NL8403374A - FIRE-RESISTANT BODY OF DELTA-STABILIZED ZIRCON DIOXIDE. - Google Patents

Description

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Refractory of partially stabilized Zirconium Dioxide 5

The invention relates to a refractory material stabilized with 2-4% by weight of CafO, MgO or Y2O3, zirconium dioxide with 94-97% by weight of ZrO2 and optionally as residues the impurities SiO2, Al2O3, Fe2O3 and / or TiO2 · 10

Zirconia compounds are used in the preparation of refractories. It is already known herein that stabilizers in the form of calcium oxide, magnesium oxide, or yttrium oxide can be added to starting material, so that the bodies, upon subsequent heating at temperatures ranging between 1600 ° C and 2000 ° C, due to their expansion ratios, are less show cracks and retain their strength to a great extent. In "Stahl und Eisen" Vol. 97, 1977, pages 945-946, the thermal behavior of partially stabilized zirconium dioxide is described, with stabilizing additives mentioned as magnesium oxide and calcium oxide. In this publication it is indicated that in the presence of oxidic impurities, in particular silicon oxide, a destabilization can start already at melting temperatures of steel. It is further indicated here that partially stabilized zirconium dioxide is more resistant to temperature changes than homogeneous, fully stabilized zirconium dioxide. In a publication in "Interceram" No. 2, 1982, pages 126-129, also discusses the influence of contaminants on the. stabilization of zirconium dioxide.

The zirconium dioxide is stabilized here with calcium oxide, to which impurities such as SiO 2, Al 2 O 2, Fe 2 O 3 Na 2 O, K 2 O or mixtures of SiO 2 and Al 2 O 3 or of SiO 2 and Na 2 O or K 2 O are added. However, it is stated in this publication that only with a slight addition of SiO 2 at lower temperatures a considerable increase in density is achieved without formation of destabilization. Also, the partial stabilization of zirconium dioxide by addition of calcium oxide or magnesium oxide in "Stahl und 84033 74 - 2 -

Requirements "Vol. 100, 1980, pages 1457-1462 written.

The object of the present invention is to provide refractory bodies based on partially stabilized zirconium dioxide according to the indicated type, which are even more resistant to temperature changes.

It has now been found that with refractory bodies the resistance to temperature fluctuations can still be substantially improved, because the mixing ratios of the individual stabilizers have been precisely adjusted and during this partial stabilization a considerable amount of silicon dioxide in addition to the constituents CaO, MgO or ¥ present as stabilizer. 2 ° 3 is present.

15

A refractory body according to the invention is characterized in that, during stabilization with only CaO, it is 1.0-1.5% by weight SiC 2. at the stabilization with MgO, Y2 ° 3 with a mixture of CaO and MgO contains 0.8-1.5 wt% SiO2, wherein the weight amount of added stabilizer is at least twice the weight amount of the SiC present is.

In preferred embodiments, the amount of SiO 3 stabilization with magnesium oxide is 1.0-1.2% by weight.

According to another preferred embodiment, the iron content of the refractory body is adjusted to 0.6-0.8% by weight by adding iron oxide, the amount of iron added being dependent on how much iron is already started in the zirconium dioxide is present as contamination.

According to another preferred embodiment, as stabilizer, a mixture of lagnesium oxide and calcium oxide is used, in a ratio of 1: 2 to 2: 1.

The invention is further elucidated on the basis of the following examples 1-5 and an example 6 outside the invention.

84033 74 _____ - 3 - • *

As a starting material, a natural Baddeleyite with the following chemical analysis is used:

ZrC> 2 Si02 A ^ 2 ° 3 T ^ ° 2 Fe2 ° 3 Ca0 5 zirconium oxide 99.1 0.40 0.17 0.07 0.22 0.04

Fine grain SiO2 (finely ground quartz flour), CaO in the form of calcium zirconate (CaZrO2), MgO, Y2 ° 3 and Fe2 ° 3 are added to Baddeleyite with a grain size below 0.063 mm. Under the use of 2% by weight dextrin (dry) and 2-2.5% water as a binder, this fine-grained mixture is homogenized in a 2 mixer, compressed into bodies at a pressure of about 1Q0N / mm, dried and then roasted at 2000 ° C. The composition of the mixtures for Examples 15 1-5 is shown in Table 1 (indications in weight%). The composition and properties of the burned bodies according to the examples are shown in Table 2.

Table 1 20 _1 2 3 4 5_ zirconium dioxide -0,063 mm 100 100 100 100 100

SiO2 + 0.8 + 0.8 + 0.5 + 0.8 + 1.0

CaZrO 3 + 12.0 + 6.5 MgO + 2.5 + 2.5 + 2.0 Y 2 O 3 + 3.5

Pe203 + 0.5 + 0.5 + 0.5 +0.5 30 35 840 33 74 r '- 4 - 4 *

Table 2 _1_2_3_4_5, _6-_

Zr02 94.6 95.3 95.7 94.7 93.9 96.7 5 Si02 1.20 1.15 0.88 1.17 1.48 0.42 A1203 0.17 0.16 0.18 0 , 18 0.17 0.19

TiO2 0.06 0.06 0.07 0.08 0.07 0.08

Pe203 0.68 0.75 0.70 0.23 0.74 0.19

CaO 3.26 0.05 0.04 0.05 1.78 0.03 10 MgO 2.45 2.52 1.86 2.30 Y203 3.52 raw density g / cm 4.75 4.95 4. 90 4.93 4.91 4.76 15 E-Modulus N / mnr 55000 36000 52000 42000 32000 90000 TWB (water) DIN 51068. > 30> 30> 30> 30> 30 10 20 temperature shock cracks 1700 ° C no cracking within 2.

min.

content of mono-klien 25

ZrO 2 wt% 87 95 90 84 92 72

The refractories according to example 1 are stabilized with CaO, 30 according to examples 2 and 3 with MgO, according to example 4 with Y 2 O 3 and according to example 5 with a mixture of MgO and Cao. SiO 2 is always added as an additional component. used in the mixture. Up to Example 4 there is also an addition to Fe2 O3.

35

The bodies according to Examples 1-5 are highly resistant to temperature changes, which is reflected in the values for the E-modulus (calculated from the ultrazone travel time), the resistance to temperature changes (determined according to 84033 74 - 5 - * f DIN 51068, Part 1: Method of cooling with water) and from the behavior with respect to temperature shocks when placing bodies (60 mm external diameter die casting nozzle) in an oven kept at 1700 ° C. It has furthermore been established that in the bodies according to the invention a relatively high content of monoclinic Baddeleyite, based on the content of stabilizers, is present. In comparison, an outside body of the invention according to Example 6, which has been partially stabilized only by the addition of MgO, achieves a low resistance to temperature changes at a simultaneously high E-modulus and a low amount of monoclinic zirconium oxide.

15 20 25 30 35 84 033 74

Claims (4)

1. Refractory material of zirconium dioxide partially stabilized with 2-4% by weight of CaO, MgO or Y203 with 94-97 5% by weight of Zr02 and optionally as a residue the contamination and SiO2, ΑΙ, ^ ΑΙ ^ 'Fe2 ° 3 and / ° f Ti ° 2 'is characterized in that on stabilization with only CaO 1.0-1.5 wt.% SiO2, or on stabilization with MgO, Y20.j with a mixture of CaO and MgO 0.8-1 1.5 weight percent SiO 2, wherein the weight amount of stabilizer added is at least twice the weight amount of SiO 2 present. Refractory body according to claim 1, characterized in that it contains 1.0-1.2% by weight SiO 2 when stabilized with MgO. Refractory material according to claim 1 or 2, characterized in that in its preparation above the iron present in the starting zirconium dioxide, its iron content is added by adding iron oxide to 0.6-0.8% by weight. set. A refractory body according to claim 1 or 3, characterized in that it has a mixture of 1: 2 to 2; 1 of MgO and CaO as a stabilizer has been prepared. 84 033 74