Lead Silicate Research Articles

Thermal behavior of lead silicate vitreous materials for sealants

The objective of our investigations consists in the thermal characterization of SiO2-PbO-Na2O vitreous materials in order to establish their properties for applications mainly as sealants. In order to evaluate the vitreous material − metal adherence, the thermal expansion coefficients (α) from experimental and theoretic data were determined. The differential thermal analysis of studied materials give the information about temperatures characteristic to glass transition, crystallization and melting. Dilatometer measurements were performed in air atmosphere in order to establish thermal coefficients of the materials. Softening and flowing characteristic of the vitreous materials were established by heating microscope measurements. The difference between thermal expansion coefficient (α) of the vitreous materials (10.2 × 10−6K−1 and 17.6 × 10−6K−1) and thermal expansion coefficient of the steel substrate OL 38 (10.8 × 10−6K−1) is under 37%. This value is fit for a good adherence between materials.

Applications of Raman spectroscopy in art and archaeology

Applications of Raman spectroscopy in art and archaeology

The microstructure of liquid Lead Silicate under PbO content

The structural characteristics of liquid lead silicate xPbO(1-x)SiO2 are performed by means of molecular dynamics simulation at ambient pressure using the Born-Mayer pairwise potentials. The simulations have been performed on the systems which include different samples with a large range of PbO content ( 0.05 ⩽ x ⩽0.75). The short and intermediate range order in liquid xPbO(1-x)SiO2 have been analysed via pair radial distribution function (PRDFs), coordination distribution, angular distribution and bond length distribution. Calculations show that most of the basic structural units in liquid lead silicate network are SiO4, PbO2 and PbO3 at low ratio of PbO and SiO4, PbO3 and PbO4 at high ratio of PbO. The distribution of O-T-O bond angle and T-O bond length (T is Si or Pb) in SiO4, PbO4 and PbO5 basic structural units are slightly changed when PbO content increase. In intermediate range order, the topology structure of OTy linkages (y=2,3,4) is also investigated in detail.

Structure of lead silicate glasses and its correlation with photoelastic properties

Short-range structures of xPbO–(100 − x)SiO2 (x = 50, 60 and 65 mol%) glasses were studied by neutron diffraction and Reverse Monte Carlo modeling. Si–O atomic pair correlation distributions are symmetrical and show peaks in the range: 1.60–1.64 ± 0.02 A. Si4+ are tetrahedrally co-ordinated with oxygen, whereas the Pb–O and O–O atomic pair correlation distributions are broad and asymmetrical due to the existence of wide range of Pb–O and O–O distances in the glass network. The peak positions in the Pb–O atomic pair correlations shift from 2.60 ± 0.05 to 2.42 ± 0.05 A on increasing PbO concentration from 50 to 65 mol%. Pb2+ exist in PbOx (x = 3, 4, 5 and 6) structural units, and the average Pb–O coordination is constant and is in the range of 4.08 ± 0.11 to 4.14 ± 0.08. The O–Si–O bond angles distributions are broad and asymmetrical with peak values in the range of 91° to 109°, and deviate significantly from the value of 109.5° in the ideal tetrahedral structural units. The short-range structural properties of glasses i.e. the cation-oxygen coordination numbers and bond lengths were used to predict the photoelastic properties of the glasses by the Zwanziger model, and it is concluded that xPbO–(100 − x)SiO2 (x = 50, 60 and 65 mol%) glasses should exhibit the properties of zero-stress birefringence.

Моделирование процессов электронного усиления в каналах умножителей на пористых структурах оксида алюминия

The secondary-emission multiplier of spatial-distributed flows of electrons – microchannel membrane – determines along with the photocathode, luminescent screen, electron-optical system determines the amplifying characteristics of the electron-optical transformers, photoelectronic multipliers. This, in its turn, determines the application areas and the operating range of the items. The actual task is an improvement of the microchannel membrane parameters and the search for new approaches to manufacture on alternative materials of the secondary-emission multipliers. In the paper the use of self-organizing high-ordered porous anode structures of aluminum oxide as the secondary-electronic emitters have been considered. The theoretical and practical approaches to development and the implementation of the computer models of processes of multiplying electrons in the channel of the based on aluminum oxide, have been offered. Based on the results of the calculations, performed using this model, the amplifying ability of such channels has been determined, their optimal caliber is 25, and the supply voltage is 300 V. A comparative analysis of these characteristics of secondary electron multipliers with corresponding parameters of microchannel plates based on lead silicate glass has been performed. It has been determined that that porous anodized alumina may be suitable for the manufacture of secondary electron multipliers. Its secondary emission ability is comparable to lead silicate glass.

Raman and X‐ray fluorescence glaze characterisation of Maria Keil's decorative tile panels

AbstractA set of decorative contemporary tile panels, created by the Portuguese artist Maria Keil (1914–2012) for the Lisbon metro stations, was studied under a noninvasive analytical methodology. This methodology combines X‐ray fluorescence spectrometry (μ‐XRF) and Raman spectroscopy in microscopic (μ‐Raman) mode for an elemental and structural composition characterisation of the glaze (glass matrix and network modifiers such as fluxes, opacifiers and colouring agents). μ‐XRF quantitative evaluation of the glassy matrix shows that all glazes have a lead silicate glass base. Results obtained by the combined use of μ‐XRF and μ‐Raman show that a zirconium‐based opacifier was used. Naples yellow (Pb2Sb2O7), lead–tin yellow type II (Pb(Sn,Si)O3), Pb–Sn–Sb triple oxide, cobalt blue (CoAl2O4), chromium oxide (Cr2O3) and malayite sphene (CaO·SnO2·SiO2) have been identified by μ‐Raman as some of the colouring agents, either used by themselves or in mixtures for obtaining the desirable colours intended by the artist.

An archaeometric investigation of glass beads decorating the reliquary of Saint Simètre from Lierneux, Belgium

The reliquary of Saint Simètre (or Symètre), which is exposed in the Saint André church of Lierneux, was produced during the middle of the 13th century. It is made of a wooden chest with a roof (77 × 28 × 39 cm) covered by silver and golden copper, and decorated by 39 stones which were analysed by Raman and pXRF techniques to determine the nature of colouring agents and of raw materials. The results confirm the identification of 39 glass beads with green, blue, red or pink colours and showing a simple cutting. They show a lead silicate composition (45–55 wt% PbO) with a high level of potassium (5–10 wt% K2O), and iron, cobalt, manganese and/or copper as coloring agents. The silver samples contain 98 wt% of Ag, and the golden border contains approximately 85 wt% of Cu and 14 wt% of Au. The brass decorations on the roof shows an average of 68 wt% of Cu and of 29 wt% of Zn. This study confirms that lead glass beads are contemporary to the reliquary and imported from central Europe.

Third-order nonlinear optical features of zirconia-added lead silicate glass ceramics embedded with Pb2Fe2O5 perovskite crystal phases and role of Fe ions

This study is aimed to identify the role of Fe2O3 in enhancing the efficiency of THG beam of Nd:YAG laser in lead zirconium silicate glass ceramics. The PbO–ZrO2–SiO2:Fe2O3 glass ceramics were synthesized by heat-treating the glasses for a prolonged time. XRD and SEM studies were performed to identify different crystalline phases in the samples. The SEM pictures have shown the presence of multiple crystallites of size in the range 0.1–0.6 µm, while characterization by XRD technique indicated the glass ceramic samples consist of perovskite Pb2FeIII2O5, FeII2SiO4, crystal phases. These studies have also demonstrated that there is an enhancement in the concentration of Fe3+ (Oh) crystalline phases with increasing quantity of Fe2O3 in the samples. Spectroscopic investigations (viz., IR and optical absorption) have further reinforced the above result and additionally indicated an increased degree of internal chaos in the material. The intensity of third harmonic generation (THG) beam of Nd:YAG laser (λ = 1064 nm) measured in the reflected regime after the pre-photopolarization of the samples indicated the largest intensity for the samples containing the highest concentration of Fe2O3. Thorough analysis of these results indicated that the tilted glass samples heat-treated with 0.5 mol% of Fe2O3 have significant chaotic internal structure and paved the way for obtaining intense THG signal with minimal phonon losses. Hence, such glass ceramics are predicted to be useful materials in the design of different optoelectronic devices.

Investigation on the radiation shielding properties of lead silicate glasses modified by ZnO and BaO

Lead glasses are a category of silicate glasses used for the absorption of electromagnetic waves. In this research, the radiation shielding properties of xSiO2.(1-x)PbO2 Glass system by adding 5, 10, and 15 mol.% of ZnO and BaO (that the value of additive decreases equally from SiO2 and PbO2 percentages) are investigated. Characterization includes XRD, SEM, EDAX, DRS (UV–vis), and density analyses. DRS analysis and XCOM software are utilized to investigate the absorption value in the range of 200–900 nm and γ-ray wavelength, respectively. It was revealed that the more ZnO and BaO percentages lead to higher absorption values. The Tauc plot showed that by increasing ZnO or BaO percentage, optical band-gap energies decrease, leading to a higher refractive index and less transparency. In the range of γ-ray wavelength, XCOM software showed that the best absorption value among all synthesized lead glasses is attributed to the glass containing 15% ZnO that for example, at 0.015 MeV provides 8.28% increase in mass absorption coefficient in comparison to the base sample. Besides, in the range of UV–vis wavelength, the highest absorption belongs to lead glass containing 15% ZnO. Therefore, 51%SiO2–34%PbO2–15%ZnO was selected as the best candidate for protective lead glasses. In this paper, the mechanisms of absorption in the base and dopped glasses have well been discussed.

Influence of macro- and microcomponent content on the color of M2O-PbO-SiO2 (M = Li, Na, K, Rb, Cs) glasses doped with copper

The dependence of lead silicate glass color, applied using copper(ii) ions, on lead content in the glass, the nature of the alkali metal, and copper content was studied. It was shown that the principal contribution to the color is made by the shift of the fundamental absorption edge, which correlates with the amount of lead and copper ions. According to EPR results for glasses with the studied compositions, copper ions have a tetragonally distorted octahedral coordination environment, which does not change considerably with composition. The Cuii d—d-transition bands also do not undergo considerable changes.

Quantification of the Fe3+ concentration in lead silicate glasses using X-band CW-EPR

The majority of the existing experimental techniques for determining the fractions of Fe3+ and Fe2+ in silicate glasses are based on X-ray or γ-ray absorption. Materials with a high lead content are not suitable for these techniques because they strongly absorb such high-energy radiation. This work investigates the feasibility and precision of X-band CW-EPR as an alternative technique for the quantification of the concentration of Fe3+ in iron containing lead silicate glasses. This could be a viable alternative since it is based on the absorption of microwaves, which are not heavily influenced by the presence of lead. A practical and robust method using standards is proposed, based on the empirical relation between the concentration of Fe3+ species and the occurrence of two distinct features in the collected EPR spectra. It was found that EPR can indeed be used for the quantification of Fe3+ concentration in lead silicate glasses up until about 8 wt.% Fe2O3, depending on the lead content of the glass. A precision of about ± 0.10 wt.% (2σ) was observed for two tested experimental set-ups. The quantification method proposed requires standards of known composition.

Compositional dependence of Stark splitting and spectroscopic properties in Yb3+-doped lead silicate glasses

In this work, we explore the effect of ionic field strength of modifiers (Li+, Na+, K+, Mg2+, Ca2+, Sr2+ and Ba2+) on room-temperature Stark splitting and spectroscopic properties of Yb3+ ions in lead silicate glasses. Our measurements show that the ‘crystal-field’ parameter and asymmetry degree of Yb3+ ion ligands are increased as a function of modifier field strength due to the corresponding higher electronegativity and bonding energy. Higher field strengths produce greater absorption σa and emission σe cross-sections, effective emission linewidth Δλeff and spontaneous emission probability Arad of Yb3+ ions. We report a 57% enhancement on σa, σe and Δλeff by doubling the field strength of the modifier cations, implying Yb3+ ion doped lead silicate glass with high field strength modifiers (Li+, Mg2+ and Ca2+) may be a promising candidate for efficient laser emission operation.

Microstructure of lead silicate melt under compression: insight from computer simulation

The microstructure of lead silicate melt (Pb2SiO4) and its change under high pressure are investigated by molecular dynamics simulation. The models are constructed at temperature of 3000 K and in the 0–50 GPa pressure range. The microstructural correlate of pair radial distribution functions is clarified. Short range order (SRO) and intermediate range order (IRO) are investigated via topology analysis of SiOx units and SiOx-clusters. Microstructural analysis, cluster-analysis and visualization techniques are applied to clarify the characteristics of -Si-O- network structure. The local environment around Pb+2, Si+4 and O−2 ions, incorporation mechanism of Pb2+ cations into -Si-O- network, the microphase separation under compression have been clarified. Specially, the storage mechanism of hazardous metal ions (heavy metal ions in industrial and nuclear wastes) in silica-based multicomponent oxide systems is also discussed in detail.

Gamma rays interactions with CdO-doped lead silicate glasses

Lead silicate glass systems with different concentrations of cadmium oxide had been prepared and characterized. The XRD analysis indicated the all samples in glassy state. The FTIRpectroscopy indicated a glass modifier role of CdO that was deduced from the formation of [CdO6] structural units. The compositional dependence of the physical parameters such as the density, the molar volume, the optical band gap, the ultrasonic velocities and the elastic moduli on CdO content were determined. The decrease of the ultrasonic velocities, the elastic moduli (experimentally determined and theoretically computed according to Makishima–Mackenzie model) with the addition of CdO was attributed to the decreased compactness and rigidity. These physical parameters revealed the glass modifier role of cadmium oxide.

Conductive mechanism of reduced lead silicate glass for micro‐channel plate

AbstractLead silicate glasses reduced by hydrogen have the characteristics of conductivity like semiconductors and surface secondary electron emission. Therefore, lead silicate glass is the important material of microchannel plate (MCP) for electron multiplier element. The change of bulk resistance (BR) of lead silicate glass (LSG) with hydrogen reducing time and temperature, and hydrogen flow was investigated. The effect of various hydrogen‐reducing parameters on BR is firstly decreasing, then keeping level, and finally increasing. The tendency presents V‐shaped curve. By analyzing the surface composition and morphology of LSG, it is found that the quantity and aggregation state of lead and bismuth are the key factors determining the conductivity of LSG. It is indicated that the electrical conduction is derived from ions and electrons of LSG. The conductive mechanism, however, is different in different stages in the V‐shaped curve. The discovery of V‐shape curve and the conduction mechanism at different stages have important theoretical guiding significance for the fabrication of microchannel plates.

Research on the Surface of Lead Silicate Glass after Resurfacing

The surfaces of lead silicate glass (LSG) S87-2 and S78-4 after resurfacing followed by washing in organic solvents are studied. It is shown that long-term treatment in organic solvents leads to the removal of the foreign layer that appears after the use of oil slurries during resurfacing.

Changes of Alkali Metal Ions and Alkaline Earth Metal Ions on The Surface of Lead Silicate Glasses

Lead silicate glasses are currently the most employed glasses for microchannel plates (MCP) and other applications. X-ray photoelectron spectroscopy was used to determine the changes of alkali metal ions and alkaline earth metal ions on glasses surface during hydrogen reduction. The results showed that the chemical states of alkali metal ions and alkaline earth metal ions did not change. However, the content of these metal ions increases, which is beneficial to secondary electron emission yield of lead silicate glasses and the gain of MCPs.

Surface Compositional Studies of Mircochannel Plates During Hydrogen Reduction by XPS

Lead silicate glasses are currently the most employed glasses for microchannel plates (MCP) and other applications. X-ray photoelectron spectroscopy was used to determine the distribution and variation of surface composition of lead silicate glasses during hydrogen reduction. The results showed that the binding energy of silicon, sodium, potassium, magnesium, barium and cesium did not change. However, the content of metal elements is gradually increased increases, while the alkali metal ions and alkaline earth metal ions migrate to the surface. At the same time, the bridge oxygen and non-bridge oxygen content also changed. All the changes of valence and content of elements on glass surface eventually lead to the change of electrical properties of MCPs.

PbO–SiO2-based glass doped with B2O3 and Na2O for coating of thermoelectric materials

Abstract

Self-Propagating High-Temperature Synthesis of a Thin-Layer CuO–B–Glass System

Experimental studies are performed and mathematical models of the wave synthesis and thermal explosion in a thin-layer CuO–B–glass system are constructed. It is established that the propagation of the combustion front occurs in a multisource mode and its rate depends on the reaction layer thickness (d) according to the parabolic law with a maximum at d = 4 × 10–4 m. An increase in the reaction layer thickness promotes the improvement of thermal explosion characteristics in this system, while its dilution with an inert component makes it possible to form copper coatings with high electrical conductivity. An X-ray phase analysis and optical microscopy showed that the coating consists of metallic copper drops fused together and surrounded by a boron–lead silicate glass melt. Coatings have high electrical conductivity comparable with that of metals. It is found that an increase in the layer thickness above 4 × 10–4 m leads to a considerable decrease in the propagation rate of the combustion wave front due to loosening the initial mixture under the effect of evaporation of water vapor and gases adsorbed on powders and, consequently, to a decrease in heat transfer in the combustion front. Such coatings are nonconductive. Mathematical models of the wave synthesis and thermal explosion in a thin-layer Cu–B–glass system are developed in a macroscopic approximation. Numerical calculations of the process dynamics are performed. Theoretical evaluations satisfactorily correspond to the experimental data. Thermal and thermokinetic process constants are determined by the inverse problem method. Experimental samples of film electric heaters with high electrical conductivity and operational temperature are fabricated based on the experimental data and mathematical models.