The determination of nitrogen in molybdenum and tungsten

The absorption vessels are measured with a y-y coincidence set-up with 2 Nal(Tl) detectors in a 180° geometry. To obtain the decay curve repeated 5 min measurements are made during 60 min starting 30 min after the irradiation. The decay curves corresponded to pure 

The results obtained were 505 + 35 ng/g (n = 4) and 74.0 + 1.2 ng/g (n = 4) for molybdenum and tungsten respectively. By deuteron activation using the B(d,n) C reaction and chemical separation of as described, upper limits for boron of 3.7 and 2.2 ng/g were found for molybdenum and tungsten respectively. This corresponds to an interference of less than 5.1 and 3.0 ng/g for nitrogen in molybdenum and tungsten, which is negligible at the actual nitrogen concentrations. 

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The molybdenum and tungsten contents were determined by atomic absorption spectrometry in areducing flame of acetylene-nitrogen protoxid at the Service Central d1 Analyse du C.N.R.S. (Lyon). 

According to Mallett (5), this procedure - melting of the sample together with solid sodium hydroxide in a nickel boat under a stream of hydrogen and determination by conventional means of ammonia, formed from the nitrogen compounds - can also be used successfully for molybdenum and tungsten. 

For tungsten and molybdenum carbides, an increase in substrate surface temperature leads to an increase of the lattice parameter of the film as a result of the increase in carbon concentration. The concentration seems to reach a maximum close to 50 mol% for 500 K in the Mo-C system and 700 K in the W-C system. At these temperatures, the respective M2C phase appears (Table 14.2). Figure 14.2 shows a plot of the carbon concentration (determined by AES) as a function of the substrate temperature. An opposite behaviour was observed for the nitrogen concentration in Mo-N films. Figure 14.3 shows that the N concentration in the a-MoN, phase (fee) decreased with substrate temperature.11 The phase domains were determined by X-ray and electron diffraction. No nitrogen was detected by AES in the Mo bee phase. No significant effect of temperature was observed on W-N films and Cr-N films. 

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