CN1092163C - Heterogeneous zirconia-mullite refractory material with sintered bound phase and its preparation - Google Patents

Abstract

The invention relates to a ZrO ₂ -mullite composite refractory material with a reaction sintering product as a binding phase and a preparation process, belonging to the field of advanced refractory materials. It uses industrial ultra-fine ZrSiO ₄ and Al ₂ O ₃ powders as raw materials, adopts reaction sintering process, uses the reaction sintering products of the two as the combined phase of refractory materials, and uses coarse-grained mullite and PSZ particles as aggregates. Composition and particle gradation design, as well as process optimization, have prepared a high-performance ZrO ₂ -mullite composite refractory material. The raw materials used in the process of the invention are cheap, the process is simple, and the obtained material has the characteristics of excellent comprehensive performance and good repeatability.

Description

Zirconia-mullite composite refractory material with reaction sintering product as binding phase and preparation method thereof

The invention relates to a zirconia (ZrO ₂ )-mullite composite refractory material with reaction sintering product as the binding phase and its preparation method. The stone and partially stabilized ZrO ₂ (PSZ) are used as the aggregate, and the reaction product of ZrSiO ₄ and α-Al ₂ O ₃ is used as the binding phase. It belongs to the field of advanced refractory materials.

As we all know, mullite (3Al ₂ O ₃ 2SiO ₂ ) has a series of excellent thermal and mechanical properties (such as low thermal conductivity and thermal expansion coefficient, excellent high temperature creep resistance and thermal shock resistance, and good Excellent chemical stability and high temperature strength), is an ideal refractory material. Adding _ZrO2 in the mullite matrix can further improve the strength, erosion resistance and thermal shock resistance of the material. ZrO ₂ -mullite composite refractories are widely used in glass smelting, iron and steel, metallurgy and other fields. In recent years, more and more attention has been paid to continuous casting of iron and steel. Although this material has been developed very early and has been extensively studied, with the continuous and rapid development of high-temperature technology, especially steel and metallurgical processes, more and more stringent requirements are placed on the performance of refractory materials. Excellent mechanical properties, corrosion resistance and thermal shock resistance, and the dependence of these properties on the material density is usually contradictory. The traditional refractory process can no longer meet this requirement. Therefore, in order to obtain ZrO ₂ -mullite composite refractory with excellent comprehensive properties, it is necessary to break through the traditional refractory structure design and traditional production technology, and it is necessary to introduce new ideas and techniques.

Since the late 1970s, people have conducted extensive and in-depth research on ZrO ₂ -mullite composite materials. Using ZrSiO ₄ and α-Al ₂ O ₃ as raw materials, it is a low-cost route to prepare ZrO ₂ -mullite composite materials by reaction sintering process, and the prepared materials have unique properties. However, because the mullite reaction in the sintering process has an adverse effect on the densification, it is difficult to obtain a dense sintered body. In 1980, Claussen used an optimized reaction sintering process to obtain ZrO ₂ -mullite composite materials with excellent mechanical properties. Since then, many scholars have studied the preparation of ZrO ₂ -mullite materials by reaction sintering process from different angles. Including the reaction sintering process, the microstructure and mechanical properties of the material, and the effect of adding sintering aids. Later, this sintering process was introduced into the preparation of refractory materials, but due to the lack of optimization in phase composition and process, good results were not achieved. Is it possible to use the reaction sintering product of ZrSiO ₄ and α-Al ₂ O ₃ —fine-grained and dense ZrO ₂ -mullite composite ceramic material—as the binding phase, and adopt a technology combining advanced ceramic technology and traditional refractory technology, The preparation of ZrO ₂ -mullite composite refractory materials with excellent properties has always been the goal pursued by material workers, and thus the idea of the present invention has been derived and useful attempts have been made.

The object of the present invention is to provide a ZrO ₂ -mullite composite refractory material with reaction sintering product as the binding phase prepared by combining advanced ceramic technology with traditional refractory material technology and its preparation method.

The object of the present invention is implemented by following technical process:

Using industrial ultra-fine ZrSiO ₄ and α-Al ₂ O ₃ powder as raw materials, adopting reaction sintering process, using the fine-grained and dense reaction sintering products of the two as the combined phase of refractory materials, and using coarse and medium-grained mullite and partially stabilized ZrO ₂ particles are aggregates, and ZrO ₂ -mullite composite refractory materials with special organizational structure are prepared through phase composition and particle gradation design and process optimization.

The specific preparation process is:

(1) The raw material used is industrial ultrafine ZrSiO ₄ powder:

ZrO ₂ content > 65%, particle size 0.2-5μm;

Industrial ultrafine α-Al ₂ O ₃ powder: particle size 0.1-3μm;

Commercially available sintered synthetic mullite particles: close to the stoichiometric composition, with a particle size of 1-3mm;

Electrofusion partially stabilized ZrO2 particles: there are two kinds of 40 mesh and 200 mesh.

(2) Multi-level particle gradation is adopted, coarse particle: medium particle: fine particle = 3-6:1-2:4-6 (volume ratio), and each particle level has a sub-level gradation. The coarse, medium and fine particles of each gradation are composed of ZrO ₂ and mullite, only the particle size and source are different.

The ZrO ₂ in the coarse and medium particles comes from the calcium oxide or yttrium oxide partially stabilized ZrO ₂ (PSZ) in (1) above, such as Ca-PSZ, Y-PSZ, etc.; the coarse and medium-sized mullite particles come from The sintering in (1) above synthesizes mullite.

Coarse-grained mullite is sintered and synthesized mullite of 1-3mm, which is milled by WC ball for 45 minutes (ball: material = 4:1), firstly removes large particles through a 20-mesh sieve, and then passes through a 40-mesh sieve to remove fine particles. Mullite particles with a particle size between 0.5-1mm are obtained.

Medium-grained mullite refers to the mullite particles with a median particle size of 19.7 μm obtained after coarse-grained mullite particles are milled by WC balls for 2 hours and passed through a 40-mesh sieve.

And fine-grained mullite and _ZrO Derived from ZrSiO ₄ and Al ₂ O ₃ superfine powders in the above (1) by the reaction product obtained by the following reaction:

           

The fine-grained ZrO ₂ and mullite formed by the above reaction are used as the binding phase of coarse and medium-grained aggregates to form a ZrO ₂ -mullite composite refractory material with a special structure. At the same time, coarse and medium-grained mullite can act as a seed crystal, which overcomes the disadvantage that the green body is difficult to sinter to a certain extent.

In the coarse particle and medium particle gradation of the present invention, the weight ratio of ZrO2 and mullite in the sub-primary gradation is equal, all 36.6: 63.4, this ratio and the ZrO2 generated after the complete reaction of ZrSiO4/Al2O3 mixed powder It is equal to the weight ratio of mullite.

(3) The specific preparation process is a mixture composed of multi-level particle gradation and proportion, using distilled water as the medium, using _ZrO2 ball milling for 24 hours, and drying through a 20-mesh sieve. Then add 5wt% PVA solution as binder, microwave drying while stirring, and adopt dry pressing, isostatic pressing or first dry pressing and then isostatic pressing after sieving, and then place it in the air at 1600- Firing at 1700°C, the reaction sintering of ZrSiO ₄ and Al ₂ O ₃ fine powder is carried out simultaneously with the sintering of the green body, and the ZrO ₂ -mullite composite refractory material with the reaction sintering product as the binding phase is obtained.

The present invention is characterized in that it adopts the process of combining advanced ceramics and traditional preparation methods of refractory materials, and combines fine-grained and dense ceramics with coarse-grained aggregates to obtain ZrO ₂ -mullite composite refractory materials with special structure. Coarse-grained mullite and _ZrO2 are embedded in the fine-grained matrix, the fine-grained area is uniform and dense, and the coarse-grained and fine-grained particles are well combined, but an obvious interface can still be observed. This structure ensures that the material has a high Mechanical properties, but also has good thermal shock resistance. In addition, the high density of the material is conducive to the improvement of corrosion resistance.

Table 1 lists the basic properties of several materials described in the examples.

Table 1 Basic properties of ZrO ₂ -mullite composite refractories

^* σ _f : flexural strength; RT: room temperature

As can be seen from Table 1, compared with traditional refractory materials, the material prepared by the process provided by the present invention has outstanding mechanical properties and good thermal shock resistance, and the raw materials used are cheap, the process is simple, and it has relatively high performance. Good prospects for industrialization.

Figure 1 is the SEM photo of the fracture of the sample numbered C.

It can be clearly seen from the figure that the coarse particles are embedded in the fine particle matrix, and there are some pores distributed on the interface between the coarse particles and the matrix, but the combination is still relatively tight. The fine-grained area is uniform and dense, and is basically transgranular fracture. As mentioned earlier, this microstructure ensures that the material not only has high mechanical properties, but also has good thermal shock resistance.

Further illustrate substantive characteristics and remarkable progress of the present invention below by specific embodiment, but be in no way limited to embodiment.

Example 1

Coarse-grained mullite (average particle size is about 0.5-1mm) and Ca-PSZ (40 mesh) are used as aggregates, the weight ratio of the two is 63.4:36.6, and the medium particles are also made of mullite (median particle size is 19.7 μm) and Ca-PSZ (200 mesh), the weight ratio is the same as above. Fine particles are composed of industrial ultrafine ZrSiO ₄ and Al ₂ O ₃ powders, according to the following reaction formula:

ingredients. The volume ratio of coarse particles, medium particles and fine particles after the reaction is complete is 5:1:4. The samples were formed by dry pressing and then isostatic pressing (200MPa), and then fired in air at 1640°C/3h. The properties of the obtained materials are shown in Table 1 (numbered A).

Example 2

The mullite with an average particle diameter of about 1 mm is used as the coarse particle, the mullite with a median particle diameter of 19.7 μm is used as the medium particle, and the composition of the fine particle is the same as in Example 1. The volume ratio of coarse particles, medium particles and fine particles is calculated as 4:1:5 according to the complete reaction. The samples were formed by dry pressing and then isostatic pressing (200MPa), and then fired in air at 1680°C/3h. The properties of the obtained material are shown in Table 1 (coded as C), and the photo of the microstructure of the material is shown in Figure 1. The thermal shock sample made of this material was repeatedly quenched (water quenching test) 20 times under the condition of ΔT=1100°C, and the sample was intact without obvious cracking and peeling on the surface. All the other are with embodiment 1.

Example 3

Coarse particles, medium particles and fine particles are calculated according to the complete reaction, and the volume ratio is determined to be 3:1:6. The samples were formed by dry pressing and then isostatic pressing (200MPa), and then fired in air at 1680°C/3h. The properties of the obtained materials are shown in Table 1 (coded as D).

Claims (4)

1. A ZrO ₂ -mullite composite refractory material, composed of ZrO ₂ and mullite phase, characterized in that: (1) The reaction sintering product of industrial ultra-fine ZrSiO ₄ and Al ₂ O ₃ powder—fine-grained and dense ZrO ₂ -mullite composite ceramics is used as the binding phase, and the particle sizes of the two powders are 0.2-5 μm respectively and 0.1-3μm; (2) Coarse-grained and medium-grained mullite and _ZrO2 aggregates are embedded in the matrix of the reaction sintered product; (3) Coarse particles, medium particles and fine particles formed by reaction sintering are calculated according to the complete reaction, and the volume ratio is 3～6:1～2:4～6; (4) The average particle size of the coarse particles of mullite is 0.5-1 mm, and the median particle size of the medium particles is 19.7 μm; the particle size of the coarse particles of ZrO ₂ is 40 mesh, and the particle size of the medium particle is 200 mesh. 2. The multiphase refractory material according to claim 1, characterized in that in the coarse and medium particle gradations, the weight ratios of _ZrO2 and mullite in the sub-primary gradation are equal, all being 36.6 : 63.4, and the weight ratio of ZrO ₂ and mullite generated after complete reaction with ZrSiO ₄ /Al ₂ O ₃ mixed fine powder is equal. 3. The preparation method of multiphase refractories according to claim 1, characterized in that the green body is formed by isostatic pressing or first dry pressing and then isostatic pressing, and the reaction sintering of ZrSiO ₄ and Al ₂ O ₃ fine powder is combined with the green body The sintering of the body is carried out at the same time, and the sintering temperature is 1600-1700°C. 4. The material preparation method according to claim 3, characterized in that said ZrO ₂ particles are ZrO ₂ partially stabilized by calcium oxide or yttrium oxide; said mullite particles are commercially available sintered synthetic mullite.

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