Development of calcium stabilized nitrogen rich α-sialon ceramics along the Si3N4:1/2Ca3N2:3AlN line using spark plasma sintering

Calcium stabilized nitrogen rich sialon ceramics having a general formula of CaxSi12-2xAl2xN16 with x value (x is the solubility of cation Ca in α-sialon structure) in the range of 0.2–2.2 for compositions lying along the Si3N4:1/2Ca3N2:3AlN line were synthesized using nano/submicron size starting powder precursors and spark plasma sintering (SPS) technique. The development of calcium stabilized nitrogen rich sialon ceramics at a significantly low sintering temperature of 1500 °C (typically reported a temperature of 1700 °C or greater) remains to be the highlight of the present study. The SPS processed sialons were characterized for their microstructure, phase and compositional analysis, and physical and mechanical properties. Furthermore, a correlation was developed between the lattice parameters and the content (x) of the alkaline metal cation in the α-sialon phase. Well-densified single-phase nitrogen rich α-sialon ceramics were achieved in the range of 0.53(3) ⩽ x ⩽ 1.27(3). A nitrogen rich α-sialon sample possessing a maximum hardness of 22.4 GPa and fracture toughness of 6.1 MPa·m1/2 was developed.

Hydration and Diffusion of H+, Li+, Na+, Cs+ Ions in Cation-Exchange Membranes Based on Polyethylene- and Sulfonated-Grafted Polystyrene Studied by NMR Technique and Ionic Conductivity Measurements

The main particularities of sulfonate groups hydration, water molecule and alkaline metal cation translation mobility as well as ionic conductivity were revealed by NMR and impedance spectroscopy techniques. Cation-exchange membranes MSC based on cross-linked sulfonated polystyrene (PS) grafted on polyethylene with ion-exchange capacity of 2.5 mg-eq/g were investigated. Alkaline metal cation hydration numbers (h) calculated from temperature dependences of 1H chemical shift of water molecule for membranes equilibrated with water vapor at RH = 95% are 5, 6, and 4 for Li+, Na+, and Cs+ ions, respectively. These values are close to h for equimolar aqueous salt solutions. Water molecules and counter ions Li+, Na+, and Cs+ diffusion coefficients were measured by pulsed field gradient NMR on the 1H, 7Li, 23Na, and 133Cs nuclei. For membranes as well as for aqueous chloride solutions, cation diffusion coefficients increased in the following sequence: Li+ < Na+ < Cs+. Cation and water molecule diffusion activation energies in temperature range from 20 °C to 80 °C were close to each other (about 20 kJ/mol). The cation conductivity of MSC membranes is in the same sequence, Li+ < Na+ < Cs+ << H+. The conductivity values calculated from the NMR diffusion coefficients with the use of the Nernst–Einstein equation are essentially higher than experimentally determined coefficients. The reason for this discrepancy is the heterogeneity of membrane pore and channel system. Ionic conductivity is limited by cation transfer in narrow channels, whereas the diffusion coefficient characterizes ion mobility in wide pores first of all.

Development of calcium stabilized nitrogen rich alpha-sialon ceramics along the Si3N4:1/2Ca3N2:3AlN line using spark plasma sintering

Calcium stabilized nitrogen rich sialon ceramics having a general formula of CaxSi12-2xAl2xN16 with x value in the range of 0.2-2.2 for compositions lying along the Si3N4:1/2Ca3N2:3AlN line were synthesized using nano/submicron size starting powder precursors and spark plasma sintering (SPS) technique. The development of calcium stabilized nitrogen rich sialon ceramics at a significantly low sintering temperature of 1500°C (typically reported a temperature of 1700°C or greater) remains to be the highlight of the present study. The SPS processed sialons were characterized for their microstructure, phase and compositional analysis, physical and mechanical properties. Furthermore, a correlation was developed between the lattice parameters and the content (x) of the alkaline metal cation in the alpha-sialon phase. Well densified single-phase nitrogen rich alpha-sialon ceramics were achieved in the range of 0.53(3) ≤ x ≤ 1.27(3). A nitrogen rich alpha-sialon sample possessing a maximum hardness of 22.4 GPa and fracture toughness of 6.1 MPa.m1/2 was developed.

Development of calcium stabilized nitrogen rich alpha-sialon ceramics along the Si3N4-1/2Ca3N2:3AlN line using spark plasma sintering

Calcium stabilized nitrogen rich sialon ceramics having a general formula of CaxSi12-2xAl2xN16 with x value in the range of 0.2-2.2 for compositions lying along the Si3N4-1/2Ca3N2:3AlN line were synthesized using nano/submicron size starting powder precursors and spark plasma sintering (SPS) technique. The development of calcium stabilized nitrogen rich sialon ceramics at a significantly low sintering temperature of 1500oC (typically reported temperature of 1700oC or greater) remains to be the highlight of the present study. The SPS processed sialons were characterized for their microstructure, phase and compositional analysis, physical and mechanical properties. Furthermore, a correlation was developed between the lattice parameters and the content (x) of alkaline metal cation in the alpha-sialon phase. Well densified single-phase nitrogen rich alpha-sialon ceramics were achieved in the range of 0.4 < x < 1.6. A nitrogen rich alpha-sialon sample possessing a maximum hardness of 22.4 GPa and fracture toughness of 6.1 MPa.m1/2 was developed.

Lewis acidic water as a new carrier for facilitating CO2 transport

We report the formation of a reversible complex between CO2 and a bound water coordinating alkaline metal cation (Lewis-acidic water) by nuclear magnetic resonance (NMR) analysis for the first time.