JP2858028B2 - Thermionic emitter and method of manufacturing the same - Google Patents

Description

The present invention relates to a thermionic emitter, and more particularly to a cation emitter for use in instruments such as, for example, an ion mobility spectrometer. .

2. Description of the Related Art An electric steam detector is described in U.S. Pat. No. 2,742,585 issued on Apr. 17, 1956.

Here a thin, hardly soluble coating made of a special metal oxide with a thickness of a few mils can be used as an insulator, or about 700
It also acts as an alkali ion emitter in the temperature range from 1200C to 1200C or higher. The hardly soluble coating includes oxides of aluminum (alumina), oxides of titanium (titania), oxides of beryllium (beryllia),
Oxides of thorium (Thria), oxides of magnesium (Magnesia), and calcium, molybdenum, iron,
Manganese, silicon, cobalt, nickel, (atomic number 57
To 71) oxides of each of the rare earth elements. In operation, at temperatures above 700 ° C., the initial ion flux from the poorly soluble coating decreases. Thereafter, the detector will detect the vapor of halogen and its compounds in a vacuum system of 1 mmHg. The entry of halogen and its compounds vapors into the poorly soluble coating surface causes an increase in cation flow that collects on the negatively charged collector. This electric vapor detector detects halogen and its compounds because the evaporation of alkali ions from the coating surface increases.

US Patent No. 2.806.991 issued September 17, 1959
Describes an electric detector for detecting a certain substance or impurity in various gases. The detector consists of a helically wound double wound heater wound on a cylindrical ceramic core impregnated with a solution of sodium hydroxide.
The electrode is inserted and fitted snugly in a hole in the ceramic core acting as a cold cathode.

The ceramic core must be impregnated with a highly conductive salt such as, for example, NaOH, NaF, LiCl. The steam detector is particularly suitable for detecting hydrogen in twistable gas, reducing gas or steam containing hydrogen.

U.S. Patent No. 3.972.480 issued August 3, 1976
Describes a method for preparing a suspension of β-alumina particles containing no additive.

U.S. Patent No. 4,166,009 issued August 28, 1979
Describes a method for measuring impurities of a specific element in a solid metal or alloy or a dissolved metal or alloy by monitoring an electromotive force generated between a substance to be measured and a control substance. The control substance is a solid electrolyte consisting of β-alumina containing the element to be detected or a compound of said element. The β-alumina pellet for the probe is formed by hot pressing at the mounting position at one end of the α-alumina tube. The powder of sodium aluminate (NaAl ₂ O ₃ ) and α-Al ₂ O ₃ are mixed well, and both are heated to 1,400 ° C. in air, and then the mixture is pulverized to a powder. Carbon rod with the same diameter as the inside diameter of α-alumina tube can reduce powder to 25kg / c
used for cooling-pressed m ^{2, and} the powder 1,150 ° C.
The load is maintained during the heating to the temperature. The load and temperature are then increased. Most of the carbon rod is cut off outside the α-Al ₂ O ₃ tube and the remaining portion is burned using a small oxygen lance. The high temperatures reached during this burning operation help to cure the pellets.

US Patent No. 4,499,054 issued February 12, 1985
Describes a halogenated carbon gas detection element comprising a cation source consisting essentially of β-alumina, a heater and an ion collector electrode. In the presence of halogen gas, the release of Na ⁺ ions increases due to the interaction of each surface.

Na ⁺ ions are attracted to the collector electrode by the voltage.
In this patent No. 4,499,654, it was observed that the release of Na ⁺ ions increased when halogenated hydrocarbons were present near the β-alumina surface.

(Problems to be solved by the invention) However, none of the references solves the problem of generating cations with low power consumption.

Accordingly, it is an object of the present invention to provide a thermionic emitter for an ion mobility spectrometer (other instruments) capable of generating cations with low power consumption and to reduce the deficiencies and disadvantages of the prior art. is there.

(Means for Solving the Problems) The thermionic emitter for supplying cations of the present invention includes a mixture of β-alumina and an inert substance, and each of the β-alumina and the inert substance forms a part thereof. The mixture has a portion exposed on the surface of the mixture. The exposed portion of the inert material provides a surface location having a high work function and increases the release of cations.
A heater (such as a filament) is then provided to heat the mixture to a predetermined temperature.

Further, in accordance with the teachings of the present invention, a method of making a thermionic emitter is disclosed that includes the step of pulverizing β-alumina to form a powder. Inert substances (such as charcoal) are ground to a powder and mixed with the ground β-alumina powder.
An inorganic binder (e.g., sodium silicate and water) is added and the mixture is allowed to cool over time (e.g.
) To form a solid or coating having exposed exterior surfaces with portions of beta-alumina and inert material.

(Example) The purpose of the present invention will be clear from the description in the following specification with the accompanying drawings.

Referring to FIG. 1, a thermionic (ion) emitter 10 that emits ions under a gaseous environment 12 is illustrated. Thermionic emitter 10 has a coating 14 on filament wire 16
Is included. The filament wire 16 is resistant;
For example, a wire made of nickel and chromium, and when current passes through the filament wire 16, heat, that is,
A predetermined temperature is supplied to the coating 14. The end 15 of the filament wire 16 is connected to the cathode of the battery 18 via the lead wire 17. The anode of the battery 18 is connected to one side of a switch 20 via a lead 19, which is a single throw single pole.

The other end of the switch 20 is connected to an end 22 of the filament 16 via a lead wire 21. When switch 20 is closed, the battery
18 passes a current through the filaments 16 through each of the leads 19 and 17, thereby heating the coating 14 to a predetermined temperature.

The coating 14 is a mixture of β-alumina 24 and an inert material 26 such as, for example, glass chips, charcoal, diatomaceous earth, ceramic powder, silica powder, alumina powder, and the like. β-alumina 24
Is represented by the chemical formula Na ₂ , 0,5Al ₂ O ₃ . Beta-alumina 24 provides the coating 14 and its surface 28 with alkali ions (such as sodium). The beta-alumina 24 is available from Ceramate, 2425 South 900 West, Salt Lake City, Utah, 84119, USA.

The coating 14 is obtained by grinding β-alumina 24 (for example,
Into fine particles (about 80-100 mesh), and the β-alumina 2
4 is prepared by mixing sodium silicate and water with an inert material (also ground to a powder).
The ratio (excluding inactive substances) is 40.98 for β-alumina.
%, Sodium silicate 1.93%, and the rest is water.
Other inorganic binders can be used instead of sodium silicate. The mixture is formed into a paste so that it can be attached to the filament to a thickness of about 1 mm, and is cured by gradually heating the filament at 100 ° C. for 2 hours, 200 ° C. for 2 hours, and 300 ° C. overnight. You. The ion source adjusted by such a method has sufficient power (0.6 to 20w)
Is supplied to the filament to release sodium ions by ion release when the coating 14 is heated to 600-1,000 ° K.

In operation, the coating 14 provides Na ion releasing sodium atoms by passing electrons to the filament 16. The sodium ions move to the surface 28 through the lattice structure of β-alumina 24. Thermal release of sodium ions into the gaseous environment 12 occurs from the surface 28 of the coating 14.

Saha-Langmuirequation
Provides the energetics for thermionic emission and includes a free energy change represented by:

That is, It is.

In the above equation, Φ is the average work function from the emission surface 28 (in other words, the energy required to extract electrons), and E
Is the electric field present at the surface 28, I (A) is the ionization potential of the alkali atom A, and D (AX) is the dissociation energy required to break the bond between the alkali atom and the surface 28. When the free energy is large and negative (in other words, accompanied by heat generation), ion emission from the surface 28 increases, so that a higher work function is required for the emission surface 28. Inert substances (which are chemically inert)
26 creates a location on the surface 28 with a high work function adjacent to the β-alumina surface, the surface of the
The cations are released more freely than the surface of the alumina 24; Alkali metal ions on the surface of β-alumina 24 lower the work function of the surface of β-alumina.

Due to the inert material 26 dispersed on the surface 28, the temperature of the filament 16 and the surface 28 is reduced by a suitable release of alkali ions, ie a saturated flow of alkali ions. In conventional thermionic sources, the release of alkali ions was dependent on the diffusion rate of the ions diffusing to the surface through the solid material. The use of beta-alumina 24 for the release of alkali ions allows sodium ions to migrate through the vacancies of the lattice structure to the surface 28, resulting in an infinite supply of sodium ions. Inert material 26 provides a plurality of release surface locations 30 dispersed throughout surface 28.

Another way to create the surface spots 30 of the inert material 26 is to use surface
This is performed by depositing an inert material 26 through a mask 28. In this case, the inert material 26 is a metal deposit, such as nickel.

One example of an inert material (performed experimentally) is charcoal, which is ground to a powder and further mixed with a mixture of β-alumina, sodium silicate and water. Charcoal may vary within the coating 14 from 0 to 100%. It was found that the use of 10% charcoal in the coating 14 required less power to release ions from the coating 14, and that the coating 14 was primarily a source of potassium cations. We believe that this low power is due to the low ionization potential of potassium as well as the high work function at the carbon surface location 30. Potassium cations are thought to be generated from charcoal impurities, resulting in more potassium ions than simultaneously released sodium ions.

This thermionic emitter 10 is also used in an ion mobility spectrometer, and provides alkali ions as reaction ions to a reaction region to react with sample ions to be detected.
One example of an ion mobility spectrometer is described in U.S. Patent No. 4,712,008 issued December 8, 1989.

In the U.S. patent, the thermionic emitter is placed in the reaction zone with the metal foil, the radioactive ion source, removed.

(Effect of the Invention) Accordingly, the thermionic emitter is a mixture of β-alumina and an inert substance (for example, charcoal), and each of the β-alumina and the inert substance causes a part of the mixture to be on the surface of the mixture It will be appreciated by those skilled in the art that a continuous flow of cations is obtained to include the exposing. The exposed portion of the inert material forms a surface location with a high work function for cation release, and the mixture is heated to a predetermined temperature. For example, a heater includes a resistive filament wire and a power source.

Obviously, many modifications may be made without departing from the basic spirit of the invention.

Accordingly, it will be appreciated by those skilled in the art that the present invention, within the scope of the appended claims, may be practiced other than as specifically described herein.

[Brief description of the drawings]

 FIG. 1 is a conceptual diagram showing one embodiment of the present invention. 10: Thermionic emitter 16: Filament wire 18: Battery 24: β-alumina 26: Inactive substance 28: Surface 30: Location

Continuing from the front page (72) Inventor Donald Noble Campbell Maryland 21093 Timonium East Padonia Road 242 (56) References JP-A-58-37556 (JP, A) JP-B-35-448 (JP, B1) (58) Field surveyed (Int.Cl. ⁶ , DB name) G01N 27/62-27/70 H01J 49/00-49/48

Claims (10)

(57) [Claims] 1. A thermoelectron emitter for supplying cations, comprising a mixture of β-alumina (24) and an inert substance (26), wherein the β-alumina (24) and the inert substance (26) are mixed. 26) exposing a portion of the mixture to the surface of the mixture, and forming portions (30) in which each portion of the exposed inert substance has a high work function for cation release; and Means for heating to a temperature (17, 18, 19, 20, 21). 2. The thermionic emitter according to claim 1, wherein said inert substance is charcoal. 3. The thermionic emitter according to claim 1, wherein said inert substance is diatomaceous earth. 4. The thermionic emitter according to claim 1, wherein said inert substance is a glass powder chip. 5. The thermionic emitter according to claim 1, wherein said inert substance is silica. 6. The thermoelectron emitter according to claim 1, wherein said inert substance is nickel. 7. The thermionic emitter according to claim 1, wherein said inert substance is a metal. 8. A step of pulverizing β-alumina to form a first powder, a step of pulverizing an inert substance to form a second powder, and mixing the first and second powders to form a mixture. And a step of adding an inorganic binder to the mixture, and a step of heating the mixture to form a solid including an outer surface having an exposed portion. 9. The method according to claim 8, wherein said inorganic binder is sodium silicate. 10. The method according to claim 8, wherein said mixture is heated to about 300 ° C. to form a solid.