hardness of tantalum
Understanding the mechanism of hardness enhancement in
The hardness of tungsten monoboride (WB) can be increased by adding tantalum and reaches a maximum at a doping level of 50 at.
Revealing the Unusual Rigid Boron Chain Substructure in Hard and Superconductive Tantalum Monoboride.
Poor electrical conductivity severely limits the diverse applications of high hardness materials in situations where electrical conductivities are highly desired.
A "covalent metal" TaB with metallic electrical conductivity and high hardness has been fabricated by high pressure and high-temperature method.
The bulk modulus, 302.0(4.9) GPa, and Vickers hardness, 21.3 GPa, approaches and even exceed that of traditional insulating hard materials.
Meanwhile, temperature-dependent electrical resistivity measurements show that TaB possesses metallic conductivity that rivals some widely-used conductors, and it will transform into a superconductor at Tc =7.8 K.
Contrary to common understanding, the hardness of TaB is higher than that of TaB2, which indicates that low boron concentration borides could be mechanically better than the higher boron concentration counterparts.
Compression behavior and first-principles calculations denote that the high hardness is associated with the ultra-rigid covalent boron chain substructure.
The hardness of TaB with different topologies of boron substructure shows that besides incorporating higher boron content, manipulating light element backbone configurations is also critical for higher hardness amongst transition metal borides with identical boron content.
Tantalum (Ta) - Properties
Tantalum is a chemical element with Ta as its symbol.
It belongs to group 5, periodic number 6 of the periodic table.
Its atomic number is 73.
Tantalum is a silvery metal that is soft in its pure form.
It is a strong and ductile metal and at temperatures below 150°C (302°F), this metal is quite immune to chemical attack.
It is known to be resistant to corrosion as it displays an oxide film on its surface.
This metal is rarely used as an alloying agent as it makes metals brittle with an exception of steel, in which case tantalum increases the ductility, strength, and melting point of steel.
Although quite rare, tantalum is obtained from minerals such as tantalite, columbite, and euxenite.
Tungsten, Tantalum & Titanium
High Temperature and Corrosion Resistant Alloys
Tungsten, Tantalum, and Titanium are part of a group of metals known as the refractory metals group.
These types of metals are used for their chemical and electrical properties.
Organizations depend on Tungsten and its alloys for their high strength, melting point, and high-density properties, and high temperatures.
Tungsten can be used as an additive to enhance physical properties in steel.
When used in the aerospace industry, Tungsten and its alloys are applied to blades used on jet engines.
In the automotive industry, they are applied to electronics.
And, in the military industry, Tungsten is applied to wear-resistant parts.
Additional applications extend much farther than these few.
In fact, Tungsten weights were used in Mars on a Mars Exploration Rover and Pathfinder.
Tantalum, Ta; Annealed
Categories: Metal; Nonferrous Metal; Refractory Metal; Pure Element. Material Notes: Annealed applies only to tensile and/or hardness.
Niobium is an excellent material for surface treatment of steel materials for chemical in Chemistry of Tantalum and Niobium Fluoride Compounds
Niobium was discovered in 1801 by an English chemist named Hatchett .
One year later, a Swedish chemist, Ekeberg, announced his discovery of tantalum .
Both tantalum and niobium were discovered in the form of oxides.
It took about 65 years until an effective method for the separation of tantalum and niobium was found by Marignac, in 1866 .
According to this method, a mixture of niobic and tantalic acid slurries is dissolved using anhydrous hydrofluoric acid (HF).
A stoichiometric quantity of potassium fluoride is added to the solution, yielding slightly soluble potassium fluorotantalate, K2TaF7, which precipitates from the solution.
Niobium, on the other hand, forms potassium oxyfluoroniobate, K2NbOF5·H2O, whose solubility is sufficiently high and remains dissolved.
The solubility of potassium fluorotantalate in a ~1% HF solution is about 10-12 times less than that of potassium oxyfluoroniobate.
Potassium fluorotantalate precipitates in the form of fine needles that can be separated from the mother solution by means of filtration, washed and dried.
This method of fractional crystallization was assumed as the basis for industrial production and was used until the middle of the 20th century, when liquid–liquid extraction processes replaced fractional crystallization .
The discovery of the process for the separation of tantalum and niobium using fluorination marked, in fact, the beginning of the development of the chemistry and technology of tantalum and niobium in general, and initiated the development of complex fluoride compound chemistry in particular.
Two main methods exist for the production of tantalum and niobium from the mineral raw material.
The first method is based on the chlorination of raw material, followed by separation and purification by distillation of tantalum and niobium in the form of pentachlorides, TaCl5, and NbCl5 [24, 29].
Boiling points of tantalum and niobium pentachlorides (236°C and 248°C, respectively) are relatively low and are far enough apart to enable separation by distillation.
Two types of chlorination processes are used for the different kinds of raw material.
The first process is a reductive process by which oxide-type raw materials in the form of ores or concentrates are chlorinated.
The essence of this process is the interaction with chlorine gas in the presence of coal or other related material.
The chlorination of ferroalloys (ferroniobium-tantalum) is a more economical and simple alternative .
The process is performed on a sodium chloride melt that contains iron trichloride, FeCl3.
Chlorine is passed through the melt yielding NaFeCl4, which interacts as a chlorination agent with the Fe-Nb-Ta alloy.
Chlorination of ferroalloys allows for the production of pure tantalum and niobium pentachlorides, which are used further in the production of high purity oxides and other products.
The performance of different types of chlorination processes is discussed comprehensively in overview .
It should be mentioned that carbon tetrachloride can also be applied successfully in the chlorination of rare refractory metal oxides, including tantalum oxide.
The second method of tantalum and niobium production is related historically to Marignac's process of tantalum and niobium separation, in the form of complex fluoride compounds, and is based on the fluorination of raw material.
The modern production process consists of slightly different steps, as described below.
The raw material is digested at a high temperature, under intensive stirring, using a mixture of highly concentrated hydrofluoric acid, HF, and sulfuric acid, H2SO4.
It is also reported that the digestion can be carried out successfully using only HF acid.
The purpose of digestion is to dissolve the tantalum and niobium as complex fluoride acids.
It is obvious that all other impurities that form soluble fluoride compounds are also dissolved.
The insoluble residual part of the slurry, which usually contains fluorides of alkaline earth and rare earth elements, is separated from the solution by filtration.
After adjustment of its acidity by the addition of sulfuric acid, the filtrated solution is processed using liquid-liquid extraction.
The process of liquid-liquid extraction was developed by Ames Laboratory together with the US Bureau of Mines and has been implemented since 1957  as an alternative to Marignac's fractional crystallization method.
Use of liquid-liquid extraction provides better separation of tantalum and niobium and allowed for the development of the production of high-purity materials.
The liquid-liquid (solvent) extraction is based on the extraction of various ions into either an organic or aqueous phase according to the complexion structure.
The structure of the complexions generally depends on the solution parameters and, first and foremost, on the acidity of the aqueous solution.
At high levels of acidity, tantalum, and niobium ions extracted from the aqueous phase into the organic phase.
At the same time, most of the impurities remain in the aqueous solution.
Lower levels of acidity lead to the stripping of tantalum and niobium ions from the organic solution into the aqueous phase.
The separation of tantalum and niobium is carried out utilizing the fact that niobium requires a higher level of acidity of the aqueous solution to pass into the organic phase and a lower level of acidity to be stripped into the aqueous solution, compared to tantalum.
Using highly acidic initial solutions originating from the digestion of the raw material, conventional technology includes collective extraction of tantalum and niobium into the organic phase, followed by scrubbing and the separation of tantalum and niobium during the stripping step.
Numerous solvents can be used in the liquid-liquid extraction of tantalum and niobium, but the most frequently used extractants are methyl isobutyl ketone (MIBK), which is the most popular extractant, tributyl phosphate (TBP), cyclohexanone and fatty alcohols (such as 2-octanol).
The products of the solvent extraction process are tantalum strip solution, niobium strip solution, and raffinate – liquid wastes containing impurities and residual acids.
Niobium hydroxide precipitates from the niobium-containing strip solution following treatment with ammonia solution.
After washing, drying, and calcinating, niobium hydroxide is converted into niobium oxide.
Tantalum oxide is produced in the same way, using a tantalum-containing strip solution.
Hydroxide precipitation and washing actually bring about the defluorination of the dissolved complex fluoride compounds to form oxide compounds by means of hydrolysis.
Another application of tantalum strip solution is in the precipitation of potassium fluorotantalate, K2TaF7, which is used as a precursor in the production of tantalum powder by sodium reduction of melts.
Very impure tantalum powder was first prepared in 1825 by Berzelius, who reduced K2TaF7 using metallic potassium.
About 40 years later, Rose produced a purer tantalum powder from Na2TaF7 using sodium as the reducing agent.
Until this day, the most applicable method of tantalum powder preparation is based on sodium reduction of melts containing potassium fluorotantalate or K-salt, as it is called commercially.
An alternative method of tantalum production is the electrolysis of alkali metal halide melts that contain K2TaF7 and periodic additions of tantalum oxide, Ta2O5.
The electrochemical reduction process was used, mainly in the US, for a long period of time, starting in 1922, for the production of tantalum metal.
In the second part of the 20th century, the tantalum capacitor industry became a major consumer of tantalum powder.
Electrochemically produced tantalum powder, which is characterized by an inconsistent dendrite structure, does not meet the requirements of the tantalum capacitor industry and thus has never been used for this purpose.
This is the reason that current production of tantalum powder is performed by sodium reduction of potassium fluorotantalate from molten systems that also contain alkali metal halides.
The development of electronics that require smaller sizes and higher capacitances drove the tantalum powder industry to the production of purer and finer powder providing a higher specific charge – CV per gram.
This trend initiated the vigorous and rapid development of a sodium reduction process.
The intensive increase in capacitor production has initiated the development of novel processes for the production of tantalum and niobium capacitor-grade powders, and the successful development of a new method, based on the reduction of tantalum or niobium oxide using magnesium vapors, was recently announced.
Nevertheless, tantalum and niobium refining technology were, and remains, a part of fluorine chemistry, since its main processes are related to the chemistry of tantalum and niobium fluorides in solid, dissolved and molten states.
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