Determination of Pb,Zr, Ti,Sr, Cr,Nb and La in lead zirconate titanate ceramics by particle‐induced X‐ray emission

A particle‐induced X‐ray emission (PIXE) technique has been used in the determination of the principal components Pb, Zr and Ti and the substituting elements Sr, Cr, Nb and La in lead zirconate titanate ceramics. In general, precision of analysis was concentration dependent from each element under study. For Pb, precision varied between 0.13% and 0.16%, at higher concentration of 59.32–64.5%. It was around 6–9% for Sr, Cr and Nb at concentrations of 1% or lower. Particular attention was devoted to the estimation of the analysis trueness. With this purpose, three methods were applied: (1) comparison of PIXE and inductively coupled plasma optical emission spectrometry concentrations, (2) recovery study and (3) comparison with a laboratory standard. Trueness of analysis was around 100 ± 10% for the evaluated elements Pb, Zr, Ti, Sr and Cr. The expected stoichiometry and elemental composition homogeneity of a wide group of produced ceramics were confirmed by the PIXE technique. Copyright © 2012 John Wiley & Sons, Ltd.     

X射线荧光光谱法测定橄榄岩主次痕量元素

本文采用熔融玻璃片和粉末压片法制样，用理论ａ系数和散射线内标法校正元素间的效应，     

A Rapid Method for the Determination of Trace Element Impurities in Silicons Oils by ICP-MS After Microwave-Assisted Digestion

Abstract

A microwave-assisted digestion procedure has been developed for the treatment of silicone oil samples. Inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the concentration level of 40 trace element impurities, like Li, Na, Mg, Al, P, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Sr, Rb, Zr, Nb, Mo, Ag, Cd, Sn, Sb, Ba, La, Ce, Nd, Hf, W, Au, Pb, Hg, Th, Bi and U in these samples, having obtained average relative standard deviation values of 9.6%. The methodology developed has been tested by recovery studies on different natural samples spiked with known amounts of Mg, Cr, Mn, Fe, Zn and Pb at concentration levels of 10, 0.5, 5, 5, 10 and 1 μg g^?1 and recovery percentage values varies from 97 to 105 %.     

Corrosion characteristics of NdFeB sintered magnets containing various alloying elements

The effect of small additions (1 at%) of some elements (P, Cr, Ti, Zr, Pb or Sn) on the corrosion behaviour and magnetic properties of Nd₁₅Fe₇₇B₈ sintered magnets has been investigated. It was established that most advantageous was the addition of 1 at% Cr which distinctly inhibited both acid and atmospheric corrosion processes while it did not deteriorate the magnetic characteristics of the magnet. Addition of Cr accelerates, however, the dissolution of the magnet at strongly cathodic polarization.     

Complete suppression of metastable phase and significant enhancement of magnetic properties of B-rich PrFeB nanocomposites prepared by devitrifying amorphous ribbons

The effect of refractory element addition on phase transformation, crystallization behavior and magnetic properties of Pr_8.5Fe_81.5B₁₀ (addition-free) and Pr_8.5Fe_81.5M₂B₁₀ (M=V, Cr, Nb, Zr, Ti) ribbons has been investigated. The annealed addition-free ribbon as well as the samples with V or Cr additions are mainly composed of the metastable Pr₂Fe₂₃B₃ phase, whereas annealed ribbons with Nb, Zr or Ti additions primarily consist of Pr₂Fe₁₄B and a minor amount of Fe₃B/boride. The complete suppression of the metastable Pr₂Fe₂₃B₃ phase due to Nb, Zr or Ti additions leads to a significant enhancement of the magnetic properties. For example, the remanence, the coercivity and the energy product are remarkably increased from 2.5 kG, 0.4 kOe and 0.2 MG Oe for the addition-free material to 9.2 kG, 4.7 kOe and 7.6 MG Oe for the specimens with Nb addition. The successful elimination of the metastable Pr₂Fe₂₃B₃ phase is believed to profit from two factors: (a) Nb, Zr or Ti atoms substitute the Pr site, comparatively increase the Pr content, and thus inhibit the nucleation of Pr-lean Pr₂Fe₂₃B₃ phases, and (b) the formation of Nb, Zr, or Ti borides consumes some part of B, which hinders the generation of the B-rich Pr₂Fe₂₃B₃ phase.     

非晶态合金FeTmB的磁矩和居里温度

本文系统地报道单辊液淬方法制备FeTmB(Tm=Ti,V,Cr,Mn,Zr,Nb,Mo,Ta,W)非晶态合金的磁性,讨论了3d,4d,5d元素的加入对非晶态FeB合金的磁矩和居里温度的影响。实验结果表明在非晶态FeTmB合金系中Fe原子磁矩都在2.0μ_B左右。Tm原子在非晶态Fe基合金中比在相应的晶态合金中显示更强的局域特性。Tm原子的磁矩与元素的外层电子数有关,IVB(Ti),VB(V),VIB(Cr),VIIB(Mn)族原子的磁矩分别约为4,5,4,3μ_B,Tm的磁矩与铁原子磁矩反平行耦合。合金磁矩随Tm含量的变化率dμ/dx与混合模型的计算值相符合。用虚拟束缚态讨论,得到IVB(Ti),VB(V)族元素的虚拟束缚态在费密面以上,VIB(Cr),VIIB(Mn)族元素的虚拟束缚态与费密面交迭。 关键词：     

High-coercivity nanocomposite permanent magnet based on Nd–Fe–B–Ti–C with Cr addition for high-temperature applications

We have investigated influences of various elements (Ti, Nb, Mo, Ta, Hf, W, V, Cr) on magnetic properties of Fe–B/Nd₂Fe₁₄B-based Nd–Fe–B–Ti–C nanocomposite magnets in order to obtain larger coercivity required for high-temperature applications. As a result, addition of Cr was found to be most effective among additive elements investigated to enhance coercivity. Thermal flux losses of high-coercivity (H_cJ=1609 kA/m) Nd–Fe–B–Ti–C–Cr nanocomposite magnet at 200 °C are less than 2%.     

Strain effects on phase transitions in transition metal dichalcogenides

We perform density functional theory calculation to investigate the structural and electronic properties of various two-dimensional transition metal dichalcogenides, MX₂ (M=Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, or W, and X=S or Se), and their strain-induced phase transitions. We evaluate the relative stability and the activation barrier between the octahedral-T and the trigonal-H phases of each MX₂. It is found that the equilibrium and phase transition characteristics of MX₂ can be classified by the group to which its metal element M belongs in the periodic table. MX₂ with M in the group 4 (Ti, Zr, or Hf), forms an octahedral-T phase, while that with an M in the group 6 (Cr, Mo, or W) does a trigonal-H phase. On the other hand, MX₂ with M in the group 5 (V, Nb, or Ta), which is in-between the groups 4 and 6, may form either phase with a similar stability. It is also found that their electronic structures are strongly correlated to the structural configurations: mostly metallic in the T phase, while semiconducting in the H phase, although there are some exceptions. We also explore the effects of an applied stress and find for some MX₂ materials that the resultant strain, either tensile or compressive, may induce a structural phase transition by reducing the transition energy barrier, which is, in some cases, accompanied by its metal-insulator transition.     

Schottky barrier properties of various metal (Zr, Ti, Cr, Pt) contact on p-GaN revealed from I-V-T measurement

Schottky barrier contact using three different metal (Zr, Ti, Cr and Pt) and Ohmic contact using Ni were made on same epitaxial growth layer of p-GaN. Measurements were carried out using current-voltage-temperature (I-V-T) in the range of 27-100°C. Under forward bias and room-temperature (RT), the ideality factors (η) were determined to be 2.38, 1.82, 1.51 and 2.63, respectively, for Zr, Ti, Cr and Pt. The Schottky barrier height (SBH) and effective Richardson coefficient A^** were measured through modified Norde plot as one of the analysis tools. Barrier heights of 0.84, 0.82, 0.77 and 0.41 eV for Zr, Ti, Cr and Pt, respectively, were obtained from the modified Norde plot. Schottky barrier heights of Zr, Ti, or Cr/p-GaN were also measured through activation energy plot, and determined to be in the same range (∼0.87 eV) and Pt at 0.49 eV. These results indicate that the Fermi level seems to be pinned due to the value of slope parameter (S) was very low (S = −0.25).     

Methodology for the Determination of Stoichiometry and Metal Impurities in New PZT Ceramics by Inductively Coupled Plasma Optical Spectrometry (ICP OES)

ABSTRACT

An inductively coupled plasma optical emission spectrometry (ICP OES) method for Pb, Zr, Ti, Sr, Cr, Fe, Cu, Mn, and Al determination in PZT-ceramics is described. Careful analytical work was carried out in order to evaluate precision, accuracy, and matrix interference. Different procedures were investigated for the ceramics decomposition. Axially viewed plasma operating conditions were evaluated for trace elements (Al, Fe, Cu, Mn, and Cr) in presence of sample matrix. The relative standard deviation (RSD) ranged from 0.7 to 3.9%, whereas the analytes recoveries in the spiked samples ranged from 92 to 119%. The detection limits (LODs) of trace elements ranged from 2.4 to 2.6 µg g^?1. The developed method is useful for evaluating the PZT-ceramics synthesis.     

Elastic properties, thermal expansion coefficients and electronic structures of Ti0.75X0.25C carbides

Elastic properties, thermal expansion coefficients and electronic structures of Ti_0.75X_0.25C carbides (X=W, Mo, Ta, Nb, V, Hf, Zr, Cr and Al) were systematically investigated using ab initio density functional theory (DFT) calculations. The calculated elastic moduli, electronic structures and thermal expansion coefficients α(T) of pure TiC are in good agreement with experimental data and other DFT calculations. Based on a phenomenological formula, the trends of elastic properties and ductile/brittle behavior of Ti_0.75X_0.25C were analyzed. It was found that alloying elements W, Mo, Ta, Nb, V and Hf can increase elastic moduli, while Zr, Cr and Al reduce moduli. The nearly free electron model and Debye approximation were applied in the evaluation of α(T). The anharmonic effect was taken into account by including volume-dependent elastic moduli and Debye temperature. Results show that alloying additions of 3d V, 4d Zr and Mo slightly reduce α(T), while 3d Cr increases α(T), Al, 4d Nb, 5d Hf and W almost keep α(T) unchanged in Ti_0.75X_0.25C at high temperatures. The electronic structures of Ti_0.75X_0.25C were calculated and analyzed, and the electronic density of states was used to interpret variations of elastic properties and ductile/brittle behavior induced by alloying additions.     

Levels and sources of heavy metal contamination in road dust in selected major highways of Accra,Ghana

Environmental studies have revealed significant contributions of vehicular exhaust emissions to high pollution levels in urban dwellings. The levels and sources of heavy metal contaminations of some major roads in Accra have been investigated in this work. Street dust samples collected from four major roads in Accra (Mallam Junction‐Weija road, John Teye‐Pokuase road, Tema Motorway and Tetteh Quarshie Interchange in Accra) were analysed for their elemental concentrations using energy‐dispersive X‐ray fluorescence. Twenty elements were identified: K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Ga, Ge, As, Se, Br, Rb, Sr, Y, Zr and Pb. Significant concentration levels were obtained for K, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Br, Rb, Sr, Y, Zr and Pb in all the samples and were used for the source identification. Enrichment factors and principal component analysis were used to verify the anthropogenic contribution to road dust. Results obtained for the enrichment factors showed moderate enrichment for V, Cr and Cu, while Zn, Br, Zr and Pb were significantly enriched. Principal component analysis identified four sources and their contributions to the elemental contents in the road dust. Natural crust, brake wear, tyre wear and vehicle exhaust emission were the four sources identified. The contribution of vehicular non‐exhaust emissions to heavy metal contamination in the road dust was found to be greater than that of exhaust emissions. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of alloying on magnetic properties of Fe-Cr-12 wt% Co permanent magnet alloys

Effect of alloying additional elements (Al, Si, Ti, V, Ni, Cu, Zr, Nb and Mo) with Fe-22/30 wt% Cr-12 wt% Co permanent magnet alloys manufactured by magnetic aging has been systematically studied with magnetic measurements and transmission electron microscopy (TEM), on a laboratory scale. It is found that the alloying shifts the optimum Cr content to a lower lever. Ti and Si show the greatest enhancement on magnetic properties yet narrow the optimum magnetic aging temperature range. Mo, Nb and Cu, when used together with Si, promote magnetic properties and widen the optimum magnetic aging temperature range. Ni and Zr are simply magnetic diluents. V is good for the magnetic properties only at a large amount of addition. The origin of alloying effects explored by TEM microscopy is attributed to the degree of particle entanglement as well as elongation.     

Atomic Scale Chemistry of α2/γ Interfaces in a Multi-Component TiAl Alloy

We report on the distribution of micro-alloying elements in a multi-component TiAl-based alloy. The specimen contains 3 at.% Nb, 1.5 at.% Cr, 0.5 at.% Mn, 0.6 at.% (W + Hf + Zr), and 0.2 at.% each of B, C, and O. The distributions of all micro-alloying elements with respect to the heterophase interface between α₂ and γ lamellae are analyzed with a three-dimensional atom-probe (3DAP) microscope. All the elements partition except boron, which resides primarily in boride precipitates. Oxygen, C, Mn, and Cr partition to the α₂-phase, whereas Nb and Zr partition to the γ-phase. Both W and Hf exhibit excess concentration values within ca. 7 nm of the lamellar interface in the α ₂-phase, and their near interfacial excesses are 0.26 and 0.35 atoms nm^?2, respectively.     

电感耦合等离子体-质谱法测定纯铪或氧化铪中的25种杂质元素

建立了用电感耦合等离子体-质谱法(ICP-MS)测定纯铪或氧化铪中的Mg、Al、Si、P、Ca、Ti、V、Cr、Mn、Fe、Ni、Co、Cu、Zn、As、Zr、Nb、Mo、Cd、Sn、Sb、Ta、W、Pb和Bi等25种杂质元素含量的方法。铪金属室温条件下混酸溶解后可直接进样分析,氧化铪采用微波消解,辅助溶解后用ICP-MS测定。利用建立的方法,对铪及氧化铪中的杂质元素进行测定,加标回收率为86%—120%。各金属杂质含量均为10ng/mL的混合标准溶液平行7次进样的相对标准偏差均小于5%。方法操作简便、快速,检出限低,能够满足纯度为99.99%的铪金属或氧化铪中杂质分析的需要。     

Theoretical investigation on the phase stability of Nd2Fe14B and site preference of V,Cr, Mn,Zr and Nb

The stability of the excellent permanent magnetic compound Nd₂Fe₁₄B and substitution of Fe in the compound by V, Cr, Mn, Zr and Nb are investigated by using interatomic pair potentials which are converted from lattice-inversion method. Calculation shows that the substitution always makes the cell volume larger, and the increase of the volume is almost linear with substituent concentration. The calculated cohesive energy shows that the preferential order of substitution of Fe is Nb, V, Cr, Mn, Zr. Nevertheless, all the five substituting elements should most preferentially replace Fe in the j₂ site, which has the greatest space among all six Fe sites.     

Effect of water vapour on particulate matter emission during oxyfuel combustion of char and in situ volatiles generated from rapid pyrolysis of chromated-copper-arsenate-treated wood

This paper reports the effect of water vapour on particulate matter (PM) during the separate combustion of in situ volatiles and char generated from chromated-copper-arsenate-treated (CCAT) wood at 1300 °C. Combustion of in situ volatiles produces only PM with aerodynamic diameter?<1?µm (i.e., PM₁), dominantly PM with aerodynamic diameter?<0.1?µm (i.e., PM_0.1). Water vapour could significantly enhance the nucleation, coagulation and condensation of fine particles and reduce the capture of Na and K by the alumina reactor tube via reduced formation of alkali aluminates, leading to increases in both yield and modal diameter of PM_0.1. Water vapour could also enhance char fragmentation hence increase the yield of PM with aerodynamic diameter between 1 and 10?µm (i.e., PM_1–10) during char combustion. For trace elements, during in situ volatiles combustion, volatile elements (As, Cr, Ni, Cu and Pb) are only presented in PM₁ and water vapour alters the particle size distributions (PSDs) but has little effect on the yields of these trace elements. During char combustion, As, Cr, Cu and Ni are present in both PM₁ and PM_1–10 while the non-volatile Mn and Ti are only present in PM_1–10. Increasing water vapour content increases the yields of As, Cr, Cu, Ni, Mn and Ti in PM_1-10 due to enhanced char fragmentation. During char combustion, water vapour also originates less oxidising conditions locally for enhancing As release, promotes the generation of gaseous chromium oxyhydroxides and inhabits the production of NiCl₂ (g), leading to increased yields of As and Cr and decreased yield of Ni in PM_0.1.     

Zur Zustandsdichte der Übergangsmetalle

X-ray isochromats of the bcc transition metals Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W have been measured with high resolution and under comparable conditions. These curves show, that the rigid-band-model is valid for these metals within one row of the periodic table. The width of the conduction band grows from the 3d- to the 5d-row. These results of the isochromat measurements are compared with conclusions about the density of states at the Fermi level, calculated from values of the electronic specific heat, magnetic susceptibility, and superconducting transition temperature. A comparison with theoretical band calculation shows, that a lowered value of the exchange term in the potential would bring into better agreement the widths of the conduction band, taken from calculation and from isochromat measurements.     

Polarization Kinetics in Transparent Pb(Mg1/3Nb2/3)O3–23Pb(Zr0.53Ti0.47)O3 Ceramic

Physics of the Solid State - The polarization kinetics in a transparent Pb(Mg1/3Nb2/3)O3–23Pb(Zr0.53Ti0.47)O3 ferroceramic is investigated in the electric fields of 0 &lt; E &lt; 6...