Verification of a mechanism for nucleating crystallization of supercooled liquids

Materials Chemistry and Physics, 25

(I 990) 199-205

199

VERIFICATION OF A MECHANISMFOR NUCLEATINGCRYSTALLIZATIONOF SUPERCOOLED

A.E.M.

ANTHONY,P.F.

Department

BARRETTand B.K. DUNNING

of Chemistry,

Received

October

17,

Trent

1989;

University,

accepted

Peterborough,

December

Dnt.

K9J 788 (Canada)

4, 1989

ABSTRACT Earlier

work has suggested

undergo

volume

between

two layers

pressure.

expansion

These

to which exposed this

of the

the

material

crystals

and the without is used

to the

in an attempt diphenylamine

Simon equation

points

for

these

are

somewhat

advanced consistent

In order

with

the

to test

to determine and phenyl

compounds.

to account

for

the

this,

by the

the

trapped point

validity

the

high

the

and the

original

hypothesis.

proposed

that

results

are

of the

crystals

of this

can be at

hypothesis,

melting

known high

pressure

determined

the

points

have been

points,

trapping

crystals

The data

temperatures melting

the

of the

pressure

salicylate.

predicted

of high

hardness

these

the

which clamped

The maximum pressure

melting

made to the

Although that

are

to nucleate

liquids.

to which

and a comparison lower

be used

is given

represent

of crystals crystals

them in regions

supercooled

can be subjected should

temperature when the

trapping

may then

maxlmum temperature

method

melting

is raised

thereby

crystals

pressure.

benzophenone,

the

corresponding

melting

elevated

method

of material trapped

crystallization

that

on melting,

of

fitted melting

using

this

explanations

a:e

shown to be entirely

INTRODUCTION We have recently supercooled the

liquids

supercooled

elevating

their

pressure

exerted

trapplng

material,

02%0584/90/$3.50

nucleation

can be achieved

compounds melting

are points

on these and that

seed

by using

trapped Ill.

crystallization

devices

in which

in regions We have

crystals

therefore

of the

further

is given the

of high

of seed

suggested

by the

crystals

pressure that

hardness

maximum temperature

of

thereby the

of the to which

0 Elsevier Sequoia/Printed

a

in The Netherlands

200 device

can be raised

and still

measure of the melting

have measured these materials

the results

melting

points

(P+a)/a

=(T/T,lC

devices

as a function

melting

our contention points

the absence

for these

To test supercool

known. salicylate

necessary

list

three

to confirm

points

our theory

points

in

to compare

trapped these

compounds which

at high pressures

have

compounds have been reported

were selected

the high pressure

which have convenient

melting data

constants

temperatures

for dfphenylamine

for these

are I51 and

as well as phenyl

We have measured the ~ximum temperatures crystals

of these

compounds may be raised

of the supercooled

maximum temperatures

of the compounds under pressures

in the trapping

(11 P, and

at pressure

to identify

and for which high pressure

that

by:

high pressure

melting

A number of organic

the crystallization

our hypothesis

points

means.

containing

point

is given

our method.

I61, and the Simon equation

nucleate

using and have

with the Simon equation

we were unable

for hiqh pressure

I71 have been determined.

and still

fit

We

[31 which expresses

deteraininq

and for which melting

points

to which devices test

hydrates,

Bridgman has reported

benzophenone

this

salt

i41, and from this

normal melting

T is the melting

[Zl.

values

The Simon equation

we were actually

using

been measured by other to supercool

hydrates

Although

it was therefore

significantly,

for a number of salt

to the Simon equation

point,

values

the theory

pressure

that

of literature

with the data obtained

elevated

of pressure.

a and c are the Simon constants.

is a

the crystallization

with a wide range of hardness

can be fitted

where T, is the normal melting supported

to nucleate

of the compound at that

maximum temperatures

in the trapping

shown that

be able

point

given

melts

represent

in order to

the melting

by the hardness

of the materials

devices.

EXPERIMENTAL The ~xi%um limiting with the following Vise-Grip carbide

pliers

was placed

investigation cooling

used since

the very process that

plate

to the other plate

of opening

result

a seed crystal

used in the devices

previously

consisted

of a pair

device jaw.

and crystals

the material. pliers

as reported

[ll of

welded to one jaw and a tungsten The material

of known

of the compound under

Following

were opened before

to see if crystallization

could sometimes

possibility Tester.

on the steel

the Vise-Grip

liquid

were deterained The clamping

were clamped into

periods

supercooled

materials

modifications. which had a steel

or diamond chip attached

hardness

liquid

temperatures

occurred.

the heating flooding

the area with

This procedure

the clamp in the presence

in crystallization was present. was determined

and

even if there

was

of supercooled was no

The Vickers

hardness

181 of the

with a Leitz

Wetzlar

Hicrohardness

201

Benzophenone

(Purum grade)

was obtained

from Fluka

and used

without

further

purification. BDH Reagent Because melt

it

and the

during

grade

did

the

Phenyl

not

clamping

molar

device

salicylate

was also

The change salicylate

enthalpy

prior

the

supercooled

in an oven maintained to prevent

obtained

of phenyl

Scanning

accompanying

the

40-45°C

without

further

phase

change

zO.5 cm3 kg-l.

was measured

and found

to use.

crystallization.

solid-liquid

to be t69.5

salicylate

Calorimeter

at

spontaneous

from BDH and was used

39°C was determined

of fusion

DSC7 Differential

hot

studies

in volume

at

and filtered

to room temperature,

were cooled

temperature

phenyl

was melted

reliably

limiting

purification. for

diphenylamine supercool

The

on a Perkin-Elmer

to be 07.75

kJ kg-l.

RESULTS AND DISCUSSION Table

I lists

benzophenone trapped

the

maximum survival

and phenyl

in materials

temperatures

salicylate

when crystals

of a variety

of hardnesses.

Table I. Maximum survival temperatures phenyl salicylate in devices of different

Vickers Hardness Material

are

assumed

7 a 0 a 9 10 31 37 42 44 50 58 65 78

the

for diphenylamine, hardnesses.

compounds survival

were temperatures

benzophenone

Temperatures

diphenylamine

and

(“C)

phenyl

60 64 60 65

salicylate

63 65 68

a2 107 95 106 157

114 127

126 105

160 165 151

191

the

high

>200

pressure

a and c can be determined to give

If

54 50 63 73

to represent

Simon constants be rearranged

benzophenone

diphenylamine,

of these

Maximum Survival

(kg mm-‘)

Lead (1) Lead (2) Tin Solder (1) Solder (2) Solder (3) Plexiglas Zinc Hagnes ium Alloy (Zn-Pb) Aluminum (11 Aluminum (2) Bakelite Gold

for

eqn.

(2)

melting as follows.

points,

the

values

for

The Simon equation

the can

P _ ac(T/T,IC

- ac

(2)

C

and an expression

for

ac,

given

in eqn.

(3) has been derived

previously

121

AHo ac = ZK where

(3)

AH, and AV, represent

change

on melting

produces

eqn.

the

standard

respectively.

enthalpy

Substitution

of fusion

from eqn.

and the

(3)

into

volume

eqn.

(2)

(4).

AH, T _-- ’ - 0AH P = AV, ( T, ) AVo

(4)

C

The constant which

gives

values for

c can be calculated the

which

the

values

best

are

fit

of the

assumed

right

process

hand side

to represent

Simon constants calculated

by an iterative

the

of eqn.

pressure.

a and c determined

by this

method,

Melting Point (T,) (‘Cl

AH, bV, (kg mm-3)

40 54 42

113a 117b 129

benzophenone diphenylamine phenyl salicylate

Figures

compare

151; b from ref.

the

seed

melting

reported

high

I51 and phenyl that

in every points

the

for

crystals

trapping

of the

are

It

dependent

the

determined

using

given

points

curves

melting will

t101.

survival

and in general

the

Simon II,

curves,

invariably

in this

study

by the

hardness

pressure

However the temperatures, decreases

with

at

I61,

is apparent

by the

which

hardnesses

so that be too that

high low.

may the

trapped

of the plastic were measured

and hardness increasing

from

survival

and a number of factors

given

is the

2.35c 2.46c 1.54c

benzophenone It

predicted

actual

large,

3.29 3.52 2.48

in Table

for

method

was assumed

that

occurs

not at

not

to a pressure

device,

material

the

by this

lit

4S.lC 40.4C 77.5=

i71 respectively.

melting

below

discrepancies.

room temperature,

be temperature

fall estimated

were subjected

in the

the

discrepancies

these

curves

salicylate

case

determinations

deformation at

from the

C

talc

i91.

pressure

the

melting

material

c from ref.

temperatures

Nevertheless account

I61;

survival

temperature pressure

values

the

Constants

mm-Z) lit

34.3 33.2 52.0

melting

figures

the

with

a and c in the

Simon Equation

calculated

diphenylamine

value

hardness

gives

along

constants

aikg talc

1 to 3 show how the

with

to the II

the

by Babb t91.

Compound

constants,

(4)

Table

Table II. Calculated and literature values for the Simon equation for high pressure melting points.

a from ref.

to determine

is known to temperature,

203

300

i 0

20 HARDNESS

40 I

PRESSURE

60

c 80

(kg/nn2)

Fig. 1. Variation of melting temperature of benzophenone with pressure. Solid line represents literature values. Bxperiaental points represent the limiting temperatures as a function of the hardness of the material used in the nucleating device. Dashed line was calculated from values of Simons constants a and c which were estimated from the limiting temperatures (see text).

3001 0

20

HARDNESS

40 *

PRESSURE

60

80

(kg/mm’ )

2. Variation of melting temperature of dipheny~amine with pressure. Experimental points represent the Solid line represents literature values. limiting temperatures as a function of the hardness of the material used in the Dashed line was calculated from values of Slmons constants nucleating device. a and c which were estimated from the limiting temperatures (see text). Fig.

204

300

!

0

I

20 40 60 HARDNESS = PRESSURE (kg/na2)

80

Fig. 3. Variation of melting temperature of phenyl salicylate with pressure. Solid and dotted lines represent literature values and their extrapolation at Experimental points represent the limiting temperatures as a higher pressures. function of the hardness of the material used in the nucleating device. Dashed line was calculated from values of Simons constants a and c which were estimated from the limiting temperatures (see text).

wfth softer experiment

materials

being more affected

with Plexiglas

at room temperature hardnesses

indicated likely

temperatures,

causing

The hardness

are particularly

suspect,

since

with increasing

temperatures In addition

it is possible

region

of the material

such that

result

possible, in data

Although

points

falling

the qualitative

for these

These

melting

curves

for Plexiglas materials

melting predicted

is quite

to soften in melting

were trapped

in a

to the maximum

of the material.

below the true

to fall

and Bakelite

resulted

the seed crystals

melting agreement

when measured

than most from the actual

points

A crude

The room temperature

they were not subjected

by the hardness

the high pressure

somewhat low, can account

given

that

121.

from 31 kg mm-*

they might be expected

temperature.

which were further

ones Ill, decreased

than the hardnesses

measurements

as plastics

curves. pressure

80 “C.

the calculated

curves.

survival

hardness

to be greater

below the actual

significantly

its

to 15 kg mm-= at about

are therefore

at the survival

than harder

that

Again this

would

curve.

good,

by this

method are

and we believe

that

discrepancies.

CONCLUSION We are therefore liquids,

as described,

confident involves

that

the mechanism for nucfeatfng

the trapping

of seed crystals

supercooled in regions

of

we

205

high

pressure

in the

temperatures

nucleating

allowing

thereby

devices,

them to survive

for

raising

subsequent

their

normal

initiation

melting

of

crystallization.

ACKNOWLEDGEMENTS The authors GE Canada and for

are

grateful

to Trent

in Peterborough

performing

the

University for

Ontario, differential

the

for

financial

use of their

scanning

support

microhardness

calorimetry

and to tester,

analysis.

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