XXXII. On the measurement of particle size by the X-ray method

Abstract

The difficulty involved in measuring the true diffraction broadening caused by the diffraction of X-rays by small crystailites is discussed. A simple relationship is shown to exist between the Jones method of determining the line broadening and the definition of Warren, which is , the latter replacing the Scherrer definition β _Scherrer=B-b, which Warren asserts is incorrect. The intermediate value is not very different from that using the Jones curve from a molybdenum calibration specimen for the particle size of colloidal gold, nor from that of the author for graphite. Thus the need for carrying out a lengthy series of graphical integrations to obtain a Jones curve no longer seems to be required. It is also shown how a sudden onset of growth in a small fraction of the crystallites in the specimen leads to extremely high values of the particle size. In order to interpret the result correctly as a real growth of the entire specimen or as merely the increase in percentage of the portion greater than 1000 A. in size, the use of a large (19 cm. diameter) Debye-Scherrer camera is shown to be essential. An approximate relationship between the apparent fractional increase in particle size and the weight fraction of the specimen greater than 1000 A. is given. An anomaly in the growth of carbon crystallites from heat-treated cellulose is cited as a specific example.