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        The chemical stability is the ability of polished surface to resist erosive substance of sorts during the glass component being processed and afterwards being applied.

3.1 Humidity resistance RC (S) (surface method)

        The humidity resistance of optical glass is classified into 3 grades according to the time required for a polished surface to form a hydrolyzing spot at the temperature of 50℃ and humidity of 85% (see table 3).

 

Table 3  

 Grade

1

2

3

 Time H

>20

5~20

<5

 

3.2 Acid resistance RA (S) (surface method)

        The acid resistance of optical glass is classified into 3 grades according to the time required for a polished surface to appear interference color or parti-color or fall-off in 0.1N (pH=2.9) acetic acid solution at the temperature of 50℃ (see table 4).

 

 Table 4

 Grade

1

2

3

  TimeH

>5

1~5

<1

3.3 Water Resistance DW (powder method) 

        Place 10g±0.0001g glass powder of grain size 450-560μm (sieved with 40~32 sized mesh) in the filter, soak into a silex glass flask filled with 80ml distilled water (pH=6.5~7.5). After constant temperature water bath ( 98~100℃) for 60 minutes, move all the glass grain to constant weight filter, wash with 80mL absolute ethyl alcohol, and then dry to constant weight at 120±5℃. Calculate the leaching percentage according to formula (13).

Where: DW—Soaking-out percentage;

B—Mass of filter and sample  g;

C—Mass of filter and soaked sample  g;

A—Mass of filter   g.

According to the calculation results, DW is classified into 6 grades as shown in Table 5.

 

Table 5  

 Grade

1

2

3

4

5

6

(%)

Soaking-out percentage

<0.04

≥0.04

<0.10

≥0.10

<0.25

≥0.25

<0.60

≥0.60

<1.10

≥1.10

 

 3.4 Acid resistance DA (powder method)

        The testing method is similar to DW, but 0.01mol/L Nitric acid aqueous solution is placed into the flask for treatment. Calculate the leaching percentage according to formula (14).

 

Where:            DA—Soaking-out percentage   %;

                        B—Mass of filter and sample   g;

               C—Mass of filter and soaked sample   g;

             A—Mass of filter   g.

According to the calculation results, DA is classified into 6 grades, as shown in Table 6.

Table 6  

 Grade

1

2

3

4

5

6

%Soaking-out percentage

<0.20

≥0.20

<0.35

≥0.35

<0.65

≥0.65

<1.20

≥1.20

<2.20

≥2.20

 

3.5 Alkali Resistance ROH(S) (surface method)  

        Dip a 40 mm×40 mm×5 mm sample polished for six surfaces into essentially stirred NaOH solution, whose constant temperature and concentration is 50±3℃, 0.01mol/L respectively, and the dipping time is fifteen hours. According to the calculated average value of the soaking mass in unit area and the unit is mg/(cm2·15h), the alkali resistance ROH (S)of optical glass is classified into 5 grades as shown in table 7.

Table 7  

 Grade

1

2

3

4

5

Soaking mass

mg/(cm2·15h)

<0.02

≥0.02

<0.10

≥0.10

<0.20

≥0.20

<0.30

≥0.30

3.6 Phosphate Resistance RP (S) (surface method)  

        Dip a 35 mm×35 mm×8 mm sample polished for six surfaces into essentially stirred Na5P3O10 solution, whose constant temperature and concentration is 50±3℃, 0.01mol/L respectively, and the dipping time is one hour. According to the calculated average value of the soaking mass in unit area and the unit is mg/(cm2·h), the phosphate resistance RP (S)of optical glass is classified into 5 grades as shown in table 8.

 

Table 8  

Grade

1

2

3

4

5

Soaking mass

mg/(cm2·15h)

<0.02

≥0.02

<0.20

≥0.20

<0.40

≥0.40

<0.60

≥0.60

 

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