Recycling process of WC-Co cermets by hydrothermal treatment

Hydrothermal extraction process of Co binder phase from WC-Co cermet was investigated in order to establish a novel recycling system of WC-Co cermet scraps. When the cermet chips were hydrothermal-treated in hydrochloric acid above 110^∘C, Co binding phase was efficiently extracted and the cermet chips were disintegrated into relatively large fragments. After hydrothermal treatment, WC sintered body become very brittle and pulverized easily by ball milling and the mean particle size of thus obtained WC particle became similar to that of virginal WC particle. The recycled WC powder was a little easier to undergo oxidation than the virginal WC powder, so that the mechanical properties of recycled WC-Co cermets were degraded. However, the degradation of mechanical properties was prevented only by drying the WC powder more carefully. This hydrothermal process will be one of the recycling systems for WC-Co cermets.     

超临界水热制备LiFePO4及煅烧碳包覆改性研究

本文以FeSO_4、H_3PO_4和LiOH为原料,采用超临界水热过程制备了亚微米级LiFePO_4颗粒.在此基础上,为了提升制备的LiFePO_4正极材料的物理和电化学性能,对其进行了后续煅烧碳包覆改性研究.同时,通过XRD、SEM、充放电测试、CV和EIS测试手段,对LiFePO_4正极材料改性前后的结构、形貌和电化学性能进行了表征.结果表明:后续固相煅烧碳包覆改性能够显著改善LiFePO_4的结晶性能,减小颗粒粒径,降低电荷传递阻抗,以及大幅度地提升放电容量和循环性能;以PVP为模板剂、蔗糖为碳源,700℃煅烧1 h得到的LiFePO_4/C颗粒粒径小、分布均一,室温0.2 C倍率的首圈放电比容量为153.1 mAh/g,1 C倍率充放电时,放电比容量可保持在144.2 mAh/g,1 C循环50次,容量保持率达到97.1%.     

铟锡氢氧化物的煅烧过程研究

采用热分析、XRD等方法,研究了用化学共沉淀法制备的铟锡氢氧化物复合粉末在煅烧过程中的变化规律.实验结果表明煅烧过程使非晶氢氧化物粉末最终转变为晶态ITO粉末,其间经历的过程是非晶氢氧化物粉末→非晶ITO粉末→晶态ITO粉末,晶化温度大约为390℃.同时分析了ITO复合粉末在煅烧过程中保温温度、加热速度、保温时间等工艺参教对晶粒度的影响,结果表明,加热温度越高,保温时间越长,晶粒直径越大;加热速度越快,晶粒直径越大.     

Crystal structure and spontaneous magnetism of BiFeO3 powder synthesized by hydrothermal method

Single-phase BiFeO3 powder was successively synthesized by a low-temperature hydrothermal method. Scanning electron microscopy and transmission electron microscopy results showed that BiFeO3 powder had several hundred nanometers to micrometer-sized particles with a broad size distribution. BiFeO3 powder showed weak-ferromagnetic behavior with a small magnetization value (Ms approximately 20 memu/g) at room temperature. Rietveld refinement results for the crystal structure show the displacive disorder of the Fe-site(6a); the Fe-site(6a) splits into two pairs, Fe(1) and Fe(2) displaced by 0.9 angstroms from each other and these sites are partially occupied. Hence the O-site(18b) also splits into the two partially occupied sites forming a distorted FeO6 octahedras. The weak ferromagnetism observed in the hydrothermal BFO powder is ascribed to the displacive disorder of FeO6 octahedras resulting in an incomplete counterbalance between the antiferromagnetic sublattices of the Fe-ions.     

Thermal behavior of copper powder prepared by hydrothermal treatment

Copper powder is synthesized by hydrothermal treatment using the copper powder obtained from the chemical reduction method as a precursor. The copper powder is also treated in benzotriazole solution. The powder X-ray diffraction patterns and SEM photomicrographs exhibit that the copper powder possesses perfect crystallinity and narrow size distribution. The thermal behavior of the three kinds of copper powder is evaluated by thermogravimetry and derivative thermogravimetry. Comparing with the sample prepared by means of the chemical reduction method, the copper powder treated under hydrothermal condition displays a peak temperature of the formation of Cu₂O shifting from 60.49 °C to higher temperatures, which indicates that it has strong antioxidation performance. However, the antioxidation effect of copper powder treated in benzotriazole solution shows only a little improvement at high temperature     

水热法合成高发光强度ZnS:Cu,Al纳米荧光粉研究

采用水热法直接合成了高发光强度的ZnS:Cu,Al纳米荧光粉.XRD和TEM测试结果表明,合成纳米晶为纯立方相结构,球形纳米晶尺寸约15nm,尺寸分布窄,分散性好.首次系统地研究了不同[S2-]/[Zn2+]和[Al3+]/[Cu2+]比值对清洗样品和不清洗样品的光致发光(PL)光谱的影响.实验结果表明,激活剂浓度不变而改变[S2-]/[Zn2+]摩尔比时,发光强度显著变化,同时未清洗样品的PL强度均比清洗样品的强,且未清洗样品强度增强的比值在低的[S2+]/[Zn2+]时更显著.这说明其发光机理为紫外光激发材料表面的发光中心,即PL强度决定于纳米材料的表面态,此外掺杂的激活剂摩尔比同样对PL光谱有影响.在我们的实验中,用343nm紫外光激发时,n[S2-]:n[Zn2+]=3,n[Al3]:n[Cu2+]=2时未清洗样品的发光最强,此时于室内照明条件下可观察到明亮的绿光.     

Structural evolution during calcination of sol-gel synthesized alumina and alumina-8 vol% zirconia composite

Alumina and alumina-8 vol% zirconia (3 mol% yttria) composite powders were synthesized via a sol-gel process using metal chlorides as precursors. Sol-gel synthesized alumina and alumina-zirconia composite powders were initially amorphous and contained structural water. Calcination was necessary to drive off the water and prompt crystallization of the powder. Calcination of synthesized powder was performed at various temperatures from 400–1300°C. Powder morphology and phase evolution during calcination were established using electron microscopy, X-ray diffraction, and thermogravimetric analysis. This revised version was published online in November 2006 with corrections to the Cover Date.     

Modifications in the microstructure of alumina porous materials by hydrothermal treatment

Thin films of microporous γ-alumina were prepared by hydrothermal treatment of boehmite which was obtained by a sol-gel process. Films of boehmite hydrothermally treated at different temperatures and times were studied by X-ray diffraction, Nitrogen Adsorption, DTA/TG Thermal Analysis and Scanning Electron Microscopy. The results showed that a well-crystallized boehmite with an anisotropic particle growth mainly in the (002) plane was obtained. The modifications introduced into the boehmite affected the microstructure, such as surface area, pore morphology, pore volume, pore size distribution and thermal stability of the corresponding alumina. Received: 30 March 2000     

Freeze casting of porous Ni-YSZ cermets

Dual-phase porous Ni-YSZ cermets were fabricated via the freeze casting of a ceramic/camphene slurry. After removing the frozen camphene via sublimation at room temperature, the green samples were sintered for 3 h in air at various temperatures, ranging from 1100 to 1350 °C, and then reduced in an Ar-5% H₂ atmosphere at 700 °C for 3 h. The fabricated Ni-YSZ cermets showed 3-D pore channels formed by the replication of the entangled camphene dendrite network and small pores in the Ni-YSZ walls produced by partial sintering of the NiO-YSZ composite. Furthermore, the fabricated samples were found to possess reasonable electrical conductivities, thus rendering them suitable for use as the basic components of planar solid oxide fuel cells (SOFCs).     

Flower-like CuO synthesized by CTAB-assisted hydrothermal method

Flower-like CuO nanostructures have been synthesized by cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal method. Here, CuCl₂·2H₂O was used as copper raw material, and sodium hydroxide was used as precipitate. The resulting CuO powders were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). X-ray diffraction (XRD) pattern exhibited the nanocrystalline nature with monoclinic structure for the as-synthesized nanostructures. FESEM images indicated that the flower-like CuO nanostructures are composed of many interconnected nanosheets in size of several micrometres in length and width and 60–80 nm in thickness. The possible formation mechanism of flower-like CuO nanostructures was discussed.     

Preparation of porous boehmite nanosolid and its composite fluorescent materials by a novel hydrothermal hot-press method

Boehmite (AlO(OH)) porous nanosolid has been successfully prepared by a novel hydrothermal hot-press (HHP) method, using Al₂O₃ nanoparticles as the starting material. Furthermore, a new organic fluorescent material (E,E)-4-{2-[P′-(N,N-di-n-butylamino)stilben-p-yl]vinyl}pyridine (DBASVP) was assembled into the pores of the boehmite porous nanosolid, thus a DBASVP/boehmite porous nanocomposite was obtained. Because of the interaction between DBASVP molecules and the surface of boehmite porous nanosolid, a red-shift of the fluorescent peak was observed in boehmite/DBASVP composite by comparing with that of DBASVP.     

Characteristics of BaTiO3 powders synthesized by hydrothermal process

Monodisperse BaTiO₃ powder was prepared by a hydrothermal process from a mixture of Ba(OH)₂ and Ti(OH)₄. In the process, the best synthesis conditions were a Ba(OH)₂/Ti(OH)₄ mole ratio of 1, the reaction temperature 180°C, which produced the cubic crystal structure of BaTiO₃ with 0.3 m size. The effects of synthesis conditions and the dispersion stability of powder were investigated. The reaction kinetics was also discussed from the experimental results.     

Synthesis of TiO2 nanotube films via pulsed laser deposition followed by a hydrothermal treatment

Titanium dioxide nanotube (TNT) films were prepared by pulsed laser deposition (PLD) of P25 and P90 TiO₂ nanoparticles onto stainless steel foils followed by a hydrothermal treatment (HT). Heating the PLD films in a TNT precursor solution at 150°C resulted in a well-adhered dense mat of TNTs that were ～10?nm in diameter with a pore size of ～4?nm. The TiO₂ nanotube films were characterised by SEM, TEM, XRD and Raman spectroscopy.     

Preparation of NixTiy compound via Ni plating followed by thermal treatment of Ti powder

In this research, Ni_xTi_y compound was prepared by thermal treatment of Ni-plated Ti powder. For this purpose, Ti powder was plated in an electroless Ni bath for various times (120, 225, 300, and 720?min). Hydrazine hydrate was used as a reductant for the deposition of pure Ni on the Ti particles. The plated powder (225?min) was heat treated under argon atmosphere to achieve Ni_xTi_y powder. Finally, the heated/plated powder was pressed by CIP followed by sintering at 980°C for prepare the Ni_xTi_y bulk sample. The plated powders as well as sintered one were characterized using scanning electron microscopy, energy dispersive spectrometer, X-ray fluorescence, X-ray diffraction and differential scanning calorimetric. The NiTi₂, NiTi, and Ni₃Ti phases were detected in the XRD patterns of heated/plated Ti powder. According to DSC data, the heated/plated Ti powder showed reversible martensitic transformation at temperature range of ?38.0°C to +38.1°C, while sintered/heated/plated Ti powder displayed reversible transformation at temperature range of 16.0°C–15.4°C.     

Monoclinic zirconium oxide nanostructures synthesized by a hydrothermal route

Zirconium oxide (ZrO(2)) nanostructures were synthesized by a hydrothermal route. Surface morphology analysis depicts the formation of rice-grain-like and fiber-like ZrO(2) nanostructures at different synthesis conditions. The structural analysis confirms that the as-synthesized ZrO(2) product is of pure monoclinic phase (m-ZrO(2)). The clear and equally spaced lattice fringes in high-resolution transmission electron microscopy (HRTEM) images and discrete spot pattern of selected area electron diffraction (SAED) confirm the high quality of the synthesized product. The product consists of monodispersed nanoparticles of uniform composition, high purity, and crystallinity. The Raman spectra are quantitatively analyzed and the observed peaks are attributed to various vibration modes of m-ZrO(2).     

Single crystalline silicon carbide nanorods synthesized by hydrothermal method

A new and simple hydrothermal process has been used to synthesize single crystalline silicon carbide nanorods. The synthesized silicon carbide nanorods have a length of about 1 μm and nearly same diameter of about 40 nm. We have observed that the nanorods possess a well-defined single crystalline structure with a thin layer of amorphous silica on the surface. The X-ray diffraction analysis demonstrates that the structure of silicon carbide nanorods is β-SiC. Raman shifts of the silicon carbide nanorods are discussed and the oxide-assisted growth mechanism is proposed to explain the formation and growth of silicon carbide nanorods.