KCl Crystals Research Articles

Theoretical studies of the spin Hamiltonian parameters and local structures for Ag2+ in AgCl and KCl crystals

The spin Hamiltonian parameters (g factors, hyperfine structure constants and superhyperfine parameters) and local structures for Ag2+ centers in AgCl and KCl crystals are theoretically studied using the high-order perturbation formulas for a tetragonally elongated 4d 9 cluster. The impurity centers undergo relative elongations (≈0.05 A and 0.23 A for Ag2+ in AgCl and KCl, respectively) along the C 4 axis owing to the Jahn–Teller effect. All the calculated spin Hamiltonian parameters show good agreement with the experimental data, and the ligand contributions to the spin Hamiltonian parameters are important and should be taken into account. The unpaired spin densities in the superhyperfine parameters are determined from molecular orbital coefficients based on the cluster approach, instead of being taken as the adjustable parameters in the previous treatments. Increasing tetragonal elongation from AgCl to KCl is attributed to a decrease in chemical bonding (or lower force constant) with increasing Ag2+–Cl distance.

The deformation stimulated luminescence in KCl, KBr and KI crystals

Currently, strengthening of the intensity of luminescence in alkali halide crystals (AHC) at lattice symmetry lowering is discussed as a promising direction for the development of scintillation detectors [1-3]. In this regard, for the study of anion excitons and radiation defects in the AHC anion sublattice at deformation, the crystals with the same sizes of cations and different sizes of anions were chosen. In the X-ray spectra of KCl at 10 K, the luminescence at 3.88 eV; 3.05 eV and 2.3 eV is clearly visible. The luminescence at 3.05 eV corresponds to the tunneling recharge [F*, H]. Luminescence at 3.88 eV is quenched in the region of thermal destruction of F′-centers and characterizes tunneling recharge of F′, VK-centers. In KCl at 90 K, the luminescence of self-trapped excitons (STE) is completely absent. In KBr at deformation not only STE luminescence, but also deformation stimulated luminescence at 3.58 eV were recorded, the last one corresponds to tunneling recharge of F′, VK-centers. In KI crystal at 10 K and 90 K at deformation, only STE luminescence is enhanced. There are no deformation luminescence bands in KI compares with KBr and KCl crystals.

The thermostimulated luminescence of radiation defects in KCl, KBr and KI crystals at elastic and plastic deformation

The efficiency of radiation defects formation in alkali halide crystals (AHC) was studied by the method of absorption spectroscopy. However, it is not possible to study the deformation-stimulated processes in detail by the absorption spectrum of radiation defects due to the limited sensitivity compared with luminescent spectroscopy. In this regard, thermally stimulated luminescence (TSL) of radiation defects at elastic and plastic deformation was applied in AHC. In the absence of deformation, the dominant peaks in TSL are -centers. After elastic deformation, low temperature peaks of TSL corresponding to F′-, VK- and VF-centers became dominant. After plastic deformation, the peaks of TSL corresponding to -centers became dominant. The elastic deformation contributes to the increase in concentration of low-temperature F′-, VK- and VF-centers, and the plastic one contributes to that of high temperature -centers (peaks of TSL in KCl at 360K, in KBr at 365K, in KI at 340K), composed by divacancies created by plastic deformation. At elastic deformation, unrelaxed interstitial halogen atoms are converted into VK- and VF-centers, and due to this fact the long-range interaction is absent, the result of which are the -centers.

ВЗАЄМОПЕРЕТВОРЕННЯ ЕЛЕКТРОННИХ ЦЕНТРІВ У ДОМІШКОВИХ ЛУЖНОГАЛОЇДНИХ КРИСТАЛАХ

Urgency of the research. Nowadays, information storage is a very important task. Thus, a new way of recording large amounts of information, when using the minimum storage size will be relevant.Target setting. Investigate the possibility of recording information in KCl + LiCl crystals, as well as a mechanism that allows doing this.Actual scientific researches and issues analysis. In the work of N.N. Baran. et al. "Dual electron-nuclear resonance of A-centers in mixed crystals of KCl + LiCl" by the DENR method confirmed the model of the FA-center, but the kinetics of the interconversion of has not been studied sufficiently.Uninvestigated parts of general matters defining. Theoretically, the mechanism of recording information when converting electronic centers by using the tunnel effect is understandable, but in reality it has not yet been realized.The research objective. Experimentally and theoretically investigate the kinetics of mutual conversion of electron centers F⇄FA in KCl crystals with an admixture of Li+ ions. In the process of research, it is necessary to show the mechanism of transformation F centers to FA-centers, as well as its practical use for recording information.The statement of basic materials. Experimental and theoretical research of the phototransformation kinetics of F⇄FA in KCl + 1 mol. % LiCl crystals in a charge are carried out. It is shown that the mechanism of transformation of F-centers to FA-centers consist in the fact that when the crystals are lighted, the F-centers go over into an excited state and give electrons to the conduction band as a result of electron-phonon interaction. During the lifetime of electrons in the conduction band, free haloid vacancies are stabilized by impurity ions because of diffusion. Then, the stabilized haloid vacancies are transformed to FA-centers by attaching electrons. It is shown that the filling of nearby haloid vacancies by tunneling of electrons of excited F-centers in the X-rays irradiated (γ-rays) crystals occurs only partially. It is proposed to use the tunnel effect to record information with a focused beam from a quantum light generator. The recorded information can be erased by a defocused light beam.Conclusions. Proposed mechanism to convert the F-centers in FA-centers in ionic crystals KCl mixed with cations Li+, and the kinetics of this transformation. This mechanism is proposed to be used for recording information.

Effect of variation in concentration of water and plant part used on physicochemical properties of Yavakṣāra

Introduction: Kṣāra Kalpanā (Ayurvedic alkali formulation) mainly deals with extraction of alkaline material from herb, animals and minerals. Kṣāra preparation mainly has variation in the concentration of Water used for extraction. Objective: To assess the effect of variation in concentration of water and plant part used on the physicochemical parameters of Yavakṣāra (YK). Materials and Methods: YK was prepared by using whole plant with seeds and without seeds. Further these batches were divided depend upon of 4, 6 and 8 times of concentration of water used for extraction. YK was analyzed by using the XRD, AAS-ICP and FTIR. Results: All samples contain Halite crystals of NaCl and Sylvine crystals of KCl. Halite and Sylvine crystals generally formed due to evaporation which is main step in the preparation of Kṣāra Kalpanā. Crystal size of NaCl and KCl is near to nanoparticles (in the range between 90 to 135 nm). YK contains other elements like Fe, Mg and Ca in small amount with slight variance in quantity in different batches. FTIR shows presence of same functional group (C-H of (Alkyl) amines) in all samples of YK. Absences (Pb, As) or traces (Hg) of heavy metal indicate care taken during harvesting and manufacturing. Conclusion: Slight variation is seen in the elements, their concentration and functional group in different batches of YK. Variation in the concentration of water alters the frequency of filtration and affect the period of sedimentation. A batch prepared with less concentration of water (4 times) and without seeds seems to be cost effective.

The role of ash content on bisphenol A sorption to biochars derived from different agricultural wastes

Inorganic minerals are important compositions in biochars, but their roles in biochar functions are investigated limitedly, which restricted our understanding on biochar applications. This study applied different biomasses to produce biochars. Their properties as well as sorption to bisphenol A (BPA) were studied, with a major focus on the role of inorganic compositions. Oxalates, carbonates, as well as KCl crystals were observed in the produced biochars depending on the feedstocks and temperatures. Oxalates and KCl formed at relatively low temperature (200–300 °C), while carbonates generally formed at pyrolysis temperature above 400 °C. The separated insoluble crystal particles and the dissolved salts have limited contribution to the apparent BPA sorption, but ash content removal altered BPA sorption. The potential impact of inorganic composition to BPA sorption should be resulted from biochar properties. Based on biochar characterization and sorption comparison before and after ash removal, we proposed that the formation of inorganic mineral compositions in biochar particles may have blocked the inner pores, which limited the significance of these sorption sites. As a result, the interactions of BPA and biochars were mostly determined by biochar surface functional groups. The acid treatment removed most of the inorganic compositions, and exposed more sorption sites, which consequently increased BPA sorption. Biochar sorption capacity may be further increased if the accessibility of the inner pores could be enhanced.

Impact of subthreshold laser defect accumulation on the optical stability of crystals

Optoacoustic means are used to study the kinetics of laser damage accumulation in potassium chloride crystals. This approach allows us to observe the accumulation of changes in KCl crystals when it is irradiated by a series of laser pulses of subthreshold intensity in a variety of actions (alloying, applying an external electric field, UV illumination). Number of laser pulses N cr required to destroy a specimen at the same density of radiation power depends on density power I as N ~ I −4. Results are explained by the formation and accumulation of structural defects during photochemical reactions under the action of laser radiation.

Bubbles facilitate ODA adsorption and improve flotation recovery at low temperature during KCl flotation

Understanding the adsorption process of collectors and the interaction between bubbles and mineral particles during KCl froth flotation are still weaknesses in our interpretation of the mechanism of flotation. In this study, we investigated in detail the adsorption kinetics and adsorption isotherm of a commonly used collector, octadecylamine hydrochloride (ODA), at the surface of KCl crystals. The effects of bubbling and temperature are discussed systematically. Our results indicated that the adsorption of ODA onto the surface of KCl crystals can be facilitated by bubbles, and that the adsorption kinetics of this process can be interpreted according to a pseudo-second order model. Both the Langmuir and Freundlich isotherm models were found to fit the adsorption isotherm of ODA on KCl crystal surface inappropriately, implying that the adsorption of ODA upon KCl crystal surfaces is a more complex process than typical monolayer, or multilayer, adsorption. This might be because the adsorption of ODA on KCl crystal surfaces takes place through an aggregated intermediate, rather than through the direct interaction of dispersed molecules. We note that the quantity of ODA adsorbed at 0°C increased markedly with increasing numbers of bubbles. Micro-flotation tests suggested that increasing the gas flow rate effectively improved flotation recovery at 0°C, consistent with the adsorption behavior. These results provide complementary information on the adsorption behavior of ODA at the surface of KCl crystals and on the effect of bubbles during froth flotation, which could help to design new flotation process and improve flotation recovery of KCl at low temperatures.

Supercrystallization of KCl from solution irradiated by soft X-rays

The X-rays influence on KCl crystallization in a saturated water solution has been investigated for the aim of comparing it with previously considered NaCl crystallization. The rate of crystallization has been measured in the drying drop in the solution activated by the irradiation. We have measured the influence of the irradiation time of the solution on the rates of KCl crystallization as well as the beginning of the crystallization processes on drying drops. For a longer irradiation time of the solution early crystallization in the drops occurs. A saturated water solution of KCl was irradiated with the diffractometer DRON-3M (Russian device) and this had a great influence on the two-step processes of crystallization. The ionization of the solution by soft X-rays can produce ions, metastable radicals in water, excited crystals' seeds and vacancies in growing crystals by Auger's effect. The X-rays generate a very fast crystallization in the drying drop.

The condensation and thermodynamic characteristics of alkali compound vapors on wall during wheat straw combustion

Alkali chlorides and sulfates are well-known species induced fouling, slagging and corrosion on the heat transfer surface in biomass combustion/gasification process. This paper aims to study the condensation behavior of alkali compound vapors (ACVs) during wheat straw combustion in laboratory, without the participation of ash particles. The effects of surface temperature of Fe-Cr-Ni alloy probe on condensation morphology, thermodynamic characteristics of mixed salt vapors, and mineralogical variation of straw ashes are also discussed. The K, Cl and S mainly existed as KCl, K2SO4 and K2Ca(CO3)2 in wheat straw ashes produced at 400°C. The main released ACVs were potassium chlorides and sulfates. The form of condensation for mixed chloride vapors at surface temperatures of 400/520/600°C is varied at 815°C. These mixed salt vapors could condense either separately as cubic crystal particles by homogeneous nucleation, or together as one or two solid solutions by heterogeneous nucleation. The side length of KCl crystal particle condensed homogeneously was less than 2μm. The aggregation and growth among crystal particles at surface temperature of 400°C were observable. The chlorides are released completely from wheat straw ashes at 815°C, and carbonates may disappear as either decomposition or sulfation with SO2/SO3. When the evaporation temperature was 1100°C, K2SO4 and Na2SO4 were released and then condensed as one solid solution with hexagonal crystal structure on the probe surface of 520°C. Finally, we propose a condensing mechanism for ACVs depending on surface temperature.

Synthesis, growth and characterization of l-Alanine Potassium Chloride single crystal: a phase-matchable semi-organic material for second and third order NLO applications

l-Alanine Potassium Chloride single crystals have been grown by slow evaporation solution growth technique. The cell parameters were estimated from single crystal X-ray diffraction analysis and it was found that the material crystallizes in orthorhombic symmetry with space group of P212121. The powder X-ray analysis proved its crystalline nature without the formation of secondary phases. The presence of functional groups and the nature of bonds appearing in the material were identified by FTIR spectroscopy. Optical constants were estimated by UV–visible spectrum and the lower cut off wavelength was observed at 330 nm. Photoluminescence emission spectrum show violet band through a strong peak centred at 380 nm. The scanning electron microscope analysis has been carried out to determine the surface morphology of the grown crystal. Energy dispersive spectrum was done to identify the composition of elements present in the title material. The second harmonic generation efficiency of the sample was confirmed and measured by Kurtz powder technique which reveals that the conversion efficiency was found to be two times that of urea crystal. Third order nonlinear optical susceptibility was identified using Z-scan technique and it is found that the crystal has a positive refractive index which is self focusing in nature. The obtained results show that l-Alanine KCl crystals are potential materials in NLO device applications.

Comparison of luminescence property of gamma‐ray irradiated Tb3+‐doped and Ce3+ co‐doped potassium halide single crystals

Single crystals of KCl and KBr singly and doubly doped with Tb3+ and Ce3+ , respectively, were successfully grown using the Bridgeman technique. This work reports the comparative luminescence behavior and optical absorption characterization of non-irradiated and γ-ray-irradiated single crystals of these materials. The existing defect and the defect created by γ-ray irradiation were monitored by optical absorption spectra. The excitation and emission spectra of these materials were measured at room temperature with a spectrofluorometer and the pertaining results were compared. The F-band comparison was made when bleached with F-light for 2mins. The trap-level changes in KCl and KBr when it is singly and doubly doped enabled us to draw conclusions on the nature of the defect and on the recombination processes involved.

Optical properties of bismuth-doped KCl and SrF2 crystals

Structural and spectroscopic properties of the pristine and γ-irradiated Bi-doped KCl and SrF2 crystals grown by the Bridgman technique were studied. New emission bands in the visible and near IR regions from the irradiated crystals were observed. An origin of optical centers responsible for near IR luminescence is discussed.

Optical, Structural, Mechanical and Magnetic Properties on Tb3+ doped KCl single crystals

ABSTRACTThis paper describes the single crystals of Tb3+ doped KCl grown by the Bridgeman–Stockbarger method. The grown crystal was subjected to Fourier transform infrared (FTIR), X-ray diffraction method (XRD), scanning electron microscopy (SEM), electron paramagnetic resonance (EPR), Vickers’s micro hardness and photoluminescence (PL). The presence of various functional groups has been identified from FTIR studies with their vibrating frequency range from 400 to 4000 cm−1. The structural studies on the grown crystals were carried out by X-ray diffraction analysis technique and found that the grown crystal crystallizes in a cubic structure. The lattice cell parameters of Tb3+-doped KCl crystals are a = b = c = 3.14260 Å and α = β = γ = 90°. The optical properties were studied by PL spectra. The excitation spectrum shows the peak at 237, 262 and 345 nm. Upon excitation at 261 nm, the emission spectrum exhibits a broad band at 377, 410 and 490 nm corresponding to 5d → 4f transition. EPR measurements showed fine structure spreading over a wide field region and the calculated g-factor value for more intense resonance signal is 2.3 and 2.2. The mechanical strength of the grown crystal was estimated by the Vicker’s micro hardness test. It confirms that the grown material is found to be a hard material. SEM shows that the particles have irregular shapes with various sizes (ranging from few microns to 20 μm) and it seem to be a cloudy like features. Owing to the high luminescence with the advantage of micrometer dimension, it can be suggested that these materials will find more applications in the field of display and lighting.

The Absorption Breakthrough Characteristics of Hydrogen Chloride Gas Mixture on Potassium-Based Solid Sorbent at High Temperature and High Pressure

In this study, the hydrogen chloride gas mixture absorption breakthrough behaviors of potassium (K)-based solid sorbents (K2CO3/Al2O3, KEPCO-RI, Korea) were studied with varying inlet HCl concentration (175–700 ppmv), temperature (200–500 °C), and pressure (1–20 bar) in a fixed-bed reactor (15 cm tall bed with 0.5 cm i.d.). The sorption capacity increases with increasing temperature and increasing pressure, whereas it was not affected by the inlet concentration. KCl crystals are formed on the sorbent surface when K+ ions from the K2CO3/Al2O3 sorbent are reacted with the Cl– ion from HCl. Its optical, physical, and chemical characterizations were examined by SEM, EDAX, BET, TGA, and XRD before and after the breakthrough tests. The main purpose of this study is to provide basic information of HCl sorption characteristics on K2CO3/Al2O3 solid sorbents for developing a high temperature and high pressure halogenide halide removal process.

Influence of elastic stresses and temperature on the dislocation unpinning from the stoppers in KCl crystals

Influence of elastic stresses and temperature on the dislocation unpinning from the stoppers in KCl crystals

Thermoluminescence and photoluminescence studies on γ-ray-irradiated Ce³⁺,Tb³⁺-doped potassium chloride single crystals.

Single crystals of KCl doped with Ce(3+),Tb(3+) were grown using the Bridgeman-Stockbarger technique. Thermoluminescence (TL), optical absorption, photoluminescence (PL), photo-stimulated luminescence (PSL), and thermal-stimulated luminescence (TSL) properties were studied after γ-ray irradiation at room temperature. The glow curve of the γ-ray-irradiated crystal exhibits three peaks at 420, 470 and 525 K. F-Light bleaching (560 nm) leads to a drastic change in the TL glow curve. The optical absorption measurements indicate that F- and V-centres are formed in the crystal during γ-ray irradiation. It was attempted to incorporate a broad band of cerium activator into the narrow band of terbium in the KCl host without a reduction in the emission intensity. Cerium co-doped KCl:Tb crystals showed broad band emission due to the d-f transition of cerium and a reduction in the intensity of the emission peak due to (5)D3 -(7)F(j) (j = 3, 4) transition of terbium, when excited at 330 nm. These results support that energy transfer occurs from cerium to terbium in the KCl host. Co-doping Ce(3+) ions greatly intensified the excitation peak at 339 nm for the emission at 400 nm of Tb(3+). The emission due to Tb(3+) ions was confirmed by PSL and TSL spectra.

Low temperature molecular dynamic simulation of water structure at sylvite crystal surface in saturated solution

The low flotation recovery of sylvite from salt lakes at low temperatures has dogged the cryogenic producer for many years. Interfacial water structure at sylvite crystal surfaces has been considered as one noticeable aspect on interpreting the selected KCl collection during flotation, and so the microscopic structure of the water membrane over KCl crystal surfaces at low temperatures was modeled through the use of molecular dynamics methods. In our simulation, the properties of the water membrane adjacent to KCl crystal surface, such as molecular mobility, water structure and preferred molecular orientation, were compared to the results for an otherwise identical system at higher temperatures or in saturated KCl solutions in the absence of a KCl crystal. In our simulation, hydrogen atoms approached the KCl crystal surface more closely, and the mobility of water molecules was more restricted compared to results for saturated KCl solutions. When the temperature decreased, the mobility of water molecules decreased, the number of hydrogen bonds made by the water molecules in the membranes was reduced and the molecules exhibited greater order than in other systems we studied. It was proposed that the property of KCl salt may change from water ‘structure breaker’ to ‘structure maker’ when temperature decreases. These results may provide complementary information which cannot be obtained from experiments on the research of flotation at low temperature directly.

Size-dependent plasticity in KCl and LiF single crystals: influence of orientation, temperature, pre-straining and doping

Size effects in plasticity are mostly studied in metallic systems, but they are rarely investigated in ionic crystals. In this study, single-crystalline KCl and LiF pillars were fabricated by focused ion beam technique and compressed using a flat punch tip in a nanoindenter. The materials were investigated with regards to crystal orientation, test temperature, pre-straining and doping. The results show: (1) [1 1 1] LiF pillars do exhibit size effect with an exponent of −0.38, in contrary to no size effect in [1 1 1] LiF reported in literature; (2) [0 0 1] LiF, and [0 0 1] and [1 1 1] KCl have similar size-effect exponents of −0.68, −0.71 and −0.65, respectively; (3) the size effect of [1 1 1] LiF pillars is more sensitive to the temperature change than that of [0 0 1] LiF pillars; (4) pre-straining of [1 1 1] LiF pillars results in a reduced size effect; (5) the 0.05 mol% CaCl2 doping in [0 0 1] KCl slightly increases strength levels and does not change the size effect much. The magnitude of the size effects in ionic crystals can be attributed to the bulk stress level, but not the slip systems. In addition, a correlation between critical temperatures and size-effect slopes is illustrated, and the additivity of strengthening mechanisms is critically discussed.

SURFACE MORPHOLOGY AND MICROSTRUCTURAL CHARACTERIZATION OF KCl CRYSTALS GROWN IN HALITE–SYLVITE BRINE SOLUTIONS BY ELECTRON BACKSCATTERED DIFFRACTION TECHNIQUES

In this paper, a study on the ternary NaCl – KCl – H 2 O system was carried out by an extractive metallurgy technique from mixed brine solutions of different compositions at room temperature (23°C). The surface morphology and microstructure were examined using a scanning electron microscope (SEM), electron backscattered diffraction (EBSD) and an energy dispersive X-ray (EDX) spectroscopy. The presence of [Formula: see text] was found to reduce the stability of the solutions and increase the crystallization induction period, interfacial energy, energy of formation of the nucleus and greatly reduce the nucleation rate of KCl crystal. The surface morphology of KCl crystals is significantly changed due to presence of 5 to 10% (w/w) of NaCl as impurities in the binary solutions and shows the formation of co-crystals of different crystallographic orientation of NaCl on the KCl surface. In addition X-ray diffraction studies performed on KCl crystals grown in halite–sylvite binary solutions reveals that these crystals are cubic in nature and its lattice constant is 6.2952 Å when the NaCl concentration is small.