Nucleation studies in supersaturated potassium dihydrogen orthophosphate solution and the effect of soluble impurities

Nucleation rates as indicated by induction period have been studied for supersaturated solutions of potassium dihydrogen orthophosphate with and without the addition of soluble impurities in the temperature range 20 to 40° C. The effects of temperature, supersaturation and impurity content are reported. The interfacial tension, energy of formation and critical radius of nuclei of the crystal are calculated based on classical nucleation theory. The presence of soluble impurities enhances the nucleation rate of potassium dihydrogen orthophosphate crystals.Nomenclature G energy of formation of nucleus - B a constant - J frequency of formation of nuclei - k Boltzmann constant - K a constant - m slope of line plot ln against 1/ln² (X/X ₀) - N Avogadro's number - R gas constant - r radius of sphere inscribed in the crystal nucleus in equilibrium with solution - T temperature (K) - U ₁ energy of activation for the molar transition from phase 1 (solution) to phase 2 (crystal) - v volume per molecule in solid phase - V molar volume of crystal - x mole fraction of solute in the supersaturated salt solution at temperaturet - x ₀ mole fraction of solute in the salt solution saturated at temperaturet - ₁ chemical potential of supersaturated solution - ₁₀ chemical potential of saturated solution - _r chemical potential of nucleus of radiusr - chemical potential of nucleus of infinite radius - interfacial tension of crystal - induction period     

Growth of unidirectional potassium dihydrogen orthophosphate single crystal by SR method and its characterization

Unidirectional <100> potassium dihydrogen orthophosphate (KDP) single crystals were grown for the first time by Sankaranarayanan-Ramasamy (SR) method. The <100> oriented seed crystals were mounted at the bottom of the glass ampoules and the crystal of 15 mm diameter, 65 mm height were grown by SR method. The grown crystals were characterized by high-resolution X-ray diffraction (HRXRD), etching studies. The HRXRD analysis indicates that the crystalline perfection is excellent without having any very low angle internal structural grain boundaries. Dislocation density is less in SR grown KDP compared to conventional method grown KDP.     

A study of the growth and growth mechanism of potassium dihydrogen orthophosphate crystals from aqueous solution

Observations made during the growth of potassium dihydrogen orthophosphate (KDP) crystals from aqueous solution are recorded. A model of the growth process is given which attempts to explain the origin of the features observed.     

Gamma irradiation effect on optical and dielectric properties of potassium dihydrogen phosphate crystals

The effect of Co⁶⁰ gamma-ray irradiation on potassium dihydrogen phosphate crystals is investigated at doses ranging from 1 kGy to 100 kGy with different diagnostics, including UV–Vis absorption spectroscopy, fluorescence spectroscopy, DC electrical conductivity, positron annihilation lifetime spectroscopy and Doppler-broadening spectroscopy. The optical absorption spectra show a wide absorption band between 250 and 400 nm after γ-irradiation and its intensity increases with the increasing irradiation dose. The simulation of radiation defects show that this absorption is assigned to the formation of substitutional impurity defects due to Al, Mg ions substituting for K ions. The fluorescence peak at 355 nm blue shifts after irradiation. The fluorescence intensity is observed to increase with the increasing irradiation dose. The positron annihilation lifetime spectroscopy is used to probe the evolution of vacancy-type defects in potassium dihydrogen phosphate crystal. The variation of size and concentration of vacancy-type defects with the different irradiation dose is investigated. The Doppler-broadening spectroscopy gives direct evidence of the formation of irradiation-induced defects. The dc electrical conductivity of γ-irradiated potassium dihydrogen phosphate crystals increases with the increasing irradiation dose when the dose is less than 10 kGy, whereas keeps constant at high irradiation dose of 100 kGy. The increase of electrical conductivity is associated with the increase of the proton defect concentration in the crystal. A possible explanation about the change of proton defect concentration with irradiation dose is presented.     

Laser-induced damage in deuterated potassium dihydrogen phosphate

Laser-induced pinpoint bulk damage of deuterated potassium dihydrogen phosphate at 351 nm is shown to depend on the propagation direction relative to the crystallographic axes and on growth temperature in addition to the previously reported dependence on continuous filtration. Pulse-length scaling is also consistent with earlier reports. The leading hypothesis for the cause of pinpoint damage is absorbing nanoparticle impurities, and our results are consistent with but not conclusive for that model. Advances in technology have led to greatly improved damage resistance.     

UV absorption in solutions and crystals of potassium dihydrogen phosphate

The effects of impurities and growth conditions on the optical quality of potassium dihydrogen phosphate (KDP) crystals were examined. The transmittance of crystals grown under various conditions was measured in the range 200–400 nm for a larger number of impurities than previously. The highest transmittance is afforded by crystals grown from solutions with the stoichiometric composition at 55‡C and a growth rate of 1 mm per day.     

Etching studies on (1 0 0) faces of gel-grown ammonium dihydrogen orthophosphate crystals

Chemical etching employing specific etchants with varying etch times (20–60 s) has been successfully applied for the first time to reveal dislocation sites on the polished (1 0 0) faces of ammonium dihydrogen orthophosphate single crystals grown at ambient temperature, using a modified gel technique of double diffusion in a U-shaped beaker assembly. The selective behaviour of the etchant for straight and inclined dislocations has been demonstrated. Growth striations due to temperature fluctuations, low-angle tilt boundary and etch channels corresponding to stacking faults were clearly observed. Surface structures of the etched faces were photographed by optical and scanning electron microscopes and are discussed.     

Nucleation and growth of potassium dihydrogen phosphate crystals in silica gels

Kinetic studies on nucleation and growth of potassium dihydrogen phosphate crystals in silica gels show that the rate-determining process for the growth of these crystals in silica gels is diffusion. Morphology, microhardness and perfection of gel grown crystals are also reported.     

Material removal mechanisms and characteristics of potassium dihydrogen phosphate crystals under nanoscratching

Potassium dihydrogen phosphate (KDP) crystals are important materials in high-energy laser systems.However,because these crystals are brittle and soft,machining...     

Elastic-plastic-brittle transitions of potassium dihydrogen phosphate crystals: characterization by nanoindentation

Potassium dihydrogen phosphate (KDP) crystals are widely used in laser ignition facilities as optical switching and frequency conversion components. These crystals are soft, brittle, and sensitive to external conditions (e.g., humidity, temperature, and applied stress). Hence, conventional characterization methods, such as transmission electron microscopy, cannot be used to study the mechanisms of material deformation. Nevertheless, understanding the mechanism of plastic-brittle transition in KDP crystals is important to prevent the fracture damage during the machining process. This study explores the plastic deformation and brittle fracture mechanisms of KDP crystals through nanoindentation experiments and theoretical calculations. The results show that dislocation nucleation and propagation are the main mechanisms of plastic deformation in KDP crystals, and dislocation pileup leads to brittle fracture during nanoindentation. Nanoindentation experiments using various indenters indicate that the external stress fields influence the plastic deformation of KDP crystals, and plastic deformation and brittle fracture are related to the material’s anisotropy. However, the effect of loading rate on the KDP crystal deformation is practically negligible. The results of this research provide important information on reducing machining-induced damage and further improving the optical performance of KDP crystal components.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00320-3     

Effect of surface degradation on optical performance of potassium dihydrogen phosphate optics

We have measured scatter produced by roughening of bare potassium dihydrogen phosphate (KDP) surfaces and by surface degradation (etch pits) that develop beneath a porous solgel coating on KDP after exposure to ambient relative humidity. The etch pits that form on coated KDP scatter incident light into strongly anisotropic angular distributions characteristic of the defect size and shape. The total integrated scatter (TIS) can be as high as 9% for a crystal with etch pits as compared with 0.05% for the as-manufactured crystal. The amount of TIS correlates with the area obscured by defects as measured by optical microscopy.     

Dilatometric and dielectric studies on phase transition of potassium dihydrogen phosphate-boric acid binary system

Linear thermal expansion coefficient, dielectric data and transition temperature of KH₂PO₄-H₃BO₃ binary are reported. The transition temperature obtained from differential scanning calorimetry (DSC) is in concurrence with the dielectric and thermal expansion data. Further, this transition is classified as first order. Thermal expansion coefficients and enthalpy values of the binary are reported and compared with the data of pure KH₂PO₄.     

Physical properties of hydrothermally grown gallium orthophosphate single crystals

GaPO₄ single crystals have been hydrothermally grown by the horizontal temperature gradient method. The physical properties of these single crystals were measured. The following results were obtained: lattice parametersa = 0.490 nm andc = 1.105 nm, density = 3.56 g cm^–3, Vickers hardnessH _v = 7.06 × 10⁹ Nm^–2, refractive indicesn _e = 1.611±0.006 andn ₀ = 1.599±0.006, and birefringence n = +0.012. GaPO₄ single crystals exhibited some similar properties to -quartz and AlPO₄ single crystals because of the similarity of their crystal structures.     

Dielectric properties of hydrothermally grown gallium orthophosphate single crystals

GaPO₄ single crystals of the low-temperature form were hydrothermally grown in 4M H₃PO₄ solution at 180 ° C. Single crystals 5.0×5.2×3.7mm³ in size could be grown in a silica glass vessel of 10 mm inner diameter. The dielectric properties of grown crystals were measured with the electric field parallel (E c) and perpendicular (E c) to thec-axis. The values of dielectric constant (ie2800-01) ofE c andE c are about 10.3 and 7.8, respectively, at frequencies from 10 kHz to 1 MHz, and these are nearly independent of frequency at room temperature. However, these values increase with temperature in the temperature range about 310 to 500 K and in the frequency region below 1 MHz. Dielectric loss (ie2800-02) increases with increasing temperature at around 300 K (E c) and 310 K (E c). From the log (conductivity) against 1/T plot in the intrinsic region at higher temperatures, the values of activation energy (E) for conduction are calculated to be about 0.17 and 0.33eV, forE c andE c, respectively.     

Investigation into the room temperature creep-deformation of potassium dihydrogen phosphate crystals using nanoindentation

It has been a tremendous challenge to manufacture damage-free and smooth surfaces of potassium dihydrogen phosphate (KDP) crystals to meet the requirements of high-energy laser systems. The intrinsic issue is whether a KDP crystal can be plastically deformed so that the material can be removed in a ductile mode during the machining of KDP. This study investigates the room temperature creep-deformation of KDP crystals with the aid of nanoindentation. A stress analysis was carried out to identify the creep mechanism. The results showed that KDP crystals could be plastically deformed at the nanoscale. Dislocation motion is responsible for creep-deformation. Both creep rate and creep depth decrease with decrease in peak force and loading rate. Dislocation nucleation and propagation bring about pop-ins in the loaddisplacement curves during nanoindentation.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-018-0234-9     

Use of potassium dihydrogen phosphate and sawdust as adsorbents of ammoniacal nitrogen in aerobic composting process

Three kinds of adsorbents-potassium dihydrogen phosphate, sawdust and mixture of potassium dihydrogen phosphate and sawdust were added respectively into composting to investigate their adsorption effect on ammonia. The experimental results showed that all the adsorbents could restrain ammonia volatilizing, with the sorption of potassium dihydrogen phosphate adsorbents being the best of all, the sorption of mixture adsorbent with potassium dihydrogen phosphate and sawdust being the second and the sorption of sawdust adsorbent being the last. Therefore, the total nitrogen loss ratios respectively reduced from 38% to 13%, 15% and 21% after adding these three kinds of adsorbents into composting. However, potassium dihydrogen phosphate produced negative influence on composting properties as its supplemented amount exceeded a quantity basis equivalent to 18% of total nitrogen in the composting, for example: pH value had been lessened, microorganism activity reduced, which finally resulted in the reduction of biodegradation ratio of organic matter. But it did not result in these problems when using the mixture of potassium dihydrogen phosphate and sawdust as adsorbent, in which the amount of potassium dihydrogen phosphate was under a quantity basis equivalent to 6% of total nitrogen in the composting. Moreover, the mixture adsorbent produced better adsorption effect on ammonia, and raised biodegradation ratio of organic matter from 26% to 33%.     

Surface micromorphology and dissolution kinetics of potassium dihydrogen phosphate (KDP) crystals in undersaturated aqueous solutions

The results of dissolution kinetics and surface micromorphology of (010) and (011) faces of potassium dihydrogen phosphate (KDP) crystals etched in undersaturated aqueous solutions are described. They are then analysed from the standpoint of the theories of dissolution and growth. It was found that Cabrera's mechanism of dislocation etch-pit formation and birthand-spread model of growth may be applied in the case of dissolution of KDP crystals.