ASTM D7667 Standard Test Method for Determination of Corrosiveness to Silver by Automotive Spark-Ignition Engine Fuel - Thin Silver Strip Method
9. Samples and Sample Preparation
9.1 Collect samples according to Practices D4057 or D4177 in clean, amber bottles made of borosilicate glass.
9.2 Close containers immediately after filling them to between 70 % to 85 % of their capacity. Adequate headspace in the container is necessary to provide room for possible thermal expansion during transport.
9.3 Take care during sampling, transportation and storage to protect the samples from exposure to direct sunlight or even diffused light.
9.4 Perform the test as soon as possible after receipt in the laboratory and immediately after opening the container. If necessary, store collected samples in a refrigerator or cold room, at a temperature not exceeding 5 °C (41 °F).
9.5 If suspended water (that is, haze) is observed in the sample, dry by filtering a sufficient volume of sample through medium rapid qualitative filter-paper, into the prescribed clean, dry test tube. Carry out this operation in a darkened room or under a light-protective shield.
NOTE 2 - Contact of the silver strip with water before, during or after completion of the test run will cause staining, making it difficult to evaluate the strips.
10. Preparation of Test Strips
10.1 Surface Preparation - To prevent possible surface contamination during preparation, do not allow fingers to come in contact with the silver strip. Wear disposable gloves, finger-tip protectors, or hold the strip in the fingers protected with ashless filter-paper.
10.2 Using a new/unused portion of a small strip of the 400-grit scouring-pad (see Note 1) first polish the ends, then the sides of the silver strip giving gentle, unidirectional strokes. Next, gently and unidirectionally, scour the long axis of the silver strip, carrying the stroke beyond the end of the strip before reversing the direction, until both surfaces demonstrate uniform asperities (roughness). Do not polish in a circular motion.
10.3 To restore the original luster of a used silver strip, it may be essential to polish it first with the 150-grit aluminum oxide cloth (using the same technique as that outlined in 10.2) followed by final polishing with the 400-grit scouring pad.
10.4 Wash the silver strip with wash-solvent (see 7.1), until it is free from metal dust and other foreign matter. Immediately store in the wash-solvent for use within 1 min.
