Calcium Oxalate Crystallization from Inhibited Solutions

The induction periods of calcium oxalate precipitation at high supersaturations were measured and the degrees of inhibition in the presence of different trace quantities of polyphosphates were determined. Crystals were grown from uninhibited and from partially inhibited solutions. The presence of both polyphosphates and of cationic impurities affects the crystal habit very strongly: rod-like crystals up to 3 mm in length grew from inhibited solutions in a week, whereas very small round particles of 10^?2 mm size sprang from the uninhibited solutions. Some previously published mechanisms are reviewed, and a new, comprehensive, heterogeneous nucleation mechanism of growth is proposed to explain the simultaneous inhibition of precipitation and inducement to growth of large crystals.     

可溶磷对常压水热法制备高强α-半水石膏的影响

研究了水热CaCl₂溶液中可溶磷对CaSO₄·2H₂O脱水形成α-半水石膏相以及晶形调控的影响,并从高强α-半水石膏相的晶体生长角度探讨了可溶磷的作用机理。结果表明:在98℃ 24%的水热CaCl₂溶液中,pH 的大小是决定二水石膏能否发生脱水相变反应形成α-半水石膏的主要因素;当pH不超过2.0时,可以得到针状的α-半水石膏,加入多元羧酸类媒晶剂NS后,可以得到长径比0.5～3.0的短柱状高强α-半水石膏,抗压强度超过20 MPa;可溶磷的存在可以降低体系的pH,增大α-半水石膏的过饱和度,降低晶体与液相界面的表面自由能,有利于α-HH相的形成;另一方面,酸根离子会影响到α-HH的结晶习性,减弱羧酸类媒晶剂的吸附效果。     

The crystallization of magnesium hydroxide

The thermodynamic association constant for the formation of the ion-pair MgOH⁺ in solutions of magnesium hydroxide has been studied by potentiometric and conductometric methods.The growth of magnesium hydroxide seed crystals in supersaturated solutions over a range of concentrations of magnesium and hydroxide ions and in the presence of phosphonate additives has been investigated by a precision conductance method. After a rapid initial surge of growth, an equation first order with respect to supersaturation can be used to explain the experimental data. A surface diffusion process is proposed as the controlling step in the crystallization process.     

Investigation of mechanism of Al(OH)3 crystal growth

Crystallization of Al(OH)₃ that occurs during the decomposition of caustic soda solutions is an important part of Bayer process for alumina production. Several phenomena, which influence the physicochemical characteristics of precipitated Al(OH)₃, occur simultaneously during this process. They are nucleation, agglomeration, and crystal growth of Al(OH)₃. In this article, we have investigated the mechanism of Al(OH)₃ crystal growth from pure caustic soda solutions and in the presence of oxalic acid. The results have shown that the growth of Al(OH)₃ crystals from caustic soda solutions follow the B + S model (birth and spread). New Al(OH)₃ particles, formed during the decomposition process of pure caustic soda solutions, are characterized by regular hexagonal shape. The nuclei have the same geometry as the contact face. However, microstructural investigations of Al(OH)₃ samples, obtained by crystallization from caustic soda solutions in the presence of oxalic acid, have shown the presence of nuclei of irregular shape in addition to regular ones. So, the presence of oxalic acid in the caustic soda solutions leads to a change in crystal habit. Besides, the results obtained by kinetic investigation confirmed the mentioned mechanism of Al(OH)₃ crystal growth.     

On the prediction of crystal shape distributions in a steady-state continuous crystallizer

Zhang and Doherty [2004. Simultaneous prediction of crystal shape and size for solution crystallization. A.I.Ch.E. Journal 50, 2101-2112] have provided a one-dimensional analysis of crystallization based on the assumption that the relative face-specific growth rates of a (2-D) crystal are independent of supersaturation and hence invariant with time. Subsequent work by these authors [Zhang, Y., Sizemore, J.P., Doherty, M.F., 2006. Shape evolution of 3-dimensional faceted crystals. A.I.Ch.E. Journal 52, 1906-1915) consider shape evolution of single three-dimensional crystals with morphological changes. In this work, we present a multidimensional population balance approach accounting for dependence of the relative face-specific growth rates on supersaturation, a situation more commonly encountered. For example, Joshi and Paul [1974. Effect of supersaturation and fluid shear on habit and homogeneity of potassium dihydrogen phosphate crystals. Journal of Crystal Growth 22, 321-327] and Mullin and Whiting [1980. Succinic acid crystal-growth rates in aqueous solution. Industrial & Engineering Chemistry Fundamentals 19, 117-121] report face-specific growth rates with different dependence on the supersaturation. Thus it has been observed that there exists significantly different crystal shapes in a crystallizer [Yang, G., Kubota, N., Sha, Z., Louhi-Kultanen, M. Wang, J., 2006. Crystal shape control by manipulating supersaturation in batch cooling crystallization. Crystal Growth and Design 6, 2799-2803]. Consequently, the population of crystals at any instant will have widely varying crystal shapes and sizes depending upon the initial crystal shape and size distribution. Computations are presented for the shape distributions of the crystal population emerging from a steady-state continuous crystallizer for two cases: (1) feed without crystals including nucleation for the formation of new crystals, and (2) feed with seed crystals of known shape, with suppressed nucleation. In the range of mean residence times investigated, the calculated crystal volume distributions for the first case show geometrically dissimilar shapes without morphological variations. However, in the second case, because the feed crystals of the chosen shape were susceptible to morphological changes, the volume distributions display this feature with shape and size distributions for each of a number of different morphologies. By varying operating conditions such as the flow rate, the inlet supersaturation, and the shapes of feed crystals, the proposed model can clearly be used to manipulate the crystal shape and size distributions and their morphologies.     

Tuning of Bi3+-related excitation and emission positions through crystal field modulation in the perovskite-structured La2(Znx, Mg1-x)TiO6 (0 ≤ x ≤ 1):Bi3+ solid solution for white LEDs

In the past year, emission-tunable crystals based on the rare-earth (RE) ions as luminescent center have been frequently reported for use in UV and blue converted white LEDs, but so far tuning the non-RE Bi³⁺ related emissions through the crystal field modulation is still not discovered in the perovskite crystals. In this work, we design and report a type of Bi³⁺ doped La₂(Zn_x,Mg_1-x)TiO₆ (0 ≤ x ≤ 1) perovskite solid solutions, which enable showing the tunable Bi³⁺ excitation and emission positions. The XRD results show that gradual substitution of smaller Mg²⁺ ions with larger Zn²⁺ ions can lead to the blue-shifting of X-ray diffraction (XRD) position, revealing the expansion of cell lattice. Together with structural analysis, our refined XRD and time-resolved spectral results reveal that there is only one type of La site available for Bi³⁺ substitution. With this regular crystal lattice change, the crystal field strength around Bi³⁺ ions is found to vary regularly, allowing to realization of the excitation and emission spectral tuning, i.e., the Bi³⁺ excitation and emission positions as the Mg ions are replaced by the Zn ions can tune from 348?nm to 392?nm and from 405?nm to 433?nm, respectively. This Bi³⁺ spectral tuning peak after calculated by the dielectric chemical bond theory features a linear relationship with the crystal field strength and, thus, is ascribed to the crystal field modulation. On basis of the La₂(Zn_0.4,Mg_0.6)TiO₆ blue, SrGa₂S₄:Eu²⁺ green and Y₂O₃:Eu³⁺ red phosphors, a UV converted warm white LED device with desirable color rendering index (CRI) of 78, correlated color temperature (CCT) of 3650 K and good luminous efficacy of 118.13?lm/W, is fabricated. This work provides new insights into using the crystal-field modulation to discover more Bi³⁺ emission-tunable crystals for white LEDs in the future.     

Co-Precipitation of Divalent Cations with KCl or NaCl and the Heterogeneous Nuclei Mechanism of Growth

Potassium chloride and sodium chloride were recrystallized in fractions. Crystallization was effected either by cooling a saturated solution or by isothermal evaporation at reduced pressure. In both cases the active cations (Pb²⁺or Cd²⁺) in the co-precipitate can be replaced by non-active cations or anions in consequent fractions of the salt crystallized. The phenomenon is attributed to heterogeneous nucleation; the active cations readily form impurity centred nuclei as soon as supersaturation is produced in the solution. The non-active ions are slow to nucleate. Co-precipitation is the result of crystal growth by impurity centred macro-nuclei.     

Effects of ionic impurities on crystallization of cobalamin

In this paper, the influence of two typical ionic impurities (Na⁺ and Mg²⁺) is investigated with the focused beam reflectance measurement (FBRM) technique. In this system, the on-line FBRM is used as a tool for monitoring the crystallization process of cobalamin by measuring the chord length distribution of particles and the particle counts. It is noted that impurity Mg²⁺ has a more significant effect than Na²⁺ in crystal growth of the whole crystallization process. From the microscopic observation of crystals, Mg²⁺ has an obvious effect on the crystal habit, while Na²⁺ has little effect. In addition, the crystal habit changes can be monitored by particle vision measurement (PVM). Understanding these effects is helpful to aid optimization and improve process control.     

Growth inhibition in calcium sulfate crystal using a copolymer in oil fields: theoretical study and experimental evaluations

A poly(itaconic acid-co-sodium vinylsulphonate) (PIASVS) was theoretically studied and experimentally evaluated as an inhibitory agent against the growth of calcium sulfate (CaSO₄) crystals, in both non-saline and saline solutions. Density functional theory revealed that the CaSO₄ crystal precipitation could be precluded through the effective pairing of Ca²⁺ and SO₄^2? ions by carboxylic group polymer heads and that, moreover, the Na⁺ cations of the sulphonate polymer heads could be easily replaced by Ca²⁺. With PIASVS concentration of 50 ppm, lower than what is required in oil recovery processes, the polymer inhibited 33% in CaSO₄ crystals growth in non-saline solution, but the salt increased the inhibitory performance of PIASVS up to 54%. Thermogravimetric analysis, scanning electron microscopy and X-ray diffractometry techniques showed that PIASVS changed the CaSO₄ crystal morphology from a bassanite phase in non-saline solution to a bassanite/gypsum mix. The crystal morphology observations along with the conductivity measurements confirmed the pairing of ions from dissolved CaSO₄ by NaCl and PIASVS. Dynamic light scattering revealed that, the PIASVS cluster size increased in non-saline solution but decreased in saline solutions, suggesting that NaCl increases the PIASVS solubility in aqueous solution. The performance of PIASVS as anti-scaling agent was found to be suitable for the conditions found in the Mexican oil reservoirs.     

Wachstumsmessungen von Kristallen in sauberen und verunreinigten Lösungen: Einzelkristall vs. Kollektiv

Information about crystal growth rates and the influence of impurities are essential for the design of industrial crystallization processes. Here, the influence of trivalent metal ions Fe³⁺ in solution and adsorbed in the crystal on the growth and dissolution rate is investigated. The results clearly show kinetic and thermodynamic effects caused by impurities which have to be taken into account in the equipment design. Furthermore, effects of growth rate dispersion must be excluded by investigation of crystal collectives. Additionally, the crystal growth data should be obtained from real starting solutions.     

Effects of magnetic field on the crystallization of CaCO3 using permanent magnets

Permanent magnets of different intensities were used to investigate the effect of a magnetic field on the crystal growth of calcite suspended in a fluidized bed. The magnets were fixed on the suspended bed where the crystal grew. The growth rates of calcite were measured at various levels of supersaturation (σ), pH, and ionic strength (I) using the constant-composition technique. The calcite growth rates in the presence of the magnetic field were lower than those in the absence of the magnetic field, and higher magnetic intensity yielded a lower growth rate. The effect of a magnetic field on CaCO₃ polymorphism was also studied. The percentage of polymorphs was dependent on the magnetization time. Aragonite was the predominant polymorphic form in the precipitate mixture, which was induced spontaneously by changing the solution pH after the supersaturated solution had been magnetized for 48 h.     

Crystallographic studies on the site selectivity of Ca<Superscript>2+</Superscript>, K<Superscript>+</Superscript>, and Rb<Superscript>+</Superscript> ions within zeolite Y (Si/Al = 1.56)

The single-crystals of Ca²⁺, K⁺-exchanged zeolite Y, and Ca²⁺, Rb⁺-exchanged zeolite Y were prepared by using flow method with mixed ion-exchange solution, whose Ca(NO₃)₂:KNO₃ mole ratios were 1:1 (crystal 1) and 1:100 (crystal 2), and Ca(NO₃)₂:RbNO₃ mole ratios were 1:1 (crystal 3) and 1:100 (crystal 4), respectively, with a total concentration of 0.05 M. They were fully dehydrated by vacuum dehydration at 723 K and 1 × 10^?6 Torr for 2 days. Their crystals were determined by single-crystal synchrotron X-ray diffraction techniques in the cubic space group \(Fd \overline{3}\) m, respectively, and were refined to the final error indices R ₁/wR ₂ = 0.057/0.196, 0.073/0.223, 0.055/0.188, and 0.049/0.175 for crystals 1, 2, 3, and 4, respectively. In the structure of crystal 1 (|Ca₂₃K₂₉|[Si₁₁₇Al₇₅O₃₈₄]-FAU), 23 Ca²⁺ ions per unit cell occupy sites I, II′, and II; 29 K⁺ ions per unit cell are at sites II′, II, and III′. In the structure of crystal 2 (|Ca_18.5K₃₈|[Si₁₁₇Al₇₅O₃₈₄]-FAU), 18.5 Ca²⁺ ions per unit cell occupy sites I, I′, and II; 38 K⁺ ions are at sites I′, II, and III′. In the structure of crystal 3 (|Ca₂₇Rb₂₁|[Si₁₁₇Al₇₅O₃₈₄]-FAU), 27 Ca²⁺ ions per unit cell occupy sites I, II′, and II; 21 Rb⁺ ions per unit cell are at sites II′, II, and III. In the structure of crystal 4 (|Ca₁₈Rb₃₉|[Si₁₁₇Al₇₅O₃₈₄]-FAU), 18 Ca²⁺ ions per unit cell occupy sites I and II; 39 Rb⁺ ions per unit cell are at sites I′, II′, II, III, and III′. In the four crystals, the Ca²⁺ ion which has much smaller size and higher charge than other cations such as K⁺ and Rb⁺ energetically preferred at site I and so the first to be filled on it. Unlike Ca²⁺ ion, no K⁺ and Rb⁺ ions are found at site I, which are clearly less favorable for K⁺ and Rb⁺ ions.     

Influences of additives on the crystal habit of potassium chloride

By means of constant control speed cooling crystallization, the influences of four additives, including lead chloride, cadmium chloride, sodium salicylate, and quaternary ammonium salt, on the crystal habit of KCl were investigated. The results show that the crystal habit of KCl is cube without additives, the crystal habit of KCl is ellipsoid-like in the presence of Pb²⁺, the crystal habit of KCl is strip in the presence of Cd²⁺, and the crystal habit of KCl is cavate cube in the presence of sodium salicylate. X-ray diffractometry analysis reveals that these additives can change the crystal habit of KCl but not its crystal structure.     

Silicalite-l Synthesis from Silicate Aqueous Solutions Including Amines as a Base

Aqueous silicate solutions could be prepared from a silicon alkoxide using amines as a base. The synthesis of silicalite-1 conducted by hydrothermally treating the solutions after the addition of NPrⁿ₄Br (TPABr), was examined focusing on triethylamine (NEt₃) as the amine. The aqueous solutions with chemical compositions of Si(OEt)₄ (TEOS) : NEt₃ : TPABr : H₂O = 1 : ≥0.5 : ≥0.8 : 200 led to silicalite-1 crystallization upon hydrothermal treatment at 130C for 4 days. The resulting crystals had a small thin coffin shape. With increasing the added amounts of NEt₃ and TPABr, the crystal size decreased. Among the investigated conditions, the smallest silicalite-1 crystal measuring about 1.0 × 0.7 × 0.4 um was obtained at starting compositions of NEt₃/TEOS ≥2.0 and TPABr/TEOS ≥3.2. The increase in the TPA content of the starting solutions accelerated the crystal nucleation of silicalite-1, so that the obtained crystals became smaller. During the hydrothermal synthesis, an amorphous silica gel was formed before the crystallization commenced. The increase in the NEt₃ content may suppress the formation of the silica gel, and/or facilitate its dissolution, thereby the supersaturation degree of silicate species in the solution was increased, giving small silicalite-1 crystals. When an aqueous suspension of the smallest silicalite-1 crystals was spread onto a glass substrate by a dip-coating method, an ordered mono-grain layer of the silicalite-1 crystals oriented with the straight channels normal to the substrate surface was obtained.     

Crystallization of calcium sulphate hemihydrate in concentrated phosphoric acid solutions

We aim to show the existence of agglomeration by measuring and modelling secondary nucleation and crystal growth rates of calcium sulphate hemihydrate, CaSO₄-0.5 H₂O, in concentrated phosphoric acid solutions. Using a batch crystallizer we measured the evolution of the population density as a function of supersaturation, H₂SO₄ excess and stirring rates. All experiments were carried out at 90 °C in solutions at 40 wt.% of P₂O₅, simulating the usual conditions for crystallizing hemihydrate in the industrial processes of phosphoric acid production. Nucleation and growth rates were calculated from the population number densities, using the moments analysis method. A model is presented for describing the crystallization process of hemihydrate. It is shown that secondary nucleation and growth rates are quadratic functions of supersaturation. H₂SO₄ concentrations affect supersaturation but at the same supersaturation the growth rates are not significantly different. Nucleation is independent of the stirring rate, whereas growth rates are slightly affected for stirring rates up to 500 rpm. Taking agglomeration into account, the moments method fits very well the experimental data.     

Tensile properties of random copolymers of propylene with ethylene and 1-butene: effect of crystallinity and crystal habit

The tensile modulus of elasticity and yield strength of semicrystalline random copolymers of propylene with different amount on ethylene or 1-butene co-units were analyzed as a function of the crystallinity and the crystal habit/shape. Samples were prepared by cooling the melt to ambient temperature, and subsequent annealing at elevated temperature. Variation of the cooling rate between 10⁻¹ and 10³ K s⁻¹ and of the temperature of annealing allowed preparation of semicrystalline specimens with either lamellar or non-lamellar crystals of different size, and with different crystallinity between about 30 and 70%. Young’s modulus and yield strength increase with increasing crystallinity and consistently are lower for samples containing nodular, that is, almost isometric, non-lamellar crystals of low aspect ratio. For samples of identical crystallinity and crystal habit, an only minor effect of presence of co-units in the crystalline and amorphous phases is observed.     

Factors influencing the phase constitution of alite in portland cement clinker

The phase constitution of alite in portland cement clinker highly depends not only in the chemical composition of a raw mix but also on the kinetics of crystallization from the interstitial melt. From the melt of high supersaturation alite can be crystallized so quickly as to take up foreign ions in quantities in favor of the occurrence of M₃ at ambient temperature. The reverse is the case for the crystallization from the melt low in supersaturation, where M₁ tends to be formed. The formation of zoned alite can be explained by the change in the degree of supersaturation during crystallization. The phase constitution of alite can be correlated with its crystal size in terms of the supersaturation of the melt. The SO₃ in clinker considerably lowers the viscosity of the interstitial melt and thus encourages the formation of M₁ along with the grain growth of alite. The relation between the phase constitution of alite and the quality of cements has been remarked in conjunction with the Ono's method.     

Chelating polymer bearing triazolylazophenol moiety as the functional group

The chelating polymer-bearing triazolylazophenol moiety as the functional group was synthesized, its metal adsorption properties for 6 divalent heavy metal ions; Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, and Pb²⁺ were investigated. The capacity of the polymer for Cu²⁺ achieved 8.7 mEq/g in pH 5.3 solution. The polymer showed remarkable color changes from orange to red violet or blue violet with its chelations to the heavy metal ions. The metal adsorption rates of the polymer were rapid in performing complete capacity saturation of heavy metal ions in about 30 min. The capacities varied little the presence of alkali or alkaline earth metal ions in solutions. The perfect elimination of metals from the polymer–M²⁺ chelates were performed with mineral acid solutions. The metal ions; Cu²⁺ and Ni²⁺ in plating-process solutions were effectively removed by the chelating polymer, and the polymer can be practically used for the removal of these ions from waste water.     

Modulation of Tubular pH by Acetazolamide in a Ca2+ Transport Deficient Mice Facilitates Calcium Nephrolithiasis

Proximal tubular (PT) acidosis, which alkalinizes the urinary filtrate, together with Ca²⁺ supersaturation in PT can induce luminal calcium phosphate (CaP) crystal formation. While such CaP crystals are known to act as a nidus for CaP/calcium oxalate (CaOx) mixed stone formation, the regulation of PT luminal Ca²⁺ concentration ([Ca²⁺]) under elevated pH and/or high [Ca²⁺] conditions are unknown. Since we found that transient receptor potential canonical 3 (TRPC3) knockout (KO; -/-) mice could produce mild hypercalciuria with CaP urine crystals, we alkalinized the tubular pH in TRPC3-/- mice by oral acetazolamide (0.08%) to develop mixed urinary crystals akin to clinical signs of calcium nephrolithiasis (CaNL). Our ratiometric (λ340/380) intracellular [Ca²⁺] measurements reveal that such alkalization not only upsurges Ca²⁺ influx into PT cells, but the mode of Ca²⁺ entry switches from receptor-operated to store-operated pathway. Electrophysiological experiments show enhanced bicarbonate related current activity in treated PT cells which may determine the stone-forming phenotypes (CaP or CaP/CaOx). Moreover, such alkalization promotes reactive oxygen species generation, and upregulation of calcification, inflammation, fibrosis, and apoptosis in PT cells, which were exacerbated in absence of TRPC3. Altogether, the pH-induced alteration of the Ca²⁺ signaling signature in PT cells from TRPC3 ablated mice exacerbated the pathophysiology of mixed urinary stone formation, which may aid in uncovering the downstream mechanism of CaNL.