Crystallized glass, substrate for magnetic disc, magnetic disc and method of producing crystallized glass

• US 6,270,876 B1
• Filed: 11/08/1999
• Issued: 08/07/2001
• Est. Priority Date: 11/09/1998
• Status: Expired due to Fees

• Current Assignee: NGK Insulators Limited
• Original Assignee: NGK Insulators Limited
• Inventors: Abe, Masahiro, Takahashi, Takahiro
• Primary Examiner(s): Resan, Stevan A.
• Application Number:
  US09/435,762
• Time in Patent Office: 638 Days
• Field of Search: 428/141, 428/64.1, 428/64.2, 428/64.3, 428/65.3, 428/694.ST, 428/694.SG, 501/4, 501/5
• US Class Current: 428/141
• CPC Class Codes: C03C 10/0027 containing SiO2, Al2O3, Li2O as main constituents
• CPC Class Codes: G11B 5/73921 Glass or ceramic substrates
• CPC Class Codes: Y10T 428/24355 Continuous and nonuniform or irregular surface on layer or component [e.g., roofing, etc.]

Abstract

A crystallized glass has a main crystal phase of α-quartz (SiO₂) and lithium disilicate (Li₂·2SiO₂) and has a thermal expansion coefficient of (90˜130)×10⁻⁷/K at −50° C.˜70° C. The crystallized glass mentioned above, has a following chemical composition; 70 wt %≦SiO₂≦80 wt %, 5 wt %≦Al₂O₃≦9 wt %, 7 wt %≦Li₂O≦10 wt %, 1 wt %≦P₂O₅≦3 wt %, 0 wt %≦K₂O≦3 wt %, 0 wt %≦CaO≦3 wt %, 0 wt %≦BaO≦4 wt %, 0 wt %≦ZnO≦4 wt %, 0 wt %≦Sb₂O₃≦1 wt %, 0 wt %≦ZrO₂≦6 wt %, 0 wt %≦Nb₂O₅≦6 wt %, 0 wt %≦SnO₂≦4 wt %, 0 wt %≦MoO₃≦3 wt %, 0.7 wt %≦(Nb₂O₅+SnO₂+MoO₃)≦6 wt %.

Claims

1. A crystallized glass, which has a main crystal phase of α

-quartz (SiO₂) and lithium disilicate (Li₂O·

2SiO₂) and has a thermal expansion coefficient of (90˜

130)×

10<sup>−

7</sup>/K at −

50°

C.˜

70 °

C., comprising a following chemical composition;

70 wt %≦

SiO₂≦

80 wt %, 5 wt %≦

Al₂O₃≦

9 wt %, 7 wt %≦

Li₂O<

10 wt %, 1 wt %≦

P₂O₅≦

3 wt %, 0 wt %≦

K₂O≦

3 wt %, 0 wt %≦

CaO≦

3 wt %, 0 wt %≦

BaO≦

4 wt %, 0 wt %≦

ZnO≦

4 wt %, 0 wt %≦

Sb₂O₃≦

1 wt %, 0 wt %≦

ZrO₂≦

6 wt %, 0 wt %≦

Nb₂O₅≦

6 wt %, 0 wt %≦

SnO₂≦

4 wt %, 0 wt %≦

MoO₃≦

3 wt %, 0.7 wt %≦

(Nb₂O₅+SnO₂+MoO₃)≦

6 wt %.

2. The crystallized glass according to claim 1, wherein the chemical composition is as follows;

71 wt %≦

SiO₂≦

78 wt %, 5 wt %≦

Al₂O₃≦

9 wt %, 7.5 wt %≦

Li₂O<

10 wt %, 1 wt %≦

P₂O₅≦

2.5 wt %, 0 wt %≦

K₂O≦

3 wt %, 0 wt %≦

CaO≦

3 wt %, 0 wt %≦

BaO≦

4 wt %, 0 wt %≦

ZnO≦

4 wt %, 0.1 wt %≦

Sb₂O₃≦

0.5 wt %, 0.5 wt %≦

ZrO₂≦

5 wt %, 0.7 wt %≦

Nb₂O₅≦

6 wt %, 0 wt %≦

SnO₂≦

4 wt %, 0 wt %≦

MoO₃≦

3 wt %, 0.7 wt %≦

(Nb₂O₅+SnO₂+MoO₃)≦

6 wt %.

3. The crystallized glass according to claim 1, wherein crystal particle sizes are 0.1˜

0.3 μ

m.

4. A substrate for magnetic disc, made of the crystallized glass set forth in claim 1, comprising a smoothened surface having a center line average roughness (Ra) of smaller than 7 angstrom.

5. A magnetic disc comprising the substrate for magnetic disc set forth in claim 4, a underlying layer formed on the smoothened surface of the substrate for magnetic disc, and a metallic magnetic layer formed on the underlying layer.

6. A method of producing a crystallized glass comprising the steps of;

preparing a parent glass having the following chemical composition, subjecting the parent glass to a heat treatment at 570°

C.˜

640°

C. so as to perform a nucleus generation, and subjecting the parent glass to a heat treatment at 670°

C.˜

750°

C. so as to crystallize the parent glass;

70 wt %≦

SiO₂23 80 wt %, 5 wt %≦

Al₂O₃≦

9 wt %, 7 wt %≦

Li₂O<

10 wt %, 1 wt %≦

P₂O₅≦

3 wt %, 0 wt %≦

K₂O≦

3 wt %, 0 wt %≦

CaO≦

3 wt %, 0 wt %≦

BaO≦

4 wt %, 0 wt %≦

ZnO≦

4 wt %, 0 wt %≦

Sb₂O₃≦

1 wt %, 0 wt %≦

ZrO₂≦

6 wt %, 0 wt %≦

Nb₂O₅≦

6 wt %, 0 wt %≦

SnO₂≦

4 wt %, 0 wt %≦

MoO₃≦

3 wt %, 0.7 wt %≦

(Nb₂O₅+SnO₂+MoO₃)≦

6 wt %.