感光乳剂颗粒中杂质中心在感光过程各阶段的演变及其诠释——(Ⅰ)感光乳剂颗粒中最大潜影中心相对大小频率分布的测定

本文根据显影过程电极理论的基本概念和单个乳剂颗粒显影过程的若干动力学特征,认为在特定的条件下,单个乳剂颗粒的显影过程可以分作两个阶段:自催化阶段和快速还原阶段。在自催化阶段,决定过程速度的是显影液/潜影中心界面上电子转移的步骤,这时过程的速度与显影中心表面积的大小成正比,反应具有自催化的性质。在快速还原阶段,乳剂颗粒内部填隙银离子向显影中心附近的迁徙成为决定过程速度的步骤;这一阶段与自催化阶段相比,持续的时间极短。在这种假设的基础上,通过乳剂颗粒显影时间的频率分布求出颗粒中最大潜影中心相对大小的频率分布。该方法适用于在同样的原始乳剂和显影的条件下比较乳剂颗粒中最大潜影中心的相对大小频率分布的情况。

EVOLUTION OF THE IMPURITY CENTRES IN PHOTOGRAPHIC GRAINS AT DIFFERENT STAGES OF THE PHOTOGRAPHIC PROCESS AND ITS MECHANISTICIMPLICATIONSPART I. DETERMINATION OF THE RELATIVE SIZE-FREQUENCY DISTRIBUTION OF THE LARGEST LATENT-IMAGE CENTRES IN PHOTOGRAPHIC EMULSION GRAINS

A method of determining the relative size-frequency distribution of the largest latent-image centres in photographic emulsion grains is proposed, based on a kinetic model of the development of individual emulsion grain under specific conditions. In the model chosen, one assumes an autocatalytic growth of the centres in the autocatalytic period, which terminates on reaching a critical mass by the largest latent-image centre with a change of the rate-determining step from electron transfer across the developer solution/developing centre interface to the interstitial silver ion migration from the interior of the grain towards the bottom of the developing centre. Then begins the fast reduction period, which is short compared with the autocatalytic period and brings the development process to its completion. Proceeding from this general concept, an expression is derived relating the relative size of the largest latent-image centre in an emulsion grain to the time required for its full development under constant emulsion grain type and specific development conditions: M_i=M_c(1-t/t_i,max)³ where M_i-mass of the largest latent-image centre in an emulsion grain,M_c——critical.mass of the development centre in an emulsion grain,t——time required for the emulsion grain to be fully developed,t_i,max ——time of development required for an emulsion grain to reach M_c in the caseof M_i = 0.Experimentally, single grain layers of a monodisperse model emulsion are developed for different lengths of time in a solvents free surface developer. The exposure and development conditions are so adjusted that, at any time of development, the vast majority of the developed grains is totally reduced, and the increase in the fraction of developed grains with time of development represents an increase in the number of totally reduced grains. The developed grains are then bleached and the residual grains counted under optical microscope over a sample area comprising not less than 3000 grains to make the data statistically meaningful. The fraction of developed grains f is plotted against time of development t, which is then transformed into the relative mass M₀ of the largest latent-image centre in the emulsion grain, using the above expression. Finally, one obtains, by numerical differentiation, the first derivatives -df/dM₀ of the f-M₀ curves atvarious points, which will represent the relative size-frequency distribution of the largestlatent-image centres in the emulsion grains. The distribution curves df/dM₀-M₀.forfive exposure levels have shown a steady increase in the number of larger centres at the expense of the smaller ones with increasing exposure. Two distinct maxima persistently appeared in the distribution curves, which will be an object of subsequent investigation.