l

‘t‘ H
H
l y

 

145 ..
766
THS_

CRYSTALUMRM CF SEUCA GEE.
if‘i E'HE
PRESEHCE 02" “WSW SALTS

Thesis for the Degzs'ee of M; S.
MICHIGAN STATE UNWERSETY
BALKUMAR P. SHAH
1970

7 IIIIII II IIIIIIIIIIIIIIIIIIIIIIIIIIIIII

312933010718314
LIBRARY

Michigan Stave
University

 

ABSTRACT

CRYSTALLIZATION OF SILICA GEL
IN THE
PRESENCE OF LITHIUM SALTS

By
Balkumar P. Shah

Silica. 5102. can exist in several different forms:
amorphous silica or silica gel; vitreous silica or silica
glass: and the crystalline forms like low and high quartz.
tridymite. and cristobalite: other less common crystalline
forms are keatite. coesite and stishovite. These crystalline
forms are stable within certain ranges of temperature and
pressure.

Zielke (1950) reported that only silica gel heated
up to 9000-10000 centrigrade do not crystallize.

An investigation was carried out to determine the
effect of lithium salts on the crystallization of amorphous
silica at 700°C. Each sample was heated for four hours at
one atmosphere of pressure. All three common polymorphs were
crystallized at this temperature. Quartz predominantes but
two high temperature forms. tridymite and crystobalite were
crystallized at temperatures below their respective thermal

stability range.

Balkumar P. Shah

Active silica gel was prepared by mixing sodium
silicate solution with hydrochloric acid. The gel was cut
into cubes. washed thoroughly with de-ionised water. and
dried at low temperature. HOmogenized mixtures of powdered
silica gel and the following salts were prepared and heated
in a platinum crucible in a high-temperature furnace.

At 700°C. and one atmospheric pressure, lithium
chloride. lithium bromide. lithium iodide. lithium nitrate.
lithium carbonate. and lithium hydroxide were used for this
study. Also ammonium hydroxide was added to lithium chloride
to make it more alkaline. Silica gel was chosen as the start-
ing material because it provided amorphous reactive condi-
tion and also assists in final x-ray analysis to determine
the phases present.

After heating. the salts were washed out with de-
ionised water and x-ray powder photographs of each sample
were taken. Polymorphs present in each sample were identi-
fied by measuring lines on powder photographs and calculat-

ing interplaner spacings.

CRYSTALLIZATION OF SILICA GEL
IN THE

PRESENCE OF LITHIUM SALTS

By .
Balkumar PI Shah

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE
Department of Geology

1970

ACKNOWLEDGEMENTS

The author wishes to express his sincere appreciation
to Dr. Harold B. Stonhouse for his suggestion of the problem
and constant assistance during the course of this research
and also for his critical review of the manuscript.

Appreciation is also extended to Dr. James W. Trow
and Dr. William J. Hinze for their guidance and constructive
criticism of the manuscript.

Acknowledgement is made to the late Dr. Justin Zinn
for his suggestions in the early part of this study. Thanks
are also extended to Dr. John A. Colwell who provided assist-

ance in spectrographic analysis.

ii

INTRODUCTION .

CONTENTS

SILICA POLYMORPHS AND THEIR TRANSFORMATIONS .

REVIEW OF PREVIOUS WORK

EXPERIMENTAL PROCEDURE .

INTERPRETATIONS AND RESULTS OF

SUMMARY . e

SPECTROGRAPHIC ANALYSIS

CONCLUSION .

RECOMMENDATIONS FOR FURTHER RESEARCH

REFERENCES 0

iii

Page

Table

II
III
IV

VI
VII

Figure

l.

2.

TABLES

POLYMORPHS OF SILICA . . . . . . . . . . . .
AMOUNT OF SALT ADDED TO SILICA GEL . . . . .
PERCENT LOSS AFTER HEATING . . . . . . . . .
X-RAY DATA FOR SILICA POLYMORPHS . . . . . .
D - SPACINGS . . . . . . . . . . . . . . . .
RESULTS OF CRYSTALLIZATION . . . . . . . . .

RESULTS OF CRYSTALLIZATION . . . . . . . .

FIGURES

STABILITY REGIONS OF THE VARIOUS FORMS OF
SILICA O O O O O O O O O O O O O O O O O O O

DIAGRAMMATIC REPRESENTATION OF PHASE
ASSEIBLAGES O O O C O O O O O O O O 0 O O 0

iv

Page

15
17
22

23
21+

27

Page

10

PLATES

Plate Page
I POWDER PHOTOGRAPHS FOR DETERMINING
SUITABLE HEATING TIME . . . . . . . . . . . . . 18
II POWDER PHOTOGRAPHS FOR 0.5 % LITHIUM . . . . . 29
III POWDER PHOTOGRAPHS FOR 2 % LITHIUM . . . . . . 32
IV POWDER PHOTOGRAPHS FOR 5 AND 10 % LITHIUM . . . 36
V POWDER PHOTOGRAPHS FOR 1 TO 5 % LITHIUM PLUS

AMMONIUM HYDROXIDE . s . . . . . . . . . . . . “0

INTRODUCTION

The name quartz is derived from a miner's word used
for massive vein quartz during the Middle Ages in Saxony.

The word has varied much in inclusiveness during its history
until the middle of the nineteenth century. When chemical
and crystallographic investigations showed the identity of
numerous varieties of natural silica the word ”Quartz” was
extended to cover them all. The discovery of the distinct
minerals tridymite and cristobalite detracted but little from
its inclusiveness.

Tridymite. the first polymorph of silica in addition
to quartz to be recognized. was described and named by G. vom
Rath in 1868. who also described and named cristobalite in
188A. The names tridymite and cristobalite are English
equivalents of German Tridymit and Cristobalit. High-quartz
was observed by Le Chatelier during laboratory experimenta-
tion in 1889. Inversions in tridymite and cristobalite were
recognized later. and also other individual polymorphs
closely related in crystal structure have been identified.
Marian discovered the high and low forms of tridymite in
188M. and Mallard discovered high and low forms of cristoba-
lite in 1890. Middle-tridymite was first recognized by Fenner
in the early 1900's. who also investigated comprehensively
the stability relations of these polymorphs of silica.

l

2
Later. three additional polymorphs of silica were synthesized
in the laboratory. Coesite. also called silica-C was the
first of these. synthesized by L. Coes in 1953. by heating a
mixture of sodium metasilicate and diammonium phosphate to
temperatures between 500°C. and 800°C. and at 35.000 atmos-
phere pressure for periods of about fifteen hours. In 1960
Coesite was first discovered in nature at Meteor Crater.
Arizona. Keatite. also called silica-K was synthesized by
P. P. Keat in 195A. It was obtained. together with small
amounts of quartz or cristobalite. over a range of tempera-
tures between 380° and 585°C. and 5.000 to 18.000 p.8.1.
Then in 1961 Stishov and P0pova synthesized stishovite at
temperatures between 12000 and lhOOOC. and at pressure report-
ed to be about 160 Kilobars. Stishovite has also been found
associated with coesite and silica glass in sandstone at
Meteor Crater. Arizona.

The development of x-ray diffraction techniques
brought an understanding of the fundamental structural rela-
tions between the various polymorphs and of the crystal
chemistry of silica. and provided a method for the discrimin-

ation of these substances.

SILICA POLYMORPHS AND THEIR TRANSFORMATIONS

One of the most striking facts about silica is the
variety of polymorphs. which are stable at different tempera-
tures and pressures. The most common of these substances
and one of the major constituents of the Earth's outer crust
is the polymorph low-quartz or simply quartz. Other two
common polymorphs are tridymite and cristobalite. Keatite.
coesite and stishovite are the less common forms existing.

which are metastable at ordinary conditions.

Table I
Polymorphs of Silica

Low-quartz -------- Stable at atmospheric pressure at
(as ) temperatures up to 573 C.

High-quartz ------- Stable from 5730 to 870°. capable of
(.5 ) existence above 870° but is then not
the stable form.

Low-tridymite ----- Capable of existence at atmospheric

(6C ) pressure at temperatures up to 117°.
but is not the stable form in this
range.

Middle-tridymite--- Capable of existence between 1170 and

(ec’) 163°. but is not the stable form in
this range.

High-tridymite ---- Capable of existence above 1630 and is

(.6 ) stable at atmospheric ressure from
870° to 1u7o°. above 1 70° is again un-
stable; melts at 16700 C.

Low-cristobalite--- Capable of existence at atmospherig 0
(ac ) pressure at temperatures up to 200 -267 .
but is not stable form in this range.

3

u

High-cristobalite - Capable of existence above 200°-267°.
(,6 ) and is stable from 14700 to l723°. its
melting point.

Keatite ----------- Metastable at ordinary conditions.
Coesite ----------- Metastable at ordinary conditions.
Stishovite -------- Metastable at ordinary conditions.

Interconversion of quartz. tridymite. and cristoba-
lite requires breaking and reforming of bonds between sili-
con and oxygen; consequently. the activation energies of
these transformations are high. and they occur only very
slowly. Thus all three polymorphs are found in nature. al-
though. of course. only one low-quartz. is thermodynamically
stable at ordinary temperatures. The other forms are meta-
stable.

The interconversions of the low (0‘ ) and high (‘6 )
forms of each structural type occur without bond breaking
and hence rapidly and at rather low temperatures.

There is a close similarity in structure between
low-quartz and high-quartz. Low-quartz undergoes a revers-
ible. rapid (displacive) inversion to high-quartz at 573°C.
This kind of rapid and displacive change takes place without
breaking any bonds. High-quartz is stable at atmospheric
pressure at temperatures from 573° to 870°C.

High-quartz converts into tridymite (high-tridymite)
at 870°C. This inversion is of the sluggish (reconstructive)
type. because in this case breaking of bonds take place.

Similarly. the sluggish (reconstructive) type of in-
version takes place between high-tridymite and high-cristobalite

Pressure. Kilobars

 

70‘

50‘

‘°I

 

Stishovite

Coesite

    
  

 

’

’fi’
.v" “\»———(not well known)

 

 

30-
’ z ’ ’ Low-Quartz / High-Quartz
2.. y
———(L.& H. Tridymite) /
(L.& H. Cristobalite) II
(E. Cristobalite) //
IOI /
I (a. Tridymite) ,’
(Keatite) ’ .. —— 1’ Liquid
-"T l
I I
7 A 4’- ~“ 1 I
“ IeaIIzefl sec 2.053 370 30 3 I410 ; I723 ;
In zoo:qu e 0 9 I200 I300 Ieoo
Temperature ° C

 

 

Figure 1. Stability Regions of the Various Forms of $102.

 

6

Liquid silica when cooled below 1723°C. crystalizes
with great difficulty. but it can be readily supercooled to
a glass. Vitreous silica or silica glass is capable of
existence at atmospheric temperatures up to 1000°C. or above.
where it slowly devitrifies and forms cristobalite as a stable
or metastable phase.

Relations between various forms of silica are ex-
plained by the phase diagram ”Stability Regions of the Vari-
ous Forms of 3102." (Figure 1)

The differences in free energy between quartz. tri-
dymite and cristobalite are very small. and the stability
relations apparently can be considerably altered by the en-
trance of H20 or of cations into interstitial positions.

The metastable formation of the relatively open. highly sym-

metric structure of cristobalite apparently is favored in

this way over tridymite and quarts (Frondel. 1962).

REVIEW OF PREVIOUS WORK

K. B. Krauskopf (1956) in his paper ”Dissolution
and Precipitation of Silica at Low Temperatures.” reviews
the earlier works of Morey and Hesselgesser (1951). Kennedy
(1950). Hitchen (19h5) and others. on the solubility of
silica at high temperatures. Also he reviews older litera-
ture on the geologic role of silica at low temperatures
cited by Roy (19h5) and Eitel (1954).

After reviewing the work of Alexander. Heston and
Iler (1953-55)} Krauskopf set up the experiments to extend
the work of Alexander..g§‘gl. in two principal directions:
the effect of temperature on the solubility equilibrium. and
the conditions under which silica is precipitated by sea
water. His effort was diverted toward obtaining many semi-
quantitative results of geologic significance rather than a
few strictly quantitative data. and he comes to the conclu-
sion about the behavior of silica in geologic environments:

In sea water amorphous silica has about the

same solubility as in fresh water. Silica in

true solution is not precipitated by electro-

lytes; colloidal-silica may be precipitated by

electrolytes. the rate and completeness of
precipitation depending on pH and on the kind

and concentration of the ions. Most of the

silica in natural waters is in true solution

rather than in colloidal diapersion. This

means that silica brought to the sea by streams

cannot be coagulated by the electrolytes of sea
water. The factors that keep the concentration

7

8

of silica below its equilibrium solubility

(with respect to amorphus silica) in most

natural waters are not completely understood:

the slowness of dissolution. the use of

silica by organisms. and slowly-established

equilibrium with crystalline silica or with

authigenic silicates doubtless all play a part.

The origin of sedimentary chert may be possibly

ascribed to dissolution of remains of siliceous

organisms and reprecipitation of the silica

(initially an amorphous silica). but not in

general to direct inorganic precipitation.

From Krauskopf's work it is not known whether or not
the polymorphs of silica were formed during dissolution of
the silica.

Similarly White. Brannock and Murata (1956) studied
the silica in hot-spring waters at Steamboat Spring. Nevada.
and in a few cold waters. Their results agree very closely
with those of Krauskopf concerning largely with the be-
habior of silica in nature. They make the following statement.

Evidence is lacking for the direct conversion

of gelatinous silica to opal. Some differences

in solubility probably exist between amorphous

Opal and opal that shows x-ray patterns like

that of cristobalite. (White. 1956)

In 1936 Fenner described tridymite of hydrothermal
origin in the Norrie Basin drill cove. At Mount Lassen.
California. Anderson (1935) found tridymite forming in lavas
that were being altered by sulphuric acid at temperatures
close to 90°C.. and Dowbraee (1876) described the alteration
of Roman bricks to opal and tridymite at temperatures as low
as 73°C. at Plombieres. France.

After taking into account above observations. White

(1956) makes the following statement:

9
The origin of cristobalite and tridymite in

hot springs is not clear. The minerals have

formed metastably. at temperatures far below

equilibrium temperatures. and in contact

with waters that were strongly supersaturated

in silica with respect to the stable mineral

quartz.

Corwin (1953) and others did some work regarding the
effects of alkali and flouride on the transformation of
amorphous silica to cristobalite or quartz. At 000°C. and
340 atmosphere silica glass was heated with aqueous solution
or water. quartz was formed in the presence of strong alkali
or flouride. However. in acidic or neutral solutions. even
when sodium or potassium chlorides were present. only cris-
tobalite was formed.

Carr and Fyfe (1958) carried out series of experi-
ments to determine the effect of pressure and temperature
on the rate of formation of quartz from silicic acid. Pres-
sure varied from 59.000 p.s.i. to 15.000 p.s.i. Temperatures
ranged between 325° to hh8°C. The time varied from minimum
6 hours at 59.000 p.s.i. to maximum 8h0 hours at 15.000 p.s.i.
They came to the conclusion that rate of crystallization is
much more sensitive to pressure than temperature and the
path followed in these reactions is: almost amorphous silica

cristobalite keatite quartz. A quali-
tative picture of this process is illustrated diagrammatic-
ally in Figure 2.

They considered the following steps in the process

of the formation of a new phase;

1. the starting material pass into solution.
2. nuclei of the new phase form.

10

3. nuclei of the new phase grow by transfer of
material from the decaying phase.

 

100

% Regions of Amorphous

Quart!
Phase 8102 or Cristobalite

 

 

 

 

 

 

 

6 aka
Time.fiours

Figure 2 Diagrammatic Representation of Phase
Assemblages During Typical Runs. (Carr. 1958)

A. G. Verduch (1958) in his paper reviews the litera-
ture on crystallization of silica by following peOple: Day
and Shepherd (1906). Kyropoulos (1917). Dwyer and Mellor
(193A). Akiyama (1901). and Cohn and Kolthoff (1948). In
these papers most of the work was done above 800°C. After
reviewing the above work he carried out a systematic series
of rate experiments at temperatures ranging from 9h5° to
1085°C.. and plotted isothermal rate curves of transforma-
tion of amorphous silica to cristobalite. His experiments
have demonstrated the existence of measurable nucleation

period. Verduch makes his final remarks as follows:

11

An intermediate metastable cristobalite phase.

having a well-defined degree of disorder. is

formed as a primary product in the heating of

silicic acid. The degree of disorder exhibit-

ed by this primary product could correSpond to

that of a superstructure having fairly well-

defined sequence rhythms of alternating three-

and two-layer structural units.

V. G. Hill and Rustum Roy (1958) considered Eitel's
(1957) review of the paper by Florke and carried out ex-
periments to demonstrate the low to high inversion in cris-
tobalite which is variable and depends on the structure of
the starting material and on the temperature and length of
heat treatment. using amorphous silica as a starting material.
differential thermal analysis was carried out and samples
were examined by powder x-ray techniques. Temperatures of
crystallization ranged from 900° to 1600°C. Time ranged
from one half hour to maximum of eleven days. Resulting x-
ray patterns showed mostly the presence of crystobalite and
very little tridymite and quartz.

Baranyai (196A) in his work shows that crystalliza-
tion of silica gel may be brought about by heating pure
silica gel to high temperature: but when heating silica gel
with various salts. crystallization to one or another form
takes place at lower temperatures. According to Zislke
(1950). if the temperature is above the melting point of the
salt. silica gel may or may not enter into chemical combina-
tion with the catalyst before crystallization takes place.
He thinks it is feasible that crystallization might take

place by the transfer of vibrational energy of an unmelted

salt. or the atoms of the silica may become arranged in a

12

certain pattern due to the presence of a salt as well as
the influence of the temperature.

Reviewing the above literature it can be seen that
the experimental work of the past few decades had yielded a
large amount of information on the chemical and physical
properties of silica and effect of pressure and temperature
on the rate of formation of quartz and other polymorphs of
silica from silicic acid. Studies of the crystallization of
silica gel using lithium salts at low temperature and vari-

ous proportions of salts are few.

EXPERIMENTAL PROCEDURE

Many commercial varieties of silica gels are avail-
able. but the silica gel used in this work was prepared by
the author. since commercial varieties may not be sufficient-
ly pure and truly amorphous.

The silica gel was prepared by mixing a solution of
sodium silicate and hydrochloric acid (Daniels. Mathews. and
Williams. 1941). Na251039°20 crystal was obtained from the
General Chemical Division of the Allied Chemical and Dye
Corporation. The impurities contained in sodium silicate
were: chloride (Cl) -0.005%. sulfate (sou) -0.01%. heavy
metals (Ast) -0.001% and iron (Fe) -0.005%. One liter of
sodium silicate solution with a density 1.15 grams per 0.0.
was prepared at room temperature 26°C.. and filtered free of
precipitated silica. 6.0N. hydrochloric acid was prepared
by diluting concentrated (12 N) hydrochloric acid. The im-
purities in hydrochloric acid were: bromide (Br) -0.005%.
sulfate (sou) -0.0001%. free chlorine (Cl) -0.00005%,
ammonium (NHu) -0.0003%. heavy metals (Ast) -0.00005%. iron
(Fe) -0.00001%. and other impurities were in negligible
amount. Twenty-five m1. of 6N hydrochloric acid was poured
into a beaker and 25 m1. sodium silicate solution was added
to this slowly. drop by drop. while continuously stirring

with a glass rod. care was taken so that the mixture remained

13

14
clear. The gel did not form immediately. The mixture
was set aside without disturbance for twelve hours at room
temperature. by which time the solution had set to a firm
clear silica gel. according to the reaction.
NaZSio3 + 2 H61 = H25103 + 2 NaCl
For the ease of preparation and thorough washing. small
(total 50 m1) batches of silica gel were prepared.
After the gel had set. it was cut into cubes and
washed with de-ionised water using succussion funnels. The
gel was washed until it was free of 01- as shown by the ab-

sence of precipitate with silver nitrate solution. It was

then soaked in four changes of de-ionised water during a four

day period. this water also being checked for 01- with silver

nitrate: all tests were negative. After four days the gel

was drained and allowed to dry at room temperature for twelve

hours. Finally the gel was dehydrated to a constant weight
in an electric oven for eight hours at 100°C. The silica gel
was shown to be completely amorphous by the presence of a
diffuse halo and the absence of lines on an x-ray powder
diffraction photograph.

Reviewing the work of Baranyai (196h) it was decided
to use the following six salts of lithium for crystalliza-
tion of amorphous silica at 700°C.

Lithium chloride
Lithium bromide
Lithium iodide

Lithium nitrate

Lithium carbonate
Lithium hydroxide

15

Table 11
Amount of Salt Added to % Lithium in the

Salt 100 ggg 9f Silica Ggl Salt Added
LiCl 3.5“ 0.5
7.08 1.0
1h.16 2.0
21.24 3.0
35-40 5.0
70.80 10.0
LiBr 6.20 0.5
12.h0 1.0
LiI 10.00 0.5
20.00 1.0
00.00 2.0
LiNO3 5.00 0.5
10.00 1.0
20.00 2.0
LIZCO 2.66 0.5
3 5.32 1.0
10.64 2.0
26.60 500
53020 10.0
LiOH 1.70 0.5
6.80 2.0
17.00 5.0
3#.00 10.0

16

For 0.5% lithium. 2.0% lithium. 5.0% lithium and
10.0% lithium in the sample. the amounts of the above salts
to be added to 100 grams of silica gel were calculated from
their atomic weight are shown in Table II.

Silica gel was ground and mixed in an agate mortar
for a period of about one hour with different amounts of the
six salts. Extreme care was taken in assuring a complete
and homogeneous mixture between the silica gel and the salts.
As shown in Table III. lithium was present in concentrates
of 0.5% and 2% as chloride. bromide. iodide. nitrate. car-
bonate and hydroxide. and in concentrates of 5% and 10% as
chloride. carbonate and hydroxide. A fifth set of 1.0 to
5.0 percent lithium as chloride with silica gel was also pre-
pared: before heating. 1.5 ml of ammonium hydroxide was
added to each sample to make it more alkaline.

The mixtures of amorphous silica and salt were heated
in covered platinum crucibles at 700°C. 1 10°C. in a furnace.
This temperature falls within the stability range of high-
quartz.

It was first decided to heat the five lithium
chloride-silica gel samples for time intervals of two. four.
six. eight and ten hours at 700°C. to determine the inter-
vals for proper crystallization and to note changes in crys-
tallization during these times.

After heating the five samples were washed with de-

ionised water to assure the complete removal of lithium

17

Table III

Sample Weight Sample Weight

 

Salt in Before Heating After Heating Percent
a Sample (Grams) Grams Loss
Set I
a. LiCl (0.5% Li) 0.0210 0.3293 21.85
b. LiBr (0.5% Li 0.0228 0.3065 18.05
0. L11 (0.5% L1 0.0232 0.3236 23.50
d. LiNO (0.5% L1) 0.0280 0.3500 17.30
e. Li 033(0.5% Li; 0.0272 0.3630 15.03
f. L1 H (0.5% L1 0.0173 0.3090 16.37
Set II
a. L101 (2% Li) 0.0200 0.2916 30.58
b. LiBr (2% Li) 0.0251 0.2679 05.50
0. L11 (2% Li) 0.0210 0.2209 07.52
d. LiNO (2% Li 0.0263 0.3073 27.92
e. L1 033(2% Li 0.0172 0.3 52 19.65
1. Li H (2% Li 0.0095 0.3 11 16.71
Set 111
a. L101 (5% Li) 0.3159 0.1795 03.11
b. L1 003(5% Li 0.0210 0.2831 32.81
0. L1 H (5% Li 0.0160 0.2899 30.38
Set IV
a. L101 (10% Li) 0.3020 0.2020 32.98
b. L1 003(10% Li) 0.017 0.2021 01.98
c. Li H (10% Li 0.011 0.2580 37.19
Set V

 

(1.5 m1 NHhOH

as
b.
ca
do
90

L101
L101
LiCl
LiCl
L101

(1%

 

added to each sample after weighing and
before heating)

Li)
Li)
Li)
Li)
Li)

0.2910
0.3025
0.3189
0.3296
0.3050

0.2199
0.2055
0.1979
0.1796
0.1675

20.53
32.06
37.90
45.50
05.08

18

.m .02 anm 09 a .oz Edam Scam ow so» mm xmos
mswsooop mam mmcHA .Hmm defiHfiw mo mumps: msonamosm

was» messages“ 0 .oz saw“ so mmCHH mo cosmmn<

mane scheme: meson 0H .mn s m.o n
meme scheme: meson m .nq a m.o e
ease scheme: meme: 6 .mg a m.o m
saws mafipmm: mason : .flq & m.o N
08H» mswpmmn mason w .«A & m.o H
mowafim msonaaoe< 0

.oz Edam

H mpmam

1-9

H can:

t.

 

 

20

chloride salt. testing the filtrate with AgNO and washing

5 to 6 times until there was no precipitate with AgMO3 solu-
tion. They were then dried for ten hours at 100°C. X-ray
diffraction powder patterns were made and it was determined
that a suitable heating time for proper crystallization was
four hours. Beyond this the lines on the powder photographs
became weaker. but there was no change in the phase crystal-
lized. the same lines being present on all the five patterns
(Plate I).

As shown in Table III each sample was weighed accurat-
ely on a chain balance (t 2.0 mg.) before and after heating.
Loss in weight of a sample can be accounted for by mostly the
loss of water and a small loss of salt.

Later. each sample was ground to approximately 200 to
300 mesh and powder mounts were prepared by coating a very
thin capillary tube. made of lead free glass with clear nail
polish. The tube was then rolled in fine powder until it
was uniformly covered. Thickness of the mount was less than
0.5 mm.and length was about 10 mm.

A 110.6 mm. diameter Debye-Scherrer camera was used
for recording x-ray powder patterns on Kodak Screen Medical
X-ray Safety Film. The film was mounted in the camera
according to the Straumanis-Ievins method. and after ex-
posure with a copper target and nickel filter for 5 hours
using 05 kilovolts and 17 milliamps. it was developed as

follows:

21

5 minutes in the x-ray developer.
é minute in the stop solution.
10 minutes in the fixer at 68°F.
From photographs x-ray diffraction powder patterns
were used to detect the crystal phase as shown in Table VI

and VII. X-ray data are shown in Tables IV and V.

22

Table IV

X-RAY DATA FOR SILICA POLYMORPHS
Most Intense Lines With Decreasing Intensity

Low quartz 3.30 0.26
(100) (35)
High-quartz 3.02 1.85
(100) (90)
Low-tridymite (Experimental 'd' spacings)
“039 “.12
(100) (100)
0.30 3.81
(100) (67)
0.30 0.08
(100) (90)
Low-cristobalite 0.05 2.09
(100) (20)
High-cristobalite 0.15 2.53
(100) (80)
Keatite 3.02 3.3;
(100) (70
Coesite 3.09 3.03
(100) (60)
Stishovite 2.96 1.5?
(100) (50

23

Table V
X-RAY DIFFRACTION PATTERN LINES FOR-SILICA POLYMORPHS

Polymogph Decreasing 'd' Spacing
Coesite 6.20
Low-tridymite 0.39
Low-tridymite 0.30
Low-quartz 0.26
High-cristobalite 0.15
Low-tridymite 0.12
Low-tridymite 0.08
Low-cristobalite 0.05
Low-tridymite 3.81
Low-tridymite 3.73
Coesite 3.03
High-quartz. Keatite 3.02
Low-quartz 3.30
Keatite 3.33
Keatite 3.11
Coesite 3.09
Stishovite 2.96
Low-cristobalite 2.80
Coesite 2.76
High-cristobalite 2.53
Low-cristobalite 2.09
Stishovite 1.98
High-quartz 1.85
Low-quartz 1.82
High-cristobalite 1.60
High-quartz 1.57
Stishovite 1.53
High-quartz 1.02
High-quartz 1.29

mowawm msonamoss
Adv epn>onmapm
“my mesmeoo
weavMox
mvwfihuwhpISOA
hwy spamsdIan:

mpnesenne-soq
spam:d:3oA

20

Ads memeormmem
va mpwpmcx
medampopmHMOIBog
mpHEhUHMvIzoA

Asemrwwq mo.oav
>H rem

vamowaww mzonmmos<

mpfipmmx
mpfiezcwuvIsoA
spamsd:cwa:
spamsUIBOQ

mpwfizvfihplzoq
spamSUIzoq

Adv mpfimmoo

Adv mpfi>onmfipm
mpwamnopmfimoIsoq
eefieaenmPIeog
spamsvnsoq

Assamemp an.mv
HHH pom

ZOHB¢NHAQ<9mNmo mo manbmmm

mowaam msonamos<
ovwshpmeI3oH
spamvaBOA

mesanm msornmoee
new eeneormmpm
menssenmp-sog
spamsdIsmH:
NBHMSUIBOA

fies eeneenmsem
fies smashes
densasaapIsoq
uvmmva3og

mowawm muonaaos<
va.mpapmmm
epmsamanpuzoq
spamsUISwwm
spamsuI3oq

moflawm msosaaoe<
memesenep-som
spamSUIsoq

hwy spamSUIanm no

Asa demands
ovwampopmwnoIsoA
mpwshcfippnzon
spamsUI3oq

AssfinmhINpSV
HH rem

 

H> manna

mowawm msozamos<
any spamsu:zog

so Ham msozamos<
v

a
As spamsdIsoA

mewESUHHPIBOA
Adv seadeasmwm
NPLMSUIZOA

womawm muonmnoe<
va spamvaanm
spamzdIsoq

moaawm msonam084
memesenmp-soa
spamDUIsoA

wowafim msonamoe<

mPAEhUwHPIBOH
spamSUIBog

AEanwHH Rm.ov
H rem

scan .0
comma .e
mOZHS .e

qu .6
mmaq .n
Hons .m
eeee<
eHem

25

vaopa>onmavm
reasseameuson
spamSUI3oq

HA fin .0

Amy epaeormnem
Amy museums
owwamnopmamoI3oA
menasenmpuzon
spadeI3oA

“A R: .c

spasmox ovdpmox
opwampovmam013og opdamnopmfiao:soq
memeseamPIrom reassesmp-sog
Asv spamsd::m«m Apv uphd:d::m«:
spamsu:sog spam:UIzoA

HA Rm .0 an RN .9

Amonzz +.eenMewmmeo.m or 6.02

avenues
ornsseane.soq
Ass epnm=6-rmn=
spamsdIBon

“A RH .m

:o :2
mafia

Howe

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Ilwn _ _ _ . .2 _ _ n __ _ m _ m _ _ . _ IOVIZ
_" .Eullé: Jilit .
e e e. _ e _ Z .03
_ _ ra_ era _ era
0 G a 0
Mi...» 2 < _
I18 _
III: x “ IO_J
lllll ._. ._. ._. m
IIIII are re .
a a so
<3 _ _
moumj
III: II.—. b. P
re
llllll a a a 8
J
--en _
II; mozj
IIIIIP P
~20
llllll G G
<
._ _
II; 3
llll»
IIIII :0 «:0
llllll O G
. _
hm]
IIIII e ‘ e
lllllll a a
"_ I- — ‘
.. _ __ _ _ _
HHHQIU u exu _ _ _ .03
IIIII a. ._. h s.
380.0. 3 .\.0.n _.._.\. 0.? _I_ e\eo.m 1.. 8 ON _I..\. 0.. 3 No.0

 

a medc.

 

27

Table VII is the condensed form of Table VI. It is

designed by using following symbols for polymorphs of

silica.

Qh

Th

Ch

Co

Low-quartz
High-quartz
Low-tridymite
High-tridymite
Low-cristobalite
High-cristobalite
Keatite

Coesite
Stishovite

Amorphous silica

INTERPRETATION AND RESULTS OF X-RAY PATTERNS

Interplaner spacings ('d' spacings) for most of the
lines on each photograph were calculated and using x-ray
data from Table IV powder photographs were interpretated as
follows:

Set I (0.5% lithium)
See Plate II)

a. LiCl

The most intense lines on the photograph are those
of low-quartz: also most of the other lines are of low-quartz.
Along with this there is a unique faint line (3.70) of low-
tridymite. Amorphous silica is present and has obscured the

lines 0.39 and 0.12 of low-tridymite.

b. LiBr

 

The three most intense lines of low-quartz (3.30,
0.26 and 1.82) are present. One faint line (3.?) of low-
tridymite is present. Most of the remaining lines are of

low-quartz.

c. _i;

Three most intense lines (3.35. 0.26 and 1.82) of
low-quartz are present. One very weak back reflected line
(1.02) of high-quartz (?) is present. Amorphous silica is
indicated by a wide diffused halo.

28

29

mvfixoapzz
opmcopamo
spams“:
scape“
opHanp

memmoare

esseeafi
esnrena
eemrpaa
ssnnema
searema
Susanna

an s m.o
“A a m.o
as a m.o
an s m.o
as a m.o
an a n.o

HH deHm

MH
0H
OH
0H
DH
0H

.02 anm

HH 090.:

 

31
d. LiNO
__2
The three most intense lines are those of low-quartz.
There is a very low intensity line (1.29) which appears to
be of high-quartz (?). A weak but unique line (3.79) of low-

tridymite appears between two intense lines of low-quartz.

e. Li2002

This sample has no sign of any of the polymorphs of
silica. Very strong diffused halo of amorphous silica is
present. There are two very weak back reflected lines pre-

sent. one of which may be of low-quartz.

1.1ngg

This x-ray powder photograph is almost identical to
that of above LiZCOB. Again amorphous silica is represented
by very strong diffused halo. One of the two back reflected
lines may be of low-quartz.

Set 11 (2.0% lithium)
See Plate III)

a. LiCl

Interplaner spacings were calculated for all lines
on a photograph. Three lines (0.25. 3.30 and 1.82) of low-
quartz are present. Three lines of low-cristobalite (0.05.
2.07 and 2.80) are present. There is a definite line (3.70)
of polymorph low-tridymite present. Keatite (?) is repre-
sented by the line (3.02). which can also be that of high-

quartz (?). There is a line (3.13) which could be accounted

32

vaKOAUh:
opmconamo
manna“:
evapow
mvdsoan

meanders

anagram
searean
seareaa
searpna
descend
anagram

en
en
es
CH
as

ea

HA R 0.N
“A R o.N
“A R 0.N
“A R o.N
«A & o.~
“A R o.~

HHH endam

MHH
mHH
UHH
OHH
DHH
mHH

.02 Saab

33

.HHH .0» Cam

 

 

30
for keatite (?). Remaining most of the lines are of low-

quartz.

b. LIB;

In this sample major phase of silica is lowbquartz.
which is represented by the three most intense lines (3.30.
0.26 and 1.82). One weak line (3.68) of low-tridymite is
present between two most intense lines of lowbquartz.

Amorphous silica is present.

0. Li;
Low tridymite is represented by the most intense and

unique line (3.73) on the photograph. All three characteris-
tic lines of low-quartz are present. Only one definite line
(1.85) of high quartz is present. Two very weak high order
lines of keatite (?) are present. Diffused halo represents

amorphous silica.

In this photograph all three most intense lines
(3.30. 0.26 and 1.82) of low-quartz are very clear. There
is one faint line (3.73) of low-tridymite present in between
two most intense lines of low-quartz. There are two weak
lines of keatite (?) and two very weak lines of stishovite (?)

are present.

e. LizCOI
Lines on this photograph are very faint. Seven

lines were measured. There are only two lines (3.30 and

35
0.26) of low-quartz present. Also there is one line (1.85)

of high-quartz present. One faint but unique line (3.70) of
low-tridymite is seen. There is a possibility of stishovite
(?) which is represented by line 1.99. Amorphous silica is

present.

f. LiOH

Lines on this photograph are very weak and most of
them are of low-quartz. Only one very faint line (3.70) of
low-tridymite is present. Amorphous silica is shown by
diffused halo.

Set III (5.0% lithium)
See Plate IV)

a. LiCl

In this sample there is a definite presence of low-
cristobalite and low-tridymite which is shown by one line
each (0.0? and 3.73 respectively). Low-quartz is represented
by only one line (3.35). Presence of stishovite (?) is
shown by lines 2.93 and 1.53. Line 6.05 may be that of
coesite (?)

e. L12003
Most of the lines on this photograph are that of
low-quartz. There is one definite line of low-tridymite

(3.72) present.

f. LiQH

Lines on this photograph are very clear. One line

(3.70) of low-tridymite is present. All three lines (3.02.

seasons»: asdnpna an as u 6.6H e>H

.1 crescendo seamen” an an a 6.60 o>H
ceasefire sadness an «a a o.oH m>H
seasons»: anagram as an a o.m «HHH
summonses sadness as an a o.m eHHH

meanders searena an an.“ 6.“ eHHH
.oz sens

>H mvmam

>H 0» nah

 

38
3.32. and 3.11) of keatite are present. Only one line (1.86)
of high-quartz is seen: line 3.02 could be that of high-
quartz. Also one line (1.82) of low-quartz is present.
Amorphous silica (?) may be present.
.Set IV (10.0% lithium)
See Plate IV)

a.‘Lin

In this sample again a definite line (0.05) of low-
cristobalite is present. Low-tridymite is shown by line
3.72. Very faint line 5.0 may be that of keatite. Stishovite
(?) may be present which is shown by two faint lines (2.91
and 1.53). Low-quartz seems to be totally absent in this

sample. which is shown by lack of lines of low-quartz.

80 L1 00
__Z__1

Most of the lines are that of low-quartz. There is

one line (3.73) of low-tridymite present.

f.lLiQfi
In this sample lowbtridymite is definitely indicated
by line 3.73. Keatite is shown by all three lines (3.02.
3.32. and 3.10). There is a possibility of high-quartz (?).
stishovite (?). and coesite (?) which are shown by faint
lines (1.88. 2.92. 2.7 respectively). Amorphous silica is
shown by diffused halo. Here again low-quartz is absent.
§23_1 (1.0 to 5.0% lithium

plus NHuOH)

(See Plate V)
a. 1% Li + NHuOH

 

This sample shows presence of low-quartz by two

39
lines (0.27 and 1.82). Low-tridymite is shown by a definite
line (3.73). Presence of keatite is indicated by strong
lines 3.00 and 3.11. High-quartz (?) may be present which
is shown by a very weak line (1.87): line 3.00 could be

accounted to high-quartz (?).

b. 2% Li + NH40H

 

This film definitely shows presence of low-quartz by
all three lines. Low-cristobalite is definitely present
which is indicated by line 0.06. Line 3.73 shows presence
of low-tridymite. Keatite is again shown by lines 3.02 and
3.11. High-quartz (?) may be present which is indicated by
very weak line 1.87.

 

Lines 0.05 and 2.09 show presence of low-cristobalite.
Low-tridymite is shown by line 3.72. Here again all three
lines of keatite are present. Low-quartz is shown by the

only line 1.82. High-quartz (?) may be present.

d. 0% Li + NHuOH

 

Low-cristobalite is present and it is indicated by
line 0.05. Line 3.72 shows presence of low-tridymite. Low-
quartz is shown by all three strong lines. Stishovite (?)
may be present which is indicated by lines 2.91 and 1.97.

One line may be accounted for keatite (?)

00

xoemz
moemz
momma
xoemz
moemz

+ 4- «0 + +1

eeamoare
seasoned
denudare
unneeded

eemmonee

museums
esserafi
senrean
Edwards
esnnpna

es
en
as
es
as

an s o.m
we a 0.:
an a o.m
“A a o.~
an a 0.0

> oPde

e>
e>
e>
p>
m>

.oz Edam

p 8.2

 

02

e. 5% L1+ NH OH

0
In this sample low-cristobalite is absent. but low-

 

tridymite is shown by presence of line 3.73. All three
lines of low-quartz are present. Possibly stishovite (?)

may be present. which is shown by lines 1.53 and 1.97.

SUMMARY

All the heating in this study was performed at 700°C.
and at one atmosphere of pressure. Temperature of 700°C.
was selected because Baranyai (1960) in his work found only
formation of low-quartz at 660°C. and 720°C. in the presence
of 2% and 5% L101: whereas temperatures above 780°C. he did
find polymorphs tridymite and cristobalite. So it was
decided to use temperature of 700°C. and several other salts
of lithium. This temperature falls within the stability
range for high-quartz.

Upon examining results in Table VI it is evident
that both low-tridymite and low-cristobalite. are present in
sets 11. III. IV and V in the presence of salt LiCl. and
more so with the addition of NHuOH. Keatite seems to be
present in samples having more alkaline conditions. Amor-
phous silica is common in sets I and II but as lithium con-
tent increases in sets III and IV most of it is crystallized:
also amorphous silica crystallized in different polymorphs
in the presence of NHuOH which is evident from set V.

Low-quartz is present in all samples except in
samples 'a' and 'f' of set IV. Even though temperature 700°C.
lies in the stability range of polymorph high-quartz. it is
obvious from Table VI that. this polymorph does not exist in

43

00
most of the samples except in questionable traces. Other
two less common polymorphs. coesite and stishovite. are also
found in questionable traces.

Low-tridymite is present in all samples except in
samples e and f of set I in which very little crystalliza-
tion occurred.

Over all examination of x-ray film study shows that
formation of polymorphs of silica was much more prominent in
samples with higher lithium content. which is shown by clear-
er x-ray patterns and also by the absence of amorphous
silica in sample with higher lithium content.

Temperature used in this study is above melting

points of all lithium salts used.

SPECTROGRAPHIC ANALYSIS

The purpose of this study was to do a qualitative
analysis of few samples to determine whether lithium salts
have entered into the structure of crystallized silica. Six
samples of set 11 (2.0% Li) were chosen for spectrographic
analysis.

All six crystallized samples were washed thoroughly
for at least 6 times with di-ionised water to assure com-
plete removal of lithium salts. until all tests for all six
salts were negative. Then they were dried for 20 hours at
100°C. in a low temperature oven. Each sample of 100 mgs.
was weighed and ground to -200 mesh in an agate mortar. An
equal amount of spectrographic graphite was added to each
sample. Mixture was then shaken vigorously in a small glass
bottle for 10 minutes to assure homogeneous mixture.

The above mixture was then tightly packed into the
cavity 3/16 inch deep and 1/0 inch in diameter. of specto-
graphically pure carbon electrodes. One electrode for one
sample was used.

The analysis was conducted to determine only lithium
in each sample. therefore it was decided to record the

spectrum of lithium using two samples of LiZCO This pro-

3.
vided faster means of detecting lithium in the sample. Two

45

46
wave-lengths 2070-3070 A° and 6000-7000 A° were used to

record the spectra of pure LiZCO It was discovered that

the photographic plate used was gore sensitive to 2070-3070
A° wavelength for lithium lines.

All six samples were arced using the conditions
described below. Iron spectra were recorded before and
after. using iron electrodes. for the purpose of orientation
on the plate. Also Li2003 spectra were recorded on the same

plate for the comparison with sample.

Samples were arced under the following conditions:

Excitation : Low voltage interrupted
Voltage : 250 volts
Current : ---------
Resistance : 30 ohms
Inductance : 60
Capacitance : 0 mfds.
Time : 15 seconds
Transmission : 100%
Slit width : 20 microns
I

Wavelength 2070-3070 A°
The following three lines of lithium were observed in all
six samples:

2562.50 weak

2701.31 strong

3232.61 very strong
Most lines were weak and they seem to be due to very little
amount of salt remaining in the sample. Although samples
were thoroughly washed there is a possibility that some salt
might have remained in the sample or very small amount of
lithium may have entered into the structure of polymorphs of

silica.

CONCLUSION

It was shown by Zielke (1950) that silica gel heated
up to 900°-1000°C. did not crystallize in any of the poly-
morphs of silica. By this study it is shown that amorphous
silica gel does crystallize in the presence of all six
lithium salts used.

High temperature polymorphs of silica. tridymite and
cristobalite can be formed far below their stability range
in the presence of lithium salts. without inverting into
quartz. which is a stable form at that temperature. This
clearly indicates that presence of lithium promoted forma-
tion of high temperature forms at 700°C.

It is evident that less common polymorphs of silica.
keatite. coesite. and stishovite can crystallize from silica
gel in the presence of lithium salts.

Crystallization of cristobalite from silica gel can
be achieved by increasing lithium content and alkalinity of
the samples.

Four hour heating time was found to be more suitable
than ten hours which may indicate that longer heating may
disrupt the structure of high temperature polymorphs.

Spectrographic studies indicate that lithium actually

may enter into the structure of various polymorphs of silica

0?

08
in very small amount. Use of x-rays prove to be the best
for identification of polymorphs of silica.
This study may not have direct implication in geo-
chemistry. but it certainly should be taken into considera-
tion while studying high-temperature polymorphs of silica in

nature or laboratory and ceramic industry.

RECOMMENDATIONS FOR FURTHER RESEARCH

The present study raises several questions regarding
the cause of crystallization of silica polymorphs at low
temperature in the presence of lithium salts. How and why
does anomalous crystallization take place? Whether it takes
place a) due to increasing amount of alkali cation like
lithium with small atomic number. or b) due to the vibra-
tional energies of (lithium) salts. or c) it is only due to
the presence of anions. or d) due to the small amount of
water present in the silica gel and salts. or 9) nuclei
with varied properties around which the different polymorphs
grow. To answer some of these questions following few
recommendations for further research may be helpful.

From Plate I it is obvious that lines on film of 10
hours heating are weaker than lines on films of 2 and 0
hours heating time. Further studies with longer time inter-
vals may prove to be beneficial for investigating the effect
of a time factor on crystallization.

Increased concentrations of lithium and mixtures of
various lithium salts should be used to see whether crystal-
lization takes place due to increase in cation or anion or
both.

Use of lithium fluoride (LiF) is recommended because

09

50
it is believed that the small size of Li and F atoms may be
more effective in promoting crystallization. Other lithium
compounds and organolithium compounds should be tried to
throw more light on the role of lithium in crystallization
of silica gel.

It is obvious from the Table VI (Set V) and Plate V
that crystallization was more pronounced in the presence of
NHuOH. which raises another question. whether ammonium ion
also promotes the crystallization of silica gel at lower
temperature and pressure. Keatite seems to crystallize more
abundantly present in samples with NHuOH added. This should
be followed up with increasing concentration of NHuOH.

In general further study should be carried out with
increased pressures and varying temperatures. This study
was carried out under dry conditions. but presence of water
may have effect on crystallization temperature and pressure.
For better workability large amounts of silica gels should
be used.

Use of a differential thermal analysis (D.T.A.) with
limited application. and infrared spectra for determining
structure and bonding characteristics within the molecule may
prove to be helpful in addition to x-ray diffraction. X-ray
diffraction is the simplest tool for polymorph identifica-
tion but provides limited data: it is strongly recommended
that a Geiger counter x-ray spectrometer be used to avoid
the difficulty of comparing line intensities of powder
photographs with each other. Use of a Geiger counter X-ray

51
spectrometer gives better qualitative and quantitative (by

using 100 % standard) results in less time.

REFERENCES

Ahrens. L. H.. 1950. Spectrochemical Analysis. Addison-
Wesley Press. nc.

Azaroff. Leonid V.. and Buerger. Martin J.. 1958. The Power

Method in X-ray prstallography. McGraw-HilI Book Co..
Inc.

Babor and Lehrman. 1957. Textbook of Chemistpy.

Baranyai. Paul D.. 1960. ”The Crystallization of Amorphous
Silica Using Salt Catalysts.” M.S. Thesis. Michigan
State University.

Berey. L. G.. and Thompson. R. M.. 1962. ”X-ray Powder Data

for Ore Minerals.” .S,A, Memoir 85. The Peacock
Atlas. New York.

Brindley. George W. (Editor). 1957. Index to the X-Ra
Powder Data File. American Society For Testing
Mater als.

Carr. R. M. and Fyfe. W. 8.. 1958. Vol. 03. ”Some Observations
on the Crystallization of Amorphous Silica.” The

American Mineralogist.

Corwin. J. F.. Herzog. H. H.. Owe. G. E.. Yalman. R. G. and
Swinnerton. A. C.. 1953. 75:3933. “The Mechanism of
the Hydrothermal Transformation of Silica Glass to
Quartz Under Isothermal Conditions." Journal of the

Aperican Chemigal Sociepy.

Cotton. F. A. and Wilkinson. G.. 1962. Advanced Inorganic

Chemist . Interscience Publishers. John Wiley and
Sons. Inc.

Frondel. Clifford. 1962. The S stem of Mineralo of James
D Dana and Edward S Dana. 7th Edition. Jofifi Wiley
W

Henry. N. F. M.. Lipson. H. and Wooster. W. A.. 1960. The

Inpeppretapion of X-Ray Diffraction Photographs.
MacMLllan and Co.. Ltd.. New York.

 

52

53

Hill. V. G.. and Roy. Rustum. 1958. ”Silica Structure
Studies. Pt. V.. The Variable Inversion in Cristo-
balite.” Journal of the American Ceramic Society.
Vol. “'1, e 5 pp. " e

Iler. R. K.. 1955. The Colloid Chemist of Silica and the
Silicates. CorneII UniversI¥§ Press. New York.

Klug. Harold P. and Alexander Leroy E.. 1950. X-Ra Diffrac-
tion Procedures for Pol c stalline and Kmo Hous
NaterIaIs. John Wiley and Sons. Inc.

Krauskopf. Konrad. 1956. “Dissolution and precipitation of
silica at low temperatures“. Geochimiga et Cosmochimic
Acta. 10:1-25. Pergamon Press. ew York.

Lange. Norbert A.. 1956. Handbpok of Chemistpy. Handbook
Publishers. Inc.

Mason. Brian. 1952. Principles of Geochemistgy. John Wiley
and Sons. New ork. pp. " 90

Pollack. S. S.. E. P. Whiteside. and D. E. van Farowe. 1950.
'X-Ray Diffraction of Common Silica Minerals and
Possible Applications to Studies of Soil Genesis.”

8911 Séience Society of America Prpceedipgs. Vol. 18.
pp. 2 ~272.

Smits. Benjamin. 1926. “Silica Gel.” Ph.D. Thesis. Michigan
State University (College).

Sosman. Robert. 1926. T 9 Pro erties of Silica. American
Chemical Society onograp er es. e Chemical
Catalog Co.. Inc.. New York.

Verduch. A. G.. 1958. ”Kinetics of Cristobalite Formation
From Silica Acid.” J urnal of the American Cera ic
Sociepy. 01:027-032. Part 11.

White. Donald E.. Brannock. W. W.. and Murata. K. J.. 1956.
“Silica in Hot—Spring Waters.” Geochimica et

Cpgppchimipa Acta. 10:27-59.
Whiteside. E. P.. 1907. "Preliminary X-Ray Studies of Loess

Deposits in Illinois.” Soil Science SO°§°§¥ of

Aperica Proceedipgs. o . . PP. - .
Zielke. Clyde W.. 1950. “The Salt Catalyzed Delegation of

Silica Gel.” B.S. Thesis. University of Wisconsin.

   

HICHIGQN STQTE UNIV. LIBRARIES

I III II III III

 

312930107 8314