JPH1095662A - Low heat expanding phosphate sintered compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a phosphate sintered compact having low thermal expansion, high strength and low hysteresis in a thermal expansion curve. SOLUTION: This phosphate sintered compact having low thermal expansion has a composition expressed by (Ba1-y Ry )1+x Zr4 P6-2x Si2x O24 (R is at least one of Mg, Ca and Sr, 0<x<0.45 and 0<y<0.2). The phosphate sintered compact having low thermal expansion, >=100MPa strength and no hysteresis is realized by substituting a part of Ba, which is an alkaline earth metal element, with a second alkaline earth element to bring to a solid solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-thermal-expansion phosphate sintered body having high strength and low hysteresis in a thermal expansion curve.

[0002]

2. Description of the Related Art Materials used at high temperatures and subjected to large thermal cycles and thermal shocks, such as diesel particulate filters, exhaust manifold heat insulating linings, and materials constituting high heat resistant honeycomb structures, have extremely low heat. Expansion properties are required.

Hitherto, cordierite, aluminum titanate and the like have been used as low thermal expansion materials used for members subjected to such a large thermal shock. However, cordierite has a relatively large coefficient of thermal expansion and insufficient thermal shock resistance, and aluminum titanate has low thermal expansion due to the occurrence of microcracks due to the anisotropy of thermal expansion. Was low.

[0004]

On the other hand, in recent years, alkaline earth zirconium phosphate sintered bodies have attracted attention as materials having very small thermal expansion characteristics. For example,
_{JP-A-2-38354, R y Zr 4 Si x} P
A phosphate represented by _6-x O ₂₄ (R is a combination of at least one kind of divalent or trivalent cation) is disclosed in JP-A-3-208807 as RZr ₄ P ₆ O ₂₄ (R is a periodic acid). Phosphate compounds represented by one or more cations of Group IIa of the Table II) are disclosed.

The alkaline earth zirconium phosphate crystal grains belong to a hexagonal system, and a system in which the thermal expansion in the a-axis direction and the c-axis direction has a large difference, that is, a system having a large thermal expansion anisotropy, is hardened. Microcracks occur in the grains and at the grain boundaries in the compact. The microcracks reduce the thermal expansion to absorb the thermal expansion of the particles in the sintered body.

However, there is a problem that the low thermal expansion body having such a micro crack mechanism has low strength.
This is because the presence of microcracks contributing to low thermal expansion, on the other hand, is a starting point of fracture and causes a decrease in strength. Therefore, in alkaline earth zirconium phosphate, there is a conflict between low thermal expansion and high strength. The realization of both of these characteristics is a major challenge.

[0007] Even in a sintered body having no microcracks, there is a problem that hysteresis occurs in the thermal expansion curve due to the phase transition of the crystal structure between space groups 1 and 2.

[0008]

(Equation 1)

[0009]

(Equation 2)

Accordingly, an object of the present invention is to obtain a low-thermal-expansion phosphate sintered body having high strength and small hysteresis in a thermal expansion curve.

[0011]

Means for Solving the Problems The present inventors diligently studied to solve the above problems, and found that (Ba _{1 -y} R _y ) _{1 + x} Zr
_Phosphorus having a composition represented by ₄ P _6-2x Si _2x O ₂₄ (R: at least one of Mg, Ca and Sr), wherein 0 <x <0.45 and 0 <y <0.2 It has been found that an acid salt sintered body is a low thermal expansion material having high strength and no hysteresis (claim 1).

[0012] The phosphate sintered body of the present invention contains Ba, which is an alkaline earth metal element, as an essential component, and a part of Ba is used as a second component.
And a solid solution substituted with Mg, Ca, and Sr, which are alkaline earth metal elements. Then, x, y in the above composition
Is set to a specific range, thereby realizing a strength of 100 MPa or more and minimizing the hysteresis.

The phosphate sintered body of the present invention having the above composition has a so-called NASICON type crystal structure. The NASICON type structure is [Z
An octahedron having [rO ₆ ] as a unit and a tetrahedron having [PO ₄ ] as a unit share and bond an oxygen atom to form a three-dimensional skeleton. The alkaline earth metal element exists in the gap between [ZrO ₆ ] in the c-axis direction when represented by a hexagonal crystal.

The thermal expansion of a substance having a NASICON-type structure is mainly affected by the type of alkali metal element or alkaline earth metal element present in the structure. In the NASICON type structure, the ionic radius and the thermal expansion of the bond between the alkaline earth metal element and oxygen are different depending on the type of the alkaline earth metal element, so that the change in the bond angle of the skeleton structure is different. A difference appears in the overall thermal expansion. Here, it is generally known that a system containing only Ba or Sr has a small thermal expansion anisotropy for an alkaline earth metal element, whereas a system containing only Ca has a large thermal expansion anisotropy. Have been. In this case, if the diameter exceeds the critical crystal grain size, microcracks are generated in the sintered body, and the thermal expansion is reduced.

The phosphate sintered body of the present invention is compositionally similar to the above-described system containing only Ba, and similarly has a small thermal expansion anisotropy, so that microcracks do not occur. Higher strength than in comparison. The thermal expansion of the bond between the alkaline earth metal element and oxygen is expressed as Ba-O> Sr
-O>Ca-O> Mg-O, and therefore, the thermal expansion is reduced by substituting a part of Ba with Sr, Ca or Mg. Further, in the composition of Ba _{1 + y} Zr ₄ P _6-2y Si _2y O ₂₄ which does not contain the second alkaline earth metal element,
Hysteresis exists in the thermal expansion curve due to a phase transition between space group numbers 1 and 2 in the temperature range of 300 to 900 ° C., but in the composition of the present invention, a part of Ba has a different ionic radius. It is considered that the substitution with the second alkaline earth metal element reduced the volume immediately before the transition, and reduced the volume change at the time of the transition from Equation 1 to Equation 2 so that hysteresis did not occur. .

More specifically, the above-mentioned phosphate sintered body is
In the above composition, coordinates (x, y) are A (0.2, 0), B (0.4
5,0), C (0.45, 0.2), D (0.35,
0.2) (excluding points A, B, C, D and the lines AB, BC, CD, DA)
It is better to choose as in In this case, the thermal expansion coefficient can be set to a particularly low range of -1 to 1 × 10 ⁻⁶ / ° C.

Resistance to thermal shock (thermal shock resistance)
It is determined by strength, Young's modulus, thermal conductivity, Poisson's ratio and coefficient of thermal expansion among the properties of the material. Among these characteristics, the coefficient of thermal expansion most governs thermal shock resistance.
The member to which the sintered body of the present invention is applied is, for example, 1400 ° C.
When used up to about the temperature, a thermal expansion coefficient of about −1 to 1 × 10 ⁻⁶ / ° C. is required to withstand a rapid thermal shock from this temperature range. Therefore, by combining the composition x and the addition amount y so as to be within the above range,
It is possible to obtain a sintered body having a sufficiently small thermal expansion coefficient and excellent thermal shock resistance.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The phosphate sintered body of the present invention has a (Ba _1-y R _y ) _{1 + x} Zr
_It has a composition represented by ₄ P _6-2x Si _2x O ₂₄ , and has a structure in which Ba as an alkaline earth metal element is partially replaced with a second alkaline earth metal element R. Where R is Mg, C
It is at least one selected from a and Sr, and a plurality of these may be used. x and y are in the ranges of 0 <x <0.45 and 0 <y <0.2, respectively.
By setting x and y in this range, high strength of 100 MPa or more can be realized, and hysteresis of the thermal expansion curve can be minimized. In a composition region in which x and y exceed the above ranges, microcracks are formed and strength is remarkably reduced, or hysteresis occurs in a thermal expansion curve.

More preferably, (x, y) in the above composition is such that x is a horizontal axis and y is a vertical axis.
A (0.2, 0), B (0.45, 0), C (0.4
5, 0.2) and D (0.35, 0.2) (points A, B, C, D and AB, BC, C-
D and DA lines are not included).
Thereby, the coefficient of thermal expansion is particularly low at -1 to 1 × 10 ^-6 /
° C, a high-strength sintered body having no hysteresis and having a very low coefficient of thermal expansion can be obtained.

More preferably, x and y are each 0 <
It is preferable that x ≦ 0.44 and 0 <y ≦ 0.2.
Thereby, the coefficient of thermal expansion can be further reduced. More preferably, (x, y) is A (0.2, 0), E (0.
44,0), F (0.44, 0.18), G (0.3
4,0.18) (points F, G and E−
The lines F, FG, and GA are included, and points A, E, and A-
(It does not include the line of E (on the x-axis)). Thereby, the coefficient of thermal expansion can be further reduced.

Next, a method of manufacturing the phosphate sintered body will be described in detail. Ba and R, ie, Mg, Ca, Sr
As a source, powders of these oxides, carbonates, sulfates, nitrates, chlorides, hydroxides and the like are used. Also, Z
Powders such as zirconium oxide, zirconium chloride, and hydroxide are used as r sources, phosphate powders such as ammonium hydrogen phosphate are used as phosphorus sources, and oxides, hydroxides, chlorides, and the like are used as Si sources. Is usually used as a starting material.

In the case of producing the sintered body of the present invention using each of the starting materials described above, these raw material powders are mixed and pulverized using an alcohol or the like as a medium using a ball mill or a vibration mill. These raw material powders usually have a particle size of 100 μm.
m or less, preferably 20 μm or less.

After drying the powder, the powder is dried in air at 1100-1000.
The solution is calcined at a temperature of 1400 ° C. for 1 to 24 hours to obtain a solid solution single phase powder. Here, when the calcination temperature is lower than 1100 ° C. or the calcination time is shorter than 1 hour, the precipitation of the solid solution phase is small, and when the calcination time is higher than 1400 ° C. and the calcination time exceeds 24 hours. , The amount of evaporation of phosphorus (P) during calcination increases.

In addition to the solid phase method, a solid solution powder can be obtained by a sol-gel method or a hydrothermal method using a water-soluble salt as a raw material.

The solid solution powder obtained as described above is subjected to a BET surface area of 10 m
Pulverize to ² / g or more. Next, the obtained mixed powder is molded by a method such as mold molding, CIP molding, casting molding, injection molding and the like, and sintered. Sintering is carried out in air at 14
This is performed in a temperature range of 00 to 1600 ° C. for 1 to 5 hours so that the crystal grain size in the sintered body becomes 20 μm or less. In the temperature range where the sintering temperature is lower than 1400 ° C., sintering does not proceed,
Decomposition occurs on the surface of the sintered body during sintering in a temperature range exceeding 1600 ° C. If the crystal grain size exceeds 20 μm, the strength of the sintered body tends to decrease.

The use of the phosphate sintered body of the present invention includes:
Dimensions of high heat-resistant honeycomb materials for automotive exhaust gas purification catalysts, diesel particulate filters, exhaust manifold thermal insulation linings, etc., members that receive large thermal shock, or supports for high-precision optical components, reflector supports for large telescopes, etc. Materials that require stability, and materials that constitute a thermal expansion measuring instrument and the like are also included.

[0027]

【Example】

(Examples 1 to 58) These powders were prepared by using barium carbonate as a Ba source, magnesium oxide, calcium carbonate or strontium carbonate as an R source, zirconium oxide as a Zr source, ammonium hydrogen phosphate as a P source, and silicon oxide as a Si source. Was mixed and pulverized for 24 hours using a pot made of silicon nitride and a ball using ethanol as a medium. After drying the obtained mixed powder, it was calcined at 1400 ° C. in the air for 10 hours to synthesize a solid solution powder. R, x, and y in the composition at this time are shown in Tables 1 to 3.

This synthetic powder was wet-pulverized for 72 hours using ethanol as a medium. 200 kg / cm ^{2 of the} obtained powder
Molding at a pressure of 3 ton / cm ² CIP at a pressure of 3 ton / cm ²
Molded. Next, this molded body was sintered in the atmosphere at a temperature of 1550 ° C. for 4 hours.

Each of the obtained sintered bodies was 3 × 4 × 40
The test piece was processed into a size of mm to obtain a test piece, and its thermal expansion coefficient was examined. The results are shown in Tables 1 to 3 above. The measurement of the thermal expansion coefficient was performed between room temperature and 1400 ° C. at a rate of 5 ° C./min by a push-rod type thermal dilatometer. Further, the open porosity and the four-point bending strength of each test piece were examined, and the results were shown in Table 1 above.
３3. Here, the open porosity was determined by the Archimedes method, and the measurement of the four-point bending strength was performed in accordance with JIS1601. As a result, as is clear from Tables 1 to 3, all the examples exhibited high values of strength of 100 MPa or more.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

When the presence or absence of hysteresis in the thermal expansion curve was examined, no hysteresis was observed in the thermal expansion curve within the measurement error range in any of the examples. As an example, a thermal expansion curve of Example 6 is shown in FIG.

(Comparative Examples 1 to 19) For comparison, in the same manner as in the above example, without adding Mg, Ca or Sr as the second alkaline earth metal element, or (Ba)
_1-y , R _y ) _{1 + x} Zr ₄ P _6-2x Si _2x O ₂₄ (R: Mg,
A solid solution in which x and y in the Ca, Sr) composition were out of the range of the present invention was prepared, and this was sintered (Comparative Examples 1-1).
7). Further, a sintered body of another composition system of the alkaline earth zirconium phosphate sintered body was produced by the same method (Comparative Examples 18 and 19). Table 4 shows their compositions. For each of the obtained sintered bodies, as in the above example, the coefficient of thermal expansion,
The open porosity and the four-point bending strength were examined and are shown in Table 4.

As a result, the strengths of the compositions containing no second alkaline earth metal element were all less than 100 MPa. Adding a second alkaline earth metal element, x,
In examples where y is out of the range of the present invention, comparative examples 9, 11, 1
In some compositions, such as Nos. 2 and 14, the strength was greatly reduced, and in the conventional compositions of Comparative Examples 18 and 19, the strength was significantly reduced. Further, when the presence or absence of hysteresis in the thermal expansion curve was examined, hysteresis was observed in the thermal expansion curves in all the comparative examples. As an example, a thermal expansion curve of Comparative Example 4 is shown in FIG.

[0036]

[Table 4]

As described above, by adding Mg, Ca, and Sr as the second alkaline earth metal elements and setting x and y within the range of the present invention, it has a strength of 100 MPa or more and a thermal expansion curve. It can be seen that a low thermal expansion phosphate sintered body with small hysteresis can be obtained.

2 to 4 show (B) based on the above embodiment.
a _1-y , R _y ) _{1 + x} Zr ₄ P _6-2x Si _2x O ₂₄ (R: M
(g, Ca, Sr) shows the relationship between x, y and the coefficient of thermal expansion in the composition. FIG. 2 shows the case where R is Mg, FIG. 3 shows the case where R is Ca, and FIG. 4 shows the case where R is Sr. is there. In the figure, the dotted line indicates the optimal range of the thermal expansion coefficient of -1 × 10 ⁻⁶ / ° C. or 1 × 10 ⁻⁶ / ° C., and as shown in the figure,
Are A (0.2,0), B (0.45,0), C (0.
45, 0.2) and a range surrounded by D (0.35, 0.2) (note that points A, B, C, D and AB, BC, C
-D and DA lines are not included), it can be seen that a very low coefficient of thermal expansion can be realized. More specifically, A (0.2, 0), E (0.44, 0), F (0.
44, 0.18), a range (points F, G and EF, FG, GA) surrounded by G (0.34, 0.18)
And on the lines of points A, E and AE (on the x-axis)
It is understood that a very low coefficient of thermal expansion can be realized. In the drawing, the range in which the coefficient of thermal expansion is 0.4 and 0.8 is shown by a solid line.

[Brief description of the drawings]

1A is a diagram showing a thermal expansion curve of a sintered body of Example 6 of the present invention, and FIG. 1B is a diagram showing a thermal expansion curve of a sintered body of Comparative Example 4. is there.

FIG. 2 shows (Ba _1−y , R _y ) _{1 + x} Zr ₄ P _6−2x S
FIG. 4 is a diagram showing a relationship between x and y and a coefficient of thermal expansion in an i _2x O ₂₄ composition, where R is Mg.

FIG. 3 shows (Ba _1-y , R _y ) _{1 + x} Zr ₄ P _6-2x S
FIG. 4 is a diagram showing a relationship between x and y and a coefficient of thermal expansion in an i _2x O ₂₄ composition, where R is Ca.

FIG. 4 shows (Ba _1-y , R _y ) _{1 + x} Zr ₄ P _6-2x S
FIG. 4 is a diagram showing a relationship between x and y and a coefficient of thermal expansion in an i _2x O ₂₄ composition, where R is Sr.

Claims (1)

[Claims] 1. (Ba _1-y R _y ) _{1 + x} Zr ₄ P _6-2x Si
_2x O _24: having a composition represented by (R Mg, Ca, at least one of Sr), 0 <x <0.45,0 < low thermal expansion phosphorus, which is a y <0.2 Acid salt sintered body.