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Silica Glass - Characteristics

Silica glass is a kind of glass as the name is implied, but silica glass is composed of by almost only SiO2, while, on the other hand, other glasses are composed of by various kinds of elements. The amount of metallic impurity contained in silica glass is extremely little, and even silica glass having large amount of metallic impurity has only several 10 ppm and silica glass having small amount of metallic impurity has less than 10 ppb. In this way, the fact that the purity is extremely high brings to silica glass the excellent characteristics of silica glass which cannot be seen in other glasses.


Features of Silica Glass

 Superb Transparency

Silica glass has excellent transmission characteristics in a wide range of wavelengths, covering not only the visible range, but ultraviolet and infrared.

High Purity

Silica glass is composed of SiO2 only, and contains very little amounts of metallic impurity.

High Heat Resistance

Deformation temperature of silica glass is as high as 1,700ºC and therefore it can be well used at such high temperatures around 1,000ºC. Further, it can be durable against rapid temperature change due to its small coefficient of thermal expansion.

Excellent Chemical Inertness

Silica glass is extremely chemically stable and it has excellent chemical resistance. However, good care must be taken in cases where it is used with hydrofluoric acid, phosphoric acid, or alkaline solutions for extended periods of time because it may be etched by those chemicals.



Lineup of Major Silica Glass Material
Category
Process Grade Features
 Fused Silica Glass
Oxy-hydrogen flame fusion
N Semiconductor standard grade, Less bubbles
NP High-purity grade of N
S High-purity grade with good light transmission
OP-1 Semiconductor standard grade opaque
OP-3 Semiconductor high-purity grade opaque
Electrical fusion
HR Semiconductor standard grade, High heat resistance
HRP High-purity grade of HR
Synthetic Silica Glass
Verneuil type process
ES Standard optical grade for optics
ESL-1 Standard optical grade with 1D striae free
ESL-1000 Enhance excimer durability for ESL-1
ESL-2
Good homogeneity with 3D striae free
ESL-2000 Enhance excimer durability for ESL-2
VAD process
ED-H Good homogeneity with 3D striae free
ED-C Very low OH content (OH content < 1ppm)

Fused silica glass is being manufactured from high-purity silica powder, and synthetic silica glass is being manufactured from high-purity SiCl4 as raw material. The levels of impurities contained are nothing more than ppm for fused silica glass and ppb for synthetic silica glass.

Impurity Level of Major Silica Glass Material

Unit: ppm
Grade Al Ca Cu Fe Na K Li Mg OH
N 8 0.6 < 0.01 0.2 0.6 0.1 < 0.07 0.04 200
NP 7 0.5 < 0.01 0.1 0.1 0.03 < 0.01 0.02 200
S 0.7 < 0.01 < 0.01 0.05 0.1 < 0.01 < 0.01 < 0.01 160
HR 15 0.6 0.02 0.2 0.8 0.6 0.5 0.1 10
HRP 15 0.6 0.01 0.2 0.2 0.6 0.2 0.1 10
OP-1 8 0.7 < 0.01 0.2 0.6 0.3 0.07 0.04 160
OP-3 8 0.6 < 0.01 0.2 0.6 0.1 0.07 0.04 160
OP-3HD 8 0.6 < 0.01 0.2 0.6 0.1 0.07 0.04 160
ES*1 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 1000
ED-C < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 1
ED-H < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 100
(Typical values. Not guaranteed
*1 Inpurity level of ESL-1, ESL-2, ESL-1000 and ESL-2000 is the same as ES.

Silica glass having the excellent resistance to chemicals is most suitable as the distillation container for various solvents and acid solutions and the dissolution and washing container for various kinds of substances, provided, however, that attention shall be taken for long-time use, because the etching and/or surface devitrification of silica glass may occur in the solution of or under the atmosphere of hydrofluoric acid, phosphoric acid, alkali, alkali metal compounds.

Chemical Reactivity with Acid/Alkaline Solutions

Solution Condition
Weight Loss (g/m2)
Concentration (%)
Temperature (ºC)
Time (Hr)
Alkali


NH4OH 10
20
100
0.19
NaOH
1
20
100
0.31
10
20
100
0.095
5
100
10
15
8
100
10
12.1
KOH 1
20
100
0.19
30
100
10
0.27
10
10
100
11.3
Na2CO3
5
20
100
0.015
10
100
10
3.7
Acid
H2SO4  98
205
24
0.06
98 20
240
0.016
HNO3
65
115
24
0.11
65
20
240
0.06
HCl
 37 66  24  0.14
 37 20  240  0.18

(Typical values. Not guaranteed

Chemical Reactivity with Other Metals

Material
Reactivity
Metal Al, Mg
Rapid reaction at 700-800º Celsius
Au, Ag, Pt
No reaction
Zn, Sn, Pb
No reaction
Si
Slight reaction when fused
Ge
No reaction at 900º Celsius
Mo, W
No reaction
Oxide
Al2O3
Gradual reaction over 900º Celsius
 CaO Reaction over 900º Celsius
CuO Reaction over 800º Celsius
Fe2O3
Reaction over 900º Celsius
PbO
Intense reaction when fused
MgO Slight reaction at 900º Celsius
 ZnO Reaction over 420º Celsius
Gas
CO, SO2 No reaction
N2, O2
No reaction
Cl2
No reaction
F2
No reaction with dried gases under 300º Celsius
H2
No reaction
HCl
No reaction
Salt BaCl2 Reaction when fused
BaSO4 Reaction over 700º Celsius
CaCl2 Slight reaction when fused at 800º Celsius
KCl Acceleration of devitrification at high temperature
KF Intense reaction when fused
NaCl Reaction visually recognized over 800º Celsius
Na2SO4  No reaction

Also available are the ES series and ED series of silica glass for optical materials. Either of them is synthetic silica glass made from high-purity SiCl4 having almost no impurities, foam or foreign materials contained, and has the excellent optical transparency in wide range of wavelength.

Optical Properties of Major Optical Grade Silica Glass Material

Grade Striae*1
Homogeneity*2
Δn(x10-6) within clear aperture
Strain
(nm/cm)
Excimer Durability
Applicable Wavelength*3 (nm)
ES
N/A
N/A
1 ~ 20
N/A
180 ~ 2,100
ESL-1
1D 3 ~ 10 (CA: φ300 mm)
1 ~ 10
N/A
180 ~ 2,100
ESL-1000 1D 3 ~ 10 (CA: φ300 mm)
1 ~ 10
Negotiable*4
180 ~ 2,100
ESL-2 3D < 10 (CA: φ300 mm)
1 ~ 10
N/A
180 ~ 2,100
ESL-2000 3D  < 10 (CA: φ300 mm)
1 ~ 10
Negotiable*4
180 ~ 2,100
ED-H 3D 5 ~ 10 (CA: φ180 mm)
1 ~ 10
N/A
170 ~ 2,600
ED-C
N/A N/A 1 ~ 10 N/A 180 ~ 3,400

(Typical values. Not guaranteed

*1: Striae specification is defined as follows: 1D: 1 direction free 3D: 3 direction free
*2: Homogeneity means refractive index homogeneity and is expressed as Δn(PV) within effective area.
*3: Applicable wavelength is defined as the wavelength range where external transmittance is more than 80%/cm.
*4: Excimer durability is specified with Tosoh SGM's KrF and ArF excimer laser damage tests.

Spectral Transmission of Major Optical Grade Silica Glass Material


Silica glass has specific properties which cannot be seen in other materials. For example, rigidity, pulling strength, bending strength and the like rise with a temperature rise, and culminate at from 800 degree C to 1,000 degree C, and suddenly decrease at the temperature exceeding such specified temperatures.

Physical Properties of Major Silica Glass Material

  Item Unit ES*1 ED-C ED-H N, NP
HR, HRP
S OP-1,3 OP-3HD

Mechanical

Density
g / cm3
2.2
2.2
2.2 2.2 2.2 2.2 2.02 2.1
Young's Modulus
GPa 74
74
74
74
74
74
-
-
Shear Modulus
GPa
31
31
31
31
31
31
-
-
Poisson's Ratio

0.18
0.18
0.18
0.17
0.17
0.17
-
-
Bending Strength*2
MPa
65 ~
95
65 ~
95
65 ~
95
65 ~
95
65 ~
95
65 ~
95
42 ~
67
42 ~
67
Compressive Strength
MPa
1,130
1,130
1,130
1,130
1,130
1,130
-
-
Tensile Strength*2
MPa
49
49
49
49
49
49
-
-
Torsion Strength
MPa
29 29
29
29
29
29
-
-
Vickers Hardness MPa
8,900
8,900
8,900
8,900
8,900
8,900
8,900
8,900
Thermal Strain Point (n=1014.5)
ºC
980
980 1,090 1,080 1,120 1,070 1,070 1,070
Annealing Point (n=1013)
ºC
1,080
1,080
1,190
1,180
1,220
1,170
1,170
1,170
Softening Point (n=107.6)*3 ºC (1,720)
(1,720) (1,720) (1,720) (1,720) (1,720) (1,720) (1,720)
Coefficient of Thermal Expansion 30 ~ 600º C x10-7 / ºC 5.8*4
5.8*4
5.8*4
5.7
5.9
5.7 6.4 6.4
Specific Heat 20º C J / kg • K
749
749
749
749
749
749
749
749
Thermal Diffusivity 19º C x10-7m2 / s
8.5
8.5
8.5
8.3
8.3
8.3
8.4
8.5
Thermal Conductivity 19º C W / mK
1.38
1.38
1.38
1.38
1.38
1.38
1.24
1.33
Viscosity (logn) 1,200º C Poise
11.4
11.4
13.0
12.7
12.18
12.5
12.6
12.6
Electrical Dielectric Constant
500 MHz

3.9
3.9
3.9
3.9
3.9
3.9
3.7
3.8
Dielectric Loss
500 MHz
x10-3
< 1
< 1
< 1
< 1
< 1
< 1
< 1
< 1
Resistivity 25º C
Ω
5x1015
8x1015
8x1015
3x1015
8x1015
4x1015
-
-
Volume Resistivity 25º C Ω • cm
1x1017
1x1017
1x1017
5x1016
1x1017
7x1016
-
-
Dielectric Breakdown
50Hz, 20º C
V/mm
 - -
-
32,000
32,000
32,000
25,500
-
  (Typical values. Not guaranteed
*1: Properties of ESL-1, ESL-2, ESL-1000 and ESL-2000 is the same as ES.
*2: Bending and Tensile strengths are affected by surface conditions.
*3: Estimate from extrapolation.
*4: Average values at 30~200º C
 NOTE: Unless otherwise stated, all values represent typical data at 25º C