ASTM B457-67 pdf free

04-16-2021 comment

ASTM B457-67 pdf free.Standard Test Method for Measurement of Impedance of Anodic Coatings on Aluminum.
The electrolyte shall be a 31/% solution of sodiumchloride prepared by dissolving 36 g of the salt in 1 L ofdistilled or deionized water. The area to be tested should be sufficiently large toaccommodate the test cell, sufficiently flat to prevent leakage of the solution from the probe,and free from mechanicaldefects such as scratches. After an anodic coating has beensealed,moisture is lost from the coating thus producing anincrease in impedance. The rate at which moisture is lostincreases as the relative humidity decreases; therefore,therelative humidity of the testing environment should be con-trolled and never below 25 %. Specimens should be testedwithin 1 h after the anodic coating has been sealed. If thiscannot be done or if the part has been subjected to an elevatedtemperature drying treatment,the test area should be conditioned as follows:Wipe the test area with acetone,methylethylketone,trichloroethylene, or similar solvent. Immerse the test area in pure boiling water for 30 s.5.1.3 Rinse in cold water.Blot dry and test without further delay. Penetrate the anodic coating in a small area with a sharpinstrument and connect the lead from the low-impedanceterminal of the bridge to the exposed aluminum substrate.Connect the other lead from the bridge to the counterelectrode of the test cell. Be certain the lead wires are nottwisted around each other. Turn on the bridge and allow it towarm up.Place the test cell on the area to be tested and applyenough pressure,490 to 1230 MPa (71 to 178 psi) to preventleakage of the electrolyte (the cell is spring-loaded to ensuresufficient and constant pressure).Make certain the bottom ofthe gasket on the test cell is level with the test surface.Fill the test cell at least half full with electrolyte andcommence a 2-min soak period. The counter electrode shouldnot contact the test specimen. Using the test cell,make at least two impedancemeasurements and average on this same area of the specimenused for standardization. Record this as B.If the two measure-ments are not within 10 %, an additional measurement shouldbe made and the two values within 10 % averaged.ASTM B457 pdf download.

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