The application research of zirconia materials in refractories and ceramic materials focuses on the phase change toughening mechanism, the study of mechanical properties at room temperature and high temperature, the friction and wear mechanism and the practical application of zirconia ceramics.
1. Toughened and strengthened ceramics
In the past ten years, many scholars have studied the use of small volume changes and microcracks in the matrix of the matrix to strengthen refractory materials. Claussen pointed out that the finer the ZrO2 particles, the lower the temperature of the tetragonal phase → monoclinic phase transition. It usually drops below room temperature from around 1000°C, or even absolute zero. When tetragonal ZrO2 transforms to monoclinic ZrO2, due to the volume change, many microcracks smaller than the critical size are formed around the transformed particles. These micro-cracks are non-expandable under the negative cutting action, so the material strength is not reduced. When large cracks expand and encounter these cracks under the action of negative cutting, a new phase transition will be induced, and the expanding cracks will be deflected to absorb energy, thereby achieving a toughening effect.
For the surface of the sintered body, because there is no matrix constraint, the tetragonal ZrO2 is easily transformed into monoclinic ZrO2, and the internal tetragonal crystal form maintains a metastable state due to the pressure from all aspects of the matrix, so the surface produces volume expansion, which causes the surface to form pressure. Stress plays a role in surface strengthening.
2. Zirconia hollow ball brick
The production method of zirconia hollow ball brick is the same as the production method of alumina hollow ball, but its melting temperature is higher, reaching 2700℃ or more. Now China widely uses CaO as a stabilizer. Zirconia hollow sphere products are completely made of zirconia hollow spheres, with good high-temperature strength and stable pore structure. They are used as insulation materials for furnace covers and other parts of ultra-high temperature equipment, such as intermediate frequency high temperature furnaces, carbon black reactors, tungsten rod furnaces, Molybdenum furnace and so on.
3. Sizing nozzle
At present, most steel products in the world are produced by continuous casting technology, so the service life and performance of refractory materials for sizing nozzles are very critical.
Zirconia sizing nozzles are widely used in small square broken continuous casting tundish. The performance of the nozzle directly affects the length of continuous casting time. The sizing nozzle is the nozzle brick in the sliding nozzle device adopted by the steel mill when casting the billet. It took nearly 80 years for the sliding nozzle device from the conception to the industrialization. The most important reason is that the material is not good enough. It has a significant comparative advantage with the stopper system. Zirconia nozzle has good corrosion resistance to molten steel and molten slag. Usually, higher purity zircon, CaO stabilized ZrO2 and industrial zirconia are used to make the nozzle.
The most critical part of the sliding nozzle device is the slide brick and the nozzle brick embedded in it. In the device, there are usually upper and lower slide bricks and upper and lower nozzle bricks. When the upper and lower nozzle bricks overlap, the casting starts, and the upper nozzle brick is installed at the bottom of the ladle. The upper slide brick is not moving, and the drain brick and the lower slide brick slide to achieve angle control. The upper nozzle brick is soaked in molten steel for a long time, and it is relatively unsuitable to be replaced, which has high requirements for products and a long life expectancy. The key to the spout is to control the speed and quality of steel pouring, and the life expectancy is low. The life of the spout brick can reach 8h or longer.
4. Film and coating
ZrO2 is a thin film material that has been developed for many years and contains a wide range of uses. Because it contains excellent heat resistance, heat insulation properties, optical properties, electrical properties, mechanical properties and chemical stability, it can be used as thermal barrier coating, insulation, wear resistance, and corrosion resistance coating. It can be widely used in aerospace, iron and steel metallurgy, machinery manufacturing, optics, electricity and other fields, and the prospects are very broad. Judging from the current data, foreign countries (especially the United States, Britain and other countries) started early in this area and have achieved certain results. As early as the 1970s, the National Aeronautics and Space Administration (NASA) began to study the preparation of Y2O3 stabilized ZrO2 ceramic thermal barrier coatings using electron beam evaporation, air plasma spraying, and plasma assisted physical vapor deposition.
Over the years, researchers from IBM companies in the United States have conducted various studies on the deposition of ZrO2 film by sputtering. They have deposited ZrO2 film by magnetron sputtering and radio frequency sputtering processes, and developed a new type of high-speed reactive magnetron sputtering equipment. The deposition rate is improved, and the target material is saved. The United States has also done a lot of research on Al2O3 and ZrO2 films with ion-assisted deposition and multi-arc ion plating. The United Kingdom and Japan have studied ZrO2 thin films as thermal barrier coatings. As an optical film, it can be used for laser mirrors, high refractive index mirrors, and broadband interference filters.
5. Zirconia kiln materials
Japan's Asahi Glass Company has successfully developed a zirconium refractory containing 94%-95% zirconia, and used it on the top and key parts of the glass kiln, greatly improving the life of the glass kiln. Zirconia is used as a refractory material in key parts of large glass kilns. In the early days, zirconium refractories were used. The content of zirconia was only 33%~35%. The zirconia was melted and blown to obtain hollow zirconia balls of different sizes. ,Prepare a variety of advanced insulation bricks to avoid the problem of dust pollution after ceramic fiber aging.
