Infiltration-mediated Combustion Research Articles

Theoretical and experimental study of cellular structures in restricted filtration combustion of porous media

Infiltration-mediated combustion of a thin porous cylinder in reactive gas was studied by mathematical modeling. Gas reagent is infiltrated through an annular gap left of the side surface. In conditions of instability, the self-sustained propagation of individual cellular spots of exothermic combustion was observed. The structure of cellular waves, their dynamics, and travel direction are defined by such factors as temperature profile, pressure gradients, heat release rate, porous structure, and heat losses. Cellular combustion of Ti powder in dish was also explored experimentally and the results were compared with theoretical predictions.

Infiltration-mediated combustion in porous media: Propagation of cellular structures in conditions of heat losses

Investigated was nonadiabatic propagation of cellular structures in conditions of unsteady infiltration-mediated combustion in porous media. The size and structure of cellular hot spots was found to be a non-linear function of governing parameters, including heat sink into environment. Quasi-stationary dynamics of cell propagation in near-critical conditions was simulated in terms of a quasi-3D mathematical model. The evolution of cellular combustion was investigated as a function of heat losses. Experimental data for cellular combustion of Ti powders in a slit-like reactor were found to agree with predictions of the model.

Spark plasma sintering of β-SiAlON–BN composites from combustion-synthesized powders

Investigated was the spark plasma sintering (SPS) of β-SiAlON/0–30 wt % BN ceramic composites. The raw materials (β-Si5AlON7 and BN powders) were prepared by infiltration-mediated combustion synthesis (CS). Experimentally established were the following process parameters for SPS of composites with high relative density (>95%) and flexural strength of 250–300 MPa: (a) heating rate 50 deg/min, (b) maximum temperature 1650–1750°C, (c) and holding time 5 min.

Infiltration-mediated cellular combustion of Ti powder in an inclined rectangular straight-through air flow reactor: Combustion wave patterning

Explored was infiltration-mediated combustion of Ti powder in an inclined rectangular straight-through air flow reactor in conditions of natural coflow and counter flow convection in the field of gravity forces. In conditions of limited supply of gaseous reagent, a continuous combustion front was found to rearrange into more complicate modes. A distinctive feature of the process under study was the presence of inert gaseous impurities that markedly affected the process of gas exchange within the reaction zone. The results may turn useful in designing reactors and in predicting fire hazards in difficult-to-access sites.

Combustion of porous solid reagent in quasi-isobaric flow of three-component gaseous reagent

A mathematical model of two-zone infiltration-mediated combustion of a porous solid reagent (Ti) in an isobaric counterflow of three-component gaseous reagent (air) was constructed and numerically analyzed. We explored structural features, stability issues, and also the influence of inert impurity gas on the initiation and structure/stability of two-zone combustion waves. The relevant experimental results are also presented.

Unsteady infiltration-mediated combustion in conditions of regulated quasi-isobaric flow of gaseous reagent

Unsteady infiltration-mediated combustion of Ti powder in air was explored in conditions of regulated quasi-isobaric flow of gaseous reagent. Variation in the parameters/geometry of air flow was found to affect the structure of reaction zone, burning velocity, composition of combustion products, and extent of conversion.

Theory of propagation limits for infiltration-mediated combustion in the absence of external gas supply

The effect of heat losses on infiltration-mediated solid-gas SHS reaction taking place in the absence of external gas supply is analyzed theoretically. It has been demonstrated that the presence of heat sink may result in disruption of combustion reactions with complete and incomplete conversion. Determined were the upper and lower limits for propagating the waves of infiltration combustion in terms of initial gas pressure and calculated were the respective critical parameters.

Combustion synthesis and tribological properties of SiALON-based ceramic composites

β-Sialon-based composite ceramics with varied BN, TiN, TiB2, SiC, and ZrO2 contents were fabricated by infiltration-mediated combustion under high pressure of nitrogen gas. Friction and wear behavior of synthesized composites were explored as a function of their microstructure, phase/elemental composition, density, and pore size distribution.

Infiltration-mediated combustion in quasi-2D geometry: Stability of front propagation

The stability of infiltration combustion was explored by mathematical modeling under the assumption that the supply rate for gas reagent to the reaction zone is defined by the rate of chemical reaction, with account of changes in the product mass and thermophysical parameters of condensed components. Investigated were the wave structure, stability limits for steady combustion, and the loss of stability caused by 1D and 3D perturbations.

Effect of batch pelletizing on a course of SHS reactions: An overview

Such a simple technological trick as pelletizing (granulating) green powder mixtures (popular in conventional powder technology) has seldom been used in SHS technology. We have demonstrated that pelletizing green powder mixtures can markedly affect the parameters of various SHS reactions (SHS in a mode of infiltration-mediated combustion, SHS with a reduction stage, combustion of thermit mixtures, SHS in aluminum melt) and properties of their products.

Surface and layer-by-layer modes of niobium combustion in nitrogen gas: Experiment and theory

Infiltration-mediated combustion of porous Nb samples in nitrogen gas under pressures of 0.12–10 MPa was investigated by thermocouple method. Measuring the velocities of front propagation over the sample surface and along the sample axis, it turned out possible to determine the combustion front concavity inside of a sample body. Combustion with a concave front was found to occur within the pressure range 0.12–1.0 MPa while that with a planar front, in the range 1–10 MPa. Elucidated was the effect of sample melting on the phase/chemical composition of combustion products. Derived was an analytical expression for parameter SL defining a limit for deviation from the mode of planar frontal combustion: the criterion SL > 1 defines the domain of combustion with a concave front while SL < 1, the domain of planar-front combustion. Theoretical predictions were found to reasonably agree with experiment.

Synthesis of silicon oxynitride by infiltration-mediated combustion

Silicon oxynitride Si2N2 O was synthesized from a mixture of Si, SiO2, and Si3N4 by infiltrationmediated combustion in nitrogen gas. The chemical/phase composition of product and process parameters (temperature and burning velocity) were studied upon variation in charge composition and initial pressure of gas reagent. Parameters of the reaction yielding single-phase Si2N2O have been optimized.

Dynamic modes of Ti combustion in a coflow of N2-Ar mixture

Combustion of bulk density Ti powder (containing 20 wt % TiN as a diluent) in a coflow of N2-Ar mixture was investigated upon variation in the nitrogen content of the gaseous mixture. The obtained data are believed to open up new horizons for fabrication of layered and composite ceramics by infiltration-mediated combustion.

Spinning waves of infiltration-mediated combustion

Infiltration-mediated combustion of powder compact with gas reagent was mathematically modeled in 3D formulation. The parameters of spinning waves were obtained as a function of ambient gas reactant pressure. At low gas pressures, combustion was found to propagate over the sample surface in the form of steady waves. At higher gas pressures, the onset of spinning waves was observed. With increasing gas pressure, parameters of these waves were found to change non-monotonically, a hot spot with a maximal temperature being inside the sample body. The results of modeling were found to qualitatively agree with the relevant experimental data.

Dynamic modes of infiltration-mediated combustion in a tubular reactor

In this work, we analyzed some regularities of frontal steady-state filtration combustion in moving porous media in tubular reactors. We analyzed the profiles temperature, concentration, pressure, rate of heat release, and velocity of combustion front propagation. Analysis was carried out in terms of 1D model from the moment of reaction ignition until onset of steady-state frontal regime. Special emphasis was made on the processes of front stabilization, non-uniqueness of steady-state regimes, and stable periodical regimes. Analyzed is the stability on combustion waves arising in the reactor. The results can be expected to extend the applicability range for the theory of filtration combustion.

Two-dimensional model of infiltration-mediated combustion: Effect of heat losses

A two-dimensional (2D) model of infiltration-mediated combustion in a porous sample with all boundaries closed to gas penetration except for one open to exchange with a large bath of gas is considered. Numerical analysis with account of heat losses through the side surface has shown that the profile of gas pressure is substantially two-dimensional. Due to heat losses, the transversal gas flow begins to occur from a cold wall (where there is no reaction and gas consumption) to the sample center (where gas is deficient). As a result, the distribution of conversion degree over sample cross sections exhibits a maximum near the side surface, which reasonably agrees with the experimental data obtained for combustion of tantalum powder in nitrogen gas in quartz tubes.