Zirconium-containing Materials Used in the Refractories

As a new material, zirconium-containing material has been developed rapidly in the recent ten years. In the field of refractories, natural zirconium containing mineral raw materials and artificial extraction or synthesis of zirconium oxide and composite oxide raw materials have also been widely used to produce a variety of excellent zirconium containing refractories.

There are about 50 kinds of zirconium minerals known to us, among which more than 20 are common. Zirconium mineral raw materials for industrial use are mainly zirconium quartz, oblique zircon, hafnium zircon, and anisotropic zircon. With the development of science and technology, zirconium oxides and composite oxides have been extracted or synthesized by various processing methods and applied in various fields.

Zirconium-containing raw materials are widely used in the refractory industry, which is mainly because of their high melting temperature and strong chemical stability. They have good corrosion resistance to metal melt, slag, or glass fluid, as well as good thermal shock resistance, so they can be used as refractories for glass kiln, metallurgical industry refractories, and so on.

Zirconium-based-products
Zirconium-based-products

Zirconium-containing refractories are mainly used in the melting part, superstructure, side wall and fluid hole of glass melting furnace. Refractories made from zirconium materials are widely used in metallurgical industry and can be divided into zirconium quartz products, zirconia products, aluminum zirconia carbon products, zirconium carbon products, calcium zirconate products, zirconium boride products, zirconia modified refractories, etc.

Zirconium quartz products have the characteristics of high-temperature resistance, good resistance to acid slag, small erosion, slight viscosity of slag, small thermal expansion coefficient, good thermal shock stability, etc., which can be better used as the lining of steel drum, but also can be masonry in the direct impact of steel, slag line parts, around the nozzle and other key parts.

The main raw material for the production of zirconium quartz products is zirconium quartz concentrate, and some clay, pyrophyllite, chromium oxide and zirconia can be also added as needed. In general, zirconium particles are small in size and are not suitable for direct brick production, which requires the raw materials of zirconium quartz and part of the combined clay to be mixed, semi-dry pressed and made into the blank. There are a wide variety of zirconia products and many molding methods, such as mud pouring method, hot pressing method, machine pressing method, isostatic pressure method, etc.

Monoclinic-Zirconium-Oxide
Monoclinic-Zirconium-Oxide

Aluminum-zirconium carbonaceous product is developed on the basis of aluminum-carbonaceous product, and it can be used as sliding nozzle brick of ladle (or tundish), long nozzle, plug rod, immersed nozzle and so on. Compared with the corresponding aluminum carbon material, aluminum zirconium carbon products have better oxidation resistance, thermal shock stability, erosion resistance, and higher strength, so the service life is longer. The addition of a certain amount of zirconia in refractory materials such as jade-quality, high-alumina, magnesium-calcium, aluminum-magnesium, magnesium-chromium and magnesium-carbon commonly used in metallurgical industry can improve the chemical stability, thermal shock stability and strength of these materials. In these materials, zirconia is usually introduced in the form of zircon sand and zirconia.

The specific production process is usually the same or slightly changed before modification. Generally speaking, zirconium-containing raw materials have been widely used in the field of refractories due to their excellent properties, and their application scope will be more and more extensive.

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An Overview of Colored Zirconia Ceramics

Zirconia ceramics, with high strength, high toughness, wear resistance, corrosion resistance and other excellent properties, are widely used in the mold, tool, ceramic bearings, electronic components, biomedical materials, and other fields. At present, with the wide application of zirconia ceramics in the field of electronic products, especially as the backboard of mobile phones, its single color has restricted its application and cannot meet people’s requirements on the appearance of structural devices. Therefore, the development of rich colors can greatly expand the application of zirconia ceramic materials in the field, which has broad prospects for development.

Overview of colored zirconia ceramics

With the development of technology, the synthesis methods of colored zirconia ceramics are becoming more and more diversified. The key to its preparation technology is that the color phase (such as CoO, Cr2O3, Fe2O3, etc.) can be evenly distributed in the ceramic matrix. The color zirconia ceramics must have a stable crystal structure, bright and uniform color, high temperature and good chemical stability without damaging its inherent properties.

For colored zirconia ceramics, the capillary force, electrostatic attraction and van der Waals force between particles are prominent due to the small size, large surface area and high surface energy of the particles forming the matrix and colorizing phase. In this environment, nano-powder particles are easily agglomerated into a larger particle body, which leads to a significant decrease in the relatively good physical and chemical properties of nano-complex phase ceramics. Therefore, the agglomeration phenomenon must be overcome to prepare zirconia ceramics with good properties and diverse colors, so that the color phase is evenly dispersed in the ceramic matrix material.

Preparation of colored zirconia ceramics

The preparation methods of color zirconia ceramics mainly include solid phase mixing, chemical co-precipitation, liquid phase impregnation, and high-temperature carburization.

  • Solid phase mixing

Color zirconia powders were prepared by solid phase mixing with ball milling technology. It mixes oxide particles such as the colorant and mineralization agent with stable zirconia nanometer powder in a certain chemical proportion and grinds them into balls. Solid particles are refined in this process, resulting in micro-cracks, lattice distortion and surface energy increase that are conducive to the realization of the low-temperature chemical reaction.

Black zirconia ceramics are used in watch straps
Black zirconia ceramics are used in watch straps
  • Chemical co-precipitation

After the solution of a zirconium salt, stabilizer salt and colorant ion salt is mixed, hydroxide or carbonate precipitation is generated by the reaction with alkali or carbonate, and then the zirconia composite powder is obtained by heating and decomposition. In coprecipitation, metal cations in a solution precipitate together to form a mixture due to an excess of precipitants. Under special circumstances, the composite oxides or their precursors that are required to be deposited must conform to a certain stoichiometric ratio, and cations are required to generate precipitation in a certain proportion.

  • Liquid phase impregnation

Liquid phase impregnation will firstly extract and degrease zirconia ceramic blank with connected pore structure after injection molding and then place it in a solution containing chromophore ions for impregnation. The colorized ions infiltrate into the surface of the billet through the pores of the solution, and the depth of infiltration is controlled by the length of infiltration time. In addition, the blank body obtained by water extraction and degreasing is directly used for infiltration, because the blank body after water extraction and degreasing will form a uniformly connected void structure, which facilitates the uniform distribution of chromophore ions in the blank body. Uniform color zirconia ceramics can be prepared only if they can be soaked completely.

  • High temperature carburizing/nitrogen

High temperature carburizing is mainly used to prepare black zirconia ceramics. The technological process is to process zirconia ceramic into a blank, normal degreasing, dewaxing, at low temperature without protective atmosphere element burning treatment, and then the processed zirconia green blank under vacuum protection conditions for high-temperature sintering. Graphite crucible is used to place workpiece during sintering, and graphite paper is placed on the workpiece surface. The black coloring of zirconia ceramics was realized by graphite infiltration into zirconia surface at high temperature.

Applications of color zirconia ceramics

  • The backplate of mobile phone

Zirconia ceramic used in mobile phone backplate has no interference, no magnetic, strong reception signal, as well as color diversity, besides, it can also be used for fingerprint identification module ceramic cover plate.

Zirconia ceramics are used in the back plate of mobile phone and the ceramic cover plate of fingerprint recognition module
Zirconia ceramics are used in the back plate of mobile phone and the ceramic cover plate of the fingerprint recognition module
  • Smart wearable appearance parts

Zirconia ceramic material has the advantages of scratch resistance, scratch resistance, no shielding, warm and moist hand texture, good corrosion resistance and bio-compatibility. It is applied to intelligent wearable appearance parts.

Smart wearable appearance parts
Smart wearable appearance parts
  • Ceramic knives

Zirconia ceramic knives have excellent characteristics such as ultra-high strength, abrasion resistance, sharp edge, no rust, no odor, and durability.

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Main Factors that Affect the Performance of Ceramics

The main raw material of zirconia ceramics is high purity zirconia powder, and its performance and content have a great impact on zirconia ceramics. Besides that, the properties of zirconia ceramics are affected by other factors. In order to prepare high-performance zirconia ceramics, we should control the main influencing factors, including raw material size, molding method, and sintering.

Forming method

Zirconia ceramics with low porosity and high density have excellent jointing properties. High density means that the grains in the ceramic body are closely arranged, and it is not easy to form a destructive breakthrough point when subjected to external loads or corrosive substances.

Ceramic-Injection-Molding
Ceramic-Injection-Molding

The forming method is the key to obtain the calcium density of ceramic embryo body. Zirconia ceramics are usually formed by means of dry pressing, isostatic pressing and hot die-casting. Different methods have different characteristics and have different effects on sintering properties as well as the microstructure of curing rate ceramics. Generally, grouting and hot die-casting are the main technologies for products with complex shapes, while the dry compression molding can be adopted for products with simple shapes. Generally speaking, the density of dry-pressed products is better than that of hot-die-cast products.

The particle size of the raw material

The particle size of raw material has a great influence on the properties of products. Only when the raw material is fine enough can the final finished product be fired into a microstructure, which makes it have a good wear resistance. The finer the zirconia powder particles are, the more active they are and the sintering can be promoted.

Due to the difference of corundum and glass phase linear expansion coefficient, the stress concentration at the grain boundary can reduce the risk of cracking. The fine grain can also hinder the development of micro-cracks, and it is not easy to break into transgranular, which is conducive to improving fracture toughness and abrasion resistance.

Zirconia Ceramic
Zirconia Ceramic

Sintering

Sintering of ceramic is the densification process of raw ceramic at high temperature. With the increase of temperature and time, the adhesion between powder particles and the strength of sintered body increase, the aggregation of powder particles becomes a strong polycrystalline sintered body with a certain microstructure, and the required physical/mechanical properties of products or materials are obtained. The densification rate and the final structure of the sample often reflect what kind of heat treatment process it has gone through.

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