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...composition of the plumes showed almost every sign that ocean water had reacted chemically with heated rock – altering the minerals of the rocky silicate seabed while the water became rich in chemicals. Presumably, the ocean water is drawn into the rock, becomes heated, reacts chemically, and escapes back up to the ocean via “hydrothermal vents”. These exist on the...

...composition akin to basalt. The global resurfacing rate by lava and fall-out from the plumes is so high that not a single impact crater has escaped burial. The heat source that powers Io’s activity is not radioactive, as for the Earth and (in the past) the Moon, but tidal. Tidal interactions between Io and the next two moons outwards, Europa and Ganymede, which take...

...composition. This is most serious for low carbon steel components, but can be avoided by coating the pattern with 2 or 3 coats of refractory slurry, then firing at approximately 1000°C. This removes the pattern, leaving a thin ceramic shell which is surrounded by sand before casting in the conventional manner. Components tend to contain less gas defects, due to vacuum...

...composition, current and voltage and shielding gas. MAG and CO2 welding CO2 welding is mainly used for welding mild steel and low-alloy steels (cheaper than argon). CO2 is really effective as a shield gas if the electrode wire contains up to 1.8% manganese, 0.5% silicon, 0.15% titanium and 0.15% zirconium, which act as deoxidising agents. Stainless steels are MAG welded...

...composition (12% silicon) the most favourable. A major problem with aluminium castings is the relatively high shrinkage that occurs during solidification. Copper-based alloys are sand cast with additions of zinc, tin and lead. When casting cast iron, the moulding material has added coal dust; this type of green sand is black. When “natural” sands are used (silica sand...