Fabrication of niobium doped Pb（Zr, Ti）O3 fibers by viscous polymer processing

A technique based on viscous polymer processing （VPP） was described, which can produce high ceramic content green fibers. PZT-5 ceramic powders were ball milled to get high dispersibility. The slurry prepared for VPP was a composition of PZT-5 powder, PVA binder and glycerin. High ceramic content PZT-5 fibers were extruded with the slurry. The results show that the ceramic powders have fine mean particle size of 0.54 pan, high specific surface area of 3.55 m^2/g and zeta potential of 8.81 mV after 16 h milling. The fibers sintered at 1 280 ℃ for 4 h have pure perovskite structure and grains of 2-5 μm in size, with little pores or cracks. The ultimate tensile strength of sintered fibers is up to 13.84 MPa compared with 2.88 MPa of green fibers. The remnant polarization （Pr） and coercive field （Ec） of the fibers are 50.65 μC/cm^2 and 2.45 kV/mm, respectively. This fiber can withstand an electric field of 9 kV/mm higher than the ceramic （5 kV/mm）, which shows high directional and compact qualities.     

Influence of Ti^4＋ doping on electrochemical properties of LiFePO4/C cathode material for lithium-ion batteries

To improve the performance of LiFePO4, single phase Li1-4xTixFePO4/C (x=0, 0.005, 0.010, 0.015) cathodes were synthesized by solid-state method. A certain content of glucose was used as carbon precursor and content of carbon in every final product was about 3.5%. The samples were characterized by X-ray diffraction(XRD), scanning electron microscopy observations(SEM), charge/discharge test, carbon analysis and electrochemical impedance spectroscopy(EIS). The results indicate that the prepared samples have ordered olivine structure and doping of the low concentration Ti~(4+) does not affect the structure of the samples. The electrochemical capabilities evaluated by charge-discharge test show that the sample with 1% Ti~(4+) (molar fraction) has good electrochemical performance delivering about an initial specific capacity of 146.7 mA·h/g at 0.3C rate. Electrochemical impedance spectroscopy measurement results show that the charge transfer resistance of the sample could be decreased greatly by doping an appropriate amount Ti~(4+).     

Effect of sintering atmosphere on corrosion resistance of Ni/(NiFe2O4–10NiO) cermet inert anode for aluminum electrolysis

A comparative study on the corrosion resistance of 17Ni/(NiFe₂O₄–10NiO) cermet inert anode prepared in different sintering atmospheres was conducted in Na₃AlF₆–Al₂O₃ melt. The results indicate that the corrosion rates of NiFe₂O₄-based cermet anodes prepared in the vacuum and the atmosphere with oxygen content of 2×10⁻³ (volume fraction) are 6.46 and 2.71 cm/a, respectively. Though there is a transition layer with lots of holes or pores, a densified layer is formed on the surface of anode due to some reactions producing aluminates. For the anode prepared in the atmosphere with oxygen content of 2×10⁻³, the thickness of the densification layer (about 50 μm) is thicker than that (about 30 μm) formed on the surface of anode prepared in the vacuum. The contents of NiO and Fe(II) in NiFe_2xO_4–y–z increase with the decrease of oxygen content in sintering atmosphere, which reduces the corrosion resistance of the material.     

Microstructure and properties of high silicon aluminum alloy with 2% Fe prepared by rheo-casting

The morphology changes of both Fe-containing intermetallic compounds and the primary Si phase of Al-20Si-2Fe- 2Cu-0.4Mg-1.0Ni-0.5Mn (mass fraction, %) alloy produced by semi-solid rheo-diecasting were studied. The semi-solid slurry of high silicon aluminum alloy was prepared by direct ultrasonic vibration (DUV) which was imposed on the alloy near the liquidus temperature for about 2 min. Then, standard test samples of 6.4 mm in diameter were formed by semi-solid rheo-diecasting. The results show that the DUV treatment suppresses the formation of needle-like β-Al₅(Fe, Mn)Si phase, and the Fe-containing intermetallic compounds exist in the form of fine Al₄(Fe, Mn)Si₂ particles. Additionally, the primary Si grows up as fine and round particles with uniform distribution in a(Al) matrix of this alloy under DUV treatment. The tensile strengths of the samples at the room temperature and 573 K are 230 MPa and 145 MPa, respectively. The coefficient of thermal expansion (CTE) between 25 °C and 300 °C is 16.052 8×10^?6 °C^?1, and the wear rate is 1.55%. The hardness of this alloy with 2% Fe reaches HB146.3. It is discovered that modified morphology and uniform distribution of the Fe-containing intermetallic compounds and the primary Si phase are the main reasons for reducing the CTE and increasing the wear resistance of this alloy.     

Catalytic graphitization of polyacrylonitrile (PAN)-based carbon fibers with Fe-Cr2O3 composite coating

The process of electrodepositing Fe-Cr2O3 composite coating on polyacrylonitrile(PAN)-based carbon fibers and its catalytic graphitization were studied.Carbon fibers with and without electrodeposited Fe-Cr2O3 composite coating were heat treated at different temperatures and the structural changes were characterized by XRD,Raman spectroscopy and SEM.The results indicate that Fe-Cr2O3 composite coating exhibits a significant catalytic effect on graphitization of carbon fibers at low temperatures.When the Fe-Cr2O3-coated carbon fibers were heat treated at 1 300°C,the interlayer spacing(d002) and ratio of relative peak area(AD/AG) reach 3.364-and 0.34,respectively.Whereas,the extent of graphitization of pristine carbon fibers is comparatively low even after heat treatment at 2 800°C and the values of d002 and AD/AG are 3.414  and 0.68,respectively.The extent of graphitization of carbon fibers increases not only with the increase of the catalyst gross but also the Cr2O3 content in Fe-Cr2O3 coating.The catalytic effect of Fe-Cr2O3 composite coating accords with the dissolution  precipitation mechanism.     

Elevated temperature properties of Mg- 12Li-Al-MgO composites

1 Introduction Mg-Li alloys have potential for use in aerospace applications because they are exceptionally light and their specific stiffness is high[1?3]. However, there are some practical difficulties, such as poor creep behavior and microstructural in…     

液料等离子热喷法制备Fe3+/TiO2纳米粉末

通过对液料等离子热喷前驱物添加掺杂成分实现了液料等离子热喷TiO2纳米粉末的掺杂改性,并利用TEM,XRD及XPS对其进行表征.结果表明,采用液料等离子热喷法可以制备Fe3 掺杂TiO2纳米粉末,所制备粉末形貌基本呈球形或近球形,粒径分布为10～35 nm,掺杂量小于2.0%时粉末为锐钛矿及金红石相混晶,Fd3 掺杂促进锐钛矿向金红石相的转变,掺杂量为10.0%时析出了Fe2Ti3O9相.Fe3 掺杂不会引起TiO2粒径的大范围波动.粉末中含有O,Ti,Fe和C等元素,Fe元素在TiO2中仍为 3价.     

Fe掺杂TiO2纳米材料的合成及光催化性能

以钛酸丁酯为钛源,Fe(NO3)3·9H2O为铁源,采用溶胶-凝胶法制备Fe/TiO2纳米粉体,利用溶胶结合静电纺丝技术制备Fe/TiO2纳米纤维,从材料改性及形貌改善两个角度共同提高TiO2纳米材料的光催化活性及实用性。借助XRD、SEM、TEM等分析技术,探究了Fe/TiO2纳米材料在可见光区的光催化活性,分析了煅烧温度及掺铁量对Fe/TiO2纳米材料光催化性能的影响。结果显示,铁的掺入及形貌的改善有助于提高TiO2的光催化性能。     

Conversion of polyaluminocarbosilane（PACS） to Si-Al-C-（O） fibers： evolutions and effect of oxygen

The evolvement of oxygen from polyaluminocarbosilane（PACS） to Si-Al-C-（O） fibers and its effect on properties were investigated by element analysis, solid-state ^27Al nuclear magnetic resonance（NMR）, Fourier transform infrared spectroscopy（FT-IR）, thermo-gravimetric analyses（TGA）, scanning electron microscope（SEM） and X-ray diffraction（XRD）. Element analysis of PACS precursor polymer gives an empirical formula of SiC2.1H11.1O0.12Al0.024. ^27Al NMR spectra mass gain shows that the oxygen of cured PACS fibers comes from aluminum aletylacctanate （Al（AcAc）3） and the curing process. Oxygen content can be regarded as a constant mass during the pyrolysis process. During the sintering process of Si-Al-C-O fibers into Si-Al-C fibers, oxygen and carbon decreases with the release of a small amount of CO and/or SiO. Oxygen has a positive effect on the ceramic yield while has a negative effect on the crystallization of Si-Al-C-O fibers. It has great influence on mechanical properties of Si-Al-C-O and excellent tensile strength is usually obtained at the oxygen content of 8%-10%. The Si-Al-C-（O） fibers have excellent thermal stability and creep resistance.     

X-ray absorption spectroscopy of iron-doped conducting polymers

X-ray absorption spectroscopy (XAS) measurements were performed at the Fe K edge to determine the iron local structure in chemically prepared polyaniline (PANI) and polypyrrole (PPy) samples prepared with FeCl₃ as an oxidant. The samples were conditioned at different pHs by an acid–base treatment. In both as synthesized-doped polymers, the observed dispersed Fe atoms were predominantly coordinated to chlorine as Fe(III)Cl_x species, where x=6 for PANI and x=4 for PPy samples suggesting that the polymer–counteranion bonding is weaker than the iron–chelate one. For the PANI samples submitted to basic treatment, three different sets of Fe distances were found: five Fe–O at 2.00 Å, three Fe–Fe at approximately 2.80 Å and five Fe–Fe at 3.00 Å and the near-edge spectra showed the presence of octahedrally coordinated Fe⁺³. These results strongly suggest the presence of small oxide/hydroxide aggregates. Similar data were obtained for PPy treated with NH₄OH.     

Microstructural evolution and mechanical properties of an Nb–16Si in-situ composite with Fe additions prepared by arc-melting

This paper deals with phase constitutions, microstructural evolutions, and mechanical properties of Nb–16Si–xFe in-situ composites (where x = 2, 4, 6 at.%, referred as to 2Fe, 4Fe and 6Fe alloys, hereafter) prepared by arc-melting. It is found that with additions of Fe, Nb₄FeSi silicide arises and microstructures of as-cast samples are consisted of dendritic-like Nb_SS phase, Nb₃Si block, and Nb₄FeSi matrix in the 2Fe and 4Fe alloys, and of the dendritic-like Nb_SS phase and Nb₄FeSi matrix in the 6Fe alloy. When heat-treated at 1350 °C for 100 h, part of the Nb₃Si phase decomposes in the 2Fe and 4Fe alloys, and the 6Fe alloy shows no change in microstructure as compared with the as-cast one. The Nb₄FeSi silicide is found to be brittle, its fracture toughness and elastic modulus are first obtained, having values about 1.22 MPa m^1/2, and 310 GPa, respectively. The fracture toughness of the bulk as-cast and heat-treated Nb–16Si–xFe samples are changed slightly by the Fe additions, which is in a range of 9.03–10.19 MPa m^1/2. It is interesting that at room temperature, strength is improved by the Fe additions, whereas at 1250 °C and 1350 °C the strength decreases. As the Fe content increased from 2 at.% to 6 at.%, for example, the 0.2% yield strength increases from 1410 MPa to 1580 MPa at room temperature, decreases from 479 MPa to 385 MPa at 1250 °C.     

Oxidation of A12O3 continuous fiber-reinforced/NiAl composites

The 1200°C and 1300°C isothermal and cyclic oxidation behavior of Al₂O₃ continuous fiber (Saphikon)-reinforced/ NiAl composites were studied. Oxidation resulted in formation of Al₂O₃ external scales in a similar manner as scales formed on monolithic NiAl. The isothermal oxidation of an Al₂O₃/NiAl composite resulted in oxidation of the matrix along the fiber/matrix interface near the fiber ends. This oxide acted as a wedge between the fiber and matrix, and, under cyclic oxidation conditions, led to further oxidation along the fiber lengths and eventual cracking of the composite. The oxidation behavior of composites in which the Al₂O₃ fibers were sputter coated with nickel prior to processing was much more severe. This was attributed to open channels around the fibers which formed during processing most likely as a result of the diffusion of the nickel coating into the matrix.     

Effect of carbon on the coefficient of thermal expansion of as-cast Fe−30wt.%Ni−12.5wt.%Co−×C invar alloys

The segregation (distribution) of nickel and the composition of its constituents influence the low thermal expansion characteristics (Invar effect) in Fe?30 wt.% Ni?12.5wt.% Co?×C Invar alloy. The change of coefficient of the thermal expansion and magnetic properties were studied as an aspect of carbon addition causing the segregation of Ni in primary austenite of as-cast Fe?30wt.% Ni?12.5wt.% Co Invar alloy. The coefficient of thermal expansion of Fe?30 wt.% Ni?12.5 wt.% Co?×C Invar alloy showed its lowest value at 0.08 wt.% carbon, increased with increasing carbon content in the range of 0.08–1.0 wt.%C, kept constant at 1.0–2.0 wt.%C and decreased at carbon higher than 2.0 wt.%. The effective distribution of the coefficient of nickel in as-cast Fe?30 wt.% Ni?12.5 wt.% Co?×C Invar alloy increased with increasing carbon content. The volume fraction of the γ phase of Fe?30 wt.% Ni?12.5 wt.% Co?×C alloy increased with increasing carbon content. The microstructure of Fe?30 wt.% Ni?12.5 wt.% Co?×C alloy changed with the carbon content was independent of the coefficient of thermal expansion. The Curie temperature changed linearly with the carbon content and was similar to the change of the coefficient of thermal expansion. Moreover, the coefficient of thermal expansion decreased when the ratio of saturation magnetization to Curie temperature (σ_s/T_c) increased, decreasing the Curie temperature and showed a specific relationship with the magnetic properties of the Fe?30 wt.% Ni?12.5 wt.% Co?×C Invar alloy.     

Application of some ferrocene derivatives in the field of corrosion inhibition

Three ferrocene derivatives, namely 1,1′-diacetylferrocene (Diacetyl Fc), 1,1′-diformylferrocene (Diformyl Fc) and 2-benzimidazolythioacetylferrocene (BIM Fc) were synthesized and their inhibitive effects against mild steel corrosion in aerated 0.5 M H₂SO₄ and 1 M HCl solutions were evaluated. Corrosion measurements based on polarization resistance (R_p), potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) indicate that Diacetyl Fc, in most cases, accelerates mild steel corrosion in HCl while Diformyl Fc and BIM Fc act as weak inhibitors. In H₂SO₄ solution, ferrocene derivatives show good inhibition performance. The efficiency of the inhibitors follows the order: BIM Fc > Diformyl Fc ? Diacetyl Fc. Adsorption of both Diacetyl Fc and Diformyl Fc obey Langmuir adsorption isotherm with very low value of free energy of adsorption ΔG^° for the Diformyl Fc (physisorption) while adsorption of BIM Fc follows that of Frumkin with high negative value of ΔG^° (chemisorption). Both Diformyl Fc and BIM Fc act as mixed-type inhibitors with predominant effect on the anodic dissolution of iron. Analysis of the polarization curves and impedance spectra indicates that charge transfer process mainly controls mild steel corrosion in H₂SO₄ solution without and with ferrocene compounds. The mechanism of corrosion inhibition or acceleration by ferrocene derivatives was discussed in the light of the molecular structure of the additives.     

Increase of TC in UFe2+x synthesized by ultrafast cooling

The uranium Laves phase UFe₂ was prepared by ultrafast cooling, which allows to incorporate excessive Fe of about 0.3 Fe/f.u. into the nanocrystalline Laves phase structure. ⁵⁷Fe Mössbauer spectroscopy reveals that such Fe atoms occupy the U sites. Stronger magnetic hyperfine field points to larger Fe moments of such antistructure Fe. Higher Fe excess leads to its segregation in the form of α-Fe. The Curie temperature of the UFe_2+x phase increases to the limit value 230–240 K.     

Effect of ultrasonic vibration on Fe-containing intermetallic compounds of hypereutectic Al–Si alloys with high Fe content

The Fe-containing intermetallic compounds with high melting point in hypereutectic Al-Si alloys can improve the heat resistance and wear resistance at elevated temperatures. However, the long needle-like Fe-containing compounds in the alloys produced by conventional casting process are detrimental to the strength of matrix. The effect of ultrasonic vibration (USV) on the morphology change of Fe-containing intermetallic compounds in the hypereutectic Al-17Si-xFe (x=2, 3, 4, 5) alloys was systematically studied. The results show that, the Fe-containing intermetallic compounds are mainly composed of long needle-like β-Al₅FeSi phase with a small amount of plate-like δ-Al₄FeSi₂ phase in Al-17Si-2Fe alloy produced by conventional casting process. With the increase of Fe content from 2% to 5% in the alloys, the amount of plate-like or coarse needle-like δ-Al₄FeSi₂ phase increases while the amount of long needle-like β-Al₅FeSi phases decreases. In Al-17Si-5Fe alloy, the Fe-containing intermetallic compounds exist mainly as coarse needle-like δ-Al₄FeSi₂ phase. After USV treatment, the Fe-containing compounds in the Al-17Si-xFe alloys are refined and exist mainly as δ-Al₄FeSi₂ particles, with average grain size ranging from 26 μm to 37 μm, and only a small amount of β-Al₅FeSi phases remain. The mechanism of USV on the morphology of Fe-containing intermetallic compounds was also discussed.     

In-situ layered double hydroxides on Mg−Ca alloy: Role of calcium in magnesium alloy

Mg?Al layered double hydroxides (LDHs), produced on cast Mg?xCa (x=0.5, 0.8, 2.0, wt.%) alloys by an in-situ growth method, showed good corrosion resistance compared to the bare magnesium substrate. The influence mechanism of the second phase (Mg₂Ca) on LDHs production was investigated. Increasing Ca content increased the amount of Mg₂Ca, decreasing the grain size and the corrosion rate of the alloys. The increased amount of the second phase particles and the grain refinement promoted the growth of LDHs, and thus led to the decreasing of corrosion rate of the Mg?xCa alloys with LDHs. A higher Mg₂Ca amount resulted in forming fluffy LDHs. Due to the dual effects of the second phase (Mg₂Ca) for LDHs growth and microgalvanic corrosion, LDHs/Mg?0.8Ca showed the lowest corrosion rate.     

含Nb元素堆焊层金属中碳化物的析出行为

以堆焊连铸辊为研究对象,研制三种不同合金元素Nb加入量的药芯焊丝,采用金相显微镜和扫描电镜对其显微组织、碳化物形貌进行了观察. 采用X射线衍射仪对其相结构进行了测定. 采用Thermo-Calc软件对含铌堆焊层金属中碳化物的析出行为进行分析. 结果表明,堆焊层金属显微组织为铁素体、M₂₃C₆和MC. 随着Nb元素含量增加,其显微组织得到细化,NbC沿晶界析出. 热力学计算结果表明,析出碳化物主要为MC,M₂₃C₆. 随着Nb元素含量的增加,MC析出量增多,M₂₃C₆析出量减小. MC中主要是Nb元素,并溶解了一定量的Mo,V,Cr和Fe元素;M₂₃C₆中主要是Fe,Cr元素,即Nb元素含量变化主要影响MC型碳化物.     

Effect of metallic phase content on mechanical properties of （85Cu- 15Ni）/（10NiO-NiFe2O4） cermet inert anode for aluminum electrolysis

（85Cu-15Ni）/（10NiO-NiFe2O4） cermets were prepared with Cu-Ni mixed powders as toughening metallic phase and 10NiO-NiFe2O4 as ceramic matrix. The phase composition, microstructure of composite and the effect of metallic phase content on bending strength, hardness, fracture toughness and thermal shock resistance were studied. X-ray diffraction analysis indicates the coexistence of （Cu-Ni）, NiO and NiFe2O4 phases in the cermets. Within the content range of metallic phase from 0% to 20% （mass fraction）, the maximal bending strength （176.4 MPa） and the minimal porosity （3.9%） of composite appear at the metallic phase content of 5%. The fracture toughness increases and Vickers＇ hardness decreases with increasing metal content. When the thermal shock temperature difference （At） is below 200 ℃, the loss rate of residual strength for 10NiO-NiFe2O4 ceramic is only 8%, but about 40% for （85Cu-15Ni）/（10NiO-NiFe2O4）cermets. As At is above 200 ℃, the residual strength sharply decreases for sample CN0 and falls slowly for samples CN5-CN20.