Search results for "silica."
showing 10 items of 1087 documents
IV.22 Servizio di cartagloria
2011
Scheda di catalogo
IV.21 Turibolo
2011
Scheda di catalogo
IV.26 Calice
2011
Scheda di catalogo
IV.23 Ostensorio
2011
Scheda di catalogo
IV.25 Servizio di cartagloria
2011
Scheda di catalogo
Le "Choral-Variationen" Bach-Stravinsky per la basilica di San Marco: simbologia e Quadrato magico
2020
Eseguite per la prima volta nella basilica di San Marco il 13 settembre 1956, le Choral-Variationen uber das Weinachtslied “Vom Himmel hoch...” (1955-56) di Stravinsky sono una reinvenzione originale e creativa delle Canonische Veränderungen BWV 796 di J.S. Bach, che presenta una profonda relazione con la struttura architettonica e i simboli della basilica, ma anche - in maniera più segreta - con il quadrato magico SATOR / AREPO / TENET / OPERA / ROTAS and e con la musica di Anton Webern. First performed in the Basilica of St. Mark on 13th September 1956, Stravinky’s Choral Variations on the Christmas Carol “Vom Himmel hoch...” (1955-56) are an original and creative reinvention of the Canon…
Amorphous Silica at Surfaces and Interfaces: Simulation Studies
2003
The structure of surfaces and interfaces of silica (SiO2) is investigated by large scale molecular dynamics computer simulations. In the case of a free silica surface, the results of a classical molecular dynamics simulation are compared to those of an ab initio method, the Car—Parrinello molecular dynamics. This comparative study allows to check the accuracy of the model potential that underlies the classical simulation. By means of a pure classical MD, the interface between amorphous and crystalline SiO2 is investigated, and as a third example the structure of a silica melt between walls is studied in equilibrium and under shear. We show that in the latter three examples important structu…
The Nature of Silanol Groups on the Surfaces of Silica, Modified Silica and Some Silica Based Materials
2014
Silica gel, a material that is produced from the condensation polymerisation of silicic acid, contains surface silanol groups formed during the condensation. The silanol groups on the surface are mostly of free and vicinal silanol groups. These silanol groups can be modified in several different ways. Thermal treatment and hydrothermal treatment can be carried out to alter the concentration proportions between free and hydrogen bonded silanol groups on the surface. They can also be chemically treated with suitable chlorosilanes to modify the silanol groups into polar or non polar materials that can be used in separation science.This article explores the chemical nature of silanol groups on …
Supported ionic liquids. New recyclable materials for the L-proline-catalyzed aldol reaction
2006
New materials for L-proline recycling have been developed. These materials have been applied to the L-proline-catalyzed aldol reaction between acetone and several aldehydes. The L-proline has been supported on the surface of modified silica gels with a monolayer of covalently attached ionic liquid with or without additional adsorbed ionic liquid. Good yields and ee values, comparable with those obtained under homogeneous conditions, have been obtained especially with imidazolinium-modified and 4-methylpyridinium-modified silica gels. Moreover, these materials have been easily recovered by simple filtration and studies about their reuse have been carried out. These studies showed that these …
Raman spectroscopy study of β-irradiated silica glass
2003
International audience; Natural and synthetic silica glass samples with different OH content have been submitted to β-irradiation at different doses from 106 to 5 × 109 Gy in a Van de Graaff accelerator. Structural changes under irradiation have been analyzed by Raman spectroscopy. The main findings are: (i) a decrease of the Si–O–Si angular dispersion and the average Si–O–Si angle as a function of dose and (ii) an increase of number of three-membered SiO4 ring concentration during irradiation. These results show therefore that purely electronic excitation from β-irradiation induces in a-SiO2 small but significant structural changes of the SiO4 membered ring statistics (size and dispersion)…