Zirconia – Page 2 – Zirconium Metal

Zirconia Ceramic Conversion Film Used in Automobile Coating Field

Phosphating is the most common pretreatment technology in the field of automobile coating. A phosphate conversion film is produced after phosphating the body steel plate, which can not only protect the base metal but also improve the adhesion between the metal and the coating. All cars are phosphated before they are painted.

A-typical-phosphating-and-E-coating-process. Source: researchgate.net

However, the traditional phosphating process has the defects of high energy consumption and high pollution. In addition, nitrite in the phosphating bath has high carcinogenicity, and its storage and use requirements are high, which increases the burden on enterprises. Therefore, under the dual drive of environmental requirements and energy cost, the phosphorus-free film-forming technology represented by the new zirconia conversion film technology has become the development consensus of green coating for automobiles.

Principle of film formation of zirconia ceramics

Zirconia ceramic film-forming technology is one-step film-forming, which means a surface treatment agent is used to treat the metal surface. The following diagram shows the film formation principle of a zirconia ceramic on the steel surface. The main materials are fluoro zirconic acid and zirconium salt. Zirconic acid and zirconium salt react directly with the metal substrate, and the zirconia ceramic film formed is attached to the surface of the metal substrate to play a role in corrosion protection.

At present, the sol-gel is the main method to produce zirconia conversion film. The so-called sol-gel refers to the formation of the three-dimensional network configuration of colloidal particles crosslinked with each other, which can mechanically wrap a large number of solvents inside the aggregate, making it no longer flow and become a semi-solid state and gel. When the density of sol particles in colloidal solution is higher than that in solution, the sol particles tend to sink under the action of gravity. If some parameters in the solution are changed to make the deposition rate of colloidal particles greater than the diffusion rate, the colloidal particles will rapidly precipitate out of the solution.

Characteristics of zirconia ceramic film

In terms of film properties, the ceramic coating formed by zirconia conversion film can completely replace the traditional phosphating film. In addition, zirconia conversion film also has the characteristic of being lightweight, while its film thickness is about 50nm. The film thickness means the low film weight, and the weight of the traditional phosphating film is usually 2-3g/m2, while that of zirconia conversion film is only 20-200mg/m2. The weight of zirconia conversion film varies according to the raw materials provided by the supplier, but in general, the weight of zirconia conversion film is about 200 times lower than that of traditional phosphating film.

In terms of technological process, the new zirconia conversion film technology is simple and fast, and generally only takes about 30s to form a complete film, which can significantly reduce the cost of water consumption, wastewater treatment, energy, and manpower.

Moreover, the new process is suitable for a variety of metals (Fe, Zn, Al, Mg), so various plates can be mixed line processing. In the process of treatment, zinc-plated plate and aluminum plate without waste slag formation, only a small amount of slag was produced in the treatment of cold-rolled plate. The resulting slag can be easily removed using a conventional phosphating system, without clogging the nozzle or adversely affecting coating properties or the appearance of the electrophoretic coating.

In daily process management, the bath of the new zirconia film-forming technology is very stable and easy to control. At ordinary times, the temperature and PH value are only needed to be controlled in production, which does not need to be like zinc phosphating that requires regular daily testing of total acid, free acid and zinc, nickel, manganese content, and many other parameters, so a lot of process management costs are saved.

Zirconia film-forming technology has been applied earlier in foreign countries. Henkel group of Germany has the absolute right to speak in this field. As early as 2002, Henkel was the first company to introduce zirconium pre-treatment materials suitable for a variety of plates; in 2008, GM used Henkel’s zirconium pretreated materials at its SanJose Dos Campos plant in Brazil; Henkel’s pretreatment materials were also used at Ford’s TwinCity plant during the same period.

Stanford Advanced Materials supplies high-quality zirconium and zirconia products to meet our customers’ R&D and production needs. Please visit http://www.samaterials.com for more information.

How is Zirconia Ceramic Cell Phone Panel Produced?

With the advent of the era of 5G signals, intelligent wearable devices are bound to shift from metal to glass and ceramics. Especially, in the mobile phone panel industry, more and more mobile phone manufacturers began to use zirconia ceramic material. So what is the manufacturing process of zirconia ceramic cell phone panel?

Ceramic powder

Microcrystalline zirconium is generally used as the raw material for the shell of 3C products. Zirconia powder is the most widely used ceramic material for the shell of 3C products due to its good appearance treatment effect and the advantages of phase change toughening.

Ceramic Machining

Ceramic shell molding processes such as mobile phones and smart wear mainly include injection molding, dry pressing molding, and tape casting. Injection molding is similar to plastic injection molding, which is mainly used to produce small and sophisticated ceramic parts with complex shapes. In general, the larger the size, the less advantageous the injection molding; dry pressing mainly produces flat products with high production efficiency; tape casting is an important forming method for thin ceramic materials. The above three molding methods can be used to produce mobile phone panels.

1. Injection molding

Ceramic Injection Molding (CIM) is a new process for ceramic parts manufacturing combining polymer Injection Molding with ceramic manufacturing.

2. Dry Pressing

Dry compression molding is a method to make the powder into a certain shape of the blank body by applying external pressure through the plunger of the press. Due to the moisture content of powder under 7%, the subsequent sintering time is reduced, so the forming efficiency is high and the cost is low, but the density is not uniform.

3. Tape casting

Tape casting is an important forming method for thin ceramic materials with high productivity and automation, but the shrinkage rate of firing is as high as 20-21%. It can be used to prepare high-quality ceramic films with a thickness of 10-1000 microns. Tape casting is used in the ceramic panel of MI 5 mobile phones and the ceramic fingerprint cover of various mobile phones.

4. Debinding and sintering

Debinding is the removal of organic matter from the body of an injection-molded billet by heating or other physicochemical means.

Under the action of high temperature, with the extension of time, the green body finally becomes a hard polycrystalline sintered body with a certain microstructure, which is called sintering. Sintering is a process to reduce the pores in the forming body, enhance the combination of particles and improve mechanical strength.

5. Postprocessing

The panel of 3C products, such as mobile phones and smart wearers, has very high requirements on the surface effect of engineering ceramics, such as smooth and clean surface, precise geometric size, fingerprint protection, and so on. This requires a complex post-processing process, including CNC machining, grinding, polishing, laser /PVD, AF processing, etc.

The above is all about the production process of the zirconia ceramic cell phone panel, I hope it can provide a reference for you. Stanford Advanced Materials supplies high-quality zirconia products to meet our customers’ R&D and production needs. Please visit http://www.samaterials.com for more information.

Zirconia Ceramics: A Hotspot in the Field of Micro-machinery

Zirconia ceramic materials are gradually being widely used in the field of micromachinery, because of its maintain excellent properties such as high-temperature resistance, oxidation resistance, acid and alkali corrosion resistance, hardness, etc.

The development of science and technology has made the miniaturization technology of zirconia ceramic materials become an important issue concerned by all countries, while the equipment tends to be miniaturized, and zirconia ceramics have a broad application prospect in the fields of automobile, medical treatment, aviation, aerospace, military, and environmental detection.

All countries in the world began to invest a lot of money, scientific research forces and too micromechanical system research. Organizations such as the National Natural Science Foundation of the United States and the Department of Defense attach great importance to MEMS（Micro-electromechanical Systems）technology and invest a lot of money in related research; The European Union has set up a multi-functional Microsystems research cooperation agency to strengthen interaction among countries; Japan has formulated the nano-manufacturing plan, the AI（artificial intelligence）technology plan, the microrobot plan, and established the micro machinery center and the micro machinery society; At present, there are more than 60 units engaged in MEMS research in China, and some scientific achievements have been made in the field of sensors and micro-actuators.

Zirconia ceramics are used in micro pressure sensors to detect engine inlet pipe pressure, micro accelerometers for vehicle safety airbag systems, and micro angular velocimeters for wheel sideslip and roll control. Microdevices such as micro pumps, microvalves, micro tweezers, and micro flowmeters applied in zirconia ceramics, and the micro-inertial measurement device, micro-whole analysis system, RF sensor, etc. are used in the military field. Moreover, zirconia ceramic materials can be used as a micro burner, a microreactor, and a pressure sensor at high temperatures and they can also be used as a composite, bone tissue scaffold, and in other biomedical fields because of their good biological solubility.

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Alumina VS Zirconia

Alumina (Al2O3) is a very common technical ceramic material. Zirconia (ZrO2), including yttrium stabilized zirconia (YSZ), is also widely used in machinery industries. Since both of them are oxide materials and could be sintered without vacuum, they share a lot in manufacturing equipment and have a similar appearance. However, there are still quite a lot of differences between these two materials.

Price: alumina VS zirconia

The most significant difference between these two materials is the price. Cost for zirconia is more than doubled for even the best alumina material. One of the reasons is the cost of the raw material. Compared with Zirconium, Aluminum is far more abundant in the crust and it’s much cheaper. On the other hand, Yttrium oxide, widely used as a stabilizer for Zirconia, is a rare earth element with limited sources.

However, it is the cost of shaping zirconia that contributes the major part. The density of zirconia is much higher than alumina and the wear resistance of zirconia is far better than alumina. To ground down the same thicknesses for zirconia takes almost 10x more time than alumina and consumes more diamond tools. Also, since the thermal shock resistance for zirconia is poor and requires a higher sintering temperature, the sintering process also costs more than alumina.

Applications: alumina VS zirconia

As the wear resistance for zirconia is much better, it is frequently used as mortar and pestles, grinding jars and grinding media, bearing balls and ceramic parts in valves and pumps. Zirconia parts will last longer in machines and have less contamination than grinding jars. Zirconia is generally better in mechanical applications but alumina is a better bulletproof material due to the lower density.

Although zirconia could withstand higher temperatures, application in industrial furnaces is rare. The advantage in working temperature is not quite significant, while the cost for zirconia is much higher.

High-density ZrO2 also provides better corrosion resistance. Zirconia could survive longer in a highly corrosive environment and is considered better material in chemistry laboratories.

Generally, zirconia performs better if the density and heat shock resistance is not considered. Stanford Advanced Materials (SAM) is a trusted supplier of customized zirconia products, such as zirconia rods, zirconia crucibles, zirconia tubes, etc. Please visit http://www.samaterials.com for more information.

Application of Zirconia in Fingerprint Identification

The Fingerprint recognition module is widely used in intelligent portable devices because of its fast, safe, convenient, and other advantages. However, due to the small area of the fingerprint module and complex application environment, it requires high identification sensitivity and speed, which also puts forward very high requirements for fingerprint identification chips and surface protection materials.

At present, there are two commonly used fingerprint identification schemes: pressing on the front of the sapphire cover and coating on the back.

Cost and Performance

In terms of cost and performance, sapphire has high hardness and corrosion resistance, but it has some weaknesses such as high cost and weak anti-falling ability, while the coated back fingerprint recognition scheme has the disadvantages of easy wear and sweat corrosion due to the low hardness of the coating.

Operation

In terms of operation, the two schemes have their own merits. The back fingerprint identification is convenient only for holding the index finger of the hand, while other fingers are inconvenient, and it can’t be used on a plane, it has to be picked up, too, which is not convenient in some special applications scenarios (such as driving). Meanwhile, the positive fingerprint is much smoother for the current hot fingerprint payment.

Appearance

In terms of appearance, the texture of backside fingerprint recognition is slightly poor, and it is easy to destroy the overall aesthetics of the backside putting fingerprints on the front not only makes the back of the phone more beautiful but also more in line with users’ habits and aesthetics.

Overall, a positive fingerprint is more popular with users, but it costs more. Many years of research have proved that zirconia ceramic cover products can be used for positive pressure fingerprint identification schemes.

The ceramic cover is zirconia ceramic (ZrO2), also known as the zirconium gem. It has superior hardness, toughness, insulation, heat conduction, and other advantages, showing abrasion resistance, fall resistance, corrosion resistance, high-temperature resistance, and other excellent characteristics, which is very suitable for pressing fingerprint identification module cover.

Zirconia ceramic is a cost-effective alternative to sapphire, and the zirconia product has been used in many well-known brands of mobile phones, which has the following advantages.

High hardness

The hardness of zirconia ceramics is 8.5 and that of single crystal alumina (sapphire) is 9, so they are quite similar in wear and scratch resistance.

High permittivity

The permittivity of zirconia is 32-35, which is three times that of sapphire, while all other materials are within 10. This characteristic is beneficial to improve the capacitance difference between the high and low levels of fingerprint identification module, so that fingerprint identification is more sensitive, the success rate is higher, and the speed is faster.

Thin in thickness

At present, the thinnest mass production thickness is as low as 0.1mm under the protection of falling strength of the zirconia protective layer, which is easier to identify than the thinnest sapphire cover with a thickness of 0.3mm. If the thickness is the same as that of sapphire, the strength and fall resistance of zirconia protective coating will be significantly better than that of sapphire.

Good processability

Zirconia ceramics are directly prepared by casting, polishing, and other ceramic processes. Its process is simple and its shape is easy to process, so it costs less than sapphire.

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Application of Chemical Zirconia Ceramics in Aeroengines

To maintain their leading position in the field of aviation power in the 21st century, aero-engine companies around the world are seeking new ways to improve the performance of military and civil engines and maintain their competitiveness. Half of that will depend on material improvements, including low-temperature polymer composites and high-temperature ceramics; the other half relies on improving design guidelines, methods, and procedures.

As the key to the improvement of military engine materials is to rely on high-temperature ceramic materials, the military engine will be the primary verifier of ceramic technology. Why is it necessary to use chemical zirconia ceramics? The operating temperature of the existing engine is already very high, and the only way to increase the temperature again is through the fine design of the cooling air circuit or the increase of cooling air volume.

However, the effects of these methods follow the law of diminishing, and only by improving the working temperature of the material can the maximum effect be achieved. Because raising the operating temperature can improve working efficiency, reduce fuel consumption and obtain the maximum thrust, using the saved high-pressure air for cooling for circulation can also improve the thrust and efficiency. Another option is to reduce weight by choosing materials with greater specific strength and greater stiffness. At present, only ceramic materials have the potential in this respect.

The application of ceramics to aero-engines will be developed with new materials and manufacturing methods. Considering the brittleness of ceramic materials and the lack of design and use experience, the process will be very long, no less than 15-20 years of metal materials. The applications of chemical zirconia ceramics in aviation are as follows.

Chemical zirconia ceramics have high-temperature resistance, low density, good oxidation resistance, corrosion resistance and wear resistance. In the case of the cooling, the working temperature of chemical zirconia ceramics can reach 1600 ℃, the density is only 40% of that in the high-temperature alloy, and the same volume of parts can reduce the weight by about 60%, which can greatly reduce the centrifugal load of the high-speed rotor. The use of ceramics also simplifies the chemical zirconia by reducing or eliminating the cooling system, making the engine compact.

The increasing turbine inlet temperature is the key to improving the thrust-to-weight ratio of the aero-engine and reducing fuel consumption. Sages for example, when the ratio is 10 level, the temperature of the engine turbine can reach above 1500 ℃, while the use temperature of high-temperature alloys and intermetallic compounds highest is less than 1200 ℃. Therefore, the research of high-temperature chemical zirconia ceramics and their ceramic matrix composites becomes one of the key technologies for high thrust-weight ratio aero-engines.

Radar remains one of the most reliable means of detecting military targets in future wars. The essence of stealth technology is to reduce the target’s RCS（Radar Cross-Section）, that is, to select materials with good radar wave absorption to reduce its RCS.

Absorbing materials can be divided into coating type and structure type according to process and bearing capacity. The former has a poor bearing capacity and low strength, while the latter is a new functional composite chemical zirconia material, which has the characteristics of absorbing waves and can be directly used as the chemical zirconia material for aircraft.

We use the excellent mechanical and physical properties of chemical zirconia ceramics to carry out the research on absorbing materials, which can not only enhance the national defense force but also is an important aspect of expanding the application of chemical zirconia ceramics. Some new nano absorbents and their composites are being applied in this field, such as nano Silicon Carbide (SiC), nano nitride, carbon nanotube (CNT), and other nanocomposites.

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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-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 the 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 drums, 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.

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 the 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 mold, tools, 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.

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 the workpiece during sintering, and graphite paper is placed on the workpiece surface. The black coloring of zirconia ceramics was realized by graphite infiltration into the zirconia surface at high temperatures.

Applications of color zirconia ceramics

The backplate of a 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.

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.

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.

The forming method is the key to obtaining the calcium density of the 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 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 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 between 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.

Sintering

Sintering of ceramic is the densification process of raw ceramic at high temperatures. With the increase in 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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7 Methods to Toughen the Zirconia Ceramics

Zirconia ceramics are characterized by unique physical and chemical properties such as high hardness, low thermal conductivity, high melting point, resistance to high temperature and corrosion, chemical inertia and amphoteric properties. As a special ceramic material, zirconia has a broad application prospect in electronics, aerospace, aviation, and nuclear industries.

At present, the toughening methods of ceramics mainly include phase transformation toughening, particle toughening, fiber toughening, self-toughening, diffusion toughening, co-toughening and nano toughening.

Phase transformation toughening

The toughening of the phase transition refers to a phase transition of t-ZrO2 of the metastable quadrilateral phase under the stress field at the crack tip, then the compressive stress is formed on the crack, which hinders the crack growth and plays a role of toughening.

Besides, external conditions (such as laser shock, fatigue fracture toughness, low temperature, grain size and content, critical transformation energy, etc.) have great influence on the toughening of zirconia ceramics. If the stress and volume produced by the phase transition are large, the product is prone to fracture. Therefore, the influence of external factors on the toughening of zirconia ceramics should be avoided in the production process.

Particles toughening

Particle toughening refers to adding ZrO2 ceramic powder as a toughening agent. Although the effect is not as good as whisker and fiber, there is still a certain toughening effect if the type, size, content and matrix materials are selected properly. The advantages of particle toughening are simple and feasible, and the toughening will bring about the improvement of high-temperature strength and high-temperature creep property. The toughening mechanism of particle toughening mainly includes grain refinement and crack turning to the bifurcation.

Fibre toughening

The toughening principle of fiber and whisker is that the closed stress is applied to the crack surface due to the deformation of crystal close to the crack tip, the external stress of the crack tip is offset, and the passivating crack growth is achieved, so as to play a toughening role. In addition, when the crack grows, the pulling out of the column crystal also overcomes the friction force, which also plays a role in toughening.

The self-toughening

Due to the existence of columnar crystals, the fracture process of zirconia ceramics can cause the crack to deflect, change and increase the crack growth path, thus passivating the crack to increase the crack growth resistance, thus achieving the purpose of toughening.

Dispersion toughening

Diffusion toughening mainly refers to the toughening of tetragonal ZrO2 particles to ceramic matrix. Besides the phase change toughening mechanism, there is also the diffusion toughening mechanism of the second phase particle. Before the crack propagation, the internal residual strain energy of the ceramics must be overcome, so as to achieve the purpose of toughening.

Microcrack toughening

Microcrack toughening refers to adding ductile materials to the stress tip of the crack to generate microcracks to disperse the stress, reduce the force of the crack forward, and thus increase the toughness of the material. When phase transition occurs, residual strain energy effects and microcracks often occur. Therefore, the effect of phase transition and toughening is remarkable.

Composite toughening

Composite toughening refers to the application of several toughening mechanisms in the actual toughening process of ZrO2 ceramics, so as to improve the toughening effect of ZrO2 ceramics. In the practical application process, the specific toughening mechanism is selected according to the different properties of zirconia ceramic materials to be prepared.

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