JP2015198034A - Cathode member for electron beam generation and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a cathode for electron beam generation, suppressed in the occurrence of a crack and a chip while maintaining uniformity in the component composition of the cathode; and a method for manufacturing the cathode.SOLUTION: A cathode member for electron beam generation contains 30 wt.% or less of cerium and the balance is iridium. The longest length of crystal grains constituting the cathode member is 500 μm or less, and the crystal grains have at least one or more crystal phases selected from among an IrCe crystal phase, an IrCe crystal phase, an IrCecrystal phase, and an IrCe crystal phase.

Description

  The present invention relates to an electron beam generating cathode member and a method for manufacturing the same.

  Conventionally, an electron beam generating cathode (cathode) member has been required to increase the current density and extend its life.

As shown in Non-Patent Document 1, tungsten (W), tantalum (Ta), and the like have been used for a long time in the hot cathode method for extracting a large current, and recently, lanthanum hexaboride (LaB ₆ ) and the like. Came to be used. LaB ₆ is known to have a large current density even at a lower cathode temperature than tungsten or the like, and at the same current density, the evaporation loss rate during use is about 1/100 and can be extended. . Furthermore, when an Ir—Ce-based alloy is used, the evaporation loss rate of the cathode material when outputting the same current density is further 1/100 to 1/1000 of the LaB ₆ cathode, and it is possible to significantly extend the life. It has been reported.

As a component composition of an iridium-cerium (Ir—Ce) -based cathode material, an alloy in which a rare earth element content such as Ce is added to Ir in an amount of about 5 to 30% by mass is effective as a cathode material, and particularly an Ir ₅ Ce compound. It has been reported that the vicinity of the composition is excellent (see Patent Documents 1 to 3, etc.).

Recently, a high energy research organization has reported that excellent characteristics can be obtained by using an Ir ₅ Ce compound alloy as a cathode member for an accelerator (Non-patent Document 2).

  Furthermore, in Non-Patent Document 3 published in 1969, the work function of Ir—Ce-based material is 2.57 eV (1300 K), and at the same time, Ir—La, Ir—Pr, Ir—Nd, Ir—Sm, etc. It is reported that the values are almost equivalent, and these compounds are expected to be effective cathodes. Among Ir-Ce-based cathode materials, the evaporation loss rate at the same current density is good when the rare earth elements are Ce, La, and Pr, and the evaporation loss rate is particularly small in the IrCe alloy. It has been reported in Non-Patent Document 1, and it is considered that the compound that becomes the center of the cathode member is an Ir—Ce system.

  Next, as a method for producing an Ir—Ce compound alloy cathode (cathode), the following method has been reported.

  First, Ir is a noble metal-based high melting point metal (melting point 2443 ° C.), and vapor pressure is low and evaporation loss at the time of melting is low, whereas Ce is a rare earth element, an active metal, and has a low melting point ( Since the vapor pressure is higher than Ir at a melting point of 798 ° C., the evaporation loss at the time of dissolution tends to be remarkable. Therefore, as the melting method, an arc melting method in an inert gas atmosphere is employed. It has been reported that an alloy having almost uniform components can be melted by repeatedly melting many times by the arc melting method (Patent Document 1). Note that the structure obtained by the arc melting-solidification method is a polycrystal.

  In order to solve the problem of defect generation at the time of solidification, in Patent Document 1, as a method for producing an Ir—Ce alloy (Ce concentration range: 5 to 15 wt%), mechanical alloying is performed using powder Ir and powder Ce as raw materials. The (MA) method is used to form an Ir—Ce alloy, which is sintered at 1300 to 1800 ° C. under vacuum to produce a sintered solidified body. It has been reported that the cathode material produced by this method has improved the current density at the same temperature by about 1.4 to 2 times that of the cathode material produced by the ordinary arc melting method. This is presumed to be due to the effect of obtaining a finer crystal structure than the material in the ingot method.

US Pat. No. 5,773,922 JP 2002-527855 A JP 2002-260520 A

G. Kuznetsov, “High temperature cathodes for high current density,” Nuclear Instruments and Methods in Physics Research A 340 (1994) 204-208. T. T. et al. Natsui, M .; Yoshida, et. al, “High Charge Low Emission RF Gun for SUPERKEK”, Proc. IPAC, 2012, 1533-1535. S. E. Rozhkov, O.M. K. Kuktashev, A .; A. Gunnin: Technical Characteristics of Thermal Emitters Based on Alloy Irwith La, Ce, Pr. Technique, Ser. 16, energy, Modulatione I Rentgenovsky Privacy, vol2, 1969, p. 81 G. I. Kuznetsov, “IrCe Cathode For EBIS”, J. Am. Physics: Conference Series 2 (2004) 35-41

  However, it is considered that the prior art described above has the following problems.

According to the study of the present inventors, by melting an Ir—Ce compound crystal having a Ce concentration equal to or higher than the Ir ₅ Ce compound composition (12.7% by weight) by an arc melting method shown in a patent document or a non-patent document, It has been found that defects such as cracks are likely to enter the solidified ingot. This is presumably because the crystal phase is almost entirely an intermetallic compound phase.

Therefore, from the viewpoint of simply producing an ingot with less cracking, it is desirable that the Ce concentration is 12.7% by weight or less, and that the composition is such that the pure Ir crystal phase coexists with the Ir ₅ Ce crystal phase. Become.

  However, on the other hand, in order to improve the characteristics as an electron beam cathode (cathode) member, it is considered that a high concentration of Ce element having a low work function is desirable. Therefore, an Ir having a Ce concentration of 12.7% by weight or more is considered. It is essential to establish a technology that can be stably manufactured even with a Ce-based alloy cathode material.

  In addition, when machining is actually performed on the shape of the cathode member from the melted and solidified ingot, cracks or chips may occur at the end during processing, or minute hole defects may occur. all right. This is presumably because, in the case of a solidified ingot, there are shrinkage defect, gas blowhole defect and the like that inevitably occur during solidification. Further, in the case of a solidified ingot, there is a problem that crystal grains tend to be large and a coarse solidified structure is formed, and cracks and chips are likely to occur during machining.

  When the present inventors manufactured a compound crystal ingot (about 500 g) having a composition of Ir-14 wt% Ce by dissolution and solidification according to a conventional method and observed the solidified structure, as shown in FIG. 1 (Photo 1). The crystal grain size is 2000 μm or more, and it turns out that the crystals grown in the shape of a dendrite-like solidified structure in the crystal grains become a coarse solidified structure grown to 2000 μm or more in the longitudinal direction. did. In addition, cracks of 500 μm or more have occurred along the grain boundaries between crystals grown in a dendrite shape, and fine cracks with a length of about 100 μm that cross the inside of the string crystals have also occurred. Was confirmed.

  For this reason, when the cathode member is machined using an Ir—Ce alloy ingot material as a raw material, cracks and chips are generated starting from crystal grain boundaries and micro cracks during processing, and the columnar shape in which strain becomes particularly large This is thought to lead to chipping and large cracks at the corners of the cathode. There is a possibility that a healthy cathode member can be obtained if it is processed from a relatively healthy area in the ingot, but it is difficult to make the cathode member stably as a raw material. I understood.

Next, it is considered that the method of Patent Document 1 in which the cathode member is manufactured by refining crystal grains is superior to the method of manufacturing from an ingot. However, in the mechanical alloying (MA) method, there remains a possibility that pure Ir and pure Ce as raw materials cannot be completely compounded. Therefore, if an Ir—Ce compound (IrCe ₄ , IrCe ₃ , Ir ₃ Ce ₇ , Ir ₃ Ce ₅ , Ir ₄ Ce _5, etc.) having a low melting point (melting point 1180 ° C. or lower) remains, it is used as a cathode. At this time, a part of the material is melted and its shape is deformed. Further, Ce is liable to be evaporated and the life of the cathode is shortened. Further, when the active metal is treated by the MA method, there is a concern that the surface oxidation of the active metal such as Ce proceeds during MA for a long time.

  Next, as a method for manufacturing a cathode member for generating an electron beam, an arc melting method has been reported as a melting method for a cathode member material alloy in the prior art such as Non-Patent Document 1 and Patent Document 1. In the melting of refractory alloys as described above, it is generally difficult to apply a refractory crucible, so that melting is performed by arc heat in an inert gas atmosphere using a water-cooled copper crucible. become. However, when using a water-cooled copper crucible, the surface temperature should be sufficient to cool the copper crucible to prevent serious accidents such as steam explosions, that is, to prevent the copper crucible from melting. It is known that it is necessary not to greatly exceed 200 ° C.

On the other hand, the temperature of the arc column (frame) in arc melting is said to reach 5000 ° C. to 10000 ° C., and the melting raw material is melted by heat transfer from the arc column, and there is a molten pool near the arc column. Will be formed. The formed molten metal flows downward and comes into contact with the surface of the water-cooled copper crucible, and the molten metal immediately solidifies and is adjacent to the water-cooled copper crucible, so that a solidified layer is formed. Therefore, the molten metal pool is in such a melting state that it is formed only directly below the arc column above the solidified phase. For this reason, the higher the melting point, the thicker the solidified layer, and the smaller the molten pool. From the above, when using the arc melting method, an alloy compound such as Ir ₃ Ce (melting point 2100 ° C.) or Ir ₂ Ce (melting point 2250 ° C.) whose melting point is remarkably increased can form a molten pool having a sufficient volume. It becomes difficult, and it is thought that the problem that it becomes difficult to equalize the components of the initial charging raw material occurs.

  Further, in the state of the metal Ce in the raw material stage before being compounded with Ir, the vapor pressure may be very high, and the Ce raw material is lost by evaporation before being alloyed with Ir by a high-temperature arc column. There is also a problem that the alloy composition tends to deviate from the target alloy composition.

  The present invention has been made in view of such a problem, and maintains a homogeneity in the component composition of the cathode member for generating an electron beam, while suppressing the occurrence of defects such as cracks and chips, and the production thereof. It aims to provide a method.

  In order to solve the above-mentioned problems, the present inventor has intensively studied and found that the above problems can be solved by the following configuration.

That is, the cathode member for generating an electron beam according to one aspect of the present invention,
Containing cerium at 30% by weight or less and the balance being iridium;
The longest length of the crystal grains constituting the cathode member is 500 μm or less,
The crystal grains are composed of at least one crystal phase selected from an Ir ₂ Ce crystal phase, an Ir ₃ Ce crystal phase, an Ir ₇ Ce ₂ crystal phase, and an Ir ₅ Ce crystal phase.

  The electron beam generating cathode member preferably further includes a pure iridium crystal phase having a maximum crystal grain length of 500 μm or less.

Further, the present invention is a method for producing the electron beam generating cathode member,
Powder that has a maximum length of 500 μm or less after iridium-cerium raw material is melt-mixed and solidified in an inert gas atmosphere using a melting method using a water-cooled copper container as a melting crucible Producing a body,
An electron beam generating cathode member comprising a step of molding the obtained powder under a high temperature and high pressure condition of a temperature of 800 ° C. or higher and 1500 ° C. or lower and a pressure of 10 MPa or higher, and a step of machining the obtained molded body. A manufacturing method is also included.

In the method for producing an electron beam generating cathode member, at least one crystal phase selected from an Ir ₂ Ce crystal phase, an Ir ₃ Ce crystal phase, an Ir ₇ Ce ₂ crystal phase, and an Ir ₅ Ce crystal phase is used. It is preferable to use an iridium-cerium raw material adjusted to the component composition to be crystallized.

  In the above method for producing an electron beam generating cathode member, it is more preferable that after the pulverization step, pure iridium crystal fine powder is added as necessary, and then the molding step is performed.

  ADVANTAGE OF THE INVENTION According to this invention, the cathode member which has few defects, such as a crack and a chip, and has a high current density, and its manufacturing method can be provided, maintaining the uniformity in the component composition of the cathode for electron beam generation.

FIG. 1 shows a structure photograph of a melt-solidified ingot of an IrCe alloy manufactured by melt-solidification according to a conventional method.

[Cathode material for electron beam generation]
Hereinafter, embodiments of the electron beam generating cathode member according to the present invention will be specifically described, but the present invention is not limited thereto.

The cathode member for generating an electron beam according to the present embodiment (hereinafter, also simply referred to as a cathode member) contains cerium in an amount of 30% by weight or less and the balance is iridium, and the longest length of crystal grains constituting the cathode member The crystal grains are composed of at least one crystal phase selected from an Ir ₂ Ce crystal phase, an Ir ₃ Ce crystal phase, an Ir ₇ Ce ₂ crystal phase, and an Ir ₅ Ce crystal phase. It is characterized by that.

  With such a configuration, a cathode member for generating an electron beam having a high current density and a long lifetime can be obtained.

In this embodiment, an Ir—Ce alloy containing cerium in an amount of 30% by weight or less and the balance being iridium is used as a cathode member, but this alloy is used as a conventional cathode material for generating an electron beam. Compared with LaB ₆ material, the current density is large and the evaporation loss is small, so that it is expected that the life can be extended.

  About cerium (Ce), it is possible to replace a part with other rare earth elements (Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc.). is there.

  The remaining iridium (Ir) is a noble metal element that is difficult to oxidize and is a high melting point (melting point 2443 ° C.) element. If it is, it will be easy to make it higher temperature, and it is thought that there exists an effect which makes large current density easy. Therefore, it is considered promising to use a noble metal alloy having a melting point higher than Ir as a base metal, and candidate elements may include osmium (Os: melting point 3027 ° C.), rhenium (Re: melting point 3160 ° C.), and the like. . However, at present, the Os-rare earth element system or the Re-rare earth element system does not have even a phase diagram, and it is considered that these elements alone cannot be fully utilized.

  However, looking at the phase diagrams of Ir-Os system, Ir-Re system, etc., it shows a tendency that the liquidus temperature and the solidus temperature can be made higher than Ir by adding Os and Re to Ir. Adding an appropriate amount of these elements may contribute to improvement of the characteristics as a cathode. About these addition amounts, since it is considered that the range in which the Ir crystal structure remains is appropriate, it is considered that the upper limit of addition concentration is 30 at% (molar fraction 0.3) or less.

  On the other hand, among rare earth elements, Ce has a small work function (2.9 eV) and at the same time has the highest boiling point among rare earth elements, so it is expected to have the lowest vapor pressure. It is thought that it is an element. Candidates for substitution are yttrium (Y (3.1 eV)), gadolinium (Gd (3.1 eV)), terbium (Tb (3.0 eV)), etc., as elements having a work function close to Ce and low vapor pressure. Is considered. However, for these elements, the work function value is slightly higher than that of Ce and the vapor pressure is also slightly higher, so it is unclear whether or not the characteristics can be improved over Ce alone. However, it is considered that there is a possibility that the effect of compounding by replacing a part of Ce can be expected.

  From the above, it is considered that the electron emission from the Ir—Ce alloy / compound is basically carried out by Ce atoms having a small work function. Therefore, in order to generate electrons more efficiently and obtain a high current density, it is considered that it is theoretically advantageous to increase the Ce concentration. In order to further increase the current density of electron emission from the cathode material, it is considered that a high concentration of Ce is desirable, and an Ir—Ce compound having a high Ce content is preferable.

  On the other hand, it is conceivable that the Ce activity in the Ir—Ce alloy increases as the Ce concentration increases, and the evaporation loss rate of Ce increases. In that case, even if the current density is increased, the life of the cathode is shortened, and as a result, practical use may not be possible. Therefore, there is an upper limit to the Ce concentration as the component composition.

  If the cerium concentration in the Ir—Ce alloy used in the present embodiment is 30% by weight or less, it is expected that an Ir—Ce alloy having a high melting point of 1880 ° C. or higher will be formed. It can be applied as a material. More preferably, from the viewpoint of further suppressing defects such as cracks that occur after solidification and extending the life, in the Ir—Ce alloy of this embodiment, the cerium concentration is 27 wt% or less, and more preferably 24 wt%. % Or less is desirable.

  The cerium concentration is not particularly limited as long as it is 30% by weight or less, but it is preferably 11% by weight or more from the viewpoint of achieving a high current density. More preferably, it is 12% by weight or more.

The crystal phase of the Ir—Ce alloy / compound of the present embodiment is one or more crystal phases of Ir ₂ Ce crystal phase, Ir ₃ Ce crystal phase, Ir ₇ Ce ₂ crystal phase, and Ir ₅ Ce crystal phase. Consists of. This is due to the following reason.

From the Ir—Ce phase diagram, when Ce (melting point 798 ° C.) is added to Ir (melting point 2443 ° C.), an Ir ₅ Ce compound (melting point 1950 ° C.) is first formed, and then Ir ₇ Ce ₂ ( Melting point 2000 ° C.), Ir ₃ Ce (melting point 2100 ° C.), Ir ₂ Ce (melting point 2250 ° C.), and as the added Ce concentration increases, the melting point tends to increase, and the compound having the highest melting point is Ir ₂ It turns out that it is Ce.

That is, the Ir ₂ Ce compound is a fairly stable compound, and it is expected that high energy is required for its decomposition. Therefore, it is estimated that the Ce activity in the Ir—Ce alloy does not increase in proportion to the concentration even when the Ce concentration increases. From the above, it is expected that the evaporation loss rate of Ce does not increase so much as long as the added Ce concentration is lower than the Ir ₂ Ce compound.

On the other hand, when Ce is added to a concentration exceeding the Ir ₂ Ce compound, the melting point is drastically lowered, such as Ir ₄ Ce ₅ , Ir ₃ Ce ₅ , Ir ₃ Ce ₇ , IrCe ₃ , IrCe _4, etc. having a high Ce concentration. This compound is presumed to be unstable as a cathode material. This is considered to indicate that the upper limit of the appropriate Ce concentration is the Ir ₂ Ce compound, and that the upper limit is reached at a certain concentration of Ce concentration in the Ir ₂ Ce compound phase having a certain concentration range.

Therefore, since the crystal phase of the Ir—Ce alloy / compound of the present embodiment is composed of a crystal phase composed of a compound having a lower Ce concentration than the Ir ₂ Ce compound, the evaporation loss rate of cerium can be kept low. it is conceivable that.

  The longest length of the crystal grains constituting the cathode member is 500 μm or less. If the maximum length of the crystal grains is 500 μm or less, there is an excellent advantage that defects such as cracks and chips during machining are reduced. More preferably, it is 250 micrometers or less, More preferably, it is 100 micrometers or less.

  The size of the crystal grains is preferably as small as possible. However, since Ce is easily oxidized when it is too small, the lower limit is 1 μm or more, and more preferably 10 μm or more, from the viewpoint of suppressing oxidation.

  Further, the crystal phase of the Ir—Ce alloy / compound of this embodiment may include a pure iridium crystal phase having a maximum crystal grain length of 500 μm or less. Thereby, although the efficiency at the time of generating the electron beam may be slightly lowered, it is considered that there is an excellent effect of suppressing the cracking of the cathode due to the thermal stress at the time of use.

  The longest length of the pure iridium crystal phase is more preferably 250 μm or less, and still more preferably 100 μm or less.

  The size of the crystal grain is preferably as small as possible, but if it is too small, the lower limit is 1 μm or more, more preferably 10 μm or more, from the viewpoint that the particle size balance with various Ir—Ce compound crystals is impaired.

[Method for producing cathode member for generating electron beam]
Next, a method for manufacturing the electron beam generating cathode member as described above will be described in detail.

The manufacturing method of the electron beam generating cathode member in the present embodiment is:
Powder that has a maximum length of 500 μm or less after iridium-cerium raw material is melt-mixed and solidified in an inert gas atmosphere using a melting method using a water-cooled copper container as a melting crucible Producing a body,
It includes a step of molding the obtained powder under a high temperature and high pressure condition at a temperature of 800 ° C. or higher and 1500 ° C. or lower and a pressure of 10 MPa or higher, and a step of machining the obtained molded body.

  More specifically, first, an iridium-cerium raw material that is a cathode member processing material is dissolved.

  As a melting method, a plasma arc melting method may be used, but a melting method using a water-cooled copper container as a melting crucible is preferably used. That is, in the plasma arc melting method, it may be difficult to perform mass production melting on a practical scale, so in this embodiment, in addition to plasma arc melting, as a melting technique assuming a mass production scale, An induction dissolution method using a water-cooled copper container is used.

  The induction melting method using a water-cooled copper container as a melting crucible is a melting method also called a cold crucible induction melting method.

  Specifically, the cold crucible induction melting method replaces the refractory crucible used in the normal vacuum induction melting method with a crucible composed of a water-cooled copper segment with a high-frequency coil arranged outside. This is a melting method that uses a high-frequency power source, generates an induced current in the melted material charged in the water-cooled copper crucible, and utilizes the resistance heat generation.

  In addition to the cold crucible induction melting method, for example, an electron beam melting method or the like can be used. However, in this melting method, Ce may be removed by evaporation, so that the Ce concentration must be adjusted in a timely manner during melting.

  Next, generally, it is known that solid crystals such as solidified ingots are very easy to break in a crystal having only a complete intermetallic compound phase, and machining of a cathode member from an Ir—Ce alloy ingot is performed. It was expected to be difficult.

  Therefore, in the present embodiment, a water-cooled copper container (crucible) is used to melt and mix in an inert gas (for example, Ar) atmosphere, and the ingot obtained by solidifying it is once crushed and pulverized. The obtained powder is molded under predetermined conditions (described later) to form a fired block, which is then machined to produce a cathode member.

  In addition, since the raw material contains a large amount of cerium, which is an active element, it is desirable to crush not only in melt mixing but also in pulverization in an inert gas atmosphere, not in an air atmosphere. As a result, accidents due to exothermic combustion of the pulverized fine powder can be prevented, and oxidation of Ce generated in the atmosphere can be prevented.

  The method for pulverization is not particularly limited, and for example, pulverization can be performed by pulverization in a glove box filled with an inert gas.

  In order to obtain a powder having a maximum length of 500 μm or less after pulverization, for example, classification using a sieve can be performed. Specifically, for example, it is separated into 500 μm super powder, 100 to 500 μm powder, or 100 μm or less powder that will be coarsely pulverized powder, and the 500 μm super powder is subjected to subsequent dissolution raw materials or subsequent pulverization.

  In the cathode in which the size of the powder (crystal grains) exceeds 500 μm, cracks and chips at corners increase, and in the cathode of 500 μm or less, defects such as cracks and chips decrease.

  In addition, since the finer the crystal grains, the smaller the defects such as fine chips tend to be reduced, it is preferable that the longest length is 250 μm or less, and further 100 μm or less is desirable.

  Next, in the molding step, molding is performed at a temperature range of 800 to 1500 ° C. and a pressurization condition of 10 MPa or more using the powder having a maximum length of 500 μm or less obtained by the pulverization step as a raw material. Under such conditions, even in the raw material after molding, the crystal grains are almost the same as the size of the raw material fine powder, and the crystal grains are not coarsened during sintering.

  For the molding, for example, hot press molding using a graphite mold can be used. Other than the hot press method, for example, a discharge plasma sintering (SPS) method can also be applied.

  When the temperature of the molding condition exceeds 1500 ° C., the Ir—Ce material and the graphite material react to fuse the fired product and the graphite mold material, which may cause a problem in taking out the molded body. Further, at 800 ° C. or lower, there is a tendency that a sufficient sintered body cannot be obtained. Regarding the pressure, if it is 10 MPa or less, there is a possibility that it cannot be sufficiently densified. The pressure is preferably higher in principle, but it is preferable to apply a pressure of at least about 50 MPa. Thereby, it is considered that a cathode member processing material (hot press molding block) having a nearly true density can be obtained.

  Thus, by forming a solidified body having fine crystal grains, it is possible to obtain a material for processing a cathode member that is hard to break and easy to machine. Furthermore, micro-shrinkage defects and gas blowhole defects associated with the difference in solid-liquid density during solidification can be suppressed.

  In this embodiment, since a polycrystalline cathode containing cerium in an amount of 30% by weight or less and the balance being iridium is manufactured, the iridium-cerium raw material may finally have a desired cerium concentration. What is necessary is just to select a material.

Specifically, for example, the component can be adjusted by setting the component composition to crystallize an Ir ₂ Ce crystal phase, an Ir ₃ Ce crystal phase, an Ir ₇ Ce ₂ crystal phase, an Ir ₅ Ce crystal phase, or the like. The Ir ₂ Ce crystal phase, the Ir ₃ Ce crystal phase, the Ir ₇ Ce ₂ crystal phase, the Ir ₅ Ce crystal phase, etc. are prepared in such a ratio that the necessary crystal phase can be obtained using, for example, commercially pure Ir or pure Ce as a melting raw material. Then, an ingot of a desired crystal phase can be obtained by dissolving.

As an example, for example, when 100 g of Ir ₅ Ce crystal phase is obtained, 87.3 g of pure Ir and 12.7 g of pure Ce are used, and these raw materials are charged into a water-cooled copper crucible by a cold crucible induction melting method. And dissolve to obtain an ingot. Then, the crystal phase is identified by subsequent analysis (X-ray diffraction method), and it is confirmed whether or not the target crystal phase is obtained.

Each crystal is pulverized to prepare fine powder adjusted so that the maximum length of the powder is 500 μm or less, and Ir ₂ Ce crystal fine powder, Ir ₃ Ce crystal so that the cerium concentration is 30 wt% or less. One or more kinds of fine powder, Ir ₇ Ce ₂ crystal fine powder, and Ir ₅ Ce crystal fine powder can be weighed and used in the next molding step.

  When the above molding is performed using the fine powder of these crystal phases as a raw material, it is not always necessary to mold in a single phase, and these mixed fine powders may be produced and molded.

  Further, depending on the purpose of use of the cathode, in order to improve the characteristics, after the above powder preparation step and before the molding step, pure Ir crystal powder or the like may be further added to perform molding. After adding fine powders such as Os, Ir-Re, Ir-Os-Re, etc., after sufficiently mixing them, molding can be performed as mixed fine powders.

  For fine powders such as pure Ir crystal powder, Ir-Os, Ir-Re, Ir-Os-Re, which can be additionally used, the maximum length of crystal grains is preferably 500 μm or less, more preferably 100 μm or less. It is. The amount added is preferably about 1 to 5%.

  Next, using the obtained molded body (molded block) as a raw material, it can be machined to produce cathodes of various shapes.

  The means for machining is not particularly limited, and a known method can be used.

  For example, the wire cutting method can be applied to the cutting of the material block. Thereby, it can be set as a cylindrical body, plate shape, etc. The circular cathode can be manufactured into a cathode shape by using, for example, an electric discharge machining method, a profile grinding method, a diamond polishing method, etc., using a cylindrical body as a material.

  According to the manufacturing method of the present embodiment as described above, a cathode (cathode) member for an electron beam made of a polycrystal composed of fine crystal grains can be produced, and a higher current density can be obtained compared to the conventional method. Therefore, it is possible to manufacture a cathode (cathode) member that can extend the life.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the scope of the present invention is not limited thereto.

(Manufacture of ingots)
Dissolved so as to be an alloy in which the cerium content is 14% by weight + balance iridium (Ir-14 wt% Ce alloy) and an alloy in which the cerium content is 26% by weight + balance iridium (Ir-26 wt% alloy) Ingot (solidified body) of each alloy was prepared by blending raw iridium and pure cerium, and mixing and homogenizing by a cold crucible induction melting method using a water-cooled copper crucible of Φ60 mm in an argon atmosphere. . Then, in order to confirm whether it was an ingot of a desired crystal phase, a small sample was taken and confirmed by an X-ray diffraction method.

  In addition, the structure photograph of the melt-solidified ingot of the Ir-14 wt% Ce alloy is as shown in FIG. 1 (Photo 1), and is composed of coarse crystal grains, in which minute cracks are observed inside the crystal. It is.

  The photograph in FIG. 1 is a reflected electron image photograph taken at a magnification of 50 times with a scanning electron microscope (SEM).

(Comparative Examples 1 and 2)
An attempt was made to produce a circular cathode (Φ8 mm, Φ9 mm, Φ10 mm, etc.) from the respective ingots of the Ir-14 wt% Ce alloy and Ir-26 wt% alloy obtained above.

(Example 1)
In an inert gas (argon) atmosphere, an Ir-14 wt% Ce alloy ingot material is pulverized and pulverized, and the powder (crystal grains) becomes a coarsely pulverized powder exceeding 500 μm, 100 to 500 μm, 100 μm. The powder was separated into powders below, and only powders of 100 μm or less were used.

  Next, a hot press (HP) molding test was performed on the obtained powder using a graphite mold. The hot press molding conditions were a temperature of 1500 ° C. and a pressure of 50 MPa.

  Thereafter, a cylindrical body was cut out by wire cutting using the obtained molded body, and processed into a circular cathode member (Φ10 mm) using a profile grinding method, a diamond polishing method, or the like.

(Examples 2-3 and Comparative Examples 3-5)
In the molding, a cathode member was obtained in the same manner as in Example 1 except that the temperature and pressure were changed as shown in Table 1.

(Example 4 and Comparative Example 6)
After separating the powder (crystal grains) into a coarsely pulverized powder of 500 μm super powder, 100-500 μm powder, 100 μm or less powder, only 100-500 μm powder (Example 4) or only 500 μm super powder (Comparative Example 6) ) Was used in the same manner as in Example 1 except that a cathode member was obtained.

(Example 5)
A cathode member was obtained in the same manner as in Example 1 except that an Ir-26 wt% alloy was used instead of the Ir-14 wt% Ce alloy.

(Comparative Example 7)
A cathode member was obtained in the same manner as in Comparative Example 3 except that an Ir-26 wt% alloy was used instead of the Ir-14 wt% Ce alloy.

(Example 6 and Comparative Example 8)
Instead of the cold crucible induction melting method, an ingot was produced by a plasma arc melting method using a water-cooled copper crucible, and only 100 to 500 μm powder (Example 6) or 500 μm super powder (Comparative Example 8) was used as the powder. Except for this, a cathode member was obtained in the same manner as in Example 5.

(Example 7 and Comparative Example 9)
Further, a compact was produced by a spark plasma sintering (SPS) method using a powder having a particle size of 100 μm or less obtained by crushing and classifying a PAM ingot of an Ir-26 wt% alloy. The molding conditions were a temperature of 800 ° C. (Example 7) and 700 ° C. (Comparative Example 9), and a pressure of 10 MPa.

(Comparative Example 10)
A cathode member was obtained in the same manner as in Comparative Example 9, except that the molding conditions of temperature and pressure were changed as shown in Table 1.

(Comparative Example 11 and Comparative Example 12)
Ir-35 wt% Ce alloy powder was produced in the same manner as Ir-14 wt% Ce alloy and Ir-26 wt% alloy, using powder of 100 μm or less, molding conditions: temperature 1000 ° C, pressure The test was carried out at 10 MPa (Comparative Example 11) and 50 MPa (Comparative Example 12).

(Evaluation method)
In the above examples and comparative examples, whether or not a molded body could be produced, whether or not a cathode member could be produced, and the current density of the obtained cathode member were evaluated.
・ Evaluation of whether or not the molded body could be produced was evaluated by taking the molded body without cracks or chips when removing the sintered molded body from the graphite mold. And the case where it was fused.
・ Evaluation of whether or not the cathode member could be manufactured is ◎ if there are no cracks or chips after machining, ◯ if there are some cracks or chips after machining, but could be processed into the shape of the cathode ○ At the time of processing (or the stage before machining), it was carried out according to the criterion of x that could not be processed to the cathode shape.
And current for the density, Ir-14 wt% Ce composition Example 1 cathode of _(Ir 5 Ce crystals) and were fabricated as the melting material of the dissolving tank _Ir 5 Ce cathode (grinding step and molding step as in Example 1 The results of showing the correlation between the generated current density and the temperature when used as a hot cathode using the non-passive ones are as shown in Table 2 below.

  The above results are shown in Tables 1 and 2.

(Discussion)
First, it was machined from a melt-solidified ingot of an Ir-14 wt% Ce alloy and formed into a cathode shape. However, in the case of a circular cathode, the corner portion at the end has many chips and cracks. Also, vacancy defects occurred, and it was determined that the cathode quality was not sufficient (Comparative Example 1). Further, in the Ir-26 wt% Ce alloy, cracks and the like were generated at the stage of cutting out the cylindrical body by wire cutting for manufacturing a circular cathode, and it was not possible to process the cathode shape (Comparative Example 2). This was presumed to be due to the fact that the crystal grains of the solidified ingot were coarse and had gas blowholes, etc., and cracks occurred at the grain boundaries and propagated during machining to the cathode.

  On the other hand, in the examples, even an alloy containing 14% by weight and 26% by weight of cerium was a sound cathode member.

  In particular, it was possible to produce a good molded body under the conditions of 800 ° C. and 1500 ° C., but in the case of 1500 ° C., a molded body denser than 800 ° C. could be produced. Further, in the subsequent cutting of the cylindrical body by wire cutting and processing into the cathode shape, a cathode member having a very good surface quality and the like could be produced from the molded body at 1500 ° C.

  On the other hand, with regard to the Ir-14 wt% Ce alloy, the molded body cannot be molded well when the molding condition is 700 ° C., and the graphite mold and the molded body are fused at 1550 ° C., and there is a problem in taking out the molded body. (Comparative Example 3, Example 1, Example 2, Comparative Example 4) occurred.

  And in the cathode member which contains cerium exceeding 30 weight%, even if molding conditions were the range of this invention, the healthy cathode member was not able to be produced (Comparative Examples 11 and 12).

  Next, in Example 3 and Comparative Example 5 in which the temperature was set to 1500 ° C., the pressure was changed to 10 MPa and 5 MPa, and the powder particle diameter was hot pressed (HP) molding under a condition of 100 μm or less, the molded body was 10 MPa. On the other hand, at 5 MPa, a sufficiently densified molded body could not be obtained, and the cathode member could not be processed.

  Next, from the comparison between Example 4 and Comparative Example 6 in which the temperature was 1500 ° C., the pressure was 50 MPa, and the powder particle size was changed to 100 to 500 μm and more than 500 μm, it is possible to produce a molded body in either powder. However, when a powder of 500 μm or more is used, a cylindrical body is cut by wire cutting and cracks and chips are generated at the stage of processing into a cathode shape, and it is difficult to manufacture a healthy cathode member. all right.

  As for the Ir-26 wt% alloy, a compact molded body was obtained at 1500 ° C. in comparison with Comparative Example 7 and Example 5 in which the temperature was 1550 ° C. and 1500 ° C., the pressure was 50 MPa, and the powder particle size was 100 μm or less. Although a good cathode member could be manufactured by wire cutting, at 1550 ° C., there was a problem that a part of the powder melted into HP and oozed out of the graphite mold material. Due to the reaction, it turned out that it was not possible to produce a sound molded body.

  In addition, in the production of an Ir-26 wt% alloy ingot, even when the plasma arc melting (PAM) method using a water-cooled copper crucible or the ingot was produced, the powder particle size was 100 to 500 μm (Example 6) and more than 500 μm (comparison) Comparing Example 8), it was possible to produce a molded body with any particle size powder, but when using a powder of 500 μm or more, a cylindrical body was cut out by wire cutting and processed into a cathode shape. It was found that cracks and chipping occurred at the stage of making, making it impossible to produce a sound cathode member.

  Next, in Example 7 and Comparative Example 9 molded by the spark plasma sintering (SPS) method using a powder having a particle size of 100 μm or less obtained by crushing and classifying a PAM ingot of an Ir-26 wt% alloy, A good molded body could be produced at 800 ° C. (Example 7), but the molded body could not be molded well at 700 ° C. (Comparative Example 9).

  In Comparative Example 10, which attempted to produce a molded body by SPS under the conditions of a powder particle size of 100 μm or less, a temperature of 800 ° C., and a pressure of 5 MPa, a sufficiently densified molded body could not be obtained, and the cathode member could not be processed. It was.

Further, in the cathode member of Example 1 relating to the present invention, as is clear from Table 2, IrB manufactured by a conventionally used LaB ₆ , Ta, W cathode or a melting method (dissolving material of a melting pot). It has been shown that a high current density can be obtained even at a low cathode temperature compared to a ₅ Ce cathode.

Claims (5)

A cathode member for generating an electron beam,
Containing cerium at 30% by weight or less and the balance being iridium;
The longest length of the crystal grains constituting the cathode member is 500 μm or less,
The crystal grain is composed of at least one crystal phase selected from an Ir ₂ Ce crystal phase, an Ir ₃ Ce crystal phase, an Ir ₇ Ce ₂ crystal phase, and an Ir ₅ Ce crystal phase, Cathode member for electron beam generation.   The cathode member for generating an electron beam according to claim 1, further comprising a pure iridium crystal phase having a maximum crystal grain length of 500 μm or less. A method for manufacturing the electron beam generating cathode member according to claim 1 or 2,
Powder that has a maximum length of 500 μm or less after iridium-cerium raw material is melt-mixed and solidified in an inert gas atmosphere using a melting method using a water-cooled copper container as a melting crucible Producing a body,
An electron beam generating cathode member comprising a step of molding the obtained powder under a high temperature and high pressure condition of a temperature of 800 ° C. or higher and 1500 ° C. or lower and a pressure of 10 MPa or higher, and a step of machining the obtained molded body. Production method. An iridium-cerium raw material adjusted to a component composition for crystallizing at least one crystal phase selected from an Ir ₂ Ce crystal phase, an Ir ₃ Ce crystal phase, an Ir ₇ Ce ₂ crystal phase, and an Ir ₅ Ce crystal phase is used. A method of manufacturing an electron beam generating cathode member according to claim 3. The manufacturing method of the cathode member for electron beam generation of Claim 3 or 4 which adds a pure iridium crystal fine powder further as needed after a grinding | pulverization process, and performs a shaping | molding process after that.