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A new thermo-chemical, low-temperature nitridation method was successfully used to introduce interstitial nitrogen into the passive layer aluminum alloy 2024 to enhance corrosion resistance. The nitridation process is based on treating the aluminum samples in potassium nitrate salt in an ultra pure nitrogen atmosphere at 475 °C. Electrochemical linear polarization and cyclic voltammetry measurements, combined with characterization of surface morphology, were used to evaluate the coating performance after two weeks of immersion in 3.5% NaCl solution. Electrochemical testing and sample examination after immersion in NaCl solution indicated that the treatment improved the resistance of AA2024 to localized corrosion, but there did not appear to be a statistically significant change in general corrosion. The effect of the quenching after nitridation was also studied. It is shown through polarization resistance, Rp, measurements that quenching increases the Rp measurably, suggesting quenching provides improved coating properties.

Newly developed low-temperature nitride synthesis route was used to introduce interstitial nitrogen into the passive layer of as-received and as-polished 316L stainless steel. The new thermochemical route is based on treating the stainless steel samples in potassium nitrate melt in an ultra pure nitrogen atmosphere at 450 °C. Electrochemical impedance spectroscopy (EIS) and dc polarization measurements have been used to evaluate the nitride layer performance in 3.5% NaCl solution. Results showed a marked increase in the corrosion resistance of nitrided stainless steel even after maintaining two weeks in NaCl solution. The effect of the treatment temperature was also studied. Data showed that the as-polished samples nitrided at 450 °C have the highest corrosion resistance. The polarization resistance ( R p ) for the as-polished and as-received blank stainless steel samples was estimated by EIS were approximately 4.0 × 10 4 Ω cm 2 and 2.0 × 10 4 Ω cm 2 , respectively. The R p increased by a factor of 2.5–5 for the nitrided samples. Increasing the nitriding temperature from 450 to 600 °C affects negatively the corrosion resistance of stainless steel in NaCl solution. The R p of the samples nitrided at 600 °C decreased sharply being almost 1/30 of the R p of the samples nitrided at 450 °C. Linear polarization measurements showed that the lowest corrosion rates and highest polarization resistances obtained from the as-polished nitrided samples at 450 °C. It has been found from the potentiodynamic measurements that the E corr of the as-polished nitrided samples at 450 °C is nobler than that measured from the other groups. The surface morphology was analysed by optical microscope and SEM-EDS under different nitriding conditions.

The reaction kinetics of ZrN and HfN immersed in a quaternary salt of composition of 28.5% LiCl–36.3% KCl–29.4% NaCl–5.8% UCl 3 (in weight percent) were assessed. Coupons of ZrN and HfN were exposed to the quaternary salt at 525–900 °C for 4–485 h. The reaction kinetics of the salt-refractory interactions were assessed through physical and microstructural characterization including scanning electron microscopy, X-ray diffraction and mass spectrometry. The results indicated that ZrN and HfN lose weight under all conditions investigated. While multiple mechanisms were evident, it is proposed that dissolution and oxidation were the dominant reactions that influence the weight loss. For the overall reaction, negative apparent activation energy values of −46 and −28 kJ/mol were observed in ZrN and HfN, respectively. These seemingly anomalous activation energies were associated with the simultaneous occurrence of electrochemical dissolution and surface oxide formation.

A high energy ball milling process was used to produce dysprosium nitride and cerium nitride powders at room temperature. Dysprosium and cerium metal flakes were milled in a 275 kPa nitrogen atmosphere for 24 h at ambient temperatures. X-ray diffraction confirmed the formation of phase pure dysprosium nitride and cerium nitride powders. The median particle size of the resultant dysprosium nitride was measured as 4 μm using a laser scattering technique. The particle size of the cerium nitride was not measured due to its reactive nature.

The characteristics of densification and distortion of a 80W–14Ni–6Cu alloy during liquid-phase sintering (LPS) were investigated in relation to the liquid-phase formation. By means of differential thermal analysis (DTA), the melting process of the Ni–Cu matrix in a die-pressed compact was examined and compared with that in a loose powder mixture. It was revealed that enhanced inter-diffusion and in situ alloying occur between the tightly compacted elemental Cu and Ni powders during heating, leading to an extended temperature range for Ni–Cu liquid formation. Dilatometry and furnace sintering tests showed that the early melting of the Ni–Cu matrix results in an onset of liquid-phase sintering at a lower temperature with die compaction. Full densification of the compact, together with satisfactory microstructure, can be achieved prior to full melting of the Ni–Cu matrix. Distortion is delayed until the end of liquid-phase formation.

A high energy, low-temperature, ball-milling route was used to directly produce uranium nitride. Pure uranium metal particles (∼100 μm) were ball milled under a 420 kPa nitrogen atmosphere for 24 h at ambient temperature to yield phase pure U 2 N 3 powder as confirmed by X-ray diffraction and energy dispersive spectroscopy. The median particle size was measured to be approximately 6 μm.