WO2006115428A1

WO2006115428A1 - Thermoemitter material for surface ionisation of organic compounds in the air and method for activating a thermoemitter

Info

Publication number: WO2006115428A1
Application number: PCT/RU2005/000229
Authority: WO
Inventors: Vladimir Ivanovich Kapustin
Original assignee: Vladimir Ivanovich Kapustin
Priority date: 2005-04-27
Filing date: 2005-04-27
Publication date: 2006-11-02

Abstract

The aim of the invention is to improve the efficiency of ionisation of organic compounds on an ion thermoemitter surface in the atmosphere air, to increase a ionisation stability in time and with the air humidity variation and to simplify a thermoemitter activating method comprising criteria for controlling the activating process termination. Said aim is attained by that the thermoemitter material is selected on the base of an alloy of vanadium, molybdenum or tungsten alloyed by 0.1-2.0 % by weight zirconium, 0.02-0.3 % by weight rhenium, and by 0.02-0.3 % by weight ruthenium or rhodium. The inventive thermoemitter activating method consists in heating the thermoemitter in an airflow whose temperature, between the thermoemitter and an additional electrode, ranges from 20 °C to +30 °C and humidity from 10 to 85 %, wherein the pumped air average rate is set-up within a range of 0.2-5.0 m/sec and the thermoemitter is heated to a temperature range of 350÷600 °C and is hold at said temperature until the thermoemitter material activating process is over. The termination of the process is determined in terms of a background ion current value in the thermoemitter and additional electrode circuit.

Description

Material of a thermal emitter for surface ionization of organic compounds in air and a method for activating a thermal emitter

The invention relates to the field of alloys for electronics and instrumentation, in particular, to the field of materials for the manufacture of surface-ionization thermoemitters of ions of organic compounds from the class of amines, hydrazines, their derivatives, a number of other nitrogen-, phosphorus- and arsine-containing compounds, as well as methods of activating such materials.

The materials of the thermal emitters of ions of organic compounds of amines, hydrazines, and a number of other organic compounds are known that work in air and are made of pure transition metals — molybdenum, tungsten, and rhenium [1]. The activation of the thermo-emitter made of these materials is carried out by heating it in air at a temperature of 450 ⁰ C for one hour, as well as by additional heating before starting the thermo-emitter for 10 - 30 minutes [1]. However, thermo-emitters made of these materials have a number of significant drawbacks — the uncontrolled growth of a loose oxide film on the surface of the thermo-emitter in an atmosphere of air, leading to a change in the ionization efficiency of the thermo-emitter over time, shedding of the oxide film, etc. In addition, the method for their activation lacks objective criteria for a thermally emitter to achieve an optimum active state.

The known material of the thermal emitter of organic compounds, working in an atmosphere of air, based on a molybdenum single crystal doped with iridium in an amount of (0.05 ÷ 0.15) weight. % The activation of such a thermoemitter is carried out in two stages: high-temperature annealing in vacuum or inert gas at a partial oxygen pressure in the range (0.0001 ÷ 0.001) Pa at a temperature (0.7 ÷ 0.8) of the melting point of iridium and subsequent oxidation in air at a temperature of (700 ÷ 1000) ⁰ K.

The material of the thermal emitter based on this alloy is devoid of the disadvantages inherent in the material of the thermal emitter of pure transition metals, but has its drawbacks. First, the ionization efficiency of such a thermal emitter changes with fluctuations in the humidity of the air pumped through a device containing a thermal emitter. Secondly, as a result of diffusion of oxygen and nitrogen in the air into the volume of a single-crystal thermal emitter and thermal cycling of the thermal emitter when it

SUBSTITUTE SHEET (RULE 26) switching on and off violates the single-crystal structure of the material, which is accompanied by its transition to a polycrystalline state, which also reduces the ionization efficiency.

In addition, the activation of the thermal emitter made of their specified material requires its two-stage heat treatment, which complicates the activation process, and the activation method of such a material also lacks objective criteria for the thermal emitter to achieve an optimum active state.

The purpose of the invention: the creation of a material for the thermal emitter of ions of organic compounds with stable and high characteristics of the efficiency of ionization of organic compounds in air, not affected by fluctuations in air humidity, resistant to thermal cycling of the thermal emitter, as well as the creation of a method of one-stage activation of the thermal emitter, characterized by the presence of objective metrological criteria for a thermally emitter to achieve an optimum active state. This goal is achieved by the fact that the transition metal VA or VlA of the subgroup of the Periodic system is selected as the basis of the alloy of the material of the thermal emitter, in addition to the higher oxides of the type Me ₂ O ₅ in the case of the transition metal VA of the subgroup or the type MeO ₃ in the case of the transition metal of the VlA subgroup, the formation is also stable on an oxide of the type MeO ₂ , which also forms intermediate oxides, which are oxidized to a higher transition metal oxide in an oxidizing gas medium, and are reduced to a lower oxide in a gas medium containing hydrogen and a transition metal, in addition to the base, the alloy contains three alloying components, while one of the transition metals of the IVA subgroup of the Periodic system, which forms a stable oxide of the type MeO ₂ in an oxidizing gas medium, in the amount of (0.1 ÷ 2.0) weight. %, as the second alloying component, the metal of the VBA subgroup forming the higher oxide of the type Me ₂ O _{7 is} selected, and as the third alloying component the metal of the VSP subgroup of the Periodic system forming the higher oxide of the type MeO _{4 is} selected, while the content of the second and third alloying components in the alloy is (0.02 ÷ 0.3) weight. % of each, and the total content of the second and third alloying components is (0.04 ÷ 0.6) weight. %

Vanadium, molybdenum, or tungsten are chosen as the basis of the alloy of the material of the thermoemitter, and cir-

SUBSTITUTE SHEET (RULE 26) conium or hafnium, rhenium is chosen as the second alloying component, and ruthenium or rhodium is selected as the third alloying component. An electrically insulated auxiliary electrode is placed near the thermo-emitter with a gap between the thermo-emitter and the auxiliary electrode, air is pumped through the gap with an external pump, having a temperature at the inlet of the gap in the range (- 20 ÷ + 30) ⁰ C and relative humidity in the range (10 ÷ 85 )%, while the average pumped air speed V = Q / S is set in the range (0.2 ÷ 5) m / s, where Q is the volumetric capacity of the external pump, m ³ / sec, S is the average cross-section of the gap between the thermal emitter and the auxiliary - a solid electrode, ^2, between the thermal emitter and the auxiliary electrode is applied a constant potential difference in the range of (30 ÷ 600) Volts plus at the thermal emitter and the minus at the auxiliary electrode, measure the amount of electric current flowing in the circuit of the thermal emitter and the auxiliary electrode, thermal emitter is heated to a temperature (350 ÷ 600) ⁰ C and held at a given temperature until the end of the process of activation of the material of the thermo-emitter, moreover, the end of the process of activation of the material of the thermo-emitter is judged by the value of the background and current in the circuit of the thermal emitter and auxiliary electrode.

The invention consists in the following. It is known [3] that the ionization of organic molecules of nitrogen-containing compounds on the surface of a thermoelectric emitter of ions containing an active layer of a transition metal oxide in an atmosphere of air occurs as a result of the capture by an organic molecule that has fallen on the surface of a thermo emitter with a stream of air, a proton, and desorption of a positively charged ion. Protons (hydrogen ions) on the surface of the thermal emitter are in turn formed as a result of dissociative adsorption on the surface of the thermal emitter of water molecules contained in atmospheric air. Therefore, the main task in creating the material of the thermoemitter, which efficiently and stably ionizes the molecules of organic compounds, is to provide a high and stable concentration of centers on the surface for the dissociative adsorption of water molecules.

It is known [4] that the centers of adsorption of water molecules on the surface of transition metal oxides can be transition metal atoms located on the surface of the oxide in a state of reduced oxidation state. Such states on the surface of transition metals characterized by variable valency

SUBSTITUTE SHEET (RULE 26) during the formation of compounds with oxygen, they can be created, for example, by annealing such oxides in hydrogen [4]. However, under atmospheric conditions, these states are unstable. These states can also be created by introducing atoms of another metal into the crystal lattice of a transition metal oxide having a lower or higher maximum valency upon interaction with oxygen than atoms of the base metal. However, the introduction into the crystal lattice of molybdenum oxide having a maximum oxidation state of +6, iridium atoms having a maximum oxidation state of +8, in an amount of 0.05 - 0.15 weight. %, as suggested in [2], is not enough to create the required surface concentration of adsorption centers of water molecules, that is, ionization centers of molecules of organic compounds. Therefore, in [2], vacuum annealing of the thermal emitter is additionally carried out (first stage of activation), lowering the oxygen concentration in the volume of the material of the thermal emitter in comparison with its equilibrium concentration in the air atmosphere, thereby creating a drain channel for oxygen from molybdenum oxide when the thermal emitter is operating in the atmosphere air in order to reduce the oxidation state of molybdenum atoms in the oxide.

New in the present invention is that a reduced oxidation state of transition element atoms in their oxides under atmospheric conditions is achieved by alloying the base metal of the alloy for a thermal emitter, in which the metal of a subgroup VlA or a VlA subgroup is selected, while the metal atoms of an IVA subgroup, VPA subgroups and VSh subgroups of the Periodic system, respectively having a maximum oxidation state of +4, +7 and +8. In this case, the metal-base of the alloy itself is selected from the additional condition that in binary systems of this metal with oxygen, firstly, there are oxides with a metal oxidation state of +4 (type MeO ₂ ) and, secondly, there are oxides with an intermediate degree oxidation between +4 and a maximum oxidation state of +5 for metals of the VA subgroup and +6 for metals of the VlA subgroup. Therefore, in accordance with these criteria and based on the available types of intermediate oxides [5], we selected vanadium, molybdenum, and tungsten as the base metal of the alloy.

The specific type of alloying components and their weight content were selected based on the results of experimental studies of the ionization efficiency of triethylamine, diphenhydramine, papaverine (test amines) on the surface of thermoemitters made of alloys of various compositions.

SUBSTITUTE SHEET (RULE 26) The essence of the process of activation of the thermoemitter, which is carried out at a temperature of 50-100 ⁰ C higher than the operating temperature of the thermoemitter, consists in the oxidation of the surface of the thermoemitter made of the proposed alloys in a flowing stream of air containing water molecules, an oxide film the base metal of the alloy, into the nodes of the crystal lattice of which atoms of the alloying components diffuse from the volume of the alloy, creating centers with a reduced oxidation state of the base metal atoms. At the same time, at the activation stage at a temperature higher than the operating temperature of the thermoemitter, water molecules, dissociatively adsorbing on the oxide surface, break the metal-oxygen chemical bonds near the oxide surface, thereby providing the possibility of enrichment of the surface of the growing oxide with alloying atoms elements, that is, enrichment of the surface with ionization centers of organic molecules. Moreover, the presence of water molecules in the flowing air stream additionally provides the ability to control the degree of activation of the surface of the thermal emitter. Indeed, at the temperature of activation of the thermal emitter, some of the hydrogen atoms are desorbed in the form of ions, and the ion current is proportional to the concentration of ionization centers on the surface of the thermal emitter and forms the so-called background ion current of the thermal emitter.

The above features meet the criteria of “new” and “material differences” in relation to this invention.

In FIG. 1 shows a diagram of the activation of a thermal emitter with a cylindrical working surface; FIG. 2 shows the activation circuit of a thermal emitter with a flat working surface, and FIG. Figure 3 shows a typical temperature dependence of the background ion current from the surface of an activated thermal emitter. In FIG. 1, FIG. 2 and FIG. 3 are marked: 1 - ion emitter, 2 - heater emitter, 3 - auxiliary electrode, 4 - source of potential difference between the emitter and auxiliary electrode, 5 - device for measuring ion current from the emitter, 6 - temperature emitter temperature sensor, 7 - average gap section between the auxiliary electrode and the thermal emitter, Q - air flow near the surface of the thermal emitter pumped external pump, the change of direction of pumping air to the contrary do not alter the essence of the invention, T ₁ - evap pa, at which there is a decline in the magnitude of the background ion current thermal emitter after its first peak, T ₂ - the temperature at

SUBSTITUTE SHEET (RULE 26) which there is a second rise in the background current of the thermal emitter, (T ₁ ÷ T ₂ ) is the interval of operating temperatures of the thermal emitter after its activation.

The ionization efficiencies of novocaine (test amine) were compared on the surface of the proposed alloys of various compositions, as well as of the known alloys. Alloys for thermo-emitters were smelted using a standard electric arc furnace. Samples for measurements were cut out by electroerosion, and their working surface was ground and polished mechanically.

Before measurements, thermoemitters were activated in the following modes: air temperature at the inlet to the measuring cell corresponding to FIG. 2, was + 18 C, relative humidity was 55%, the average velocity of the pumped air was 2 m / s, the potential difference between the thermal emitter and the auxiliary electrode was 300 Volts, the thermal emitter was heated to a temperature of 500 ⁰ C. Before the activation of the thermal emitter, the background current in the thermal emitter circuit did not exceed 10 ^"13 A for all alloy compositions. After 10–30 minutes of heating of thermal emitters of different compositions at the activation temperature, the background current from the thermal emitters reached a value of (5 * 10 ^{" 10} ÷ 10 * 10 ^"9 ) A in depending on the composition of the alloys, after which the background current stabilized. This signaled the end of the activation of the thermoemitter. The ionization efficiency was measured by feeding samples of novocaine with a mass in the range of (10 ^"10 ÷ 10 ^{" 6} ) grams. The results are shown in the Table.

Alloys of compositions from N ° 3 to Na 12 after activation had a dense layer of dark gray oxide on the surface, resistant to vibrations and mechanical

SUBSTITUTE SHEET (RULE 26) abrasion. Tests of activated alloys showed that within 200 hours

(test time) the ionization efficiency of test amines on their surface at an operating temperature of 450 ^° C changed by no more than 2%. During the tests, air having 100% humidity was periodically fed to the inlet of the measuring cell periodically for 1 minute (barbating air through boiling water). In this case, the ionization efficiency remained constant. After testing, a dense gray oxide layer remained on the surface of the thermoemitters. The proposed material and the method of its activation in comparison with the known technical solutions made it possible to provide a higher ionization efficiency of organic compounds, stable in time and not sensitive to fluctuations in air humidity, to drastically simplify the activation process of the thermal emitter and to provide the ability to control the end of the activation process

When the alloy contains more than 2% of the IVA metal of the subgroup of the Periodic system, an oxide layer of the metal of the form MeO _{2 is} formed on the surface of the oxide film, which prevents the activation of the thermal emitter. When the content of this component in the alloy is less than 0.1%, the activation process takes up to 2 to 3 hours, while on the surface there is an increase in loose inclusions in the oxide film.

If the alloy contains more than 0.3% of the metal of the VCA subgroup of the Periodic system after the activation process, the ionization efficiency of organic molecules on the surface of the thermoemitter is not stable over time. When the content of this component in the alloy is less than 0.02%, the activation process is not observed when the thermoemitter is exposed to activation up to 10 hours.

If the alloy contains more than 0.3% metal of VHA subgroup of the Periodic system, the ionization efficiency of organic molecules on the surface of the thermoemitter is not stable when the air humidity changes. When the content in the alloy is less than 0.02% of this component, the activation of the thermal emitter does not occur in the entire range of activation temperatures.

If we use VA or VlA metal as the base metal, the intermediate oxides of which cannot be reduced with hydrogen to lower oxides at temperatures up to 600 ^° C or whose higher oxides are inert in solid-phase reactions with other metal oxides or whose oxides have low thermal stability, for example, chromium, tantalum, niobium [6], alloys based on such metals do not provide ionization of molecules of organic compounds.

SUBSTITUTE SHEET (RULE 26) To ensure effective activation of the surface of the thermal emitter, it is necessary that the number of water molecules falling on a surface unit of the thermal emitter from the air atmosphere per unit time is (5 * 10 ¹⁹ ÷ 2 * 10 ²² ) CM ^-2 CeK ^"1 , which is in the temperature range of the pumped air ( - 20 ÷ + 30) ⁰ C corresponds to air humidity in the range of (10 ÷ 85)%. When the humidity value is less than 10%, the thermoemitter is not activated, when the humidity value is more than 85%, the end of the activation process is difficult to fix in time.

At an activation temperature of less than 350 ° C, the activation process does not occur. At an activation temperature of more than 600 ⁰ C, there is a growth of needle structures on the surface of the oxide film, which adversely affects the stability of the thermal emitter.

At a speed of pumping air through the device for activation of less than 0.2 m / s, it is not possible to register a background ion current due to the action of the space charge of ions. At a pumping speed of more than 5 m / s, the ions formed on the surface of the emitter “grow” in the air stream and recombine without reaching the auxiliary electrode.

The foregoing shows that in the scientific, technical and patent literature there are no technical solutions to achieve the indicated technical results using the above methods and means, which allows us to conclude that the claimed invention meets the patentability conditions: “novelty” and “inventive law”. The claimed material and the method of its activation can be implemented in industry, which allows us to conclude that the claimed invention meets the patentability condition: industrial applicability ”.

Sources of information taken into account.

1. Golovnya P.B., Zhuravleva I. L., Terenina M. B. et al., Gas chromatographic functional analysis of amines in parallel detection by surface-ionization and flame-ionization detectors. Journal of Analytical Chemistry, 1981, Volume 34, no. 3, pp. 533 - 538 (analogue of the material and method).

SUBSTITUTE SHEET (RULE 26) 2. Patent of the Russian Federation N ° 2138877, priority of 08/12/97 (prototype material and method).

3. Bannykh O.A., Povarova KB, Kapustin B.I., A new approach to surface ionization and drift spectroscopy of organic molecules. Zhtf, 2002, Volume 72, no. 12, p. 88 - 93.

4. Krylov O.B., Kiselev B.F., Adsorption and catalysis on transition metals and their oxides. M .: "Chemistry", 1981, 288 p.

5. Lazarev B. B., Krasov V. G., Shaplygin I. S., Electrical conductivity of oxide systems and film structures. M .: "Hayka", 1979, 168 p. 6. Lazarev V. B., Sobolev B. B., Shaplygin I. S. Chemical and physical properties of simple metal oxides. M .: "Hayka", 1983, 239 p.

SUBSTITUTE SHEET (RULE 26)

Claims

CLAIM

1. The material of the thermal emitter for surface ionization of organic compounds in air based on a transition metal alloy containing the metal of the VH subgroup of the Periodic system as an alloying component, characterized in that the transition metal VA or VlA of the subgroup of the Periodic system is selected as the basis for the alloy of the material of the thermal emitter, in addition to higher oxides of the type Me ₂ O ₅ in the case of a transition metal of the VA subgroup or of the type MeO ₃ in the case of the transition metal of the VlA subgroup also forms an air-stable oxide of the type MeO ₂ , vol which also produces intermediate oxides, which are oxidized to a higher transition metal oxide in an oxidizing gas medium, and are reduced to a lower transition metal oxide in a hydrogen-containing gas, moreover, the alloy contains three alloying components in addition to the base, while the first alloying component alloy choose one of the transition metals of the IVA subgroup of the Periodic system, forming in an oxidizing gas medium a stable oxide of the form MeO ₂ , in the amount of (OD ÷ 2.0) weight. %, as the second alloying component, the metal of the VBA subgroup forming the higher oxide of the type Me ₂ O _{7 is} selected, and as the third alloying component the metal of the VSP subgroup of the Periodic system forming the higher oxide of the type MeO _{4 is} selected, while the contents of the second and third alloying components in the alloy is (0.02 ÷ 0.3) weight. % of each, and the total content of the second and third alloying components is (0.04 ÷ 0.6) weight. %

2. The material according to p. 1, characterized in that vanadium, molybdenum or tungsten are selected as the basis for the alloy of the material of the thermal emitter, zirconium or hafnium is selected as the first alloying component, rhenium is selected as the second alloying component, and rhenium is selected as the third alloying component ruthenium or rhodium.

3. A method for activating a thermal emitter of ions of organic compounds made of a material based on an alloy of a transition metal VA or VlA subgroups of the Periodic system doped with metals IVA subgroups and metals VHA and VSh subgroups of the Periodic system, comprising annealing the material of the thermal emitter in an oxidizing medium at a fixed temperature, characterized in that electrically insulating

SUBSTITUTE SHEET (RULE 26) the auxiliary electrode with a gap between the thermal emitter and the auxiliary electrode, air is pumped through the gap using an external pump, having a temperature at the inlet of the gap in the range (- 20 ÷ + 30) ⁰ C and relative humidity in the range (10 ÷ 85)%, at the average air velocity V = Q / S is set in the range (0.2 ÷ 5) m / s, where Q is the volumetric capacity of the external pump, m ³ / sec, S is the average cross-section of the gap between the thermal emitter and the auxiliary electrode, m ² , between the thermal emitter and the auxiliary electrode ohms apply a constant potential difference in the range (30 ÷ 600) Volts with a plus on the thermo-emitter and minus on the auxiliary electrode, measure the amount of electric current flowing in the circuit of the thermo-emitter and auxiliary electrode, the thermo-emitter is heated to a temperature in the range (350 ÷ 600) ⁰ C and maintained at a given temperature until the end of the activation process of the material of the thermal emitter, and the end of the activation process of the material of the thermal emitter is judged by the value of the background ion current in the circuit of the thermal emitter and auxiliary lektroda.

SUBSTITUTE SHEET (RULE 26)