Six Boride Lanthanum Nanometer Powder Preparation And Heat Insulation Performance Study

As the society pays more and more attention to problems of energy resources and the environment,the reasonable use of the sun energy is a very important research topic.LaB6 nanopowder which has obvious absorbing and scattering effect to NIR due to the localized surface plasmon resonance (LSPR) of conduction electrons is believed to be a new energy-saving and heat-insulating material. The synthesis of LaB6 nanopowder by solid-state reaction at a low temperature through microwave heating using LaCl3 and KBH4 as main starting materials was studied in this paper. The influence of processing parameters on the microstructure of LaB6 nanopowder, Fourier transform Infrared spectra (FTIR), Roman diffraction spectra and Thermal stability were also studied. In addition, Dispersion containing LaB6 nanopowder as well as LaB6/PVB thermal insulation coatings were prepared and the relationship between optical performance, microstructure and the effect of heat insulating was investigated.The reaction mechanism and change of microstructures during synthesis process of LaB6 were studied by DSC-TG, XRD and SEM. Results showed that reactions of LaCl3 and KBH4 occurred at 580℃. The grain size coarsed and crystallinity was higher with the temperature increasing; LaB6 nanocrystalline tended towards consummation as the holding time prolonged. In addition, additive adjuvant could reduce the reaction temperature and increase the production yeild. Finally, the synthesis process was optimized and LaB6 nanopowder was successfully achieved.The prepared products were refined by washing with deionized water and hydrochloric acid repeatedly, thus pure monophase LaB6 nanopowder. Results of XRD, SEM and TEM show that the synthesized LaB6 nanopowder is well crystallized and the particles are spheres-like with particle size between 10-60nm. The sample has a structure of Pm3m cubic crystal system, which is consistent with LaB6 synthesized by high-temperature reaction.FTIR results showed that there were two distinct absorption peaks at 1634 and 3436 cm-1, which corresponded to the two infrared active phonon T1u. In Raman spectra of LaB6 nanopowder, there were five peaks at 209,658,1107,1214 and 1130cm-1, of which peaks at 658,1107and 1214cm-1 corresponded to Raman active phonons of T2g, Eg and A1g respectively. Other two bands around 209 and 1130cm-1 were characteristic peaks of LaB6 sample. Compared with the aborption of micron-powder, obvious Einstein shift and band broadening occurred in nanopowder FTIR and Raman spectrum, which was thought to be related to the presence of lattice distortion and internal stress.The results indicated that the stability of LaB6 nanopowder decreased with reducing of the crystallinity. LaB6 nanopowder was oxidized dramatically at a high temperature. Transitional products La(BO3)2 and LaBO3 as well as a final product La2O3 were produced, which were oxidized slowly in the air to produce La(BO3)2, LaBO3, H3BO3 and so on.Ethanol dispersion containing LaB6 nonaparticles was prepared. The influence of different dispersion methods, process conditions an d dispersion agents on LaB6 ethanol dispersion were studied. The r esults showed that the optimal dispersion process was that adding p olyethylene glycol as a dispersing agent after a ball mill dispersing period for 12h, then ultrasonicly dispersing for 30min. The results o f optical performance measurement showed that for ethanol dispersi on containing LaB6 nanoparticles had high transmittance at visible li ght zone and could obviously block near-infrared radiation. The blo cking effect was more distinct with LaB6 content higher. Polyvinyl butyral resin (PVB) transparent thermal insulation coatings containin g LaB6 nanoparticles were obtained by coating methode. When the r atio of LaB6 is 0.05%, the transmittance is about 79% at visible lig ht zone (380-780nm) and the shielding efficiency of near-infrared r adiation (780-1000nm) was 54%, thus the PVB coatings containing LaB6 nanoparticles can block near infrared radiation. The temperatur e of the chamberloaded with the insulating glass was lower than th at of the one with theconventional glass for 5.0℃under the irradiati on of iodine-tungstenlamp for 60 minitues.Thus LaB6 nanoparticlesca n significantly reduce solar heat gain.