Shape-Controlled Synthesis of ZnS Nanostructures: A Simple and Rapid Method for One-Dimensional Materials by Plasma

In this paper, ZnS one-dimensional (1D) nanostructures including tetrapods, nanorods, nanobelts, and nanoslices were selectively synthesized by using RF thermal plasma in a wall-free way. The feeding rate and the cooling flow rate were the critical experimental parameters for defining the morphology of the final products. The detailed structures of synthesized ZnS nanostructures were studied through transmission electron microscope, X-ray diffraction, and high-resolution transmission electron microscope. A collision-controlled growth mechanism was proposed to explain the growth process that occurred exclusively in the gas current by a flowing way, and the whole process was completed in several seconds. In conclusion, the present synthetic route provides a facile way to synthesize ZnS and other hexagonal-structured 1D nanostructures in a rapid and scalable way

Preparation and characterization of Ni-Cu composite nanoparticles for conductive paints

Ni and Cu are the two most promising alternatives to noble metals used in electrical conductive materials. However, Cu is susceptible to oxidation, while Ni exhibits poorer electrical conductivity. To solve this problem, Cu-Ni composite nanoparticles have been prepared in the present work by successive hydrazine reduction based on the different oxidation potential between Cu (II) and Ni (II). The as-prepared products were characterized by XRD, FE-SEM, EDS, and TG, and the electrical resistivity of which was measured by four-probe method. A formation process of the composite particles was proposed and demonstrated. The Cu-Ni composite nanoparticles have a uniform diameter of about 50nm, and exhibit higher oxidation temperature than Cu and lower electrical resistivity than Ni. This novel Ni-Cu structure and method might help solve the problems associated with the oxidation of Cu and the low electrical conductivity of Ni, which would further promote the application of base metal conductive powders

RF Thermal Plasma Synthesis of Ultrafine ZrB2-ZrC Composite Powders

Ultrafine ZrB2-ZrC composite powders were synthesized via a radiofrequency (RF) thermal plasma process. Numerical simulation and thermodynamic analysis were conducted to predict the synthesis process, and experimental work was performed accordingly to demonstrate its feasibility. The as-prepared samples were characterized by XRD, FESEM, particle size analyzer, nitrogen/oxygen analyzer, Hall flowmeter, and the Brunner-Emmet-Teller (BET) measurements. The thermodynamic analysis indicated that ZrB2 was preferentially generated, rather than ZrC, and numerical simulation revealed that the solid raw materials could disperse well in the gaseous reactants, and experimental work showed that free carbon particles were easily removed from the products and the elements of Zr, B, C, and O exhibited a uniform distribution. Finally, ZrB2-ZrC composite powders with a particle size of about 100 nm were obtained, the surface area of which was 32.15 m2/g and the apparent density was 0.57 g/cm3

Mater. Lett.

Well dispersed nickel nanoparticles with uniform size were synthesized via a modified hydrazine reduction route without any surfactant introduced. Ethanol was used as solvent and played the complementary reducing role. The as-prepared samples were characterized by XRD, FESEM, TEM and TG. Pure metallic Ni could be easily obtained when ethanol instead of water was used as solvent. The particle surface was much improved when ethanol was involved in the reduction process at high temperature. The resultant particles have smooth surface and uniform size of about 50 nm. The nickel powders have an oxidization temperature of about 200 degrees C. The formation process was discussed based on the experimental results. (c) 2007 Elsevier B.V. All rights reserved.Well dispersed nickel nanoparticles with uniform size were synthesized via a modified hydrazine reduction route without any surfactant introduced. Ethanol was used as solvent and played the complementary reducing role. The as-prepared samples were characterized by XRD, FESEM, TEM and TG. Pure metallic Ni could be easily obtained when ethanol instead of water was used as solvent. The particle surface was much improved when ethanol was involved in the reduction process at high temperature. The resultant particles have smooth surface and uniform size of about 50 nm. The nickel powders have an oxidization temperature of about 200 degrees C. The formation process was discussed based on the experimental results. (c) 2007 Elsevier B.V. All rights reserved

Progress in Preparation of ZrB2 Nanopowders Based on Traditional Solid-State Synthesis

ZrB2 is of particular interest among ultra-high temperature ceramics because it exhibits excellent thermal resistance at high temperature, as well as chemical stability, high hardness, low cost, and good electrical and thermal conductivity, which meet the requirements of high-temperature components of hyper-sonic aircraft in extreme environments. As raw materials and basic units of ultra-high temperature ceramics and their composites, ZrB2 powders provide an important way for researchers to improve material properties and explore new properties by way of synthesis design and innovation. In recent years, the development of ZrB2 powders’ synthesis method has broken through the classification of traditional solid-phase method, liquid-phase method, and gas-phase method, and there is a trend of integration of them. The present review covers the most important methods used in ZrB2 nanopowder synthesis, focusing on the solid-phase synthesis and its improved process, including modified self-propagating high-temperature synthesis, solution-derived precursor method, and plasma-enhanced exothermic reaction. Specific examples and strategies in synthesis of ZrB2 nano powders are introduced, followed by challenges and the perspectives on future directions. The integration of various synthesis methods, the combination of different material components, and the connection between synthesis and its subsequent application process is the trend of development in the future

Synthesis of Nickel Powders: From Spheres to Monodispersed Clusters

Well dispersed nickel powders with uniform size were synthesized using hydrazine hydrate as reducing reagent, with no surfactant introduced. The morphology of the products could be controlled from smooth spheres to flowerlike clusters by simply choosing solvent and adjusting the molar ratio of NaOH/Ni or N2H4/Ni. A two-step reduction process was proposed for the formation mechanism based on the experimental results. The crystal phase of the as-prepared sample was characterized by XRD. The morphology and microstructure were inspected with FESEM. The magnetic properties were recorded using VSM. The novel flowerlike clusters exhibit unique magnetic properties

Large-scale production of well-dispersed submicro ZrB2 and ZrC powders

ZrB2 and ZrC powders were synthesized via metallothermic reduction route using ZrO2, B/C, and Mg as raw materials. Low packing density of the green mixture and high heating temperature of the furnace are crucial for the formation of well-dispersed submicro powders. Optimum reaction time helped achieve good crystallization and high purity. The as-prepared samples were characterized by XRD, FESEM, TEM, and particle size analyzer. Results showed that well-dispersed ZrB2 powders with mean particle size of 0.534m and ZrC powders with mean particle size of 0.376m can be obtained. Oxygen content can be controlled lower than 1.0 wt%. The bench-scale output is about 10kg/d

Optimization of tungsten particles spheroidization with different size in thermal plasma reactor based on numerical simulation

Micro-size tungsten particles have been prepared by radio-frequency (RF) thermal plasma reactor. SEM images show that spheroidization ratio of small particles is obviously lower than that of big particles. Numerical model has been founded to simulate the spheroidization system to explain this phenomenon based on FLEUNT software. The calculation results indicate that small particles are easy to diffuse and &#39;back-mix&#39;, which will urge small particles to escape from the high temperature area, while big particles are flowing straightly through the high temperature area, as a result that small particles cannot absorb enough heat and cannot be spheroidized well. The forces of diffusion and &#39;back-mixing&#39; are each radial velocity and axial velocity. With some calculations based on the change of each gas flow, it can be found that appropriate combinations of gas flow can improve the spheroidization ratio of small particles. (C) 2016 Elsevier B.V. All rights reserved.</p

Fabrication of homogeneous Mo-Cu composites using spherical molybdenum powders prepared by thermal plasma spheroidization process

In this work, spherical and dense molybdenum particles with the average particle size of 16.6 mu m were synthesized by thermal plasma spheroidization process, and further used to fabricate homogeneous Mo-25 wt% Cu composites by infiltration method. The influence of infiltration temperature and holding time on the microstructure and properties of obtained Mo-Cu composites was investigated, and experimental results show that homogeneous Mo-Cu composites with high densification are obtained and the smooth surface of pores could facilitate the infiltration process. Specially, 98.6% of relative density of Mo-Cu composites is achieved and less than 10% irregular particles existing in spherical powders induce closed or half-connected pores in porous Mo skeleton, which shows adverse effect on full dense Mo-Cu composites obtaining. In addition, the highest microhardness of Mo-Cu composites (199 +/- 3.6 Hv) is obtained when infiltrated at 1300 degrees C for 1 h. Moreover, the maximum value of thermal conductivity (TC) of Mo-Cu composites is 154 W/(m.K), and this is lower than that predicted by theoretical models, which may be due to the small amounts of carbon in Mo-Cu composites and non-full dense of Mo-Cu composites. Furthermore, the carbon in porous skeleton could be well removed by controlling the atmosphere of sintering process. Importantly, Mo-25 wt% Cu composites fabricated by irregular particles exhibit non-uniform microstructure and low TC compared to that prepared by spherical particles, which would be due to the uneven pore distribution and closed pores in porous skeleton fabricated by irregular particles. These results well illustrate the superiority of spherical molybdenum particles on fabrication homogeneous Mo-Cu composites.</p

J. Mater. Sci.

Well-dispersed spherical nickel powders with uniform size were synthesized via a mild solvothermal route in which aqueous hydrazine was used as reducing agent without any alkaline reagent or surfactant introduced. The as-prepared products were characterized by XRD, FESEM, XPS, and TG. Different influencing factors including solvent, concentration, reaction time, and temperature on the morphology and size of the final products were examined. The size of the spherical nickel powders is tunable from 150 to 800 nm. The obtained nickel powders have little Ni(OH)(2) on the surface and exhibit excellent oxidation resistance. In addition, the formation process was discussed on the basis of the experimental results.Well-dispersed spherical nickel powders with uniform size were synthesized via a mild solvothermal route in which aqueous hydrazine was used as reducing agent without any alkaline reagent or surfactant introduced. The as-prepared products were characterized by XRD, FESEM, XPS, and TG. Different influencing factors including solvent, concentration, reaction time, and temperature on the morphology and size of the final products were examined. The size of the spherical nickel powders is tunable from 150 to 800 nm. The obtained nickel powders have little Ni(OH)(2) on the surface and exhibit excellent oxidation resistance. In addition, the formation process was discussed on the basis of the experimental results