PbCl2 Crystals Research Articles

Growth and characterization of a new inorganic metal-halide crystal structure, InPb2Cl5.

A new solid-state inorganic compound, indium dilead penta-chloride, InPb2Cl5, was synthesized by melting InCl and PbCl2 in a vacuum-sealed quartz ampoule. The ampoule was heated to 793 K and then slowly cooled to room temperature to induce crystallization of InPb2Cl5. InPb2Cl5 crystallizes in the monoclinic crystal system adopting a space group of type P21/c, which is isostructural with other metal halides such as RbPb2Cl5, KPb2Cl5 and TlPb2Cl5. The bulk InPb2Cl5 exhibits a metallic black/grey colour, allowing it to be separated from white/yellow PbCl2 crystals. Due to the incongruent nature of the compound, the pure bulk InPb2Cl5 was not obtained. The black/grey InPb2Cl5 crystals were characterized by powder and single-crystal X-ray diffraction. InPbCl3 was also explored, however the growth was unsuccessful.

Hydrometallurgical recovery of critical metals from an incinerated fly ash of municipal solid waste from western India

ABSTRACT The global generation of 2.2 billion tons of municipal solid waste (MSW) as a result of population growth, rapid urbanization, and industrial development has highlighted an urgent need for MSW management. Incineration is widely accepted as one alternative to landfilling; however, the recovery of heavy metals from the incinerated fly ash (IFA) before its final disposal is highly desirable to make the process sustainable. In this study, we studied the recovery of zinc and lead from typical MSW-IFA employing hydrometallurgical techniques. Sulfuric acid leaching was performed to selectively leach out zinc over the lead at the optimal condition of H2SO4 concentration = 1.5 M, temperature = 30°C, S/L ratio = 150 g/L, time = 2 h, and stirring speed = 300 rpm. The sulfate leach liquor was treated with a 5% stoichiometric excess of oxalic acid to precipitate>99% of zinc to be recovered as ZnC2O4·2 H2O. Further, the remaining lead in leach residue was subsequently leached in 50 g/L NaCl solution for 2 h yielded>94% efficiency. The dissolved lead was crystallized to recover the crystals of PbCl2. The demonstrated process leads towards the recovery of critical metals from an alternative source of MSW-IFA.

Facile generation of rod‐like PbCl2 crystals from Pb(II) aqueous solutions induced by Aliquat 336 at room temperature

AbstractBACKGROUNDLead is one of the frequent contaminants of industrial wastewater. This work presents a novel approach for the removal of lead from aqueous solutions through generation of rod‐like PbCl2 crystals induced by Aliquat 336 at room temperature.RESULTSRegular rod‐like PbCl2 crystals formation was rapid and the reaction could be described by a second‐order kinetic model very well. PbCl2 crystals were obtained when Pb(II) concentration was more than 15 g L‐1, but the maximum PbCl2 production was achieved at 60 g L‐1 for the solution/Aliquat ratio of 5. Increase of Aliquat 336 volume could increase PbCl2 production, but an optimal volume existed for different Pb(II) solutions. The formation of rod‐like PbCl2 was strongly dependent on pH, but the yield of crystals was uncorrelated with pH. The presence of ethanol led to high yields of PbCl2, but the crystal size became smaller.CONCLUSIONSThe results indicate that PbCl2 crystals form at the interface of the organic and aqueous phases, and the reaction rate is proportional to the Pb(II) in aqueous phase and Cl‐ in Aliquat 336. H+ promotes the orientated PbCl2 growth with a rod‐like shape. The high yield of PbCl2 crystals with ethanol is due to the increases of interface area. Aliquat 336 can be used as an effective PbCl2 crystals inducer for the removal of lead from wastewaters. © 2017 Society of Chemical Industry

Electron and hole trapping in irradiated PbBr2:Tl single crystals

Several hole trapped centres, namely Tl2+, self-trapped hole and A-type centres, were observed by ESR in PbBr2:Tl single crystals after X-ray irradiation at 77K. The corresponding spectra are visible up to 200K for all three defect centres. The STH centres are observed at higher temperatures than in the undoped PbBr2 single crystals, probably due to the stabilising effect of the Tl+ impurities. The ESR parameters of the Tl2+ centre point to stronger covalency effects in PbBr2 than in the isostructural PbCl2 crystals. All hole trapped centres started decaying around 160K, probably due to recombination with nonparamagnetic electron trapped centres. Besides a small concentration of self-trapped electron centres, no other electron trapped centres were observed.

Synthesis and spectroscopic properties of neodymium doped lead chloride

The crystal growth and infrared spectroscopic properties of Nd doped lead chloride (Nd:PbCl2) are reported. Lead halide based materials have recently emerged as laser hosts with low maximum phonon energies. In this work, Nd:PbCl2 crystals were grown by a self-seeded Bridgman technique. Following optical pumping at 750 and 808nm, Nd:PbCl2 exhibited several infrared (IR) emission lines between 800 and 1600nm as well as a broad mid-IR band centered at ∼5.19μm. It was found that for Nd3+ concentrations larger than ∼1×1019cm−3, the mid-IR emission is predominantly due to the transition I11∕24→I9∕24. From a Judd-Ofelt analysis, the radiative quantum efficiency of the 5.19μm emission was determined to be ∼27%. The multiphonon decay rates of several closely spaced Nd3+ transitions were modeled using the well known energy-gap law and the host dependent parameters B and β were determined to be 9.5×109s−1 and 1.26×10−2cm, respectively. The obtained energy-gap law parameters were subsequently used to describe the temperature dependence of the 5.19μm mid-IR emission lifetime for a range from 77to450K.

Thermal behavior of holes in lead-chloride crystal

Temperature dependence of emission spectra in PbCl2 has been measured under steady optical excitation in the region above the band gap energy. Emission spectra below 85 K are made up of a broad band (BG band) locating at 2.60 eV, which is attributed to luminescence due to electron—hole recombination between the (Pb2)3+ self-trapped electron (STEL) center and some hole trapping center. With raising temperature, two emission bands with their peaks at 2.79 and 2.08 eV appear newly, growing in intensity at the expense of the BG emission band. The two emission bands are not produced by optical or thermal stimulation in PbCl2 crystals irradiated with UV-light. This results suggests that most of holes are not trapped individuaily at high temperatures. The change from the BG emission band to the two emission bands will be explained in terms of the change in the electronic state of holes.

Electronic structure of lead (II) fluoride and lead (II) chloride crystals

The method of complete neglect of differential overlap was used to calculate the electronic structure of α PbF2, β PbF2, and PbCl2 crystals which form the basic matrices for the synthesis of new superionic conductors. It was shown that the electronic subsystem is fairly stable on transition from the high-symmetry β PbF2 crystal to the low-symmetry α PbF2. The electronic structure of the cotunnite crystal PbCl2 was calculated for the first time.

Acid Leaching of Indium-Lead-Tin Alloy Wire Scrap.

Acid leaching of indium-lead-tin alloy wire scrap has been studied. Anexperimental study was excuted to produce leaching liquor for subsequent separationof the concerned metals from the scrap material. Two leaching solutions were investigatedhydrochloric acid and hydrochloric-nitric acid oxidationleaching. Parameters affecting leaching processes such as time, temperature, acid concentration and acid: scrap stoichiometric ratio havebeen evaluated. Results obtained revealed that hydrochloric acid failed toextract metals completely, the maximum extraction efficiency was in the orderof indium 97.1, lead 94.1 and tin 89.2% by using 5M HCl for 6 hours at 95°C, HCl: scrap ratio was 5. Addition of nitric acid as oxidizing agent resulted incomplete extraction for metals, the optimum leaching conditions were conductedby addition of 0.6ml of 1:1HNO3/g scrap to the leachate of 5M HClfor 1.45 hours at 80°C with HCl: scrap ratio of 2.5. Another advantage forusing of HCl-HNO3 leaching was that about 71% of the lead content was separatedas pure crystals of PbCl2 on cooling the resulting solution.

Electron self-trapping and photolysis in Pbcl2crystals

Abstract Strongly anisotropic paramagnetic centers produced by X-ray or UV-irradiation of PbCl2 crystals at T = 80 K have been attributed to Pb3+ 2 self-trapped electron (STEL) centers. The self-trapping of free (conduction) electrons at pure cation sites is further supported by production experiments using selective optical excitation in the fundamental absorption band. Optical bleaching experiments suggest the STEL center to be the primary defect responsible for the photolysis in PbCl2, with the g ≈ 2 centers representing hole-trapped centers. P.A.C.S. numbers: 61.72.Ji; 63.20.Kr; 76.30.Mi; 78.50.Ec; 61.80.Ba, Cb.

Consistent Analysis of the Tl and Pb Center ESR Parameters

AbstractThe electron spin resonance parameters of the Tl and Pb dimer centers produced by electron trapping at pairs of neighboring Tl+ or Pb2+ impurity ions in alkali chlorides are reanalyzed. The analysis which uses a consistent set of molecular parameters is based on the molecular modcl previously employed to describe the ESR properties of the homonuclear Vk self‐trapped hole center, which has a complcrnentary electronic configuration. In a rough approximation the analysis is extended to the self‐trapped electron (STEL) center in PbCl2 crystals, which is a bent Pb molecular ion in a low symmetry crystal field.

Growth and Characterisation of Gel‐grown Lead(II)Chloride and Lead(II)Bromide Single Crystals

AbstractSingle crystals of pure and doped lead(II)chloride and lead(II)bromide were grown by gel technique employing a modified two‐stage chemical reaction. Methods to minimise the predomination of needle morphology during the growth of these crystals have been investigated and the results are discussed. The grown crystals were characterised by optical transmission spectrum. Undoped and monovalent cation (K+, Na+, Cu+, Ag+ and Hg+) doped crystals of PbCl2 and PbBr2 were subjected to d.c. electrical conductivity studies. Using the log σT versus T−1 plot, the activation energies for the migration of anion vacancies in lead(II)halides are calculated. They are found to be less for the doped crystals than those of undoped ones.

Electron Spin Resonance Study of Centers Formed in γ-Irradiated PbCl2 Crystals

An analisis is presented by utilizing the electron spin resonance spectra of new defects which are produced in PbCl2 single crystals irradiated at liquid nitrogen temperatures with γ-rays from a 60Co source. One of the g tensor axes of the defects corresponds to the crystallographic c-axis, and the other two make an angle of about 12° with the a- and b-axes. The components of the g-factor are gx=1.494±0.005, gy=1.322±0.005 and gz=1.662±0.005. The principal axes of the hyperfine coupling tensor A are collinear with neither the g tensor axes nor the crystallographic axes. The resolved hyperfine structure indicates that these defects fit a model of the paramagnetic centers consisting essentially of an electron trapped at paired lead ions, that is, the Pb23+ centers.

Hartman–Perdok theory: influence of crystal structure and crystalline interface on crystal growth

Hartman–Perdok theory enables classification of crystal faces as F, S or K faces. Only F faces should be present on growth forms as they grow slowly according to a layer mechanism. Such a classification can be quantified for ionic crystals by the calculation of attachment energies in electrostatic point-charge models. The attachment energy of a crystal face (hkl)Ehkla, is the energy released per mole, when a new elementary growth layer, called a slice, with a thickness of dhkl crystallizes on an existing crystal face. Theoretical growth forms can be constructed by making use of the supposition that Ehkla is directly proportional to the growth rate. Often these growth forms are very similar to the morphologies of crystals grown in nature or in laboratory experiments {zircon (ZrSiO4), alkali feldspars ((K,Na)AlSi3O8), natural silicate garnets [A2+3 B3+2(SiO4)3]}. The structure of the crystalline interface is very important for the crystal growth processes. The derivation of F faces provides the atomic topology of the crystalline interface as well. Sometimes there is more than one possible surface of a slice with a thickness of dhkl, e.g. zircon (011), garnets (110) and (112), which may lead to growth via slices of thickness ½dhkl, causing a significant increase of the growth rate. Ordering of the ions which are situated on the slice boundaries may reduce the growth rate (alkali feldspars and YBa2Cu3O7 –x). Experimental crystal growth of PbCl2 shows that adsorption of OH– and H3O+ ions on special sites of the crystalline interfaces may cause habit modifications. This effect can be explained for PbCl2 in terms of adsorption of Pb(OH)Cl on {211}. The influence of the solvent on the growth can also be explained in terms of impurity adsorption on the crystalline interface. The growth of flattened PbCl2 crystals from HCl due to the reduction of the growth rates of {010} and {121} is such an example.

Identification by ESR of Pb+-type centres in lead-doped SrCl2

Several Pb+-type centres are produced in SrCl2:PbCl2 crystals by X-ray irradiation at 80 K and subsequent thermal and optical treatments. From the analysis of the electron-spin-resonance (ESR) and production properties, the dominant spectrum, with trigonal symmetry around (111), is attributed to a Pb+ ion located on a cation site with an anion vacancy in a nearest-neighbour position: the so-called Pb+ (1) centre with the laser-active-type structure. Specific thermal treatments lead to two more Pb+ centres with the same symmetry. The analysis of their hyperfine interaction parameters shows that in both centres the Pb+ ion is subject to a strong odd crystal field too, but their defect structures could not be further elucidated. An additional spectrum with a small orthorhombic distortion is observed in a more heavily doped crystal and is attributed to a lead dimer centre consisting of a Pb+ (1) defect perturbed by a nearest-neighbour substitutional Pb2+ impurity.

Growth and microhardness studies of melt‐grown lead (II) chloride single crystals

AbstractIn the present work, lead (II) chloride material is purified by directional solidification and single crystals of PbCl2 are grown by vertical Bridgman technique employing double zone furnace. The growth conditions and the problems overcome are discussed. The grown crystals of pure and K+‐doped crystals are cleaved and subjected to microindentation tests. The validity of Kick's relation is checked, the value of K1 the standard hardness number and n the work‐hardening coefficient are discussed. The microhardness behaviour of pure and K+‐doped lead(II) chloride have been compared.

Allowed and Forbidden Transitions in ESR of Mn2+ in PbCl2 Crystals

Single crystals of PbCl2 doped with Mn2+ have been investigated by ESR at X band and room temperature. The Mn2+ ion is found to be replaced for the Pb2+ ion. The spectrum can be described by a spin Hamiltonian for an ion in an orthorhombic crystal field. The parameters are found to be gz=1.9996±0.0002, gy=2.0004±0.0002, gx=2.003±0.001, D=-495.9±0.1 G, E=-137.0±0.1 G, Az=-84.8±0.2 G, Ay=-85.2±0.2 G, Ax=-85.2±0.5 G, a∼0 G and F∼0 G. The hyperfine structure splitting depends on the angle θ between the static magnetic field H and the z axis. the linear relation between the hyperfine constant A and the ionicity of the lattice holds even in PbCl2. The experimental angular variation of intensities is in good agreement with the calculation by numerical diagonalization. The measured intensity is asymmetric about the nuclear quantum number m=0.

Decay Kinetics of UV Luminescence from Undoped PbCl2 Crystals

AbstractThe kinetics of the UV luminescence from PbCl2 crystals are measured from 3.8 to 25 K. Two components in UV luminescence are found. The form of the long time component of the UV luminescence decay curve is thoroughly investigated and compared with theoretical predictions. A model based upon exciton—exciton annihilation leading to free electron—hole pairs is used to describe the decay at temperatures above 15 K.

Polarized Luminescence of Lead Ions Associated with Interstitial Radiation Defects in KCl:PbCl2 Crsytals

AbstractTwo types of lead ion and interstitial chlorine atom associates (Hz(Pb2+) centres) are found and investigated by optical methods in X‐irradiated KCl:PbCl2 crystals. The polarized 3.35 and 1.8 eV emission of these centres and the absorption bands near 5.55 and 4.4 eV are caused by electronic transitions in the Pb2+ ion perturbed by Cl molecular ion, which occupies a cation vacancy and an anion site. The broad absorption band at 3.7 eV is due to the transitions in the Cl ion perturbed by Pb2+. Using the ESR data obtained by Schoemaker et al. it is concluded that the centres with 3.35 and 1.8 eV emission are interstitial chlorine atoms trapped by Pb2+ ions associated with the nearest neighbouring (Hz[110](Pb2+) centres) and with the next nearest neighbouring (Hz[100](Pb2+) centres) cation vacancies, respectively. Lead ion and Cl molecular ion associates (V2z(Pb2+) centres) are found. The polarized 3.05 eV emission and the 4.3 eV absorption band of these centres are caused by the electronic transitions in Pb2+ ions perturbed by Cl. The broad 5.27 eV absorption band is due to the electronic transitions in the Cl ions perturbed by Pb2+. It is assumed that the V2z(Pb2+) centre may be represented as a Cl molecular ion which occupies two anion and one cation sites and is associated with a Pb2+ ion located (according to Itoh et al.) at a face‐centred position as well as with an interstitial chlorine ion and cation vacancy.

Far infrared reflection spectra of lead (II) chloride and iodide

Far infrared reflection spectra of single crystals of PbCl2 and PbI2 have been measured using a Hitschi 070 for infrared interferometer. AIP

Determination of the distribution coefficient of Pb in NaCl crystals by estimation of the lead concentration from the optical absorption in aqueous solutions

AbstractIt is shown that the intensity of a UV absorption band of lead ions in aqueous solution of NaCl is linear dependent on the concentration of lead. This can be developed to a simple determination method of lead in NaCl crystals even in the ppm region. Its application on melt grown NaCl:PbCl2 crystals was used for a calculation of the distribution coefficient, for which was found k = 0.24. Furthermore it could be shown that an essential part of lead is evaporated from the melt before the growth process starts so that the real initial concentrations are drastically lower than the nominal concentrations of the melts.