November 2022 – Zirconium Metal

Comparison of zirconia ceramic teeth and metal ceramic teeth

Broken or missing teeth usually require fillings. The two conventional options are zirconia ceramic teeth and metal-ceramic teeth. This article will analyze the difference between the two and help those in need to choose the one that suits them.

Metal ceramic teeth

Metal-ceramic crowns are accepted by most patients because of their good strength, but they have many disadvantages. The metal substrate is easily oxidized to form gray oxides, which are scattered and deposited on the edge of the gums, causing the gums to turn gray and affecting the appearance; at the same time, metal porcelain teeth may have a strong stimulating effect on the gums, and even cause gum swelling, bleeding, allergies and other symptoms; the color of the metal-ceramic crown should be covered with opaque porcelain, so that the ceramic crown can block the light to a certain extent, thus affecting the aesthetics of the teeth.

Zirconia all-ceramic teeth

At present, there are many types of all-ceramic dental materials, such as leucite, lithium-based porcelain, alumina, zirconia, etc. There are also a variety of fabrication methods, such as infiltrated ceramics, hot pressure casting ceramics, porcelain deposition, computer-aided design, and computer-aided fabrication. In comparison, among all all-ceramic restoration materials, zirconia material has higher flexural strength, so it is accepted by more and more patients and doctors.

Zirconium dioxide all-ceramic crown has its own unique advantages. Since there is no metal bottom crown, its restoration has permeability and aesthetics, which provides a guarantee for aesthetic restoration. At the same time, zirconium dioxide has strong biocompatibility and is non-irritating to the gums. Most patients will not experience symptoms such as gum swelling, bleeding, and allergies, which meet the clinical requirements.

Advantages of zirconium dioxide

(1) Good mechanical properties: it has a flexural strength greater than 900MPa, so it can also be used for the repair of posterior teeth and porcelain bridges with more than 6 units.

(2) Good biocompatibility: The zirconia all-ceramic crown itself does not contain metal, which can exclude metal allergic reactions; zirconia also has good biocompatibility.

(3) No obstruction to X-rays: There is no need to remove the dentures when performing cranial X-rays, CT, and MRI examinations, because zirconia ceramic teeth have no obstruction to X-rays.

(4) Good strength and density: Zirconium dioxide is widely used, especially in high-precision instruments, such as aviation equipment. Because of its good crack resistance and tough curing after cracking, it can be made into a porcelain bridge with more than 6 units, and it can also solve the problem that the all-ceramic system cannot be used as a long bridge.

(5) The color is comparable to real teeth: the color of the base crown of the ceramic is white, so the neck of the porcelain tooth will not become black and darkened for a period of time after the porcelain tooth is inserted, thus avoiding the problem of discoloration of the metal porcelain crown.

(6) Healthy biological material: Zirconium dioxide is an excellent high-tech biological material with good biocompatibility, which is healthy and safe to use.

(7) High-tech quality: Zirconium dioxide ceramic teeth are made by good computer-aided design, laser scanning, and then controlled by computer-aided program grinding.

Hopefully, the above analysis will help you a lot in making your choice between metal ceramic teeth and ceramic teeth.

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.

For more information, please visit https://www.samaterials.com/70-zirconium.html.

Methods for Zircon Beneficiation

What is Zircon?

Zircon (also known as zircon) is zirconium orthosilicate with a chemical formula of ZrSiO4, which is the most common type of zirconium-containing mineral. Zircon is mainly used as a raw material for zirconate refractory bricks, and can also be used for precision casting sand and ceramic utensils.

What is Zircon Beneficiation?

Zircon beneficiation refers to the process of removing impurities in zircon ore and increasing the content of zircon. Most of the zircon deposits are coastal placers. In the heavy sand containing zircon, there are usually heavy minerals such as magnetite, ilmenite, rutile, and monazite. Generally, when zircon is selected, these heavy minerals are also recovered as target minerals.

What are Zircon Beneficiation Methods?

Zircon beneficiation methods mainly include gravity separation, magnetic separation, electrostatic separation, and flotation.

Gravity separation

Zircon mostly occurs in ilmenite and is often accompanied by heavy minerals such as hematite, chromite, and garnet. Therefore, in the initial stage of enriching zircon, gravity separation is often used, such as using a shaking table to separate heavy minerals from gangue (quartz, feldspar, biotite), etc., and then using other beneficiation methods to separate them from other heavy minerals.

Flotation

The commonly used collectors in this method are fatty acids (oleic acid, sodium oleate), etc.; the slurry conditioner is sodium carbonate; the inhibitor is sodium silicate; the activator is sodium sulfide and heavy metal salts (zirconium chloride, ferric chloride) ); this method also uses oxalic acid to adjust the pulp to acidity and uses amine collectors for flotation.

Electric selection

Conductive minerals such as ilmenite, hematite, chromite, cassiterite, and rutile are separated from non-conductive minerals such as zircon, monazite, garnet, and apatite by utilizing the difference in mineral conductivity. Desliming, grading, drying, and dosing should be done in advance before electrification.

Magnetic separation

Magnetic minerals in heavy minerals include ilmenite, hematite, chromite, garnet, biotite, monazite, etc. Zircon is a non-magnetic mineral or a weak magnetic mineral (the iron in zircon in some deposits is weak magnetic). Magnetic separation is divided into dry and wet. In dry magnetic separation, the selected materials need to be heated, dried, and classified before they can be sorted. The wet type strong magnetic field magnetic separator has a wide separation particle size, and the lower limit of particle size can reach 20um. Therefore, it is more appropriate to use a wet magnetic separator when the zircon particle size is fine.

Wrap up

Since there are many associated minerals in zircon ore, gravity separation, magnetic separation, flotation, electric separation, and other methods should be used in combination. For more information, please visit https://www.samaterials.com/70-zirconium.html.

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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