How to Ensure the Welding Quality of Zirconium Alloy

In the previous article, we introduced the basic properties of zirconium alloys and the problems that easily occur during the welding process. Next, we will explain how to ensure the welding quality of zirconium alloys and some precautions.

welded zirconium

Precautions for zirconium alloy welding

  • In the welding prefabrication stage of a large number of welds, a special closed clean place needs to be set up, and strict control of environmental dust pollution and air humidity. For example, when entering the construction site, measures such as wearing clean labor insurance shoes must be worn to ensure the cleanness of the welding environment. In the outdoor installation environment, make a temporary operating room to achieve clean conditions.
  • Strengthening the requirements for the weld joint groove and within 70mm of both sides of the groove and the cleanliness of the surface of the welding wire is an important factor to ensure the welding quality.
  • In the welding process of zirconium alloy, pores are the most prone to defects, and it is mostly concentrated near the fusion line and the centerline of the weld. The most critical steps to prevent the occurrence of welding porosity defects are to strengthen the control of the cleanliness and humidity of the welding environment, and to enhance the cleaning of the bevel and the surface of the welding material, so as to improve the quality of the internal and external protection of high purity argon in the weld zone.
  • The zirconium alloy has a low thermal expansion coefficient, a small amount of thermal deformation, and a small volume change during phase change. It has a low content of impurities such as sulfur, phosphorus, and carbon, so there is no obvious tendency to form cracks during welding. However, when the welding seam absorbs a certain amount of oxygen, nitrogen and hydrogen gas impurities, the performance of the welding seam and the heat-affected zone will become brittle. If there is stress in the weld in the peer group, a cold crack will occur. In addition, the hydrogen atoms have the property of diffusing and accumulating to the high-stress parts in the heat-affected zone at a relatively low temperature, which promotes the formation of relatively weak links in these parts, which may lead to the occurrence of delayed welding cracks.
  • In the welding test, manual tungsten argon arc welding with low welding line energy and convenient gas welding protection should be selected; The larger-diameter welding torch nozzle, the outer surface of the weld seam, and the internal argon filling method of the pipe are used for air isolation to achieve the purpose of the weld seam not being oxidized and absorbing harmful gases.
  • The filler wire used for zirconium alloy welding should be selected according to the principle of matching the composition of the base metal. The surface of the welding wire must be free from defects such as heavy skin, cracks, oxidation, and metal or non-metallic inclusions. The welding wire should be cleaned and dried before use.
  • Zirconium alloy tungsten arc welding requires high-purity argon with a purity of not less than 99.999%, and its impurity content meets the requirements of the current GB / T4842 standard. Due to the extremely high requirements for the purity of the welding protective gas, the welding process needs to be continuously inflated and cannot be interrupted halfway, otherwise, the argon filling must be replaced again. The method of using an ordinary single bottle of argon direct gas supply cannot meet the protection requirements. Multiple bottles of argon gas need to be connected in series to increase the gas supply capacity, and multiple welders can be operated simultaneously by dividing the cylinder.
  • Because zirconium alloys are active at high temperatures, relying solely on the argon gas supplied by the argon arc welding torch nozzle to protect the molten pool and high-temperature bead and heat-affected zone during welding cannot guarantee the welding quality. In order to ensure that the requirements for gas isolation in high-temperature areas and prolonged argon protection time are met, special external gas protection devices for pipes must be added to provide high-purity argon isolation protection for weld pools, high-temperature weld beads and heat-affected zones at high temperatures.

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

Problems Prone to Welding of Zirconium Alloys at High Temperatures

Zirconium is an expensive corrosion-resistant metal material with excellent resistance to corrosion by acids and alkalis. In some media, it even exceeds metals with good corrosion resistance such as niobium and titanium. Zirconium alloys have been gradually used in recent years as structural materials for equipment and pipelines in the chemical industry due to their good corrosion resistance.

The commonly used zirconium alloy grades include Zr702 (UNSR60702), Zr704 (UNSR60704), and Zr705 (UNSR60705). Among them, Zr702 (UNSR60702) is widely used in chemical projects.

zirconium-tubes

Basic characteristics of zirconium alloy

Zirconium alloy has good welding performance, stable chemical properties at room temperature, and outstanding corrosion resistance. However, its high-temperature chemical properties are lively and have a strong affinity for the pollution of oxygen, nitrogen, hydrogen in the ambient gas, and dust and humidity in the operating environment. As the temperature rises, its chemical activity sharply increases, and it forms ZrH2 with hydrogen at 200 ℃; it can form ZrO3 with oxygen at 300 ℃; it reacts with oxygen in the air above 550 ℃ to form a porous brittle oxide film; at 600 ° C, zirconium absorbs nitrogen to form ZrN; it absorbs oxygen and severely embrittles the material at above 700 ℃. As the temperature increases, its absorption capacity and reaction speed increase. Therefore, the high temperature environment and welding seams generated by welding are the key to restrict chemical equipment.

The excellent corrosion resistance of zirconium alloys comes from the oxide film formed on its surface and depends on the integrity and robustness of the oxide film. When zirconium alloy absorbs a certain amount of oxygen, nitrogen, hydrogen and other gas impurities, its mechanical properties and corrosion resistance will drop sharply. Therefore, strengthening the protection of environmental dust, humidity and heat-affected zone surfaces and the back of welds is a key element of quality control during welding.

Problems prone to welding of zirconium alloys

High temperature is the natural enemy of zirconium alloys with great changes in corrosion performance. Zirconium generally reacts easily with the atmosphere at high temperatures. It starts to absorb oxygen at 200 ℃, hydrogen at 300 ℃, and nitrogen at 400 ℃. The higher the temperature, the more intense the reaction. Because zirconium is active against oxygen, nitrogen and hydrogen, it must be protected with a high-purity inert gas or welded in a good vacuum chamber.

zirconium-alloy-welded

During zirconium welding, the weld seam and heat-affected zone are easily polluted by oxygen, hydrogen, nitrogen and other elements in the air, forming hard and brittle compounds, and producing brittle needle-like structure, which increases the hardness and strength of the welded joint , while the plasticity declines, and the corrosion resistance is also greatly reduced. Therefore, zirconium welding should fully protect the molten pool, weld and heat affected zone to completely isolate the air.

The welding of zirconium alloys is generally performed by the welding method of tungsten inert gas shielded arc. Other welding methods include electron beam welding, plasma arc welding and resistance welding. Its welding performance is close to that of titanium metal welding. Due to the small thermal expansion coefficient and elastic modulus of zirconium, the welding deformation and weld residual stress are relatively small. It is recommended that the stress relief time of the weld at 1100 ° F (594 ℃) be 1 hour / inch thickness.

Another major problem of zirconium welding is that the weld is prone to soften too much and cause the weldment to be distorted. When welding zirconium, the welding piece should be properly fixed and double-sided welding should be used as much as possible. Except for titanium, niobium, silver, and vanadium, zirconium cannot be directly welded to other metals. Therefore, choosing a clean operating environment and strengthening the isolation and protection of welds and heat-affected zones are the keys to ensuring the quality of zirconium alloy welding.

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

Basic Info | Toughening Methods of Zirconia Ceramics

Zirconia (ZrO2) ceramics are special ceramics with unique physical and chemical properties, and their applications in electronic ceramics, functional ceramics and structural ceramics have developed rapidly. However, the fatal shortcomings of zirconia ceramic materials are brittleness, low reliability, and low repeatability, which seriously affect its application range. Only by improving the fracture toughness of zirconia ceramics, strengthening the material and improving its reliability and service life, can zirconia ceramics truly become a widely used new material.

Toughening technology of zirconia ceramics has been a hot spot in ceramics research. At present, ceramic toughening methods mainly include phase change toughening, particle toughening, fiber toughening, self-toughening, diffusion toughening, synergistic toughening, nano-toughening, etc.

Transformation_Toughening
Transformation-Toughening

Phase toughening

Phase toughening refers to the metastable tetragonal phase t-ZrO2 undergoing a phase change under the action of the stress field at the crack tip, forming a monoclinic phase, resulting in volume expansion, thereby forming compressive stress on the crack, hindering crack growth, and increasing the role of toughness. In addition, external conditions (such as laser shock, fatigue fracture toughness, low temperature, grain size and content, critical transition energy, etc.) have a great effect on the phase toughening of zirconia ceramics. If the phase transition produces large stress and volume changes, the product is prone to fracture. Therefore, the influence of external factors on the phase toughening of zirconia ceramics should be avoided during production.

Particle toughening

Particle toughening refers to the method of using particles as a toughening agent and adding it to ZrO2 ceramic powder. Although its effect is not as good as whiskers and fibers, if the particle type, particle size, content and matrix material are properly selected, there is still a certain strong effect. The advantage is that it is simple and easy to implement, and it will also improve the high-temperature strength and high temperature creep performance while toughening. The toughening mechanism of particle toughening mainly includes refinement of matrix grains and crack turning bifurcation.

zirconia-overview

Fiber toughening

The principle of fiber and whisker toughening is that the crystal close to the crack tip adds closing stress to the crack surface due to deformation, offsets the external stress at the crack tip, and passivates the crack propagation, thereby strengthening the toughness. In addition, when cracks are propagated, the frictional force must be overcome when the columnar crystals are pulled out, which also plays the role of toughening.

Self-toughening

Due to the existence of columnar crystals, cracks will be deflected during the fracture process of zirconia ceramics, which will change and increase the path of crack growth, thereby passivating the cracks, increasing the crack growth resistance and achieving toughening.

Diffuse toughening

Diffusion toughening mainly refers to the toughening of the ceramic matrix by the tetragonal ZrO2 particles. In addition to the phase toughening mechanism, there is also a diffusion toughening mechanism of the second phase particles. Before cracks propagate, the internal residual strain energy of the ceramic itself must first be overcome to achieve the purpose of toughening.

Microcrack toughening

Micro-crack toughening refers to adding a tough material at the crack stress tip to cause micro-cracks to achieve the purpose of dispersing stress, reducing the force of crack advance, and thereby increasing the toughness of the material. When a material undergoes a phase transition, it often results in residual strain energy effects and microcracks. Therefore, the effect of phase transition toughening is significant.

Composite toughening

Composite toughening refers to the simultaneous use of several toughening mechanisms during the actual toughening of ZrO2 ceramics, thereby improving the toughening effect of ZrO2 ceramics. In the actual application process, the specific toughening mechanism is selected according to the different properties of the zirconia ceramic material to be prepared.

Alumina-toughened-Zirconia
Alumina-toughened-Zirconia

Nano toughening

At present, there are three main academic viewpoints of nano-toughening, namely: the theory of refinement, trans-crystalline, and “pinning”.

  • The refinement theory believes that the introduction of nano-phases can suppress the abnormal growth of the matrix grains, refine the matrix structure uniformly, and improve the strength and toughness of the nano-oxide ceramic composites.
  • The trans-crystalline theory holds that in nanocomposite materials, the matrix particles are densified with the nanoparticles as the core, and the nanoparticles are encapsulated inside the matrix grains to form an “intracrystalline” structure. In this way, the effect of the main grain boundary can be weakened, transgranular fracture is induced, and transgranular fracture instead of intergranular fracture occurs when the material is fractured, thereby improving the strength and toughness of the nano-zirconia ceramic composite material.
  • The “pinning” theory believes that the nanoparticles existing in the grain boundaries of the matrix produce a “pinning” effect, which limits the occurrence of grain boundary slippage, pores, and creep. The enhancement of grain boundaries leads to the improvement of the toughness of nano-zirconia multiphase ceramic.

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

What Are the New Sintering Methods of Zirconia Ceramics?

With the continuous development of science, sintering methods of zirconia ceramics are continuously introduced.

Electric field sintering

Electric field sintering refers to the sintering of the ceramic body under the action of a DC electric field. Some high-curie-point ferroelectric ceramics, such as lithium niobate ceramics, apply a DC field to both ends of the green body at their sintering temperature. After cooling to a temperature below the Curie point (Te-1210 ℃) and removing the electric field, you can obtain Piezoelectric ceramic samples.

sintering

Ultrahigh pressure sintering

Ultra-high pressure sintering is sintering at a pressure of several hundred thousand atmospheres or more. Its characteristics are that it cannot only make the material reach high density quickly, have fine grains (less than 1um), but also change the crystal structure and even the atomic and electronic states, so that the material cannot be reached under the usual sintering or hot-pressing sintering process Performance, and can synthesize new artificial minerals. This process is relatively complicated, which requires higher mold materials, vacuum sealing technology, and fineness and purity of raw materials.

Activated sintering

The principle of activated sintering is to use some physical or chemical methods to make the atoms or molecules of the reactants in a high-energy state before or during sintering. With the instability of this high-energy state, it is easy to release energy Low energy state. The physical methods used in activated sintering include electric field sintering, magnetic field sintering, sintering under the action of ultrasound or radiation, and so on; the chemical methods used are: chemical reactions based on redox reactions, dissociation of oxides, halides, and hydroxides, and atmospheric sintering. Activated sintering has the advantages of reducing the sintering temperature, shortening the sintering time, and improving the sintering effect.

activated-sintering

For some ceramic materials, activated sintering is another effective texturing technique. There is also the use of substances in the phase change, dehydration and other decomposition processes, the atom or ion bond is destroyed, making it in an unstable active state. For example, increase the specific surface area; add substances that can generate new erbium molecules during the sintering process; add substances that can promote the sintering material to form a solid solution; increase the lattice defect substances, all of which are activated sintering. In addition, activated sintering also includes adding a small number of substances that can form an active liquid phase, promote the vitrification of materials, appropriately reduce the viscosity of the liquid phase, wet the solid phase, and promote solid-phase dissolution and recrystallization.

Activated hot sintering

Activated hot-pressing sintering is a new process developed on the basis of activated sintering. It utilizes an activated state with higher energy during the decomposition reaction or phase change of the reactants to perform hot-pressing treatment, which can be performed at lower temperature and lower pressure. It is a high-efficiency hot pressing technology to obtain high-density ceramic materials in a short time. For example, barium titanate, lead zirconium titanate, ferrite, and other electronic ceramics are made by hot pressing by the decomposition reaction of hydroxide and oxide; high-density beryllium oxide, thorium oxide and uranium oxide ceramics were prepared by hot pressing of carbonate decomposition reaction; high-density alumina ceramics are made by hot pressing during phase transition of some materials.

Stanford Advanced Materials (SAM) is a global supplier of pure metals, alloys, ceramics, minerals, and rare earth materials since 1994. Headquartered in Lake Forest, California, SAM specializes in providing high-purity chemicals (up to 99.99999%) for research institutes and technical grade materials for advanced industries, such as pharmaceutical, capacitor, metallurgy, semiconductor, and aviation. Please visit https://www.samaterials.com/ for more information.

Advantages of Zirconia Ceramic Rods

Zirconium oxide ceramic rods have the common advantages of both metal and polymer materials, and they play a very important role because of their numerous advantages and applications. The production process of ceramic rods is cumbersome and requires production processes such as cutting, grinding, grinding and polishing. Despite this, ceramic rods are in high demand compared to other materials of the same type, which has a tendency to go higher because of its advantages.

zirconia-ceramic-rods

Excellent Weatherability

Ceramic rods using zirconia or alumina as production materials have obvious advantages over products of the same category. They are highly weather-resistant and have no effect on the surface and substrate of the ceramic rod, whether it is sunlight, rain or moisture. Corrosion-resistant ceramic rods are also very stable in color under ultraviolet light and are in good compliance with international standards in terms of impact resistance, strength, and elasticity.

Strong Stability

Ceramic rods are generally made of zirconia, which is currently a leading technology in the industry. First of all, a zirconia ceramic rod is simpler to clean, with good fire resistance, neither melting nor falling or exploding, and it can remain stable for a long time. Secondly, the ceramic rod is easy to maintain, no need to add any anti-corrosion paint or protective layer on the surface, it is easy to use and has a long service life.

High Abradability

The ceramic rods are made of high-precision materials, which enhance the mechanical strength and hardness of the ceramics during high-temperature firing. Therefore, the ceramic rod has a good performance in terms of impact resistance. After a long period of proof and a number of tests, the wear resistance is also strong, and the shape is not damaged in the long-term use. In a variety of harsh working environments, the advantages of ceramic rods are even more pronounced, making acid-resistant ceramic rods the best choice for harsh conditions.

kitchen-knives

Ceramic rods are widely used in various fields due to their weather resistance, stability, and high wear resistance. In addition to being able to be used in normal environments, the use of ceramic rods not only ensures the normal operation of the instrument, but also does not cause breakage, wear, corrosion, etc., nor damage to the instrument.

Stanford Advanced Materials (SAM) is a global supplier of pure metals, alloys, ceramics, minerals, and rare earth materials since 1994. We supply high-quality zirconia ceramic materials used in aerospace components, medical devices, surgical and dental implants, etc. Please visit http://www.samaterials.com for more information.

How is the Zirconia Industry Laid Out?

Globally, zirconia producers are mainly concentrated in a few countries, mainly including China, Japan, France, the United Kingdom, the United States, and Australia. Companies with comprehensive zirconia industrial layout include Saint-Gobain, Japan’s Tosoh, Japan’s First Element, Showa Denko, France’s Suvi, and Japan’s Sumitomo Osaka Cement. Among them, the main business of First Element is zirconium-based, and most of the other companies are large-scale integrated enterprises.

With zirconia as the main component, after adding rare earth elements (mainly cerium oxide) and other oxides, composite zirconia powders with different performance characteristics can be formed. The nature of the composite zirconia depends on the type of material or crystal structure to which it is combined. Depending on the specific needs of the application, different formulations of composite zirconia materials with different properties can be prepared using different formulations.

zirconia

In general, zirconia ceramics are divided into three categories: PSZ partially stabilized zirconia, also known as ceramic steel (with superior impact resistance); TZP tetragonal polycrystalline zirconia (better mechanical strength and fracture toughness); FSZ fully stabilized zirconia, crystalline phase cubic phase, with high temperature conductivity, but high thermal expansion coefficient and poor thermal shock resistance.

Catalyst

Since zirconia is the only metal oxide that has both acidic and basic and oxidizing and reducing properties and is also a p-type semiconductor, it is easy to generate oxygen vacancies. As a catalyst carrier, it can interact with the active component, so its supported catalyst has more excellent properties than other materials supported catalysts.

Precise ceramic parts

Zirconia ceramics can have excellent mechanical properties and fracture toughness, chemical resistance, and biocompatibility, so you can see the back of zirconia ceramic materials in industry and life.

Typical applications for zirconia ceramics: tools, dentures, bearings, etc.
Typical applications

Battery material

Solid oxide fuel cells (SOFC) are a new type of green energy that developed rapidly in the 1980s. Due to its high energy conversion efficiency (up to 65%) and the use of various fuels such as hydrogen, carbon monoxide, methane, etc., the system design is simple, and the pollution-free emission is low, which will be applied to the power generation system. The solid electrolyte is the core component of SOFC.

Schematic diagram of a solid fuel cell
Schematic diagram of a solid fuel cell

Zirconium oxide ceramics have become the most researched and widely used solid electrolyte materials because of their high ionic conductivity, good chemical stability, and structural stability.

Refractory

Zirconium oxide is an excellent special oxide refractory material and used at a high temperature (2300 ℃ – 2400 ℃). It has good chemical stability and is not easy to decompose, and is highly corrosive and resistant to acid and alkali slag. The industry uses zirconia-based refractories to produce refractory materials with excellent thermal shock resistance, corrosion resistance and wears resistance, which can make refractories have better performance and longer service life. It has been applied to the manufacturing process of industrial continuous casting steel and alloy materials and has important significance for improving the quality and cost of metal materials such as steel.

Zirconia foam ceramics for steel water filtration
Zirconia foam ceramics for steel water filtration

Optical material

Zirconium dioxide ZrO2 is a high refractive index, low absorptive material that can be used in coatings in the near-ultraviolet (<300 nm) to infrared (~8 μm) spectral regions. Nano-zirconia is added to the special coating material to increase the refractive index of the coating without changing the light transmittance. In the field of optical materials, in addition to being used as a coating, nano zirconia can also be used as a polishing material for optical lenses.

Electronic materials

For engines that use three-way catalytic converters to reduce pollution emissions, oxygen sensors are essential in the automotive industry. It uses the ceramic sensitive component to measure the oxygen potential in the exhaust pipe of the automobile, and calculates the corresponding oxygen concentration by the principle of chemical balance, and achieves the measuring component that monitors and controls the combustion air-fuel ratio to ensure the product quality and the exhaust gas emission standard. There are two types of oxygen sensors currently in use: titanium oxide and zirconium oxide. The core component is a porous zirconia ceramic tube, which is a solid electrolyte with sintered porous platinum (Pt) electrodes on both sides.

Plumbum zirconate titanate (PbZrxTi1-xO3, PZT) ceramics are a commercially important class of piezoelectric materials. Compared with other piezoelectric ceramics, PZT ceramics not only have high Curie temperature and piezoelectric coefficient, but also are easy to be doped and modified, and have good stability, so they have an important position in the electronic machinery manufacturing industry. They are the basic material for the preparation of most electromechanical devices such as sonar, hydrophone, ultrasonic generator, volt generator, and position trimmer.

Brake material

Ceramic materials have high heat resistance, thermal stability, and hardness. As an important member of advanced ceramics, zirconia ceramics certainly have similar characteristics. In view of the excellent quality of advanced ceramics, researchers have introduced it into friction materials to obtain longer-lasting and more durable friction materials under the most extreme working conditions. Today, more and more composite formulations for brake pads and clutch linings contain ceramic materials.

Many ceramic materials can be added to the brake material, including the zirconia ceramics we introduce today, in addition to silicon carbide, alumina, silica, and magnesia

Example of the microstructure of the brake pad material
Example of the microstructure of the brake pad material

Thermal spray material

Using thermal spraying technology, the ceramic coating is deposited on the metal collective, and the characteristics of high-temperature resistance, heat insulation, wear resistance, corrosion resistance and insulation of the ceramic are combined with the toughness, workability, the electrical and thermal conductivity of the metal material. The ideal composite coating product has become an important development direction in the field of composite materials and product development.

Aviation surface protection technology is a hotspot of thermal spraying for many years. The key components of aero-engines are high-temperature alloy turbine blades and turbine disks. The current engine turbine inlet temperature is close to or exceeds the melting point of the alloy, and such high temperatures will affect the function of the engine and dye. Therefore, an important development trend of superalloys is to coat the surface of the alloy with a high-melting ceramic coating (Thermal Barrier Coatings – TBCS) with good thermal insulation properties. At present, the most widely used TBCS is yttria-stabilized zirconia materials.

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.

Zirconia Ceramic Phone Backplane Stands Out in 5G Era

By the end of 2018, 154 mobile operators around the world are carrying out 5G technology tests or trials, and the number of countries participating in 5G has been expanded to 66. With the advent of 5G era, the mobile phone industry will usher in a new round of reform, and the mobile phone backboard market is facing a reshuffle.

Zirconia ceramic phone backplane stands out

5G era requires faster signal transmission, 1 to 100 times faster than 4G. 5G communications will use a spectrum of more than 3Ghz, with shorter millimeter-wave wavelengths. Compared with the metal backplane, ceramic backplane has no interference to signal and has incomparable superior performance of other materials, which is favored by mobile phone manufacturers.

MIUI Backplane
MIUI Backplane

The contrast of the backplane of several kinds of mobile phones

Among all-ceramic materials, zirconia ceramic has the advantages of high strength, high hardness, acid and alkali resistance, corrosion resistance and high chemical stability, as well as the characteristics of scratch and wear resistance, no signal shielding, excellent heat dissipation performance, and good appearance. Therefore, it becomes a new mobile phone body material after plastic, metal, and glass. The application of zirconia ceramic in the mobile phone is mainly two parts: backplane and fingerprint identification cover.

Preparation and difficulty analysis of zirconia cell phone ceramics

The preparation of zirconia ceramic backplane mainly includes the preparation, molding, sintering, grinding and polishing process of zirconia ceramic powder, in which the preparation of zirconia ceramic powder is the most important and most difficult part of the whole process.

Active Ceramic Membranes
Active Ceramic Membranes

Technological difficulties

The phone backplane powder of zirconia ceramic is nanocomposite zirconia. In the preparation of ceramics, the quality requirements include that the particle size distribution is normal, the particle shape is close to circular, the dispersion is good, and the purity is high. The preparation methods of nano-composite zirconia powders include the hydrothermal method, precipitation method, alcohol-brine hydrolysis method, and low-temperature gas-phase hydrolysis method.

The quality of powder directly affects the intrinsic quality and performance of finished products. High purity, ultra-fine particle size, narrow particle size distribution, and good dispersibility are important bases for evaluating the quality of ceramic powders. The powder agglomeration and surface modification of nano-composite zirconia have become two major problems. With the development of technology, researchers have found corresponding solutions.

Firstly, the agglomeration of zirconia powder is a big problem. Gan Xuexian et al. investigated the final depolymerization effect by designing and using different grinding equipment and process parameters. With d50=1.355μm zirconia powder as the research object, when using vertical ball mill, vertical ball mill and horizontal sand mill as the grinding equipment, serving with φ2mm zirconia ball as the grinding medium, with m medium: m material = 5:1 medium material ratio grinding for 15h, detection zirconia slurry size after grinding, the results show that: the horizontal sanding machine has the best grinding effect, and the d50 of zirconia slurry is 0.303μm. When the horizontal sand mill is adopted as the grinding equipment, the grinding effect is best under the conditions that the ratio of medium material (m medium: m material) is 4:1, the solid content of slurry (w) is 45%, the linear speed is 10m•s-1, and the grinding time is 25h.

Secondly, in terms of surface modification of zirconia powder, Yue Liang et al. drew the following conclusions through experiments: the sintering activity of zirconia powder was significantly improved after horizontal stirring grinding and manual granulation, and the sintering density was close to 99.5% at 1400℃; after grinding zirconia powder, the bending strength of sintered samples was lower than that of the original powder mainly because of the large size defect. Therefore, it is necessary to have appropriate granulation technology to improve the powder forming performance; it is suggested that improving the stability of phase transition is beneficial to obtain high-performance zirconia powders.

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.

Application of Zirconia Electrolyte in Oxygen Sensor

With the gradual improvement of people’s awareness of environmental protection and energy conservation, many large and medium-sized enterprises, such as iron and steel metallurgy, petrochemical industry, thermal power plants, etc., have taken improving combustion efficiency, reducing energy consumption, reducing pollutant emissions, protecting the environment as an important way to improve product quality and enhance enterprise competitiveness.

oxygen-sensor

Generally speaking, the direct way to improve the combustion efficiency is to continuously monitor the composition of flue gas in the flue gas analysis instrument (such as flue gas analyzer, combustion efficiency tester, zirconia oxygen content detector), then analyze O2 content and CO content in flue gas, adjust the flow rate of combustion air and fuel, and determine better air consumption coefficient. Therefore, as an industrial tool to improve combustion efficiency, oxygen sensor’s response time and measurement accuracy become key performance indicators. Due to its simple structure, short response time, wide measurement range (from PPM to percentage), high operating temperature (600℃-1200℃) and small maintenance, zirconia oxygen sensor has been widely used in metallurgy, chemical industry, electric power, automobile, and other fields.

Principle of zirconia sensor

The figure below is the schematic diagram of oxygen measurement with an oxygen probe. Porous platinum (Pt) electrodes were sintered on the two sides of the zirconia electrolyte (usually a zirconia tube). At a certain temperature, when the oxygen concentration on both sides of the electrolyte is different, the oxygen molecules on the high concentration side (air) are adsorbed on the platinum electrode and combine with electrons to form oxygen ions, making the electrode positively charged. The oxygen ions then migrate through the oxygen ion vacancy in the electrolyte to the Pt electrode on the low oxygen concentration side, releasing electrons and transforming them into oxygen molecules, making the electrode negatively charged.

 

zirconia-sensor

This creates a certain electromotive force between the two electrodes. The zirconia electrolyte, the platinum electrode, and the gas with different oxygen concentrations on both sides constitute the oxygen probe, which is called the zirconia concentration difference cell. Then, by measuring the gas temperature and the output electromotive force, the oxygen partial pressure (concentration) can be calculated by the nengst equation, which is the basic detection principle of the zirconia oxygen sensor.

Common types of zirconia oxygen sensors

At present, the commonly used zirconia oxygen sensor includes a detection probe and direct insertion oxygen probe.

Detector probe

The sampling method is to introduce the measured gas into zirconia through a guide tube and then heat the zirconia to the working temperature (above 750℃) through a heating element. Zirconia is typically tubular and the electrode is porous platinum. Its advantage is that it is not affected by the temperature of the gas detected, and the oxygen content of the gas can be detected by using different flow guides at different temperatures.

This flexibility is used in much industrial on-line detection. Its disadvantages are slow response; the structure is complex and easy to affect the detection accuracy; when there are many impurities in the measured gas, the sampling tube is easy to be blocked; the porous platinum electrode is easy to be corroded by sulfur and arsenic or blocked by fine dust, etc. When the temperature of the detected gas is low (0-650℃), or when the measured gas is clean, it is suitable to use this detection method, such as oxygen measurement by nitrogen production machine and laboratory.

oxygen-sensors

Direct probe

Direct insertion method is to directly insert zirconia into the gas measured at high temperature and directly detect the oxygen content in the gas. It uses the high temperature of the measured gas to bring zirconia to its operating temperature without the need for additional heaters.

The key technology of direct insertion oxygen probe is the high-temperature sealing of ceramic material and the electrode. Due to the need to insert zirconia directly into the detection gas, the length of the oxygen probe is required to be relatively high. The effective length is about 500mm ~ 1000mm, and the special environment length is up to 1500mm, as well as high requirements for detection accuracy, working stability and service life. Therefore, it is difficult to adopt the whole zirconia tubular structure of the traditional zirconia oxygen probe with direct insert oxygen probe, and the zirconia and alumina tube connection structure with high technical requirements are mostly adopted. The sealing performance is one of the most important technologies for the zirconia oxygen probe. Currently, the most advanced connection mode in the world is the permanent welding of zirconia and alumina tubes together.

Compared with the method of sampling pattern detection, the direct insertion method has obvious advantages: zirconia directly contacts with gas; high detection accuracy; fast reaction speed and small maintenance.

Brief summary

The regulation of oxygen content is a powerful means to monitor combustion conditions and improve combustion efficiency, and the accuracy and time of the measurement of the sensor have put forward certain requirements. Zirconia, as a solid electrolyte, is used to transport conductive ions in oxygen sensors. At present, there are two kinds of zirconia oxygen sensors: detection type and direct insertion type. The direct insertion type probes are widely used because of their direct contact with the measured gas, high measurement accuracy and fast reaction time.

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.

Why Does Zirconium Explode? How to Solve It?

Zirconium (Zr) is estimated to make up about 0.017% of the lithosphere. Because zirconium is chemically active at temperatures only slightly above normal atmospheric temperatures, it exists only in a bound state. The most common ores are zircon (ZrO2) and barium lead (ZrSiO4).

The hafnium (Hf) coexists with zirconium in all its terrestrial ores. The content of hafnium fluctuates greatly, accounting for 2% (the total amount of hafnium and zirconium). The two elements are chemically closer than any other in the periodic table, and the similarities are so great that no difference in mass has been found to separate them.

Hafnium
Hafnium

Zircon

Zircon has been considered a gem since ancient times because it is usually found in large single crystals. However, most commercial deposits of zirconium ore are in beach sand, where the relatively heavy and chemically inert zirconium minerals are retained, while the lighter parts are broken down and washed away by water. India, Malaya, Australia and the United States are known to have large deposits of this sand. Harmful substances have been found in commercially useful deposits, first in Brazil and later in other places, including Sweden, India, and Italy, while some zirconium ores are also commercially mined in Madagascar, Nigeria, Senegal, and South Africa.

Zircon is used as a component of foundry sand, abrasive, and laboratory crucible zircon and zirconia refractories. It is found in ceramic compositions and acts as an emulsifier in glazes and enamels. Zirconium and zirconia bricks are used as glass linings, zirconia templates are also used for extrusion iron and non-ferrous metal molds and injection metal nozzle linings, especially for continuous casting.

zircon-crystals
Zircon-crystals

Zirconium metal

More than 90% of zirconium is now used in nuclear power generation because zirconium has a low neutron absorption cross-section and is highly resistant to corrosion in atomic reactors, provided it contains no hafnium. In addition, zirconium is used in the manufacture of cast iron, steel, and surgical instruments, as well as in arc lamps, fireworks, special solder, plastic pigments, etc.

The powdered zirconium metal is used as a “getter” in thermionic tubes that absorb traces of residual gas after it has been drained and expelled. The metal, in the form of filaments or wool, is also used as a filter for camera flashes. Block metals can be used in the lining of reaction vessels, either pure or alloyed. It is also used as lining for pumps and piping systems in chemical processes. Excellent zirconium and niobium superconducting alloys are used in the magnetic field of 6.7T.

Zirconium-metal-strip
Zirconium-metal-strip

Zirconium compounds

Zirconium carbide and zirconium diboride are hard, refractory, metallic compounds that have been used in metal cutting tools. Diboride is also used as the shell of open-hearth thermocouple with long life. Zirconium tetrachloride is used in organic synthesis and water repellent in textiles, and it is also useful as a tanning agent.

The metal hafnium has been used as a coating for the tantalum components of rocket engines, which must work at very high temperatures and under corrosive conditions. Because of its high thermal cross-section, it is also used as control rod material in nuclear reactors. In addition, hafnium is used in the manufacture of electrodes and filament bulbs.

The harm of zirconium

It is not accurate to say that zirconium compounds are physiologically inert, but most organisms seem to tolerate zirconium quite well compared to most heavy metals. Zirconium salts have been used to treat plutonium poisoning to replace the deposition of plutonium (and yttrium) in the skeleton and to prevent precipitation when early processing begins.

Zirconium-salts
Zirconium-salts

Some studies have shown that more than 20% of zirconia can be absorbed in rats for a long time without harmful effects. LD50 of rats injected with sodium zirconium citrate is about 171mg/kg. Other investigators found an intraperitoneal injection of LD50 rats with zirconium lactate 670mg/kg, barium zirconium 420mg/kg, and mice with sodium zirconium lactate 51mg/kg.

Zirconium compounds have been recommended for topical treatment of suede dermatitis and body deodorants, among which are zirconia carbide hydrate, zirconia hydrate, and sodium zirconium lactate. There have been some reports of persistent granulomas on the skin as a result of these applications.

More immediate interest in occupational exposure is the effect of inhaled zirconium compounds, which has not been studied as extensively as other approaches to drug administration. However, there are several experiments and at least one report on human exposure. In this case, a chemical engineer who had been at a zirconium and hafnium processing plant for seven years was found to have granulomatous lung disease. As no similar damage was found on all other employees, it was concluded that the situation was most likely due to relatively high levels of beryllium prior to zirconium contact.

Animal exposure to zirconium compounds has shown that severe persistent chronic interstitial pneumonia occurs in both zirconium lactate and barium zirconium at atmospheric concentrations of about 5mg/m3. Short exposure to sodium zirconium lactate at a higher air concentration of 4900mg/m3 resulted in peribronchoabscess, peribronchogranuloma, and lobular pneumonia. Despite the lack of literature on human zirconia pneumoconiosis, the authors of one study suggest that zirconium should be considered as a possible cause of pneumoconiosis and recommend appropriate precautions in the workplace.

A small number of studies on the toxicity of hafnium compounds indicate that their acute toxicity is slightly higher than that of zirconium salts. Like soluble zirconium salts, hafnium chloride-induced cardiovascular failure and respiratory arrest in cats at 10mg/kg.

Safety and health measures

  • Zirconium is burned as a fine powder in air, nitrogen or carbon dioxide. The spontaneous air explosion of these powders at concentrations of 45,000 to 300,000 mg/m3 may be caused by static electricity generated by the separation of the disturbed particles.
Zirconium-powder-in-flame
Zirconium-powder-in-flame
  • Metal powders should be transported and treated in a wet state; water is usually used for wetting. When the powder is dried before use, the amount used should be as small as possible and should be operated in a separate compartment to prevent the spread of the explosion.
  • All ignition sources including electrostatic charges should be eliminated. All surfaces in the area should be impermeable and seamless so that they can be washed down with water and completely free from dust. Any spilled powder should be washed with water immediately so that it has no chance to dry. Old paper and cloth contaminated with powder should be kept moist in a covered container until they are removed and burned, at least daily.
  • Dry powders should be treated with as little interference as possible, and then only sparkless tools should be used. Rubber or plastic aprons, if worn on overalls, should be treated with antistatic compounds. Work clothes shall be made of non-synthetic fibers unless effectively treated with antistatic materials.
  • All processes using zirconium and hafnium should be designed and ventilated to keep air pollution below exposure limits.

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

What Are the Main Industrial Uses of Zircon?

Zircons are highly resistant to high temperatures and acid corrosion, and its melting can reach 2,750℃. 80% of the world’s zircons are used directly in the foundry, ceramics, glass, and refractories industries, while a small amount is used in ferroalloys, pharmaceuticals, paint, leather, abrasive, chemical, and nuclear industries. The main industrial uses of zircon are as follows.

Zircon sand

Zircon sand containing ZrO2 65~66% is directly used as casting material for the iron metal in foundry due to its melting resistance (melting point above 2500℃). Zircon sand has the lower thermal expansion, higher thermal conductivity, and stronger chemical stability than other common refractory materials, and high-quality zircon and other adhesives have a good bond and used in the foundry industry. Zircon sand is also used as bricks in glass kilns. Zircon sand and powder are mixed with other refractory materials for other purposes.

zircon-sand
Zircon-sand

Zirconium oxide

Zirconium and dolomite react together at high temperatures to produce zirconia or zirconium oxide (ZrO2). Zirconium oxide is also a good melting material, although its crystal shape varies with temperature. Stable zirconium oxide also contains small amounts of oxides of magnesium, calcium, scandium, or yttrium. The stable melting point of zirconium oxide is close to 2700℃, and it is more resistant to thermal shock than zirconium in some metallurgical applications. Stable zirconium oxide has low thermal conductivity, and the use of hafnium dioxide as fusible in industrial zirconium oxide is harmless.

Zirconium metal

Zirconium metal is mainly used in the chemical and nuclear reactor industries, as well as in other industries requiring corrosion resistance, high-temperature resistance, special fusion properties or special neutron absorption. In the United States, about 8% of the total consumption of zirconium metal is used in these industries, while the only meaningful application of the hafnium metal is in the nuclear reactors of warships.

zirconium-metal
Zirconium metal products

Zirconium metal is obtained by multistage extraction. Initially, zircon reacts with coke in an electric furnace to produce zirconium hydrocarbons and then chlorinates to produce zirconium tetrachloride. The magnesium reduction of the zirconium tetrachloride process involves the reduction of tetrachloride by placing magnesium metal in an inert gas to obtain spongy zirconium.

High purity zirconium metal can be refined by iodide thermal dissociation. In this process, metal and iodine vapors react at 200℃ and send volatile iodine to the connector, separating zirconium in the form of volatile iodine from most impurities. At about 1300℃, iodide is separated on a heated filament attached to highly purified zirconium. The released iodine is transferred from the filament, and the product is called a zirconium crystal rod.

Zirconium sponge

More than 90% of zirconium sponge is used as a zirconium-based alloy for structural and cladding materials in nuclear reactors. Zirconium is used in the chemical industry, pesticide industry, printing, and dyeing industry to manufacture corrosion-resistant reaction tower, pump, heat exchanger, valve, stirrer, nozzle, pipe, and container lining. It can also be used as a deoxidizing and denitrifying agent in the process of steelmaking and grain finisher of aluminum alloy. Zirconium wire can be used as grid support, cathode support and grid material, as well as air plasma cutting machine electrode head. Zirconium powder is mainly used as a deflagrant in the arms industry, a degassing agent in electronic devices, and it can also be used to make igniters, fireworks and flash powder.

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