semi合集-English.pdf - 第4709页

SEMI C3.22-1000 © SEMI 1983, 2004 4 4.5.6 Standardiza tion 4.5.6.1 The method of analysis stated above can be used as a primary standard, meaning cylinders analyzed by this m ethod can be used as st andards of measuremen…

SEMI C3.22-1000 © SEMI 1983, 2004 3

4.5 Assay of Oxygen — This procedure describes the

assay of oxygen using an “Orsat” device. This is a

volumetric determination of nonabsorbable/reactable

gas.

4.5.1 Method Capability — 99.9% Oxygen.

4.5.2 Instrument Parameters — See Diagram A.

4.5.2.1 Equipment:

1. 1-100 mL calibrated certified buret, calibrated every

0.1 mL for the top 5 mL equipped with a 3-way

stopcock on the top.

2. 3-250 mL aspirator bottles.

3. 1 one-hole rubber stop.

4. 1-1/16 in OD soft copper wire made into hollow

coils 3/8 in OD by 3/4 in long.

5. Sufficient 3/8 in OD tygon tubing.

6. Sufficient surgical rubber tubing.

7. 1 gallon distilled water.

8. 2 lbs technical grade ammonium chloride.

9. 1 gallon 27% ammonium hydroxide.

4.5.2.2 Test Solution Preparation

4.5.2.2.1 Two pounds of technical grade ammonium

chloride are dissolved in one gallon of distilled water

and stored in a glass jar. One-half gallon of this solution

shall be combined with one-half gallon of 27%

ammonium hydroxide.

4.5.3 Equipment Assembly — The equipment is to be

assembled, as per Diagram A, in a suitable wood or

metal frame so arranged that the aspirator bottle

connected to the buret can be raised and lowered, as

required, to transfer the gas being analyzed to and from

the center aspirator bottle which is filled with copper

coils. The two leveling bottles should be filled half full

of testing solution and the buret and aspirator bottle,

which contains the copper coils, should be completely

filled.

4.5.4 Operating Procedure

4.5.4.1 Before analyzing the sample, perform a series

of analyses using a source of oxygen of which the

purity has been previously determined. This procedure

is necessary to age the test solution properly and

eliminate any air bubbles which may become trapped in

the apparatus. Only after three consecutive analyses

have been run, indicating the known purity, should you

proceed with testing. (See Note 7.)

4.5.4.2 Attach rubber tubing from the regulator of the

cylinder being tested to the stopcock of the buret.

Rotate the stopcock so as to draw the sample into the

gas measuring buret. Collect a little more than 100 mL

(i.e., below the zero mark) in the buret, and then rotate

the stopcock so as to shut off the oxygen flow and

remove the rubber tubing attached to the intake of the

buret. If the gas sample in the buret is below the zero

mark raise the leveling bottle #1 so that its “water”

level is even atmosphere so as to raise the “water” level

in the buret to exactly zero (Diagram B, Fig. #1).

4.5.4.3 Rotate the stopcock to connect the aspirator

bottle #3 containing the copper coils, and transfer the

oxygen into this aspirator bottle by raising the leveling

bottle #1 (Diagram B, Fig. #2). Invert bottle #3

containing the copper coils so that both the inlet stopper

and the sided outlet are in a downward position and

shake gently for 1 to 2 minutes. Stand test bottle #3 on

its base and lower the leveling bottle so as to withdraw

any residual gases into the gas measuring buret

(Diagram B, Fig. #3). Transfer at least 25 to 30 mL of

test solution from the left-hand leveling bottle #2 into

the right-hand leveling bottle #l, through the copper coil

bottle #3, and the gas buret while, at the same time,

gently rocking and tapping the center bottle (Diagram

B, Fig. #4). This will move any bubbles which might

cling to the copper coil into the gas measuring buret.

4.5.4.4 Turn the stopcock off and raise the leveling

bottle #l so that its liquid level is the same as the liquid

level inside the upper portion of the gas buret. When

the levels of the leveling bottle and the gas buret are the

same, read the gas purity markings on the buret at the

liquid level at this point.

4.5.5 Maintenance

4.5.5.1 Copper coils should be added to the test bottle

as required to keep the bottles completely full. The gas

buret should be kept clean with a strong detergent

solution to eliminate drops of liquid that might hang up

in the gas space and give incorrect purity readings. No

readings should be taken when the space above the

liquid level of the gas buret has any liquid drops

hanging in it, as this will give an erroneous purity

reading.

4.5.5.2 The solution must be replaced occasionally as

it becomes exhausted. The necessity of replacement

may be determined when the color begins to turn green,

and by the increased length of shaking time required to

get a minimum acceptable purity from the oxygen in a

cylinder of known purity. Suspect an exhausted solution

if analysis of a cylinder of known purity does not read

the correct purity.

4.5.6 Standardization

4.5.6.1 The method of analysis stated above can be

used as a primary standard, meaning cylinders analyzed

by this method can be used as standards of

measurement on electronic analyzers used to measure

oxygen.

4.5.6.2 This method is specific to oxygen when carbon

dioxide is not present in the sample gas. When carbon

dioxide is one of the components of the sample gas, the

carbon dioxide must first be scrubbed from the sample.

4.6 Notes

Note 1: The 0–1 range can be used provided that zero

and span gas standards in oxygen with known levels of

hydrocarbons between 0–1 ppm are used in the

calibration of the analyzer.

Note 2: As the flow rate and heat capacity of the matrix

gas affect the instrument output, the zero and span gas

matrices must coincide with that of the sample gas.

Note 3: The effective response of a flame ionization

detector-equipped total hydrocarbon analyzer to

different hydrocarbons can vary and must be

approximated. However, the response of the most

common hydrocarbon impurities in oxygen can be

accurately totaled and compared to methane.

Note 4: The sampling system and hygrometer must be

designed to operate under the sample pressure, or the

sample pressure must be reduced (by a regulator with

diaphragm of stainless steel or other suitable material)

to accommodate the pressure restrictions of the

analytical hygrometer.

Note 5: The National Institute of Standards and

Technology (NIST) provides calibration services for the

thermometers used in dewpoint/frostpoint hygrometers.

Note 6: This method is not applicable if other

constituents in the gas will condense before water

vapor, e.g., carbon dioxide and/or oil contamination.

Note 7: This procedure will be required only

immediately after changing the test solution or

contaminating the apparatus with air.

Buret

Diagram A