Appeal No. 95-3422
Application 07/891,132
grams of the silicon carbide-silicon nitride mixture
which was spread level; then the center was scraped out
with a flat edge scraper to provide a thin section 4 in
Fig. 1. This results in the end portions 5 having twice
the thickness of the center 4. This was then followed by
a 77.3 gram quantity of the silicon nitride powder which
was uniformly spread and leveled. The graphite mold
plate
was put in position and the tri-layered content of the
mold cavity was hot-pressed at 2,000 p.s.i. at 1,750 C forO
60 minutes.
Electrical leads were connected to the silicon
nitride-silicon carbide resistor core of the plate thus
producing an insulated heating element . . . .
On the other hand, referring to the reactor depicted in
Fig. 1, Levin teaches (Levin, col. 5, l. 17-24):
[T]he outer cylinder 12 is provided with suitable entry
ports for copper or like conduits 28 which conduct
current
for energizing graphite, “picket fence” type resistance
heaters 30 surrounding the inner reactor apparatus 10.
The resistance heaters 30 and the inner reactor apparatus
32 are separated from one another by a high temperature
resistant electrical insulator 31.
We have considered the teachings of Levin and Richerson
as a whole. We fail to see why persons having ordinary skill
in the art would have been led by the combined teachings to
insulate Levin’s energizing graphite, “picket fence” type
resistance heaters 30 from the graphite or other carbon
reactor material which forms the walls of Levin’s reactor 32
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