Polymorphic Phase Transformation of Lead Monoxide and Its Influence on Lead Zirconate Titanate Formation

The polymorphic phase transformation of PbO from massicot to litharge phase is easily produced by mechanical force. The transformation is relatively quick by wet ball-milling. The additions of TiO₂ and ZrO₂ tend to retard it. A second-order exponential relation is observed between the fractional conversion and the milling time for pure PbO, PbO-TiO₂, and PbO-ZrO₂-TiO₂ systems with a rutile constituent. This exponential relation is changed into a first-order logarithmic relation when anatase instead of rutile is used. Although the PbO _ss phase is observed irrespective of the phase of the PbO in the raw materials, this PbO _ss peak is more obvious when massicot PbO or anatase TiO₂ is used. The formation of PbO _ss phase is also dependent on the reactivity of the ZrO₂, and its presence can affect the formation and piezoelectric properties of PZT ceramics.     

Topotatic-Like Phase Transformation of Amorphous Lead Titanate to Cubic Lead Titanate

The crystallization process of lead titanate (PT) prepared using the polymeric precursor method was investigated using X-ray diffractometry, Raman spectroscopy, electron microscopy, and X-ray absorption spectroscopy techniques. The results showed that amorphous PT was formed by an O–Ti–O structure composed of fivefold and sixfold oxygen-coordinated titanium. The local structure of the amorphous PT phase was similar to that of the cubic PT phase, i.e., similar coordination number and similar bond lengths, leading to a topotactic-like transformation during the phase transformation from amorphous to cubic perovskite PT. Because of the low crystallization temperature, every transformation observed during the crystallization process was associated with a short-range rearrangement process.     

Modification of Surface Texture by Grinding and Polishing Lead Zirconate Titanate Ceramics

Grinding and polishing affected the orientation of 90° domains at the surface of lead zirconate titanate (PZT) ceramics. This was quantified by using changes in the intensity ratio of the {002} and {200} X-ray reflections. Grinding unpoled PZT with 600-grit SiC paper gave X-ray intensity ratios similar to those of poled material. This implies that 90° domain realignments had occurred in the near surface region probed by the X-rays. Grinding poled samples with 600-grit SiC further increased the X-ray intensity ratio beyond that caused by poling, indicating that additional surface reorientation of 90° domains had occurred. The effects of diamond polishing depended on the size of the diamond particles. The use of 6-μm diamond had no effect on the {002}/{200} intensity ratio of either poled or unpoled samples, while polishing with 15- or 45-μm diamond significantly enhanced the 90° domain rotation. In unpoled samples, the increase in the X-ray intensity ratio then approached that induced by poling or grinding with 600-grit SiC paper. While the observed increase in X-ray intensity ratio upon grinding is attributed to the rotation of 90° domains, the simultaneous formation of 180° domains appears to minimize or reduce the increase in electrical polarization.     

Nanocrystalline Lead Titanate and Lead Titanate/Vinylidene Fluoride-Trifluoroethylene 0-3 Nanocomposites

Lead titanate (PT) powders of nanometer particle sizes were prepared using a sol-gel process. The PT gel was annealed at various temperatures to produce powders with different particle sizes. X-ray diffractometry (XRD), thermogravimetric analysis (TGA), and differential thermal analysis (DTA) revealed that the PT gel initially crystallized at an annealing temperature of 500°C. The crystallite diameter measured by XRD increased from 27 to 54 nm, while the size of PT particles increased from 30 to 270 nm as the annealing temperature increased from 500° to 900°C. Lead titanate/vinylidene fluoride-trifluoroethylene (PT/P(VDF-TrFE)) 0-3 nanocomposites with PT volume fractions of 0.18 and 0.41 were prepared using PT powders annealed at various temperatures. Because the pyroelectric coefficients of the ceramic and polymer phases had like signs and the piezoelectric coefficients had opposite signs, the poled composite had high pyroelectric but very low piezoelectric activity, thereby reducing vibration-induced electrical noise in pyroelectric sensor applications.     

Low-Temperature Preparation of Nanocrystalline Lead Zirconate Titanate and Lead Lanthanum Zirconate Titanate Powders Using Triethanolamine

Nanocrystalline lead zirconate titanate (PZT) powders, with a Zr:Ti ratio of 60:40, have been prepared from a solution of triethanolamine (TEA) and Ti⁴⁺, Zr⁴⁺, and Pb²⁺ ions. The metal ions were in solution through complex formation with TEA. The soluble metal-ion–TEA complex formed the precursor material when it was completely dehydrated. Heat treatment of the precursor at 450°C resulted in single-phase PZT powders. The precursor and the heat-treated powders have been characterized by using thermal analysis and X-ray diffractometry (XRD) studies. The average particle size, as measured from X-ray line broadening and transmission electron microscopy studies, was ∼20 nm. PZT powders modified with 3 mol% of lanthanum (PLZT) also were prepared through this route and were investigated via XRD studies. The dielectric constants of the PZT and PLZT powders were 12475 and 11262, and their corresponding Curie temperatures were 362° and 315°C, respectively.     

牛粪生物炭的活化及其吸附铅的研究

以Na OH活化牛粪生物炭,分析了活化对牛粪生物炭理化性质的影响,并以生物炭吸附溶液中Pb2+(以0.01 mol/L为背景电解质)。结果表明活化处理能提高生物炭对Pb2+的吸附效果,吸附容量达到192.2 mg/g,相比未活化牛粪生物炭(50.4 mg/g)提高了约4倍。     

Ferroelectric Properties of Lead Titanate

The eutectic and solidus temperatures of the PbTiO₃-KF binary system were investigated by DTA for four compositions. Optical studies of crystal habit as a function of crystallization conditions were used to determine favorable conditions for growing PbTiO₃ crystals from a KF flux. Results of X-ray studies of these crystals agree closely with those of earlier studies. Interferometric measurements of thermal expansion confirmed the ferroelectric transition at 490° C. Specific heat studies indicated a transition energy of about 1550 cal/mole with an entropy change of 2.055 cal/mole °C. Spontaneous polarization was calculated as 66 μcoulombs/cm².     

Solution Chemistry,Substrate, and Processing Effects on Chemical Homogeneity in Lead Zirconate Titanate Thin Films

The effects of chemistry, substrate, and processing conditions on through‐thickness cation distributions are explored in solution‐derived morphotropic composition lead zirconate titanate (PZT) films. Films prepared from chelate‐based and conventional sol–gel chemistries were spin cast onto Pt/ZnO/SiO₂/Si and Pt/Ti/SiO₂/Si substrates and pyrolyzed at 300°C, 350°C, and 400°C prior to crystallization at 700°C either in a preheated furnace or via rapid thermal processing. For films crystallized within a conventional furnace on Pt/ZnO/SiO₂/Si substrates no chemical gradients were observed. All films prepared on Pt/Ti/SiO₂/Si substrates had increased titanium concentrations near the PZT/Pt interfaces, and the source is shown to be titanium diffusing from the substrate metallization stack. The effect of heating method and rate was explored in films prepared on Pt/ZnO/SiO₂/Si substrates with 15°C, 50°C, and 100°C/s heating rates within a rapid thermal annealer. Only one solution chemistry‐heating rate combination resulted in the formation of a chemical gradient: a conventional sol–gel chemistry and a 50°C/s heating rate. Infrared spectroscopy of pyrolyzed gel films showed absorption spectra differences in the bonding structure between the two chemistries with the conventional sol–gel‐derived films exhibiting a signature more similar to that of a PbTiO₃ gel, suggestive of a gel‐structure source of gradient formation during crystallization.     

Organic Acid Adsorption on Lead Titanate Surfaces

Several carboxylic acids were adsorbed on the surface of lead titanate. The total amount of adsorbed acid was determined and characterized by diffuse reflectance infrared Fourier transmission spectroscopy (DRIFTS). The acids were found to be chemisorbed on the lead titanate surface by a metal carboxylate bond. This bond forms by reaction between surface hydroxyls and the organic acid functional group. The amount of adsorbed species per unit surface area varied with each carboxylic acid studied and generally correlated with the size of the individual molecules. The experiments also demonstrate an application of a sensitive method for carbon analysis, oxygen-based coulombic titration.     

在高压下制备单相钛酸铅体陶瓷的研究

阐述了用高压法制备致密钛酸铅陶瓷的原理;用纳米二氧化钛替代了普通的二氧化钛,降低了烧结温度;对PbTiO3陶瓷粉体的合成方法进行了筛选,采用了固相合成法的PbTiO3陶瓷粉体;并对高压下烧结PbTiO3陶瓷的工艺参数进行了全方位的考察,在5~5.5GPa的高压条件下,使晶粒的连接强度得到提高;采用780℃的温度,烧结10~15min,通过手动缓慢降温,得到单相、致密、无开裂的PbTiO3体陶瓷。通过X射线衍射分析和SEM的形貌分析,对所制得的PbTiO3体陶瓷进行了密度测试,只有晶体尺寸较小时,样品才能有较高的密度,并且内应力较小,可作为位移型铁电相变体。     

Densification and Crystallization of Lead Titanate Aerogels

Crack-free monolithic lead titanate (PbTiO₃, or PT) aerogels were prepared via a sol-gel process and drying in supercritical carbon dioxide. The material was characterized by thermogravimetric analysis, dilatometry, helium pycnometry, and X-ray diffraction. Skeletal densification was the main reason for the observed shrinkage of the heat-treated porous material at temperatures <450°C. The transition (at temperatures of 500°-600°C) from an amorphous state to the crystalline (tetragonal) PT was accompanied by significant particle coarsening, as revealed by transmission electron microscopy. Nitrogen adsorption measurements confirmed that crystallization was preceded by the formation of interparticle necks.     

Effect of Additives on Properties of Lead Titanate

The effect of additives on the properties of lead titanate was investigated. The additives employed were selected on the basis of potential solid solution or liquid formation with PbTiO₃ during sintering. Most of these additives aided sintering and produced dense polycrystalline specimens of PbTiO₃ with densities in the range 89 to 95% of theoretical. The dielectric constant and dissipation factor were found to vary considerably, depending on the additive employed. Some poled specimens exhibited a piezoelectric coefficient, d₃₃, as high as 130 × 10⁻¹² coulombs per newton with a dielectric constant of about 160 at room temperature. The microstructure of some of the specimens was also studied and a texture similar to that of barium titanate was observed for those specimens which gave the higher piezoelectric response.     

Oxygen Delignification Chemistry and Its Impact on Pulp Fibers

Abstract

Two southern pine kraft pulps with kappa numbers of 30.0 (SW1-0) and 48.0 (SW2-0) were oxygen delignified by 30–60% by varying the reaction temperature (78–110°C) and charge of sodium hydroxide (1.6–4.4%). O-bleachability was found to be correlated to the incoming kappa number and charge of sodium hydroxide employed. In general, a lower charge of caustic and a higher brownstock kappa number improved pulp bleachability. The residual lignin in the brownstocks and O-delignified kraft pulp samples was isolated and characterized by ¹³C and ³¹P NMR. ¹³C NMR analysis of the residual lignin samples indicated that the post-oxygen delignified pulps were enriched with α-carbonyl groups and carboxylic acid groups. The content of β-O-aryl structures was increased by 23–36% depending on the extent of oxygen delignification. The post-oxygen delignified pulps were also shown to have increased substituted aryl carbons. ³¹P NMR indicated that the relative content of condensed phenolic units increased by 9–20% after the oxygen delignification, depending on the severity of the O-stage. This observation was probably due to the accumulation or formation of 5,5-biphenyl structures in the process. The physical strength properties of brownstock and post-oxygen delignified pulps were assessed in terms of zero-span strength, tensile strength, tear strength, and burst strength. Oxygen delignification led to a slight increase in the curls and kinks of the pulp fibers. The O-stage was shown to cause a 4.8–15.6% decrease in zero-span strength. In contrast, oxygen delignification increased tensile strength. This result could be explained as the improvement of fiber bonding after the oxygen bleaching.     

Vaporization of Lead Zirconate-Lead Titanate Materials

A thermogravimetric investigation of the vaporization of cold-pressed Pb(Zr_0.65Ti_0.35)O₃ in vacuum from 690° to 1130°C shows that the vaporization occurs in two steps. An initial loss of 1 to 7 wt% proceeds by a mechanism with a logarithmic time dependence and represents the vaporization of the unreacted PbO that remains after the initial calcining. The second step proceeds by a slower, diffusion-controlled mechanism with a parabolic time dependence. It is shown that this rate-determining step is bulk diffusion across a thickening lead-depleted layer in the cold-pressed pellet, despite pore volumes of 24 to 42%. The rate constant, g/cm² sec½, for the parabolic weight loss process is expressed by: log K = (3.37 ± 0.14) - (8.46 ± 0.16) (10³/ T _K). The activation energy is 38.7 ± 2.0 kcal/mole.     

钛酸铅微晶玻璃介电性能研究

主要对钛酸铅系铁电性微晶玻璃的介电性能做了研究,研制的微晶玻璃初始组成由形成主晶相的氧化物和形成玻璃相的氧化物构成,经过熔融、热处理可以得到以钛酸铅为主晶相的微晶玻璃,分析了不同组成情况下微晶玻璃的介电性能.     

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.     

Formation of Lead Zirconate-Lead Titanate Solid Solutions

Formation of the Pb(Zr,Ti)O₃ solid solution in the system PbO-TiO₂-ZrO₂ was studied by chemical analysis and X-ray powder diffrac-tometry. Only PbTiO₃ and Pb(Zr,Ti)O₃ were found as reaction products. The following three elementary reactions seemed to be reasonable for the formation of the Pb(Zr,Ti)O₃ phase: PbO + TiO₂→ PbTiO₃, PbTiO₃+ PbO + ZrO₂→Pb(Zr_1-λTi_λ)O₃, and Pb(Zr_l-λTi_λ)O₃+ PbTiO₃→ Pb(Zr_1-λ'Ti_λ')O₃ (λ<λ').     

Electrophoretic Deposition of Lead Zirconate Titanate Ceramics

Electrophoretic deposition (EPD) of submicrometer lead zirconate titanate (PZT) powders in ethanol was conducted to form thick green PZT films up to 160 μm thick. The PZT colloid stability, as a function of pH, was studied by zeta-potential measurement. The electrical condition of the suspension was quantified by conductivity measurement at various pH values. The effect of different applied current densities on the deposition mass was investigated. A kinetic model for the constant-current-density EPD process, taking into account the particle concentration variation, was also examined, based on the experimental results obtained in the present work. An empirical relationship between the kinetic constant and the applied current density has been proposed.