Zhao Wen-Yu

Preparation and characterization of monodisperse nickel nanoparticles by polyol process

Polymer-protected monodisperse nickel nanoparticles were synthesized by a modified polyol reduction method in the presence of poly (N-vinyl-2-pyrrolidone). These nanoparticles were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), selected area electron diffraction (SAED), as well as vibrating sample magnetometer (VSM). The experimental results show that the addition of PVP and the concentration of NaOH have strong influences on the size, agglomeration and uniformity of nanoparticles. In the presence of PVP and NaOH with low concentrations, monodisperse nickel nanoparticles with average diameters about 42 nm were obtained and characterized to be pure nickel crystalline with fee structure. Secondary structures such as clusters, loops, and strings resulted from magnetic interactions between particles were observed. The chemical interaction between the PVP and nickel nanoparticles was found by FTIR. The saturation magnetization (Ms), remarem magnetization (Mr) and coercivity (HC) of these nickel nanoparticles are lower than those of balk nickel.

Thermal instability and microstructure of strontium M-type hexaferrite nanoparticles synthesized by citrate approach

The dried gel of SrFe12O19, prepared by citrate approach, was investigated by means of infrared spectroscopy (IR), thermograimetric analysis (TG), differential scanning calorinetry (DSC), X-ray diffraction (XRD) techniques, energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). The thermal instability and the thermal decomposition of low-temperature strontium M-type hexaferrite crystallized at about 600°C were confirmed for the first time by XRD method. The decomposition of the low-temperature strontium M-type hexaferrite took place at about 688.6°C determined by DSC investigation. The low-temperature strontium M-type hexaferrite nanoparticles were decomposed into SrFeO2.5 with an orthorthombic cell and Fe2O3 with a tetragonal cell as well as possible α-Fe2O3. The agglomerated particles with sizes less than 200 nm obtained at 800°C were plesiomorphous to strontium M-type hexaferrite. The thermally stable strontium M-type hexaferrite nanoparticles with size less than 100 nm could take place at 900°C. Up to 1000°C, the phase transformation to form strontium M-type hexaferrite was ended, the calcinations with the sizes more than 1 μm were composed of α-Fe2O3 and strontium M-type hexaferrite. The method of distinguishing γ-Fe2O3 with a spinel structure from Fe2O3 with tetragonal cells by using powder XRD method was proposed. Fe2O3 with tetragonal cells to be crystallized before the crystallization of thermally stable strontium M-type hexaferrite was confirmed for the first time. The reason why α-Fe2O3 as an additional phase appears in the calcinations is the cationic vacancy of strontium M-type hexaferrite,SrFel2-x▭xO19(0⩽x⩽0.5). 3

Factors of impacting the coprecipitation process for synthesizing CoTi-substitued Barium M-type ferrite ultrafine powder

The effect of pH values on synthesizing single-phase CoTi-substituted barium M-type ferrite ultrafine powders, and BaCoTiFe10O19, was investigated employing corrosion versus pH plot (E-pH plot) for metal element, thermodynamic calculation, and co-dump coprecipitation. The pH values of complete coprecipitation of all Fe3+, Ti4+, Co2+ and Ba2+ and Ba2+ cations are9–12 and higher than7.9 on the basis of E-pH plot analysis and thermodynamic calculation, respectively. The miniumum pH value necessary to the formation of single-phase BaCoTiFe10O19 is8.5 in the light of the co-dump coprecipitation. These results indicate that the coprecipitation process for synthesizing CoTi-substituted barium M-type ferrite ultrafine powders is simultaneously influenced by synergetic coprecipation effect of cations and coordination effect of Cl− anions. The test time of the minimum pH value corresponding to forming a series of single-phase CoTi-substituted barium M-type ferrite ultrafine powders, and Ba-CoxTixFe12−2xO19. may be significantly reduced by using the effects of two new factors on the coprecipitation process.

In掺杂β-Zn4Sb 3 热电材料的制备与电热输运

设计了一系列名义组成为Zn 4 Sb 3- x In x (0~0.08, ?x=0.02)的In掺杂β-Zn 4 Sb 3 基块体材料, 并用真空熔融-随炉冷却-放电等离子体烧结工艺成功制备出无裂纹的In掺杂单相β--Zn 4 Sb 3 基块体材料. 300~700 K内材料的电热输运特性表明, In杂质对Zn 4 Sb 3 化合物的Sb位掺杂可导致载流子浓度和电导率大幅度增大、高温下本征激发几乎消失和晶格热导率显著降低, x =0.04和0.08的Zn 4 Sb 3- x In x 的In掺杂beta-Zn 4 Sb 3 化合物700K时晶格热导率均仅为0.21 W/(m·K). 与纯β-Zn 4 Sb 3 块体材料相比, 所有In掺杂β-Zn 4 Sb 3 基块体材料的ZT值均显著增大, x =0.06的Zn 4 Sb 3- x In x 的In掺杂β-Zn 4 Sb 3 基块体材料700K时 ZT 值达到1.13, 提高了69%.设计了一系列名义组成为Zn 4 Sb 3- x In x (0~0.08, ?x=0.02)的In掺杂β-Zn 4 Sb 3 基块体材料, 并用真空熔融-随炉冷却-放电等离子体烧结工艺成功制备出无裂纹的In掺杂单相β--Zn 4 Sb 3 基块体材料. 300~700 K内材料的电热输运特性表明, In杂质对Zn 4 Sb 3 化合物的Sb位掺杂可导致载流子浓度和电导率大幅度增大、高温下本征激发几乎消失和晶格热导率显著降低, x =0.04和0.08的Zn 4 Sb 3- x In x 的In掺杂beta-Zn 4 Sb 3 化合物700K时晶格热导率均仅为0.21 W/(m·K). 与纯β-Zn 4 Sb 3 块体材料相比, 所有In掺杂β-Zn 4 Sb 3 基块体材料的ZT值均显著增大, x =0.06的Zn 4 Sb 3- x In x 的In掺杂β-Zn 4 Sb 3 基块体材料700K时 ZT 值达到1.13, 提高了69%.

纳米SiO 2 包覆提高填充方钴矿热电材料热稳定性

Single-phase Ba0.3In0.2Ni0.05Co3.95Sb12 bulk materials were synthesized by melting and spark plasma sintering (SPS) methods. Ba0.3In0.2Ni0.05Co3.95Sb12/SiO2 nanocomposite material with nano-SiO2 coating was prepared by wet chemical coating processing. Emphases were given on the evolution of microstructure, chemical composition, and thermoelectric properties of two kinds of (Ba,In) double-atom filled skutterudite based bulk materials during periodic thermal cycling 2000 times in the range of 300-723-300 K. It was found that the thermal stability of (Ba,In) double-atom filled skutterudite was remarkably improved after nano-SiO2 coated. The microstructure and chemical composition along the grain boundaries of single-phase Ba0.3In0.2Ni0.05Co3.95Sb12 bulk material obviously changed, while the thermal cycling had no effect on Ba0.3In0.2Ni0.05Co3.95Sb12/SiO2 nanocomposite. Thus the nano-SiO2 stabilized the grain boundary and prevented the elements diffusing and volatilizing from intra-grain. The ZT values of two kinds of materials were very close and kept unchanged at 300 K and 500 K during the thermal cycling. The ZT values of single-phase bulk materials gradually decreased at 800 K. However, the ZT values of nanocomposite mainly depended on the complex changes in thermal conductivity and increased with prolonging of quenching time, then reached 1.12 at 800 K after quenching for 1800 times, which was even higher than those of 578 无 机 材 料 学 报 第 25 卷 unquenched Ba0.3In0.2Co3.95Ni0.05Sb12/SiO2 nanocomposite (ZT=1.08) and single-phase Ba0.3In0.2Co3.95Ni0.05Sb12 bulk material(ZT=1.10) quenched for 1800 times.采用熔融结合放电等离子体烧结制备了单相Ba 0.3 In 0.2 Ni 0.05 Co 3.95 Sb 12 块体材料, 并用湿化学包覆处理方法制备了纳米SiO 2 包覆的Ba 0.3 In 0.2 Ni 0.05 Co 3.95 Sb 12 /SiO 2 纳米复合材料, 重点研究了两种(Ba,In)双原子填充方钴矿基块体材料在300~723~300 K范围热循环2000次过程中其显微结构、化学成分和热电性能的演变特征. 结果发现, 纳米SiO 2 包覆可以显著提高(Ba,In)双原子填充方钴矿块体材料的热稳定性, 单相Ba0.3In0.2Ni0.05Co3.95Sb12块体材料晶界处的显微结构和化学成分发生显著变化, Ba 0.3 In 0.2 Ni 0.05 Co 3.95 Sb 12 /SiO 2 纳米复合材料几乎没有影响, 纳米SiO 2 起着稳定晶界和抑制晶内元素扩散与挥发的作用. 热循环过程中, 两种材料在300和500 K时的综合热电性能ZT值相近, 变化很小; 800 K时, 单相块体材料的ZT值呈逐渐降低趋势, 纳米复合材料由于受热导率的复杂变化影响其ZT值, 随淬火次数增加而逐渐增大, 淬火1800次时ZT值达到1.12, 甚至高于未淬火的Ba 0.3 In 0.2 Co 3.95 Ni 0.05 Sb 12 /SiO 2 纳米复合材料(1.08)和淬火1800次后的单相Ba 0.3 In 0.2 Co 3.95 Ni 0.05 Sb 12 块体材料(1.10)的ZT值.采用熔融结合放电等离子体烧结制备了单相Ba 0.3 In 0.2 Ni 0.05 Co 3.95 Sb 12 块体材料, 并用湿化学包覆处理方法制备了纳米SiO 2 包覆的Ba 0.3 In 0.2 Ni 0.05 Co 3.95 Sb 12 /SiO 2 纳米复合材料, 重点研究了两种(Ba,In)双原子填充方钴矿基块体材料在300~723~300 K范围热循环2000次过程中其显微结构、化学成分和热电性能的演变特征. 结果发现, 纳米SiO 2 包覆可以显著提高(Ba,In)双原子填充方钴矿块体材料的热稳定性, 单相Ba0.3In0.2Ni0.05Co3.95Sb12块体材料晶界处的显微结构和化学成分发生显著变化, Ba 0.3 In 0.2 Ni 0.05 Co 3.95 Sb 12 /SiO 2 纳米复合材料几乎没有影响, 纳米SiO 2 起着稳定晶界和抑制晶内元素扩散与挥发的作用. 热循环过程中, 两种材料在300和500 K时的综合热电性能ZT值相近, 变化很小; 800 K时, 单相块体材料的ZT值呈逐渐降低趋势, 纳米复合材料由于受热导率的复杂变化影响其ZT值, 随淬火次数增加而逐渐增大, 淬火1800次时ZT值达到1.12, 甚至高于未淬火的Ba 0.3 In 0.2 Co 3.95 Ni 0.05 Sb 12 /SiO 2 纳米复合材料(1.08)和淬火1800次后的单相Ba 0.3 In 0.2 Co 3.95 Ni 0.05 Sb 12 块体材料(1.10)的ZT值.

Model of coherent interface formation in cement-based composites containing polyblend of polyvinyl alcohol and methylcellulose

The texture of interfacial zone between cement paste and quartz in the cement-based composites containing polyvinyl alcohol (PVA), methylcellulose (MC) and their polyblend in an amount of 10 wt % with respect to cement, as well as the texture of dehydrated bodies of PVA, MC, and the polyblend solutions, were investigated with SEM. The network texture of the dehydrated polyblend is confirmed by comparing the texture of dehydrated bodies of PVA and MC. The network texture has restrained the movement of polyblend molecules in the cement mortar but is helpful to forming a coherent interface between cement paste and quartz. The key factor of forming the coherent interface is not the neutralization reaction between H+ from hydrolysis of quartz and OH− from hydration of cement, but the electrostatic attraction and the chemical reaction between polar groups on the polyblend molecule and cations and anions from hydrolysis of quartz and hydration of cement, respectively. The model of the coherent interface formation is that excessive [HSiO3]− and [SiO3]2− anions are bonded with the hydrated cations such as Ca2+ and Al3+, which is confirmed by the gel containing Ca and Si on the quartz surface.

Determination of space groupPncm of prehnite using electron diffraction method

Space symmetry of prehnite, which occurs in cavities and veins within Skarn from the Tieshan iron mineral deposit, Daye, Hubei province, Central China, has been determined using selected area electron diffraction (SAED) and convergent-beam electron diffraction (CBED) on the submicrometer scale. Our results confirm that the natural prehnite may have the structure with symmetry Pncm. The unit-cell parameters of investigated prehnite (a=0.458 nm, b=0.555 nm, and c=1.853 nm) have been calculated by using the multicrystal diffraction rings of gold, the internal standard.