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What is Hafnium Carbide? Hafnium carburide (HfC), a chemical compound composed of hafnium, is a combination of carbon and hafnium. It has a melting point of 3900degC. The oxidation resistance of this compound is extremely low. At 430degC, oxidation begins. This compound might be used in the heat shield of future spacecraft.
Carbonizations are usually devoid of carbon. Therefore, their composition is typically expressed as HfCx (x = 0,5 to 1,0). The crystal structure is cubic (salt).
Hafnium carburide is normally synthesized in an atmosphere of inertness or reduction with hafnium (HfO2) oxide and carbon. The reaction is carried out at a temperature between 1900-2300degC. Hafnium carburide can form solid solutions with many compounds such as ZrC or TaC. ).
Hafnium oxide (IV) is obtained by reducing powdered hafnium with carbon at a temperature of 18002000degC. To remove all the oxygen, it takes a lot of time. Chemical vapor deposition can be used to obtain a coating of high purity HfC from a mixture containing methane, hydrogen and vaporized chlorine chloride (IV). HfC’s limited use is due to its technical complexity and high synthesis costs, despite its advantageous properties, including high hardness and melting point (>9 Mohs).
HfC-x undergoes a change from paramagnetism to diamagnetism when x is increased. TaC has the same structure as HfC but exhibits the opposite behavior.

What is hafnium carbide used for?
Hafnium carbide is an excellent material for rockets. It can also be used for ceramics, other industries and as the nose of space rockets which re-enter our atmosphere.

How powerful is hafnium carbide?
W-based or Mo-based alloys that are dispersed with Hafnium Carbide exhibit superior tensile strength and stress rupture properties to those without the HfC. MoHfC is stronger than WHfC at 1400K pressure, based on density compensation.
Hafnium carbide has a density 12.7g/cm3 as well as a melting temp of 3890degC. It is the most melting point known among single compounds. Volume resistivity of hafnium carbide is 1.95×10-4O*cm (2990) and thermal expansion coefficient 6.73×10-6/. In general, hafnium (HfO2) is combined with carbon to create powders in an inert environment. The reaction temperature for hafnium carburide is between 1900 and 2300°C. It can form a solution solid with many compounds, such as ZrC or TaC. It is characterized by a high melting temperature and high elastic co-efficient, as well as good thermal and electrical conductivity.

Is hafnium carbide poisonous?
In studies on animals, the intraperitoneal routes of trichlorooxidation were toxic. No industrial poisoning has been reported. Carbide : Pure carbon is very low in toxicity for humans. It may be processed into graphite and charcoal, or it can even be safely consumed.
Why does hafnium carburide have a melting point so high?
Hafnium carburide is resistant to corrosion as it forms an oxide layer on the surface. According to a report from “Chemical World”, among the three-element compounds, the mixed carbide of tungsten and hafnium has the highest melting point of any known compound at 7,457 degrees Fahrenheit (4,125 degrees Celsius).

Introduction to Hafnium-What is Hafnium?
In nature, hafnium often co-exists with zirconium, and zirconium-containing minerals contain hafnium. Hafnium and zirconium are similar in nature, and hafnium is mainly found in zircon. The amount of HfO2 in zircon used in industry is 0.5-2%. The beryllium zircon in secondary zirconium ore can contain up to 15% HfO2. There is also a metamorphic zircon using stone, which contains more than 5% HfO2. The latter two minerals have small reserves and have not been used in the industry. Hafnium is mainly recovered in the process of producing zirconium.

The smelting of hafnium is basically the same as that of zirconium, generally divided into five steps.
The first step is the decomposition of ore. There are three methods: 1 Zircon is chlorinated to obtain (Zr, Hf)Cl4. 2 Alkaline fusion of zircon, zircon and NaOH melt at about 600 , more than 90% of (Zr, Hf) O2 is transformed into Na2 (Zr, Hf) O3, and the SiO2 becomes Na2SiO3, which is removed by water solution. Na2(Zr, Hf)O3 can be used as the original solution for the separation of zirconium and hafnium after being dissolved in HNO3. However, it contains SiO2 colloid, which makes solvent extraction and separation difficult. 3Sinter with K2SiF6, and get K2(Zr, Hf)F6 solution after water immersion. The solution can separate zirconium and hafnium by fractional crystallization.

The second step is the separation of zirconium and hafnium, which can be separated by solvent extraction with the hydrochloric acid-MIBK (methyl isobutyl ketone) system and the HNO3-TBP (tributyl phosphate) system. The technology of multi-stage fractionation using the difference in vapor pressure of HfCl4 and ZrCl4 melts under high pressure (above 20 atmospheres) has long been studied, which can eliminate the secondary chlorination process and reduce costs. However, due to the corrosion problems of (Zr, Hf)Cl4 and HCl, it is not easy to find a suitable fractionation column material, and it will also reduce the quality of ZrCl4 and HfCl4 and increase the purification cost.

The third step is the second chlorination of HfO2 to prepare crude HfCl4 for reduction. The fourth step is the purification of HfCl4 and magnesium reduction. This process is the same as the purification and reduction of ZrCl4, and the obtained semi-finished product is crude sponge hafnium. The fifth step is vacuum distillation of crude sponge hafnium to remove MgCl2 and recover excess metal magnesium. The finished product is sponge metal hafnium. If the reducing agent uses sodium instead of magnesium, the fifth step is changed to water immersion.

Take extra care when removing the hafnium sponge from the crucible to avoid spontaneous combustion. Large pieces of sponge hafnium must be broken into small pieces of a certain size in order to be pressed into consumable electrodes, and then melted into ingots. Spontaneous combustion should also be prevented when broken. The further purification of sponge hafnium is the same as titanium and zirconium by the iodide thermal decomposition method. The control conditions are slightly different from those of zirconium. The small pieces of sponge hafnium around the iodination tank are kept at a temperature of 600degC, while the temperature of the hot wire in the center is 1600degC, which is higher than the 1300degC when the zirconium “crystal rod” is made. . The processing and forming of hafnium include forging, extrusion, drawing and other steps, the same as the method of processing zirconium. The main purpose of hafnium is to make control rods for nuclear reactors.
Hafnium application
Pure hafnium has plasticity, easy processing, high-temperature resistance and corrosion resistance, and is an important material in the atomic energy industry. Hafnium has a large thermal neutron capture section and is an ideal neutron absorber, which can be used as a control rod and protection device for an atomic reactor. Hafnium powder can be used as a rocket propeller. The cathode of X-ray tubes can be manufactured in the electrical industry. The alloy of hafnium can be used as the front protective layer of rocket nozzles and gliding re-entry aircraft, and the alloy of Hf-Ta can be used to make tool steel and resistance materials. Hafnium is used as an additional element in heat-resistant alloys, such as tungsten, molybdenum, and tantalum alloys. HFC can be used as cemented carbide additive due to its high hardness and melting point. The melting point of 4TaC*HfC is about 4215degC, which is the highest melting point compound known.

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