Niobium diboride

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Niobium diboride (NbB2) is a highly covalent refractory ceramic material with a hexagonal crystal structure.

Contents

Niobium diboride
Magnesium-diboride-3D-balls.png
Names
IUPAC name
niobium diboride
Systematic IUPAC name
boron; niobium
Other names
NbB2
Identifiers
3D model (JSmol)
ChemSpider
EC Number
PubChem CID
  • InChI=1S/2B.Nb
    Key: WCJIBJJSTRKWNY-UHFFFAOYSA-N
  • [B].[B].[Nb]
Properties
NbB2
Molar mass 114.526 g/mol
Appearancegrey powder
Density 6.97 g/cm3
Melting point ~3050°C
Boiling point N/A
Insoluble
Structure
Hexagonal, hP3 a = 3.085 Å, c = 3.311 Å and c/a = 1.071 Å
P6/mmm, No. 191
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
Uninvestigated
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Preparation

NbB2 can be synthesized by stoichiometric reaction between constituent elements, in this case Nb and B. This reaction provides for precise stoichiometric control of the materials. [2] Reduction of Nb2O5 (or NbO2) to niobium diboride can also be achieved via metallothermic reduction. Inexpensive precursor materials are used and reacted according to the reaction below:

Nb2O5 + 2 B2O3 + 11 Mg → 2 NbB2 + 11 MgO

Mg is used as a reactant in order to allow for acid leaching of unwanted oxide products. Stoichiometric excesses of Mg and B2O3 are often required during metallothermic reductions in order to consume all available niobium oxide.

Borothermal reduction of NbO2 with elemental boron via solid‐state reaction was proposed by Jha and coworker to obtain nanorods (40 × 800 nm2), [3]

A variation of the borothermal reduction in molten salt was proposed by Ran and co‐worker using Nb2O5 with elemental boron to produce nanocrystals (61 nm). [4]

Nanocrystals of NbB2 were successfully synthesized by Zoli's reaction, a reduction of Nb2O5 with NaBH4 using a molar ratio M:B of 1:4 at 700 °C for 30 min under argon flow. [5]

Nb2O5 + 13/2 NaBH4 → 2 NbB2 + 4Na(g,l) + 5/2 NaBO2 + 13 H2(g)

Properties and use

NbB2 is an ultra high temperature ceramic (UHTC) with a melting point of 3050 °C. [6] This along with its relatively low density of ~6.97 g/cm3 and good high temperature strength makes it a candidate for high temperature aerospace applications such as hypersonic flight or rocket propulsion systems. It is an unusual ceramic, having relatively high thermal and electrical conductivities (Electrical resistivity of 25.7 μΩ⋅cm, CTE of 7.7⋅10−6/°C), properties it shares with isostructural titanium diboride, zirconium diboride, hafnium diboride and tantalum diboride. [7]

NbB2 parts are usually hot pressed [8] or spark plasma sintering [9] (mechanical pressure applied to the heated powder) and then machined to shape. Sintering of NbB2 is hindered by the material's covalent nature and presence of surface oxides which increase grain coarsening before densification during sintering. Pressureless sintering of NbB2 is possible with sintering additives such as boron carbide and carbon which react with the surface oxides to increase the driving force for sintering but mechanical properties are degraded compared to hot pressed NbB2.

Related Research Articles

<span class="mw-page-title-main">Magnesium diboride</span> Chemical compound

Magnesium diboride is the inorganic compound with the formula MgB2. It is a dark gray, water-insoluble solid. The compound has attracted attention because it becomes superconducting at 39 K (−234 °C). In terms of its composition, MgB2 differs strikingly from most low-temperature superconductors, which feature mainly transition metals. Its superconducting mechanism is primarily described by BCS theory.

<span class="mw-page-title-main">Titanium diboride</span> Chemical compound

Titanium diboride (TiB2) is an extremely hard ceramic which has excellent heat conductivity, oxidation stability and wear resistance. TiB2 is also a reasonable electrical conductor, so it can be used as a cathode material in aluminium smelting and can be shaped by electrical discharge machining.

<span class="mw-page-title-main">Superhard material</span> Material with Vickers hardness exceeding 40 gigapascals

A superhard material is a material with a hardness value exceeding 40 gigapascals (GPa) when measured by the Vickers hardness test. They are virtually incompressible solids with high electron density and high bond covalency. As a result of their unique properties, these materials are of great interest in many industrial areas including, but not limited to, abrasives, polishing and cutting tools, disc brakes, and wear-resistant and protective coatings.

<span class="mw-page-title-main">Hafnium diboride</span> Chemical compound

Hafnium diboride is a type of ceramic composed of hafnium and boron that belongs to the class of ultra-high temperature ceramics. It has a melting temperature of about 3250 °C. It is an unusual ceramic, having relatively high thermal and electrical conductivities, properties it shares with isostructural titanium diboride and zirconium diboride. It is a grey, metallic looking material. Hafnium diboride has a hexagonal crystal structure, a molar mass of 200.11 grams per mole, and a density of 11.2 g/cm3.

<span class="mw-page-title-main">Zirconium carbide</span> Chemical compound

Zirconium carbide (ZrC) is an extremely hard refractory ceramic material, commercially used in tool bits for cutting tools. It is usually processed by sintering.

<span class="mw-page-title-main">Boron compounds</span>

Boron compounds are compounds containing the element boron. In the most familiar compounds, boron has the formal oxidation state +3. These include oxides, sulfides, nitrides, and halides.

<span class="mw-page-title-main">Calcium hexaboride</span> Chemical compound

Calcium hexaboride (sometimes calcium boride) is a compound of calcium and boron with the chemical formula CaB6. It is an important material due to its high electrical conductivity, hardness, chemical stability, and melting point. It is a black, lustrous, chemically inert powder with a low density. It has the cubic structure typical for metal hexaborides, with octahedral units of 6 boron atoms combined with calcium atoms. CaB6 and lanthanum-doped CaB6 both show weak ferromagnetic properties, which is a remarkable fact because calcium and boron are neither magnetic, nor have inner 3d or 4f electronic shells, which are usually required for ferromagnetism.

<span class="mw-page-title-main">Rhenium diboride</span> Chemical compound

Rhenium diboride (ReB2) is a synthetic high-hardness material that was first synthesized in 1962. The compound is formed from a mixture of rhenium, noted for its resistance to high pressure, and boron, which forms short, strong covalent bonds with rhenium. It has regained popularity in recent times in hopes of finding a material that possesses hardness comparable to that of diamond.

<span class="mw-page-title-main">Boron suboxide</span> Chemical compound

Boron suboxide (chemical formula B6O) is a solid compound with a structure built of eight icosahedra at the apexes of the rhombohedral unit cell. Each icosahedron is composed of twelve boron atoms. Two oxygen atoms are located in the interstices along the [111] rhombohedral direction. Due to its short interatomic bond lengths and strongly covalent character, B6O displays a range of outstanding physical and chemical properties such as great hardness (close to that of rhenium diboride and boron nitride), low mass density, high thermal conductivity, high chemical inertness, and excellent wear resistance.

<span class="mw-page-title-main">Niobium pentoxide</span> Chemical compound

Niobium pentoxide is the inorganic compound with the formula Nb2O5. A colorless, insoluble, and fairly unreactive solid, it is the most widespread precursor for other compounds and materials containing niobium. It is predominantly used in alloying, with other specialized applications in capacitors, optical glasses, and the production of lithium niobate.

<span class="mw-page-title-main">Zirconium diboride</span> Chemical compound

Zirconium diboride (ZrB2) is a highly covalent refractory ceramic material with a hexagonal crystal structure. ZrB2 is an ultra-high temperature ceramic (UHTC) with a melting point of 3246 °C. This along with its relatively low density of ~6.09 g/cm3 (measured density may be higher due to hafnium impurities) and good high temperature strength makes it a candidate for high temperature aerospace applications such as hypersonic flight or rocket propulsion systems. It is an unusual ceramic, having relatively high thermal and electrical conductivities, properties it shares with isostructural titanium diboride and hafnium diboride.

<span class="mw-page-title-main">Niobium monoxide</span> Chemical compound

Niobium monoxide is the inorganic compound with the formula NbO. It is a grey solid with metallic conductivity.

<span class="mw-page-title-main">Niobium dioxide</span> Chemical compound

Niobium dioxide, is the chemical compound with the formula NbO2. It is a bluish-black non-stoichiometric solid with a composition range of NbO1.94-NbO2.09. It can be prepared by reducing Nb2O5 with H2 at 800–1350 °C. An alternative method is reaction of Nb2O5 with Nb powder at 1100 °C.

<span class="mw-page-title-main">Sodium metaborate</span> Chemical compound

Sodium metaborate is a chemical compound of sodium, boron, and oxygen with formula NaBO2. However, the metaborate ion is trimeric in the anhydrous solid, therefore a more correct formula is Na3B3O6 or (Na+)3[B3O6]3−. The formula can be written also as Na2O·B2O3 to highlight the relation to the main oxides of sodium and boron. The name is also applied to several hydrates whose formulas can be written NaBO2·nH2O for various values of n.

Aluminium magnesium boride or Al3Mg3B56, colloquially known as BAM, is a chemical compound of aluminium, magnesium and boron. Whereas its nominal formula is AlMgB14, the chemical composition is closer to Al0.75Mg0.75B14. It is a ceramic alloy that is highly resistive to wear and has an extremely low coefficient of sliding friction, reaching a record value of 0.04 in unlubricated and 0.02 in lubricated AlMgB14−TiB2 composites. First reported in 1970, BAM has an orthorhombic structure with four icosahedral B12 units per unit cell. This ultrahard material has a coefficient of thermal expansion comparable to that of other widely used materials such as steel and concrete.

<span class="mw-page-title-main">Tantalum boride</span>

Tantalum borides are compounds of tantalum and boron most remarkable for their extreme hardness.

<span class="mw-page-title-main">Tungsten borides</span>

Tungsten borides are compounds of tungsten and boron. Their most remarkable property is high hardness. The Vickers hardness of WB or WB2 crystals is ~20 GPa and that of WB4 is ~30 GPa for loads exceeding 3 N.

Diboride may refer to:

Ultra-high-temperature ceramics (UHTCs) are a type of refractory ceramics that can withstand extremely high temperatures without degrading, often above 2,000 °C. They also often have high thermal conductivities and are highly resistant to thermal shock, meaning they can withstand sudden and extreme changes in temperature without cracking or breaking. Chemically, they are usually borides, carbides, nitrides, and oxides of early transition metals.

Hafnium compounds are compounds containing the element hafnium (Hf). Due to the lanthanide contraction, the ionic radius of hafnium(IV) (0.78 ångström) is almost the same as that of zirconium(IV) (0.79 angstroms). Consequently, compounds of hafnium(IV) and zirconium(IV) have very similar chemical and physical properties. Hafnium and zirconium tend to occur together in nature and the similarity of their ionic radii makes their chemical separation rather difficult. Hafnium tends to form inorganic compounds in the oxidation state of +4. Halogens react with it to form hafnium tetrahalides. At higher temperatures, hafnium reacts with oxygen, nitrogen, carbon, boron, sulfur, and silicon. Some compounds of hafnium in lower oxidation states are known.

References

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  3. Jha, Menaka; Ramanujachary, Kandalam V.; Lofland, Samuel E.; Gupta, Govind; Ganguli, Ashok K. (2011-07-26). "Novel borothermal process for the synthesis of nanocrystalline oxides and borides of niobium". Dalton Transactions. 40 (31): 7879–88. doi:10.1039/c1dt10468c. ISSN   1477-9234. PMID   21743887. S2CID   45554692.
  4. Ran, Songlin; Sun, Huifeng; Wei, Ya'nan; Wang, Dewen; Zhou, Niming; Huang, Qing (2014-11-01). "Low-Temperature Synthesis of Nanocrystalline NbB2Powders by Borothermal Reduction in Molten Salt". Journal of the American Ceramic Society. 97 (11): 3384–3387. doi:10.1111/jace.13298. ISSN   1551-2916.
  5. Zoli, Luca; Galizia, Pietro; Silvestroni, Laura; Sciti, Diletta (23 January 2018). "Synthesis of group IV and V metal diboride nanocrystals via borothermal reduction with sodium borohydride". Journal of the American Ceramic Society. 101 (6): 2627–2637. doi: 10.1111/jace.15401 .
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  9. Sairam, K.; Sonber, J.K.; Murthy, T.S.R.Ch.; Subramanian, C.; Fotedar, R.K.; Hubli, R.C. (2014). "Reaction spark plasma sintering of niobium diboride". International Journal of Refractory Metals and Hard Materials. 43: 259–262. doi:10.1016/j.ijrmhm.2013.12.011.