Chinese name: Hafnium, English name: Hafnium, element symbol Hf, atomic number 72, atomic weight 178.49, belongs to group ⅣB in the periodic table. Hafnium is a lustrous silver-gray transition metal with a density of 13.31g/cm³(20 °C), a melting point of 2233 °C (2506 K, 4051 °F) and a boiling point of 4603 °C (4876 K, 8317 °F). The compact hafnium metal is inactive and reacts with air to form an oxide coating, which is stable at room temperature, whereas the powdered hafnium is prone to spontaneous combustion in air. Hafnium does not react with dilute hydrochloric acid, dilute sulfuric acid, and strong alkali solutions, but is soluble in hydrofluoric acid and aqua regia. Hafnium is found in small amounts in the earth's crust and often coexists with zirconium. Hafnium has high temperature resistance, corrosion resistance, oxidation resistance, easy processing, rapid heat-absorbing and heat-releasing properties, and is used as atomic materials, alloy materials, high temperature resistant materials, electronic materials, etc.

Hafnium target material hafnium can react with air to form an oxide film protective layer. When the temperature is 500 ~ 750℃, the oxide film will lose its protective effect and combine with oxygen, nitrogen and other gases to form oxides and nitides when heated. At temperatures above 800℃, hafnium is rapidly oxidized to form HfO2.

Hafnium has good corrosion resistance and does not react with dilute hydrochloric acid, dilute sulfuric acid and strong alkali solutions, but is soluble in hydrofluoric acid and aqua regia.

Hafnium is often +4 valence in compounds, the main compound being hafnium oxide HfO2, which comes in three different variants: monoclinic, tetragonal, and cubic. +4 hafnium also easily forms complexes with fluoride consisting of K2HfF6, K3HfF7, (NH4)2HfF6, (NH4)3HfF7.

Fields of hafnium use and application

Electronic material

Hafnium can be used as the cathode of an X-ray tube because of its tendency to emit electrons. In addition, alloys of hafnium and tungsten or molybdenum are also used as electrodes for high voltage discharge tubes. In 2012, a research team led by Andrew Flovit of the Department of Engineering at the University of Cambridge, UK, developed a new type of hafnium oxide with a higher dielectric constant, which is expected to be used in the manufacture of the next generation of smaller electronic devices, photovoltaic manufacturing equipment, and more efficient photovoltaic cells.

Atomic energy industry

Hafnium applied to reactor Hafnium metal has excellent welding performance, processing performance, high temperature resistance and corrosion resistance, so it has become an important material in the atomic energy industry. Hafnium is an ideal neutron absorber with a large thermal neutron capture cross section, and can be used as control rods and protective devices in atomic reactors.

Chemistry field

Hafnium can be used as an getter in many aeration systems. Hafnium getter can remove oxygen, nitrogen, etc. present in the system without the need for gases. In addition, hafnium has a strong resistance to volatility, commonly used as an additive for hydraulic oil, to prevent the volatilization of hydraulic oil in high-risk operations.

Alloy material

Hafnium applications to spacecraft Hafnium has properties such as malleability, oxidation resistance and high temperature resistance, and is also a good alloy material, which is used in a variety of alloys. For example, niobium hafnium alloy containing hafnium 10% can be used as the nozzles of lunar rockets, while tantalum tungsten alloy containing hafnium 2% can be used as the protective layer material of spacecraft due to its high creep strength.

Effects of hafnium on health and the environment

Hafnium metal generally has no effect on human health, but some compounds of hafnium are toxic and can have adverse effects on human health, such as hafnium chloride which corrodes skin and mucous membranes. Therefore, when we come into contact with hafnium compounds, we should first understand whether the compound is toxic, and whether we need to take protective measures when in contact, such as wearing masks, gloves, etc. Persons who are in regular contact with hafnium compounds should undergo regular medical examinations, especially liver examinations, as damage to the liver of animals has been reported from animal studies. In addition, the hafnium compound production site shall have good ventilation and regular dust removal to reduce the concentration of hafnium compound dust in the air to avoid irritation to the skin, eyes and mucosa due to contact or inhalation.

Although the compact hafnium metal properties are not active, the surface forms an oxide covering layer, stable at room temperature, but the powder of hafnium in the air is easy to spontaneous combustion, so whether in the hafnium powder production workshop, or we in the use of hafnium powder, should properly keep hafnium powder, ensure good ventilation, avoid spontaneous combustion.

Plants absorb small amounts of hafnium from the soil, but it has no effect on plant growth. Hafnium compounds have been shown in animal studies to irritate the eyes, skin, and mucous membranes. To date, no other negative environmental effects of hafnium have been reported.