Structural characterization of silicon orthophosphate

Improving the Ablation Properties of Liquid Silicone Rubber Composites by Incorporating Hexaphenoxycyclotriphosphonitrile

The ablative properties of epoxy-modified vinyl silicone rubber (EMVSR) composites containing hexaphenoxycyclotriphosphonitrile (HPCTP) have been systematically studied. The strength of the ablation char layer was greatly enhanced with the addition of HPCTP, which induced the formation of a more complete, denser, and thicker char during oxyacetylene ablation tests. Moreover, the HPCTP-containing EMVSR composites demonstrated lower thermal conductivity and pyrolysis rate when compared with those without HPTCP. At the same time, the thermal insulation properties of HPCTP-filled composites were improved under low heat flow ablation scenarios. The reduction of graphitic carbon content, the formation of phosphate-like crystals as well as the increase of SiC content contributed to strengthening the char layer, which was critical for improving the ablation properties. The optimum char layer strength and thermal insulation properties were achieved when the content of HPCTP was 15 phr, whereas an optimum ablation resistance was achieved at 25 phr HPCTP. This suggests that HPCTP-modified EMVSR composites can be used for thermal protection purposes, especially in the fields of aerospace and aeronautics.

Rationalization of the crystal structure of eudidymite Na2Be2[Si[4]6O15]·H2O in light of the extended Zintl-Klemm concept

The structure of eudidymite is described in light of the extended Zintl-Klemm concept which considers that Na and Be atoms transfer their six valence electrons to the six Si atoms, converting them into Ψ-P which forms a skeleton characteristic of pentels (Group 15 elements) and is similar to that described in the compound (NH₄)₂Ge^[6][Ge^[4]₆O₁₅] when analysed in the same manner. The Si^[4] skeleton is formed of bilayers that are connected through Be₂O₆ groups which are in fact fragments of the β-BeO structure which bridge the two contiguous Si-bilayers by sharing O atoms. In this context, the Be atoms play a dual role, i.e. on the one hand converting the Si atoms into Ψ-P, on the other hand replicating fragments of its own β-BeO structure. The Be atoms partially reproduce their own structure despite it being enclosed in a more complex network such as in Na₂Be₂[Si^[4]₆O₁₅]·H₂O. Calculations of the ionic strength I considering Si as Ψ-P is energetically more favourable than when I is calculated on the basis of tetravalent Si in the silicate, justifying this new approach of developing the theory of pseudo-structure generation. This approach offers a major new development in the study of crystal structures.

Five- and six-fold coordinated silicon in silicodiphosphonates: short range order investigation by solid-state NMR spectroscopy

Silicodiphosphonates synthesized by two different pathways show interesting chemical shifts of five- and sixfold coordinated silicon.

Orthophosphate and Sulfate Utilization for C-E (E = P, S) Bond Formation via Trichlorosilyl Phosphide and Sulfide Anions

Reduction of phosphoric acid (H₃PO₄) or tetra- n-butylammonium bisulfate ([TBA][HSO₄]) with trichlorosilane leads to the formation of the bis(trichlorosilyl)phosphide ([P(SiCl₃)₂]^-, 1) and trichlorosilylsulfide ([Cl₃SiS]^-, 2) anions, respectively. Balanced equations for the formation of the TBA salts of anions 1 and 2 were formulated based on the identification of hexachlorodisiloxane and hydrogen gas as byproducts arising from these reductive processes: i) [H₂PO₄]^- + 10HSiCl₃ → 1 + 4O(SiCl₃)₂ + 6H₂ for P and ii) [HSO₄]^- + 9HSiCl₃ → 2 + 4O(SiCl₃)₂ + 5H₂ for S. Hydrogen gas was identified by its subsequent use to hydrogenate an alkene ((-)-terpinen-4-ol) using Crabtree's catalyst ([(COD)Ir(py)(PCy₃)][PF₆], COD = 1,5-cyclooctadiene, py = pyridine, Cy = cyclohexyl). Phosphide 1 was generated in situ by the reaction of phosphoric acid and trichlorosilane and used to convert an alkyl chloride (1-chlorooctane) to the corresponding primary phosphine, which was isolated in 41% yield. Anion 1 was also prepared from [TBA][H₂PO₄] and isolated in 62% yield on a gram scale. Treatment of [TBA]1 with an excess of benzyl chloride leads to the formation of tetrabenzylphosphonium chloride, which was isolated in 61% yield. Sulfide 2 was used as a thionation reagent, converting benzophenone to thiobenzophenone in 62% yield. It also converted benzyl bromide to benzyl mercaptan in 55% yield. The TBA salt of trimetaphosphate ([TBA]₃[P₃O₉]·2H₂O), also a precursor to anion 1, was found to react with either trichlorosilane or silicon(IV) chloride to provide bis(trimetaphosphate)silicate, [TBA]₂[Si(P₃O₉)₂], characterized by NMR spectroscopy, X-ray crystallography, and elemental analysis. Trichlorosilane reduction of [TBA]₂[Si(P₃O₉)₂] also provided anion 1. The electronic structures of 1 and 2 were investigated using a suite of theoretical methods; the computational studies suggest that the trichlorosilyl ligand is a good π-acceptor and forms σ-bonds with a high degree of s character.

Investigation of the effects of phosphorus on the selective hydrodeoxygenation of anisole over an Fe/SiO2 catalyst

Hydrodeoxygenation (HDO) of lignin derivatives offers an effective approach to produce aromatics.

Non-aqueous template-assisted synthesis of mesoporous nanocrystalline silicon orthophosphate

Mesoporous nanocrystalline silicon orthophosphate Si₅P₆O₂₅ was synthesized by the non-hydrolytic sol–gel reaction in the presence of Pluronic P123 template and displays superior catalytic activity and selectivity in methylstyrene dimerization.

Studies of silicophosphate derivatives by 31P-->29Si CP MAS NMR

We show that it is possible to efficiently transfer magnetization from 31P to 29Si, using variable amplitude CP MAS experiment. This experiment is demonstrated by using Si5O(PO4)6, the synthesis protocol of which is described. From the obtained results, we show that the experiment allows the spectral edition of 29Si spectra from 31P-->29Si CP, enabling the studies of derivatives involving Si-O-P linkages, such as phosphosilicate glasses, microporous silicoaluminophosphates (SAPO) and bioactive phosphosilicates.