DE3725170A1 - STABILIZED CERAMIC MATERIALS, METHOD FOR THE PRODUCTION AND USE THEREOF - Google Patents

Abstract

The invention relates to a process for manufacturing thermal shock-resistant and refractory ceramic materials based on the system aluminium oxide/titanium dioxide by customary methods of ceramic technology, characterised in that the starting materials used are mixtures of Al2O3 and TiO2 with additions of from 0.1 to 15 % by weight of niobium pentoxide and/or tantalum pentoxide; stabilised ceramic materials obtained by this process and also their use.

Description

The present invention relates to an improved ceramic Material based on the Al₂O₃ / TiO₂ system preferably aluminum titanate ("tialite"), its temperature resistance to changes, mechanical strength and sintering hold by the entry of niobium and / or tantalum oxide can be improved.

Aluminum titanate is a new type of ceramic material recently found versatile applications and ge is gaining increasing importance in engineering ceramics whether there are some fundamental shortcomings:

As is known, takes place in the temperature range below 1300 ° C in ceramic Shaped bodies made of aluminum titanate by decomposing the chemical Species a decay of the ceramic parts from this material instead of how to from numerous references.

These temperatures are e.g. B. in exhaust systems of thermal engineering, in which Aluminum titanate is advantageous because of its low thermal expansion is used, unavoidable. But also in other areas of fire solid ceramics, e.g. B. as crucible material for iron metallurgy, in the glass industry and for heat engines and as a material for grinding ceramics or as an insulating material, this area is subject to temperature changes Persistence of acute importance.

The critical one maintains particularly on the surfaces of the ceramic components Temperature range to occur most frequently.

The use of sintered ceramic made of aluminum titanate as a high temperature material is therefore under temperature change conditions in the above critical temperature range is not without problems, because the mechanical Firmness of  Ceramic components are declining sharply.

Remedy against such undesirable decomposition effects offer additives of various foreign metal oxides that in small to large amounts as a dopant stabilizing effect the aluminum titanate or the Aus materials (aluminum oxide and titanium dioxide) before sintering be added. On the one hand, these additives reduce the Decomposition tendency of the material in critical temperature range and on the other hand increase the strength that pure aluminum titanate because of its known heat strain anisotropy and the resulting micro Cracking in the structure of the ceramic parts very unsatisfactory is.

To the known stabilizers or dopants ge hear z. B. alkali oxides, iron oxide, alkaline earth oxides, rare earth oxides, tin dioxide, zirconium silicate or glass-forming oxides such as boron trioxide, phosphorus pentoxide or silicon dioxide.

A comprehensive literature review on the state of the art is in the magazine SPRECHSAAL, volume 118, No. 12, pages 1157-1166.

With the previously known doping additives you can now achieve however, in most areas of application only an unrelated one peaceful improvement in resistance to temperature changes and mechanical strength. So it was the job of the present invention, over the known additives to find other dopants for aluminum titanate, what additional improvements in material properties of the aluminum titanate.

In particular, the object of the invention was ge judges the resistance of the aluminum titanate below  of 1300 ° C, the sintering behavior in relation to elongation or shrinkage of the moldings when processing the Aluminum titanate materials, but also the strength under Changes in temperature of the finished sintered parts improve.

It has now surprisingly been found that the Sintering behavior of ceramic materials in the Alu system minium oxide / titanium dioxide, especially of aluminum ti tanats, as well as the mechanical strength and at the same time the Surface hardness of the sintered body made of aluminum titanate by adding 0.1 to 15% by weight of niobium oxide and / or Tantalum oxide, preferably 1 to 10, in particular 1.5 to 7.5% by weight of niobium pentoxide or 2.0 to 12.5% by weight of tantalum pentoxide or 1.5 to 12.5% by weight of a mixture of Nb₂O₅ and Ta₂O₅ in any ratio, can significantly improve.

Furthermore, it was found that not only undoped Aluminum oxide / titanium dioxide starting mixtures or undo tied (i.e. pure) aluminum titanate but also with the known doping additives already applied aluminum Titanate formulations through the addition of niobium and / or tantalum Pentoxide improved for use as a ceramic material can be.

The invention therefore relates to a process for the preparation position of thermal shock-resistant and refractory ceramic Materials based on the aluminum oxide / titanium system dioxide by the usual methods of ceramic technology, because characterized in that mixtures are used as starting materials of Al₂O₃ and TiO₂ with additions of 0.1 to 15 wt .-% niobium Pentoxide and / or tantalum pentoxide is used.

To stabilize the system's ceramic materials Aluminum oxide / titanium dioxide are generally fiction  according to aluminum oxide and titanium dioxide in usual proportions such as the 0.7 to 1.3 times stoichiometric amounts of aluminum oxide (Al₂O₃) with 1.3 to 0.7 times stoichiometric amounts Titanium dioxide (TiO₂) and with an additional 0.1 to 15 wt .-% niobium oxide and / or tantalum oxide intimately mixed, with one another Conventional mixing method, preferably a grinding mixer operated.

Said mixing process can also be carried out in a known manner Form of suspensions in water or in special inert Solvents are carried out. The shape of the ceramic body takes place in the usual way such. B. in Schlickergußver drive or with the help of ceramic presses, if simple geometric shapes are desired.

Preferred mixing ratios of the oxide mixture are Ranges 40-60 wt .-% Al₂O₃ with 50-30 wt .-% TiO₂ under Zu Set of 1-10 wt .-% Nb₂O₅ or 2-12.5 wt .-% Ta₂O₅ or 1-12.5 wt .-% of a mixture of Nb₂O₅ and Ta₂O₅ in be loving relationship. (All data in% by weight are based on the Ge velvet composition.)

In particular, mixtures of the simple stoichiometric Ratio of Al₂O₃ / TiO₂ - according to the formula Al₂TiO₅ - with 0.1 to 15 wt .-% Nb₂O₅ and / or Ta₂O₅, based on the overall composition are preferred.

Such mixtures of the system also come Al₂O₃ / TiO₂ as starting materials in question, which already beta aluminum titanate formed by chemical reaction Contain phases, d. H. their implementation from the undoped Starting materials Al₂O₃ and TiO₂ has already been carried out.

According to an embodiment of the present method are already with known additives, especially foreign metal oxides, doped starting mixtures of the system  Aluminum oxide / titanium dioxide with niobium oxide and / or tantalum oxide acted upon.

For sintering the "green" Al₂O₃ / TiO₂ ceramic molded body usual conditions are applied. To the training of the aluminum titanate structure with the highest possible To achieve conversion rate, temperatures of the distillate oven from 1300 to 1450 ° C required. The holding times are between 10 minutes and 12 hours depending on the firing temperature.

Exemplary embodiments and test results:

For the investigation of the aluminum oxide / Titanium dioxide ceramic materials have been some exemplary Mixtures of Al₂O₃, TiO₂ and Nb₂O₅ or Ta₂O₅ used, whose grain sizes were below 2 micrometers. The Oxidge mix with those given in Table I below Parts by weight (% by weight) were in white spirit of an intense, subjected to mixed milling for one hour and after separation the grinding fluid dried. Samples of the 6 mixes and a comparison sample made of pure aluminum titanate (Al₂TiO₅) were sintered at 1300 ° C for 1 h; the sinter samples were examined by X-ray.

To test the thermal shock resistance, all were Sintered bodies of samples No. 1 to No. 6 each 120 tem subjected to temperature change cycles between 1000 and 1300 ° C, one cycle lasting about 2 hours.

After this treatment, the test samples were X-rayed again ogographically analyzed and the changes in structure determined by the thermal cycling. The Test results are in the overview below summarized:  

Table I

Stabilization of aluminum titanate of the additions of various amounts of Nb₂O₅ and Ta₂O₅ to the starting materials.

It means:
00 = no measurable change in the beta-aluminum titanate structure
01 = main component: Beta-Al₂TiO₅ with small amounts of aluminum niobate as a new phase;
02 = main component: Beta-Al₂TiO₅ with small amounts of aluminum tantalate as a new phase;
03 = significant change in the test sample; as phases predominantly occur Al₂O₃ (corundum) and TiO₂ (rutile).

Result of the tests:

Finding (I) after 1300 ° sintering: the beta Aluminum titanate without stabilizing additives has already shown after the first sintering, clear signs of decomposition in the starting components Al₂O₃ and TiO₂, while the samples No. 1 to No. 6 in addition to niobium oxide or tantalum oxide as the main phase contained the beta aluminum titanate.

Findings (II) after the temperature change treatment; In the rehearsals No. 2 and No. 3 showed the X-ray analysis that to a very small extent an implementation of the originally ge formed Al₂TiO₅ with niobium oxide has taken place. As a reaction However, aluminum niobate could be detected in the product. Samples No. 5 and No. 6 also showed small amounts Aluminum tantalate as a new foreign phase, which by Um conversion of the aluminum titanate with Ta₂O₅ was created. The reaction products aluminum niobate or tantalate affect however, do not affect the mechanical strength of the ker amikteile; Surprisingly, the new foreign phases work additionally as stabilizing components of the Invention modern ceramic materials (synergistic effect).

Claims (7)

1. Process for the preparation of thermal shock-resistant and refractory ceramic materials based on the system aluminum oxide / titanium dioxide by conventional methods of ceramic technology, characterized in that mixtures of Al₂O₃ and TiO₂ with additions of 0.1 to 15 wt .-% Niobium pentoxide and / or tantalum pentoxide is used. 2. The method according to claim 1, characterized in that a composition of 40 to 60% by weight of aluminum oxide, 30 to 50% by weight of titanium dioxide and 1 to 10% by weight of niobium pentoxide or 2 to 12.5% by weight tantalum pentoxide or 1 to 12.5% by weight a mixture of Nb₂O₅ with Ta₂O₅ in any ratio starts. 3. The method according to claims 1 and 2, characterized in that that one already with known foreign metal oxides doped starting mixtures of the system alumina / Titanium dioxide additionally with 0.1 to 15 wt .-% niobium oxide and / or Tantalum oxide applied. 4. Ceramic materials according to claims 1 to 3, characterized ge  indicates that one of aluminum oxide / titanium dioxide Ge mix according to the stoichiometric composition Al₂TiO₅ goes out. 5. The method according to claims 1 to 4, characterized records that one of an aluminum titanate stoichio metric composition containing Al₂TiO₅ starting mix runs out. 6. Stabilized ceramic materials based on the system Aluminum oxide / titanium dioxide, available after a ver drive according to one of claims 1 to 5. 7. Use of the according to a method according to one of the An Proverbs 1 to 5 available ceramic materials as fire solid material for internal combustion engines and their exhaust systems, as crucible material for non-ferrous metallurgy, as grinding ceramic, as an insulating material, in powder form as a ceramic work substance in thermal wettable powders.