Fluorides etching test

Fluoride. A portion of the dried residue (or of the original mixture) may be decomposed with concentrated sulphuric acid. Heat in a lead capsule or crucible with concentrated sulphuric acid and apply the etching test (Section IV.17, reaction 2). Alternatively, the water test (Section V.18, reaction 8) may be used. 

Fluoride, (i) Etching test (IV.17, 2). (ii) Silicon tetrafluoride test heat with concentrated sulphuric acid in a test-tube (IV.17, 1) better, test 8 in VII.16. 

FIGURE 16.3 Typical bond durability data for Ti-6 Al-4 V adherends bonded with an epoxy adhesive and aged at 60°C and 100 percent RH. (a) Crack propagation versus time for the wedge crack propagation test. (b) Applied stress versus time to failure for the lap shear geometry. PF—phosphate fluoride MPF—modified phosphate fluoride DP—PasaJell 109 dry hone LP—PasaJell 107 liquid hone CAA-5—-5% solution CAA-10—10% solution TU—Turco 5578 etch DA—Dapcotreat.50... 

The test may also be conducted in a small lead capsule, provided with a close-fitting lid made from lead foil. A small hole of about 3 mm diameter is pierced in the lid. About 0-1 g suspected fluoride and a few drops concentrated sulphuric acid are placed in the clean capsule, and a small piece of glass (e.g. a microscope slide) is placed over the hole in the lid. Upon warming very gently (best on a water bath) it will be found that an etched spot appears on the glass where it covers the hole. 

Wash well with cold water. Divide into two parts. (i) Smaller portion. Add excess dilute acetic acid and boil (this will dissolve any lead fluoride). White residue indicates sulphate. The residue is soluble in ammonium acetate solution. (ii) Larger portion. Treat cautiously with concentrated sulphuric acid and test with a moist glass rod. Milkiness of the water and etching of the tube indicate fluoride. Add Ba(N02)2 solution and warm gently. White crystalline precipitate indicates hexafluoro-silicate. 

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