PHOTOGRAPHIC DEVELOPMENT BY HYDROXYLAMINE
597
THE KINETICS OF PHOTOGRAPHIC DEVELOPMENT BY HYDROXYLAMINE' T. H. JAMES Kodak Research Laboratories, Rochester, New York Received ma^ 17, 1948
The reaction between silver ions and hydroxylamine in acid and alkaline solutions and the reaction between various solid silver salts and hydroxylamine in alkaline solutions have been dealt with in previous publications (1, 3, 8, 10). The kinetic studies (1, 2) mere carried out as part of an investigation of the mechanism of photographic development. The choice of hydroxylamine for this purpose was determined by the fact that its gaseous oxidation product permitted a marked simplification of the kinetic technique. The present paper deals with the reaction between hydroxylamine and the silver bromide grains of a simple commercial photographic emulsion, i.e., with development of the latent image and formation of photographic fog. The results, taken together with the previous work, support the interpretation of development as a catalyzed heterogeneous process taking place preferentially at the interface between the silver and silver halide (5, 6, 7). HYDROXYLAMINE AS A DEVELOPING AGENT
Although hydroxylamine is a relatively unfamiliar developing agent, its developing properties are not atypical. It yields somewhat lower contrast and lower emulsion speed than the simplest organic agents of its type. It is, however, capable of producing relatively fog-free development of good quality. Satisfactory prints can be made on both chloride and bromide papers with hydroxylamine. It is not a practical developemfor ordinary bromide film, but only because the nitrogen evolved during development disrupts the gelatin layer. Even this can be avoided by working at pH values of 11 or less, but then the time required for development becomes excessive for ordinary purposes. EXPERIMENTAL PROCEDURE
The general experimental procedure was similar to that employed in previous work with hydroquinone (2). Oxygen-free solutions were used, and development was carried out at 20°C. f 0.05" under an atmosphere of nitrogen. The photographic material was a normal motion-picture positive emulsion. Exposures were made on the standard Eastman type IIb sensitometer, and the exposures, E , are in terms of meter-candle-seconds. Gamma refers to the sloDe of the straight-line portion of the curve obtained by plotting density, D, against log E (7). THE SILVER-DENSITY
RELATIONSHIP
The most convenient method of measuring the extent of development makes use of the optical densities of the sensitometer steps. For kinetic purposes, 1
Communication No. 933 from the I h d a k Research Laboratories.
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T. H. JAMES
however, it is important to knoiv the amounts of silver formed. In the present invest,igation, simple relations vere found between density and silver under most, of the experimental conditions. Density, therefore, could be used as a quantitative measure of the progress of development. -4t constant exposure and varying degrees of development, a linear relation exists between log ;ig and log P. This is illustrated by the plot in figure 1, Tyhich may be expressed by the linear equation : log Ag = 1.42 log D
+ Constant
This is approximately the same relation as that found previously for development by hydroquinone under simple experimental conditions. The theory covering this relation has already been given (2).
05t
I
I
"
I
"
'
0 1 030'
06
I
+
08
IO
I2
I4
L O G hy
FIG.1
FIG.
2
FIG.1. Silver-density relation for constant esposure FIO.2. Effect of bromide on development by hydroxylamine: 0 , R , pH = 10.55; R , pH = 9.96; X , 4 j t , pH = 10.55,
a,
The density-,silrer ratio did not vary greatly with exposure for a fixed degree of development, but the data show a definite trend. A plot of D/Ag against log E gave a substantially straight line. This is the same relationship which Sheppard reported (9) as holding for the same emulsion developed in certain conventional developing solutions. Data for hydroxylamine are given in table 1. KINETICS
The rate of development above a pH of about 10.0 increases in a regular iashion with pH. Below a pI-1 of 10.0, development of the silver bromide emulsion ivas very sloiv, and changes occurred in the color of the reduced silver and in the density-silver relation. This change wra,s accompanied by indications t,hat a solvent action of the hydroxylamine wvas encroaching upon the normal development reaction. Data for the "normal del-elopment" range are given in table 2 for different amounts of excess bromide-ion concentration. >lost of the data are for an exposure of log E = 1.45. Similar results were obtained for
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PHOTOGRAPHIC DEVELOPMENT BY HYDROXYLAMINE
other exposure values. Rates are given in terms of R = bD/At, where t is in minutes and the increment is taken a t D = 0.80, and l/t, where t is the time in minutes required to attain a density of 0.20. (The column headed R' gives some rate values for D = 0.40 and log E = 0.85.)
"?OH,
TABLE 1 Density-silver ratio ,for development by hydrozylamine 0.Ot M ; p l l , 10.8;development, 40 min. to gamma 1.22; Ag in terms of micromoles per circular area of 0.794om.diameter LOG
1
E
1.75 1.45 1.15 0.85 0.55
I
D
D/Ag
Ag
1.96 1.74 1.31 1.00 0.635
1.03 0.98 0.75 0.58 0.3%
1.90 1.83 1.78 1.72 1.65
TABLE 2 Effect of p H , hydroxulamine concentration, and bromide-ion concentration on rate of development PH
9.96 10.55
1l.W 12.7
Br-
NHiOH
M
M 0.04
0 0 0 0
0.10
0.04 0.04
0.025 0.058 0.32
0.04
0.90
0.25 0.84 3.23
0.04 0.04
0.021 0.054
0.038 0.125
0.044
0.067 0.100 0.588 1.0 2.7
9.96 10.55
0.0002
10.55
0.00067 0.00067 O.OOO67 0.00067 0. GOO67
0.04 0.04
0.0002
R'
R
0.04 0.04
0.061 0.253 0.40
0.04
0.80
0.02
0.039 0.067 0.112
0.050
10.8
0. 00067 0.0006i 0.00067
12.7 12.7 12.7 12.7 12.7
0.00067 0. OOO67 0.0006i 0. W 6 7 0.00067
0.0033 0.005 0.010 0.020
0.140
0.32 0.52
0.040
0.80
0.29 0.43 0.91 1.5 2.7
10.8
11.9 12.3 12.7 10.8 10.8
0.04 0.08
0 20
0.025 0.040 0.176 0.28 0.54
0.100 0.196 0.102 0.155 0.22 0.38 0.54
A plot of log R against pH yields a reasonably straight line with a slope of about 0.6. The slope increases somewhat at the lowest pH values. Likewise, a plot of log R against log [NH20H] yields a line with slope 0.65 for a, pH of 12.7, and slope 0.75 for a pH of 10.8. These results imply that the active species
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T. H. JAMES
in the hydroxylamine developer is the ion, NH20-, and that this ion reacts in the adsorbed state (Freundlich isotherm). The results are in complete agreement with previous findings for the catalyzed reduction of pure silver chloride precipitates ( 5 ) . The l / t rates are complicated by the presence of an electrical barrier effect (5, lo), and the values given in table 2 show some raggedness. However, the general results indicate a weaker adsorption of hydroxylamine ion during the “induction period” of development. An analysis of the effect of excess bromide ion on the rate of development shows a linear decrease in R with increase in bromide-ion concentration (figure 2). The effect upon the l / t rates, however, is relatively much larger a t small bromidpion concentrations. This is analogous to results obtained with simple hydroquinone developers, and may be explained on the basis of the electric barrier effect during the induction period. Sodium sulfite is a normal constituent of the conventional developing solution. When added in moderate amounts, its primary purpose is to retard the oxygen oxidation of the developing agent and to combine with the oxidation products (either of oxygen oxidation or of development) to form harmless substances. The oxidation products, if left to themselves, may have a marked effect upon the development kinetics ( 2 ) and may also produce stain. The two primary functions of sulfite in the conventional developer are absent in the case of a hydroxylamine developer. Hence, hydroxylamine is useful for a study of the secondary effects of sulfite in development, such as those resulting from the solvent action upon the silver halide. The addition of small amounts of sodium sulfite to a hydroxylamine deiTeloper had no measurable effect upon the rate of development or the character of deielopment. Larger amounts produced a decrease in rate and, in extreme cases, a shift in the character of development completely to that of the so-called “physical” type. Apparently, the solvent action of the sulfite can isolate the development centers from the main body of the silver bromide if the development action a t the silver-silver halide interface is too slow. Development in that caye proceeds by x-ay of solution of the silver halide, followed by catalytic reduction of the silver ions at the development centers. This catalytzc reduction of silver ions adsorbed from sdution onto silver nuclei is the probable mechanism of normal “physical” development. Table 3 gives data on the change in rate with sulfite concentration at pH = 10.8 and a hydroxylamine concentration of 0.04 -11. Evidently the decrease in rate is due primarily to the solvent action of the sulfite. Sodium sulfate, used in place of the sulfite, produced only a slight decrease in rate (column 3). A complete transition to physical development occurred between sulfite concentrations of 0.05 and 0.20. The transition region shifted to higher sulfite concentrations with increasing hydroxylamine concentration. This is due to the increase in rate of the interface reaction, When hydroxylamine was used a t a pH of 12.7, where development is relatively rapid, no transition was observed
GO 1
PHOTOGRAPHIC DEVELOPMEKT BY HYDROXTLShfINE
even when the sulfite concentration was increased to 0.80 and the hydroxylamine concentration decreased to 0.005. Similar results were obtained when ammonia was added to the developer in place of sulfite. The transition in this case occul*red a t lower ammonia concentrations than the corresponding sulfite concentrations. The observed decrease in reaction rate caused by these two agents indicates a more rapid reaction a t the solid silver-silver halide interface during normal development (absence TABLE 3 Effect of sulfite upon hydroxylamine development “SOH, 0.04 M ; pH, 10.8; excess Br-, 0.00067 . I I
1
SALT CONCENTBATION
R WanSO4
R (NaiSO4
-
M
0.062 0.063 0.062 0.055 0.027 0.003
0 0.0025
0.010 0.050 0.100 0.200
0.062 0.061 0.060
TABLE 4 Effect of bromide and pH upon relative fog formation DEVELOPED TO GAMMA
KBr Fog a t pH
0 0.0002 0.00067 0.0020 0 .IN67
-
0.14 0.02 0.015 0.01
j
= 0.80
Fog at pH = 12.7
10.55
I
0.42
1
DEVELOPED TO
1
D
* 1 5 , LOG E = 1.45
__
Fog at pH = 10.55
Fog a t pH = I2 7
0.17
0.40
*
0.02 0.02 0.02
0.19 0.01
0.01
TABLE 5 Rates of initiation of fog at pH = 18.7
h”%OH coneentration.~., , , , . . . . . . . . . . . . . . . . . 1,inminutes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
0.04
0.25
j
0.02 0.45
I
0.01 0.85
~
0.005 0.0025 1.70 13.30
of solvent effect) than can be produced by the aid of even a strong solvent when development is proceeding according to the mechanism of the “physical” type. FOG PRODUCTION BY HYDROXYLAMINE
Fog production on a comparatively insensitive, slightly ripened emulsion, such as the one used in this work, is likely to be initiated by an uncatalyzed reaction (4). I n the case of silver chloride and bromide precipitates, the conditions which favor the uncatalyzed reaction relative to the catalyzed are, primarily,
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T. E. JAMES
high pH values and low excess chloride or bromide concentrations. These are likewise the factors which fay~or fog formation during development by hydroxylamine. The effect of bromide in suppressing fog relative to image density is particularly marked. Data are given in table 4 for development carried to equal gamma and to equal density. A comparison of the fog densities at pH values of 10.55 and 12.7 likewise shows a definite increase in fog with pH for constant bromide excess. Probably the rate of the uncatalyzed reaction increases proportionally with the concentration of the hydroxylamine (1). The actual rate of fog formation in the visible region, however, will be complex. The silver formed by the initial uncatalyzed reaction n-ill eventually form nuclei which can act as catalysts, so that the measured rates will depend upon both the catalyzed and the uncatalyzed reactions. Some tentative rates for the uncatalyzed initiation of fog were obtained by extrapolating fog curves to D = 0.01, and following the experimental procedure previously used for hydroquinone (4). Table 5 gives the t)imes required to obtain a density of 0.01 (intensified as previously described) for various hydroxylamine concentrations. A plot of t against the reciprocal of the hydroxylamine concentration yields a straight line, which is evidence of a direct proportionality between the rate of initiation of the fogging reaction and the hydroxylamine concentration. However, the data must be regarded as of doubtful quantitative significance, even though they support the expected relation. SUMMARY
The kinetics of development of an actual photographic emulsion by hydroxylamine were studied. The results are in accord with those of previous studies of the reduction of pure silver chloride and bromide. The catalytic mechanism of the latter reactions applies also to photographic development. Fog formation is due primarily to an uncatalyzed reaction. REFERESCES (1) JAMES, T. H.: J. .in]. Chcm. Soc. 61, 2375 (1930); 62, 536, 1645 (1940); 64, 731 (1942). (2) JAMES, T. H . : J. Phys. Chem. 43, 701 (1935); 44, 42 (1940). (3) JAMES,T. H . : J . Chem. Phys. 10, 464, 744 (1942). (4) JAMES,T. H.: J. Franklin. Inst. 234, 3 i l (1942). (5) JAMES,T. ?I.: J . Chem. Phys. 11, 338 (1543). (6) J . ~ M E S T. , H., A X D KORNFELD, G . : Chem. Rev. 30, 1 (1942). ( i ) MEES, C. E. K.: The T h e o r y of the Photogyaphie Pvocess. The Macmillan Company, New York (1042). (8) XICHOLS, M. L.: J. 6 m . Cheni. Sor. 56, s-il (1031). (0) SHEPPARD, 6 . E . : “Colloid-Chemical Aspects of Photographic Development” t o appear in Colloid C h e m i s t q t , Tlieorelical and A p p l i e d , Vol. V, edited by Jerome Alexander. Reinhold Publishing Corporation, Sew Toric. (10) S H E P P A ~P.DE., , . ~ S DMEES,C. E. K . : Iiiaestigcltiotis of the T h e o i . ~of Ihe Photographic Process, p. 141 ff. Longmans, Green and Company, S e w York (1907).
