February 2023 – Zirconium Metal

Does Zirconium Have Any Effect on Human Health?

Zirconia ceramics and jewelry made of zirconium are widely used in daily life, and it is generally believed that zirconium is not harmful to human health. However, some people suspect that zirconium in tiles can cause cancer.

It is possible for radioactive elements to cause malignant tumors, usually by inducing cell lesions, leading to leukemia, lymphoma, skin cancer and other blood cancers. As for the malignant tumor caused by excessive radioactivity of ceramic tiles, there are no such cases and related records in clinical experience and domestic and foreign case literature.

Adding zirconium silicate to ceramics is mainly used to increase the whiteness of ceramics. If you are still concerned about its safety, don’t blindly pursue whiteness when buying tiles.

How to Distinguish Zircon from Diamond?

Colorless and transparent zircon is a good substitute for diamonds after careful consideration. The refractive index of zircon is close to 2, and the dispersion is similar to that of the diamond. Therefore, from the appearance, zircon will also shine with colorful light, which is very similar to diamond. Before the advent of man-made diamonds, zircon was the best diamond substitute.

Zircon is very similar to diamond in appearance, but zircon is far from diamond in price. Because the two are not easy to distinguish, some unscrupulous merchants use zircon as a diamond to deceive consumers and make huge profits. So as consumers, how do we differentiate them?

The main identification features of zircon are high refractive index, strong luster, high birefringence, high density, high dispersion, and typical spectral characteristics, etc., resulting in a very special optical phenomenon: When the polished zircon is observed with a magnifying glass, it can be seen from the top surface that there are obvious double shadows on the bottom surface and the ridge line. Because diamonds are “homogeneous”, there will never be a double shadow phenomenon, so zircons can be distinguished from real diamonds.

Diamond is a homogeneous body, completely black and hard under-crossed polarizers; while zircon appears as four bright and four dark under-crossed polarizers. Diamonds are lipophilic, and a ballpoint pen can easily leave uninterrupted marks on the surface of the diamond. Of course, this mark can be easily wiped off. Zircon is not lipophilic, and a ballpoint pen cannot leave uninterrupted marks on its surface. Sharpness marks.

Hydrogenation Method: A Method for Preparing Zirconium Powder

Introduction

Hydrogenation is one of the main methods for producing zirconium powder in the industry. This method refers to the process of preparing metal zirconium powder by hydrogenating and dehydrogenating bulk metal zirconium. The product metal zirconium powder prepared by the method has a purity of more than 98%, and can be mainly used in powder metallurgy additives and pyrotechnic industries.

Reaction Process

Zirconium has good plasticity and is difficult to be crushed by mechanical means, but it can be transformed into a brittle intermediate product zirconium hydride for further processing.

When hydrogen is sufficient, zirconium reacts with hydrogen to form zirconium hydride, releasing a lot of heat. The reaction formula is:

Zr+H2→ZrH2

When dehydrogenated by heating under a vacuum, zirconium hydride decomposes into metallic zirconium. The reaction formula is:

ZrH2→Zr+H2

Zirconium hydride is a non-stoichiometric substance in the interstitial phase, and the hydrogen content (x) can vary from zero to 2 with different process conditions. When x>1.65, it is brittle zirconium hydride, and the brittleness increases with the increase of x value. Zirconium powder can be obtained by grinding the brittle zirconium hydride finely and then dehydrogenating it in a high-temperature vacuum.

According to the requirements for product purity, the bulk zirconium raw materials used for hydrogenation include sponge zirconium, zirconium ingots, or zirconium scraps in zirconium processing; in order to ensure product quality, high-purity hydrogen must be used; the hydrogenation process should be in a well-airtight environment in a stainless steel reaction tank.

Specific steps are as follows:

After the reaction tank is filled, vacuum until the pressure is lower than 0.1Pa, heat to a temperature of 873-973K, and stop vacuuming.
Introduce high-purity hydrogen for hydrogenation. Sponge zirconium and zirconium shavings have a large specific surface area, which can be met by hydrogenation once. The dense zirconium with a large size needs to undergo multiple hydrogenation and dehydrogenation treatments at high temperatures to make it fully burst to ensure that the product is easy to grind. As long as the temperature and pressure of the hydrogenation process are well controlled, zirconium hydride with the desired hydrogen content can be obtained.
After the hydrogenation reaction is completed, continue to pass hydrogen to cool to room temperature, then extract the residual hydrogen, slowly fill in argon or air, and start unloading.
Put block zirconium hydride into a grinding tank, add the appropriate amount of water or ethanol to grind, then sieve and dry to get zirconium hydride powder. This zirconium hydride powder can be used as a heat-burning agent or powder metallurgy additive.
Spread the dried zirconium hydride powder into a thin layer in a tray, then put it into a dehydrogenation tank, and heat it slowly under a vacuum. Zirconium hydride releases a large amount of hydrogen at a temperature of about 673K.
When the temperature rises to 873-973K and the vacuum pressure reaches below 0.1Pa again, cool the dehydrogenation tank to room temperature, slowly pour water or ethanol into it, and then unload.
After grinding, sieving, and drying, the product zirconium powder is obtained.

Advantages

The zirconium powder produced by this method can maintain the content of metal impurities at the level of the raw material while ensuring that it is not contaminated by the container, and the content of some volatile impurities will be reduced, but the content of gas impurities, especially oxygen, will be reduced. Increase. The average particle size of zirconium powder can reach 5-10μm, and finer particle sizes can be separated through liquid countercurrent classification. The finer the particle size of the zirconium powder, the higher the oxygen content.

Attention

Zirconium powder, zirconium hydride powder, and hydrogen are flammable and explosive substances, and fine zirconium powder can oxidize, spontaneously ignite or explode even at room temperature. Explosion-proof measures should be taken during the production, storage, transportation, and use of zirconium powder to ensure safety.

For more information, please visit https://www.samaterials.com/.

4 Methods for Making Metal Zirconium

Zirconium and its alloys not only have good machinability, moderate mechanical strength, and high corrosion resistance, but also have a low neutron cross-section. In the nuclear energy industry, they are widely used as structural materials for water reactors. Zirconium widely exists in zircon, so most methods of preparing metal Zr use zircon as a raw material for extracting zircon. This article will mainly introduce four methods for purifying zirconium.

Metal Thermal Reduction Method

The reducing agents used in the thermal reduction method are mainly calcium and magnesium.

(1) Calcithermic reduction

Using ZrO2 as raw material and calcium as a reducing agent, the reduction reaction is carried out at 1273-1373K under vacuum. The reduction product is a powdery mixture of Zr, CaCl2, CaO, and Ca, which can be pickled, washed with water, filtered, dried, and sieved to obtain metal zirconium.

(2) Magnesium reduction method

The magnesium reduction method mainly includes steps such as the preparation of zirconium tetrachloride, purification, magnesium reduction, and vacuum distillation. Chloride zirconium dioxide or zircon sand to obtain zirconium tetrachloride, purify, remove impurities such as SiCl4, TiCl4, AlCl3, FeCl3, and then use molten magnesium to reduce ZrCl4 to obtain a mixture of metal zirconium, magnesium, and magnesium chloride, and finally, Zirconium metal is obtained by distillation and purification.

Hydrodehydrogenation

This method uses the reversible absorption characteristics of zirconium to hydrogen to prepare zirconium powder. At a certain temperature, zirconium and zirconium alloys absorb hydrogen to form hydrides or solid solutions. When reaching a certain level, the material will produce microcracks, become brittle, and contain a lot of hydrogen. Such powder is called zirconium hydride powder. Zirconium hydride powder is dehydrogenated under high temperature and vacuum conditions to obtain zirconium powder. After years of improvement and promotion, this method has become the main method for producing zirconium powder.

Molten Salt Electrolysis

Metals or alloys that are difficult to electrodeposit in an aqueous solution usually use molten salt electrodeposition. Insoluble anodes are usually used, stainless steel or other refractory metals are used as cathodes, and molten salts of electrodeposited metals and alkali metal chlorides or fluorides are used as electrolytes. During the electrolytic reduction process, they are decomposed by the electrolytic metal molten salts. and deposited at the cathode.

Direct Electro-Deoxidation Method

The direct electro-deoxidation method uses a single or mixed metal oxide as the raw material, presses it into a block as the cathode, removes the oxygen in the cathode by electrolytic deoxidation, and obtains a metal element or alloy with low impurity content in a high-temperature molten salt, also known as FFC Law. The metals successfully prepared by the FFC method include Zr, Hf, Be, Mg, Ca, Ba, V, Nb, W, Fe, and Cu.

Among the four methods, the magnesium reduction method and hydrogenation-dehydrogenation method are the main production methods in the industry.

For more information about zirconium materials, please visit https://www.samaterials.com/.

The Importance of Surface Coatings for Zirconium Alloy Cladding

Safety Issues in The Application of Zirconium Alloys

In the past few decades, zirconium alloy cladding has been successfully applied to light water reactors (LWR), and has shown good radiation resistance and corrosion resistance. However, a major problem in the application of zirconium alloys in stacks is that they react violently with water vapor at high temperatures, and when the temperature is greater than 1200 °C, a large amount of hydrogen and heat will be released. After the Fukushima nuclear power accident in Japan, the safety of nuclear power has once again been placed in front of all nuclear workers. How to further improve the safety and reliability of light water reactor nuclear fuel elements under accident conditions has become an urgent problem to be solved. Research and development directions include accident-resistant fuel cores and accident-resistant cladding materials.

Cladding Material for Zirconium

The accident-resistant cladding material has good thermodynamic properties, which can improve the reaction kinetics of zirconium and water vapor and reduce the hydrogen release rate. The development of this material is mainly reflected in two aspects: one is to improve the high-temperature oxidation resistance and strength of the zirconium alloy cladding; the other is to develop non-zirconium alloys with high strength and oxidation resistance. This paper discusses the research on the surface coating of zirconium alloy cladding for the former.

The main advantage of the application of coated zirconium cladding is economical. The technical challenge it faces is to meet various performance requirements of the fuel cladding and components without changing the size of the fuel cladding. During long-term operation, the coating should have certain stability under corrosion, creep, and abrasion conditions.

Research Status of Zirconium Alloy Cladding Surface Coating

The anti-oxidation coating technology on the surface of zirconium alloy is the main method to improve the anti-oxidation ability of the surface of zirconium cladding. The outer surface of the zirconium alloy is coated with a layer of material to enhance the wear resistance and high-temperature oxidation resistance of the cladding, thereby improving the accident resistance of the zirconium cladding under normal working conditions and accident conditions. At present, some preliminary screening results have been obtained in international research on the surface coating of zirconium alloy cladding, and the coating materials mainly involve MAX phase and metal Cr.

MAX-phase coating

A series of studies have shown that:

The essence of the MAX phase coating is the dressing effect, and the key to the problem is to solve the diffusion of oxygen atoms to the zirconium substrate.
No matter whether in a fast neutron reactor or thermal neutron reactor, under the three activation time conditions, the activity of MAX phase material is similar to that of SiC, but three orders of magnitude lower than that of 617 alloys.
The thickness of the MAX phase coating should be controlled at 10~30 μm to limit the loss of neutrons.
Ti3SiC2 shows better prospects than Ti2AlC as a candidate material for MAX-phase coatings for high-temperature nuclear energy applications.
At room temperature, the radiation resistance of Ti3AlC2 is better than that of Ti3SiC2, and the radiation stability of the two MAX phase materials at 600 ℃ is better than that at room temperature.

Metal Cr Coating

A series of studies have shown that:

The high-temperature oxidation resistance of the coated zirconium alloy is obviously better than that of the Zr-4 substrate.
The high-temperature oxidation resistance of the coated zirconium alloy is significantly stronger than that of the zirconium alloy substrate, and the Cr-coated zirconium cladding has better ductility.
The metal Cr coating has good high-temperature oxidation resistance and can be used as a candidate coating material for accident-resistant zirconium alloy cladding.

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

If you are interested in coating materials, you can find more information at https://www.sputtertargets.net/.