Abstract: A porous body including an inorganic fiber and an organic binder, wherein the average fiber diameter of the inorganic fiber is 2.0 ?m or less, the amount of the inorganic fiber is 90% by mass or more, the amount of the organic binder is 0.5% by mass or more and 10% by mass or less, the organic binder contains an elastomer, and the bulk density of the porous body is 30 kg/m3 or less.

Abstract: Inorganic fibers including the following composition, SiO2, Al2O3, MgO and CaO being main components, and the inorganic fibers being produced by a melting method: SiO2: 3.0 wt % or more and less than 48.0 wt %, Al2O3: more than 20.0 wt % and 80.0 wt % or less, MgO: 1.0 wt % or more and 50.0 wt % or less, CaO: 1.0 wt % or more and 50.0 wt % or less, and Fe2O3: 0.0 wt % or more and less than 1.0 wt %.

Abstract: Inorganic fibers including the following composition, SiO2, MgO and CaO being main components: SiO2: 73.6 wt % to 85.9 wt %, MgO: 9.0 wt % to 21.3 wt %, CaO: 5.1 wt % to 12.4 wt %, Al2O3: 0 wt % or more and less than 2.3 wt %, and Fe2O3: 0 wt % to 0.50 wt %.

Abstract: Inorganic fibers including the following composition, SiO2, MgO and CaO being main components: SiO2: 73.6 wt % to 85.9 wt %, MgO: 9.0 wt % to 21.3 wt %, CaO: 5.1 wt % to 12.4 wt %, Al2O3: 0 wt % or more and less than 2.3 wt %, and Fe2O3: 0 wt % to 0.50 wt %.

Abstract: Inorganic fibers including the following composition, SiO2, Al2O3, MgO and CaO being main components, and the inorganic fibers being produced by a melting method: SiO2: 3.0 wt % or more and less than 48.0 wt %, Al2O3: more than 20.0 wt % and 80.0 wt % or less, MgO: 1.0 wt % or more and 50.0 wt % or less, CaO: 1.0 wt % or more and 50.0 wt % or less, and Fe2O3: 0.0 wt % or more and less than 1.0 wt %.

Abstract: A method of etching capable of rapidly and flatly performing wet etching on a Si substrate using fluonitric acid represented by HF(a)HNO3(b)H2O(c) (where the unit of a, b and c is wt % and a+b+c=100). The etching rate of an SiO2 layer with the highly concentrated fluonitric acid is significantly lowered by the appropriate selection of its composition as compared with the etching rate of the Si substrate, and etch the Si substrate until the SiO2 layer is exposed. In this way, it is possible to rapidly etch the Si substrate and significantly enhance the flatness of the etched surface.

Abstract: There is provided with an etching method using an etching apparatus. Four arms can be positioned in a direction substantially from a center of the stage toward a peripheral portion with an angle difference of about 90°. Etchant is supplied to a first position nearest to the center of the object which is rotating, from a first etchant supply nozzle placed on a first arm. Etchant is further supplied to a second position second nearest to the center of the object, from a second etchant supply nozzle placed on a second arm. The second arm is substantially symmetrically positioned with respect to the first arm and the second arm has an angle difference of about 180° with respect to the first arm.

Abstract: A method of etching capable of rapidly and flatly performing wet etching on a Si substrate using fluonitric acid represented by HF(a)HNO3(b)H2O(c) (where the unit of a, b and c is wt % and a+b+c=100). The etching rate of an SiO2 layer with the highly concentrated fluonitric acid is significantly lowered by the appropriate selection of its composition as compared with the etching rate of the Si substrate, and etch the Si substrate until the SiO2 layer is exposed. In this way, it is possible to rapidly etch the Si substrate and significantly enhance the flatness of the etched surface.