Zirconium materials – Page 3

3 Manufacturing Methods of Zirconium-containing Refractories

What is Zirconium-containing Refractory Material?

Zirconium-containing refractory materials are made of zirconia (ZrO2) and zircon (ZrSiO4) as raw materials. “Zirconium-containing” usually refers to materials containing the following zirconium products: zirconia, zircon, zirconium mullite and zirconium corundum. Zirconium-containing products have good corrosion resistance to various molten metals, acidic reagents and liquid glass.

Zirconium-containing refractory materials can be divided into the sintered, fused cast, and non-fired products based on different manufacturing methods.

What are the Different Manufacturing Methods?

Sintered Zr-Containing Refractory Product

The basic steps to manufacture zirconium-containing sintered bricks are to prepare raw materials, press green bodies, and sinter at high temperatures.

Another method is to obtain blanks by granulation, kneading, machine pressing or extrusion molding, and the clinker fired at high temperature is used as aggregate, and the clinker fine powder is used for batching, kneading, molding, drying, and sintering to finally obtain the finished product.

Cast Zr-Containing Refractory Product

1) Use zircon concentrate or industrial zirconia and industrial alumina powder as raw materials.

2) Add sodium oxide, calcium oxide, boron oxide and rare earth metal oxides as additives.

3) The powder is melted at a temperature above 2500°C by means of electric arc melting, cast in a mold, cooled, annealed, and machined.

Non-fired Zr-Containing Refractory Product

The manufacturing process of zirconium-containing refractory products without firing is simple, and the product qualification rate is high.

1) Use stabilized zirconia clinker or zircon as raw material.

2) Use water glass, phosphoric acid, phosphate, or sulfate as the cementing agent.

3) Mix the raw materials and cementing agents, and undergo high-pressure molding and low-temperature heat treatment to make zirconium-containing non-fired materials.

The heat treatment temperature varies with different binders. When aluminum dihydrogen phosphate is used as the cement, the heat treatment temperature is about 300°C; when phosphoric acid is used as the cement, the heat treatment is carried out at a temperature of about 600°C.

What Are These Products Used for?

Zirconium-containing refractory products can be widely used in metallurgy, building materials, the chemical industry, machinery and other professional fields due to their high refractoriness, mechanical strength and chemical stability.

Zirconia bricks can be used in thermal equipment in the building materials industry and metallurgical industry, such as billet continuous casting sizing nozzles, submerged nozzles and slag lines in long nozzles.
Zircon bricks are resistant to low-alkali glass corrosion. They can be used for the kiln wall of the glass melting furnace, as well as the arch feet of the upper structure of the glass melting furnace or the intermediate transition layer between silica bricks and corundum bricks.
Zirconia-mullite fused cast bricks can be used in heating furnaces, soaking furnaces in the metallurgical industry, glass melting furnaces in the building materials industry, etc.
Zirconium corundum bricks have good resistance to melt erosion. As a high-grade abrasive, it has a good grinding effect on steel, cast iron, heat-resistant steel, and various alloy materials.

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10 Common Zirconium Products and Their Applications

1. Zirconium Silicate

Zirconium silicate is an important variety in traditional zirconium products. The product is made of zircon sand, which can be obtained after grinding, calcining and powdering. It is a high-quality and cheap opacifying agent for ceramic glazes.

Zirconium silicate is mainly used for color glazes of architectural ceramics, daily-use ceramics and electric porcelain. It is also widely used in high-grade refractory materials, precision casting, emulsified glass and other industries.

2. Zirconium Carbonate

Zirconium carbonate is a source of zirconium that is insoluble in water but is easily transformed into other zirconium compounds. It is mainly used as an additive for cosmetics, waterproofing agent, flame retardant, opacifying agent, and surface aid for fibers and paper, and can also be used to prepare zirconium-cerium composite catalytic materials. It is an important raw material in the textile, papermaking, paint, and cosmetic industries, and its consumption has been increasing in recent years.

3. Zirconium Oxychloride

Zirconium oxychloride is the main raw material for the production of other zirconium products such as zirconium dioxide, zirconium carbonate, zirconium sulfate, composite zirconium oxide, and the separation of zirconium and hafnium to prepare metal zirconium and hafnium. In addition, it can be used in textiles, leather, rubber additives, metal surface treatment agents, paint drying agents, refractory materials, ceramics, catalysts, fire retardants, and other products. The primary source material for zirconium oxychloride is zircon sand.

4. Fused Zirconia

Fused zirconia is mainly used in the production of glazes and refractory materials. Due to the high content of impurities in fused zirconium, its use is sometimes limited.

5. Zirconium Sulfate

Zirconium sulfate is an intermediate raw material for the production of zirconium chemicals and metal zirconium and hafnium. It is also an important raw material for the production of leather tanning agents, wool treatment agents and paint surface oxidants. Additionally, it can be used as a catalyst carrier, amino acid and protein, precipitant and deodorant.

Consumption Structure of Zirconium Products

6. Zirconium Dioxide

Zirconium dioxide, or zirconia, is a non-toxic, odorless white solid. It has sufficient stability in alkaline solutions and many acidic solutions. ZrO2 ceramic is suitable for precision ceramics, electronic ceramics, optical lenses, glass additives, electrolytic zirconia bricks, ceramic pigments, enamel, artificial gemstones, refractory materials, grinding and polishing and other industries and products.

7. Composite Zirconia

Composite zirconia, referring to stabilized zirconia, is a non-toxic, odorless white powder. It has stable chemical properties and controllable specific surface area. It is the basic raw material for the manufacture of various special ceramics, advanced refractory materials, optical communication devices, and new energy materials.

8. Nuclear Grade Zirconium

Nuclear-grade zirconium is mainly used as the structural material of nuclear-powered aircraft carriers, nuclear submarines, and civil power reactors, and the cladding of uranium fuel elements. It is an important strategic metal.

9. Industrial Grade Zirconium

Industrial-grade zirconium is mainly used in the production of chemical acid and alkali-resistant equipment, the military industry, the electronics industry, pipeline valve materials, special high-strength, and high-temperature alloy materials, and getters for electric vacuum and lighting bulb industries.

10. Metallurgical Grade Zirconium

Metallurgical grade zirconium is used as a firearms sponge zirconium combustion agent and is also suitable for alloy additives and metallurgical deoxidizers, the chemical industry, civilian flash fireworks, etc.

Purification of Zirconium by Vacuum Distillation

Vacuum distillation refers to the process of removing metal magnesium and MgCl2 in sponge zirconium by distillation under the condition of lower pressure than normal pressure. The zirconium sponge produced by distillation is then vacuum cast into metal or alloy, which is used in industrial sectors such as atomic energy, metallurgy, and chemistry.

Principle of Vacuum Distillation

The raw material of vacuum distillation is generally the product of the reduction of zirconium tetrachloride and magnesium, containing 55% to 60% of zirconium, 25% to 30% of magnesium, 10% to 15% of MgCl2 and a small amount of Zrcl3 and ZrCl2.

The vapor pressures of these components are different at a certain temperature and pressure. For example, in the standard state, the boiling point of magnesium is 1380K, MgCl2 is 1691K, and zirconium is 4673K; at normal pressure and 1173K temperature, the equilibrium vapor pressure of magnesium is 13332.2Pa, MgCl2 is 999.9Pa, and zirconium is less than 130μPa. Therefore, by controlling the appropriate distillation temperature and pressure, zirconium and other components can be separated.

In addition, under a 10Pa vacuum, the boiling points of magnesium and magnesium chloride dropped to 789K and 950K, respectively, and the volatilization rate was many times greater than that of atmospheric distillation. Therefore, the use of vacuum distillation can shorten the distillation time, reduce the distillation temperature, improve the separation effect, and avoid the formation of Zr–Fe alloys that contaminate the zirconium sponge and iron.

System for vacuum distillation

The vacuum distillation system is mainly composed of a distillation furnace, a distillation tank, a condensation sleeve, a condenser, a heat shield, and a vacuum system.

According to the installation position of the condenser, it can be divided into two types: upper cooling type and lower cooling type, and the structure of the two is basically the same. In industrial production, the distillation furnace and the reduction reactor are the same. Therefore, the structural design and material selection of the reduction reactor should take into account the requirements of the reduction and distillation processes.

The condenser is a hoistable bell-shaped cylindrical tank with a cooling water jacket. The condensing sleeve is cylindrical, and the condensing area is set according to the amount of condensate discharged by distillation. A heat shield is arranged between the distillation tank and the condenser, the function of which is to reduce the radiant heat from the heating area to the condenser, without hindering the passage of the airflow escaping from the distillation tank. In order to improve the thermal insulation effect, most of the heat shields are multi-layer structures.

The structure of the distillation furnace is the same as that of the reduction reactor, but the furnace shell of the former should be sealed and connected to a vacuum device. During operation, the furnace is in a low vacuum state to reduce the external pressure on the distillation tank and prevent the latter from deforming.

Process of vacuum distillation

The reducing crucible together with the reaction product is placed upside down in the distillation pot of the distillation furnace.
The distillation tank was evacuated to 13.3-1mPa, and then the distillation furnace was heated to a temperature of 573-673K and kept at a constant temperature for 1-4 hours to remove the crystal water adsorbed by MgCl2 during the assembly process of the distillation equipment.
Then the furnace temperature was raised to 1023-1073K. At this time, since the metal magnesium and MgCl2 begin to volatilize in large quantities, the vacuum degree drops sharply, and the heating rate needs to be controlled well.
After the distillation enters the constant temperature stage, the temperature should be controlled at 1223-1273K.
After 20-25 hours of constant temperature, when the vacuum in the distillation tank rises to less than 1Pa and tends to be stable for a certain period of time, the residual amount of volatiles is very small, and the distillation operation is over.

In the whole distillation process, process parameters such as distillation temperature, vacuum degree and distillation time should be well controlled. It takes about 50 to 60 hours to distill 700 to 800 kg of zirconium. The zirconium sponge produced by distillation is self-igniting. When the distillation tank is cooled to 323K temperature, a mixed gas consisting of 60% dry air and 40% indoor air should be slowly introduced to reduce the surface activity of the sponge zirconium and make it passivated before it is released.

Product handling after vacuum distillation

Zirconium sponge is a hard and tough metal. Usually, the zirconium lump is cut into pieces by a vertical hydraulic press equipped with a cutter, and then it is medium and finely crushed to make the particle size reach 5-25mm, and then sieved, classified, mixed in batches, and packed with argon. The typical impurity content (mass fraction ω/%) of sponge zirconium is Fe 0.08, Al 0.006, Mg 0.002-0.02, Cl 0.001-0.04, O 0.08-0.1, N 0.002-0.004.

Sponge zirconium taken out from the reduction crucible can be divided into four types: A, B, C, and D.

A type of zirconium sponge accounts for about 35% of the total and is a bulk dense metal that contains almost no metal magnesium and MgCl2.
B-type zirconium sponge accounts for about 20% of the total. It is the product formed in the initial stage of the reaction, which is plate-shaped and about 10mm thick. In addition to metal magnesium, it contains a lot of iron and nitrogen impurities.
C-type sponge zirconium accounts for about 35% of the total, is a light and porous sponge with the least impurities but contains a considerable amount of metal magnesium and chloride in the pores.
D-type zirconium sponge is a product that is close to the crucible wall and contains a lot of impurities. Generally, it is returned to the chlorination treatment to recover the zirconium in it.

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What are Zirconium Containing Refractory Materials?

Description of zirconium-containing refractory products

Zirconium-containing refractory products refer to refractory products made of zirconia (ZrO2) and zircon (ZrSiO4) as raw materials, including zirconia products, zircon products, zirconium mullite, and zirconium corundum products. According to different production processes, zirconium-containing refractory products are divided into sintered products, fused cast products, and non-fired products. Zirconium-containing refractory products have the characteristics of high melting point, low thermal conductivity, and good chemical stability, especially good corrosion resistance to molten glass and liquid metal.

Properties of zirconium-containing refractory products

Dense, stabilized zirconia has a melting point of 2677°C and a service temperature of 2500°C. The bulk density fluctuates between 4.5 and 5.5 g/cm3 due to the purity of the raw materials and the different manufacturing methods. The bulk density of dense zirconia products can reach 5.75g/cm3. Sintered zirconia products do not chemically react with molten metal and liquid glass. Caustic alkali solutions, carbonate solutions, and acids (except concentrated H2SO4 and HF) do not chemically react to zirconia. When carbon reacts with sintered zirconia, zirconium carbide is formed only on the surface. Therefore, under the condition of oxidizing atmosphere, zirconia products can be used at high temperatures without chemical change.

The main component of zircon products is ZrO2•SiO. Zircon is decomposed into ZrO2 and SiO when heated at 1680℃. Quartz stone products have good corrosion resistance to various molten metals, acidic reagents, and liquid glass, but they are prone to erosion reactions when they come into contact with alkaline slag or alkaline refractory materials. Aluminum-zirconium-silicon (AZS) cast bricks and fired bricks have good resistance to glass liquid erosion, and can be used in the pool wall and upper structure of glass melting pool kilns.

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Uses of zirconium-containing refractory products

Zirconium-containing refractory products have high refractoriness, mechanical strength, and chemical stability. It can be widely used in metallurgy, building materials, the chemical industry, machinery, and other professional fields.

Zircon bricks have good resistance to acid slag, small corrosion loss, and slight sticking of slag. They can be used in the slag line of the ladle and have a long service life. Zircon products can also be used as continuous-casting intermediate tank base bricks, cushion bricks, and nozzle bricks. Zircon bricks are corrosion-resistant to low alkali glass and can be used in the kiln walls of glass-melting furnaces. It can also be used for the arch foot of the upper structure of the glass melting furnace or the intermediate transition layer between the silica brick and the corundum brick and is also an important material for the comprehensive masonry bottom.

Zirconia bricks can be used in thermal equipment for the building materials industry and metallurgical industry, such as sizing nozzles for billet continuous casting, submerged nozzles, and slag lines in long nozzles.

Fused-cast bricks with a ZrO2 content of more than 90% can be used for side walls, partition walls and flow holes of borosilicate glass melting furnaces and aluminosilicate glass melting furnaces. AZS-fired bricks and fused cast bricks can be used in soda-lime glass melting kilns, such as flow holes and side walls. The use of this brick to build liquid flow holes and side walls can reduce the contamination of glass liquid by refractory materials. In addition, zirconium mullite fused cast bricks can be used in the metallurgical industry heating furnaces, soaking furnaces, glass melting furnaces in the building materials industry, etc.

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How to Purify Zirconium Tetrachloride? – 3 Methods

The purification of zirconium tetrachloride is the process of removing the impurities of crude zirconium tetrachloride. Zirconium tetrachloride is generally prepared by chlorination of zirconium carbide, zircon, or zirconium dioxide. At this time, the finished product also contains a considerable amount of impurities such as FeCl3, AICl3, TiCl4, SiCl4, ZrOCl2, and carbon powder. To obtain high-purity zirconium tetrachloride, these impurities must be removed. The mainstream methods for purifying zirconium tetrachloride mainly include the hydrogen reduction method, the molten salt purification method.

Hydrogen Reduction

Principles

The basic principles on which this law is based are:

(1) Since Zrcl4 and TiCl4 and SiCI4 have different vapor pressure differences at the same temperature, by controlling a specific temperature, TiCl4, SiCl4 and H2O can be sublimated and removed;

(2) Since ferrous chloride or chromium chloride has a high boiling point (the former is 1303K, the latter is 1573K), trivalent iron and chromium can be reduced to divalent with hydrogen. At the sublimation temperature of ZrCl4 (723-933K), FeCl2, CrCl2 and ZrOCl2 do not sublime and remain in the residue and separate from zirconium.

Process

The purification furnace of the hydrogen reduction method consists of a sublimation furnace and a condenser. The sublimation furnace is a stainless steel container with a cylinder inside, and a multi-layer tray is placed in the cylinder. The zirconium tetrachloride is packed on the tray with an appropriate thickness, and the top of the sublimation furnace is sealed with the condenser to collect the purified ZrCl4.

The work is carried out in three steps.

Step 1

Evacuate the furnace and heat it to a temperature of 423-473K, while the pressure continued to rise. TiCl4, SiCl4, HCI, H2O and adsorbed chlorine gas are discharged out of the furnace by timing exhaust method.

Step 2

Evacuate the furnace and fill it with hydrogen, and raise the temperature to 573K. The iron and chromium in FeCl2 and CrCl2 are reduced to a low-price state.

Step 3

Gradually heat the furnace to 873-933K, and keep the temperature of the condenser at 523K. At this time, ZrCl4 continuously enters the condenser from the sublimation furnace and condenses into a solid, while FeCl3 and CrCl3 do not volatilize and remain in the slag.

Summary

The purification operation time depends on the physical state, impurity content and processing volume of the raw materials. 2.0～2.5t ZrCl4 generally needs to be purified for 100～120h, and the recovery rate of zirconium is 97%～98%. The main impurity content (mass fraction ω/%) of refined ZrCl4 is as follows:

Impurities	After purification (mass fraction ω/%)
Fe	0．001
Al	0．008
Ti	<0．003
Si	0．006

Molten Salt Purification

Principle

The basic principle on which this method is based is that zirconium, iron and aluminum form Na2ZrCl6, K2ZrCl6, NaFeCl4, KFeCl4, NaAlCl4 and KAlCl4 double salts in the NaCl-KCl molten salt system, respectively.

Zirconium double salt can be re-decomposed to ZrCl4 at the set temperature, while Na(K)FeCl4 and Na(K)AlCl4 are stable compounds with high boiling point. Due to the different partial pressures of zirconium salts and iron and aluminum salts at the same temperature, it can be separated from them by controlling a specific temperature to only volatilize ZrCl4. Crude ZrCl4 is purified by washing with molten salt and filtering.

Process

There are two methods of industrial production: intermittent operation and continuous operation.

Intermittent operation

First, make ZrCl4, NaCl, and KCl into molten salt in proportion, remove volatile components at a temperature of 573K, and then raise the temperature of the salt pool to a temperature of 773-873K, so that ZrCl4 is continuously volatilized to the condenser for collection.

Continuous operation

Add the crude ZrCl4 to the molten salt pool with a temperature of 623-723K by a screw feeder for washing and purification, and then transfer the ZrCl4 gas to a bubbling molten salt pool with a temperature of 773-873K for secondary purification. The gaseous product enters the baghouse and condenser for collection.

Summary

This method is suitable for processing raw materials with high iron and aluminum impurities. The main impurity content (mass fraction ω/%) of ZrCl4 product after purification is:

Impurities	After purification (mass fraction ω/%)
Fe	0．01～0．002
Al	0．003～0．008
Ti	0．002～0．009
Si	0．002～0．008。

Liquid Purification Method

In addition to the above two mainstream purification methods, there is also a liquid purification method. The process is to pass hydrogen and nitrogen mixed gas into the bottom of the purification furnace with a structure similar to that of the fluidized chlorination furnace, so that the coarse ZrCl4 powder in the furnace forms a fluidized layer, and trivalent chlorides such as iron and chromium are reduced to two due to reduction. The high boiling point chlorides remain in the slag and separate from ZrCl4. The refined ZrCI4 gas enters the condenser for cooling and collection after being filtered.

For more information about zirconium tetrachloride or othe

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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. 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. 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.

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. 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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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.

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.

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.

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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