KCl Crystals Research Articles

Mechanisms of radiation defect formation in KCl crystals under the influence of local and plastic deformation

This work proposes an original approach to the study of trihalide centers in a KCl matrix in the field of local and plastic deformation. Local lattice deformation is carried out by purposeful doping of the KCl crystal with light homologous cations, as well as bivalent impurities, which create dipole strontium complexes to maintain the electroneutrality of the lattice. Plastic deformation, which creates paired vacancy defects in the lattice, divacancies and vacancy quartets, is realized at room temperature within the degree of relative uniaxial deformation of 3–5%. After subsequent cooling down to 80 K the deformed crystal was additionally irradiated with X-rays. The absorption spectra of the crystals subjected to two types of deformation and additional isodose irradiation by X-rays were recorded in a special cryostat at 80 K. The spectral characteristics and formation efficiency of V-type centers, lithium- and strontium-containing centers in the field of pre-irradiation dipole complexes have been considered.

Porous Carbon Nanosheets Derived from ZIF‐8 Treated with KCl as Highly Efficient Electrocatalysts for the Oxygen Reduction Reaction

Developing advanced electrocatalysts for the oxygen reduction reaction (ORR) is a critical reaction in fuel cells. Metal–organic framework (MOF)‐derived nitrogen‐doped carbons have been widely reported as promising electrocatalysts for ORR. Herein, a KCl‐assisted pyrolysis method is reported to prepare N‐doped porous carbon nanosheets (NCNS). During pyrolysis preparation, KCl crystals act as templates and activator, penetrating the ZIF‐8‐derived carbon material via capillarity, which facilitates the formation of micro‐ and mesopores carbon nanosheets. By adjusting the KCl dosage and pyrolysis temperature, the carbon material structure, nitrogen species, and graphitization degree are effectively controlled. The optimal NCNS‐10‐900 catalyst exhibits a higher half‐wave potential (≈0.88 V) in alkaline solution, which is even better than Pt/C (≈0.86 V). The NCNS‐10‐900 also exhibits outstanding long‐term stability with an only 17 mV shift in half‐wave potential after a 10K cycle durability test. All of these high properties are ascribed to the high specific surface area, the abundant microporous and mesoporous nanosheet structure, and the synergistic effects of the N species with intrinsic activity. This strategy of using a KCl‐assisted pyrolysis MOF provides a feasible method to explore highly efficient and robust non‐noble metal catalysts for energy‐conversion reactions.

SUITABILITY OF BI-VACANCY TRAP FOR TL EMISSION IN KCl

In KCl crystals, the 2s energy level of F-center within an anion-cation vacancy pair has been proposed as a suitable trap for thermoluminescence (TL) emission. It is further seen that the 2s – level of F-center situated in cation – anion vacancy pair has large trap depth. The observed trap depth of F-center is explainable on the basis of Herman and Barnett model, modified presently and supports bi-vacancy configuration for traps in KCl lattice.

Statistical Theory of Two-Component Crystal I-Case of One Dimensional Crystal

The Unsymmetrized Self-Consistent Field Method (USCFM) has applied to a linear infinite chain consisting of two different particles. Expanding the self-consistent potential in power series of the lattice displacement, and taking the anharmonicity up to the fifth order, we show that all thermodynamic properties can be found in terms of two universal functions M1(α)M1(β), which can be implicitly expressed in terms of parabolic cylinder functions. We have applied this approach to study one dimensional system of KCl crystal using Born-Mayer-Huggins pair potential, and have determined some thermoelastic properties of this system.

General and Efficient Synthesis of Two-Dimensional Monolayer Mesoporous Materials with Diverse Framework Compositions.

Two-dimensional (2D) mesoporous materials have received substantial research interest due to their highly exposed active sites and unusual nanoconfinement effect. However, controllable and efficient synthesis of 2D mesoporous materials and investigation of their intrinsic properties have remained quite rare. Herein, a general and effective surface-limited cooperative assembly (SLCA) method enabled by leveling precursor solutions on KCl crystals via centrifugation is employed to conveniently synthesize two-dimensional (2D) monolayer mesoporous materials with different compositions. This novel strategy is performed in a manner similar to spin coating, not only enabling generation of ultrathin mesostructured composite film on KCl particles and recycling excessive precursor solution but also providing favorable solvent annealing environment for the film to form ordered mesostructures. Taking monolayer mesoporous Ce0.8Zr0.2O2 solid solutions as a sample, they display ultrathin nanosheet morphology with a thickness of ∼20 nm, highly open porous structure, and easily accessible active sites of surface superoxide species. Upon decoration of 2D mesoporous Ce0.8Zr0.2O2 nanosheets with Pt nanoparticles, the obtained catalyst exhibits superior catalytic activity and stability toward CO oxidation with a low onset temperature of 30 °C and a 100% conversion temperature of 95 °C, which are 35-70 °C lower than those for their counterpart materials, namely, three-dimensional (3D) mesoporous Pt/Ce0.8Zr0.2O2. Moreover, their TOFPt value is ∼11.3 times higher than that of 3D mesoporous Pt/Ce0.8Zr0.2O2. Characterizations based on various techniques indicate that such an outstanding catalytic performance is due to the ultrashort distance (20 nm) of mass diffusion, highly exposed active sites, rich surface-chemisorbed oxygen, and the synergistic effect between the Ce0.8Zr0.2O2 matrix and Pt species.

Luminescent and Mechanical Properties of Cerium Doped Potassium Chloride Single Crystal

AbstractLarge size cerium (Ce3+)‐doped potassium chloride single crystal is grown by the resistance heating Czochralski method and characterized structurally, mechanically, and optically by carrying out X‐ray diffraction (XRD), micro‐hardness, photoluminescence (PL), PL excitation (PLE), thermo‐luminescence (TL), and decay time measurements. XRD measurements reveal the incorporation of Ce atoms into the KCl host lattice. Microhardness measurements indicate an improvement in the hardness due to Ce3+‐doping and a decrease of hardness with increasing temperature. Two intense PL emission peaks are observed at wavelengths 343 and 367 nm, attributed, respectively, to the 5d→2F5/2 and 5d→2F7/2 transitions of Ce3+. Energy level scheme for the Ce3+ ion in the KCl crystal is proposed through PL and PLE analyses. The observed TL glow curve of KCl:Ce3+ shows a sharp peak located at about 244 °C. XRD, PL, and TL studies confirm the trivalent state of Ce3+ ion in the KCl host lattice. The luminescence decay time of KCl:Ce3+ crystal is found to be 35.14 ± 0.17 ns. The present study indicates that the KCl:Ce3+ crystal grown exhibiting suitable PL and TL emissions is expected to be a potential material for radiation dosimetry and scintillation applications.

Cu-Doped KCl Unfolded Band Structure and Optical Properties Studied by DFT Calculations.

The unfolded band structure and optical properties of Cu-doped KCl crystals were computed by first principles within the framework of density functional theory, implemented in the ABINIT software program, utilizing pseudopotential approximation and a plane-wave basis set. From a theoretical point of view, Cu substitution into pristine KCl crystals requires calculation by the supercell (SC) method. This procedure shrinks the Brillouin zone, resulting in a folded band structure that is difficult to interpret. To solve this problem and gain insight into the effect of copper ions (Cu+) on electronic properties, the band structure of SC KCl:Cu was unfolded to make a direct comparison with the band structure of the primitive cell (PC) of pristine KCl. To understand the effect of Cu substitution on optical absorption, we calculated the imaginary part of the dielectric function of KCl:Cu through a sum-over-states formalism and broke it down into different band contributions by partially making an iterated cumulative sum (ICS) of selected valence and conduction bands. Consequently, we identified those interband transitions that give rise to the absorption peaks due to the Cu+ ion. These transitions involve valence and conduction bands formed by the Cu-3d and Cu-4s electronic states.

Positron Annihilation Spectroscopy of KCl (Zn) crystals

Four samples of nominally pure KCl crystals and doped with Zn2+ impurities are grown by the Czochralski method and characterized by X-ray diffraction and Proton Induced X-ray Emission techniques. Positron Annihilation Lifetime Spectroscopy (PALS) is performed to obtain information on the cation vacancy type defects and their evolution under doping. The results of the PALS experiment indicate that doping KCl by Zn2+ ions, at first increases the concentration of mono vacancies and in the second stage leads the creation of divacancy sites. Coincidence Doppler Broadening Spectroscopy (CDBS) is carried out to obtain the chemical environment of positron annihilation sites. The results of CDBS show that cation vacancies have a significant role in the annihilation process. An interesting observation is the participation of Zn2+ cations in the positron annihilation process which confirms that positrons are not completely localized on the anion sites. The internal consistency between the results of PALS and CDBS experiments is also clarified.

Temperature and pH-Dependent Response of Poly(Acrylic Acid) and Poly(Acrylic Acid-co-Methyl Acrylate) in Highly Concentrated Potassium Chloride Aqueous Solutions.

In this study, the phase transition phenomena of linear poly(acrylic acid) (PAA) and linear or star-shaped poly(acrylic acid-co-methyl acrylate) (P(AA-co-MA)) in highly concentrated KCl solutions were investigated. The effects of polymer molecular weight, topology, and composition on their phase transition behavior in solution were investigated. The cloud point temperature (TCP) of polymers drastically increased as the KCl concentration (CKCl) and solution pH increased. CKCl strongly influenced the temperature range at which the phase transition of PAA occurred: CKCl of 1.0–2.2 M allowed the phase transition to occur between 30 and 75 °C. Unfortunately, at CKCl above 2.6 M, the TCP of PAA was too high to theoretically trigger the crystallization of KCl. The addition of hydrophobic methyl acrylate moieties decreased the TCP into a temperature region where KCl crystallization could occur. Additionally, the hydrodynamic diameters (Dh) and zeta potentials of commercial PAA samples were examined at room temperature and at their TCP using dynamic light scattering. The salt concentration (from 1 to 3 M) did not impact the hydrodynamic diameter of the molecules. Dh values were 1500 and 15 nm at room temperature and at TCP, respectively.

Influence of aliovalent impurity doping and effect of sensitized luminescence in KCl single crystals for dosimetry applications

Sensitized luminescence properties of various alkali halide single crystals of dosimetric importance doped with aliovalent impurities are studied. Single crystals of KCl co-doped with (Ce,Mn), (Ce,Mg) (Ce,Tb) and (Eu,Tb) are grown using the Czochralski technique. The XRD of grown crystals showed good crystalline nature with face-centred cubic KCl structure. Thermally stimulated luminescence (TSL) and optically stimulated luminescence (OSL) characteristics of grown crystals are investigated after subjecting to gamma dose. TSL response of KCl:Eu,Tb and KCl:Ce,Tb showed an enhancement of 6.5 times and 3.5 times, respectively, compared to singly doped KCl:Tb. Co-doping of the divalent activators such as Mn and Mg did not result in enhanced TSL response with rare earth sensitizers. Notwithstanding the low TSL response, KCl:Ce,Mn showed very high OSL response, six times than that of single-doped KCl:Tb and 3.5 times than that of KCl:Ce,Tb and KCl:Eu,Tb. However, KCl:Ce,Mg did not exhibit noticeable OSL intensity enhancement compared to single doping. The high TSL and OSL response is apparently the conclusive evidence of the energy transfer mechanism between dopants, which is confirmed by photoluminescence studies. The dose–response curve of KCl:Ce,Mn that exhibited very high OSL response showed linearity up to 100 Gy, which indicated the material is a good candidate for dosimetric applications. The growth and characterisation of aliovalent impurity-doped KCl single crystals and mechanism of resonance energy transfer between the dopants are discussed in this paper.

Strategies to control product characteristics in simultaneous crystallization of NaCl and KCl from aqueous solution: seeding with NaCl and KCl

In this work we developed an approach for the simultaneous crystallization of NaCl and KCl from their aqueous solution by concomitantly seeding both salts. Results highlight the possibility of retrieving relatively pure solid fractions of each salt.

Mechanisms of micro-voids formation caused by optical breakdown in KCl single crystals

The phenomenon of optical breakdown has been studied experimentally for KCl single crystals exposed to laser emission focused on the neodymium glass with modulated quality-factor, pulse duration 5·10-8 s, wavelength λ= 1054 nm, and pulse energy of the order 1 J in the regime of local intrinsic absorption of the laser emission by the single crystal. Evaluations of local heat flash energetic constituents and characteristic durations for both local area heating and relaxation processes and following comparison with experimental results have shown that the relaxation process takes place in two stages: the first is fast phasefollowed by crowdion mass transfer with shock wave participation, and the second is slow phase with participation also dislocation mass transfer. The energy losses for heat radiation and thermal conductivity are found to be by orders of value less than the absorption energy flux Iabs that provides fast local heating and plasma formation. From the viewpoint of the mechanics of continua the process under study where the pressure achieves value exceeding the theoretical strength limit for the time less 10-6 s, should be considered as explosion-like or shock process. The general scheme of plastic deformation arising from abovementioned estimations and observations is seemed as follows. In the beginning, under action of the shock wave the crowdions are generated which carry the substance from the high pressure area and move along close-packed atomic rows (<110> type directions in KCl crystals); the void is formed almost completely during the shock wave passing the relaxation zone crosssection. This time is of the order of τrel, i. e. 10-9…10-8 s. After falling temperature and pressure and vapor condensation into liquid, at the end of relaxation process, the void boundaries expand already under liquid melt pressure, and the mass transfer dislocation mechanism comes into action providing additionally some enlarging the void volume. This process continues also after stopping the laser emission, during the crystal cooling down to the melt crystallization in the void and formation of a pore with size observed.

A Novel Route for a Fluorescent Temperature Sensor Based on the Reabsorption Process in Sm2+‐Doped KCl

Fluorescent temperature sensors have attracted attention in recent years, due to their potential for use in situations where conventional temperature sensors are unsuitable. There are a lack of appropriate sensors at the microscale for industrial, laboratory, and medical applications. Sm2+:KCl crystals possess luminescence properties that enable them to be used as sensors in a new approach for local temperature measurements, by determining the blueshift or the ratio between the intensities from the allowed 4f–5d transitions. A broad emission band centered at 750 nm at 300 K, with high quantum yield (1.00 ± 0.05), is observed when exciting these crystals in the ultraviolet (UV)–vis range. This emission lies within the optical response range of commercial Si‐based photodetectors, which are readily available at relatively low costs. Furthermore, the crystals can be excited using red light‐emitting diodes (LEDs) or a solid‐state laser at 600–650 nm, which are used to produce fluorescent thermometers with a relative sensitivity of 0.24% K−1 (A1/A2 ratio) at 299 K and 1.43 cm−1 K−1 (blueshift).

Fabrication of low-dimensional microstructures with distyrylbenzene derivatives

Microneedle crystals of 1,4-bis-(4-methylstyryl)benzene (DSB-4Me) and amorphous microdots of bis (N,N-di-p-tolylamino-p-styryl)benzene (DADSB) are fabricated by using mask-shadowing and conventional vapor deposition techniques. By interaction between π-conjugated electronic chains and ionic lattice of a KCl crystal substrate, DSB-4Me molecules grow into needle crystals epitaxially orienting in four directions making ±60° against [110]KCl and [−110]KCl. As for DADSB, self-assembly into microdots by heating the KCl substrate at 180 °C during deposition is attributed to the impact of bulky peripheral groups in DADSB and surface migration of the deposited molecules. Moreover, while amplified spontaneous emission is observed above an excitation threshold of 362 μJ cm−2 in the DSB-4Me microneedle crystals, a lower threshold whispering-gallery mode lasing is observed above 37 μJ cm−2 for DADSB microdots owing to the higher waveguide quality.

ZnO-doped KCl single crystal with enhanced UV emission lines

The embedded bulk KCl single crystal with the ZnO nanocrystal was grown using Czochralski technique. Various structural and optical analyses were employed to characterize the grown sample. X-ray diffraction confirmed the diffusion of ZnO NCs in the KCl bulk lattice. The crystal structure and the lattice parameters were estimated for both ZnO NCs and KCl matrix by Rietveld analysis. The bond formation of KCl:ZnO was demonstrated by Fourier transform infrared (FTIR) spectroscopy. FE-SEM was carried out for the morphological study of ZnO NCs and estimation of particle size distributions. Energy-dispersive X-ray (EDX) analysis was used to investigate the elemental composition of the prepared sample. The experimental results confirmed the improvement in optical properties of KCl single crystal was found when it was doped by ZnO. The second derivative of absorption spectrum confirmed the band gap of 6.06 eV for KCl single crystal. In PL spectrum, several intense UV light emission peaks at 297 and 360 nm were observed in which the emission peaks of KCl:ZnO samples were very sharp in comparison with the pure KCl single crystal. It seems that the UV peaks at 297 and 360 nm emission lines of ZnO-doped KCl crystals originated from electron capturing from F center.

Optical properties of the Eu2+-ion immersed as a doping impurity into a KCl:KBr:RbBr solid solution: Influence of the different aggregation-precipitation states of the doping ions

The optical properties of the Eu2+-ion immersed as a doping impurity in mixed KCl–KBr–RbBr crystals were investigated together with the changes that these properties suffer by thermal quenching at liquid-N2 temperature and, also, during thermal annealing at 523 K. The crystal matrix, as characterised by X-ray diffraction, consists of a strongly-textured F-type cubic ternary KCl:KBr:RbBr solid solution (a0 = 6.59 ± 0.02 Å). The absorption spectrum of freshly-quenched samples shows two broad absorption bands peaking at about 328 and 247 nm (10Dq = 9998 ± 143 cm−1) whereas the fluorescence spectrum of these samples shows a single nearly-symmetric emission band peaking at about 420 nm. These spectra, being similar in general to the corresponding ones of freshly-quenched single crystals of KCl:Eu2+, KBr:Eu2+ and RbBr:Eu2+, change during the annealing treatment so that, for well-annealed samples, the absorption bands peak at 277 and 333 nm (10Dq = 6689 ± 91 cm−1) whereas the fluorescence spectrum consists of four emission bands peaking at about 420, 427, 449 and 480 nm. These changes, indicating that the doping ion environment evolves during annealing, are discussed to be due to the occurrence of different precipitation states of the doping ions. The structural nature of these states, and, also, an aggregation-precipitation kinetics, is proposed.

Influence of KCl and HCl on a laser clad FeCrAl alloy: In-Situ SEM and controlled environment High temperature corrosion

This study investigated the effects of HCl and KCl on a laser-clad FeCrAl coating at 450 °C in an in-situ ESEM followed by a furnace exposure. In all in-situ TEM cross-sections, three major phases were identified: an iron rich oxide, an iron-chromium mixed oxide and an aluminium enriched layer. HCl allowed chlorine based corrosion to occur which suggests interaction from its gas phase. EDX of the regions around KCl crystals showed a decrease in chromium which is an indication of chlorine selectively removing chromium. Moreover, the mass gain in HCl with KCl was significantly lower than that observed in air with KCl.

Formation of Sodium and Potassium Nanoparticles upon Local Electron Bombardment of Alkali-Halide Crystals

It has been shown experimentally that upon local bombardment of NaCl, KCl, and KBr crystals with 50-keV electrons, sodium and potassium nanoparticles with plasmon resonances in the visible spectral region are formed in these crystals. We have obtained optical-density spectra of crystals after the bombardment with electrons in various doses. The probability of location of nanoparticles in the solid or liquid phase, as well as interference effects emerging in the irradiated zone of crystals, have been studied using numerical simulation.

Selective adsorption of octadecylamine hydrochloride on the surface of KCl crystal: adsorption energy based on density functional theory

Flotation has become a significant technique for the KCl separation from NaCl-containing complex systems, but the true nature of adsorption selectivity of collector on the crystal surface of KCl is still unclear. In this study, using density functional theory calculations, we investigated the adsorption behaviors of a commonly used collector, octadecylamine hydrochloride (ODA), on the crystal surfaces of KCl and NaCl, respectively. The results demonstrate that the structure of built crystals for calculation is validity and the crystal surfaces containing two-layer atoms are most stable. All adsorption energies of ODA+ cation and H2O molecule on the crystal surfaces of KCl and NaCl are negative with the decreased absolute value according to the sequence of KCl-ODA+ >NaCl-H2O > KCl-H2O > NaCl-ODA+, suggesting that the interaction between ODA and KCl is stronger than that in the other considered systems. The differences of interaction energies demonstrate the adsorption selectivity of ODA on KCl, resulting in the selectively flotation. Therefore, we construct accurate models to simulate the actual crystal surface structures of KCl and NaCl, and we provide adsorption energies as complementary evidences to interpret the floatability of KCl from the NaCl mixture, which can help to design new collectors for the flotation of soluble salts.

Properties of the model for radiation induced optically stimulated luminescence (OSL) in sodium and potassium chlorides

The complex kinetics of optically stimulated luminescence (OSL) in certain salts is associated with the effect of regeneration (RE). Until now, the RE effect was found in sodium and potassium chlorides (NaCl, KCl). The model of OSL kinetics explaining regeneration and fading was previously proposed in pure NaCl. However, it can be referred also to other materials. Verification of the model was performed based on the experimental results obtained for halite (rock salt mineral) and pure KCl crystals. Determination of the characteristic lifetimes of regeneration and fading was performed by adjusting the model solutions for a special case (without stimulation) to the data obtained from the VD-OSL method. In the case when stimulation is on during OSL readout, differential equations describing the model have no analytical solution. Therefore in order to model OSL decays the numerical simulations for various parameters were carried out. The obtained theoretical OSL decays are compatible with the measurement data.