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Holland, L. R.

Publications and source records attributed to Holland, L. R..

Two-Step Vapor/Liquid/Solid Purification

Vertical distillation system combines in single operation advantages of multiple zone refining with those of distillation. Developed specifically to load Bridgman-Stockbarger (vertical-solidification) growth ampoules with ultrapure tellurium and cadmium, system, with suitable modifications, serves as material refiner. In first phase of purification process, ampoule heated to drive off absorbed volatiles. Second phase, evaporator heated to drive off volatiles in charge. Third phase, slowly descending heater causes distillation from evaporator to growing crystal in ampoule.

Holland, L. R.

High-temperature, high-pressure optical cell

The invention is an optical cell for containment of chemicals under conditions of high temperature and high pressure. The cell is formed of a vitreous silica tube, two optical windows comprising a vitreous silica rod inserted into the ends of a tube, and fused into position in the tube ends. Windows are spaced apart to form a cavity enclosed by the tube and the windows. A hole is drilled radially through the tube and into the cavity. Another vitreous silica tube is fused to the silica tube around the hole to form the stem, which is perpendicular to the long axis of the tube. The open end of the stem is used to load chemicals into the cavity. Then the stem may be sealed, and if desired, it may be shortened in order to reduce the volume of the cavity, which extends into the stem.

Harris, R. P.

Accommodation requirements for microgravity science and applications research on space station

Scientific research conducted in the microgravity environment of space represents a unique opportunity to explore and exploit the benefits of materials processing in the virtual abscence of gravity induced forces. NASA has initiated the preliminary design of a permanently manned space station that will support technological advances in process science and stimulate the development of new and improved materials having applications across the commercial spectrum. A study is performed to define from the researchers' perspective, the requirements for laboratory equipment to accommodate microgravity experiments on the space station. The accommodation requirements focus on the microgravity science disciplines including combustion science, electronic materials, metals and alloys, fluids and transport phenomena, glasses and ceramics, and polymer science. User requirements have been identified in eleven research classes, each of which contain an envelope of functional requirements for related experiments having similar characteristics, objectives, and equipment needs. Based on these functional requirements seventeen items of experiment apparatus and twenty items of core supporting equipment have been defined which represent currently identified equipment requirements for a pressurized laboratory module at the initial operating capability of the NASA space station.

Uhran, M. L.

High-Temperature, High-Pressure Optical Cells

Optical cell constructed for measurement of thermal diffusivity of HgCdTe semiconductor by laser pulses. Container allows radiation from laser to enter one side of alloy sample, while allowing lower-energy infrared radiation to leave opposite side of sample so temperature rise read by sensor. Composed entirely of fused silica, cell includes two optical windows joined by tube. Cell withstands 1,000 degrees C cell-operating temperature and contains molten alloy at its 100-atmosphere vapor pressure. Finally, allows alloy to solidify without bursting even though alloy expands on cooling.

Harris, R. P.

Growth of Solid Solution Crystals

The major objective of this program is to determine the conditions under which single crystals of solid solutions can be grown from the melt in a Bridgman configuration with a high degree of chemical homogeneity. The central aim is to assess the role of gravity in the growth process and to explore the possible advantages for growth in the absence of gravity. The alloy system being investigated is the solid solution semiconductor with x-values appropriate for infrared detector applications in Hg sub (1-x) Cd sub x Te the 8 to 14 micro m wavelength region. Both melt and Te-solvent growth are being considered. The study consists of an extensive ground-based experimental and theoretical research effort followed by flight experimentation where appropriate. Experimental facilities have been established for the purification, casting, and crystal growth of the alloy system. Facilities have been also established for the metallurgical, compositional, electric and optical characterization of the alloys. Crystals are being grown by the Bridgman-Stockbarger method and are analyzed by various experimental techniques to evaluate the effects of growth conditions on the longitudinal and radial compositional variations and defect densities in the crystals.

Lehoczky, S. L.

Sealed silica pressure ampoules for crystal growth

The properties of vitreous silica and the mechanics of thick walled pressure vessels are reviewed with regard to the construction of sealed silica crucibles such as are used in the growth of mercury-cadmium telluride crystals. Data from destructive rupture tests are reported, failure modes discussed, and recommendations for design given. Ordinary commercial clear vitreous silica from flame fused quartz can withstand a surface stress of 20 MPa or more in this application.

Holland, L. R.

Combined distillation and normal freezing to purify elements of groups II and VI

A practical system and its application to the purification of Te and Cd is described. Single crystals are grown directly in vitreous silica ampoules subsequently used for sealed Bridgman growth of (Hg-Cd)Te. The system also prepares the ampoules by heating in high vacuum. Purification of the elements is by the combined effect of distillation and normal freezing. Transport and segregation are discussed.

Holland, L. R.

Apparatus and method for heating a material in a transparent ampoule

An improved process for heating a material within a fused silica ampoule by radiation through the wall of the ampoule, while simultaneously passing a cooling gas around the ampoule is described. The radiation passes through a screen of fused silica so as to remove those components capable of directly heating the silica, therby increasing the temperature of the material within the ampoule above the strain point of the ampoule, while maintaining the exterior of the ampoule cool enough to prevent rupturing the amp.

Holland, L. R.

Holder for Fragile Parts

Fixture with many springfingers holds irregularly-shaped parts. Gripping fixture has hundreds of springfingers, each applies minute force. Total force approximates hydrostatic pressure, resulting in well-distributed load that maintains firm grip without high stress concentrations. Applied to industrial robot manipulators, fixutre enhances ability to grasp delicate parts.

Holland, L. R.

Measured thermal diffusivity of Hg(1-x)Cd(x)Te solids and melts

The thermal diffusivity of Hg(1-x)Cd(x)Te melts is found to rise rapidly with temperature to values characteristic of metals. Solid and melt diffusivities for values of x from 0 to 0.3 and over a temperature range from 150 to 900 C have been determined by the laser flash method of Parker, Taylor, and Cowan. The diffusivity decreases from a maximum at x = 0 in both the solid and the liquid, with the values observed at x = 0.3 being about 40 percent of those for x = 0. The solid diffusivity for x = 0 is 1.7 sq mm/s at 150 C, decreasing to 0.7 sq mm/s at the melting point. The x = 0 liquid diffusivity increases from 0.7 sq mm/s at the melting point to 3.5 sq mm/s at 900 C.

Holland, L. R.

Density of liquid Hg(1-x)Cd(x)Te

Negative thermal expansion has been established in liquid Hg(1-x)Cd(x)Te for x less than 0.2 employing a pycnometric method. Pure HgTe increases in density from its melting point at 670 C to a maximum value at 750 C, where normal thermal expansion progressively resumes. The dependence of density on temperature for liquid Hg(1-x)Cd(x)Te arises almost exclusively from the HgTe portion of the melt, while CdTe acts as a diluent. The temperature corresponding to the maximum density changes slightly with composition, increasing by about 5 C for x = 0.1.

Chandra, D.

High-temperature, high-pressure optical cells

For measuring the thermal diffusivity of HgCdTe melts by the laser-pulse method, an infrared transparent cell with flat windows of sufficient strength to withstand the high-vapor pressure of mercury had to be developed. Since mercury telluride expands on freezing, certain difficulties arose in returning the cell to room temperature without cracking it. T08 commercial fused silica is used in the construction of the cell, and the cells are transparent for wavelengths from about 3.5 microns in the infrared to 260 nm in the ultraviolet. The construction procedure for the required cells has been laborious. However, the obtained cell has routinely withstood internal pressures in excess of 60 atm at 900 C. Attention is given to the design of the windows, aspects of cell construction, and questions of loading.

Holland, L. R.

Radiant Heating of Ampoule contents

Ampoule charge heating system exploits spectral properties of blackbody radiation and ampoule material transparency to heat charge to high temperature. Cooling gas prevents softening of outside wall of ampoule. Use of proposed method may be limited by tendency of silica (or any other viteous material) to devitrify on prolonged exposure to temperatures near softening point.

Holland, L. R.

Space processing of electronic materials

The bulk growth of solid solution alloys of mercury telluride and cadmium telluride is discussed. These alloys are usually described by the formula Hg1-xCdxTe, and are useful for the construction of infrared detectors. The electronic energy band gap can be controlled between zero and 1.6 electron volts by adjusting the composition x. The most useful materials are at x approximately 20%, suitable for detection wavelengths of about 10 micrometers. The problems of growing large crystals are rooted in the wide phase diagram of the HgTe-CdTe pseudobinary system which leads to exaggerate segregation in freezing, constitutional supercooling, and other difficulties, and in the high vapor pressure of mercury at the growth temperatures, which leads to loss of stoichiometry and to the necessity of working in strong, pressure resistant sealed containers.

Holland, L. R.

Space processing of electronic materials

The relative values of thermal conductivity of solid and liquid HgCdTe are critically important in the design configuration of the furnaces used for Bridgman crystal growth. The thermal diffusivity of the material is closely linked to the conductivity by the defining relation D = k/rho c, where D is the diffusivity, K is the thermal conductivity, rho is the density, and c is the specific heat. The use of transient and periodic heating approaches to measure the diffusivity are explored. A system for securing and extracting heat from silica or glass tubes under high C vacuum conditions is described.

Workman, G. L.

Zone-refining encapsulated semiconductors

Reflector directs intense, sharply focused heat precisely where it is needed for zone-refining semiconductor materials. Reflector is especially suited for compound semiconductors which must be sealed inside capsule to prevent vaporizing during zone refining. Device is flattened toroid with elliptical-cross-section, much like horizontal partly-inflated inner tube.

Davidson, M. C.

Narrow zone heating by a new radiation focusing technique - Toroidal ellipsoid furnace

The paper describes the design of a toroidal ellipsoid furnace for narrow zone heating of materials in sealed transparent ampoules. The heater is a toroid flattened to an elliptical cross section like a partially inflated inner tube resting on a horizontal surface. The foci of the ellipsoid are two concentric rings. The outer focus is occupied by a heater wire, and the inner focus is arranged to fall on the surface of the cylindrical ingot within its transparent capsule. One advantage of the new furnace is that the wire heater closely approximates the ideal shape, lying along an extended line focus, as opposed to the elusive point source of the Costello furnace. Also, the ingot is heated uniformly around its circumference.

Davidson, M. C.