Both initial concentrations of Fe(II) and monovalent cations jointly determine the formation of biogenic iron hydroxysulfate precipitates in acidic sulfate-rich environments

In order to accurately predict the types of biogenic iron hydroxysulfate precipitates in acidic, sulfate-rich environments facilitated by Acidithiobacillus ferrooxidans, different initial concentrations of Fe^2 +, K⁺, Na⁺, and NH₄⁺ are selected and tested in batch experiments for the formation of the precipitates. The critical equations of jarosite formation in FeSO₄–K₂SO₄–H₂O system or FeSO₄–(NH₄)₂SO₄–H₂O system could be described as Y = ? 22120.8077 ? 0.04257x + 0.006170x² (R² = 0.9979) or Y = 0.03540 ? 0.002950x + 7.407E ? 5x² (R² = 0.9934), respectively, where Y is the threshold or critical values of the molar ratio of Fe/K or Fe/NH₄ for jarosite formation, and x (mmol/L) is the initial concentration of Fe(II). Schwertmannite is the sole biogenic secondary ferric mineral when molar ratio of Fe/K or Fe/NH₄ is higher than Y in the system with a given initial Fe(II) concentration. The precipitates are an admixture of schwertmannite and jarosite, or pure jarosite when the Fe/M molar ratio is lower than Y. The crystallinity of the secondary ferric minerals increased with the increase of initial Fe(II) concentration in the medium with a fixed K⁺ concentration. It is observed that the capacity of monovalent cation in promoting jarosite formation is K⁺ > NH₄⁺ > Na⁺, as exhibiting that the capacity of K⁺ in this process is about 75 and 200 times greater than NH₄⁺ and Na⁺, respectively. Obviously, both the initial concentration of Fe(II) and molar ratio of Fe to monovalent cation determine the types of biogenic iron hydroxysulfate precipitates.     

Improved optical photoluminescence by charge compensation in the phosphor system CaMoO4:Eu3+

It has been found that charge compensated CaMoO₄:Eu³⁺ phosphors show greatly enhanced red emission under 393 and 467 nm-excitation, compared with CaMoO₄:Eu³⁺ without charge compensation. Two approaches to charge compensation, (a) 2Ca²⁺ → Eu³⁺ + M⁺, where M⁺ is a monovalent cation like Li⁺, Na⁺ and K⁺ acting as a charge compensator; (b) 3Ca²⁺ → 2Eu³⁺ + vacancy, are investigated. The influence of sintering temperature and Eu³⁺ concentration on the luminescent property of phosphor samples is also discussed.     

X-ray powder diffraction,vibration and thermal studies of [A0.92(NH4)0.08]2TeCl4Br2 with A = Cs,Rb: Influence of mixed cationic and anionic substitutions

The crystal structures of [A_0.92(NH₄)_0.08]₂TeCl₄Br₂ with A = Cs, Rb have been determined using X-ray powder diffraction techniques. The two compounds crystallize in the tetragonal space group P4/mnc, with the unit cell parameters: a = 7.452(1) Å, c = 10.544(3) Å, Z = 2 and a = 7.315(2) Å, c = 10.354(4) Å, Z = 2 in the presence of Cs and Rb, respectively. These two compounds have an antifluorite-type arrangement of NH₄⁺/Rb⁺/Cs⁺ and octahedral TeCl₄Br₂^2? anions. The stability of these structure is by ionic and hydrogen bonding contacts: A?Cl, A?Br and N–H?Cl, N–H?Br. The different vibrational modes of these powders were analysed by FTIR and Raman spectroscopic studies. A DTA/TGA experiment reveals one endothermic peak at 780 K implicating the decomposition of the sample. At low temperature, one endothermic peak in thermal behavior is detected at around 213 K by DSC experiment. This transition was confirmed by dielectric measurements.     

Investigation of La3 + Doped Yb2Sn2O7 as new thermal barrier materials

Low thermal conductivity is one of the key requirements for thermal barrier coating materials. From the consideration of crystal structure and ion radius, La^3 + Doped Yb₂Sn₂O₇ ceramics with pyrochlore crystal structures were synthesized by sol–gel method as candidates of thermal barrier materials in aero-engines. As La^3 + and Yb^3 + ions have the largest radius difference in lanthanoid group, La^3 + ions were expected to produce significant disorders by replacing Yb^3 + ions in cation layers of Yb₂Sn₂O₇. Both experimental and computational phase analyses were carried out, and good agreement had been obtained. The lattice constants of solid solution (La_xYb_1 − x)₂Sn₂O₇ (x = 0.3, 0.5, 0.7) increased linearly when the content of La^3 + was increased. The thermal properties (thermal conductivity and coefficients of thermal expansion) of the synthesized materials had been compared with traditional 8 wt.% yttria stabilized zirconia (8YSZ) and La₂Zr₂O₇ (LZ). It was found that La^3 + Doped Yb₂Sn₂O₇ exhibited lower thermal conductivities than un-doped stannates. Amongst all compositions studied, (La_0.5Yb_0.5)₂Sn₂O₇ exhibited the lowest thermal conductivity (0.851 W·m^− 1·K^− 1 at room temperature), which was much lower than that of 8YSZ (1.353 W·m^− 1·K^− 1), and possessed a high coefficient of thermal expansion (CTE), 13.530 × 10^− 6 K^− 1 at 950 °C.     

Spectroscopic investigations on Eu3+ ions in Li–K–Zn fluorotellurite glasses

Eu³⁺ ions incorporated Li–K–Zn fluorotellurite glasses, (70 − x)TeO₂ + 10Li₂O + 10K₂O + 10ZnF₂ + xEu₂O₃, (0 ⩽ x ⩽ 2 mol%) were prepared via melt quenching technique. Optical absorption from ⁷F₀ and ⁷F₁ levels of the Eu³⁺-doped glass has been studied to examine the covalent bonding characteristics, energy band gap and Judd–Ofelt intensity parameters. The emission spectra (⁵D₀ → ⁷F_0,1,2,3,4) of the glasses were used to estimate the luminescence enhancement, asymmetric environment in the vicinity of Eu³⁺ ions, stimulated emission cross section and branching ratios. The phonon side band mechanism of ⁵D₂ level of the Eu³⁺ ions in the prepared glass was examined by considering the excitation and Raman spectra. The radiative lifetime calculated using Judd–Ofelt parameters was compared with the experimental lifetime to estimate the quantum efficiency of ⁵D₀ level of Eu³⁺ ions in Li–K–Zn fluorotellurite glass.     

Synthesis and crystal structure of tetramethylammonium fluoride octadecasil

Octadecasil, a clathrate-type inclusion compound, has been synthesized hydrothermally at 453 K with a gel having the composition 1.0SiO₂:0.53tetramethylammonium (TMA⁺):0.54fluoride:86H₂O. The crystal structure has been determined based on powder X-ray diffraction data taken at 298 K, and has been refined using Rietveld method. The result confirms the AST-type, all-silica framework model developed by Caullet et al. [P. Caullet, J.L. Guth, J. Hazm, J.M. Lamblin, H. Gies, Eur. J. Solid State Inorg. Chem. 28 (1991) 345]. Furthermore, by using a rigid body model the position and orientation of the occluded TMA⁺ cation in the rhombododecahedral [4⁶6¹²] cage can be determined; F⁻ anion has been located in the hexahedral [4⁶] cage. The unit cell parameters, in the tetragonal space group I4/m, have been refined as: a = b = 9.07 Å, c = 13.44 Å, cell volume = 1104.97 Å³. The refined unit cell composition is |[N(CH₃)₄⁺]_2.0F⁻_1.9|[Si₂₀O₄₀], i.e., both TMA⁺ and F⁻ ions possess near full occupancies, and compensate each other's electronic charges. The crystallization of the AST framework structure is the result of a cooperative structure-directing effect of both ions.     

Fabrication of (Ca + Yb)- and (Ca + Sr)-stabilized α-SiAlON by combustion synthesis

In this paper, (Ca + Yb)- and (Ca + Sr)-stabilized α-SiAlON powders were fabricated by combustion synthesis. The influence of Ca²⁺ incorporation on the phase composition and grain morphology of combustion products was discussed. The experimental results showed that with the incorporation of Ca²⁺ well-developed rod-like (Ca + Yb) α-SiAlON crystals could be produced. It was also found that, when only Sr²⁺ was used as stabilizing cation, the reaction product was (α + β)-SiAlON composite, in which β-SiAlON was the predominant phase and the relative content of α-SiAlON was low. With the incorporation of Ca²⁺, however, both the relative content and the lattice parameters of α-SiAlON were clearly increased. These results indicated that the incorporation of Ca²⁺ could assist Sr²⁺ into the α-SiAlON lattice structure.     

Calcium metal to synthesize amorphous or cryptocrystalline calcium phosphates

Metallic calcium was never used before as the calcium source in synthesizing bioceramics. Amorphous calcium phosphate (ACP) powders were synthesized at room temperature, in synthetic mineralization solutions which contained Na⁺, K⁺, Mg^2 +, Cl^?, HCO₃^? and HPO₄^2 ? ions at concentrations similar to those found in human blood plasma, by using calcium (Ca) metal as the only calcium source. The experimental conditions leading to the formation of PCA (cryptocrystalline or poorly crystallized apatite) or CaCO₃ powders were also determined when using metallic Ca in aqueous synthesis in the mineralization solutions. The formation of calcium phosphate (CaP) in synthesis solutions was immediately initiated by the addition of calcium metal granules (or shots), at appropriate amounts, into the solutions while the solutions were being continuously stirred in glass bottles at room temperature (22 ± 1 °C). The synthesis reactions were reaching completion in less than 30 min with the final solution pH values ranging from 9 to 12, without a necessity for any external pH adjustment in the form of any strong base (such as NH₄OH, LiOH, NaOH or KOH) additions. ACP or PCA powders are useful for dentin and enamel re-mineralization applications or orthopedic (bone) defect-filling applications.     

Impact of Nd3+ ions on physical and optical properties of Lithium Magnesium Borate glass

Enhancing the up-conversion efficiency of borate glass via optimized doping of rare earth ions is an ever-ending quest in lasing glass. Neodymium (Nd³⁺) doped Lithium Magnesium Borate (LMB) glasses are prepared using the melt-quenching method. X-ray diffraction (XRD), Fourier transformed infrared (FTIR), UV–Vis–NIR absorption and Photoluminescence (PL) spectroscopic characterizations are made to examine the influence of Nd³⁺ concentration on physical properties and optical properties. Nd³⁺ contents dependent density, molar volume, refractive index, ion concentration, Polaron radius, inter nuclear distance, field strength, energy band gap and oscillator strength are calculated. XRD patterns confirm the amorphous nature of all glasses and the FTIR spectra reveal the presence of BO₃ and BO₄ functional groups. UV–Vis–IR spectra exhibit ten prominent bands centered at 871, 799, 741, 677, 625, 580, 522, 468, 426, 349 nm corresponding to the transitions from the ground state to ⁴F_3/2, (⁴F_5/2 + ²H_9/2), (⁴F_7/2 + ⁴S_3/2), ⁴F_9/2, ²H_11/2, (⁴G_5/2 + ²G_7/2), (²K_13/2 + ⁴G_7/2 + ⁴G_9/2), (²G_9/2 + ²D_3/2 + ²P_3/2), (²P_1/2 + ²D_5/2), (⁴D_3/2 + ⁴D_5/2) excited states, respectively. A hyper-sensitive transition related to (⁴G_5/2 + ²G_7/2) level is evidenced at 580 nm. The room temperature up-conversion emission spectra at 800 nm excitation displays three peaks centered at 660, 610 and 540 nm. Glass with 0.5 mol% of Nd³⁺ showing an emission enhancement by a factor to two is attributed to the energy transfer between Mg²⁺ and Nd³⁺ ions. Our results suggest that these glasses can be nominated for solid state lasers and other photonic devices.     

Synthesis and characterization of a new p-phenylenediammonium dihydrogenmonophosphate [p-NH3C6H4NH3][H2PO4]2

Chemical preparation, crystal structure and NMR spectroscopy of a new organic cation p-phenylenediammonium monophosphate [p-NH₃C₆H₄NH₃][H₂PO₄]₂ are presented. This new compound crystallizes in the orthorhombic system, with the space group Pnma and the following parameters: a = 7.970 (2) Å; b = 22.770 (7) Å; c = 7.000 (7) Å, V = 1270.3 (11) Å³, Z = 4 and D_x = 1.590 g cm⁻³. The crystal structure has been determined and refined to R = 0.043 and R_(w) = 0.057 using 2623 independent reflections. The structural arrangement can be described as inorganic layers of (H₈P₄O₁₆)⁴⁻ units, parallel to (a, c) planes. The organic groups (p-H₃NC₆H₄NH₃)²⁺are anchored between the phosphoric layers to form a three-dimensional infinite network. This compound is also investigated by IR and solid-state ¹H, ¹³C and ³¹P MAS NMR spectroscopies. The ab initio method is used in the calculation of chemical shifts.     

Facile synthesis of cubic fluorite nano-Ce1−xZrxO2 via hydrothermal crystallization method

Nano-Ce_1?xZr_xO₂ (x = 0.15, 0.25, 0.5) were synthesized via co-precipitation using NH₄OH as precipitant and hydrothermal crystallization. The XRD results confirmed that the cubic fluorite nano-Ce_1?xZr_xO₂ can form in NH₄OH solution (pH > 10) at 150 °C for 12 h, and well crystallized 20–50 nm nano-Ce_1?xZr_xO₂ were obtained at 200 °C for 22 h. The crystal growth of Ce_1?xZr_xO₂ was suppressed under higher OH^? concentration and crystallite size decreased with increasing concentration of NH₄OH. Ce3d XP spectra showed that the main valence state of the cerium on Ce_1?xZr_xO₂ surface is +4, and substituting Ce⁴⁺ with Zr⁴⁺ has no obvious influence on Ce³⁺/Ce⁴⁺ ratio.     

Selective recognition of Pr3 + based on fluorescence enhancement sensor

(E)-2-(1-(4-hydroxy-2-oxo-2H-chromen-3-yl)ethylidene)hydrazinecarbothioamide (L) has been used to detect trace amounts of praseodymium ion in acetonitrile–water solution (MeCN/H₂O) by fluorescence spectroscopy. The fluorescent probe undergoes fluorescent emission intensity enhancement upon binding to Pr^3 + ions in MeCN/H₂O (9/1:v/v) solution. The fluorescence enhancement of L is attributed to a 1:1 complex formation between L and Pr^3 +, which has been utilized as the basis for selective detection of Pr^3 +. The sensor can be applied to the quantification of praseodymium ion with a linear range of 1.6 × 10^? 7 to 1.0 × 10^? 5 M. The limit of detection was 8.3 × 10^? 8 M. The sensor exhibits high selectivity toward praseodymium ions in comparison with common metal ions. The proposed fluorescent sensor was successfully used for determination of Pr^3 + in water samples.     

Characterization of chemically treated titanium using soft X-ray fluorescence

High energy resolution soft X-ray fluorescence measurements of commercially pure (cp-Ti) and chemically treated Ti (Ti + HCl and Ti + HCl + NaOH) are presented. They show the formation of thick hydrogen-(TiH₂) and oxygen-passivated (TiO₂) layers on Ti + HCl and Ti + HCl + NaOH, respectively; it is shown that the oxygen-passivated layer has primarily anatase structure. A bone-like carbonated apatite layer is found to be formed on the surface of chemically treated Ti after exposure to simulated body fluid (SBF). The spectroscopic results indicate that (CO₃)^2? substitutes both OH^? (type A substitution) and (PO₄)^3? (type B substitution) sites in the apatite structure.     

Multicolor-emitting Ca3 -x-ySry(PO4)2:xEu2 + (0 ≤ x ≤ 0.075, 0 ≤ y ≤ 2.2) phosphors for light-emitting diodes

In this paper, a series of Ca_3 -x-ySr_y(PO₄)₂:xEu^2 +, (0 ≤ x ≤ 0.075, 0 ≤ y ≤ 2.2) phosphors were prepared by flux assisted solid-state reaction method, and their photoluminescence properties were investigated. The β- to β′-phase transition of Ca_3 -ySr_y(PO₄)₂ for high Sr^2 + content was observed from the XRD patterns, and the corresponding optical bandgaps were obtained experimentally. Various Eu^2 + emission centers were found, which generate tunable emission depending on the Sr^2 + concentration. Broad and intense excitation bands exist in Eu^2 + activated Ca₃(PO₄)₂, and the introduction of Sr^2 + further extends and enhances the excitation bands beyond 350 nm, which is beneficial to the applications on near ultraviolet LEDs. The morphology measurement reveals that the average size of particles with smooth surface is about 11.2 μm, which is suitable for the practical applications. These results indicate that the Ca_3 -x-ySr_y(PO₄)₂:xEu^2 + phosphors could be promising candidates for LEDs.     

Fluorescence spectroscopy of Er3+:LaOBr prepared by NH4Br solid state reaction

The steady luminescent materials La_1−xEr_xOBr (x = 0, 0.0003, 0.01) were synthesized by a new NH₄Br solid state reaction, and the structures were studied using XRD and Raman methods. Under 514.5 nm Ar⁺ laser excitation, the upconversion fluorescence spectra in LaOBr:Er³⁺ were recorded and investigated. It was found that four upconverted emission bands with peaks at 388 nm, 399 nm, 405 nm (violet) and 477 nm (blue) were observed. All these upconverted emissions were assigned, and the upconversion mechanism was deduced to be excited state absorption (ESA), by analyzing the energy level structures of Er³⁺ ions and measuring the power dependence of upconverted emission intensities.     

High work-hardening effect of the pure NiAl intermetallic compound fabricated by the combustion synthesis and hot pressing technique

The pure NiAl intermetallic compound was fabricated by the combustion synthesis and hot pressing technique. Microstructure examination showed that the NiAl intermetallic compound contained fine grains. Analysis of the X-ray diffraction and the HRTEM studies showed that the phase in the intermetallics was the only NiAl phase. The NiAl showed prominent compression properties. The true ultimate compression strength and the fracture strain of the NiAl are 1002_? 94^+ 72 MPa and 21.6_? 1.8^+ 1.8%, respectively. The work-hardening capacity (H_c) is 1.40_? 0.07^+ 0.09 and the Vickers micro-hardness is 360_? 19^+ 15 HV. The finer grains, the high density dislocation and the seriously distorted lattices in the matrix, and the intense interactions between dislocations contribute to the prominent compression properties.     

Microstructure and photoluminescent properties of Sr2SiO4:Eu3+ phosphors with various NH4Cl flux concentrations

In this paper, effect of NH₄Cl flux concentrations (0, 1, 2, 3 and 4 wt%) on the crystal structure, morphology and photoluminescent properties of Sr₂SiO₄:Eu³⁺ phosphors synthesized by a microwave sintering at 1200 °C for 1 h was investigated and discussed. X-ray powder diffraction analysis showed the crystal structure was not affected and the pure Sr₂SiO₄ phase was formed without second phase or phases of starting materials when adding with the NH₄Cl flux. The SEM images indicated that increase of the NH₄Cl flux enlarged the particle size of the phosphor particles. The photo-luminescence results showed the addition of 1 wt% NH₄Cl flux much improved the emission intensity at λ_em of 617 nm as the excitation spectrum at λ_ex of 395 nm. The decay times of Sr₂SiO₄:Eu³⁺ phosphors with different NH₄Cl flux concentrations were obtained around 2.47–2.52 ms.     

Biomimetic mineralization of calcium phosphate crystals in polyacrylamide hydrogel: Effect of concentrations of calcium and phosphate ions on crystalline phases and morphology

Calcium phosphate crystals were synthesized in polyacrylamide (PAAm) hydrogel, and the effects of the concentrations of calcium and phosphate ions on the crystalline phases and morphology were investigated. PAAm hydrogels containing diammonium hydrogen phosphate ((NH₄)₂HPO₄) were transformed into calcified materials by diffusion of calcium ions from calcium nitrate (Ca(NO₃)₂) aqueous solution into the gels. Several kinds of calcium phosphate crystals were precipitated at various Ca(NO₃)₂ concentrations (0.5–4.0 mol·dm^? 3), or (NH₄)₂HPO₄ contents (3.6–21.6 mmol) in the gels. The crystalline phases were mainly determined by the (NH₄)₂HPO₄ content in the gels. When the (NH₄)₂HPO₄ content was ≥ 10.8 mmol, hydroxyapatite (HAp) formed near the interfaces between Ca(NO₃)₂ solution and the gels, whereas octacalcium phosphate (OCP) formed in gels with ≤ 10.8 mmol (NH₄)₂HPO₄. HAp crystals were granular in form and about 200 nm in diameter, and OCP crystals were spherulitic with diameter 10–70 μm.     

Li doping effects on the upconversion luminescence of Yb3+/Er3+-doped ABO4 (A = Ca,Sr; B = W,Mo) phosphors

ABO₄ (A = Ca, Sr; B = W, Mo):Er³⁺/Yb³⁺/Li⁺ phosphors tri-doped with different concentrations of Li⁺ ion ranging from 0 to 22.5 mol% were prepared by using a solid-state reaction method. And their upconversion (UC) luminescence properties were in estimated under a 975 nm laser-diode excitation. The four kinds of phosphors (CaWO₄, CaMoO₄, SrWO₄, and SrMoO₄) tri-doped with Er³⁺, Yb³⁺ and Li⁺ ions showed strong green UC emission peaks at 530 nm and 550 nm and weak red UC emission. The intensity of green UC emission of Li⁺ doped samples was several higher than that of Li⁺ un-doped samples due to the reduction of lattice constant and the local crystal field distortion around rare-earth ions. The optimum doping concentration of Li⁺ ions was investigated and the effects of Li⁺ concentration for UC emission intensity were studied in detail.