Nanorods of HfB2 from mechanically-activated HfCl4 and B-based powder mixtures

Mechanically activated solid-state synthesis of hafnium carbide and hafnium nitride nanoparticles

“…• Thermal reactions above 700 • C. From the TGA curve (Fig. 1), the excess of Mg evaporates from 700 • C and that of anhydrous MgCl 2 from 900 • C [7]. The dehydrogenation of HfH x occurs below 800 • C. Thus above 500 • C, MgCl 2 ·6H 2 O decomposition gives MgCl 2 and MgO and the powders contain further an excess of magnesium and HfH x .…”

“…1a) shows that the first step, from room temperature up to 400 • C corresponds to dehydration and decomposition of HfOCl 2 ·nH 2 O with n > 4 [25]. Then the weight losses which occur in the ranges 700-900 and 900-1100 • C correspond, respectively, to the evaporation of Mg and to that of anhydrous MgCl 2 [7,32,33]. A weak weight loss occurs between 100 and 500 • C as seen on the TGA curve of the ground powder mixture (Fig.…”

“…For instance, boron nitride nanotubes were prepared by annealing, under nitrogen, boron powders ground in NH 3 [6]. Similarly, nanorods of HfB 2 were produced by annealing of ground HfCl 4 + B powder mixtures [7] and nanosized CeO 2 particles were obtained after annealing of mechanically activated powders of cerium carbonate with sodium hydroxide [8]. Many studies are, however, based on mechanically activated exchange reactions between, for example, metallic chlorides and MOH (with M = Li or Na) which lead to nanosized monocrystalline particles embedded within a salt matrix which is further removed by washing [9], or between metallic chlorides and CaO [10] or Li 2 O [11] or between lithium and cobalt hydroxides [12].…”

Screw Dislocation Assisted Spontaneous Growth of HfB2 Tubes and Rods

“…Anisotropic growth of diborides has been encountered in several synthesis routes involving carbothermal reduction reactions. Barraud et al . obtained defect free mono‐crystalline rods of HfB 2 from mixtures of ph‐HfCl 4 + B.…”

Mechanical activation-assisted autoclave processing and sintering of HfB2-HfO2 ceramic powders

“…In an investigation on the high-energy ball milling of HfCl 4 -B-Mg powder mixtures,Barraud et al [37]. reported the reduction of partially hydrated HfCl 4 mainly to the HfH x and subsequently to the HfB 2 phase.…”