Zirconia – Page 3 – Zirconium Metal

Applications of Zirconia in Structural And Functional Ceramics

Zirconia is a kind of inorganic nonmetallic material with high-temperature resistance, corrosion resistance, abrasion resistance, and excellent electrical conductivity. Since the mid-1970s, developed countries have invested heavily in the research and development of zirconia products, extending the application field of zirconia to structural and functional materials. Zirconia is also one of the new high-performance materials in the national industrial policy, which is widely used in various industries.

Applications of zirconia in structural ceramics

In 1975, R.G.Garvie, Australia, prepared partially stabilized zirconia with calcium oxide as a stabilizer, and improved the toughness and strength of zirconia for the first time, which greatly expanded its application in the field of structural ceramics.

1. Zirconia ceramic bearings

Zirconia ceramic bearing has the characteristics of wear resistance, corrosion resistance, high-temperature resistance, high cold resistance, oil-free self-lubrication, resistance to magnetoelectric insulation, etc. It can be used in an extremely harsh environment and under special working conditions.

Zirconia ceramic bearings have been used in micro cooling fans, and the product life and noise stability are better than traditional ball and sliding bearing systems. Foxconn is the first company to use zirconia ceramic bearings in computer cooling fans.

2. Zirconia ceramic valve

At present, valves commonly used in various industries are made of metal materials. Due to the limitation of metal material itself, the corrosion damage of metal has a considerable impact on the working life, reliability and service life of valve wear resistance.

The working climate of the valve pipeline is very complicated. Hydrogen sulfide, carbon dioxide, and some organic acids in oil, gas, and reservoir water increase the destructive power of their surfaces, rapidly disabling them. Zirconia ceramic valve has excellent wear resistance, corrosion resistance, high-temperature resistance, and thermal shock resistance, so it is suitable for this field.

3. Zirconia abrasive material

Zirconia ball has the advantages of high hardness, low wear rate and long service life, which can greatly reduce the pollution of grinding materials and ensure the quality of products. Besides that, zirconia material has high density and strong impact energy when used as a grinding medium, which can greatly improve the grinding dispersion efficiency. Good chemical stability determines its corrosion resistance and can be used in acidic and alkaline media.

Applications of zirconia in functional ceramics

1. Zirconia ceramic knives

Zirconia ceramic knife has the characteristics of high strength, wear resistance, no rust, no oxidation, acid and alkali resistance, anti-static, and no reaction with the food. Its body is as shiny as jade, which also makes it an ideal high-tech green knife. At present, the main products on the market are zirconia ceramic knife, scissors, razor, scalpel and so on, which has become popular in Europe, America, and Japan in recent years.

2. Zirconia high-temperature heating element

Zirconia is an insulating material at room temperature, its resistivity is as high as 1015 Ω cm, and it can conduct electricity when the temperature to 600 ℃. When the temperature reaches 1000℃ above, it is a good conductor and can be used as 1800℃ high-temperature heating element, with the highest operating temperature of 2400℃. At present, zirconia has been successfully used in heating elements and equipment with an oxidation atmosphere above 2000℃.

3. Zirconia bioceramics

The quality of ceramic tooth material directly affects its quality and patients’ health. The inner crown of porcelain teeth is made of different metal materials, which is easy to oxidize with saliva. Since there is no metal inner canopy, zirconia ceramic teeth have good transparency, excellent gloss, and effectively avoid tooth allergies and gum black lines.

4. Zirconia coating material

Zirconia thermal barrier ceramic coating material with a high-performance stabilizer such as yttrium oxide (Y2O3) is mainly used in high-performance turbine aero-engine. The thermal barrier coating uses ceramic insulation and corrosion resistance to protect the metal material, which can not only improve the fuel combustion efficiency but also greatly extend the life of the engine. Thermal barrier coating has important application value in aviation, aerospace, surface ships, large thermal power generation, and automobile power, etc. It is one of the most important technologies in modern national defense.

5. Zirconia oxygen sensor

Oxygen sensors are essential in the automotive industry for engines that use three-way catalytic converters to reduce pollution emissions. Currently, there are two kinds of oxygen sensors in use: titanium oxide and zirconia. Japanese scientists made a porous oxygen sensor out of zirconia, which is installed in an engine to automatically detect the ratio of oxygen to combustion gas in the engine, and automatically control the ratio of input gas and output gas, thus greatly reducing the harmful gas emissions from cars.

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

Why Are Zirconia Ceramic Teeth So Expensive?

The all-ceramic dental prosthesis has excellent mechanical properties, no gingival inflammation, and excellent biocompatibility, and it has no obstruction to X-ray rays. In addition, it has excellent wear resistance, corrosion resistance, and aesthetic properties of no gingival black edge and emulating natural teeth, all of these make it the first choice of dental repair materials.

Zirconia ceramic teeth

At present, there are three kinds of materials used in all-ceramic dental restorations, namely, zirconia all-ceramic dental restorations, cast ceramic dental restorations and alumina all-ceramic dental restorations.

Among the three kinds of all-ceramic teeth, zirconia all-ceramic teeth are the strongest dental restorations. Its fracture toughness ratio is two or three times that of alumina all-ceramic, and it is not easy to break the teeth with it; secondly, it can be used for cosmetic dentistry and restoration of missing teeth. It can be used to repair multiple teeth, which can be used to repair even crowns, which can perfectly solve the problem that the strength of ceramic casting material is too poor to make continuous crown; moreover, its color is perfectly adjustable, so it can be used to make very realistic dentures.

Zirconia denture, as such an excellent product, should have been favored by the public. But zirconia restorations are expensive, costing thousands or even thousands of dollars for a single crown, which makes it unaffordable for ordinary people.

Why are zirconia ceramic teeth so expensive?

The main reason for the high price of zirconia ceramic teeth is that the overall production cost of zirconia teeth is really high.

The zirconia prosthesis underwent a series of complex processes before it was put into the patient’s mouth to achieve its chewing, vocal and aesthetic functions, including raw material production of raw material manufacturers, production of zirconia block manufacturers, dental surgeons’ spare tooth mold, processing design, selection of the right zirconium block, cutting, dyeing, sintering, dyeing, polishing, dental doctor’s grinding, etc. As long as one of the above processes goes wrong, it will affect the currently visible quality of the restoration or the currently invisible but potential quality problems in the future.

Zirconium blocks used for all-ceramic teeth can cost anywhere from hundreds to thousands of dollars just from the cost of materials alone. From the above analysis, we can see that the proportion of the raw material cost is not large, but the difficulty of processing leads to an increase in the overall preparation cost.

At present, the forming of zirconia ceramic crowns is dominated by CNC processing technology, which has advantages in product precision and processing efficiency. However, due to the material removal by cutting tools on zirconium plates (blocks) during processing, the cost of ceramic crowns remains high due to the waste of materials and the wear of cutting needles, and microcracks are easily introduced in the cutting process, leading to the failure of the restoration. The current zirconia denture is semi-machined, and the zirconia teeth processed by a professional milling machine need to be used to repair the maxillofacial fossae and furrows with a crack drill or a ball drill to achieve a realistic effect. If human ingenuity is lacking, it can also be said that it has a little personality in shape and edge treatment.

To sum up, the waste of raw materials and the high labor cost of advanced technical workers inevitably increase the preparation cost of zirconia teeth due to the inevitable mistakes in manual processing. Therefore, seeking a new dental ceramic prosthesis forming technology is the characteristic of dental ceramic research and the key point of the clinical prosthesis.

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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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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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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Can Zirconia Ceramics be used as Wearables?

Zirconia ceramics enter the consumer electronics represented by mobile phones in three subdivisions.

The main application area is the back cover of the mobile phone, which is mainly used to upgrade and supplement plastic, glass and metal materials.
The second is the patch or the case of the wearable device used for fingerprint identification, which mainly benefits from the increase in the installed rate of the fingerprint reader and the replacement of sapphire.
Finally, it is used for small structural parts such as lock screen and volume button, which is a continuation of the ceramic button business in the era of the functional machine.

In contrast, zirconia has a density of 6 grams per cubic meter, the heaviest of all materials. Fortunately, zirconia ceramics can be controlled by thickness, keeping the total weight to a level lighter than glass. Besides, the back set of fine CNC processing required time and high cost because of the superior wear-resisting performance of ceramics. As a result, zirconia has exploded more quickly in areas such as fingerprint recognition, wearable devices and the back cover of mobile phones, where it is more cost-effective.

Apple Watch

As early as April 2015, the Apple Watch went on the market and used zirconia ceramic material as the rear cover appearance for the first time, which brings the wearables’ ceramic facade to a climax. Compared with metals and plastics, zirconia ceramics are wear-resistant and skin-friendly, making them more suitable for use on wearable devices. In addition, the airtightness and waterproof of wearable devices determine that most of them adopt wireless charging mode, and the ceramic material is used as the rear cover with small signal shielding, which is obviously superior to the metal material.

Due to the aesthetic and waterproof considerations, most wearable devices have the function of wireless charging, and the wireless charging scheme of the non-metal back shell is easier to design. From the perspective of shielding efficiency, zirconia ceramics, as a non-metal material, have no shielding effect on electromagnetic signals, and will not affect the internal antenna layout at all. Therefore, it can be conveniently shaped into a whole, instead of making an ugly segmented structure like aluminum magnesium alloy. Arguably, Apple’s Apple Watch led the trend of zirconia ceramics being the back cover of wearables.

Wearable devices

In addition, zirconia ceramics also have the following advantages as wearable devices. As mentioned above, zirconia ceramics have higher dielectric constants that make fingerprint scanners work more sensitively and cost significantly less than sapphires. The Mohs hardness of zirconia ceramics is around 8.5, which is very close to that of sapphire 9. Given all the advantages of zirconia ceramics, it is expected that it will become the preferred rear cover material in the field of wearable devices in the future.

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