CAPTIONS FOR ILLUSTRATIONS
October 26, 1959
[no photos, no attachments, text only]
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A group of specimens typical of those studied in the dielectrics laboratory of the National Bureau of Standards. Small disk: electrode-plated poly(methyl methacrylate); large disk: polystyrene; opaque rods (first and third from left): polychlorotrifluoroethyleme; clear rods: polystyrene.
Graph of the dielectric loss index vs. frequency for polyclorotrifluorothyleme at room temperature and selected temperatures from -50 degrees to 200 degrees C. The degree of crystallinity in these specimens measured at the National Bureau of Standards was 80 percent. For each temperature value, there is a frequency at which the loss factor reaches a peak. As this frequency increases with temperature, the height of the peak also increases.
Dielectric specimen holder developed by the National Bureau of Standards for use at temperatures up to 500 degrees C. The controls for the electrode spacing and the measurement of the position of the movable electrode are located outside the heated space to eliminate the effects of such temperatures. This holder is constructed of stainless steel
A. J. Curtis of the National Bureau of Standards is using a special holder designed for use from the liquid-nitrogen range up to 300 degrees C. To achieve the very low temperatures, the holder (center) is placed in a Dewar containing liquid nitrogen. The top of the Dewar, which can be conveniently raised up to the holder, can be seen at table level. At left is a modified commercial resonant circuit and directly in front of the scientist a capacitance bridge.
Electrode system employed at the National Bureau of Standards in making standard dielectric measurements on solids up to approximately 40 Mc by bridge and resonance methods. The middle electrode system is equipped for regulating the temperature of the material under test.
J. J. Weeks is shown making a micrometer reading to determine the dielectric properties of a material undergoing a change of state. A special fusion cell designed by the National Bureau of Standards is used for this work either with the bridge shown at right or the higher frequency resonant circuit located beneath the fusion cell housing.
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E. C. Bamberger of the National Bureau of Standards, Boulder Laboratories, is shown making dielectric measurements using the 100 to 500 Mc re-entrant variable-length cavity resonator.
Wavemeter with a precision of about 3 parts in a million developed by the National Bureau of Standards for accurate dielectric measurements.
Disassembled fusion cell. The outermost housing for this special holder designed by the National Bureau of Standards is shown in the upper left of the photograph. The principal unit, lying horizontal in the center of the picture, consists of the cell itself (lower end) and the controls. At the lower right is a unit which houses the cell.
Barium titanate crystals used at the National Bureau of Standards in the study of conductivity and instability in ferroelectric materials. The crystals are observed with polarized light to show domain formations.
By lowering a key, R. W. Dickson inserts one of 19 dielectric samples into a bridge circuit. The specimens are in a constant-temperature holder designed by the National Bureau of Standards to provide the controlled conditions needed in measuring ceramic materials.
Growing single crystals of inorganic non-metallic materials at the National Bureau of Standards. Powdered material drops from above through the flame, melts, and forms a crystal on the vertical rod at the base of the furnace. After closing the furnace, operator Katherine King will continue to check on the process, using an optical filter to look through a slit in the furnace wall.
Studying the crystallization of dielectrics at the National Bureau of Standards. As the specific volume of a specimen is affected by crystallinity, studies involve weighing the sample in silicone oil--a medium of known density. J. J. Weeks is about to lower the sample, suspended by a wire, into the oil.
In studies of poly(chlorotrifluorethylene) at the National Bureau of Standards, this graph showing the effect of crystallinity at 23 degrees C on loss index curves was obtained. As the degree of crystallinity (indicated on curves) increases, the frequency at which the loss index reaches a peak increases and the height of this peak decreases.
As part of the dielectric studies that the National Bureau of Standards is conducting on nylon, a viscosity determination is employed to check on polymer degradation which would greatly affect loss index and other dielectric measurements. R. H. Meyersburg is shown adding a solution containing the polymer to a viscometer in a constant temperature bath.
S. J. Kryder of the National Bureau of Standards tunes a resonant cavity containing a gas sample in preparation for determining dielectric properties by a microwave absorption technique.
Measuring the dimensions of a dielectric sample under consideration as a reference standard. To insure the greatest accuracy possible, the National Bureau of Standards employs special techniques such as the traveling microscope which W. P. Harris is using here.
Humidity cabinet employed at the National Bureau of Standards to determine the effect of atmospheric conditions on dielectrics under consideration as reference standards. A. H. Scott is introducing a sample into the cabinet, which is equipped with a measurement cell. A rubber glove, like the one on the left side of the box, will seal the opening. Once the desired humidity is established, all further manipulation is done by an operator working through these gloves.
An 18-in. diameter resonator used by the National Bureau of Standards to investigate hole errors in dielectric measurements.
NOTE TO EDITOR:
Glossy prints of listed illustrations are available to editors upon request. Address the National Bureau of Standards, Office of Technical Information, Washington 25, D. C.
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Original Caption by Science Service