U.S. patent application number 09/395186 was filed with the patent office on 2001-12-27 for glass with high specific rigidity for recording medium.
Invention is credited to KANAMARU, MORIYOSHI, KAWANAKA, TAKAO, KUNII, KAZUTAKA, TAKAHASHI, TOMOJI.
Application Number | 20010056029 09/395186 |
Document ID | / |
Family ID | 26438124 |
Filed Date | 2001-12-27 |
United States Patent
Application |
20010056029 |
Kind Code |
A1 |
KANAMARU, MORIYOSHI ; et
al. |
December 27, 2001 |
GLASS WITH HIGH SPECIFIC RIGIDITY FOR RECORDING MEDIUM
Abstract
Oxynitride glass whose composition is represented by
Al--Si--O--N or M--Al--Si--O--N (where M denotes Ca, Mg, or rare
earth element), wherein the content of O and N as non-metallic
components is in the range of O eq %<N.ltoreq.30 eq %, with
O+N=100 eq %, the content of M, Al, and Si as metallic components
is in the range of 20 eq %.ltoreq.Al.ltoreq.30 eq % and 70 eq
%.ltoreq.Si.ltoreq.80 eq %, respectively, with Al+Si=100 eq % (if M
does not exist) and the content of M, Al, and Si as metallic
components is within the hatched area in the composition diagrams
shown in FIGS. 1 to 3, if M is Ca, Mg, or rare earth metal, or
within the hatched area in the composition diagrams shown in FIGS.
4 to 8, if the content of N is in the range of 5 eq
%.ltoreq.N.ltoreq.25 eq %. This glass is superior in specific
rigidity and fabricability. It contains nitrogen in a controlled
amount so that it has improved specific rigidity without its
specific gravity increasing.
Inventors: |
KANAMARU, MORIYOSHI;
(KOBE-SHI, JP) ; TAKAHASHI, TOMOJI; (KOBE-SHI,
JP) ; KUNII, KAZUTAKA; (KOBE-SHI, JP) ;
KAWANAKA, TAKAO; (KOBE-SHI, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Family ID: |
26438124 |
Appl. No.: |
09/395186 |
Filed: |
September 14, 1999 |
Current U.S.
Class: |
501/56 ; 501/64;
501/68; 501/69; 501/70; G9B/5.288; G9B/5.299 |
Current CPC
Class: |
G11B 5/73921 20190501;
G11B 5/8404 20130101; C03C 3/111 20130101 |
Class at
Publication: |
501/56 ; 501/64;
501/68; 501/69; 501/70 |
International
Class: |
C03C 003/11 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 1998 |
JP |
10-279038 |
Apr 2, 1999 |
JP |
11-096987 |
Claims
What is claimed is:
1. Oxynitride glass whose composition is represented by
Al--Si--O--N, wherein the content of Al and Si as metallic
components is in the range of 20 eq %.ltoreq.Al.ltoreq.30 eq % and
70 eq %.ltoreq.Si.ltoreq.80 eq %, respectively, with Al+Si=100 eq
%, and the content of O and N as non-metallic components is in the
range of 0 eq %<N.ltoreq.30 eq %, with O+N=100 eq %.
2. Oxynitride glass whose composition is represented by
Ca--Al--Si--O--N, wherein the content of Ca, Al, and Si as metallic
components is within the hatched area in the composition diagram
shown in FIG. 1, and the content of O and N as non-metallic
components is in the range of 0 eq %<N.ltoreq.30 eq %, with
O+N=100 eq %.
3. Oxynitride glass whose composition is represented by
Mg--Al--Si--O--N, wherein the content of Mg, Al, and Si as metallic
components is within the hatched area in the composition diagram
shown in FIG. 2, and the content of O and N as non-metallic
components is in the range of 0 eq %<N.ltoreq.30 eq %, with
O+N=100 eq %.
4. Oxynitride glass whose composition is represented by
Re--Al--Si--O--N (where Re denotes one or more members selected
from rare earth elements), wherein the content of Re, Al, and Si as
metallic components is within the hatched area in the composition
diagram shown in FIG. 3, and the content of O and N as non-metallic
components is in the range of 0 eq %<N.ltoreq.30 eq %, with
O+N=100 eq %.
5. Oxynitride glass whose composition is represented by
Ca--Al--Si--O--N, wherein the content of Ca, Al, and Si as metallic
components is within the hatched area in the composition diagram
shown in FIG. 4, and the content of C and N as non-metallic
components is in the range of 5 eq %.ltoreq.N.ltoreq.25 eq %, with
C+N=100 eq %.
6. Oxynitride glass whose composition is represented by
Mg--Al--Si--O--N, wherein the content of Mg, Al, and Si as metallic
components is within the hatched area in the composition diagram
shown in FIG. 5, and the content of C and N as non-metallic
components is in the range of 5 eq %.ltoreq.N.ltoreq.25 eq %, with
O+N=100 eq %.
7. oxynitride glass whose composition is represented by
Y--Al--Si--O--N, wherein the content of Y, Al, and Si as metallic
components is within the hatched area in the composition diagram
shown in FIG. 6, and the content of C and N as non-metallic
components is in the range of 5 eq %.ltoreq.N.ltoreq.25 eq %, with
O+N=100 eq %.
8. Oxynitride glass whose composition is represented by
Gd--Al--Si--O--N, wherein the content of Y, Al, and Si as metallic
components is within the hatched area in the composition diagram
shown in FIG. 7, and the content of C and N as non-metallic
components is in the range of 5 eq %.ltoreq.N.ltoreq.25 eq %, with
O+N=100 eq %.
9. Oxynitride glass whose composition is represented by
Ce--Al--Si--O--N, wherein the content of C, Al, and Si as metallic
components is within the hatched area in the composition diagram
shown in FIG. 7, and the content of C and N as non-metallic
components is in the range of 5 eq %.ltoreq.N.ltoreq.25 eq %, with
O+N=100 eq %.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a glass suitable for use as
a disk for recording medium such as magnetic disk.
[0003] 2. Description of the Related Art
[0004] In the field of magnetic disk, technical development is
being made rapidly toward increasing the recording density and
transfer rate. Nowadays, it is urgent to develop a high-speed disk
for rapid transfer. Hence, there is a demand for a disk material
with a high specific rigidity which will not vibrate during
high-speed running. Conventional aluminum disks have a specific
rigidity of 26.7 (Young's modulus [72 GPa] divided by density [2.7
g/cm.sup.3]). It is said that aluminum disks need more than twice
that specific rigidity if they are to be used at high speeds of
10000 rpm. The only way to double the specific rigidity of aluminum
disks is to combine aluminum with ceramics. This is not practical
from the standpoint of production cost.
[0005] On the other hand, glass disks (2.5-inch in size) are
attracting attention because it is easy to increase their specific
rigidity. This object is achieved by heating glass at an adequate
temperature, thereby causing a crystalline phase with a high
Young's modulus to separate out. The resulting glass ceramic has a
high Young's modulus. For example, Japanese Patent Laid-open Nos.
329440/1994, 111024/1996, and 221747/1996 disclose a process for
causing lithium dioxide crystals and .alpha.-quartz crystals to
separate out. And Japanese Patent Laid-open No. 77531/1998
discloses a process for causing spinel crystals to separate out,
thereby increasing Young's modulus to 109-144 GPa and specific
rigidity to 36-47.
[0006] The disadvantage of the disclosed technology is that
crystallization increases the specific rigidity of glass but it
also gives rise to a composite structure (composed of the hard
crystalline phase and the soft glass phase). Such a composite
structure produces minute steps at the time of polishing, making it
difficult to obtain a super-mirror required of disks.
[0007] There is a way to increase the specific rigidity of glass
per se by incorporation with a rare earth metal which improves
Young's modulus of glass. The disadvantage of this technology is
that incorporation with a rare earth metal increases not only
Young's modulus but also specific gravity, with the result that the
specific rigidity of glass does not increase as expected.
[0008] One way to increase Young's modulus without remarkably
increasing the specific gravity of glass is to replace nitrogen
with oxygen in glass, thereby producing oxynitride glass. Japanese
Patent Laid-open No. 1327/1998 discloses using oxynitride glass as
a disk substrate. It indicates in its example that the glass has an
extremely high Young's modulus of 139-185 GPa and a comparatively
low specific gravity of 2.9-3.4 g/cm.sup.3, with the specific
rigidity being as high as 47-55. However, the composition disclosed
in its example suggests that the glass contains nitrogen in such a
large amount as to form inhomogeneous glass, with the glass partly
crystallized. As in the case of glass ceramics mentioned above,
such glass gives rise to steps at the time of polishing, making it
difficult to obtain a super-mirror. Another disadvantage of glass
with microcrystals which have separated out is a slow polishing
rate. This leads to a high production cost because time required
for fabrication accounts for a large portion of production cost,
particularly in the case of mirror-finishing. Glass containing
microcrystals increases in fracture toughness to such an extent
that abrasive grains do not readily produce minute cracks during
polishing. This is the reason why the polishing rate is extremely
low in the case of inhomogeneous glass or crystallized glass
containing microcrystals.
OBJECT AND SUMMARY OF THE INVENTION
[0009] If oxynitride glass is to have an increased Young's modulus
with its specific gravity kept low so that it is used as a glass
substrate, it is necessary to carefully establish the range of its
composition. The present inventors studied this subject and
acquired specific knowledge about it. The present invention is
based on this knowledge.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a composition diagram of metallic components (Ca,
Al, and Si) in the oxynitride glass represented by Ca--Al--Si--O--N
in which 0 eq %<N.ltoreq.30 eq %.
[0011] FIG. 2 is a composition diagram of metallic components (Mg,
Al, and Si) in the oxynitride glass represented by Mg--Al--Si--O--N
in which 0 eq %<N.ltoreq.30 eq %.
[0012] FIG. 3 is a composition diagram of metallic components (Re,
Al, and Si) in the oxynitride glass represented by Re--Al--Si--O--N
in which 0 eq %<N.ltoreq.30 eq %.
[0013] FIG. 4 is a composition diagram of metallic components (Ca,
Al, and Si) in the oxynitride glass represented by Ca--Al--Si--O--N
in which 5 eq %.ltoreq.N.ltoreq.25 eq %.
[0014] FIG. 5 is a composition diagram of metallic components (Mg,
Al, and Si) in the oxynitride glass represented by Mg--Al--Si--O--N
in which 5 eq %.ltoreq.N.ltoreq.25 eq %.
[0015] FIG. 6 is a composition diagram of metallic components (Y,
Al, and Si) in the oxynitride glass represented by Y--Al--Si--O--N
in which 5 eq %.ltoreq.N.ltoreq.25 eq %.
[0016] FIG. 7 is a composition diagram of metallic components (Gd,
Al, and Si) in the oxynitride glass represented by Gd--Al--Si--O--N
in which 5 eq %.ltoreq.N.ltoreq.25 eq %.
[0017] FIG. 8 is a composition diagram of metallic components (Ce,
Al, and Si) in the oxynitride glass represented by Ce--Al--Si--O--N
in which 5 eq %.ltoreq.N.ltoreq.25 eq %.
DETAILED DESCRIPTION OF THE INVENTION
[0018] In order to address the above-mentioned problems, the
present inventors carried out a series of researches which led to
the finding that oxynitride glass can be used as a glass substrate
if it has a specific range of composition for homogeneity.
According to the present invention, the glass with a high Young's
modulus falls under the classes of Al--Si--O--N, Ca--Al--Si--O--N,
Mg--Al--Si--O--N, and Re--Al--Si--O--N (where Re stands for one or
more members selected from rare earth elements). Each of these
glasses has the range of composition as specified in the
following.
[0019] The oxynitride glass represented by Al--Si--O--N contains Al
and Si as metallic components in an amount of 20 eq
%.ltoreq.Al.ltoreq.30 eq % and 70 eq %.ltoreq.Si.ltoreq.80 eq %,
with Al+Si=100 eq %, and also contains O and N as non-metallic
components in an amount of 0 eq %<N.ltoreq.30 eq %, with O+N=100
eq %.
[0020] The oxynitride glass represented by Ca--Al--Si--O--N
contains Ca, Al, and Si as metallic components in an amount within
the hatched area in the composition diagram shown in FIG. 1, and
also contains O and N as non-metallic components in an amount of 0
eq %<N.ltoreq.30 eq %, with O+N=100 eq %, as in the case of the
oxynitride glass represented by Al--Si--O--N.
[0021] The oxynitride glass represented by Mg--Al--Si--O--N
contains Mg, Al, and Si as metallic components in an amount within
the hatched area in the composition diagram shown in FIG. 2, and
also contains O and N as non-metallic components in an amount of 0
eq %<N.ltoreq.30 eq %, with O+N=100 eq %, as in the case of the
oxynitride glass represented by Al--Si--O--N.
[0022] The oxynitride glass represented by Re--Al--Si--O--N
contains Re, Al, and Si as metallic components in an amount within
the hatched area in the composition diagram shown in FIG. 3, and
also contains O and N as non-metallic components in an amount of 0
eq %<N.ltoreq.30 eq %, with O+N=100 eq %, as in the case of the
oxynitride glass represented by Al--Si--O--N.
[0023] Each of the Ca--Al--Si--O--N, Mg--Al--Si--O--N, and
Re--Al--Si--O--N glasses should preferably have the range of
composition as specified in the following.
[0024] The oxynitride glass represented by Ca--Al--Si--O--N
contains Ca, Al, and Si as metallic components in an amount within
the hatched area in the composition diagram shown in FIG. 4, and
also contains O and N as non-metallic components in an amount of 5
eq %.ltoreq.N.ltoreq.25 eq %, with O+N=100 eq %.
[0025] The oxynitride glass represented by Mg--Al--Si--O--N
contains Mg, Al, and Si as metallic components in an amount within
the hatched area in the composition diagram shown in FIG. 5, and
also contains O and N as non-metallic components in an amount of 5
eq %.ltoreq.N.ltoreq.25 eq %, with O+N=100 eq %.
[0026] The oxynitride glass represented by Y--Al--Si--O--N contains
Y, Al, and Si as metallic components in an amount within the
hatched area in the composition diagram shown in FIG. 6, and also
contains O and N as non-metallic components in an amount of 5 eq
%.ltoreq.N.ltoreq.25 eq %, with O+N=100 eq %.
[0027] The oxynitride glass represented by Gd--Al--Si--O--N
contains Gd, Al, and Si as metallic components in an amount within
the hatched area in the composition diagram shown in FIG. 7, and
also contains O and N as non-metallic components in an amount of 5
eq %.ltoreq.N.ltoreq.25 eq %, with O+N=100 eq %.
[0028] The oxynitride glass represented by Ce--Al--Si--O--N
contains Ce, Al, and Si as metallic components in an amount within
the hatched area in the composition diagram shown in FIG. 8, and
also contains O and N as non-metallic components in an amount of 5
eq %.ltoreq.N.ltoreq.25 eq %, with O+N=100 eq %.
[0029] The glasses specified above are superior in specific
rigidity and fabricability.
EXAMPLES
[0030] According to the present invention, the oxynitride glass
contains nitrogen and metal components in an adequate amount (the
former affecting Young's modulus and the latter affecting specific
gravity) so that it has a high specific rigidity. Moreover, the
controlled content yields homogeneous glass which permits stable
workability.
[0031] According to the present invention, the nitrogen content
should be 0 eq %<N.ltoreq.30 eq %, with O+N 100 eq %. In
practice, only a small amount of nitrogen will suffice. An adequate
nitrogen content is more than 1 eq %, preferably more than 5 eq %,
more preferably more than 10 eq %.
[0032] The adequate content of each of Ca, Mg, and Re is shown
respectively in FIGS. 1 to 3. The ranges shown in these figures are
recommended when the nitrogen content is 15 eq %.
[0033] In the case where the nitrogen content is 5 eq
%.ltoreq.N.ltoreq.25 eq %, it is necessary to restrict the content
of Ca, Mg and Re (such as Y, Ge, and Ce) so as to produce a better
effect.
Example 1
[0034] Samples were prepared each containing Ca, Mg, Y, Ce, La, Nd,
or Gd in an amount (eq %) as shown in Table 1. In Table 1, M stands
for any one or more of Ca, Mg, Y, Ce, La, Nd, and Gd. For example,
E-1 embraces seven samples each containing Ca, Mg, Y, Ce, La, Nd,
and Gd alone or in combination with one another in an amount of 10
eq %. Those samples in which M=0, such as E-2, E-5, E-8, E-12,
E-21, and E-26, contain none of these metals; in other words, they
are oxynitride glass represented by Al--Si--O--N.
[0035] These glass samples were prepared by weighing CaCO.sub.3,
MgO, Y.sub.2O.sub.3, CeO.sub.2, La.sub.2O.sub.3, Nd.sub.2O.sub.3,
Gd.sub.2O.sub.3, Al.sub.2O.sub.3, SiO.sub.2, and AlN, mixing them
in a ball mill, drying, shaping by CIP, melting in a BN crucible at
1750.degree. C., and finally cooling.
1 TABLE 1 Sample No. Si Al M O N E-1 90 0 10 85 15 E-2 90 10 0 85
15 E-3 80 0 20 85 15 E-4 80 10 10 85 15 E-5 80 20 0 85 15 E-6 70 0
30 85 15 E-7 70 20 10 85 15 E-8 70 30 0 85 15 E-9 50 0 50 85 15
E-10 50 20 30 85 15 E-11 50 40 10 85 15 E-12 50 50 0 85 15 E-13 40
0 60 85 15 E-14 40 10 50 85 15 E-15 30 10 60 85 15 E-16 30 20 50 85
15 E-17 30 30 40 85 15 E-18 30 40 30 85 15 E-19 30 50 20 85 15 E-20
30 60 10 85 15 E-21 30 70 0 85 15 E-22 20 10 70 85 15 E-23 20 20 60
85 15 E-24 20 50 30 85 15 E-25 20 70 10 85 15 E-26 20 80 0 85 15
E-27 10 30 60 85 15 E-28 10 50 40 85 15 E-29 10 70 20 85 15 E-30 10
80 10 85 15 E-31 0 40 60 85 15 E-32 0 60 40 85 15
[0036] The glass samples with compositions shown in Table 1 were
examined for the presence or absence of crystallization and
foaming. The results are shown in Table 2. Foaming (indicated by
.cndot.) means that the glass contains a large number of bubbles
because the molten glass has a high viscosity or the molten glass
evolves a gas. In the case of large bubbles, the foamed glass may
have twice its original volume. Anyway, foamed glass is not
suitable for disk because it does not give a smooth surface after
polishing. Devitrification (indicated by x) means that the glass
becomes opaque due to crystallization.
2 TABLE 2 M = Ca M = Mg M = Y M = Ce M = La M = Nd M = Gd M = Y +
La M = Y + Gd E-1 .circle-solid. .circle-solid. .circle-solid.
.circle-solid. .circle-solid. .circle-solid. .circle-solid.
.circle-solid. .circle-solid. E-2 .circle-solid. .circle-solid.
.circle-solid. .circle-solid. .circle-solid. .circle-solid.
.circle-solid. .circle-solid. .circle-solid. E-3 .largecircle.
.largecircle. .circle-solid. .circle-solid. .circle-solid.
.circle-solid. .circle-solid. .circle-solid. .circle-solid. E-4
.largecircle. .largecircle. .circle-solid. .circle-solid.
.circle-solid. .circle-solid. .circle-solid. .circle-solid.
.circle-solid. E-5 .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. E-6 .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. E-7 .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. E-8
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. E-9 .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. E-10 .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. E-11 .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. E-12
.circle-solid. .circle-solid. .circle-solid. .circle-solid.
.circle-solid. .circle-solid. .circle-solid. .circle-solid.
.circle-solid. E-13 .largecircle. X .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. E-14 .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. E-15 .largecircle. X .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. E-16 .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. E-17 .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. E-18
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. E-19 .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. E-20 .largecircle. .largecircle. X X X
X X X X E-21 X .largecircle. X X X X X X X E-22 X X X X X X X X X
E-23 .largecircle. X X X X X X X X E-24 .largecircle. X X X X X X X
X E-25 .largecircle. X X X X X X X X E-26 X X X X X X X X X E-27
.largecircle. X X X X X X X X E-28 .largecircle. X X X X X X X X
E-29 .largecircle. X X X X X X X X E-30 X X X X X X X X X E-31 X X
X X X X X X X E-32 X X X X X X X X X .circle-solid.: foaming,
.largecircle.: homogeneous, x: devitrified
[0037] The results shown in Table 2 are interpreted as follows.
E-1, E-2, etc., which have an Si-rich composition, contains not
only glass phase but also crystalline phases such as SiO.sub.2
phase and Si.sub.2N.sub.2O phase; in other words, they have a
comparatively soft glass phase and a hard crystalline phase which
are mixed together. This is detrimental to the surface smoothness.
In addition, glass with such a composition has a high viscosity and
hence is liable to contain a large number of bubbles. Residual
bubbles prevent the glass from being finished smooth by
polishing.
[0038] E-22 etc., which have an M-rich composition, are not
suitable for use as glass substrate because they are liable to
precipitation of Ca.sub.2SiO.sub.4+CaSiN.sub.2 phase or
Mg.sub.2SiO+MgSiN.sub.2 phase (in the case of Ca- or Mg-containing
composition) or they are liable to precipitation of
Y.sub.4Si.sub.2O.sub.7N.sub.2+Y.sub.2SiO.sub.5 phase (in the case
of Y-containing composition).
[0039] E-30 etc, which have an Al-rich composition, are liable to
precipitation of corundum phase (Al.sub.2O.sub.3).
[0040] E-12 etc., whose composition is close to the Al--Si line,
are liable to precipitation of mullite phase (Al.sub.2SiO.sub.5).
M-12 is particularly inadequate because it contains a large number
of bubbles.
[0041] E-31, E-32, etc., whose composition is close to the Al--Re
line, are not suitable for use as glass substrate because they are
liable to precipitation of YAG phase (Y.sub.3Al.sub.16O.sub.12) in
the case of M=Y or they are liable to precipitation of
Ca.sub.2SiO.sub.4 and Mg.sub.2SiO.sub.4 in the case of M=Ca or
Mg.
[0042] Those samples with an N-rich composition are not suitable
for use as glass substrate because they are liable to precipitation
of silicon nitride (e.g., Si.sub.3N.sub.4).
[0043] Another six samples were prepared each having a composition
of M=20 eq %, Si=60 eq %, and Al=20 eq %, with the nitrogen content
varied from 1 to 35%. They were examined for glass formation. The
results are shown in Table 3 below.
3TABLE 3 Nitrogen Sample content State of glass No. (eq %) M = Ca M
= Mg M = Y M = Ce M = La M = Nd M = Gd E-N-1 1 .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. E-N-2 5 .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. E-N-3 10 .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. E-N-4 20
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. E-N-5 30 .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. E-N-6 35 X X X X X X X .largecircle.:
homogeneous glass, x: devitrified
[0044] The same procedure as above was repeated to prepare glass
samples each having a composition of Si=60 eq %, Al=20 eq %, M=20
eq %, O=80 eq %, and N=20 eq %. They were tested for Young's
modulus, density, hardness, and surface smoothness after polishing.
The results are shown in Table 4 below.
4 TABLE 4 Ca Mg Y Ce La Nd Gd Ra (.ANG.) 3 4 3 3 4 3 3 Young's
modulus 120 115 141 153 147 145 155 (GPa) Density 2.87 2.78 3.53
3.69 3.69 4.10 4.25 Hardness 910 780 1050 1100 1030 1040 1170
[0045] It is noted that the glass samples containing nitrogen are
high in Young's modulus and hence suitable for use for high-speed
disk. By contrast, the oxynitride glass incorporated with a rare
earth element has a high Young's modulus and also has a high
density. Hence, Ca-containing glass or Mg-containing glass is
preferable from the standpoint of improvement in specific rigidity.
These samples are homogeneous (without crystalline phase) and hence
have a small surface roughness (Ra=3-4 .ANG.) after polishing.
[0046] Glass samples containing Ca, Mg, and rare earth element (Y,
Gd, or Ce), with nitrogen content being in the range of 5 eq
%.ltoreq.N.ltoreq.25 eq %, were studied. The composition of each
sample is shown in Table 5. Each sample contains Si, Al, M', and 10
or 20 eq % nitrogen, where M' stands for any of Ca, Mg, Y, Gd, and
Ce. Therefore, F-1 embraces five samples each containing Ca, Mg, Y,
Gd, and Ce, alone or in combination with one another in an amount
of 10 eq %. "M'=0" means that the sample is oxynitride glass
containing none of these metals.
[0047] These glass samples were prepared by weighing CaCO.sub.3,
MgCO.sub.3, Y.sub.2O.sub.3, CeO.sub.2, Gd2O.sub.3, Al.sub.2O.sub.3,
SiO.sub.2, and Si.sub.3O.sub.4, mixing them a ball mill, drying,
shaping by CIP, melting in a BN crucible at 1750.degree. C., and
finally cooling.
5 TABLE 5 Sample No. Si Al M' F-1 90 0 10 F-2 90 10 0 F-3 80 0 20
F-4 80 10 10 F-5 80 20 0 F-6 70 0 30 F-7 70 10 20 F-8 70 20 10 F-9
70 30 0 F-10 60 0 40 F-11 60 10 30 F-12 60 20 20 F-13 60 30 10 F-14
60 40 0 F-15 50 10 40 F-16 50 20 30 F-17 50 30 20 F-18 50 40 10
F-19 50 50 0 F-20 40 10 50 F-21 40 20 40 F-22 40 30 30 F-23 40 40
20 F-24 40 50 10 F-25 40 60 0 F-26 30 30 40 F-27 30 40 30 F-28 30
50 20 F-29 30 60 10 F-30 20 40 40 F-31 20 50 30 F-32 20 60 20 F-33
20 70 10
[0048] The glass samples of the composition shown in Table 5 were
examined for the presence or absence of crystallization and
foaming, and some of them were also tested for surface roughness
(Ra). They include F-5, F-12, F-14, F-15, F-19, and F-29, which
contain 10 eq % nitrogen, and F-2, F-5, F-8, F-12, F-14, F-15, and
F-23, which contain 20 eq % nitrogen. Table 6 shows the results of
tests on the samples containing 10 eq % nitrogen, and Table 7 shows
the results of tests on the samples containing 20 eq % nitrogen.
The samples were rated according to the following criteria.
[0049] Good:homogeneous
[0050] Poor:less than 50% crystalline (C) or foamed (F)
[0051] Bad:more than 50% crystalline (C) or foamed (F)
6TABLE 6 (N = 10 eq%) Sample No. M' = Ca M' = Mg M' = Y M' = Gd M'
= Ce F-1 Bad (F) Bad (F) Bad (F) Bad (F) Bad (F) F-2 Bad (F) Bad
(F) Bad (F) Bad (F) Bad (F) F-3 Poor (F) Poor (F) Bad (F) Bad (F)
Bad (F) F-4 Poor (F) Poor (F) Bad (F) Bad (F) Bad (F) F-5 Poor (F)
Poor (F) Poor (F) Poor (F) Poor (F) Ra: 17 .ANG. Ra: 16 .ANG. Ra:
17 .ANG. Ra: 15 .ANG. Ra: 15 .ANG. F-6 Poor (C) Poor (C) Poor (C)
Poor (C) Poor (C) F-7 Good Good Good Poor (C) Poor (C) F-8 Good
Good Good Good Good F-9 Poor (F) Poor (F) Poor (F) Poor (F) Poor
(F) F-10 Poor (C) Poor (C) Good Poor (C) Poor (C) F-11 Poor (C)
Poor (C) Good Good Good F-12 Good Good Good Good Good Ra: 4 .ANG.
Ra: 5 .ANG. Ra: 3 .ANG. Ra: 4 .ANG. Ra: 3 .ANG. F-13 Good Good Good
Good Poor (F) F-14 Bad (F) Bad (F) Bad (F) Bad (F) Bad (F) Ra: *
Ra: * Ra: * Ra: * Ra: * F-15 Poor (C) Poor (C) Poor (C) Poor (C)
Poor (C) Ra: 10 .ANG. Ra: 15 .ANG. Ra: 13 .ANG. Ra: 13 .ANG. Ra: 15
.ANG. F-16 Poor (C) Poor (C) Good Good Good F-17 Good Poor (C) Good
Good Good F-18 Good Poor (C) Good Good Poor (F) F-19 Bad (C) Bad
(C) Bad (C) Bad (C) Bad (C) Ra: 36 .ANG. Ra: 49 .ANG. Ra: 31 .ANG.
Ra: 34 .ANG. F-20 Poor (C) Poor (C) Poor (C) Poor (C) Poor (C) F-21
Poor (C) Poor (C) Poor (C) Poor (C) Poor (C) F-22 Poor (C) Poor (C)
Good Good Good F-23 Good Poor (C) Good Good Good F-24 Good Poor (C)
Good Good Poor (F) F-25 Bad (C) Bad (C) Bad (C) Bad (C) Bad (C)
F-26 Poor (C) Poor (C) Poor (C) Poor (C) Poor (C) F-27 Poor (C)
Poor (C) Good Good Good F-28 Good Poor (C) Good Good Good F-29 Poor
(C) Poor (C) Bad (C) Bad (C) Bad (C) Ra: 52 .ANG. F-30 Poor (C) Bad
(C) Bad (C) Bad (C) Bad (C) F-31 Poor (C) Bad (C) Bad (C) Bad (C)
Bad (C) F-32 Poor (C) Bad (C) Bad (C) Bad (C) Bad (C) F-33 Poor (C)
Bad (C) Bad (C) Bad (C) Bad (C) *unmeasurable
[0052]
7TABLE 7 (N = 20 eq%) Sample No. M' = Ca M' = Mg M' = Y M' = Gd M'
= Ce F-1 Bad (F) Bad (F) Bad (F) Bad (F) Bad (F) F-2 Bad (F) Bad
(F) Bad (F) Bad (F) Bad (F) Ra: * Ra: * Ra: * Ra: * Ra: * F-3 Poor
(F) Poor (F) Bad (F) Bad (F) Bad (F) F-4 Poor (F) Poor (F) Bad (F)
Bad (F) Bad (F) F-5 Poor (F) Poor (F) Poor (F) Poor (F) Poor (F)
Ra: 15 .ANG. Ra: 13 .ANG. Ra: 15 .ANG. Ra: 16 .ANG. Ra: 14 .ANG.
F-6 Poor (C) Poor (C) Poor (C) Poor (C) Poor (C) F-7 Good Good Good
Poor (C) Poor (C) F-8 Good Good Good Good Good Ra: 6 .ANG. F-9 Poor
(C) Poor (C) Poor (C) Poor (C) Poor (C) F-10 Poor (C) Poor (C) Good
Poor (C) Poor (C) F-11 Poor (C) Poor (C) Good Good Good F-12 Good
Good Good Good Good Ra: 3 .ANG. Ra: 4 .ANG. Ra: 5 .ANG. F-13 Good
Good Good Good Poor (F) F-14 Bad (C) Bad (C) Bad (C) Bad (C) Bad
(C) Ra: 52 .ANG. Ra: 44 .ANG. Ra: 50 .ANG. Ra: 39 .ANG. Ra: 45
.ANG. F-15 Poor (C) Poor (C) Poor (C) Poor (C) Poor (C) Ra: 12
.ANG. Ra: 10 .ANG. Ra: 13 .ANG. Ra: 12 .ANG. Ra: 11 .ANG. F-16 Poor
(C) Poor (C) Good Good Good F-17 Good Poor (C) Good Good Good F-18
Good Poor (C) Good Good Poor (F) F-19 Bad (C) Bad (C) Bad (C) Bad
(C) Bad (C) F-20 Poor (C) Poor (C) Poor (C) Poor (C) Poor (C) F-21
Poor (C) Poor (C) Poor (C) Poor (C) Poor (C) F-22 Poor (C) Poor (C)
Good Good Good F-23 Good Poor (C) Good Good Good Ra: 4 .ANG. F-24
Good Poor (C) Good Good Poor (F) F-25 Bad (C) Bad (C) Bad (C) Bad
(C) Bad (C) F-26 Poor (C) Poor (C) Poor (C) Poor (C) Poor (C) F-27
Poor (C) Poor (C) Good Good Good F-28 Good Poor (C) Good Good Good
F-29 Poor (C) Poor (C) Bad (C) Bad (C) Bad (C) F-30 Poor (C) Bad
(C) Bad (C) Bad (C) Bad (C) F-31 Poor (C) Bad (C) Bad (C) Bad (C)
Bad (C) F-32 Poor (C) Bad (C) Bad (C) Bad (C) Bad (C) F-33 Poor (C)
Bad (C) Bad (C) Bad (C) Bad (C) *unmeasurable
[0053] Samples were prepared each containing nitrogen 5 eq %, 25 eq
%, or 30 eq %. They were examined for glass state. The results are
shown in Table 8 below.
8 TABLE 8 Si Al M' O N Rating M' = Ca F-34 70 20 10 95 5 Good F-35
40 40 20 95 5 Good F-36 70 10 20 75 25 Good F-37 30 50 20 75 25
Good F-38 70 10 20 70 30 Poor (C) F-39 30 50 20 70 30 Poor (C) M' =
Mg F-34 70 10 20 95 5 Good F-35 60 30 10 95 5 Good F-36 70 10 20 75
25 Good F-37 70 20 10 75 25 Good F-38 70 10 20 70 30 Poor (C) F-39
70 20 10 70 30 Poor (C) M' = Y F-34 60 10 30 95 5 Good F-35 30 50
20 95 5 Good F-36 60 0 40 75 25 Good F-37 30 50 20 75 25 Good F-38
60 0 40 70 30 Poor (C) F-39 30 50 20 70 30 Poor (C) M' = Gd F-34 60
10 30 95 5 Good F-35 30 50 20 95 5 Good F-36 50 30 20 75 25 Good
F-37 30 50 20 75 25 Good F-38 50 30 20 70 30 Poor (C) F-39 30 50 20
70 30 Poor (C) M' = Ce F-34 70 20 10 95 5 Good F-35 30 50 20 95 5
Good F-36 60 10 30 75 25 Good F-37 40 40 20 75 25 Good F-38 60 10
30 70 30 Poor (C) F-39 40 40 20 70 30 Poor (C)
[0054] It is noted from Table 8 that samples F-34 to F-37, which
contain 5 eq % or 25 eq % nitrogen, are homogeneous glass
regardless of the kind of metallic elements they contain. By
contrast, samples F-38 and F-39, which contain less than 30 eq %
nitrogen, are inhomogeneous glass containing less than 50%
crystals.
[0055] A base plate measuring 95 mm in diameter and 1.2 mm thick
was prepared from glass having a composition of (Si, Al, M', O,
N)=(50, 30, 20, 75, 25). This base plate was chamfered by using an
edge grinder. The base plate, fixed to a carrier, underwent primary
lapping by a double-sided lapping machine "18B" equipped with a
cast iron lap containing 20 wt % alumina (20 .mu.m in average
particle diameter), at a rotary speed of 40 rpm under a finishing
pressure of 100 gf/cm.sup.2. Then, the base plate underwent
secondary lapping by a cast iron lap containing 20 wt % alumina (8
.mu.m in average particle diameter) under the same conditions as in
primary lapping. After washing, the base plate underwent primary
polishing by a double-sided lapping machine (the same one as used
as above) equipped with a lap covered with a rigid foamed
polyurethane pad, while supplying a polishing liquid containing 20
wt % cerium oxide (2 .mu.m in average particle diameter), at a
rotary speed of 30 rpm under a finishing pressure of 250
gf/cm.sup.2. After simple washing, the base plate underwent
secondary polishing by a lap covered with a rigid polyurethane pad
having a nap layer while supplying a polishing liquid containing 20
wt % cerium oxide (1 .mu.m in average particle diameter), at a
rotary speed of 25 rpm under a finishing pressure of 200
gf/cm.sup.2. Thus there was obtained a finished disk 0.8 mm in
thickness. This disk was examined for surface roughness by using a
contact-type surface roughness meter. The results are shown in
Table 9.
9 TABLE 9 M' = Ca M' = Mg M' = Y M' = Gd M' = Ce F-34 5 5 4 5 3
F-35 3 4 4 3 5 F-36 5 3 5 4 4 F-37 5 4 5 4 3 F-38 14 44 32 14 34
F-39 35 53 43 40 54 Unit: .ANG.
[0056] It is noted from Table 9 that those disks made of any of
glass samples F-34 to F-37, each containing 5 eq % or 25 eq %
nitrogen, have a good surface with a surface roughness of 3-5
.ANG.. By contrast, those disks made of any of glass samples F-38
and F-39, each containing 30 eq % nitrogen, have a surface
roughness greater than 14 .ANG. regardless of the kind of metal
they contain, and hence they are not suitable for practical
use.
[0057] A base sheet was made from glass having the composition of
F-37, and it was fabricated into a disk in the same manner as
above. The disk was examined for surface roughness (Ra), Young's
modulus, density, and hardness. The results are shown in Table
10.
10 TABLE 10 M' = Ca M' = Mg M' = Y M' = Gd M' = Ce Ra (.ANG.) 4 4 3
4 3 Young's 130 119 145 157 160 modulus (GPa) Density 2.98 2.60
3.39 3.88 3.89 Hardness 925 790 1,062 1,120 1,200
[0058] It is noted from Table 10 that those disks containing 25 eq
% nitrogen have a good surface roughness and a high value of
Young's modulus and hence they are suitable for use as high-speed
disk. Oxynitride glass containing Y, Gd, or Ce (rare earth element)
have a high value of Young's modulus but they also have a high
density; therefore, oxynitride glass containing Ca or Mg is
desirable from the standpoint of improvement in specific
rigidity.
[0059] [Effect of the invention] As mentioned above, the present
invention provides a special kind of glass with high specific
rigidity for a disk for recording medium. This glass is oxynitride
glass containing a special component within a specific range, and
hence it can be made into a homogeneous base plate with a high
Young's modulus which can be fabricated into the disk for
high-density recording, high-speed transfer, and high-speed
rotation.
* * * * *