to relative and absolute emf corrections for thermocouples due to the effect of high pressure are evaluated in the present paper. These factors include contamination, plastic deformation, electrical shunting, and pressure and temperature gradients. The relative correction data from different experiments and different types of cells are compared. A method for obtaining the proper absolute corrections for Pt/Pt10Rh and Chromel‐Alumel thermocouples for any type of high‐pressure cell is presented.

Catalytic Effects in the Transformation of Graphite to Diamond

The transformation graphite to diamond is catalyzed by the Group VIII metals, manganese and chromium. The fact that these metals are good solvents for carbon tends to obscure their catalytic role in this transformation. It was found that copper‐rich copper—nickel alloys capable of dissolving less than 0.06 at. % carbon catalyzed the formation of diamond whereas lead and antimony having about equal solvent capacity did not. The diamond nucleation rate increased exponentially with nickel concentration in the copper‐rich alloys. Hence, on the basis of the theory that nucleation catalysts provide surfaces of low interfacial energy, one important role of the nickel in these alloys may be interpreted as that of reducing the interfacial energy between diamond and alloy.

Measurement of Temperatures in Flames of Complex Structure by Resonance Line Radiation. I. General Theory and Application to Sodium Line Reversal Methods

Sodium line reversal temperature measurement by low resolving power spectroscopic instruments on complex flame structures gives temperatures intermediate between the highest and lowest temperature in the line of sight. This intermediate temperature is determined by the temperatures, optical depths and arrangement of the individual zones. By taking into account these factors, it is possible to derive temperatures for the inner zones of a complex flame. The theory, numerical data needed to apply the theory, and experimental examples are given.

Measurement of Temperatures in Flames of Complex Structure by Resonance Line Radiation. II. Sodium Line Reversal by High‐Resolution Spectroscopy

Sodium line reversal temperature measurement by low resolving power spectroscopic instruments on complex flame structures gives temperatures intermediate between the highest and lowest temperature in the line of sight. An apparatus is described which was designed especially for determining the temperature structure in a complex flame by a modified sodium line reversal technique. Experimental data testing the validity of the method and a description of how it may be applied to complex flames is given.

Measurement of Temperatures in Flames of Complex Structure by Resonance Line Radiation. III. From Absolute Intensity Measurements at High Resolution

A method for measuring flame temperatures is described which requires the determination of the intensity and emissivity of the flame at wavelengths within the intensity contour of a resonance spectral line such as a D line of sodium. An experiment is cited to illustrate the method in which a Fabry‐Perot interferometer was used as the spectroscopic dispersion instrument. The emissivities were determined by comparing the brightnesses of the mirrored and unmirrored flame. The theory, procedure, and an example of using the method to find the temperature of a submerged zone of a flame are given.