This document discusses methods for measuring the hydrophobicity of various AEROSIL products. It begins with an overview of how AEROSIL R 972 was the first industrially produced hydrophobic silica in 1962. Several new hydrophobic AEROSIL grades have since been developed with different surface treatments and starting materials. The document then examines various techniques for quantifying the hydrophobicity of these products, including water vapor adsorption, contact angle measurement, and infrared spectroscopy. It explores applications of hydrophobic AEROSIL in the coatings industry, focusing on their effects on rheology, dispersion, coating properties, corrosion protection and more.

2. The series of TechnicalBulletinPigments
issuedby the InorganicChemical
ProductsDivisiondiscusses fields of
application inthe lacquerand paintindus-
try in the followingeditions:
No. 3
Degussa Pigments for the
Coatings Industry*)
No. 15
Carbon Blacksfor Coatings and Printing
Inks -A Survey
No. 17
Degussa Pigment Blacks and Pigment
Black Preparationsfor Coating Materials
No. 21
Degussa FlattingAgents for the Coatings
Industry
No. 22
Basic CharacteristicsandApplications of
Colour Black Part 14,
FloridaTest Resultsof CoatingsColoured
with Pigment Blacks
No. 34
Aluminium Silicate P 820
for Emulsionand DecorativePaints
No. 36
DifferencesbetweenNatural Fillers
and Synthetic Micro-Extenders
in EmulsionPaints*)
No. 37
Basic CharacteristicsandApplications of
Colour Black Parts 10and 16,
Coloristic Measurements of Jet-Black
and Grey Coatings
No.39
Basic CharacteristicsandApplications of
AEROSIL@
Part 17,
ReflectionMeasurements on Synthetic
Silica Products
No. 68
AEROSIL@
for Lacquersand Paints
Our cover shows:
demonstrationof typicaleffectsattainable
withAEROSIL R 972: hydrophobic
behaviour,effectiveness as a free-flow
additive, applicationas an anti-settling
agent. *) not yet publishedin English

3. Basic Characteristics andApplications
of AEROSIL@
Part32:
The Use of HydrophobicAEROSIL@
inthe Coatings Industry
Dr. Horst Ferch
Department ofAppliedResearchand
TechnicalServices, Silicasand Pigments,
DegussaAG
Followinga brief descriptionof howthe
hydrophobic grades ofAEROSIL@
are pro-
duced, the author goes intosome detail to
describeways of measuringthis stateof
hydrophobicity. Possibleapplicationsin
which hydrophobicAEROSlLisusedinthe
coatings industryarethendescribedanda
brief mention is made of further uses in
other branchesof industry.
Basedonlecturesheldbytheauthoratthe
47th Conventionof the specialist group
“API” of the GesellschaftDeutscher
Chemiker heldin Hannoverin 1979and on
the occasion of the 13thEUROCOAT
Congress of AFTPV in Nicein 1987.
Thiseditionof theTechnicalBulletinPig-
ments issuedby theInorganicChemical
Products Divisionis printed usingthe
Degussa carbon black PRINTEX@
55.
1

4. Table of Contents
3
1 Introduction
2 ProductionandPropertiesof HydrophobicAEROSIL 4
3 Howto MeasureHvdroDhobicitv 10
3.1 GeneralInformation 10
3.2 MeasuringMethods 11
~
3.2.1 WaterVapourAdsorption 11
3.2.2 ContactAngle 12
3.2.3 MethanolWettability 14
3.2.4 Infra-RedSpectroscopy 15
3.2.5 TotaEilanol GroupDensity 15
3.2.6 CarbonContent 15
3.2.7 Water-SolublePart 16
3.2.8 CalorificQuantities 16
~~
3.2.9 “Residual SurfaceArea” 16
3.2.10 SAPPOK’s Degreeof Hydrophilicity 16
3.3 Evaluation 17
4 Applications intheCoatings Industry 18
18
4.1 Rheology
4.1.1 ThickeningBehaviourandThixotropy 19
4.1.2 UseasanAnti-SettlingAgent 21
4.2 DisDersionAdditive 23
25
4.3 CoatingEffect
4.4 CorrosionProtection 28
4.5 Adhesion 29
4.6 Uniformity 29
4.7 Free-FlowProperties 34
5 FurtherApplications 34
6 PracticalAdvice 35
7 Toxicological Information 35
8 Literature 37
Brief List of TechnicalTerms 39
Phvsico-ChemicalDataof HvdroDhobicAEROSIL 43
Additional DegussaProducts 44
2

5. 1
Introduction for example
by usingthe hydrophilic products,
Overthe past 25 years synthetic hydro- - inthe production Of free-flowing Pow-
ders for fireextinguishers(1);
defoamers(2);
fluoroelastomers(3);
tems (4);
printing inks (5).
phobic silicashavecome to be used in
numerous branchesof industry.This new
class of products offeredthe solution
to problems which could not besolved
- inthe development of highly-active
- inthe reinforcement of special
- to achievespecialeffects incoating sys-
- to regulatethe water balanceof offset
Inthis brochure,these newer products are
compared with the oldest of the hydro-
phobic silicas,AEROSILR972, which was
introducedin 1962and isnow producedon
an industrialscale.Themanufacturingpro-
cess was described in 1965(6).Technical
Bulletin Pigments No. 6 inthis series deals
with this product in moredetail.
Additional hydrophobic silicashavebeen
developedin orderto increasethe pos-
sibilitiesof application andtoopen upnew
markets.
3

6. 2
Productionand Propertiesof
HydrophobicAEROSIL
As mentioned before,thefirst industrially-
manufactured hydrophobic silica was
broughtontothe market in 1962 and was
known as “Filler R 972”.After reportsby
KLOSTERKOlTERin 1965 (7),based on a
one-year long-terminhalationtest carried
out with laboratory animals, showed that
this new materialdid not cause silicosis,
the namewas changedto “AEROSIL
R 972”.This hydrophobic special product
isconvertedwith dimethyldichlorosilanein
a fluid-bed reactorwhich is heatedto
approximately 400°C.As a result of this,
around 70% of the previouslyexisting
silanolgroups reactwith the silaneand
form Si-0-Si (CH& groups(6);thematerial
acquiresa hydrophobiccharacter, see
Figure 1.When analysed,AEROSIL R 972
differsfromthebasic productasa resultof
its carboncontentof approximately 1YO.
However,nodifferencecan beobservedas
regardsthe average primary particlesize
whenAEROSIL R 972 is compared with its
hydrophiliccounterpartin electronmicro-
graphs.
Figures2and3show atransmissionelec-
tron micrograph (TEM)and a scanning
electronmicrograph(SEM)of this product.
These picturesillustratethe tendency of
AEROS!L R 972 to aggregateand agglom-
erate,as isthecasewiththe basic product
AEROSIL 130.This statement is also valid
for all of the other hydrophobicgrades of
AEROSIL dealt with inthis editionofTech-
nicalBulletin Pigments.The question re-
garding the existenceof primary particles
inAEROSIL, as defined in DIN53206,
Figure 1: Schematicrepresentation of the reactionof dimethyl dichlorosilanewith the silica surface:
conversionof “hydrophilic”to “hydrophobic”
was treated back in 1984(10).Technical
Bulletin Pigments No. 60 is dedicatedto
this subject.
The properties of and special effects to be
attainedwithAEROSIL R972when applied
in coatingsystemswere described in
1979 (4)and further applicational pos-
sibiiitiesoithis speciaisiiicawere reported
on in 1980 (11).
Over the years it became apparent that
AEROSIL R 972 was unableto fulfil all of
the demands placedon it by various
aspects of the different applications. What
was wanted above all was a low-priced
hydrophobic version.
Dueto the fact that all of the hydrophilic
gradesofAEROSIL must be classifiedas
high-quality productsfrom a pointof view
of price, it was necessaryto fall back on a
lessexpensivestartingproductas a basis.
For obvious reasons,the choice fell on a
precipitatedsilica.An appropriate product
was brought ontothe market in 1964(12)
and is now known as SiPERNAT@
D 17.

7. Figure2
: TEM of AEROSIL R 972
5

8. Figure3 SEM of AEROSIL R 972
~~ ~
6

9. This hydrophobicspecial silica is used in
particularto improvethefree flow be-
haviourof substances inpowderform, e.g.
fire extinguishingpowder basedon sodium
bicarbonate(1).The commercial products
AEROSIL R 972 and SIPERNATD 17were
able to satisfy virtually all the market
demands for a periodof nearlyfifteen
years. SIPERNATD 17was unableto find
access to the coatingssector.
However,there are now severalnew com-
mercial productsavailable on the market
whichcan beusedfor further applications,
and whose data are compiled inTable 1.
All of these hydrophobicgradesofAEROSIL
are characterized by the additionalletter
“R” intheir name, which servesas a refer-
enceto the locationoftheGermanproduc-
tion plantin RheinfeldedBaden.Similar to
the productionofAEROSIL R 972,the new
AEROSILgrades are also manufactured
accordingto atechnical process.The
natureof the chemical aftertreatment is
shown inTable 1 inthe form of the chemi-
cal residuessituatedon the surface of the
silica; these can be easily detected by
means of infra-red spectroscopy, e.g.
(4, 13),as demonstrated in Figure4. The
left-handside of this figure depictsthe
rangeoftheOHstretchingvibrationbands
for the untreatedbasic product
- at 3750 cm-1 (freeSiOH groups)
- between3800 and2800 cm-I
(bridged silanol groups);
Figure4 Infra-red spectra of hydrophilicAEROSIL 300 and hydrophobicAEROSIL R 812 (13)
thesamefrequency rangeofthissampleis
shown on the right-handside followingan
in situ treatment of the silicawith the cor-
respondingsilane.A reduction inthe
number of both isolated and bridged
silanolgroups can be observed here inthe
right-handdiagram, and at the sametime,
the CH stretching vibrationbands of the
newly-anchoredmethyl groups become
apparent at 237Ccn-I.
7

10. Table 1: Specificationsand further data on the hydrophobicAEROSIL grades.AEROSIL R 812S differsfromAEROSIL R 812 as a resultof havinga higher degree of
hydrophobicitywhich is achieved by means of an additionalprocessingstep
8

11. All of the hydrophobic gradesof AEROSIL
listed inTable 1arethermallystableas far
asapplicationsinthecoatings industryare
concerned,as Figures 5 and 6confirm.
Figure5 shows the weight loss of the
undriedhydrophobicAEROSIL grades,
which was determinedby meansofthermo-
gravimetric analysis, as a functionof the
temperature. Onthe basisof infra-red
measurements, Figure 6confirmsthe fact
that bothAEROSIL R 972 andAEROSIL
R 812 only undergochanges as a resultof
oxidationat temperaturesexceeding
400°C.
Asuggestion put forward in 1976(15)
servesto classify the hydrophobic grades
of AEROSIL in the wide range of synthetic
silicas currently availableonthe market.
Figure5: Weight lossof hydrophobicAEROSILgradeswhich wereslowly heatedina nitrogen atmosphere
(14). (PERKIN-ELMERthermo-balance, modelTGS-2)
Figure6 Reductioninthe IR absorption of the
methyl groups as a measureof the thermal stability
ofAEROSlLR972andAEROSlLR812(13).Measure-
ments were carried out on self-supporting discs
with adiameter of 13mmand6mgIcm2inweight
9

12. 3
How to MeasureHydrophobicity
3.1
General Information
What exactlydoestheterm “hydrophobic”
mean?Expressedsimply, hydrophobic
meanswater-repellent.The plumageof
aquatic birdsor the cuticles of leaves
on the plantsare well-known natural
examples of this. Furtherexamples of
hydrophobicityin daily use comefromthe
technicalfield:TEFLONa-coatedfrying
pansandtop coatsfor automobiles.The
opposite of hydrophobic is “hydrophilic”.
Intechnology, use is often made of a
combinationof hydrophobicand hydro-
philic properties.Inthe molecular range,
the surfactantsin householddetergents
shouldbe mentioned;the increasingly
importantoffset printingprocess operates
with largerparticles,andcoarsepiecesare
used inthe flotation of ore.
The useof hydrophobic substances in
powderform has provedsuccessful in
numerousapplications, with synthetic
silicas playinga particularly importantrole
here. Productsof this natureattaintheir
hydrophobic characteristics as a resultof
many different methods of surfacetreat-
ment,such as coating with wax or chemi-
cal reactionof the surfacegroupswith
appropriate silanes. It should be repeated
at this point,however,that all of the hydro-
phobicgrades of AEROSIL mentionedin
this brochurearerenderedhydrophobic by
means of a chemical reactionon the sur-
face of the solid.The hydrophilic or hydro-
phobiccharacter of an amorphous silica
canbeeasilyjudged byshaking ittogether
with water in atest tube; hydrophobic
AEROSIL floatsto the surface.All of the
hydrophobicAEROSIL grades react inthe
same way duringthis test, Le. it is not
possibleto differentiate betweenthem.
Although theterm “hydrophobic” appears
to be easy to understandwhen taken to
meanwater-repellent,it is neverthelessdif-
ficult to accurately define or to quantita-
tivelydeterminethis property. Itisoftenthe
casethat the differentmethodsdo not lead
to thesameconclusions(14).Aselectionof
methodsof determinationaregivenbelow.
10

13. 3.2
Measuring Methods
3.2.1
WaterVapourAdsorption
A methodwhich is somewhat time-con-
suming, but definitely relatedto practiceis
the intakeof the water vapour adsorption
isothermsmeasuredat varying levelsof
relativemoisture.Correspondingmeasure-
mentsaregenerallymadeat roomtempera-
ture, e.g. inthe case ofAEROSIL R 972 (4).
Figures7-10 depict the corresponding
curvesfor the productsAEROSIL R 202,
R 812, R 805, R 972 and R 974, each in
comparisonwiththe respectivehydrophilic
basesilica.
It is understandablethat the adsorptionof
the latter is always higher.The numerical
values which are obtained withAEROSIL
R 972 (FigureIO) demonstrate an even
loweradsorptionthanthat shown inFigure
7 for AEROSIL R 202. If the shapes of the
curves shown inthe four diagramsare
compared, it ispossibleto observedefinite
and also characteristic differenceswhich
occur independentof the size of the
specificsurface area.When measured
accordingtothis method,the hydrophobic
character of the individual grades declines
inthe followingorder:AEROSIL R 972 >
R 202 > R 812 > R 805 > R 974.
Figure 7: Water vapour adsorptionisothermsat roomtemperature of AEROSIL 150 (basic hydrophilic
substance) andthe hydrophobic grade AEROSIL R 202, measured usingsmall samples
Figure8 Water vapour adsorptionisothermsat roomtemperature ofAEROSIL 300 (basic hydrophilic
substance)andthe hydrophobic grade AEROSIL R 812, measuredusingsmallsamples
~
11
. "I

14. 3.2.2
ContactAngle
The so-calledcontact angle methodcan
be usedto determinethe hydrophobicityor
“wettability” of smoothsurfaces (16).This
method involves placinga droplet of water
of a certain volume under specifiedcondi-
tions ontothesurfaceto beexamined.The
contact angle is then measuredwith the
aid of a horizontally-positioned
micro-
scopewithagraduatedscale. Ifthedropis
predominantlysphericalinshape,thecon-
tact angle is 8 > 90” and, accordingto
YOUNG’Sequation, the interfacial energy
is Ewater/soiid > Ewater/air Wetting does not
takeplace,or onlyto a limitedextent. Ifthe
drop resemblesmore of a hemisphereor
even spreads out (8 <go”),the expression
EwateVsolid < Ewater/air applies and wetting
takes place.This behaviour is illustratedin
Figure 11. Difficultiesarisingfrom the
productionof suitable mouldedtablets
with “smooth” surfaces are experienced
when the contactangle methodis usedto
determinethe wettabilityof hydrophobic
powder(17).
Figure9 Water vapour adsorptionisothermsat roomtemperature of AEROSIL 200 (basic hydrophilic
substance)andthe hydrophobicgradesAEROSIL R805andAEROSIL R974,measuredusingsmall samples
Figure 1 0 Water vapour adsorptionisothermsat roomtemperature of AEROSIL 130(basic hydrophilic
substance)and the hydrophobic grade AEROSIL R 972, measuredusing small samples
12

15. Of allthesilica gradestestedhere,it isonly
possibleto produceasuitable moulded
discwithAEROSlL R972.Theotherhydro-
phobicAEROSIL grades can be compres-
sedto mouldeddiscsunderhighpressure,
but these crumble on releasewithoutthe
applicationof any externalforce. For this
reason, it is only possibleto give contact
angles for the Degussasilicas listed in
Table 2. Hencethe contact angle method
is not suitable for the characterizationof
hydrophobicsilicas.
Contactangle given indegreesof
Water Glycerine Siliconeoil Mineraloil
hydrophilicsilica <20" <20* <20* <20*
SIPERNATD17 144 113 <20" c20*
AEROSIL R972 124 78 <20" <20"
*
Table 2 Contactanglesofdifferentliquidson mouldeddiscs(2mmthick,28mm indiameter)madeof some
Degussasilicas
soaks intothe mouldedtablet after a short time
13

16. 3.2.3
MethanolWettability
A suitableway of determiningthewettabil-
ity of hydrophobicpowders appears to be
with the aid of alcohol/water mixtures.
The higherthe proportionof alcohol inthe
liquid mixture inwhich wetting istaking
place,-Le. the immersionof the powder
intothe liquid-, the “greater” the degreeof
hydrophobicity(18). In principle,this
methodcan also be used to test the
homogeneity of the hydrophobicity.For
this purpose, samples are shaken with
various mixtures of methanoland water
and are then centrifuged.
Ifthe height of the sediment is plotted
against the proportionof alcohol inthe li-
quid,an ascendingcurveresults.Agradual
risedenotes that the powder particlesare
not uniformly hydrophobic.
On the other hand, a steep rise indicatesa
uniformsurface modification,see
Figure12.
14

17. Furthermore,it seemsjustifiedto inferthat
an increasedmethanol requirement sig-
nifies a higher degree of hydrophobicity.
A relativelysimple method, which is attri-
butedto K. KLEIN(19),hasproveneffective
in practicewith hydrophobic silicas.
200 mg of the substance are addedto
50 ml water in a separatingfunnel.As the
mixtureis shaken,a burette-which is
immersedto the bottom of the water -is
then usedto slowly add methanol until all
of the silica has beenwetted. The portion
by weight of the methanol inthe mixture
neededfor this purpose is a measurefor
the hydrophobicityof the silica.The values
attainedinthisway arerecordedinTable1.
However,it should be pointedout that,
within the meaning of an exact analysis,
this methodyields very fluctuatingvalues.
Forcomparative purposes, a measure-
mentof this nature must be carried out by
the sametester andif possibleinthesame
laboratory.
3.2.4
Infra-RedSoectroscoov
3.2.6
CarbonContent
Two methodsof characterizingsynthetic
hydrophobic silicas are availablewhen
using infra-red spectroscopy:
- determinationof the remainingsilanol
groups situated on the surface in iso-
lated state,
group density on the surface.
- determinationof the relativemethyl
Numericalvaluesfor the relativemethyl
group density are given inTable 1.Accord-
ingto bothofthese criteria,AEROSIL R 812
is more hydrophobic than, for instance,
AEROSIL R 972.
The infra-redtest methodistime-consum-
ing and a spectrometer with good resolv-
ing power (e.g. 2.5 cm-I) is needed. How-
ever, oncethis methodhas been “mas-
tered”, it providesaccurate comparative
values for characterizationpurposes.
3.2.5
Total Silanol Group Density
The LiAIH4methodcan be employedto
determinethetotal silanolgroupdensityof
syntheticsilicas(9,13).Inaccordancewith
Table 1,the increasinghydrophobicityis
given in the followingorder:
AEROSIL R 805 <R 812S <R 972 <R812
< R 202.
This methodisnotsuitablefor testingonan
occasional basis,as especiallythe drying
of the synthetic silica is of great signifi-
cance here.
An obvious way of characterizinga hydro-
phobicAEROSIL grade isto determinethe
Ccontent.Thisisthefirst steptowardsgiv-
ingan impressionof theamountof organic
groupsthat are present on the silica sur-
face. However,this value does notseemto
tell usvery much because
- the sizeof the specificsurface area of
- in additionto a chemicalfixing of the
the basicsilicaisnottaken intoaccount,
organic groups, afurther adsorptionof
organic substances can alsotake place
on the silica.
Boththe analytically-determinedtotal car-
bon content andthe C content relatedto
the surface are includedinTable 1.When
the specific carbondistributionis taken as
abasis,thefollowingsequenceisobtained
in view of the increasinghydrophobicity:
AEROSIL R974 <R972 <R 812or R812S
<R202 or R805.
AEROSIL R 812 andAEROSIL R 812 S are
silicas which are also capableof firmly
adsorbing organic substancesby physical
means.This is notthe casewithAEROSIL
R 972, R 974 and R 805.
15

18. 3.2.7
Water-Soluble Part
The proportionof hydrophobicsynthetic
silica which is wetted by water is deter-
mined analytically.The lower this value is,
the higherthe degree of hydrophobicity.
However,this methodis relativelyinaccu-
rateand can only providevalues which
enablea differentiationof hydrophobic
silicas in truly routinestudies.
3.2.8
CalorificQuantities
Another processwhich can be usedto
characterize hydrophobic grades of
AEROSIL isthe determination of the heats
of wetting invarious liquids.The extent to
which a methodof this naturecan be used
to explainthe gradualapplicational differ-
ences of finely-dividedhydrophobicmate-
rials is uncertain at present.The method
appears to betoo expensive for purposes
of qualitycontrol (20,21,22).
3.2.9
“ResidualSurfaceArea”
3.2.10
SAPPOK’s Degreeof Hydrophilicity
Aspecial feature of the pyrogenicsilica
AEROSIL isthatthe N2adsorptionaccord-
ingto BET(23)reflectsthesurfacechemis-
try inthe form of the concentration of iso-
lated silanolgroups (24).It seems logical,
therefore,to usethis specificsurface area,
determinedwith N2according to the BET
method, and the “reduced”specific sur-
face followingthe chemicalaftertreatment
as a criterion for the surface coverage (13).
Numericalvalues for the “residualsurface
area” relatedto the basic silica are given in
Table 1.The followingorder is obtained
when this methodisapplied:
AEROSIL R972 <R812 <R 805 <R 812S
< R 202.
Nevertheless,itshould bepointedout here
that this “residual surfacearea” method is
somewhat inaccurate.This is due in par-
ticular to the alteredform of the BETad-
sorptionisothermswhich arises duringthe
chemicalsurfacemodification.This makes
it difficult to evaluatethe curves and re-
ducesthevalue ofthestatement regarding
the degreeof coverage.
The expression“degree of hydrophilicity
according to SAPPOK may also befound
incertain literature(53-55).This isthe quo-
tient ofthespecificsurfaceareaaccording
to BETmeasuredwith H20,and the same
value measuredwith N2.Thisdegreeofhy-
drophilicityaccording to SAPPOK issup-
posedto give indicationsastothewettabil-
ity, dispersion and stability behaviourof
pigments.
Onthe basisofthe BETtheory,itshouldnot
be possibleto usethis quotient to charac-
terize hydrophobic silicas, becausethis
theory works on the principlethat all the
valueswhich areobtainedareindependent
of the properties of the solid surface.
However.this is notthe case.
16

19. 3
.
3
Evaluation
Followinga brief descriptionof thevarious
ways of characterizinghydrophobicity, an
attempt will now be madeto list the
AEROSIL R grades inthe order of their
hydrophobicity.This is done inTable3by
compilingan “order of rank” based on the
methodspermittingsuchstatementsto be
made; the smallervalues signify the high-
est degree of hydrophobicity.Once the
meanvalue hasbeencalculated,the grade
with the lowest value must representthe
product withthe most pronouncedhydro-
phobic propertiesoverall.This results in
the followingorder:
AEROSIL R 202 > R 812 > R 805 > R 972
> R 974.
Acertaindegreeof randomnessisalsopre-
sent in this list, due to thefact that a com-
parisonofthe individualmethodsdoes not
always result inthe same order. Hence
itisnoteasyto giveaclear-cutdefinitionof
the term “hydrophobicity”(14).
Table3 Procedurefor drawing up a “hydrophobicorderof rank”with the hydrophobicgrades of AEROSIL

20. Table 4 Effectson the gloss of water-thinnable stoving enamels caused byadditions of
AEROSIL R 972 (4).
Composition: RESIMENE 5.5; CHEMPOL 10-0500 - solution 65.0; TiOpRKB2 27.8;
2-ethyl hexanol 1.0; defoamerTROY999 0.3; FluorchemicalFCI-430 0.4
4
Applicationsinthe CoatingsIndustry
Hydrophobicgradesof AEROSIL may be
used in numerousways to improvethe ap-
plicationalpropertiesof paintsand other
coatings,andto reducethe addedamount
of silica in certain formulations. Effectsof
this naturewere compiledin a report back
in 1979(4). Recently-acquiredknowledge
relatingto these new specialproducts
will be includedinthe familiar applications
dealtwith inthis section.
Nowandagainobjectionsare raisedto the
effectthat the additionofAEROSILre-
ducesthe glossoftop coatsto suchan ex-
tent that practicalapplicationis rendered
impossible.Usingas an examplea black
and awhite stovingenamelbased on a
water-thinnable binder,Table 4 illustrates
that this argument is not valid if the
AEROSIL issufficiently dispersed. Only
very slight reductions in gloss occur,
seeTable4.
4.1
Rheology
~
18
The influenceon the rheologicalbehaviour
of liquid systems exerted by hydrophilic
AEROSILwas describedway back in 1969
(25).Acompany publicationissuedin 1986
also discussesthe possibleinteraction
mechanismsof hydrophobic grades of
AEROSIL (26).
Figure 13: Viscosity behaviourof an ethanol-water
mixture 1:l followingthe addition of different
AEROSIL grades (14)

21. 4.1.1
Thickeninn Behaviour andThixotropy
In a large numberof systems, higher in-
creases in viscositycan be attainedwith
hydrophobicsilicas than with the same
added amount of hydrophilicsilicas.
This is the case, for instance,in a 1:1
ethanol-water mixture,as illustratedin Fi-
gure 13,whereAEROSIL R 972 serves as
an example.It isalsopossibleto recognize
from this example howthe likewisehydro-
phobicAEROSIL R 812 does not display
this behaviourto anywhere near suchan
extent. It is not possibleto predictwhich
hydrophobicsilica will demonstratethe
bestbehaviour inaparticularcase,andfor
this reason, practicaltests are unavoid-
able.This statement isvalid for pure
solventsand mixturesof suchaswell asfor
bindersystems.
Three epoxy esters of the same composi-
tion butfrom different manufacturersare
shown in Figure14,which depictsthe
increasesinthe viscosity andthe corres-
pondingthixotropic index values of these
threesystems, inducedby the additionof
hydrophobicsilicas. The thixotropic index
was calculatedfrom the viscosityvalues
attainedat a shear rate ratio of 1:I 0.
Figure14showsthat
- the three binders used display different
behaviouralthoughthe initialviscosity
was comparable;
- AEROSIL R 812 providesthe best result
ineach of the cases;
- the differenceinthethixotropyisgreater
than that of theviscosity.
Figure 1 4 Increaseinthe viscosity andthixotropy of epoxy ester-basedzinc dust paintsfrom different
manufacturersafter the additionof hydrophobicAEROSIL (14). Dissolver dispersionat 4000 r.p.m.
Peripheralvelocity =8.4 m/s
Figure 1 5 Viscosity behaviour of epoxy resinsolutionsthickenedwith 3% by weight of AEROSIL during
12weeks of storage at roomtemperature (14)
19

22. Afurther examplewill be usedto de-
monstratehow, in additionto the levelof
viscosityand a possiblethixotropiceffect,
the time-dependentviscosity behaviour
can also be changed to advantage.
Figure15 illustratesthe viscosity be-
haviourof 50% epoxy resinsolutions con-
taining different grades of AEROSIL.
3% by weight of silica was added ineach
case.Thethickeningeffect ofAEROSIL
R 972 is very slight; the hydrophilicgrade
AEROSIL 200 only demonstratesa high
initial viscosity; good long-termviscosity
behaviour is attained solely withAEROSIL
R 805.
Some results in a white highsolidscoating
will nowbediscussed.Figure16illustrates
the increases inviscosity attainable with
additionsof 0.3% of hydrophobic silica
and also the calculatedthixotropic index.
AEROSIL R 805 also providedthe most
favourable result as regardsthe gloss at-
tained (87%) andthe sagging behaviour.
The latter was measuredby coatingplates
of glass with a 150 pm film applicatorover
a lengthof 16 cm and then placingthe
platesin a vertical position.The only
system which demonstrated no sagging
was that containingAEROSlL R 805.
without the additionofAEROSIL at roomtemperature (14). Composition: BAYER-TITAN RKB3 28.00;
AEROSIL ineach case 0.28; ALKYDAL F261 hs43.90; RESIMENE740 13.00; ethyl glycol acetate 5.22;
ethyl glycol 5.00; butylglycol2.30; xylene 2.50.48 hoursinthe ball mill KU 1 using porcelainballs
Special mentionshould be made at this
point about the orange peel effect which
occurredon the surface of the coatings
containingAEROSIL R 202.This effect can
only occurwithAEROSIL R 202 and not
with any other grades ofAEROSIL referred
to inthis publication.AEROSIL R 202
is producedwith the aid of polydimethyl
siloxanes, which are knownto cause such
an effect.
Ina company publicationissuedback in
1986(27),it was pointedout that AEROSIL
R 202 can cause:
- levellingproblems, e.g. the orange peel
- adhesionproblems,e.g.with multi-layer
effect,
systems,etc.
Ifthe best rheological resultsare obtained
withAEROSIL R202,testsmustbecarried
out priorto applicationin practicein order
to determine whether or not side-effects
occur.
- ~~~ ~
20

23. 4.1.2
Use as anAnti-Settling Agent
The useof AEROSIL as a suspending
agent for pigmentsand fillers inthe coat-
ings industryisthe oldest field of applica-
tion for this class of products(29).In
general,the additionof small amounts is
sufficientto obtainthedesiredanti-settling
effect which is accompanied, as a rule,by
acertain increaseintheviscosity.
It is importantto establishthat theimprove-
ment inthe suspensionbehaviour cannot
be explainedentirely bythe increaseinthe
viscosity. Paralleltests servedto demon-
strate how a subsequent adjustment of
the viscosity up to the same levelof the
samples inthe controltest only produceda
gradualimprovementand notthe positive
effect of improvingthe suspension
behaviour,such as is shown in Figure 17.
The advantage of all of the hydrophobic
grades overAEROSIL 200 isthat -due to
their havinga lower silanolgroup density
(seeTable1)-agglomeration is not so
great and they may therefore be dispersed
more easily,see Figure23.If the cost-
benefitratio isconsidered, all of the argu-
mentsspeak infavour of the use of
AEROSILR 972.
Figure 1 8 Sediment consistency measurements
carried out on zinc dust paints(composition see
sub-titleto Figure17)after three monthsof storage
at roomtemperature(4)
Figure 17: Comparison of the sedimentation tendency of epoxy ester-based zinc dust paintsafterfour
weeks of storageat roomtemperature.Left:control paint, right: paint producedwith an addition of 2% of
AEROSIL R 972 (4).
Composition:JAGALYD ED4,50% inxylene 19.6; zinc dust super-fine 72.5; butanol1.0;SHELLSOLA9.4;
Co octoate,6% Co 0.2
JAGALYD ED4
21

24. The optimumadditionof AEROSIL can be
readily determined in practicewith the aid
of a DYNOMETER (30,31).Usingzinc
dust paintsas an example, Figure 18
demonstrates the effect which may be
obtainedwithAEROSIL R 972.
It isofsignificancethatthecontrolsample,
which containedno additionof AEROSIL,
had becomeso hard after only four weeks
of storagethat it was no longer possible
to carry out a measurementwith the
DYNOMETER.-If 2% by weight of
AEROSIL R 972 is addedto these paints,
the power input in the DYNOMETER
requiredto reachthe bottom of the test
apparatus is nil.This value corresponds to
the addedamount of AEROSIL R 972
determinedin practice(4).
LikeAEROSIL 200,AEROSIL R 972 has
also been usedas athixotropein special
effectcoatingsfor manyyears (28).This
statement is still valid today. By preventing
the occurrenceof sagging, it is possibleto
producea well-defined specialeffectin
this application, which is naturally based
on the useof an appropriate silicone oil.
This statement is illustratedclearly in
Figure 19.Finally,special mention should
be madeof the fact that hammerfinish
coatingscontainingAEROSIL show no
sign of greying even after storage.
Figure 19: Saggingbehaviourof hammerfinishcoatings.Above: controlcoating,below:containing0.8% of
AEROSIL R972 (4).Composition:ALKYDAL R 4050.0;PLASTOPALEBS200,6O% inbutanol3.6; MAPRENAL
MF750,55% in isobutanol18.0; EFWEKO NC 18/2,20% inethyl acetate 5.0; butanol 13.5; SHELLSOL A 4.0;
ethyl glycolacetate 2.0; STAPA POLYCHROM3 3.6; silicone hammerfinish solutionTRS 0.3
22

25. An improvementinthe long-termsuspen-
sion behaviourcannot only be achieved
with specificallyheavypigments. Products
with a low specificdensity,such as SiOn-
basedflatting agents with a density of
1.9 g/cm3, can also be held effectively in
suspension, as demonstrated in
Figure20.
The resultsshown inFigures17and20are
representativeof the findings of numerous
othertests, inwhich AEROSIL grades lead
to the realsolutionof problems in other
systems.
AEROSIL R 972, for example, is effective
as an anti-settlingagent, improving impor-
tant properties, even after application
of a coatingonto the respectivesubstrate,
see Figures34 and 35.
4.2
DispersionAdditive
Figure 2 0 Improvement inthe suspension behaviourof FlattingAgentTS 100inacoating resultingfromthe
addition of 0.5% of AEROSIL R 972
Thestateof dispersionof mainlyhighqual-
ity pigmentscan be greatly improved by
slight additionsof hydrophobicAEROSIL.
This is demonstratedwith a pigmentblack
in Figure21wherethejetnessandblueun-
dertoneattainableserveas an example.
Figure 21: Blackvalue MYand bluecomponent M
, of stoving enamelscontaining 5% of Pigment Black
FW200 and 0.6% of AEROSILas a function of the dispersion time inthe ball mill (14).
Composition: MAPRENALMF800,55% in isobutanol13.3; butanol 0.6; Colour Black FW200 2.2; AEROSIL
0.264; ALKYDAL F310,6O% in MAPRENALMF800,55% in isobutanollO.7; solvent mixture RL938/9 21.9
23

26. Figure22: Increaseinthe degree of gloss of alkyd/
melamine-basedstoving enamels containingcol-
oured pigmentsresulting from the addition of 0.1 YO
and 0.5% ofAEROSIL R 972 (14).
Composition:ALFTALATAS502,6O% inxylene 46.6;
MAPRENAL MF800,55% in isobutanol21.8; diluent
15.8; Paliotolyellow 1770o
r HeliogenblueNFB or
cobalt blue5002 12.0; Bayertitan R-KB3 10.0 with
Paliotolyellow, otherwise 1.5
This modeof actionis demonstrated in
Figure22byan increaseinglosswithtints
of inorganicand organic coloured
pigments.
time. Peripheralvelocity of the stirrer: 8.4 m/s. Bothgrades of AEROSIL had already been predispersed.
Composition:see sub-titleto Figure 17
The grindometer values of zinc dust paints
which maybeobtainedas afunction of the
dispersion time are recorded in Figure23.
This diagram illustrates how much more
easily hydrophobic silica may bedis-
persed. For practicalpurposes, no more
differencescan be detectedbetweenthe
hydrophobicgradeandthecontrolsample
after 20 minutesof dispersion.
All of thefindingsdiscussed inthis section
are alwaysdependent onthe dispersing
conditions. It is by no meansthe casethat
the presenceof one of theAEROSIL
grades necessarily leadsto an increasein
gloss or improvementinthe optimum
efficiencyineveryapplication,seeTable4.
24

27. .
4.3
CoatingEffect
Ifzinc dustismixedinahouseholdblender
with 0.5% of AEROSIL R 972 inthe dry
stage, the hydrophobicsilica completely
envelops the Zn particles,as demon-
strated in Figure24.The same effect is
also observed inthe correspondingzinc
dust paints(4), see Figure25.This coating
effectof solidshas been knownfor quite a
longtime (32), and is also usedas a basis
for the preventionof the “gassing” of zinc
dust paintsduringstorage,which isshown
in Figure26.Theenvelopmentof zinc dust
with AEROSIL R 972 can possiblybe
attributedto purely electricalinteractions,
becausesynthetic silicas are always
negativelycharged (33)and metals are
always charged positively.
AEROSIL R 972 (right)(4)
-
-
Figure 2 5 SEMs of etchedzinc dust paints, lek control, right:containing2% ofAEROSIL R 972 relatedto
zinc dust (4).
Composition: JAGALYD ED4,50% inxylene 19.6; zinc dust sups-fine 72.5; butanol 1.0; SHELLSOLA9.4;
Co-octoate, 6% Co 0.2
25

28. However, non-metallicanti-corrosive pig-
ments can also be coated, as illustrated in
Figure27 by usingzinc phosphate as an
example. The theory of electrostatic in-
teractionscannot be usedto explainthis
particularphenomenon.It isalso possible
to attributethis coatingeffect to the better
dispersibility, discussed in 4.2, which
bringsaboutan improvementintheoptical
effectiveness of the different pigments.
Figure 2 6 Prevention of gassing of a zinc dust paint on a basis of epoxy ester following storage at
roomtemperature for four weeks. Left no addition; right: containing2% of AEROSIL R 972 related to zinc
dust (14).
Composition: JAGALYD ED4,50% inxylene 19.6; zinc dust super-fine 72.5; butanol 1.0; SHELLSOLA9.4;
Co-octoate, 6% Co 0.2
Figure 27:
phosphate
(right) (14)
SEMs of zinc phosphate(left) and zinc
together with 1YOof AEROSIL R 972
26

29. Hydrophobicsilica may also be usedto
stabilizea particular state reachedduring
dispersion. Table5 gives evidenceof a
morestabledistributionofthered pigment
frequentlyused intop coats for auto-
mobilesafter 48 hours of dispersion in a
laboratory ballmill. Inadditionto thetrans-
parency,which is higherthan that of the
control sample, and which indicates a bet-
ter pigment distribution,Table 5 also in-
cludesthechanged rheologicalmeasuring
data of the mill base broughtabout by the
addition of AEROSIL.
Not only solidscan be coatedwith
AEROSIL.The use of hydrophobic silicas
also enableswater to beenveloped. News
about this world sensationwas published
in 1966underthe motto “Degussa
chemistsinvent dry water” (34).Attempts
were made at this timeto mix 10% of
AEROSIL R 972 into water with the aid of a
high-shear powder mixer.
This resulted in afree-flowingwhite pow-
der. Whilst 10% of AEROSIL R 972 were
requiredinthose days, smaller quantities
are now sufficient to produce“dry water”.
The resultscompiledinTable6 are ob-
tainedwith 5% of hydrophobicAEROSIL.
Ifthistest hadbeenincludedintheevalua-
tion described in 3.3, the order of hydro-
phobicitydeterminedwould nothavebeen
changed, butthere would have been less
difference betweenAEROSIL R 202 and
AEROSIL R 812.
Paliogenred AEROSIL AEROSIL
L3885 R972 R805
viscosityof millbase mPas at Dm 4%s-1 3711 8834 8162
(HaslkeRV 11, SV I) mPas at Dm433s-’ 1352 1785 1406
Thixotropicindex 2.9 5
.
4 6.3
Transparency(redhigh solidsstovingenamel) 105.6 141.5 140
(LangeKMVLt 12/ grey filter 2)
I
Table 5 Increaseinthe viscosity and thixotropic index of a mill base based on Paliogen red” L 3885
and inthe transparency of a highsolids stoving enamelfollowing the addition of AEROSIL (14)
AEFFOSIL
R202 R805 R812 R812S R972
Formulationpossible no nQ Yes Yes no
Shearingstability in min - -
- 0.5 5
Table 6 Practicaltest to determinewhich hydrohobic gradesof AEROSIL are suitable for producing “dry
water” using 5% byweight (35). The shearing stabilitywas tested ina householdblender. The formation
of a clearly compacted,“smearable” masswas considered as signifying a collapseof the formulation
27

30. 4.4
Corrosion Protection
The useofAEROSlLR 972 as an additiveto
increasethe resistanceto corrosion was
describedin 1974(29).The positiveeffects
which may be obtainedwithAEROSIL
R 972 are illustrated in Figures28 and29
using zinc dust paintsand zinc chromate
primingcoatsas examples.
However,AEROSIL R 972 canalso improve
formulationswhich do notcontainanti-cor-
rosivepigments. For example, Figure30
depicts an industrial coatingbased on a
water-thinnable, oil-free alkyd resin
(s. Table 4 for formulation),which de-
monstrateda greatly improved resistance
followingstresses imposedduring the
accelerated durability test (dewcycle)
accordingto DIN 50018. -Results of this
natureare confirmedby independent
laboratories, such as theTransportation
Laboratoryof the Californian Department
ofTransportation(38).-
Figure3 0 Stovingenamel based ona water-thinn-
able binderfollowing7 dew cycles, to conform with
DIN50018(14). Left control sample, right: contain-
ing0.5% of AEROSIL R 972 related to the total for-
mulation
Figure 2 8 Zinc dust paintsbasedonanepoxyester
after a 168-hoursalt spray test inaccordancewith
DIN50021 andASTM B 117-64. Left:control paint,
right: containing 2% of AEROSIL R 972 related to
zinc dust (14).
Composition:JAGALYD 4,50% inxylene 19.6; zinc
dust super-fine 72.5; butanol 1.0; SHELLSOLA 9.4;
Co-octoate,6% Co 0.2. CompareFigure31
Figure 29: Zinc chromate primersafter a 168-hour
salt spray test in accordancewith DIN50021 and
ASTM B117-64. Left control paint, right: containing
1.3% of AEROSIL R 972 related to pigment (14).
Composition: LAROFLEXMP35 19.5; zinc white,
red seal 2.9; zinc phosphateZIN P 1.4; zinc chro-
mate1W6.8; ironoxide red130M6.8; talc AT1 13.5;
SHELLSOLA11.6; xylene 32.6; ethyl glycol acetate
2.4; chlorinatedparaffin40 2.0; castor oil derivate
0.6. CompareFigure32
28

31. 4.5
Adhesion
An additionofAEROSlL is knownto im-
prove the applicational propertiesof stov-
ing enamels, e.g. during the performance
of the mandrelbendtest, as definedin DIN
53152 (36). Figure31 demonstratesthe
improvedadhesion of epoxyester which
was appliedontoasteel plate. It isinterest-
ingto note that the hydrophobicgrades
ofAEROSIL bringabout an improvementin
the adhesion of the epoxy resins by an
averageof 13%.
4.6
Uniformity
The results of numeroustests have de-
monstratedatremendous improvementin
the uniformity or homogeneityof coating
Systemsthat includehydrophilic or hydro-
phobic grades ofAEROSJL.This section
includesseveralrepresentativeexamples
of applications containing hydrophobic
AEROSIL grades.
Figure 31: Increaseinthe adhesivestrength of epoxy esters on steel plates bythe addition of 1.5%of
hydrophobicsilica. Measuredfollowingtwo days Of storageat roomtemperature(14). See Figure28
To beginwith, these claims are supported
by surface representationsof priming
coats depictedin Figures32and 33. For
this purpose,we returnedto examples
which were already usedfor a different
representationin section4.4.
Figure32: Scanning electron micrographsof an etchedzinc chromateprimer (4). Left control paint, right:
containing 1
.
3
% ofAEROSIL R 972 related to pigment content. See Figure29
29

32. Figure32depictsa zinc chromate primer
and Figure33a zinc dust paint.The left-
handside ofthis pictureis notout offocus;
the blurredeffect is dueto the fact that the
upper layers of the controlpaint not con-
tainingAEROSlLarevirtuallyfreefrom zinc
dust, see Figure34.
The depthof focus of
the scanning electron microscopeis not
sufficientto obtaina moresharply defined
photograph,suchastheoneshownonthe
right-handside of Figure33.Evena top
view of this sample, which contains 2% of
AEROSILR972,showsthecompletelyuni-
form distributioninthe zinc dust coating
film.Thisfact isclearlyconfirmedinFigure
34which depictsphotographsof micro-
tome sections.The upper half of Figure34
also illustrates clearly how sedimentation
hasoccurredintherelativelyshort timebe-
tween applicationof the coatingand dry-
ing.Thiscanbe preventedbyanadditionof
2% of AEROSIL R 972.
The more uniform distributionof the zinc
dust can definitely be usedto explain the
improvementinthe anti-corrosive effect
(4).This statement isvalid regardlessof
which theoriesare drawn upon as a basis
to explain the protectionmechanismof
zinc dust paints.
Thisgoesfor boththe “sealingtheory” and
the “cathodic protectionmechanism
theory”which were compared in 1964(40).
Figure3 3 SEMs of etched zinc dust paints(4). Left: control paint,right: containing2% of AEROSIL R 972
relatedto zinc dust. See Figure26
30

33. Figure 34: Optical micrographsof cry0 microtome sectionsof zinc dust paintsamples (14). Paintwas appliedto a PVCfilm,the surfacewas vapour-blastedwith
gold.Above: control paint, below:containing2% of AEROSIL R 972 relatedto zinc dust
31

34. Figure 3 5 SEMs depicting microtomesectionsof wood glazeson absorbent wood. Left:control paint, right:containing 1.5%
ofAEROSIL R 972 relatedto the total coating (37). Basis: 8% ofALFTALAT AF 641 and 9% of FlattingAgent OK 412
A more uniform distributioncan also bring
about definiteimprovementsinthe caseof
applicationscontaining flatting agents
(37). Figure35likewisedepictsmicrotome
sections of wood glazes on a porous
wooden substrate.The coatingon the left-
hand side of the picturehas penetrated
intothesubstrateto suchan extentthat the
SiOn-basedflattingagent particlesarenow
lying on the coatingsurface without any
binderto envelopthem.This producesan
extremely poor opticaleffect, compare the
left-hand side of Figure36.
32

35. Figure 36: Photographsof the wood finishes shown in Figure 35
The additionofkEROSli R 972 prevents
an excessivepenetrationof the binder
solutionintothe surface of the wood.This
meansthat adequate binder remains in
the coating to completely embed eventhe
flattingagentparticleslyingonthesurface.
Aperfect opticaleffect is obtained,com-
parethe right-handside of Figure36.

36. 4.7
Free-Flow Properties
Synthetic silicas, especiallythevarious
AEROSILgrades,are used in many
branches of industry to improvethe free-
flow behaviourof substances in powder
form (32,39). Hydrophobic silicasare
particularly effective here(4).The free-flow
properties of powder coatings can also
be considerably improved,as shown in
Table 7. Inaddition to this, small amounts
of AEROSIL R 972 can also be usedto
reducethe unwantedelectrostatic charge
of coating materialsin powder form.
This occurs regardlessof whether the
basic substance hasa positive or a nega-
tive charge.The very slight additions of
AEROSIL R972 usedto improvethe flow
properties of ready-ground powder coat-
ings have littleor no effect on the levelling
properties of the powder coating during
the film forming and curing processes.
Table 7: Free-flow cone height and electrostatic charge of commercial powder coatings before and after
the additionof AEROSIL R 972(4).The measurementof the electrostatic charge isdescribedin (33)
5
FurtherApplications
HydrophobicAEROSIL gradesare also
used in numerousother applications, for
exampleoutside the coatings sector in:
- toners, to stabilizethe triboelectric
characteristics (41,42)
- deodorants(43),to converttheaqueous
phasecontaining the active substances
into8 !oose,sprz!yablepowder;
- silicone-based sealing compounds;
- protective cable fillersfor light-conduc-
tive cables as a water-repellent thicken-
ingagent (44)(so-called “cable gels”);
- waterproof gel greases;
- specialgreasesfor packagingmachines
used inthe food industry.
The application of hydrophobic silicasin
the production of powdered rubber mix-
tures (45)isalsoconceivable.Thispossible
application andthe above-mentioneduse
indeodorantsarebasedonthe conception
of “dry water” which was published in (46).
This list is by no meanscomplete and is
intendedto givesome exampleswhich
could encourageideasfor further applica-
tions.
34

37. 6
PracticalAdvice
Which gradesofAEROSlLshouldthepaint
chemistuse in practice?It is easy to
answer this question (14):
The most significant product is
AEROSIL 200.
If the results obtained with this standard
grade are not satisfactory,AEROSIL
R 972 shouldbe applied,particularlyfor
anti-corrosionpurposes.
Only in cases where evenAEROSIL
R 972 is unableto producethe desired
effect should one resortto other grades
of AEROSIL, e.g. inthe followingorder:
- AEROSIL R 805
- AEROSIL R 812.
For example, these grades may be
used to advantage in certainvinyl
ester resinsforcastingresinsor adhe-
sives.
AEROSIL R 202 shouldonly be used in
the coatingsindustryif extensivetests
bythe consumer have provedthat no
applicational problemsoccuras regards
levelling,recoating or adhesion.
AEROSIL R202 is recommendedfor use
inepoxysystems(27),andespeciallyfor
casting resins.
7
ToxicologicalInformation
All of the hydrophobic silicas mentioned in
this brochureareX-ray amorphous. Like
the basic hydrophilicproducts,they do not
causesilicosis (47-49). AEROSIL R 972
andAEROSIL R 974 are knownto be
expelledfrom the lungsof rats soon after
intake(7,50).The occurrenceof fibrosis
inanimal experimentswas only observed
followinghighdoses ofthesubstance.This
cannot occur if a low dust concentration
attheplaceofwork isensured.Thegeneral
dust limit value of 4 mg/m3has beenvalid
inthe FederalRepublicof Germanysince
1989.Similar values are also inforce in
other western industrialstates.
Knowndata are compiledinTable8.The
“PatchTest” and the test for irritatingef-
fects on the mucous membranes proved
negativeinall cases,i.e.were without find-
ings. It should be pointedout that the
numericalvalues given for the acute oral
LD50
dependto a large extent on the bulk
densityofthematerialbeingexaminedand
on the testinglaboratory.It was not possi-
bleunderthetest conditionsto apply more
silica in any of the cases.
All of the recommendedhydrophobic
silicas are deliveredin papersacks. Inten-
sive handlingtests have beencarried out
Upuntilnowtherehasbeennoevidenceto
show that hydrophobic silicas damagethe
skin in any way. Dueto a certain water
adsorptioncapacity,hydrophobic silicas
can withdraw water from the humanskin.
The “dry feeling” which is experienced
during direct contactwith the productis
basedon this effect.The normal state can
hands.
-
-
-
be restoredby simply washing one’s -
with synthetic silicas in order to avoidany
in-plant dust problemsthat a customer
might experience. Most of these results
have been published(51,52)and include:
the manualor fully-automaticemptying
of sacks;
the transportationof the hydrophobic
silicaswithintheworks, which iseasiest
inthis case by meansof a suction con-
veyor;
the automatic weighing and dosing;
the dust-freetransferofthesilicato mix-
ing and dispersing appliances.
35

38. Table 8 Toxicologicaldata of hydrophobic grades of AEROSIL accordingto (49)

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Lackeund Beschichtungen,Bd. 2,
VerlagW
. A. Colomb, Schwandorf
(1974)
30) U.VEIEL,W. PAPENROTH,
IX. FATIPECCongressBook, Sect. 3,
19(1968)
31) W. PAPENROTH,XI. FATIPEC
CongressBook595 (1972)
32) TechnicalBulletin Pigments No. 31,
DegussaAG, Frankfurt/M., 1st edition
(1969),2nd edition (1978)
33) H. FERCH, Seifen, Ole, Fette,Wachse
101,17(1975)and 101,51(1975)
34) Frankfurter Rundschaufrom 8. 10.
1966, p. 8; e.g. Suddeutsche Z. from
12. 10.1966,p. 33;Abendpost-
Nachtausgabefrom 12.10.1966, p. 3;
HanauerAnzeiger from 8.10. 1966,
p. 19
35) J. Mathias, lectureheld at Colloid
ChemistrySymposiumVCV-STI,
Antwerpen, Sept. 1987
36) Technical Bulletin PigmentsNo. 68,
DegussaAG, Frankfurt/M.,2ndedition
(1985)
38) ReportFHWA-CA-TL-78-21,obtainable
from US-NationalTechnical Informa-
tion Service, Springfield,VA22 161
39) K. KLEIN,Seifen, Ole, Fette,Wachse
94, 12(1968)
40) K.M.OESTERLE,DeutscheFarbenZ.
18, 151(1964)
41) Xerox Corp. US-PS3.819.367 (1974)
42) Kodak DE-PS2.821.565 A 1(1978)
43) S. PRUSSIN,EU-PS18.137 (1980)
44) RaychemCorp. EU-PS67.009 (1981)
45) R. CASPARY, I.HESKE,J.Appl.
Polym.Sci. 24, 345 (1979)
46) H. FERCH, Pharm. Ind.32,478 (1970)
47) 0.ISAAC,H.FERCH,Dtsch.Apoth. Z.
116, 1867(1976)
48) H. FERCH, S. HABERSANG, Seifen,
Ole, Fette,Wachse 108,487 (1982)
49) H. FERCH, H. GEROFKE, H. ITZEL,
H. KLEBE,Sozialmed. Praventivmed.
Arbeitsmed. 22,6 and 33 (1987)
50) P
. I. REUZEL,ClVO Inst.TNO,
NL-ZEIST, pers. Mitt. (1985)
51) Technical Bulletin PigmentsNo. 70
DegussaAG, Frankfurt/M. (1978)
52) H. FERCH,W. SCHMITZ,J. Chem.
Techn. Biotechn.30,699 (1980)
53) ,,EinfluO physikalischerEigenschaften
organischer Pigmenteauf ihr an-
wendungstechnischesVerhalten".
BASFAG, Ludwigshafen/Rh.
54) 0.J.SCHMITZ,defazet26,422(1972)
55) G. R. JOPPIEN,farbe + lack 81,1102
(1975)
37) H. FERCH,25th Meeting OCCA.New
Zealand, Rotorua, (1987),Congress
Book.
38

41. Brief List of Technical Terms
AEROSILB Binder Cry0 Microtome Section
Trade mark usedby DegussaAG,
FrankfurVM. for a-+ submicron synthetic
silica which is producedaccording to the
processof high-temperature hydrolysis.
Aaalomerates
Aredefined inDIN53206as looseclusters
of +aggregates which may be broken
down duringdispersion.
Aggregates
Interwoven union of particlesjoinedat the
interfaceswhose surface area is lessthan
the sum of the surface areas of the-
primaryparticles(DIN53206).As a rule,
aggregatesarenotbrokendownduringthe
-+dispersion of +pigments.
Anti-Settling Agent
Product designedto keep-+ pigments
whichareproneto settlinginsuspensionin
a coatingsystem.
Application
Here-+ coating.
ASTM
Abbreviation for theAmerican Societyfor
Testingand Materials.
isthe non-volatilepartof acoating material
excluding+pigment and4 filler, but in-
cludingplasticizers,+surface driers and
other non-volatileadditives.The binder
connects the individual pigment particles
andthe substrate thus combiningto make
upthe finished coating (DIN55945).
Bridged Silanol Groups
Here:shorterexpressionusedfor+ silanol
groupswhich haveenteredintoa hydrogen
bridgelinkage.
BS
Abbreviationfor BritishStandard.
Coating
Collectiveterm for oneor moreconnecting
layerson a substrate, which are manufac-
tured from coating materials.
Corrosion Protection
is made using a pieceof equipment called
a microtome.The sample is cooledand
then cut with a diamondknife.
Defoamers
Namegivento substances which are
added to frothy liquidsystems in order to
reduceor inhibit the formation of foam.
Dispersion
istheuniformdistributionof- pigmentsin
+binders or powderedformulation
components with the aid of dispersing
equipment.
DryingAgents, better:Surface Driers
are organic, soluble metallic compounds
which are addedto oils inorder to consid-
erably shortenthe dryingtime.
Dynometer
Measurestaken in order to preventcorro-
sive damage.
Combined measuringapparatuswhich
can be usedto determinethe surfaceten-
sion of liquid systems andthe depthand
consistency of sediment. Manufacturer:
Byk Labotron MeOtechnikAG,D-8192
Geretsried.
39

42. Elastomers Film Formation Gloss
are wide-meshed, cross-linked macro-
molecular substances with reversible
expansibility.
ElectronMicroscope
isthetransition of anappliedcoating mate-
rialfrom liquidto solidstate.Thefilm forma-
tion resultsfrom drying or curing. Both
processescantake place simultaneously
or one after another (DIN55945).
isthe sensory impressionfor the moreor
lessdirected reflectionof beamsof lighton
a surface.
Hammer FinishCoating
Microscopeusing electron beamsto de-
pict very small objects.
Epoxy Resins
are reaction resinswith an adequate
number of epoxy groups for curing
purposes.
Fibrosis
Increasein connectivetissue.
Filler
is a substancewhich is practically insolu-
ble inthe applied medium.The refractive
index of white fillers is generally < 1.7.
In certain media,a filler can also serve as
a-pigment (DIN55943).
Gas Black
Carbonblack whose manufactureis
characterizedbythe evaporationby heat-
ing of the hydrocarbonsserving as raw
materials,followed by combustion of the
gas with the aid of a burnablecarrier gas.
Gassing
Term usedto describe the development of
hydrogenoccurring inzinc dust paints,
which is caused bythe reactionof water
with the zinc dust.
GeneralDust LimitValue
is the maximumpermissibledust concen-
tration for “non-hazardous substances”
at the place of work, valid inthe Federal
Republicof Germany.
is one of the special effect coatings, which
can be usedto achieve intentional,visible
and uniformly-distributed irregularitieson
the surface of a coating film.
Highly Dispersed
Finelydivided.
Hydrophilic
Havingan affinityto water; wettable by
water.
Hydrophobic
Water-repellent;not wettable by water.
lanitionLoss
~
istheterm givenin DIN55921 forthe differ-
enceinweight betweenthe dryweight and
the weight of the ignition residue.Values
given as a percentage.
40

43. Infra-RedSpectroscopy MillBase
Modernoptical process inwhich the infra-
redrangeof absorptionspectraof mainly
organic compoundsin solid, liquid or
gaseousform are used for qualitativeand
quantitativeanalysis and for determining
the structure.
in situ
meansthe formation of a substance at the
time when it is required.
JIS
Abbreviation for
Japanese IndustrialStandard.
LD50
LethalDose= dose leadingto death.
Inexperiments on animals,this is usually
fixedat LD50,whichisthedosethat leads
to the deathof 50% of the animalswithin
a certainperiodof time.
Concentratedmixtureof --f pigments,
+fillers (anddispersionadditives)in a
-+binder: solvent ratio chosento suit the
respectivemethodof dispersion.
Monomolecular
Monomolecularlayersare made up of a
single moleculethicknessofthe substance
concerned;they playa significant rolein
corrosionand in many interfacial
phenomena.
Offset PrintingInks
or flat-bedprintinginks,arepaste-likesys-
tems whichdry asa resultof oxidativeand/
or physical processes.The water stability
of these systems is particularly good as a
resultof the printingprocess,which is
basedonan interactionbetweenthewater
andthe ink.
Oranae PeelEffects
Levelling
The term denotesthe ability of a coating
that is still inthe liquidstate, to self-
regulatethe irregularitieswhich occurred
during application(DIN55945).
is aterm used in IS04618 to describe
irregularitiesin the surface of a coating
film which givethe latterthe crinkled
appearanceof orange peel.
PatchTest
MAKValue
(German: MaximaleArbeitsplatz-Konzen-
tration) isthe highest permissible concen-
tration inthe air of a materialbeingused at
the place of work which, accordingto the
present levelof knowledge, must not be
exceededeven as a resultof repeatedor
long-termeffects.+General Dust Limit
Value.
Tolerancetest carried out by observingthe
localeffectof substancesontheconjuncti-
val sac of NewZealandWhite rabbits.
Pigment
~~
is defined in DIN 55945, BS 2015 and
ASTM D 16as an organic or inorganiccol-
ourant which can be chromatic or achro-
matic and is insoluble in solvents.
Powder Coatings
arepaintsinpowderform which producea
coating on a substrate followingapplica-
tion and melting.
PreciDitatedSilicas
arevirtually non-porous synthetic silicas
which are formedduring the conversionof
water glass and sulphuric acid.
PrimaryParticles
according to DIN 53206,arethe smallest
particleswhich make up powdered solids.
Recognizableas individual particlesby
means-ofelectron microscopy.
PrimingCoat (Primer)
The primer is made up of coatinglayers
designedto connectthe substrate and the
coating layersapplied to the priming coat.
It may also fulfil other specialfunctions,
e.g. +corrosion protection.
41

44. ResidualSurfaceArea Silicosis ThermogravimetricAnalysis
Mathematicalquantity which is deter-
minedas the difference betweenthe+
specific surfaceof the basic hydrophilic
silica andthat of the hydrophobic
(= aftertreated)silica.
ScanningElectronMicroscope
Analyticalappliancewhichscansanobject
linefor linewithanelectronbeam, resulting
in impulseswhich are convertedinto
scanner dots to givethe finished picture.
Sediment
Matterthat settlesto the bottom of a liquid
system if not held in suspension.
SEM
Scanning Electron Microscopy.
SilanolGroup Density
Densityofthe- silanolgroupssituatedon
the silica surface.
SilanolGroups
Progressivepneumoconiosisas a result of
inhalingdust containingquartz: occupa-
tional disease.
SIPERNAT@
Term usedto describeathermoanalytical
processwhich makesuse of the changes
inweight that occur as a resultof the
conversionof substancescaused by
heating.
Registeredtrade markused by Degussa
AG, Frankfurt/Mainfor +precipitated
silicas and silicates.
SDecific Surface
isthe surfacearea of a solid, relativeto its
mass,given in mVg.Generally determined
accordingto the BETmethod(DIN66 131).
Substrate
is an insoluble,generally achromatic
substancewhich is involvedinthecompo-
sition of certaincolouredcoatings
(DIN55945).
SuspendingAgent
-t Anti-SettlingAgent.
TEM
=Si-OH groupssituatedon the silica
surface.
Transmission ElectronMicroscopy.
Thixotropic Index
Viscosityquotientestablishedbyusingthe
measuringequipment at two different
shear ratesand rotationalspeeds.
If possible,the rotationalspeedsshould
be in a ratio of 1:lo.
Thixotropy
Time-dependentgel-sol-gelconversion
which is reversible underisothermalcondi-
tions.
Toner
Pigmentedresinpowder.The particlesize
is approximately 10-20 pm.Toner isthe
colouringsubstanceusedin photocopying
processes.
Toxicology
The scienceof harmful,in somecases
fatal, effectsof substancesin excessive
amounts.
Triboelectric Effect
occurswhen different materialsare
brought into contact with one another
(non-conductorse.g. polymerglass).
Frictioncauseselectronsto be removed
from or conveyedto the surface.
42

45. Physico-ChemicalDataof
HydrophobicAEROSlL
acc. to DIN66131
acc. to DINIS0787/XloderJIS K5101/18 (not sieved)
acc. to DIN IS0 787/11,ASTM D280, JIS K 5101/21
acc. to DIN55921,ASTM D 1208,JIS K 5101/23
acc.to DIN IS0787/1X, ASTM D1208,JIS K5101/24
acc.to DIN IS0787/XVlll,JIS K5101/20
The sieve residueacc. to Mockercannot bedetermined
withwater inthe caseof hydrophobicAEROSILgrades
relatedto materialignitedfor 2 hoursat 1000"C
relatedto materialdriedfor 2 hoursat 105"C
HCIcontentisa partof the ignitionloss
10) containsapprox. 1% of chemicallyboundcarbon
11) containsapprox. 3.5-5.0% of chemicallybound carbon
12) containsapprox. 4.5-6.5% of chemicallybound carbon
13) containsapprox. 2.0-3.0% of chemicallybound carbon
14) containsapprox. 3.0-4.0% of chemicallybound carbon
15) containsapprox. 0.6-1.2% of chemicallybound carbon
16) containsapprox. 0.7-1.3% of chemicallybound carbon
43

46. Additional Degussa Products
Active oxygen compounds Copper compounds Silanes
~
Adhesives Flattinaaaents
Barium compounds
Bluepigments
Carbon blacksand pigment black
preparations
Catalvsts
Ceramic colours
Colouredpigments
Highlydispersedmetallicoxides
Hvdrocvanicacid and its derivatives
Silicadispersions
Silicates
Strontiumcompounds
~~
Leadcompounds Titaniumcompounds
Methacrylicacid and its derivatives
Powdercellulose
PreciDitatedsilicas
Seleniumcompounds
Semi-finishedplastic products
Toner resins
Zeolites
Zinc compounds
The Industrialand FineChemical DEGALAN@
LP DEGACUFtE@
ProductsDivisionof DegussaAG supplies
the Coatings Industrywith:
Thermoplasticmethacrylic resin in solid
form usedinthe manufactureof protective
coatings for concrete, road markingpaint
and marinepaint; heat-seal coatings for
aluminiumfoils, imitationleathertop coat-
ings, etc.
Cyclo-aliphaticepoxides and Photo-
initiatorKJ85 for usein cationic radiation
curing.
DEGADUW
Cold curing, low-viscositymethacrylic-
resinfor floor and wall coatings.
DEGARQUTE@
Cold curing, low-viscositymethacrylic
resin used inthe manufactureof 2-com-
ponent cold plasticsfor lanemarkingson
city streets and country roads, and for
colouredmarkingson cycle paths.
44

47. The product rangeof DegussaAG’s
InorganicChemical Products Division
includesthefollowingregistered
trademarks:
The informationand statements contained
hereinare providedfree of charge.
They arebelievedto beaccurateatthetime
of publication,but Degussamakesno
warranty with respectthereto, including
butnotlimitedto any resultsto beobtained
ortheinfringementof any proprietaryrights.
Useor applicationof such information
or statements is at user’s sole discretion,
withoutany liabilityonthepartof Degussa.
Nothinghereinshall be construedas a
licenseof or recommendation for use
whichinfringesuponanyproprietaryrights.
All sales are subject to Degussa’s General
Conditionsof Saleand Delivery.