Separation of Zirconium and Hafnium by Solvent Extraction

Solvent extraction of zirconium and hafnium is one of the common methods for separating zirconium and hafnium. Compared with other zirconium and hafnium separation methods (such as pyrolysis separation and solvent extraction separation), this method has the advantages of large production capacity, simple process and easy to achieve continuously.

Principle

The extraction agents used for the separation of zirconium and hafnium mainly include ketone extractants, neutral phosphorus-containing extractants and amine extractants.

A commonly used ketone extractant is methyl isobutyl ketone (MIBK), which can form a neutral extract with hafnium thiocyanate and is preferentially extracted into the organic phase.

Methyl isobutyl ketone 3D ball
Methyl isobutyl ketone 3D ball. Source: Wikipedia

A typical neutral phosphorus-containing extractant is tributyl phosphate (TBP), which is preferentially extracted into the organic phase through the coordination of oxygen atoms in chemical bonds with zirconium metal atoms to form a neutral extract compound Zr(NO3)4•2TBP.

Ball and stick model of Tributyl phosphate
Ball and stick model of Tributyl phosphate. Source: Wikipedia

The commonly used amine extractant is trioctylamine (TOA). Trioctylamine forms an extract with zirconium ions in an acidic medium, and is preferentially extracted into the organic phase.

Process flow

There are three extraction processes: MIBK, TBP, and N235.

MIBK extraction

It uses ZrCI4 as raw material, adds water and NH4CNS ingredients. MIBK preferentially extracts hafnium, leaving a large amount of zirconium in the aqueous phase. This is the earliest extraction process used to separate zirconium and hafnium, and it is adopted by major producers of zirconium and hafnium such as the United States, France, Germany, and Japan.

TBP extraction

There are two aqueous feed systems for this process: nitric acid, and a mixed acid of nitric & hydrochloric acid. The former is to convert the product of zircon decomposed by alkali fusion method into nitric acid aqueous phase feed liquid, and use TBP to preferentially extract zirconium; the latter use Zr-CI4 as raw material, add water, nitric acid and hydrochloric acid as ingredients, and then use TBP to preferentially extract zirconium.

The separation coefficient of zirconium and hafnium in the TBP extraction process is large, and the number of extraction stages is small, and atomic-level zirconium oxide and hafnium oxide can be obtained at the same time. However, the water-phase feed liquid is highly corrosive, and the emulsification problem in the extraction process has not been completely solved, thus affecting its popularization and application.

N235 extraction

First, the zircon is decomposed by alkali fusion method, and the product is washed with water to remove silicon, and then leached with sulfuric acid to obtain a sulfuric acid solution of zirconium, and then the zirconium is preferentially extracted with N235. After washing, atomic-level zirconia containing hafnium <0.01% can be obtained. The hafnium in the raffinate is enriched to 50% to 70%, and then extracted by P204, and the zirconium and hafnium are further separated to obtain atomic energy level hafnium oxide containing more than 96% of hafnium.

This process has low material toxicity, light equipment corrosion, stable operation, and easy disposal of waste, so it is currently recognized as one of the best extraction processes.

Extraction equipment

There are two main types of extraction equipment, one is the extraction tower, and the other is the box-type mixer-settler. The former is used by the MIBK process, and the latter is used by TBP and N235 extraction process. The extraction tower occupies a small area and has a large production capacity. The box-type mixer-clarifier is simple in structure and stable in operation, and is generally made of acid-resistant materials such as plastic or plexiglass.

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3 Methods to Separate Zirconium & Hafnium

The two elements of zirconium and hafnium are symbiotic resources, which means that zirconium generally contains 0.5% to 2% of hafnium. However, the application of zirconium products in various industries requires high purity. For example, zirconium, which is a structural and cladding material for nuclear reactors, must contain less than 0.01% hafnium. In general, the metallurgical process of separating zirconium and hafnium is an important part of the zirconium metallurgical process.

The separation methods of zirconium and hafnium include pyrolysis separation, solvent extraction separation, and ion exchange separation. This article will briefly introduce these three separation methods.

Zirconium and Hafnium Pyrolysis Separation

Pyro separation is a method of separating zirconium and hafnium at high temperature or high pressure by using the difference in vapor pressure of zirconium and hafnium chloride. Zirconium and hafnium pyrolysis can replace the three production stages of extraction, calcination and chlorination in common separation methods. It has the characteristics of a short production process, high efficiency, low reagent cost and light pollution to the environment, and is a promising method for separating zirconium and hafnium.

The pyrolysis method is mainly realized by high-pressure rectification and molten salt rectification. High-pressure rectification is a process of directly separating zirconium and hafnium by using the difference in vapor pressure of Zrcl4 and HfCl4. Molten salt rectification is a process of separating zirconium and hafnium in a rectifying tower by using the difference in saturated vapor pressure of ZrCl4 and HfCl4 in KAlCl4 molten salt.

3 Methods to Separate Zirconium & Hafnium

Zirconium and Hafnium Solvent Extraction

This is a method for the separation of zirconium and hafnium using solvent leather. Compared with other separation methods of zirconium and hafnium, this method has the advantages of large production capacity, simple process, and easy to achieve continuously. It is the most important method for the separation of zirconium and hafnium.

The reagents used in this method mainly include ketone extractant, neutral phosphorus-containing extractant and amine extractant. There are three extraction processes of MIBK, TBP and N235. There are two main types of extraction equipment, one is the extraction tower, and the other is the box-type mixer-settler. The former is used by the MIBK process, and the latter is used by TBP and N235 extraction process. The extraction tower occupies a small area and has a large production capacity. The box-type mixer-clarifier is simple in structure and stable in operation, and is generally made of acid-resistant materials such as plastic or plexiglass.

Further Reading: Separation of Zirconium and Hafnium by Solvent Extraction

Zirconium and Hafnium Ion Exchange Separation

As the name suggests, this is a method for the separation of zirconium and hafnium by ion exchange. The production volume of this method is small. Only the former Soviet Union has used it to further separate zirconium and hafnium from the hafnium-rich material separated by the zirconium-hafnium recrystallization method to obtain hafnium oxide, which is used as the raw material for the production of atomic-level sponge hafnium.

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2 Methods of Refining Zirconium

Zone melting and purification

This method does not use crucibles, so it can largely protect the product from contamination by the crucible.

The process of zirconium zone smelting and purification generally includes three stages: raw material preparation, zone smelting and product quality inspection.

Stage 1 Prepare raw materials

The sponge zirconium or zirconium iodide is made into rods by electron beam melting, extrusion, machining and other steps.

Stage 2 Zone smelting

Fix the zirconium rod vertically in the vacuum chamber, use the high-frequency induction coil (or electron gun) as the heat source to melt one end of the rod into a melting zone, and then slowly move the melting zone from one end to the other.

Zirconium is a high melting point metal with strong chemical activity. The vapor pressure at its melting point of 2125K is low, and zone smelting is easier to carry out at this time.

The main factors affecting this stage are the purity of raw materials, vacuum pressure, zone melting speed and zone melting times.

Schematic-representation-of-the-zone-melting-process-with-single-heater
Schematic representation of the zone melting process with single heater. Curtolo, Danilo & Friedrich, Semiramis & Friedrich, Bernd. (2017). High Purity Germanium, a Review on Principle Theories and Technical Production Methodologies. Journal of Crystallization Process and Technology. 07. 65-84. 10.4236/jcpt.2017.74005.

Stage 3 Inspect Product Quality

The head and tail sections of the zirconium rod obtained in the previous stage were excised for sampling. Its various parameters are measured by mass spectrometry, hardness determination or specific resistance.

E-beam melting and purification

Zirconium has a great affinity for oxygen and nitrogen, and 0.2% nitrogen or oxygen in zirconium becomes brittle, making it difficult to process into materials. In this method, the metal to be purified is bombarded with electrons in a vacuum to melt it. In the purification process, in addition to avoiding the oxidation and nitridation of zirconium, the gas dissolved in the zirconium can also escape, the mixed oxide can be decomposed or evaporated, and metal impurities (such as copper, aluminum, gold, iron, manganese, chromium, etc.). The processing properties, electrical properties, magnetic properties and mechanical properties of the zirconium ingot purified by electron beam smelting are obviously better than the raw zirconium.

Scheme of Electron beam melting and refining (EBMR) process
Scheme of Electron beam melting and refining (EBMR) process. Vutova, Katia & Donchev, Veliko. (2013). Electron Beam Melting and Refining of Metals: Computational Modeling and Optimization. Materials. 6. 4626-4640. 10.3390/ma6104626.

An electron beam melting furnace is composed of an electron gun system, furnace body, vacuum system, raw material adding system, mold mechanical device, operation control system, and high voltage power supply device. The larger the scale is, the lower the product smelting cost is. At present, the smelting process is developing into a semi-continuous or continuous production mode to improve production efficiency and production capacity.

The quality of zirconium ingot purified by electron beam melting depends on the raw material, the melting speed, and the power of the melting furnace.

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3 Types of Zirconium Based Getter Materials

Zirconium-based getter material refers to the alloy with high absorption active gas characteristics formed by adding other elements based on zirconium.

Before sealing in vacuum tubes and devices, the material must be heated and activated under vacuum conditions for fast and effective gettering. The function of activation is to remove the passivation film formed on the surface during the manufacturing and storage process to expose the fresh surface, which is conducive to the overall gettering, so as to achieve the purpose of absorbing a large amount of oxygen, nitrogen, hydrogen, carbon monoxide, carbon dioxide, hydrocarbons, and water vapor.

Zirconium-aluminum alloy, zirconium-graphite, and zirconium-vanadium-iron alloy are widely used zirconium-based getter materials today.

Zirconium-aluminum alloy getter

Zirconium-aluminum alloy getter can be made into ring-shaped material and composite strip-shaped material.

(1) Ring-shaped material. The material has poor gettering performance at room temperature and is usually not used for gettering at room temperature. This material is commonly used in electronic tubes, various vacuum devices, special lamps, inert gas purification, zirconium-aluminum getter pumps, etc.

(2) Composite strip material. The advantage is that the amount of mercury can be accurately controlled, and it does not decompose or generate mercury vapor below 500°C, thereby greatly reducing environmental pollution, preventing workers from mercury poisoning, and improving lamp quality and life. It has been widely used in fluorescent lamps and energy-saving lamps.

ZR1422 Zirconium Aluminum Alloy, ZrAl Alloy
ZR1422 Zirconium Aluminum Alloy, ZrAl Alloy

Zirconium graphite getter

Zirconium graphite getter is often used in high-reliability and long-life vacuum tubes and devices for long-term operation and storage, such as traveling wave tubes, X-ray tubes, trigger tubes, ceramic tubes, and laser tubes.

Zirconium-vanadium-iron alloy getter

Zirconium-vanadium-iron alloy getter is a low-temperature activated getter material composed of zirconium, vanadium, and a small amount of iron. It is divided into two types:

(1) Zirconium vanadium ferroalloy getter material, smelted by 70%zr+24.6%V+5.4%Fe in electric arc furnace or medium frequency induction furnace under vacuum or filled with inert gas, then crushed, pulverized, and then pressed into getter elements.

(2) (Zirconium vanadium ferro)/zirconium getter material. It is made by adding the zirconium vanadium ferroalloy powder prepared in (1), adding zirconium powder in a certain proportion, mixing evenly, and then pressing, high temperature and high vacuum sintering and other processes. into a suction element. Product forms are powder, flakes, rings, and strips.

These two zirconium-vanadium-iron alloy getters are low-temperature activated getters, and the activation process is as follows: the temperature is 400-600°C, the vacuum degree is 10-2-10-4Pa, and the maintenance is 10-30min. The working temperature is from room temperature to 350℃.

Zirconium-vanadium-iron alloy getter is widely used in stainless steel vacuum insulated cups (bottles), solar vacuum water heaters, high-efficiency oil-insulated pipes, and vacuum tube containers that are only allowed to operate at 500°C.

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Zirconium Carbide and Its Composite Functional Materials

Introduction

Zirconium carbide, with the chemical formula ZrC, has a theoretical carbon content of 11.64%. It belongs to the typical NaCl type face-centered cubic structure. The atomic radius ratio of C atoms and Zr atoms is 0.481, which is less than 0.59, forming a simple interstitial phase. The Zr atoms form a compact cubic lattice, and the C atoms are located in the octahedral interstitial positions of the lattice.

The melting point of zirconium carbide is 3540℃, the theoretical density is 6.66g/cm3, and the thermal expansion coefficient is 6.7×10-6℃-1. It is insoluble in hydrochloric acid, but soluble in nitric acid. Zirconium carbide is a key material for the preparation of high-performance cemented carbide, aerospace, atomic energy, textiles, electronics, coatings, hard films and metallurgical automation and other high-tech fields.

ZR1394 Zirconium Carbide (ZrC) Powder

Advantages

Zirconium carbide has the advantages of high surface activity, high temperature resistance, oxidation resistance, high hardness, good thermal conductivity, good toughness, etc., and has the characteristics of efficient absorption of visible light, a reflection of infrared rays, and energy storage. It is an important high-temperature structural material.

Using ultra-high-purity zirconium dioxide and high-purity carbon black as raw materials, and applying core technology and alloying and sintering technology to prepare, can ensure the purity, low oxygen content, and low free carbon of zirconium carbide powder. The prepared ZrC powder has densified grains, stable phase composition, uniform particle size, and stable quality.

Application

1. Zirconium carbide is added to rubber, plastics, polyethylene, acrylonitrile-butadiene-styrene copolymer ABS plastics, transparent plastics, resins, polyurethane materials, and other materials for manufacturing related products. As an additive, zirconium carbide can greatly improve the strength, high-temperature resistance, and drop resistance of plastics and related materials.

2. Adding a certain proportion of zirconium carbide to Zr-Ti alloy, C/C-(Zr-Ti-C-B/SiC) composite material, and Zr-Ti-C-B ceramic material can be made into a ceramic coating resistant to 3000℃ ablation and its composite materials. The composite material made in this way exhibits superior ablation resistance and thermal shock resistance and is a new type of material for key components of hypersonic aircraft, which is now widely used in the military and aerospace fields.

3. Zirconium carbide has the characteristics of heat absorption and heat storage. Therefore, it can be used to manufacture solid propellants in rocket engines, to produce metal zirconium and zirconium tetrachloride, and as abrasive.

4. Zirconium carbide is used for U-shaped ZrC-graphite composite ceramic combined heating element. This heating element has high heating efficiency, good energy saving effect, small occupied volume, low cold end temperature, and stable electrical performance; under vacuum, neutral or reducing atmosphere, it can provide a high-temperature environment above 2000 ℃; it has good It has excellent thermal shock resistance, high thermal efficiency, and fast heating rate, and can be raised from room temperature to 2000 ° C in 120 minutes; it can be used for thermal shock resistance test of ultra-high temperature refractory materials.

5. Zirconium carbide is used for zirconium carbide composite ceramic sensors. This sensor has high mechanical strength, is not easy to deform and volatilize at high temperatures, and has stable electrical performance and long service life; in a vacuum or protective atmosphere, it can more accurately measure ultra-high temperature ambient temperature below 3000 °C; it is the temperature sensing element with the highest temperature measurable in the contact sensor.

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Zirconium – A Vacuum Material

Properties of Zirconium

Zirconium easily absorbs hydrogen, nitrogen, and oxygen; zirconium has a strong affinity for oxygen, and oxygen dissolved in zirconium at 1000°C can significantly increase its volume. The surface of zirconium is easy to form an oxide film with luster, so its appearance is similar to that of steel. Zirconium is resistant to corrosion but is soluble in hydrofluoric acid and aqua regia. At high temperatures, zirconium can react with non-metallic elements and many metal elements to form solid solutions. Zirconium has good plasticity and is easy to be processed into plates, wires, etc. Zirconium can absorb a large amount of oxygen, hydrogen, nitrogen, and other gases when heated, and can be used as a hydrogen storage material. The corrosion resistance of zirconium is better than that of titanium, and it is close to niobium and tantalum. Zirconium and hafnium are two metals with similar chemical properties that are symbiotic together and contain radioactive substances.

Applications of Zirconium

Like lithium and titanium, zirconium can strongly absorb nitrogen, hydrogen, oxygen, and other gases. When the temperature exceeds 900 degrees Celsius, zirconium can absorb nitrogen violently; under the condition of 200 degrees Celsius, 100 grams of metal zirconium can absorb 817 liters of hydrogen, which is equivalent to more than 800,000 times that of iron. This characteristic of zirconium makes it widely used in the electric vacuum industry. People use zirconium powder to coat the surface of the anode and other heated parts of electric vacuum components and instruments to absorb residual gas in vacuum tubes. The high vacuum tubes and other electric vacuum instruments made in this way have high quality and long service life.

high vacuum tubes

Zirconium has a small thermal neutron capture cross-section and has outstanding nuclear properties, so it is an indispensable material for the development of the atomic energy industry and can be used as a reactor core structural material. Zirconium powder is easy to burn in the air and can be used as a detonator and smokeless powder. Zirconium can be used as an additive for deoxidation and desulfurization of high-quality steel and is also a component of armor steel, cannon steel, stainless steel, and heat-resistant steel.

Zirconium can also be used as a “vitamin” in the metallurgical industry to exert its powerful deoxidation, nitrogen removal, and sulfur removal effects. Adding 1/1000 zirconium to steel will increase the hardness and strength amazingly; zirconium-containing armored steel, stainless steel, and heat-resistant steel are important materials for the manufacture of defense weapons such as armored vehicles, tanks, cannons, and bulletproof panels. When zirconium is mixed into copper and drawn into copper wire, the conductivity is not weakened, while the melting point is greatly improved, which is very suitable for high-voltage wires. Zirconium-containing zinc-magnesium alloy is light and resistant to high temperatures, and its strength is twice that of ordinary magnesium alloys. It can be used in the manufacture of jet engine components.

Zirconium powder is characterized by a low ignition point and fast burning speed and can be used as a primer for detonating detonators, which can explode even underwater. Zirconium powder plus oxidant is like adding fuel to the fire, it burns with strong light and dazzling, and it is a good material for making tracer and flare.

Zirconium alloys and their applications

Zirconium alloy is a non-ferrous alloy composed of zirconium as the matrix and other elements are added. The main alloying elements are tin, niobium, iron, and so on. Zirconium alloy has good corrosion resistance, moderate mechanical properties, low atomic thermal neutron absorption cross-section in high temperature and high-pressure water and steam at 300-400 °C, and has good compatibility with nuclear fuel. In addition, zirconium alloy has excellent corrosion resistance to various acids, alkalis, and salts, and has a strong affinity with oxygen, nitrogen, and other gases, so it is also used in the manufacture of corrosion-resistant parts and pharmaceutical machinery parts. For example, it is widely used as a non-evaporable getter in the electric vacuum and light bulb industries.

zirconium alloy

There are two types of zirconium alloys produced on an industrial scale: the zirconium-tin series and the zirconium-niobium series. The former alloy grades are Zr-2 and Zr-4, and the typical representative of the latter is Zr-2.5Nb. In zirconium-tin alloys, the alloying elements tin, iron, chromium, and nickel can improve the strength, corrosion resistance, and thermal conductivity of the corrosion-resistant film, and reduce the sensitivity of the surface state to corrosion. Usually, Zr-2 alloys are used in boiling water reactors, and Zr-4 alloys are used in pressurized water reactors. In zirconium-niobium-based alloys, the corrosion resistance of the alloy is the best when the addition amount of niobium reaches the solid solution limit of the crystal structure of zirconium at the service temperature. Zirconium alloy has isomorphous transformation, the crystal structure is body-centered cubic at high temperature, and hexagonal close-packed at low temperature. Zirconium alloy has good plasticity and can be made into pipes, plates, bars and wires by plastic processing; its weldability is also good and can be used for welding.

Other Zirconium Compounds

Zirconium dioxide and zircon are the most valuable compounds in refractory materials. Zirconium dioxide is the main material of new ceramics and cannot be used as a heating material that resists high-temperature oxidation. Zirconium dioxide can be used as an additive for acid-resistant enamel and glass, which can significantly improve the elasticity, chemical stability, and heat resistance of glass. Zircon has a strong light reflection performance and good thermal stability and can be used as sunscreen in ceramics and glass. Zirconium can absorb a large amount of oxygen, hydrogen, ammonia, and other gases when heated, and is an ideal getter. For example, zirconium powder is used as a degassing agent in electronic tubes, and zirconium wire and zirconium sheets are used as grid supports and anode supports.

Powdered iron mixed with zirconium nitrate can be used as glitter powder. Zirconium metal is used almost exclusively as the cladding for uranium fuel elements in nuclear reactors. It is also used to make photographic flashes, as well as corrosion-resistant containers and pipes, especially hydrochloric and sulfuric acids. Zirconium chemicals can be used as crosslinking agents for polymers.

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Applications of Zirconium Silicate Grinding Media

Zirconium Silicate is a high-quality and inexpensive opacifier with a high refractive index of 1.93-2.01 and chemical stability. It is widely used in the production of various ceramics. Besides, Zirconium Silicate has a high melting point, so it is also widely used in refractory materials, zirconium ramming materials for glass furnaces, casting materials, and spray coatings.

The zirconium silicate media ball is one of its kind, offering users the highest quality and superior grinding levels with improved abrasion resistance, better cost-effectiveness and lower overall contamination rates. Zirconium silicate beads are formulated in strict quality-controlled laboratory containers, in which they undergo specialized instillation techniques, followed by high-temperature sintering and final surface treatment. Compared to other alternative grinding media options such as glass beads or alumina, this ultra-hard media is an ideal solution for grinding special and complex products.

Zirconium Silicate Grinding Media
Zirconium Silicate Grinding Media

The basic characteristics of a good quality zirconium silicate grinding media are that they are high in density, shiny and smooth in appearance, and consist of a uniform solid spherical shape which in turn assures better efficiencies, decreased media wear, and a much longer life span respectively. Additional specialized techniques such as solidifying the media from surface to center result in further strengthening of the molecular structure of ZrSi beads. Zirconium silicate media balls exist in varying sizes and diameters in accordance with each buyer’s prerequisites.

ZrSi04 applications and uses are tremendous and widespread from everyday products such as paints and inks to ceramics, pharmaceuticals, and even in controlled quantities within edible food materials. Zirconium Silicate grinding media plays an integral role as an emulsion agent in order to achieve a ceramic glaze in refractory’s and on cutlery etc. Also being chemically inert and nonreactive allows ZiSi04 media to be used for grinding plastic on a mass level and at economical costs. Moreover, zirconium casting refractories of all kinds utilize this media for operational purposes within glass melting furnaces, cement production and heat/fire resistant porcelain among many others. On a generalized level, Zirconium Silicate grinding media performs numerous operations including mold cleaning of stainless steel, plastic as well as nonferrous materials, mechanical polishing, buffing and eventual after-cleaning processing.

On an overall rating scale, the benefits of this industrial product being extremely dense and strong results in creating an ideal surface roughness and metallic depth with a much lower breakage or contamination rate comparatively. These attributes in turn render Zirconium Silicate milling balls suitable for application on all types of materials and within both wet and dry environments easily.

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Two Surface Treatment Technologies for Zirconium Materials

The surface of the zirconium rod and zirconium alloy must be clean and smooth before joining, heat treatment, electroplating and forming. This article introduces 2 types of surface treatment methods for zirconium materials.

  1. Surface decontamination

Grease, oil, and lubricants produced during zirconium machining or other processing can be removed in a number of ways. Commonly used cleaning methods are

1) cleaning with alkaline or milky detergent in a soaking tank;

2) cleaning with ultrasonic vibration;

3) rinsing with acetone or trichloroethylene or steam degreasing and

4) cleaning with other cleaning agents.

Small stains can also be removed by hand wiping with some solvents such as acetone, alcohol, trichloroethylene, or a trichloroethylene substitute. In the electrolyte system, if the voltage and current can be controlled to avoid anodic polarization or spark discharge and pitting, positive or negative polarity decontamination can be used. Before heat treatment and bonding, the surface of the zirconium material must be cleaned to prevent metal contamination and the resulting deterioration of ductility.

Surface Treatment Technologies for Zirconium Materials

  1. Blast cleaning

Mechanical decontamination methods such as sandblasting, shot blasting, and evaporative cleaning can remove dirt and lubricants from zirconium and hafnium surfaces. Alumina, silicon carbide, silica and steel grit are ideal media for mechanical decontamination. The decontamination medium used should be replaced regularly to avoid increased workload due to particle passivation.

Grinding or shot peening may cause residual compressive stress and thermal deformation on the surface of the material, especially the surface of the sheet. Hot deformation may also occur during subsequent rolling and profile machining.

Blast cleaning is not a substitute for pickling. Blast cleaning cannot remove surfaces contaminated with interstitial elements such as carbon, oxygen, and nitrogen. In general, blast cleaning followed by pickling can ensure the complete removal of surface contamination and cold-worked layers, resulting in a smooth, shiny metal surface.

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Application of Zirconium Silicate in Ceramic Industry

Introduction of Zirconium Silicate

Zirconium silicate is a non-toxic, odorless white powder. It is usually made of natural high-purity zircon sand concentrate, which needs to be processed by ultra-fine grinding, iron removal, titanium processing, surface modification treatment and other processes. Zirconium silicate powder is a high-quality and inexpensive ceramic glaze opacifier, brightener, anti-seepage agent and stabilizer.

Main roles of Zirconium Silicate

  1. Improve the hardness of ceramic glaze

Zirconium silicate has good chemical stability, and can significantly improve the separation performance of ceramic glaze and improve the hardness of ceramic glaze;

  1. Whitening effect

Zirconium silicate powder can whiten ceramic glazes.

Application of zirconium silicate in the traditional ceramic industry

Zirconium silicate is mainly used for high-temperature opaque glaze in daily ceramics and sanitary ware.

Application of zirconium silicate

Many companies add a small amount of zirconium silicate or zircon powder to polished tiles and glazed products to increase stability.

Another function of zirconium silicate in the traditional ceramic glaze is to increase the hardness of the ceramic glaze and improve its wear resistance of the glaze. Zirconium silicate is generally used in raw glazes with little or no zircon powder. Compared with zircon powder, zirconium silicate powder is finer and brighter.

Engobe generally uses zirconium silicate, which can increase the whiteness of the engobe and adjust its expansion coefficient and stability.

Zirconium silicate has a good effect when added to the medium and high-temperature glaze of raw materials. A certain amount of zirconium silicate is generally added to the high-gloss and matt glazes of sanitary ware and glazed porcelain tiles.

Conclusion

Zirconium silicate is a high-quality and inexpensive opacifier, which is widely used in various architectural ceramics, sanitary ceramics, daily-use ceramics, and first-class ceramics. Zirconium silicate has also been further used in the production of color picture tubes in the TV industry, emulsified glass in the glass industry, and enamel glaze production. Zirconium silicate is also widely used in refractory materials, glass furnace zirconium ramming materials, castables and spray coatings due to its high melting point.

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.

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.

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