FORMATION OF ALUMINIUM TITANATE

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FORMATION OF ALUMINIUM TITANATE

H. Hennicke, W. Lingenberg

To cite this version:

H. Hennicke, W. Lingenberg. FORMATION OF ALUMINIUM TITANATE. Journal de Physique

Colloques, 1986, 47 (C1), pp.C1-533-C1-536. �10.1051/jphyscol:1986180�. �jpa-00225611�

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JOURNAL D E PHYSIQUE

Colloque C1, suppl6ment au n 0 2 , Tame 47, f6vrier 1986 page c1-533

FORMATION OF ALUMINIUM TITANATE

H.W. HENNICKE and W. LINGENBERG

Institut fiir Nichtmetallische Werkstoffe der Technischen Universitgt Clausthal, Zehntnerstrasse 2a,

0-3392 Clausthal-Zellerfeld, F.R.G.

Resume

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La formation de A12TiO5 se fait en deux &tapes de vi- tesse de rgaction dif ferentes;

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La phase de germination qui ne cause que des effets thermi

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ques et volum6triques limit&s, a lieu entre 1230 OC et 1280°C

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La psriode de croissance qui est d&terminee par une crois

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sance des grains importante, commence au dessus de 1280 OC.

Les taux de reaction les plus &levEs peuvent Gtre observ&s entre 1300°C et 1400°C.

Abstract

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The formation of Aluminium Titanate takes place in two steps of different reaction rates:

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The nucleation phase, which causes only little thermic and volumetric effects, occurs between 1230/1240 OC and 1280 OC.

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The growth period, that is accompanied by a strong grain growth, starts above 1280 OC.

The highest reaction rates are observed between 1300 OC and 1400 OC.

I

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INTRODUCTION

Aluminium Titanate (A12Ti0 ; Tielite) is a compound formed by one mole of A1203 and T i 0 2 . Since ?t has a low thermal expansion, an excellent thermal shock resistance and a low thermal conductivity, it is of high technical interest.

Therefore Aluminium Titante is being tested as an insulating material in engines for portliner, piston bottom and turbo charger.

I1

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EXPERIMENTAL METHODS

1 1 equimolar mixtures of Ti0 and A1 0 (purity 2 99 %) with different specific surfaces ( S

,

see ?igures)2aad mineral contents were investigated by DTA, diyatometric and microstructural analyses in the temperature range from 1200 OC up to 1400 OC.

The contents of Tielite, Corundum and Rutile were determined by X-ray.

The specific surface was investigated by gas adsorbtion.

To investigate the sintering behaviour of the specimens, a Laser dila- tometer / I / was used, which measures their absolute lengths.

All samples (except of those for the DTA) were about 8 mm in diameter.

The given temperatures correspond to the surface temperatures.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986180

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JOURNAL DE PHYSIQUE

111

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LITERATURE SURVEY

By rapid heating Kato et a1 121 detected small amounts of Tielite in specimens by X-ray analysis, being held at 1250 OC for 1 min. If the soaking time was increased, Tielite disappeared forming Corundum and Rutile. This appears to be a metastable nucleation process.

Their results implied the equilibrium temperature to be 1280

+

^{1 OC.}

In a further study 131, using mixed aluminium and titanium sulfates as raw materials, they demonstrated, that the formation is dependent on the calcination temperature. Mixtures being calcinated at 800 OC showed a strong formation above 1260 OC.

Kim and Hummel /4/ found the equilibrium temperature at 1237 -1- 10 OC.

By thermodynamic means 151, the formation of Aluminium Titanate should be possible over the whole temperature range from 20 OC to 1860 OC

(fig. 1 ) .

T' T

" Temp.

fig. 1: Gibbs Energy for the fig. 2: Used way to differentiate formation of Tielite as a the dilatometric curves

function of temperature

IV

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^RESULTS

As the theoretical density of Tielite is about 10 % less than that of Corundum/Rutile mixtures, the formation can be easily seen by dilatometric investigations.

The dilatometric curves

( ?

= const) were differentiated by calculating the average slope as f(T) of nine neighboured points (see fig. 2).

Fig. 3 a and b shows pl'otts of two equimolar mixtures with different specific surfaces.

Below 1230 OC the sintering rate increases with increasing temperature.

Then a beginning reaction is indicated. This reaction seems to be de- vided into two parts; i. e. 1230 OC to 1280 OC and 1280 OC to 1360 OC.

Even the DTA

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curves (fig. 4 ) show these two parts of the reaction, but shift to higher temperatures because of higher heating rates

(T = 10 K/min and 2 Klmin respectively).

With X-ray analysis Tielite can be determined above 1275 OC. With increasing temperature Corundum and Rutile disappear quickly forming Tielite (fig. 5).

During the reaction, grain growth appears, being strongest above 1280 OC (Fig. 6).

At 1260 OC after two hours annealing .time nuclei of Tielite are found on both surfaces of Corundum (smaller crystals) and Rutile crystals with a SEM (fig. 7).

As the nuclei are not located on contact areas of the two crystal types but on free surfaces, evaporation/condensation or surface diffusion must have taken place.

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fig. 3: Sinteringlreaction behaviour of two equimolar CorundumIRutile mixtures with different specific surfaces S

('f

= 2 K/rnin)

(Slope of diJatometric curve vs temperaturey

a. Sv = 73 m Ig b. Sv = 7.5 m /g

fig. 4: Typical DTA-curve of R~tileICorundum mixtures

(T = 10 Klmin, S v = 5.2 m Ig)

10.

30

20 ..

4- tielite

-P rutile

'-0- corundum

YO

10 h

-50 -60 Q70 080 nS0

TI "c

fig. 5: Mineral contents of Rutile/Corundum bodies as a function of temperatyre (ta = 2h, S v = 8.3 m /g)

V

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DISCUSSION

The results imply, that the formation of Aluminium Titanate is de- vided into two phases:

1. The nucleation period between 1230 OC and approximately 1280 OC

2 . The growth period, that begins above 1280 OC.

The formation rate has its maximum between 1300 OC and 1400 O C depen- ding on the reactivity of the used powders and the heating rate.

As the nucleation process starts on free surfaces of Corundum and Rutile crystals, the transport path must be the atmosphere or the sur-

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C1-536 JOURNAL DE PHYSIQUE

f a c e s . S i n c e on R u t i l e c r y s t a l s a r e a s much n u c l e i t o b e s e e n a s on Corundum s u r f a c e s a n d t h e e v a p o r a t i o n p r e s s u r e o f b o t h o x i d e s i s l o w , s u r f a c e d i f f u s i o n i s t h e m o s t p r o b a b l e mechanism.

f i g . 6 : G r a i n g r o w t h d u r i n g t h e r e a c t i o n

a . T = 1 2 5 0 ^{O C} b. T = 1270 ^{O C} c . T = 1290 ^{O C}

f i g . 7 : a . T i e l i t e n u c l e i b . T i e l i t e n u c l e i

( T = 1260 O C , ta = 2 h ) ( m a g n i f i c a t i o n o f f i g . 7 a . )

REFERENCES

/ I / B i n k e r t , B. a n d H e n n i c k e , H. W. c f i / B e r . D t . Ker. Ges 59 ( 1 9 8 2 ) 365 / 2 / K a t o , E . , Daimon, K. a n d T a k a h a s h i , J. _Arner

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Kate,

155 E . , Dairnon, K. a n d Harnano, K. R e p t . Res. Lab. Eng. Mat.

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( 1 9 8 4 ) 7'5

/ 4 / K i m , K . H . a n d G l a s s e r , F. A. T r a n s . B r i t . Ceram. Soc.

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( 1 9 6 8 ) 581 / 5 / B a r i n , 0. a n d Knacke, H. T h e r m o c h e m i c a l P r o p e r t i e s o f I n o r g a n i c

S u b s t a n c e s S p r i n g e r V e r l a g ( 1 9 7 3 ) 3 2 , 4 2 , 7 8 6 , 787