Potassium Chloride Crystals Research Articles

Magnetic Gyration Studies of Mixed Crystals of Potassium Chloride and Potassium Bromide

Magneto-optical rotary dispersion studies have been made on mixed crystals of potassium chloride and potassium bromide. The data obtained are explained on the basis of a model which assumes an asymmetric distribution of anions about the cations.

The temperature dependence of dislocation charge in calcium doped single crystals of potassium chloride

Abstract Using the ultrasonic piezoelectric composite oscillator technique we have measured the temperature dependence of dislocation charge in bent KCl single crystals as a function of Ca impurity concentration. In each case the charge changes sign at an extrinsic isoelectric temperature, Te , and the shift in Te with impurity concentration allows the calculation of the individual thermodynamic vacancy formation parameters. We obtain h+ = 1.244±0.014 eV, s+ = 4.50±0.19 k, h- = 1.346∓ 0.014 eV and s- = 5.11∓0.19K.

Electrical conductivity and colour centres in Tl-doped KCl crystal

The electrical conductivity and optical absorption of potassium chloride crystals doped with different concentrations of thallium have been measured before and after X-irradiation. The optical absorption spectrum exhibits the characteristic Tl+ ion band at 247 nm. The extrinsic conductivity and the absorption coefficient at 247 nm increase with impurity addition upto a certain concentration. Further increase in impurities decreases them. Room temperature X-irradiation decreases the Tl+ ion band and produces the F band. F centre concentration is higher in lightly doped crystal compared to pure or heavily doped KCl. These results have been interpreted in terms of formation of interstitial potassium ions and positive ion vacancies in the Tl-doped KCl lattice due to large ionic radius of Tl+ ions. The impurity ions precipitate into TlCl phase when the doping is heavy.

Matrix phyllosilicates and associated minerals in C2M carbonaceous chondrites

TEM, HRTEM, HVEM and SEM methods, coupled with energy dispersive X-ray analysis, have been used to study the microstructure and the phases comprising the matrix of carbonaceous chondrites Murchison, Cold Bokkeveld, Nawapali and Cochabamba. A wide variety of phyllosilicate morphologies occurs in each. Very small crystals and clasts of olivine, pyroxene and other unhydrated minerals are mixed intimately with the phyllosilicates. Intergrowths of carbonates and Sulfides within the phyllosilicates also occur, as well as a ubiquitous spongey material which is difficult to characterize, but contains elementary phyllosilicate units and embryo crystals. The identifiable large crystalline phyllosilicates are principally Fe-rich serpentine-group minerals and intermediate more Mg-rich chrysotilelike group members, with characteristic ~ 7.0–7.4 Å basal layer spacings. Complex interlayered and intergrown hydrous minerals also occur associated with the spongey material, and other poorly crystalline silicates and finely divided Fe-Ni sulphides. Fe/Si and Mg/Si ratios vary on a sub-micron scale, and the morphologies of the larger phyllosilicate crystals correlate broadly with these variations. Small crystals of sodium chloride and potassium chloride have been identified, occluded within a predominantly organic mass. The matrix minerals have a multistage history of formation in which the effects of aqueous alteration are dominant. Few, if any, of matrix minerals can be unmodified nebular condensates, although some clasts and inclusions have escaped alteration and predate the alteration process.

Micromorphology of spruce timber after long-term service in a potash store house

Sprucewood samples from construction timber in a 40 year old store house were examined for microstructural and chemical changes effected on the exposed surface. A degradation of the surface cells extending to a depth of only 5 mm was the most predominant feature, resulting in their separation. Analysis of the fine structure of the tracheids revealed a deposition of potassium chloride crystals leading to a pattern of degradation resembling alkaline cooking. All the wall components including lignin, cellulose and hemicelluloses of these disintegrated tracheids seem to become affected. Deeper in the wood (3 mm) the hemicelluloses are the main components that become hydrolyzed. The degradation is limited to the outermost surface layers of the timber event after such a long service life, so that repairs are not very extensive. In general sprucewood can be considered as highly resistant in such storage houses for mineral fertilizers

Optical and Thermal Stability of Ag Centres in RT X‐Irradiated KCl:Ag Crystals

AbstractThe optical absorption, thermoluminescence (TL), monochromatic TL, and TL spectra of potassium chloride crystals doped heavily with silver are measured after X‐irradiation at RT. The effect of optical bleaching on X‐irradiated crystals with light in the F, E, and B bands both, separately and together, as well as thermal annealing effects of the defect centres are studied. It is found that in the heavily doped crystals the role of holes in the form of doubly charged impurity ions (Ag++) is predominant compared to holes of the host lattice in the form of Cletc. The Ag ions stabilised only at cation sites in different valence states are involved in the recombination‐luminescence process. From the TL spectral data of the glow peaks preferential redistribution of the excess electron centres on optical bleaching is evident. The results support that tunnelling of electrons is responsible for the observed TL and TL spectral data.

Anomaly in electron channeling due to imperfections produced thermally in a potassium chloride crystal

Lattice imperfections were produced in KCl crystals by a thermal process. The heat treated specimen was irradiated with 50 KeV electrons and the corresponding range of electrons in the crystal has been estimated. It was found that the electron range in the crystal depends upon the temperature of heat treatment, being a decreasing function of this temperature up to about 625 K, above which it becomes an increasing function. This anomaly has been explained in terms of dissolution of vacancies through dislocation loops.

The role of double poison in the etching of potassium chloride crystals

The authors give an experimental account of how additions of calcium chloride to the etchant, consisting of cadmium chloride and methanol, modifies the etch pits formed on the freshly cleaved surfaces of potassium chloride crystals. As the concentration of calcium chloride is increased in the etchant, the etched samples show the following essential features. A progressive increase in the degree of surface roughness. A gradual increase in the shallowness of etch pits. A systematic variation in the morphology of the etch pits and finally the orientation changes from the (100) directions to the (110) directions. Also, the effect of decreasing the cadmium chloride concentration in the etchant is observed. These observations suggest that calcium chloride inhibits the action of the poison, i.e. cadmium chloride, during etching.

Heterogeneous nucleation of bubbles at solid surfaces in gas-supersaturated aqueous solutions

CH 4, Ar, and N 2 supersaturation thresholds for cavitation in saturated aqueous solutions of succinic acid, potassium nitrate, and potassium chloride were determined at room temperature in the presence and absence of crystalline precipitates. To avoid the introduction and interference of preformed gaseous nuclei, crystals were formed in situ by cooling prior to decompression, after the solutions had been equilibrated with gas at elevated pressure and temperature. In the succinic acid and potassium nitrate systems, bubbles first occurred during decompressions in exclusive association with crystals. At ambient pressure, such cavitation occurred with supersaturations below 10 atm, while cavitation without crystals required supersaturations over 100 atm. In contrast, cavitation with potassium chloride crystals required supersaturations exceeding 100 atm. It is concluded that thresholds with succinic acid and potassium chloride crystals accurately reflected particular properties of the crystal-liquid interfaces, while the low thresholds observed with potassium nitrate crystals may also have reflected certain effects of the preceding crystallization processes per se. Results may be of particular biological significance because thresholds with succinic acid crystals at atmospheric pressure were within 5 atm of the supersaturations which elicit bubble-induced trauma in animals and man.

ESR on the triplet state of Fz centres in potassium chloride crystals doped with strontium

Z2 centres are produced in KCl:Sr by various methods and their optically excited triplet state is investigated by means of ESR measurements. In general the ESR spectra are very complicated and contain a large number of lines. Analysis is only made possible by varying the impurity and F-centre concentrations and by variation of the optical excitation conditions. Five different types of triplet centres are found and interpreted as Z2 centres. Three types have triplet lifetimes of about 20 ms and absorptions in the usual Z2 absorption region >or=1.8 eV. The two others possess triplet lifetimes of 100 ms and 1.6 s, not previously reported. They exhibit additional absorptions at low energies (<or=1.5 eV). All the types of Z2 centres have large fine-structure parameters ( mod D mod >0.3 cm-1) and none of them show simple axial symmetry. At very low temperatures (1.6K) a remarkable optical electron-spin polarisation can be detected. It is used for the determination of the absolute sign of the axial fine structure parameter of two Z2 centre types.

Agglomeration of potassium chloride crystals from supersaturated aqueous solutions

Agglomerates of potassium chloride crystals grown in the presence of lead ions were studied by SEM and by sieve analysis. Spherulites grown in industrial crystallizers have characteristics of agglomerates, as was shown by SEM studies of their cross sections. The assembling of spherulites with hard core and attached peripherial crystallites was achieved in laboratory experiments with non-linear programmed cooling. An attempt was made to relate the variation of the internal structure of spherulites obtained industrially to the cyclic behaviour of supersaturation levels in crystallizers.

A large unit cell semiempirical molecular orbital approach to the properties of solids. III. Ionic crystals: lithium fluoride and potassium chloride

For pt.II see ibid., vol.12, p.2497 (1979). A large unit cell-complete neglect of differential overlap (LUC-CNDO) method has been used to predict some properties of lithium fluoride and potassium chloride crystals. A 16 atom cell and a parameter set chosen to match the properties of the relevant diatomic molecules form a basis for the calculation. The results are compared with predictions from a 27 atom cluster model, with previous band-structure calculations and with experiment. It is concluded that the approach has great potential for the study of ionic solids with and without defects.

Исследование статики и динамики решетки хлористого калия

A really consistent and comprehensive approach has been adopted to derive the framework of a three-body force shell model (TSM) which is capable to explain successfully the lattice statics and dynamics of ionic crystals. The model contains eleven parameters which have been determined from those physical constants whose prediction is not intended for. The application of this model to the case of potassium chloride crystal has reproduced fairly well the phonon dispersion, two-phonon Raman and infra-red spectra, cohesive energy, relative stability, phase transition pressure and volume, photoelastic constants and anharmonic elastic constants. The successful description of this series of various properties with the same set of model parameters may be considered as a remarkable feature of TSM. It may also be pointed out that the original TSM developed by Singh and Verma was formulated only to explain the lattice dynamics of ionic crystals.

Spectroscopic and optically detected magnetic resonance studies of PO2− in potassium chloride. II. Magnetic resonance analysis

The optically detected magnetic resonance (ODMR) spectrum of phosphorus activated potassium chloride crystals obtained at 2 K in zero and weak applied external magnetic fields is reported and analyzed. A theoretical fit to the observed field and angular dependence ofthe ODMR spectrum is obtained using a phenomenological spin hamiltonian, assuming the center to be the paramagnetic photoexcited 3B1 state of the C2v ion PO2−. The components of the phosphorus nuclear hyperfine structure tensor are obtained from the theoretical analysis and compared with those of other AB2 ions and radicals. Optical polarization measurements and weak field ODMR spectra are used to determine the orientation of the PO2− chemical impurity center in the cubic KCl lattice and the orientation is compared with those of other isostructural impurities in KCl. The PO2− chemical impurity center exhibits a dramatic photo-orientation effect at 2 K and is shown to be in thermal equilibrium between twelve crystallographically equivalent orientations at temperatures above 45 K.

Spectroscopic and optically detected magnetic resonance studies of PO 2−in potassium chloride. I. Electronic and vibrational states

The phosphorescence and phosphorescence excitation spectra of phosphorus activated single crystals of potassium chloride have been examined at 4.2 K. The “color center” responsible for the blue emission in these samples is identified as PO 2 − by isotopic substitution and optically detected magnetic resonance measurements. The observed vibrational frequencies of the PO 2 − ion have been used to compute the normal coordinates of the ground state totally symmetric modes as well as the valuence angle in the valence force approximation. The vibrational analysis of the phosphorescence spectrum has been used together with the computed ground state normal coordinate description to compute the geometrical changes associated with excitation to the lowest triplet state of PO 2 −. The results for PO 2 − are compared with the results of similar calculations and measurements for other 18-electron AB 2 type molecules of the isoelectronic sequence PO 2 −, SO 2, NO 2 − and O 3.

Croissance des cristaux de chlorure de potassium en couche fluidisée: Comparaison avec la dissolution

The authors present data of an experimental study relative to the growth of potassium chloride crystals in a fluidized bed at 25 °C. Under the operating conditions (0.07 × 10 −2 ⩽ ΔC ⩽ 0.87 × 10 −2 kg KCl/kg H 2O, 8.2 × 10 −3 ⩽ U ⩽ 15.9 × 10 −3 m s −1 and 0.357 × 10 −3 ⩽ L i ⩽ 0.715 × 10 −3 m) the growth rate can be considered as quite independent of the crystal size and superficial velocity of the solution.

Discussion of “On Thermally Stimulated Space‐Charge Decay in Sn2+‐doped Sodium Chloride and Potassium Chloride Crystals” [Ah Mee Hor and P. W. M. Jacobs (pp. 430–432, Vol. 125, No. 3)

not Available.

Holograms in irradiated crystals of potassium chloride

Holograms in irradiated crystals of potassium chloride

First stage f centre formation in pure and doped KCl crystals by room temperaure X-irradiation

The electrical conductivity and optical absorption of potassium chloride crystals, pure and doped with divalent cation impurities, have been measured before and after X-irradiation at room temperature. The concentration of free positive ion vacancies at room temperature has been calculated from conductivity for each crystal before irradiation and is found to be much less than the first stage F centre concentration. This shows that both free and associated positive ion vacancies are the latent source of F centres in the first stage colouration. Pb+ + ions trap electrons producing Pb+ + and Pb0 centres and making free the associated cation vacancies. Such centres are not produced in Ca-doped crystals where impurity-vacancy complexes trap F centres producing Z centres. The higher ratio of F centres to positive ion vacancies in Pb-doped crystals indicates that free cation vacancies are more effective in producing F centres. However, the concentration of divalent cations is found to decrease in both the crystals after irradiation, the decrease being more in Ca-doped crystals.

On Thermally Stimulated Space‐Charge Decay in Sn2+‐doped Sodium Chloride and Potassium Chloride Crystals

When quenched crystals of or are warmed at a constant rate and the voltage appearing across platinum electrodes in contact with the crystal is monitored, as in a thermal depolarization experiment, large d‐c currents are measured even when the crystals have not previously been polarized. This charge release is believed to be associated with the crystallization of precipitates of within the crystal. The appearance of depolarization currents of the “wrong” sign during heating of previously polarized crystals is commented upon briefly.