When a laser beam is used to perform shape processing on an edge surface of a disk-shaped glass plate, in order to suppress strain (retardation values) in the main surface of the glass plate, the disk-shaped glass plate is floated above a base, and the edge surface of the glass plate is processed into a target shape by irradiating the edge surface with the laser beam while contactlessly heating the glass plate in a state where the glass plate is floated, and moving the laser beam relative to the edge surface in the circumferential direction of the disk-shaped glass plate.

A magnetic-disk glass substrate contains an alkaline earth metal component as a glass composition and includes a pair of main surfaces, and an outer circumferential side edge surface that is a mirror surface. The outer circumferential side edge surface includes a surface having a roughness percentage of 40% or more when a bearing ratio of a roughness cross-sectional area is 50% in a bearing ratio curve of roughness cross-sectional areas obtained when a surface roughness of the outer circumferential side edge surface obtained after the outer circumferential side edge surface is etched by 2.5 μm is measured.

A glass for magnetic recording medium substrate is an amorphous oxide glass. In terms of mol %, SiO.sub.2 content ranges from 45 to 68%, Al.sub.2O.sub.3 from 5 to 20%, total content of SiO.sub.2 and Al.sub.2O.sub.3 60 to 80%, B.sub.2O.sub.3 from 0 to 5%, MgO from 3 to 28%, CaO from 0 to 18%, total content of BaO and SrO 0 to 2%, total content of alkali earth metal oxides from 12 to 30%, total content of alkali metal oxides from 3.5 to 15%, and at least one kind selected from the group made of Sn oxide and Ce oxide being included, a total content of Sn oxide and Ce oxide ranges from 0.05 to 2.00%, a glass transition temperature ≥625° C., a Young's modulus ≥83 GPa, a specific gravity ≤2.85, and an average linear expansion coefficient at 100 to 300° C.≥48×10.sup.−7/° C.

A method for plating nickel onto a glass surface of a substrate by sequentially contacting the surface with a solution having an oxidizing agent, a solution containing a silane compound, a Pd/Sn solution, and a nickel ion-containing solution, thereby accomplishing an electroless nickel plating process.

A magnetic-disk substrate has a pair of main surfaces, and an arithmetic average roughness Ra of each of the main surfaces is 0.11 nm or less. The arithmetic average roughness Ra is a value obtained through measurement using an atomic force microscope provided with a probe having a probe tip provided with a carbon nanofiber rod-shaped member. The magnetic-disk substrate is made of glass or aluminum alloy.

A filamentation process uses ultrafast laser pulses to form a line of filaments or perforations in a glass material in sheet form. The glass material is then cleaved using mechanical or thermal stress to form a glass substrate with a planar doughnut shape having an inner circular edge and an outer circular edge. The inner and outer edges may exhibit filamentary damage from the filamentation process, including microcracks and pillar shaped funnels along an entire length of the edge. The inner and/or outer edges may then be treated by polishing only, by etching only, or by etching and polishing to remove a portion of the filamentary damage to improve the strength of the edges. The resulting glass substrate may be used in a magnetic medium for a magnetic recording device, wherein it provides an edge strength sufficient to withstand high force shocks to the device.

A non-metallic media substrate includes a disc-shaped substrate body having at least one media storage surface on a face thereof. The substrate body has a center opening having an inner diameter and an outer diameter surface, and the substrate body has a thickness. The substrate further includes an annular groove at the outer diameter of the media substrate, the annular groove having chamfered edges and an internal concavity extending toward the inner diameter.

The present invention relates to a glass composition that includes: 57 to 75 percent by weight of SiO.sub.2; 3 to 11 percent by weight of Al.sub.2O.sub.3; 6 to 11 percent by weight of Na.sub.2O; 16 to 21 percent by weight of CaO; 0.01 to 0.1 percent by weight of Li.sub.2O; and less than 0.05 percent by weight of K.sub.2O. Each percent by weight is based on total weight of the glass composition. Glass products are also provided that have a bulk glass composition as described above. The glass products, such as flat glass products and glass substrates, have a strain point of at least 590° C. and a thermal expansion of at least 7.4 ppm/° C. The present invention also relates to magnetic recording articles and photovoltaic cells that include a glass substrate that has a bulk glass composition as described above.

The present invention provides a glass composition including, as components, in mol %: 50 to 70% SiO.sub.2; 10 to 20% Al.sub.2O.sub.3; 2 to 5% MgO; 3 to 15% CaO; 3 to 15% Li.sub.2O; 3 to 15% Na.sub.2O; and 0 to 5% K.sub.2O, wherein when a content of a component X in mol % is expressed as [X], [Al.sub.2O.sub.3]— [R.sub.2O] is less than −0.5%, where [R.sub.2O] is the sum of [Li.sub.2O], [Na.sub.2O], and [K.sub.2O].

A substrate for a magnetic disk has a disk shape. The substrate has a diameter D of 85 mm or more and a thickness T of 0.6 mm or less. When an impact is applied to the substrate under conditions of 70 (G) and 2 (msec) in a normal direction of main surfaces of the substrate in a state in which an inner circumferential end portion of the substrate is fixed, the maximum amplitude of vibration in a thickness direction of an outer circumferential end portion of the substrate is 0.25 mm or less, the substrate is a non-magnetic metal substrate, and regarding the Young's modulus E and the thickness T of the substrate, a value of E.Math.T.sup.3 is 3 to 18 (GPa.Math.mm.sup.3).