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A study on the effect of comminuting treatment of ZTA Powders
The treatment of ZTA( zirconia toughened alumina) ceramic
powders bycomminuting operations during manufacturing process is
the scope of this study.The raw material of ZTA powders is
prepared by chemical coprecipitation via-gel method. Before
calcination, ZTA powders are comminuted by tumbling mill,
vibration mill and planetary mill. The energy accumulated from
the impact andattrition actions of comminuting ZTA gel
powders to occur mechano- chemicalreaction and enhance the
sintering body. Meant me, The chips loosening fromalumina
grinding ball will become the nucleating seeds during sintering
of ZTAceramic of ZTA powders. In this study, the dry
coprecipitation gel are treated by vibrationmill and tumbling
ball mill with different grinding duration. The alumina
andzirconia grinding balls are adopted for comminution tests.
The wear of grindingball and the chips loosening from ball
surface are examined during everycomminution test. The function
of comminution treatment is evaluated by thespecific surface
area phase transformation and sintering density of finalceramic
products.The results of this study are listed as following： 1.
We discover the comminuted ZTA gel can produce mechano-chemical
reaction.The predominant phase observed in the ZTA gels are
boehmite and bayerite. Thecomminuted treatment can make ZTA
gel dehydroxyation and transformation toboehmite phase.
However, Planetary ball milling above 9.5hrs can make ZTA
gelamorphous. 2. ZTA gel powder has the phase transformation
of γ ( η ) →δ ( θ ) →α-Al2O3 during annealing treatment.
Large comminuted energy can make its crystaldestructive and
amorphous. Except the the destruction of crystal by
comminutedtreatment, high energy ball milling can prolong the
forming temperature ofmetastable phase of Al2O3 and t-ZrO2,
reduce the content metastable phase ofAl2O3,and directly
transform δ ( θ ) →α -Al2O3. The intensity of α -Al2O3is
intensive with perfect crystal. 3. BET surface area of ZTA gel
markly decreases after comminuted treatment.This phenomemon
is the result that ZTA particle aggregated each other,
BETsurface area of calcined powders are not affected.
After planetary ballmilling, has occur phase transformationand
re-dispersed, agglomerate. 4. ZTA powders with tumbling ball
milling of 12 hours duration can reduce thephase transformation
of θ -Al2O3 to α -Al2O3 to 1200 ℃. Vibrating ballmilling
of 24 hours duration and planetary ball milling 1.5 hours
duration canmake it reduce to 1100 ℃. This result appears that
planetary ball milling ofhiger comminution energy can
shorten the grinding time to cause thetransformation of
θ→α -Al2O3. However, both the energy and chips seeding
inmilling process are the main reason of affecting the transform
ation of θ→α-Al2O3. 5. The vibrating ball milling with
Al2O3 balls above 24 hrs and with ZrO2balls above 34 hrs of
the ZTA ceramic body which sintering at 1550 ℃ with 4hour
duration can obtain the relative density of final ceramic body
is measuredof 99.5 ％ T.D.
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