Methods for the measurement of surface areas of aerosols by adsorption

15 (1982) 223--249 Ekevier Scientific Publishing Company, Amsterdam - Printed in The Netherknds

223

Aduances in Colioid and Interface Science,

flETHOl?S FOR THE F1EASlJREMENT OF SURFACE AREAS OF AEROSOLS BY ADSORPTIOEJ

S-J.

ROTHENBERG,

Inhalation nental

P.B.

DENEE,

Toxicology Research

Y-S_

Research

Institute,

CHEEJG, P.-L_

P.

0.

HAEJSON, H-C.

Lovelace

Institute, Box 5890,

YEH AND A-F_

Biomedical

Albuquerque,

and

EIDSON

Environ-

NM 87’185

COF!TEt!TS 223

......................................................

I.

ABSTRACT

11.

IE.!TRODLlCTIOE!..................................................

III.

PRINCIPLES

IV.

METHODS ....................................................... A.

Vol unetri

B.

Radionetric

226 226

.........................................

c nethod

..zz

......................................

nethod

FLOWING GAS METHODS ...........................................

V.

Thermal

A.

Gas

B.

.....................................

chronatographic

A.

Vacuum

B.

Piezo-gravinetri

C.

Millikan

0

..23

1

..23

2

2

c ......................................

...23

4

......................................

...23

....................................

oil-drop

6

238

VII.

CONCLUSIONS

VIII.

ACKNObJLEDGEI!ENTS ..............................................

...................................................

236

240

....................................................

IX.

REFERENCES APPENDIX

XI.

APPENDIX

XII.

SUflHARY TABLE

1.

Equations

for

Calculation

of

Specific ..~..2~

Area ............................................

Surface

..23

...23

.........................................

nicrobalance

X.

2.

Sample

9 230

..................................

conductinetric

GRAVIMETRIC NETHODS

VI.

1

243

...................................

Handling

247

.................................................

ABSTRACT

I. Basic

design,

determining reviewed. ing

224

.224

.....................

OF SURFACE AREA DETERI’IINATION

The

gas

of

precedes

advantages of

which

powder are

conductinetric

microbalance,

discussion niques

areas

methods

(thermal

(vacuun

limitations,

surface

the

discussed and

gas

piezo-gravinetric principles

the

detailed

OOOI-8686/82/0000-0000/$06.75

and

and

samples

are

less

volunetric,

chronatographic), and

procedures

discussion

disadvantages

weighing

of

the each

to

nethod.

methods 10 ng

method).

adsorption The

flow-

gravinetric,

oil-drop all

for are

radionetric, and

Millikan

comon

of than

precision

0 1982 Elsevier Scientific Publishing Company

techof

A

22a

volumetric, flowing gas and radionetric nethods is limited by the blank corThe smallest reported blank correction is equivalent to an area rection. of 4 2 0.1 cm2. Powder transfer and sampling problems limit the precision Precision of nicrobal ante determinations for samples less than 1 ng. determinations is limited by the thermomole&ular flow and houyancy corrections, which &an be determined to 2 0.3 pg. Potential advantages of peizo-gravinetric adsorption methods and an adaptation oil-drop method (pica-balance) are also discussed.

of the llillikan

If.

surface area (surface area per unit mass, m’ g ‘1) of an The specific aerosol is important because it influences rates of dissolution of particles and the adsorptive and catalytic properties of aerosols (ref. l-6). Specific surface area is frequently estimated from projected area diameters or from aerodynamic diameters rather than actually being measured. However, direct For coal combustion fly ash and ambient aerosol measurement is preferable. samples, specific surface areas obtained by direct measurement nay be ten times larger than estimates from particle size alone as a result of surface roughness and porosity (ref. 6,7). At least five methods are used for direct determination of the specific surface area of aerosol sanples. however, only three are cozszercially available. See SummaryTable. The following factors must be considered in choosing a method; (A) the weight of sample required and whether it can be co1 lected in a reasonable amount of time (methods suitable for mill igran and submilligram size samples are important, particularly for size-selected sanples); (61 restrictions on sanple size and experinental techniques for radioactive aerosols; and (C) re-aerosolization of the same during the The authors have used the reviews of Vercer measurement must be avoided. (ref. 1), Gregg and Sing (ref. 5), Gregg (ref. 8), Khan (ref. 9), Campbell and Thomson (ref. lo), Choudhary (ref. ll), Lundgren et al., (ref. 12) Gregg and Stock (ref. 13), and Fuller (ref. 14) as well as their own experiences, in writing this review_ III.

PRINCIPLESOF SURFACEAREADETEPJIINATION When gas is admitted into an evacuated chamber containing a solid, gas molecules attach to the solid surfaces and thus decreases the gas pressure and increases the weight of the solid. The amount of gas attached to the sample (adsorbed) can be determined by: weighing the sample (gravinetric method). counting the sample lradiometric method), or measuring the change in pressure (volumetric

method).

225 gas methods use an adsorbate

Flowing mixture

passes

adsorption which

is

compared

with

run with walls

a ‘layer

of

adsorbed

holder.

adsorbed

adsorbed

gases

process

surface

is

partial

called

deterni

the

final

partial

the

by the is

(BET) established the

required

is

of

of

gas required

of

a standard

pressure.

procedure

in

100

at

1

OO

a2 %a

an Fig.

of

the

Fig. 1. Adsorption of nitrogen (77°K) by a 48 ng sample of fly ash, showing “knee”

1).

the

adsorption

adsorption cover

of monolayer of

layer

at reduced

the basic

caTcu7ation

samp?e,

usually

adsorption the

amount

called

They also

area

if

the

deve7oped

surface (the

and the

given

(ref.

of

the

which

specific

with

are widely of

surface

They demonstrated

to the mass of

sample

“BET method”

as m2g-‘)

15).

corresponds

equations

weights

sample

normally

isotherms

isotherm

used

area

(surface

of

The area/unit

from the mass

to form a monolayer and an assumed size (area or Methods of calculation have been

discussed

(ref.

detaiied

gas

in the

calcu7ation).

can be calculated

gas

a monolayer

cross-section) for the adsorbed molecule_ are

by

These

gas is

(e.g.,

mol ecu1 es. surface

during

covered

dioxide.

measured.

to conp’letefy

mass of

sample

sample,

(or

sample

interpretation “knee”

the

becomes

2 x

Emmett and Teller

of

surface and carbon

200

gas adsorbed

isotherm

Brunauer,

a

(or

reached

and the

obtained

adsorption

its

vapor

and has become

adsorbed

is

of

new pressure

The curve

of

involve

at which

of

in steps

gas absorbed

theory

the

The pressure

pressure)

increased

by a known quantity gas methods

are made simpler

the

from

detector,

adsorbate pressure

of

quantity sample.

by heating

resulting

from the

The

measurements

equi?ibriun

and the

of

gas.

nations.

temperature

adsorption

water

area

carrier

for the gas adsorbed by the

atmosphere,

behavior

surface

outgassing

of

pressure)

the

the of

produced

to correct

to the

signal

and flowing

principally

removed

sanple,

are made of

that

gases,

admission

gas to the

each

exposed

influence

is

area

After

of

is

in signal

an inert

gas composition

in the

radiometric present

Measurements

by the

change

no sample

gases

studies.

a change

and sample

When a sample

gas,

the

mixed with

Change of

causes

The volumetric,

chamber

This

a detector.

or desorption

adsorbate. blank

through

by Gregg and Sing in Appendix

1_

(ref.

51,

Sing

16)

and Fuller

(ref.

‘14) and

226

The neasurenent of the mars of gas adsorbed at a fixed pressure and tenperature is the principal experimental difficulty in the determination of (1) the specific surface area. Precautions are necessary to ensure that: adsorbate pressure measured at the pressure gauge equals that in equilibriuln with the sanple; (2) the sanple is brought into equilibrium with the constant temperature bath surrounding the sanple container or corrections are made for differences between sample tenperature and bath temperature.

These pre-

cautions have been discussed by Fuller (ref. 141, Gregg and Sing (ref, 5) and by Cutting and Parkyns (ref. 17). Measurements of particle surface area are significantly affected by particle handling. technique:

Three sources of error can occur because of poor handling

(1) loss of part of the sample (in most instances mall

particles

will be more readily aerosolized than large ones, causing sanple bias and systematic errors in the data), (2) contamination of the sample, (3) crushing, leaching or other transformation of the particles, changing their surface norSanple handling is discussed in

phology and adsorption properties. Appendix 2. IV.

METHODS

A.

Volunetric nethod This is the oldest, sinplest and probably the most popular nethod for

determining adsorption isotherms.

The quantity of gas adsorbed is detemined

from the decrease in pressure (at fixed volume) caused by adsorption.

simple volumetric systen is show known

bath.

volune,

a furnace,

A

(Fig. Z), and includes a bulb of accurately

precision pressure gauges and constant

temperature

Criteria for selection of these are discussed elsewhere (ref. 5,11,14,

17).

c

Main

Vacuum

/

Manifold

Ni?rogen Cylinder

--

,iquid Nitrogen Trap

Helium Cylinder

8 '&mValve

@ 8

Fig, 2. nethod.

PValve Glass Slopcock

A simple apparatus for determination of adsorption by the volumetric

227

The advantages

of

structed

from glass;

mination

is

readily

several

flow

sealed

studied

samples

forces;

(6)

quantity

correction

and (7)

on small

The disadvantages the

is

for

(3)

if

the

adsorbate

pressure

difference

between

requires

correction

(ref.

of

77°K.

the

container

adsorption. problem see

Fig.

joint ing

to

3.

The powder

in the cell

the

procedure

ensures

powder

cooled-

is

have found either

Apiezon

of

sure

of Apiezon above to

the

can be determined a calibrated

pressure correction

nitrogen

to the

sample

level,

which are

when equili-

by using sets

pressure

necessary

Krypton

up a finite

gauge which adhere

to

not cooled

mass but not to

the to

the measured

includ-

all

the

coated

MANIFOLD

to

vacuum. 200°C

the

(for

vapor

FI exceeds

temGloss Stopcock Liquid Nitrogen

pres-

10m5

-Ground

Gloss

200°C.

The quantity admitted

phase

reduced

particles

is

a dead space

this

be used with

since

Torr

and the

1 iquid

11 or Silicone

exceeding

outgassing)

those

(2j

transpiration

gauge.

of

adsorbate

outgassed with

sample

precision

volume

and a

The dead space

must be reduced

to a

Jointed Fig. 3. work on powders, loading the cell

of

78).

This

can be cooled loss

t! cannot

peratures

using

joints

Apiezon

vacuum grease 77°K without

sample

a throughput

(ref.

gaseous is

(5) and

the most precise

correction

container;

in the

samples; manifold

The authors

that

with

with

some of

which

the

cell,

that

available

or cell

is

cooled.

is

outJet

correction

deter-

cell;

below

entire

joint,

the

to

use a jointed

and the

cold

and (4)

contribute

One soJution

is

inserted

the

radioactive

a blank

sample

thermal

below),

above

Such particles

by the

(1)

the

in a glass

muJtipJe

has given

gas remaining

18);

contained of

can be con-

(3)

electrostatic

have been reported

dead space

(see

is

transfer

method are:

the

apparatus

shock,

commercially

which

the

determination;

a single

the method

gas adsorbed

required

at 77°K as the

this

sample

in the

is

most of

direct

nechanical

using

samples

of

of

brium is reached;

walls

the

equipment

per day;

determinations for

(4)

can be outgassed

in 1 day;

three

uses

by vibration,

and can be used

samples

(1)

are:

the method

not affected

thermonolecular is

method

this

(2)

ceJJ for designed easier.

adsorption to make

228

minimum, is

not

between bore

so that

tubing

space

adsorption

as a small

two 1 arge

lengths

difference

quantities.

as well

Harrow

as minimum tube

have been used to reduce volume,

Fig.

the measured

determined

4).

e.g.,

Hayes

The quantity

adsorbed

by

a given

coverage

is

constant.

dead

(ref.

of

19 and

a given

sample

at

gas

nonolayer

The quantity

of

gas in the dead space is proportional the

pressure

of

a mono1 ayer. method

for

rection

is

which

gas in equilibrium

Therefore, reducing

has a lower

an additional

the

to choose

dead space

a gas

dead

space

correction

example 20)

for

container is

area

varied

nitrogen bath. areas

_

level

of

nitrogen

level

Chenebaul t jacket

cell

surface

of

+ 10

across

Fig.

5.

within

at 77°K \lith

instead for

a given

1 iquid

Air

B

2

surface an

when he

the

liquid

to -+ 0.1 cm. used a double

in which

area

The blank

independent

Vacuum \

---__-

constant

design, the

surface

the

cm

to maintain

(ref _ 18)

correction

used

temperature

area was determined

flow

dead space

(ref.

whose cooled

the

precautions

the

is

(Peq = 2x10m4 Torr),

An

by Aylnore

in the constant

precision

than when krypton

by the

essential

a cell with

reduce

He was able to determine as small as 200 cm2 with

apparent

used

be greater

adsorption

is

discussed

who used

Fig. 4Hayes vol unetric method, employing capillary tubes and “Hake” valves to mi ninize dead space.

at

Use of Xe at 77°K

would r 3~10~.

by ca.

Correction sample

used the

will

P = 0.1-0.3 Torr. eq of nitrogen at 77”K, apparatus

pressure, For

coverage.

Peq. i nstence , if nitrogen is 77°K with P,, = 60 Torr,

cor-

(adsorbate)

equilibrium

at non01 ayer

to with

the

cooled

by heat

marked C in

correction experimental

was error

-

--p Fig. 5. Cell design of ChiSnebault. The blank correction is almost independent of nitrogen 1 iquid 1 eve1 , provided it remains between points A and B.

229

of

the

points B.

liquid

nitrogen

A and B.

nethod

The quantity

r-detector. of

dead

correction

space

eliminate

previously

correction

l eve1

ned between

renai

was 4 cm2 5 0.1

a radioactive

gas adsorbed

when conpared

is

eliminated;

which

need for

the

described.

The method counting the

uses of

the nethod

disadvantages, are

cn2.

such as a5Kr , as

gas,

is to

(2)

determined

the

using

(ref.

211,

volunetric

wide

cell

are

a blank In addition,

connon

to

bore

are

calibrated

or as a relative

With that

of

a standard

all

correction

a 6 or Fig_

nethod

tubing

variants

and care

counting

can be used as an absolute

geonetry

sanple

conpared

providedthe

The

6.

(1)

are:

the

nay be used to

themonolecular flow and reduce pumping resistance; and (3) samples 2 total surface area (< 10 cm ) can be determined.

of mall The

blank

Dewar,

The Rethod was first used by Clarke

advantages

nethod,

the

method

The radionetric _

in

Chenebault’s

Radionetric

a dsorbate

level

geometry

nethod

by condensing

of

(ref.

21) when the

a known quantity

in which

adsorption

sample

which

exposed

is

Pressure

volunetric

of to the

of

cell

and

a5Kr in

an unknown is saliie a5Kr.

Gouge

-To

Manifold

‘Cap

as

must be reproducible.

nethod

Q-

the

in powder transfer

Ptimps

3 -Moin.*5Kr

Storoge Reservoir

Liquid Nitrogen Counter Weight

n

Sample-

Lead

Shield

Fig.

6.

l?adionetric

-Solid

\Liquid

Nitrogen

Filled Thermostat 1 -Glass

lPhotorriuItiplier --+----Preamplifier --

Method - Apparatus

used by Clark.

Stopcock

1

230

smallest

The

probably

ng,

blank

sample

because

(Fig.

5)

is

to

date,

Counts

desirable

- 10 Ci gn-’

0.1

cm2 monolayer readily

ciency,

based

both

are

area

surface

area

precision of

of

aerosol

sanples

(micro-bal

ante)

gravinetric

because

equipment

is

comercially

technique

is

more suitable

the

on which we have as yet that

we have probably

a specific

85Kr adsorbed

in a

a level

correction,

not counting

which

Most measurements the

mall

samples.

weighed

3 ng,

linits

probably suggests

the

The ma1 lest but it

of

effi-

of

“classical”

Our experience

available.

the

how-

acti-

per ninute.

have used either

approached

and 18)

nethods,

or f 1 owing gas nethods,

nade neasurenents not yet

(ref.

this

sample

appears

to

us

nethod.

FLOHI NG GAS METHODS

V. A.

Conductinetrfc

Thermal

One flowing overnight, sample.

A steady

then

up and the

set

there

is

the

flow

the

nitrogen

adsorbed.

Dewar of

liquid

desorption

of

measured

this

samples

of

nixed

with

the

cooled

from the

the

is

then

gas

flow

sign)

produced

off,

is by

caused

The advantages are

using

in turn

injecting

pressure, 1 hour

by

adsorption

stream.

effects

of

the

by

(overnight)

transferred

is

the quantity

produced

in approxinately

detemined

and

opposite peaks

peaks

carrier

sinultaneously

(Quantector/Quantasorb)

(of

used at atmospheric

and themonolecular be

leveled

has

nitro-

hence,

response

detector

is

of

and,

to

conductivity

into

Adsorption

gas mixture

The detector

the

with

adsorbate)

proportional

thermal compared

preferably from the

other

nitrogen.

and a peak

are

(or

flowing

removed

equipnent

outgassed

of

at atnospheric

outgassed, desorbed

nitrogen

detector. peak is

response

The

can

the

is

gases

in liquid of

adsorption is

dead space be

is

conductivity

nitrogen

(1)

isotherm can

helium

nitrogen

are:

for

a conplete

of

When the

volumes

rections

renoves

nitrogen. of

method

which

nitrogen

desorption

such as helium

The sanple

heliun

signal

of

gas,

adsorbates.

sanp?e

in

area

on Cooling)

an inert

of

thermal

a change

recorded,

uses

for

in a stream

gen changes

(Adsorption

gas method

as a carrier

pressure,

or

TII

method.

for

500

85Yr . used , counting

Kr having

blank

this

volunetric, radionetric

the

was

geometry

radionetric

of

sanple.

Thus,

to + 5%.

the

by activity the

counting

have been reported.

10 3 disintegrations

give

determined

and absolute

al 1y avai 1 abl e _

‘I_s comerci will

both

used by Chenebault

Reasurenents

of

made neasurenents

of

on that

relative

detemined

surface

determines

specific

reproducibility

design

for

per minute

vity is

Cl ark successfully

of

no such radionetric

, and the

geonetry

lack

A cell

correction_

ever,

on which

of

(2)

not and

of

cor-

required, (4)

a commercial

(3)

several system

to the neasuring

i nstrunent, The disadvantages rarely

yield

of

reproducible

the

flowing

results,

gas technique (2)

thermal

are:

diffusion

(1)

adsorption

distorts

peaks

peak shapes

231

(ref.

ZZ),

carrier

(3)

systenatic the

Several less

flowing

sample liters

for

paring

pure

of

“tail

nitrogen

” of

for

total

oxide,

the

area

of

haps might

reduce

the

(personal could

ments,

this

8.

design the

are

in the

contanination

and

principles

The basic

equipnent

The particle

10 cm length,

sample

1 mm i-d)

is

the

flowing

that

repetition

intervals

should

or wave-form be used

Adsorption and the conDesorp-

measured.

the peak produced (ref.

tlininun The

22).

sanpies

as a chromatography

cell

to + 0.2

cm’.

of

13,

a small column.

of per-

the

generate

a signal

With such improvewhose total

gas method

in ref.

into

to a U-tube

eductor.

for

flowing

described packed

23).

was 175 m2, for a 4.5 mg sample correction was 12 to 17 cm2. by Chenebault

but does

surface

not

require

23 and shown in

length

of

tubing

A carrier

gas is

(e.g., passed

Thermostats

Fig.

7.

Basic

from C.I?.C.

Apparatus

“Handbook

for

Gas Chromatography.

of Chromatography,

” Vol II.

or

in pre-

gas mixture.

and Carp

suggested

another is

141,

against

correction

by computer

method

into

100 cc

(ref.

kinetics.

he accurately

by Lowell

to

and care

samples

(ref.

blank

method might 2 20 cm _ (GC) is

a minute

in the

at regular

Gas chromatographic

mall

contact

methods.

compared

by adsorption

used

uncertainty

be analyzed

used,

into

in other

techniques,

and are calibrated nitrogen

gas brought used

are

peak nay not

was measured The blank

cycle

of

in work with

determined

of

Gas chromatography 7.

pressure

essential

communication)

than

quantity quahtities

at 77°K nay exceed

m2g-‘_

convenient

was greater

cooling. Fig.

impurities

sample

or micro-ba7ance

adsorption

adsorption/desorption

area

is

which

S = 3.88

which

total

the method was studied

Adaptation Whitby

gases

a known volume

size

smallest

radionetric

are more reproducible

by injecting

zinc

and (4)

causing

than the

gas at atmospheric

peak shapes

for

peaks

sample

required

sanple,

the

much greater

carrier

Adsorption sequent

is

by the

gas method,

is

vol metric,

half-tines tion

correction

errors.

In the with

a blank

gas nay he adsorbed

Redrawn, with (ref. 23)

permission,

232

through is

the

column

desired

using

is

to

added

a permeation

unadsorbed

tube

(ref

is

allowed

conpound

the

equilibrium

the

column to elute

the

24,25).

The advantages

florr

of

several

inert

adsorbates

sanples

carrier

Sing

for

(rsf.

several

(2)

i s required, size

of

and (4)

sample

1 ng/cn3, of

benzene

funnel ) _ detemi

Thus,

VI, A.

from the caused

G.C.

of

at

through

trace

completed

(ref.

within

(overnight)

day and (3)

1

in a

a kJide range

temperatures

Thus,

the

tine

and desorption

(-50

specific

to

surface

as recomended are:

(1)

of

300°C)

areas

by Gregg and

it

must be calculated, be uniformly

detectors

is

(3)

packed,

respond adsorbs

A 5 ng sample

a column that

nil1

(1 m*g-‘)

coverage. into

an indirect

a blank

liniting

correction nininun

(using

column

as little

vJas the least

a 20 gauge

packing,

to

or desorbs

not

as 300 ng

we were

syringe

needle

detector

as a

sensitivity,

sanpl e size.

ante

sample

bean of

is

transferred

a sensitive

by adsorption

are

8a.

The method has been

this

vJidely

wide bore

for (sample

blank

correction

studies

weight

for

studies

of

the

becones

by Fuller

elininating constant

the empty balance adsorbates. curves

pan is

small

as adsorbate of

changes

ShOvJn in Fig.

14).

Advantages

is

measured

the

can be noni-

conplete),

(4)

the

(5)

can be supplenented

by

for

can be studied

a nore

complete

sur(ref.

character-

sample. of

the method

to one per nicrobalance

per

are: day,

(1) (2)

the throughput any disturbing

of

(2)

and reproducible,

adsorption

determined

suspended

are eliminated,

procedures

rrhen outgassing

Rates

is

need to correct

outgassing

is

and weight

(ref.

corrections

the

(3)

weight

The apparatus

dead space

transpiration,

decomposition

The disadvantages limited

recently

(1)

pan which

Both sample directly.

%Jhich use nitrogen

vJith additional

and thermal

ization

can be used,

thermal

tored,

area

determined reviewed

a balance

into

balance.

used method are;

tubing

pressure

25)

passed

chronatographic outgassed

range

of

Gl?AVIFlETRICMETHODS Vacuum nicrobal The powder

face

then

are easily

GC technique

adsorbent

appears

nes ni ninun

period

by to

5 ng.

1 mg of

it

the

13,23).

column nust

available

in packing

GC detector

gas is

often

14).

of the

at monolayer

successful

the

of

in a single

a wide

isotherm

the

gas,

an extended

can be compared,

(ref.

to about

Mhereas

of

experiments

(ref.

sorbates

adsorption

Commercially

(1)

shape

isothem

carrier

The adsorption

conpound.

because

disadvantages the

for

Pure carrier

available

5) and Fuller

The nain method,

off

gas and studied

are

the

can be simultaneously

can be studied

and GC detectors obtained

to level

from the are;

to

The response

13,23).

adsorbed

can be calculated

(2)

concentration

gas concentration.

isotherm hour,

The compound vJhose adsorption

a GC detector.

at constant

of force

samples on the

is

233 such as those

balance

bean or pan,

charge,

buoyancy

and themonolecular

(3)

standard

one-piece

the

long)

gust

1 tss-

be removed

This Balances

Gregg

and Sing

(ref.

care

both

determined

sources

is

studied

perature,

8.

nitrogen,

areas

molecule

-Ho~Q-Dow~

Fig.

flow

adsorbed

surface

The benzene

of

a sanpl e which

insert

a tube Joe8

g are

the

nitrogen

Benzene

standard

mall

samples

has an area

of

with

18 inches

nay cause base

sanple

[Fig-

8~).

available. caused

by buoyancy

and monolayer

as adsorbate

effects is

in readings,

(about

to + 1 rrg,. however,

are

readily

adsorbate,

at room temperature. of

comercially

can be reduced using

8b)

a detachable

precision

and buoyancy

the

(Fig.

uncertainties

useful

uncertainty effects

with

electric

a change

to

that

14,17)

static

produce tube

at room temperature,

whereas

significantly dardize

to

will

hang-down

(THF) limit

ug (ref.

Both themonolecular tion

sensitive

flow

to + 0.3

by using

5) estimated

and themonolecular with

and rep1 aced

are

by vibration,

flow

balance

can be avoided which

caused

(area

It nay prove benzene

reduced

adsorbed 16.2

necessary

Wire-

a) Vacuum Micro-Balance and Accessories. b) Standard tube supplied by Cahn-Ventron. c) Tube with Detachable base for easy sanple

insertion.

if

adsorp-

at rooT;1 ten-

A2) is

as a secondary

40 A2 (ref _ 5).

weights

at 77°K.

to

not stan-

standard.

234

A monolayer

weight

of

2 lo%,

corresponds

to

sample

of

surface

sample

transferred

the B.

specific

into

1 ower 1 ini t of Piezo-gravinetric

Af,

of

to

area

pan can be detemined

determined

by the

to + 1 pg,

buoyancy

thus

and TMF effects.

method

According to the

vibrating

to

caused

Sauerbrey

change

in a thickness-shear (ref.

by deposition

of

of mass,

27),

the

aerosols

node

change

of

constitutes

a

frequency,

or adsorption

of

vapor

is

Am:

where G is

(1)

the

sensitivity three

factor.

angles

to the

ties.

Both Y and AT cut The Y cut

28). is

usually

principal

is

easiest

preferred

For a commercial

the Eass

sensitivity

sensitivity

is

The detection

28). crystal

s is,

1 Hz.

A lower

carefully

limit

useful

Measurement (ref.

301,

Daley

(ref.

reported

of

of

aerosol

of

a quartz

adsorption

of

vapor

311, of

using

Lundgren

vapors

isotherm

and Wade is

particulate reported

sanples

samples

by Lundgren

surfaces

al.

33)

as mall

shown in Fig. et --

of

10) (ref.

9.

collected

sensitivity,

as 1 cn2. Adsorption directly

two types

of

particles;

8’

for

the

area

The of on a

12).

application of this nettrod is the calculation 2 -1 30 P g and 45 m’g-’ for the specific surface

14.8

were

who demonstrated

of

of

by Chuan

surface

the

(ref.

very

and Sen and

of

by Lundgren

is

particulate.

values

Data pub1 ished

of

who used (QCN),

12,281

a smooth crystal

(Fig.

its

shift

the QCM was developed

and Wade (ref. for

of

micro-balance

et al . (ref.

onto

ref.

a frequency

by Leenhorst

on small

1 cn2,

available

Because

crystal

crystals

area

comercially

29).

AT

the tenperature AT cut

surface

to

(ref.

but the

and Lundgren,

reported

s (ref.

9) and by Slutsky

on various

An example approximate

a value

usually

used by Slutsky was

for

(Daley

using

gran has been crystal

Adsorption

QCM mass noni tor

of

10-l’

of measuring

vacuum chamber

be 200 Hz/vg

propernode

crystal,

since

smaller

crystal

mass change

the

pork,

quartz

at various

thickness-sheer

shattering

mass concentration

by Khan (ref.

vapor

for

and Sem (ref.

32).

possibility

areas

of

study

Olin

to

crystals,

have different

5 x 1 Oe9 gram corresponding

sensor,

in the

in the

(G) is

AT-cut

and tested

a piezo-electric

water

limit

selected

factor

found

therefore,

vibrate

of

axes,

piezo-gravinetric

for

(ref.

cuts

lographic

to make without

of

28).

the

Different

crystal

crystals

coefficient

the

can be detemined

= - G Af,

An

cut

which

or to the area of a 10 ng of 100 cn’, 2 -1 weight of the 1 r;l g . The outgassed

the balance

crystal

a crystal

proportional

nitrogen,

area

the method is

A piezo-electric ni crobal ante.

3 vg of

a total

of

Arizona road dust and a room aerosol sanple. 12), (reproduced with permission in Fig. lo), occupied by a water molecule and Eq. 3

235 (hppendix

1) were used

have been

suggested

hexane of

are

surface

for

in this the

better

adsorbates

area,

as discussed

calculation.

area

of

to use

a water (at

Values

ranging

molecule

(ref.

(ref.

dry --wCj KllSS

Fig. 9. Vacuum chamber used by Slutsky and Wade for piezo-gravinetric detemination of adsorption on single crystals.

The piezo-gravinetric the

conventional

direct

monitoring

advantages:

(1)

of the

outgassing

of

less

than ten microgram),

crystals (ref. aerosol

these

forces

(2)

sanpl es.

Stiiber

in the

centrifuge

Chap.

PERCENT

advantages

There

three

orders

(thus

reducing

buoyancy

have no detectable

can be incorporated 341 or the

is

nicrobalances,

the

such as nininun

procedures.

sensitivity

that since

conventional

methods

0

Benzene

in the

5,

A2 or

determination

2).

R&WE

HUMIDITY

loo

Fig. 10. Adsorption isotherms for water on aerosol sanales. T-10 ~a sample size, reproduced from data of Lundgren [ref. 12).

method has some of

gravinetric

5).

room tenperature)

by Gregg and Sing

from 8-20

collecting (ref.

are

35),

of

several

greater

the mininun

on crystal surfaces to obtain

are

than

sample mass to not

frequencies of a cascade size

with

dead space, other

of nagnitude

and TtlF corrections

effect

associated

effects

classified

required and (3) inpactor

236

The disadvantages netri c method, sensitivity, the

(2) (3)

gas mixture

9,12,28,33). the

outgassing

which

and (5)

a critical

the

crystal the

crystal

correction

for

samples

will

uniformly

cover

surface

the

incorporated of

10 pg sanple,

S = 10 n2g-‘,

approximately

30 ng,

the

28)

type

desirable

size

area

of

fre-

surface

areas

and be tightly

normally complicate

thus,

it

bound

used

to

the

blank

appears

preferable

bounce (ref.

36),

the

linited

by

range.

which

can be determined

is

(2)

10 ug,

which

a change

hence

R is

in the

for

precise oil -drop

A charged

particle

of

gravity

in the

position

in the particle_

nay

benzene)

to i_ 20% using

at a

A of

a commercial

crys-

QCrl.

(ref.

be held

balanced

by the

current

Thus,

direct

(for

2 x 103.

For a 10 vg sample, S = 0.1 approximately 0.3 ng, which cannot be

neasurenents

chemical

mass.

5 ng and overload

than

to better

29).

than 2 10% using

An R value

greater

on samples

of

low specific

stationary

in ah electrical

than

the 1 O4 is

surface

area.

method

field-coil

during

in particle

is

of

less

capacity

can be determined

by Leenhorst

Mill ikan

single

surface

particle

has a monolayer

incorporated

described

a

range

specific

both

can be

change

approximately

equipment

be used

linits

a mall

and,

is lX2g-’ , the monolayer capacity detected on the QCf-1, but could be neasured

change

and this

over

coatings

increases

in the QCM detect

sample weight

force

(refquartz

R where:

The crystals

C,

of

250°C for adsorption

of

the mass

shift

which

entire

Grease

a narrow

Sanple weight detectable weight

of

affect

over

range

gravi-

constant

frequency

destroyed

linear

(ref.

If this

R = SRal lest

tal

are

QCMmass monitors

studies

crystals. specific

particles

(approxinately

and the

cover

in commercial

no longer

an indirect

dielectric

cause

range

is

size

is

below)).

adsorption

The ninimun ratio

response

Eq. 1 to be valid.

adhesion

use uncoated

both

tenperature

sample

(see

should for

crystal

characteristics

both

can be neasured

enhance

the

of

and in the

and the temperature

linits

the nethod

characteristics

with

piezoelectric

(this

to the

the

above

(1)

are;

in temperature

in contact

The deposit

to

collection

procedures

studied. quency

the

the method

changes

(4)

crystals)

of

reaction the

electrical

required

or adsorption

instrment

gravinetric

force

to hold is

is

on the

the

of

the

if

particle.

particle

picobalance adsorption

the The

in a stationary

proportional

a sensitive

determination

field

to the

change

which nay isotherm

of

237

LEIGH HORN

Fig. JJ. MiJJikan CeJJ, with Laser sensing device, aj. b) Circuit diagram for The ccl 7, diagrammatic, currents. Laser the

beans

used to

in the field

current

or days

are

(ref.

39)

shown in Fig.

pattern)

curves

to

coils

in the

JJb.

tering

sense

obtain

A pattern

very

Adsorption

does

(ref.

ceJJ

is obtained

the

of

light

precise

vaJues

not cause

but scattering

dropJets

of known density

required detemi

to hold

38).

possibJe,

tic’les foi7 mined

p’laced (ref.

401 are

from the

refractive

index

37)

the

change

as it

particle

theoretically radius

determine

and hence, in the

hours

circuits (Hie

scat-

derived

(ref.

in particJe

adsorbs

nethod caused

sane baJance

are;

(1)

size

37). or Mie

the mass of to calibrate

field

coil

the

currents

gas nay be used to

pan (ref.

coil

current

at the

to a Mie pattern

rates

of

5,7)

the mass of

and aerodynamic

measurements

by formation

(3)

coupled

adsorption

in place

(ref.

avoided,

fieJd

is

this

artifacts

in the

instrument and (5)

of

(2)

from the

particJe

change

can be held for control

to

control

i sothems.

The advantages ore

the

and to

the

can be used to

Subsequently,

a particJe

ne adsorption

of

particle

A particJe J Ja using

scattered

significant

pattern, (ref.

the

which nay be compared

honogenous coiJs

of

37,38).

shown in Fig.

scattering fieJd

position

used by Ray and Davis. control of field coiJ

outgassed of

analyzer,

diameter

can be determined.

of

the

particJe

particle

reaJ

par-

on an inpactor

an experiment, thus,

particles

between

or coJJected

the

start

on single

interstices

size,

is (4)

deterthe

density,

nay be determined

23s

The disadvantages designed

for

(2)

to

samples

200°C) is

therefore, equipment

is

charge

(ref.

the

are

limited

to a small cell

aerosol

(4)

the

size

required (3)

the

show marked

approximately

cells

of

can be

generator,

most aerosols

thus,

range

(which

The minimum sample

41,42),

and (5)

ccl 1 s now in use were

in a separate

available,

(ref. 42)

(1)

in a dry dust

commercially

variation

be measured

and thus

reaerosolized.

to the

not yet

that;

must be outgassed

and then

equal

particle-particle should

the method are

use at room temperature

adsorbates, heated

of

20-200

now available

particles

have a sensi-

tivity

approximately 5 x lo-l5 g and can be used for particles of -12 mass = 5 x 10 g or have an R factor (see above) of approximately 103. than

This value is adequate for samples of 10 m’g-’ but for samples whose specific

1 m2ge1 , an i? value If

mean and variance measurement Fuller’s

of

will

(ref.

sample

weight,

the

take

method

weights data

exceeding

1 O4 is

the minimum number (20)

for the

the

plot

to equilibrium

rate

is

(as

are

properties This

5 days.

extrapolation

If

surface area is

area less

greater than

necessary.

particles

adsorption

at least

the

14).

of

specific surface

of

gain

Hence,

demonstrated

of

in Fig.

to

plot

8 of

the

aerosol

may be reduced obtain

(dw/dt)

the

to obtain

a single

tine

readings

of weight

linear.

studied

is

range,

sample,

the

by applying

equilibrium plotted

against

can be used to extrapolate ref.

14).

CONCLUSIONS

VII.

Methods

exist

samples

weighing

samples

less

1.

Table

precision

measurement

with

which

the

Methods

both

various

specific

suggest

appears

corrections

to extending that

radionetric

size

QCM) w-ill

probably

prove

area

are

powder

summarized

in

by the

can be determined.

for

deposited

Our

measurements

problems

methods

the most

of

on powder

to be limited

radiometric

powder handling

and volumetric

in which the sample is directly

(pica-balance,

surface

measurements

Methods

reported. blank

preparatory

samples, of

the

and minimum sample

trials,

subnilligran precision

of

than 10 ng but few reliable

than 10 ng have been

Precision

manipulative

ng.

for less

to

1 imit

Will

samples

less

than

from the aerosol

reliable

for

1

strean

subnilligran

samples. ACKNOWLEDGMENTS

VIII.

We wish manuscript for

to

discussion

respectively; gestions Clark,

thank

our co1 leagues

and A. Ferris of

the

E. L. Fuller

Slutsky, Figs.

editing;

for of

L. J.

10-12.

suggestions

Slutsky,

and modified

a preprint

glassware

Sherman and C.&C., 5-8,

fo r helpful

piezo-gravinetric

on constructi,on

reproduce

for

of

reference

and sample Lundgren

and review

E. J.

Davis

Millikan 14,

handling,

and Ray for

of

the

and A. K. Ray

apparatus,

A. Noensch Hayes,

permission

for

sug-

Chcnebault, to

239

Uork

was

performed

DE-AC04-76EVOl073,

and

.Mational

of

Institute

under also

0. in

S. part

Environmental

Department under Health

of

an

Energy

interagency

Sciences.

Contract agreenent

Number with

the

240 REFEREWCES

IX. 1

14

T-T. t’lercer, “Aerosol Technology in Hazard Evaluation,” Academic Press, flew York (1973). 3-R. Hodkinson, in “Aerosol Science,” (C. H. Pavies, Ed.) p. 287 Academic Press, t!err York (1966). G.tq. Kanapilly and C.H.T. Goh. Health Phys. 25(1973)225. T-T. Kercer, Health Phys. 13(1967)1211, S.J. Gregg and K.S.W. Sing, “Adsorption, Surface Area and Porosity,” Acadenic Press, Hell York (1967). M. Corn, T-L. Montgonery and H.A. Esnan, Env. Sci. Technol-, 5(1971)155. S.J. Rothenberg, Atnos. Env., 14(1X0)445. S.J. Gregg, in ‘*Surface Chemistry and Colloids,” (!I. Kerker, Ed.) -Vol. 7, University Park Press, Baltimore (1975) _ G.W. Khan, Pakistan J. Ind. Res., 17(1974)103. K.C. Campbell and S.J. Thomson, Prog. Surf. tlenhr. Sci., 9(1975)163. V.R. Choudhary, J. Sci. Ind. Res., 33(1974)634. D.A. Lundgren, L-D. Carter and P.S. Daley, in “Fine Particles,” (B. Y. H Liu, Ed.) p. 485, Academic Press, l!ew York (1976). S-J. Gregg and R. Stock, in “Gas Chromatography.” (D-H. Destry, Ed.) Chapter VI, Butterworths, London (195B) _ E-L. Fuller Jr., in "Microweighing in Vacuum and Controlled Environnents,"

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(R.N. Czanderna, Ed-) Chapter 0, Elsevier (in press)_ 5. Rrunauer, P-H. Emett and E. Teller, J. An. Chen. Sot.,

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$7” 30 39 40 41 42 43 44 45

Oxide Nuclear Fuel Materials m Colorado Springs (1979). D-J. Cram and G.S. Hammond, “Organic Chemistry” 2nd Ed. IlcGrarr-Hill, (1964). J.C.D. Brand and J.C. Speaknan, “tlolecular Structure - the Physical Approach, ” Edward Arnold, London, (1960) _ P-0. Hednan, L.D. Stloots, R.N. Hanks, J-R. Thurgood and F-D. Skinner, BY0 Rate Resolution Coal Furnace and Coal Gasifier,” Presented at 3rd Rocky tlountain Fuel Symposium, Albuquerque, Ml Feb. 10-11, 19X.

t!.

Y.

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241

46 47 48 49 50

C-f!. 921. R.L.

Davies,

Brit.

J.

Appl . Phys.

(J.

Phys.

0.1,

1968,

Ser 2,

Vol.

1,

Carpenter. G.J. Newton, S-J. Rothenberg and P-B. DeNee. Env. Sci. . , 14(198O)B54. P.B. DeHee, Scanning Electron tlicroscopy 1978, Vo7. 7, 479. and references cited therein, SEfl Inc., ArlF O’Hare, Illinois, 197C. by the International Atomic “Safe Hand1 ing of P.adionucl ides" Sponsored Energy Agency and the World Health Organization. Vienna. 1973. Atomic Energy Agency, Vienna, “Safe Hand1 i ng of Pl utoni urn,” International 1974.

Technol

APPENDIX I

X.

Equations

A.

for

The specific molecules

Calculation surface

required

molecule

to

of

area

Specific

(.S) is

for-n a monolayer

where w is the

sample

weight

in A2 , values

tabulated

(nm) and the

5) area

from the

number of

occupied

hy each

of

A D

n “;

(1)

in grams. Values of An are 2 -1 S in n g , thus, a conversion

conventionally factor

of

i s required_

If

the monolayer

weight

(x,1

n

where the

Area (ref.

(A,).

S=

1 o-20

Surface

calculated

El is

Avogadros

n

is

=

E!unher (6.0225

deternined

xm x !!

(21

fi

x 1 0z3),

t! is

the “o7ecular

weight

of

adsorbate,

(3)

thus,

which

is

the

gravinetric usually

basic work,

employed

equation in which

for

detemination

nitrogen

of

(A” = 16.2

specific

k2,

surface

tl = 20.02)

area.

For

is

as adsorhate, s = 3.4B

x 103X”

(4)

7

For benzene,

!I = 70.1

and Am = 40_OA*,

(ref

5,

s = 3.013 x 103xm

p. 7B),

hence:

(5 )

242 Values values

for

for

lengths

other

ar structure

The value

of

tabulated

(ref. s

BET equation

is is

adsorbates

in texts obtained

normally

P/X(P”

-

intercept

at which

p/p”

i = l/xmc,

gives

are

at monolayer

one gram-mole

tution

in equation

of

BET plot_

p” the

If

saturation

and c a constant.

line

El

of

slope

of

A plot

s = (c - 1 l/xmc

and

(71

1

f S+l

used to

determine

the monolayer

In the volumetric (Vm) is measured in cc,

coverage occupies

(3)

22,414

cc

at N.T.P.

coverage

method, reduced

and weighs

in the

the volume to N.T.P.

M grams,

substi -

gives: V

nitrogen

or

(61

adsorbed,

adsorption,

N3-l

s=*x* With

43)

hence,

equations

Since

bond

(ref.

isotherm:

vol umetri c and radi onetri c methods. adsorbed

approximate

-I- (c - 11 E xmc PO

a straight

X

Similar

chemistry

a five-point

adsorption

x grams are

at the temperature

pl against

organic

using

to the

applicable

the pressure

pressure

of

5,

from models,

441.

1

vapor

in i?ef.

may be estimated

XRC where p is

are tabulated

hydrocarbons

and bond angles

nolecul the

several

most aromatic

as adsorbate

(81

(Am = 76.2A21, s = 4.35

vm

(9)

= For Krypton, low vapor

pressure

which

is

at 7i°K,

frequently

used

Am = 19.5A2 S = 5.24

in volumetric

(ref.

5,

work because

P. 86-871,

of

its

hence:

Vm

(10)

w Although gas

the method of

(Quantasorb) For the

known weight

method,

radiometric (wsl

obtaining Equations

method,

of 85 Kr/Kr,

if then

Vm is

very

6 - 10 are the

counting

the monolayer

different

in the

flowing

applicable. geometry weight

is is

calibrated obtained

with as:

a

243

(11)

where

c B is

rate

for

the

count

rate

ws grams of

for

labeled

the

sanple

Krypton.

cnk’s

s =

at monolayer

Thus,

If face

for

the

which

A,, = 19.5A2,

radionetric

area

S”,

method

weight

is is

count 3, (12)

-e

= 5ll ws x 7.40 7z-F

85Kr,

c the

in Equation

q-l

x

--e-t7

if

coverage,

substituting

used

x lo3

(13)

as adsorbate.

used with

a standard

sample

of

specific

sur-

W”, then (14)

where C,, sanple

are the

C”,

and standard

XI.

counts

per minute

respectively,

at monolayer

determined

coverage

by Equation

for

the

6 and 7.

APPENDIX 2

Sample Handling A portion, (a)

rapid

bulence,

or the entire

adnission (b)

of

rapid

the

than 7 Torr)

causing

both

force),

(c)

off

moisture

with

turbing

the

sample

strikes

the walls

driving

adsorbate

evacuation

an explosive

of

the

(from

and rapid

sanple

great

aerosol

determinations)

causing

the

sample

to

tur-

to

(with

convection

less

almost

currents

The sample nay al so be 1 ost

micro-balance

by;

causing

pressure

of moisture

causing

ization

system,

atmospheric loss

heating,

force.

apparatus,

through

gas to an evacuated

a system

turbulence rapid

pan (during of

can be lost

sample,

so that be tipped

and

by disit out

of

the

pan. Sample transformation chosen

for

However, or

outgassing if

particles

ture

involves

been

employed,

a very sintered

during

should high

temperature

together

compromise, dependent

outgassing

thus, ‘upon

must be avoided.

be sufficiently (ref.

is

high

employed,

5).

the

nature

the

Selection

temperatures

ranging of

the

The

temperature

to remove adsorbed surface of

an outgassing

fron

materials

gases.

may be damaged,

25OC to involved.

tenpera1000°C Most

have

ambient aerosols tile

at less

dures sinilar

to

deteminations to

those

considerable

The particle very

mall

impinger,

errors

it

is

of

a single

distill

led

successive

a large

tenperature

can be altered

by the

vola-

proce-

surface

number of

outgassing

of

the container contaminated Some sanpling

handled.

to entrain

the

composition

of

adsorption water

area from 0°C

samples

results

from a

in

transform

a?.

The aforementioned or eliminated

sampling

(ref.

or bias et --

of

with

45).

the

sanple

(ref.

471.

sources

of

it

the

adhesion sample

particles

fron

the liquid

and quench

the

of

this

is

hot

fly

ash

have been

by Davies

discussed surface

several

surface

systematic

which

in the

the

nay not

both

creating

An exanple

following

of

is

such as a midget

can affect

sample

probes

the

Methods of sampling

error

by carefully

dirt

system,

Although

sample)

selective

in which

area neasurenents.

to cool

liquids,

sample.

the

properties

surface

from a conbustor

and by Carpenter

etc.,

to adopt

samples at 100°C intervals

studying

can al so become

obtained

reduced

one is

sulfates,

necessary

in which

being

chemical and the

14)

outgassing

if

distribution

in subsequent

cold

[ref.

to the walls

use liquids

the

morphology of

size

The sample

in which

change

Ful’ier

is

in tine.

particles

stored. area

of

selection savings

it

For such samples,

were made after

source,

conposed of organics,

particles

Nonetheless,

7ooo”c.

single

include

than 100°C.

do not

the use

(ref.

area measurement important

steps

use

461 can be

in the

procedures; a.

Admission

resultant

flow-ate

is

tubing.

the

instrument

flow

rate

tines

(5 point

must exceed

radioriietric dp/dt

for

are being rates

ash samples

of 1 Torr diameter

Rapid initial

Convection

avai‘lable currents

of

required

will

resu‘lt

pressure

for

set-’

apparaa

procedure

(760 Torr)

_

again Lmless

of

in a dp/dt of 10 to

less

than

and twenty seconds for

This

the

corn-

the

Normal operating

steps)

10 Torr

are

so that

turbu?ence

dimensions

two seconds

sample tubes].

corresponds kinetics

the

to a of

there is litle need to exceed puI3p-dovm or set -1 = since very fine ponders nay aerosol i ze at

than those stated,

These rates

were obtained

far

f7y

= 2 IKI. heating

of the sample should be avoided by reducing

so that the sample will

than 5 minutes and preferably

comercia77y

on the

tubes).

long

at which

a micro-balance

of about

heat input to the furnace no less

for

rate

studied,

flow-rates of

of

sample

from atmospheric minute

be sufficiently

dependent

BET and 20 Torr

the microbalance

even snal ler C_

one

nust

critical

in excess

method (10 m i.d.

adsorption adnission

is

(76 ma i.d.

Torr set-' or less. b. l%.mp-dOwI tines 1 Torr

adsorbate

than the

Admission

vacuum micro-balance

for

less

The critical

tlences. tus

tines

in no less

programmable furnaces

than

10 ninutes.

can e7ininate

can be avoided by reducing

the

t-i se fron 20”~ to 200°C in

pressure

this

to less

The use of problem. than 10S4

245 Torr

before

heating

by weight), the

it

water

has

precede

Sanp?e

disturbance

vibration

in

liquid

the

loss.

This

or

“boil-off”

the

liquid

or

nay

for can

in

e. very

difficult

size

and

f.

The

bench,

Janinar

flow prevent

to

Standard

(ref.

regulations Sanple

We have

fron

in

the

which

be

sample

sample

upright

sanple

is

and

and

free

must

from

cooled

motion

slol-J?Y

of

in

These

which

co?d than

gross

rapidly con-

is

causing

rather

sample

nitrogen

gas,

directly

SJOVJ cooling, the

can

in

liquid

Rapid

sample

heating

the

sample

is

sample

increase

was

greatly

reduced

partic?e

a clean

center

is

the

decreasing

using

the

stored

bias since

with by

near

during

sample

of

the

con-

used faci?itates

bag,

or of

contain

“bagged”

lead,

either The

to

prevent

is

vibration-free ShOMn

of

This

is

and

surface

those

both

is

made.

The

during

of for

bagged

and

best

radionetric during

handled,

to

the

glove

sanple,

in

its

ho?der,

transfer

or

is

baterials. samples.

containment

betLVeen

2”~4”x4”,

(a

unbagged

provide the

has

adequate

2 and

Fiaure

glove

sample

are

for

in

is

glove and

holders

and

box

space 72

box

half-brick]

shielding

and

are

area the

other

volunetric

sample

UnJess

in Table

be

safety Jaws

requirements

sample

half-bricks

spillage.

can

Energy

Local

toxicity

fron in

Atomic

interest.

specific

measuring the

a

box

appropriate

1 icensing

potential

hoJders

measurement

the

of

any

differ

the

made

isotopes

the

which

flow

If

samples.

International

determine

determination

in

a laninar

plexiglass

radioactive

of the to

so that

of

free

handling

publications

the

draft

using

manipulation.

sample.

in

the

by

sample

a clean,

be consulted

box

those

in

somewhat

on the

necessary

handling.

as

which

material

off

procedures

p?astic

to

nass)

be

available, settling

because

area

in result

reduced

turned

sanp7e

holder

obtained such

or

into

sanp’le

nay

powdered

easily,

glove

drilled

for

procedures

of

wall.

fan

box,

surface

A sample

the

5% ltater

most

ninutes

an area

apparatus,

position.

unit be

investigated

that

the

in a clean

useful

the

as the

sealed

placed

holes

(per can

weighing

boxes. with

ten

heated

the

minutes

Adhesion

are

a glove

be

transfer

to

should

found

can

four

equipment needed for

As a consequence,

methods

container

not

handling

in

the

the

from

such

should

performed

over until

currents may occur.

of

final

the

is

49,501 and

wall

its

the

precautions

procedures

net.

with

dust

texts,

Agency

least

a micro-balance

or

effect

near

bench

Special

of the

contamination

but

used

is

convection

into

sampling

than

Specimen

clean

(i.e.,

= 60°C

by using

sample

three

on particles

by

rather

at

avoided

the

by cooling

overcome.

48).

container

pan

strike

adhesion

forces

tainer

takes

wet at

above.

to

(ref.

very

sample

liquid nitrogen in a Dewar,

raised

Partic?e

adhesion

the

After

(c)

be

If

strong

to

from

is

is

the

usually

should

be avoided

Dewar

discussed

This

shock.

set

pan

nitrogen.

nitrogen

a sample

maintain

200°C.

nitrogen),

currents

sufficient

to

renoved. at

d.

vection

been

If

samp?e.

necessary

outgassing

nechanica? (e-g.,

the

is

also

which

hold the

a ba?ance,

necessary.

is

246

tube

w

and

into in

two bags

glove

spare

Monitor,

9

tube

accept/reject

box

bag outside glove-box

Surface study

Area in

glove-box

Fig.

12.

Flow chart

The sample of

the

glove

procedure

loaded

into

procedures a sample

The outside

If

level the

sample

the

preparatory

outside

the

bagged

pass-through considered sample topes

of

However,

if is

box also

is

unacceptable

registering

over to the

area

higher

levels

(ref.

49,

is

level

returned

radioactive

and the

tube

pouder bagged

glove of

with

page 84).

may be permissible

box. glove

isotope

clean

The sample is

Levels

used.

If (ref

the the 49,

balance balance

is

for

(ref.

radio49,

is

pp_ 85-91).

50)

bag which then

reweighed for

transand the

of contamination

We recommend that is

out

handling

decontamination

6 or T or l-l 0 dpn/cn’

box if

and passed

unacceptable

box for

decontaminated. the

small

a second

contamination

to the

100 cpn for glove

sufficiently

inside

samples.

in the

is monitored

therefore, is

placed

carefully vary

be returned

“clean”

contamination

the

sample

tube

box and,

the

(Tab1 e 2).

of

for

of the bag nay be contaminated

bag containing

remains fer

transfer

or in the pass-through

activity. the

is

box.

of

for

any

a iso-

in an uncontrolled in a controlled

area,

or

1 mg 5 mg

Gas Chronatographic

0.1mg

Flowinggas

kadiometric

Columnpacking uniformity

Olankcorrection Peakshapeanomalies

Blankcorrection

blankcorrection Deadspacecorrection

Volumetric 1 mg

MainLdmitations on Precision Method

Wethods/ Estimated minimum Characteristic SampleSize

TABLEla, Volumetric and BelatedMethods

ZOO"C,M,V

200"C,M,A

/OO"C,M,V

200"C,M,V

Outgassing Method

M.A-

M.A.

P.M.

P.M.

Main Advantage

~o~erciallyavailable. (Quantasorb)

Equipment is easy to construct and set up.

Equipment is easy to construct and set up. Commercially available. (Micromeritics)

OtherCommentsa

10-CrJg

Stability of field coil currents

2OO"C,S,A

Sample Size

Sample Size

MaIn Advantage

Kineticsof adsorptfon can be studied.

kineticsof adsorption can be studied, also size-selected saples,

Commercially available, Cahn-Ventron, SartorIus, Perkin-Elmer, Kinetics of adsorption can be studied,Otherdata possible,

OtherCommentsa

aMentionof a inanuhcturer's namedoesnot constitute endorsement of the product.ho attemptat a comprehensive directoryhas beenmade. ~fanufa~turers instructions may suggestthatoutgassing timesas shortas 5 minutesare satisfactory, ktith a corresponding high dailythroughput of samples.Hostof the productstestedgaveunsatisfactory dataif five minuteoutgassing timeswereused. However,a markedimprovement r/as demanstrated when sampleswere outgassed overnight as re~o~endedby Fuller,Greggand Sing (ref.S,llr),As disc~tssed e~se~/here, (ref.26),desorption half-times may exceed30 mfnutes, S = Singlesampleoutgassed overnight. t-1 = ~u~tjpJesamplesoutgasse~ overnight, V J Vacuumoutgassing. A = Atmospheric pressureo~ltgassing, flowinggas usedto removedesorbedgases. R = Suitably for radioactive samples,

Mi~likanOil-Drop

Uniformity of deposition ZOO"C,S on crystal A or V

2rlO"C,S,V

T.M.F.and buoyancy corrections

Vacuum ~iicro-balance

2 Pg

Out~~~~~~g

t4ain Linitations on Precision Nethod

estimated minimum Methods/ Characteristic SampleSize

TABLElb, Gravjnetric Ftethods

249

TABLE 2.

Exanple

of

Objects

Neighing

Procedure

Weight,

hei ghed

22.57149

Empty sample ho1 der, cap, spring Empty sample holder, cap? spring and a 50 ng class Fl weight Enpty sanple holder, cap, spring and 2 bags with ties Empty sample holder, cap, spring, 2 bags with ties and a 50 ng class M weight Sanple holder, cap, spring, 2 bags with ties and a sanp?e Sample height

Gram

22.62152 29.03025 29.08065 29.08861 =

50.0

2 0.1

ng