Mixed systems of silver halides, silver cyanide and silver thiocyanate were investigated by means of electron microscope. The shape of the particles formed depends greatly on the ratio of concentrations of the reacting components. Even quite small amount of one substance can change the particle shape of another one. The most characteristic electron micrographs are reproduced

B. Černicki

M. Wrischer

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CR 0 AT I CA CHEM I CA A C TA 30 (1958) 163 CCA -130 546.571.2 :541 .182.6 :621.385.833 Investigation on Mixed Silver Halide, Silver Cyanide and Silver Thiocyanate Systems by means of Electron Microscope M. Wrischer and B. Cernicki Laboratory of Etectron M icroscopy, Institute »Rud.er Boskovic«, and Laboratory -Of Physicai Chemistry*, Facuity of Science, University of Zagreb, Croatia, Yugosiavia Received June 3, 1958 Mixed systems of silver halides, silver cyanide and silver thiocyanate were investigated by means of electron microscope. The shape of the particles formed depends greatly on the ratio of concentrations of the reacting components. Even quite small amount of one substance can change the particle shape of another one. The most characteristic electron micrographs are reproduced. In previous papers1•2 we described our tyndallometric investigation on ihe simultaneous precipitation of silver halides, silver cyanide and silver ihiocyanate. The interpretation of the results obtained was difficult since only statistical phenomena of colloidal systems can be measured by tyndal-]ometry and it is not possible to have any direct insight into the micro-:mechanism of the processes involved. For this reason we tried to apply .another technique which would enable us to observe individual particles of our systems. Thus we investigated all systems, possessing characteristic tyndal-]ometric features, by means of electron microscope. The results of this investigation and the most characteristic of over a hundred pictures obtained .are represented in this paper. EXPERIMENTAL We prepared our systems according to the scheme: AgN03 + KA + KB---+ AgA .j. + AgB .j. + KN03, .AgA representing the more soluble component of the system, AgB the less soluble ·One. The concentration of AgNOa was always 2Xl0-4N, that of KA 4X l0-4N ·(except with A= CN = 3X l0-4N}, and that of KB was varied from 3X10-4 to "3X lo-8N. The concentration gradient of B-ions included the point of equivalence ·where there was CB = CAg· Tite systems were prepared for microscopic observation ·one hour after the mixing of the reacting components, always in the same way. 'The pictures were made with electron microscopic magnification 1,300x using the whole resolving power of the microscope and finally magnified to 13,000x. 'They are characteristic for t,he systems one hour old. The electron micrographs are reproduced on Figs. 1 to 18 (see the plates ·included) and described in Table I. DISCUSSION In trying to interpret the results described one has to bear in mind that ihese systems suffer strong deformation when prepared for electron micro-:scopic observation (because of enormous concentration change) and during the * Contribution No. 74 from the Laboratory of Physical Chemistry. ,_,:-~-~y--r-~-~~···-~:--~•r·-~; ,.,•" ... . • ,_ . ' .: . .. .. . ' · . 4 ... . · Fig . 1. KC!: 4X l 0- 4 N . Fi g . 4. KBr: 4X lO-- ' N. Fi g . 7. KC!: 4X 10- ' N . K CN : 5X JO- '• N . • · . In a ll system s AgNO , : 2x 10- ' N. Fig. 2. KCN: 31< 10- ' N. Fi g. 5. KI: 4 X l0- ' N. F ig . 8. KC!: 4 X l0- ' N. NH,SCN: 3X l 0- 4 N. \ • ' \ ' Fig. 3. NH4SCN : 4X l0- 4 N . Fig. 6. KC!: 4X l0- 4 N; KCN: 3X l0- 4 N . Fig. 9. KC!: 4 X lO- • N; NH<SCN: 1.5 X l0- 4 N. (izmeclu str. 163 i 164) /II 10 • . ·• 1 ~·· • In a]] systems AgN03 : 2Xl0- 4 N. Fig. 10. KC!: 4X lO-• N; Fig. 11. KC!: 4X lO- • N ; Kl: 3X lO- ' N. KI: 3X l0- 7 N. Fig. 13. KCN: 3 X lO- • N; NH,SCN: 5X !O- ' N. Fig. 14. KCN: 3 X !0- 4 N ; KBr: 6 X Io- •; N. F ig. lG. NH,1SCN: 4X !0- 4 N; KBr: 3X !0- 4 N. Fig. 17. NH4SCN: 4X J0- 4 N; Kl: IXJO- • N. • • . . l.. . Fig. 12. KC!: 4X !O-' N ; KI: 3 X IQ - S N. Fi g . 15. KCN: 3X lO- • N; Kl:6 X lo- c. N. Fig. 18. KBr. 4X IO- ' N. KI: 3 X lO- ' N. (izm eau str. 163 164) 164 System Pure AgCl Pure AgCN Pure AgSCN Pure AgBr Pure AgI AgCl-AgCN AgCl-AgSCN AgCl-AgBr AgCl-AgI AgCN-AgSCN AgCN-AgBr AgCN-AgI AgSCN-AgBr AgSCN-AgI AgBr-AgI M. WRISCHER AND B. CERNICKI TABLE I smnil parallelograms ; recrystallization into larger particles (Fig. 1) rhombohedric needles3 •4 ; tiny semi-transparent particles (Fig. 2) large particles (about 1 µ long) with various shapes (Fig. 3) small particles with irrecognizable shape (Fig. 4) small particles with irrecognizable shape (Fig. 5) needles of AgCN; a few parall. of Ag81 (Fig. 6) parallelogram slates, some very thin (semi-transp.); AgSCN part1s.; small partls . with irrecogniza-ble shape (Fig. 8) small particles with irre-cognizable shape small particles with irre-cogniza ble shape typical AgSCN particles small particles with irre-cognizable shape small particles with irr. shape AgSCN particles; smaller partls. with irr. shape (Fig. 16) small pts. with irr. shape small pts. with irr. shape parallelograms of various sizes (Fig. 7) AgSCN and AgCl particles inde-pendently, their ratio varying with changing CB (Fig. 9) parallelograms of various sizes small particles with irr. shap.e and larger ones (hexagonal* and paralls.); then only larger parti-cles (Fig. 10-12) firstly only AgSCN partls., then partls. with hexagonal* shape, finally tiny semi-trpt. and larger ones (Fig. 13) aggregates of small partls. with irr. shape; tiny semi-trp. partls. Fig. 14) aggregates of small particles with irr. shape; tiny semi-trp. particles (Fig. 15) AgSCN particles AgSCN partls. and small pts. with irr. shape; finally only AgSCN particles (Fig. 17) small and larger partls. with irr. shape, their ratio varying with changing CB (Fig. 18) • the term pertaining only to the shape of the particles, not necessarily to their crystal structure observation itself (because of the impacts._ of i=lectr;ons). The first obstacle is inevitable and the second one can be greatly reduced by careful operation with the electron beam. In spite of that, the pictures obtained were repro-ducible and -the. shape .of . the particles formed·· seems to be charateristic for the systems (one hour old). There is a definite change of the particle shape when .the ratio b etween KA and KB is altered. · . The most interesting features of the results described are a) the difference between the systems above the equivalence of Ag-ions and B-ions (CB > C Ag) INVESTIGATION ON MIXED SILVER HALIDES 165 and those below it (CB < CAg); b) the appearance of particles having shapes which correspond neither to AgA nor to AgB; c) the totally inhibited appea-rance of AgB in some systems, when quite sm all amount of AgA is present. The pictures obtained cannot be a basis for any definite conclusions pertaining to the structure of the mixed precipitates. However, the mixed precipitates certainly show strong mutual influence of the components precipitated. This paper represents the first attempt to give an electron microscopic insight into these mixed systems (only AgCl- AgBr and AgBr-Agl have been investigated by the means of electron m icroscope3). Other workers have investigated the systems with other t echniques. There have also been electron microscopic investigations of the pure silver halides and silver thio-cyanate systems4-6. REF'ERENCES 1. B. Cerni ck i and B. Te z ak, Croat. Chem. Acta 29 (1957) 7. 2. B . C e r n i c k i and B . T e z a k, Croat Chem. Acta 30 (1 958) 1. 3. C. R. Berry and S. J . M a rino, Phot. Sci. Tech . II. 4 (1917) 22. 4. H . Ammann - Br a s s, Z. Naturforsch. 6a (1951) 372. 5. H. Ammann - Brass, Chimia 10 (1956) 173. 6. E. A. Gu 1 brans en, R. T. P he 1 p s and A . Lan ge r, Ing. Eng. Chem ., Anai. Ed. 17 (1945) 646. IZVOD Istrazivanja mi.lesanih sistema argentum ha!ogenida, argentum cianida i argentum t.iocianata pomocu eiektronskog mikroskopa M . Wrischer i B. Cernicki Istrazivani su mijesani sistemi argentum halogenida, argentum cianida i argen-tum tiocian ata pomocu elektronskog mikroskopa. Oblik n astalih eestica uvelike ovisi o om .ieru l<oncent racija reagenc>.ta. Vee m alene kolicine neke komponente mogu p ro-mijeniti oblik cestica druge komponente. Reprod ucirane su najka rakteristicnije slike dobivene pomocu elektronskog mikroskopa. LABORATORIJ ZA ELEKTRONSKU MIKROSKOPIJU I NSTI TUT »RUDER BOS KOVIC« I F'IZICKO-KEMIJSKI INSTITUT PRIRODOSLOVNO-MA TEMA TICK! F AKULTET ZAGR EB 

Investigation on Mixed Silver Halide, Silver Cyanide and Silver Thiocyanate Systems by means of Electron Microscope

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