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 special working conditions.

Zirconia-ceramic-bearings
Zirconia-ceramic-bearings

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 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, thermal shock resistance, so it is suitable for this field.

ceramic-ball-valve
Ceramic-ball-valve

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.

Zirconia-ceramic-knife
Zirconia-ceramic-knife

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.

Biomedical-uses-of-zirconia-ceramics
Biomedical-uses-of-zirconia-ceramics

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 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-teeth

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 of the overall preparation cost.

crown

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 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 the human ingenuity is lacked, 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.

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

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.

Phosphating
Phosphating

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 of enterprises. Therefore, under the dual drive of environmental requirements and energy cost, the phosphorous-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.

Film formation process of zirconium salt conversion film on steel surface
The film formation process of zirconium salt conversion film on the steel surface

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 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 light weight, 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 more 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.

Ceramic-film
Ceramic-film

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 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 Did Nuclear Zirconium Alloys Develop?

Zirconium alloys have a small thermal neutron capture cross-section (0.185b) and are surprisingly resistant to corrosion, so they are widely used in fission reactors, such as core-clad tubes, grids, and guide tubes in boiling water reactors, as well as pressure pipes and exhaust reactor vessels in pressurized water reactors.

Nuclear zirconium alloy

With the application of zirconium alloys in the nuclear energy industry, the zirconium industry has developed rapidly.

In the nuclear giant change reactor, nuclear fuel is fission reaction all the time. In the reaction, the neutron bombards the nucleus of U235, which splits into Ba140 and Kr93, and releases two or three neutrons at the same time; other U235 nuclei are bombarded by these neutrons and re-fission. This is the chain reaction of fission.

nuclear-reactor
Nuclear Reactor

A material with a large neutron capture cross section will absorb many neutrons when they hit the wall, reducing the efficiency of the chain reaction. Meanwhile, the chain reaction produces a lot of heat, which is removed by circulating cooling water (or other coolants) to avoid overheating and damage to the reactor. When metals come into contact with high-temperature water, they can be corroded (oxidized). Materials with poor corrosion resistance need to be replaced frequently, which increases the cost and easily leads to safety accidents. Therefore, as core-cladding and structural materials, zirconium alloys are required to have low neutron capture cross-section and excellent corrosion resistance, so the development of zirconium alloys should be attributed to the nuclear industry.

Origin of zirconium alloys

Initially, zirconium was not considered a suitable material for use in the nuclear industry, because studies have shown that zirconium’s effect on thermal neutron absorption can affect the efficiency of nuclear reactors. Later, researchers at the Oak Ridge Institute found that 2.5% of the hafnium in zirconium was responsible for its large thermal neutron capture cross-section.

Zirconium Alloy
Zirconium Alloy

Zirconium and hafnium are associated with ore and are generally difficult to separate. Until the 1850s, Admiral in the Naval Nuclear Propulsion project decided to use zirconium in the water-cooled reactor of the Nautilus Nuclear Submarine. Although zirconium had already been used for the project by that time, there were no strict standards for the use of zirconium, and the researchers only knew that improving the purity of zirconium would be good for the properties of the alloy. Some processes are used to purify strip zirconium, but it still contains small amounts of nitrogen, making it less resistant to corrosion at high temperatures. Finally, the researchers realized that purity was not the key to zirconium’s corrosion resistance, because they found that some zirconium materials containing impurities (such as tin, iron, chromium, and nickel) were more resistant to corrosion than higher-purity zirconium materials. Therefore, the development of zirconium alloys is put on the agenda.

Development of zirconium alloys

The first alloy, Zircaloy-1, contains 2.5% tin. It was found that the corrosion rate of Zircaloy-1 alloy was increasing and not consistent with the expected decrease. This was similar to a normal sponge zirconium material, so Zircaloy-1 was quickly abandoned.

At the same time, the researchers found that adding iron and nickel to the Zircaloy-2 could improve corrosion resistance. The tin content was reduced to 1.5% and 0.15% iron, 0.05% nickel and 0.10% chromium were added. It was found that Zircaloy-2 had the same mechanical properties as Zircaloy-1, but the high-temperature corrosion resistance of Zircaloy-2 was much better than that of Zircaloy-1. However, during the service of the pressurized water reactor, the alloy produces a lot of hydrides, resulting in hydrogen embrittlement.

By studying the binding technique, the researchers found that nickel greatly enhanced the hydrogen absorption capacity of zirconium alloys. The researchers removed the nickel from the Zircaloy-2, creating a Zircaloy-3. But Zircaloy 3 was quickly abandoned because its strength was too low. In addition, Zircaloy-3 produced many striated Fe-Cr binary intermetallic compounds when it was processed in the two-phase zone, so it could not provide sufficient corrosion resistance. The strength of Zircaloy-3 was still too low, although changes in the heat treatment process prevented the production of the striated compound.

Zircaloy-2 Composition
Zircaloy-2 Composition

The researchers compensated for the nickel by increasing the iron content by 0.22 percent and found that the corrosion resistance of the new alloy was similar to that of zircaloy-2, which had only half the hydrogen absorption rate. The new alloy quickly became a major part of the pressurized water reactor, the first Zircaloy-4.

Zirconium alloys for the nuclear industry have been developed into the third generation of products, which are used in various reactors.

The first generation is the standard zircaloy-4 and Zircaloy-2, whose composition and process requirements are specified in the ASTM standard. This generation zirconium alloy is still in use.

The second generation is low tin Zircaloy-4 and optimized Zircaloy-4. The tin content of low tin Zircaloy 4 decreased from 1.2% ~ 1.70% to 1.20% ~ 1.50%, and the carbon and silicon were controlled at 0.008% ~ 0.020% and 0.005% ~ 0.012%, and the cumulative annealing process parameters in the alpha phase after quenching in the beta phase were strictly controlled; the optimized zircaloy-4 is based on the low tin zircaloy-4, and the content of alloy elements and process parameters are more strictly controlled, so as to improve the uniformity of materials.

The third generation of zirconium alloy has excellent properties and is widely used as a fuel rod cladding tube and fuel assembly guide tube. NDA and MDA from Japan, HANA from South Korea and composite casings from Siemens are also examples of this generation of products.

Prospect of zirconium alloys

Zirconium alloys above 620℃ (depending on composition) convert to body-centered cubic β-zirconium. After the transformation, the mechanical properties and corrosion resistance of the alloy will be greatly reduced, and it cannot continue to maintain the safe operation of the nuclear reactor. The famous event is the accident at the Fukushima nuclear power plant in Japan. Affected by the big earthquake in eastern Japan, the reaction water of Fukushima nuclear power plant leaked, and the cladding temperature increased significantly. The zirconium alloy cladding softened quickly, and brittle material formed with the leakage of air, leading to the leakage of nuclear fuel. Large amounts of nuclear-contaminated water flow into the sea have caused great damage to the ecology of the world.

As a nuclear reactor cladding material, it needs to have a small thermal neutron capture cross-section, which leads to the zirconium alloy cannot be highly alloyed, so it is bound to be difficult to break through the zirconium alloy’s high-temperature performance. At present, countries attach great importance to this problem. On the one hand, they are trying their best to make a breakthrough in the high-temperature performance of zirconium alloy; on the other hand, they are looking for alternative products of existing fuel cladding, such as silicon carbide (SiC) composite material, molybdenum alloy, cobalt alloy and so on. Molybdenum alloys and cobalt alloys were originally intended as structural materials for fusion reactors. Although they do not have the same low thermal neutron absorption cross-section as zirconium alloys, they have excellent high-temperature stability.

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