Transpiration Cooled Porous Type Vi Silica Rocket Windows
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TRANSPIRATION COOLED POROUS TYPE VI SILICA ROCKET WINDOWS ALBERT G FOSMOE II AND LARRY L. HENCH Advanced Materials Research Center, Progress Blvd., #14, Alachua, Fl 32615
University
of Florida,
One
ABSTRACT A novel use of sol-gel derived porous Type VI silica for high performance rocket guidance system windows is evaluated. The samples produced for this study were optically transparent hydrofluoric and/or nitric acid catalyzed tetramethylorthosilicate (TMOS) xerogel monoliths with average pore radii of 1.2, 5.0, and 8.Onm. Maximum He transpiration velocities of up to 3 cm/sec, 3 times the velocity needed for transpiration cooling, are measured for a 5.0 nm sample at 3.2 MPa. Transpiration velocities of 0.6 cm/sec result in cooling effects as large as 44 0 C from 0 160 C.
INTRODUCTION The sol-gel method provides many unique possibilities in the design of modern optical materials not available by the traditional melt methods[1-3]. Of interest here is the ultraporous structure of Type VI silica, an intermediate product of Type V fully dense gel-silica[3] . Recent advances at the Advanced Materials Research Center (AMRC) in the development of sol-gel technology has made possible the reliable production of Type VI ultra-pure silica monoliths with a wide controllable range of porosity and pore morphology[4-6]. This porosity may potentially be used and modified advantageously for rocket window applications. Specifically, the transpiration of gases through the interconnecting permeable structure should provide a significant cooling effect, thus increasing the working performance of hypersonic (mach > 5) rocket guidance system windows. The properties needed in the severe operating conditions of optically transmitting rocket windows include: structural strength, high temperature stability, thermal shock resistance, and broad band optical transmission over wide temperature ranges. Previous work in this area by the authors concentrated on the first steps in proving the conceptsCl]. These steps included the demonstration of UV transmission at elevated temperatures and determination that transpiration flow is possible through optically transparent monoliths. UV transmission was qualitatively shown to exist at temperatures >1000 0 C. Transpiration data was also presented, however, velocities were incorrectly reported low by a factor of ten. It is the intent of this work to evaluate samples with average pore radius in the low mesopore range, approximately 5 nm, in an attempt to increase transpiration velocities to well above the approximately 1 cm/sec needed for transpiration cooling[7] . Cooling effects resulting from He transpiration will also be explored.
Mat. Res. Soc. Symp. Proc. Vol. 180. @1990 Materials Research Society
844
The shock wave preceding a rocket under high mach conditions involves an intense thermal boundary next to the exterior surface an optical exterior surface is If this of the rocket[8] . transmission window with a temperature dependant bandpass, the conductive heat increased temperature resulting
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