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.

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.

Alumina VS Zirconia

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

Price: alumina VS zirconia

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

Alumina-Oxide-Balls
Alumina-Balls

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

Applications: alumina VS zirconia

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

YSZ-ceramic-cylinders
YSZ-ceramic-cylinders

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

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

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

10 Applications of Zirconium You Should Know

Zirconium, chemical symbol Zr, atomic number 40, melting point 1852°C, is one of the high melting point metals. Zirconium with special excellent properties, such as the resistance from high temperature, oxidation, corrosion, and abrasion, all of which made it a wide range of application as the structured and functional ceramic material in many industrial sectors, especially in the high-tech industry.

Zirconium products and their applications

  1. Zirconium silicate

Zirconium silicate is an important kind of traditional zirconium products. Products can be prepared with zircon sand as raw material, after grinding, calcination, powder, is a kind of high quality and inexpensive ceramic glaze opacifying agent, mainly used in ceramics and porcelain, building ceramics color glaze production, has been widely used in high-grade refractory materials, precision casting, emulsified glass and other industries.

zirconium-silicate-powder

  1. Zirconium carbonate

Zirconium carbonate mainly used as cosmetic additives and waterproof agent, flame retardant, sunscreen, fiber and paper surface additives, and can be used for preparing zirconium cerium catalytic composite material, is an important raw material for textile, papermaking, paint, cosmetics industry, the amount of growth in recent years.

  1. Zirconium oxychloride

It can be used other zirconium products such as two – zirconium oxide, zirconium carbonate, zirconium sulfate, zirconium and hafnium compound preparation and separation of zirconium and hafnium metal material, can also be used for textile, leather, rubber additives, metal surface treatment agent, coating driers, refractories, ceramics, catalyst, fire retardant, and other products.

  1. Fused zirconia

Fused zirconia, mainly used in the production of glazes and refractories. Due to the high content of impurities in the fused zirconia, the use is limited.

  1. Zirconium sulfate

It is the important raw material in the production of leather tanning agent, wool processing agent and paint surface oxidation agent, can be used as a catalyst carrier, amino acid, and protein, precipitant, and deodorant, intermediate raw materials are for zirconium chemicals and metal zirconium and hafnium.

  1. Zirconium oxide

The white solid, non-toxic, tasteless, has enough stability of alkali solution and many acidic solutions, suitable for precision ceramics, electronic ceramics, optical lenses, glass additives, dissolving zirconia brick, ceramic pigment, glaze, artificial stone, refractory materials, grinding and polishing industry and products.

It is also known as semi-stable, stable zirconia is white powder non-toxic, tasteless, stable chemical properties, the specific surface area is controllable, manufacturing all kinds of special ceramics, advanced refractories, new energy materials, optical communication devices, based on raw materials.

  1. Zirconia structural ceramics

Using the composite zirconium oxide as the raw material, including two kinds of products such as zirconia grinding and zirconia structure, the structure of zirconia mainly includes the zirconia special ceramic valves, fiber optic connectors, ceramic knives, watches accessories, ceramic scissors, textile porcelain, etc.

Since Zirconium has very good chemical corrosion resistance, zirconium shapes, such as zirconium tubes and zirconium rods are used to make equipment for the chemical industry.

zirconium-tube

  1. Nuclear grade zirconium

It is an important strategic metal used primarily for nuclear-powered aircraft carriers, nuclear submarines, and civilian power reactors, as well as the cladding of uranium fuel elements.

  1. Industrial grade zirconium

It is mainly used for the production of industrial grade zirconium – chemical corrosion resistance equipment, military industry, electronic industry, pipeline valve materials, special high strength and high-temperature alloy materials, electric vacuum and lighting industry getter.

  1. Firearm zirconium

It is also used in the combustion of the flame zirconium sponge, and also can be used in alloy additives and metallurgical deoxidizer, chemical industry, civil flash fireworks and so on.

Please visit http://www.samaterials.com for more information.

What Are the Uses of Advanced Composite Ceramic Substrates in Missiles?

In the mid-1980s, the United States developed an aerospace aircraft program that required both high-temperature tolerance and light mass. For this purpose, a variety of new high-temperature materials were developed, including advanced resin matrix composites, metal matrix composites, ceramic matrix composites, and carbon/carbon composites. Ceramic material is the preferred material for missile radome because of its excellent mechanical, thermal and electrical properties. The radome is the most widely used ceramic matrix composite material in missile structure.

Missile radome

The missile radome is located at the front end of the missile. Its function is to protect the navigation antenna from damage so that the missile can effectively hit the target. It is not only an important part of the aerodynamic shape of the missile but also the protection device of the antenna. During the flight of the missile, the radome should not only withstand aerodynamic heating and mechanical overload, resist the erosion of rain, sand, and other adverse working conditions, but also meet the stringent requirements of electrical performance proposed by the missile control loop. Therefore, the missile radome material should have the following properties:

Missile-radome

  • Excellent dielectric properties

In the guidance system, the transmission efficiency and aiming error of the radome are very sensitive to the dielectric properties of the material and its relationship with temperature and frequency. It is required that the material has low dielectric constant (10) and dielectric loss, and the dielectric properties do not change obviously with temperature and frequency.

  • Good heat resistance and thermal shock resistance

The high Mach number of missile can make the radome of instantaneous heating rate is as high as above 120 ℃ / s, so the material is required to have good thermal shock resistance, and the molecular structure of the material is required to be stable when the temperature is raised, and the material properties (such as dielectric properties and mechanical properties) change little to ensure that the radome can work normally when the temperature is raised.

  • High strength structural properties

The strength of the radome material should be high and rigid enough to satisfy the mechanical stress and bending moment caused by the longitudinal or transverse acceleration of the aerodynamic forces in the spacetime of the missile flying at high speed.

  • Resistance to rain erosion

It plays a decisive role in the design allowable range of impact Angle and the sensitivity of aircraft in rain erosion.

  • Low-temperature sensitivity

The dielectric properties and strength properties of general materials change obviously when they work at high temperature. Therefore, the properties of the radome material, especially the dielectric properties and strength, are affected by the temperature change as little as possible.

Ceramic-based missile radome

Ceramic-based missile radome materials mainly include silicon nitride based, a silicon oxide based and phosphate-based materials. Silicon nitride ceramics have not only excellent mechanical properties and high thermal stability but also low dielectric constant. Its decomposition temperature is 1900 ℃, and its erosion resistance is better than fused silica, and it can withstand 6 ~ 7 Ma rating of flight conditions. Silicon nitride ceramic composite radome is one of the main research targets in various countries, which has been identified as the most promising radome material by the test of the Georgia Institute of Technology. Yttria Stabilized Zirconia (YTZ), also known as yttria-zirconia, is the strongest ceramic material. This material offers the highest flexural strength of all zirconia-based materials, and the research on zirconia-based materials as missile radome is in progress.

Ceramic-based-missile-radome

  • Silica-based material

Because of the high flying Mach number of the missile and the relatively long heating time, if the radome of the medium-range missile is made of a single quartz ceramic material, it cannot meet the bearing requirement of thermal stress. In order to meet the requirements of medium and long-range ground-to-ground tactical and strategic missile radome, quartz glass, high-silica puncture fabric and orthogonal tri-directional quartz fabric reinforced silica matrix composites have been developed and successfully applied.

  • Phosphate-based materials

Phosphate matrix composite material is a kind of Russian characteristic permeable material, which is made by impregnating cloth or fabric with a phosphate solution and then curing under pressure. Aluminum phosphate has stable performance in 1500 ~ 1800 ℃. At present, such materials have been used in cruise missiles, anti-missile missiles, tactical missiles and space shuttles. The most obvious disadvantage of phosphate is that it is highly hygroscopic, so the surface of the composite material needs to be coated with an organic coating for moisture-proof treatment.

  • Silicon carbide ceramic matrix composites

Silicon carbide ceramic matrix composites have a series of excellent properties, such as low density, high-temperature resistance, ablation resistance, erosion resistance, and oxidation resistance, and it has a wide application prospect in the field of aerospace. Since the late 1980s, the United States has successfully developed a series of C/SiC, SiC/SiC ceramic matrix composites, which can be applied to the re-entry nose cone of missiles, the front end of wings and other heat-resistant structures.

Please visit http://www.samaterials.com for more information.

Zirconium-containing Materials Used in the Refractories

As a new material, zirconium-containing material has been developed rapidly in the recent ten years. In the field of refractories, natural zirconium containing mineral raw materials and artificial extraction or synthesis of zirconium oxide and composite oxide raw materials have also been widely used to produce a variety of excellent zirconium containing refractories.

There are about 50 kinds of zirconium minerals known to us, among which more than 20 are common. Zirconium mineral raw materials for industrial use are mainly zirconium quartz, oblique zircon, hafnium zircon, and anisotropic zircon. With the development of science and technology, zirconium oxides and composite oxides have been extracted or synthesized by various processing methods and applied in various fields.

Zirconium-containing raw materials are widely used in the refractory industry, which is mainly because of their high melting temperature and strong chemical stability. They have good corrosion resistance to metal melt, slag, or glass fluid, as well as good thermal shock resistance, so they can be used as refractories for glass kiln, metallurgical industry refractories, and so on.

Zirconium-based-products
Zirconium-based-products

Zirconium-containing refractories are mainly used in the melting part, superstructure, side wall and fluid hole of glass melting furnace. Refractories made from zirconium materials are widely used in metallurgical industry and can be divided into zirconium quartz products, zirconia products, aluminum zirconia carbon products, zirconium carbon products, calcium zirconate products, zirconium boride products, zirconia modified refractories, etc.

Zirconium quartz products have the characteristics of high-temperature resistance, good resistance to acid slag, small erosion, slight viscosity of slag, small thermal expansion coefficient, good thermal shock stability, etc., which can be better used as the lining of steel drum, but also can be masonry in the direct impact of steel, slag line parts, around the nozzle and other key parts.

The main raw material for the production of zirconium quartz products is zirconium quartz concentrate, and some clay, pyrophyllite, chromium oxide and zirconia can be also added as needed. In general, zirconium particles are small in size and are not suitable for direct brick production, which requires the raw materials of zirconium quartz and part of the combined clay to be mixed, semi-dry pressed and made into the blank. There are a wide variety of zirconia products and many molding methods, such as mud pouring method, hot pressing method, machine pressing method, isostatic pressure method, etc.

Monoclinic-Zirconium-Oxide
Monoclinic-Zirconium-Oxide

Aluminum-zirconium carbonaceous product is developed on the basis of aluminum-carbonaceous product, and it can be used as sliding nozzle brick of ladle (or tundish), long nozzle, plug rod, immersed nozzle and so on. Compared with the corresponding aluminum carbon material, aluminum zirconium carbon products have better oxidation resistance, thermal shock stability, erosion resistance, and higher strength, so the service life is longer. The addition of a certain amount of zirconia in refractory materials such as jade-quality, high-alumina, magnesium-calcium, aluminum-magnesium, magnesium-chromium and magnesium-carbon commonly used in metallurgical industry can improve the chemical stability, thermal shock stability and strength of these materials. In these materials, zirconia is usually introduced in the form of zircon sand and zirconia.

The specific production process is usually the same or slightly changed before modification. Generally speaking, zirconium-containing raw materials have been widely used in the field of refractories due to their excellent properties, and their application scope will be more and more extensive.

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Rare Metals Indispensable to Modern Industries: Zirconium

The 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 carrier, nuclear submarine and civil power reactor, and the hull of 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, nickel zirconium alloy, zirconium tin alloy, and niobium zirconium alloy and so on.

aluminum zirconium alloy

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 a 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.

aluminum zirconium alloy

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.

What are the uses of Zirconium in the Vacuum Industry?

As a rare metal, zirconium is widely used in the fields of aerospace, military industry, nuclear reaction and atomic energy due to its remarkable corrosion resistance, extremely high melting point, ultra-high hardness, and strength.

The surface of zirconium is easy to form a glossy layer of the oxide film, so its appearance is similar to that of steel. Zirconium is resistant to corrosion but dissolves in hydrofluoric acid and aqua regia, and it can react with non-metallic elements and many metallic elements to form the solid solution at high temperature. Zirconium has good plasticity and is easy to be processed into zirconium plate and zirconium wire. Besides that, zirconium can absorb a lot of gases such as oxygen, hydrogen, and nitrogen when heated, and can be used as hydrogen storage material. Zirconium and hafnium are two metals with similar chemical properties, which are symbiotic and contain radioactive materials.

Zirconium Rod

The zirconium can absorb nitrogen violently when the temperature exceeds 900 degrees Celsius. At 200 degrees Celsius, 100 grams of metal zirconium can absorb 817 liters of hydrogen, equivalent to more than 800,000 times the hydrogen absorption capacity of iron. This characteristic of zirconium has been widely used. In the electric vacuum industry, for example, zirconium powder is coated on the surfaces of the anodes and other heated parts of the electric vacuum elements and instruments to absorb the residual gas in the vacuum tube, thus making the vacuum tube and other vacuum instruments, which have better quality and longer service life.

Zirconium can also be used as a “Vitamin” in the metallurgical industry, playing a powerful role in deoxygenation, nitrogen removal, and sulfur removal. For example, if a thousandth of zirconium is added to steel, its hardness and strength will increase dramatically. Zirconium-containing armor steel, stainless steel, and heat-resistant steel are important materials for the manufacture of defense weapons such as armored vehicles, tanks, artillery and bulletproof panels. When zirconium is mixed into copper and drawn into copper wire, its electrical conductivity does not weaken but the melting point is greatly improved, so it is very suitable to be used as a high-voltage wire. Zinc-magnesium alloys containing zirconium, which are light and high temperature resistant, are twice as strong as conventional magnesium alloys and can be used in the manufacture of jet engine components.

Zirconium alloy is a nonferrous alloy which is composed of zirconium as the matrix and other elements are added, and the main alloy elements are tin, niobium, iron and so on. Zirconium alloys have good corrosion resistance, moderate mechanical properties, low atomic thermal neutron absorption cross-section and good compatibility with nuclear fuel in the high-pressure water and steam of 300 ~ 400 ℃, which is mainly used as core structure material of water-cooled nuclear reactor. Besides that, zirconium has excellent corrosion resistance to a variety of acids, bases, and salts, and has a strong affinity with gases such as oxygen and nitrogen, and they are also used in the manufacture of corrosion-resistant and pharmaceutical mechanical components, as well as the non-evapotranspiration disinfectant in the electric vacuum and light bulb industries.

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.