Sum/de type Single cryslul Siugle crystal Siugle A vcrngc cvystnz Sample size (mg) f00.0 100.0 100.0 100.0 100.0 Tungsten, rcsiduc (mg) 74.5 7fi.G 7.b.8 75.9 Tungsten, Hz01 (rng) 75.4 2.54 2.14 2.2G 2.38 2.35 Silicon. rcsiduc (mg) 22.0 22.4 22.5 22.2 22.3 Silicon, 1-1~02 (mg) 0.22 O.?O 0.20 0.21 0.21 Mntcrial balzmcc (nig) 99.3 IO1 ..I 90.8 100.7 x00.3 n/0 Free tungsten I .82 1.58 I.GO r.Gg 1.67 ----___.. ---__ _-_---.--Spectrographic analysis showed that the total impurity was approximately 1250 p.p.m. The major impurities, molybdenum and iron, were each in the approximate concentration range 500 p.p.m. Since the rccommcncled procedure requires only IOO rng of sample, complete extraction of the molybdenum and iron by hydrogen peroxide would yield about 50 pg of each. Tests with the clithiol extraction spectrophotometric method for molybdenum
showed that no molybdenum was in fact extracted. Therefore, molybdenum was probably present as the silicide and not as free molybdenum.
By means of the o-phenanthrolinc method, the level of iron in the hydrogen peroxide fraction was found to be insignificant.
S-Ray diffraction analysis indicated that free tungsten, i.f present, was less than 5%. Reportedly, this tcchniquc is not sensitive enough to determine fret tungsten in the I+.(~, concentration range.