Ring Deposit Research Articles

Semiempirical method for process analysis on electric arc spray forming of Fe-0.06%C steel rings

A numerical program, which calculates the temperature profiles of electric arc spray formed (EASF) preforms, is coded on the basis of a shape forming model, droplet flight dynamics, and the boundary fitted coordinate (BFC) method for the calculation of heat transfer equations. Some thermophysical input data for the calculations, such as average droplet temperature impinging on the deposit surface, effective thermal conductivity of the deposit, and heat transfer coefficient at the interface and surface, are given by matching the experimental results with the numerical calculation results. Using the program, the temperature changes of the Fe-0 06%C steel ring deposit during the EASF process are calculated. The effects of the EASF parameters, such as substrate rotation velocity, average droplet temperature, and wire feedrate, on the temperature changes of the Fe-0.06%C steel ring preforms are also estimated.

Dark ring in southwestern Orientale Basin: Origin as a single pyroclastic eruption

A large, 154 km diameter dark annular ring, located in the southwestern part of the Orientale Basin along the Montes Rook ring, was first discovered and documented in Soviet Zond 8 images. Clementine UV‐visible multispectral data indicate that the dark ring consists of material similar to the pyroclastic glasses collected by the Apollo astronauts, with the glasses being more closely related to the orange glass beads that comprise the Aristarchus Plateau than to the crystallized black beads typical of Taurus‐Littrow. This implies relatively rapid cooling times for the eruption products. We propose that the dark ring is the manifestation of a pyroclastic eruption originating at a fissure vent, an elongate 7.5 km by 16 km depression, located near the center of the ring. The event producing the eruption began with a dike rapidly emplaced from subcrustal depths to within ∼3–4 km of the surface. The dike stabilized and degassed over ∼1.7 years to form an upper foam layer which then penetrated to the surface to cause an eruption, lasting ∼1–2 weeks. The eruption produced a ∼38 km high symmetrical spray of pyroclasts into the lunar vacuum at velocities of ∼350 to ∼420 m/s, and the pyroclastic material accumulated in a symmetrical ring around the vent. The geometry of eruption caused the deposits to accumulate preferentially in a ring representing the material ejected at 45°. The paucity of pyroclastic rings of this type on the Moon can be attributed to the low probability of a dike stalling at just the right depth (∼3–4 km) to create these eruption conditions. The detailed characteristics of this ring provide important new insight into the emplacement of pyroclastics in the more regionally continuous lunar dark mantle deposits, suggesting that their sources are dominated by effusive and Hawaiian‐style eruptions. The Orientale dark ring deposit has similarities to the pyroclastic rings on the Galilean satellite Io. Both the Orientale dark ring and Ionian eruptions involve acceleration of small particles to a high velocity in an expanding gas stream, silicate pyroclasts derived from the disrupted foam layer in the lunar case, and a mixture of silicate pyroclasts and “snowflakes” of condensing SO2 solids on Io. In both cases the silicate pyroclasts ejected from the vent are accelerated by the gas until they become decoupled and continue on ballistic trajectories controlled only by gravity. Differences in mass flux and cloud opacity between the Moon and Io are the direct result of the origin and mass fraction of the volatile phase: the accumulation of a magmatic foam layer on top of a silicate intrusion in the lunar case and the intimate mixing on Io of a steadily erupting magma and liquid SO2. The interpretation of the Orientale dark mantle ring as a pyroclastic eruption provides an alternative to the hypothesis that the dark ring represents the presence of an ancient pre‐Orientale impact structure and that the Orientale Basin cavity of excavation must therefore lie within the Outer Rook Mountain ring.

Transmission electron microscope observations of planar defects in ferrierite from Kamloops Lake, British Columbia

Transmission electron microscope observations of planar defects in ferrierite from Kamloops Lake, British Columbia