JP2015040692A - Molybdenum crucible for metal evaporation and manufacturing method and use method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molybdenum crucible for metal evaporation hard to react with a molten metal at high temperature.SOLUTION: A molybdenum crucible for metal evaporation is subjected to carbonization in a state where the inner wall surface of a crucible substrate 1-a composed of molybdenum has at least approximate 800°C or more, and thus a surface layer becomes molybdenum carbide 1-b. Since the contact angles of the surface layer of the molybdenum carbide and many molten metals 5 is beyond 100 degrees at 1000°C and wettability relatively becomes worse, react with the molten metal can be suppressed.

Description

The present invention relates to a metal evaporation molybdenum crucible having a surface layer excellent in corrosion resistance against molten metal. In addition, it relates to the manufacturing method and the usage method.

When the temperature of the metal is raised to a high temperature for the purpose of evaporating the metal, it becomes a molten state when a certain temperature is exceeded, and a container having a recess for holding the molten metal is required. The high temperature holding container is generally made of a material that does not melt or deform at a high temperature and does not easily react with a molten metal or alloy.
Molybdenum has a high melting point of 2430 ° C. and is excellent in corrosion resistance against many molten metals. For example, as described in Patent Document 1, as a crucible for metal evaporation or a crucible for producing a sapphire single crystal, Widely used in the past.

Patent Document 2 discloses that ceramics and glass are melted and therefore suitable as a molybdenum crucible having a porosity of 0.8 to 8%. There is a description that by setting the porosity within this range, the strength is hardly deteriorated and the heat stress resistance can be maintained.

Patent Document 3 discloses a technique in which a melting crucible is made of molybdenum containing La or a compound thereof instead of molybdenum alone. This crucible has a small amount of deformation, does not contain components that become gas impurities like molybdenum with conventional aluminum, silicon, and potassium added. There is a description. Therefore, there is a description that it is particularly excellent as a crucible for dissolving metals and oxides at 1800 ° C. or higher.

Patent Document 4 discloses a crucible in which molybdenum crystal grains are hardly coarsened by adding 1 to 5% by weight of tungsten to molybdenum. There is a description that the crucible is not easily weakened due to the coarsening of the particles, and the content is hardly leaked out, which is suitable for high temperature use at 1800 ° C. or higher. As an example, a crucible for producing a single crystal is shown.

JP 2003-060348 A JP-A-53-070012 JP-A-63-171847 JP 09-196570 A

The present invention has been made to solve the above-described problems, and it is an object of the present invention to provide a molybdenum crucible for metal evaporation that hardly reacts with molten metal at a high temperature necessary for metal evaporation.

The techniques disclosed in Patent Documents 1 to 4 all relate to molybdenum crucibles used at high temperatures, and are used in containers for melting and evaporating ceramics such as metal and sapphire. It has been improved by focusing on the weakening of the molybdenum material at high temperature. In particular, the cited document 1 describes the use of metal evaporation.

However, none of the documents describes the reaction between the molten metal and the crucible when melting the metal. This is because even if the grain boundary strength of molybdenum is increased or the coarsening of particles at high temperatures is prevented, alloying with aluminum, nickel, scandium, etc. occurs independently of the strength. It cannot be used as a crucible for melting or evaporating metals.

Molybdenum has a melting point of 2620 ° C., which is higher in the metal, and its boiling point is as high as 4600 ° C. or higher. Further, the vapor pressure is as low as 1 × 10 ⁻² (Pa) at 2530 ° C., and it has excellent characteristics as a high temperature material. However, usually, a single metal is highly reactive especially at a high temperature, and when two or more metals come into contact with each other at a high temperature, many of them are alloyed and dissolved. Making the metal evaporation crucible made of metal may cause alloying or solid solution with the crucible and the metal to be evaporated, leading to breakage of the crucible. In particular, in order to melt a metal and obtain a certain amount of evaporation, a temperature higher than the melting point is usually required, and a treatment at a higher temperature is required as the evaporation efficiency is increased. Therefore, when considering an evaporation crucible for evaporating a metal or an alloy, it is necessary to mainly examine “reaction between the metal and the evaporation crucible”.

The molybdenum crucible for metal evaporation of the present invention is converted to molybdenum carbide by carbonizing at least a portion of the crucible base made of molybdenum that is in contact with the molten metal at about 800 ° C. or more, and almost reacts with many metals and alloys. do not do. This molybdenum carbide is typically MoC, but molybdenum carbide having a different ratio of Mo and C, such as Mo ₂ C, may occupy part or all of it. Except for the carbonized layer, it is molybdenum without change.

  Molybdenum carbide (MoC) has a melting point of about 2430 ° C., which is higher than the temperature at which the vapor pressure of many metals becomes sufficiently high (that is, the use temperature). Therefore, not only melting but also deformation is small.

  Further, since the contact angle between the surface layer of molybdenum carbide and many molten metals exceeds 100 ° at 1000 ° C. and has relatively low wettability, the reaction with the molten metal can be suppressed.

Examples of metals to be evaporated include Ag (silver), Al (aluminum), Au (gold), Ba (barium), Be (beryllium), Ce (cerium), Co (cobalt), Cr (chromium), Cu (Copper), Fe (iron), Ge (germanium), In (indium), La (lanthanum), Mn (manganese), Ni (nickel), Pd (palladium), Sc (scandium), Sn (tin), Ti (Titanium), U (uranium), Y (yttrium) and the like. These metals have a melting point of about 660 to 1750 ° C., and the temperature at which the vapor pressure becomes 10 ⁻² (torr) is at most 1900 ° C. The molybdenum crucible of the present invention is sufficient as these metal evaporation crucibles. Can be used. Moreover, the metal which evaporates is not restricted to the above-mentioned metal simple substance, but can also use those alloys.

The metal evaporation molybdenum crucible of the present invention can be used in a reduced pressure atmosphere including a vacuum atmosphere, a nitrogen atmosphere, a hydrogen gas atmosphere, an inert gas (such as a rare gas or CO ₂ gas) atmosphere, or the like. The oxygen-containing atmosphere may oxidize the molybdenum of the crucible base material for evaporation and the molybdenum carbide of the surface layer thereof, and is not desirable, and has a high risk of generating oxides and metal or alloy components to be evaporated. A vacuum atmosphere is often used because the lower the pressure of the atmosphere, the higher the evaporation rate of the metal and the higher the productivity.

Molybdenum used for the base material for the evaporation crucible has a thermal conductivity of 138 (W / m · K), which is relatively high among metals, and molybdenum carbide in the surface layer is also 50 to 70 (W / m · K) (MoC ) And relatively high thermal conductivity among ceramics. Moreover, since molybdenum carbide is only a surface layer, it is extremely small as an inhibition of heat conduction. Therefore, even if the heating method is such that the molybdenum crucible for metal evaporation is heated and the heat is conducted to the metal, the temperature of the crucible and the metal tends to work together. Therefore, the temperature control of the metal is easy and the temperature follow-up is fast, so that the productivity can be increased.

In the present invention, a molybdenum crucible for metal evaporation that hardly reacts with molten metal is provided by carbonizing at least a portion of the molybdenum crucible that is in contact with the molten metal.

It is a figure which shows the molybdenum crucible for metal evaporation which carbonized the crucible inner wall surface as an example of this invention. It is a figure which shows the molybdenum crucible for metal evaporation which carbonized the whole crucible surface as another example of this invention. It is a figure which shows an example of the metal evaporation method of this invention.

  As a molybdenum crucible for metal evaporation, a crucible-shaped molybdenum sintered body having a density of 90% or more is prepared as a base material. As for the component, it is better not to contain a metal component having a low melting point other than molybdenum (excluding metals having a higher melting point than Mo such as W) as much as possible. When the metal component is present as a simple substance or an alloy, it may evaporate and evaporate together with the metal, and may be mixed into the molten metal. An acceptable low-melting-point metal is approximately 1000 ppm or less by mass, and in particular close to 0 is desirable as an evaporation crucible. On the other hand, transition metal carbides, nitrides, and carbonitrides may be contained within a range of 3 mass% or less. Above this, it is not desirable because it significantly affects the thermal conductivity.

  A molybdenum carbide layer is formed at least at a position in contact with the molten metal crucible for metal evaporation described above. As a carbonization method, a powder containing carbon as a carbon source is placed around a crucible and heated to 800 to 2500 ° C. in a non-oxidizing atmosphere. A crucible is placed in a carbon container and heated to 800 to 2500 ° C. in a non-oxidizing atmosphere. Either a liquid containing carbon is applied to the crucible and heated to 800-2500 ° C. in a non-oxidizing atmosphere, or heated to 800-2500 ° C. in a non-oxidizing atmosphere using an organic gas, etc. may be selected. The method is not limited as long as at least a portion of the crucible that contacts the molten metal can be carbonized.

The part to be carbonized may be only the part in contact with the molten metal, or the entire surface of the crucible. The carbonized layer may be MoC, or may be a simple substance of molybdenum carbide having a different ratio of Mo and C, or a mixture thereof. The thickness of the carbonized layer needs to be such that metal molybdenum is not exposed to the surface at least in a portion in contact with the molten metal. This thickness is about 0.1 μm. In addition, when the entire crucible is carbonized, the thermal conductivity is lowered, and cracking and peeling are caused by the volume change. Therefore, a carbonized layer thickness of 500 μm or less is preferable.

  In the molybdenum crucible for metal evaporation obtained as described above, the metal in the solid state is placed in the recess, and is put into the evaporation furnace.

  Next, one or both of the crucible and the metal are heated. A known method may be used as a heating method, but it can be roughly divided into a method of directly heating a metal or an alloy like electron beam heating and a method of heating a metal by conduction of heat by heating a crucible. The molybdenum crucible for metal evaporation of the present invention can be used in any method. Specific examples include high-frequency induction heating, heating with a heater such as carbon or molybdenum, electron beam heating, laser heating, microwave heating, energization heating to a crucible, arc discharge heating, and the like.

In addition, the atmosphere during heating (1) does not react with the evaporating metal, (2) does not react with the crucible, and (3) the characteristics that the evaporation amount can be increased to a certain level or more are required.

Most suitable is a non-oxidizing and reduced pressure atmosphere. Since the evaporation amount depends on the temperature and the atmosphere, the evaporation efficiency is high when a reduced pressure or vacuum atmosphere is used. It is also possible to adjust the evaporation amount by flowing a certain amount of an inert gas such as a rare gas. On the other hand, an atmosphere containing oxygen is undesirable because it reacts with a metal evaporation molybdenum crucible containing molybdenum as a main component to produce an oxide. In addition, a gas such as nitrogen may be used if it does not produce a reactive organism with the metal to be evaporated.

Example 1
Molybdenum powder having an average particle diameter of 3 μm, a purity of 99.9% or more and a metal impurity ratio of 500 ppm or less was used as a starting material for the molybdenum crucible for evaporation.

  Molybdenum powder was molded at 100 MPa to obtain a cylindrical press body. Subsequently, a blind hole was drilled with a milling machine in the center of one end face of the obtained pressed body.

The sample was put into a sintering furnace, and sintered in a H ₂ gas flow at a maximum temperature of 2100 ° C. for 180 minutes.

The obtained sintered body is processed into a tapered bowl shape as shown in FIG. 1 using a lathe, and then a liquid in which carbon is dispersed is applied to the entire inner wall surface of the crucible including the portion in contact with the molten metal. In an H ₂ gas flow, heating was performed at 1600 ° C. to obtain a molybdenum crucible for metal evaporation whose inner wall surface was carbonized with a thickness of 5 μm. When this carbonized layer was analyzed by an X-ray diffraction method, it was a MoC phase.

As shown in FIG. 3, the obtained molybdenum crucible for evaporation was placed in a high-frequency induction heating type evaporation furnace 10 with the crucible side facing up. This evaporation furnace is provided with a vacuum pump 2 for reducing the pressure and a vacuum atmosphere, and a film formation target 3 for forming a film with evaporated metal or alloy is provided above the metal evaporation molybdenum crucible. High frequency induction is performed by the coil 4.

  Nickel powder was put into the blind hole of the metal evaporation molybdenum crucible, the vacuum pump was operated, and then the temperature was raised by a high frequency induction heating method.

The melting point of nickel is about 1455 ° C., and the vapor pressure can be sufficiently increased near the melting point. The melted nickel is 5 in FIG. The temperature of the molten nickel was measured by a temperature sensor (not shown) and set so as to maintain a constant temperature at 1600 ° C. As a result, a nickel film could be formed at a sufficient rate on the film formation target 3, and no components other than nickel were detected from the formed film. The molybdenum crucible for metal evaporation can be used for a long time with few defects such as deformation and reaction even after repeated use.

(Example 2)
Using the same molybdenum powder as in Example 1, the molybdenum powder was molded at 100 MPa, put into a sintering furnace, and sintered in a H ₂ gas flow at a maximum temperature of 2100 ° C. for 180 minutes. did. After forging the obtained sintered body and processing it into a tapered bowl shape as shown in FIG. 2, it was put into a carbon container and heated at 1400 ° C. in an H ₂ gas flow, and the entire surface was A molybdenum crucible for evaporation having a thickness of 2 μm was obtained. When this carbonized layer was analyzed by an X-ray diffraction method, it was a MoC phase and a Mo ₂ C phase.

  With the molybdenum crucible for evaporation spread upward, aluminum powder was charged therein, and after operating the vacuum pump, the temperature was raised by high frequency induction heating.

  The melting point of aluminum is 660 ° C., and the vapor pressure can be extremely increased near 1300 ° C. The molten aluminum is 5 in FIG. The temperature of the molten aluminum was measured by a temperature sensor (not shown) and set to be kept at a constant temperature at 1300 ° C. As a result, an aluminum film could be formed at a sufficient rate on the film formation target 3, and no components other than aluminum were detected from the formed film.

  Compared to Example 1, since the entire surface was carbonized, the reaction of raising and lowering took some time, but the carbonization treatment could be manufactured more easily.

Even when the metal evaporation molybdenum crucible was repeatedly used for several tens of hours, defects such as deformation and reaction hardly occurred, and it could be used without any problem.

Example 3
Using the same molybdenum sintered body as in Example 1, heating was performed at a maximum temperature of 1800 ° C. in a CH ₄ gas flow to obtain a molybdenum crucible for evaporation whose entire surface layer was carbonized by about 150 μm. When this carbonized layer was analyzed by an X-ray diffraction method, it was a Mo ₂ C phase.

  Scandium powder was put into a molybdenum crucible for metal evaporation, and after operating the vacuum pump, the temperature was raised by a high frequency induction heating method.

  The melting point of scandium is 1541 ° C., and the vapor pressure can be sufficiently increased near the melting point. The melted scandium is 5 in FIG. The temperature of molten manganese was measured with a temperature sensor (not shown), and was set to maintain a constant temperature at 1300 ° C. As a result, a film of scandium could be formed at a sufficient rate on the film formation target 3, and components other than scandium were not detected from the formed film.

The molybdenum crucible for metal evaporation could be used without any problems, such as deformation and reaction, even after repeated use.

(Comparative example)
As a comparative example, nickel powder was put into a metal evaporation molybdenum crucible having the same shape as that described above, which was not carbonized, and heated and formed under the same conditions as in Example 1. The nickel powder could be melted and evaporated, but at the same time it melted, the nickel molten metal and the molybdenum crucible started to react, forming an intermetallic compound, and cracking occurred in a part of the crucible, which could be reused. It became difficult. Actual use is considered unsuitable.

DESCRIPTION OF SYMBOLS 1-a Molybdenum crucible base material for metal evaporation 1-b Molybdenum carbide layer 2 Vacuum pump 3 Film-forming object 4 Heating coil 5 Metal 6 Gas supply part 10 Evaporating furnace

Claims (7)

  A molybdenum crucible for metal evaporation, having a molybdenum carbide layer at least in contact with the molten metal.   The molybdenum crucible for metal evaporation according to claim 1, wherein the entire surface has a molybdenum carbide layer.   The molybdenum crucible for metal evaporation according to claim 1, wherein the molybdenum carbide layer has a thickness of 0.1 to 500 μm. The molybdenum crucible for metal evaporation according to any one of claims 1 to 3, wherein the molybdenum carbide contains one or both of MoC and Mo ₂ C.   A method for producing a molybdenum crucible for metal evaporation, wherein a molybdenum carbide layer is formed by carbonizing at least a portion of a crucible-shaped molybdenum in contact with a molten metal at 800 to 2500 ° C.   6. The method for producing a molybdenum crucible for metal evaporation according to claim 5, wherein the carbon source for carbonization is one or more of solid, powder, liquid and organic gas containing carbon.   Heat the metal evaporation molybdenum crucible and / or the metal with a heating device in a reduced pressure or vacuum atmosphere to maintain the metal melt at 600 ° C or higher, and generate the metal vapor from the melt. A method of using a molybdenum crucible for evaporating metal having a molybdenum carbide layer at least at a location in contact with the molten metal.

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