Solid State Chemistry: A Contemporary Overview - ACS Publications

20 Phase Equilibria Research in Portions of the System K O - M g O - F e O 3 - A l O 3 - S i O 2 Downloaded by UNIV OF CALIFORNIA SAN DIEGO on August 26, 2015 | http://pubs.acs.org Publication Date: June 1, 1980 | doi: 10.1021/ba-1970-0186.ch020

2

R O B E R T S.

2

2

ROTH

National Bureau of Standards, Washington, DC 20234

Preliminary

phase

binary

ternary

and

equilibria joins

diagrams

and

are given

cuts through

ponent system K O-MgO-Fe O3-Al O3-SiO . 2

2

2

2

for

some

the

five-com-

The

diagrams

are those that are most pertinent

to the chemical

reactions

taking

seed and

four-com-

place

between

ponent synthetic

potassium

slag of importance

a magnetohydrodynamics KAlO -SiO , 2

KFeO -SiO ,

2

2

ently true binary only kalsilite The

system. 2

3

magnesia

containing

ternary

that might be expected

appar-

are generally

not

Thus

binary.

liquidus

into

leucite

is a

temperatures

and quaternary

to exhibit

involving

at low temperatures

phase plus leucite.

even just below

cuts

of

systems

2

types of end members

a second kalsilite-like

studies the

and K M g S i O 4 - S i O 2 are

phase K M g S i O 8 dissociates

major component

in corrosion Although

joins, other pseudobinary

2

the

of

compositions

only kalsilite-like

phases.

' T p h e d e v e l o p m e n t of n e w m a t e r i a l s w i t h u s e f u l p r o p e r t i e s f o r a p p l i c a -•- tions i n the a r e a of e l e c t r o n i c c e r a m i c s , catalysts, electrolytes, elec trodes, a n d so o n is s t r o n g l y d e p e n d e n t o n a k n o w l e d g e of t h e c h e m i s t r y of m a n y u n u s u a l o x i d e systems. A better u n d e r s t a n d i n g of t h e m e c h a nisms of c o r r o s i o n , w e a r , f r a c t u r e , a n d the g e n e r a l b e h a v i o r of m a t e r i a l s u n d e r use c o n d i t i o n s of severe e n v i r o n m e n t s is also d e p e n d e n t

on

a

k n o w l e d g e of c h e m i c a l c o m p a t i b i l i t y . T h e p r e d i c t i o n of p h y s i c a l a n d c h e m i c a l p r o p e r t i e s of m a t e r i a l s is l i m i t e d b y o u r k n o w l e d g e or a b i l i t y to p r e d i c t c h e m i c a l reactions a n d g e n e r a l c r y s t a l c h e m i c a l relations.

A

d e t a i l e d e x p e r i m e n t a l s t u d y o f a f e w selected systems o f t e n enables us to p r e d i c t t h e c r y s t a l c h e m i c a l p r i n c i p l e s g o v e r n i n g the c h e m i c a l reactions i n m o r e c o m p l e x i n d u s t r i a l systems. T h i s c h a p t e r not subject P u b l i s h e d 1980

to U . S .

copyright.

American Chemical

Society

In Solid State Chemistry: A Contemporary Overview; Holt, S., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1980.

392

SOLID S T A T E

CHEMISTRY: A

CONTEMPORARY OVERVIEW

I n a s t u d y of the p h a s e e q u i l i b r i a relations of a m o d e l system, i t is a l w a y s d e s i r a b l e to p r e p a r e s i n g l e crystals of a l l the p r e v i o u s l y u n k n o w n phases to b e c e r t a i n of h a v i n g i d e n t i f i e d a l l the reactions. E v e n a k n o w l e d g e of the c r y s t a l s t r u c t u r e of m a n y of t h e phases is n e e d e d to u n d e r s t a n d t h e m e c h a n i s m s i n v o l v e d i n the c h e m i c a l reactions.

A s t u d y of

p h a s e e q u i l i b r i a , c r y s t a l g r o w t h , a n d c r y s t a l c h e m i s t r y is c u r r e n t l y b e i n g conducted

i n p o r t i o n s of the system K 0 - M g O - F e 2 0 3 - A l 0 3 - S i 0 2 2

2

to

u n d e r s t a n d t h e c h e m i c a l c o r r o s i o n of r e f r a c t o r y c o m p o n e n t s b y s e e d / s l a g Downloaded by UNIV OF CALIFORNIA SAN DIEGO on August 26, 2015 | http://pubs.acs.org Publication Date: June 1, 1980 | doi: 10.1021/ba-1970-0186.ch020

i n a c o a l - f u e l e d m a g n e t o h y d r o d y n a m i c s system. P r e v i o u s studies i n this c o m p l e x system h a v e b e e n c o n f i n e d m a i n l y to the t e r n a r y systems.

T h e m o s t i m p o r t a n t of these

(1-5)

have

been

c o n c e r n e d m a i n l y w i t h the h i g h - s i l i c a p o r t i o n s of the system because of t h e o b v i o u s g e o l o g i c a l interest. H o w e v e r , the m a i n object of the present s t u d y is to u n d e r s t a n d the r e a c t i o n b e t w e e n m o l t e n c o a l s l a g a n d p o t a s s i u m o x i d e , u s e d to e n h a n c e t h e c o n d u c t i v i t y of t h e p l a s m a i n a M H D c h a n n e l . T K e r e f o r e , o u r m a j o r interest is i n those phases i n e q u i l i b r i u m w i t h the h i g h e r K 0 c o m p o s i t i o n s a n d the m i n e r a l s k a l s i l i t e a n d l e u c i t e , 2

w h i c h h a v e the c o m p o s i t i o n s K A l S i 0

4

a n d K A l S i 0 , respectively. 2

Iron

6

a n d / o r m a g n e s i u m c o n t a i n i n g analogues also c a n b e f o r m u l a t e d . first

results

of

these

studies, i n v o l v i n g t h e

published recently (6),

join

KA10 -Si0 , 2

2

as w e l l as several abstracts ( 7 , 8 , 9 )

The were

o n other

p o r t i o n s of the system. S o m e o f the other d a t a m e n t i o n e d i n this p a p e r h a v e b e e n p r e v i o u s l y r e p o r t e d o n l y i n project reports to sponsors, i f at a l l . M u c h o f the w o r k r e p o r t e d i n t h e present p a p e r is p r e l i m i n a r y i n n a t u r e , a n d i m p o r t a n t p o r t i o n s of the phase d i a g r a m s m a y b e

changed

i n f u t u r e p u b l i c a t i o n s . A l l t h e e x p e r i m e n t a l p o i n t s are s h o w n i n the d i a g r a m s , so that the r e a d e r c a n j u d g e w h e r e f u r t h e r w o r k m a y b e n e e d e d to u n a m b i g u o u s l y u n d e r s t a n d t h e n a t u r e of the e q u i l i b r i u m reactions. A s a l l corrosion

and stability problems

i n a w o r k i n g M H D system

necessarily i n v o l v e relations w i t h the K 0 - c o n t a i n i n g c o m p o u n d 2

as seed ( s u c h as K C 0 2

3

added

a n d K S 0 ) , o n l y those p o r t i o n s of t h e system 2

4

c o n t a i n i n g K 0 are discussed. 2

Experimental A l l specimens f o r this s t u d y w e r e p r e p a r e d f r o m r e a g e n t - g r a d e m a t e r i a l s , of n o m i n a l 9 9 % p u r i t y or better. S t a r t i n g m a t e r i a l s u s e d w e r e K C 0 , a - F e 0 ( h e m a t i t e , - 0 . 5 fim), M g C 0 , y - A 1 0 ( 0.05 / i i n ) , a n d S i 0 ( q u a r t z , less t h a n 5 jum). B a t c h e s w e r e w e i g h e d to the nearest 0.01 m g , m i x e d , a n d c a l c i n e d s e v e r a l times b e f o r e final h e a t treatments. M a n y experiments were duplicated b y approaching e q u i l i b r i u m i n the s o l i d state o n l y a n d b y a n n e a l i n g a p r e m e l t e d glass. S p e c i m e n s w e r e a n n e a l e d f o r p e r i o d s v a r y i n g f r o m s e v e r a l h o u r s to s e v e r a l m o n t h s u n t i l 2

3

2

3

3

2

3

2


20.

ROTH

Phase Equilibria

393

Research

e q u i l i b r i u m w a s a c h i e v e d . M o s t specimens h e a t e d a b o v e a b o u t 9 0 0 ° C w e r e e n c l o s e d i n sealed P t tubes i n o r d e r to m i n i m i z e K 0 v o l a t i l i z a t i o n a n d g e n e r a l l y q u e n c h e d after t h e h e a t treatment. A l l specimens w e r e e x a m i n e d after e a c h h e a t t r e a t m e n t b y X - r a y p o w d e r d i f f r a c t i o n analyses u s i n g a h i g h - a n g l e diffractometer e q u i p p e d w i t h a graphite single-crystal monochromator using C u K a radiation. I n g e n e r a l , e q u i l i b r i u m w a s b e l i e v e d to h a v e b e e n a c h i e v e d w h e n f u r t h e r heat t r e a t m e n t at the same ( a n d / o r h i g h e r ) t e m p e r a t u r e s c a u s e d n o c h a n g e i n the X - r a y d i f f r a c t i o n p a t t e r n . D u e to the v e r y s l u g g i s h r a t e of r e a c t i o n i n silicate systems, specimens w e r e h e l d at t e m p e r a t u r e for m u c h l o n g e r times t h a n is c o m m o n f o r most s o l i d state c h e m i s t r y p h a s e e q u i l i b r i a experiments. F o r p r o p e r i n t e r p r e t a t i o n of the X - r a y d i f f r a c t i o n p o w d e r p a t t e r n s , i t is e x t r e m e l y i m p o r t a n t that every p e a k i n the p a t t e r n b e m a t h e m a t i c a l l y a c c o u n t e d for b y i n d e x i n g a l l the single-phase patterns. I t is not sufficient to s i m p l y assign p e a k s to a k a l s i l i t e - l i k e p h a s e w i t h o u t k n o w i n g the t r u e u n i t c e l l , as s m a l l peaks i n the p a t t e r n often m a y represent a s m a l l a m o u n t of a p r e v i o u s l y u n k n o w n s e c o n d phase. C o n s e q u e n t l y , attempts w e r e m a d e to g r o w s m a l l , single crystals, sufficient for the X - r a y d i f f r a c t i o n precession t e c h n i q u e , for e v e r y u n k n o w n p h a s e i n the system. B y a d h e r i n g to this p r i n c i p l e , w e f o u n d a n e w c o m p o u n d w i t h t e t r a g o n a l s y m m e t r y i n the K A 1 0 - S i 0 system, r e f e r r e d to as K i . A l i . S i i . 0 b y C o o k e t al. (6). M o s t of the single crystals p r e p a r e d to s t u d y these silicate systems w e r e m a d e b y H . S. P a r k e r ( J O ) , u s i n g the flux t e c h n i q u e . T h e flux u s e d w a s g e n e r a l l y either K F as i n C o o k et a l . ( 6 ) or K M o 6 w i t h or w i t h o u t a d d i t i o n s of either V 0 or K V 0 i n v a r i o u s p r o p o r t i o n s . T h e f u l l details of the c r y s t a l g r o w t h of each of the phases w i l l b e f o u n d i n later p u b l i cations. M a n y of the crystals w e r e e x a m i n e d i n a s c a n n i n g e l e c t r o n m i c r o s c o p e e q u i p p e d w i t h X - r a y d i s p e r s i v e analysis a n d a w i n d o w l e s s detector, e n a b l i n g s e m i q u a n t i t a t i v e d e t e r m i n a t i o n of elements d o w n t o a t o m i c n u m b e r 6. N e i t h e r m o l y b d e n u m [ a t o m i c n u m b e r 42] n o r fluorine [ a t o m i c n u m b e r 9] w a s f o u n d i n the crystals, a l t h o u g h a s t r o n g o x y g e n p e a k w a s a l w a y s seen w i t h the w i n d o w o p e n . T h e d e t e c t i o n l i m i t f o r fluorine w a s a b o u t 1,4 w t % F , a n d the K A l S i 0 a n d r e l a t e d c o m p o u n d s c o n t a i n e d less t h a n 0.2 u n i t s of F w h e n d e s c r i b e d as K i . A l S i 0 . . F . . H o w e v e r , i t s h o u l d b e r e m e m b e r e d t h a t i t is v e r y difficult to d e t e r m i n e F b y this t e c h n i q u e i n the p r e s e n c e of F e b e c a u s e of the o v e r l a p of t h e m a j o r peaks of the c h a r a c t e r i s t i c spectra. I n o r d e r to b e c e r t a i n t h a t t h e t y p e of u n i t c e l l i n the single crystals g r o w n w a s not b i a s e d b y i m p u r i t i e s f r o m t h e flux, b o t h K F - a n d K M o 0 - b a s e d fluxes w e r e often u s e d t o g r o w crystals of the same phase. I n g e n e r a l , the size (less t h a n 0.2 m m i n d i a m e t e r ) a n d t o t a l a m o u n t of the crystals w e r e insufficient f o r a n y w e t c h e m i c a l analysis.

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on August 26, 2015 | http://pubs.acs.org Publication Date: June 1, 1980 | doi: 10.1021/ba-1970-0186.ch020

2

2

2

+ a

2

2

5

+ a

x

4

4

3

4

+ f l

2

4

a

a

4

S i n g l e - c r y s t a l X - r a y s t r u c t u r e d e t e r m i n a t i o n is p r e s e n t l y u n d e r w a y o n most of the phases i n these systems. N e u t r o n d i f f r a c t i o n t o t a l profile analysis w i l l b e a t t e m p t e d t o d e t e r m i n e t h e n a t u r e of t h e n o n s t o i c h i o m e t r y b u t m u s t a w a i t some p r e v i o u s X - r a y structure d e t e r m i n a t i o n . High-resolution, electron microscope lattice-imaging techniques w o u l d b e v e r y v a l u a b l e to s t u d y t h e n a t u r e of the o r d e r i n g of a l k a l i a n d v a c a n c i e s i n the kalsilite-like polymorphs.


394 The

SOLID

Quaternary

STATE CHEMISTRY:

System

A

CONTEMPORARY

OVERVIEW

K 0-Al O —Fe 0 —Si02 2

2

s

2

&

T h e T e r n a r y S y s t e m K 0 - A l 0 - S i 0 . T h e latest v e r s i o n of this t e r n a r y system w a s p u b l i s h e d b y S c h a i r e r a n d B o w e n i n 1955 ( 2 ) , a n d a c o m p o s i t e d i a g r a m w a s p u b l i s h e d as one of a series of large-scale phase d i a g r a m s b y the A m e r i c a n C e r a m i c Society a n d as F i g u r e 407 i n t h e b o o k " P h a s e D i a g r a m s for C e r a m i s t s " (11). T h i s d i a g r a m is n o w i n n e e d of r e v i s i o n , especially i n the r e g i o n c o n t a i n i n g / ? - A l 0 as a n e q u i l i b r i u m phase a n d i n the h i g h - K 0 p o r t i o n of the system. 2

2

3

2

2

3


2

T h e b i n a r y j o i n K 0 - S i 0 w a s s t u d i e d b y K r a c e k ( 1 2 ) , a n d the latest v e r s i o n of the system A l 0 - S i 0 is that of A k s a y a n d P a s k (13). U n f o r t u n a t e l y , n o e x p e r i m e n t a l s t u d y of the system K 0 - A 1 0 has a p p e a r e d i n the l i t e r a t u r e . T h e present i n v e s t i g a t i o n has established the l i m i t s of s o l i d s o l u t i o n of t h e £ - A l 0 phase as v a r y i n g f r o m a b o u t 1 5 % K 0 to a b o u t 1 0 % K 0 f r o m 1000° to 1 6 0 0 ° C , d e c r e a s i n g s l i g h t l y at the h i g h e r temperatures. T h e m e l t i n g p o i n t of K A 1 0 has not y e t b e e n established, b u t p r e l i m i n a r y d a t a o b t a i n e d b y u s i n g a n u n s e a l e d I r c r u c i b l e i n d i c a t e a v a l u e greater t h a n 2 1 0 0 ° C , a n d a v a l u e of 2150 ± 1 0 0 ° C is o u r best e s t i m a t e d at this t i m e . ( E x p e r i m e n t s h a v e b e e n p e r f o r m e d n o w to d e t e r m i n e t h e m e l t i n g p o i n t of K A 1 0 i n sealed M o tubes ( O D , 3.0 m m ; I D , 1.5 m m ) a n d the t e m p e r a t u r e at w h i c h t h e i n t e r n a l pressure f r o m t h e K A 1 0 e x c e e d e d the r u p t u r e s t r e n g t h of t h e tubes w a s f o u n d to b e ~ 2 2 6 0 ° C . ) T h e eutectic b e t w e e n K A 1 0 a n d / ? - A l 0 w a s f o u n d to o c c u r at a b o u t 1910 ° C , b u t the c o m p o s i t i o n has not yet been established. 2

2

2

3

2

2

2

2

2

3

3

2

2

2

2

2

a

3

K A 1 0 - S i 0 . A n i n v e s t i g a t i o n of the c r y s t a l c h e m i s t r y of the system K A 1 0 - K A l S i 0 w a s r e p o r t e d b y C o o k et a l . (6) as t h e first p a r t of the present study. T h e m a i n c o n t r i b u t i o n s of this w o r k w e r e the d i s c o v e r y of the h i g h - t e m p e r a t u r e f o r m of K A l S i 0 , o r t h o r h o m b i c , w i t h u n i t - c e l l p a r a m e t e r s a = 18.110 A , b = 15.600 A , a n d c = 8.560 A , the t e t r a g o n a l phase K i ^ A l i ^ S i i . ^ (x « 0.1) a = 8.943 A a n d c — 5.5221 A , a n d the i n v e s t i g a t i o n of the s o l i d s o l u t i o n of S i 0 i n K A 1 0 , s t a b i l i z i n g the p s e u d o c u b i c m o d i f i c a t i o n of t h i s structure. 2

2

2

4

4

2

2

S i n c e the s u b m i s s i o n o f the m a n u s c r i p t of C o o k et a l . (6), a c o n s i d e r a b l e a m o u n t of e x p e r i m e n t a l d a t a has b e e n a c c u m u l a t e d o n this b i n a r y j o i n . T h e i n f o r m a t i o n i n t e r p r e t e d f r o m these experiments is s u m m a r i z e d i n F i g u r e 1 as the system K A l 0 - K L A l S i 0 . A m o r e c o m p l e t e d e s c r i p t i o n of this system w i l l be p u b l i s h e d , w h e n c o m p l e t e d , b y J . L . W a r i n g et a l . (14). I n this d i a g r a m the n e w t e t r a g o n a l phase is f o u n d to o c c u r at a r a t i o v e r y close to the c o m p o s i t i o n 4 K A 1 0 : 3 S i 0 . H o w e v e r , i t seems d o u b t f u l that this r a t i o has a n y significance w i t h respect to A l / S i o r d e r i n g w h e n c o m p a r e d w i t h the s m a l l size of the u n i t c e l l . I m m e d i a t e l y after p u b l i c a t i o n of the p a p e r b y C o o k et a l . (6), J . V . S m i t h b r o u g h t to 2

2

6

2

2



20.

ROTH

Phase Equilibria

Research

395

Figure 1. Preliminary phase equilibria diagram of the system KA10 KAlSi O : (9), no melting; (Q), partially melted; (Q), completely melted. TET = tetragonal phase; ORTH b X 3 = low-temperature orthorhombic form of KAlSi0 ; ORTH a X 2, b X 3 = high-temperature orthorhombic form of KAlSiO^ 2

2

e

4

o u r a t t e n t i o n a classification of f r a m e w o r k silicates d e s c r i b i n g p o s s i b l e l i n k a g e s f r o m a s i m p l e h e x a g o n a l net, p u b l i s h e d a short t i m e earlier ( 1 5 ) . H e p o i n t e d out that this t e t r a g o n a l phase c o u l d c o r r e s p o n d to his p o s s i b l e structure d e s i g n a t e d S C C S C C .

I n d e e d , i t seems l i k e l y t h a t t h e s t r u c t u r e

of this p h a s e m a y c o r r e s p o n d to t h i s f o r m , w h i c h is c o m p o s e d of t e t r a h e d r a l u n i t s , as s h o w n i n F i g u r e s 2 ( a )

and 2(b).

refinement of this p h a s e is c u r r e n t l y u n d e r w a y structure analysis of

the t w o

orthorhombic

double

A structural

along w i t h a crystal'

polymorphs

of

KAlSi0 , 4

p r e v i o u s l y r e p o r t e d b y C o o k et a l . ( 6 ) , i n a n a t t e m p t to l e a r n m o r e a b o u t the possible A l / S i o r d e r i n g as w e l l as the K v a c a n c y o r d e r i n g i n t h e k a l s i l i t e - l i k e phases. T h e T e r n a r y System K 0 - F e 0 - S i 0 2 . 2

2

3

T h i s t e r n a r y s y s t e m has n o t

b e e n p r e v i o u s l y s t u d i e d i n a n y great d e t a i l . F a u s t (16)

reported

the

presence of c o m p o u n d s e q u i v a l e n t to k a l s i l i t e , l e u c i t e , a n d f e l d s p a r , b u t a l l w e r e l o c a t e d o n l y i n the presence of glass o n t h e j o i n K 0 : 6 S i 0 2

Fe 0 . 2

3

2

Potassium-iron feldspar, K F e S i 0 , was synthesized hydrother3

8

mally and structurally analyzed by Wones and A p p l e m a n

(17).

T h e system F e 0 - S i 0 contains n o b i n a r y c o m p o u n d s unless a c c o m 2

3

p a n i e d b y r e d u c t i o n of F e

2

3 +

-> F e * .

s t u d i e d b y T a k a h a s h i et a l . (18)

2

H o w e v e r , t h e system K 0 - F e 0

contains K F e 0

2

2

and a £ - A l 0 2

3

2

3

t y p e of

phase. A n u n k n o w n p h a s e r e p o r t e d o n the h i g h - F e 0 e n d of t h e system 2

3

has b e e n f o u n d i n the present w o r k to a c t u a l l y b e a j8"'-type of c o m p o u n d ,



396

SOLID S T A T E

CHEMISTRY:

A

CONTEMPORARY

OVERVIEW

Figure 2a. Tetrahedral model of the structure of the phase designated SCCSCC (15). View looking down one of the a-axes showing pseudohexagonal symmetry. t h a t is, six s p i n e l - l i k e l a y e r s b e t w e e n t h e a l k a l i l a y e r s , w i t h h e x a g o n a l symmetry a =

5.927 A a n d c =

33.45 A . T h i s p h a s e u n d o u b t e d l y has

some F e

2 +

/?-Al 0

t y p e of c o m p o u n d p r o b a b l y also contains some F e , t h e F e

2

Fe

2 +

3

ions as a n i n t e g r a l p a r t of the s t r u c t u r e . I n d e e d , t h e r e g u l a r 2 +

3 +

/

ratio d e p e n d i n g on the heat treatment. T h e current study indicates

t h a t the c o m p o s i t i o n of t h e p p h a s e o c c u r s at t h e 1/5.75 K / F e r a t i o at 800°C, w i d e n i n g slightly w i t h increasing temperature. experimental data a n d phase e v e n t u a l l y b y P a r k e r et a l . KFE0 -SI0 . 2

The

e q u i h b r i u m d i a g r a m w i l l be

complete published

(19).

T h e system K F e O - j - S i C ^ has b e e n e x a m i n e d i n t h e

2

present s t u d y (8),

a n d t h e i n t e r p r e t a t i o n of t h e e x p e r i m e n t a l d a t a is

s h o w n i n F i g u r e 3. 5.278 A a n d c —

T h e hexagonal kalsilite-like phase, K F e S i 0 , a 4

8.824 A , w a s f o u n d to exist b e l o w

=

9 4 5 ° C a n d to

t r a n s f o r m r e v e r s i b l y to a n o r t h o r h o m b i c f o r m w i t h a c-axis seven times t h e size of t h e p s e u d o o r t h o r h o m b i c c e l l , a = c =

59.61 ( 7 X

9.115 A , b =

5.433 A , a n d

8.516) A . T h e l a r g e s u p e r s t r u c t u r e c a n n o t b e seen i n



20.

Phase Equilibria

ROTH

Research

397

Figure 2b. Tetrahedral model of the structure of the phase designated SCCSCC (15). View looking down the c-axis snowing the real bodycentered tetragonal nature of the unit cell. X - r a y d i f f r a c t i o n p o w d e r patterns, a n d i t is necessary to e x a m i n e s i n g l e crystals (10) 2 to 5 m o l %

to see t h e l a r g e c e l l . T h e k a l s i l i t e - l i k e p o l y m o r p h s Si0

2

accept

i n s o l i d s o l u t i o n d e p e n d i n g o n the t e m p e r a t u r e .

b o d y - c e n t e r e d t e t r a g o n a l phase, a =

9.09 A a n d c =

A

5.33 A , a p p a r e n t l y

i s o s t r u c t u r a l w i t h t h a t i n the a l u m i n a system, occurs at a p p r o x i m a t e l y t h e same s i l i c a c o n t e n t n e a r 4 K F e 0 : 3 S i 0 . I t s h o u l d b e n o t e d t h a t a 2

2

f e l d s p a r t y p e of p h a s e c a n b e f o r m e d b y a n n e a l i n g a glass of c o m p o s i t i o n KFeSi 0 3

8

b e l o w the solidus at a t m o s p h e r i c pressure.

S i a g l e crystals of

the t e t r a g o n a l p h a s e , of b o t h p o l y m o r p h s of k a l s i l i t e , w i t h a n d w i t h o u t excess s i l i c a , a n d of K F e S i O , the i r o n l e u c i t e - l i k e phase, w e r e p r o d u c e d 2

e

i n s e a l e d P t tubes u s i n g b o t h K F a n d K M o 0 : K V 0 2

4

3

as fluxes ( J O ) .

The

high-temperature orthorhombic kalsilite p o l y m o r p h containing 2-4 m o l % excess s i l i c a , w h e n first t r e a t e d w i t h K F i n a n a t t e m p t to increase the g r a i n size, f o r m e d a n e w phase o n attempts to reverse the e q u i l i b r i a at 850°C.

P u r e K F e S i 0 , w h e t h e r or not t r e a t e d w i t h K F , a n d the s o l i d 4

solutions not t r e a t e d w i t h K F s h o w e d no s u c h a n o m a l y . N o s i n g l e crystals



398

SOLID S T A T E C H E M I S T R Y :

1 KFe0

1

1

I

20

2

l

I

i

40 60 Mole % S i 0

A CONTEMPORARY

I l

I

l

l

80

Si0

OVERVIEW

2

2

Figure 3. Preliminary phase equilibria diagram of the system KFe0 Si0 : (%), no melting; (O), partial melting; (M), completely melted. C . = cubic KFe0 solid solution; T = tetragonal phase; H = hexagonal kalsilite-like phase; ORTH c X 7 = high-temperature orthorhombic form of KFeSiO . 2

2

8

2

h

h a v e y e t b e e n s y n t h e s i z e d w i t h this n e w u n k n o w n s t r u c t u r e . ( T h i s p h a s e n o w has b e e n i d e n t i f i e d as i s o s t r u c t u r a l w i t h the k a l s i l i t e - l i k e p o l y m o r p h s of K F e G e 0

a n d R b A l G e 0 , hevagonal w i t h a «

4

times the value i n

4

the low-temperature form.)

T h e complete experimental data a n d

v e r s i o n of t h i s p h a s e d i a g r a m w i l l b e p u b l i s h e d i n a n o t h e r p a p e r The

T e r n a r y System K O ^ A l O j r - F e 0 3 . 2

2

2

No

compositions

final (20). were

s t u d i e d i n the present w o r k t h a t d i d n o t c o n t a i n s i l i c a as one of t h e ingredients.

H o w e v e r , s e v e r a l c o m p o s i t i o n s i n t h e q u a t e r n a r y system

e s t a b l i s h e d t h a t s o l i d solutions are f o r m e d b e t w e e n t h e phases a n d b e t w e e n t h e £ - A l 0 2

3

KA10 -KFe0 2

2

types of phases i n t h e a l u m i n u m a n d

i r o n o x i d e systems. N o t h r e e p h a s e r e g i o n s w e r e i d e n t i f i e d . KAlSi0 -KFeSi0 . 4

of K A l S i 0 - K F e S i 0 4

expected

T h r e e c o m p o s i t i o n s at 3 : 1 , 1:1, a n d 1:3 ratios

4

4

w e r e i n i t i a l l y p r e p a r e d to c h e c k t h e s o l i d s o l u t i o n

i n these k a l s i l i t e - l i k e phases.

i n t e r p r e t e d i n F i g u r e 4.

T h e e x p e r i m e n t a l results are

A f e w m o r e c o m p o s i t i o n s are b e i n g p r e p a r e d

a n d e x a m i n e d i n o r d e r to c h e c k t h e p h a s e b o u n d a r i e s . p h a s e w a s f o u n d t o o c c u r at 7 5 K F e S i 0 : 2 5 K A l S i 0 4

S i n g l e crystals of this p h a s e (10) m e t a s t a b l e v a r i e t y of K A l S i 0 (21),

4

4

A n e w stable

(KFe .75Al . SiO ). 0

0

2 5

4

p r o v e d to b e i s o s t r u c t u r a l , w i t h

a

p r o d u c e d b y ion exchange f r o m R b A l S i 0

4

a n d are m o n o c l i n i c w i t h a p s e u d o o r t h o r h o m b i c C - c e n t e r e d c e l l ,

with a =

18.45 A , b =

10.73 A , a n d c =

8.55 A . A t t e m p t s to reverse t h e

p h a s e t r a n s i t i o n of t h e h i g h t e m p e r a t u r e p o l y m o r p h s at 8 0 0 ° C

were

successful, b u t r e v e r s a l e x p e r i m e n t s at 8 5 0 ° C p r o d u c e d the n e w p h a s e



20.

ROTH

Phase Equilibria

399

Research

Figure 4. Preliminary phase equilibria diagram of the system KFeSi0 KAlSiOj^: (%), no melting; (&), partial melting; (O), completely melted. HEX = hexagonal kalsilitelike phase; ORTH c X 7 = orthorhombic KFeSiO^ type of phase; MON = monoclinic distortion of the kalsilite-like phase; ORTH b X 3 = low-temperature orthorhombic kalsiliterlike phase; ORTH a X 2, b X 3 = high-temperature orthorhombic kalsilite-like phase; ? = kalsilite-like phase of unknown symmetry. 4

KAI0

2

KFe0

2

Figure S. Preliminary phase equilibria diagram of the system KA10 KFeOg-SiOg representing an isotherm at about 1050°C: (•), compositions studied. O' = low-temperature orthorhombic b X 3 kalsilite-like phase; M = monoclinic distortion of the kalsilite-like phase; O" = orthorhombic c X 7 KFeSi0 type o fphase; T = tetragonal kalsilite-like phase. 2

4


400

SOLID S T A T E C H E M I S T R Y :

f o u n d for K F e S i 0 (see

A CONTEMPORARY

OVERVIEW

w i t h excess s i l i c a i n s o l i d s o l u t i o n p r e r e a c t e d w i t h K F

4

section titled " K F e O ^ S i C V ' ) .

A s this phase apparently forms only

d u r i n g reversal from the high-temperature forms, it m a y be o n l y w i t h respect to the o r t h o r h o m b i c f o r m .

metastable

T h e exact n a t u r e of t h i s

p h a s e m u s t a w a i t e x a m i n a t i o n of s i n g l e crystals t h a t h a v e gone t h r o u g h the same r e v e r s a l attempts. KAl02-KFe02-Si0 .

Although many

2

experimental

compositions

h a v e b e e n s t u d i e d o n e a c h b i n a r y c o n t a i n i n g SiOo as one e n d m e m b e r ,


n o c o m p o s i t i o n s i n the t e r n a r y field h a v e b e e n s t u d i e d except those o n t h e join K A l S i 0 - K F e S i 0 . 4

Nevertheless, a subsolidus ternary phase d i a g r a m

4

c a n b e h y p o t h e s i z e d b y c o m p a r i s o n w i t h k n o w n reactions i n t h e b i n a r y systems, as s h o w n i n F i g u r e 5. T h i s d i a g r a m needs e x p e r i m e n t a l v e r i f i c a tion a n d probably w i l l be modified considerably i n the near future.

The

Quaternary

System

K 0-MgO^Te Os-Si0 2

2

T h e T e r n a r y System K 0 - M g O - S i 0 . 2

was studied b y Roedder ternary compounds K 0-MgO.

T h e K 0 - M g O - S i 0 system

2

(3,

4).

and noted

2

2

2

H e r e p o r t e d t h e existence of t h a t n o phases

appeared

several

on the

H o w e v e r , he f o u n d that several ternary compounds

2

join

existed

that w e r e essentially i s o s t r u c t u r a l w i t h t h e phases o n the j o i n K A 1 0 - S i 0 . 2

2

A p p a r e n t l y a s t r u c t u r a l s u b s t i t u t i o n of 2A1 M g S i c a n take p l a c e , so that a c o m p o u n d

is f o r m e d essentially i s o s t r u c t u r a l w i t h K A 1 0

c o m p o s i t i o n K [ M g . 5 S i o . 5 ] 0 or K M g S i 0 . 2

0

2

the join K M g S i 0 - S i 0 , a ternary c o m p o u n d 2

4

2

composition K M g S i i O 2

5

2

3 0

at t h e

was reported w i t h

the

.

T H E SYSTEM K M G S I 0 - S I 0 . 2

2

I n a d d i t i o n to the phases o n

4

4

2

M a n y experiments were conducted on

t h e j o i n K M g S i 0 - S i 0 . T h e results of these e x p e r i m e n t s are i n t e r p r e t e d 2

and

4

2

s h o w n i n F i g u r e 6, p l o t t e d as the system K [ M g . 5 S i o . 5 ] 0 - S i 0 to 2

0

s h o w t h e a n a l o g y to t h e system K A 1 0 - S i 0 2

2

( F i g u r e 1) a n d K F e 0 - S i 0

2

2

( F i g u r e 3 ) . T h e solidus a n d l i q u i d u s v a l u e s d e t e r m i n e d b y R o e d d e r

2

(3)

are i n d i c a t e d o n the d i a g r a m . T h e present d a t a differ f r o m that of R o e d d e r

(3, 4) i n several i m

p o r t a n t d e t a i l s . F i r s t of a l l , t h e k a l s i l i t e - l i k e c o m p o s i t i o n r e p r e s e n t e d b y t h e f o r m u l a K [ M g . S i o . 5 ] S i 0 or K M g S i 0 0

5

4

as suggested i n R o e d d e r ( 3 ) .

2

3

8

does n o t m e l t c o n g r u e n t l y

I n s t e a d , i t m e l t s i n c o n g r u e n t l y to a n o t h e r

k a l s i l i t e - l i k e p h a s e deficient i n s i l i c a . T h e r e is a p p a r e n t l y a c o n g r u e n t t y p e of c o m p o s i t i o n r e p r e s e n t e d b y a m o n o t e c t i c

(The term "monotectic"

is

u s e d w h e n there is insufficient e x p e r i m e n t a l e v i d e n c e to d e t e r m i n e i f t h e c o m p o u n d melts just s l i g h t l y i n c o n g r u e n t l y or c o n g r u e n t l y or r e a l l y r e p resents t h e l i m i t i n g case b e t w e e n t h e t w o ) Sio.5]0 :3Si0 2

(10)

2

or 2 K 0 • 2 M g O • 5 S i 0 . 2

2

at a b o u t t h e r a t i o 4 K [ M g . 5 0

S i n g l e crystals h a v e b e e n

grown

of t h e l o w - t e m p e r a t u r e f o r m of t h e k a l s i l i t e - l i k e c o m p o s i t i o n , w h i c h

is h e x a g o n a l , just as for the c o m p o u n d s K A l S i 0

4

and K F e S i 0 . 4

The high-



20.

ROTH

Phase Equilibria

401

Research

Figure 6. Preliminary phase equilibria diagram of the system K[Mg gSi ]O -SiOg: (%), no melting; (Q), partial melting; (G), completely melted; (M), liquidus values of Roedder (3). T = tetragonal kalsilite-like phase; O = orthorhombic kalsilite-like phase; M = monoclinic kalsilite-like phase; H = hexagonal kalsilite-like phase; L = leucite-like phase. 0

05

2

temperature form existing between

about

9 0 0 ° C a n d 1 0 7 0 ° C has

an

X - r a y d i f f r a c t i o n p o w d e r p a t t e r n essentially i d e n t i c a l to t h a t of 7 5 K F e Si0 :25KAlSi0 4

(21)].

4

[see

I t therefore

section t i t l e d " K A l S i 0 - K F e S i 0 " a n d M i n o r et a l . 4

4

is r e f e r r e d to as a m o n o c l i n i c p h a s e , a l t h o u g h

s i n g l e crystals h a v e y e t b e e n g r o w n

(10).

T h e p o w d e r p a t t e r n of

p h a s e o c c u r r i n g at t h e 4 : 3 r a t i o s t r o n g l y resembles t h a t of K F e S i 0

4

no the and

is l a b e l e d o r t h o r h o m b i c , a l t h o u g h a g a i n n o single crystals are a v a i l a b l e a n d i t is v e r y d o u b t f u l t h a t this phase has t h e same c X 7 s u p e r s t r u c t u r e found in K F e S i 0

4

(8,20). A l l these k a l s i l i t e - l i k e phases exist as s o l i d s o l u

tions h a v i n g s m a l l b u t e x p e r i m e n t a l l y d e t e r m i n a b l e ranges of s t o i c h i o m e t r y . I t is i n t e r e s t i n g to n o t e i n t h e p h a s e d i a g r a m i n F i g u r e 6 t h a t t h e composition corresponding

to K [ M g . 5 S i . 5 ] S i O 0

0

4

or K O M g 0 3 S i 0 2

n o t q u i t e single p h a s e at t e m p e r a t u r e s b e l o w a b o u t 9 5 0 ° C . phase

specimen

prepared

at h i g h e r t e m p e r a t u r e s

A

2

a c t u a l l y exsolves

s m a l l a m o u n t of l e u c i t e w h e n h e a t e d at l o w e r t e m p e r a t u r e .

is

singlea

T h i s insta

b i l i t y of t h e k a l s i l i t e - l i k e c o m p o s i t i o n i n the M g O s y s t e m b e c o m e s v e r y i m p o r t a n t i n the e q u i l i b r i u m relations of m o r e c o m p l e x systems (see tion titled " T h e Quaternary System K ^ - M g O - A l a O a - S i C V ) .


sec

402

SOLID S T A T E

CHEMISTRY:

A

CONTEMPORARY OVERVIEW

T h e t e t r a g o n a l p h a s e first f o u n d b y C o o k et a l . ( 6 , 7 ) i n the system KA10 -Si0 2

Si0

2

F i g u r e s 1, 2 ( a ) , a n d 2 ( b ) ]

[see

2

a n d i n the system K F e 0 2

( F i g u r e 3 ) also occurs i n this s y s t e m , except t h a t i t occurs at t h e r a t i o

5K[Mgo. Si .5]0 :3Si0 5

2

0

( 5 K 0 : 5 M g O : l l S i 0 ) i n s t e a d of at 4 : 3 as i n t h e

2

2

2

a l u m i n a a n d i r o n o x i d e systems.

T h e c o m p l e t e e x p e r i m e n t a l d e t a i l s of

this s y s t e m w i l l be p u b l i s h e d e l s e w h e r e i n t h e near f u t u r e K MgSi 08-KFeSi0 . 2

It

4

3

K[Mgo.5Si .5]Si0 -KFeSi0 4

0

4

can

be

seen

from

system is a l m o s t a b i n a r y j o i n .


a m o u n t of l e u c i t e t h a t occurs at t e m p e r a t u r e s b e l o w K MgSi 0 2

3

8

(22).

Figure 7

that The

the small

about 950°C for

a p p a r e n t l y d i s a p p e a r s w h e n a s m a l l a m o u n t of K F e S i 0

4

is

a d d e d i n s o l i d s o l u t i o n . H o w e v e r , the i n s t a b i l i t y of the m a g n e s i a p h a s e is reflected i n t h e n o n b i n a r y n a t u r e of t h e m e l t i n g r e l a t i o n s i n t h e r e g i o n u p to a b o u t 2 0 - 2 5 m o l %

KFeSi0 .

T h e low-temperature

4

p h a s e is s t a b i l i z e d b y the a d d i t i o n of K F e S i 0

hexagonal

a n d the o r t h o r h o m b i c a n d

4

m o n o c l i n i c p o l y m o r p h s f o u n d i n t h e K [ M g . 5 S i . 5 ] O - S i O s y s t e m are 0

eliminated.

0

2

2

T h u s t h e h e x a g o n a l p h a s e is stable u p to the solidus f r o m

about 5 m o l %

to a b o u t 30 m o l %

KFeSi0 .

a d i d t i o n of K [ M g . 5 S i o . 5 ] S i 0 to K F e S i 0 4

0

4

4

O n the other side, the

causes b o t h t h e h e x a g o n a l a n d

h i g h - t e m p e r a t u r e o r t h o r h o m b i c (c X 7 ) forms to b e e l i m i n a t e d f r o m t h e d i a g r a m . Instead, a n e w phase appears w i t h a n X - r a y diffraction p o w d e r pattern

very

KAlSi0 . 4

similar

to

the

low-temperature

orthorhombic

form

of

H o w e v e r , there are a f e w extra lines i n t h e p a t t e r n , a n d i t c a n -

1300

Figure 7. Preliminary phase equilibria diagram of the system K[Mg SiogjSiO^-KFeSiO^. Note nonbinary nature of this system up to about 30% KFeSi0 . (%), no melting; (Q), partially melted; (Q), completely melted. HEX = hexagonal kalsilitelike phase; MON = monoclinic kalsilite-like phase; ORTH b X 3 = orthorhombic phase similar to the lowtemperature b X 3 phase of KAlSiO^; ORTH c X 7 = orthorhombic KFeSiO} type of phase. 0tS

4


20.

Phase Equilibria

ROTH

403

Research

n o t b e c o m p l e t e l y i n d e x e d o n the basis of t h e o r t h o r h o m b i c c e l l w i t h & X 3. S i n g l e crystals of this p h a s e h a v e not y e t b e e n p r e p a r e d ( 1 0 ) , as the M g O a p p a r e n t l y does n o t enter easily i n t o t h e s t r u c t u r e , w i t h a l l experiments resulting i n either K F e S i 0 2

or K F e S i 0 .

6

4

C o m p l e t e details

w i l l be p u b l i s h e d later (22). K MgSi0 -KFe0 -Si0 . 2

4

2

2

0

2

t r a t e d i n F i g u r e 7.

E x a m i n a t i o n of s p e c i m e n s

2

K[Mg .5Sio.5]0 -KFe0 -Si0

2

i n the

system

thus f a r h a v e b e e n l i m i t e d to t h e j o i n i l l u s

N e v e r t h e l e s s , i t is p o s s i b l e f r o m t h e d a t a a l r e a d y


d e t e r m i n e d to m a k e a g o o d guess as to the g e n e r a l n a t u r e of a n i s o t h e r m a l s e c t i o n just b e l o w the solidus ( a b o u t 1 0 5 0 ° C ) , as s h o w n i n F i g u r e 8.

It

s h o u l d b e r e m e m b e r e d t h a t this d i a g r a m is v e r y p r e l i m i n a r y i n n a t u r e a n d b o u n d a r i e s m a y c h a n g e c o n s i d e r a b l y as m o r e e x p e r i m e n t a l d a t a is o b t a i n e d . F u r t h e r details w i l l be r e p o r t e d i n t h e n e a r f u t u r e

KFeO,

2

^ !s

K

S

) 0

(22).

2

Figure 8. Preliminary phase equilibria diagram of the system K[Mg Si JO -KFeO -SiO . Isothermal section at about 1000°C. (%), compositions studied. T = tetragonal kalsilite-like phase; O" = orthorhombic KFeSiO type of phase; O' = orthorhombic phase similar to the lowtemperature b X 3 phase of KAlSiO^ H = hexagonal kalsilite-like phase; M = monoclinic kalsilite-like phase; O = orthorhombic kalsilite-like phase. 0

0

2

2

5

2

h

The

Quaternary

System

K 0-MgO*-Al Os--SiO 2

2

B

T h e h i g h - s i l i c a p o r t i o n of this q u a t e r n a r y system w a s d i s c u s s e d i n d e t a i l b y S c h a i r e r ( 5 ) . H o w e v e r , t h e h i g h e r - K 0 - c o n t a i n i n g phases h a v e 2

not been examined i n any detail i n previous papers. T h e T e r n a r y System K 0 - M g 0 - A l 0 . 2

2

3

T h i s t e r n a r y s y s t e m has

n o t b e e n r e p o r t e d i n a n y d e t a i l e v e n i n reports to sponsors.

A few pre

l i m i n a r y e x p e r i m e n t s , h o w e v e r , h a v e s h o w n t h a t t h i s system is analogous to t h e N a 0 - M g O - A l 0 system i n its c o m p o u n d

formation.

t e r n a r y / ? A l 0 - r e l a t e d phases l a b e l e d 0 " ,

can be found i n the

2

2

2

3

3

and 0

l v


A l l the

404

SOLID S T A T E

CHEMISTRY: A CONTEMPORARY OVERVIEW

s y s t e m , b u t t h e i r exact c o m p o s i t i o n a l l i m i t s h a v e n o t b e e n d e t e r m i n e d . I t has also b e e n e s t a b l i s h e d b y T . N e g a s (23) +

accurately

that M g A l 0 2

4

K 0 - » M g O + 2 K A 1 0 . T h i s has b e e n f o u n d to b e t h e m e c h a n i s m for 2

2

d e g r a d a t i o n of M g A l 0 2

i n s u l a t i o n i n a n M H D system.

4

K MgSi 0 -KAlSi0 . 2

3

8

T h e system K [ M g o . S i . 5 ] S i 0 - K A l S i 0

4

5

i n F i g u r e 9 is not a b i n a r y j o i n .

4

0

T h e tendency

4

shown

for instability i n the

k a l s i l i t e - l i k e h e x a g o n a l f o r m of K [ M g . 5 S i . 5 ] S i O is e n h a n c e d b y t h e a d d i 0

t i o n of K A l S i 0 . 4

4

0

A l l c o m p o s i t i o n s that h a v e b e e n e x a m i n e d so f a r s h o w


some l e u c i t e b o t h a b o v e a n d b e l o w the s o l i d u s . A l t h o u g h t h i s w a s a c o m p l e t e l y u n e x p e c t e d result, i t s h o u l d not b e s u r p r i s i n g i n v i e w of t h e state m e n t m a d e b y R o e d d e r i n f o o t n o t e n u m b e r 42, p a g e 2 3 6 : . . t h e system

K 0 •MgO •3 S i 0 - K 0•A1 0 •2Si0 2

2

2

2

3

is

2

p a r t i a l l y b i n a r y at l i q u i d u s t e m p e r a t u r e s , f o r m i n g l e u c i t e c c o n s i d e r a b l e r a n g e of t e m p e r a t u r e s "

(4).

A s a m a t t e r of fact, the a m o u n t of l e u c i t e present i n these a c t u a l l y increases w i t h i n c r e a s i n g K A l S i 0 5%

l e u c i t e w i t h no K A l S i 0

to a b o u t 5 0 %

4

25K[Mgo.5Sio.5]Si0 :75KAlSi0 . 4

f u r t h e r a d d i t i o n of K A l S i 0

4

4

4

only

over

specimens

content, v a r y i n g f r o m l e u c i t e at t h e

about

composition

O f course, i t m u s t decrease a g a i n w i t h

as t h a t e n d m e m b e r shows n o l e u c i t e .

There

is n o e v i d e n c e i n t h e present d a t a to i n d i c a t e a n y n e w k a l s i l i t e - l i k e phases i n this system.

Mole%KAISI() 4

KAISiO, 4

Figure 9. Preliminary phase equilibria diagram of the system K[Mg Si ]SiO^-KAlSiO^. Note that this is not a binary join, as a leucite-like phase exists at all compositions studied. (%), no melting; (Q), partially melted; (Q), completely melted. L = leucite type of phase; M = monoclinic kalsilite-like phase; H — hexagonal kalsilite-like phase; O b X 3 = low-temperature orthorhombic KAlSiO^ type of phase; G a X 2 , b X 3 = high-temperature orthorhombic KAlSiO^ type of phase; Liq = liquid. 05

0

5


20.

Phase Equilibria

ROTH

405

Research

KaMgSiOi-KAlOa-SiOa.

T h e system K [ M g o . 5 S i o . 5 ] 0 - K A 1 0 - S i 0 , 2

2

s h o w n i n F i g u r e 10, is m u c h m o r e c o m p l e x t h a n t h e c o r r e s p o n d i n g

2

system

c o n t a i n i n g i r o n o x i d e i n s t e a d of a l u m i n a . T h i s c o m p l e x i t y is c a u s e d

by

the l a r g e d e v i a t i o n of the j o i n , s h o w n i n F i g u r e 9, f r o m b i n a r y e q u i l i b r i a . M a n y c o m p o s i t i o n s i n the t e r n a r y m u s t b e e x a m i n e d b e f o r e this d i a g r a m can be considered

determined

even approximately.

c u m u l a t e d so far, no conclusions

F r o m the data

ac

c a n b e d r a w n as to the reason f o r t h e

l a r g e a m o u n t of l e u c i t e o c c u r r i n g i n c o m p o s i t i o n s o n t h e j o i n K M g S i 0 2

3

8

KAlSi0 .


4

K^OrMgO-KAlO^SiO^ compositions discussed KAlSi0

One

e a r l i e r to

logical reason

for

kalsilite-like

s h o w l e u c i t e is to assume t h a t

s t r u c t u r e w i l l not tolerate m u c h excess s i l i c a .

4

the

s o l u t i o n m a y exist i n the d i r e c t i o n K i A l _ . M g . S i 0 + a

1

a

a

4

the

T h e true solid

i n s t e a d of

KAli_

2 a ?

-

M g a . S i i . 0 , or at least i n some c o m p r o m i s e b e t w e e n these t w o alternates. + a

4

If the p r e v i o u s d i a g r a m , F i g u r e 10, is r e d r a w n so t h a t all t h e s i l i c a is p l o t t e d at one apex, as s h o w n i n F i g u r e 11, t h e n the r i g h t - h a n d corner becomes K M g . O or l / 2 [ K 0 : M g O ] . 0

5

2

I f the t r u e s o l i d s o l u t i o n is r e a l l y

K i a A l i . , M g * S i 0 , the d i a g r a m s i n F i g u r e s 10 a n d 11 w o u l d +

4

i l l u s t r a t e these c o m p o s i t i o n s .

s t i l l not

N e v e r t h e l e s s , F i g u r e 11 does s h o w t h a t t h e

o b s e r v e d c o m p o s i t i o n s m a y w e l l b e single p h a s e w h e n t h e t o t a l s i l i c a c o n tent is n o m o r e t h a n 5 0 %

of t h e t o t a l n u m b e r of s m a l l c a t i o n

oxides.

M u c h m o r e w o r k r e m a i n s to b e d o n e o n s o l i d solutions i n t h e k a l s i l i t e - l i k e phases i n v o l v i n g M g O .

Figure 10. Preliminary phase equilibria diagram of the system K[Mg Si ]O -KAlO2-SiOg. Isotherm section at about 1000°C. (%), compositions studied. T = tetragonal kalsilite?like phase; O' = low-temperature orthorhombic b X 3 kalsilite-like phase; M = monoclinic kalsilite-like phase; O = orthorhombic kalsilite-like phase. 0B

0B

2



406

SOLID

STATE CHEMISTRY:

A

CONTEMPORARY

OVERVIEW

Figure 11. The same system as illustrated in Figure 10 except redrawn to show total Si0 content at upper apex of the diagram: HEX = hexagonal kalsilite-like phase; MON = monoclinic kalsilite-like phase; ORTH = orthorhombic kalsilite-like phase; TET = tetragonal kalsilite-like phase. 2

The

Five-Component This

System

five-component

K 0-MgO-Al Os-Fe Os-Si0 2

2

2

2

system has not b e e n s t u d i e d i n d e t a i l as yet.

In

the p r e s e n t s t u d y no a t t e m p t has b e e n m a d e to s t u d y s y s t e m a t i c a l l y effect of the p o s s i b l e r e d u c t i o n of i r o n f r o m F e

3 +

to F e . 2 +

l i m i n a r y studies w e r e m a d e b y R o e d d e r i n the system

Previous

the pre

K 0:FeO:Si0 2

Figure 12. Preliminary phase equilibria diagram of the system K[Mg SioJSiO^-KAlSiO^-KFeSiO^. Isotherm at about 1000°C. Note that a leucite-like phase extends into the ternary system. MON = monoclinic kalsilite-like phase; H and HEX = hexagonal kalsilite-like phase; L = leucite-like phase; O and OTH b X 3 = low-temperature orthorhombic KAISiO ^ type of phase; M = monoclinic kalsilite-like phase; ORTH c X 7 = orthorhombic KFeSiO type of phase. 0

u


5

2

20. (24)

Phase Equilibria

ROTH

and K 0 : F e O : A l 0 : S i 0 2

2

407

Research

3

(25).

2

H e indicated that e q u i l i b r i u m

i n v o l v i n g F e O , at least i n c o m p o u n d f o r m a t i o n , w a s s i m i l a r to t h a t of t h e systems i n v o l v i n g M g O . KAlSi0 -KFeSi0

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