Anion water in gypsum (CaSO4·2H2O) and hemihydrate (CaSO4·1/2H2O)

The bonding nature of water in gypsum, CaSO₄·2H₂O, and hemihydrate, CaSO₄·1/2H₂O, was suggested by characteristic absorption bands of water and sulphate ions. The infrared spectral data indicate the presence of anion water in gypsum and hemihydrate through hydrogen bonding. Negative shifting of bending vibration of SO₄ ion and lowering and broadening of the O-H stretching vibration at around 3600 cm⁻¹ indicate the presence of both anion water and hydrogen bonding in gypsum and hemihydrate     

Atom transfer radical polymerizations of methyl methacrylate catalyzed by EBiB/SnCl2·2H2O(FeCl2·4H2O)/FeCl3·6H2O/MA5-DETA systems

The ATRP of methyl methacrylate (MMA) with the system of FeCl₂·4H₂O, N,N,N′,N″,N″-penta(methyl acylate)diethylenetriamine (MA₅-DETA) and ethyl 2-bromoisobutyrate (EBiB) showed high activity and is not well-controlled. The addition of a certain amount of FeCl₃·6H₂O as the additive into the above system results in the decrease of the polymerization rate and the improvement of the controllability. When SnCl₂·2H₂O was added instead of FeCl₂·4H₂O, a novel catalyst system SnCl₂·2H₂O/FeCl₃·6H₂O/EBiB/MA₅-DETA formed shows better controllability, higher catalytic activity and higher initiating efficiencies (more than 90%) in comparison with the system FeCl₂·2H₂O/FeCl₃·6H₂O/EBiB/MA₅-DETA. The polydispersities of the polymers kept range from M_w/M_n=1.18-1.26. The real active species in the new system is Fe (II) formed from the reaction of FeCl₃·6H₂O with the active radical species produced from the reaction of SnCl₂·2H₂O with EBiB.     

Solubility of Na2SO4, Na2CO3 and their mixture in supercritical water

The solubility of many salts in water decreases dramatically with temperature in the vicinity of the critical point of pure water. Examples of these salts are sulfates of sodium, potassium, lithium and sodium carbonate. These salts are usually produced during supercritical water oxidation (SCWO) and contribute to fouling. The solubility of Na₂CO₃ and Na₂SO₄ has been determined in pure form and in the presence of each other, for the temperature range relevant to SCWO. The experimental procedure was to pass the salt solution through a tube at constant temperature. After a brief initiation period during which no salt sticks to the tube, the salt above the solubility limit deposited on the tube surface. The solution leaving the section was thus at the solubility limit. A rapid decrease in the salt solubility was observed just above the pseudo-critical temperature. For supercritical conditions, the solubility of each salt in the form of a mixture was quite close to the solubility of pure salt. At the highest fluid density considered (480 kg/m³) the presence of Na₂CO₃ reduces the solubility of Na₂SO₄, as might be expected from the “common-ion effect”.     

Removal of methyl orange dye and Na2SO4 salt from synthetic waste water using reverse osmosis

The efficiency of reverse osmosis (RO) membranes used for treatment of colored water effluents can be affected by the presence of both salt and dyes. Concentration polarization of each of the dye and the salt and the possibility of a dynamic membrane formed by the concentrated dye can affect the performance of the RO membrane. The objective of the current work was to study the effect of varying the Na₂SO₄ salt and methyl orange (MO) dye concentrations on the performance of a spiral wound polyamide membrane. The work also involved the development of a theoretical model based on the solution diffusion (SD) mass transport theory that takes into consideration a pressure dependent dynamic membrane resistance as well as both salt and dye concentration polarizations. Control tests were performed using distilled water, dye/water and salt/water feeds to determine the parameters for the model. The experimental results showed that increasing the dye concentration from 500 to 1000 ppm resulted in a decrease in the salt rejection at all of the operating pressures and for both feed salt concentrations of 5000 and 10,000 ppm. Increasing the salt concentration from 5000 to 10,000 ppm resulted in a slight decrease in the percent dye removal. The model’s results agreed well with these general trends.     

Structural transition of Friedel's salt 3CaO·Al2O3·CaCl2·10H2O studied by synchrotron powder diffraction

The structural phase transition occurring in Friedel's salt, the chlorinated compound 3CaO·Al₂O₃·CaCl₂·10H₂O (AFm phase), was studied by synchrotron and standard X-ray powder diffraction. The compound transforms at 35 °C from a rhombohedral (rh) high-temperature (HT) phase [R−3c; a=5.744(2) Å, c=46.890(3) Å] to a monoclinic (m) low-temperature (LT) phase [C2/c; a=9.960(4) Å, b=5.7320(2) Å, c=16.268(7) Å, β=104.471(2)°]. The LT and HT phases were refined with the Rietveld method from synchrotron data recorded at 20 and 40 °C. Variations of the lattice parameters as a function of temperature are reported between 8 and 48 °C. The rh→m transition is characterized by a unit cell volume expansion of 1% and a movement of the interlayer species: a shift of 0.45 Å of the Cl⁻ anions along [010]_h and a shift of 0.25 Å of the water molecules along [210]_h of the hexagonal cell. The m phase distortion is due to an ordering of the hydrogen bonds between chloride anions and H-atoms of the water molecules.     

Grass blade-like microparticle MnPO4·H2O prepared by a simple precipitation at room temperature

Grass blade-like microparticle MnPO₄·H₂O was synthesized by a simple precipitation at room temperature using a mixture of manganese sulphate monohydrate, phosphoric acid and water at pH = 7. The thermogravimetric study indicates that the synthesized compound is stable below 500 °C and its final decomposed product is Mn₂P₂O₇. The pure monoclinic phases of the synthesized MnPO₄·H₂O and its final decomposed product Mn₂P₂O₇ are verified by XRD data. FTIR spectra indicate the presences of the PO₄³⁻ ion and water molecules in the MnPO₄·H₂O structure and the P₂O₇⁴⁻ ion in the Mn₂P₂O₇ structure. The thermal stability, crystallite size, and grass blade-like microparticle of MnPO₄·H₂O in this work are different from previous reports, which may be caused by the starting reagents and reaction condition for the precipitation.     

The solubility of selenate-AFt (3CaO·Al2O3·3CaSeO4·37.5H2O) and selenate-AFm (3CaO·Al2O3·CaSeO4·xH2O)

The Se(VI)-analogues of ettringite and monosulfate, selenate-AFt (3CaO·Al₂O₃·3CaSeO₄·37.5H₂O), and selenate-AFm (3CaO·Al₂O₃·CaSeO₄·xH₂O) were synthesised and characterised by bulk chemical analysis and X-ray diffraction. Their solubility products were determined from a series of batch and resuspension experiments conducted at 25 °C. For selenate-AFt suspensions, the pH varied between 11.37 and 11.61, and a solubility product, log K_so=61.29±0.60 (I=0 M), was determined for the reaction 3CaO·Al₂O₃·3CaSeO₄·37.5H₂O+12 H⁺⇔6Ca²⁺+2Al³⁺+3SeO₄²⁻+43.5H₂O. Selenate-AFm synthesis resulted in the uptake of Na, which was leached during equilibration and resuspension. For the pH range of 11.75 to 11.90, a solubility product, log K_so=73.40±0.22 (I=0 M), was determined for the reaction 3CaO·Al₂O₃·CaSeO₄·xH₂O+12 H⁺⇔4Ca²⁺+2Al³⁺+SeO₄²⁻+(x+6)H₂O. Thermodynamic modelling suggested that both selenate-AFt and selenate-AFm are stable in the cementitious matrix; and that in a cement limited in sulfate, selenate concentration may be limited by selenate-AFm to below the millimolar range above pH 12.     

Crystal structure of Kuzel's salt 3CaO·Al2O3·1/2CaSO4·1/2CaCl2·11H2O determined by synchrotron powder diffraction

The crystal structure of Kuzel's salt has been successfully determined by synchrotron powder diffraction. It crystallizes in the rhombohedral R3? symmetry with a = 5.7508 (2) Å, c = 50.418 (3) Å, V = 1444.04 (11) ų. Joint Rietveld refinement was realized using three X-ray powder patterns recorded with a unique wavelength and three different sample-to-detector distances. Kuzel's salt is the chloro-sulfoaluminate AFm phase and belongs to the layered double hydroxide (LDH) large family. Its structure is composed of positively charged main layer [Ca₂Al(OH)₆]⁺ and negatively charged interlayer [Cl_0.50·(SO₄)_0.25·2.5H₂O]⁻. Chloride and sulfate anions are ordered into two independent crystallographic sites and fill successive interlayer leading to the formation of a second-stage compound. The two kinds of interlayer have the compositions [Cl·2H₂O]⁻ and [(SO₄)_0.5·3H₂O]⁻. The crystal structure explains why chloride and sulfate anions are not substituted and why the formation of extended solid solution in the chloro-sulfate AFm system does not occur.     

Thermodynamic modeling of CO2 solubility in aqueous solutions of NaCl and Na2SO4

A thermodynamic model based on the electrolyte NRTL activity coefficient equation and PC-SAFT equation-of-state is developed for CO₂ solubility in aqueous solutions of NaCl and Na₂SO₄ with temperature up to 473.15 K, pressure up to 150 MPa, and salt concentrations up to saturation. The Henry's constant parameters of CO₂ in H₂O and the characteristic volume parameters for CO₂ required for pressure correction of Henry's constant are identified from fitting the experimental gas solubility of CO₂ in pure water with temperature up to 473.15 K and pressure up to 150 MPa. The NRTL binary parameters for the CO₂-(Na⁺, Cl⁻) pair and the CO₂-(Na⁺, SO₄²⁻) pair are regressed against the experimental VLE data for the CO₂-NaCl-H₂O ternary system up to 373.15 K and 20 MPa and the CO₂-Na₂SO₄-H₂O ternary system up to 433.15 K and 13 MPa, respectively. Model calculations on solubility and heat of solution of CO₂ in pure water and aqueous solutions of NaCl and Na₂SO₄ are compared to the available experimental data of the CO₂-H₂O binary, CO₂-NaCl-H₂O ternary and CO₂-Na₂SO₄-H₂O ternary systems with excellent results.     

Repeated use of MgNH4PO4·6H2O residues for ammonium removal by acid dipping

A novel process was developed to repeatedly utilize MgNH₄PO₄·₆H₂O (MAP) for ammonium removal from wastewater by releasing ammonium in MAP through acid dipping. In acid solutions, ammonium can be released to solution from MAP while MAP was transformed to MgHPO₄, which can be used to remove ammonium again. Ammonium-N concentration in acid solutions increased with the decreasing pH and increasing temperature, up to 3.27× 10⁴ mg/1 at 60°C and pH 4.8. MAP also dissolved into acid solutions when transformation to MgHPO₄·N:P, indicating the ratio of MAP transformation to MAP dissolution, was maximum at pH 6.0 and increased with the temperature. N:P was up to 38.8 at 60°C and pH 6.0. Recycling experiments were done. Ammonium-N in effluents was lower than 20 mg/l in the first five cycles, which indicates the feasibility of this process. XRD spectra also validate the transformation between MAP and MgHPO₄.     

Numerical simulation of electrode process in Cu/CuSO4 + H2SO4 system

In the present work, electrode process in the system Cu/CuSO₄+H₂SO₄ is considered as a sum of two single-electron electrochemical reactions that occur simultaneously on copper electrode. Numerical modelling of this process was performed taking into account diffusion, electromigration, and chemical interactions between the components of the solution. The results of calculations do not contradict the experimental facts known for this system. The behaviour in the region close to the open circuit potential can be explained by the differences in the partial currents of the reactions proceeding on the electrode. The behaviour of the surface concentrations of the components of solution in the region of the anodic overpotential points to a substantial role of electromigration processes that can be played by them in copper passivation in sulphate solutions.     

Synthesis of FePO4·2H2O nanoplates and their usage for fabricating superior high-rate performance LiFePO4

Monoclinic phase FePO₄·2H₂O nanoplates are synthesized very easily in a waterbath and are lithiated to LiFePO₄/C nanoparticles by a simple rheological phase method. The thickness of the nanoplates can be tuned simply by changing the concentrations of the reactants. The LiFePO₄/C nanoparticles lithiated from the thin FePO₄·2H₂O nanoplates, with the sizes about 50 nm and the carbon coating layer at the surface 1–2 nm, show excellent high-rate performance and long-term cyclability as the cathode for lithium ion batteries, delivering discharge capacities of more than 150, 120, 110, 100, and 75 mAh g⁻¹ at rates of 5 C, 10 C, 15 C, 20 C and 30 C, respectively.     

Chemical Processing of CaHPO4·2H2O:

The aim of this paper is to develop a robust chemical process to synthesize Na- and K-doped brushite (DCPD: dicalcium phosphate dihydrate, CaHPO₄·2H₂O), a potential starting material for bone substitutes. The powders were synthesized by using sodium phosphate and potassium phosphate and aqueous solutions containing calcium chloride at room temperature, followed by drying at 37°C. DCPD powders thus formed were found to contain 460 ppm K and 945 ppm Na. On calcination in air, these powders readily transformed into monetite (DCPA: dicalcium phosphate anhydrous, CaHPO₄) first, and then into Ca₂P₂O₇ (calcium pyrophosphate). Na- and K-doped DCPD powders were shown to completely transform, in less than 1 week, into poorly crystalline carbonated apatite on immersion in an acellular simulated/synthetic body fluid (SBF) solution at 37°C. The Tris (i.e., tris(hydroxymethyl)aminomethane) buffered SBF solution used in this study had a carbonate ion concentration of 27 m M equal to that of human plasma. DCPD powders of this study displayed a notable apatite-inducing ability. This finding suggests the use of these DCPD powders as the starting materials for potential bone substitutes, which can be easily manufactured in aqueous solutions friendly to living tissues, at temperatures between room temperature and 37°C.     

Bulk modulus of basic sodalite, Na8[AlSiO4]6(OH)2·2H2O, a possible zeolitic precursor in coal-fly-ash-based geopolymers

Synthetic basic sodalite, Na₈[AlSiO₄]₆(OH)₂·2H₂O, cubic, P43n, (also known as hydroxysodalite hydrate) was prepared by the alkaline activation of amorphous aluminosilicate glass, obtained from the phase separation of Class F fly ash. The sample was subjected to a process similar to geopolymerization, using high concentrations of a NaOH solution at 90 °C for 24 hours. Basic sodalite was chosen as a representative analogue of the zeolite precursor existing in Na-based Class F fly ash geopolymers. To determine its bulk modulus, high-pressure synchrotron X-ray powder diffraction was applied using a diamond anvil cell (DAC) up to a pressure of 4.5 GPa. A curve-fit with a truncated third-order Birch–Murnaghan equation of state with a fixed K'_o = 4 to pressure-normalized volume data yielded the isothermal bulk modulus, K_o = 43 ± 4 GPa, indicating that basic sodalite is more compressible than sodalite, possibly due to a difference in interactions between the framework host and the guest molecules.     

Resurrection of dead lacquer—Cupric potassium chloride dihydrate (K2CuCl4·2H2O) used as the mimic laccase

Oriental lacquer collected from lacquer trees is widely used as surface coatings for centuries. The lacquer with little activity of laccase is called dead lacquer vividly which cannot be cured automatically. In this study, the cheap copper chloride dihydrate (K₂CuCl₄·2H₂O) was used as a novel catalyst to cure the dead lacquer at room temperature. The redox property of K₂CuCl₄·2H₂O was studied by cyclic voltammetry. The process of oxidative polymerization of urushiol was confirmed by FT-IR, ¹H NMR, UV–vis, and electron spin-resonance spectroscopy. At 75% relative humidity, the dead lacquer film with the gloss of 101.0% and hardness of 0.84 (glass value) could be obtained when the K₂CuCl₄·2H₂O content was 0.6 wt%. The results of the thermal properties and the chemical resistance tests showed that the dead lacquer film catalyzed by K₂CuCl₄·2H₂O had better thermal stability and chemical resistance than those of the raw lacquer film catalyzed by laccase.     

Hydrothermal synthesis and characterizations of 2D and 3D 4ZnO·B2O3·H2O nano/microstructures with different morphologies

2D and 3D nano/microstructures of 4ZnO·B₂O₃·H₂O with different morphologies have been successfully synthesized by a hydrothermal route in the presence of surfactant polyethylene glycol-300 (PEG-300). Lamellar-like nanoparticles and microsphere organizations of nano and microrods are fabricated by varying the reaction conditions. The products have been characterized by XRD, FT-IR, TG-DTA and SEM. The XRD data indicate the as-prepared samples present at pure phase 4ZnO·B₂O₃·H₂O with monoclinic symmetry. The SEM results reveal that the lamellar-like particles are about 30 nm in thickness and around several hundred nanometers in diameter. The microsphere organizations have different diameters, and the secondary structures are made from rod-like particles with different size and mode, respectively. The morphologies of products strongly depend on surfactant, hydrothermal temperature and time.     

Resistance of sodium polyphosphate-modified fly ash/calcium aluminate blend cements to hot H2SO4 solution

Sodium polyphosphate-modified Class F fly ash/calcium aluminate blend (SFCB) cements were prepared at room temperature and their resistance to hot acid erosion was evaluated by submerging them in H₂SO₄ solution (pH 1.6) at 90°C. Sodium polyphosphate preferentially reacted with calcium aluminate cement (CAC) to form amorphous Ca(HPO₄).xH₂O and Al₂O₃.xH₂O gel, rather than fly ash. These amorphous reaction products, which bound the partially reacted and unreacted CAC and fly ash particles into a coherent mass, were responsible for strengthening and densifying the SFCB specimens at room temperature, playing an essential role in mitigating their acid erosion. In these cements, the extent of acid erosion depended primarily on the ratio of fly ash/CAC; namely, those with a higher ratio underwent a severe erosion. This effect was due to the formation of a porous structure, which allowed acid to permeate the cement easily, diminishing the protective activity of Ca(HPO₄).xH₂O and Al₂O₃.xH₂O gel against H₂SO₄.     

Controllable synthesis and flame retardant properties of bunch-, chrysanthemum-, and plumy-like 4ZnO·B2O3·H2O nanostructures

Three kinds of new 4ZnO·B₂O₃·H₂O nanostructures of bunch-, chrysanthemum-, and plumy-like morphologies have been synthesized under hydrothermal conditions at 140 °C in the presence of ethanol. The as-synthesized products were characterized by the chemical analysis, TG, XRD, FT-IR, SEM and TEM. All the synthesized 4ZnO·B₂O₃·H₂O nanostructures consist of nanoribbons. A series of control experiments confirmed that the morphologies of the products were influenced by the reaction time, temperature, and the presence of the surfactant of PEG-300. Furthermore, the flame retardant properties of the synthesized 4ZnO·B₂O₃·H₂O nanostructures were investigated by the thermal analysis method, demonstrating that they had the better behaviors than the non-nanostructure sample.     

Synthesis of an industrially important zinc borate, 2ZnO·3B2O3·3H2O, by a rheological phase reaction method

2ZnO·3B₂O₃·3H₂O is an industrially important zinc borate. Herein, 2ZnO·3B₂O₃·3H₂O has been prepared via a rheological phase reaction method using zinc oxide and boric acid as starting materials. This route is facile and acceptable for green chemical synthesis, producing no pollution and giving a yield of near 100% of theoretical value. And in this method, the complete conversion of the starting materials can be achieved in the presence of only 0.04 mL water (one drop of water). The products have been characterized by X-ray powder diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA), scanning electron microscopy (SEM) and particle size distribution. The effects of experimental conditions on the products were investigated. The main factors that affect the formation of zinc borate are water volume, sealing state, reaction time and temperature.     

Medium-term phase stability of Na2O–Al2O3–SiO2–H2O geopolymer systems

The phase evolution and microstructural development of a series of geopolymer mixtures comprising SiO₂, Al₂O₃, Na₂O and H₂O prepared by alkali reaction of metakaolin, have been studied. The study also included the effects of cure duration and its impact on physical properties such as compressive strength. The characteristic molar ratios of the geopolymer mixtures were of the range SiO₂/Al₂O₃ [2.50–5.01] and Al₂O₃/Na₂O [0.60–1.70], respectively. The formulations were subjected to continuous curing at 40 °C for 7 months, and were analyzed periodically by XRD and SEM techniques.

Amorphous Na–Al–Si phase(s), observed at early ages, gradually transformed to crystalline phase(s) with prolonged curing. The initial SiO₂, Na₂O, and Al₂O₃ contents of mixtures appeared to be critical factors governing the observed amorphous → crystalline transformation. Well-developed crystalline zeolitic phases, including chabazite, faujasite, zeolite A and zeolite P, were identified in some of the mixtures investigated. In most cases, with prolonged curing, some correlation emerged relating compressive strength development with corresponding phase changes. In essence, the mixture formulations that developed crystalline phases after prolonged curing tended to produce low strengths. The relevance of these findings on the phase development of mild- to warm-temperature prolonged curing of geopolymer systems is discussed.