A new tungsten-free gamma-gamma ` Co-Al-Mo-Nb-based superalloy

We present the first report of a tungsten-free cobalt-based superalloy having a composition Co-10Al-5Mo-2Nb. The alloy is strengthened by cuboidal precipitates of metastable Co-3(Al,Mo,Nb) distributed throughout the microstructure. The precipitates are coherent with the face-centred cubic gamma-Co matrix and possess ordered Ll(2) structure. The microstructure is identical to the popular gamma-gamma' type nickel-based superalloys and that of recently reported Co-Al-W-based alloys. Being tungsten free, the reported alloy has higher specific proof stress compared to existing cobalt-based superalloys. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Wave propagation of phonon and phason displacement modes in quasicrystals: Determination of wave parameters

The paper presents the study of wave propagation in quasicrystals. Our interest is in the computation of the wavenumber (k(n)) and group speed (c(g)) of the phonon and phason displacement modes of one, two, and three dimensional quasicrystals. These wave parameter expressions are derived and computed using the elasto-hydrodynamic equations for quasicrystals. For the computation of the wavenumber and group speeds, we use Fourier transform approximation of the phonon and the phason displacement modes. The characteristic equations obtained are a polynomial equation of the wavenumber (k(n)), with frequency as a parameter. The corresponding group speeds (c(g)) for different frequencies are then computed from the wavenumber k(n). The variation of wavenumber and group speeds with frequency is plotted for the 1-D quasicrystal, 2-D decagonal Al-Ni-Co quasicrystals, and 3-D icosahedral Al-Pd-Mn and Zn-Mg-Sc quasicrystals. From the wavenumber and group speeds plots, we obtain the cut-off frequencies for different spatial wavenumber eta(m). The results show that for 1-D, 2-D, and 3-D quasicrystals, the phonon displacement modes are non-dispersive for low values of eta(m) and becomes dispersive for increasing values of eta(m). The cut-off frequencies are not observed for very low values of eta(m), whereas the cut-off frequency starts to appear with increasing eta(m). The group speeds of the phason displacement modes are orders of magnitude lower than that of the phonon displacement modes, showing that the phason modes do not propagate, and they are essentially the diffusive modes. The group speeds of the phason modes are also not influenced by eta(m). The group speeds for the 2-D quasicrystal at 35 kHz is also simulated numerically using Galerkin spectral finite element methods in frequency domain and is compared with the results obtained using wave propagation analysis. The effect of the phonon and phason elastic constants on the group speeds is studied using 3-D icosahedral Al-Pd-Mn and Zn-Mg-Sc quasicrystals. It is also shown that the phason elastic constants and the coupling coefficient do not affect the group speeds of the phonon displacement modes. (C) 2015 AIP Publishing LLC.

New Deformation Twinning Mechanism Generates Zero Macroscopic Strain In Nanocrystalline Metals

Macroscopic strain was hitherto considered a necessary corollary of deformation twinning in coarse-grained metals. Recently, twinning has been found to be a preeminent deformation mechanism in nanocrystalline face-centered-cubic (fcc) metals with medium-to-high stacking fault energies. Here we report a surprising discovery that the vast majority of deformation twins in nanocrystalline Al, Ni, and Cu, contrary to popular belief, yield zero net macroscopic strain. We propose a new twinning mechanism, random activation of partials, to explain this unusual phenomenon. The random activation of partials mechanism appears to be the most plausible mechanism and may be unique to nanocrystalline fcc metals with implications for their deformation behavior and mechanical properties.

Digested sludge: delineation and modeling for ocean disposal

Experimental work was performed to delineate the system of digested sludge particles and associated trace metals and also to measure the interactions of sludge with seawater. Particle-size and particle number distributions were measured with a Coulter Counter. Number counts in excess of 10¹² particles per liter were found in both the City of Los Angeles Hyperion mesophilic digested sludge and the Los Angeles County Sanitation Districts (LACSD) digested primary sludge. More than 90 percent of the particles had diameters less than 10 microns.

Total and dissolved trace metals (Ag, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) were measured in LACSD sludge. Manganese was the only metal whose dissolved fraction exceeded one percent of the total metal. Sedimentation experiments for several dilutions of LACSD sludge in seawater showed that the sedimentation velocities of the sludge particles decreased as the dilution factor increased. A tenfold increase in dilution shifted the sedimentation velocity distribution by an order of magnitude. Chromium, Cu, Fe, Ni, Pb, and Zn were also followed during sedimentation. To a first approximation these metals behaved like the particles.

Solids and selected trace metals (Cr, Cu, Fe, Ni, Pb, and Zn) were monitored in oxic mixtures of both Hyperion and LACSD sludges for periods of 10 to 28 days. Less than 10 percent of the filterable solids dissolved or were oxidized. Only Ni was mobilized away from the particles. The majority of the mobilization was complete in less than one day.

The experimental data of this work were combined with oceanographic, biological, and geochemical information to propose and model the discharge of digested sludge to the San Pedro and Santa Monica Basins. A hydraulic computer simulation for a round buoyant jet in a density stratified medium showed that discharges of sludge effluent mixture at depths of 730 m would rise no more than 120 m. Initial jet mixing provided dilution estimates of 450 to 2600. Sedimentation analyses indicated that the solids would reach the sediments within 10 km of the point discharge.

Mass balances on the oxidizable chemical constituents in sludge indicated that the nearly anoxic waters of the basins would become wholly anoxic as a result of proposed discharges. From chemical-equilibrium computer modeling of the sludge digester and dilutions of sludge in anoxic seawater, it was predicted that the chemistry of all trace metals except Cr and Mn will be controlled by the precipitation of metal sulfide solids. This metal speciation held for dilutions up to 3000.

The net environmental impacts of this scheme should be salutary. The trace metals in the sludge should be immobilized in the anaerobic bottom sediments of the basins. Apparently no lifeforms higher than bacteria are there to be disrupted. The proposed deep-water discharges would remove the need for potentially expensive and energy-intensive land disposal alternatives and would end the discharge to the highly productive water near the ocean surface.

Band structure and transport properties of simple cubic tellurium-base alloys

The electrical transport properties and lattice spacings of simple cubic Te-Au, Te-Au-Fe, and Te-Au-Mn alloys, prepared by rapid quenching from the liquid state, hove been measured and correlated with a proposed bond structure. The variations of superconducting transition temperature, absolute thermoelectric power, and lattice spacing with Te concentration all showed related anomalies in the binary Te-Au alloys. The unusual behavior of these properties has been interpreted by using nearly free electron theory to predict the effect of the second Brillouin zone boundary on the area of the Fermi surface, and the electronic density of states. The behavior of the superconducting transition temperature and the lattice parameter as Fe and Mn ore added further supports the proposed interpretation as well as providing information on the existence of localized magnetic states in the ternary alloys. In addition, it was found that a very distinct bond structure effect on the transition temperatures of the Te-Au-Fe alloys could be identified.

Homo- and Heteronuclear Transition Metal Complexes Supported by Multinucleating Ligands

This dissertation is mainly divided into two sub-parts: organometallic and bioinorganic/materials projects. The approach for the projects involves the use of two different multinucleating ligands to synthesize mono- and multinuclear complexes. Chapter 2 describes the synthesis of a multinucleating tris(phosphinoaryl)benzene ligand used to support mono-nickel and palladium complexes. The isolated mononuclear complexes were observed to undergo intramolecular arene C¬–H to C–P functionalization. The transformation was studied by nuclear magnetic resonance spectroscopy and X-ray crystallography, and represents a rare type of C–H functionalization mechanism, facilitated by the interactions of the group 10 metal with the arene π–system.

Chapter 3 describes the construction of multinickel complexes supported by the same triphosphine ligand from Chapter 2. This chapter shows how the central arene in the ligand’s triarylbenzene framework can interact with dinickel and trinickel moieties in various binding modes. X-ray diffraction studies indicated that all compounds display strong metal–arene interactions. A cofacial triangulo nickel(0) complex supported by this ligand scaffold was also isolated and characterized. This chapter demonstrates the use of an arene as versatile ligand design element for small molecular clusters.

Chapter 4 presents the syntheses of a series of discrete mixed transition metal Mn oxido clusters and their characterization. The synthesis of these oxide clusters displaying two types of transition metals were targeted for systematic metal composition-property studies relevant to mixed transition metal oxides employed in electrocatalysis. A series of heterometallic trimanganese tetraoxido cubanes capped with a redox-active metal [MMn₃O₄] (M = Fe, Co, Ni, Cu) was synthesized starting from a [CaMn₃O₄] precursor and structurally characterized by X-ray crystallography and anomalous diffraction to conclusively determine that M is incorporated at a single position in the cluster. The electrochemical properties of these complexes were studied via cyclic voltammetry. The redox chemistry of the series of complexes was investigated by the addition of a reductant and oxidant. X-ray absorption and electron paramagnetic resonance spectroscopies were also employed to evaluate the product of the oxidation/reduction reaction to determine the site of electron transfer given the presence of two types of redox-active metals. Additional studies on oxygen atom transfer reactivities of [MMn₃O₄] and [MMn₃O₂] series were performed to investigate the effect of the heterometal M in the reaction rates.

Chapter 5 focuses on the use of [CoMn₃O₄] and [NiMn₃O₄] cubane complexes discussed in Chapter 4 as precursors to heterogeneous oxygen evolution reaction (OER) electrocatalysts. These well-defined complexes were dropcasted on electrodes with/without heat treatment, and the OER activities of the resulting films were evaluated. Multiple spectroscopic techniques were performed on the surface of the electrocatalysts to gain insight into the structure-function relationships based on the heterometallic composition. Depending on film preparation, the Co-Mn-oxide was found to change metal composition during catalysis, while the Ni-Mn oxide maintained the NiMn3 ratio. These studies represent the use of discrete heterometallic-oxide clusters as precursors for heterogeneous water oxidation catalysts.

Appendix A describes the ongoing effort to synthesize a series of heteromultimetallic [MMn₃X] clusters (X = O, S, F). Complexes such as [ZnMn₃O], [CoMn₃O], [Mn₃S], and [Mn₄F] have been synthesized and structurally characterized. An amino-bis-oxime ligand (PRABO) has been installed on the [ZnMn₃O] cluster. Upon the addition of O₂, the desymmetrized [ZnMn₃O] cluster only underwent an outer-sphere, one-electron oxidation. Efforts to build and manipulate other heterometallic [MMn₃X] clusters are still ongoing, targeting O₂ binding and reduction. Appendix B summarizes the multiple synthetic approaches to build a [Co₄O₄]-cubane complex relevant to heterogeneous OER electrocatalysis. Starting with the tricobalt cluster [LCo₃(O₂CR)₃] and treatment various strong oxidants that can serve as oxygen atom source in the presence Co²⁺ salt only yielded tricobalt mono–oxo complexes. Appendix C presents the efforts to model the H-cluster framework of [FeFe]-hydrogenase by incorporating a synthetic diiron complex onto a protein-supported or a synthetic ligand-supported [Fe₄S₄]-cluster. The mutant ferredoxin with a [Fe₄S₄]-cluster and triscarbene ligand have been characterized by multiple spectroscopic techniques. The reconstruction of an H-cluster mimic has not yet been achieved, due to the difficulty of obtaining crystallographic evidence and the ambiguity of the EPR results.

Materiais tipo hidrotalcita contendo Cu como precursores de catalisadores para a redução de NO pelo CO

Dentre os óxidos de nitrogênio, o N2O é um gás do efeito estufa altamente nocivo. Devido ao potencial contaminante que este possui, torna-se importante a implementação de processos capazes de reduzir a sua emissão, bem como a dos NOx. Tradicionalmente, têm-se empregado catalisadores baseados em metais nobres, porém estes apresentam como principal desvantagem o elevado custo. Desse modo, sempre houve o interesse pelo uso de outros tipos de catalisadores e metais neste sistema de reação. Nesse contexto, na presente dissertação procurou-se sintetizar precursores de catalisadores tipo hidrotalcita Cu-AlCO3 e avaliar o seu desempenho na reação de redução do NO pelo CO, visando melhorar a atividade e a seletividade a N2. Foram estudados diversos parâmetros de síntese e diferentes composições. Os parâmetros mais influentes na síntese foram a relação molar H2O/(Al+Cu) e a temperatura de secagem do sólido, cujos melhores valores foram 434 e 25C, respectivamente. Testaram-se dois sólidos, o primeiro composto pela fase hidrotalcita quase pura e o segundo com uma clara mistura entre fases hidrotalcita e malaquita. As análises térmica e química revelaram presença da fase malaquita em ambos os materiais com porcentagens de 14 e 40%, respectivamente. Os resultados de difração de raios X indicaram a presença da fase CuO para os catalisadores provenientes da calcinação dos materiais tipo hidrotalcita, porém a espectroscopia Raman evidenciou a presença de Cu2O no catalisador proveniente do material com maior mistura de fases. Os ciclos redox mostraram uma melhora na redutibilidade dos catalisadores após um ciclo de oxidação-redução. Além disso, foi estudado o impacto do envelhecimento térmico a 900C por 12 h no desempenho dos catalisadores. Pelos resultados de teste catalítico os melhores desempenhos foram alcançados pelos catalisadores envelhecidos, contudo o catalisador proveniente do precursor mais puro apresentou-se melhor tanto novo como envelhecido em termos de menor rendimento de N2O. Uma comparação com catalisadores à base de metal nobre mostrou um bom desempenho dos catalisadores à base de cobre, com a vantagem destes apresentarem menor emissão de N2O em temperaturas menores

The zonation of soft-bottom sediments in Gorgan Bay (Caspian Sea) using macrobenthos as indicator of ecological health

In this study, in order to assess the ecological health status and zoning of soft bottom of Gorgan Bay, the spatial and temporal distribution of macrofauna and their relationship with environmental stress were investigated. Sediment samples were collected using a Van Veen grab at 22 sampling points, seasonally during 2012-2013. The averages (±SD) of the percentages of sand, silt, clay and TOM (Total Organic Matter) in the sediment samples were determined (44.4± 15, 53.4 ± 14, and 2.2 ±2.2 and 7.2% ± 1.6, respectively). Our results showed that mean (range) of Al, As, Cu, Fe, Ni, Pb and Zn in the sediment samples were 1.2 % (0.4-2.1), 4.8 (2.5- 10.3) ppm, 10.5 (4.4-16.9) ppm, 1 (0.4 – 1.6) % , 13.6 (6.2-21.5) ppm, 9.1 (4.7-12.9) ppm and 23.9 (3.1-39.4) ppm, respectively. In spring, both Al and Ni were higher than the guideline level. In the event that arsenic was exceeds the guidelines in summer. In this study, 14 species of macrofauna from 12 families were identified. Polychaeta with 3 species was the most dominant group in terms of abundance. The four most abundant taxa making up 85% of all specimens (Streblospio gynobranchiata, Tubificidae, Hediste versicolor and Abra segmentum). The western area were characterized by the higher species diversity (H', 1.94). So Gorgan Bay presents transitional macrobenthic assemblages that are spatially distributed along substrate gradients .The mean of Shannon index, BENTIX, BO2A, AMBI and M-AMBI in the bay was 1.3, 2.2, 0.4, 3.2 and 0.65 respectively. According to the results of these indices, ecological status of the western part of the bay assessed better than the other parts. According to the results of the nmMDS (non-metric Multidimensional Scaling), PCA (Principal Components Analysis), the map of distribution of heavy metals and the map of the ecological status , it seems Gorgan Bay is divided into two separate zones (the eastern and the western parts).M-AMBI finaly introduced reliable index for assessing the ecological status of the Bay.

PH-dependent leaching behaviour and other performance properties of cement-treated mixed contaminated soil

Portland cement has been widely used for stabilisation/solidification (S/S) treatment of contaminated soils. However, there is a dearth of literature on pH-dependent leaching of contaminants from cement-treated soils. This study investigates the leachability of Cu, Pb, Ni, Zn and total petroleum hydrocarbons (TPH) from a mixed contaminated soil. A sandy soil was spiked with 3000 mg/kg each of Cd, Cu, Pb, Ni and Zn, and 10,000 mg/kg of diesel, and treated with ordinary Portland cement (CEM I). Four different binder dosages, 5%, 10%, 15% and 20% (m/m) and different water contents ranging from 13%-19% dry weight were used in order to find a safe operating envelope for the treatment process. The pH-dependent leaching behaviour of the treated soil was monitored over an 84-day period using a 3-point acid neutralisation capacity (ANC) test. The monolithic leaching test was also conducted. Geotechnical properties such as unconfined compressive strength (UCS), hydraulic conductivity and porosity were assessed over time. The treated soils recorded lower leachate concentrations of Ni and Zn compared to the untreated soil at the same pH depending on binder dosage. The binder had problems with Pb stabilisation and TPH leachability was independent of pH and binder dosage. The hydraulic conductivity of the mixes was generally of the order, 10-8 m/sec, while the porosity ranged from 26%-44%. The results of selected performance properties are compared with regulatory limits and the range of operating variables that lead to acceptable performance described. © 2012 The Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences.

Cement-fly ash stabilisation/solidification of contaminated soil: Performance properties and initiation of operating envelopes

This study was aimed at evaluating the mechanical and pH-dependent leaching performance of a mixed contaminated soil treated with a mixture of Portland cement (CEMI) and pulverised fuel ash (PFA). It also sought to develop operating envelopes, which define the range(s) of operating variables that result in acceptable performance. A real site soil with low contaminant concentrations, spiked with 3000mg/kg each of Cd, Cu, Pb, Ni and Zn, and 10,000mg/kg of diesel, was treated with one part CEMI and four parts PFA (CEMI:PFA=1:4) using different binder and water contents. The performance was assessed over time using unconfined compressive strength (UCS), hydraulic conductivity, acid neutralisation capacity (ANC) and pH-dependent leachability of contaminants. With binder dosages ranging from 5% to 20% and water contents ranging from 14% to 21% dry weight, the 28-day UCS was up to 500kPa and hydraulic conductivity was around 10-8m/s. With leachant pH extremes of 7.2 and 0.85, leachability of the contaminants was in the range: 0.02-3500mg/kg for Cd, 0.35-1550mg/kg for Cu, 0.03-92mg/kg for Pb, 0.01-3300mg/kg for Ni, 0.02-4010mg/kg for Zn, and 7-4884mg/kg for total petroleum hydrocarbons (TPHs), over time. Design charts were produced from the results of the study, which show the water and/or binder proportions that could be used to achieve relevant performance criteria. The charts would be useful for the scale-up and design of stabilisation/solidification (S/S) treatment of similar soil types impacted with the same types of contaminants. © 2013 Elsevier Ltd.

Relating monolithic and granular leaching from contaminated soil treated with different cementitious binders.

This work employed a clayey, silty, sandy gravel contaminated with a mixture of metals (Cd, Cu, Pb, Ni and Zn) and diesel. The contaminated soil was treated with 5 and 10% dosages of different cementitious binders. The binders include Portland cement, cement-fly ash, cement-slag and lime-slag mixtures. Monolithic leaching from the treated soils was evaluated over a 64-day period alongside granular leachability of 49- and 84-day old samples. Surface wash-off was the predominant leaching mechanism for monolithic samples. In this condition, with data from different binders and curing ages combined, granular leachability as a function of monolithic leaching generally followed degrees 4 and 6 polynomial functions. The only exception was for Cu, which followed the multistage dose-response model. The relationship between both leaching tests varied with the type of metal, curing age/residence time of monolithic samples in the leachant, and binder formulation. The results provide useful design information on the relationship between leachability of metals from monolithic forms of S/S treated soils and the ultimate leachability in the eventual breakdown of the stabilized/solidified soil.

Comparisons of operating envelopes for contaminated soil stabilised/solidified with different cementitious binders

This work initiated the development of operating envelopes for stabilised/solidified contaminated soils. The operating envelopes define the range of operating variables for acceptable performance of the treated soils. The study employed a soil spiked with 3,000 mg/kg each of Cd, Cu, Pb, Ni and Zn, and 10,000 mg/kg of diesel. The binders used for treatment involved Portland cement (CEMI), pulverised fuel ash (PFA), ground granulated blast furnace slag (GGBS) and hydrated lime (hlime). The specific binder formulations were CEMI, CEMI/PFA = 1:4, CEMI/GGBS = 1:9 and hlime/GGBS = 1:4. The water contents employed ranged from 13 % to 21 % (dry weight), while binder dosages ranged from 5 % to 20 % (w/w). We monitored the stabilised/solidified soils for up to 84 days using different performance tests. The tests include unconfined compressive strength (UCS), hydraulic conductivity, acid neutralisation capacity (ANC) and pH-dependent leachability of contaminants. The water content range resulted in adequate workability of the mixes but had no significant effect on leachability of contaminants. We produced design charts, representing operating envelopes, from the results generated. The charts establish relationships between water content, binder dosage and UCS; and binder dosage, leachant pH and leachability of contaminants. The work also highlights the strengths and weaknesses of the different binder formulations. © 2013 Springer-Verlag Berlin Heidelberg.

Efficiency of constructed wetlands in decontamination of water polluted by heavy metals

A twin-shaped constructed wetland (CW) comprising a vertical flow (inflow) chamber with Cyperus alternifolius followed by a reverse-vertical flow (outflow) chamber with Villarsia exaltata was assessed for decontamination of artificial wastewater polluted by heavy metals. After application of Cd, Cu, Pb, Zn over 150 days, together with Al and Mn during the final 114 days, no heavy metals with the exception of Mn could be detected in either the drainage zone at the bottom, shared by both chambers, or in the effluent. The inflow chamber was, therefore, seen to be predominantly responsible for the decontamination process of more toxic metal species with final concentrations far below WHO drinking-water standards. About one-third of the applied Cu and Mn was absorbed, predominantly by lateral roots of C. alternifolius. Lower accumulation levels were observed for Zn (5%), Cd (6%), Al (13%). and Pb (14%). Contents of Cd, Cu, Mn, and Zn in soil were highest in top layer, while Al and Pb were evenly distributed through the whole soil column. Metal species accumulating mainly in the top layer can be removed mechanically. A vertical flow CW with C. alternifolius is an effective tool in phytoremediation for treatment of water polluted with heavy metals. (C) 2002 Elsevier Science B.V. All rights reserved.

异丁烷/丁烯烷基化新型固体强酸催化剂的研究

异丁烷和丁烯在酸催化剂的作用下反应生成的烷基化油，是车用汽油的理想调合组分。工业上的烷基化过程采用硫酸和氢氟酸为催化剂，存在着设备腐蚀、废酸处理和毒性等问题，因此开发对环境友好的固体酸催化剂对于推动传统催化剂的改革具有重要意义。本文研究了WO_3/ZrO_2、Zr(SO_4)_2/Al_2O_3(SiO_2)及M_xO_y/Hβ分子筛等固体酸催化剂的制备、性质表征及其在异丁烷—丁烷基化反应中的催化性能。结果表明WO_3的加入对稳定ZrO_2的四方晶相起着重要作用，分散于ZrO_2表面上的氧化钨主要呈单层分散和析出的WO_3晶粒，部分可能与ZrO_2作用形成Zr-O-W键起强酸作用。与其它固体酸相比，具有较好的起始活性和i-C_8~0选择性。用过渡金属M (M = Pt、Co、Ni、Mn、Fe、Cu)活化的M-WO_3/ZrO_2固体强酸催化剂与WO_3/ZrO_2相比，结构、表面状态和酸量均有不同和度的改变。从反应机理上分析了添加过渡金属元素无显著效果的原因。以超细ZrO_2为载体的WO_3/ZrO_2等催化剂，具有更大的比表面、酸强度和对金属氧化物的负载能力，因而具有更好的反应活性，在烷基化产物中C_5～C_7裂解产物较多，使i-C_8~0的选择性有所下降。阐明了不同焙烧温度的Zr(SO_4)_2及Zr(SO_4)_2负载量不同的Zr(SO_4)_2/Al_2O_3(SiO_2)固体强酸催化剂的晶型结构、比表面、酸量及酸强度随焙烧温度和负载量变化的规律。将Zr(SO_4)_2负载在Al_2O_3和SiO_2两种载体上，呈现不同的特性。尤其在Al_2O_3上明显地延缓了Zr(SO_4)_2的分解和ZrO_2的晶相转变。并且使酸量、酸强充和反应活性有所提高，各种样品均具有较高的i-C_8~0选择性。负载各种氧化物的M_xO_y/Hβ(M = Li, Ca, La…)样品仍然保持Hβ的基本特性，但酸性和催化性能也发生了不同程度的改变，其中在Tm_2O_3/Hβ等样品上具有更好的稳定性，烷基化产物i-C_8~0的比例也有所增加。

旋流雾室-气动雾化-氢化物发生-ICP-AES同时测定氢化物元素及非氢化物元素

电感耦合等离子体发射光谱法具有灵敏度高，测定精度好，线性范围宽以及多元素同时测定等优点，目前在分析领域已经得到较为普遍的应用。本文对ICP-AES研究中较为活跃的领域—进样系统方面的最新工作（氢化物发生技术，电热蒸发进样技术和样品直接插入等离子体进样技术）进行了比较详细的综述。为了较好地满足氢化物元素和非氢化物元素同时测定的要求，本文提出了一种新型的旋流雾室—气动雾化—氢化物发生系统。该系统以同心雾化器将样品溶液雾化，沿切线方向引入旋流雾室，筛分出的大雾滴同泵入系统中的KBH_4溶浓反应生成气态氢化物，与经筛分后的较细的雾滴—同进入等离子体中，因而可进行氢化物元素和非氢化物元素的同时测定。砷，铋，锑，硒，锡，碲和锗的检出限分别为：4.6，0.4，7.8，2.1，1.8，1.5和15ng/mL。比用双筒雾室气动雾化非氢化物发生方法得到的检出限好20～30倍，非氢化物元素的检出限也有一定程度的改善。同文献中已见报导的三种同时测定方法相比，该系统具有如下特点：结构简单，操作方便；信号平稳，因溶液溅射造成雾化器堵塞的可能性很小，而且不会向等离子体中引入大量盐份而造成信号漂移和背景强度增加；冲洗及信号平衡较为迅速，样品需要量较小；该系统在实际情况需要时，不经任何拆卸，只需以蒸馏水代替KBH_4溶液泵入系统冲洗干净，便可轻易地转化为普通的旋流雾室，因而使用的灵活性较大。但是由于样品的进样量受同心雾化器的提升率限制，所以对氢化物元素的检测灵敏度的继续提高有一定影响。我们用这种旋流雾室—气动雾化—氢化物发生装置研究了等离子体射频正向功率，载气流量，观测高度，样品溶浓介质酸度，硼氢化钾溶液浓度对待测元素信号强度，线背比和检出限的影响，研究了样品溶液中氢化物元素的浓度对其光谱通道信号强度及谱线净强度的相对标准偏差（测量精度）的影响。我们还对一些较为严重的共存干扰元素对氢化物生成过程中的化学干扰进行了研究，并从近十种络合剂中选出以草酸（0.5%）—硫脲（0.5%）的混合络合体系，较好地消除了Al，Co，Cr，Cu，Fe和Ni的化学干扰。我们利用该旋流雾室—气动雾化—氢化物发生系统对河流沉积物81-101标准参考物质进行分析。结果与标准值比较接近。