Impurities In Crystals Research Articles

A microscopic mechanism of efflorescence on hemihydrate gypsum: Insight into the formation and diffusion of sodium impurities in hemihydrate gypsum crystals

Using phosphogypsum (mainly composed of dihydrate gypsum) as raw material to prepare α-hemihydrate gypsum (α-HH) is an effective way for high-value utilization of phosphogypsum solid waste. Sodium ions can effectively promote the transformation of dihydrate gypsum to α-HH and enhance the driving force of crystal transformation. However, during this process, sodium impurities may be doped into the α-HH crystals, resulting in an efflorescence phenomenon when α-HH products are used, which affects the use of the products. In this paper, the formation of sodium impurities in the process of preparing α-HH in NaCl solution was studied by the laboratory test, XRD, XPS, SEM and XRF. Possible forms and diffusion paths of sodium impurities in hemihydrate gypsum crystals are studied by density functional based tight binding methods. The results show that sodium impurities tend to exist in hemihydrate gypsum crystals by doping at interstitial sites. Moreover, there are a large number of interstitial sites in hemihydrate gypsum, which are critical for the diffusion of sodium impurities.

Study the metal impurities in potassium dihydrogen phosphate crystal by ion beam analysis

KDP (Potassium dihydrogen phosphate) crystal is one of the artificially grown crystals that has attracted the most attention. Now the fast growth method, which may easily introduce the metal impurities, is widely investigated. These metal impurity ions seriously affect growth rate and optical properties of the crystal. In this paper, the metal impurities Fe3+, Ba2+ and Cu2+ were doped into the growth solution of KDP crystals. The content and distribution of these metal impurities in KDP crystals were analyzed by a 3 MeV proton beam. The results indicate the chemical composition of elements O, K and P did not change by the impact from the ion beam. The limit of detection of Fe3+ was calculated. The results show that the trivalent metal ions in KDP crystals are easier to enter the crystals versus divalent ions and most of them distributed uniformly in the crystal.

Antisolvent crystallization of ammonium dihydrogen phosphate (ADP) from aqueous solutions containing Al(III) and Fe(III) impurities by addition of ethanol

Experimental results of a study of the effect of concentration of Al(III) and Fe(III) ions on the metastable zone width (MSZW) of aqueous ADP saturated solutions, as determined by the maximum antisolvent content Δxmax in them for spontaneous three-dimensional (3D) nucleation, by feeding ethanol antisolvent to them at different rates RA and the nucleation and growth of crystals from these solutions are described and discussed. Crystal structure and segregation coefficients of impurity in the crystals were also studied by X-ray diffraction analysis and microwave plasma atomic absorption spectrometry, respectively. It was observed that: (1) the value of Δxmax for spontaneous 3D nucleation increases with an increase in ethanol feeding rate RA as well as impurity concentration ci, (2) the morphology and size of the ADP crystals changes with an increase in impurity concentration ci and antisolvent feeding rate RA, and (3) the effective segregation coefficients keff of the impurities in ADP crystals at a constant RA of ethanol feeding decreases with an increase in impurity concentration ci in the solution. The experimental data of the dependence of Δxmax on RA for solutions containing different impurity concentration ci were analyzed according to the approach based on the classical theory for 3D nucleation to calculate values of the preexponential factor A and the effective interfacial energy γeff of the theory, those of the morphology of ADP crystals from consideration of adsorption of impurity particles on the surfaces of growing crystals, and those of the dependence of segregation coefficient keff of the impurities on their concentration ci in the solution using a model based on competitive adsorption of solute and impurity molecules. It is argued that the formation of 3D nuclei of ADP during MSZW measurements and growth of these ADP nuclei as large crystals from aqueous solutions containing impurities and segregation of impurities in the crystals may be explained from consideration of different rates of ligand exchange of the surface-adsorbed complexes formed by interaction between univalently-charged cation complex present in aqueous solution and the H2PO4− ions of kinks in steps.

Fractal model-based crystal pillar structure simulation and mechanism analysis of impurity migration process in layer melt crystallization

Layer melt crystallization (LMC) is regarded as a green purification technique and is widespread in the separation of isomers. Based on the highly efficient separation, this work combined the experiments and models to explore the crystal pillar structure and impurity migration. Firstly, we established the crystallization process kinetic model to reveal the crystal growth rules and pointed out the correlations of growth rate and supercooling degree. Then the fractal porous model was used to analyze the crystal pillar structure, where the fractal characteristics tended to the Euclidean geometric features with porosity increase in both crystallization and sweating processes. Next, we simulated the melt seepage rate through the pore channel, where the modeling results showed high consistency with the experiments. Finally, the effects of pore structure, kinetics, and sweating intensity on the separation and impurity migration in both crystallization and sweating processes were revealed, to guide the technical design.

Macroscopic helicity of a suspension of chiral magnetic particles based on nematic liquid crystal

The basic state of a suspension of chiral ferroparticles based on a nematic liquid crystal is studied when the finite coupling between the impurity and liquid crystal subsystems is considered. An additional contribution to the free energy functional due to the chiral shape of impurity particles, which describes the formation of spontaneous macroscopic helicity of the orientational structure of a nematic liquid crystal, is proposed.

Quantitative analysis of low content polymorphic impurities in canagliflozin tablets by PXRD, NIR, ATR-FITR and Raman solid-state analysis techniques combined with stoichiometry

Canagliflozin (CFZ) was a commercially new class of anti-diabetic drug, which had various anhydrate crystal forms and two hydrate crystal forms (Canagliflozin hemihydrate (Hemi-CFZ) and Canagliflozin monohydrate (Mono-CFZ) crystal form). Commercially available CFZ tablets’ active pharmaceutical ingredient (API) was Hemi-CFZ, which was easy conversion to CFZ or Mono-CFZ under the influence of temperature, pressure, humidity and other factors in tablets processing, storage, and transportation, thus affected bioavailability and efficacy of tablets. Therefore, quantitative analysis low content of CFZ and Mono-CFZ in tablets was essential to control tablets’ quality. The main objective of this study was to examine the feasibility of Powder X-ray Diffraction (PXRD), Near Infrared Spectroscopy (NIR), Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Raman for quantitative analysis the low content of CFZ or Mono-CFZ in ternary mixtures. PLSR calibration models for low content of CFZ and Mono-CFZ were established by the solid analysis techniques of PXRD, NIR, ATR-FTIR and Raman combined with various pretreatments (such as Multiplicative Scatter Correction (MSC), Standard Normal Variate (SNV), Savitzky-Golay First Derivative (SG1st), Savitzky-Golay Second Derivative (SG2nd) and Wavelet Transform (WT)), and the correction models were verified. However, compared with PXRD, ATR-FTIR and Raman, NIR due to its water sensitivity was the most suitable for the quantitative analysis low content of CFZ or Mono-CFZ in tablets. Partial Least Squares Regression (PLSR) model for quantitative analysis low content of CFZ in tablets was as follow: Y = 0.0480 + 0.9928 X, R2 = 0.9986, LOD = 0.1596 %, LOQ = 0.4838 %, SG1st + WT pretreated. And that of Mono-CFZ were Y = 0.0050 + 0.9996 X, R2 = 0.9996, LOD = 0.0164 %, LOQ = 0.0498 %, MSC + WT pretreated and Y = 0.0051 + 0.9996 X, R2 = 0.9996, LOD = 0.0167 %, LOQ = 0.0505 %, SNV + WT pretreated, respectively. That can be used for quantitative analysis of impurity crystal content in drug production to ensure drug quality.

Federated-Learning-Based Synchrotron X-Ray Microdiffraction Image Screening for Industry Materials

Synchrotron X-ray microdiffraction ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> XRD) services are conducted for industrial minerals to identify their crystal impurities in terms of crystallinity and potential impurities. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> XRD services generate huge loads of images that have to be screened before further processing and storage. However, there are insufficient effective labeled samples to train a screening model since service consumers are unwilling to share their original experimental images. In this article, we propose a physics law-informed federated learning (FL) based <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> XRD image screening method to improve the screening while protecting data privacy. In our method, we handle the unbalanced data distribution challenge incurred by service consumers with different categories and amounts of samples with novel client sampling algorithms. We also propose hybrid training schemes to handle asynchronous data communications between FL clients and servers. The experiments show that our method can ensure effective screening for industrial users conducting industrial material testing while keeping commercially confidential information.

Relationship between Co-related optical centres and nitrogen impurities in large single crystals of diamond grown in Co–C system under HPHT conditions

Diamonds with Co-related optical centers were prepared in a Co–C system and the effect of N impurities was analysed.

Control and characterization of defects and impurities in bulk crystals

Control and characterization of defects and impurities in bulk crystals

Application of optical velocity measurements including a novel calibration technique for micron-resolution to investigate the gas flow in a model experiment for crystal growth

An important step in the fabrication of many modern semiconductor materials and devices is the crystal growth process. These processes take place in high-temperature furnaces using inert gas and other atmospheres. The flow in the gas phase influences the transport of crystal components, dopants and impurities and hence has a significant impact on the grown crystals. In this work, we study the flow in a simplified model of a crystal growth furnace. This model is made of PMMA filled with a Diesel mixture as a model fluid to match the refractive index of PMMA and to allow for measurements in the complex geometry. The comparability to the flow in a real furnace is ensured by matching the Reynolds number. Two optical measurement methods, Particle Image Velocimetry (PIV) and the Laser Doppler Velocity Profile Sensor (LDV-PS) are used to investigate the global flow field as well as the small-scale flow structures. A calibration model is developed for the LDV-PS to reduce systematic measurement errors caused by the refractive index of the model fluid from up to 1% to less than 0,1%. The results obtained in this study improve the understanding of the gas flow behavior inside a crystal growth furnace and provide reference data for simulation. The first analysis shows a highly unsteady flow with unexpected flow direction along the crystal and melt surfaces. The near-surface flow patterns are of particular relevance in crystal growth because of their large influence on the local heat and mass transport during the crystallization process.

Influence of Mn2+ doping on refractive and electronic properties of β-LiNH4SO4 crystals

β-LiNH4SO4:Mn2+ crystals with 2 and 5 wt% Mn2+ concentration have been synthesized. The crystalline structure of impurity crystals was identified and refined by means of X-ray diffraction analysis. Experimentally studied dispersions of the refractive indices and birefringence showed that the introduction of the impurity leads to an increase in the absolute values of refractive indices without changing the nature of the dispersion; the anisotropy of the optical indicatrix increases along with a significant changes of birefringence absolute values. The optical birefringence temperature dependence reveals shifts in the phase transition point of the impurity crystals towards lower temperatures; the temperature interval of the existence of the “intermediate” phase in the β-LiNH4SO4:Mn2+ also shifts. The results of optical studies are independently confirmed by experimental studies of thermal expansion and differential thermal analysis. Band structure and optical spectra of β-LiNH4SO4:Mn2+ crystal are calculated using the density functional theory.

Parts-per-Million Detection of Trace Crystal Forms Using AF-PTIR Microscopy.

Autofluorescence-detected photothermal mid-infrared (AF-PTIR) microscopy was shown to enable parts-per-million detection of α-indomethacin impurity in γ-indomethacin samples. Subtle differences in the photothermal response of the UV-autofluorescence of two indomethacin crystal polymorphs were used for sub-micron chemical discrimination based on fingerprint region mid-IR spectroscopy. The AF-PTIR assignment was independently confirmed by second harmonic generation (SHG) microscopy, which was shown to reduce the total analysis time by rapidly identifying the suitable fields of view. AF-PTIR microscopy has the potential to assist in the early identification of crystal form impurities in the solid dosage forms development pipeline.

Method to detect carbon in silicon crystals in the concentration range down to 5 × 1014 cm−3 by Fourier transform infrared absorption at room temperature

The procedure of Fourier transform infrared absorption (FT-IR) at room temperature for quantifying C impurities in Si crystals was reexamined to improve the detection limit down to 5 × 1014 cm−3. Since the substitutional C absorption peak overlaps with a strong two-phonon absorption, the difference spectroscopy is necessary with using a C-lean reference sample. A baseline flatness of less than 0.0005 in absorbance and a thickness uniformity of less than 0.001 mm are required to realize a detection limit of 5 × 1014 cm−3 for 2 mm thick samples. To check the flatness, we define the Si/Si baseline which is the difference in the absorbance spectra measured twice with the removal and attachment of the same Si sample. Four organizations participated in the FT-IR round-robin test for ten samples with the C concentration ranging from 3.6 × 1014 to 3.3 × 1015 cm−3. The obtained C concentrations were almost within 30% deviation from the values determined by reliable secondary ion mass spectroscopy.

Photocatalytic and antibacterial activity of Yttrium doped TiO2 nanostructure

In this study, TiO2 nanostructures were doped with Yttrium (Y) at various doping concentrations using a low-cost approach called chemical co-precipitation, and then used for photocatalysis and antibacterial activity application. The effects of yttrium doping on TiO2 nanostructure properties such as crystal structure, chemical impurities, and optical features were investigated using EDAX, XRD, TEM, SAED, RAMAN, UV–Vis, and PL techniques. X-ray diffraction (XRD) confirmed the presence of the Rutile tetragonal crystalline phase in both pure and Y doped-TiO2 nanostructure. TEM images of synthesised nanomaterials depict typical nanoellipsoid morphology. UV–Vis absorption spectroscopy revealed that due to doping, the optical band gap was reduced from 3.28 eV to 3.11 eV. Low temperature Raman spectroscopy was used to determine variations in the isobaric Gruneisen parameter for both pure and Y doped materials. The photocatalytic activities of samples were evaluated by the photodegradation of methyl blue (MB) aqueous solution under 250 W UV lamp irradiation. The photodegradation efficiency of TiO2 has been found to vary with Y doping, despite 6% Y doped TiO2 nanostructure are most efficient than other samples. Furthermore, antibacterial analysis indicated that the doping exhibits excellent antibacterial properties when evaluated against E. coli culture.

Uncovering the role of impurity sugars on the crystallization of d-tagatose crystal: Experiments and molecular dynamics simulations

Impurity sugars produced in upstream process of functional sugars are significantly impacting the product quality. In this work, the effect of congeners (d-maltose (d-MAL), d-fructose (d-FRU), d-glucose (d-GLU)) on primary and secondary nucleation of d-tagatose (d-TAG) crystals was investigated. The impurity sugars showed an inhibition on primary nucleation of d-TAG crystals, while a promotion on the secondary nucleation of d-TAG. Interestingly, the impact of impurity sugars on d-TAG crystal growth was similar to that on primary nucleation. The diffusion ability, hydrogen bonding forming ability, interaction energy of d-TAG crystal surfaces and impurity sugars were evaluated by molecular dynamics (MD) simulations to reveal the nucleation and growth behavior. Based on the above findings, we designed the d-TAG crystallization experiments, and obtained d-TAG crystals with uniform particle size distribution and regular morphology. This study helps to understand the influence of impurity sugars on crystallization, guiding the industrial manufacturing of functional sugars.

Colossal In-Plane and Out-of-Plane Shift Photocurrents in Single-Layer Two-Dimensional α-Antimonide Phosphorus.

For materials lacking inversion symmetries, an interband transition induced by a photon may result in excited electrons (holes) experiencing a spatial shift leading to generation of directional photocurrents. This phenomenon known as bulk photovoltaic effect (BPVE) shift photocurrent (SPC) has recently attracted immense attention owing to its potential in generating photovoltages that are not restricted by Shockley-Queisser limitations imposed by materials' electronic band gaps. The BPVE was recently reformulated in a quantum mechanics viewpoint as the change in the geometrical phase upon photoexcitation and can now be promptly calculated from Bloch wave functions generated by first-principles calculations. The SPC of an electron (hole) is robust against crystal defects and impurities both in the interior and the surface and can be less dissipative and ultrafast. Herein, an emergence of colossal SPC in a pristine two-dimensional (2D) single-layer α-SbP crystal is predicted from first-principles calculations. An external electric field is further applied on the 2D crystal, and a large SPC enhancement is achieved. The locations of the SPC peaks due to both in-plane and out-of-plane responses suggest that α-SbP can generate a large photocurrent both in visible-light and ultraviolet regions. Single-layer 2D α-SbP is thus an excellent material for strong SPC. This finding is thus expected to open a pathway to exploring efficient photovoltaic devices based on monolayer α-SbP and similar materials.

Dispersion effects and real atomic vibrations of impure crystals studied based on interatomic effective potential

The dispersion effects and real atomic vibrations of crystals containing doping atoms have been studied using the interatomic effective potential which includes the many-body effects based on the contributions of nearest neighbors of the host and doping atoms. The analytical expressions are derived for the dispersion relations describing the dispersion effects consisting of the acoustic and optic branches, forbidden zone, as well as for the amplitude and phase shift of the real atomic vibrations of impure crystals. The Morse potential is assumed to describe the single-pair atomic interaction. The interrupts of wave propagation caused by doping atoms and the changes of thermodynamic properties due to the real atomic vibrations, as well as the areas of localization of forbidden zones and doping atoms have been specified. The numerical results for Fe doped by atoms of W calculated by the present theory using the interatomic effective potential are found to be in good agreement with experiment obtained from the measured Morse potential parameters and quite different from those of its inverse doping process (W doped by atoms of Fe), while they are the same if the single-pair potential is used.

Recovery of Lanthanum from Aqueous Solutions by Crystallization as Lanthanum Sodium Sulfate Double Salt

The recovery of rare earth elements from spent nickel-metal hydride batteries by hydrometallurgical processing has become increasingly important in recent years. The present work investigated the effect of temperature, systems of adding the reactant, the molar ratio of sodium and lanthanum, and the initial concentration of six sulfate impurities (Ni, Co, Al, Mn, Fe, and Zn) on the crystallization of the monohydrate of sodium lanthanum sulfate double salt (NaLa(SO4)2·H2O) crystals from synthetic leachate solutions. The sodium sulfate reactant was added as an acidic solution by pumping or batchwise as a solid anhydrate salt to a pregnant lanthanum sulfate solution. Compared to precipitation with acidic sodium sulfate solution, precipitation with solid sodium sulfate yielded smaller single crystals, a greater tendency to form aggregates, and lower crystal purity. The lowest overall impurity and highest lanthanum quantity in crystals were obtained by semi-batch reactant adding performance of Na2SO4 solution at 70°C with Na/La molar ratio of 3. Real-time monitoring of the count rates of different chord length fractions clearly showed the influence of crystallization temperature on the precipitation kinetics.

Experimental and CFD study on influence of viscosity on layer melt crystallization

• Layer melt crystallization of aqueous sucrose solutions with different viscosities. • Viscosity influence on freezing based on ice crystal yield and purity results. • CFD study on heat transfer inside melt crystallizer prior to ice crystallization. • Temperature distributions and thermal boundary layers of undercooled solutions. In the present work, the influence of solution viscosity on growth kinetics and purification efficiency in layer melt crystallization was investigated. Melt crystallization experiments were conducted for three different types of aqueous sucrose solution as they are ideal solutions and a relatively wide viscosity range can be investigated with a moderate change of freezing points. The aqueous 10 wt%, 23 wt%, and 30 wt% sucrose solutions have a dynamic viscosity value of 2.01 mPas, 4.74 mPas, and 7.21 mPas at their respective freezing points of −0.63 °C, −1.78 °C, and −2.64 °C. The solution temperature distribution was predicted by computational fluid dynamics (CFD) simulations run in COMSOL Multiphysics 5.6 software. Experimental results showed that a higher solution viscosity caused a higher crystal layer impurity and lower crystal yields in static layer melt crystallization. The cooling process of different solutions predicted by a CFD heat transfer study showed that the supersaturation region is wider for less concentrated solutions as cooling proceeds more rapidly. Hence, the temperature gradients obtained follow the boundary layer theory, i.e., the thinner the boundary layer, the faster the heat transfer.

Elastic forces drive nonequilibrium pattern formation in a model of nanocrystal ion exchange

Chemical transformations, such as ion exchange, are commonly employed to modify nanocrystal compositions. Yet the mechanisms of these transformations, which often operate far from equilibrium and entail mixing diverse chemical species, remain poorly understood. Here we explore an idealized model for ion exchange in which a chemical potential drives compositional defects to accumulate at a crystal's surface. These impurities subsequently diffuse inward. We find that the nature of interactions between sites in a compositionally impure crystal strongly impacts exchange trajectories. In particular, elastic deformations which accompany lattice-mismatched species promote spatially modulated patterns in the composition. These same patterns can be produced at equilibrium in core/shell nanocrystals, whose structure mimics transient motifs observed in nonequilibrium trajectories. Moreover, the core of such nanocrystals undergoes a phase transition-from modulated to unstructured-as the thickness or stiffness of the shell is decreased. Our results help explain the varied patterns observed in heterostructured nanocrystals produced by ion exchange and suggest principles for the rational design of compositionally patterned nanomaterials.