Fused Quartz Used for SPI Supplies® Brand Quartz Slides and Cover Slips
Technical details and specifications for GE 124 electrically fused quartz
Quartz is far from a "unique material", as there are many different grades
of quartz available in the world, with various different additives and
impurities, different transmittances in different ranges of the
electromagnetic spectrum, level of "bubbles", etc. And as would be expected,
there is a wide variation in prices for these different quartz products. For example,
what is nominally called "quartz" in the laboratory field, is really what is more
precisely called "fused quartz", electrically fused quartz not to
be confused with "fused silica" or "synthetic flame fused silica".
The quartz used for the production of the SPI Supplies slides and cover
slips is considered to be "high purity" and is the same purity used in the
electronics industry, which is recognized as having the highest
specifications for quality in quartz products. This is the same grade of
quartz for example generally used to fabricate, for the electronics industry,
wafer carriers, flanges, and a variety of other demanding optical
applications.
Special Note:
All SPI Supplies quartz products that are produced in GE 124 are also available in Corning 7980, a synthetic
flame fused silica, and which has even lower impurity levels and therefore, less fluorescence and therefore even
higher transmittance. At first, we had a hard time being convinced
that the typical user of UV microscopy techniques would
benefit from this slight increase in transmittance. But with the passing of
time, we have come to meet some of our customers who have convinced us
otherwise. We now believe that it is very application specific.
We can produce all of our product line in Corning 7980, but the
cost as well as minimum quantities make the total budgetary outlay considerably higher.
We at SPI Supplies believe it is important that a researcher always have
the technical details associated with the quartz they are using in their
critical experiments. All too often, one has not the slightest clue as to
the grade or purity of the quartz they might be using in their experiments
and then when one tries to reproduce such experiments, perhaps in another
part of the world, an unsatisfactory result of obtained that is the result
of different grades of quartz being used. Hence the point might not be so
much that one grade is better than another grade but that the same grade be
used in order to ensure reproducibility of results.
Typical Trace Element Composition (ppm by weight): Analysis by
direct reading spectrometer
SPI Fused Quartz Products
Al 14
As <0.002
B <0.02
Ca 0.4
Cd <0.01
Cr <0.05
Cu <0.05
Fe 0.2
K 0.6
Li 0.6
Mg 0.1
Mn <0.05
Na 0.7
Ni <0.1
P <0.2
Sb <0.003
Ti 1.1
Zr 0.8
OH <5
Reactivity:
Most acids, metals, chlorine and bromine are unreactive with fused quartz
at ordinary temperatures. It is slightly attacked by alkaline solutions,
the reaction rate increasing with temperature and concentration of
solution. Phosphoric acid will attack fused quartz at temperatures above
about 150° C / 302° F. Hydrofluoric acid alone will attack it at all
temperatures. Carbon and some metals will reduce fused quartz; basic
oxides, carbonates, sulfates, etc. will react with it at elevated
temperatures. For general use, however, it can be concluded that fused
quartz is quite unreactive.
Permeability:
Fused quartz is essentially impermeable to most gases, but helium, hydrogen,
deuterium and neon may diffuse through the material. The rate of diffusion
increases at higher temperatures and differential pressures.
The selective diffusion of helium through fused quartz is the basis for a
method of purifying helium by essentially "screening out" contaminants by
passing the gas through thin-walled quartz tubes.
The diffusion of helium, hydrogen, deuterium and neon through fused quartz
is accelerated with increasing temperature. The permeability constants for
these gases through the SPI fused silica at 700° C are estimated to be:
Helium: 2.1 x 10-8 cc/sec/cm2/mm/cm Hg
Hydrogen: 2.1 x 10-9 cc/sec/cm2/mm/cm Hg
Deuterium: 1.7 x 10-9 cc/sec/cm2/mm/cm Hg
Neon: 9.5 x 10-10 cc/sec/cm2/mm/cm Hg
Mechanical properties:
Mechanical properties of fused quartz are much the same as those of other
glasses. The material is extremely strong in compression with design
compressive strength of better than 1.9x109Pa
(160,000 psi).
Surface flaws can drastically reduce the inherent strength of any glass, so
tensile properties are greatly influenced by these defects. The design
tensile strength for fused quartz with good surface quality is in excess of
4.8 x 107 Pa (7000 psi). In practice a
design strength of 68 x 107 Pa (1000 psi)
is generally recommended.
Typical Physical Properties:
Density: 2.2 x 103 kg/m3
Hardness: 5.5 - 6.5 Mohs Scale 570 KHN
Design Tensile Strength: 4.8 x 107 Pa (N/m2), 160,000 psi
Design Compressive Strength: Greater than 1.1 x 108 Pa (160,000 psi)
Bulk Modulus: 3.1 x 1010 Pa (5.3 x 103 psi)
Poissons ratio: 0.17
Coefficient of thermal expansion (20 - 320° C): 5.5 x 10-7 cm/cm °C. Thermal
conductivity: 1.4 W/m° C
Specific heat: (20°C) 670 J/kg °C
Softening point: 1683° C
Annealing point: 1215° C
Strain point: 1120° C
Electrical resistivity (350° C): 7 x 107 ohm cm
Index of refraction: 1.4585
Constringence (Nu value): 67.56
Thermal properties:
One of the most important properties of fused quartz is its extremely low
coefficient of expansion (20-320° C): 5.5 x 10-7
mm° C. Its coefficient is 1/34 that of copper and only 1/7 of borosilicate
glass. This makes the material particularly useful for optical flats,
mirrors, furnace windows and critical optical applications which require
minimum sensitivity to thermal changes. Thermal conductivity information is given below
as a function of temperature:
A related property is its unusually high thermal shock resistance. For
example, thin sections can be heated rapidly to above 1500° C and then
plunged into water without cracking.
Empirical Annealing Rates:
Cooling from two sides:
Rate °C/minute: 4274.7 x residual stress Pa/(thickness, mm)2
Cooling from one side:
Rate °C/minute: 4274.7 x residual stress Pa/(2 x thickness, mm)2.
The residual stress or design, depending on the application, may be in the
range of 1.7 x 107 to 20.4 x 107
Pa (25-300 psi).
As a general rule, it is possible to cool up to 100° C/hour for sections
less than 25 mm thick.
Effects of temperature
Fused quartz is a solid material at room temperature, but at high
temperatures, it behaves like all glasses. It does not experience a
distinct melting point as crystalline materials do, but softens over a
fairly broad temperature range. This transition from a solid to a
plastic-like behavior, called the transformation range, is distinguished
by a continuous change in viscosity with temperature.
Viscosity:
Viscosity is the measure of the resistance to flow of a material when
exposed to a shear stress. Since the range in "flowability" is extremely
wide, the viscosity scale is generally expressed logarithmically. Common
glass terms for expressing viscosity include strain point, annealing point,
and softening point which are defined as follows:
Strain point:
The temperature at which the internal stress is substantially relieved
in four hours. This corresponds to a viscosity of 1014
poise where poise = dynes/cm2 sec.
Annealing point:
The temperature at which the internal stress is substantially relieved
in 15 minutes, and at a viscosity of 1013 poise.
Softening point:
The temperature at which glass will deform under its own weight, a viscosity
of approximately 107.6 poise. The softening point
of fused quartz has been variously reported from 1500° C to 1670° C, the range
resulting from differing conditions of measurement.
Optical Properties:
Optical transmission properties provide a means for distinguishing among
various types of vitreous silica as the degree of transparency reflects
material purity and the method of manufacture.
Specific indicators are the UV cutoff and the presence or absence of bands
at 245 nm and 2.73 µm. The UV cutoff ranges from ~155 to 175 nm for a 10 mm
thick specimen and for pure fused quartz is a reflection of material purity.
The presence of transition metallic impurities will shift the cutoff toward
longer wavelengths. When desired, intentional doping, e. g. with Ti in the
case of Type 219 quartz may be employed. The absorption band at 245 nm
characterizes a reduced glass and typifies material made by electric fusion.
If a vitreous silica is formed by a "wet" process, either flame fusion or
synthetic material, for example, the fundamental vibrational band of
incorporated structural hydroxyl ions will absorb strongly at 2.73 µm.
UV Cutoff
As the transmission curve illustrates,
GE Type 214 fused quartz has a UV cutoff (1 mm thickness) at < 160 nm, a small absorption at
245 nm and no appreciable absorption due to hydroxyl ions. Type 219, which contains
approximately 100 ppm Ti, has a UV cutoff at about 230 nm for a 1 mm thick sample.
High IR Transmission
The IR edge falls between 4.5 and 5.0 micrometers for a 1 mm thick sample.
Type 214/124 electrically fused quartz is a very efficient material for the transmission of
infrared radiation. Its infrared transmission extends out to about 4 µm with little absorption
in the "water band" at 2.73 µm. This makes GE electrically fused quartz different than flame
fused quartz (often referred to as = "wet" quartz). This difference is seen in the
transmission for the IR range. The IR Transmission figure illustrates this difference.
Conversion to other thicknesses can be accomplished with the following formula:
T = 3D (1-R)2 e - at
Where:
T = 3D percent transmission expressed as a decimal.
R = 3D surface reflection loss for one surface.
e = 3D base of natural logarithms
a = 3D absorption coefficient, cm-1
t =3D thickness, cm
To aid in the calculation of the transmission for GE materials at different thicknesses, try
the GE Transmission Calculator.
Optical transmission properties provide a means for distinguishing among various types of
vitreous silica as the degree of transparency reflects material purity and the method of
manufacture. Specific indicators are the UV cutoff and the presence or absence of bands at
245 nm and 2.73 µm. The UV cutoff ranges from about 155 to 175 nm for a 10 mm thick specimen
and for pure fused quartz is a reflection of material purity.
The presence of transition metallic impurities will shift the cutoff toward longer wavelengths.
When desired, intentional doping, e.g., with Ti in the case of Type 219, may be employed to
increase absorption in the UV. The absorption band at 245 nm characterizes a reduced glass
and typifies material made by electric fusion. If a vitreous silica is formed by a "wet"
process, either flame fusion or synthetic material, for example, the fundamental vibrational
band of incorporated structural hydroxyl ions will absorb strongly at 2.73 µm.
As the transmission curve illustrates, GE Type 214 fused quartz has a UV cutoff (1 mm thickness)
at 160 nm, a=small absorption at 245 nm and no appreciable absorption due to hydroxyl ions.
Type 219, which contains approximately 100 ppm Ti, has a UV cutoff at about 230 nm for a 1 mm
thick sample.
High IR Transmission
The IR edge falls between 4.5 and 5.0 µm for a 1 mm thick sample.
Type (214/124 electrically) fused quartz is a very efficient material for the transmission of
infrared radiation. Its infrared transmission extends out to about 4 µm with little absorption
in the "water band" at 2.73 µm This makes GE electrically fused quartz different than flame
fused quartz (often referred to as "wet" quartz). This difference is seen in the transmission
for the IR range. The IR Transmission figure illustrates this difference.
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Sunday March 21, 2010
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