Nanophase Composite Materials for Magnetic Refrigeration

该计划的目标是：(1)通过激光诱导气相颗粒形成过程生成相对单分散的含铁和铬的纳米颗粒；(2)通过表面放电/液氮电极组件有效去除颗粒。(3)将纳米颗粒固化成纳米相复合材料，并在不同的外加磁场下测量其增强的磁热效应；(4)将最大磁热制冷量的实验数据与理论数据进行比较。三种技术用于纳米级颗粒的生成：激光烧蚀，光解离解和热解。在激光烧蚀和光解离实验中，将使用工作在紫外频率范围内的准分子激光器。为了控制单分散纳米颗粒的生成，将优化反应室的结构、气体压力和流动模式。利用CO2激光的光解热解技术将被用于最终大规模生产高速率的纳米复合材料。利用CO2激光诱导热解工艺，可以大量制备新型纳米复合材料，用于构建室温下工作的磁性冰箱原型。采用气相成核工艺制备纳米复合制冷剂颗粒，并将其固结成磁矩增强的超顺磁性材料，将产生具有显著磁热效应的材料。

The objectives of the proposed program are (1) to generate relatively monodispersed nanoparticles containing Fe and Cr by laser-induced gas-phase particle formation processes, (2) to effectively remove particles by a surface discharge/liquid nitrogen electrode assembly , (3) to consolidate nanoparticles into nanophase composites and measure their enhanced magnetocaloric effect under varying external magnetic field, and (4) to compare the experimental data with theory for maximum magnetocaloric refrigerating capacity. Three techniques are used for the generation of nanometer- sized particles: laser ablation, photolytic dissociation, and pyrolysis. For both the laser ablation and photolytic dissociation experiments, excimer lasers operating in the ultraviolet frequency range will be used. The reaction chamber configuration, gas pressure and flow patterns will be optimized for controlled generation of monodispersed nanoparticles. The photolytic pyrolysis technique using CO2 lasers will be developed for the eventual scale-up production of nanocomposite at high rates. Using CO2 laser-induced pyrolytic process, the proposed new nanocomposite material may be prepared in large quantities for the construction of prototype magnetic refrigerators operating near room temperature. The creation of nanocomposite refrigerant particles by gas- phase nucleation processes and their consolidation into superparamagnetic materials with enhanced magnetic moments will result in significant materials with increases of the magnetocaloric effect.