Page 16 - PR 2014 2016 10 Materials and Nanotechnology

292 Materials and Nanotechnology | Progress Report

Mullite-based coating on silicon carbide were used with different distributions sizes.
refractory These compositions were heat treated at dif-
ferent thermal cycles to determine a suitable
Silicon carbide (SiC) presents low thermal ex- condition to obtain a high mullite content. The
pansion, high strength and thermal conductiv- composition with 20% of the smaller particle
ity. For this reason, it is used as kiln furniture size Al powder was selected and used to be
for materials sintering. On the other hand, SiC applied as a suspension over SiC refractory.
degrades at high temperature under aggressive The applied suspension, after dried, crosslinked
atmosphere. The use of protective coatings and heat treated, formed a mullite coating
can avoid the right exposition of SiC surface over SiC refractory. Cycles of thermal shock
to the furnace atmosphere. Mullite can be a were performed in coated and uncoated SiC
suitable material as protective coating because samples(Figure 23) to compare each other.
of its high corrosion resistance and thermal They were carried out 26 cycles of thermal
expansion coefficient matching that of SiC (4,7 shock, in the following conditions: 600°C/30
x10-6/°C e 5,3 x10-6/°C, respectively). In the min. and air cooling to room temperature. After
present work, a mullite coating obtained from each thermal shock, samples were analyzed
ceramic precursor polymer and aluminium by mean of optical and electron microscopy
powder was studied to be applied over SiC (Figure 24), elastic modulus was also deter-
refractories. Compositions were prepared with mined. After thermal shock cycles, the coating
10, 20, 30 and 50% (vol.) of aluminium powder presented good adhesion and no significant
added to the polymer. Aluminium powders damage were observed.

Figure 23: Coated (a) and uncoated (b) SiC refractory bars.

Instituto de Pesquisas Energéticas e Nucleares