Тепловой баланс помещения с электрической кабельной системой отопления

Solvothermal oxidation of metallic gallium in monoethanolamine for 72 h at 240 °C yields a crystalline sample of γ-Ga₂O₃ (∼30 nm crystallites). While Rietveld refinement (cubic spinel structure, <i>Fd</i>3̅<i>m</i>; <i>a</i> = 8.23760(9) Å) reveals that Ga occupies two pairs of octahedral and tetrahedral sites (ideal spinel and nonspinel), it provides no information about their local distribution, which cannot be statistical owing to the short Ga–Ga contacts produced if neighboring ideal spinel and nonspinel sites are simultaneously occupied. To create an atomistic model to reconcile this situation, a 6 × 6 × 6 supercell of the crystal structure is constructed and refined against neutron total scattering data using a reverse Monte Carlo (RMC) approach. This accounts well for the local as well as long-range structure and reveals significant local distortion in the octahedral sites that resembles the structure of thermodynamically stable β-Ga₂O₃. ⁷¹Ga solid-state NMR results reveal a octahedral:tetrahedral Ga ratio that is consistent with the model obtained from RMC. Nanocrystalline samples of γ-Ga₂O₃ are produced by either a short solvothermal reaction (240 °C for 11 h in diethanolamine; ∼15 nm crystallites) or by precipitation from an ethanolic solution of gallium nitrate (∼5 nm crystallites). For these samples, the Bragg scattering profile is broadened by their smaller crystallite size, consistent with transmission electron microscopy results, and analysis of the relative Bragg peak intensities provides evidence that a greater proportion of tetrahedral versus octahedral sites are filled. In contrast, neutron total scattering shows the same average Ga–O distance with decreasing particle size, consistent with ⁷¹Ga solid-state NMR results that indicate that all samples contain the same overall proportion of octahedral:tetrahedral Ga. It is postulated that increased occupation of tetrahedral sites within the smaller crystallites is balanced by an increased proportion of octahedral surface Ga sites, owing to termination by bound solvent or hydroxide

Proglašen Zakonik kanona istočnih crkava

The hydrothermal synthesis of a zeolite with properties suitable for use in the assembly–disassembly–organization–reassembly (ADOR) process was designed, and a zeolite called SAZ-1 was successfully prepared. This zeolite was then used as a parent in the ADOR process, and two new daughter zeolites, IPC-15 and IPC-16, were prepared. The X-ray powder diffraction patterns of the new zeolites match well with those predicted using computational methods. The three materials form an isoreticular series with decreasing pores size from 14-ring to 12-ring to 10-ring

A Multinuclear Solid-State NMR Study of Templated and Calcined Chabazite-Type GaPO-34

The open-framework gallophosphate GaPO-34 is prepared with either 1-methylimidazole or pyridine as the structure-directing agent. ¹³C and ¹H NMR spectra for these two variants of the as-made GaPO-34 are fully assigned, confirming the presence of the protonated amine and water within the pores of both materials. ³¹P MAS NMR confirms the presence of three crystallographic P sites, while ⁷¹Ga MAS and MQMAS NMR spectra reveal three crystallographic Ga sites: two tetrahedral and one six-coordinate. Simulations of ⁶⁹Ga MAS NMR spectra from these results are in good agreement with spectra acquired at <i>B</i>₀ = 20.0 T, and assignments are supported by first-principles calculations. ¹⁹F MAS NMR proves the presence of Ga-bridging fluoride within the as-made materials, leading to the six-coordinate gallium. Calcination removes the organic species and fluoride, yielding a microporous chabazite-type GaPO₄, containing one tetrahedral Ga site. Exposure to moist air yields calcined, rehydrated GaPO-34 containing four-, five-, and six-coordinate gallium. Upon heating this material, loss of crystallinity is observed by powder X-ray diffraction and NMR, with the latter revealing a range of P and Ga environments. The thermal instability of calcined, rehydrated GaPO-34 contrasts with the isomorphous aluminophosphate, showing that apparently analogous materials may have important differences in reactivity

Synthesis, Isotopic Enrichment, and Solid-State NMR Characterization of Zeolites Derived from the Assembly, Disassembly, Organization, Reassembly Process

The great utility and importance of zeolites in fields as diverse as industrial catalysis and medicine has driven considerable interest in the ability to target new framework types with novel properties and applications. The recently introduced and unconventional assembly, disassembly, organization, reassembly (ADOR) method represents one exciting new approach to obtain solids with targeted structures by selectively disassembling preprepared hydrolytically unstable frameworks and then reassembling the resulting products to form materials with new topologies. However, the hydrolytic mechanisms underlying such a powerful synthetic method are not understood in detail, requiring further investigation of the kinetic behavior and the outcome of reactions under differing conditions. In this work, we report the optimized ADOR synthesis, and subsequent solid-state characterization, of ¹⁷O- and doubly ¹⁷O- and ²⁹Si-enriched UTL-derived zeolites, by synthesis of ²⁹Si-enriched starting Ge-UTL frameworks and incorporation of ¹⁷O from ¹⁷O-enriched water during hydrolysis. ¹⁷O and ²⁹Si NMR experiments are able to demonstrate that the hydrolysis and rearrangement process occurs over a much longer time scale than seen by diffraction. The observation of unexpectedly high levels of ¹⁷O in the bulk zeolitic layers, rather than being confined only to the interlayer spacing, reveals a much more extensive hydrolytic rearrangement than previously thought. This work sheds new light on the role played by water in the ADOR process and provides insight into the detailed mechanism of the structural changes involved

Unusual Intermolecular “Through-Space” <i>J</i> Couplings in P–Se Heterocycles

Solid-state NMR spectra of new P–Se heterocycles based on <i>peri</i>-substituted naphthalene motifs show the presence of unusual <i>J</i> couplings between Se and P. These couplings are between atoms in adjacent molecules and occur “through space”, rather than through conventional covalent bonds. Experimental measurements are supported by relativistic DFT calculations, which confirm the presence of couplings between nonbonded atoms, and provide information on the pathway of the interaction. This observation improves the understanding of <i>J</i> couplings and offers insight into the factors that affect crystal packing in solids, for future synthetic exploitation

Unusual Intermolecular “Through-Space” <i>J</i> Couplings in P–Se Heterocycles

Solid-state NMR spectra of new P–Se heterocycles based on <i>peri</i>-substituted naphthalene motifs show the presence of unusual <i>J</i> couplings between Se and P. These couplings are between atoms in adjacent molecules and occur “through space”, rather than through conventional covalent bonds. Experimental measurements are supported by relativistic DFT calculations, which confirm the presence of couplings between nonbonded atoms, and provide information on the pathway of the interaction. This observation improves the understanding of <i>J</i> couplings and offers insight into the factors that affect crystal packing in solids, for future synthetic exploitation