The Behavior of Sulfur in Silver Chloride at Chlorine Atmosphere

J. Soc. Photogr. Sci. Technol. Japan, Vol.50, No.3, 1987

研究 The Behavior of Sulfur in Silver Chloride at Chlorine Atmosphere

Sanemi S0N0IKE

Faculty of Science and Engineering, Chuo University 1-13-27 Kasuga, Bunkyo-ku, Tokyo

(Received 21th January, 1987. Accepted for Publication 20th April, 1987)

Abstract

Silver chloride crystals containing silver sulfide 1-10 mol% are annealed in a chlorine at-

mosphere above 400•Ž. The crystals expand their volume and become white brittle bulks which are porous with numerous gas-bubbles. By means of X-ray analysis, S35 tracer technique

and weighing in chlorine atmosphere with a quartz spring, it is verified that the silver sulfide in the chlorine atmosphere are decomposed into silver chloride and sulfur chloride vapor.

The chlorination of metallic silver is also studied.

measured by the X-ray diffraction, showed 1. Introduction the perfect AgC1 in its diffraction patterns. It is well known that the silver sulfide In this case, the amount of silver chloride added to fused silver halide crystals can en- was much larger than that of silver sulfide, hance the photosensitivity of the crystals1). so the existence of sulfide would be masked The function of the sulfide has long been in a bulk structure. It was, however, ob- studied based on several hypotheses such as served that even with a pure silver sulfide

electron traps2), hole traps, or silver traps4). powder the chlorine atmosphere converted As to the hole traps, early in 1927 K. C. D. it into silver chloride in X-ray patterns, Hickman') proposed a decomposition of Ag2S though when it was made at room tempera- by light through an intermediate stage of ture, the diffraction lines were slightly de- AgSBr in AgBr crystals. The theory was viated from that of pure silver chloride in lately cited in 1954 by J. H. Burrow and J. their intensities as shown in Fig. 1. W. Mitchell6) to be modified to their hole In order to study the process of chemical trapping theory with silver liberation. Now reactions, we measured the change of weight we are showing a function of chlorine at- of the samples in chlorine atmosphere with mosphere instead holes on the decomposition a quartz spring as shown in Fig. 2. At room of silver sulfide, that may be useful to ex- temperature, the calculated percentage of

plain the mechanism of sulfur sensitization. produced silver chloride liberating sulfur in the reaction that Ag2S+2C12=2AgCl+SC12•ª 2. Experimental reached about 50% in a couple of days, and Silver chloride crystals containing 1-10% after elevated temperature at 220•Ž, the silver sulfide made from melt show a dark percentage of silver chloride was almost 100 color and black precipitates. When the crys- % as shown in Fig. 3. If the sulfur was tals are annealed in a chlorine atmosphere remained in the specimens in any forms, the above 400•Ž, they expanded their volume weight changes would indicate the reactions and became white brittle bulks like a chalk overestimated. In order to estimate the which were porous with numerous gas- amount of residual sulfur in the final stage bubbles. The bulk, when it was ground and of the elevated temperature we traced the

― 179 ― ― 180 ― Sanemi SONOIKE J. Soc. Photogr. Sci. Technol. Japan

Fig. 1 The X-ray diffraction patterns. 1) Ag2S powder. 2) Ag2S powder exposed to chlorine atmosphere for two days at R.T. 3) AgC1 powder.

Table 1 RI detection of residual sulfur after

chlorine annealing at 220•Ž for Ag2S

powder containing S35.

Fig. 2 The apparatus for the measurements of S35 Half life 87.9d

weight changes in the chlorine atmos- β-0.167 MeV phere. The elongation of the spring is about 60 mm/1g or 30 mm/0.1g. as shown in Table 1. The self absorption of radiation would make the residual sulfur radioactivity of S35 added in the sulfide under-estimated. It seems, however, unlikely powder. The amount of residual sulfur that the residual sulfur is larger owing to measured from the radioactivity was less the self absorption than the calculated value than that calculated from the weight changes from the weight changes. Then the reac- Vol.50, No.3, 1987 The Behavior of Sulfur in Silver Chloride at Chlorine Atmosphere ― 181 ―

rine atmosphere. At room temperature the sulfur in chlorine atmosphere vanished per- fectly in several hours. Initially the sulfur looked unchanged, but after once started changing, it rapidly liquefied to a brown liquid. When the solid sulfur resolved and the weight exceeded a maximum, the liquid evaporated rapidly, but in a while the liquid changed its color to yellow and the evapo- ration rate became slow. But at last the color of liquid became brown again and evaporated rapidly to the empty. A typical change is shown in Fig. 4. The initial unchanged stages and the last rapid evaporat- ing processes were sensitively affected by the room temperatures and chlorine pressures. The dependence of the reaction rates on the chlorine pressure for a similar room temperature is shown in Fig. 5. It seems Fig. 3 The weight changes of Ag2S and Ag there is a optimum chlorine pressure to powders exposed to chlorine atmosphere at R.T., and that after heating at 220•Ž. evaporate the sulfur most rapidly. The ordinate are calculated from the

ratios of weight changes to the final weight changes(see Table 1). The

actual weight change are proportional to the % of the figure.

Fig. 5 The weight changes of sulfur powder in various chlorine pressures for a similar room temperature. The chlorine pressures were reduced with the volume ratios of the evacuated traps to the reaction chamber.

The brown liquid and yellow one seem to be SCl2 and S2Cl2 if we consider that there Fig. 4 A typical example of weight changes are only two components of the sulfur chlo- of sulfur powder in chlorine atmos- ride in this case and compare the thickness phere. of their colors referring to the Table in Fig. 4. Therefore we may consider that in the tion seemed almost completed within the initial reactions or in the excess chlorine experimented error. atmosphere, the sulfur makes SCl2 which In order to study how the sulfur vanished, evaporates rapidly, or the else S2Cl2 which we treated pure sulfur powder in the chlo- evaporates slowly. ― 182 ― Sanemi SONOIKE J. Soc. Photogr. Sci. Technol. Japan

On the other hand, the reaction of silver the electron traps. We have several evi- powder into silver chloride in the chlorine dences that the sulfur is concerned with the atmosphere is much slower than that of electron traps'". It should be thought that silver sulfide, and it is hard to reach 100% in the excess chlorine atmosphere the nature even in the elevated temperature of 220•Ž of sulfur is restrained. The more detailed as shown in Fig. 3. To chlorinate the silver study will be given later. metals completely, it is necessary either that The author would like to express his sin- the holes liberated from the adsorbed chlo- cere thanks to T. Nagashima for his assis- rine atoms reach the metallic silver through tance throughout the experiments, and to the reaction layer and liberate silver ions to S. Horie for his assistance in the isotope form silver chloride at the surface, or that the experiments, and also to H. Nemoto, S. adsorbed chlorine atoms diffuse to the me- Hosaka and other many students in my tallic silver to form silver chloride directly. laboratory and T. Mochiku in Fukai labora- It seems, however, that the diffused holes tory for their assistance to the experiments. hardly attack the metallic silver owing to that the silver metals are electron traps. References Then the experimental facts suggest that 1) O. Stasiw and J. Telton: Ann. d. Phys., 40 the diffusion of sulfur ions is faster than (1941) 181 that of chlorine atoms to explain the differ- 2) H. E. Spencer, R. E. Atwell and M. Levy: J. ence of reaction rates of silver and silver Photogr. Sci., 31(1983) 158 3) J. W. Mitchell and N. F. Mott: Phil. Mag.,(8) sulfide. In this opinion the sulfur ions are 2(1957) 1149 considered hole traps. 4) T. Evance, J. M. Hedges and J. W. Mitchell: 3. Conclusion J. Photogr. Sci., 3(1955) 73 5) K. C. D. Hickman: Photo. J., 67(1927) 34 The above experimental results is useful 6) J. H. Burrow and J. W. Mitchell: Phil. Mag., to explain the nature of sulfur as a hole trap 45(1954) 208 in the silver chloride. However, it does not 7) S. Sonoike and T. Nagashima: J. Imaging Sci., mean that the sulfur is not responsible to 30(1986) 127