Synthesis, Sintering, and Oxidative Behavior of HfB₂–HfSi₂ Ceramics

Abstract

The self-propagating high-temperature synthesis (SHS) of (1 − x)HfB 2 −xHfSi 2 (x from 0 to 1) ceramics is successfully performed in this work starting from elemental reactants. The presence of HfSi 2 in the composite system progressively reduces the exothermic character of the synthesis reaction. Bulk ceramics are then obtained after consolidation by spark plasma sintering (SPS) of the SHS crashed products. It is found that the HfB 2 −xHfSi 2 composite powders synthesized in a single step by SHS require milder sintering conditions as compared to the mixtures consisting of the ceramic constituents obtained separately by the same route. In addition, 15 vol % is the minimum percentage of HfSi 2 required to achieve the complete densification of the starting powders, under the SPS conditions investigated in the present work (I = 1350 A, P = 50 MPa, 30 min total time). Thermogravimetric analysis experiments performed in air flow up to 1450 °C clearly indicate that the introduction of HfSi 2 plays a beneficial role for protecting the obtained material from oxidation.

Titanium diboride ceramics for solar thermal absorbers

“…More specifically, the Rietveld analysis provided that the relative amount of TiB2 in the SHS-obtained product was above 96 wt.%. As recently reported in the literature to justify the presence of unreacted Hf and Zr, respectively, in HfB2 [59] and ZrB2 [58] ceramics obtained by SHS, the formation of TiB is likely due to some deficiency of B in the reaction environment. This could be caused by some expulsion of the latter reactant during the evolution of the SHS reaction and/or by their partial consumption to reduce some oxides often present on the starting powders surface.…”

“…The present investigation is first aimed to the optimization of the SPS conditions for the full densification of additive free TiB2 powders synthesized by SHS. In this regard, it should be noted that the combination of the SHS and the SPS techniques was recently exploited for the fabrication of other UHTC systems, both in monolithic [11,53,54] and composite forms [55][56][57][58][59].…”

“…Indeed, the only literature source is limited to the spectral range from 0.4 to 1.0μm and is referred to thin films [52].The present investigation is first aimed to the optimization of the SPS conditions for the full densification of additive free TiB2 powders synthesized by SHS. In this regard, it should be noted that the combination of the SHS and the SPS techniques was recently exploited for the fabrication of other UHTC systems, both in monolithic [11,53,54] and composite forms [55][56][57][58][59].Subsequently, in the present work we report on microstructure, topological characterization, and hemispherical reflectance spectra in the wavelength range 0.3-15 μm of TiB2 produced by the twosteps SHS-SPS technique, with the aim to evaluate the material potential for solar absorber applications.…”

Experimental and Theoretical Studies for Mild Steel Corrosion Inhibition in 1.0 M HCl by Two Stereoisomers of Benzothiazinone Derivatives

“…Conversely, LUMO energy (ELUMO) indicates the molecules' electron accepting ability; therefore, inhibitors with low ELUMO values have a tendency to accept electrons. The gap energy between the frontier orbitals (∆E) is another important factor in describing the molecular activity, so, when the gap energy decreases, the inhibitor efficiency is improved [42]. Khaled has investigated the adsorption of thiourea and their derivatives on iron surface in nitric acid media, and he has found that the gap energy decreases with the increase in the inhibition efficiency [43].…”

Processing Conditions Optimization for the Synthesis and Consolidation of High-Entropy Diborides

“…), also used in combination with some additives (SiC, MoSi 2 , HfSi 2 , fiber/whisker reinforcements, etc.) to improve their properties [1][2][3][6][7][8][9][10]. Binary solid solutions, such as (Zr,Ta)B 2 and (Hf,Ta)B 2 , have been also investigated [11][12][13].…”