Download Rocks, various soils, clays and sands are composed almost entirely

i
PREFACE
Rocks, various soils, clays and sands are composed almost
entirely of silicate minerals and
silica.
This predominance of sili-
cates and alumino silicates is reflected
in the abundance of oxygen,
silicon
and
aluminium
which
are
commonest
in
the
Silica has stoichiometric composition presented as S10
includes
o tn 2).
hydrated
species
with
composition
earth I s
2
crust.
which sometimes
SI0 2 :XH 20
(where
X
=
Tho mlnnrnl AlllcntflA. TlArticulnrly clny minerals 1.e. layer"d
silicates also known as "phyllosilicates" (phyllo = leaflike), are essential
components
of so11,
to
which
we owe our survival.
They are
also raw materials for some of the mankind I s most ancient and essential artefacts: bricks,
social
pottery,
developments and
tiles
etc.
However,
growth,~ the
industrial
synthetic materials is rising in enormous rate.
with
continuing
need of artificial or
The increasing demand
of synthetic silica and alumino silicates in the market since last four
decades
is
applications
due
of
to the rapid
different
changes taking
types
of
amorphous
place in the industrial
and
crystalline
silica
and alumino silicates.
In
the
present
investigations related
study
the
stress
has
to amorphous silica and
been given on
the
modification of natural
Alumino AlllcAtOA pArticularly clay minerals of Amectite group.
Properties
of
amorphous
silica
such
as
specific
surface
and porosity can be varied within a largo range which are attributed
ii
to ultimate particles of colloid
in aggregates.
range,
of
their packing
(arrangement)
The clay minerals also have particulate matter in colloid
the plate like structure and large surface area.
mnko
tins
size and
slllcn
applications
compounding,
onel
like
liquid
alumino
silicates uniquely
surface
coa tings,
carrier,
thickeners, free-flow aid,
These proper-
suitable
for number
rubber-reinforcement,
beer-stabilizer,
toothpaste
dessicant adsorbent etc.
plastic
abrasives,
Since these mate-
rials are chemically inert and non-toxic they find growing applications
in food
and pharmaceutical industries.
blocking
agent
in
plastic
They are also used as anti-
industries and
matting agent
in
paint and
The clays are widely used in drilling fluid in petroleum
varnishes.
industry.
The dissertation consists of two parts.
Part-I
includes
studies
on
synthesis
of amorphous
silica
precipitated
silica
by acldulRtJon of sodJum sJ]jcate.
As
sillca
gels,
pyrogenic
are industrially important products,
synthesis is found
pyrogenic
much
silica
silicas
and
majority of the literature on the
in the patent archives.
However, silica gels and
have been intensively studied academically,
but not
information is available in literature on the systematic studies
of the changes in surface properties of precipitated silica under different conditions with academic interest.
efforts
silica
have
varying
been
the
focussed
synthetic
to
In the present investigation,
understand
parameters
the
of
surface
properties of
precipitation
procedure.
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Part-II
silicates
i. e.
includes
clay
modification
minerals
for
the
studies
of
preparation
natural
of
alumino
pillared
inter-
lnyered ClAY" (PIl.e).
The
swelling
phyllosilicate
are naturally occurring catalysts.
minerals,
known
as
smectites
Acid mOdified smectites were used
as petroleum cracking catalyst until mid 60' s when they were replaced
by more thermally stable and shape selective zeolite catalysts.
inherent problem
with zeolite catalyst/adsorbent
crude oil is its relatively small pore size
escalation of oil prices in early 70 I S
in processing heavy
(0.2 to 0.9 nm).
having
stable structure
with
The
prompted the investigation of
catalytic material for processing of heavy crude oils.
material
The
large
pores,
In search for
basic concept
of
pillared clay gradually emerged and consequently a new class of smectite intercalated compounds was synthesized which makes use of robust
poly-hydroxy
metal cation as molecular props or pillars between the
Rillentn InynrR.
The
cationic
clays
hydroxy
of
smectite
groups
oligomers of different
can
metals
be
intercalated
(AI,
Si,
Zr,
with
Ti
and
transition metals) as pillars and thus properties of the products also
can be widely varied.
been
studied
The intercalation of clay with Al and Zr has
extensively
and
AI-pillared
smectite
is
thought
to
be
the best understood one.
In
the
present
investigation,
modification study of Indian
bentonite for the preparation of thermally stable PILC has been undertaken by intercalating cationic oligomer of hydroxy aluminium (COHA).