Description - Colorless optical glass

Classification and naming of optical glass grades

1.1 Classification of Optical Glass Grades

According to the position and glass composition of the refractive index nd and dispersion coefficient ν d in the nd ν d domain diagram, colorless optical glasses are classified into 19 categories according to Table 1.

Table 1

1.2 Naming of Optical Glass Grades

Optical glass is composed of the code and serial number of the glass category it belongs to; In addition, six digits are used as codes to represent each grade, with the first three digits representing the decimal point of the refractive index of the glass and the last three digits representing the Abbe number of the glass. For example, H-K9L has nd=1.516800 and ν d=64.20, and its code is "517642".

1.3 Naming of lead-free, arsenic free, and cadmium free glass grades

Glass grades without lead, arsenic, cadmium, and other radioactive elements are represented by the initials "H" and "-" of the Chinese Pinyin letter "Huan", for example: H-K9L.

1.4 Naming of low softening point glass grades

Low softening point lead-free, arsenic free, cadmium free, and other radioactive element glass grades used for compression molding are represented by the initials "D" and "-" of the Chinese Pinyin letters for "low", such as D-K9.

1.5 High transparency glass brand naming

High transmittance and ultra-high transmittance glass grades are named by the letters (GT, TT) after the grade. Use the first letter of "GT" in Chinese Pinyin to represent high transmittance glass; The first letter of "TT" in Chinese Pinyin, which means "special" and "transparent", is used to represent ultra-high transmittance glass, such as H-ZF52GT and H-ZF52TT.

1.6 Other Naming

L: Add "L" after the serial number of the grade to indicate that the refractive index standard deviation of the grade is within ± 100 × 10-5 compared to the same grade in GB/T 903, for example: H-K9L; Add "L" before the serial number to indicate the brand and GB/T

The refractive index of the same brand in 903 is basically the same, but there are differences in dispersion, such as H-LaFL5, whose physical and chemical properties remain basically unchanged.

A. B, C, D, E: The number of times the formula composition is improved by adding letters in alphabetical order after the serial number of the brand. The main optical properties are the same or equivalent, but the physical and chemical properties have changed.

N: In order to improve process performance, reduce the use of rare and precious chemical raw materials, and achieve excellent glass properties, an "N" symbol is added after the grade number. Its main optical and physicochemical properties have changed, such as H-ZLaF68N.

-25: Adding "-25" after the serial number of the low softening point optical glass grade indicates that the refractive index is data at -25 ℃/h annealing rate, such as D-K9-25 indicating that the refractive index is data at -25 ℃/h annealing rate.

2 Optical performance

2.1 Refractive Index

The refractive index of optical glass is given by the 20 spectral lines listed in Table 2 and measured according to the method specified in GB/T 7962.11-2010.

2.2 Dispersion and Abbe number

The central dispersion is nF nC or nF '- nC', and the dispersion coefficient (i.e. Abbe number) is defined as follows:

ν d=(nd-1)/(nF nC) or ν e=(ne-1)/(nF ′ - nC ′)

2.3 Dispersion formula

At 302 In the spectral range of 15nm to 2325.42nm, the refractive index of other wavelengths can be calculated using the Sellmeier 1 formula, which is as follows:

image.png 

In the formula: K1, L1, K2, L2, K3, L3- calculation constants;

λ - wavelength, μm；

N λ - the desired refractive index.

For non extended refractive index grades, in the spectral range of 365.01nm to 1013.98nm, the Schott formula can be used to calculate the refractive index of other wavelengths. The Schott formula is as follows:

nλ2=A0＋A1λ2＋A2λ-2＋A3λ-4＋A4λ-6＋A5λ-8

In the formula: A0 to A5- calculation constants;

λ - wavelength, μm；

N λ - the desired refractive index.

Table 2

2.4 Relative Partial Dispersion

The relative partial dispersion Px and y of wavelengths x and y can be expressed by the following equation:

Px,y= (nx- ny)/ (nF-nC)   P′x,y= (nx- ny)/ (nF′-nC′)

The data table provides information by brand Ps,t 、PC,s 、Pd, C 、Pe ,d、Pg,F   、Pi,h    、P ′s,t 、P ′C’,s 、P ′d ,C’、 P′e ,d、P′g,F’ 、P′i,h。

According to the Abbe formula, for most so-called "normal glasses" (selecting H-K6 and F4 as "normal glasses"), the following linear relationship holds:

image.png 

This linear relationship is represented by Px and y as the vertical axis and υ d as the horizontal axis, where mx and y are the slopes and bx and y are the intercepts.

As is well known, the correction of secondary spectra, that is, the chromatic aberration reduction of two or more wavelengths, requires at least one type of glass that does not conform to the above formula (i.e., its Px, y values deviate from the Abbe empirical formula), and its deviation value is represented by Δ Px, y. Therefore, each Px, y-υ d point is shifted by Δ Px, y relative to the "normal line" that conforms to the above formula. In this way, the Δ Px and y values of each grade of glass can be calculated using the following formula:

Px,y   = mx,y ·υd  ＋bx,y   +ΔPx,y

Therefore, Δ Px, y quantitatively represent the deviation characteristics of the special dispersion compared to "normal glass".

The data table provides Δ PC, t, Δ PC, s, Δ Pg, F, Δ PF, e by brand, and their calculation formulas are as follows:

ΔPC,t= PC,t-0.5462-0.004713·υd   ΔPC,s= PC,s -0.4017-0.002365·υd

ΔPF ,e  = PF ,e   -0.4894＋0.000541·υd

ΔPg,F  = Pg,F -0.6457＋0.001703·υd

2.5 Stress optical coefficient B

The stress in glass can cause birefringence of light. The stress optical coefficient represents the relationship between stress and the optical path difference caused by stress birefringence:

δ= B·d·F

In the formula: δ - total optical path difference, nm；

B - Stress optical coefficient,/Pa;

D - the distance traveled by light through glass, cm；

F - stress, Pa。

2.6 Internal transmittance τ

The internal transmittance is the transmittance without surface reflection loss of the sample. Measure according to the method specified in GB/T 7962.12-2010. The internal transmittance values listed in the data table are for sample thicknesses of 10mm and 5mm, and the values listed in the data table are the average of multiple melting batches.

2.7 Chromaticity (λ 80/λ 5)

The short wave transmission spectral characteristics of optical glass are represented by chromaticity (λ 80/λ 5). The sample thickness is 10mm. λ 80 refers to the wavelength corresponding to the glass transmittance reaching 80%, and λ 5 refers to the wavelength corresponding to the glass transmittance reaching 5%, expressed in units of 5nm. For example, the wavelength corresponding to the glass transmittance reaching 80% is 368nm

When the transmittance reaches 5%, the corresponding wavelength is 313nm, and the chromaticity λ 80/λ 5 is 370/315, as shown in Figure 1.

When ne ≥ 1.85, due to the large reflection loss of glass, the coloring degree is replaced by the wavelength λ 70 corresponding to the glass transmittance of 70% instead of λ 80. The variation range of coloring degree is generally within ± 10nm.

Figure 1

2.8 Refractive Index Temperature Coefficient (dn/dT)

The refractive index of optical glass varies with temperature. The refractive index temperature coefficient in vacuum is called the absolute refractive index temperature coefficient, and the refractive index temperature coefficient in media such as air is called the relative refractive index temperature coefficient. The catalog lists the spectral lines t（1013.98nm）、 C ’（643.85nm）、d（587.56nm）、e（546.07nm）、 F’(479.99nm) And the relative refractive index temperature coefficient (dn/dT) rel of 6 spectral lines of g (435.83nm).

The relative refractive index temperature coefficient is calculated using the following formula:

In the formula: nrel - relative refractive index of the tested sample;

Dnair/dT - temperature coefficient of refractive index of air.

The temperature coefficient of air refractive index is shown in Table 3.

Within the wavelength range of 435.83~1013.98nm and temperature range of -60~140 ℃, the absolute refractive index temperature coefficient (dn/dT) abs corresponding to different temperatures and wavelengths can be calculated according to the following formula:

In the formula: (dn/dT) abs - absolute refractive index temperature coefficient;

D0, D1, D2, E0, E1, λ TK - Calculation constants related to glass grades;

λ - wavelength, μm；

T0- reference temperature, 20 ℃;

T - Temperature, ℃;

Δ T - temperature difference between T0;

N (λ, T0) - refractive index at wavelength λ and temperature T0.  

Table 3

3 Chemical properties

The ability of polished surfaces of optical glass components to resist various corrosive media during manufacturing and use is called the chemical stability of optical glass.

3.1 Moisture resistance stability RC (S) (surface method)

According to the testing method of GB/T 7962.15-2010, the moisture resistance stability is classified into four categories based on the comparison of turbidity values with standard samples H (BaK7) and H (ZK9), as shown in Table 4.

3.2 Acid stability RA (S) (surface method)

According to the testing method of GB/T 7962.14-2010, acid solutions are classified into 6 categories based on their stability, as shown in Table 5.

3.3 Water resistance stability DW (powder method)

According to the testing method of GB/T 17129, calculate according to the following formula:

Dw = image.png× 100%

In the formula: DW - glass leaching percentage,%;

B - Mass of filter and sample, g;

C - Quality of filter and corroded sample, g；

A - Filter quality, g。

According to the calculated leaching percentage, the water resistance stability Dw of optical glass is divided into 6 categories, as shown in Table 6:

Table 4

Table 5

Table 6

3.4 Acid resistance stability DA (powder method)

According to the testing method of GB/T 17129, calculate according to the following formula:

image.png 

In the formula: DA - glass leaching percentage,%;

B - Mass of filter and sample, g;

C - Quality of filter and corroded sample, g；

A - Filter quality, g。

According to the calculated leaching percentage, the acid resistance stability DA of optical glass is classified into 6 categories, as shown in Table 7:

Table 7

3.5 Weather resistance (CR)

Place the sample in a testing chamber with a saturated water vapor environment at a relative humidity of 90%, and cycle alternately every 1 hour between 40 ℃ and 50 ℃ for 15 cycles. According to the turbidity change before and after the placement of the sample, the weather resistance category is classified. Table 8 shows the classification of weather resistance.

Table 8

4 Thermal properties

4.1 Thermal expansion coefficient α

The thermal expansion coefficient of optical glass refers to the elongation per unit length of glass when the temperature rises by 1 ℃ within a certain temperature range. Measure according to the method specified in GB/T 7962.16-2010. The data table provides -30 ℃~+70 ℃

The average coefficient of thermal expansion between+100 ℃ and+300 ℃.

4.2 Transition temperature Tg

Optical glass gradually transitions from a solid state to a plastic state within a certain temperature range, and its transition temperature Tg refers to the temperature corresponding to the intersection point of the extension lines of the low temperature and high temperature regions of the glass sample from room temperature to the sag temperature Ts, as shown in Figure 2. Measure according to the method specified in GB/T 7962.16-2010.

Figure 2

4.3 Relaxation temperature Ts

As shown in Figure 2, the relaxation temperature Ts refers to the temperature at which the glass sample stops expanding during the heating process. Measure according to the method specified in GB/T 7962.16-2010.

4.4 Strain point T1014.5

The strain point is the temperature at which the glass viscosity is 1014.5dpa · s (or 1013.5pa · s), which is the temperature at which the internal stress in the glass can be eliminated after several hours, also known as the lower limit temperature of glass annealing.

4.5 Annealing point T1013

The annealing point is the temperature at which the glass viscosity is 1013dpa · s (or 1012pa · s), which can eliminate the internal stress of the glass within a few minutes, also known as the upper limit temperature of glass annealing.

4.6 Softening point T107.6

The softening point is the temperature at which the viscosity of the glass is 107.6 dpa · s (or 106.6 pa · s). The temperature at which the glass visibly softens and deforms under its own weight.

4.7 Thermal conductivity coefficient λ

The thermal conductivity coefficient is equal to the quotient obtained by dividing the heat flux density by the temperature gradient, that is, the heat per unit area per unit time divided by the temperature difference per unit distance, expressed in units of w/(m · k).

Note: 1 w/(m · k)=8.6000 × 10-1kcal/(h · m ·℃)=2.38889 × 10-3cal/(s · cm ·℃)

5 Mechanical properties

5.1 Young's modulus E, shear modulus G, and Poisson's ratio μ

The Young's modulus, shear modulus, and Poisson's ratio of optical glass are calculated using the following formula:

G = Vs2ρ

In the formula: E - Young's modulus, Pa；

G - Shear modulus, Pa；

μ - Poisson's ratio;

VT - longitudinal wave velocity, m/s；

Vs - transverse wave velocity, m/s；

ρ - glass density, g/cm3。

5.2 Knoop hardness HK

Knoop hardness is measured according to the testing method specified in GB/T 7962.18-2010. This method uses a four cornered diamond indenter with symmetrical edges of 172 °, 309 °, and 130 °. A certain load is applied vertically to the specimen and held for a certain period of time. After removing the load, the diagonal length of the indentation on the specimen is observed and measured under a microscope. The Knoop hardness is calculated according to the following formula:

In the formula: F - load, N；

D - the length of the diagonal of the indentation, mm；

HK - Knoop hardness, 107Pa.

5.3 Abrasion degree FA

Abrasion degree refers to the value obtained by multiplying the ratio of the wear amount (volume) of a sample to the wear amount (volume) of a standard sample (K9 glass) under identical conditions by 100, expressed by the formula as follows:

In the formula: V - volume wear of the tested sample;

V0- standard sample volume abrasion;

W - mass abrasion of the tested sample;

Wo - standard sample quality wear amount;

ρ - density of the tested sample;

ρ 0- standard sample density.

5.4 Density ρ

The density of optical glass refers to the mass per unit volume at a temperature of 20 ℃. The density of optical glass is measured according to the method specified in GB/T 7962.20-2010, expressed in g/cm3.

6 Glass Quality Indicators

6.1 Allowable deviation of refractive index nd and Abbe number ν d from standard values

The general allowable tolerances for refractive index nd and Abbe number ν d are:

Refractive index nd: ± 30 × 10-5

Abbe number ν d: ± 0.5%

When customers have requirements, the allowable tolerances for nd and ν d can be controlled within ± 20 × 10-5 and ± 0.3%; The allowable tolerances for nd and ν d of precision annealed products such as H-K9L, H-K9LGT, H-BaK7, and H-BaK7GT can be controlled within ± 10 × 10-5 and ± 0.2%. When customers have special requirements, please contact the sales personnel.

The refractive index and Abbe number are measured according to the testing method specified in GB/T 7962.1-2010, with a refractive index measurement accuracy of ± 3 × 10-5 and a central dispersion measurement accuracy of ± 2 × 10-5.

6.2 Optical Uniformity

6.2.1 Large caliber glass

Optical uniformity is represented by the maximum refractive index difference Δ nmax between different parts of the same glass, measured according to the testing method specified in GB/T7962.2-2010, and divided into 6 categories, as shown in Table 9.

Table 9

6.2.2 Ordinary optical glass strip material

The optical uniformity of ordinary optical glass strips is measured using the parallel light tube method, which is specified based on the change in resolution of the device caused by the glass sample placed in the parallel light tube beam. Assuming the theoretical resolution of the collimator is α 0, and when the glass sample is placed, the resolution becomes α, the non-uniformity of the glass is represented by the resolution method α/α 0 ratio and the star point method, divided into four levels, as shown in Table 10.

Table 10

6.3 Stress birefringence

6.3.1 Central stress

The stress birefringence of glass blanks is represented by the optical path difference δ per unit length in the middle of the longest edge, and is measured according to the method specified in GB/T 7962.5-2010. It is divided into four categories, as shown in Table 11.

Table 11

6.3.2 Edge stress

The stress birefringence of glass blanks is represented by the maximum optical path difference δ max per unit thickness at a distance of 5% from the edge diameter or edge length. It is measured according to the testing method specified in GB/T 7962.5-2010 and is divided into four categories, as shown in Table 12.

Table 12

6.3.3 Stress birefringence requirements for coarse annealed glass

Coarse annealed glass with a thickness of less than or equal to 20mm has an edge stress birefringence of less than or equal to 100nm/cm, while coarse annealed glass with a thickness greater than 20mm has an edge stress birefringence of less than or equal to 80nm/cm.

6.4 Stripe degree

The stripe meter composed of a point light source and a lens is used to compare and inspect the stripes with the standard sample from the direction where the stripes are most easily visible. It is divided into four levels, as shown in Table 13.

Table 13

6.5 Inclusions

The quality of inclusions in optical glass is measured according to the testing method specified in GB/T 7962.8-2010. The allowable inclusion content level in glass is determined by the total cross-sectional area of inclusions (diameter φ ≥ 0.03mm) contained in 100cm3 glass, divided into 5 levels, as shown in Table 14. Calculate the cross-sectional area of a flat inclusion by taking the arithmetic mean of its longest and shortest axes as the diameter.

Table 14

6.6 Light absorption coefficient

The light absorption coefficient is measured using a spherical photometer according to the testing method specified in GB/T 7962.9-2010. The light absorption coefficient is equal to the negative value of the natural logarithm of the internal transmittance of white light passing through glass per centimeter of distance. Divided into 8 categories, see Table 15.

Table 15

7 X-ray resistant glass and its X-ray resistance performance

The X-ray resistance performance of X-ray resistant optical glass, numbered 500-599, shall comply with the provisions of Table 16 when irradiated with X-rays at a total dose of 2.58 × 101C/kg (or 1 × 105R). The increase in optical density per centimeter thickness shall be expressed as Δ D1.

Table 16

8 Forms of Glass Supply

8.1 Optical Glass Blocks

Two major surfaces are finely ground, while the other four surfaces are roughly ground. The edges and corners are slightly chamfered and undergo precision annealing.

8.2 Optical Glass Strip Material

Two end faces are blasted surfaces, while the other four sides are naturally formed surfaces, which have undergone rough or fine annealing.

8.3 Optical Glass Molding Materials

8.3.1 Optical glass one-time molding blank

A one-time pressed billet is a billet formed by direct drip pressing through melting, and then subjected to precision annealing.

8.3.2 Optical glass secondary molding blank

The secondary pressing blank is processed and hot pressed again, and then subjected to precision annealing. The specifications and dimensional tolerances are shown in Table 17.

Table 17

8.4 Optical glass fruit shaped material (also known as Gobs material)

Gobs material, also known as fruit shaped material, is a rough material with a nearly circular cross-sectional area. Its weight or volume is determined according to customer needs and has not undergone precision annealing.

8.5 Other

Different melting processes have a significant impact on the infrared transmittance of optical glass. If there are special requirements for infrared transmittance, please contact the sales personnel in advance.

Please also contact the sales personnel in advance for any special requirements or large-sized glass requested by the customer.

F1, ZF1 and other non environmental optical glasses that have stopped production and H-ZK10 and other environmental optical glass brands with low production frequency have not provided printed data sheets. The company's website www.cdgmgd.com and WeChat official account have provided electronic data sheets. If you need relevant data, please log in and query.

For more product information, please visit the company's website www.cdgmgd.com or WeChat official account.

9 Mutual Search Catalog

The corresponding grades in the optical glass mutual retrieval table only refer to glass codes that are the same or similar, while glass components such as CDGM, HOYA, OHARA, and SCHOTT are different.