FCC汽油中硫醚硫的测定--四乙酸铅电位滴定法

Compared with conventional method of violet spectrum, determination of the content of sulfides in fluid catalytic cracking (FCC) gasoline by using the potentiometric titration of lead tetraacetate has some advantages such as clear potentiometric abrupt change at the stoichiometric point, stable potentiometric value, exact and credible results, and simple operation. The content of sulfides in FCC gasoline of Shenghua refinery is 0.136% by this method. The standard deviation about this method is less than 0.01% and the relative standard deviation is less than 2.42%.     

Low-Temperature Synthesis of Lead Tantalate Pyrochlore Solid Solutions Pb1.5+x(Ta2−yPby)O7−δ (0.0 < x < 0.5; 0.0 < y < 0.6)

Synthesis of lead tantalate pyrochlores by the reaction of PbO and Ta₂O₅ in various molar ratios between 1.5 and 4.0 at low temperatures (500–650°C) has been carried out. It has been shown that when PbO is reacted with Ta₂O₅ in various molar ratios at low temperatures, metastable lead tantalate pyrochlore solid solutions having cubic symmetry are formed. X-ray diffraction data give evidence for an increase in the a lattice parameter with increasing PbO content and partial occupancy of Pb in the Ta sites leading to the formula Pb_{1.5+ x} ²⁺(Ta_{2− y} Pb _y ⁴⁺)O_7−δ (0.0 < x < 0.5; 0.0 < y < 0.6) for this phase. It has also been found that the intermediate members of the solid solutions are metastable and tend to segregate into Pb-deficient and Pb-excess compositions leading to significant compositional inhomogeneity for the intermediate members.     

Combustion synthesis of PbO from lead carboxylate precursors relevant to developing a new method for recovering components from spent lead–acid batteries

BACKGROUND: In the conventional recycling process, lead battery pastes are recovered as metallic lead by using an energy intensive decomposition and reduction process. Decomposition of PbSO₄ requires the use of relatively high temperature and causes environmental pollution, i.e. emission of SO₂ and lead particulates. A new process for treating the pastes at low temperature has been developed. RESULTS: Three major lead compounds are individually reacted with an aqueous solution of citric acid in order to leach and to crystallize lead citrate precursors, which are then subjected to calcination at relatively low temperatures to recover the lead directly as PbO the most common active material for preparing pastes for a new battery. Characterization of the citrate precursors have been carried out using DSC, XRD, and SEM. The combustion products were characterized by XRD and SEM. CONCLUSION: Lead(II) oxides along with a small amount of lead metal are the combustion products, which can be produced at a relatively low temperature of 350 °C. Resulting morphologies show that combustion products are in the 100–200 nm size range, providing high‐surface‐area PbO for making new battery paste materials. The work is aimed to develop a sustainable process for recovering lead from spent lead battery paste. Copyright © 2012 Society of Chemical Industry     

Properties of 0–3 Lead Zirconate Titanate–Polymer Composites Prepared in a Centrifuge

The purpose of this work was to present the electrical and piezoelectric properties of the 0-3 piezoceramic–polymer composites prepared by spinning the lead zirconate titanate (PZT) powders with polyester resin in a centrifuge. PZT powders with average sizes of 55 and 160 μm were used and mixed in the resin with different volumetric percentages. The dielectric and piezoelectric properties such as permittivity, loss angle, electromechanical coupling factor, and piezoelectric coefficient were measured. The mechanical quality factor was calculated. The acoustic impedance was accessed by the echo-shift method. The results were analyzed and fit to mechanical models. Distribution of the ceramic particles in the polyester-resin phase was examined by scanning electron microscopy. Smaller-ceramic-particle composites seemed to form denser samples. Most of the properties showed linearly varying as the volumetric percentage of the ceramic phase. The fabrication using the centrifuging techniques resulted in more homogeneity of the ceramic and polymer phases, and the fabricated samples could be loaded up to 65% or more with the ceramic powders.     

Low-Temperature Reactive Sintering of 0.65PMN·0.35PT

Dense, fine-grained 0.65PMN·0.35PT ceramics were fabricated by reactive sintering of a mixture of metal oxides at 1000°C. The fine nature of the precursor powder resulted in rapid, direct transformation to perovskite PMN–PT at 600°C. Because of the fine structure of the perovskite, no excess PbO was required for sintering.     

利用硝酸回收机械化学活化后的硫化物浓缩液中的铅

Decomposition of lead sulfide concentrates in nitric acidic solutions after ferric (Ⅲ) nitrate addition and mechanical preparation has been investigated. It was found out that the decomposition can be achieved in HNO3 solution (>1.5mol-L-1) at the temperature above 85℃. The leaching rate of lead can be increased by means of mechanochemical activation. The use of [Fe(NO3)3-HNO3-H2O] aqueous salt system allows the decomposition of lead sulfide concentrate at room temperature and in this case the concentration of HNO3 does not exceed 0.05-0.1mol·L-1. The degree of lead recovery into solution from PbS concentrate reaches 99.3%-99.6% with the mechanochemical activation of this concentrate. The insoluble residues after the leaching contain SiO2, S0, FeCO3 and PbSO4.     

Properties of Lead Zirconate Titanate Thin Films Prepared Using a Triol Sol–Gel Route

Microstructure and phase development during the thermal decomposition of sol–gel precursor coatings of PbZr_0.53Ti_0.47O₃ on platinized silicon substrates have been investigated for a triol sol–gel route. The single-layer, 0.4 μm PZT films were heated from below the substrate, over the temperature range 350–600°C, using a calibrated hot plate. The first crystalline phase to appear was a PbPt₃ intermetallic phase at the Pt/PZT interface. Although perovskite PZT formed at ca. 500°C, heating at higher temperatures, for example 550°C for 30 min, was required to develop ferroelectric hysteresis loops. However, the rather low value of remanent polarization, P _r= 11 μC·cm⁻², was consistent with incomplete crystallization at 550°C. The values of remanent polarization increased with increasing processing temperatures, reaching 21 μC·cm⁻² for samples heated at 600°C, with a corresponding E _c value of 57 kV·cm⁻¹. Distinctive spherical precipitates up to ca. 50 nm in size have been identified by TEM in the lower portions of otherwise amorphous coatings, after heating at around 350–400°C. Although their precise composition could not be identified, they were mostly Pb-rich, and it is speculated that they form due to reduction of some of the lead(II) acetate starting reagent, to atomic Pb during the early stages of thermal decomposition of the organic components of the gel; it is possible that subsequent reactions occur to form lead oxides or carbonates. High levels of porosity were present in many of the fully crystallized films. The possible reasons for this are discussed.     

Surface Breakaway Decomposition of Perovskite 0.91PZN–0.09PT during High-Temperature Annealing

The thermal stability of crystallite powder and bulk single crystals of relaxor 0.91Pb(Zn_1/3Nb_2/3)O₃–0.09PbTiO₃ (0.91PZN–0.09PT) solid solution in air and an PbO-rich environment has been investigated. At 700°C, perovskite PZN–PT decomposes only slightly to the pyrochlore phase. At 800°C, the rate of decomposition is accelerated, promoted by a surface breakaway decomposition process. This process occurs via the inward growth of faceted pyrochlore grains from the particle surface. At a certain point of the growth process, they will break away and detach themselves from the perovskite phase. The transformation stress also causes the adjacent perovskite phase to fracture concurrently, contributing to the breakaway event. At higher annealing temperatures (i.e., 900°–1000°C) and/or in the PbO-rich environment, a layer of PbO-rich liquid phase is formed on the surface of the particle. Because of limited wetting between the PbO-rich liquid phase and the earlier-formed pyrochlore grains, the latter detach themselves from the perovskite substrate. This action frees the substrate from the pyrochlore nuclei to initiate the breakaway decomposition event, which causes the rate of decomposition to slow substantially. At 1100°C both in air and the PbO-rich environment, the PbO-rich liquid formed vaporizes readily, which causes the decomposition rate to accelerate again. The present work shows that (i) the decomposition of perovskite PZN–PT to the pyrochlore phase during high-temperature annealing is a surface phenomenon and (ii) its rate is controlled by the relative rate of formation and vaporization of the protective liquid layer that is present under the annealing conditions.     

Effect of Ba2+ Substitution on Dielectric and Electric-Field-Induced Strain Properties of PMN–PZ–PT Ceramics

Effect of Ba²⁺ substitution for Pb²⁺ on the dielectric and electric-field-induced strain characteristics of the PMN–PZ–PT ceramics has been investigated in the compositions of the tetragonal-rich 0.2PMN–0.36PZ–0.44PT and rhombohedral-rich 0.2PMN–0.4PZ–0.4PT ceramics. The phase approached cubic structure from the tetragonal and rhombohedral, and grain size was reduced when the Ba²⁺ cation was substituted. As Ba²⁺ content increased, frequency-dependent relaxor-like behavior of the dielectric constant was observed at temperatures below the dielectric maximum ( T _max) for compositions with 20 and 25 mol% Ba²⁺. Electric-field-induced strain was maximized in the 12 mol% Ba²⁺-substituted 0.2PMN–0.4PZ–0.4PT specimen ( S _max= 0.15%), and maximum piezoelectric, d ₃₁, was 300 in the 14 mol% Ba²⁺-substituted 0.2PMN–0.4PZ–0.4PT specimen.     

Processing and Sol Chemistry of a Triol-Based Sol–Gel Route for Preparing Lead Zirconate Titanate Thin Films

A triol-based sol–gel system has been developed for the fabrication of thin films of lead zirconate titanate (PZT). Starting reagents were lead acetate, zirconium and titanium isopropoxides, acetylacetone, and 1,1,1-tris(hydroxymethyl)ethane (THOME), with 2-methoxyethanol (MOE) being used to dilute the sols for spin coating purposes. Preliminary characterization by NMR spectroscopy suggested that the gels consisted of the metal ions and bound THOME, acetylacetonate, and acetate residues, with some possible M–O–M bridges. Uncracked 0.4 μm single-layer PZT films of nominal composition PbZr_0.53Ti_0.47O₃ were prepared on platinized substrates. Dielectric and ferroelectric properties were determined for samples made from sols containing 10 and 15 mol% excess lead acetate. Improved values were obtained for samples made from sols containing the higher excess; these exhibited a remanent polarization of 34 μC·cm⁻¹, a coercive field of 54 kV·cm⁻¹, and a relative permittivity of 1000.     

Development of a fixed‐bed column with cellulose/chitin beads to remove heavy‐metal ions

Environmental friendly cellulose/chitin beads, having relatively high mechanical properties, were successfully prepared from a blend of cellulose and chitin in 6 wt % NaOH/5 wt % thiourea aqueous solution by coagulating with 5% H₂SO₄ aqueous solution. The ability of the beads to adsorb Pb²⁺ in an aqueous solution was measured with a fixed‐bed column. The effects of important parameters, to design an adsorption column of the cellulose/chitin beads for fixed‐bed columns, were investigated. The breakthrough curves for the adsorption behavior indicated that the column performance was improved with decreasing initial lead concentration, ionic strength, flow velocity or bead size, as well as increasing pH dependence and bed height. Column studies showed that constants, calculated from the experimental data, and the Bed Depth Service Time (BDST) model had a good correlation. The columns were easily regenerated by treating with 0.1 mol/L HCl aqueous solution after the adsorption of metals, providing a simple and economical method for removal and recovery of heavy metals. After four adsorption–desorption cycles, the efficiency of column for the removal of lead was not significantly reduced (not more than 5%). It is shown that heavy‐metal biosorption processes in fixed‐bed columns could give a broad range of potential industrial applications. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 684–691, 2004     

Microstructures and Pyroelectric Properties of Multicomposition 0.9PbZrO3·xPbTiO3·(0.1−x)Pb(Zn1/3Nb2/3)O3 Ceramics

The microstructures and pyroelectric properties of multicomposition 0.9PbZrO₃· x PbTiO₃·(0.1− x )Pb(Zn_1/3Nb_2/3)O₃ (PZ–PT–PZN) ceramics were investigated. The PZ–PT–PZN ceramics with nearly theoretical density were prepared by spark plasma sintering at low temperature (800°C) for a very short time (10 min) from two original compositions with x = 0.025 and x = 0.050. The heat treatment was successfully used to control the diffusion between the different compositions in such ceramics. For ceramics heat-treated at 900°C, two pyroelectric peaks corresponding to the original compositions were observed. When the heat-treatment temperature was increased to 1200°C, these two pyroelectric peaks combined into one sharp pyroelectric peak, which corresponds to average composition. When the spark-plasma-sintered ceramics were heat-treated at 950°C, a high and stable pyroelectric coefficient (>100 nC·cm⁻²·K⁻¹) over a wide temperature range (23°–47°C) was obtained. It was found that the pyroelectric properties strongly depended on the microstructures.     

Chemical Heterogeneity in PMN–35PT Ceramics and Effects on Dielectric and Piezoelectric Properties

Pb[(Mg_1/3Nb_2/3)_0.65Ti_0.35]O₃ (PMN–35PT) powder was prepared using the columbite precursor method. Fully dense compacts were formed by hot-pressing the powder at 950°C, and then the compacts were annealed at 1150°C for 5 and 10 h, respectively. Dielectric and piezoelectric properties of the as-hot-pressed and annealed samples were measured and correlated with microstructure. The as-hot-pressed material exhibited relaxor–ferroelectric-like behavior, with a relatively low dielectric constant maximum measured at 1 kHz ( K _m@1kHz) of 8160. Annealing resulted in a transition to weak normal-ferroelectric behavior, a shift in the dielectric maximum temperature from 190°C to 169°C, and a dramatic increase of K _m@1kHz to a maximum value of 41 720 for the longer anneal. The as-hot-pressed microstructure was chemically heterogeneous, characterized by submicrometer-sized regions of varying magnesium, niobium, and titanium content that likely originated from chemical heterogeneities that were present in the as-prepared PMN-PT powder. The as-hot-pressed properties have been explained as being the integrated response of many discrete ferroelectric responses as dictated for each of these regions by the local chemistry. The transition on annealing has been explained in terms of chemical homogenization to a near-morphotropic phase-boundary composition that is intrinsically weak normal-ferroelectric. Differences in polarization-versus-electric-field and strain-versus-electric-field behavior between the hot-pressed and annealed materials have been discussed in terms of differences in domain mobility.     

Composition‐Dependent Microstructures and Properties of La‐, Zn‐, and Cr‐Modified 0.675BiFeO3–0.325BaTiO3 Ceramics

Pure and 1.0 mol% La₂O₃, ZnO, and Cr₂O₃‐modified 0.675BiFeO₃–0.325BaTiO₃ (BF–BT) multiferroic ceramics were prepared and comparatively investigated. For pure and La‐, Zn‐, and Cr‐modified BF–BT, the average grain size is 415, 325, 580, and 395 nm, and the maximum dielectric constant temperature is 460°C, 430°C, 465°C, and 445°C, respectively. All additives weaken the ferroelectricity slightly. Zn‐ and Cr‐modifications dramatically enhance the room‐temperature magnetic properties, whereas La‐modification has almost no effect on magnetic property. Especially, the Cr‐modified BF–BT ceramics show switchable polarization and magnetization of 4.9 μC/cm² and 0.27 emu/g at room temperature, the magnetoelectric coupling is confirmed by the magnetization‐magnetic field curves measured on ceramics before and after electric poling. The mechanism responsible for the different effects of additive on microstructures and properties are discussed based on additive‐induced point defect and second phase as well as diffusion‐induced substitution. These results not only provide a promising room‐temperature multiferroic material candidate, but also are helpful to design new multiferroic materials with enhanced properties.     

Coupled transport of Pb2+ through tri‐n‐octylamine‐xylene‐polypropylene supported liquid membranes

Transport of Pb²⁺ was carried from acidic solution into alkaline stripping phase through tri‐n‐octylamine‐xylene‐polypropylene supported liquid membrane. The transport of Pb²⁺ through the membrane was studied by varying the concentration of Pb²⁺ and HNO₃ in feed solution, NaOH concentration in strip solution and TOA concentration in membrane phase. The flux data obtained has been used to study the stoichiometry of complex Pb(NO₃)_n+2(HNR₃)_n. The supported liquid membrane (SLM) has been found stable for 10 runs with 24 h between each run. This SLM has been used effectively to extract lead ions along with chromium, copper and zinc ions from aqueous acidic leached solution of paint and industrial effluents. © 2012 Canadian Society for Chemical Engineering     

Development of a lead‐free copper co‐fired BNT‐based piezoceramic sintered at low temperature

Compatibility of Bi‐based piezoelectric ceramic and copper electrodes is demonstrated by co‐firing 0.88Bi_1/2Na_1/2TiO₃–0.08Bi_1/2K_1/2TiO₃–0.04BaTiO₃ (BNKBT88) with copper. A combination of Bi₂O₃, CuO, ZnO, Li₂CO₃, and B₂O₃ are used as additives to reduce firing temperature to 900°C with minimal effect on the electromechanical properties compared to sintering at 1150°C without additives. Co‐firing with copper electrodes requires controlled oxygen sintering at low temperature. The atmosphere is controlled using carbon dioxide and hydrogen gas to maintain an oxygen partial pressure of 6.1 × 10^?8 atm, which is necessary for the coexistence of Cu metal and Bi₂O₃. The thermodynamic activity of bismuth oxide in BNKBT88 is calculated to be 0.38. BNKBT88 ceramics were successfully co‐fired with internal as well as surface Cu metal electrodes. The copper co‐fired ceramics were successfully polarized and the dielectric and piezoelectric properties are evaluated.     

Crack–Tip Toughness of a Soft Lead Zirconate Titanate

Crack–opening displacement (COD) measurements were performed on a commercial lead zirconate titanate (PZT). The intrinsic fracture toughness (or crack–tip toughness) of this material was determined using a new evaluation procedure, which takes into account the near–tip CODs and complete crack profile CODs. The crack–tip toughness K _I0 was determined from an extrapolation of COD data obtained at various loading stages, thus avoiding the complications caused by subcritical crack growth in PZT. Results for plane strain and plane stress condition are presented.     

Influence of Lead in the Processing of High-Temperature 2223 Bi─Sr─Ca─Cu─O Superconductor

Difficulty in reproducibility of results has often been encountered in the Pb-doped 2223 Bi─Sr─Ca─Cu─O superconductor compound due to lead vaporization in samples prepared by standard ceramic methods. Various processing parameters such as quenching, slow cooling, or closed vs open sintering containers were found to affect the properties significantly in samples prepared by standard ceramic methods. In contrast, samples prepared by spray-drying of nitrate solutions were very homogeneous and reproducible because of the rapid and uniform reaction of Pb with other constituents. The magnetic susceptibility and X-ray diffraction data remained unchanged for spray-dried samples processed with or without quenching and sintered in open or closed containers.     

Preparation and Spontaneous Polarization–Magnetization of a New Ceramic Ferroelectric–Ferromagnetic Composite

Ceramic composites with the composition of x PMZNT·(1 – x )NiCuZn have been prepared using a standard ceramic technique, in which x varies as 0, 0.1, 0.2, 0.4, 0.6, 0.9, and 1.0. PMZNT is the abbreviated form of 0.92Pb(Mg_1/3Nb_2/3)O₃·0.04Pb(Zn_1/3Nb_2/3)O₃·0.04PbTiO₃ (PMN-PZN-PT). NiCuZn is the abbreviated form of Ni_0.2Cu_0.2Zn_0.6Fe₂O₄. The presence of ferroelectric PMZNT phase and ferromagnetic NiCuZn ferrite phase has been confirmed using X-ray diffractometry. Ferroelectric hysteresis loops and magnetic hysteresis loops have been observed and studied. In polarization–electric-field curves, the remnant polarization and coercive fields display little asymmetric characterization because of the existence of the internal electric field. When the amount of NiCuZn ferrite phase increases, the coercive field increases. Meanwhile, the saturation magnetization decreases and the coercivity of the composites increases with the increase of phase fraction of PMZNT, because the interaction between magnetic grains (or magnetic connectivity) is weakened by the existence of nonmagnetic PMZNT phase distributed in the magnetic phases. Under an applied magnetic and electric field, the magnetization and polarization of the composites can be easily tuned. The sintered composites possess high density and fine-grained microstructure. The average grain size of NiCuZn ferrite grains is slightly larger than that of the PMZNT grains.