Physicochemical simulation of fusion processes of basalt and diabase with Na<Subscript>2</Subscript>CO<Subscript>3</Subscript> and Na<Subscript>2</Subscript>CO<Subscript>3</Subscript> + CaO

Fusion processes of basalt and diabase with sodium carbonate and its mixture with calcium oxide are investigated by methods of physicochemical simulation. Equilibrium compositions of the Si-Al-Fe-Ca-Mg-Na system are calculated at various ratios Na₂CO₃: basalt (diabase) and (Na₂CO₃ + CaO): basalt (diabase) in the temperature range of 1270–1470 K. It is shown that, on fusion with sodium carbonate, depending on conditions, the main components of fusion products are sodium metasilicate (Na₂SiO₃) and sodium metaaluminate (NaAlO₂), magnesium orthosilicate (CaMgSiO₄), sodium ferrite(III) (NaFeO₂), iron(III) oxide (Fe₂O₃), and sodium-aluminum orthosilicate (Na₂AlSiO₄). On fusion with the mixture of sodium carbonate and calcium oxide, respectively, the products are sodium metaaluminate, calcium pyrosilicate (Ca₃Si₂O₇), calcium-magnesium orthosilicate, and calcium ferrite (CaFe₂O₄).     

Low temperature fabrication of spherical brushite granules by cement paste emulsion

Secondary protonated calcium phosphates such as brushite (CaHPO₄·2H₂O) or monetite (CaHPO₄) have a higher resorption potential in bone defects than sintered ceramics, e.g. tricalcium phosphate or hydroxyapatite. However, processing of these phosphates to monolithic blocks or granules is not possible by sintering due to thermal decomposition of protonated phosphates at higher temperatures. In this study a low temperature technique for the preparation of spherical brushite granules in a cement setting reaction is presented. These granules were synthesized by dispersing a calcium phosphate cement paste composed of β-tricalcium phosphate and monocalcium phosphate together with a surfactant to an oil/water emulsion. The reaction products were characterized regarding their size distribution, morphology, and phase composition. Clinically relevant granule sizes ranging from 200?μm to 1?mm were obtained, whereas generally smaller granules were received with higher oil viscosity, increasing temperature or higher powder to liquid ratios of the cement paste. The hardened granules were microporous with a specific surface area of 0.7?m²/g and consisted of plate-like brushite (>95?% according to XRD) crystals of 0.5–7?μm size. Furthermore it was shown that the granules may be also used for drug delivery applications. This was demonstrated by adsorption of vancomycin from an aqueous solution, where a load of 1.45–1.88?mg drug per g granules and an almost complete release within 2?h was obtained.     

High-temperature crystal chemistry of Na<Subscript>6</Subscript>(UO<Subscript>2</Subscript>)<Subscript>2</Subscript>O(MoO<Subscript>4</Subscript>)<Subscript>4</Subscript>

Thermal deformations of Na₆(UO₂)₂O(MoO₄)₄ were studied by high-temperature powder X-ray diffraction. The compound crystallizes in the triclinic system, space group Р\(\bar 1\), a = 7.636(7), b = 8.163(6), c = 8.746(4) Å, α = 72.32(9)°, β = 79.36(4)°, γ = 65.79(5)°, V = 472.74(4) ų. It is stable in the temperature interval 20–700°С. The thermal expansion coefficients (TECs) are α₁₁ = 25.5 × 10^–6, α₂₂ = 7.8 × 10^–6, and α₃₃ = 1.1 × 10^–6 (°C)^–1. The orientation of the TEC pattern relative to the crystallographic axes is a₃₃^Z = 45°, a₃₃^X = 122°, a₂₂^Z = 59°, and a₂₂^X = 66°. The anisotropy of the thermal expansion is due to specific features of the crystal structure of the compound.     

High performance films obtained from PVA/Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>/H<Subscript>2</Subscript>O and PVA/CH<Subscript>3</Subscript>COONa/H<Subscript>2</Subscript>O systems

The atactic poly(vinyl alcohol) (a-PVA) aqueous solutions with Na₂SO₄ or CH₃COONa were cast to prepare films and then the Na₂SO₄ or CH₃COONa in the films was removed. Both films prepared by removing Na₂SO₄ or CH₃COONa in water had a water-resistance property. The degree of crystallization of the films increased with an increase of the contents of Na₂SO₄ and CH₃COONa in the solutions up to 0.05 and 0.1 wt%, respectively. However, the melting temperature (226–228°C) was independent of the content of Na₂SO₄ and CH₃COONa in the solutions. The draw ratio and tensile modulus of the films prepared from the solutions with 0.01 wt% Na₂SO₄ and 0.1 wt% CH₃COONa were 1.3–1.6 times more than that of the films obtained from an aqueous solution. Namely, in case of the films obtained from a-PVA/H₂O/Na₂SO₄ and a-PVA/H₂O/CH₃COONa systems, both the drawability and mechanical properties as well as the degree of crystallization were higher than those for the film obtained from an aqueous a-PVA solution.     

Thermochemistry of sodium uranomolybdates formed in the system Na<Subscript>2</Subscript>O-UO<Subscript>3</Subscript>-MoO<Subscript>3</Subscript>

Sodium uranomolybdates Na₂U₃Mo₉O₃₇, Na₄U₃Mo₂O₁₇, Na₂U₃Mo₄O₂₂, Na₆UMo₄O₁₈, and Na₆U₂Mo₄O₂₁ were synthesized and studied by reaction calorimetry. The enthalpies of their formation were calculated from the calorimetric data.     

Crystallization from high-temperature solutions in the Na<Subscript>2</Subscript>O-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript>-M<Superscript>VI</Superscript>O<Subscript>3</Subscript> (M = Mo,W) systems

We have studied the crystallization behavior of Na₂O-NaPO₃-M^VIO₃(M^VI = Mo, W) high-temperature solutions containing 15 mol % Bi₂O₃ in the pseudoquaternary systems Na₂O-Bi₂O₃-P₂O₅-M^VIO₃ and have established the conditions for the formation of Na₃Bi(PO₄)₂, high-temperature BiPO₄, NaBi(MoO₄)₂, Bi₂WO₆, and NaMoO₂PO₄. The compounds identified have been characterized by powder x-ray diffraction and IR spectroscopy.     

Growth and properties of LiCu<Subscript>2</Subscript>O<Subscript>2</Subscript>-NaCu<Subscript>2</Subscript>O<Subscript>2</Subscript> crystals

Platelike Li_{1 ? x} Na _x Cu₂O₂ single crystals up to 2 × 10 × 10 mm in dimensions have been grown by slowly cooling (1 ? x)Li₂CO₃·xNa₂O₂·4CuO melts in alundum crucibles in air. Li_{1 ? x} Na _x Cu₂O₂ solid solutions in the LiCu₂O₂-NaCu₂O₂ system have been shown to exist in the composition range 0.78 < x < 1. The temperature stability ranges of NaCu₂O₂ and LiCu₂O₂ are 780–930 and 890–1050°C, respectively. The Mössbauer spectra and electrical conductivity of the crystals have been measured.     

Giant dielectric and electrical properties of sodium yttrium copper titanate: Na<Subscript>1/2</Subscript>Y<Subscript>1/2</Subscript>Cu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript>

The electrical properties and dielectric response in Na_1/2Y_1/2Cu₃Ti₄O₁₂ ceramic prepared by conventional solid-state reaction method and sintered at 1,090 °C for 5 h were investigated as functions of frequency and temperature. Main phase of Na_1/2Y_1/2Cu₃Ti₄O₁₂ with CaCu₃Ti₄O₁₂-like crystallographic structure and CuO secondary phase were observed in the X-ray diffraction pattern. Abnormal grain growth was observed just as observed in CaCu₃Ti₄O₁₂ ceramics. The Na_1/2Y_1/2Cu₃Ti₄O₁₂ ceramic exhibits a high ε′ of ~2.04 × 10⁴ at 20 °C and 1 kHz and low tan δ (with the minimum 0.080 at 5 kHz). Impedance spectroscopy analysis reveals that Na_1/2Y_1/2Cu₃Ti₄O₁₂ ceramic is electrically heterogeneous, consisting of semiconducting grains and insulating grain boundaries. Giant ε′ response in Na_1/2Y_1/2Cu₃Ti₄O₁₂ ceramic is therefore attributed to an internal barrier layer capacitor effect.     

Dielectric and piezoelectric properties of MnO<Subscript>2</Subscript>-doped K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>Nb<Subscript>0.92</Subscript>Sb<Subscript>0.08</Subscript>O<Subscript>3</Subscript> lead-free ceramics

Lead-free MnO₂-doped K_0.5Na_0.5Nb_0.92Sb_0.08O₃ ceramics have been fabricated by a conventional ceramic technique and their dielectric and piezoelectric properties have been studied. Our results show that a small amount of MnO₂ (0.5–1.0 mol%) is enough to improve the densification of the ceramics and decrease the sintering temperature of the ceramics. The co-effects of MnO₂ doping and Sb-substitution lead to significant improvements in the ferroelectric and piezoelectric properties. The K_0.5Na_0.5Nb_0.92Sb_0.08O₃ ceramic with 0.5 mol%MnO₂ doping possesses optimum propeties: d ₃₃ = 187 pC/N, k _P = 47.2%, ε _r = 980, tanδ = 2.71% and T _c = 287 °C. Due to high tetragonal-orthorhombic phase transition temperature (T _O-T ~ 150 °C), the K_0.5Na_0.5Nb_0.92Sb_0.08O₃ ceramic with 0.5 mol%MnO₂ doping exhibits a good thermal stability of piezoelectric properties.     

Spectral diagnostics of vapor composition over molten Na<Subscript>2</Subscript>WO<Subscript>4</Subscript> and Na<Subscript>2</Subscript>O-BaO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The high-temperature Raman spectra recording technique was found applicable also to study luminescence of atoms and individual molecular groups in vapors over some overheated molten compounds. Sodium atomic luminescence excited with a yellow (578.2 nm) copper vapor laser line was detected in vapors over overheated molten Na₂WO₄ and Na₂O-BaO-B₂O₃ system. The possibility of recording the sodium doublet spectrum by excitation with the 578.2 nm copper vapor laser line in vapors of any melts containing sodium was shown. Overheated melts in the Na₂O-BaO-B₂O₃ system disproportionate and lose boron oxide as evidenced by the recording of luminescent spectra of BO₂ molecular radicals in vapors over relevant melts.     

Synthesis of nanocrystalline TiB<Subscript>2</Subscript> powder from TiO<Subscript>2</Subscript>, B<Subscript>2</Subscript>O<Subscript>3</Subscript> and Mg reactants through microwave-assisted self-propagating high-temperature synthesis method

In this research work, microwave-assisted self-propagating high-temperature synthesis (SHS) process was employed for the fabrication of titanium diboride (TiB₂) compound from TiO₂–B₂O₃–Mg mixtures. Thermodynamic evaluations of this system and its relevant subsystems revealed that TiB₂–MgO composite powder can be easily produced by a SHS reaction. However, experimental results of a TiO₂ : B₂O₃ : 5Mg mixture heated in a domestic oven showed the formation of some intermediate compounds such as Mg₃B₂O₆, presumably due to some degree of Mg loss. The optimum amount of Mg in TiO₂ : B₂O₃ : xMg mixtures, yielding the highest amount of TiB₂ phase, was found to be around 7 mol, i.e., 40 mol% more than the stoichiometric amount. Experimental results revealed that a pure TiB₂ compound could be obtained by leaching the unwanted by-products in an HCl acid solution. Scanning electron microscopic observations and Scherrer calculations showed that the produced TiB₂ contains sub-micron (150–200 nm) particles, where each particle consists of a number of nanosized (32 nm) crystallites.     

Crystallization from high-temperature solutions in the K<Subscript>2</Subscript>O-P<Subscript>2</Subscript>O<Subscript>5</Subscript>-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> system

We have studied general trends of crystallization from high-temperature solutions in the K₂O-P₂O₅-V₂O₅-Bi₂O₃ system at P/V = 0.5?2.0, K/(P + V) = 0.7?1.4, and Bi₂O₃ contents from 25 to 50 wt % and identified the stability regions of BiPO₄, K₃Bi₅(PO₄)₆, K₂Bi₃O(PO₄)₃, and K₃Bi₂(PO₄)_{3 ? x} (VO₄) _x (x = 0?3) solid solutions. The synthesized compounds have been characterized by X-ray powder diffraction and IR spectroscopy, and the structure of two solid solutions has been determined by single-crystal X-ray diffraction (sp. gr. C ₂/c): K₃Bi₂(PO₄)₂(VO₄), a = 13.8857(8), b = 13.5432(5), c = 6.8679(4) Å, β = 114.031(7)°; K₃Bi₂(PO₄)_1.25(VO₄)_1.75, a = 13.907(4), b = 13.615(2), c = 6.956(2) Å, β = 113.52(4)°.     

Preparation and characterization of bioactive sol-gel-derived Na<Subscript>2</Subscript>Ca<Subscript>2</Subscript>Si<Subscript>3</Subscript>O<Subscript>9</Subscript>

In this study, pure Na₂Ca₂Si₃O₉ was synthesized by a sol-gel method, and Na₂Ca₂Si₃O₉ cuboids and disks were prepared by uniaxial pressing and calcining at 700 °C. The porosity and mechanical strength of the Na₂Ca₂Si₃O₉ cuboids were measured, and the results showed that the Na₂Ca₂Si₃O₉ cuboids were porous with an average porosity of 44%, and the 3-point bending strength of the cuboids was 6.08 MPa. The in vitro bioactivity of Na₂Ca₂Si₃O₉ was carried out by soaking Na₂Ca₂Si₃O₉ disks in simulated body fluid (SBF). The results showed that hydroxyapatite (HA) formed on the surface of Na₂Ca₂Si₃O₉ samples after soaking for 1 day, which indicated good bioactivity of Na₂Ca₂Si₃O₉.     

Dielectric responses of Na<Subscript>0.65</Subscript>Bi<Subscript>0.45</Subscript>Cu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics based on the composition design of changing the Na/Bi ratio

Na_0.65Bi_0.45Cu₃Ti₄O₁₂ ceramics were successful prepared by the conventional solid-state reaction technique. Compared to Na_0.50Bi_0.50Cu₃Ti₄O₁₂ (NBCTO), the composition of Na_0.65Bi_0.45Cu₃Ti₄O₁₂ was designed in terms of changing the Na/Bi ratio. Colossal dielectric permittivity of ~1.2 × 10⁴ at 1 kHz was obtained in Na_0.65Bi_0.45Cu₃Ti₄O₁₂ ceramics. Interestingly, three frequency dispersions were observed in the frequency dependence of dielectric constant measured at different temperatures. The investigation of electric modulus displayed that the giant low-frequency dielectric constant was attributed to Maxwell–Wagner polarization at the grain boundaries and the frequency dispersion in middle-frequency range was due to the grain polarization. Except grain response and grain boundaries response reflected by two semicircles in the impedance spectroscopy, another electrical response associated with nonzero high frequency intercept was found. The grain resistance Rg and grain boundaries resistance R _gb was ~600 Ω and 3.9 × 10⁵ Ω, respectively. The large intrinsic permittivity as high as ~700 was obtained. Furthermore, two dielectric anomalies observed in the temperature dependent of dielectric constant were discussed in detail. The results indicated change in the Na/Bi ratio had a significant effect on the electrical properties of NBCTO ceramics.     

Unique hyper-kagome atomic order in the noncentrosymmetric structure of Na<Subscript>3</Subscript>Ir<Subscript>3</Subscript>O<Subscript>8</Subscript>

The formation of a unique hyper-kagome atomic order in the structure of the ordered spinel phase Na₃Ir₃O₈ has been analyzed in terms of the Landau theory of phase transitions. We have identified a critical six-component order parameter generating a phase transformation of the spinel parent phase to ordered P4₁32 (P4₃32) spinel-like enantiomorphs and examined the structural mechanism behind the development of hyper-kagome order and the detailed crystal chemistry of Na₃Ir₃O₈.     

Microstructure and electrical properties of K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>NbO<Subscript>3</Subscript> lead-free piezoelectric ceramics sintered in low pO<Subscript>2</Subscript> atmosphere

Pure K_0.5Na_0.5NbO₃ lead-free piezoelectric ceramics without any dopants/additives were sintered at various temperatures (950–1125 °C) in low pO₂ atmosphere (pO₂?~?10^?6 atm). All ceramics exhibit high relative densities (>?94%) and low weight loss (<?0.6%). Compared to the ceramics sintered in air, the ceramics sintered in low pO₂ exhibit improved electrical properties. The piezoelectric constant d₃₃ and converse piezoelectric constant d₃₃* are 112 pC/N and 119 pm/V, respectively. The ceramics show typical ferroelectric behavior with the remnant polarization of 21.6 µC/cm² and coercive field of 15.5 kV/cm under measurement electric field of 70 kV/cm. The good electrical properties of the present samples are related to the suppression of volatility of the alkali cations during the sintering process in low pO₂ atmosphere.     

Mechanisms of the formation of a surface phase with the matrix composition in a Ca<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>7</Subscript> single crystal

We have studied the local composition and nanoscale surface morphology of a calcium niobate, Сa₂Nb₂O₇, single crystal after thermally stimulated heterosegregation with the aim of identifying the mechanisms underlying the formation of a surface phase with the matrix composition. The identity of the compositions of the surface phase and matrix is accounted for in terms of a liquid-phase model for surface segregation, which includes diffusion, melting, and crystallization processes.     

Synthesis of anisotropic NaNbO<Subscript>3</Subscript> seed crystals and fabrication of textured (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript>-based ceramics

High aspect ratio patelike NaNbO₃ particles with pure perovskite structure have been successfully synthesized by topochemical microcrystal conversion (TMC) from plate-like precursor particles of the layer-structured Bi_2.5Na_3.5Nb₅O₁₈. By changing the Bi_2.5Na_3.5Nb₅O₁₈/Na₂CO₃ ratio, large and thin NaNbO₃ particles with a thickness of approximately 0.5 μm and a width of approximately 20 μm were obtained. The obtained NaNbO₃ particles is quite suitable for fabricating textured (K_0.5Na_0.5)NbO₃-based ceramics. Using the fine platelike NaNbO₃ particles as templates, dense <001> -oriented (K_0.5Na_0.5)NbO₃-0.5 mol %MnO₂ ceramics with high texture quality (Lotgering factor F ₀₀₁ = 87 %) and excellent piezoelectric properties were produced by templated grain growth. Compared with randomly oriented ceramics, textured samples show greatly enhanced properties. The room-temperature strain S, the piezoelectric coefficient d ₃₃ ^* and d ₃₃ reach up to 0.093 %, 233 pm/V and 195pC/N, respectively, which are all about 1.5 times larger than those of non-textured ceramics.     

Photoluminescence properties and charge compensation investigations of novel orange-emitting Eu<Superscript>3+</Superscript> doped Na<Subscript>4</Subscript>Ca<Subscript>4</Subscript>(Si<Subscript>6</Subscript>O<Subscript>18</Subscript>) phosphors

A series of polycrystalline Na₄Ca₄(Si₆O₁₈):Eu³⁺ orange emitting phosphors were synthesized by a conventional high-temperature solid-state reaction. The phase formation was confirmed by X-ray power diffraction analysis. The excitation spectra show a strong host absorption indicating an efficient energy transfer process from O^2? to Eu³⁺ ions. Upon NUV radiation, the phosphors showed strong red emission around 610 nm (⁵D₀ → ⁷F₂) and orange emission around 591 nm (⁵D₀ → ⁷F₁), but the ⁵D_1,2,3 emission nearly can not be seen. Compared with the luminescence properties of Li⁺, Na⁺, and K⁺ co-doped samples, we deduced that Na⁺ ions probably prefer to dope into the intrinsic Na vacancies rather than Ca²⁺ ions vacancies in Na₄Ca₄(Si₆O₁₈) crystal. Thermal stability properties, quantum efficiency and chromaticity coordinates of the phosphors have been investigated for the potential application in white LEDs.     

Microstructure and properties of lead-free (Bi<Subscript>1/2</Subscript>Na<Subscript>1/2</Subscript>)TiO<Subscript>3 </Subscript>based piezoelectric ceramics doped with different cations

Different cations doped lead-free piezoelectric (Bi_1/2Na_1/2)TiO₃ ceramics with the general formula Na_0.4995Bi_0.4995Ba_0.001Ti_0.998M_0.002O₃ (M = Nb, Ta, and Sb) were fabricated. The effects of processing parameters and doping on phase content, microstructure, dielectric and piezoelectric properties of the materials were discussed. Experimental results show that Nb doped (Bi_1/2Na_1/2)TiO₃ exhibits superior polarization performance over the existing lead-free ceramics with a d₃₃ value of 122 pC/N obtained when poled at 60 kV/cm at room temperature. The best piezoelectric properties were achieved in (Bi_1/2Na_1/2)TiO₃ doped with Ta having a measured d₃₃ value of 164 pC/N for samples poled at 100 °C under the applied field of 50 kV/cm.