Kyanite Mining Corporation

Kyanite Mining CorporationKyanite Mining Corporation

Mullite FormationMullite Formation

A myth or Reality?A myth or Reality?

Dilip JainDilip JainKyanite Mining CorporationKyanite Mining Corporation

Virginia, U.S.A Virginia, U.S.A

St Louis Section MeetingSt Louis Section Meetingof the American Ceramic of the American Ceramic

SocietySociety

March 29, 2007March 29, 2007


It is very well known that when ever there is a It is very well known that when ever there is a source of free silica and alumina in any refractory, source of free silica and alumina in any refractory, Mullite is formed upon heating at high temperatures. Mullite is formed upon heating at high temperatures. Generally it is believed that this can happen at as low a Generally it is believed that this can happen at as low a temperature as 1200C. It is not certain however if this temperature as 1200C. It is not certain however if this actually happens in any appreciable amounts. All actually happens in any appreciable amounts. All monolithics have source of either reactive or calcined monolithics have source of either reactive or calcined alumina, silica fume and other sources of silica and alumina, silica fume and other sources of silica and alumina in the matrix.alumina in the matrix.


Monolithics are very complex with many Monolithics are very complex with many sources of Corundum and Mullite and hence it is very sources of Corundum and Mullite and hence it is very difficult to know when and how much mullite is difficult to know when and how much mullite is being formed at any given temperature. A controlled being formed at any given temperature. A controlled study was undertaken to see when and how much study was undertaken to see when and how much mullite is actually formed. mullite is actually formed.

Several sources of alumina, silica, mullite and Several sources of alumina, silica, mullite and Kyanite were used to make mixtures that has an Kyanite were used to make mixtures that has an alumina content of about 70%. These were then alumina content of about 70%. These were then heated to a series of temperatures starting from heated to a series of temperatures starting from 1000 c and up to 1650 c in 100c increments. 1000 c and up to 1650 c in 100c increments.


After mixing with water and using 2% Norlig A After mixing with water and using 2% Norlig A binder, bars 6x1x1/4 inch were pressed then dried binder, bars 6x1x1/4 inch were pressed then dried and fired in a lab electric furnace at various and fired in a lab electric furnace at various temperatures. The rate of rise of temperature was temperatures. The rate of rise of temperature was 10c per minute and were held at the temperature for 10c per minute and were held at the temperature for one hour. After the heat treatment both XRF and one hour. After the heat treatment both XRF and XRD analysis was conducted to see when and how XRD analysis was conducted to see when and how much mullite was being formed. much mullite was being formed.

..


For the XRD a slow scan of 20For the XRD a slow scan of 20--60 degrees was 60 degrees was performed and then all the phases were identified performed and then all the phases were identified using Xpert High Score Plus software. After identifying using Xpert High Score Plus software. After identifying all the peaks, the peak height of the Mullite peak at all the peaks, the peak height of the Mullite peak at 40.87 degrees (60) and Corundum peak at 52.55 40.87 degrees (60) and Corundum peak at 52.55 degrees (48) were used to measure the peak height. degrees (48) were used to measure the peak height. These two peaks were chosen as no interference from These two peaks were chosen as no interference from any other mineral at these peaks were found. Peaks any other mineral at these peaks were found. Peaks with most intensity for both had interference with other with most intensity for both had interference with other phases. phases.


The peak height was measured using the The peak height was measured using the software and the background was subtracted from the software and the background was subtracted from the peak height and then the ratio of the Mullite to peak height and then the ratio of the Mullite to Corundum peak was calculated. This was done to more Corundum peak was calculated. This was done to more accurately determine the amount of Mullite and accurately determine the amount of Mullite and corundum present rather than the absolute intensities corundum present rather than the absolute intensities of each.of each.

Table I lists the various mix designs, Table II Table I lists the various mix designs, Table II lists the chemical analysis of various mixeslists the chemical analysis of various mixes


, , It is interesting to note that for pure alumina and It is interesting to note that for pure alumina and

silica no mullite formation was seen till a temperature silica no mullite formation was seen till a temperature of 1500c. Also even after 1650 c heat treatment, some of 1500c. Also even after 1650 c heat treatment, some corundum was present that still had not reacted with corundum was present that still had not reacted with silica to form Mullite. It is understood that presence of silica to form Mullite. It is understood that presence of impurities will lower the formation of Mullite some what impurities will lower the formation of Mullite some what but not to an appreciable amount.but not to an appreciable amount.


MixMix Table IA C90 LSB /Colloidal Silica 1140B C90 LSB / Silica Fume 971C A35-325 / Silica Fume 971D A35-325 / Colloidal Silica 1140E Micronized Kyanite / C90 LSBF Micronized Kyanite / A35-325 AluminaG Va Mullite 325M / C90 LSBHA Mulcoa 60 325m / C90 LSB

K Va Kyanite 325m


Table II

Mix Al2O3 SiO2 Fe2O3 TiO2 Alkalies

A 70 29.6 0.01 0.18 0.19

B 71.2 28.4 0.03 0.16 0.19

C 68.5 31.1 0.01 0.16 0.23

D 68.4 31.1 0.02 0.16 0.23

E 67.4 30.7 0.7 0.93 0.19

F 68.7 29.4 0.66 0.97 0.18

G 70.7 26.6 0.33 0.83 0.24

HA 70.4 28.2 0.83 1.44 0.35

K 58.6 39.3 0.66 1.11 0.19


Mullite Peak

0

5000

10000

15000

20000

25000A

5 (1

400C

)

A7

(160

0C)

B6

(150

0C)

B8

(165

0C)

C6

(150

0C)

C8

(165

0C)

D5(

140

0C)

D7

(160

0C)

E6

(150

0C)

E8

(165

0C)

F5 (1

400C

)

F7 (1

600C

)

G6

(150

0C)

G8

(165

0C)

HA

5 (1

400C

)

HA

7 (1

600C

)

Mullite Peak


Corundum Peak

0

1000

2000

3000

4000

5000

6000

7000

A5 (14

00C)

A8 (16

50C)

B6 (15

00C)

C8 (165

0C)D6 ( 1

500C)

E7 (16

00C)

F5 (14

00C)

F8 (16

50C)

G6 (150

0C)

HA7 (160

0C)

Corundum Peak


M/C Ratio

0

5

10

15

20

25

30A

5 (1

400C

)

A7

(160

0C)

B6

(150

0C)

B8

(165

0C)

C6

(150

0C)

C8

(165

0C)

D5(

140

0C)

D7

(160

0C)

E6

(150

0C)

E8

(165

0C)

F5 (1

400C

)

F7 (1

600C

)

G6

(150

0C)

G8

(165

0C)

HA

5 (1

400C

)

HA

7 (1

600C

)

M/C Ratio




, , In series A that is reactive Alumina with Colloidal In series A that is reactive Alumina with Colloidal

Silica, there is a very small amount of Mullite formation Silica, there is a very small amount of Mullite formation at 1500C. At 1650C there still is residual Corundum left at 1500C. At 1650C there still is residual Corundum left that has not reacted with silica to form Mullite.that has not reacted with silica to form Mullite.




, , In series B that is a mixture of reactive Alumina In series B that is a mixture of reactive Alumina

and silica fume, there is small amount of Mullite and silica fume, there is small amount of Mullite formation at 1500 C. Even at 1650C there still is formation at 1500 C. Even at 1650C there still is residual Corundum left that has not combined with residual Corundum left that has not combined with silica to form Mullite.silica to form Mullite.




, , In series C that is a mixture of calcined alumina In series C that is a mixture of calcined alumina

and silica fume Mullite formation starts after 1500 C. and silica fume Mullite formation starts after 1500 C. At 1650 C there still is residual Corundum that has not At 1650 C there still is residual Corundum that has not reacted with silica.reacted with silica.




, , In series D that is a mixture of calcined alumina In series D that is a mixture of calcined alumina

and colloidal silica, small amount of Mullite is formed at and colloidal silica, small amount of Mullite is formed at 1500C. At 1650 C there still is residual Corundum that 1500C. At 1650 C there still is residual Corundum that has not reacted with silica to form Mullite.has not reacted with silica to form Mullite.




, , In series E that is a mixture of Micronized In series E that is a mixture of Micronized

Kyanite and reactive Alumina, fair amount of Mullite Kyanite and reactive Alumina, fair amount of Mullite formation has taken place even at 1400C. This mixture formation has taken place even at 1400C. This mixture shows the maximum amount of Mullite formed. But at shows the maximum amount of Mullite formed. But at 1650 C still a very small amount of residual Corundum 1650 C still a very small amount of residual Corundum is left that has not reacted with silica to form Mullite.is left that has not reacted with silica to form Mullite.




, , In series F that is a mixture of Micronized In series F that is a mixture of Micronized

Kyanite and calcined Alumina, fair amount of Mullite is Kyanite and calcined Alumina, fair amount of Mullite is seen at 1400C. But even at 1650c some residual seen at 1400C. But even at 1650c some residual Corundum is left that has not reacted with silica to Corundum is left that has not reacted with silica to form Mullite.form Mullite.




, , In series G that is a mixture of VA Mullite 325m In series G that is a mixture of VA Mullite 325m

and reactive Alumina more Mullite is formed than and reactive Alumina more Mullite is formed than Mulcoa 60. This is because the silica that is released Mulcoa 60. This is because the silica that is released during conversion is very finely distributed and is during conversion is very finely distributed and is amorphous in nature and quite reactive. But even at amorphous in nature and quite reactive. But even at 1650C some residual Corundum is present that has not 1650C some residual Corundum is present that has not reacted with silica to form Mullite.reacted with silica to form Mullite.




, , In series HA that is a mixture of Mulcoa 60 325m In series HA that is a mixture of Mulcoa 60 325m

and reactive Alumina, less Mullite is formed than Va and reactive Alumina, less Mullite is formed than Va Mullite as all the silica is in a glass state and not quite Mullite as all the silica is in a glass state and not quite reactive. Even at 1650 C residual Corundum is left reactive. Even at 1650 C residual Corundum is left that has not reacted with silica to form Mullite.that has not reacted with silica to form Mullite.




, , In series K that is Kyanite 325m, Mullite In series K that is Kyanite 325m, Mullite

formation starts at about 1250 C and is complete at formation starts at about 1250 C and is complete at about 1450C. It is the lowest temperature than either about 1450C. It is the lowest temperature than either AndalusiteAndalusite or Sillimanite.or Sillimanite.




, , In this comparison, all of the series at 1500 are In this comparison, all of the series at 1500 are

compared. From this one can see the relative amounts compared. From this one can see the relative amounts of Mullite and Corundum are present in each.of Mullite and Corundum are present in each.




, , In this comparison all of the series at 1600 are In this comparison all of the series at 1600 are

shown. This shows the relative amount of Mullite and shown. This shows the relative amount of Mullite and Corundum in each.Corundum in each.




, , In this comparison all of the series at 1650 are In this comparison all of the series at 1650 are

shown. One can see the relative amounts of Mullite and shown. One can see the relative amounts of Mullite and Corundum in each.Corundum in each.




, , In this comparison all of the series with Kyanite In this comparison all of the series with Kyanite

and Mullite at 1400 are shown. One can see the and Mullite at 1400 are shown. One can see the relative amounts of Mullite and Corundum in each.relative amounts of Mullite and Corundum in each.


, , In order to see what happens to the Mullite In order to see what happens to the Mullite

formation in the presence of Cement, mixture was formation in the presence of Cement, mixture was made with 30% cement, and balance with either made with 30% cement, and balance with either alumina and silica or Micronized alumina and silica or Micronized kyanitekyanite and Alumina and Alumina was prepared and fired to 1400C.was prepared and fired to 1400C.


Table III

Kyanite Secar Reactive Silica

% 71%Alumina % Fume %

KAS 49 30 21 0SAS 0 30 49 21





It is interesting to note that there wasIt is interesting to note that there washardly any Mullite present when a hardly any Mullite present when a mixture if Secar 71 cement, silica fume mixture if Secar 71 cement, silica fume and reactive alumina was fired to 1400 c. and reactive alumina was fired to 1400 c. It shows only Anorthite and Corundum. It shows only Anorthite and Corundum. Where as a mixture of micronized Where as a mixture of micronized Kyanite, Secar 71 cement and reactive Kyanite, Secar 71 cement and reactive alumina shows Mullite, Anorthite and alumina shows Mullite, Anorthite and Corundum.Corundum.


ConclusionConclusion

1) Alumina and Silica do not begin to 1) Alumina and Silica do not begin to form Mullite at a temperature lower than form Mullite at a temperature lower than 1500c. Certainly presence of impurities 1500c. Certainly presence of impurities may change this some what but not may change this some what but not dramatically.dramatically.


Conclusion (cont.)Conclusion (cont.)

2) As to be expected Colloidal silica 2) As to be expected Colloidal silica combines with both calcined alumina and combines with both calcined alumina and reactive alumina to form Mullite at slightly reactive alumina to form Mullite at slightly lower temperature and in larger amounts lower temperature and in larger amounts than silica fume. Also as to be expected, than silica fume. Also as to be expected, Colloidal Silica and reactive alumina Colloidal Silica and reactive alumina formed more Mullite than the other two formed more Mullite than the other two combinations.combinations.



3) Free Silica in Virginia Kyanite in 3) Free Silica in Virginia Kyanite in presence of Alumina coverts to Mullite presence of Alumina coverts to Mullite readily and at a much lower temperature. readily and at a much lower temperature. This is because the excess silica that is This is because the excess silica that is ejected during conversion of Kyanite is ejected during conversion of Kyanite is amorphous in nature and is quite reactive amorphous in nature and is quite reactive similar to Andalucite. This combination similar to Andalucite. This combination produced by far the most Mullite of the produced by far the most Mullite of the series.series.



4) Virginia Mullite combines with Alumina 4) Virginia Mullite combines with Alumina to form Mullite more readily than Mulcoa to form Mullite more readily than Mulcoa 60. This is because Virginia Mullite does 60. This is because Virginia Mullite does not have any glass phase. All excess silica not have any glass phase. All excess silica is in the form of Quartz, Cristobalite and is in the form of Quartz, Cristobalite and amorphous silica that is finely distributed amorphous silica that is finely distributed and is more reactive than Silica in glass.and is more reactive than Silica in glass.



5) It is clear that presence of finer 5) It is clear that presence of finer Kyanite and Alumina in the matrix will Kyanite and Alumina in the matrix will produce Mullite at lower temperatures produce Mullite at lower temperatures and in larger amount than other forms of and in larger amount than other forms of Alumina and Silica that is beneficial.Alumina and Silica that is beneficial.



6) A separate study has shown that part 6) A separate study has shown that part of the silica fume and alumina can be of the silica fume and alumina can be replaced with micronized Kyanite that will replaced with micronized Kyanite that will enhance Mullite formation at lower enhance Mullite formation at lower temperature and provide better hot temperature and provide better hot properties.properties.



7) Virginia Kyanite converts to Mullite in a 7) Virginia Kyanite converts to Mullite in a very narrow range of 1250 c to 1450 c, a very narrow range of 1250 c to 1450 c, a temperature much lower than either temperature much lower than either Andalucite or Sillimanite.Andalucite or Sillimanite.

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