Low-Temperature Synthesis of Nano-AlN Based on Solid Nitrogen Source by Plasma-Assisted Ball Milling

Plasma-assisted ball milling was carried out on the Al+C3H6N6 system and Al+C_(4)H_(4)N_(4) system,respectively.The phase structure,functional groups and synthesis mechanism were analyzed by XRD and FT-IR,and the differences in the synthesis process of nano-AlN with different solid nitrogen sources were discussed.The results show that C3H6N6 has a stable triazine ring structure,and its chemical bond is firm and difficult to break,so AlN cannot be synthesized directly by solid-solid reaction at room temperature.However,there are a large number of nitrile groups(-CN)and amino groups(-NH_(2))in C_(4)H_(4)N_(4) molecules.Under the combined action of plasma bombardment and mechanical energy activation,C_(4)H_(4)N_(4) molecules undergo polycondensation and deamination,so that the ball milling tank is filled with a large number of active nitrogen-containing groups such as N=,≡N,etc.These groups and ball milling activated Al can synthesize nano-AlN at room temperature,with a conversion rate of 92%.SEM,DSC/TG analysis showed that the powder obtained by ball milling was formed by soft agglomeration of many fine primary particles about 50–80 nm.The surface morphology of the powder was loose and porous,and it had strong activity.After annealing at 800℃,the conversion rate of the Al+C_(4)H_(4)N_(4) system reached 99%.

Behavior of Fe Powder During High-Energy Ball Milling Cooperated with Dielectric Barrier Discharge Plasma

In this study, nanostructured Fe powders were synthesized following 10 hours of high-energy ball milling with a superimposed dielectric barrier discharge plasma （DBDP）. The mean size of the milled powder was approximately 100 nm with an average grain size of 16.2 nm. The influence of DBDP on the underlying grain refinement mechanisms during ball milling was investigated by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD） and BET methods. Our results show that the Fe particles displayed an extraordinary plasticity during the early milling stages under the action of DBDP, and that the plastic deformation experienced by the Fe particles during this stage was more severe than that present in normal milling. A high concentration of spherical Fe particles, approximately 50-100 nm in diameter, was documented via TEM. We propose that these spherical particles were generated via high temperature disintegration as a result of DBDP electron bombardment during ball milling. Our results suggest that it may be possible to significantly refine metallic powders during milling via the superimposition of DBDP.

Modeling and analysis of a dual-channel solar thermal storage wall system with phase change material in hot summer and cold winter area

A dual-channel solar thermal storage wall system with eutectic phase change material is studied.The full-day cooling load in summer and heating load in winter can be both decreased by this novel system.To investigate the airflow in the dual channel,mixed area assumptions based on the experimental results are summarized.Dynamic mathematical models of the system under four work modes are established and verified by the experimental results.The average RMSD(root mean square deviation)value is 0.35%in summer and 0.95% in winter.By analyzing the heat flux,the combination of dual channel and PCM is proven to decrease and delay cooling load both in the daytime and nighttime of summer.In winter's daytime,the thermal efficiency is promoted by the dual channel.And in winter’s nighttime,the system is able to heat the room constantly by the PCM boards.Based on parameter researches,the optimum phase change temperature range and the optimum thickness of the PCM are 26-30℃,1.5 cm in summer and 16-22℃,0.6 cm in winter respectively.To reach the optimum annual thermal performance,the coverage area is 2 m^(2) for this system.