12007-35-1Relevant articles and documents
Bulk monolithic zirconium and tantalum diborides by reactive and non-reactive spark plasma sintering
Licheri, Roberta,Musa, Clara,Orrù, Roberto,Cao, Giacomo,Sciti, Diletta,Silvestroni, Laura
, p. 351 - 359 (2016)
Monolithic ZrB2 and TaB2 were produced starting from the precursors through Self-propagating High temperature Synthesis followed by Spark Plasma Sintering (SHS-SPS) and by means of Reactive Spark Plasma Sintering (RSPS). Both methods enabled to achieve almost fully dense ceramics with mean grain size typical of pure bulks. ZrB2 materials displayed significant differences in the final mean grain size of the products obtained by the two routes, while a satisfactory homogeneity was reached in both cases. This was confirmed by good mechanical strength values, about 400 MPa at room temperature, basically maintained up to 1200°C. On the other hand, TaB2 sintered materials were quite diverse, in particular TaB2/RSPS showed a dual distribution of mean grain size, along with an almost no residual porosity, whilst TaB2/SHS-SPS had more homogeneous grain size distribution and diffused trapped porosity which corrupted the mechanical and oxidation performances.
Solution-based synthesis of submicrometer ZrB2 and ZrB 2-TaB2
Xie, Yanli,Sanders Jr., Thomas H.,Speyer, Robert F.
, p. 1469 - 1474 (2008)
Zirconium diboride and a zirconium diboride/tantalum diboride mixture were synthesized by solution-based processing. Zirconium n-propoxide was refluxed with 2,4-pentanedione to form zirconium diketonate. This compound hydrolyzed in a controllable fashion to form a zirconia precursor. Boria and carbon precursors were formed via solution additions of phenol-formaldehyde and boric acid, respectively. Tantalum oxide precursors were formed similarly as zirconia precursors, in which tantalum ethoxide was used. Solutions were concentrated, dried, pyrolyzed (800°-1100°C, 2 h, flowing argon), and exposed to carbothermal reduction heat treatments (1150°-1800°C, 2 h, flowing argon). Spherical particles of 200-600 nm for pure ZrB2 and ZrB 2-TaB2 mixtures were formed.
Superhard Tungsten Diboride-Based Solid Solutions
Pangilinan, Lisa E.,Turner, Christopher L.,Akopov, Georgiy,Anderson, Mackenzie,Mohammadi, Reza,Kaner, Richard B.
, p. 15305 - 15313 (2018)
Solid solutions of tungsten diboride (WB2) with increasing substitution of tungsten (W) by tantalum (Ta) and niobium (Nb) - ranging from 0 to 50 at. % on a metals basis - were synthesized through resistive arc melting. Samples were characterized using a combination of powder X-ray diffraction (PXRD) for phase identification, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy for elemental composition, Vickers microindentation for hardness measurements, and thermogravimetric analysis for thermal stability. The solubility limit was found to be less than 8 at. % for Nb and less than 10 at. % for Ta, as determined by PXRD. Vickers hardness (Hv) values were measured to be 40.3 ± 1.6 and 41.0 ± 1.2 GPa at 0.49 N for 6 at. % Nb and for 8 at. % Ta substitution, respectively. In addition, the hardest solid solution (W0.92Ta0.08B2) showed oxidation resistance up to ～570 °C, approximately 70 °C higher than that of tungsten carbide (WC). Although pure WB2 is known not to be superhard, these results demonstrate the formation of superhard solid solutions through the substitution of tungsten by small amounts of transition metals. This increase in hardness can be attributed to solid solution hardening.
The unexpected formation of MB2 layers (M = refractory metal) on metal surfaces
Friedhoff, Wibke,Milke, Edgar,Binnewies, Michael
, p. 3398 - 3402 (2011)
The reactions between refractory metals (Ti, Zr, V, Nb, Ta, Mo, W) and BCl3 vapour at high temperatures have been studied. For this purpose, the metal wires were heated up by an electrical current in a BCl3 atmosphere for a couple of hours. Optical and X-ray diffraction methods were used to analyze the solid products, whereas mass spectrometry was used to study the gas phase composition. In the reactions with Ti, Zr, V, Nb and Ta, we observed the formation of MB2 layers on the metal surfaces. Molybdenum reacted with formation of MoB, with tungsten no reaction was observed at all. This is contrary to the thermodynamic expectations. The mechanism of the coating process is discussed from a thermodynamic viewpoint. In the course of reactions between refractory metals (Ti, Zr, V, Nb, Ta) with boron(III) chloride at temperatures of about 1500 K, layers of the diborides of these metals are formed. The coexistence of the refractory metal with its diboride is impossible from a thermodynamic viewpoint. The formation of metal diborides in the presence of the metal is discussed. Copyright
A convenient inorganic solvent thermal route to nanocrystalline tantalum diboride
Ma, Jianhua,Du, Yihong
, p. 510 - 511 (2008)
Nanocrystalline TaB2 has been prepared via a simple inorganic solvent thermal route by the reaction of metallic magnesium powders with tantalum pentoxide and boric acid in an autoclave at 650°C. X-ray powder diffraction patterns indicate that the product was hexagonal tantalum diboride. Scanning electron microscopy images show that it consisted of particles with an average size of about 40 nm. The product was also studied by BET and TGA. Copyright
REACTION BETWEEN REFRACTORY METALS AND INSULATING NITRIDES AT HIGH TEMPERATURE
SATA T,URANO T
, p. 21 - 29 (2008/10/08)
Some nitrides, BN, AIN and Si//3N//4, are used as electric insulators up to moderate temperatures. The difficult problems occur when they are to be employed at higher temperatures than 2000 C. In this paper the reactions between these insulators and conductors of refractory metals, tungsten and tantalum, are investigated up to 2100 C in a tungsten furnace under argon atmosphere.
