Nitrogen-to-metal ratio

Ion implantation techniqnes can lead to nitrides having extremely high nitrogen to metal ratio snch as TiNu bnt these phases are probably metastable. 

Much more so than the carbides, the interstitial nitrides are susceptible to the presence of even minute amounts of impurities particularly oxygen, vdiich tend to distort the structure. Like the carbides, the interstitial nitrides allow norunetal vacancies (i.e., nitrogen) in the lattice, but unlike the carbides, they also tolerate metal-atom vacancies. This means that, if the metal-atom vacancies are more numerous than the nitrcgen-atom vacancies, the nitrogen-to-metal ratio will be >1. As a result, the structure of interstitial nitrides is sometimes difficult to identify with certainty. 

Figure 11.4 Hardnesses of the interstitial nitrides vs. nitrogen-to-metal atomic ratio.

The pH was maintained at 5.0 by the addition of 2 M NaOH (Micro DCU-300 B. Braun Biotech). The fermentation temperature was 30°C and the stirrer speed was 500 rpm (MCU-200 B. Braun Biotech). Cell mass was produced in an initial batch phase using a glucose concentration of 64 g/L. The concentrations of mineral salts, trace metals, vitamins, and Ergosterol/ Tween-80 were the same as in the fed-batch experiments. When the glucose in the batch medium was completely consumed, 1.9 L of dilute-acid hydrolysate was pumped into the reactor at maximum pump speed, by using a peristaltic pump (Ul-M Alitea AB). The ratio between batch volume and the final volume (i.e., after all the hydrolysate had been added) was similar to the ratio in the PDU fed-batch experiments, approx 1 4. The reactor medium was sparged with nitrogen (600 mL/min). The C02 content in the exhaust gas was measured with a gas analyzer (TanDem Adaptive Biosystems, Luton, UK). 

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