Defect structures in zirconium diboride powder prepared by self-propagating high-temperature synthesis (original) (raw)
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Production of Zirconium Diboride Powder by Self Propagating High Temperature Synthesis
Advances in Science and Technology, 2010
In this study, the self-propagating high-temperature synthesis (SHS) and following acid leaching techniques were carried out to produce zirconium diboride (ZrB 2 ) powder. In the SHS experiments, technical grade ZrO 2 powder, and different amounts of B 2 O 3 and Mg powders were used. The SHS products were obtained in the form of black, spongy solid. In the leaching step, the effect of different acid concentrations on selective leaching was investigated by using optimum SHS product to eliminate the impurities such as MgO, Mg 3 B 2 O 6 and Mg 2 B 2 O 5 . The products obtained were characterized by using XRD, ICP and SEM techniques.
Formation of zirconium diboride–zirconium nitride composite powders by self propagating high temperature reaction of zirconium, boron and hexagonal boron nitride powders was investigated. Zirconium diboride– zirconium nitride powder mixtures with varying proportions were produced by changing the amount of boron nitride in the reactants. Products were subjected to powder X-ray diffraction analysis; and grain size and morphology was examined by scanning electron microscope. It was seen that the velocity of the wave front, adiabatic temperature of the reaction and grain size of the products decreased by increasing the boron nitride amount in the reactants. It was deduced from the scanning electron microscope examinations and crystal size calculations performed from the broadening of the peaks on the X-ray diffractions patterns that zirconium nitride grains were much finer than zirconium diboride grains.
Materials Letters, 2005
The addition of TiC (5-10 wt.%) and C (5 wt.%) was found to enhance the sinterability of SHS produced ZrB 2 powder. The densification increased to 94% of the theoretical density with the addition of carbon and TiC. The oxygen impurities normally present on the surface of this diboride powder leads to exaggerated grain-growth during sintering and hinders densification. The addition of C and TiC reduced the surface oxide layer and resulted in improved densification. Less grain-growth was also observed during sintering.
Zirconium diboride (ZrB 2) was synthesized by a solution-based technique using zirconyl chloride (ZrOCl 2 Á 8H 2 O, ZOO), boric acid (H 3 BO 3 , BA) and gum karaya (GK) as the sources of zirconium, boron and carbon, respectively. The initial formation temperature of ZrB 2 was 1200 °C and complete conversion was achieved by 1400 °C. Preceramic precursors and as-synthesized ZrB 2 powders were characterized by XRD, TG-DTA, SEM, TEM, EDX and compared with commercial ZrB 2 powder made by carbothermic reduction. FT-IR of as-synthesized dried preceramic precursor revealed the formation of Zr–O–C and Zr–O– B whereas SEM showed agglomerated spherical particles with mean diameter of o 1 mm. Commercial ZrB 2 and as-synthesized fine ZrB 2 powder were spark plasma sintered (SPS) at 1900 °C for 10 min. Addition of 10 wt% of synthesized fine powder improved the fired density from 87% to 93% of theoretical. A significant cost benefit arises for the utilization of cheap synthesized fine powder as an additive for the densification of the more expensive commercial powder.
Ceramics International
Zirconium diboride (ZrB 2 )-zirconium dioxide (ZrO 2 ) ceramic powders were prepared by comparing two different boron sources as boron oxide (B 2 O 3 ) and elemental boron (B). The production method was high-energy ball milling and subsequent annealing of powder blends containing stoichiometric amounts of ZrO 2 , B 2 O 3 /B powders in the presence of graphite as a reductant. The effects of milling duration (0, 2 and 6 h), annealing duration (6 and 12 h) and annealing temperature (1200-1400 8C) on the formation and microstructure of ceramic powders were investigated. Phase, thermal and microstructural characterizations of the milled and annealed powders were performed by X-ray diffractometer (XRD), differential scanning calorimeter (DSC) and transmission electron microscope (TEM). The formation of ZrB 2 starts after milling for 2 h and annealing at 1300 8C if B 2 O 3 is used as boron source and after milling for 2 h and annealing at 1200 8C if B is used as boron source. #
Preparation of nano-size ZrB 2 powder by self-propagating high-temperature synthesis
Preparation of nano-size ZrB 2 powder by SHS has been investigated. Zr and B elemental powders were mixed with 10–50 wt.% NaCl, and prepared pellets were reacted under argon. Adiabatic temperatures were calculated by HSC software. Increasing NaCl content led to a continuous decrease in adiabatic temperatures and reaction wave velocity. Products were subjected to XRD, SEM and FESEM analyses. Average crystallite size of ZrB 2 , which was 303 nm without NaCl, decreased to 32 nm with 40% NaCl addition. Distinct decrease in ZrB 2 particle size was also observed from SEM analyses. 30% NaCl addition was found to be optimum for ensuring a stable SHS reaction and providing the formation of nano-size ZrB 2 particles. It was revealed from particle size distribution measurements that ZrB 2 powder obtained by 30 wt.% NaCl addition contained particles mostly finer than 200 nm. A mechanism, similar to solution-precipitation was proposed for the particle size refining effect of NaCl.
2015
The synthesis of ZrB2 from elemental reactants via reactive spark plasma sintering (SPS) process is markedly affected by the heating rate conditions adopted. Specifically, when the temperature during SPS is increased at 500 °C/min or faster, the synthesis reaction proceeds under the combustion regime. On the other hand, if heating rates equal or lower than 200 °C/min are considered, the process is governed by a gradual solid-state diffusion mechanism. Although the route involving the combustion synthesis event permits the obtainment of pure dense products at relatively milder conditions, the gradual evolution of the synthesis reaction is preferable. Indeed, the inconveniences encountered during the process (gas pressure increase, powder expulsion, product inhomogeneity, abrupt sample displacement, die/punches breakage) make its practical exploitation difficult. In contrast, safety conditions are preserved when sufficiently lowering the heating rates to suppress the combustion reacti...
International Journal of Refractory Metals and Hard Materials, 2015
In this study, microstructure-densification relations were investigated for zirconium diboride ceramics. Billets of ZrB 2 were densified by hot pressing at 1700, 1775 or 1850°C for 30, 60 or 90 min under 8, 12 or 16 MPa. SEM micrographs of polished and fracture surfaces as well as density and porosity measurements were used to study the influences of hot pressing parameters (temperature, dwell time and applied pressure) on the final microstructure and densification behavior of ZrB 2. A design of experiment approach, Taguchi methodology, was used to optimize the hot pressing of ZrB 2. In this way, an L9 orthogonal array procedure, which comprises the signal to noise ratio and the analysis of variance, was employed. The significances of temperature, dwell time, pressure as well as unknown parameters, affecting the mean ZrB 2 grain size, were recognized about 56, 33, 1.5 and 9.5%, respectively. The controlling densification mechanisms were shown to vary from ZrB 2 particles rearrangement to diffusion-based mechanisms with increasing hot pressing factors. In addition, by approaching the optimal hot pressing conditions, the fracture surfaces of the samples changed from intergranular to transgranular state, dominantly.
Nanocrystalline ZrB2 powders prepared by mechanical alloying
Journal of Asian Ceramic Societies
ZrB 2 powders were synthesized by mechanical alloying (MA) of the mixture of elemental Zr and B powders using WC vial and balls. The effect of the initial composition, the milling time on MA and the phase changes during MA were investigated. Well-crystallized ZrB 2 powder with micrometer size was received by directly ball milling the Zr/B powder mixtures. Nanocrystalline ZrB 2 powders were received by adding ZrB 2 powder into the Zr/B powder mixture as a diluent to exhibit the ignition of the raw powders. The phase transformation and the morphology of the powders were characterized by XRD analysis and SEM and TEM observation.
Novel Synthesis of ZrB2 Powder Via Molten‐Salt‐Mediated Magnesiothermic Reduction
Journal of the American Ceramic Society, 2014
Zirconium diboride (ZrB2) powder was synthesized at a low temperature via a molten‐salt‐mediated reduction route using ZrO2, Na2B4O7 and Mg powders as starting raw materials. By using appropriately excessive amounts of Mg and Na2B4O7 to compensate for their evaporation losses, ZrO2 could be completely converted into ZrB2 after 3 h at 1200°C. In addition, the formation of undesirable Mg3B2O6 could be effectively avoided. As‐prepared ZrB2 powders were phase pure, 300–400 nm in size and generally well dispersed. SEM images showed that to a large extent the reactively formed ZrB2 retained the morphology and size of the starting ZrO2. The salt melt formed from MgCl2 and Na2B4O7 at test temperatures is believed to be responsible for the reduced synthesis temperature and good dispersion of the final ZrB2 product powder.