Dysprosium nitride was synthesized by the reactive milling of the rare earth metal under 400 kPa nitrogen gas in a planetary ball mill. The nitrogen consumption rate was calculated from in situ temperature and pressure measurements to find the reaction extent as a function of milling time at milling speeds from 350 to 650 rpm. The results are analyzed in terms of a fundamental milling dynamics model in which the input milling energy is the primary driving force for reaction and the rate limiting step of the nitridation kinetics is the formation of chemically active surfaces. The model differs from traditional gas-solid reactions which are often limited by diffusion of a species through a surface layer or by dissociation of the gas molecule. These results give fresh insight into reactive gas-solid milling kinetics. (C) 2014 Elsevier B.V. All rights reserved.

Processing of advanced nitride ceramics traditionally requires long durations at high temperatures and, in some cases, in hazardous atmospheres. In this study, dysprosium mononitride (DyN) was rapidly formed from elemental dysprosium in a closed system at ambient temperatures. An experimental procedure was developed to quantify the progress of the nitridation reaction during mechanochemical processing in a high energy planetary ball mill (HEBM) as a function of milling time and intensity using in situ temperature and pressure measurements, SEM, XRD, and particle size analysis. No intermediate phases were formed. It was found that the creation of fresh dysprosium surfaces dictates the rate of the nitridation reaction, which is a function of milling intensity and the number of milling media. These results show clearly that high purity nitrides can be synthesized with short processing times at low temperatures in a closed system requiring a relatively small processing footprint. Published by Elsevier B.V.

Polycrystalline 3 C silicon carbide ( SiC ) was implanted at room temperature with 400 keV cesium ions to a dose of 10 16 ions/cm 2 . The samples were annealed at 600°C–1000°C for times up to 48 h to observe changes in the implantation zone crystallinity and density. The implanted regions were characterized by transmission electron microscopy ( TEM ) and secondary ion mass spectroscopy ( SIMS ) before and after annealing. It is shown that the implantation resulted in a 217 ± 2 nm amorphous region with microstructural damage extending to ~250 nm below the surface. Recrystallization of the amorphous region was observed to begin at 725°C. Densification was determined indirectly through changes in the measured implantation zone thickness. Measurable thickness, or densification, of the implanted region was not observed until temperatures greater than ~800°C. The SiC recrystallization began at the interface between the amorphous, damaged region, and the underlying polycrystalline material. Image analysis was used to quantify the fraction of crystalline phase as a function of time and temperature. The recrystallization kinetics exhibited Arrhenius dependency with an apparent activation energy of 480 kJ/mol. SIMS demonstrated that 60%–70% of the cesium was retained within the recrystallized microstructure after thermal annealing.

The influence of dysprosia addition on the sintering and resulting microstructure of nano-grained CeO2 ceramics was investigated as functions of the spark plasma sintering parameters. The addition of Dy2O3 (forming a solid solution) resulted in an increase in relative density and a decrease in grain size in sintered samples. The relative density of samples with Dy2O3 content of 6 and 10mol% was over 95% when sintered at 1050 degrees C under 500MPa for holding times as short as 5min. The application of high pressure facilitated the consolidation to relatively high densities with minimal grain growth. Heating rate and holding time, however, had insignificant effect on density but a measurable effect on grain size.

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 275kPa nitrogen atmosphere for 24h 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 4μm using a laser scattering technique. The particle size of the cerium nitride was not measured due to its reactive nature.