JP2500809B2 - Heat-resistant phosphate compound sintered body and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat-resistant phosphate compound sintered body and a method for producing the same, and more specifically, it is excellent in heat resistance and low expansion and has high temperature stability. The present invention relates to an excellent sintered body of a phosphate compound and a method for producing the same.

[Prior Art] In recent years, with the progress of industrial technology, there has been an increasing demand for materials excellent in heat resistance and low expansion.

Under these demands, zirconyl phosphate [(ZrO) ₂ P
₂ O ₇ ] has been found to be promising as a material excellent in heat resistance and low expansion.

Recently, zirconium phosphate, which is an alkali metal such as sodium, has been proposed as a substance having heat resistance and a low coefficient of thermal expansion. (Mat.Res.Bull., Vol.19, pp.1451
-1456 (1984), Journal of Materials Science 16,1633
-1642 (1981), and the Ceramic Society of Japan 95 [5], Nos. 531 to 537.
(Pp. 1987) Further, a phosphate compound of an alkaline earth metal having a specific composition has been proposed as having a low expansion property. (Mat.Res.Bull., Vol.20, pp.99-106,1985, and JA
m.Geram.Soc., 70 [10] C-232 to C-236 (1987)) In addition, U.S. Pat. No. 4,675,302 describes Ca _0.5 Ti ₂ P ₃ O.
Ceramic materials having ₁₂ basic compositions have been proposed as having excellent low expansion properties.

[Problems to be Solved by the Invention] However, although the above-mentioned phosphate compounds such as zirconyl phosphate have an advantage of being excellent in low expansion property, a common problem with these phosphate compounds is as follows.
Thermal decomposition occurs at high temperatures above 00 ° C, resulting in phosphorus (P)
It is mentioned that the minutes evaporate. For example, at 1400 ° C
19% of zirconyl phosphate when heat treated for 100 hours
There is a problem that it shows a weight loss.

Further, the ceramic material proposed in U.S. Pat. No. 4,675,302 is mainly used for a substrate of a low expansion optical reflector which is not deformed by a temperature change for artificial satellites. As shown in the figure, the temperature change is intended to be up to about 500 ° C., and no consideration is given to stability, heat resistance, etc. at a high temperature of 1200 ° C. or higher.

On the other hand, as a method for producing a phosphate compound, Na ₂ CO ₃ , Zr
_{O 2, ZrOCl 2 · 8H 2} O, SiO 2, (NH 4) 2 HPO 4, H 3 PO 4, Nb 2 O 5, Y
_{A method using a combination of 2} O ₃ , SrCO ₃ , K ₂ CO ₃ , CaCO _{3 and the} like is known. (T. Oota and I. Yamai, Journal of the
American Ceramic Society, 69 , 1, (1986)] However, in the above production method, the P ₂ O ₅ component is independently generated during the process of decomposing ammonium phosphate or H ₃ PO ₄ , and the phosphorus concentration is locally increased. Of the low melting point compound is formed during sintering. For this reason, there are huge pores (voids) in the sintered body, centering on the low melting point compound.
Will result in serious defects.

[Means for Solving the Problem] Therefore, the present inventor has conducted various studies in order to solve the above-mentioned problems of the conventional technique, and as a result, in order to suppress the weight loss due to the evaporation of phosphorus, a certain amount of addition is added. It is effective to add an agent and calcinate. In that case, it was found that a predetermined crystal phase was formed in the sintered body, and the present invention was accomplished.

That is, according to the present invention, R _y Zr ₄ Si _x P _6-x O ₂₄ (R is 2 to
A crystal phase having a composition selected from one or more elements capable of becoming trivalent ions, x has a numerical value of 0 or more and less than 6 and y has a numerical value of 2/3 or more and less than 4 that satisfies the electrical neutrality condition of the chemical formula) A heat-resistant phosphate compound sintered body containing 10% by weight or more and having a weight loss rate of 10% or less when heat-treated at 1400 ° C. for 100 hours, and ZrP ₂ O ₇ , (ZrO) ₂ P ₂ O ₇ , ZrO ₂ , ZrSiO ₄ , Si
A batch mixture composed of a substance selected from O ₂ , R phosphate, R silicate, and RO (R is an element that can be a divalent to trivalent ion) is molded and fired to give the above-mentioned specific composition and Provided is a method for producing a heat-resistant phosphate compound sintered body, which comprises obtaining a heat-resistant phosphate compound having physical properties.

In the phosphate compound sintered body of the present invention, it is necessary that the sintered body contains a crystal phase represented by the general formula of R _y Zr ₄ Si _x P _{6 -x} O ₂₄ . Depending on the presence or absence of this crystal phase, the thermal stability at high temperatures greatly differs, as will be described below.

Further, R is one or more elements capable of becoming 2-3 valent ions, and generally represents an element belonging to Group IIa of the periodic table, but one of barium (Ba), strontium (Sr), and calcium (Ca) It is preferable that the above is configured.

Furthermore, according to the sintered body of the present invention, in the range where the open porosity is 50% or less, after heat treatment at 1400 ° C. for 100 hours,
The weight reduction rate due to the evaporation of phosphorus can be as low as 10% or less, and the bending strength can be 100 kg / cm ² or more. That is, when the open porosity exceeds 50%, the bending strength becomes less than 100 kg / cm ^2, and the strength required when using ceramics as a practical material cannot be satisfied.
Further, this sintered body has a self-weight softening rate of 0.3% or less after heat treatment at 1400 ° C. for 5 hours, which satisfies the requirements as a heat resistant material.

Further, this sinter has a small dimensional change rate, and when heat-treated at 1400 ° C. for 100 hours, the dimensional change rate is 1% or less, which also satisfies the requirements as a heat resistant material.
Furthermore, this sintered body has a low coefficient of thermal expansion of 25 × 10 ⁻⁷ / ° C. or less from room temperature to 1400 ° C., and is excellent in thermal shock resistance. Therefore, the sintered body of the present invention having the characteristics as described above is a ceramic honeycomb structure such as an automobile exhaust gas purification catalyst carrier, a rotary heat storage type ceramic heat exchange body, a heat transfer type heat exchange body, a housing for a turbocharger rotor, and It is preferably applied to materials that require heat resistance and thermal stability at high temperatures such as engine manifold heat insulating materials.

Next, in the method for producing a heat-resistant phosphate compound sintered body according to the present invention, the raw materials are ZrP ₂ O ₇ , (ZrO) ₂ P ₂ O ₇ , and Zr
O ₂ , ZrSiO ₄ , SiO ₂ , R phosphate, R silicate, and RO
It is characterized in that it is a batch mixture of powders made of a substance selected from (R is an element that can be a divalent to trivalent ion).
That, ZrP ₂ O _7, a _{(ZrO) 2 P 2 O 7} , ZrO 2, ZrSiO 4, SiO 2, R phosphates, silicates of R, and RO are each stable compound, forming firing process Therefore, it is possible to obtain ceramics which are less likely to cause non-uniformity, can be fired at high temperature, and have excellent heat resistance.

On the other hand, when a conventional phosphoric acid was used as the P ₂ O ₅ source, the phosphoric acid was a liquid, so it became non-uniform during the mixing process, forming a locally high phosphorus concentration portion as described above. Yields a low melting point compound. For this reason, a serious defect occurs in which a huge bore is formed in the sintered body centering on the low melting point compound. When a kneaded material containing phosphoric acid is extruded to obtain a honeycomb structure, the corrosiveness of phosphoric acid causes the die for extrusion and the cylinder of the extruder to corrode or corrode, resulting in significant formation. It will be difficult. Furthermore,
In the case of application to press molding, there is a drawback that molding as powder is essentially impossible due to the phosphoric acid content.

Further, ZrP ₂ O ₇ , (ZrO) ₂ P ₂ O ₇ , ZrO ₂ , ZrSiO ₄ , SiO ₂ , R phosphates, R silicates and RO usually have a ZrP ₂ O ₇ content of 0 to 84.2.
% By weight, (ZrO) ₂ P ₂ O ₇ 0-82.3% by weight, ZrO ₂ 0-51.7
% By weight, 0 to 77.2% by weight of ZrSiO ₄ , 0 to 37.8% by weight of SiO _{2, 0} to 44.6% by weight of R phosphate and 0 of R silicate.
˜53.0% by weight and RO are blended in a ratio of 0 to 42.1% by weight. Of these, one of ZrP ₂ O ₇ and (ZrO) ₂ P ₂ O ₇ and R phosphate, and RO , R silicate or R phosphate must be included in the batch mixture.

Further, as the raw material RO, it is also possible to select and use RO during the firing, that is, stable compounds such as hydroxides, carbonates and sulfates which are converted into oxides.

It should be noted that the raw material usually has an average particle size of 50 μm or less, preferably 10 μm or less.

The firing conditions for the sintered body of the present invention include a firing temperature of 1400 ° C.
The above is preferably 1400 to 1800 ° C., and the firing time is 1 to 24 hours, preferably 2 to 10 hours. By setting the firing temperature to 1400 ° C. or higher, R _y Zr ₄ Si _x P _6-x O ₂₄ can be used as a crystalline phase.
The phosphate compound sintered body of the present invention containing 0% by weight or more can be obtained. Further, if the firing time is less than 1 hour, the sintering is insufficient, and if it exceeds 24 hours, the strength is lowered due to abnormal grain growth and the precipitation of a different phase is caused by the phosphorus content evaporation.

The preferred embodiments of the present invention described above will be summarized as follows.

(A) A phosphate compound sintered body in which R is composed of one or more of Ba, Sr, and Ca.

(B) A phosphate compound sintered body having an open porosity of 50% or less and a bending strength of 100 kg / cm ² or more.

(C) The self-weight softening rate after heat treatment at 1400 ℃ for 5 hours is 0.3%
The following is a phosphate compound sintered body.

(D) A phosphate compound sintered body having a dimensional change rate of 1% or less when heat-treated at 1400 ° C. for 100 hours.

(E) Thermal expansion coefficient from room temperature to 1400 ℃ is 25 × 10 ^-7 /
A phosphate compound sintered body having a temperature of ℃ or less.

(F) A phosphate compound sintered body used as a ceramic honeycomb structure.

(G) A method for producing a phosphate compound sintered body, wherein R is composed of one or more of Ba, Sr, and Ca.

(H) Hydroxide, carbonate, which RO transforms into RO during firing,
A method for producing a phosphate compound sintered body selected from sulfates.

(I) A method for producing a phosphate compound fired body, which has a firing temperature of 1400 ° C. or higher and a firing time of 1 to 24 hours.

[Examples] Hereinafter, the present invention will be described based on Examples, but it will be apparent that the present invention is not limited to these Examples.

(Examples and Comparative Examples) Zirconyl phosphate [(ZrO) ₂ P ₂ O ₇ ], ZrP ₂ O ₇ , calcium carbonate, strontium carbonate, barium carbonate, the particle size of which was adjusted in advance according to the blending ratio shown in Table 1. Yttria, zircon, sodium carbonate, ceria, titania,
Silica, calcium phosphate and zirconia were mixed. A vibrating mill filled with ZrO ₂ sintered boulders having a diameter of about 5 mm was used to adjust the particle size of zirconyl phosphate, but the particle size can also be adjusted using a pot mill or an attritor. As the ZrO ₂ sintered boulders, those stabilized with MgO and those stabilized with Y ₂ O ₃ were used. Table 2 shows the chemical composition of the boulders used. Table 3 shows the chemical analysis values of the raw materials used.

To 100 parts by weight of the mixture shown in Table 1, 5 parts by weight of 10% PVA aqueous solution was added and mixed well, and after press molding with a mold of 25 × 80 × 6 mm at a pressure of 100 kg / cm ² , It was dried by rubber pressing at a pressure of 2 ton / cm ² . After this molded body was dried, it was fired in the air in an electric furnace under the conditions shown in Table 1. The temperature rising rate was 5 to 1700 ° C / hr. After firing, this sintered body was processed into a bending test piece of 3 × 4 × 40 mm shown in JIS R1601 (1981), and the weight reduction amount and the dimensional change rate during heat treatment at 1400 ° C. for 100 hours, 40 to 1400 ° C. Coefficient of thermal expansion up to,
The four-point bending strength, the self-weight softening amount, the open porosity, and the melting point were measured. A push rod differential thermal expansion meter using a high-purity alumina sintered body was used to measure the thermal expansion coefficient. Measuring temperature range is 40
~ 1400 ° C. The 4-point bending strength was measured according to the method shown in JIS R1601. The self-weight softening rate is as shown in FIG. 6, where the bending test piece of 3 × 4 × 40 mm is placed between supports of 30 mm width, and heat treatment is performed at 1400 ° C. for 5 hours in the atmosphere.
The weight deformation amount Δx at that time was measured to obtain the following equation.

Self-weight softening rate = Δx / l × 100 (%) The open porosity was measured by the Archimedes method. The melting point is
The sintered body cut out in a shape of 3 × 4 × 5 mm was heat-treated in an electric furnace at 1650 ° C. for 10 minutes, and it was visually judged whether or not it was melted. Further, the crystal phase amount of the sintered body is zirconyl phosphate [β- (ZrO) ₂ P ₂ O ₇ ] [Communications of the American
Ceramic Society, C-80 (1984)] (200) plane reflection peak value, R _y Zr ₄ P _6-x Si _x O ₂₄ (113) plane reflection peak value [The above composition crystal phase index is JCPDS 33- 321, CaZr ₄ (PO ₄ ) ₆ , JCP
DS 33-1360, SrZr ₄ (PO ₄ ) ₆ , JCPDS 34-95, BaZr ₄ (PO ₄ ) ₆
Indexed according to. ], Zircon JCPDS 6-266 (312) plane reflection peak value, and m-ZrO ₂ JCPDS 34-95
It was quantified using the (011) plane reflection pork value of. Where m
(011) plane reflection of -ZrO ₂ because relative strength is low and 18/100, was used to the 5.6-fold as a peak value. Regarding other heterogeneous crystal phases, only the presence or absence thereof was identified by an X-ray diffraction pattern.

As is clear from the results of Examples 1 to 18 and Comparative Examples 19 to 27 shown in Table 1, R _y Zr ₄ P _6-x Si _x O ₂₄ (R can be a divalent or trivalent ion) as a crystal phase. When one or more elements are contained in an amount of 10% by weight or more, a phosphate compound sintered body having a weight loss rate of 10% or less when heat-treated in the air at 1400 ° C. for 100 hours, which is the object of the present invention, is obtained. It was Further, such a sintered body is made of a material selected from ZrP ₂ O ₇ , (ZrO) ₂ P ₂ O ₇ , ZrO ₂ , ZrSiO ₄ , SiO ₂ , R phosphate, R silicate and RO. It was obtained when the following mixture was sintered under the firing conditions shown in Table 1. Fig. 1 shows the relationship of the weight reduction rate when various oxides are added to the phosphate compound, and Fig. 2 shows the relation of the R _y Zr ₄ P _6-x Si _x O ₂₄ phase contained in the phosphate compound. The relationship between the weight% and the weight reduction rate of the sintered body is shown. FIG. 3 shows the relationship between the weight percentage of the R _y Zr ₄ P _6-x Si _x O ₂₄ crystal phase contained in the phosphate compound sintered body and the dimensional change rate of the sintered body.

From the above, R _y Zr ₄ P is contained in the phosphate compound sintered body.
By including 10% by weight or more of _6-x Si _x O ₂₄ crystalline phase, 1
It can be seen that it is possible to obtain a phosphate compound sintered body which is excellent in heat resistance with a small weight reduction rate and a small dimensional change rate when heat-treated in the air at 400 ° C. for 100 hours.

FIG. 4 is a graph showing the relationship between open porosity and bending strength of the phosphate compound sintered body.

Further, FIG. 5 shows an X-ray diffraction pattern of the phosphoric acid compound sintered body of Example 3. From this figure, (ZrO) ₂ P ₂ O ₇
And CaZr ₄ (PO ₄ ) ₆ are contained.

[Effects of the Invention] As described above, according to the heat-resistant phosphate compound sintered body of the present invention and the method for producing the same, R _y Zr ₄ P _6-x Si _x O ₂₄ (R
Is a heat-resistant phosphate that contains 10% by weight or more of a crystalline phase of one or more elements that can become divalent to trivalent ions, and the weight loss rate is 10% or less when heat-treated at 1400 ° C for 100 hours. A compound sintered body can be obtained.

Therefore, this phosphate compound sintered body is required to have heat resistance, low expansion property, and high temperature stability. For example, when it is formed into a honeycomb structure by extrusion molding, etc. The present invention can be widely applied to a heat exchanger, a ceramic turbocharger rotor housing formed by a slurry casting method, a press molding method, an injection molding method, or an insulating material in an engine manifold.

[Brief description of drawings]

FIG. 1 is a graph showing the weight reduction rate when various oxides are added to the phosphate compound sintered body at 1400 ° C. for 100 hours, and FIG. 2 is R _y in the phosphate compound sintered body. Zr ₄ P _6-x Si _x
A graph showing the amount of O ₂₄ crystal phase and the weight loss rate at 100 ° C. for 100 hours, FIG. 3 shows R _y Zr ₄ P in the phosphate compound sintered body.
A graph showing the amount of _6-x Si _x O ₂₄ crystalline phase and the dimensional change rate at the time of heat treatment at 1400 ° C. for 100 hours. FIG. 4 is a graph showing the relationship between the open porosity and the bending strength of the phosphate compound sintered body, FIG. 5 is a graph showing an X-ray diffraction pattern of the phosphoric acid compound of Example 3, and FIG. 6 is a view showing a method for measuring the self-weight softening rate.

Claims (2)

(57) [Claims] 1. R _y Zr ₄ Si _x P _6-x O ₂₄ (R is selected from one or more elements capable of becoming 2-3 valent ions, x is a numerical value of 0 or more and less than 6, and y is an electrical formula. A heat-resistant phosphorus containing 10% by weight or more of a crystal phase having a composition satisfying the neutral condition and having a numerical value of 2/3 or more and less than 4 and having a weight loss rate of 10% or less when heat-treated at 1400 ° C. for 100 hours. Acid salt compound sintered body. 2. ZrP ₂ O ₇ , (ZrO) ₂ P ₂ O ₇ , ZrO ₂ , ZrSiO ₄ , Si
The heat resistance according to claim 1, wherein a batch mixture made of a substance selected from O ₂ , R phosphate, R silicate, and RO (R is an element that can be a divalent to trivalent ion) is molded and fired. A method for producing a heat-resistant phosphate compound sintered body, which comprises obtaining a heat-resistant phosphate compound.