PbO Content Research Articles

Experimental studies on the gamma photons-shielding competence of TeO2–PbO–BaO–Na2O–B2O3 glasses

In this work, glass composed of (40 + x) PbO–5 TeO2–15 BaO–(20 − x) Na2O–20 B2O3 (x = 0, 5, 10, 15, and 20 mol%) was prepared via melt-quenching and the gamma-shielding competency was studied. The results showed that the density and molecular weight increased from 5.006 to 7.121 (gcm−3) and 146.579 to 178.823 (g) as Na2O was replaced by PbO. The direct and indirect bandgap energies decreased from 3.512 to 3.357 and 2.791 to 2.525 eV as the lead concentration increased from Pb40Na20–Pb60Na0. We employed the Geant4 simulation code for narrow-beam geometry with a mono-energetic photon beam imposed on a glass specimen. The mass attenuation coefficient (µ/ρ) for the fabricated glass was determined using the Geant4 simulation code. The difference between the theoretical values (XCOM) and simulated values (Geant4) was less than 7%, confirming the accuracy of the present results. The µ/ρ values increased quickly with the increasing PbO content at low photon energies, while increasing the energy reduced the increase of the µ/ρ values. The linear attenuation coefficient (LAC) was also evaluated and the results showed that increasing the density increased the attenuation behavior. The Pb60Na0 sample with the highest density (7.121 g/cm3) had the largest LAC values at all energies (in the range of 0.29–1.69 cm−1). The effective atomic number values of the fabricated samples were in the range of 33–70. Pb60Na0 glass with the lowest half-value layer is a promising candidate for radiation-shielding applications among Pb40Na20–Pb60Na0 glass.

Effect of gamma irradiation and lead content on the physical and shielding properties of PVC/NBR polymer blends

In the present work, polyvinylchloride/acrylonitrile butadiene rubber PVC/NBR was blended on a Brabender mixer. The blends obtained were cured with peroxide curing systems and loaded with different concentrations of lead monoxide (PbO) for increasing shielding properties of the investigated blends. The physicomechanical and the shielding properties of the prepared blends were evaluated. The surface morphology and structure of the blends were studied by SEM, XRD and FTIR spectroscopy. The morphological analysis of the blends shows that PbO material exhibited homogeneous dispersion in polymer matrix. The gamma attenuation performance of the composites was evaluated by 232Th gamma radiation source. Mass attenuation coefficients of the blends were found to be increased with the increase in PbO content. The tensile strength was found to be enhanced in the presence of the lead oxide filler till 60 phr. The investigated blends were irradiated by 60Co gamma radiation source. The dielectric properties of the prepared blends were evaluated by broadband dielectric spectroscopy. The physicomechanical and dielectric properties of the irradiated blends were investigated. Based on the present obtained results, PVC/NBR/PbO blends are promising materials for low gamma radiation doses.

Electrochemical Investigation of the Effect of Activated Coconut Shells in the Negative Plate of Lead Carbon Battery

The addition of certain types of carbon or graphite to the negative electrode paste mix of lead acid batteries has been reported to substantially slow down the capacity limiting accumulation of insoluble lead sulfate. The resulting lead carbon battery provides improved capacity and cycle life. This report presents the results obtained from recycling of some used lead acid cells into lead carbon battery negative electrodes through the addition of activated coconut shells mixed with graphite powder. Lead metal pieces and sulfated plate materials were obtained from used batteries. The lead pieces were melted and casted to form new grids. The plate materials were desulfurized and calcined to generate the lead oxide used for the new plates. Five new negative plates (30 mm 2 ) composed of the carbon in the proportions (0, 2, 4, 6, 8) % by volume to the PbO contents were prepared. The plates were cured at 60 0 C in high humidity for 12 hrs. and formed at 5 mA/cm 2 for 12 hrs. Cyclic Voltammetry tests implemented with a Gamry 600+ Potentiostat indicated progressive increase in discharge current output with increase in the content of the electroactive carbon up to 4% carbon loading. Keywords: Lead Carbon battery, Desulfurization, Cyclic Voltammetry, Potentiostat. DOI : 10.7176/JNSR/9-20-08 Publication date :October 31 st 2019

Magnetic Properties of Glass Systems (Lead Bismuthate)

XPS has been used to find structural information on the xPbO.(1-X)Bi2O5 glass system where x=0.23, 0.36, 0.44 and 0.55. The binding energies from the Pbf7/2 and 4f5/2 core levels decrease with increasing PbO content while the full-width at half concentrated of these peaks increase. The Ois spectra show an asymmetryfor samples having composition x<0.6, which results from oxygen atomare the B-O-B conformationas well asoxygen atom in the Bi-O-Pb and Pb-O-Pbconfiguration. The no of non-bridging O was establish to grow thing 82% near 93% with grow thingPbOcomfortable.The documents aresteadybyresolves from magnetic susceptibility dimensions on the similarcrystalexamples.PbObond are appropriateextra covalent in environmentallyPbOandfinallyPbOaltered its role of glass. In addition to the paramagnetic involvementin Bi4+, The Susceptibility of Oxide Glasses Covers Of +ve Constant Contribution

Investigation of the physical properties and gamma-ray shielding capability of borate glasses containing PbO, Al2O3 and Na2O

Six glass samples of new lead borate with chemical formula 5Al2O3–5Na2O–(90-x)B2O3–xPbO, where 0 ≤ x ≤ 50 mol% have been synthesized using the melt quenching technique. The prepared glasses distinguished by codes as x = 0 (ANBP00)—x = 50 (ANBP50) mol%. The physical properties and gamma-ray shielding capability of the glasses have been investigated. To achieve these aims, the amorphous structure of all glasses was examined using X-ray diffraction (XRD) measurements. The density and molar volume have been calculated. Density of the glasses increases from 2.133 (g/cm3) for ANBP00 glass sample to 5.010 (g/cm3) for ANBP50 sample. The XMuDat and XCOM programs were used to calculate the mass attenuation coefficient (μ/ρ) in the photon energy range of 0.015–10 MeV for all glasses. The difference between the obtained values of XMuDat and XCOM is found to be less than 1%. Half value layer (HVL), effective atomic number (Zeff), and mean free path (MFP) as γ-ray shielding features have been evaluated using values of the (μ/ρ) for all proposed glasses. Results reveal that ANBP50 and ANBP00 samples possess a maximum Zeff and a minimum Zeff, respectively. Indeed, ANBP50 glass has lowest values of (HVL) and (MFP). Therefore, addition of PbO content in the prepared glasses has a considerable effect to improve the shielding effectiveness for these glasses. Finally, ANBP50 glass can be considered as a promising candidate for gamma-ray protection applications among different types of concretes, commercial glasses, and HMO glasses.

Fabrication, optical, structural and gamma radiation shielding characterizations of GeO2-PbO-Al2O3–CaO glasses

(90-x)GeO2-xPbO-5Al2O3–5CaO: 0 ≤ x ≤ 40 mol%) glasses have been fabricated by conventional melt quenching technique and coded as GACPb00 to GACPb40. The structure of the prepared glasses has been examined using X-ray diffraction measurements. The UV–vis spectra in the range of 190–1100 nm wavelength for the proposed glasses have been recorded. Based on the absorption spectra, the band gap of optical energy (Egap) has been evaluated using the direct method and absorption spectrum fitting (ASF) model. Index of refraction (n), molar polarizability (αMolar), molar refractivity (RMolar), metallization criterion (MCriterion), dielectric constants (εStatic and εOptical), optical transmission (TOptical), reflection loss (RLoss) have been evaluated. WinXcom program was applied to study the photons shielding behavior of the present samples. The mass attenuation coefficient of the samples increases with the increase of PbO content at all energies. However, this increase is more notable at low energies. The current samples have relatively high effective atomic number (Zeff) at low energy due to the photoelectric phenomenon. The Zeff for GACPb00 and GACPb40 at 0.356 MeV is 16.02 and 30.76 respectively, and at 0.662 MeV these values are 15.58 and 23.71. The results also revealed that the density of the samples plays a very important rule of the half value thickness (HVT), and as well the thickness of the samples that are used to block or attenuate the photons. Interestingly, we found that GACPb40 has the biggest μ/ρ and lowest HVT which implies that this sample has superior photon attenuation capability.

Microstructure and Properties of PZT Films with Different PbO Content-Ionic Mechanism of Built-In Fields Formation.

Experimental studies were conducted on the effects of lead oxide on the microstructure and the ferroelectric properties of lead zirconate-titanate (PZT) films obtained by the method of radio frequency (RF) magnetron sputtering of a ceramic PZT target and PbO2 powder with subsequent heat treatment. It is shown that the change in ferroelectric properties of polycrystalline PZT films is attributable to their heterophase structure with impurities of lead oxide. It is also shown that, even in the original stoichiometric PZT film, under certain conditions (temperature above 580 °C, duration greater than 70 min), impurities of lead oxide may be formed. The presence of a sublayer of lead oxide leads to a denser formation of crystallization centers of the perovskite phase, resulting in a reduction of the grain size as well as the emergence of a charge on the lower interface. The formation of the perovskite structure under high-temperature annealing is accompanied by the diffusion of lead into the surface of the film. Also shown is the effect of the lead ions segregation on the formation of the self-polarized state of thin PZT films.

Insight into Oxidation of Ultra-Fine Lead Powder By Electrodeposition

Pure lead powder has multiple application such as oil and gas exploration, X-ray shield, golf club manufacture, paints, lubricating grease and anti-friction products. Electrochemical deposition of lead powder can be obtained from both the acid electrolytes based on fluoroborate, acetate, fluorosilicate, nitrate, etc. and an alkaline solution. Morphological characteristics of lead powder with overpotential have been detailed in previous literatures. Nevertheless, oxidation of lead powder during electrodepositing process was out of view, which actually decreased the purity and quality of lead powders compared to atomized ones. In this investigation, ultra-fine lead powders with a minimum median diameter of 4.5 μm were electrodeposited in solution consisting of 2 M CH3COONa, 2 mM Pb(CH3COO)2 and pH values adjusted by acetic acid. The degree of as-deposited lead powder was defined as the content of PbO in wt %, and was determined by complexometric titration with EDTA. The morphology of lead powders shown by SEM was a classical dendrite and branches, which resemble a tree. The oxidation of lead powder reached to about 16% when pH value of electrolyte was 1 and decreased abruptly to around 6 % at pH from 3 to 7. The oxidation of lead powder was stable at ~5.5 % with the cathodic current densities from 23 mA cm-2 to 36 mA cm-2 and increased to 9 % and 13% at current densities of 10 and 45 mA cm-2 respectively. The concentration of gelatin as an additive accelerated the oxidation of lead powder. When ultrasonic was applied, the oxidation degree of lead powder became 3-fold larger than that of the stirred one. More importantly, the average sizes of powder have a directly relationship with the degree of oxidation. The smaller median diameter is, the larger degree of oxidation is. However, the XRD of the lead powder with about 16 % oxidation shows only metallic Pb with strongly preferred orientation in (111) plane, which indicated the amorphous PbO powders. The results of TEM confirmed the amorphous materials around lead particles, which suggested metallic Pb was partly transformed from PbO. Therefore, we suggested a mechanism of lead electrodeposition result in oxidation of lead as follows: Deprotonation: [Pb(H2O)]2+ → [PbOH]+ + H+ Electrochemical reduction: Lead reduction— Directly：[PbOH]+ + H+ + 2e- → Pb + H2O Indirectly: [PbOH]+ → PbO + H+ PbO + 2H+ + 2e- → Pb + H2O Hydrogen evolution— 2[PbOH]+ + 2e- → 2PbO + H2 2H+ + 2e- → H2 The reason of forming [PbOH]+ complex is due to the stability constant, lgβ=13.3, which is about 10 order of magnitude large than that of acetate complexes, lgβ=3.60. Figure 1

Glass Formation in the PbO–GeO2 System

The glass-forming region in the PbO–GeO2 system is studied. To increase the glass-forming limit in this system, the tempering rate of the samples has to be increased using special methodological practices. The dependence of the temperature of the synthesis of lead germanate glass on the PbO content is obtained. It is shown that the corrosion of alumina crucibles proceeded during the synthesis of lead germanate glass. The dependence of the thickness of the corroded layer of the alumina crucible wall on the time of the synthesis of the glass of the 55PbO · 45GeO2 composition, mol % at 900°С is obtained. It is proved that the obtained glass is X-ray amorphous within the whole range of compositions in the PbO–GeO2 system.

The influence of PbO on the radiation attenuation features of tellurite glass

Tellurite based glasses have been of considerable interest in the last decades due to their interesting mechanical, physical and chemical features. Presently, different investigators and engineers are being devoted for developing the Tellurite based glasses to be used as effective radiation shielding materials. Our aim is to study the energy as well as PbO content dependence on the gamma rays attenuation behavior of lead tellurite glasses when the PbO content changes from 0 to 30 mol% between 0.356 and 2.506 MeV photon energies. This was achieved by considering the lead tellurite glass system with the composition x(PbO)-(100-x)(TeO2). The photon attenuation factors of the lead tellurite glasses were evaluated at five energies utilizing Monte Carlo simulation (Geant4 code). The reative difference values between Geant4 and XCOM data for the six glasses are less than 7% and this validates the accuracy of the obtained results. The mass attenuation coefficient (μ/ρ) reduces with an increase in the energy whereas it increases when TeO2 is replaced by PbO. The influence of PbO on the μ/ρ is significant only at 0.356 and 0.511 MeV, but at the other energies it is found that PbO slightly affects the attenuation factor. The linear attenuation coefficient of 30PbO–70TeO2 (coded as TePb6) is higher than the other samples. The effective atomic number has the maximum value at 0.356 MeV (in the range of 27.76–41.25). We compared the mean free path for the tellurite glasses with RS-520 and RS-360, Osmani, nasir and PHP glasses. The results reveal that the lead tellurite glasses (especially the samples with high PbO content) are a candidate as protection materials from hazardous radiation and have better attenuation in comparison to some nuclear engineering materials.

Comparison between MCNP5, Geant4 and experimental data for gamma rays attenuation of PbO–BaO–B2O3 glasses

Monte Carlo simulations, MCNP5 and Geant4 codes were developed to investigate radiation shielding properties of xPbO–(50-x) BaO–50B2O3 (where 5 ≤ x ≤ 45 mol%) consider to be glass systems. The mass attenuation coefficients were evaluated for different PbO concentration in the glass samples for varies photon energies of 0.356, 0.662, 1.173 and 1.332 MeV. The obtained mass attenuation coefficient values used to calculate half-value layer, effective atomic number, and electron density. The simulation parameters were compared with experimental data. Results show that the simulation results of mass attenuation coefficients for all PbO concentrations were generally in good agreement with experimental results, however, mass attenuation coefficient values calculated using Geant4 were slightly lower than MCNP5 and experimental data on the low energy of 0.356 MeV. The results obtained from MCNP5 and Geant4 codes might be able to assessment mass attenuation for different glass systems. Furthermore, gamma ray, fast neutron and charged particle interaction for the glass systems were studied using buildup factors, fast neutron removal cross sections and ranges respectively.

Gamma ray shielding and structural properties of iron alkali alumino-phosphate glasses modified by PbO

The glasses with the chemical formula 55 P2O5 – 5 Al2O3 - 20 Na2O - (20-x) Fe2O3- x PbO (0 ≤ x ≤ 20 mol%) as proposed shielding for gamma radiation were synthesized and explored. The investigations of the FTIR variations of the glasses are discussed in the view of the variations of the phosphate and lead structural units. These changes were determined by the evolution of the PbO on the expense of Fe2O3 concentrations. According to this analysis, non-bridging oxygens were created as the Pb2+ ions were occupied between the P–O–P layers. This process revealed the glass modifier role of PbO. The narrow beam transmission method was used utilizing different photon energies 356, 662, 1173 and 1332 keV to determine the mass attenuation coefficient (μm) of each glass sample of the studied glasses. For the investigated glasses, there is an increment in the values of the physical parameters μm, Zeff and Nel with the increment of PbO contents. This relation turns out that the studied glasses are improved shields for gamma-radiations with the increment of PbO.

Optical and Electrical Properties of Lead Borate Glasses

Lead borate glass matrix of composition (x PbO-10 ZnO-(90 − x) B2O3), (x = 50–90 wt.%) was prepared by the melt quenching technique. The amorphous nature of these glasses was confirmed via x-ray diffraction (XRD) measurements. Both infrared spectra (400–4000 cm−1) and UV–visible absorption 200–1100 nm have been measured for all prepared samples in order to study the optical properties of samples. We found that the optical energy gap ( $$ E_{\rm{gap}}^{\rm{optical}} $$ ) decreased, however, Urbach’s energy (EU) increased with increasing PbO content. By using UV–visible absorption, electrical conductivity ( $$ \sigma_{\rm{electrical}} $$ ), optical conductivity ( $$ \sigma_{\rm{optical}} $$ ), refractive index (n), extinction coefficient (k), optical complex dielectric constant (e), surface and volume energy loss functions (SELF and VELF) have been calculated. In addition to optical basicity (Λth), optical basicity on the basis of optical band gap ( $$ \varLambda_{{E_{\rm{gap}} }} $$ ), and electronic polarizability on the basis of optical band gap ( $$ \alpha E_{\rm{gap}}^{\rm{optical}} $$ ) have been calculated. Dielectric parameters (e′ and e″) and ac conductivity (σac) have been carried out in (100 Hz–100 kHz).

Extensive study of newly developed highly dense transparent PbO-WO3-BaO-Na2O-B2O3 glasses for radiation shielding applications

Amorphous PbO – WO3 – BaO – Na2O – B2O3 glass system have fabricated using traditional melt quenching method. The XRD and FTIR spectra confirm the amorphous nature and the various structural properties of the glasses respectively. The various optical properties have been measured in the spectral range 400–4000 cm−1. Also, to understand the shielding ability of the fabricated glasses, we used the Geant4 model of a HPGe detector and WinXcom program to calculate the mass attenuation coefficient (MAC) at six energies between 356 and 2510 keV. In order to confirm the agreement between both methods, we used correlation theory and calculated the correlation coefficients (R2) for each sample. It is found that the R2 values are close to 1 for all samples. The MAC values at 356 keV for the prepared samples lies between 0.221 and 0.246 cm2/g. It is found that the usage of different concentration of PbO (from 50 to 70 mol%) affects the MAC values and thus the attenuation ability of the samples due to the heavier density of the PbO in comparison to B2O3. The effective atomic number results showed that Pb70B10 sample (contains 70 mol% of PbO) was higher than the other samples. Hence, Pb70B10 absorbs more photons than the rest of the prepared glasses.

Optically transparent newly developed glass materials for gamma ray shielding applications

Five amorphous heavy metal oxide borate glasses have been fabricated by melt quenching method. The density of the fabricated samples changes from 5.411–7.075 (g/cm3) whereas molar volume decreases from 33.806–30.198 (cm3 mol−1) as lead concentration increases from 40 to 60 mol%. The FTIR spectra reveals the various structural properties of the samples. The indirect and direct band gap energies have been obtained from the UV spectra. Both values of Eg decrease as the PbO content increases. These indirect band gap energy values are further used for the calculation of the other optical parameters. The gamma shielding features of the prepared samples were evaluated and the results revealed that the mass attenuation coefficient increased with increasing the content of PbO and the sample coded as Pb60B10 has the highest protection efficiency. The effective atomic number values for the samples are high between 0.015 and 0.2 MeV and in order of 78.18–60.11 for Pb40B30.

Evaluation of the inhibiting effect of graphene oxide on lead leaching from waste cathode-ray tube glass incorporated in cement mortar

A huge volume of waste cathode-ray tube (CRT) glass (containing a large content of PbO) is generated annually. In this study, evaluation of lead leaching in waste CRT glass within cement-based materials is addressed, and the role of graphene oxide (GO) in inhibiting lead leaching is studied. Lead leaching was evaluated using the toxicity characteristic leaching procedure (TCLP) and electrochemical impedance spectroscopy (EIS), and the microstructure was also characterized with scanning electron microscopy (SEM). The TCLP results indicated that Pb leaching of waste CRT mortar with GO addition was significantly controlled below the regulatory limit (5 mg/L) specified by United States Environmental Protection Agency (USEPA) and the Chinese Standard. A novel circuit model R0(Q1W(Q2R1)(Q3R2)) was successfully applied to evaluate the transport of lead in GO-waste CRT mortar by using EIS. The electrochemical parameters revealed that the microstructure of the bulk cover and waste CRT-mortar interface was improved by adding GO, indicating that lead transfer within the bulk cover and waste CRT-mortar interface was inhibited. Better attachment between waste CRT glass/bulk paste and higher density hardened structure with 0.1 wt% GO were observed in SEM images, indicating that the hardened structure can effectively encapsulate lead ions out of waste CRT glass in the interface and bulk paste.

Experimental studies and Monte Carlo simulations on gamma ray shielding competence of (30+x)PbO[sbnd]10WO3[sbnd] 10Na2O − 10MgO – (40-x)B2O3 glasses

In the present study, we utilized the melt quenching method to fabricate (30 + x)PbO10WO310Na2O 10MgO–(40-x)B2O3 (where x = 0, 5, 10, 15 and 20 mol %) glasses. The mass attenuation coefficients (μ/ρ) have been measured at four energies using gamma spectrometric system and the measured values were validated by MCNPX code and XCOM software. The variation in the experimental, theoretical and MCNPX μ/ρ values coincided with each other in all energy regions. The linear attenuation coefficient values for the prepared glasses are proportional to the increase of PbO concentration; however reduce with the increasing photon energy. Besides, we found that the addition of PbO to the glasses leads to reduce in HVL values in the photon energy range, which suggested that the addition of PbO in the synthesized glasses enhances property of more photons absorption of the glass samples. The effective atomic number (Zeff) for the prepared glasses was also calculated and then, we discussed the effect of PbO on the Zeff. The Zeff values lie within range of 29.95–42.77, 20.90 to 30.88, 17.99 to 26.46, and 17.74 to 26.07 for 0.356, 0.662, 1.173 and 1.33 MeV, respectively.

Influence of PbO stoichiometry on the properties of PZT ceramics and multilayer actuators

AbstractLead‐oxide stoichiometry of lead‐zirconate‐titanate (PZT) ceramics and multilayer actuators is a critical issue for fabrication and performance. During sintering, the high vapor pressure and the corresponding volatility of lead oxide (PbO) require a careful design of sintering setup and parameters, as both may significantly impact on the PbO content in ceramics and devices. In order to investigate the effects of PbO stoichiometry, PZT compositions with different PbO contents have been synthesized and were sintered under varying temperature conditions and sintering setups. Structure and microstructure of the material was characterized using X‐ray diffraction and scanning electron microscopy (SEM). Dielectric properties and high field strain behavior were analyzed with respect to their relation to PbO content and grain size. Corresponding experiments with multilayer actuators were carried out, whereby the PbO content was varied by controlling the sintering atmosphere. The results indicate that there is a pronounced correlation between PbO content, structure and high field strain in both, PZT ceramics, and multilayer actuators.

Microstructure properties of lead silicate glasses

In the present work, lead silicate glasses have been prepared withdifferent amount of lead oxide content. Structure properties such asX-ray diffraction, AFM, and FTIR analyses have been done. Theexceeding of PbO content more than 25wt% revealed a decreasing indensity. The X- ray revealed that the strongest peak related toHexagonal silica dioxide and the other crystal phases formed wererelated to silica oxide (SiO2) and lead oxide (PbO). Growth anddecayed phases in X-ray have been observed with changing leadoxide content. Homogeneous surface was obtained using AFManalyzer with an average diameter around 100 nm. Infrared spectrumis characterized by the presence of large absorption band between1200 and 900cm-1 and have its maximum at 1080 cm-1 which istypical to stretching vibrations of Si–O–Si bonds, another bandsnoticed were attributed to Pb–O–Pb, Pb–O–Si, [AlO4]-tetrahedron,and to Si–O–Al bond.

Synthesis of praseodymium trioxide doped lead-boro-tellurite glasses and their optical and physical properties

This paper presents the influence of TeO2 on the optical and physical properties of rare earth ion Pr3+ doped 75PbO - (24-x) B2O3 - xTeO2 - 1Pr2O3 glass matrix. Using the absorption coefficient measurements, optical band gap energies of the studied glasses are estimated. Oxide ion polarizability, refractive index, optical basicity, reflection loss and transmission coefficient are discussed and reported for the investigated glasses. Physical parameters like the optical dielectric constant, polaron radius, interatomic separation, molar refraction and the metallization criterion are also studied through molar density and molar volume. The FTIR analysis reveals the shift of the band appearing at 1029 to 870 cm−1 because of the high concentration of PbO (75 mol% in the present glass) in the matrix. The Pb-O-B linkage is considered to be the important in the network structure of these glasses. For the present glasses metallization parameter values are <1. The polarizability values are high but decrease with increasing value of TeO2 concentration. This may be due to densification of restricted or localized states caused by the creation of dangling bonds.