Document B8N17QVmZ4QJdNEYpxGv37EzL

^fietum' to: jjp' FILBRCOM TO: Betum to: <7. L. FILEBOCM ,: TO: Betum to: J. L. FTLEBOCM \ COMPANY Serial No. _ .. 7S~3 Copy No. / cf TO: 'Betum to: J. L. .FILEBOCM T" TO: , \ !f Betum to: ' J. L. l^isBoasi . v ; r et ur n t o JACKSON LABORATORY FILE RQO*V TO: Return to: MO-1780 J. L. PILEROOM NEWARK PLANT PIGMENT COLOR RESEARCH REPORT INSTRUMENTAL COLOR MONITORING OF MOLYBDATE ORANGE STRIKES Period Covered May 1976 - November 1976 FILE: 210.3 DATE: 11/17/76 NJ 3049 N35365 DUP050109082 Jr--. KN-76-8 Issued -11/17/76 Copy No. NEWARK PLANT PIGMENT COLORS RESEARCH AND. DEVELOPMENT REPORT E. 1, DP PONT PE NEMOURS AND COMPANY TITLE - : COLOR MONITORING Og MOLYBDATE ORANGE STRIKES FINAL REPORT Work Done by - A* R. Hanke Report Written by * A. R, Hanke/ Previous Related Reports ~ KM-76-7 Project Code - 4671-290 Period Covered <* 1976 - November 1976 Notebook Nos * E61S9, E6158 ABSTRACT Instrumental color measurement cm be used to study the Influence of various factors in the production -of molybdate orange* Sie factors studied in this report .ate temperature, sodium chloride, .addition,. W** mddifioa, effect of pH, effect of rate of addition of the CrO^/MoOr* mixture, and the effect of a Pb^** excess. DU P050109083 TABLE OP CONTENTS I. INTRODUCTION II. PATENT SITUATION III. SUMMARY. AND CONCESSIONS IV. EXPERIMENTAL DETAILSAND DISCUSSIONS Page X Page 1 Page 1 Page 2 Distribution on last page DU P050109084 -i- I. INTRODUCTION This work was undertaken to show that instrumental color measurement can prove useful in monitoring the production of molybdate orange from the beginning of the strike to the final vat control. The basic idea of monitoring production of many pigments by on-the-spot instrumental color measurement is an obvious extension of this work. II. PATENT SITUATION No patent action is intended for any of this work. III.SUMMARY AND CONCLUSIONS A. The color monitoring technique involves placing a 2 liter beaker over the viewing Prt of the DU-COLOR meter. The Quantities are adjusted So that the final volume is around 1 liter. An electric stirrer supplies sufficient vertical mixing to give reproducible and steady readings. The formations of a vortex that reaches the bottom of the beaker or the formation of air bubbles must be avoided. From the DU-COLOR data, calculations are made of lightness, hue, and color intensity in U*V*W* color space. In most cases, it was the change in hue that was followed as Various other factors were changed for a molybdate orange strike. B. The following variables associated with molybdate orange production were studied using instrumental cdlor measurement. 1. Effect of temperature during the strike and development of YE-698-D. 2. Effect of NaCl during strike and development of YE-698-D. 3. Effect of pH on molybdate orange with, and without silica/alum treatment, 4. Effect of amount of Sb+++ added during YE-698-D production. 5. Effect of rate of addition of the CrO* /MoO* solution. 6. Effect of Pb++ excess on the development step of YE-698-D, C. The desired temperature during strike and development is around 65F. At a temperature of 73F, the color is noticeably yellower than at 65F by an amount about equal to the shipping limit. This difference is apparent immediately after the strike and persists through all subsequent steps, D. The addition of NaCl accomplishes two desirable effects. It causes the development of a redder product and it slow the subsequent degradation of molybdate orange. E. For wide swings in pH, such as from 2.5 to 9.5, there is a reversible shift in hue with the high pH giving the redder hue. A permanent change due to pH is associated with the degradation of molybdate orange. At a pH of 3.5, after an induction period of around 100 minutes, there is rapid degradation of the silicate/alma treated molybdate orange slurry At a pH of 6,0, the slurry is stable for at least two weeks and very likely, indefinitely. At a pH of 10 there is no severe degradation up to around a day but x-rays show evidence of the formation of some basic lead chromate. DUP050109085 2- - F. The addition of Sb111 causes yellowness and dullness* A plot of hue vs amount of Sb444- shows a rapid change towards yellow in the range of zero to 1/2 the normal amount of Sb444, For increased amounts, the change is less rapid* The same holds true for color intensity. From the point of view of a subjective color change, there is a greater change in color intensity than in hue. The difference in hue between no Sb1 1 * and four times the normal amount is about that of a shipping limit unit. Hie difference in color intensity between no Sb444 and the normal amount is about three times the shipping limit. G. If the CrO* /MoO* mixture is dumped into the lead nitrate solution rather than added over a period of 18 minutes, the hue reaches a redder value and main tains this red advantage through all subsequent treatments. This holds for YE-698-D, YE-816-D, and YE-421-D type Strikes. For YE-698-D type strikes, the difference amounts to around two shipping limit units. A possible explanation is that there is more molybdate orange degradation in the case of the 18 min. strike than for the dump strike because of longer exposure to a low pH in the case of the 18 min. strike. H. A Pb excess has a marked effect in slowing the rate of formation of molybdate orange and the rate of degradation. The greater the Pb44 excess, the longer it takes to develop maximum redness. After reaching a red maximum, the greater the lead excess the longer it takes to degrade back to yellow. In the range of 2.5% to 8% Pb44 excess the maximum redness is about the same and is greater than that reached for smaller or larger Pb"1-** excesses. At a Pb44 excess of 0.5%, the red maximum is considerably yellower than at 2.5% Pb'*"*' excess, it is more detrimental to let the Pb44 excess get in the mage of 0.5% than in the range of 21% Pb44- excess. These observations relate to the mechanism of molybdate orange formation and degradation. The intial precipitate of rhombic PbCrO* and tetragonal solid solution converts to molybdate orange but there is also degradation of the molybdate orange crystal. The rate of degradation becomes so great as the Pb44* excess approaches zero that very little molybdate orange remains. IV, EXPERIMENTAL DETAILS AM) DISCUSSION This section is a compilation of monthly summaries dealing with the application of instrumental color measurement to molybdate orange formation and degradation. The summaries contain notebook references where one can obtain further experimental details. The summaries have been edited to correct some typographical errors and show some re-calculated values for Pb44 excess including an estimate for sulfate in the chroma liquor. DUP050109086 r in s t r u me n t a l c o l o r me a s u r e me n t a s a t o o s ^c n mo l y b d a t e o r a n g e p r o c e s s c o n t r o l a r h - 1 ! 71-200 NB E6153-17 It has been shown previously (KN-75-2) that instrumental color measurement on the final vat eontrol of molybdate oranges is useful in predicting the tinctor ial properties of the dry color. The attempt is now being made to monitor the slurry color from the beginning to the end of a molybdate orange strike, This is being accomplished by carrying out a strike in a beaker on the DU-COLOR allowing continuous color monitoring through the bottom of the beaker. A trial YE-698-D strike was carried out with no serious technical difficulties. Work will continue in the attempt toshow that some characteristic of the color changing profile can provide a useful monitor.for moly orange production. INSTRUMENTAL COLOR MEASUREMENT FOR MOLYBDATE ORANGE PROCESS CONTROL 71-900 NB E6153-15, E6158-1,2 ARH Instrumental color measurements are being made on laboratory strikes of YE-698-D molybdate orange. The color is being monitored by carrying out the complete strike in a beaker placed over the viewing po,rt of the DU-COLOR meter. Figure 1 shows the change in hue with time for strikes run at 65F and 73F. The hue is calculated as an angle in U*V*W* color space. The vertical regions on the. plot signify hue readings immediately before and after the addition of the indicated ingredient. It can be seen that the DU-COLOR is sensitive enough to pick up the almost immediate eoior changes that occur when the various ingredients are added. The abrupt change to redness when soda ash is added is related to the pH Change from the acid to the alkaline side. Other abrupt color changes are undoubtedly related to the precipitation of hydrous silica, alumina, and the reducing action of the trivalent antimony Solution. Another point to be observed is that the 73 strike is yellower, prior to the first addition of soda ash, than the 65 strike. This yellowness persists throughout the strike and is due to the higher temperature. A strike run at 80F, not shown in the figure, shows a bend in the curve at a higher hue value (yellower) than the 73F curve. This means that at a point during development, even before the addition of the first soda ash, it will be possible to tell that the final product will be substandard. Unfortunately, there is i j; f- DUP050109087 BHP Mb. Summ. -5- July 23, 1976 nothing one can do to "save" such a strike but it may be possible to establish the cause for the failure to develop sufficient redness and correct it for the following strike. These experiments show that color measurements during a strike can be rapidly obtained and can give early warning of trouble. .Color monitoring could also be used as part of the strike procedure. For example, instead of using a pre-set time during development before adding the. other reagents, begin adding them at the time of maximum redness. An inspection of the curves shows a general slope to yellowness after the point of maximum redness is reached. This suggests a slow deterioration of the molybdate orange crystal while in the mother liquor and indeed, without the silicate treatment, overnight standing shows considerable loss of redness. This Suggests that subsequent addition of the reagents after development should not be delayed. Jk Observing the color profiles of other strikes while modifying some parameter will undoubtedly give rise to other thoughts that could aid in quality control. Work along this line will be continued. This will include the actual monitoring of plant strikes. DU P050109088 t E> DU P050109089 ' " tl i w m (Miui.wKaag?giJ4 T ' _-. "h u 3j h j u 'j v ~ hm INSTRUMENTAL COLOR MEASUREMENT OF MOLYBDATE ORANGE STRIKES " "TM= "" E6153-1V. E615S-I thru 7 ARH Plant and laboratory strikes of YE-698-D and YE-421-D have been color monitored with the intent of learning what the color readings should be during a strike that will result in a product close to the standard. Such information is now available for YE-698-D and YE-421-D. In addition to monitoring slurry color for quality.control, inprocess color measurement can serve as a topi to study the effect of variables on molybdate orange formation. Such measurements have the considerable advantage of being made almost immediately and hence are not influenced by inadvertent variable treatment given later. For example* if one is studying the influence of a variable early in a. strike and it is being followed by the color of the final dried pigment, this final color will also be influenced by all subsequent treatments such as pigment DUP050109090 BHP Mo . fiiinmi. -4* Sept. 1, 1976 surface treatments, grinding,and drying conditions. An on-the-spot color meas urement of the slurry circumvents all this. Furthermore, color measurement is one of the most sensitive measuring tools that we possess. It is often more sensi tive to changes in the physical and chemical makeup of a pigment than other tools such as X-ray diffraction and electron microscopy. Following are.some examples of how "inprocees" color measurement can serve as a tool to study molybdate orange formation and hopefully optimize certain tinctorial properties. A. Effect of NaCl on Molybdate Orange Formation E6153-17 A YE-698-D type strike was run with the NaCl added at the customary time during the strike. None of the following customary additions were made and the color changes were followed with the DtJ-COLQR. Another strike was run hut 'no NaCl was added. Figure 1 shows the plot of hue in U* V* W# color space with time. ' It can be seen that the NaCl accomp lishes two things, both desirable. First, with NaCl the slurry becomes redder than without NaCl before it turns around and becomes yellower again. Second, with NaCl the rate of increase in yellowness after the turn around is far less than without NaCl. The presence of NaCl allows a redder product and also acts to inhibit the degradation of the molybdate orange crystal. B. Influence of pH on Slurry Color 1. Zigzag Change in pH E615S-1 A YE-698-D strike Was carried out. At the time where soda ash would normally be added, caustic was used instead, to adjust the pH to 9. Period ically thereafter, the pH was shifted in zigzag fashion from around 9 to 2,5 . using caustic and nitric acid. Figure 2 shows a plot of the hue in It can be seen that the pH change, over this range appears to have a reversible effect on the color. This reversible effect is riding on an irrevers ible color change towards yellow which undoubtedly relates to the degradation of the molybdate orange crystal. 2. Effect on Molybdate Orange Slurry of Stepwise pH Change E615S-6 A YE-698-D strike was celled out that included the addition of silicate and plant alum but did not include the addition of Sb+++, After the second addition of soda ash the pH was adjusted to 9 with caustic and then changed in step fashion from 9 to 2.5 and back to 9 using nitric acid and caustic. There was a 1 to 3 minutes interval between each step. ' Figure 3 shows a plot of hue in U#V#W# color space vs time with Indicated pH at each time. It is seen that there is very little change in hue as the pH is dropped from 9 to 3 but in the vicinity of pH 3 there is a sharp turn to. yellow. This shift to yellow continues even when the pH is reversed and moved back up. When the pH reaches the region of 7, the rate of yellowing decreases but by now the molybdate orange has been severely degraded. DU P050109091 BfP Mo. Suimn. -5. Sept. 1, 1976 .Tills experiment serves to illustrate how color measurement on slurries can indicate the degree of stability of molybdate orange as a function of pH. This experiment suggests that even with a silica/slum treatment, discernible degradation of molybdate orange can take place in a few minutes at a pH of around 4 to 3. A repeat experiment giving more attention to the pH range 5 to 3 with time intervals greater than three minutes will allow a more precise measure of the influence of pH on molybdate orange stability. C. Influence of Amount of Sb*** on Color E6158-7 +++ A YE-698-D strike was carried out but when it Came time to add the Sb , the pH was adjusted to 6.5 with HNOo and only & the normal amount of Sb+++ was added. After again adjusting to pH 6.5 with caustic, another . portion was added. This was continued,jjrith time intervals around two minutes to give a ladder series of total Sb** of 0, 1/2, 1, 1|, 2, 3, 4 times the customary amount. The pH adjustments to 6.5 were made tadqprevent any reversible pH effect on hue from influencing the results, * Figure 4 shows a plot of hue and color intensity.vs amount of Sb+++ expressed as a fraction of the customary amount. It is seen that the hue changes towards yellow quite steeply in the range of zero to \ the normal amount of Sb++. From then on, the change is less rapid but the trend toward yellowness continues almost linearly up to at least four times the normal amount of Sb+++, The color intensity also falls off quite steeply in the low Sb+++range and then falls off to a lesser extent as the Sb+++ increases. These changes can he considered in terms of visual color differences by realizing that an instrumental hue difference of around 0.33 represents the shipping limit for visual hue and an instrumental color intensity difference of around 1,4 represents the shipping limit for the visual intense/dull color reading. From this point of view the hue difference between no Sb*-++ and four times the normal amount of Sb+++ will be about that of the shipping limit. This is not the case with color intensity, however. Here the difference between no Sb+++ and the normal amount is about three times the shipping limit. This means that the Sb+++ has a greater visual effect on color intensity than on hue. The curves also show that the normal amount of Sb+++ is well chosen to lie in the region where a variat ion in the amount added, will have the least tinctorial effect. D. Influence of Rate of Addition of Cr077MC)7-on Molybdate Orange Color '' 1 1 y" E&158-2,3 Two YE-698-D strikes were carried out. For one, the time of addition of the Crsolution was the normal 18 minutes and for the other, the solution was dumped in. In each case the NaCl was added immediately after the addition of the CrO^/MO/-- solution. In the case of the dump strike, the first soda ash was added near the time of reddest hue. S' , Figure^irshow3 the BUE/TIME profile for both strikes. For both strikes, the hue reaches its reddest point at about the same time (around 32 minutes) but the dump strike slurry is redder than the 18 minute strike. This hue advantage is maintained throughout all the subsequent additions of the usual reagents. The two products finish with a hue difference that would exceed shipping limits. The 'difference in hue cannot be attributed to the fact that for the dump strike, the DU P050109092 BHP Mb, Summ. -6- Sept. 1, 1976 flrst soda ash was added at the point of maximum redness because the slurry was redder than the 18 minute strike .even before the addition of the first soda ash, A possible explanation is more Molybdate Orange degradation in the ease of the 18 minute strike than for the dump strike because of longer exposure to a low pH in the case of the 18 minute strike. 4 Work is continuing to more rigidly define the conditions for molybdate orange formation and degradation using inprocess color measurements. DUP050109093  & OH 3 %l \ <$> & 4 <5) r-i \ 1\ -&P t \ SS&A oo"\ H O Cr-M4 iiOHH O s OO' 0o- FIGURE 1 . YE-698-D S tr ik e S lu r r y In flu e n ce ' o f NaCl 1 \ o 4 NO $ i o| \ tor\ 4 \ \ Q , <?> -o<r 4 o ,/ ...0 0 / oC'l ...o 0 // lOTiai -5- aaa --1 o -& o CM uc-\ 'H4- C<-'Nt anH Cr4M Cu~M\ orH DUP050109094 11.25 11.10 _j 10.95 _ FIGURE 2 9 YE-698-D strike Slurry Influence of pH on Hue. Illustrated reversible Hue change. 4 NaCl 2.65 <?) / // 10.80 _ 0) 10.65 _ tA \j 10.50 10.35 10 i j# \\ \\ HNO, A pH 214 \\ \ pH 2.65.. \\ /i \\'X &/ iI// yw ^.5 / / .1 H r A NaOHy PH 9.3 0-9.2 "" i...... ... 20 1 ....... 1 ....... .. 30 40 TIME (min.) T.. ........... 50 1.....~ ' . .....' 60 70 DUP050109095 n.2 11.0 10.8 10.6 FIGURE 3 YE-698-D strike slurry Influence of pH on Hue Illustrated Mply. Or. Degradation. S 6 '7 / / 05 #. i i i i 03 <& 8 13 * r 10.4 10.2 pH 9 0- p 9 2.5 'b . & 10.0. t V ii -J- - - - - - J...J- - - - - - - r 32 40 48 56 64 72 80 TIME (MIN. ) y ! DUP050109096 10.48 FIGURE 4 10.40 4\ ?/ 6 YE-698-D Strike Slurry Influence of Sb+++ 10.32 4 ..-fir 6....,- ' / " /\ / Hue 10.24 10.16. s. \ j* /' /\ Q. customary "t o * Sb+< \^ c 132.0 JS> 130.5 129.0 127. 5 emcwsos~ rr* a 126,0 8 10.08 10.00. \0 x. ..T" Color Intensity . 124.5 ..... 0-.... --------- q 123.0 i Multiples of customary amount of Sb+++ DUP050109097 * |rT * DUP050109098 B. Rate of Molybdate Orange Degradation as Function of pH E6158-II ARK Laboratory YE-698-D type strikes were carried out that included the addition of silicate and alum but the S'o+++ was omitted. At the point in the strike where the second soda ash is normally added, the pH was adjusted to a pre-selected value using nitric acid or caustic. Stirring was continued and the color monitored with the OT-COLOR. The selected pH's were 3, 3*5* 4.0, 4.5, 10. Figure 1 shows the HDE/TIME profiles for the various pH's. There is sane evidence that at a lower pH there is an induction period where the change is slight and after this period there is rapid degradation. This could relate to the tine required to strip off the protective coating and this could constitute a test for the effectiveness of the coating. It is also of interest to note that the curve at pH 4,5 is much the same as that of pH. 10. The degradation is slight but . ^ unmistakable over around 300 minutes but over a much longer period of time the^-^l molybdate orange severely degrades at a pH of 4.5 but does not at a pH of $. It is already well established that at a pH of ground 6.5, coated molybdate orange slurries are stable practically indefinitely?The fact that even coated molybdate orange is unstable at a pH of 4.5 can be of some concern, if in its end use it will be subjected to a pH 4,5 environment for a long time, C. Bate of Molybdate Orange Degradation as Function of Lead Excess E 6158-12 ARH YE-698-D type strikes were carried out in the laboratory but the CrOy`"/ MoOij 1 solution was dumped into the PbCNOs)^ solution rather than added over a set period of time. After addition, the pH was adjusted to 2.3 which is close to the pH expected at that point in the strike. Hone of the subsequent reagents was added. The color change with time was monitored with the DU-COIDR. The only variable between strikes was the amount of CrOiTbolution added. For each strike a different amount of crcvRloO* solution was added creating a ladder series with different amounts of Pb++ excess. Hie excess was calculated as a per cent in DUP050109099 BHP Mo. Sunsnary More TMS4,_ Ui---< 30, 1976 excess of the stoiehimetric amount based on the reaction with Cr057 MoO^ and. 'TMn^infm~"{ ^ Chrome li^Qg-^s~ignered. beeansft-.bpnp> 1 tiiatuised-in~bhe-QalcuIatonT- aA . , * -- /* r.? us the HUE/TIMSf profile for the various Pb 6JKsessesv. It can jnt of Pb++ excess has a profound effect on the rate of molyb- Lon. At lflof$`/Pb++ excess, 'the rate of degradation is far less than that at %3? Pb++ excess. In the region the rate of degradation is reduced still further. But note that the development time to reach maximuin redness becomes longer as the Pb++ excess increases . Also at higher Pb++ excesses, the slurry does not reach as red a point as at lower Fb++ excesses. In the range^A-??# ~ -IQ-&% the slurry reaches about the same degree of redness but at higher percentage this degree- of redness jgfr never reached even with an extended hz.r%-7.f%, >, t,ry,, -zf0 These data suggest that/ although a Pb++ excess^slows degradation, which is desirable, it does not allow as full a development of redness as that which occurs at a lower_Pb++ excessand this is^undesirable. The data also suggest that in the range, of "there is very xittle change injraximum redness but a large change in the rate of degradation. This means that if the Pb++ excess is not allowed to get much above -l^T^here will be very little sacrifice in redness but some advantage in increased stability. Another observation relates to the question, "How long can an uncoated molybdate orange be exposed to a pH of 2.3 before there is a discernible change in hue?". A reasonable detectable limit on the hue scale 'JS'b is around 0.1. Tj^,4-ff#"Pb++ excess curve shows a rate of degradation such that in about threj^mmAtes there would be a discernible change in hue. This points up the importance of not allowing the molybdate orange to be exposed to the develop ment"pH of around 2,3 with a low Pb++ excess for a length of time exceeding three minutes. Recall, hovxever, that it was shown previously that the addition of NaCl slows degradation and does not impair the development of redness. The addition of NaCl can, therefore, be considered as a safeguard against excessive degradation. This experiment serves as an excellent example of the use of instrumental color measurements. In this experiment the molybdate orange is unstable and at times is changing rapidly. It would have to be isolated, dried, a rubout made and measured under conditions that would allow very little degradation. These are rather difficult technical requirements. Gening immediate color measurements on the slurry completely eliminates these difficulties. We will continue to aid Manufacturing in applying instrumental color measurement to "in-process" control. BISMUTH VANADATE YB-200-D NB 6154 JiH Bismuth Vanadate, formerly PGL-20, is now coded YB-200-D. Appropriate SP numbers for intermediate stages have also been assigned. * The second four pound sanple prepared was sent to P&P Troy, Michigan who reported the acid resistance as unacceptable. A decision was made to proceed with a Saml-Works run from Semi-Works oxidecoated base. Thirty-five pounds (SW 76-00811) was prepared. The quality by the M. r k k >. iK C- v wm DUP050109100 9 OCcsf\ ``oK?vfl PH o C 48-> O PS CcdO 'aroi 4J CO <&D Mto *Wo a Ocn i V* <D $>, & H,n i n "Q------- O0v ttonax afiH aaa "o b o O 00 t+) c4 CsHN CO m rf-4ii- rH CO o! DUP050109101 DUP050109102 INSTRUMENTAL COLOR MEASUREMENTS OF MOLYBDATE ORANGE STRIKES ARH A. Rate of Molybdate Orange Degradation as Function of pH E6158-11 In the previous summary an experiment was described in which a series of YE-698-D type slurries, exclusive of Sb+ , was allowed to stir at pre-selected pH Values. The slurry, pre-set at pH 4.5, showed severe degradation- within 3.7 days. Continuing experiments show that at a pH of 5.0 and 5.5 there is severe degradation within four days. At a pH of 6.0 the slurry did not degrade even after a week. This means that final vat controls adjusted to a pH.no lower than 6 can be considered stable for at least a week and very likely longer.. It is of interest to note tint at a pH of 10.0, there is no severe tinctorial degradation up to 0.8 days, but an x-ray record shows evidence of a small amount of basic lead chromate of the Y0-34-D type. No further work is planned for this experiment. DUP050109103 BHP Mb, Summary -4- October 21, 1976 B. Rate of Molybdate Orange Degradation as a Function- of Lead .access E6158-12 ASH In the previous siopiary it was shown that the formation and degradation of molybdate orange was slowed 'considerably as the Fb++ excess increased. Furthermore, increased redness was observed at the lower Bb++ excesses with the redness about the same in the region of 4to-lQrS#- Fb+ excess, All of the strikes in this ladder series were dump strikes. [The experiment has been extended to still 1 Pb++ excesses, namely 3w and 3$-. \ Figure Y shows the change yin hue with timi It also includes the curves for -4t 7# and 16t 6$ Pb+ excess (from the previous xperiments for comparison purposes. It can be seen that at the 3JS* Pb++ excess le- 1, l--e--s--s- redness is developed and the rate of degradation is greater than]at^452# Pb++ excess. At the *2$ ITr excess level, a maximum redness was not caught by the DU-COLOR, it prpbably^exists but is too transient to be easily observed. At any rate, it would "be at a point far yellower than the maximum redness atVrT#- Pb++ excess. Notice, too, that at- ,,++ excess, molybdate orange is degrading at the most rapid rate of all and the reddest point is already far yellower than the reddest point of the 46r6jS'Pb++ excess curve. Too great a Fb++ excess and too small a Pb++ excess both contribute to yellowness but the effect is most pronounced at a low Fb excess. s This can he explained by realizing that after the initial precipitation of rhombic PbCrO/ and tetragonal solid solution, molybdate orange is both being formed and degraded. The rate of degradation increases so rapidly, with decrease in Pb++ excess that at the iSJf-vLevel it is so large that no acceptable amount of molybdate orange is ever produced. '--_ This means that' for a dump strike, it is necessary to have a higher Pb++ excess than for a strike where the chrome molybdate solution is added over a period of time. It also suggests that with a higher Pb++ excess, the addition of NaCl becomes less critical because the increased Pb++ excess will impart some stability making it less imperative to rapidly invoke the stabilizing action of the NaCl. No further work is planned for this experiment. BHPtmnm ate, % DUP050109104 DUP050109105 DISTRIBUTION 1. E. Gonick, Pigm., Wilmington/Newark Library 2. E. E. Jaffe, Pigm., Newport/Circulate and Pile 3. Newport Library 4. W, S. Struve/J. P, Galvin/H. Matrick/Library 5. A. P. Smith 6. B. H. Perkins 7. J. Jackson 8. A. R. Hanke 9. F. F, Ehrich, Pigm., Wilmington 10. 0. C. Gero, Pigm., Newark 11. I, H. Dunn, Pigm., Newark 12. T, R. Becker, Pigm., Newark 13. E. J. Mead/C.H.Muendel, Pigm., Exp. Station 14. Newark Numerical File - 210.3 15. Newark Library - Central Report Index 16. Newark Library - Central Report Index 17. Extra 18. Extra 19. Extra icn-J& DUP050109106