Effect of Particle Size on the Reaction Wave Propagation in the Combustion Synthesis of Al₂O₃‐ZrO₂‐Nb Composites

Abstract

The effect of reactant particle size on the kinetics of wave propagation in the thermite system Nb2O5+ Al2Zr + nuAl2O3 (with alumina being a diluent) was investigated. Reactants in three size ranges were utilized: fine (1–3 µm), medium (<10 µm), and coarse (10–45 µm). Particle size had an effect on the mode and velocity of the self‐propagating combustion wave. For fine particles, the combustion wave propagated in a steady‐state mode for all values of dilutions investigated (0 ≤ nu ≤ 0.8). For medium particles with nu > 0.1 and for all coarse particles, wave propagation was in the spin mode. A significantly large difference between the calculated adiabatic combustion temperatures and the measured values was observed and is attributed to large heat losses arising from very wide reaction zones. For fine particles, the temperature dependence of the wave velocity showed a discontinuity at a temperature corresponding to the formation of the eutectic in the binary ZrO2‐Al2O3. The velocity can be more than a factor of 3 higher at the same temperature, depending on the amount of the eutectic liquid. The dependence of the wave velocity on particle size (r) was found to have the form v is proportional to 1/rm with 0.5 < m < 0.8. The upper limit approximates that of m= 1.0 for diffusion‐controlled reaction kinetics, according to reported modeling studies. In all cases, regardless of the mode of wave propagation the reactions resulted in the desired products, Nb + ZrO2+ Al2O3 with a microstructure exhibiting the eutectic of the binary ZrO2‐Al2O3.

Effects of C particle size on the ignition and combustion characteristics of the SHS reaction in the 20wt.% Ni–Ti–C system

“…doi:10.1016/j.jallcom.2007.06.010 Table 1 The compositions of the investigated systems as well as corresponding weight ratio of every element of 20 wt.% Ni- Ti-C systems Sample Material composition Weight ratio of every element 1 Ni, Ti, C Ni:Ti:C = 20:64:16 2 Ni, Ti Ni:Ti = 20:64 3 Ni, C Ni:C = 20: 16 4 Ti, C Ti:C = 64:16 300 m radius. Tomasi and Munir [25] conducted an extensive study on the effect of micron-scale reactant particle size on the dynamics of wave propagation in Al 2 O 3 -ZrO-Nb composites. And they found that the burn rate (μ) is inversely proportional to particle radius (r) according to μ = (1/r m ) with 0.5 < m < 0.8 [25].…”

“…Tomasi and Munir [25] conducted an extensive study on the effect of micron-scale reactant particle size on the dynamics of wave propagation in Al 2 O 3 -ZrO-Nb composites. And they found that the burn rate (μ) is inversely proportional to particle radius (r) according to μ = (1/r m ) with 0.5 < m < 0.8 [25]. Unfortunately, effects of C particle size on the kinetics of SHS reaction, the phase constituents and microstructure of final SHS products in the Ni-Ti-C system are rarely studied.…”

Kinetics of Heterogeneous Self-Propagating High-Temperature Reactions

“…Because of the relative simplicity in using these techniques, they have found widespread use within SHS reactions. These layer velocity approaches have been used to describe the kinetics in the Ni/Al system [69,70], in boride systems, including Nb/B [71][72][73], Ta/B [71], Zr/B [71,74,75], Hf/B [71], Ti/B [76], Mo/B [77], along with other binary systems such as Ti/C [78], Ti/Si [79,80], thermites [81][82][83][84][85][86][87][88][89] and more complex ternary systems [78,[90][91][92][93].…”

Effect of Reactant Particle Size on the Self-Propagating High-Temperature Synthesis Reaction Behaviors in the Ni-Ti-B4C System

“…In addition to the composition of reactants, material parameters such as particle size and packing also play an important role in the SHS reaction behaviors, which have been studied in many research papers. [17][18][19] Therefore, it can be assumed that the reactant powder particle size can influence the SHS reaction behaviors in the Ni-Ti-B 4 C system greatly. Knowledge of the parameters that can control the reaction behaviors, the resultant phases and their microstructure, and a quick estimation of those are practically very useful in the optimization of both the composites' processing technology and their mechanical properties.…”