Preparation Of Nano-size AlN Powders With Solid Nitrogen-containing Organic Compounds As Nitrogen Source By Wet Chemical Method

As an important member of Group III nitride,aluminum nitride?AlN?has attracted much attention from many scholars and research units for its excellent comprehensive properties.For instance,AlN is an important structural ceramic material owing to good mechanical strength and high melting temperature.AlN is an excellent electronic substrate material for its high thermal conductivity,low dielectric constant and low linear thermal expansion coefficient with silicon.AlN holds promising applications in both deep ultraviolet?UV?optical devices and photoluminescent?PL?host matrix materials for its largest bandgap?6.2 eV?in Group III nitrides.However,High quality AlN powder is the prerequisite for the preparation of high-performance Al N ceramics.Therefore,it is of great significance to explore the new methods for the synthesis and morphology control of AlN.In addition to traditional processing routes,a new method has been developed recently to synthesize nitride with solid nitrogen-organic compounds?SNCOCs?as N source,such as urea?CH₄N₂O?,cyanamide?CH₂N₂?,dicyandiamide?C₂N₄H₄?and melamine?C₃H₆N₆?.Compared with the methods of carbothermal nitridation and direct nitridation of aluminum powders,this method has the advantages of easy availability of raw materials,low cost and low synthesis temperature,and powders with higher purity can be directly obtained without post-processing by dangerous ammonia or decarburization.Therefore,the objective of this research was to introduce the solid nitrogen-containing organic compounds as N source to synthesis nano-size AlN powder.In this research,urea was selected as N source to explore the process of synthesizing nano-size AlN powder.The influence of the calcination mode,holding time,nitrogen flow rate,reaction temperature and molar ratio of urea to metal on the purity and morphology of synthesized nano-size AlN powder were studied.The optimal process route to synthesise AlN powder is determined as follows:The AlN powder was synthesized by calcining the precursor salt powder with urea/metal molar ratio of 6 at a nitrogen flow rate of 0.4l L/min,holding time of 6h and reaction temperature of 1000?.The Fourier-transform infrared spectrometer?FT-IR?and thermogravimetric differential scanning calorimetry analyzer?DSC-TG?were used to analyze the structure and thermogravimetric of AlN precursor salts,the phase and morphology of the final obtained AlN powder were characterized by X-ray diffractometer?XRD?,scanning electron microscopy?SEM?and transmission electron microscope?TEM?,the optical properties of AlN were analyzed in detail by Ultraviolet visible spectrophotometer?UV-Vis?and fluorescence spectrometer?PL?.Then,we also selected dicyandiamide and melamine as N source to synthesis nano-size AlN powder according to the higher nitrogen content of cyanamide carbonitride.By analyzing the characterization results of calcined products such as XRD?SEM and TEM,the effects of the molar ratio of N source/metal and the reaction temperature on the structure and morphology of the calcined products were discussed.The mechanism of reaction with aluminum salt to form AlN during the decomposition of dicyandiamide and melamine is summarized.Finally,the photoluminescence properties of AlN are discussed in detail via PL and UV-Vis test analysis.Finally,the following conclusions are obtained through experimental research and analysis:1.In the experiment of using urea as N source,the precursor was mainly aluminum-urea chloride complexes.when the molar ratio value of urea/metal reaches 4,66.37%AlN powder was obtained,and when the molar ratio of urea/metal reaches 6,pure AlN powder can be obtained;When the calcination temperature rises from 900?to1000?,the carbonitride of AlN layer decreases rapidly and the crystallinity of AlN becomes better;In addition,with the increase of urea content,spherical agglomeration of AlN powders appeared,and the crystallinity of the powder becomes better and the band gap increases;2.In the experiment of using dicyandiamide as N source,the precursor was mainly a mixture of dicyandiamide and aluminium chloride hydrate.when the molar ratio of dicyandiamide/metal reaches 2,61.44%AlN powder was obtained,and when the molar ratio of urea/metal reaches 3,pure AlN powder can be obtained;When the calcination temperature rises from 900?to 1000?,the crystallinity of AlN becomes better;With the increase of the content of dicyandiamide,the crystallinity of AlN becomes better,its particle size increases,and the optical band gap increases firstly?R3-R5?and then decreases?R5-R7?.3.In the experiment of using dicyandiamide as N source,the precursor was mainly a polymer of melamine and aluminium chloride hexahydrate.When the molar ratio value of melamine/metal reaches 3 and the temperature reaches 1000?,pure AlN powder was obtained;With the increase of melamine content,the crystallinity of AlN becomes better,and the optical band gap increases firstly?R3-R5?and then decreases?R5-R6?.4.The comparative study on the preparation of Al N nanocrystalline powders with three nitrogen sources shows that they have some regularity in the regulation of grain size and band gap width.Among them,the nano-size AlN powder prepared by dicyandiamide have better crystallinity,the average particle size is the largest and the optical band gap width is the smallest,while the crystallinity of the nano-size Al N powder prepared by melamine is not enough,the average particle size is the smallest and the optical band gap width is the largest.The crystallinity and particle size of AlN powder prepared by urea as nitrogen source almost remained unchanged when the molar ratio value of urea to metal reaches 8.In addition,the optical band gap showed a linear change with the increase of urea content.