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Journal of Re sea rch of the No tion al Bureau of Standards Vo l. 62, No. 2, February 1959 Re sear ch Paper 2930
Properties of Zinc Borosilicate Glasses 1
Edgar H. Hamilton , Roy M. Waxler / and Joseph M. Nivert, Jr.
The glass -f or min g rcg ion of thc sys tcm ZnO -B 2 0 3 -Si0 2 wa s s urveyed. G lasses ,,·e rc Ina de wit h compo sit ions within the fo ll owing lim its in mole per cent: 50 to 62.5 Zn O 20 to 43.5 B (^2 0) 3, a nd 0 to 20 S i0 (^) 2 • They can be me lted a nd p Ol lI· cd bclow 1,400° C. The g lasses have lo w coe ffi cie nt s of t he rm a l expans ion , high va lucs of clast ic modu li and Po isson 's ratio , an d refra ct ive indi ces fr om 1.6409 to 1.6798.
1. Introduction
In a sear ch for heat-r es ista n t glasses, for which a low coefficient of t h ermal ex pan sion is desirable, it was found that Winklemann [1] 2 reported a low, ex pan sion zinc borat e glass conta ining 4] percent of B 2 0 3 and 59 per ce n t of ZnO by weigh t. H e r epor ted a coe ffi cie nt of cub ic expansion of 110 X lO - i over the tempe ra ture range of 10. 35 to 92.88° C, whi ch is eq uivalent to a co efficient of linear ex pan sion of 3.7 X l0 - 6. Th e glass h as b ee n r eport ed to h ave other ext rem e properti es including gr eat ha r dn ess, large values of cl ast ic modu l i, and Poi sso n's r atio [1, p. 1 93 ]. A glass-form ing system , with a glass th at. is so hi ghl)' r eco mm end ed, seemed worth)- of further stud ~T to dete rmin e jf t h ere were other glasses with sim il ar or mor e d es irab le properties.
E. In ge rs on , G. W. ~tor ey, and O. F. Tu tt le [2]
s urv eyed the ZnO-B 2 0 3 a nd ZnO-B (^) z 0 3 -S i0 2 systems and identified two zinc boraLe co mpound s, ZnO·B 20 3 an d 5ZnO·2B (^2 0) 3 , and a ve ry lar ge region of two- liquid immiscibility. Th ey found that ZnO ·B (^) Z (^0 ) h as an extr em ely flat pr imary fi eld- so fl at that t he determined values of liquidus te mp erat ur e within th e fi eld wer e all th e sa m e, 1,000° C, within the limi ts of error of the ir determination. Th e ex- tremely flat prim ar)- field indicatf's a hi gh degree of dissoc iation of ZnO ·B 2 0 3 at th e liquidus. In a numbe r of oth er multicomponent systems the r eg ions where sta ble glasses are obtain ed are in and adjacent to flat primary fields l3]. Th e ZnO-Si0 2 s)-ste m was
st ud ied by E. N. Bun ting [4] who iden tifi ed one
compou nd, 2Z110· Si0 2"
2. Experimental Procedure
Th e glasses wer e mad e in 500-g melt s from bat ch materia ls of sufficient pur i ty to sat isfy the r equire- m ents for optical glass. Th e m elt s we re mad e in pla t inum crucibl es and stirre d with pl atinum - l p ercen t-rhodium propeller-typ e stirrers. Th e d et ails of th e melting proce dur e ar e pub lished else wh er e [5 , 6]. rrhe sag points (acc urat e to ± 7° C) [7] of th e gla sses were used to esta blish annealing temperat.ur es from which the glasses wer e c oo led at 2.5° C per hour to 350° C. R ef rac tive indices were meas ur ed with th e Grauer refra ct om eter l8 ] on s ma ll cub es c ut from the ann ealed glasses. With this apparatu s the refractive i ndi ces can b e determin ed to ± 2 X l0 - 5 without additional processing of the glass spec im en. 1 Th e work described i ll this report was s ponsored by the Wright Air Develop· ment Cent er, United Stat es Air Force. 2 Fi gures ill brackets indicate th e litera tur e references at the end of tbis paper.
Th e liquidus tem peratm e of each glass was deter- min ed b)' a temp erat urc g radient m et hod [9 ]. Th e probable error of a s in gle dcter min at ion is ± 4° C, bu L th e abso lut e error in the pre se n t data ma:v be g re a ter. Comparison wi th the data of In ge l" son et al. , to be discussed later, ind icates t haL the error is less than 30° C. Th e thermal ex pa nsions of sel ecLe d gl assC's wer e de termined to with in ± 0.l X IO - 6 b~- at; int erferom et ric met hod [10]. Ch emical durabilit~ 1 was determin ed by the i llL erferom et ri c m et hod of Hubb a rd a nd Harililton [ 11]. Elast ic modu li were m eas ur ed by the d)Tnami c method described by Sp i nn er [12]. Th e accurac.I' of a single (l eter mination is ± 0.4 pcrc C' n t for Young 's and Sh ea r modu li , and ± ] pcr ce nL for Poisso n's ratio. Th e co mp os itions lisLe d in table 1 a re calc ul aLed from the bat ch formu l at ions. The. ZnO a nd Si0 2 co nt ent s of four of the glasses were dcte rmin ed by ch em ical a naI)-si s. Th e cal- cul ate d and an alyzed co mpo sitions of these gla sses arc co mpared in table 2. Th c res ult s indi cate that thc ch a nges. in co mpos ition du ring m el ting of th e glasses us ua lly werc less than 0.5 mo le p er cent, but for a few of the glasses they ma y have b een as hi gh as 1 mole perce nt.
3. Results and Discussion
3 .1. Gla ss-Fo rmi ng Re gi on of t he Sys te m ZnO -B20 a- Si0 (^2)
The compo siL ions of the m cl ts are give n in table 1 and are plotted in fi g ur e 1. Cl car binar y zinc bor ate glasses were m ade co ntainin g from 50 to 60 mole p erce nt of ZnO. Th is compos ition ran ge co incides with t h at of the ex tr em ely fl at prim ary field of ZnO ·B 20 3 as determined by In ger so n ct al. [2]. All of the gla sses c ou ld b e m elt ed b elow 1,4 00 ° C. Th e mel ts wer e ve ry fluid and eas il y fined.
3 .2. Liquidus Temperature s
Th e liquidus temperatures of man y of the glasses are given in tab le 1. Ther e is a g radual cha nge in the co mpo sition of the gla sses at and above their liquidus temperatures. Th e lengtll of time that a sample is h eld in this temperature rang e will hav e a b ea rin g on the liquidus temperature obtained. Suc- cessively high er va lu es wer e obtain ed on repeat det ermination s. Th e liquidu s va l ue s given in the ta bl e are the highest temperat ures at whi ch c ry sta ls
wer e observed after a 30-min hol ding period. The
T ABLE 1. Compositions and p l' op erlies of zi nc bo rosilicate glasse s
Compos i tion Refl'ac - (^) Coefficien t Jin ear Glas s Live (^) Liquidu s Sag (^) t h er mal ex pan sio n Youn g's Shear POi SS Oll' S (^) ..'\ ppcaral1 CC of glass :\0. injcx (^) po in t. (^) a X H/6 m odul us modulu s (^) ratio 8 iO, B ,0 .1 ZnO nl) --------------------- (^) --- , IIolp. (^) .W ole .1I ole (^) 25° to (^100) ° 10 % % % °C (^) ° C 100 ° (^) C 1.00° C I{ ilO ' Jll TS a ]( ilobnrs a (^35 65) Opaque. (^5 30 65) St reak s of cr~ 's t :!ls in ~bss. (^10 25 65) Do. (^15 20 65) Do. 20 15 ()5 (^) Glass an d cr ystals.
- .5 62.5 (^) D o. .5 32. .5 62. .5 (^) - ~ --
I
10 27. !) 62 .5 I. (^6772) I. 020 618 Streak s^ of^ cl'~^ 'sta^ l^ s^ in^ glass. 15 22 .5 62. 5 I. G7 98 --^ Clear.^ no^ seeds.
- 1 (^51 608) - -- (^) -- Cry s tal s in LOp ~t1l'fnc(' of (^10 20) li.5 62 .5 glass. Glass an d cr~·st;)ls. Il (^25 12) .5 62.5 (^) Do. (^12 40 60) l. G6iO 972 (;,J (^2) o. N ii. 19 84 8. :j 32 .~. (^0 0) .3 05 Dull s urface. (^13 5) ;J5 60 I. (^6684) 06~ (j02 (^) Clear, no seeds. 14 R :,2^60 I. (^668 7 950 588) 3.2 (^1) 5.04 (^) Do. 15 10 30 60 l. (^) 6G91 998 G50 3.(\5 (^) 5 09 (^) Do. (^16 15 25 50) I. (^66 98) 1, 108 (i I i (^) Do. 1 i (^20 20 50) l. (^6 721) 1, 19S G,17 (^3) .3 i 4. 9r; C r ystals (^) in t op surfaco of 18 25 \ f) 50 gl^ a ss. 10 18 2:j (^59) l. f'J()62 Gla^ ss^ and^ cr)-stn ls. 20 Gl^5 856 ..^ 02f,.9^.^ ;J^ IO^ C^ ry^ sta^ ls^ in^ top^ ~urL1e('. 4 2.5 57. 5 l. (^6608 970) Gl o (^) Cle aJ', pin p o int s{'(' d ~. 21 f) (^) 3i.5 57.5 l. 6()J i (^9 50 625) Cle ar , few s(lr ct s. (^22 10) ;J2.5 57 .5 1. (^66 14 9) 5i G (^50) D o. (^23 15) 2i.5 57. .5 I. 61i l4 (^) 1. 0..\ (^591) D o. (^24 20) 22.5 57.5 (^) 1. 66 19 1, 1 (^25) Ct'~ r s tal s in (^) lOp surface of (^25) 44.8 55.2 (^) 1. 65 48 J .77 (^) 5.28 Dullgl^ ass. su rfa ce. (^26) ' 1.. 55 1.6.150 (^) 91i.\ ()();j (^) 3. 71 ..2 (^1) 859.4 330.4 .300 Do. :n (^5 40 55) 1. 1i544 (^900) (i2 (^5) C lea r , fe\' seeds. (^28 10) 3.1 .\5 1. 6.\4 (^1 964 642 3) .5·1 (^) 5.0 1 83 G.6 322. 7. 2 9G Do. (^29 15 30 55) '1' wo immi scihlc liquid s. (^30 20 25 55) Do. :11 (^10) 3fi.5 50.. 1 1. (^6499) C l eGt', t ran spn rrn t fillll (^) on (^32 10 37 53) 1. (i185 top^ surfa^ cC'. :J3 (^47). .\ 52.5 1. 64 i8 D o. 34 9G^8 610 C]ra^ r ,^ pin^ po^ int^ seeds. 12.5 52.5 1. (^6479) .\9! (^) C lenr, pin poi nt (^) I ~ rt'd s. 'rr an sp are n t film en (^) .to p (^35 10) 3i. 5 52 .5 1. 5· 16 5 s^ urf^ ace. (^646) Do. (^36 15) 32.5 52. 5 (^) Opaq ue, t,,·o immisrib !e (^37 10 38 52 1) ,6 455 liq u ids. (^60 8) Cl ea r, tran spa rent film (^) on (^38 43). 5 fi l ,,\ 1. 6449 t^ op^ su^ rfacc. 6 15 (^) Do. 39 JO (^) 38. 5 5 1. 5 I. C-139 (^) (^585) Do. ·10 (^) !i0 (^50) '1' \"0 i mmi scible liq ui ds. (^41 45 50) l. (^6409) 6 15 3. 49 5. (^18) Clear , t ranslXlrent film on 12 to 40 50 top^ s^ ur^ face. Opaqu e, t,'o jmmisr-ib!r liquid s. a On e kilob ar = l. X lO ll d~ r n c~.'c I1l 2.
T A BL I'; 2. C ompa rison of ana lyze d and calculated compo siti o ns of se lerted glasses.
valucs are abou t 30° C low!'l' than those' re ported by Inger son et al. [2 ]. In ei th er of the se inYes tigation s, failur e to obta in cquilibl ium 01' losses du e to vol ati- lizatiOll c ould accoun t for su ch diffcren ces.
G lass num her (^2110) 8 iO , _·------11--------- 1 2{CaAna lc l ul yze atcd d _____________ ______ _ _ __ __ 16{Ca lc nl a tcd ____ __ _____ _ Ana ly zed ____________ __ 26{Ca lc ul ate d ____________ _ An a lyz ed _____________ _ 28{Ca lcul atcd. ______ _• ___ _ An a lY7,e ci _____________ _
."f ole 0/, 50
50
55
55
.11"ole 0/, 40
- 2 25
45
35
.H ole %
15 1 5. 1
10
- 0
a Ana lyzed va lu es for B 20 a ,n:l r c obt a ined by di fT crcnc('.
All the clcar glasses, fr ee from cr ys tal defects OJI the surface or in the body of th e g la ss, had liq uidu s te mperature s betwe en 900 0 a nd 1,110° C. A melt of th e co mpo sition ZnO ·B 20 3, :L\o. 40, wa s opaqu e at pouring tempe r atures. After coolin g it was discove red that the ca st block consis ted of a thin opaqu e sh ell sUl'l'ounding a ma ss of d ea l' , transpa]'en t glass. Th e ZnO con te nt s of the tran s- parent glass and the opaqur sh ell were d ete rmin ed with th e following r es ults: transparcnt glass 52. mole percen t, and opaqu e shell 0.9 mole p er ce n l. So it appears that th e r eg i on of liquid immi se ibjli t ~ is slightly lar ger than indi c at ed by Inger son et a l.
TABLE 3. Chemical durability of selected glasses
Com position Surface a lt eration In fringes, • at pH : Glass (e^ xposure, 6^ hr^ at^ SO^ O^ C) No.
S lO , I B,O, ZnO^2 4 1_ 6 1_ 8 10 12
"'10 1e %
12 :~~O{;:~:I M:g % 60 Severe^ b^ ______ _^ 1.
I 0. 1 I 0. e ND Se \7ere. 26 I
55 __^ ___^ do ____^ ___^ __^0 .6. 1. 1 O. 1 Do. 28 10 35 55 _____^ do^ ______^ ___^ 2. 4. 2 .2 e N D^ dO .1 (SC ).
- One fringe Is approxim ately eq ui valent to depth of attack of 0.291'. b Severe : Att ack so gr eat it was inlpossible to determ ine the s urface alteration in terms of frin ges.
- ND : Not detectable. d SC: In a ddit ion to the indicat ed surface a lt eration there was severe attac k at the air-liquid interface.
3 .6. Chem i cal Durabilit y
Using an interferometric method [11] the chemical durabilities of three of the glasses were det ermin ed
in solutions buffer ed at pH values of 2, 4, 6, 8, 10,
and 12. Th e results ar e given in tab le 3. Th e addi- tion of SiO (^) z to the zinc borate glasses did not improve t he resistanc e to attack by acids but did increase the r es i st an ce to strong alkali. The re sults indicat e that
the glasses s hou ld be serviceable in the pH range
of 6 to 10 , inclusive. A polished sample of glass No. 28 was ex posed to alternate cycles of wetting and drying. Each cycle was of 30 min. duration. During the wetting cycle the samp le was heated from 60° to 65° C while the humidity was maintain ed at the s aturation point , then the temperature was lowered to 60 ° C and the r el ative humidity to 84 percent for the drying cycle. After 96 hI' exposure there wa s no det ectable change in the appearan ce, lig ht transmission, or weight of the polis hed pl at e.
3.7. Surface Devitrification
During annea ling, the two co mpon ent ZnO- B20 3 glasses always developed a dull appearan ce on their ex posed surfaces. The amount of this surface devitrification var ied with the time and temperature of heat treatment. The three component glasses, conta,ining as little as 5 mo le percent of Si0 (^) 2 , always maintain ed a br ill iant transparent surface dur ing annealing. The tarnishing of the ZnO- B 2 0 3 glasses during heat treatment is probab ly one of the rea s on s why 'Vink l emann's glass has not been adopted for c omm ercial use. Thi s tarnishing may be caused by a loss of B 2 0 3 from the s urfa ce of the glass at the annealing tempera ture.
4. Summary
The glass-forming area of the system ZnO-B 2 (^0) 3- Si0 2 wa s s urv eyed. Clear glasses are obtain ed in or adjacent to th e primary fi eld of the compound ZnO ·B 2 0 3. Thi s prim a ry fi eld is extremely fia t,
indicating a high degree of dissociation 01 the primary
c ompound a t the liquidus. Such a co ndition app eit rs to b e favorabl e for t he formation of sta ble multi- c ompon e nt gla sses.
Th e glasses h'tv e modera tely low t hermal expan- sions and high va lues of elastic moduli and Poii" son 's ratio.
The authors thank Thoma s Scuderi for determin- ing the ch emi ca l durabiliti es of the gla sses and H. A. B erman for makin g the chemical analysis.
5. References
[11 H. Ho vesta d t, J e na Gla ss, pp. 146, 193, an d 216 ( Mac- Millan and Co., Ltd ., London , 1902). [2] E. Ing erson, G. W. Mor ey, an d O. F. Tuttl e, Th e systems K zO-Si0 (^) 2, ZnO-BzOa-SiOz, a nd Zn2SiO.-Zn2Ge O" Am. J. Sci. 246 ,31 (1948). [3] E. H. H a milton an d G. W. Cleek, Th e sha pe of t he liquidu s surface as a criter ion of s tabl e gl ass form ation, J. R esearch N BS 60, 593 (11158 ) RP. [4] E. N. Bunting , Ph ase equ ilibria in t he sys tem SiOz-ZnO, BS J. R esea rch 4, 131 (1930) RP136 ; J. Am. Ceram. Soc. 13 ,5 (1930). [5] G. ' V. Cleek an d E. H. Hamilton, Propertie s of barium titanium silicate glasses, J. R esea rch NBS 57, 317 (1956) RP. [6] E. H. Hamil ton, G. W. Cleek, and O. H. Grauer, Some prop e rti es of gl asses in t he barium oxide-boric oxide- silica syste m, J. Am. Cera m. Soc. 41, 209 (1958). [7] S. Spi nner, G. W. Cleek, an d E. H. H a milton , D et ermi na- t i on an d use of t he sa g point as a re ference poi nt in t he h eating of glasses, J. R esearch NBS 59, 227 (1957) RP27 9 1. [8] O. H. Grauer z..!'recision r efr acto m eter - U. S. Pat ent No. 2,772,597 (v ece mb er 4, 1956). [9] O. H. Grauer an d E. H. Hamilt on, An improved a ppa- I r at us for t he d ete rmin atio n of liquidus temperature a nd r ates of cr ysta l grow t h in glass, J. R esea rch N BS, 44, 495 (1950) RP. [10] J. B. Saund ers, An a pp aratu s fo r photographing i nte r- ference ph enomena, J. R esea rch NBS 35, 157 (1945) RP. [11] D. Hubb ar d and E. H. H a milton , Stu dies of the ch em ical dur ab ility of glass by an int erferom ete r me thod , J. Rese arc h N ES 27, 143 (1941) RP1409. [12] S. Spinn er , Ela stic mo duli of glasses by a d yna mic m et hod, J. Am. Ce ram. Soc. 37, 231 (1954).
'VA S HI~wro ~, O cto b er 27, 1958.
