Zirconia – Page 3 – Zirconium Metal

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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Zirconia Ceramic Structural Parts VS Auto Parts

As we all know, a car is a product with an extremely demanding operating environment and working conditions, so the various components that make up this giant must have very superior functions. The zirconia ceramic structure has been widely used in auto parts.

Zirconia ceramic structure parts with excellent performance just make up for the lack of metal materials, so they began to be accepted by the automobile. For example, it has a long vibration tolerance of 20 grams; as parts used in combustion and exhaust systems, it can endure 50 ~ 60 ℃/S of thermal shock for a long time; due to the strong mechanical reliability of the zirconia ceramic, the failure rate is usually between 10 and 5; it can also be mass-produced and low in price, which is convenient for the formation of industrial management.

In recent years, scientists in the international special ceramics field have developed a large number of automobile special ceramics through hard research, and experiments and industrial applications have proved that the superior mechanical properties and high-temperature chemical properties of ceramic materials have far surpassed those of metal materials or other materials. At present, the applications of zirconia ceramic structure parts in auto parts industry are as follows.

Zirconia ceramic oxygen sensor

The zirconia ceramic oxygen sensor has high mechanical properties and reliability. As a component of clean exhaust, O2 concentration in automobile exhaust is measured, and the measured value is fed back to the gas and fuel supply system of the engine to keep the fuel always in full combustion state. Since all phases of the ceramic material are partially stabilized zirconia mixed with fully cubic, tetragonal and monoclinic crystals, the mechanical properties are superior during use and the heat generated by friction can be reduced.

Zirconia ceramic valve heater

In order to make the engine burn completely when starting, a heating device, the valve heater, is installed on the suction side of the engine, which is used to heat the air so that the fuel vaporizes and mixes completely. In order to control the temperature and improve the reliability of the device, the barium titanate ceramic PTC (thermistor) is used as the valve heater. After adopting the ceramic valve heater, the engine is in full combustion state when it starts, so as to improve thermal efficiency, energy saving, and purification and exhaust efficiency.

Zirconia ceramic engine

The application of special ceramics in the automobile has been popularized by the piston engine, and there will also be an auxiliary combustion chamber, piston head, cylinder liner, cylinder head, pressurized rotor, etc. Special ceramic materials such as silicon nitride, silicon carbide, and partially stabilized zirconia are also being considered for these parts.

Zirconia ceramic sensor

The shock absorber of the high-class car is a smart shock absorber that is developed by using the positive piezoelectric effect, inverse piezoelectric effect and electrostrictive effect of sensitive ceramics. The smart shock absorber, with its ability to recognize and self-regulate the road, minimizes the vibration of cars on rough roads, making them comfortable for the passenger.

Intelligent ceramic wipers

The intelligent ceramic windshield wiper is made of barium titanate, which can automatically sense rainfall and adjust the windshield wiper to the best speed. Some other ceramic sensing elements, such as thermal, pressure, humidity and magnetic ceramic materials, can also be sensitive to temperature, humidity, condensation, anti-freezing, etc. with automatic control and adjustment.

In addition, many parts, and small devices used in automobiles are made of special ceramic materials, such as the electronic buzzer, ultrasonic vibrator, heat-absorbing glass, photocell, oil plug ring, oil seal, etc. These kinds of automobile products made of new special ceramic materials generally have high physical and chemical properties, such as anti-seismic, wear-resisting, anti-corrosion, high-temperature resistant, lightweight and easy to process and produce.

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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.

How did people come up with Zirconia Ceramics for Tableware?

Most people think they are very strange to zirconia ceramics and have little contact with them, but in fact, we only need a few examples to make it clear. The simplest examples are the utensils we use in our daily lives, such as zirconia ceramic chopsticks, zirconia ceramic soup spoons, zirconia ceramic teacups, and so on, all of which are made from zirconia ceramics.

But how did people come up with this material for tableware? This is because traditional ceramics have problems such as poor resistance to fall and durability, and the appearance and application of zirconia ceramics completely solve these problems. This special material is not only resistant to acid, alkali, and rust, but also has good environmental protection. It is the ideal choice of tableware materials.

Zirconia ceramics are by far the most resilient of ceramic materials, so you don’t have to worry about breaking them when you make your cutlery. Besides, it has an excellent high-temperature solid electrolyte, oxygen ions can also pass through at a high temperature, which is a very special ceramic material. The following is a special case of zirconia ceramic knife to explain in detail the application of zirconia ceramics in kitchen utensils.

Zirconia ceramic knife is made from zirconia ceramic material which belongs to nonmetal material. Since the material purity and particle size were controlled, and various carbides, nitride, boride, and oxides were added to improve their properties, not only did the bending strength of the zirconia ceramic knife increase to 0.9~1.0GPa, but also the fracture toughness and impact resistance were greatly improved. In recent years, the application range of zirconia ceramic knives has been expanding, from high-tech fields such as aerospace to the industrial ceramic knife.

Characteristics of zirconia ceramic knife

Clean

The ceramic knife is designed in a close manner with no gaps and pores, no sticky bacteria and foreign body, and will not become a breeding ground for bacteria. The super antibacterial function of the ceramic knife is very suitable for cutting food which can be eaten directly.

Resistance to food oxidation

The ceramic knife will not react with any food, maintaining the original taste of the food, allowing you to fully experience the enjoyment of the delicious food. By the way, ceramic knives are very suitable for cutting raw fish, fruits, vegetables, boneless meat, and cooked food.

Healthy and Eco-friendly

The ceramic knife, which does not emit metal ions, has excellent non-metal properties, making it never rust. Besides, the healthy and environmentally friendly ceramic knives are resistant to various acid-base organics, and will not be corroded by acids and oils in fruits and vegetables. It is non-toxic, pollution-free, non-oxidizing and non-rusting.

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Is the Zirconia Full-porcelain Teeth Safe?

Zirconia is an excellent high-tech biological material with good biocompatibility that is superior to various metal alloys, including gold. Zirconia has no irritation or allergic reaction to the gingiva, and is suitable for oral application, avoiding allergic, stimulative, and corrosive reactions of metal in the oral cavity.

Excellent mechanical properties

The zirconia full porcelain dental material has a winding strength greater than 900MPa, so it can also be used to repair the posterior tooth and the all-ceramic bridge with more than 6 units.

Good biocompatibility

In the latest clinical evaluation report of CRAI, a U.S. clinical research association, it was found that the zirconia all-ceramic crown itself had no metal, and the restoration of the zirconia all-ceramic crown could exclude the metal allergic reaction and have good biocompatibility. Therefore, zirconia all-ceramic crowns are superior to various metal alloys in terms of biocompatibility, including gold materials.

Safe non-metallic materials

At present, zirconia is the only mineral in the natural world, which does not contain any metal, and it is safer after medical clean processing.

No obstruction to the X-Ray

If cranial X-ray, CT, and MRI examinations are needed after inserting the zirconia porcelain teeth, the dentures do not need to be removed in the future, because the zirconia porcelain teeth do not have any obstruction to X-ray, so a lot of trouble is avoided.

High intensity and density

Zirconia is widely used, especially in high-precision instruments, such as aviation equipment, because of its ultra-high-strength and density. Among them, the unique resistance to rupture and the strong firmness after rupture can be made into all-ceramic Bridges of more than 6 units, thus solving the problem that all all-ceramic systems cannot be long Bridges. Therefore, they are favored by doctors and patients.

Perfect color

Due to the white color of the base crown of structural ceramics, the neck will not become dark for a period of time after the insert, which solves the extremely difficult problem of the metal crown.

Healthy biomaterials

Zirconia is an excellent high-tech biological material with excellent biocompatibility and no irritation or allergic reactions to the gums. It is very suitable for the mouth.

PFM (porcelain fused to metal) is accepted by most patients for its good strength, but it has its fatal disadvantages. The metal base of low-end porcelain teeth is easy to oxidize and form gray oxides. When scattered and deposited at the edge of the gingiva, the gingiva will turn gray and affect its appearance. At the same time, it has a strong stimulation effect on the gingiva, and some patients may also have gingiva swelling, bleeding, allergy, and other symptoms, which is difficult to meet the clinical requirements. High-end metal porcelain teeth (gold alloy) are expensive without these drawbacks.

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How to tell the Zirconia from Diamonds?

Diamond is the product of adamas finishing, which is the hardest and simplest gemstone in the world. It is a natural crystal with a cubic structure made of carbon. The bigger the diamond, the rarer it is. Diamond often contains 0.05%-0.2% impurity elements, among which N and B are the most important. The pure diamond is colorless and transparent, which presents different colors due to the mixing of trace elements.

Natural diamonds are expensive due to their scarcity, especially the larger ones. However, artificial diamonds (synthetic diamonds) are difficult to achieve large size gemstones. Generally, synthetic diamonds are used in cutting and polishing tools. Therefore, in order to meet the design needs of jewelry and some products, there are usually some substitutes, such as glass, artificial spinel, artificial sapphire, zircon, scheelite, strontium titanate, cubic zirconia and so on. Among them, cubic zirconia is very close to diamond in terms of its optical and hardness properties and is the most common diamond substitute.

The cubic zirconia was first developed by the Soviets, also known as Soviet Stone. Cubic zirconia in cubic crystals is rare in nature and is usually synthesized artificially. Synthetic cubic zirconia is a hard, colorless and optically immaculate crystal, and it has been a replacement for diamonds since 1976 because of its low cost, durability and its resemblance to diamonds. Cubic zirconia is known as a “fake” diamond or CZ diamond. The following is a brief analysis of the difference between diamonds and “fake” diamonds and how they are identified.

Difference in hardness

Natural diamonds have a Mohs hardness of 10 and are difficult to process, and the cubic zirconia has a Mohs hardness of 8.5 to 9.0, while quartz sand is 7 and stainless steel is only 5.5. Therefore, the treatment of gem-level cubic zirconia can meet the requirements of daily use and is easier to process.

Differences in dispersion

The dispersion of cubic zirconia was 0.060, which is higher than that of diamond, so cubic zirconia looks more brilliant than diamonds.

The index of refraction

Cubic zirconia has a refractive index of 2.176, which is slightly lower than diamond’s 2.417. Depending on the refractive index, cubic zirconia cuts slightly differently from a diamond, which can be seen under a magnifying glass.

Color

Completely colorless diamonds are very rare, and usually, they are pale yellow. However, the cubic zirconia can be made into diamonds of the highest grade, or D-grade color. A variety of trace elements can also be added to the cubic zirconia to render it in different colors to meet customers’ demand for colored gems.

The crystals of different colors can be obtained by adding different metal oxides to the raw materials. For example, cerium: yellow, orange, red; chromium: green; neodymium: purple; erbium: pink; titanium: golden brown.

Specific gravity

Cubic zirconia is 1.7 times heavier than a diamond, so they can be distinguished by differences in specific gravity, but can only be used to separate unencrusted gems.

The heat-transfer capability

The thermal conductivity of cubic zirconia and diamond are two extremes. Cubic zirconia is a good insulator and can be used as an insulator for jet engines, while diamond is one of the best heat conducting bodies, its heat-conducting ability surpasses copper.

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.

How is the Zirconia Ceramic Made?

As the most important type of advanced ceramics, zirconia ceramic material is an important basic material for the development of the modern high-tech industry. Zirconia is widely used in the market, and its specific applications include the solid fuel cell, automobile exhaust treatment, dental materials, ceramic cutting tools, and zirconia fiber core plug.

However, as mobile 5G era approaches at any time, zirconia ceramics become the hot spot of the industry again due to its characteristics such as warm feeling, anti-scratch and wear resistance, no signal shielding, and excellent heat dissipation performance.

Zirconia is insoluble in water, sulfuric acid, hydrochloric acid, and nitric acid. It is slightly soluble in hydrofluoric acid and concentrated sulfuric acid when heated. Pure zirconia is an insulator at room temperature. Adding a stabilizer can increase its conductivity and show ionic conductivity at high temperatures. There are three crystal types of zirconia. The crystal parameters and the schematic diagram of the structure of the three crystal types are shown below.

Zirconia ceramics have high hardness, wear resistance, high-temperature thermal stability and impact resistance. The preparation of high-performance zirconia ceramics depends on high-quality zirconia powder and optimized sintering process parameters.

Preparation of high-quality zirconia powder

The preparation methods of high-quality zirconia powder mainly include the physical method and the chemical method. The physical methods include high-temperature spray pyrolysis, spray induction coupled plasma pyrolysis and freeze-drying; chemical methods include gas phase, liquid phase, and solid-phase method. Among them, the liquid phase synthesis method has high efficiency, fine powder particle quality, and simple equipment, so it has been widely used.

The sintering method

Sintering process parameters include sintering temperature, sintering pressure and sintering time. Ceramic materials with very different microstructures and properties can be obtained when the same ceramic materials adopt different sintering processes. At present, the sintering process of zirconia ceramics at home and abroad has pressureless sintering, hot pressing sintering, hot isostatic sintering, and discharge plasma sintering. Pressureless sintering, also known as traditional atmospheric sintering, is the sintering of a prefabricated ceramic body under atmospheric pressure and high-temperature conditions; hot press sintering is a sintering method for applying axial pressure to the powder in the mold; spark plasma sintering (SPS), also known as plasma-activated sintering, is a new rapid sintering technology.

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

How Does the Fused Zirconia Work in Modern Industry?

Zirconia and zirconite are the main raw materials of zirconia in nature. Pure zirconia is a white solid that will appear grey or light yellow when it contains impurities, and various other colors can be displayed by adding a developer. Pure zirconium oxide is a kind of advanced refractory raw material with a melting temperature of about 2900 ℃. Zirconia usually contains a small amount of hafnium oxide, which is difficult to separate but has no obvious effect on the properties of zirconia.

Zirconia has three crystalline forms: monoclinic, tetragonal and cubic. The zirconia at room temperature only appears in monoclinic phase, and it will be transformed into the tetragonal phase when heated to 1100 ℃ or so, and it will turn into a cubic phase when heated up to a higher temperature. Due to large volume changes when the monoclinic phase changes to the square phase, and large volume changes in the opposite direction when cooling, it is easy to cause product cracking, which limits the use of pure zirconia at high temperatures. However, the tetragonal phase can be stabilized at room temperature after adding stabilizer, so the volume mutation will not occur after heating, which greatly expands the application range of zirconia.

Refractory materials and casting

There are two main refractory markets for the fused zirconia. The first is the cast steel refractories in the steel industry, particularly for the production of isostatic pressure molding products, which include intermediate flow slots and ladle outlets and immersion nozzles.

The second major market is the refractory produced by the electric melting and burning method in the special glass industry. Zirconia gives the molten glass good resistance to high temperature and corrosion. As there is no reaction area, there is no gravel in the glass. Aluminum-zirconium silicon refractories are graded by the content of zirconia, which is determined by the content of zirconia in the product.

Investment casting

For fused zirconia, investment casting is another major specialized market. For example, zirconia is commonly used as a model coating for the casting of special products such as aerospace engines, turbine engines, and golf clubs. Zirconite is used in investment casting because it can form actual contact with hot metal alloy to protect the die from thermal shock.

Abrasive substance

The polishing tools used in the ceramic industry, such as grinding wheel pieces and non-metal blades used in stone cutting, are made into coarse abrasive particles by mixing zirconia and alumina according to a certain formula, and then made into a grinding wheel or coated on the surface of grinding tool after thermal processing. This method can be used to polish steel and metal alloys.

Advanced ceramics and special products

For stable zirconia, the roasting control board for electronic components is a major market. Stable zirconia is also used in oxygen sensors and fuel cell partitions because it has the ability to allow oxygen ions to move freely in the crystalline structure at high temperatures, and the high ionic conductivity makes it one of the most promising materials for electrical ceramics. Chemical-grade zirconia is often used in electric melting products, and other special product markets include vacuum pumps and high-value components, special tool parts and brake lining. Fully stable cubic phase yttrium stabilized zirconia is used in the jewelry industry as a cheap alternative to diamonds.

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.

Rare Metals Indispensable to Modern Industries: Zirconium

Zirconium has been regarded as a precious stone since ancient times due to its rich and colorful color, playing a decorative role in human life. As people’s understanding of zirconium deepens, the application of zirconium has penetrated into every aspect of our life. For example, all kinds of buildings, ceramics, knives, ornaments, etc., as well as the military and nuclear power fields are also featured with zirconium.

Zirconium is mainly used in ceramics and refractories in the form of zirconium silicate and zirconia. Only 3 to 4 percent of zirconium ore is processed into metallic zirconium, or sponge zirconium, which is further processed into various zirconium materials. Zirconium has excellent nuclear properties because of its small thermal neutron absorption section, and the nuclear grade zirconium is used as the structural material of nuclear power aircraft carriers, nuclear submarine and civil power reactors, and the hull of the uranium fuel element. Another important use of zirconium metals is in the manufacture of alloys with excellent properties, such as aluminum zirconium alloy, copper zirconium alloy, iron zirconium alloy, and nickel zirconium alloy, zirconium tin alloy, and niobium zirconium alloy and so on.

Currently, the most used materials in the industry are zircon, while a small number of zirconium compounds and metals. Zirconium ore and mineral powder are mainly used in refractory, casting, abrasive, ceramic and electronic industries. Zirconium compounds, mainly zirconia, are used in refractories, abrasives, electronic materials, glass additives, gemstones, sensitive materials and precision ceramics.

Zirconium metals can be classified into atomic and industrial grades by use. Atomic energy grade zirconium refers to the zirconium with content of hafnium less than 0.01% in the metal, also known as hafnium zirconium or reactor-grade zirconium, which is mainly used in nuclear reactors as nuclear fuel sheathing materials and core structural materials. In the chemical industry, smelting, and other industries, zirconium does not need to be separated. Generally, zirconium containing about 2.5% of hafnium is classified as industrial-grade zirconium.

As an active metal, zirconium forms an oxide film at room temperature, which gives zirconium and its alloys excellent corrosion resistance. Moreover, zirconium also has good mechanical and heat transfer properties, as well as significant cost advantages, which makes it an excellent corrosion-resistant structural material in today’s petrochemical industry.

The zirconium applied in chemical acid-resistant equipment, military industry, and electronic industry is called industrial grade zirconium. In terms of processing difficulty and technological level, zirconium metal and its alloy products are at the top of the industrial chain.

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