JP3988981B2 - Method for producing linear expansion control composite material - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a thermal expansion control material.
[0002]
[Prior art]
It has a negative thermal expansion coefficient and has the chemical formula (A _{1 -Z} D _Z ) (W _{1 -X} R _X ) ₂ O ₈ (A is Zr or Hf or a mixture thereof, D is a solid solution in ZrO ₂ or HfO ₂ Elements selected from possible elements, Z is a value equal to or less than the maximum solid solution atomic ratio limited by each element, R is an element selected from elements that can be dissolved in WO ₃ , and X is limited by each element The oxide represented by the value below the maximum solid solution atomic ratio is a stable substance at 1105 to 1257 ° C., and exhibits isotropic negative thermal expansion in a temperature range below the nonequilibrium decomposition temperature of 777 ° C. It is known. The oxide can be combined with other substances to form a sintered body of the composition, whereby the thermal expansion coefficient of the sintered body of the composition can be controlled.
[0003]
As a method for producing a sintered body of the composition containing the oxide, ZrW ₂ O ₈ (hereinafter referred to as zirconium tungstate), which is a kind of this oxide, is described in Scripta Materialia Vol. 36, No. 9, No. 1075-1080. ) And pure copper are mixed and sintered by hot isostatic pressing (hereinafter referred to as HIP) to form a composite material. In addition, J.H. Mater. Res. Magazine Vol. 14, No. 3, pages 780-789 include a method in which zirconium tungstate and pure copper are mixed and solidified by hot pressing, and zirconium tungstate and pure copper are bonded by mechanical alloying. There are proposed a method of solidifying by sol-gel and a method of plating pure copper on the surface of zirconium tungstate and solidifying by HIP.
[0004]
However, in the method in which zirconium tungstate and copper powder are mixed and solidified by HIP, it is necessary to hold at 600 ° C. under a pressure of 103 MPa for 3 hours. There was a problem that a copper oxide was generated by mutual diffusion of oxygen atoms and copper atoms in zirconium, and zirconium tungstate was decomposed, so that a composite material having a desired thermal expansion coefficient could not be obtained.
[0005]
Further, a method of mixing zirconium tungstate and pure copper and solidifying by hot pressing, and a method of bonding zirconium tungstate and pure copper by mechanical alloying and solidifying by hot pressing are 1.4 GPa at 250 ° C. Since the decomposition does not occur by holding for 13 hours under the pressure of, a high-density solidified body can be obtained. However, since the time of 13 hours is spent only for holding, there is a problem that productivity is low, and The material bonded by the mechanical alloying method has a problem that it does not exhibit a desired thermal expansion coefficient.
[0006]
Further, in the method of plating pure copper on the surface of zirconium tungstate and solidifying by HIP, the problem of the HIP method is solved, but the composite material of zirconium tungstate and copper having a desired thermal expansion coefficient It is necessary to control the surface coating to obtain this, but this control is difficult. In addition, this method is not always efficient in terms of process.
[0007]
[Problems to be solved by the invention]
The present invention provides a composition sintered body having a desired thermal expansion coefficient containing an oxide represented by the chemical formula (A _1-Z D _Z ) (W _1-X R _X ) ₂ O ₈ as a component, It is an object of the present invention to provide a production method that enables efficient and easy production.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have studied a method for producing a sintered body of the composition containing the oxide, and as a result, (1) the heating rate during sintering and (2) during sintering. The inventors have found that the above-mentioned object can be achieved by setting the pressure conditions to an appropriate value, and have made the present invention.
That is, the aspects of the present invention are as follows.
[0009]
(1) has a negative thermal expansion coefficient, chemical formula _{(A 1-Z D Z)} (W 1-X R X) 2 O 8 (A is Zr or Hf or mixtures thereof, D is ZrO ₂ or HfO ₂ At least one element selected from elements that can be dissolved in Z, Z is a value that is less than or equal to the maximum solid solution atomic ratio limited by each element (including 0), and R is selected from elements that can be dissolved in WO ₃ Sintering of a composition of an oxide and an Al, Cu, or Al—Cu alloy represented by at least one element, X being a value less than the maximum solid solution atomic ratio (including 0) limited by each element In the method for producing a body, the composition of the oxide and Al, Cu or Al—Cu alloy is heated to generate heat, the temperature increase rate during sintering is 20 to 1000 ° C./min, and the sintering temperature is 777 ° C. The manufacturing method of the sintered compact characterized by sintering below.
[0010]
(2) The method for producing a sintered body according to (1) above, wherein the pressure during sintering is 0.1 to 1000 MPa.
[0011]
(3) The method for producing a sintered body according to (1) or (2) above, wherein heat treatment is performed at a temperature of 100 to 777 ° C. after sintering at a pressure of 200 MPa or less for 1 minute or more.
[0012]
Hereinafter, embodiments of the present invention will be described in more detail.
Oxide _{(A 1-Z D Z)} (W 1-X R X) 2 O 8 A is Zr or Hf or mixtures thereof having a negative thermal expansion coefficient of the present invention, D is solid in ZrO ₂ or HfO ₂ At least one element selected from elements that can be dissolved, Z is a value that is less than or equal to the maximum solid solution atomic ratio limited by each element (including 0), and R is at least selected from elements that can be dissolved in WO ₃ With respect to one element, X is a value less than the maximum solid solution atomic ratio (including 0) limited by each element, an element that can be dissolved in ZrO ₂ or HfO ₂ is an alkaline earth metal such as Ca, Elements such as rare earth metals such as Y.
[0013]
The value of Z is specifically 0.2 or less, and typically 0 to 0.1. Moreover, the element which can be dissolved in WO ₃ is an element such as IIIA group, VA group or VIA group. The value of X is specifically 0.25 or less, and more specifically 0 to 0.2. If Z is larger than 0.2 or X is larger than 0.25, the negative thermal expansion characteristics may not be remarkable, which is not preferable. It is known that when Z = 0 and X = 0, it has a remarkable negative thermal expansion characteristic.
[0014]
As one aspect of the production method of the present invention, the sintering is performed at a heating rate of 20 to 1000 ° C./min during sintering and a sintering temperature of 777 ° C. or less. (Aspect (1))
Sintering the composition containing the oxide and Al, Cu or Al-Cu alloy at a heating rate of 20 to 1000 ° C./min during sintering and a sintering temperature of 777 ° C. or less, A chemical reaction between the oxide and other constituent elements can be suppressed. In order to control the sintering temperature to 777 ° C. or lower, the temperature rising rate is preferably 20 to 500 ° C./min, more preferably 30 to 300 ° C./min, and further preferably 50 to 200 ° C./min.
[0015]
When a composition containing the oxide and Al, Cu, or an Al—Cu alloy is sintered at a temperature of 777 ° C. or lower, non-equilibrium decomposition of the oxide can be suppressed.
[0016]
Moreover, as an aspect of the production method of the present invention, sintering is performed at a pressure during sintering of 0.1 to 1000 MPa. (Aspect (2))
When a composition containing the oxide and Al, Cu, or an Al—Cu alloy is sintered under pressure, the time required for the sintering can be shortened, and the chemical reaction between the oxide and other constituent elements. Can be suppressed. However, a large press is required to apply a larger pressing force, and the size of the thermal expansion control material of the present invention is limited if the press has the same capacity. For this reason, the applied pressure is preferably 30 to 800 MPa, more preferably 50 to 500 MPa, and still more preferably 100 to 400 MPa.
[0017]
In addition, as an aspect of the production method of the present invention, in order to satisfy the production conditions described above, sintering is performed by generating heat by energizing the composition and raising the temperature. (Aspect (1))
Examples of the sintering method for generating heat by energizing the composition containing the oxide include a discharge plasma method disclosed in Japanese Patent No. 2762225. Compared to a general heating method such as an electric furnace, when the composition is energized to generate heat, the rate of temperature rise can be increased, and the composition containing the oxide is a surface like aluminum. Even with a material having an oxide layer, a dense sintered body can be produced by causing a discharge when energized and destroying the oxide layer.
[0018]
As still another aspect of the production method of the present invention, heat treatment is performed at a temperature of 100 to 777 ° C. after sintering at a pressure of 200 MPa or less for 1 minute or more. (Aspect (3))
Zirconium tungstate, which is a typical composition of the oxide, is known to have three phases by applying temperature and pressure. In general, the α phase is stable at normal temperature and pressure, but it is known that the γ phase is induced by pressurization of 200 MPa or more, and changes to the β phase at a temperature of 155 ° C. or more. Since these three phases have different crystal structures and lattice spacings, their thermal expansion coefficients are different.
[0019]
The α phase is cubic and has a coefficient of thermal expansion of −8.8 × 10 ⁻⁶ / ° C. isotropically in a temperature range of −273 to 127 ° C. The β phase is also cubic and has a thermal expansion coefficient of −4.9 × 10 ⁻⁶ / ° C. in the temperature range of −157 to 677 ° C. The γ phase is orthorhombic and exhibits a thermal expansion coefficient of −0.68 to −1.88 × 10 ⁻⁶ / ° C. at 20 ° C.
[0020]
The γ phase may be induced under the sintering conditions of the production method of the present invention. The γ phase is preferably changed to an α phase or a β phase. For this reason, after sintering, heat treatment is performed at a temperature of 100 to 777 ° C., preferably 120 to 777 ° C., more preferably 150 ° C. to 777 ° C. At that time, heat treatment is performed for 1 minute or more at a pressure of 200 MPa or less. This pressure is preferably 100 MPa or less, and more preferably 50 MPa or less.
[0021]
The heat treatment can also be carried out by holding the sintered body in the above pressure range within the above temperature range during cooling after sintering. That is, after the current sintering, when heating is stopped by reducing the current, the current is cooled by thermal diffusion through the sintering jig. When the sintered body is cooled to an appropriate temperature, by placing the pressure on the sintered body in the pressure range, an oxide having a negative thermal expansion coefficient undergoes a phase change to obtain a desired phase. be able to.
[0022]
Moreover, a metal is included in a composition as an aspect of the manufacturing method of this invention. (Aspect (1))
Metals generally have a lower softening point and better spreadability than materials such as oxides and nitrides. For this reason, the metal is effective as a sintering aid for the composition containing the oxide. As the metal here, Cu, Al, and alloys thereof can be appropriately selected.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention does not limit a technical scope at all by these specific examples.
[0024]
[Example 1]
As the oxide, zirconium tungstate powder (average particle size 2 μm) and commercially available pure aluminum powder (manufactured by Kojundo Chemical Laboratory Co., Ltd .: purity 99.9%, average particle size 10 μm) are used. Mix in a mortar so that the volume ratio is 50%, fill in a cemented carbide sintering jig (inner diameter 10 mmφ), and use a pulse current sintering apparatus (SPS-1050L manufactured by Sumitomo Coal Mining Co., Ltd.). Then, pulse electric current sintering was performed in a vacuum atmosphere to produce a sintered body of zirconium tungstate and aluminum. The conditions for pulsed current sintering were a heating rate of 100 ° C./min, an applied pressure of 300 MPa, a sintering temperature of 400 ° C., and a holding time of 3 minutes.
[0025]
The obtained sintered body was subjected to density measurement by Archimedes method, and as a result, it was 97% or more of the density calculated from the theoretical density and composition ratio of aluminum and zirconium tungstate, and was in a good sintered state. .
Next, as a result of identifying the constituent phases and reactants by X-ray diffraction (XRD), the peaks of α-phase, γ-phase and aluminum of zirconium tungstate were observed, and peaks of decomposition products and reactants were observed. There wasn't.
Moreover, from the observation result of the structure | tissue by an optical microscope and a scanning electron microscope (SEM), a void and a reaction layer were not observed in the joining interface of zirconium tungstate and aluminum, and it was a favorable sintered state.
[0026]
[Example 2]
As in Example 1, as the oxide, zirconium tungstate powder and pure aluminum powder were mixed in a mortar so that the volume ratio of zirconium tungstate was 25%, 50%, and 75%. A sintered body was produced under the same sintering conditions as in Example 1.
[0027]
As a result of carrying out density measurement by the Archimedes method for the obtained sintered body, it was 97% or more of the density obtained by calculation from the theoretical density and composition ratio of aluminum and zirconium tungstate in all the sintered bodies, and good Sintered state.
Next, the sintered body was heat-treated at 300 ° C. and 0.1 MPa in the air for 1 hour.
Then, as a result of identifying the constituent phases and reactants by X-ray diffraction (XRD), the α phase of zirconium tungstate and the aluminum peak were observed in all sintered bodies, and the peaks of decomposition products and reactants were observed. Was not recognized.
Next, each composite material was processed into dimensions of 3 × 3 × 6 mm ³ , and the amount of thermal expansion was measured with TMA. The measurement results are shown in FIG. A desired thermal expansion coefficient was obtained by the mixing ratio of the oxide and aluminum.
[0028]
[Example 3]
As the oxide, zirconium tungstate powder (average particle size 2 μm) and commercially available pure copper powder (Fukuda Metal Foil Powder Co., Ltd .: purity 99.9%, average particle size 5 μm) were used. Were mixed in a mortar so as to be 10%, 25%, 50%, 75% and 90%, and a sintered body of zirconium tungstate and copper was produced in the same manner as in Example 1. The conditions for pulsed electric current sintering were a heating rate of 80 ° C./min, an applied pressure of 350 MPa, a sintering temperature of 500 ° C., and a holding time of 3 minutes.
[0029]
As a result of carrying out density measurement by the Archimedes method for the obtained sintered body, it was 97% or more of the density calculated from the theoretical density and composition ratio of pure copper and zirconium tungstate, and was in a good sintered state. .
Then, as a result of identifying the constituent phases and reactants by X-ray diffraction (XRD), the α phase of zirconium tungstate and the peak of pure copper were observed in all the sintered bodies, and the peaks of decomposition products and reactants were I was not able to admit.
[0030]
Next, for each composite material, the thermal expansion amount was measured by TMA in the same manner as in Example 2. As a result, the same result as in Example 2 was obtained. A desired thermal expansion coefficient was obtained by the mixing ratio of the oxide and the pure copper component.
[0031]
【The invention's effect】
According to the present invention, it has become possible to efficiently and easily produce a material having a desired thermal expansion coefficient by combining an oxide having a negative thermal expansion coefficient with another material.
[Brief description of the drawings]
FIG. 1 is a graph showing thermal expansion characteristics of a composite sintered body of zirconium tungstate and aluminum at each mixing ratio.

Claims (3)

It has a negative thermal expansion coefficient and has the chemical formula (A _{1 -Z} D _Z ) (W _{1 -X} R _X ) ₂ O ₈ (A is Zr or Hf or a mixture thereof, D is a solid solution in ZrO ₂ or HfO ₂ At least one element selected from possible elements, Z is a value equal to or less than the maximum solid solution atomic ratio limited by each element (including 0), and R is at least one selected from elements that can be dissolved in WO ₃ Manufactures a sintered body of a composition of an oxide and an Al, Cu or Al-Cu alloy represented by two elements, X being a value less than the maximum solid solution atomic ratio limited by each element (including 0) In this method, the composition of the oxide and Al, Cu or Al—Cu alloy is energized to generate heat, and the temperature rise rate during sintering is 20 to 1000 ° C./min, and the sintering temperature is 777 ° C. or less. A method for producing a sintered body, characterized by comprising:   The method for producing a sintered body according to claim 1, wherein the pressure during sintering is 0.1 to 1000 MPa.   The method for producing a sintered body according to claim 1 or 2, wherein a heat treatment is performed at a temperature of 100 to 777 ° C after sintering at a pressure of 200 MPa or less for 1 minute or more.

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