Process for the preparation of homogeneous metal oxide varistors

Claim 2

A process for making a homogeneous metal oxide varistor power comprising the steps of: (A) dissolving in an aqueous solvent from about 6.9 w/o to about 33.0 w/o of soluble compounds, which are soluble in water or acid, to form an aqueous solution, said soluble compounds containing metals which are desired in a homogeneous metal oxide varistor powder, said metals being selected from the group consisting of Al, B, Bi, Co, Cr, K, Mn, Ni, Pb, Sb and combinations thereof; (B) mixing from about 68.0 w/o to about 93.2 w/o of insoluble compounds, as a powder, which are not soluble in water or acid, into the aqueous solution of step (A) to form a solution containing a suspension, said insoluble compounds being selected from the group consisting of ZnO, TiO 2 and combinations thereof; (C) evaporating to dryness the solution containing the suspension from step (B) to form a homogeneous material; and (D) calcining the homogeneous material from step (C) to an oxide of each metal contained therein at temperatures up to 800° C. to form a homogeneous metal oxide varistor powder.

Claim 3

A process for making a homogeneous metal oxide varistor powder comprising the steps of: (A) dissolving in an aqueous solvent from about 6.8 w/o to about 33.0 w/o of soluble compounds which are soluble in water or acid to form an aqueous solution, said soluble compounds containing metals which are desired in a homogeneous metal oxide varistor powder, said metals being selected from the group consisting of Al, B, Bi, Co, Cr, K, Mn, Ni, Pb, Sb and combinations thereof; (B) mixing from about 68.0 w/o to about 93.2 w/o of insoluble compounds which are not soluble in water or acid, as a powder, into the aqueous solution of step (A) to form a solution containing a suspension, said insoluble compounds being selected from the group consisting of ZnO, TiO 2 and combinations thereof; (C) evaporating to dryness the solution containing the suspension from step (B) to form a homogeneous dried cake; (D) comminuting the dried cake of step (C) to form a powder; (E) calcining the powder of step (D) up to about 800° C. to remove volatiles and to convert the powder to the oxides of each metal present to form a sintered powder; (F) comminuting the sintered powder of step (E) to form a fine sintered powder; (G) adding and mixing binders to the fine sintered powder from step (F) to form a homogeneous slurry; (H) drying the slurry from step (G) to form a dried powder; (I) pressing the dried power of step (H) at a temperature up to about 1400° C. to form a sintered body; (J) applying an electrically conductive coating for attaching electrical leads to the sintered body of step (I); (K) attaching electrical leads to the sintered body of step (J); and (L) encapsulating the body from step (K) to form an encapsulated homogeneous metal oxide varistor.

Claim 4

A process for making a homogeneous metal oxide varistor powder comprising the steps of: (A) dissolving in an aqueous solvent from about 6.8 w/o to about 33.0 w/o of soluble compounds which are soluble in water or acid to form an aqueous solution, said soluble compounds containing metals which are desired in a homogeneous metal oxide varistor powder, said metals being selected from the group consisting of Al, B, Bi, Co, Cr, K, Mn, Ni, Pb, Sb and combinations thereof; (B) mixing from about 68.0 w/o to about 93.2 w/o of insoluble compounds which are not soluble in water or acid, as a powder, into the aqueous solution of step (A) to form a solution containing a suspension, said insoluble compounds being selected from the group consisting of ZnO, TiO 2 and combinations thereof; (C) evaporating to dryness the solution containing the suspension from step (B) to form a homogeneous dried cake; (D) comminuting the dried cake of step (C) to form a powder; (E) calcining the powder of step (D) up to about 800° C. to remove volatiles and to convert the powder to the oxides of each metal present to form a sintered powder; (F) comminuting the sintered powder of step (E) to form a fine sintered powder; (G) adding and mixing binders to the fine sintered powder from step (F) to form a homogeneous slurry; (H) drying the slurry from step (G) to form a dried powder; (I) pressing the dried power of step (H) at a temperature up to about 1400° C. to form a sintered body; (J) applying an electrically conductive coating for attaching electrical leads to the sintered body of step (I); (K) attaching electrical leads to the sintered body of step (J); and (L) encapsulating the body from step (K) to form an encapsulated homogeneous metal oxide varistor.

Claim 5

A process in accordance with claim 2 wherein said drying in step (H) is pan drying.

Claim 6

A process in accordance with claim 2 wherein said drying in step (H) is spray drying.

Claim 7

A encapsulated homogeneous metal oxide varistor made by the process in accordance with claim 2.