Provided is a blade dicing device for wafers that cuts (dices) a wafer with the grit on a cutting blade and separates the wafer into individual chips, and that can minimize process defects when dicing compound semiconductor wafers made of high-hardness materials such as SiC. The device includes a body, a cutting blade protruding from the outer periphery of the body, and grit bonded and attached to the outer periphery of the cutting blade and cutting a wafer, wherein the length of the grit is 2 m to 4 m.

Provided is a blade dicing device for wafers that cuts (dices) a wafer with the grit on a cutting blade and separates the wafer into individual chips, and that can minimize process defects when dicing compound semiconductor wafers made of high-hardness materials such as SiC. The device includes a body, a cutting blade protruding from the outer periphery of the body, and grit bonded and attached to the outer periphery of the cutting blade and cutting a wafer, wherein the length of the grit is 2 m to 4 m.

Provided is a glass for a magnetic recording medium substrate or for a glass spacer for a magnetic recording/reproducing apparatus, in which a mole ratio of the total content of Al.sub.2O.sub.3 and MgO relative to the total content of SiO.sub.2 and CaO [(Al.sub.2O.sub.3+MgO)/(SiO.sub.2+CaO)] is in a range of 0.417 or more and 0.6 or less, the total content of SiO.sub.2 and Al.sub.2O.sub.3 (SiO.sub.2+Al.sub.2O.sub.3) is in a range of 64 mol % or more and 85 mol % or less, the total content of SiO.sub.2, Al.sub.2O.sub.3, MgO, and CaO (SiO.sub.2+Al.sub.2O.sub.3+MgO+CaO) is in a range of 87 mol % or more and 98 mol % or less, the Na.sub.2O content is 0 mol %, and an average linear expansion coefficient of the glass at 100 C. to 300 C. is 6810.sup.7/ C. or less.

Provided is a glass for a magnetic recording medium substrate or for a glass spacer for a magnetic recording/reproducing apparatus, in which the total content of Li.sub.2O, Na.sub.2O, K.sub.2O, B.sub.2O.sub.3, and ZnO (Li.sub.2O + Na.sub.2O + K.sub.2O + B.sub.2O.sub.3 + ZnO) is in a range of 0 mol% or more and 3 mol% or less, the mole ratio of the total content of Al.sub.2O.sub.3 and MgO relative to the total content of SiO.sub.2 and CaO [(Al.sub.2O.sub.3 + MgO) / (SiO.sub.2 + CaO)] is in a range of 0.30 or more and 0.6 or less, the total content of SiO.sub.2 and Al.sub.2O.sub.3 (SiO.sub.2 + Al.sub.2O.sub.3) is in a range of 64 mol% or more and 85 mol% or less, and the total content of SiO.sub.2, Al.sub.2O.sub.3, MgO, and CaO (SiO.sub.2 + Al.sub.2O.sub.3 + MgO + CaO) is in a range of 87 mol% or more and 98 mol% or less.