Silica Glass - Characteristics | https://www.tosoheurope.com

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
	Electrical fusion	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
	VAD process	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)
Solution		Concentration (%)	Temperature (ºC)	Time (Hr)	Weight Loss (g/m²)
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
	Na₂CO₃	10	100	10	3.7
Acid	H₂SO₄	98	205	24	0.06
	H₂SO₄	98	20	240	0.016
	HNO₃	65	115	24	0.11
	HNO₃	65	20	240	0.06
	HCl	37	66	24	0.14
	HCl	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=10^14.5)	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=10^7.6)^*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 (log_n) 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