Magnesium chloride particles with a truncated structure, catalytic component supported on these particles, polyolefins obtained by employing this catalytic component, procedures for manufacturing these products

The process for the preparation of the MgCl.sub.2 having the shape essentially of two truncated right cones connected by their larger bases, which truncated cones are incurved towards the axis of symmetry, perpendicular to the bases, at the intersection of the envelope of the truncated cones with two orthogonal planes passing through the said axis of symmetry comprising dissolving MgCl.sub.2 in an alcohol, emulsifying the alcohol solution in a liquid dispersant which is a nonsolvent and inert in relation to the solution and precipitating the MgCl.sub.2 in the form of a MgCl.sub.2 -1,4-dioxane complex by addition to the emulsion of 1,4-dioxane.

A catalytic component comprising MgCl.sub.2 particles impregnated with a transition metal compound, said particles having essentially the shape of two truncated right cones connected by their larger bases, which truncated cones are incurved towards the axis of symmetry perpendicular to the bases, at the intersection of the envelope of the truncated cones with two orthogonal planes passing through the said axis of symmetry.