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-,
Journal
of
Research of the National
Burea
u
of
Standard
s Vol. 53,
No.6,
December
1954
Re
se
arch
Paper
2554
Some
Properties of Strontium
Hydroxide
and
Its
Monohydrate
Elmer T.
Carlson
Strontium
hydroxide,
Sr
(
OH
)2,
was
prepared
by
hydration
of
st
rontium
oxide
under
pressure
at
4000 C.
Th
e
monohydrate
was
prepared
by
h
ydration
of
the
oxide
at
1680 C.
and
also
by
evaporation
of a boiling sol
ution
of
strontium
hydroxide
.
Optical
properties
and
X-ray
powder
diffr
action
pattern
s
are
given.
1. Introduction
Str
ontium
h
yd
roxide,
in
the
form
of iis
oeta-
hydrate
, Sr (
OH
)2
·8H
20 , is a sub
sta
nce familial' to
the
chemist. Various low er h
ydrates
have been
postulated
front
time
to time, bu t there seems to be
li
tt
le evidence of th e
ex
i
stc
nce of
any
excep t
th
e
monohydrate,
Sr(
OH
h·
H2
0.
De
hydration
st
udies
by
several investigators [1,2,3) 1 give fairly de rinite
data
concerning
the
dissociation of the
ortahydrate
and
of
the
unb
ydrated
hy droxid
e.
Equation
s
relating
the dissociation
pr
essures of
stro
ntium
hydroxide a
nd
its
octa
h
ydrate
to
te
mp
era-
ture
are given
by
Tamaw
and
Siomi
[3).
From
t
he
se equations,
the
temperature
at
which
the
disso-
ciation
pre
ss
ure
reac
he
s 760
111m
is calculated
to
be
92° 0 for Sr(OH)2·8
II
2
0
and
701° 0 for
Sr(OHh
The
s
hap
e of the
di
ssociation c
urve
i
ndi
cates
that
it
monohydrate
exists,
but
its dissociation
temperature
is
not
clearly defined.
In
view of
the
amo
un
t of work done
on
Sr (OH)2
and
its
monohydrate,
it
is somewh
at
surprising t
ha
t
there
appears to
be
no published
data
on
the
optical
properties of these compounds.
X-ray
dif
l"
raction
patt~rns
were
published
by
Huttig
and
Arbes
[1),
but
III
such
form
that
they
are
very
difficult to
translate
in
terms
of in
lerplanar
spacings, or even
to use as a basis for iclentification.
In
connection
with
some h
ydrotherma
l studies of
stronti
um
compound
s,
it
was necessary
to
be
able
to identify
the
various forms of
the
hydroxide.
Accordingly,
the
hydroxide
and
its
monohydrate
were prepared, a
nd
t,
heir
more useful identifying
properties determined.
2.
Procedure
and
Results
Stro
n
tium
carbonate,
reagent
g
rade
, was
heated
at
1
,3
00
° 0 to conve
rt
it
to t he oxid
e.
The
dry
oxide was th
en
exposed to
water
vapor
in a pressure
bomb
at
400° 0 for 3
day
s.
The
product
wa
s a
dry
powder
containing
0.98 mole of
water
per
mole of
SrO, closely
approximating
the
composition of
1 Figur
es
in brackets indicate litemture references
at
the
en
d
of
this paper.
371
Sr (
OH
h
Th
e
crysta
ls averaged
about
20
p.
in
diameter
,
b
u
~
were somewh
at
rounded
and
irregular,
so t
ha
t t he
Iel
eal s hape
co
uld
not
be
determined
.
The
y apPcflrecl to be
in
th e
form
of relatively thi
ck
pla
tes. T he
crysta
ls dc
cr
ib
ed were
pr
e
par
ed
wit
h
a
modcr
atc excess of w
ater
in
the
bomb
.
l~edu('ing
the
water
to the stoic
hi
om
et
ri
e
quantity
resulted
in
crysta
ls th
at
were
m1
.1
ch
sma
ll
er
but
of th e same
composition. The opt ical
pr
opcrt
ies are as follows:
Rcfraetive
incli
ces,
0'
= I.S88,
/J
= 1.S99, a
nd
')'
= 1
.61
O'
charactcr, biaxial ; sign, p
os
iti vc; aml
opt
ic axial
angle 2V,
nearly
90
°.
Hydrothe
rmal
treatment
of
stronti
um
oxide
at
168
°
0,
in the pre
se
nce of a s
light
excess
of
watcl',
res
ulteclm
a procluct having 1.9S moles of H2
0 pel'
mole of
81"0,
a
ppr
oxim
ately
the
composition of
Sr(OI-Ih
·H
2
0.
The
crystals wcre
lar
ger
than
th ose
~les~ribed
above
but
quite irreg
ular
in shape.
Th
e
mehees
are
0'
=1.S70,
/J
=1.589,
and
,),
=1.610 '
c
h
~ract;r,
?ia.xia~;
sign,
l?o
sitiye ;
aJ~d
2V nearl);
90.
1:
he
s
lmll
ant~'
m optlcal
proper
tl
('s
point
s to a
dose
re
lationship between
the
hyclroxide
an<l
it
monohydrate
, which is
borne
out
'by
the
similarit"
of th e
X-ray
patterns.
.
The
monohydrat
e was also obtainell
b,
" slow
evaporation
of a
saturated
solution of str'o
ntium
hydroxide
at
the
boiling
point
.
Many
of
the
larger
crysta
ls
\~
r
er?
in.
the
form
of hexagonal prisms,
although
It
IS
eVIdent from
the
optical
propertie
s
th
at
t
he
symmetry
cannot
be
truly
hexagonal. T he
prel?aration,
when
dried
at
110°
0,
lo
st
weight
eq
mval
e
nt
to
1.23 moles of watel'.
At
900° 0
it
lost
an
a
ddi
tiona
l 1.02 moles, correspo
nding
to con-
version to
Sr
O.
The
loss
at
110° 0 is
evidently
due
t?
the expulsion of
the
1 molecule of
water
of hy
dra-
tIOn,
the
sma
ll cxcess
presumably
resulting eith
er
from
entrapped
moisture
or
from
the
presence of a
small
amount
of
the
octahydrate
. :
Most
of
the
pr
ec
ipitated
hydroxide
adhered
tenaciously
to
the
fl
ask,
and
there was microscopic evidence of
reaction
\\
'
ith
the
glass,
with
the
formation
of
minute
c
ry
sta
ls
of
strontium
silicate h
ydrate
(3SrO.2Si02·4H2
0 )
[4).
The
fact
that
strontium
h~
T
droxicle
monohydrate
is
formed
under
these con
di
tions indicates
that
it
is
the
stable
phase
at
th e boiling
point
.
