Alumina glass composition and magnetic head incorporating same

In a glass composition suitable for bonding to metal alloys or metal oxides, the composition comprising oxides of phosphorus, zinc or copper or boron, aluminum, an alkali metal or alkaline earth, and having a coefficient of thermal expansion that is from about 80.degree. to about 170.times.10.sup.-7 .degree.C..sup.-1 ;

• the improvement wherein
• (a) said oxide of aluminum comprises from about 5 to about 15 mole % of said composition,
• (b) about 10 to about 35 mole % of oxide of phosphorus is present as a glass former so that said oxide of aluminum is soluble in said composition, and
• (c) said composition contains substantially zero mole % of volatiles that cause bubbling.

In a glass composition suitable for fusing to metal alloys or metal oxides, the composition having a coefficient of thermal expansion that is from about 80.degree. to about 170.times.10.sup.-7 .degree.C..sup.-1 ;

• the improvement wherein said composition comprises as mole percentages of said composition,
• 1- 40% alkali metal or alkaline earth oxide,
• 5-15% oxide of aluminum,
• 0-25% oxide of zinc or copper,
• 0-25% oxide of boron,
• 0-30% oxide of silicon, and
• 10-35% oxide of phosphorus,
• provided that an oxide of at least one of said boron, zinc, copper, and silicon is present in an amount sufficient to provide to the composition said coefficient of thermal expansion.

In a magnetic head for a magnetic recorder and reader, the head comprising magnetic metal or metal oxide bonded to a glass composition comprising oxides of an alkali metal or alkaline earth, and at least one metal oxide of a non-alkali metal in an amount sufficient to provide a coefficient of thermal expansion to said composition that is from about 80.degree. to about 170.times.10.sup.-7 .degree.C..sup.-1 ;

• the improvement wherein
• (a) from about 5 to about 15 mole % of said composition comprises an oxide of aluminum;
• (b) said composition further includes about 10 to about 35 mole % of a compatible glass former for said oxide of aluminum to render said oxide of aluminum soluble in said composition;
• and
• (c) said composition contains substantially zero mole % of volatiles that cause bubbling.

In a magnetic head for a magnetic recorder and reader, the head comprising magnetic metal or metal oxide bonded to a glass composition comprising oxides of phosphorus, zinc or copper, boron, aluminum, an alkali metal or alkaline earth;

• said composition having a coefficient of thermal expansion that is from about 80.degree. to about 170.times.10.sup.-7 .degree.C..sup.-1 ;
• the improvement wherein
• (a) said oxide of aluminum comprises from about 5 to about 15 mole % of said composition,
• (b) about 10 to about 35 mole % of oxide of phosphorus is present so that said oxide of aluminum is soluble in said composition, and
• (c) said composition contains substantially zero mole % of lead oxide and of fluorine.

In a magnetic head for a magnetic recorder and reader, the head comprising ferromagnetic metal alloy wafers laminated together with a bonding composition,

• the improvement wherein said bonding composition comprises, as mole percentages of said composition,
• 10-35% oxide of potassium,
• 5-15% oxide of aluminum,
• 5-15% oxide of zinc or copper,
• 5-15% oxide of boron,
• 0-30% oxide of silicon, and
• 10-30% oxide of phosphorus,
• said composition being further characterized by a coefficient of thermal expansion that is from about 120.degree. to about 170.times.10.sup.-7 .degree.C..sup.-1, and containing substantially zero mole % of each of lead oxide and fluorine.

In a magnetic head for a magnetic recorder and reader, the head comprising magnetic metal oxide bonded to a glass composition;

• the improvement wherein said bonding composition comprises, as mole percentages of said composition,
• 1- 30% oxide of sodium,
• 5-15% oxide of aluminum,
• 10-25% oxide of zinc or copper,
• 10-25% oxide of boron,
• 0-30% oxide of silicon and
• 10-30% oxide of phosphorus,
• said composition being further characterized by a coefficient of thermal expansion that is from about 80.degree. to about 120.times.10.sup.-7 .degree.C..sup.-1, and containing substantially zero mole % of each of lead oxide and fluorine.