Submicron-grade powders of Na1-xZr2(PO4)3-x(XO4)x compounds (hereafter referred to as NZP) and Ca1-xZr2(PO4)3-x(XO4)x compounds (hereafter, CZP), X = Mo, W (0 ≤ x ≤ 0.5) were obtained by sol-gel synthesis. The compounds obtained were studied by X-ray diffraction phase analysis and electron microscopy. An increase in the W or Mo contents was shown to result in an increase in the unit cell volume of the NZP and CZP crystal lattices and in a decrease in the coherent scattering region sizes. Thermal expansion behavior at high temperatures of synthesized NZP and CZP compounds has been investigated. The dependencies of the parameters a and c on the heating temperature, as well as the temperature dependence of the crystal lattice unit cell volume V in the range from the room temperature up to 800 °C, were obtained. The dependencies of the average thermal expansion coefficient (αav) and of the volume coefficient (β) on the W and Mo contents in the compositions of NZP and CZP compounds were studied. Ceramics Na1-xZr2(PO4)3-x(XO4)x with relatively high density (more than 97.5%) were produced by spark plasma sintering (SPS). The increase in the W or Mo contents in the ceramics leads to an increase in the relative density of NZP and to a decrease of the optimum sintering temperature. The mean grain size in the NZP ceramics decreases with increasing W or Mo contents. The study of strength characteristics has revealed that the hardness of the NZP ceramics is greater than 5 GPa, and that the minimum fracture toughness factor was 1 MPa·m1/2.

The structure, microstructure, coefficient of thermal expansion (CTE), and mechanical properties of Na1+2xZr2−xCox(PO4)3 ceramics (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) were studied. Na1+2xZr2−xCox(PO4)3 submicron powders with the NaZr2(PO4)3 structure (NZP, kosnarite type) were obtained by the solid-phase method. The starting reagents (NaNO3, ZrOCl2·8H2O, NH4H2PO4, CoCl2·6H2O, ethanol) were mixed with the addition of ethyl alcohol. The resulting mixtures were annealed at 600 °C (20 h) and 700 °C (20 h). The obtained phosphates crystallized in the expected structure of the NaZr2(PO4)3 type (trigonal system, space group R3¯c). Thermal expansion of the powders was studied with high-temperature X-ray diffraction at temperatures ranging from 25 to 700 °C. CTEs were calculated, and their dependence on the cobalt content was analyzed. Na1+2xZr2−xCox(PO4)3 ceramics with high relative density (93.67–99.70%) were obtained by Spark Plasma Sintering (SPS). Ceramics poor in cobalt (x = 0.1) were found to have a high relative density (98.87%) and a uniform fine-grained microstructure with a grain size of 0.5–1 µm. Bigger cobalt content leads to a smaller relative density of ceramics. During the sintering of ceramics with high cobalt content, anomalous grain growth was observed. The powder compaction rate was shown to be determined by creep and diffusion intensity in the Na1+2xZr2−xCox(PO4)3 crystal lattice. SPS activation energy in ceramics increased as the cobalt content grew. The microhardness and fracture toughness of ceramics did not depend on their cobalt content.

We have synthesized Na1 – xZr2(PO4)3 – x(ХO4)x and Сa0.5 – xZr2(PO4)3 – x(ХO4)x (X = Mo, W; 0 ≤ x ≤ 0.5) compounds with the NZP structure. Their thermal expansion has been studied in the temperature range 25–800°C using high-temperature X-ray diffraction and shown to have a tendency to decrease as the occupancy of the extraframework sites in their structure decreases. Ceramic samples with a relative density above 97.5% have been prepared from the synthesized phosphate molybdates and phosphate tungstates by spark plasma sintering. Their strength characteristics (microhardness and fracture toughness) have been determined and they have been characterized by hydrolytic stability tests.

— New NZP-type solid solutions, Na 1+2 x Zr 2– x Ni x (PO 4 ) 3 and Ca 0.5+ x Zr 2– x Ni x (PO 4 ) 3 with x = 0.10, 0.25, and 0.50, have been prepared by solid-state reactions. The synthesized samples have been characterized by X-ray diffraction and IR spectroscopy. Crystal structure of the compound CaZr 1.5 Ni 0.5 (PO 4 ) 3 has been refined by full-profile X-ray diffraction analysis method, reliability factors is R p = 4.78% and R wp = 6.45%, respectively. Thermal expansion of the phosphates has been studied by high-temperature X-ray diffraction in the temperature range 25–700°C. The synthesized compounds have been shown to be intermediate- and low-thermal-expansion materials. Using SPS method we have produced ceramic samples with a high relative density (ρ rel > 97%), based on phosphate powders. Strength characteristics (microhardness and fracture toughness) of the ceramics have been determined.

Thermal expansion behavior at high temperatures of synthesized Na1-xZr2(PO4)3-x(ХO4)x, Сa1-xZr2(PO4)3-x(ХO4)x, Х = Mo, W (0 ≤ x ≤ 0.5) compounds has been investigated. Ceramics with relatively high density (more than 97.5%) were produced by Spark Plasma Sintering (SPS) of submicron powders obtained by sol-gel synthesis. The study of strength characteristics has revealed that hardness the ceramics are greater than 5 GPa, and minimum fracture toughness factor was 1 (*) Corresponding author (23/3 Gagarina ave., Nizhniy Novgorod, 603022, Russian Federation, nokhrin@nifti.unn.ru)

A method for preconcentration and simultaneous determination of trace heavy metals in water media by core-shell superparamagnetic nanoparticles with the immobilized derivative of ethylenediaminetriacetic acid (referred to as MNPs/SiO2-EDTA) is proposed. The specific layer-by-layer covering of magnetite endowed the new material with essentially increased chemical stability of MNPs including acidic media and improved the affinity toward traces of toxic metal ions. The initial and modified materials were characterized by X-ray powder diffraction, Fourier transform infrared spectroscopy, transmission and scanning electron microscopies, elemental analysis, and vibrating sample magnetometry. The obtained particles were nanodimensional with a 7–12-nm magnetic core and a 4–6-nm silica shell. The MNPs/SiO2-EDTA quantitatively removes heavy metals from contaminated media at pH ≥ 3.5 within 15 min. The adsorption data were successfully fitted to the pseudo-second-order kinetic model. The preconcentration factor was 150 and maximum adsorption capacity was 36.9 mg g−1 for Cu(II), 108.8 mg g−1 for Pb(II), 30.9 mg g−1 for Zn(II), 34.32 mg g−1 for Cr(III), and 59.5 mg g−1 for Cd(II). Due to high stability in the wide range of pH, the magnetic adsorbent can be regenerated at least six times using 0.1 M HNO3. Following adsorption/desorption, determination of metal ions is provided by inductively coupled plasma optical emission spectrometry (ICP-OES) . The linear range of the proposed method is 0.1 - 200 μg L−1. The limits of detection (LOD) are 0.12 μg L−1 for Zn(II); 0.06 μg L−1 for Cd(II); 0.39 for Cu(II); 0.15 μg L−1 for Cr(III); and 0.76 μg L−1 for Pb(II). The method performance was evaluated in the analysis of environmental, tap, and wastewater samples with recoveries in the range of 94.0–104.0%.

The crystal-chemical approach has been applied to design materials with regulated thermal expansion. To that end, model simulations have been performed for compositions of phosphates that yield solid solutions of the following type Na1 + 2xZr2 –xCux(PO4)3 and Ca0.5 +xZr2 –xCux(PO4)3, 0.1 ≤ x ≤ 0.5 with the expected structure of NaZr2(PO4)3 (NZP). The new phosphates have been prepared by solid-state reactions and characterized by X‑ray diffraction, IR spectroscopy, and scanning electron microscopy. The compounds have been shown to crystallize in the NZP structure, with a particle size from 0.1 to 1 μm. The thermal expansion of the compounds has been studied by high-temperature X-ray diffraction in the temperature range from 25 to 700°C. Linear, average, and volume coefficients of thermal expansion and anisotropy of thermal expansion have been calculated and analyzed in relation to composition of Na, Zr, Cu and Ca, Zr, Cu phosphates in the studied sets.

Two adsorbents with covalently bound aminomethylenephosphonic acid functions (and referred to as MNPs/AMPA and MNPs/SiO2-AMPA) were synthesized from two types of amino-functionalized magnetic nanoparticles (MNPs) via Moedritzer-Irani reaction. The sorbents with anchored dopamine ligand (MNPs/dopa) or aminopropyl groups (MNPs/SiO2-NH2), and the MNPs/AMPA were characterized by X-ray diffraction, FTIR, transmission electron microscopy and vibrating sample magnetometry. Surface modification does not adversely impact the physical properties of the starting magnetite. Compared to the size of the unmodified Fe3O4 (magnetite) nanoparticles (7–12 nm), the average size of functionalized nanoparticles is increased to 10–16 nm. Similarly, the magnetic saturation decreased from 67.5 emu g-1 to 42.0 emu g−1, and the surface area is increased up to 205 m2 g−1 for MNPs/SiO2-AMPA. The kinetics of the adsorption of Eu(III) on the sorbent is ultra-fast, and equilibria are attained within 5–10 min at room temperature. The adsorption kinetics can be described by a pseudo-second-order model. Adsorption and desorption conditions were tested with respect to the removal of Eu(III) ions from water solution. The adsorption capacities for Eu(III) at pH 7.0 are 77 mg g−1 and 69 mg g−1 for MNPs/AMPA and MNPs/SiO2-AMPA nanoparticles, respectively. Eu(III) was quantified by ICP-MS. The limit of detection (LOD) for Eu(III) is 0.05 ng L−1 (based on the 3σ criterion), with an enrichment factor of 150. The selectivity over ions such as Tb(III), Fe(III), Zn(II), Cu(II), and Ca(II) ions was studied. Under optimal condition the distribution coefficient for Eu(III) relative to these ions is near 105 mL g−1. The sorbents can be easily retrieved from even large volumes of aqueous solutions by magnetic separations. The method was tested for spiked water samples (with recoveries from 96.6–102.5%) and for rock minerals.

— Na x Sr 1 – 2 x Nd x MoO 4 ( x = 0–0.5, Δ x = 0.1) solid solutions with the scheelite structure have been synthesized for the first time and their crystallographic parameters have been determined as functions of composition and temperature. Their thermal expansion coefficients have been determined in the temperature range 25–1000°C: α a = (12.9–14.9) × 10 –6 °C –1 and α c = (24.9–25.9) × 10 –6 °C –1 . Using spark plasma sintering at t max ≈ 872–985°C and τ ≈ 650–750 s, we have prepared ceramics with relative densities in the range 97–99%.

Ca0.75 + 0.5xZr1.5Fe0.5(PO4)3 –x(SiO4)x (x = 0–0.5) solid solutions have been synthesized by a sol–gel process and characterized by X-ray diffraction, IR spectroscopy, and differential scanning calorimetry. As expected, the synthesized phosphatosilicates crystallize in a NaZr2(PO4)3-type structure (trigonal symmetry, sp. gr. R\(\bar {3}\)c). The thermal expansion of the solid solutions has been studied by high-temperature X-ray diffraction in the temperature range from 25 to 800°C. Their thermal expansion parameters have been calculated and analyzed as functions of composition. High-density ceramics based on the Ca0.875Zr1.5Fe0.5(PO4)2.75(SiO4)0.25 phosphatosilicate have been produced by spark plasma sintering and their structure and properties have been studied in detail.

of structural mechanisms responsible for their formation, -12 , CaCu Ga 2 Sn 2 12 , CaMn Mn 12 , Ce 1/2 Cu 12 , LaMn Mn 12 -structure.

Ca0.5(1 + x)Zr2–xFe x (PO4)3 phosphates have been synthesized by a sol–gel process. The individual compounds and solid solutions obtained crystallize in the NaZr2(PO4)3 structure (trigonal symmetry, sp. gr. R\(\bar 3\)). Using high-temperature X-ray diffraction, we have determined their thermal expansion parameters in the temperature range from 25 to 800°C. With increasing x, the magnitudes of their linear thermal expansion coefficients and thermal expansion anisotropy decrease. Most of the synthesized phosphates can be rated as low-thermal-expansion compounds and can be regarded as materials capable of withstanding thermal “stress.”

NaZr2–xBx(PO4)3–2x(SO4)2x (0 ≤ x ≤ 1.25, B = Mg, Co, Ni, Cu, Zn), and NaZr2–xRx(PO4)3–x(SO4)x (0 ≤ x ≤ 1.25, R = Al, Fe) phosphate-sulfates series have been prepared by a sol–gel process. These compounds belong to the NaZr2(PO4)3 (NZP) structure family and crystallize in hexagonal crystal system, space group R\(\bar 3\)c. Limited solid solution series were found to exist; their formation temperatures and thermal stability limits were determined. Particle sizes as determined by microstructure observation were 50–200 nm, and for Cu- and Zn-containing samples, 200–500 nm. The thermal expansion of phosphate-sulfate NaZr1.25Cu0.75(PO4)1.5(SO4)1.5 was studied in the range 25–700°C. Thermal expansion coefficients and thermal expansion anisotropy were found to be αa =–5.40 × 10–6 °C–1, αс = 18.88 × 10–6 °C–1, αavg = 2.69 × 10–6 °C–1, and Δα = 24.28 × 10–6 °C–1.