The flux of tritiated water (HTO) through pieces of stratum corneum at four different levels of hydration has been measured. The concentration of water in the stratum corneum, the concentration of HTO in the presenting solution, and the thickness, density, and weight per unit area of the dry stratum corneum are known. The thickness of the hydrated stratum corneum and the permeability and diffusion constants of HTO were calculated. From these in vitro data it is possible to calculate the in vivo thickness of the stratum corneum, its water concentration profile, and the flux of water (transepidermal water loss) at environments of different relative humidities. Both the transepidermal water loss and the water concentration profile change very little as the environmental relative humidity increases from 0 to 80%. The small decrease in the water concentration of the surface layers of cells as the relative humidity becomes very low, however, may cause an observable alteration in the physical characteristics of the surface layers.
In contrast to other inorganic solids, glasses may be permanently compacted by application of pressures of the order of 104 to 105 atmospheres. This effect was studied on two simple oxide glasses (SiO2 and B2O3) and several silicate glasses. The effect of compacting was studied by measuring the densities, dimensions, and x-ray diffraction patterns. A definite threshold pressure is observed in vitreous silica and silicate glasses, under which no effect takes place and above which the collapse takes place readily. Vitreous boric oxide behaves in a different manner, collapsing gradually, starting at the lowest pressures. Vitreous boric oxide exhibits also plastic flow with subsequent strain hardening. X-ray diffraction measurements performed on vitreous silica and boric oxide indicate that the compacting proceeds on the atomic scale, leaving, however, the short-range order of the basic structural units unchanged. The density of compacted glass can be restored to the original value by annealing to sufficiently high temperatures. Activation energy of this process was determined in the case of vitreous boric oxide.
The structure of quartz and vitreous silica disordered by heavy irradiation (1020 neutrons per cm.2) of fast neutrons was studied by means of X-ray diffraction and infrared spectroscopy. The results indicate that the structure of the disordered amorphous form of silica resembles closely that of vitreous silica. The average Si-0 distance (1.61 a.u.) remains unchanged, but the average Si-0-Si bond angle decreases from 142' to 138'; the radial distances of the more distant neighbor atoms show a wider distribution in the disordered material. It is suggested that the disordered form of silica results from thermal effects (thermal spikes) accompanying the passage of knocked-on atoms through the solid.
Infrared spectra of α- and β-quartz, α- and β-cristobalite, and vitreous silica were studied by the reflection method using natural and polarized radiation in the 700 to 1400 cm−1 wave number interval. By measuring the reflecting powers at two different angles of incidence, the indices of refraction and extinction were obtained and the absorption bands could be correctly located, sometimes at variance with the existing data, based on reflection maxima alone. The strong band at 1055 cm−1 in α-quartz and at 1095 cm−1 in α-cristobalite and vitreous silica can be assigned as a valence stretching Si lim ←–O lim →–Si lim ← vibration. Other observed bands are consistent with the already existing assignments. The effect of temperature on the total intensity and width of the bands was studied in a temperature interval between 4°K and 880°K.
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