PbO Content Research Articles

Glass formation in the MoO3–CuO–PbO system

Abstract Glasses in the MoO 3 –CuO–PbO system are obtained at high cooling rates (10 4 –10 5 K/s) and characterized using X-ray diffraction (XRD), differential thermal analysis (DTA), infrared (IR) and X-ray photoelectron spectroscopy (XPS). Two glass formation regions are determined: one with compositions having a high MoO 3 content (50–80 mol%) and the other in the PbO-rich compositions (65–80 mol%). In the region of MoO 3 -rich compositions the building units of the amorphous network are МоО 6 , МоО 4 and CuO 4 groups. For these high MoO 3 contents and respectively low PbO concentrations, the lead oxide is supposed to act as a network modifier while at high content PbO is found to be the main glass network former. In latter case the structure of glasses is formed by chains of PbO n ( n = 3, 4) polyhedra, between which there are isolated MoO 4 and CuO 4 complexes. IR and XPS data reveal the existence of Mo–O–Mo, Mo–O–Me(Me’) (where Me = Cu 2+ , Cu 1+ and Me’ = Pb) and Me(Me’)–O–Me(Me’) bonds in the amorphous network. Surprising result is found for low PbO content (10 mol%) where the lead oxide acts as glass network modifier: the actual MoO 3 content drops strongly which is accompanied with a significant increase of the actual CuO content with respect to their nominal MoO 3 –CuO composition. Such effect is not observed in PbO-rich composition (70 mol%) where PbO has a role of network former.

The investigation of the influence of lead oxide on the formation and on the structure of lithium diborate glasses

Pseudo-binary (100 − x) Li 2B 4O 7· xPbO, where x = 0, 5, 15, 25, 35, 45, 55 and 65 mol%. PbO have been investigated. The glass transition temperatures, density and molar volume have been determined. Both T g's values and molar volume decreased non-linearly while the density increased by increase the PbO content. Infrared spectra of the glasses reveal that the strong network consisting of diborate units is break open by PbO. The absorption bands below 620 cm −1 show that PbO is one of the network former of glasses 65 ≥ PbO ≥ 5 which can be associated with vibrations due to [PbO 4] 2− type of grouping are become sharp and high intensities by increase PbO content. PbO plays the dual role in the glass network. The calculated values of N 4 slightly decreased by increase PbO content up to 25 mol% and then increased up to 45 mol% PbO, then decreases above it. Proving that three-coordinated boron atoms are predominant in these glass samples. The Vicker's hardness values of the glasses vary as a function of the PbO content in a manner that N 4 varied. The dc conductivity decreased by increase PbO concentration up to about 25 mol% and then increased by increase the concentration of lead oxide.

Chemical corrosion and gamma-ray attenuation properties of Zr and Ti containing lead silicate glasses

Lead silicate glasses (LSGs) have high gamma-ray attenuation but low chemical durability properties. In this work, LSGs with (55.5–68.5 wt%) PbO content containing ZrO 2 and TiO 2 additions were produced. The chemical corrosion of various produced LSGs in 0.5 N HNO 3 aqueous solution and determination of their gamma-ray attenuation coefficients for 60Co and 137Cs sources were investigated. The weight loss measurements, the SEM micrographs, the EDS analysis of the sample surfaces and the ICP analysis of solution were used to characterize the dissolution process. The effects of PbO content, ZrO 2 and TiO 2 additives on chemical corrosion, and also the effect of PbO on gamma-ray attenuation coefficient, glass transition temperature (Tg), and density of LSG glasses were determined. The results showed that by increasing the lead content of glass the gamma-ray attenuation coefficient, chemical corrosion and density were increased, but the Tg decreased. One of the samples with PbO contents of 65.4 wt% and SiO 2 content of 26.9 wt% showed a very low chemical corrosion behavior and good gamma-ray absorption property.

Thermoluminescence kinetic study of binary lead-silicate glasses

This paper describes a detailed experimental study of the thermoluminescence (TL) properties of four binary lead-silicate glasses, with PbO concentrations ranging from 32% to 62% in mole percent. The TL glow peaks between room temperature and 300 °C were analyzed using a systematic thermal cleaning technique. The T max– T stop and E– T stop methods of analysis were used to identify the number of peaks under the glow curves, and to obtain the activation energy E for each TL trap. A computerized glow curve fitting analysis is used to fit the experimental data to four first-order peaks with maxima at temperatures of 54, 80, 110 and 210 °C, as measured with a heating rate of 2 °C/s. The kinetic parameters of the glow-peak at 210 °C were confirmed by using phosphorescence decay methods of analysis. The TL traps associated with the low-temperature TL peak at 54 °C are found to depend strongly on the PbO concentration of the samples, while the higher-temperature TL peaks show a behavior independent of the PbO concentration. The activation energy E and frequency factor s of the low-temperature TL trap associated with the peak at 54 °C are consistent with a trap involving a delocalized transition through the conduction band. However, the activation energies and frequency factors for the higher-temperature TL traps are consistent with traps involving localized transitions via an excited state below the conduction band. The data suggest that these higher-temperature TL traps are associated with the common silicate matrix in these binary silicate glasses.

Raman and infrared structural investigation of (PbO)x(ZnO)(0.6−x)(P2O5)0.4 glasses

AbstractThe structure of ternary (PbO)x(ZnO)(0.6−x)(P2O5)0.4glasses was investigated using Raman scattering and infrared spectroscopy over the compositional range x = 0–0.6. No significant change of the average chain length composed by PO4 tetrahedral units with the substitution of zinc for the lead cation was observed. The linewidth and wavenumber variations of the Raman high‐wavenumber bands reflect the Zn/Pb substitution in these glasses and are correlated with the metal–oxygen force constant and local disorder. The infrared reflectivity spectra have been fitted with the four‐parameter dielectric function model. The variation in the 1000–1200 cm−1wavenumber range has been attributed to an increase of the oscillator damping ΓLO(PO3)2− as with PbO content vibrations rather than a variation of the chain length. Copyright © 2008 John Wiley & Sons, Ltd.

Mechanism for the formation of Ag crystallites in the Ag thick-film contacts of crystalline Si solar cells

This study examined the interfacial reactions between various Ag pastes and (100) Si wafers with and without an SiN x layer during firing at 800 °C for extended times in order to better understand the mechanism for the formation of Ag crystallites in Ag thick-film contacts of crystalline Si solar cells. The results showed that, in contrast to the model proposed previously, the Ag crystallites were formed by a direct reaction between Ag + ions dissolved in the glass frit and the Si wafer without an aid of liquid-Pb formation. The redox reactions between PbO and Si as well as between PbO and SiN x were suppressed by adding a few weight percent of Ag powder into the glass frit. The size and distribution of the inverted pyramidal Ag crystallites formed at the glass/Si interface were found to depend critically on the PbO content in the glass frit. The role of PbO in Ag crystallite formation was discussed in terms of the solubility of Ag and the viscosity of the glass frit at the firing temperature.

LOW SINTERING TEMPERATURE OF LEAD MAGNESIUM NIOBATE-LEAD TITANATE (0.9PMN–0.1PT) BY ADDING OXIDE ADDITIVES

This research work is aimed at lowering the sintering temperature of 0.9PMN–0.1PT ceramics by adding oxide additives. The oxides used for this purpose were Bi 2 O 3 and Li 2 CO 3 with various amounts, following the formula of xBi 2 O 3+y Li 2 CO 3, where x+y = 10 mol % and x = 1, 3, 5 and the mixed oxide additive powders were then added to the dried powder of 0.9PMN–0.1PT with 1 wt% concentration. An excess PbO content of approximately 3 wtadded to all compositions to compensate the lead loss. After that, the mixed powders were pressed into pellets and subsequently sintered to form the ceramic samples. The results showed that the sintering temperature of 0.9PMN–0.1PT ceramics could be lowered down from 1250°C to 900–1000°C by the addition of small amount of the oxide additives, where the optimum composition was found in the sample with x : y = 1 : 9 at sintering temperature of 1000°C. Moreover, the densification, dielectric and ferroelectric properties of this sample remain acceptable in particular uses, promising positive future for reduction of lead loss from electrical and electronic industries.

Effect of Excess PbO on Crystal Structure, Microstructure and Phase Transition of Lead Titanate Ceramics

In this work, we studied the effect of excess PbO on crystal structure, microstructure and phase transition of lead titanate (PT). PT was prepared via a mixed oxide method with various PbO levels (0, 1, 3 and 5 wt.%). The raw materials were calcined at 750 oC for 2 h and sintered at 1225 oC for 2 h. The characteristics of PT were analyzed by a X-ray diffractometer (XRD), scanning electron microscopy (SEM) and differential scanning calorimeter (DSC). It was found that calcined powders and sintered ceramics indexed in a tetragonal structure. For PT powders, the impurity phases of lead oxide (PbO) and lead dioxide (PbO2) were detected in 3 and 5 wt.% of excess PbO samples, but they were not detected in all sintered ceramic samples. The increase of excess PbO levels resulted in a decreased c/a ratio in both calcined powders and sintered ceramics. Average particle sizes increased from 0.64 to 4.24 µm when excess PbO levels increased from 0 to 5 wt.%. It was also clearly seen that the liquid phase of the sintering process was obtained in the PT calcined powders which had an excess of PbO. The DSC result indicated that the phase transition temperature, from a ferroelectric to a paraelectric phase with a high PbO content (5 wt.%), was higher than those with low PbO contents (0, 1 and 3 wt.%).

Effect of Li 2O on the heterogeneous structure of equi-molar lead borate glasses

Different glass samples in the Li 2O, PbO and B 2O 3 system have been prepared by melt quenching method. These glasses were classified in two groups such as 0.5 B 2O 3, (0.5 − x) PbO, xLi 2O and (0.5 + y) B 2O 3; (0.25 − y)PbO; 0.25Li 2O. The IR spectra almost show broad bands in the frequency range (800–1050) cm −1 and (1100–1500) cm −1, together with different weak bands over the range of investigation (2400–3000) cm −1. The deconvolution analyses of these IR spectra reveals presence of multi structure arrangements from BO 4 and BO 3 groups, such as penta, tri, and diborates grouping together with meta; ortho borates as well as PbO n groups. Partial replacement of PbO by Li 2O causes decrease in microhardness, a change which is attributed to the decrease in the concentration of ortho borate groups as is it revealed from the bands area analysis. The IR analysis shows also that the total concentration of (meta + ortho) borates is nearly constant while their individual concentrations is proportional depending on the relative concentration of PbO and Li 2O.

Shear flow behaviors of poly(p‐phenylene benzobisoxazole) spinning dope

AbstractIn this study, the shear flow properties of Poly(p‐phenylene benzobisoxazole) (PBO)/poly(phosphoric acid) (PPA) spinning dope were studied by means of capillary rheometer. The effect of shear stress, temperature, PBO concentration, and PBO molecular weight on the apparent viscosity of PBO/PPA dope was discussed. The results showed that the apparent viscosity of the dope decreased with the increase of the shear stress and the temperature. The flow behavior index increased with the increase of temperature, which indicated that the non‐Newtonian behavior of the dope became weaker at high temperature. Moreover, it was also found that at high shear stress, the apparent viscosity of the dope was insensitive to the temperature, PBO molecular weight, and PBO concentration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Effects of PbO and SrO contents on crystallization and dielectric properties of PbO–SrO–Na 2O–Nb 2O 5–SiO 2 glass–ceramics system

PbO–SrO–Na 2O–Nb 2O 5–SiO 2 glass–ceramics were prepared via roll-quenching followed by controlled crystallization from 700 °C to 900 °C. The effects of PbO and SrO contents on crystallization and dielectric properties were investigated. The results show that Pb 2Nb 2O 7, Sr 2Nb 2O 7 and their solid solutions crystallize at 700 °C, NaNbO 3 is the primary phase at 800 °C, Pb 2Nb 2O 7 disappears and PbNb 2O 6 forms at 900 °C. The dielectric properties of the glass–ceramics formed through controlled crystallization has a strong dependence on the phase compositions that were developed during heat treatment. The highest dielectric constants (∼600) are found in samples with 6.0 mol% SrO annealed at 900 °C for 3 h. The dielectric–temperature characteristics of the samples show stability over the range from −60 °C to 180 °C, except the sample without SrO heated at 900 °C.

Interface controlled active fracture modes in glass-ceramics

The active fracture modes in glass-ceramics, produced by controlled crystallization from three starting vitreous products containing PbO and SiO2, were studied and compared. The goal was to examine the active fracture modes in PbO-rich glass-ceramic materials, where the main glass former was PbO, and compare these results with those reported in the literature, where the main glass former was SiO2. The influence of composition, shape and mean size of the ceramic phase on the active fracture modes of the glass-ceramics was also examined. It was observed that the microhardness and fracture toughness of the starting vitreous products decrease with increasing PbO content. Increase in the relative amount of SiO2 resulted in a decrease of the percentage of the ceramic phase. Glass-ceramics with higher PbO content showed typical behaviour of high toughness material, i.e. intergranular fracture mode, with lower microhardness value. Glass-ceramics with lower PbO content showed typical behaviour of high-strength material, i.e. transgranular fracture mode, with higher microhardness value.

Spectral properties of PbO–P 2O 5 glasses

The optical absorption spectra of xPbO–(100 − x) P 2O 5 glasses where x = 5, 10, 15, 20, 25, and 30 is reported. The spectral absorption of these glasses was measured in the spectral range 300–900 nm at room temperature. Optical absorption spectra show that the absorption edge has a tail extending towards lower energies. The edge shifts nearly linearly towards higher energies with increasing PbO content. The degree of the edge shift was found to depend on the PbO content and is mostly related to the structural rearrangement and the relative concentrations of the glass basic units. The optical energy gap increases, from 2.55 to 3.05 eV by increasing PbO content from 5 to 30 mol%. The width of the localized states is decreased by increasing PbO content.

Origin of Rayleigh scattering and anomaly of elastic properties in vitreous and molten GeO 2

Vitreous (v) and molten (m) GeO 2 were studied by Rayleigh and Mandel’shtam–Brillouin scattering spectroscopy and high-temperature acoustics. Original measurement apparatus and procedure were used that included Bayseian deconvolution of light scattering spectra of vGeO 2 and a specially designed high-temperature (up to 1500 °C) acoustic interferometer to measure temperature and frequency dependence of ultrasonic (US) velocity and attenuation in mGeO 2. Landau–Placzek ratios for vGeO 2 were found optically (from the light scattering spectrum) and acoustically (through the Schroeder’s formalism). Dispersion of optical and other physical parameters of vGeO 2 found by many authors is explained by the existence of small amount of GeO in the samples. It means that properties of vGeO 2 are under the influence of redox synthesis conditions controlling the GeO 2 ↔ GeO and coordination [GeO 4] ↔ [GeO 6] equilibrium in vGeO 2. Measurements of temperature dependencies of longitudinal ultrasonic velocities in mGeO 2 and in the PbO–GeO 2 glass melts as a function of PbO concentration shows existence of ‘water-like anomaly’ in mGeO 2 and in liquid germanates with the rich content of GeO 2 where equilibrium sound velocity increases with the temperature.

Antiferroelectric-ferroelectric phase transitions in Pb1−xBaxZrO3 ceramics: Effect of PbO content

The irreversibility of the antiferroelectric (AFE) to FE phase transition in Pb1−xBaxZrO3, x=0.75–0.1, compositions is shown to be a consequence of lattice vacancies arising from PbO evaporation during ceramic processing. Previously, the absence of a FE→AFE cooling transition was thought to be due to the transformational strain and the fragmentation of ferroelectric domains. Appropriate compensating levels of excess PbO added to starting powders generate the FE→AFE transition. For lower levels of Ba2+ substitution, x=0.05, the transition is reversible in noncompensated samples, but PbO compensation raises the FE→AFE transition temperature by ∼25°C.

Effect of PbO Concentration on the Templated Grain Growth of PMN-32.5PT Ceramics

<001> textured 0.675Pb(Mg1/3Nb2/3)O3-0.325PbTiO3 (PMN-32.5PT) ceramics were prepared by templated grain growth with micron scale BaTiO3 platelet templates. 0%~7% excess PbO was added to form liquid phase. The influence of liquid phase concentration on the growth of matrix and templated grains was investigated. The growth process was controlled by a dissolution-precipitation mechanism. The templated grain growth was accelerated by the formed liquid phase and resulted in highly textured PMN-32.5PT ceramics.

Preparation of Highly Dense PZN–PZT Thick Films by the Aerosol Deposition Method Using Excess‐PbO Powder

Lead zinc niobate–lead zirconate titanate thick films with a thickness of 50–100 μm were deposited on silicon and alumina substrates using the aerosol deposition method. The effects of excess lead oxide (PbO) on stress relaxation during postannealing were studied. Excess PbO content was varied from 0 to 5 mol%. The as‐deposited film had a fairly dense microstructure with nanosized grains. The films deposited on silicon were annealed at temperatures of 700°C, and the films deposited on sapphire were annealed at 900°C in an electrical furnace. The annealed film was detached and cracks were generated due to the high residual compressive stress and thermal stress induced by thermal expansion coefficient mismatch. However, the film deposited using powder containing 2% of excess PbO showed no cracking or detachment from the substrate after the postannealing process. The PbO evaporation at elevated temperature during the postannealing process seemed to have reduced the residual compressive stress. The remanent polarization and relative dielectric constant of the 50 μm thick films annealed at 900°C were 43.1 μC/cm2 and 1400, respectively, which were comparable with the values of a bulk specimen prepared by a powder sintering process.

Aureoles of Pb(II)-enriched feldspar around monazite in paragneiss and anatectic pods of the Napier Complex, Enderby Land, East Antarctica: the roles of dissolution-reprecipitation and diffusion

Extraordinarily high Pb content in K-feldspar and plagioclase has been found contiguous to monazite in two occurrences in the ultrahigh-temperature Napier Complex of Antarctica. Monazite shows a variety of textures and compositions. In a garnet-sillimanite-orthopyroxene paragneiss at Mount Pardoe (Amundsen Bay), grains range 80–150 μm across and are anhedral; two grains are Th- and Si-dominant. In pods that crystallized from anatectic melts at 2500 Ma at Zircon Point, Casey Bay, monazite grains range 0.05 mm–1 cm in length and are highly variable in texture. The coarsest grains (>0.7 cm) are skeletal and euhedral, whereas the smallest grains are anhedral and associated with fine- to medium-grained quartz, K-feldspar, plagioclase, garnet, sillimanite and rutile in aggregates that form interstitial veinlets interpreted to be a second generation of anatexis during an event at 1100 Ma. The huttonite component (ThSiO4) reaches 30 mole% in the cores of the coarsest skeletal grains, whereas other grains, particularly smaller ones, show complex and irregular zoning in Th and U. The latter zoning is attributed to dissolution-reprecipitation, which also resulted in complete Pb loss during the 1100 Ma event. In the paragneiss at Mount Pardoe, K-feldspar and myrmekitic plagioclase (An16) are found in a 70–80 μm band between monazite and orthopyroxene and contain up to 12.7 wt.% and 2.7 wt.% PbO, respectively, corresponding to 18.5% and 3.4% PbAl2Si2O8 component, respectively. Cathodoluminescence of both feldspars increases with distance from a nearby monazite grain and is not correlated with Pb content. Incorporation of Pb in K-feldspar and plagioclase could be a result of diffusion, even though the monazite adjacent to feldspar apparently lost little Pb, i.e., Pb could have been transported by fluid from the Th-rich grains, which did lose Pb. In contrast to the paragneiss, cathodoluminescence correlates with Pb content of K-feldspar in aureoles surrounding skeletal monazite grains 0.7–1 cm across in anatectic pods at Zircon Point. Pb content of K-feldspar decreases monotonically to near detection limits within several millimetres of monazite grains; the greatest PbO concentration is attained in K-feldspar inliers and embayments in monazite, 8.8 wt.%, corresponding to 11.7% PbAl2Si2O8 component. Fine-grained quartz in the K-feldspar suggests that the mechanism for Pb incorporation involved breakdown of feldspar: Pb2+ + 2(K,Na)AlSi3O8 → PbAl2Si2O8 + 4SiO2 + 2(K,Na)+ . The smooth decrease of Pb in the aureoles is not characteristic of dissolution-reprecipitation, which is characterized by abrupt changes of composition, and it seems more likely that Pb was incorporated in K-feldspar by diffusion at 1100 Ma. We suggest a model whereby fluid introduced during the 1100 Ma event flowed along grain boundaries and penetrated mineral grains. Temperatures were sufficiently high, i.e., 700°C, assuming burial in the mid-crust, for the fluid to induce localized melting of quartzofeldspathic matrix of the anatectic pods. Loss of radiogenic Pb was complete. Some penetration of K-feldspar by aqueous fluid is suggested by the presence of scattered galena specks and by rays of turbidity emanating from monazite. Aqueous fluid or water-rich granitic melt may have mediated the diffusion of Pb in feldspar, but it did not cause dissolution-reprecipitation. Although Pb was mobilized by aqueous fluid or water-rich granitic melt, it was not entirely flushed from the immediate vicinity of the monazite, but nearly half was incorporated in adjacent feldspar. Fluid activity that could cause Pb loss in monazite does not always leave an obvious trace, i.e., hydrous minerals, such as sericite, are very sparse, and biotite is absent in the anatectic pods at Zircon Point. Nonetheless, electron microprobe dating of monazite from the pods could not detect the 2500 Ma age of original crystallization determined by isotopic dating.

Properties of fluorine-doped PbMg1/3Nb2/3O3 ceramics

We report the first fluorine doping of lead magnesium niobate in the PbMg (1 + x)/3Nb(2 − x)/3O3 − x F x system in a wide composition range, x = 0.025 to 0.625. The fluorine content of the samples is shown to be substantially lower than the intended one because of the fluorine volatilization in the form of HF during synthesis and sintering in air. The ceramics consist of magnesium and lead oxides undetectable by x-ray diffraction, and a perovskite phase whose composition can be represented by the formula PbMg(1 + m)/3Nb(2 − m)/3O3 − m F m , where the fluorine content after sintering is m ≤ 0.12. The PbO and MgO contents of the ceramics depend on the starting mixture composition (x) and heat-treatment conditions (hydrogen fluoride and lead oxide volatilization). As a result of the low fluorine content, the diffraction patterns of the samples show no superlattice reflections, and their lattice parameter varies insignificantly with x. Data are presented on the temperaturedependent dielectric permittivity of ceramic samples sintered and annealed under different conditions.

Energy transfer and upconversion luminescence in Tm 3+/Yb 3+ co-doped lanthanum–zinc–lead–tellurite glasses

A series of Tm 3+/Yb 3+ co-doped lanthanum–zinc–lead–tellurite (TPZL) glasses pumped by a 980 nm laser diode (LD) were demonstrated to obtain a high efficiency of infrared-to-visible upconversion. Effects of PbO content on the thermal stability, structure and upconversion properties of Tm 3+/Yb 3+ co-doped TPZL glasses had been investigated. The efficient visible upconversion fluorescences corresponding to the 1G 4→ 3H 6, 1G 4→ 3F 4 and 3H 4→ 3H 6 transitions of Tm 3+ were observed under 980 nm excitation. The upconversion intensities of blue, red and near infrared emissions in Tm 3+/Yb 3+ co-doped TPZL glasses were obviously enhanced with increasing PbO content. The dependence of upconversion intensities on excitation power and the possible upconversion mechanisms had been evaluated by a proper rate equation model. Population density in different levels and coefficients of the energy transfer rate C Di ( i=2, 4, 6) between Tm 3+ and Yb 3+ were estimated by fitting the simulated curves to the measured ones. The obtained three energy transfer coefficients C D 2, C D 4, and C D 6 were determined to be 5.7×10 −17, 1.3×10 −16 and 8.6×10 −17 cm 3/s, respectively.