Abstract: A catalyst for polymerizing ethylene, especially at high temperature and high pressure, comprising at least two halogen compounds of transition metals, one of which is a titanium trichloride syncrystallized with aluminum chloride. The catalyst has the formula(TiCl.sub.3, 1/3AlCl.sub.3)(MX.sub.3).sub.x (MgX.sub.2).sub.ywherein 0.3.ltoreq.x.ltoreq.3, 0.ltoreq.y.ltoreq.20, M is a transition metal of Groups V B and VI B of the Periodic System, and X is a halogen. The second transition metal is preferably vanadium, chromium, molybdenum, or tungsten. The catalyst is made by subjecting titanium trichloride syncrystallized with aluminum chloride, the trivalent halide of M, and, optionally, anhydrous magnesium halide to a milling step in which the milling energy is at least equal to three kWh per kg of solid material treated, which results in a binary solid solution structure Ti-M of which the dimension of crystallites is less than or equal to 100 Angstroms.

Abstract: An organometallic halide having the formula:(RMX)(MX.sub.2).sub.a (MR.sub.2).sub.b (MH.sub.2).sub.cwherein a.congruent.0.45, b.congruent.0.15, and c.congruent.0.30, X is a halogen, R is a hydrocarbon radical, and M is a metal selected from the group consisting of magnesium, zinc, beryllium, and calcium is prepared by a continuous dry process by reacting an organic monohalide RX and a metal M in the form of convex solid grains of a size between 1 and 15 mm. The reaction temperature is lower than the temperature at which decomposition of the organometallic halide RMX begins and at least 10.degree. C. higher than the boiling point of the organic monohalide. The reaction may also take place in the presence of an organometallic derivative comprising a hydroxy group or an enolysable ketone group. The resulting organometallic halide may be used for the synthesis of anhydrous magnesium halide or for the reduction of titanium tetrachloride.

Abstract: A catalytic component having the formula(MX.sub.a) (MgX.sub.2).sub.b (RMgX).sub.c (MHgX).sub.dwherein M is a metal selected from group VI B and group V B of the Periodic Classification, X is a halogen, R is a hydrocarbon radical, 2.ltoreq.a .ltoreq.3.5, 1.ltoreq.b.ltoreq.30, 1.ltoreq.c.ltoreq.8 and 0.ltoreq.d.ltoreq.10 is prepared by reducing a metallic halide of the metal M, the valency of said metal being 4 if a metal of group IV B is concerned and 4 or 5 if a metal of group V B is concerned, by means of at least one organomagnesium compound having the formula RMgX, the said organomagnesium compound being used in the solid state and reduction of the metallic halide being carried out under a pressure lower than or equal to atmospheric pressure and at a temperature lower than the decomposition point of said organomagnesium compound under the pressure concerned but at least 10.degree. higher than the boiling point or sublimation point of the metallic halide under the pressure concerned.

Abstract: A catalyst comprising the product obtained by bringing into contact (a) a compound of magnesium comprising at least one species selected from the group consisting of magnesium monohalides (MgX), halo-magnesium hydrides (HMgX) and magnesium hydride (MgH.sub.2), X being a halogen and the said species MgX or HMgX being obtained by thermal decomposition of a powdery organo-magnesium halide R.sub.1 MgX wherein R.sub.1 is an organic radical; and (b) at least one halide of a transistion metal selected from the group consisting of titanium and vandium, the valency of said metal in said halide being lower than or equal to 3, the quantities of (a) and (b) being such that the atomic ratio of magnesium to said transistion metal is between 1 and 25, and a catalyst system including the catalyst that is suitable for use in the polymerization of olefins and particularly ethylene.

Abstract: An organometallic halide having the formula:(RMX)(MX.sub.2).sub.a (MR.sub.2).sub.b (MH.sub.2).sub.cwherein a.ltoreq.0.45, b.ltoreq.0.15, and c.ltoreq.0.30, X is a halogen, R is a hydrocarbon radical, and M is a metal selected from the group consisting of magnesium, zinc, beryllium, and calcium is prepared by a continuous dry process by reacting an organic monohalide RX and a metal M in the form of convex solid grains of a size between 1 and 15 mm. The reaction temperature is lower than the temperature at which decomposition of the organometallic halide RMX begins and at least 10.degree. C. higher than the boiling point of the organic monohalide. The reaction may also take place in the presence of an organometallic derivative comprising a hydroxy group or an enolysable ketone group. The resulting organometallic halide may be used for the synthesis of anhydrous magnesium halide or for the reduction of titanium tetrachloride.