Document nNb82OMbyNo2wqZDan67OOqER

E. I. DU PONT DE NEMOURS & COMPANY PIGMENTS DEPARTMENT 256 VANDERPOOL STREET NEWARK, NEW JERSEY Copy No. 1 A V ^ -3 / NEWARK PLANT PIGMENT COLOR RESEARCH REPORT THE DETERMINATION OF FREE ZING OXIDE IN ZING CHROMATE PIGMENTS Period Covered: October 1942 to April 1943 FILE: DATE: 7/5/46 NJ3699 N41553 fr*rl&2 3?o K'---'46^31 Copy Roo X Copy t-e> $1 Shiseyiaal FX1 a = E#38.ro* 0meg (2X2} 3 - Msrery nift (2X2) 4 Sasosd*! Chomioal ,, W <* * $ . * * '| if. Ft Spngraag Brassek 3 - Sxiffa e Ltda * * SPJ&EK PMlif KflHC !M EBSSARGE EEFCR1* Pryms Final Ropwt TitUt THS 1SSHUBKME7Q1I OF FfGSE 7Sm OESPB X.!5 ZSHS c e r o mm p i? Farit 4 Ceroroda Osio'j!* .154-2 to April 1943 SUBETflEB BTa A. R. Hanks AFJROFB SI s A, A0 Srisaolcm* Ml* 8U3J.HTTED* 7/2/46 DAS ISSUES a 7/5/46 N41553.01 DUP050150493 THE mTERffiMTXQH OF FREE 2XHC OXIDE JSKJ msm mMMsmm The following report is based on email mount e? work performed off and o% with ike purpose la mind of showing the presence of free sine aside ia *ino yellow or related pigments. The presets# of sine aside ia sine yellow aa he due to the deliberate mixing ia of siao oxide or t'o the use of slao oxide during manufacture end incomplete oonTcreioa to the desired pigment la either ease the detection of sins oxide by chemical means Is complicated by the fast that any chemical action on the pl&sent will so change the pigment that it will be difficult to state whether the chemical evidence for V&& presence or abseaoe of Zino Oxide indicates the condition of the plgpent before or after the chemical treatment. j Seecuse of thls^atleailea was turned primarily to physical method*. Xray diffraction and fluorescence under the action of ultraviolet light were the physical methods examined. A chemical method was also investigated not that it could indicate with certainty the presence of free *iao oxide but be cause it could give an easy measure of the basicity of the plgaeat. duch a basicity is expressible as free sine oxide and any increase over the expected basicity of the pigment would point i the possible presence of free sin* oxideo suiat&Fnr mo comwsiom / / 1. . X-ray diffraction can detect with certainty SjC or more of free sins oxide In sine yellow. / / 2. Fluorescence induced by filtered ultraviolet light ms used te detect as little as 0 aino oxide dry ground into sine' yellow. Hotfever, two oonpetative samples which contained around 1 to 1 l/S$ ZaO by X**ray diffraction SLiialyels should no flueroeoeaca. This can be considered as same evidence that the slao oxl.de present in Eeiolthold* s Sine tallow $1420 (C-46530) and a sin yellow of unknown manufacture 0-45839 ms not introduced by dry mixing 3o It is possible to dissolve a sine chromate pigment in aa excess of standard sulfuric acid and bach titrate with standard sodium hydroxide solution. There are two points of inflection ia the pH curve, one at a pH of 4.0 and the other at about a pH of 8.2* Using the point of inflection at the low p3 and knowing the chromate content, 11 becomes possible to calculate the basicity of the pigment and express it as SnO. If this turns out to be mob higher than expected, free sine oxide say be present. If the basicity is about that expected, it is very unlikely that any sine oxide is present, 4. Using these three methods in conjunction with each other can threw ame light on the nature of the sine yellow pigment and how the free sine oxide, if any, ms ihtrodueed into the pigment. 5. The most reliable method for detecting Z* in xino yellow Is by means of X-ray diffraction. Table I shows the results on ths samples examined hj X^ray dif&aotiojft* DUP050150494 . HSJL Diffraction Zlne Teller SsaalM Reiohheldt8* 1420 (C-46530) Xii^oriaV* 1-1910 (C-46315) Imperial0 X-2062 <0-46632} Unknown Xfgt from W* P. Ml#r (0-45039) K-18U - Lot 61*9 * * 963*5 * 606S M&SMSmsSm1 Nerffi&l Slig&fcly charter MerMl ?t %ereent 1.0 *0o5 *o<,5 1.5 Probably absent te"5 Probably absent &Anything 1 than 1$ ZxiO is In the doubtful range. a. Samples were prepared by double mis grinding in & ieiorcpulveriaer mixtures of nine yellow and tine exid. ' The slac yellow -me T-232-C hot 93266 and the ino oxide ms Boras Head XX sine oxide 50 from Rev Jersey fine Go. (B-4213). The samples were saad 4a contain 09 0.5 10 2.0 and 4<# Za0c X-ray diffraction patterns using oeryper rYtietion were obtained of those 8,xaplas along with a sample of the fine Oxide. One percent and above could be detected f&th certainty. One half percent wan in the doubtful range* The results when applied to unknown camples of line yellow are given in fable X. For this study, the same samples were used as deenibsl in section *AW0 1st addition, samples werej .Tepared containing 0.3, 0.2, 0.1, 0S0$ Zia* Oxideo A quarts awreury taper tube ms employed in connection with a suitable Corning light filter to rectos the visible light. Snail portions of the sample wore irecisd out on dull Uaek paper and the characteristic fluoresceaa# of the fins oxidi observed in a suitably darkened room. The ssasitlvity of the tost 1 is adraittedly dependent as t ie intensity of the ultraviolet light, frsedan fro visible light, etc, but wiit <tist ordinary precautions, it ms possible t observe a differsue festwDc. 1 0 snd Q 2$> ZaO ia sine yellcwo t i DUP050150495 O^cts When this test was applied to th* two samples la whioh ZnO me found toy X**ray diffbaotien, aassely C-46530 mad C-4583? , ho fluorescence wr.s observed The emplm were extracted with chloroform to remove any treating agrnt which it me fait say interfere, hut still no fluorescence ms observed* he sample ms also heated for several dry* at 165*0 It was thought that th sine oxide say need to he mere nearly dehydrated to properly exhibit fluorescence* Still no fluorescence ms bservedo Perhaps the sine oxide is so effectively coated with sins yellow that the ultraviolet light and fluorescent light are effectively screened* iLt any rate #0 further work me done because Xray diffraction gave results suitable to our purp&soo Nevertheloec, the fluorescent method me the most sensitive method studied for detecting sine oxide* the lower limit for the conditions of the axperiaeat being OoZfc ZaO* SsMs. This method is admittedly not specific for *ino oxide tut if the basicity turns out to be about that espostefc* the pigment will very likely contain so free sine oxide* Since sine oxide is a basio substance free sine oxide will increate the basicity of the pigment* If the pigment is dissolved in an excess of a standard acid, the more trine oxide, the less will be the back titration with standard alkali* X normal sine yellow pigment very yearly corresponds to the formula, 4 CrOa, a># KgO, 3g0 Mol Wt, 873082 This may also be written,. 3 Zn CrOe.KaCrOeo fcaQ ,3HgQ . Thus it is scon that normal sine yellow already contains the equivalent of one mole of sine oxideu If chromic acid is titrated with otsmdard alkali, two points of inflection of pH are observed, one around pH 4 and one around p8 802 Ohroaie acid can then be considered as a dibasio sold ionising stepwise thusf % CrQ* 5 HSrO* > *$* **** H GrOe * H CrO* The idea of the disfcrojssat ion will not Invalidate this sitaplififd picture since the diohrcaxrt ion can be ooadidcrod m singly & dehydrated H CrOg ion. 2 H OrE*-* Cra0v BaO Whoa titrating' chromic asid to tL-s first pointof-- inflection. of pH .(assume pH ), chromic acid say be considered as a saonebasic-acid, ie, with only one replaoaBle hydrogen lea ^ Ha Cr04 e OH -* BgO B CrOe ifi DUP050150496 Every equivalent of sino oxide $dxed with the chromate will moan ten equivalent less f alkali required to back titrate to the point of inflection around a pH of 4 It then becosies poeeibln, kaowtigg the ehroaaata concentration, to calculate the <quivalent sine cr.lda* Such titrations were carried out with the fire samplee containing 0, 0*5, 1,0, 2*0, 4.0$ 4a0. The procedure ms to take a I gra samples add 30 i of H/3 H*0o end war until the sine yellow was completely dieaolTed. Cool, dilute to >200 ml*, and baektitrat with H/3 MaOH to two Inflections in the pH surra* She pH was measured with a glass * ealosel electrode system.* She second point of inflection was also measured ia most eases but no use was made of it la the calculations* Since precipitation always started between the first and eecsad points of inflection, the position of the second point of inflection would be influenced by hew much ohroaate and sine were token out of solution* Equilibrium conditions were probably sot established which-would also tend to make the second point of iafleetios a mriftbl#* hi any rate, nothing could be dene with the second point of inflection but it is Included In the data for the soke of completeness* Following are sene typical calculations to illustrate the sthod iS^i*J^a32^J^LB4 By analysis, chromate aa CrOs * 41*1235 m 4i.i2 Killhequivalcnts CrOs per gran sg & Koao*** 0,1 basis acid) A 1 gram sasple dissolved in 30 1 of 0*38998 BgSO* required 13^3 ml of 0*38168 HaoB back titration to the firet point of inflection of pR 3C at 0*3899 13 o3 * 0,3816 * 11*69? ndlliequitalence of B^BOa added * 5*096 H&OS backtltratefi _ -6*621 i* ~ %* due to chromate S*509 % " attributable to ;5aD MiUlequiwalent ft* of Za6 * 0*04069 100 s 2*509 * 0*04069 10*2135 ZsD fh figure 30*21^ 2n0 is then the calculated InO basicity of the p.lg'jint with no sine oxide present* If it gets- moh above this, irve sin oxide ray be present* Chroaaai 39.48$ CrO Same procedure used as for above sample* Baofc titration * 11*65 1*,, U*W7f 11*65 x 0*3816 * 4.444 7.251 3*303 x 4*069 - 13*4^5 f^nO "10*21 3*23$ ?*aO DUP050150497 Th* amount of ZaO la *2.0*00 of that xpet*d for a typical zin yallow cat 323$ Za0o This whan oomp&red to 4% la not a good ehesk hut t~-m precision ef th method is admittedly pssrg th purpose fcoing eteply t* indicat* th possible pratte of fra sine oxide,, , For other sasaples th procedure an sometlm*# modified to th. extent of using sraplo weights other tia&a 1 gram and Tcrying th amount of standard tulfurle add used to dlssolr th eaj8pl#0 Table 22 shows all of the data for all samples titrated,, Graph* 1 and shm typical titration o u x t o for sin yellow and *in yellow sin oxid mixture DUP050150498 c o m m ? M TA FOR TES BASICITY SgTEBMIMTIOa OF ZIHS ItSLLOa AMD BBIATS2? K M S O^o w\ ^e* ^w\ m<ro* O O O H <n <M CM H 2 SS o 9 ao * ac s o9 S3 9 so m0 focft c*n Os Os 2 2H^a 3 H HI 5 ^ Ve vu%\ Jj* ^ 9 i*s ;*&*9 m<93 fmt %*0Q $ *0 *Hg ->Hg *H5 ft ft . V\ O' nOa9fr' 90a^--0b3* CM e *ao <cn9* *> uS0H\ OA nO V\ H S'** 8?* ^ &** &r s> $ && I* Ho H m MCM H life ** mO hOi a9 2 2 222 * ft cn* <n* frh * 59 ft fiO cn CM *s 3* w% 9 CM *M* * *CO vd &* nH O H O H %ff% o &*" * CM H H HKH *4 8 o %F\ <5 H :( DUP050150499 DUP050150500 DUP050150501 As eca trm the tote?, la the first m a typical fine yellow Isas & basicity of 10o2l 2aO Em tlecretloal percent assuming ih forml.8. 3 $ CrOas KaPr0&.Zttv*3H*0 is only 93$ JisO, fhia ladieate that small enount of a acre basic alao chromate is eslt?<3 present wfciah is a reascn&bl# supposition sines acre basic *ie ohrosatas do asirt* fhe result* in tfco last celion mk the assunptien that 10o2lS Ze.0 rapraeeat* a typical basiolty for sine yellow in spit* of the 9.32J& theoretical figure* The knowledge of this &r gumption dsore&ses the quantitative sigaiffislcnoa of the feta la the last column bacau.ee a mixture of also fellow with a acre basic sine darosmts *uoh as the tri oxyehroimte will very aotleafely increase the tesloiiy without adding say "aO* 5h* high basicity off cure basic sine chrejsfties Is indicated in the last tm re***, AgsuaiHg sine trioxyebreshve as y<30rS&3S03S# the theorileal basicity i XaO. fh* observed figure of 49 *4? it in fair agreement end ie obviously mash higher than 10.21/S which is that for a typical sine yellow,. X-ray diffraction of a typical sin trioxyehromste shored so &0 Assualng sins tetroaychromte as 2^r0ao4Zn0'*4HsQ# the tbecretioal basiolty becomeit 5623Jt 2n0 fh obswved ffigur# of 55*34 is also in fair agreement. Her* though, Xul ms found by X-ray diffraction analysis when examining^ typical sine tetrosyohrdaate so at least part of the basiolty east be attributed/!x*e sine oxide, Osmpsriag X-ray diffraction results on Reiobholdg 1420 ^3-4253$) with the basicity result* gives l.<$ against 2*1<^ &i0* This is la hotter ayrsensni.. than the result# os C-45839* wfe the eompafeiaon la 1*5$ as against 6*17^ 29,, Sine* the swiss where sine oxide ms ground into the sampls had a tendency to sire basicity figures on the lew side, the high results when comparing the coajssiaiiwa staples lends support to the idea that the sasplo# contain ocro basic sino chromates in addition to freo sine oxide. It, also loads widens to the idea that the sine oxide in these pigments was not ground late the plants but that the pigments were prepared v. u er such eonditiouc off basicity that sot only ms a acre 'basic sin# dhromts pigaurat produced but sow free ZaO was also left in the pi|prvt* Failure to observe ray fluorescence i tfcace pigmsnta also tends to chaw that the free foO ms intretutsd in seas manner other than dry nixing* lino orJ.de ground into sin yellow. Them and oojspetatlTe swales titrated with add end alkali. JMLx 4u M fluorescent method used. SH.im.. A competitive susrpl*, a sine trloxyekrcante, and a titrated with sold and alkali* (piraefa chromate Bmplm of sine side ground into sino yellow exassiaed with X-ray diffraction* Competitive samples and maples examined with X-ray diffraction* DUP050150502