Solid-state Synthesis,Characterization And Properties Of Carbides And Nitrides

In this paper, based on the investigation of the synthesis and properties of carbides and nitrides, a series of carbides and nitrides have been prepared in mild temperature and their electric property has been researched preliminarily. The main points are summarized as follows:1. The preparation of metal carbides with metal oxides as metal source has the advantage of cheaper raw materials and simple operation, In the paper, we use different carbon sources (carbide and discarded PTFE), to synthesise a series of transition metal carbides with the assistant of metal reduction. Several carbides (TiC, V2C, Mo2C) were prepared by using the corresponding oxides (TiO2, V2O5, MoO3), CaC2and Mg as starting materials in a stainless steel autoclave at600℃. In addition, using Na as a reducing agent, a series of carbides (TiC, VC, NbC, Mo2C) were prepared from waste PTFE and the corresponding oxides (TiO2, V2O5, Nb2O5, MoO3). This Na reduction-thermal treatment method provides an efficient way to turn the waste PTFE to valuable transition metal carbides. Related research results were pubished on International Journal of Refractory Metals and Hard Materials and Materials Chemistry and Physics.2. GaN nanocystalline was synthesized in a stainless steel autoclave at400-550℃by using Ga2O3as gallium source and NaNH2as nitrogen source. X-ray powder diffraction (XRD) pattern indicated that the product was hexagonal GaN, which is consistent with the database of standard card (JCPDS card No.76-0703). In addition, the GaN nanoparticles recrystallize and grow with increasing reaction temperature. The product was also studied by the thermogravimetric analysis (TGA). The results indicated that it had good thermal stability and oxidation resistance below750℃in air and1000℃in nitrogen atmosphere.3. Cubic NbN and hexagonal NaNbN2were selectively synthesized in a stainless steel autoclave at400-700℃by using Nb2O5, NaN3and different metal reducing agent (magnesium or aluninium) as starting materials. When magnesium was used as a metallic reductant, NbN can be synthesized at400℃for10h. If the metallic reductant was replaced by aluminum, NaNbN2was obtained at700℃for40h. The resistivity curve against temperature of NbN sample indicated that the superconducting transition of the NbN sample is found to occur at17K. The obtained NaNbN2sample can be indicated as a semiconductor. Related research results were pubished on Journal of Nanoscience and Nanotechnology.4. With the solid state reaction of molybdenum trioxide, sodium azide and magnesium powder, we prepared MgMoN2micromeshes and cubic Mo2N by adjusting the amount of magnesium,The new layered structure ternary nitride (MgMoN2) was synthesized by using MoO3, Mg and NaN3in a stainless steel autoclave at700℃. The crystal structure of MgMoN2was investigated through powder X-ray analysis. The nitride crystallized in the hexagonal system P63/mmc. SEM shows that the obtained MgMoN2are composed of micromeshes with average pore size of1μm. The formation mechanism of MgMoN2was considered through an oriented aggregation process, in which the in-situ produced MgO microparticles served as template. As MoO3was substituted by other Mo source (such as (NH4)6Mo7O24·4H2O or Na2MoO4·4H2O), MgMoN2micromeshes with different pore sizes could also be produced. It is a general way for the convenient synthesis of MgMoN2micromeshes. This porous material might be valuable for a range of potential applications, including catalyst supports, separations and chemical filtration. Furthermore, as the amount of magnesium powder was reduced, cubic Mo2N irregular nanocrystals can be selectively synthesized. Related research results were pubished on Journal of Materials Chemistry.