JPH01164760A - Sintered moldings - Google Patents

Abstract

PURPOSE: To produce a sintered compact consisting of Al₂TiO₅ as a base material produced from a starting material mixture consisting of TiO₂, Al₂O₃ and SiO₂ in a prescribed ratio respectively and specifying an Al₂O₃/TiO₂ ratio in which a TiO₂ phase is dispersed homogeneously and an abrasive structure without a crack is obtained.

CONSTITUTION: A starting material mixture is composed of ≥46% TiO₂, ≤49.5% Al₂O₃, 3-5% quartz (SiO₂) and ≤0.2% impurity by a weight ratio. In this case, Al₂O₃/TiO₂ is 1:(0.95-11.05) and the total weight is 100%. Then the starting material mixture is wet-ground to particles being (D50-) and having ≤0.5 μm grain size and the produced slurry is dried and molded. Then an objective sintered compact consisting of 15-35% TiO₂, 60-85% Al₂TiO₅, ≤5% Al₂O₃, ≤0.2% impurity and ≤17% mullite by a weight ratio is obtained by sintering and holding the molded matter at 1350-1490°C.

COPYRIGHT: (C)1989,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is based on the subject matter of claim 1. The invention furthermore relates to the preparation of the object of the invention and its use.

Aluminum titanate containing silicate is DE-AS
27 50 290. When producing this known aluminum titanate, 50-60% by weight AL203, 40-45% by weight TiO2, 2-5% by weight kaolin and 0.5% by weight are used. 1 to 1% by weight of magnesium silicate is used as a raw material. The thermal stability of pure aluminum titanate is improved by the addition of SiO2;
It is stated that a higher calcining temperature is required to obtain the same aluminum titanate content, since at the same time the thermal extensibility increases and the aluminum titanate formation slows down. To improve the physical properties, M2O
- component is considered necessary, for which purpose, for example, Sepiolith has been proposed. By doing so, a relatively flat elongation curve is obtained, with an elongation factor of 1.5x10-11 up to 1000'C.
i/' Located below C. As can be seen from the examples in this specification, the stoichiometric range of AL2O2 and TiO2 (AL2O2
O2:TiO2=1:0.78), young, Ti
The mixing should be carried out with a slight excess of O2. This means that AL2O2:TiO2=1:
For a ratio of 0°81, it is clear from example 5 of the specification that the best value is given.

The teaching of DE-As 27 50 290 can thus be interpreted in such a way that the content of aluminum titanate in the finished molded body should be as high as possible.

According to DE-AS 12 38 376, it has also already been proposed to produce ceramic materials from AL2O2, SiO2 and TiO2. As raw material components, kaolinite and also aluminum hydroxide are used as plastics, and lithium carbonate and other metal oxides are also used as other additives. This DE
- The achieved low hardness of the materials described in AS 12 38 376 is DE-AS 27 502 90
According to the authors, this is due to the lack of magnesium oxide compounds in the raw material mixture. On the other hand, this known substance has a temperature range of -o,i to -0,8x up to 1000°C.
It has a thermal elongation coefficient α of 10-67°C.

EP-A 133 021 contains 60-75% by weight A
L203.15-35% by weight TiO2 and 1-16.
Aluminum titanate lit ceramics combined with 5% by weight SiO2 are described. Additionally, 0.5 to 5% by weight, Fe2O3 and/or 0.5 to 5% by weight.
Rare metal oxides have been proposed. The above composition of the sintered ceramics includes a murite proportion of 20 to 40% by weight,
- an AL2TiO3 proportion of from 50 to 70% by weight and from 10 to
It contains an AL203 proportion of 12% by weight. In addition, a total of more than 3% by weight of iron oxide, lanthanum and neodimus oxides are described. The thermal expansion coefficient should be less than or equal to 2.5 x 10-G10C in the range between room temperature and 1000C.

EP-A 37 868 relates to a ceramic material with low thermal elongation, produced from aluminum titanate as a base material and with the addition of magnesium oxide and iron oxide.

The main components of this crystalline material phase are described as magnesium oxide/aluminum oxide/titanium oxide/silicon oxide/iron oxide in the solid solution flow. Many compounds are used as raw materials. For example, aorin is used to obtain aluminum oxide or magnesium carbonate is used to obtain magnesium oxide. The minimum achievable value of the flexural crushing strength is estimated to be extremely low at about 5 MPa at room temperature. The thermal expansion coefficient should not exceed a value of 2XIO-6°C in the range 25-800°C.

According to US-P 2872 72B, for silicate-free workpieces made using AL2O2 and TiO2, the addition of chromium oxide in an amount of, in particular, 25 to 60% by weight is proposed. The achieved flexural crush strength is relatively high and much greater than the strengths commonly known for aluminum titanate materials.

The proportions of aluminum oxide and titanium oxide are not mentioned either in the raw material mixture or in the composition of the finished material. Rather, the proportions of oxygen to the elemental metal oxides obtained, such as aluminum, titanium and chromium, are stated here.

US-PS 35 34 286 describes a material in which AL2O2 is one of the main components, in which case the typical composition is 75.2% by weight AL203.22° 8% by weight AL2-TiO5 and 2% by weight It is made of SiO2. There is no mention of the presence of free TiO2 in the finished material. This material is used for microwave control and must have fewer pores. Regarding this point, a value of 7% or less is stated.

It is clear from US-PS 3607 343 that
TiO2 has also already been used to coat AL203 particles in amounts of 1-50% by volume. This coated particle is
For example, they are used for coating by flame jetting with the addition of suitable binders based on phenolic resins.

In order to produce sinterable aluminum titanate powder, according to US-PS 38 25 853, a halide or alkoxy compound of aluminum and a hydroxide of titanium are co-precipitated, and the co-precipitate is dried. and has been proposed for use in the sintering of aluminum titanate products. The product made in this way has an I
It should have a thermal elongation rate of 0-610°C or less. The specific gravity is 70-85% of the theoretical specific gravity of 3°73 depending on the manufacturing method.
That is, it should be about 2.6-3.2. AL2O2
:TiO2 is mixed in a ratio of 1:1.1:3 to 3:1. No mention is made of mixing silicate compounds.

The powder described in the above US-PS specification is
According to PS 39 90 140, it is used for the production of uranium and this molten brick for uranium metallurgy. When manufacturing molten bricks by hot pressing method, 10~
One should start from aluminum titanate powder with a size of 70 μm. A ratio of 50 mol% AL203/TiO2 is considered suitable.

US-PS 41 18 240 essentially describes aluminum titanate containing 1.5 to 10% by weight of tin oxide (Sn
02) and with the addition of 2-3% by weight of SiO2. Instead of 5n02, rare earth oxides such as L a 1Ce N and Y oxides can also be used. A synergistic effect between SiO2 and these rare earth oxides, especially tin oxide, is expected. Use TiO
2 amount is 37 to 55% by weight of AL2O2.
It is 39% by weight. AL2 as described in this specification
For compositions consisting of O2, TiO2 and SiO2, 20~
The expansion coefficient is 1.2x10- in the temperature range of 1000'C.
8 and a reported strength at room temperature of 18 MPa (not calculated) has been achieved.

According to DD-PS 29 794, good temperature change stability is achieved by a very low, especially negative, linear thermal expansion coefficient. According to the specification, in order to produce an oxide material with high fire resistance and good temperature change stability, a composition consisting of Mg0-AL2O2-TiO2-mer or Mg0-AL2O2-TiO2-8i02 is required. A product has been proposed in which the proportion of TiO2 is 15-75% by weight and the proportion of AL2O2- is 70-35% by weight.
% by weight and the proportion of SiO2 and MgO should be up to 40, or even 20%. The linear thermal expansion coefficients achieved in this specification range from 20 to 700 oC and 4
It should be less than or equal to x 10-6/' C, and in particular should be negative or not too far from O. AL2O2 described in this specification: T i
The mixing ratio of 02 covers a wide range from 1:0.7 to 1:1.7, the latter range also being true for compositions without silicate with an MgO proportion of 8% by weight. .

The last specification describes the ideas that have been dominant in the past,
In other words, the temperature change stability of aluminum titanate material is
This is a typical example of the idea of improving by adjusting the thermal expansion coefficient as little as possible. As noted in this specification, their temperature change stability, however, also directly depends, inter alia, on the thermal conductivity, the tensile strength and the elastic modulus. However, as can be seen from DE-AS 27 50 290 mentioned at the outset, which forms the closest state of the art in this case, a low coefficient of thermal expansion always has advantages. The known proposals, however, suggest that the produced sintered moldings do not in any case have sufficient temperature stability at their disposal, so that even during their casting, depending on the circumstances, the sintered moldings are Defects only appear after long-term use. The defects may begin already during one contact, for example during recasting with the metal melt, or they may occur later. The sintered molded product in question is
Careful monitoring of the physical values of the sintered moldings often leads to premature failure of the molded moldings while they are used under their own unaltered loads, since they have some quality differences. wake up In particular, the reason for this unexpected defectiveness of the sintered compacts has not necessarily been proven, or it has been assumed that some non-uniformity of the seams of the sintered compacts is the cause.

It is an object of the present invention to further improve the known sintered bodies based on aluminum titanate and to use them in production operations, in particular with melts of non-ferrous metals in the temperature range below 800 °C. Its stability upon recasting lies in its further expansion as configured.

Surprisingly, contrary to the prevailing conventional wisdom, the solution to the problem at hand is that the composition of the raw material mixture is such that a relatively high amount of free TiO2 is present in the finished sintered body. This is achieved using a mixture of raw materials.

Therefore, contrary to the known state of the art, no attached aluminum oxide or titanium oxide remains and is not reacted with aluminum titanate, and a certain amount of TiO2
Care has been taken to ensure that there is an excess of TiO2, so that there is no TiO2 that reacts with the aluminum titanate. It has also been found that the quality and homogeneity of the sintered bodies in question can be further improved by minimizing the magnesium oxide content and other impurities that are partly unavoidably formed. Based on the above findings, the present invention provides the following:
In the case of a sintered body according to the generic concept of claim 1,
In order to solve the current problem, we are planning the features described in the characteristics section.

Although it has not yet been elucidated in detail what the excellent effect of the sintered compact of the present invention is, it has been found that the following characteristics are important. It is thus important that the composition of the raw material mixture consists of very pure substances without using kaolin, which is known from the state of the art, as a component of the raw material mixture; aluminum oxide with a purity of at least 99% is preferably used. The presence of impurities of up to 0.2% by weight, such as magnesium oxide, is by no means necessary, but
．． Up to 1% by weight may be present. This is because the presence of this substance in the raw material mixture cannot necessarily be excluded. This is because impurities, such as crushed or powdered particles, are unavoidable. What is of essential importance is a homogeneous distribution of the TiO2 phase in the sintered compact. This is because it has been found that when using the raw material mixture according to the invention, a crack-free abrasive structure is obtained due to the presence of a homogeneously dispersed TiO2 phase. The presence of a crack-free abrasive structure is extremely important. This is because the high reliability of the use of the sintered bodies according to the invention in production operations is attributed to this.

A moderate particle size of aluminum titanate particles of 5 to 20 μm is also important. In particular, its value is 8 to 15 μm
Even. The average particle size of titanium oxide is smaller, between 0.5 and 10 μm, but in any case smaller than the average particle size of aluminum titanate particles. The sintered bodies known from this practice and corresponding to the generic concept of patent claim 1, on the other hand, have a grain size of aluminum titanate of 1 to 3 μm.

The sintered compact of the present invention has the following composition.

15-35% by weight TiO2 60-85'' AL2TiO5 (aluminum titanate) up to 5% by weight AL2O2 up to 17% by weight Murlit max. 0.5% by weight impurities, the total weight% being 100% by weight.

The specific gravity of the sintered compact is at least 3.0, but unlike known sintered compacts, it can be increased to 3.6 g/c+n3. A specific gravity in the range of 3.3 to 3.5 g/cm3 is preferable. The flexural breaking strength is at least up to 25 MPa, preferably within the range of 33 to 47 MPa. E
- The module is 14000-25000 MPa. The elongation coefficient is from about 1.5 to about 3.0 x 10-11iK-1 in the temperature range from 400 to 800°C, thus essentially for the known sintered compacts of DE-AS 275°290. Higher in nature. Thermal insulation (Waermed)
aemmung ) is 1 to 3 W/mK.

Further advantageous embodiments characterized in the dependent claims are particularly directed to the method of the invention for producing sintered shaped bodies. Using a raw material mixture of extremely pure substances, the kaolin that has been proposed so far is absolutely excluded, and the necessary supply of SiO2 is provided by quartz, but the presence of other impurities is eliminated as completely as possible, and the impurities are The maximum content of magnesium oxide does not exceed 0.2% by weight of the raw material mixture, allowing a maximum of 0.1% by weight of magnesium oxide, mixing these oxides to a particle size D50 of less than 0.5 μm. By grinding and using auxiliaries known per se, a raw material with a specific gravity of at least 2.4 g/cm3 is produced from the slurry. Sintering is carried out at a temperature of 1350-1490'C for a holding time of 1-5 hours.

Alternatively, the production can also be carried out by shaping and pressing a powder mixture comprising the composition of the invention, containing customary binders, and produced by spray drying.

The sintered compact is sintered using a method known per se.
For example, using a diamond machine tool, the final shape is created through hard machining. A particularly interesting area of use for the sintered moldings of the invention is their use in the production of composite bodies made of metal or ceramics. Such a connection is, for example, a waste gas pipe in a combustion motor, in particular in a combustion chamber. In that case, it is particularly advantageous if the sintered shaped body is round or oval in each cross section, avoiding concave shapes and having all edges rounded - 1! ;-, a wall thickness of 3-4+am is particularly advantageous.

The following examples provide a detailed illustration of the invention.

Kayu JL-1゜49% by weight AL2O2 47// TiO2 4 A raw material mixture consisting of quartz (Si02) was dispersed in water, and the sinker was
．． Grind to D50-particle size below 5 μm.

The mixture is spray-dried and pressed out of itself at a pressure of 1000 bar to form a green body, with the addition of a common temporary binder. The binder is heated to 300°C and the green compact is then sintered at 1430°C for 3 hours. The following values were measured for this sintered compact.

Specific gravity 3.43g/cm3 Flexural breaking strength δB: 38MPa Elastic modulus: 18000MPa Thermal elongation coefficient α in the temperature range of 400-800℃: 2.3x10-B/-1 This sintered compact has the following composition .

68% by weight AL2TiO3 18// TiO2 - i/ b - 1// AL2O2 Residual Murlit Example-2 - Contains 75% by weight of solids and has a particle size of D50 of 0.5 μm or less and defects in the milling operation. Create an aqueous soil with a specific composition.

48.5% by weight AL2O2 48,5// TiO2 3 〃 Quartz (Si02) A hollow tube-shaped molded body was formed from the soiled material by casting, and this resulting carving was held at 1440'C for 2.5 hours. Time to sinter.

The following values were measured for this sintered compact.

Specific gravity 3-4g/c+++3 Flexural breaking strength δB: 36MPa Elastic module: 15000MPa Thermal elongation coefficient in the temperature range of 400-800'C (1: 2.1x10-6/k-1 Composition F deficiency of this sintered compact It is as follows.

75% by weight AL2T i 05 18 // TiO2 1 n AL2O2 Residual Murlisoto Among the attached photos, Photo 1 shows the natural untreated surface of the sintered compact of the present invention, and Photo 2 shows the natural untreated surface of the commercially available sintered compact. Photo 3 shows the polished structure of the sintered compact in Photo 1, and Photo 4 shows the polished structure of the sintered compact in Photo 2. Comparing Photos 1 and 2, it is clear that the sintered compact of the present invention has a polished structure. An essentially sparse grain surface can be seen.

Comparing Photos 3 and 4, it is clear that the sintered compact of the present invention has a crack-free polished structure in which TiO2 is homogeneously dispersed, whereas the polished structure in Photo 4 shows cracks. .

[Brief explanation of the drawing]

Attached photos 1 and 3 show the product of the invention, photos 2 and 4
indicates a commercially available product. There is no other way to prove this effect than by using photographs.

Claims (1)

[Scope of Claims] (1) The composition of the starting materials is 46% by weight or more of TiO2, 49.5% by weight or less of AL2O3, 3 to 5% by weight of quartz (SiO2), and 0.2% by weight or less of impurities; At this time, the ratio of AL2O3 and TiO2 is 1:0.95.
In addition to the SiO2-compound, which is characterized in that it is present in an amount of from 11.05% to 100% by weight, aluminum titanate produced from a raw material mixture containing aluminum oxide and titanium oxide is also used. Sintered molded body as a substrate (2) 15-35% by weight of TiO2 60-85% by weight of AL2TiO5 (aluminum titanate) Up to 5% by weight of AL2O3 Up to 0.2% by weight of impurities and up to 17% by weight of mullite The sintered compact according to claim 1, characterized in that the sintered compact (3) has a specific gravity of 3.0 to 3.6 g/cm3. (4) A sintered compact according to claims 1 to 3 characterized by an abrasive structure with a homogeneous distribution of the TiO2 phase (5) 400-800°C temperature range of 1.5 to 3
．． Sintered shaped body according to one of claims 1 to 4, characterized by an average thermal elongation coefficient α of 0x10-6/k-1 (6) Aluminum titanate particles having an average particle size of 5
-20 μm (7) 46% by weight or more of TiO2 49.5% by weight or less of AL2O3 3 to 5% by weight of quartz (SiO2) A starting mixture consisting of impurities of 0.2% by weight or less, the total weight of which is 100% by weight, is wet-pulverized to a particle size of D50- of 0.5 μm or less,
The resulting slurry is used as a raw material, and after drying, at least 2
．． According to one of claims 1 to 6, characterized in that a product having a mud specific gravity of 4 g/cm3 is molded and the product is sintered by holding it at a temperature of 1350 to 1490 °C for 1 to 5 hours. Method for producing a sintered compact (8) Consisting of 48% by weight or more of TiO2, 49.5% by weight or less of AL2O3, 3 to 5% by weight of quartz (SiO2), 0.2% by weight or less of impurities, in which case the total weight% The starting mixture containing 100% by weight of
Press a product having a mud specific gravity of 1.
A method for producing a sintered shaped body according to claims 1 to 6, characterized in that the sintering is carried out by holding at a temperature of 1350 to 1490 °C for a period of 5 to 5 hours (9) Hollow tubular metal in an exhaust gas pipe of a combustion motor - Use of a sintered compact according to one of claims 1 to 6 for producing a ceramic composite body