摘要
纳米Mo-ZrO_(2)(Y_(2)O_(3))复合粉末是一种很有发展前景的粉末冶金材料。采用溶胶凝胶法制备前驱体复合粉末,并对得到的前驱体复合粉末采用高温氢还原工艺制备Mo-ZrO_(2)(Y_(2)O_(3))复合粉末。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和能谱分析(EDS)等分析检测技术对前驱体复合粉末的物相组成和微观结构进行表征,并分析不同的还原时间和温度对高温氢还原后Mo-ZrO_(2)(Y_(2)O_(3))复合粉末的物相组成及微观组织结构的影响。结果表明,在400-650℃下煅烧后的前驱体粉末物相均由MoO3组成;随着煅烧温度的升高,粉末形貌按照薄片状-片层状-长棒状规律演变;在保温3 h条件下,MoO3还原成Mo的起始温度为550℃;如果采用一步还原的方法,煅烧产物MoO3完全转换为Mo的还原温度必须高于650℃;溶胶凝胶结合高温氢还原能够制备纳米级别且纯度较高的Mo-ZrO_(2)(Y_(2)O_(3))复合粉末,团聚的复合粉末由80-100 nm细小颗粒组成,ZrO_(2)(Y_(2)O_(3))均匀地分布在Mo基体粉末中。
Molybdenum and its alloys had a low coefficient of thermal expansion,superior electrical and thermal conductivities,good high-temperature strength and creep resistance,and excellent high-temperature dimensional stability. Therefore,as high-temperature components,molybdenum and its alloys were widely used in aerospace,electronic communications,electrical equipment,space vehicles and other high-temperature parts. However,to some extent,the low recrystallization temperature(about 1000 ℃),inherent brittleness and insufficient strength hindered their practical application. It was well known that ultrafine grained or nanocrystalline materials have better mechanical properties than that of the conventional coarse-grained materials. Therefore,preparing ultrafine grained or nanocrystalline composite materials was an effective way to enhance the mechanical properties. Moreover,Y_(2)O_(3) partially stabilized ZrO_(2) had a great potential in improving the comprehensive mechanical properties of molybdenum and its alloys. However,the study had not yet reported the preparation of the Mo-ZrO_(2)(Y_(2)O_(3))nanometer composite powders. The nanometer Mo-ZrO_(2)(Y_(2)O_(3))powders were prepared by sol-gel and high temperature hydrogen reduction,the details were as follows:Firstly,the raw materials of Zr(NO3)4·5H2O,Y(NO3)3·6 H2O and C6H8O7·H2O were dissolved in the distilled water according to a certain proportion and continuously heated with thermostat water bath cauldron at 85 ℃ to form wet gel. Secondly,the wet gel was dried at 110 ℃ for 10 h to obtain the dry precursor powder,and the powder subsequently calcinated at 400~650 ℃ for 5 h in a muffle furnace. At last,the effects of different reduction time and temperatures on the phase composition and microstructure of the Mo-ZrO_(2)(Y_(2)O_(3))composite powders after high temperature hydrogen reduction were also analyzed. The reduction parameters were discussed as follows:(1)reduction time:the powders were reduced at 550 ℃ for 1~5 h in H2 atmosphere;(2)reduction temperature:the powders were reduced at 350~900 ℃ for 3 h in H2 atmosphere. Phase composition and microstructure of the precursor composite powders were investigated by X-ray diffraction(XRD),scanning electron microscope(SEM),transmission electron microscope(TEM)and energy dispersive spectroscopy(EDS). The calcinated powders were composed of single MoO3 when the dry precursor powders were calcined at 400 to 650 ℃ for 5 h. An increase in the grain size of the calcined powders was observed with the enhancement of the calcination temperature. When the calcination temperature was varying from 400 to 550 ℃,the calcined MoO3 powders showed the characterization of lamellar and smooth microstructure,and the agglomeration phenomenon appeared in the powders. When the calcination temperature increased up to 600 or 650 ℃,the grain size of MoO3 powders continued to grow. The powders showed the shape of rod after the dry precursor powders were calcined at 650 ℃. It indicated that the particle size distribution of the composite powders was relatively uniform after the dry precursor powders were calcined at 550 ℃ for 5 h. When the calcined powders were reduced at 550 ℃ for 1 h,the powders were composed of MoO3 and a small amount of MoO_(2),and the particles of the reduced powders showed the characterization of lamellar(MoO3)and granular(MoO_(2))morphologies. With extending the reduction time to 3 or 5 h,the diffraction peak of MoO3 disappeared and the MoO_(2) phase appeared,and a small amount of the Mo phase formed,which indicated that the reduction time of transforming MoO3 to Mo phase at 550 ℃ needed at least 3 h. According to the relationship between reduction temperature and products,the reduction temperature could be divided into three stages. With an increase of the temperature from 350 to 600 ℃,MoO3 powders were first reduced to Mo4O11 and subsequently amount of Mo. When the reduction temperature varied from 650 to 900 ℃,the products were composed of Mo. It was obvious that the temperature of reducing all the calcined MoO3 powders to Mo should be over 650 ℃. When the reduction temperature was 350 ℃,the morphologies of the powders were lamellar(MoO3)and granular(MoO_(2)). When the reduction temperature increased up to 450 ℃,the morphology of the powders gradually changed from lamellar to granular structure. After reducing at 550 ℃,the powder exhibited the irregular granular. When the reduction temperature was 600 ℃,the irregular granular particles gradually decreased and changed into the spherical Mo particles. When the reduction temperature was further increased up to 650-850 ℃,the agglomeration phenomenon of the powders was more obvious,and the agglomerated particles were composed of fine near-spherical particles. The Mo powder particles tended to grow up due to the high reduction temperature. The TEM image indicated that the agglomerated composite powders were made of nanometer Mo-ZrO_(2)(Y_(2)O_(3))particle with the size of 80~100 nm,and the EDS results further proved that the composite powders were composed of Mo and ZrO_(2)(Y_(2)O_(3))particles. In addition,Mo-ZrO_(2)(Y_(2)O_(3))powders contained 0.11% C,1.53% O and 0.07% N. It indicated that the combination of sol-gel and high temperature hydrogen reduction could prepare the nano-grained and high purity MoZrO_(2)(Y_(2)O_(3))composite powders. TEM analysis of Mo-ZrO_(2)(Y_(2)O_(3))composite powders reduced at 750 ℃ for 3 h further confirmed that the composite powders were composed of nano-Mo and ZrO_(2)(Y_(2)O_(3)),and the elements of Zr and Y were uniformly distributed in the Mo matrix in the form of oxide ZrO_(2) and Y_(2)O_(3). The results showed that the compositions of the precursors,which were calcined at 400-650 ℃,were composed of MoO3. With an increase in the calcination temperature,the morphologies of the powders evolved in the form of flakes-lamellar-long rods. The reduction temperature was 550 ℃ when MoO3 were initially reduced to Mo. The temperature should be over 650 ℃ using a one-step reduction method when the MoO3 was completely reduced to Mo powder. Nanometer Mo-ZrO_(2)(Y_(2)O_(3))composite powder with high purity was prepared by sol-gel and high-temperature hydrogen reduction method. The agglomerated composite powder was made of nanometer Mo-ZrO_(2)(Y_(2)O_(3))particle with the size of 80~100 nm,and ZrO_(2)(Y_(2)O_(3))particles were uniformly distributed in the Mo matrix powder.
作者
康蓉
颜建辉
李茂键
Kang Rong;Yan Jianhui;Li Maojian(College of Materials Science and Technology,Hunan University ofScience and Technology,Xiangtan 411201,China;Hunan Provincial Key Defense Laboratory of High Temperature Wear Resisting Materials and Preparation Technology,Hunan University of Science and Technology,Xiangtan 411201,China;Hunan Provincial Key Laboratory of Advanced Materialsfor New Energy Storage and Conversion,Hunan University of Science and Technology,Xiangtan411201,China)
出处
《稀有金属》
EI
CAS
CSCD
北大核心
2021年第3期288-296,共9页
Chinese Journal of Rare Metals
基金
国家自然科学基金项目(51475161)
湖南省自然科学基金项目(2020JJ4025)
湖南省研究生科研创新项目(CX20190837)资助。
作者简介
康蓉(1995-),女,陕西省渭南人,硕士研究生,研究方向:难熔金属及其化合物,E-mail:657974926@qq.com;通信作者:颜建辉,教授,电话:0731-58290847,E-mail:yanjianhui88@163.com。
