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Journal of Colloid and Interface Science, 25, 2, pp. 255-262, 1968-03-01
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Surface features observed during thermal etching of ice
Krausz, A. S.; Gold, L. W.
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https://nrc-publications.canada.ca/eng/view/object/?id=48699fb3-ba59-4dd1-b402-a84e7e095d03 https://publications-cnrc.canada.ca/fra/voir/objet/?id=48699fb3-ba59-4dd1-b402-a84e7e095d03lteprintcd from J o n n x . ~ ~ 01.. COI.LOID A X L I IWERI?.LCE SCIESCE, Volullle 25, NO. 2, O c t o l ~ c r 10137
Copyrigl~t 0 1067 by Ac:ldcll~ic Prcss l n c . I>ri111ed ?'7~ U . S ..A.
A N A L Y Z E D
Surface Features O b s e r v e d during Thermal Etching of lce'
I-'olyrryst:illi~re- and s ~ ~ ~ g l e - c r y s t : ~ l ice specirlle~~s were etchetl in a saturateti :ur ntmosphere. O b s e r v a t i o ~ ~ s were 1n:lde a t nbor~t 50s m a g ~ ~ i f i c a t i o ~ ~ after etchill:, t ~ n ~ e s of :i fcw r n i ~ ~ t ~ t e s to scveral weeks.
IIigh-:inglc bol~~ltlaries bec:lme visible :IS grooves within the first few ~ n i ~ l u t e s . Straight low-angle I > o u ~ ~ d : ~ v ~ e s , which fo~metl tlurillg soliclific~at~o~l or in the cor~rsc of plastic defor~nntion, were :llso observed
Sharply defined short s t r a ~ g h t lines, ~aisetl above the surface of the s p e c i m e ~ ~ , were f r e ~ ~ ~ ~ e ~ l t l y observed :iud have bee11 iuvestigated in detail. These f e a t u ~ e s developed within a few miur~tes a i d were very stable, retni~liilg their iuilinl appenr:zi~ce for as loug as several hours of etchiug time. The liues formed either a t r ~ n ~ l g i ~ l n r or a rec- tai~gular patter11 that was related to the crystallographic orie11t:~t ion of the exposed s t i r f : ~ ~ ~ . I t was established t h:~t one family of these lines was parallel a ~ ~ t l a s c c o ~ ~ t l was perpendicular to the C :ixis.
Occasioi~ally small r o u ~ ~ d hillocks with a sm:ill ce11tr:~l f e n l ~ ~ r e that nppe:~red to be a cr:itcr formed during etching. The coirce~lt ratio11 of hillocks :ippe:~retl to be grei~test : ~ l o ~ ~ g subhoui~daries. -4 ho~~eycoinb-like ~ ~ c t w o r k of hillocks was someti~nes observed.
Tri:l~lgulnr hillocks were o1)scrvetl to form 011 the s~rrface of some gr:ii~~s. The bisectov of the :icl~te angle associated with the raised part of the t r ~ : l ~ ~ g l e was ~ ) e r l ) e ~ ~ c l i c l ~ l a r to the basal p l n ~ ~ c . After e x t e ~ ~ s i v e thcr111:11 c t c h i ~ ~ g , 1erla11gu1:ir pits with well-developctl f:icets :~ppe:ircd.
The ctchi~rg techniqr~c w:is 11scc1 to s t ~ ~ t l y s t r u c t ~ ~ r a l chn~iges that o c c ~ ~ r r e t l i l l ~ c c d u r i ~ ~ g creep :l~ld t ' r : ~ c t ~ ~ i ~ C S I ) ~ ~ ~ I I ~ C I I ~ S .
1XTItOI)UCTION relevarlt to the u~iderstaiidi~ig of the proper- Ill :,ssociatioll ]\.itll a of ,,he ill- ties and behavior of ice at its surface. fiuelice of structure on the plastic deforma-
tion 1)ehavior of ice, i~ thermal elching.
method \\as clcveloped for observing grain boundary migratioll and the formation of :ow-angle boundaries (1). Thc etching proc- ess brought out other fcxtures that 11-cre considered to be of general interest. This paper reports thcse features, ns they may bc
1Prese11tcd at the A r n e r ~ c a ~ ~ Chemical Society S y m p o s i ~ i ~ n " I ~ ~ t c r f a c ~ a l a i ~ t l Surfarc I'roperlies of Ice," Pittsb~rrgh, M:irch, 10(i(j.
2Itesearch Officer, SIIV\V a i ~ t l Ice Section, Ili- visioii of Buildii~g Itese:irch, N:iliol~al Itesenrch C o u ~ ~ c i l , Ot tnw:i, Ca11:itln.
3IIead, S i ~ o w and Ice S e c l i o ~ ~ , D B R / N R C , Ottawa, Canada.
r 7
I ransparent, air-buhble-free ice plates were groxn fro111 deacratcd tap water by slo\v, unidirectionizl freezing. Columnar-icc \\-it11 grains of cross-sectional area about 0.013 scl. in. \\-as obtained by seeding the coolcd ~vater ivith fine ice particles. Large single cqst~nls \\-ere obtained by freezing 11-ithout seeding..
The surfacc of speci~llerls \\.as prepared b y nlelti~ig bricfly 011 a plate kept at a tempera-
ture slightly above 0°C. or by pouring al- cohol over it,. S o ~ n e spccinlerls were subsc- cluently polished to a "mirror" surface wit11 tissue paper or soft Icatller. The specimen
FIGURE I (a)
FIGURE I (b)
Be JIU.,
F I G . 1. Slcetrh of profiles o f high-:~llple g r : ~ i ~ ~
boulltlnrics : ( a ) sgm~nc( ricanl; (1)) :~synlmetric~nl,
\\-as then placed rvith the 1)repared sl~rface facing upn:lrds in an air-tight plastic box lillccl \\it11 crusl~ccl ice to ensure a salu- r:~tcd atmosphere. Obsmvatioiis \\-ere nladc Ihrougll the transpai~cllt t,op of the box using a biuocular n~icroscope a t magnificatiol~ of iiot greater than XSO. The 1)criotl of tinlc ovcr ~vl~icll observations \vcrc I I I ~ L C ~ C 011 a
surface varied froill spccilneil to specimen, begillrii~lg as soon as 1 minute after placii~g it \\ithill the hos aild estciitling a t times over several ~veclis.
Both the prcparatioii of spccin~cns :111tl the obscrvntioiis were n1:~cle in :L cold roo111 a t a tc111j1crat1u.e of - 10°C. f 0.3". Uiidcr the couclitions esisting in tllc cold room, a cliff'crcnce in temperatulbc clcvcloped betivecn the i~isiclc top nrld bottom surfaces of tllc 110s alnou~itillg
-
to about 2 X 10-'"C. ovcr adistance of 9 cm. The spccin~el~s were sup- ported or1 a platfol-n~ about '3 cm. above tllc bottom of the box, nrlcl their upper surfacc ~v:~s usually I\-ithiri a11out 1 cm. of the top of the bos.
Surface features \yere usually i l l u i l ~ i ~ ~ a t c d by transn~itted light by reflecting the light, off a sheet of 11 hite paper placed under the
specimen. Tlle focus of the light, \\-as ad- justed t o give lnaxilllum contrast
Tllcrlllal el ching of ice at - 10°C. i r ~ the co~lditioris ohtai~lecl in the plastic 11os pro- duced sharply defined surface features. Il'ea- tures obscrvccl a t low mag~lificatio~i were high- and 1011 -angle boundaries and net -
\vorl<s of cr~~stallograpl~ically orjented short straiglit lilies a1id 111110~1i~ ol various regular shal~cs. I t is s~pprcciatecl that sublimatloii and depositioii of water vapor on the surfacc a t high energy sites, as well ns surfacc or bulk migration, lnay all play a part in the forlnat,ion of these fcaturcs. The observations iiidicatcd that the solidificatioii of :L thin
layer of water that formccl when tlle surface
n as prepared p1nj.c.d a sigriifica~lt role ill the formation of some of the features, as will be poi~ilecl out later.
Gl,airt Boz~nclat,!j Obscr~uatiotrs. The etching lechniclue proved to be \\ell suited for grain b o u i ~ d t ~ r y studies; high-angle boundaries could all\ ays be observed uithin a fen- min- utes as clearly clcfiiiecl lines. The profile of grain bou~idary grooves was similar to that observed a t high tenlpel.at~ues in metals. Observations sho~ved tlls~t the cross-sectional s11:~pe of grooves \\as del~endellt oil t,he orientatioii of the grain bou~idary ]dative l o the c~~ystallograpl~ic orie~itation. The fn- miliar symmetrical profile dcvclopecl only 1vl1c11 the arigle bct~vceli the bou~idary and tllc trace of the basal pln~ic on the surfacc was sigriificn~~tly diffcl.cnt from 0" (Fig. l a ) .
IVlleii the trncc of the basal 1)lane was :ipprosimately ]~:uallcl, an asymmdl.icu1 pro- file dcvclopecl :IS hhonii ill Fig. 16. Etchi~ig
ovcr long periods of time usually caused the bou1iclnl.y regio11 to bccoll~c steeper and to be elevated :~bove the surfacc of the atljaccilt grains.
I,o\v-angle boulldaries could be obscrved \vit,hi~i a Sew ininutcs alter thc initiation of etching. The grooves associatccl n-it11 t,llcsc boundnrics 11 ere distinctly shallo~\-cr. W11eii
fornlcd ill surface.; almost pcrpelidicular to basal planes lo\\ -angle boundaries \\ ere
straiglit, arid those TI ithi11 the same grain
\\-ere usually parallel. A11 esamplc of this is s h o ~ n in Fig. 3a. When fo1.111ecl in surfaces alillost parallel t o tllc bast1 plarie, these boundaries were not usuall~ straight and P those in the sanle grai~i were not parallel.
IJitzs F C ~ ~ Z L Y P S . T11cril1~1 etc11i11g l r e q ~ ~ e ~ i t l y proclucccl a tri:~~lgul:~r or rectangular pattern of short straight lilies (Fig. 2). Obscrvations s l ~ o ~ v c d t11:~t the lilies \\ ere raised above the
surfacc. Studies nladc oil single crystals of lino~vn orientatioii, and on polycrystnlline specimens lor \\llicll the orientation of in-
SURF.ICE EE,YrURES I ) U I t I N ( ; T I l E I t M A L E T C I I I N G OF I C E 237
F I G . 2. Typic:ll es:~rnples of p ~ t t ~ 1 . 1 1 s of short s l r i ~ i g h t lilies: ( a ) t l . i a ~ l g u l i ~ r ; ( b ) rcct:i~lgtlli~r.
dividual g r ~ ~ i n s n as detmmincd using the plastic hlm technicluc of Higuchi
(3,
estutl- lishcd that the rectangular pattern dcvclopcd on surfaces I hat 11 ere perpendicular t o t hcbasal pl:~nc; the lines being parallel to the t~asal and prismatic planes. If the C nsis w:ls il~cliilcd to the surface, a tri:~ngul:lr 1)attcril dcvclopecl, thc lines being p~lrnllcl to the edges of the c1lar:~ctcristic tri:utgular et,ch
pits lormcd tor this oricntatio~i using the plastic fill11 icchni~~uc. This i~ldicatccl that the lines ncrc again parallel t o the basal and prism p1:trics.
The line features nere quite stable. They fornled sllortlj- after the initiation of the etching process and retained thcir appear- ance for several days. I'rolongcd etchirlg coarscncd the pattern 1 ) ~ - i11crc:lsing the
ORIENTATION
\
OF T H EPRIMARY LINES
\
FIGURE 3(b)
FIG. 3 . Ex\-aml)lr: of the seconcl:~ry set of short, l i ~ l e s . ( N o t e l o w - n ~ ~ g l e bou~ltlaries p ~ r r ~ l l c l t o one of tlic prirnnrj- sets of s h o r t l i ~ l c f c n t ~ ~ r c s ) ( b ) Slielch i l l \ ~ s l r a t i ~ l g l h c geomctricnl rclntio~lshil) betwee11 t h e primary :111d S C C O I I ~ ~ I ~ S C ~ S
\\idill of the lines. Lilies grnduallv disap- penrcd in an area. s~vcpt through by :i inigrnt-
ing boundary as ~vould be espcctcd frorn the change ill crystallogri~phic o~ientatio~i. Sell- lines, corresponding to the iicn- orientatioli, \\-ere not observed to dcvclop. Except for this obscrvation, plastic deformatiorl of up t o about 2 % did riot appear to have any effect on the line fc:~tures.
It \\-as observed that somctiines a shortcr and dcnscr system of lirics covered the slope of grain boundary grooves. The grain bouncl- ary region \\-as often a preferred site for the
clcvelopmcnt of both the rect,angular and triangular patteriis.
A secondary set of lincs, a t an angle t o thc fanlilies ptirallcl to the bnsnl arid pris- matic planes, \v:ts occasio~iall~~ observed. I n
n few cases it \\-as fou~icl on closc~. i~ispcctiorl that the seco~idiir~r set \\-as made up of very short lilies parallel t,o the primnrj7 set as she\\-ii i11 Fig. 3.
JIillocli Fortllatio~l. Itouncl hillocks \\;ere obscrvccl to form or1 the surf:~ce of some grains. These hilloclis appeared t,o be initiat,ed during the freezing of the thin film of \\-at,er
SURFACE FEATURES IIURINC: TIIERMXL ETCIIING OF ICE 239
FIG. 4. ( a ) Example of ccll-likc arrnl~gernel~t of hillocks. (0) Esnml>le of r:ludomly (list rihut ed hillocks with higher co~lccu(r:~lion a l o l ~ g sl~bboundary. Notice dark, craicr-like, cell1 rnl region.
formcd when preparing a surface on the warm platc.
Two distinctlv different types of hillocli systems were observed. One typc consisted of a cell-like armngement as show11 i11 Fig.
4a. The sccond had n more random distri- bution of the hillocli~, with a higher thali average concentration along subboundaries
(Fig. 46). I n both tppcs, thc hi1locl;s had a small dark central region that had the ap- pcarance of a crater.
After ctchiiig for a pcriod of about 24 hr., triangular-shaped h i l l ~ c l i ~ were sometimes observed, as shon-11 in Fig. 5. These features n-crc so orientcd that the plane bisecting the apex angle was parallel to the C axis.
F I G . 5. Example of trii11igul:~r I~illoclrs. (Note oriel~t:ltiol~ of rect:u~g~ll:~l. e t c h pits for~lled b y pl:~stic
film technique.)
F I ~ ; . (i. 1~;x:~mplc of p r i s m i ~ t i c pits lol.~nctl n l t c r cx(cusivc c t c h i t ~ g . ( K o t c r c c t n ~ l g ~ l l n r pits formccl by t h e plastic film t c c h l ~ i c l \ ~ r , bo1111tl:~ry legloll clcvntctl :~bovc, surf:rcc c o ~ ~ t : ~ i l ~ i l ~ g C ~ C I I pits.)
r 7
Ihis car1 bc sccrl in Fig. .S, wherc thc biscct- thc triangular 11illocl;s clevelopecl Irom hill- ing plane is perpendicular to one cclgc of the ocks that werc rouncl initially.
rectnngul:~ ctch pits Eormccl over part of Alist~ellnneous Obso~untions. Thcrc np- the surfncc of the grain by thc plastic fill11 1)c:~rcd t o bc :L le~icle~icy for thcrillal ctchillg
SURFACE FEATURES DURIKG TIIEI1hTX1, ETCTIIS(; OF ICE
FIG. 7. l%s:~mplc of threadlikc feature obscrvetl at some grain b o ~ u ~ t l a r y triple points.
i~lclined to the surface, and to 1,rodnce a rough surfacc if thc C nsis was pxr:~llel to the surface. Thc ~*ough surface :~ppcarccl to be raiscd above thc surlace of grains that ctched smooth. Etchiiig ovcr a period of sevcral ~vecks produccd prislnatic pits, \\ hosc shapc :~nd orientation ~vcrc rc1:ltccl to thc cr~~stallogrnphic oricntatioli. 1\11 csnmplc is
sho\vn iri Fig. 6, 11 hcrc the rcctaligular pits
formcd by thc plastic film technicjuc sho~v that in this casc the C :wis is parallel to thc surt'acc.
i \ ~ ~ iliteresti~lg "thrcadlikc" fcaturc was observcd to form a t somc graili bounc1:u.y triplc points; :111 es:~mplc is sho\vil in Fig. 7.
This fcnturc had ~ i o nl)parcnt depcndciicc on cl~ystallographic oricut,ation. Observations ~ v i t h the microscope shon ccl a line of cavitics extciidi~lg intfo the speciincli allnost vcrtical to thc surface a t the sitc ~vhcrc thc feature joined to the triple point,. For one casc ob- served, thc thrcad fcsturc tc~.minatcd at, a
boundary ivcll an-ay from the tiiple point.
A colnmli of cavitics cstcnded into the icc a t thc intcrseclio~i of the fcaturc :~11(1 the boundary in this casc as ~rcll.
The anthols are not prcpared to olTcr : ~ t this tinlc an csp1an:~tion for the line arid 1,hrcacl fcatures that have bccn obscrvcd. It
is of intcrcst that 110 line fcnturcs n-crc ob-
scrvccl to form on stu4'accs that had becn prepared hy carcful machining only, ~vithout subsccluent inciting or dissolvirig with alco- hol. This suggcsts that thc features may bc a~sociatcd nit11 Ihc f'ornlation aiid subsc- qucnt frccxing of a 1 liin lilm of lratcr fornled \vhc~i thc surf:~cc \\as bcing prcpnred. 011 the
othcr hand, thc similarity I)ct\vccrl soinc oC the observdioiis reportcd licrc 2nd thc ap- pcarancc of impurity scgrcgation in mctals
i.; strikilig (3).
IIillocl;~, similar in appc:walicc to those discussed in this papcr, llavc bccii obscrvcd by I31,yniit and ;\Inson (4) on thc basal ~ ~ l t ~ n c of ice crystals gro\vn from the vapor. A t p1.csent thcrc is not enough i~iforinatio~i available to corrclatc tlic ttro obscrvatio~is.
S o obscrvntio~is were ulldcrt,nlicrl to deter- mine ho\v the clevelopmci~t of the thcrmal etch fcaturcs war affected by changing such factors as tcmpcraturc, temperature diffm- cncc bet\vccn the top and bottoln of thc bos, niid the degree ol satur:~tion of thc air.
Thermal etching
roved
to be a vcqr con- vcnient tcchliicluc for studying certairi struc- tural fcaturcs that pl:~y a role in thc dcfor- lllatiorl behavior ol icc. 13~pcricncc h ~ t s sho\v~i that, ill addition, it is a pot,entiillly262 ICRAUSZ .IN11 G O I J I ~
useful method for deternuning crystnllo- graphic orientation and for studies of the surfacc of ice, such as determining the de- penclcncc of surfncc energy on crystallo- graphic orient,at,ion. I t is hopccl that the obscrvatio~is reported here \\-ill proviclc a stinmlus for such ilivestigations.
ACKNOWLEDGMENT
This is a cotrtributiotl from the Divisiotl of B ~ ~ i l d i n g Research, Natiorral Reseal.ch Coutrcil, Carrada, and is published with the approval of the Ilirector of the Divisioti.
R E F E R E N C E S
1. I < R \ I ~ S Z , A. S.," Etching techiiiclue to study plastic deformatiotr of ice," J . Glaciologt/
3, 30, 1003-1005 (1961).
2. 111cuc111, I<., "The etching of ice c-rysti~ls,"
ilcla M e l . 6 , 636 (1958).
3 . I<IEVITS, I?. J., "The ageing characteristics of aluminium-mag~~esium alloys coiltaiiritrg sil- ver and cadmium," J. Insl. ilfelals 93, 517
(1965). k
4. BRY.LNT, G . W., .\ND MLSOS, B. J., "Etch pits arrd dislocatior~s in ice crystals," P l ~ i l !\fag.
