[meteorite-list] Tile Glows

[MexicoDoug]

Wow ! Nice links, James. Still aren't clear what the heat-exposed 
surface looks like on a microscopic scale after use, but it certainly 
sounds on paper like the tiles are near perfectly resistant/stable. Can 
you imagine an artificial bolide made of a sphere of this material?

My favorite size, a basketball sized-sphere of it falling from orbit 
would have the following characteristics:

1024 gram mass
59 mph (95 km/h) impact velocity
NOT TOO HOT AND NOT TOO COLD - BUT JUST RIGHT TO TOUCH!
...and apparently no ablation loss!

For comparison, a real inflated basketball, on the other hand would 
theoretically be:

650 gram initial mass
47 mph (75 km/h) impact velocity, theoretically: if it could withstand 
the atmospheric passage
but you'd end up with an exploded smelly burnt cinder instead that you 
wouldn't really want to touch ;-)
...if not complete ablation loss!

This stuff is only 57% heavier than the bulk density of an inflated 
basketball! Space Hoops, anyone ... a chance for games out of the pages 
of an Asimov, Clark or Heinlein novel for those brave enough to play 
space-catch!

Best wishes
Doug


-----Original Message-----
From: James Beauchamp <falcon99 at sbcglobal.net>
To: cdtucson at cox.net; meteoritemike at gmail.com; John at Cabassi.net; 
rickmont at earthlink.net; MexicoDoug <mexicodoug at aim.com>
Cc: Meteorite-list at meteoritecentral.com
Sent: Mon, Jun 27, 2011 7:58 am
Subject: A better link.. Re: [meteorite-list] Tile Glows


http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts_sys.html

The HRSI tiles are made of a low-density, high-purity silica 
99.8-percent amorphous fiber (fibers derived from common sand, 1 to 2 
mils thick) insulation that is made rigid by ceramic bonding. Because 
90 percent of the tile is void and the remaining 10 percent is 
material, the tile weighs approximately 9 pounds per cubic foot. A 
slurry containing fibers mixed with water is frame-cast to form soft, 
porous blocks to which a collodial silica binder solution is added. 
When it is sintered, a rigid block is produced that is cut into 
quarters and then machined to the precise dimensions required for 
individual tiles.
HRSI tiles vary in thickness from 1 inch to 5 inches. The variable 
thickness is determined by the heat load encountered during entry. 
Generally, the HRSI tiles are thicker at the forward areas of the 
orbiter and thinner toward the aft end. Except for closeout areas, 
theHRSI tiles are nominally 6- by 6-inch squares. The HRSI tiles vary 
in sizes and shapes in the closeout areas on the orbiter. The HRSI 
tiles withstand on-orbit cold soak conditions, repeated heating and 
cooling thermal shock and extreme acoustic environments (165 decibels) 
at launch.
For example, an HRSI tile taken from a 2,300 F oven can be immersed in 
cold water without damage. Surface heat dissipates so quickly that an 
uncoated tile can be held by its edges with an ungloved hand seconds 
after removal from the oven while its interior still glows red.
The HRSI tiles are coated on the top and sides with a mixture of 
powdered tetrasilicide and borosilicate glass with a liquid carrier. 
This material is sprayed on the tile to coating thicknesses of 16 to 18 
mils. The coated tiles then are placed in an oven and heated to a 
temperature of 2,300 F. This results in a black, waterproof glossy 
coating that has a surface emittance of 0.85 and a solar absorptance of 
about 0.85. After the ceramic coating heating process, the remaining 
silica fibers are treated with a silicon resin to provide bulk 
waterproofing.
Note that the tiles cannot withstand airframe load deformation; 
therefore, stress isolation is necessary between the tiles and the 
orbiter structure. This isolation is provided by a strain isolation 
pad. SIPs isolate the tiles from the orbiter's structural deflections, 
expansions and acoustic excitation, thereby preventing stress failure 
in the tiles. The SIPs are thermal isolators made of Nomex felt 
material supplied in thicknesses of 0.090, 0.115 or 0.160 inch. SIPs 
are bonded to the tiles, and the SIP and tile assembly is bonded to the 
orbiterstructure by an RTV process.
Nomex felt is a basic aramid fiber. The fibers are 2 deniers in 
fineness, 3 inches long and crimped. They are loaded into a carding 
machine that untangles the clumps of fibers and combs them to make a 
tenuous mass of lengthwise-oriented, relatively parallel fibers called 
a web. The cross-lapped web is fed into a loom, where it is lightly 
needled into a batt. Generally, two such batts are placed face-to-face 
and needled together to form felt. The felt then is subjected to a 
multineedle pass process until the desired strength is reached. The 
needled felt is calendered to stabilize at a thickness of 0.16 inch to 
0.40 inch by passing through heated rollers at selected pressures. The 
calendered material is heat-set at approximately 500 F to thermally 
stabilize the felt.
The RTV silicon adhesive is applied to the orbiter surface in a layer 
approximately 0.008 inch thick. The very thin bond line reduces weight 
and minimizes the thermal expansion at temperatures of 500 F during 
entry and temperatures below minus 170 F on orbit. The tile/SIP bond is 
cured at room temperature under pressure applied by vacuum bags.
Since the tiles thermally expand or contract very little compared to 
the orbiter structure, it is necessary to leave gaps of 25 to 65 mils 
between them to prevent tile-to-tile contact. Nomex felt material 
insulation is required in the bottom of the gap between tiles. It is 
referred to as a filler bar. The material, supplied in thicknesses 
corresponding to the SIPs', is cut into strips 0.75 inch wide and is 
bonded to the structure. The filler bar is waterproof and 
temperature-resistant up to approximately 800 F, topside exposure.
SIP introduces stress concentrations at the needled fiber bundles. This 
results in localized failure in the tile just above the RTV bond line. 
To solve this problem, the inner surface of the tile is densified to 
distribute the load more uniformly. The densification process was 
developed from a Ludox ammonia-stabilized binder. When mixed with 
silica slip particles, it becomes a cement. When mixed with water, it 
dries to a finished hard surface. A silica-tetraboride coloring agent 
is mixed with the compound for penetration identification. Several 
coats of the pigmented Ludox slip slurry are brush-painted on the 
SIP/tile bond interface and allowed to air-dry for 24 hours. A heat 
treatment and other processing are done before installation. The 
densification coating penetrates the tile to a depth of 0.125 inch, and 
the strength and stiffness of the tile and SIP system are increased by 
a factor of two.
There are two different densities of HRSI tiles. The first weighs 22 
pounds per cubic foot and is used in all areas around the nose and main 
landing gears, nose cap interface, wing leading edge, RCC/HRSI 
interface, external tank/orbiter umbilical doors, vent doors 
andvertical stabilizer leading edge. The remaining areas use tiles that 
weigh 9 pounds per cubic foot.

--- On Sun, 6/26/11, MexicoDoug <mexicodoug at aim.com> wrote:

From: MexicoDoug <mexicodoug at aim.com>
Subject: Re: [meteorite-list] Tile Glows
To: falcon99 at sbcglobal.net, cdtucson at cox.net, meteoritemike at gmail.com, 
John at Cabassi.net, rickmont at earthlink.net
Cc: Meteorite-list at meteoritecentral.com
Date: Sunday, June 26, 2011, 11:36 PM

Richard, James, very cool ... and especially being a witness of history
in the making for you guys ...

Does anyone know if these tiles show any signs of fusion (Is there
evidence of a fusion crust in this material or is is so structurally
pure and aerodynamically designed that a tile in proper service never
reaches a temperature for that to occur) as they wear out, or how
exactly material disappears as they wear out in old age (vs. a defect)?

Best wishes
Doug