Ammonia synthesized using hydrogen from renewable sources offers a vast potential for the storage as well as transportation of renewable energy from regions with high intensity to regions lean in renewable sources. Ammonia can be used as an energy vector for an emissionless energy cycle in a variety of ways. Ammonia at the point of end use can be converted to hydrogen for fuel cell vehicles or alternatively utilized directly in solid oxide fuel cells, in an internal combustion engine or a gas turbine. One ton of ammonia production requires 9–15 MWh of energy. However, its conversion back to useful form or direct utilization can lead to substantial energy losses. In this paper, we present an overview of the current processes and technologies for ammonia synthesis and its utilization as an energy carrier. We have performed an estimation of the round-trip efficiency of different routes for ammonia utilization at the point of end use along with some sensitivity analysis, and we discuss the outcomes resulting from the best and worst case scenarios.

No abstract

No abstract

No abstract

The α, β, γ, and δ polymorphs of Y2Si2O7 were synthesized using sol-gel and solid-state methods. The structures of the α and γ polymorphs were determined by identification of isostructural rare-earth disilicates, and the structures were refined using Rietveld analysis of X-ray powder diffraction data. The α polymorph crystallizes in space group P1, with a=6.5872(6) Å, b=6.6387(7) Å, c=12.032(1) Å, α=94.501(7)°, β=90.984(8)°, γ=91.771(7)°, and volume=524.16(9) Å3. The γ form is described by space group P21/c, a=4.68824(5) Å, b=10.84072(9) Å, c=5.58219(6) Å, and γ=96.0325(3)°. The anisotropic thermal expansion of each phase was measured using high temperature diffraction up to 1200 or 1400 °C, depending on the stability of the polymorph. The thermal expansion is highly anisotropic for all polymorphs, with the low-expansion direction normal to the long axis of the corner-shared SiO4 tetrahedra.

No abstract

No abstract

No abstract