CR 0 AT I CA CHEM I CA A C TA 28 (1956) 13

CCA-3 541.18.041 :546.571.2

Methorics of the Precipitation Processes. XII. Mutual Influence of Silver Halides in Precipitation Processes*

B. Cernicki and B. Tefak

Laboratory of Physical Chemistry, Faculty of Science, University of Zagreb, Zagreb, Croatia, Yugoslavia.

R eceived January 29, 1956

Our investigations into the mutual influence of silver halides on precipitation processes, using sols in statu nascendi, included the systems AgBr-AgI and AgCl-AgI.

The general result of our investigations is that those halide ions which make the least soluble salt with Ag-ions are preferred in building up the crystal lattice of silver halides. If such ions are in excess over the Ag-ions in the system, then neither the crystal growth nor the coagulati-0n of sol :Particles will much depend upon the presence of other halide ions. This dependence is small i!'Il the system AgBr-AgI and almost vanishes in the system AgCl-AgI.

INTRODUCTION

lit has been known for a 1ong ttl.me that small addition of Agl to the bromil!le iphoto:graphic emulsion cornsLderaibly incre.a1ses its sensitivity. Mixed crystals of silver halides have, therefore, been investigated by many authors using various techniques 1- 11 . The~r results are very different. We approached the problem from the point of ".'iew of co·1loLd chemisbry and tried to solve it by using a method described in previous papers. 12•13•14 The problem was interestmg, since even small quantities of iodLdes, for instance, could widely change the course of the fo'l'iffiaHon and coagulation of AgBr owing to ithe much smaller solubility of Agl. The sol.JuJbilities of si1ver halides lin the s er ies AgCl­AgBr-AgI have the ratios 1 : 5.5 X 10-2 : 7.7 X 10-4

EXPERIMENTAL

The 1system AgBr-AgI was investigated first. With 2 X 10- 4 N AgN03 we obse1rved that al:ready aJn adddtion of 1 N-0/o** KI to KBr ~noreased the coagulation. v1ail.1Ue of the :system from 3.8 X 1Qr 2 N to 8 X 10"' N (Fig. 1). Th~s effect was constant even when KI additions were decreased to 0.4 N-0/o.

The change of the one hour coagulation curve was characteristic too. While pure AgBr coaigulated in one hour in the whole concentration region of counter­ions used (introduced as KBr) , the so•l obtained with small additions of I-ions remained stable for more than one hour in lower regions of the gradient. _

When the percenitage of I--additions was varied foom series to series, a shift of a new maximum wi'th changes in the quanhty -of I-ions added was observed (4-hours coagulation curves in fig. 2). This maximum aipipeared strictly at the point where KI was equivalent to AgN03.

• Contribution No. 58 from the Laboratory of Physical Chemistry. Paper XI: J. Kratohvil and B. Tefak, Arhiv kem. 26 (1954) 243.

•• N-0/o denotes the percentage of one halide component in the mixture of halides when their concentrations are expressed in normalities.

14

L.LI

3 <l: >

B. CERNICKI AND B. TEZAK

10mln. AgN0 1:2x10- 4 N I 0.091----------+-

1

_ _ J1

•

J\ ••'""'""' l<I

I \ 'I'"'"' KBc with!•~ I ' lj N-% Kl I I ~KBr 6 I I I

u 0061--~-i-~'-it--l--~~~-4-~l--~~

er f­uJ .L 9 -' <t 0

I a I i

z ~031-------+1c..:;_--}'------l~>-+-------l >-f-

-1 -1.5 -2.

LOG . CONC. K+ CNl

Fig. 1. The influence of KI addition to the system AgNO"-KBr.

w 3 <t >

AgN03 :2)( 10-'N

K Br wirh addition

•• 11 •• 0.4N-%Kl o'\ 0.6 I \--- 1.0

!:< O.O&l-+..1'--4-l'l---l-:tt---+--t---1-----i er t-­w :;: 0 -' -' <i: 0

0

\ \ \ \ \

:; o.Q3:1-+--~---+:----"--l.----''-t----t t-- o,

-1

\ \

', I .,

-;1.5 -2

LOG. CONC . KBr CNl

Fig. 2. Isoelectric maxima of AgI appearing in the system AgN03-KBr-KI.

~ 2 200

PRECIPITATION PROCESSES OF MIXED SILVER HALIDES

~ KBr with t ~ N-9'~ Kl

- 1.5 LOG. CONC. K+tN l

Fig. 3.

:::1, E

AgN03 : 2•10-~N K+:sx10-2 N

! ~ 200>----+--------+-- .,._ _ _ _ ,__,

0 <(

°" w -' I.)

t­Si 1oor----+-----.i-t------+-+-~ 0.. I

I I

.. o' . I

.,D£J •• • KBr Vl lth

•' •' 1 N-% Kl O'--...._~.___._._~.._~._~__...._.

2 4 5 .. 10 · 20 liO

LOG. TIME IN MIN.

Fig. 4.

Fig. 3. Concentration d yspersoidograms of the systems AgN03-KBr, A gNO,,-KI and A g N03-KBr -KI.

15

·Fig. 4. Time dyspersoidograms of the systems AgN03-KBr, AgNO, -KI and A gNOa-KBr-Kf.

w ::i -' -et >

0.12

0.05

10 mi n ...

I AgN0

3: 2x10-~ N

:0

\ K (I with add it[o n of

,.ct'f-%f..,\ I --• 0.1 N-% Kl I 'i I I ____ ....... 0.15

fo ... u I n-! • • "" 0.25 .... !I ..... ~-o.4 ~,·. i1 -1.0

~ \ f;I :1 '1!. 0.06t---1.--lf'.i---.&f-------·-+------!

g \Ji -' <( 0 z >­t-

-1 -1.5 • 2

LOG. CO NC. KCL LN l

Fig. 5. Isoetectric yt1axim a of AgI appearing in the system AgNOa-KCl-KI.

16 B. CERNICKI AND B. TEZAK

Small r--additions also affected the size of colloidal particles and the rate of their growth (fig. 3 and 4).

After this we started to investigate the influence of KI additions to KCl. Here the iodide character of the coagulation curves was still more pronounced, with the coagulati()[l value of 16 X 10-2 N KCl. We also observed a regular shift of the AgI maximum with changes in the quantity of KI addition. Both phenomena are shown in fig. 5.

Then we performed many measurements with counter-ions introduced as KN0 3 while the concentrations of halide ions were consfant i. e. C B,.- + c1_ = const. =

~· 2 X C Ag + = 4 X 10-4 N. A shift in coagu.J.ation values of the systems with an increase in the ratio between I- and Er-ions was observed again. 12 Additions of the order 1 N-0/o KI to KBr rapidly pushed the coagulation values towards higher concentrations. With larger additions (of the order 10 N-0/o) the coagiulati:on values only slowly increased until the value for pure AgI was reached at 50 N-0/o Kl (equivalence with AgN03) .

w ::::> _J <r >

~

0'09r----------,-------, -1/. 10m«n AgNOi 2.><'10 N

KCl +Kl : 4><10-4N

~ 006 l--~~-~-.o'-'!.:.''0-00

-0

l------~ w :L 0 _J _J

C3 z :>-

60Y. KC[+ 40.Y.KI ·"'b·-·0-o.._

I- 0''13 1--~~-+----tl-----+-------=-l 90o/.KQ ... 10Y.KI

uO-"""'"oe.

100%KI ~~""'i"..;g:.:b;::~ 0'----_-0~·5-------~~------~~·5

LOG. CONG. KN03 CN)

Fig . 6.

u ~.0.06 w 2:

9 .-J <( 0

10 min .

-100% KBr ... •••• '10 96 Kl

-·-• 50% Kl ---100 % Kl

~ O.o31--.0-c>-"""..,;0.1k"""rt------1 .....

-3.S -4 4.!I

LOG. CONC. La.CN03l3 CNl

Fig. 7.

Fig. 6. The influe n ce of Kl addition to the syst e m A gNO.,-KCl-KN03 •

Fig. 7. The influence of Kl addition to the system A gN03-KBr-La(N03) 3•

With AgCl these influences were much more pronounced. In the whole c oncentration gradient (5- 50 X 10- 2 N KN0 3) pure AgCl coaigulated completely (fig. 6). Already 1 N-0/o KI ~n •the halide mixture considerably decreased the turbi­dity but the systems coagulated in the whole region. Further additions, up to 40 N-0/o KI, did not change the picture essentially. At 50 N-0/o KI, however, the cu:·ves rapidly acquired an iodide character with a decline in concentra,tion maxi­mum and a coagulation value of 18 X 10-,2 N.

The situation was quite reverse wben trivalent La-ion was taken instead o·f monovalent K-ion, as counter-ion. The coagulation value for ipure AgBr was at very low concentrations, 12 X 10-0 N La(N03)a. The additions of I-ions decreased it gradually to the coagulation value for pure AgI, 4 X 10- ' N (fig. 7). With the AgCl-AgI systems the situation was similar.

PRECIPITATION PROCESSES OF MIXED SILVER HALIDES 17

DISCUSSION

The principal ques,tion to be expJa.ined i:s the st11ong influence of very s mall additions of some halide ~ons to 1the other ones dUJring the coagulation :process of thei'r s ilver s alts. The comparison of our ·r esults with those of 'Taboury and hi1s collaborators15•16•17 and the senior author (B. T.) 18 and S. Kratohvil19 suggests thait induced formation of solid phase occurred in our s ystems fo.o. Here, however, aipart £,rom the difference in the ease of crystal formation, the diifferences in solubility and adsorbabiJ.ity requi1r e consideration.

When the concentration gradient of counter-ions was obtained by KBr ·or KCl, there was an excess of I-ions over Ag-ions in srpite of their small concentration. ThUJs &gl wais prefeirably formed and I-ions w ere preferably adsol'bed on Ag! partic1les. The coaigulation curves, therefore, had a predomi­nantly 1odide character (high coagulation value and a much im.ereased sol stability). Yet Br-i'Ons had also a share, fo :som e ,extent, in thes.e processes, because of their great excess.

'Dhe particles o.f Ag! w ere much smaller than tho1se of AgBr, but prevailed widely in number (Ag! having a much smaller solubility product). The particles of our sy:stems with small r--additions were, in turn, smaller than those of Ag! itself, and even the rate of their growth was 1smaller. This may be explain ed by the fact that in such mixed sys tems the comparatively low concentration of I-ions caused no apipreciaJble complex solubility of Ag! particles formed and there was, ·therefore, a much larger number od nuclei which cou1d only slowly re-grnw int·o coarser particles.

The ipreferability o.f I-ions in th e formation of solid rpha,se and in the adsoription 01n it was a lso confirmed by the appearance of n ew maxima at that point on the halide ions gradien t wh er e I-ions were in equivalence with Ag~ions,

and by the fact that t h ese maxima shifted regularly with the change in 1--percentage, following exactly the equivalence point with Ag- ions. There is no doubt that they were i:soelectric :maxima of AgI.

In AgCl-AgI systems the influence of iodide additions was more pronounced because of the great er difference in solubLli1ty between AgCl and Ag! than between AgBr and AgI.

When the concentration gradient of counter-ions was obtained by KNOR, and twice as many h alide ions were taiken as Ag-ions, there was not enough I-ions to react with all Ag-ions and th us Br- or Cl-ions participated in building up the crystal lattice also. At 50 N-0/o iodides the I-ions were in equivalence with Ag-ions. The systems, therefore, d id not behave as pure iodide systems before this composition was reached.

With tri:valen t L a-ions as cournter-ions th e effects w er e different. The coagulation values of our systems were shifted to a much lower concentration region of counter-ions (two powers of 10 lowe:r). This is in agreement with the Schulze-Ha11dy rule. The coagulation vatlues decreased wi:th th e increase in t he number of I-ions. This is natural, for trivalen t ions have a lower coagu­lation value for Ag! than for AgBr or AgCl. The reason for that has been discussed in a previous paper by the senior author (B.T.)20 .

18 B. CER NICKI AND B. TEZAK

REFERENCES

1. J. Te It o w, Fundamentai Mechanisms of Photographic Sensitivity, London 1951, p. 33. 0. St as i w and J. Te Ito w, Z. anorg. Chem. 257 (1948) 103.

2. P. V. Mei k I y a r, Dokiady Akad. Nauk SSSR 77 (1 951) 391. 3. N . K ame yam a and K. Mi z u ta, J. Soc. Chem. I nd., Japan 42 (1939) 426. 4. A . Haut o t and H . Sauve n i er, Science et inds. phot. 24 (1953) 257.

A. Hau t o t and H . Sauve n i er, Science et inds. phot. 23 (1952) 169. 5. G. M. S c h w a b, Naturwissenschaften 31 (1943) 322.

G. M. Schw ab, Trans. Faraday Soc. 43 (1947) 715. G. M. Schwab, KoHoid-Z. 101 (1942) 204. G. M. Schwab, Z. physik. Chem. B-51 (194.2) 245.

6. C h. R. Berry, Acta Cryst. 2 (1949) 393. 7. H . Ch a t ea u and J. Pour a.die r, Science et inds. phot. 25 (1954) 3. 8. H . F 1 o o d, Nord. Kemikermode, Forh. 5 (1939) 211.

H . FI o o d, KgL Norske V i denskab. Seiskabs, Skr. 1941, 23. H. FI o o d and B . Brunn, Z. anorg. ang. Chem. 229 (1936) 85.

9. 0. Ru ff a nd E. Ascher, Z . anorg. ang. Chem. 185 (1930) 369. 10. H . C. Yutzy and I. M. Ko Ith off, J. Am. Chem. Soc. 59 (1937) 91 6.

I. M. Ko Ith o ff and F . T. Egge r t s en, J. Am. Chem. Soc. 61 (1939) 1036. 11. K. Schau m and 0. Scheid, Z . wiss. Phot. 36 (1937) 121. 12. B. Tezak, E. Mat i j e v i c, K. Sc h u I z, J. K rat oh v i I, R. W o If and B.

C e r n i c k i, J . CoHoid Sci., Supl. 1 (19'54) 118. 13. E. M a t i j e v i c and B. Tezak, KoHoid-Z. 125 (1952) 1. 14. B. T e z a k , E. Ma t i j e v i c and K. S c h u I z, J. Phys. & CoHoid Chem. 55·

(1951) 1557. 15. F . T ab our y and R. Echard, Bun. soc. chim. France 51 (1932) 1377. 16. F. Tab our y and R. Echard, BuU. soc. chim. France (5) 1 (1934) 1525. 17. F. T a. b our y .and X. S a Iv in i en, Bun. soc. chim. France 51 (1932) 1340. 18. B. T ezak, KoHoid-Z. 68 (1934) 60 19. B. T ezak and S. K r at oh v i 1 - Babic, Arhiv kem. 24 (1952) 67. 20. B. Tezak, Arhiv kem. 22 (1950) 26.

B. Te zak, E. Mat i j e v i c, K. F. S c h u 1 z, J. K rat oh v i 1, M. Mir n i le

and V. B. Vo u k, Discussions Faraday So c. 18 (1954) 63, 194, 199.

IZVOD

Metorika precipitacionih 1)rocesa. XII. Medusobni utjecaj argentum h alogenida kod precipitacionih procesa

B. Cernfrki i B. Te:Zak

Nasa istrazivanja medusobnog utjecaja argentum h alogenida kod precipitacionih procesa obuhvartila su sis.teme AgBr-AgI i AgCI-AgI. R adili smo tSa solovima in. statu nascendi.

Opceniti je rezultat nasih istr azivanja, da prilikom izgradnje kristalne resetke a rgen1mm halogenida prvenstvo imaju on i halogentd ioni, koji s argentum ionima daju n aj t eze topljivu sol. Ako takvih iona ima u sistemu u suviSku natl argentum ionima, ne ce ni kristalni ras.t ni koagulacija cestica sola u znatnoj mjeri ovisiti o prisutnosti drugih halogenidnih iona . Kod sistema AgBr-AgI t a je ovisnost ma­lena, a kod sistema AgCl-AgI gotovo iscezava.

FIZICKO- KEMIJSKI INSTITUT

PRIRODOSLOVNO-MATEMATICKI FAKULTET

ZAGREB

Primljeno 29. · j anuara 1951> .