New diamond anvils with conical support are introduced. Compared to conventional anvils the new design offers superior alignment stability, larger aperture, and reduced cost owing to significantly smaller anvil diameters. Except for table and culet, all surfaces are precision ground on a lathe, which lowers cost compared to faceted anvils. The conical design allows for steel supports, which are significantly easier and cheaper to manufacture than tungsten carbide supports. Conical support also prevents seat damage upon diamond failure. An additional new feature of the anvils is the roughened outer portion of the culet, which increases friction between the anvils and the gasket. This increases the height to diameter ratio of the pressure cell and prevents bonding between gasket and diamond, which causes ring cracks during pressure release. This technique replaces complicated diamond coating procedures. The anvils have been extensively tested for culets ranging from 0.1 to 1 mm diameter up to megabar pressures. A new anvil shape with cup-shaped culets to further increase the cell volume and gasket stability is also introduced.

We report high-pressure measurements for the melting curve of Ti, V, Cr, Mo, Ta, W, Fe, Co, and Ni. Measurements were made in a laser-heated diamond-anvil-cell to nearly 100 GPa and 4000 K. The bcc metals have surprisingly small melting slopes which approach zero at high pressure. The melting curves of Co, Ni, and Fe are nearly parallel. Several ab-initio calculations for the melting of Fe are incompatible with the present results.