Oxidation Behavior of Siliconcarbide-Based Materials by Using New Probe Techniques

Abstract

Hysteresis of passive to active and active to passive transition of SiC oxidation behavior has been investigated theoretically, numerically, and experimentally. Theoretical and experimental investigations show a strong interaction between transition and catalysis. Dependence on plasma composition is shown. A recently developed reaction model has been implemented in the advanced nonequilibrium Navier-Stokes code URANUS. Results are presented for the highly dissociated flow around the MIRKA capsule. In this case, radiation adiabatic surface temperatures have been found to be 120 K higher for active oxidation conditions as compared to passive oxidation conditions. To investigate transition behavior in detail, various new probe measurement techniques have been developed. Important additional observations have been made in chemical nonequilibrium. Within plasma wind-tunnel testing, a sudden temperature increase of up to 400 K was found with the transition from passive to active oxidation. Theoretical and numerical predictions show good qualitative and quantitative agreement with experimental results. Nomenclature= distance from plasma generator outlet plane γ = ratio of heat capacities H = reaction enthalpy δ = boundary-layer thickness ε = emissivity ρ = density = angle Subscripts amb = ambient (g) = gaseous in = related to temperature of water coming into cooling system -und Konstruktionsforschung. Member AIAA. out = related to temperature of water leaving cooling system (s) = solid tot = total W = related to wall 1 = situation before shock 2 = situation behind shock

Ultra-high-temperature testing of sintered ZrB2-based ceramic composites in atmospheric re-entry environment

“…This phenomenon has been observed by several authors for SiC-containing UHTCs and C-SiC, but a widely agreed interpretation is still lacking. The mechanisms proposed as possible triggers for the jump include transition from passive to active oxidation of silicon carbide [44, 45], triggering of catalytic recombination of nitrogen atoms due to the presence of gaseous silicon [46], formation of cracks promoting oxygen diffusion to inner SiC particles and carbon fibers, resulting in carbon exothermic oxidation and nitridation [44,47], surface modifications altering properties of the samples such as emissivity and catalycity. All these factors could lead to completely different surface heat flows even under the same test conditions (same arc power, in the present case).…”

High-enthalpy test environments, flow modeling and in situ diagnostics for characterizing ultra-high temperature ceramics

“…Hirsch et al, 52 Altman et al, 53 and Jentschke et al 54 have monitored Si atom densities in front of C/C-SiC composites exposed to nitrogen-oxygen plasma flows, using high-resolution spectroscopy of Si I multiplet emissions in the 250-253-nm range. Herdrich et al 55 observed Si emission near 252 nm and 288 nm while testing SiC specimens in oxygen-nitrogen plasmas, and also captured emission from SiO 2 molecules near 423 nm. Emission from SiO molecules was not reported in any of these studies, which is surprising given that reaction mechanism (5) should have been operating under some of the test conditions reported.…”

Exploratory numerical experiments with a macroscopic theory of interfacial interactions

“…We refer readers wishing to acquire deeper familiarity with the subject matter to the thorough surveys of methods and literature provided by Kovalev and Kolesnikov [74] and Viviani [133]. Although there are attempts [26,27,30,111,112,140] to determine ACs from quantum-mechanical, molecular-dynamics (MD) and Monte-Carlo calculations, efforts and energies (financial form included) have been invested prevalently in experimental investigations [6,7,8,15,35,54,58,65,69,70,72,82,83,100,101,102,104,117].…”