US1456532A - Selenium crystals and method of preparing the same - Google Patents

Description

?atented Mayne, teas.

teaser meta care.

FAY C(LUFF) BROWN, 01E IOWA CITY, IOWA.

SELENIUM CRYSTALS AND METHOD OF PREPARING THE SAME.

Ho Drawing.

To all whom it may concern:

Be it known that I, FAY C. BnowN, a citizen of the United States, residing at Iowa City, in the county of Johnson and State of Iowa, have invented new and useful Selenium Crystals and Methods of Preparing the Same, of whichthe following is a speclfication.

This invention has reference to selenium crystals and its object is to produce light sensitive selenium crystals of greatly increased sensitiveness.

It has long been known that selenium in some of its forms is less resistant to the passage of an electric current when under the influence of light than when in the dark, that is, protected from the action of light. Ad-

vantage has been taken of this property of selenium for various purposes and the devicesfor utilizing the selenium in such manner have been customarily known as selenium cells, but such term is somewhat of a misnomer, wherefore the term selenium bridge isused throughout this specification, becausethe selenium is utilized to bridge a gap in the electric circuit, whereby the variable resistance'represented by the selenium ma be utilized, 7 1 l r ior to the present invention crystallized selenium has been produced, but the crystals have been of comparatively small size. For

this reason there can be no control of the arrangement ,of the crystals which because of their-extremely small size are'present in great multitudes in the ordinary selenium bridge. Such crystals have their axes pointing in all directions.

By the production of crystals of selenium of large size, that is, readily visible individually to the unaided eye and easy to handle,

it is quite possible. to produce a selenium bridge of suitable capacity from a single crystal, and the capacity may be increased by the em loyment of twoor three or more crystals, or the crystals are of size as to be readily oriented. It has been found that-a single hexagonal crystal shows a greater sensibility to light when the illuminationim linges on. the end of the crystal and-trave s in the direction of the principal axisof the crystal.

'Iaoreover, it has been found that such I crystals whenjsnbiectedto pressu-re'exhibit a many fold increase sensitiveness' to the action ot 'lighnsolthat a selemum crystal so arrangedthat the .lightstrikes it in the dismdi large Application filed March 7, 1916. Serial No. 82,782.

rection of its principal axis and under compression .to a considerable degree, 18 increased in light sensitiveness, say, a thou-' sand times over the sensitiveness of selenium bridges as heretofore constructed.

' The selenium bridge of the present invention, therefore may comprise one or more crystals of selenium with means for subjecting such crystal or crystals to pressure and at the same time having the crystals so presented that the light rays strike them in the direction of their principal axes.

' The invention will be best understood from a consideration of the following detailed description.

In using selenium crystals, made after the manner herein described, for selenium bridges whose resistance varies in accordance with the amount of light impinging thereon, certain precautions should be observed, if the best results are to be secured. The selenium crystal is placed in the circuit between the electrodes of any suitable material, for example, those hereinafter mentloned. Increased sensitivity results from applying pressure to the crystal and in the case of hexagonal crystals it is advantageous to apply the light ray in the direction of the principal axis of the crystal. The crystal may be shielded from extraneous light in any suitable manner and a window or opening may be provided through which the varying light ray may impinge upon the crystal. For a more detailed description of the possible uses to which such crystals may be put and of the precautions to be observed in using them reference may be made to the specification of my United States Patent 1,219,432, patented March Q0, 1917.

Selenium exists in the amorphous or nonconducting form, in the red crystalline form, also non-conducting, and in a crystalline metallic state with the crystals of monoclinic or hexagonal shape very sensitive to light and with properties peculiar to the various axes of the crystals and also due to the manses, wherefore the sealed receptacle con tains nothing but selenium which becomes vaporized by the heat employed and from which vapor the crystals are deposited. The crystals are of the monoclinic form when the temperature is about 171 C. Hexagonal crystals of a maximum sensibility to light are obtained when the vapor is sublimed at a temperature of about 183 A high sensitiveness hasbeen obtained when occluded gases have been driven 0H from the selenium by repeated boiling and condensing in a high vacuum. For some purposes it is advantageous to have argon, neon, helium and other gases mixed with the vapor of selenium either separately or in combination, and, again, it is advantageous to form the crystals in an atmosphere of selenium vapor only and afterward allow them to absorb any one gas'or a mixture of the gases at temperatures below the temperature of formation.

While the temperatures named have been found to produce most excellent results, it is to be understood that the invention is not in any manner limited to any precise temperatures. 1 I

One method of producing the herein described sensitive selenium crystals of high sensitivity will be described in. detail. V treous selenium which i s,to be transformed into crystals is .placed inone end of a glass tube of about mm. inside diameter and of about'30 to 60 cm. length. This tube is placed in a cylindrical electrical oven of about 30 cm. length closed at one end. A suitable current is used to heat the selenium to a suficiently high temperature to cause it to vaporize. The glass tube may'behlghly evacuated, filled with some of the various gases hereinbefore mentioned, or filled with ordinary air at atmospheric or lower pressures. In general the use of air is not recommended, but its elimination is not essential for all purposes Where theg'lass tube 1projects from the oven will be a region of igh temperature gradient. The apparatus should be set up and maintained quietly for a long period which may vary in accordance with circumstances from a minimum of one day to a maximum of one week or more. Along the part of the tube where the temper- .ature grad ent is the greatest will be found numerous crystals.

In general the largest crystals will be formed at the point of highest temperature at which the selenium will sublime. In various parts of the region in which crystallization takes place'there. will occur various forms of selenium crystals. It is not possible to determine in advance or predict with certainty the form which the crystals will take in any particular instance or the relative quantities or sizes of the various types, or the size of individual crystals. It will happen, however, that certain crystals will be relatively large, that is asses smaller crystals and the selenium which is deposited in non-crystalline form may be resublimed either with or without the addition of other selenium. The resublimation may be performed under thesame or difierent conditions as the first sublimation as may be desired.

For further and more detailed information reference may be made to an article by me on the Crystal forms of metallic selenium and some of their hysical roperties, plublished in Physical view, S., Vol.4,

0. 2,1lu ust 1914.

A sing e crystal of a substance is more likely to be pure and of the same crystalline structure throughout than is the case with a heterogeneous mass of material, wherefore such crystal has the advantage of a uniform molecular structure throu hout, that is, a uniform and regular spacing of the molecules. Such uniformity of structure contributes to the stability of the crystal and of the selenium bridge in which the crystal is included.

Large crystals are advantageous in that because of the parallel plane faces of the crystal it is possible to apply pressure on the electrodes after the crystals are formed.

The pressure on a single crystal or an assembla e of single crystals is more likely to pro'.uce a uniform stress in the crystal or crystals than is the case where pressure is applied to a mass-aggregate of sub-microsco ic crystals.

arge crystals permit ressure to be applied with so simple a evice as a screw, and also permit the control of the axis along which the crystal may be illuminated. Not only is the sensibility difi'erent, dependent upon the orientation of the axis to beilluminated, but this orientation determines which region of the spectrum will produce the maximum change of conductivity. I I Experience has shown great stability of the new crystals of selenium over selenium as hertofore used in selenium bridges. A selenium crystal as produced and employed in accordance with the present invention has been exposed to most intense light for twenty-four hours a day for thirty-five days without showing deterioration. Such a crystal mounted for a year has now the same sensibility as when first mounted.

The electrodes may be made of a material 1 iso intense selenium vapor. It is not imperative that the light afiecting the bridge shall reach the crystal or crystals in the direction of the principal ax s thereof. lFor instance,

are described in my V patent referred toabove.

What is claimed is 1. 'lhe method of reparing selenium for use in selenium hri ges, Which consists. in freein selenium from occluded see, then vaporizing the selenium by heat in a high vacuum, and causing the deposition ofcrystals from the selenium vapor so produced.

yecu n a 5. e method of ma nng selemerysp 2. The method of preparin seleni crystals for use in selenium bri ges, which consists in freeing the selenium from cccluded gases, then heating the selenium in a high vacuum to produce selenium vapor, and causing the deposition of crystals of selenium from such selenium vapor, und

finally causing the 'crymal'sso formed to ehsorh one. or more gases.

3. Themethod of making selenium crystels by sublimation comprising vaporizing the seleni in u' vucuum.

4. The method of memn seleni crystals trom selenium h 'subhmution comprising eliminating occ uded gases from the selenium and vaporizing the selenium in a sion of undesired .crystels comprisin? e tals from selenium which comprises vaporizing selenium end precipitating the vepor under conditions which prevent the occlugas in the resulting crystals."

65. The ethod of making seleni crystals from selenium comprising vaporizing the selenii end precipitating the vapor at a temperuture of approximately 180 C.

7. A seleni cr stel having occluded therein inert gas su stantially exclusively. 8. A selenium crystal heving occluded therein gus principally of the helium group.

9. The method of making selenium crystals from selenium by sublimation, comprising vuporizing the selenium in a closed vessel at suhstentially less than atmospheric pressure, and maintaining the vessel under,

uniform conditions of temperature and pressure for a long period of time to cause the deition of the selenium vapor in the to of the desired crystals.

1d. The method of preparing selenium repeatedly vaporizin and'condensing nium in an evacuate vessel.

11. The method of producing sensitive seleni crystals, comprising repeated suhlimation of selenium in a vessel from which to f the larger pert of the atmosphere has been rev otters nnovv u.

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