Absorption isotherms have been determined for methylene blue absorbed from aqueous solutions on montmorillonites saturated with various cations. Surface areas are determined from observations of the amount of methylene blue absorbed on the clay required to produce optimum flocculation; this condition corresponds to in behavior is observed between a clay from Wyoming and one from Texas. The Wyoming clay gives much smaller effective flocculation areas and clearly defined saturation absorptions are not obtained. These results are attributed to relatively large particle sizes, so that external surfaces are covered when internal surfaces are only partially covered, and ultimate saturation is hindered by the large particles. With finer particles, the Texas clay gives flocculation areas nearer to those obtained with Li-and Na-clays and the apparent exchange capacities also are nearer to those obtained for the monovalent ion clays. A limitation on surface area measurements for montmorillonites with exchange capacities less than about 100 meq/100 g is discussed.

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The comminution of blocky planetary surfaces into fine‐grained regoliths was simulated by impacting a fragmental gabbro target 200 times with stainless steel projectiles (diameter = 6.35 mm; mass = 1.2g; Vi = 1.35 km/s). Initially the target fragments were 2–32 mm in size with a mean diameter of 15.2 mm, which was reduced to 0.4 mm after 200 shots. For the first 60 shots, comminution was linear with cumulative kinetic energy and, thus, essentially linear with time. The comminution efficiency, however, decreased at later stages. This could be due to a change in fracture mechanism from predominantly intergranular to predominantly intragranular and/or due to a change in partitioning of the projectile's kinetic energy from collisional fragmentation or large fragments at early times to cratering in a progressively finer‐grained medium at later stages. Mineral‐specific, preferential comminution is abundantly observed in the modal make‐up of various grain‐size fractions: plagioclase comminutes more readily than pyroxenes. Plagioclase—initially present at 54% (vol.)—comprises typically 65–70% of the 125–250 μm fraction; pyroxenes (initially at 33%) are depleted to 20–25%. This fractionation occurs in the earliest samples analyzed and is not a time‐dependent phenomenon. Bulk chemical analyses reveal a corresponding increase in Al2O3, CaO, and Na2O, and a decrease in FeO and MgO. The finest grain sizes are generally the most severely affected by differential comminution. Similar, if not exactly identical, trends are abundantly documented for lunar soil samples. These experimental findings illustrate that differential comminution is capable of producing fractionation in the finest grain sizes. They diminish the need for prominent lateral and vertical transport of components otherwise “foreign” to a lunar soil‐sampling site as postulated by some workers on the basis of multivariate chemical mixing models.

A compensation of stress induced in silicon epitaxial films heavily doped with boron was investigated. Addition of a controlled amount of germanium during the film growth allows one to attain a desired compressive or tensile stress in the film, or its complete elimination. The data shows very good correlation with a theoretical model adapted from Herzog et al. [J. Electrochem. Soc. 131, 2969 (1984)]. A 6.45 : 1 ratio of atomic concentrations of Ge and B completely eliminates stress in these films. We determined a critical amount of strain in the films, ≂2–4 μm thick, beyond which misfit dislocations are generated.

Abstract-The oxidative power of a smectite can be measured quantitatively by oxidation of hydroquinone to p-benzoquinone in a clay slurry. Oxidation takes place in the presence of 02 (air) but not N2 unless Fe 3 § or Cu 2+ are the exchangeable cations. This study examined 26 smectite samples with varying compositions and processing. The oxidative power increases with decreasing Li-fixation and increasing cation exchange capacity. Li-fixation does not depend upon the tetrahedral A1. The cation exchange capacity can decrease markedly by mere storage in water.The oxidation proceeds principally on the surface by adsorbed oxygen molecules or radicals. A mechanism is proposed. With Fe 3 § or Cu z § present, even under N2, oxidation occurs via electron transfer. With smectites containing Fe z § both the Fe and the hydroquinone are oxidized in the same reaction.