JP2004084069A - Inorganic oxide coated metal powder and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide inorganic oxide coated metal powder having shrinkage resistance, and to provide its manufacturing method. <P>SOLUTION: The inorganic oxide coated metal powder has an inorganic oxide layer on the surface of particles of metal powder and the inorganic oxide layer is constituted of silicon oxide, aluminum oxide, magnesium oxide, etc., and in which the diameter of crystallites of the metal powder particles is ≥50 nm. In the method for manufacturing the inorganic oxide coated metal powder, the inorganic oxide is caused to adhere to the surface of the metal powder particles by a mechanochemical technique to form the inorganic oxide layer on the surface of the particles and then heat treatment is carried out to regulate the diameter of the crystallites of the metal powder to ≥50 nm. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The invention according to the present application relates to an inorganic oxide-coated metal powder and a method for producing the inorganic oxide-coated metal powder. It is an object of the present invention to provide an inorganic oxide-coated metal powder particularly suitable for ceramic material applications.
[0002]
[Prior art]
Conventionally, copper powder and silver powder have been widely used as raw materials for copper paste and silver paste and as raw materials for low-temperature fired ceramic substrates. Because of the ease of handling, the former metal paste has been used to easily form a conductor circuit in a wide range from use for experimental purposes to use in the electronics industry. For example, there are a method of adjusting a sample of an electron microscope, a routing of a conductor circuit of a printed wiring board, a formation of an interlayer conduction conductor as a substitute for a through hole for obtaining an interlayer conduction of a multilayer printed wiring board, and an electrode formation of a ceramic capacitor. Among various uses, particularly when used for a low-temperature fired ceramic substrate, dimensional stability when processed into a green sheet and sintered is an important issue.
[0003]
The production of such metal powder for low-temperature firing ceramics can be roughly classified into a dry production method and a wet production method. It is reasonable to think that the latter wet manufacturing method is a method of manufacturing by directly depositing metal powder from a solution containing a target metal element. Therefore, the former dry manufacturing method includes not only a pulverization method using a completely mechanical method but also an atomizing method using a molten metal.
[0004]
As a feature of the metal powder obtained by these methods, the metal powder obtained by the former dry manufacturing method has a relatively large crystallite diameter of 40 to 50 nm, and the metal powder is fired at a low-temperature firing ceramic substrate. It has the advantage of excellent oxidation resistance and shrinkage resistance in such cases. On the other hand, metal powder produced by the wet production method generally has a crystallite diameter of 35 nm or less and is smaller than metal powder obtained by the dry production method, and is resistant to oxidation during firing of a low-temperature fired ceramic substrate. It has the drawback of poor heat resistance and shrink resistance. It is said that shrink resistance depends on the size of crystallites of the metal powder. That is, the larger the crystallite diameter, the smaller the shrinkage when heated at a high temperature and the more excellent the shrinkage resistance.
[0005]
The metal powder referred to in the present specification is used for producing a metal powder-containing slurry, and is mainly used for applications in which a green sheet of a low-temperature fired ceramic is processed and fired to obtain a low-temperature fired ceramic. Therefore, a metal powder that is easily oxidized and has poor oxidation resistance significantly alters the quality of a low-temperature fired ceramic. Furthermore, when the crystallite diameter is small, the shrinkage is large and the metal powder is inferior in shrinkage resistance. Is difficult to maintain satisfactorily. Considering these facts, it seems to be desirable to use metal powder produced by a dry production method.
[0006]
[Problems to be solved by the invention]
However, as a characteristic of the powder obtained by the dry production method, there is a defect that the particle size distribution is broad and it is difficult to produce a fine powder with high accuracy. In recent years, the demand for the finishing accuracy of the surface of low-temperature fired ceramics has become more and more severe, and the weight cumulative particle size D by the laser diffraction scattering type particle size distribution measuring method has been increasing. ₅₀ The demand for metal powder having a narrow particle size distribution with a value of 10 μm or less and excellent in dispersibility is becoming remarkable.
[0007]
In addition, even in the case of such fine metal powder, it is desired in the market that the powder is excellent in oxidation resistance during firing of low-temperature fired ceramics and shrinkage resistance with small shrinkage behavior during firing. It has come. In order to satisfy this requirement, it is desirable to satisfy these requirements by using a metal powder having a fine particle size and a sharp particle size distribution obtained by a wet manufacturing method.
[0008]
When the crystallite diameter of the metal powder obtained by the wet method is to be increased in order to improve the shrinkage resistance, the metal powder is heated to grow the grain size inside the powder particle. Just fine. Therefore, it is considered that the metal powder obtained by the wet method may be simply heated.
[0009]
However, simply heating in the state of ordinary metal powder oxidizes the surface of the metal powder, forms an oxide film on the surface, and causes a remarkable agglomeration state. Properties will be significantly impaired. The use of such powders in the production of low-temperature fired ceramics results in a rough surface condition of the resulting low-temperature fired ceramic. Therefore, by simply heating ordinary copper powder, it is possible to provide metal powder having both excellent oxidation resistance and shrinkage resistance, sharp particle size distribution, and small particle size while securing the dispersibility of the powder particles. It was difficult.
[0010]
[Means for Solving the Problems]
Therefore, as a result of earnest research, the present inventors have found that it is possible to obtain a metal powder having a large crystallite diameter by pre-coating the metal powder obtained by the wet manufacturing method with an inorganic oxide layer. It came to mind. Hereinafter, the present invention will be described.
[0011]
In the claims, "an inorganic oxide-coated metal powder having an inorganic oxide layer on the surface of the metal powder particles, wherein the inorganic oxide layer comprises silicon oxide, aluminum oxide, magnesium oxide, zirconium oxide, zinc oxide. And an inorganic oxide-coated metal powder characterized in that the metal powder has a crystallite diameter of 50 nm or more. " That is, the structure is such that an inorganic oxide layer is provided on the surface of a metal powder particle having a crystallite diameter of 50 nm or more. By making the crystallite diameter larger than the crystallite diameter of the metal powder obtained by the conventional wet manufacturing method, it becomes possible to improve the shrink resistance.
[0012]
The metal powder at this stage is not particularly limited as long as it is a metal material that can be used for the low-temperature fired ceramic. However, in view of the powder characteristics required for metal powders used in the production of low-temperature fired ceramics in recent years, it is preferable to use either copper powder or silver powder obtained by a wet production method.
[0013]
The inorganic oxide layer uses any one of silicon oxide, aluminum oxide, magnesium oxide, zirconium oxide, and zinc oxide. Among them, it is preferable to use any of silicon oxide, aluminum oxide, and magnesium oxide. Zinc oxide is particularly preferable when silver powder is used for the core material. Silicon oxide, aluminum oxide, and magnesium oxide are easily fixed to the surface of the metal powder particles uniformly. In addition, at the same time, considering that the firing temperature of the low-temperature fired ceramic is generally 900 ° C. or higher, it functions most effectively as a barrier layer for preventing aggregation of metal powder as a core material.
[0014]
However, it is difficult to physically indicate the thickness of the inorganic oxide layer as a gauge thickness because of the nature of metal powder which is an aggregate of fine powder particles. Accordingly, the present inventors have determined that the thickness of the inorganic oxide layer is represented as a reduced mass thickness. The reduced mass thickness is expressed as a percentage by mass of the inorganic oxide layer in the weight of the inorganic oxide-coated metal powder. Strictly speaking, when applying the reduced mass thickness, it is necessary to consider the particle size of the metal powder. If the weight of the metal powder is constant and there is a metal powder with a small particle size and a metal powder with a large particle size, the former has a larger specific surface area, and the same amount of inorganic oxide covers the surface of the powder. This is because the former method makes the former inorganic oxide layer of metal powder thinner.
[0015]
Therefore, the present inventors consider the particle size of the metal powder required for the current low-temperature fired ceramics and consider the weight cumulative particle size D by a laser diffraction scattering type particle size distribution measuring method. ₅₀ The thickness (converted mass thickness) of the inorganic oxide layer in the case of a metal powder having a value of 0.1 μm to 10 μm is 0.1 mass of the inorganic oxide coated metal powder. % To 10% by mass.
[0016]
When the coating amount is less than 0.1% by mass, it does not serve as a barrier layer for preventing the progress of agglomeration of powder particles due to heating during firing of the low-temperature fired ceramic. On the other hand, when the thickness exceeds 10% by mass, the dispersibility of the obtained inorganic oxide-coated metal powder becomes poor. By forming the inorganic oxide layer having such a uniform thickness, the inorganic oxide-coated metal powder according to the present invention does not have conductivity by itself. Further, in order to ensure stable non-conductivity by eliminating manufacturing variations and to stabilize the obtained shrink resistance, it is more preferable to employ 1% by mass to 10% by mass. By adopting the coating amount of the inorganic oxide as described above, sufficient heat treatment can be performed for the first time, so that the crystallite diameter can be adjusted.
[0017]
The production of the inorganic oxide-coated metal powder described above is performed by the following method. The method for producing an inorganic oxide-coated metal powder for forming a conductive circuit according to the present invention comprises the steps of: fixing an inorganic oxide to the surface of the metal powder by a mechanochemical method; The method is characterized in that a crystallite diameter of the metal powder is adjusted to 50 nm or more by forming an oxide layer and performing heat treatment. That is, by coating the surface of the metal powder with the inorganic oxide layer, the heat treatment temperature can be set high. As a result, the crystallite diameter can be made equal to or larger than the crystallite diameter of the metal powder obtained by the dry manufacturing method.
[0018]
In this manufacturing method, "to fix the inorganic oxide to the surface of the metal powder particles by a mechanochemical method" means that the metal powder and the inorganic oxide powder to be fixed to the surface thereof are: The inorganic oxide is fixed to the surface of the metal powder particles by stirring and mixing or using a ball mill type medium, and the metal powder particles and the inorganic oxide powder particles are mixed and collided. Any device capable of performing such operations is sufficient, and does not require special equipment. The inorganic oxide powder used at this time has a specific surface area of 50 m. ² / G or more is preferably used. This specific surface area mainly depends on the particle diameter of the inorganic oxide powder, and it can be said that the larger the specific surface area, the smaller the particle diameter.
[0019]
The heat treatment is performed under the following conditions. Strictly speaking, the condition is changed according to the type of the metal powder. This heat treatment promotes so-called recrystallization and increases the crystallite diameter. However, this heat treatment must not promote aggregation of the surface of the metal powder itself so as not to deteriorate the quality of the inorganic oxide-coated metal powder.
[0020]
In consideration of these facts, when copper powder is used as the metal powder, the heat treatment is desirably performed in a reducing atmosphere or an inert gas atmosphere at 500 ° C. to 1000 ° C. Heating at a temperature lower than 500 ° C. makes it difficult to recrystallize crystals of the copper powder obtained by the wet production method. On the other hand, when the heating is performed at a temperature exceeding 1000 ° C., even if the inorganic oxide layer is present, the aggregation of the copper powder as the core material progresses, and the copper powder itself is softened to form a powder. Will worsen. Since copper itself tends to be very easily oxidized, it is preferable to employ a reducing atmosphere or an inert gas atmosphere as a heating atmosphere.
[0021]
When silver powder is used as the metal powder, the heat treatment is preferably performed at a temperature of 350 ° C. to 900 ° C. in any one of an air atmosphere, a reducing atmosphere, or an inert gas atmosphere. This heat treatment is performed for the purpose of adjusting the crystallite diameter and vaporizing and degassing organic impurities contained in the silver powder and causing thermal expansion. Therefore, when the heating is performed at a temperature lower than 350 ° C., the degassing treatment of impurities cannot be performed satisfactorily, and it becomes difficult to recrystallize silver powder crystals obtained by a wet production method. On the other hand, when heating is performed at a temperature exceeding 900 ° C., even if the inorganic oxide layer is present, the oxidation progresses significantly to the surface of the silver powder as the core material, and the silver powder itself is softened. The powder shape will be degraded. Since silver is harder to oxidize than copper, it is possible to use an air atmosphere for the heating atmosphere. Naturally, a reducing atmosphere or an inert gas atmosphere can also be used to increase the safety of quality. It is preferable if you think about it.
[0022]
By adopting such a manufacturing method, it is possible to prevent the agglomeration of the inorganic oxide-coated metal powder from progressing, and to obtain the “average particle diameter D by a laser diffraction scattering type particle size distribution measuring method”. ₅₀ Formula SD / D between the particle size distribution and the standard deviation SD ₅₀ The process variation index CV value represented by × 100 ”can be prevented from being deteriorated. The “standard deviation SD” is a standard deviation obtained from a particle size distribution of a powder obtained as a result of measurement using a laser diffraction scattering type particle size distribution measuring method, and the value of this CV value is small. This means that the powder particles have a uniform particle size, are excellent in dispersibility, and do not have a large variation.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to a comparative example through embodiments.
[0024]
First Embodiment First, a method for producing copper powder used as a core material will be described. 4 kg of copper sulfate (pentahydrate) and 120 g of aminoacetic acid were dissolved in water to prepare an 8 L (liter) aqueous solution of copper salt at a liquid temperature of 60 ° C. Then, while stirring the aqueous solution, 5.75 kg (1.15 equivalents) of a 25 wt% sodium hydroxide solution was quantitatively added over about 30 minutes, and the mixture was stirred at a liquid temperature of 60 ° C. for 60 minutes. Aged until the color was completely black to produce cupric oxide. Thereafter, the mixture was left for 30 minutes, 1.5 kg of glucose was added, and the mixture was aged for 1 hour to reduce cupric oxide to cuprous oxide. Further, 1 kg of hydrated hydrazine was quantitatively added over 5 minutes to reduce cuprous oxide to obtain metallic copper, thereby producing a copper powder slurry.
[0025]
Then, the obtained copper powder slurry was filtered, sufficiently washed with pure water, filtered again, and dried to obtain a copper powder. The weight cumulative particle size D of the copper powder measured by a laser diffraction scattering particle size distribution measuring method ₅₀ Was 0.93 μm, the process variation index CV was 0.22, and the crystallite diameter was 32.2 nm. As a result of measuring the coefficient of thermal expansion, the shrinkage at 900 ° C. was 13.0%.
[0026]
The measurement of the crystallite diameter in the present specification is obtained by using RINT200V manufactured by RIGAKU and using an average crystallite diameter using crystallite analysis software. The crystallite diameter in the present specification means the average crystallite diameter. It is the diameter of the child. The shrinkage ratio is measured by putting 20 g of the powder used for the measurement in 20 g of a solution of 95 wt% of terpineol C and 5 wt% of ethyl cellulose, kneading with a three-roll mill, and then heating at 80 ° C. for 1 hour. It was dried and made into a powder again. Then, the obtained powder was continuously heated in a predetermined atmosphere using a thermomechanical analyzer (TMA / SS6000 manufactured by Seiko Denshi Kogyo KK) at a rate of temperature increase of 10 ° C./min while continuously measuring the coefficient of thermal expansion. Then, the thermal shrinkage when the ambient temperature was 900 ° C. was measured.
[0027]
Then, 1 kg of the copper powder and 0.05 kg of the silicon oxide powder, which is an inorganic oxide, are subjected to a mechanochemical fixing treatment at 6,000 rpm for 5 minutes using a hybridizer to produce silicon oxide-coated copper powder. did. At this stage, the coating amount of the silicon oxide coated on the surface of the silicon oxide-coated copper powder was 5% by mass. The weight-accumulated particle diameter D of the silicon oxide-coated copper powder before heating is measured by a laser diffraction scattering particle size distribution measuring method. ₅₀ Was 0.94 μm, the process variation index CV was 0.25, and the crystallite diameter was 28.2 nm. As a result of measuring the thermal expansion coefficient, the shrinkage at 900 ° C. was 6.3%. In other words, the copper powder is subjected to mechanochemical processing, so that the crystallite diameter is smaller than that of the copper powder obtained by the original wet manufacturing method, but the thermal expansion is caused by the presence of the oxide coating layer. Although the shrinkage at the time was small, it did not reach the shrinkage within the range required by the market.
[0028]
Thus, the silicon oxide-coated copper powder obtained as described above is heated at 500 ° C., 700 ° C., and 900 ° C. for 1 hour in a nitrogen gas atmosphere having a hydrogen concentration of 1 wt% to reduce the crystallite diameter. Three types of adjusted silicon oxide-coated copper powder were obtained. As a result, (1) when a temperature of 500 ° C. was adopted, the weight cumulative particle diameter D of the heated silicon oxide-coated copper powder measured by a laser diffraction scattering particle size distribution method ₅₀ Is 0.92 μm, the crystallite diameter is 52.6 nm, the process variation index CV value is 0.24, and (2) when a temperature of 700 ° C. is adopted, the silicon oxide-coated copper powder after heating is Weight cumulative particle size D by laser diffraction scattering type particle size distribution measurement method ₅₀ Is 0.93 μm, the crystallite diameter is 58.4 nm, the process variation index CV value is 0.25, and (3) when the temperature of 900 ° C. is adopted, the silicon oxide-coated copper powder after heating is Weight cumulative particle size D by laser diffraction scattering type particle size distribution measurement method ₅₀ Was 0.94 μm, the crystallite diameter was 66.8 nm, and the process variation index CV value was 0.24.
[0029]
From these results, when the crystallite diameter was 500 ° C. and 700 ° C., a crystallite diameter equivalent to that of copper powder obtained by the dry manufacturing method was obtained. It can be seen that a crystallite diameter larger than the copper powder obtained by the production method was obtained. In addition, it can be seen that the CV value of the copper powder before the formation of the inorganic oxide layer did not significantly deteriorate regardless of the heating temperature.
[0030]
Furthermore, the thermal expansion coefficient was measured in the same manner as described above using three types of silicon oxide-coated copper powder. As a result, the shrinkage at 900 ° C. was (1) the heating temperature of 500 ° C. In this case, the shrinkage ratio of the silicon oxide-coated copper powder after heating is 2.5%, and (2) the shrinkage ratio of the silicon oxide-coated copper powder after heating is 2.0% when a heating temperature of 700 ° C. is adopted. (3) When a heating temperature of 900 ° C. is employed, the shrinkage ratio of the silicon oxide-coated copper powder after heating is 1.2%, and all are within the ideal shrinkage ratio of 3% or less. .
[0031]
Second Embodiment: The copper powder used in this embodiment is obtained by the same manufacturing method as that used in the first embodiment, and therefore, description thereof is omitted here to avoid redundant description. That is, the weight cumulative particle diameter D of the laser diffraction scattering particle size distribution measuring method ₅₀ Is 0.93 μm, the process variation index CV value is 0.22, the crystallite diameter is 32.2 nm, and the shrinkage ratio at 900 ° C. is 13.0%.
[0032]
Then, 1 kg of this copper powder and 0.03 kg of aluminum oxide powder, which is an inorganic oxide, are subjected to a mechanochemical fixing treatment at 6000 rpm for 5 minutes using a hybridizer to produce aluminum oxide-coated copper powder. did. The coating amount of aluminum oxide coated on the surface of the aluminum oxide-coated copper powder at this stage was 3% by mass. The weight cumulative particle size D of the aluminum oxide-coated copper powder before heating by the laser diffraction scattering particle size distribution measurement method ₅₀ Was 0.92 μm, the process variation index CV was 0.25, and the crystallite diameter was 27.8 nm. As a result of measuring the thermal expansion coefficient, the shrinkage at 900 ° C. was 4.2%. In other words, the copper powder is subjected to mechanochemical processing, so that the crystallite diameter is smaller than that of the copper powder obtained by the original wet manufacturing method, but the thermal expansion is caused by the presence of the oxide coating layer. Although the shrinkage at the time was small, it did not reach the shrinkage within the range required by the market.
[0033]
Therefore, the aluminum oxide-coated copper powder obtained as described above was heated at 900 ° C. for 1 hour in a reducing atmosphere having a hydrogen concentration of 1 wt% to adjust the crystallite diameter. As a result, the weight-accumulated particle diameter D of the heated aluminum oxide-coated copper powder was measured by a laser diffraction scattering particle size distribution measuring method. ₅₀ Was 0.93 μm, the crystallite diameter was 68.0 nm, and the process variation index CV value was 0.26. It can be seen that the crystallite diameter is larger than the copper powder obtained by the dry production method. Further, the coefficient of thermal expansion was measured using the above-described aluminum oxide-coated copper powder in the same manner as described above. As a result, the shrinkage at 900 ° C. was 0.6%, and the shrinkage was within 3%. It was in.
[0034]
Third Embodiment The copper powder used in this embodiment is obtained by the same manufacturing method as that used in the first embodiment, and therefore, description thereof will be omitted to avoid redundant description. That is, the weight cumulative particle diameter D of the laser diffraction scattering particle size distribution measuring method ₅₀ Is 0.93 μm, the process variation index CV value is 0.22, the crystallite diameter is 32.2 nm, and the shrinkage ratio at 900 ° C. is 13.0%.
[0035]
Then, 1 kg of this copper powder and 0.03 kg of magnesium oxide powder, which is an inorganic oxide, are subjected to a mechanochemical fixing treatment at 6,000 rpm for 5 minutes using a hybridizer to produce a magnesium oxide-coated copper powder. did. The coating amount of magnesium oxide coated on the surface of the magnesium oxide-coated copper powder at this stage was 3% by mass. The weight-accumulated particle diameter D of the magnesium oxide-coated copper powder before heating was measured by a laser diffraction scattering particle size distribution measuring method. ₅₀ Was 0.92 μm, the process variation index CV was 0.28, and the crystallite diameter was 28.2 nm. As a result of measuring the coefficient of thermal expansion, the shrinkage at 900 ° C. was 5.8%. In other words, the copper powder is subjected to mechanochemical processing, so that the crystallite diameter is smaller than that of the copper powder obtained by the original wet manufacturing method, but the thermal expansion is caused by the presence of the oxide coating layer. Although the shrinkage at the time was small, it did not reach the shrinkage within the range required by the market.
[0036]
Therefore, the magnesium oxide-coated copper powder obtained as described above was heated at 900 ° C. for 1 hour in a reducing atmosphere having a hydrogen concentration of 1 wt% to adjust the crystallite diameter. As a result, the weight cumulative particle diameter D of the heated magnesium oxide-coated copper powder measured by a laser diffraction scattering particle size distribution method was determined. ₅₀ Was 0.93 μm, the crystallite diameter was 60.6 nm, and the process variation index CV value was 0.26. It can be seen that the crystallite diameter is larger than the copper powder obtained by the dry production method. Further, the coefficient of thermal expansion was measured using the above-described aluminum oxide-coated copper powder in the same manner as described above. As a result, the shrinkage at 900 ° C. was 1.1%, and the shrinkage was within 3%. It was in.
[0037]
Fourth Embodiment First, a method for producing silver powder used as a core material will be described. Here, 300 g of silver nitrate was added to 360 ml of ion-exchanged water in the reaction vessel and completely dissolved, and then 300 ml of 25 wt% ammonia water was added, followed by stirring to adjust the aqueous solution of the ammine silver complex. Temperature controlled. Then, the aqueous ammine silver complex solution was added in about 3 seconds, and stirred for about 3 minutes to complete the reductive precipitation of silver particles. Thereafter, silver particles were collected by filtration, washed sufficiently with pure water, and dried to obtain silver powder.
[0038]
The weight-accumulated particle diameter D of this silver powder measured by a laser diffraction scattering particle size distribution measuring method ₅₀ Was 1.51 μm, the process variation index CV was 0.34, and the crystallite diameter was 7.7 nm. As a result of measuring the thermal expansion coefficient, the shrinkage at 900 ° C. was 16.0%. The measurement of the coefficient of thermal expansion was performed by the same method as described in the first embodiment.
[0039]
Then, 1 kg of the silver powder and 0.05 kg of the silicon oxide powder as an inorganic oxide were subjected to a mechanochemical fixing treatment at 6000 rpm for 5 minutes using a hybridizer to produce a silicon oxide-coated silver powder. At this stage, the coating amount of the silicon oxide coated on the surface of the silicon oxide-coated silver powder was 5% by mass. The weight-accumulated particle diameter D of the silicon oxide-coated silver powder before heating is measured by a laser diffraction scattering particle size distribution measuring method. ₅₀ Was 1.30 μm, the process variation index CV was 0.27, and the crystallite diameter was 6.8 nm. As a result of measuring the thermal expansion coefficient, the shrinkage at 900 ° C. was 7.0%. In other words, the silver powder undergoes mechanochemical processing, the crystallite diameter becomes smaller than the silver powder obtained by the original wet manufacturing method, but the presence of the oxide coating layer causes Although the shrinkage was small, it did not reach the shrinkage within the range required by the market.
[0040]
Thus, the silicon oxide-coated silver powder obtained as described above was heated at 450 ° C. for 1 hour in an air atmosphere to obtain a silicon oxide-coated silver powder whose crystallite diameter was adjusted. As a result, the weight cumulative particle diameter D of the silicon oxide-coated silver powder after heating was measured by a laser diffraction scattering particle size distribution measuring method. ₅₀ Was 1.32 μm, the crystallite diameter was 60.0 nm, and the process variation index CV value was 0.33.
[0041]
From these results, a crystallite diameter of silver powder obtained by the dry production method (the crystallite diameter of the silver powder obtained by the dry production method is generally 30 to 40 nm) or more is obtained. I can understand that. In addition, it can be seen that even after heating, the CV value of the silver powder before forming the inorganic oxide layer did not significantly deteriorate.
[0042]
Further, the coefficient of thermal expansion was measured using the silicon oxide-coated silver powder after heating in the same manner as described above. As a result, the shrinkage at 900 ° C. was 2.1%, which was 5% which is said to be ideal. Within the shrinkage rate.
[0043]
Fifth Embodiment: The silver powder used in this embodiment is obtained by the same manufacturing method as that used in the fourth embodiment, and therefore, description thereof is omitted here to avoid redundant description. That is, the weight cumulative particle diameter D of the laser diffraction scattering particle size distribution measuring method ₅₀ Was 1.51 μm, the process variation index CV value was 0.34, the crystallite diameter was 7.7 nm, and the shrinkage ratio at 900 ° C. was 16.0%. Silver powder was used as the core material.
[0044]
Then, 1 kg of this silver powder and 0.05 kg of aluminum oxide powder, which is an inorganic oxide, were subjected to a mechanochemical fixing treatment at 6000 rpm for 5 minutes using a hybridizer to produce an aluminum oxide-coated silver powder. At this stage, the coating amount of aluminum oxide coated on the surface of the aluminum oxide-coated silver powder was 5% by mass. The weight cumulative particle size D of the aluminum oxide-coated silver powder before heating by the laser diffraction scattering type particle size distribution measurement method ₅₀ Was 1.33 μm, the process variation index CV was 0.27, and the crystallite diameter was 6.3 nm. Then, as a result of measuring the coefficient of thermal expansion, the shrinkage at 900 ° C. was 6.5%. In other words, the silver powder undergoes mechanochemical processing, the crystallite diameter becomes smaller than the silver powder obtained by the original wet manufacturing method, but the presence of the oxide coating layer causes Although the shrinkage was small, it did not reach the shrinkage within the range required by the market.
[0045]
Therefore, the aluminum oxide-coated silver powder obtained as described above was heated at 450 ° C. for 1 hour in an air atmosphere to adjust the crystallite diameter. As a result, the weight cumulative particle size D of the heated aluminum oxide-coated silver powder measured by a laser diffraction scattering type particle size distribution measurement method was determined. ₅₀ Was 1.31 μm, the crystallite diameter was 68.0 nm, and the process variation index CV value was 0.32. It can be seen that the crystallite diameter is larger than the silver powder obtained by the dry production method. Also, it can be seen that even after heating, the CV value of the silver powder after forming the inorganic oxide layer before heating is a rather good value. Further, the coefficient of thermal expansion was measured using the above-described aluminum oxide-coated silver powder in the same manner as described above. As a result, the shrinkage at 900 ° C. was 1.8%, which was within 5%. It was settled.
[0046]
Sixth Embodiment: The silver powder used in this embodiment is obtained by the same manufacturing method as that used in the fourth embodiment, and therefore, description thereof will be omitted to avoid redundant description. That is, the weight cumulative particle diameter D of the laser diffraction scattering particle size distribution measuring method ₅₀ Was 1.51 μm, the process variation index CV value was 0.34, the crystallite diameter was 7.7 nm, and the shrinkage ratio at 900 ° C. was 16.0%. Silver powder was used as the core material.
[0047]
Then, 1 kg of the silver powder and 0.05 kg of magnesium oxide powder as an inorganic oxide were subjected to a mechanochemical fixing treatment at 6000 rpm for 5 minutes using a hybridizer to produce a magnesium oxide-coated silver powder. At this stage, the coating amount of magnesium oxide coated on the surface of the magnesium oxide-coated silver powder was 5% by mass. The weight-accumulated particle size D of the magnesium oxide-coated silver powder before heating is measured by a laser diffraction scattering particle size distribution measuring method. ₅₀ Was 1.21 μm, the process variation index CV value was 0.28, and the crystallite diameter was 6.5 nm. Then, as a result of measuring the coefficient of thermal expansion, the shrinkage at 900 ° C. was 7.1%. In other words, the silver powder undergoes mechanochemical processing, the crystallite diameter becomes smaller than the silver powder obtained by the original wet manufacturing method, but the presence of the oxide coating layer causes Although the shrinkage was small, it did not reach the shrinkage within the range required by the market.
[0048]
Thus, the magnesium oxide-coated silver powder obtained as described above was heated at 450 ° C. for 1 hour in an air atmosphere to adjust the crystallite diameter. As a result, the weight cumulative particle diameter D of the heated magnesium oxide-coated silver powder was measured by a laser diffraction scattering particle size distribution measuring method. ₅₀ Was 1.23 μm, the crystallite diameter was 60.6 nm, and the process variation index CV value was 0.33. It can be seen that the crystallite diameter is larger than the silver powder obtained by the dry production method. Further, it can be seen that even after the heating, the CV value of the silver powder after the formation of the inorganic oxide layer before the heating is rather good. Further, the coefficient of thermal expansion was measured using the above-described magnesium oxide-coated silver powder in the same manner as described above. As a result, the shrinkage at 900 ° C. was 2.0%, It was settled.
[0049]
【The invention's effect】
Since the inorganic oxide-coated metal powder according to the present invention has a large crystallite diameter while maintaining uniform fineness and excellent dispersibility, which are advantages of the metal powder obtained by the wet manufacturing method, it is subjected to high-temperature heating. It has a quality that is excellent in resistance to shrinkage when exposed. By using this inorganic oxide-coated metal powder, it is possible to improve the dimensional stability of a sintered body containing a metal powder such as a low-temperature fired ceramic, and it is possible to dramatically improve the product yield. . In addition, the inorganic oxide-coated metal powder has a structure in which copper powder, silver powder, or the like is used for the core material and an inorganic oxide layer is provided on the surface thereof, so that aggregation of the metal powder of the core material does not proceed, and Since heating is possible, it is easy to adjust the crystallite diameter of the metal powder of the core material, and the unique manufacturing method described above can be adopted.

Claims (6)

An inorganic oxide-coated metal powder having an inorganic oxide layer on the surface of the metal powder particles,
The inorganic oxide layer is composed of any one of silicon oxide, aluminum oxide, magnesium oxide, zirconium oxide, and zinc oxide, and has a crystallite diameter of metal powder of 50 nm or more. Inorganic oxide coated metal powder. The inorganic oxide-coated metal powder according to claim 1, wherein the metal powder is copper powder or silver powder. In the case where the value of weight-cumulative particle diameter D ₅₀ by laser diffraction scattering particle size distribution measuring method using a metal powder of 0.1 m to 10 m, the thickness of the inorganic oxide layer (in terms of mass thickness), an inorganic oxide The inorganic oxide-coated metal powder according to claim 1, which is 0.1% by mass to 10% by mass of the weight of the substance-coated metal powder. A method for producing an inorganic oxide-coated metal powder according to any one of claims 1 to 3,
Forming an inorganic oxide layer on the surface of the metal particles by fixing the inorganic oxide to the surface of the particles by a mechanochemical method,
Thereafter, a heat treatment is performed to adjust the crystallite diameter of the metal powder to 50 nm or more. The method for producing an inorganic oxide-coated metal powder according to claim 4, wherein when the copper powder is used as the metal powder, the heat treatment is performed in a reducing atmosphere or an inert gas atmosphere at 500C to 1000C. 5. The inorganic material according to claim 4, wherein when the silver powder is used as the metal powder, the heat treatment is performed at a temperature of 350 ° C. to 900 ° C. in any one of an air atmosphere, a reducing atmosphere, or an inert gas atmosphere. A method for producing an oxide-coated metal powder.