US2744629A

US2744629A - Method and apparatus for processing chemicals

Info

Publication number: US2744629A
Application number: US291227A
Authority: US
Inventors: Benjamin H Vine
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1952-06-02
Filing date: 1952-06-02
Publication date: 1956-05-08
Anticipated expiration: 1973-05-08

Description

May 8, 1956l B. H. VINE METHOD AND APPARATUS FOR PROCESSING CHEMICALS Filed June 2, 1952 INVENTOR. BENJHMINH. VlNE:

United States Patent O METHOD AND APPARATUS FOR PROCESSING CHEMICALS Benjamin H. Vine, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application June Z, 1952, SerialNo. 291,227

9 claims. (cl. 21041) This invention relates to a method and apparatus for purifying and processing chemicals and particularly to such a method and apparatus for use in the treatment of photoelectric materials.

In the electronic arts, many devices such as camera pickup tubes, phototubes and the like utilize targets or photocathodes or other elements having lms or layers of photoelectric material. Suchv photoelectric Vfilms or photolayers may be deposited on a supportr member by an evaporation process.

Some typical photoelectric materials which may be evaporated and utilized in such devices include antimony, caesium, antimony trisulide, selenium and the like. Ordinarily inthe preparation of a photoelectric chemical for evaporation, the chemical materialy is ground into a ne powder by mechanical means and mixed with a suitable binder, for example nitrocellulose.k `Aquantity of the chemical thus prepared is deposited in a boat or container which forms part of an evaporator' assembly from which the chemical is evaporated onto the support member.

Such procedure has certain disadvantages. For example, when the photoelectric material is thus mixed with the binder, the mixture is unavoidably contaminated by agents which 'are of the same order of volatility as the photoelectric material. In addition when aquantity of the chemical is'deposited in a container, contaminants are unavoidably included. When such a mixture is heated, in order to evaporate the photoelectric chemical, such contaminants are also evaporated or released by decomposition and may condense on the target area along with the photoelectric material. Such contaminants may also increase :the'gas'pressure in the tube and thus adversely affect the structure of the deposited layer.

Since most photoelectric films are subject to deleterious changesif heated, it is not possible, thereafter, to adequately degas the film carrying support member and thereby remove the agents which had condensed or been absorbed thereon. Such contamination adversely aiects the operation'of the photoelectric ilm and in. the case of photoconductive lms used in pickup tubes for example, the lag of the film is increased.

By lag is meant the rate of response of the photocon ductorto changes in light, i. e. the ability of the photo layer to erase a signal in a given period of time without showing ashadow or trail of light. The problems arising from an unfavorable lag become acute when a lightcolored moving object is televised against a'dark background.

In addition, when the powdered photoelectric materialr is heated and evaporated, unavoidably, some of the particles of the' powder and other minute solid materials are carried toward the-target assembly and adhere to the condensed photoelectric ilm. This prevents proper operation of the tube sinceV the trapped particles appear in the transmitted picture. 'AIn addition, such particles may fall out of the evaporator during handling and be scatice tered throughout the tube envelope thereby contaminating electrode surfaces and the like.

The principles of the invention may also be applied to the preparation of other materials for evaporation or for other purposes where a comparatively pure and homogeneous mass of material is desirable. For example silver, silver bismuth alloy and the like are often formed as beads on a heater wire from which the beads are evaporated. Such a procedure may be carried out by this invention.

Accordingly, an important object of this invention is to provide an improved method and apparatus for preparing chemicals to be evaporated onto a target assembly.

A further object is to provide an improved method and apparatus for preparing chemicals which are free of undesirable gases and contaminant including particles of chemical material.

Another object is to provide an improved method and apparatus for charging receptacles with chemicals to be used in making a photoelectric lm, said chemicals being free of undesirable contaminants including particles of chemical material.

Another object is to provide an improved method and apparatus for filling a container or capsule to be used in evaporating apparatus for forming a pure and homogeneous ilm of photoelectric material.

In general the purposes and objects of this invention are accomplished by the provision of apparatus for heating and thoroughly melting the material to be evaporated. At the same time, a stream of gas is bubbled through the molten material and undesirable volatile contaminants are thereby carried away. The apparatus is provided with means for controlling the flow of the molten chemical processed. i

The invention is described in detail with reference to the drawings wherein:

Fig. 1 isa schematic diagram in elevation of the apparatus `of the invention;

Fig. 2 is an elevation view partly in section of a boat orcapsule for carrying a quantity of chemical prepared in accordance with the inventionl and a support device for the boat; and,

Fig. 3 is a sectional view along the line 3-3 in Fig. 2.

According to the invention, apparatus is provided for melting and purifying a chemical material to be evaporated and for charging a receptacle with a quantity of the puried chemical. The apparatus includes a vertically disposed heating device 10 which is provided for heating and melting the photo electric material or other chemical to be evaporated. The heating device comprises a tubular chamber 12, which may be made of glass or any other suitable material, and which is surrounded by a wire heating coil 14. The heating coil is connected to the usual current control means and either an alternating or direct current source of energy. The coil is positioned approximately in the middle portion of the tubular chamber 12 and is thus adapted to provide localized heating within the chamber generally in the center thereof. By this arrangement cool zones 16 are provided in the chamber above and below the area surrounded by the coil 14. The chamber 12 has an opening at each end and a side arm 18 projecting laterally near the upper end thereof. A tubular insulating member 19 made of glass or the like is positioned around the heating coil 14 to limit heat loss due to radiation.

A generally tubular container or pouring tube 20 is provided for containing the material to be processed' and prepared for evaporation. The pouring tube is made of glass or some similar material which will not react with the chemical being processed. The pouring tube comprises a tubular portion 22 of substantially constant diameter having an opening 24 at one end thereof. At the other end of the tubular portion 22 the pouring tube is provided with an expanded portion 26 in which the chemical 28 is placed after insertion through the opening 24. The expanded portion 26 is narrowed gradually into a constricted portion which has a fine opening 30 defining the other end of the pouring tube. The fine opening constitutes a pouring spout for the processed chemical.

When the apparatus is assembled, the pouring tube 20 is inserted into the tubular chamber 12 in air-tight engagement with the upper end thereof. The air-tight attachment is effected by means of a rubber stopper 32 or some similar means in which the pouring tube is inserted. The tube is thus inserted with the expanded portion 26 disposed within the heating coil 14 and with the opening 24 extended out of the tubular chamber. The lower end of the tubular chamber 12 remains open.

The side arm 18 is provided with a valve 34 for opening and closing the passageway through the arm and for throttling the ow of gas therethrough. The arm 18 is connected through a suitable coupling means 36 to one end of a pipe member V40. The pipe or tube 4t) has a lateral extension 44 which is provided with a pressure regulating control valve 46. The extension 4'4 is connected to a conventional source 47 of a gas which is used to provide the desired atmosphere in the tubular chamber and which is bubbled through the chemical as it is being processed. The gas is bubbled through the chemical in order to remove volatile impurities. The gas employed must be one which will not react with the chemical or any of the apparatus and will not dissolve in the molten chemical. The nas may be an inert gas such as argon or the like.

The pipe member 40 is also connected through a coupling 48 to a tube or pipe 50 having a valve 52 for controlling the passageway through the pipe and throttling the flow of gas therethrough. This valve may be similar to the valve 34 provided in the side arm 18. The pipe 50 is connected in turn by means of a lateral extension line 54 and a suitable coupling 55 to the large opening 24 of the pouring tube 20 which extends out of the tubular chamber 12. The tube 50 is also connected by means of an extension pipe or line 56 to a conventional exhaust device 57. The line 56 is provided with a quick acting valve 58 for opening or closing the passageway therethrough and a valve 60 for throttling theow-of gas through the line 56 when the valve 58 is open. The

valves

52, 58 and 60 are arranged so that, after the apparatus and valves are preliminarily adjusted, a single valve may be employed to carry out all necessary operations This is described in detail below.

A receptacle or boat or other suitable means is provided for receiving a quantity of the treated chemical. One such receptacle or capsule 62 is shown in Figures 2, 3 and 4 and comprises a generally tubular member made of glass or some material which will not react with the chemical or gas. The boat is provided with a slotted opening 64 which leads to an inner channel 66 in which the chemical charge is retained preparatory to and during the evaporation procedure. The glass boat, when charged with the material to be evaporated, may be carried by an evaporator or any other suitable apparatus for use in evaporating the chemical. One suitable evaporator is shown and described in the copending B. H. Vine application, Serial Number 279,883 and tiled April 1, 1952 now Patent 2,701,597. It is to be understood that other suitable containers for the purified chemical and other suitable cvaporators may be employed for receiving a chemical charge and for use in an evaporation process.

For supporting the glass boat 62 during the charging cr loading operation there is provided a support member 68 comprising a generally rod-like base portion 70 having a pair of spring clip members 72 mounted in spaced relation thereon. The spring clips 72 are adapted to grasp and support the glass boat 62. Also mounted on the cylindrical support and extending oppositely to the aforementioned spring clips 72 is an assembly of a plurality of other spring clip members 74 which are arranged in a generally circular grouping and are adapted to receive and grasp a support rod 76 by means of which thc glass boat may be inserted into the tubular chamber 12. The support rod is made of an insulating material such as glass or the like.

In operation of the apparatus of the invention, a quantity of chemical to be processed is inserted into the pouring tube 20 through the large opening 24 thereof and positioned in the expanded portion 26. Next the pouring tube is inserted into airtight engagement with the tubular chamber as previously described and the pipe 54 is connected to the large opening 24 of the pouring tube through the coupling 55. The pouring tube is positioned with the expanded portion carrying the chemical material within the effective heating area of the coil 14.

At the beginning of the operation all of the valves are closed. First, valves 46 and 34 are opened and retained open in order to maintain a continual ow of gas through the tubular chamber 12 and out through the bottom opening thereof. By this means a constant gas atmosphere is retained in the chamber and air is prevented from entering and contaminating the chemical. Next, valves 52 and 60 are adjusted so that the operation of the gas source 47 and exhaust device 57 are combined to provide a slight vacuum above the chemical in the pouring tube 20. This vacuum is sutlicient to draw gas from the tubular chamber 12 through the chemical material within the pouring tube. This reduced pressure above the chemical is also sufficient to retain the chemical material within the tube as the chemical is heated and melted. The heating coil 14 is then energized sufficiently to heat and melt the chemical charge. For antimony trisulfide this temperature is on the order of 500 C. and for selenium it is on the order of 225 C. This condition of the apparatus is retained for a time on the order of two minutes while the gas is allowed to bubble through the molten chemical whereby volatile impurities therein are picked up and removed. The combination of heating and the bubbling gas also serve to remove moisture from the chemical.

The glass boat 62 carried by the support rod 76 is then inserted through the open lower end of the tubular charnber 12. The boat is preheated for a time on the order of l5 seconds before it is moved up into contact with the pouring spout. If the glass boat were not so preheated and was at a sufliciently low temperature, the chemical in the pouring spout 30 might be solidified and operation of the apparatus might thus be temporarily halted. After the boat has been thus heated, it is moved up to the pouring tube until the pouring spout lies within the channel 66 within the boat.

Valve 58 is then closed and the exhaust apparatus 57 is thereby effectively disconnected from the system and gas ows from the gas source 47 through the open valve 52 and into the tube 54. The gas pressure thus increases above the molten chemical so that a quantity of the chemical is forced out of the pouring spout 30 and into the channel 66 of the glass boat or capsule 62. After the desired quantity of chemical has been deposited in the boat the valve 58 is opened and the exhaust apparatus is thereby again connected to the system. By this means the balance previously achieved between the valves 52 and 60 is restored and the pressure above the molten chemical reduced sufficiently to prevent further flow from the pouring tube.

After it has been thus charged with chemical, the glass boat 62 is removed from the vicinity of the pouring tube 20 to the lower cool zone in the oven where it is allowed to cool for approximately 45 seconds before it is exposed to the air. This is done in order to prevent oxidation of the hotchemical by the air. Finally the supporting rod and boat are removed from serted in a suitable evaporator from which evaporation may be effected asdesired;

What is claimed is: 1. The method of preparing uncontaminated a restricted orifice, said method comprising surrounding said containerwith an atmosphere of inert gas, reducing molten material to retain the V,material within said con'- tainer, and thereafter increasing the pressure above the surface of said material to force said material through said orice and into a heated capsule in the presence ofl said inert atmosphere.

2. The method of preparing uncontaminated chemical material in apparatus having a container'provided with a restricted discharge orifice in the bottom thereof, said method comprising introducing solid material to ber purified into said container, establishing an atmosphere of an inert gas around said container and discharge orifice, reducing the pressure above said material to allow a flow of said gas through said discharge orifice and into said container, heating said material to a molten state to allow passage of said gas through said ymaterial for removing volatile impurities therefrom, maintaining said reduced pressure above said molten material to prevent premature discharge -of said material, increasing the pressure' above the surface of said material to discharge said material through said orifice and into a heated vessel in the presence of said gas atmosphere, and thereafter cooling the material in said vessel before exposing the same to air,

3. Apparatus for removing contaminants from chemicals to be evaporated from a receptacle and for charging the receptacle with the `resultant purified chemicals, said apparatus including a hollow member; a container in said hollow member, said container having an aperture therein communicating with the interior of said hollow member, and a portion adjacent said aperture for receiving and holding the chemical to be treated; a source of inert gas connected to said hollow member for supplying gas thereto; means connected to said container to reduce the pressure in said container above the surface of said chemical and to permit the flow of gas therethrough; and means adjacent to said container for heating the chemical there- 4. Apparatus for removing contaminants from chemicals to be evaporated from a receptacle and for charging a receptacle with the resultant puned chemicals, said ap'- paratus comprising a hollow member; a container posi-` tioned within said hollow member'and extending there through, said container having at least a pair of openings therein and a portion for receiving a quantity of chemical to be treated; means adjacent to said hollow member for heating said chemical; a source of inert gas, means coupling said gas source to said hollow member whereby a gas atmosphere -may be established in said member; exhaust means connected to said container and to said gas the chamber, and the boat and its charge of purified chemical are ready vto be in *chemicalV material in apparatus having a container provided with said container having the chemical therein; exhaust means;

a ,sourceof inert gas; means coupling said source of inert gaswith said hollow member for directing inert gas into `saiclhollow member; a conduit connecting said exhaust means with said gas source and coupled to said container member; an adjustable valve in the portion of said conduit'.V intermediate said gas source and said container; a secondr adjustable'valve in the portion of -said conduit intermediate said exhaust means and said container; and a control valve in said last mentioned conduit portion.

6.' Apparatus for removing contaminants from chemicals to be evaporated from a receptacle and for charging a receptacle with the resultant purified chemicals, said ap- A paratus comprising a hollow member verticallydisposed and having an opening at each end; a hollow container having a large opening at one end, a restricted opening at the other end and a portion for receiving the chemical to be treated, -said container being disposed in air-tight engagement with said hollow member with said restricted 2'0" v means forheating said portion of saiducontainer having source; and valve means intermediate said gas source and said exhaust means for regulating the gas pressure above the chemical insaid container.

5. Apparatus for removing contaminants from chemicals to be evaporated from a receptacle and for charging a receptacle with the resultant purified chemicals, said apparatus including a hollow member having an opening at one end; a container member positioned within'said hollow member, said container member including a portion for receiving the chemical to be treated and having a restricted aperture at a lower portion thereof communicating with the interior of said hollow member; means adjacent to said hollow member for heating said portion of the chemical therein; a source of inert gas; means coupling said gas source to said hollow member and for controlling the flow of gas into said hollow member; an exhaust device; a conduit coupled to said hollow container and connected between said exhaust device and said gas source, and having valve means for controlling the gas pressure in said container and for controlling the ow of gas therethrough; and independent control valve means in the connection between said exhaust device and said container for regulating the ow of gas to said container.

7. Apparatus for removing contaminants from chemicals to be evaporated from a receptacle and for charging a receptacle with the resultant purified chemicals, said apparatus comprising a hollow member vertically disposed and having an opening at each end; a hollow container having a large opening at one end, a restricted opening at the other end and an intermediateportion for receiving the chemical to be treated, said container being disposed in air-tight engagement with said hollow member with said restricted opening inside the member and said large opening extending out of said member; means associated with said hollow member for heating said portion of said container having the chemical therein; an insulating member surrounding said heating means and said hollow member; a source of inert gas; means coupling said gas source to said hollow member and for controlling the flow of gas into said hollow member; an exhaust device; a conduit extending from said gas source tosaid exhaust device and connected to ysaid hollow container for reducing the gas pressure above said chemical and for promoting the flow of gas through said chemical; ka first valve means in said conduit associated with said gas source and said exhaust device for establishing an equilibrium relationship between said gas source and said exhaust device; and a second valve means in said conduit associated with said first valve means for upsetting said equilibrium whereby the gas pressure above said chemical is increased and a quantity of chemical is forced out of the restricted opening of said yhollow container.

8. Apparatus for removing contaminants from chemical materials to be evaporated from a receptacle and for charging a receptacle with the resultant purified chemicals, saidapparatus comprising a container for said material, a tubular member, means for heating the interiorof said tubular member, a source of inert gas, means coupling said gals source to said tubular member and for controlling the flow of gas into said tubular member, an exhaust device, said container comprising a tube-like portion and a bulb-like portion, said bulb-like portion extending into the space defined by said tubular member, means for closing the end of said tubular member through which said bulk-like portion is extended, said bulb-like portion -having a restricted opening adjacent to one end thereof, and `means for alternately coupling said exhaust device andsaid gas source to said tubelike portion, saidmeans including a conduit connected between said exhaust device and said gas source and coupled to said tube-like portion, and a plurality of valves in said conduit for controlling the flow of gas therethrough whereby while said exhaust device is coupled to said tube-like portion gas from said tubular member will be drawn through said restricted opening and while said gas source is coupled to said tube-like portion any of said material which is melted is discharged through said restricted opening.

9. Apparatus for removing contaminants from chemicals to be evaporated from a receptacle and for charging a receptacle with the resultant purified chemicals, said apparatus comprising a tubular chamber having an opening at each end, a tubular container having an upper portion for receiving the chemical to be treated and a restricted opening at a lower portion thereof, said container being disposed within said chamber with said restricted opening communicating with the interior of said chamber, means adjacent to said chamber for heating said upper portion of said container, a source of References Cited inthe tile of this patent UNITED STATES PATENTS 1,921,060 Williams Aug. 8, 1933 2,054,923 Betterton Sept, 22, 1936 2,274,643 Adams Mar. 3, 1942 2,533,149 Stand Dec. 5, 1950 2,583,438 Nieman et al Ian. 22, 1952 FOREIGN PATENTS 't 338,409 Great Britain Nov. 20, 1930 OTHER REFERENCES Gas Free Metals, The Metals Research Staff, National Research Corp., Cambridge 42, Mass.

Claims

1. THE METHOD OF PREPARING UNCONTAMINATED CHEMICAL MATERIAL IN APPARATUS HAVING A CONTAINER PROVIDED WITH A RESTRICTED ORIFICE, SAID METHOD COMPRISING SURROUNDING SAID CONTAINER WITH AN ATMOSPHERE OF INERT GAS, REDUCING THE PRESSURE ABOVE SAID MINERAL TO ALLOW A FLOW OF SAID GAS THROUGH SAID ORIFICE AND INTO SAID CONTAINER, HEATING SAID MATERIAL TO A MOLTEN STATE TO ALLOW PASSAGE OF SAID GAS THROUGH SAID MATERIAL FOR REMOVING VOLATILE IMPURITIES THEREFROM, MAINTAINING SAID REDUCED PRESSURE ABOVE SAID MOLTEN MATERIAL TO RETAIN THE MATERIAL WITHIN SAID CONTAINER, AND THEREAFTER INCREASING THE PRESSURE ABOVE THE SURFACE OF SAID MATERIAL TO FORCE SAID MATERIAL THROUGH SAID ORIFICE AND INTO A HEATED CAPSULE IN THE PRESENCE OF SAID INERT ATMOSPHERE.