Search results for "silica"
showing 10 items of 1092 documents
Phase change and O2 loading in mesoporous silica MCM41, MSU-H and MSU-F
2014
Near-Infrared emission of O2 embedded in amorphous SiO2 nanoparticles
2011
We report an experimental study on the emission properties of O2 molecules loaded by a thermal diffusion process at 200 °C into high-purity silica nanoparticles with mean diameters of 7 and 40 nm. The embedded O2 features a singlet to triplet emission band peaked at 1272 nm in agreement with the band observed for bulk silica materials. The photoluminescence excitation spectra have been determined in the visible and in the infrared range and are characterized by narrow bands peaked at 691, 764,and 1069 nm, respectively. By comparison of the transition energies, the vibrational quanta have been determined for the ground and for both the excited states; the values found are lower than the corr…
Near infrared emitting silica nanoparticles: O2 diffusion properties and excited state relaxation
2013
O2 trapping in silica nano-structures with high specific surfaces
2014
We report an experimental investigation regarding the entrapping of O2 molecules inside various silica nano– structured systems having specific surfaces from 50 to 1000 m2/g. By recording Raman spectra and Near Infrared O2 emission we studied the O2 content per mass unit. Our data show that the internal voids of these nanostructured systems can trap O2 molecules diffusing from the surrounding air or from a pure O2 atmosphere, whereas the concentration of O2 that can be trapped in the silica near–surface layer is at least one order of magnitude lower. This low ability is consistently observed in non–porous and porous silica nanoparticles and in mesoporous silica systems. Furthermore, we obse…
Prediction of concrete materials compressive strength using surrogate models
2022
Using soft computing methods could be of great interest in predicting the compressive strength of Ultra-High-Performance Fibre Reinforced Concrete (UHPFRC). Therefore, this study developed four soft computing techniques. The models are the Linear- relationship (LR), pure quadratic, M5P-tree (M5P), and artificial neural network (ANN). The models were trained and developed using 306 datasets comprising 11 input parameters, including the curing temperature (T), the water-to-cement ratio (w/c), silica fume (SF), cement content (C), fiber content (Fb), water (W), sand content (S), superplasticizer (SP), fiber aspect ratio (AR) and curing time (t). Experimental results were used and compared to t…
PROCESSO INNOVATIVO SONOCHIMICO CHE IMPIEGA CAVITAZIONE ULTRASONICA PER LA SINTESI DI NANOPARTICELLE AMORFE MONODISPERSE DI SILICIO BIOSSIDO E METODO…
2011
La presente invenzione è stata stimolata dalla necessità di produrre nanomateriali da impiegare per il consolidamento e, più segnatamente, per la conservazione e la protezione dei materiali lapidei o lignei di strutture antiche
DIO SALVI IL RESTAURO. L’apporto inglese alla cultura della conservazione dei monumenti
2020
Sebbene già riuscissimo a percepire quanto rilevante fosse l’apporto inglese per aver contribuito alla definizione del restauro modernamente inteso, sino ad oggi mancavano ancora sia una chiara visione d’insieme delle articolate vicende connesse all'affermazione dei princìpi conservativi, sia una più approfondita conoscenza delle fonti documentarie, necessarie al fine di tracciare i profili culturali dei protagonisti e scandagliarne i contributi teorici. La ricostruzione delle vicende è sviluppata entro margini temporali estesi all'incirca per tre secoli, dalla fine del Seicento al principio del Nove-cento, e strutturata attraverso la traduzione e lo studio di testi perlopiù mai circolati i…
Lithium silicate admixture in mortars to be used as putty for limestone
2018
Marble is a very common material in artworks for its softness, relative isotropy and homogeneity and its characteristic waxy look that gives "life" to sculptures. Even if in geology the term "marble" refers to metamorphosed limestone, commonly the term ‘marble’ is used more broadly encompassing hard unmetamorphosed limestone that can be polished assuming a glossy aspect. In the restoration field when marble artworks have cracks that alter the smoothness of their surface, a putty is used to fill them, for both aesthetic and conservative reasons. Putties usually consist of epoxy resin mixed with marble powder. The use of a synthetic resin raises some doubts on compatibility and durability of …
INDAGINI SPERIMENTALI SU MALTE TRATTATE CON SILICATO DI LITIO NANODISPERSO DA UTILIZZARE PER STUCCATURE DI MATERIALI LAPIDEI COMPATTI
2018
In questo lavoro di ricerca, sviluppato all’interno della tesi di laurea magistrale in Conservazione e Restauro dei Beni Culturali presso l’accademia Galli di Como con la supervisione della restauratrice Gisella Bianconi, si è sperimentato l’uso del silicato di litio come additivo per il miglioramento delle prestazioni di malte a base di leganti inorganici, e in particolare calci aeree e idrauliche, utilizzate nel restauro dei materiali lapidei. Spesso per le stuccature di materiali lapidei compatti vengono utilizzate malte con leganti organici, ed in particolare di tipo epossidico, che offrono certamente ottime proprietà meccaniche e un’eccellente adesività, garantendo al contempo una acce…
Silicate and Hydroxide Concentration Influencing the Properties of Composite Al2O3-TiO2 PEO Coatings on AA7075 Alloy
2021
This work evaluates the effect of sodium meta-silicate pentahydrate (SMS) and potassium hydroxide concentrations on properties of Al2O3-TiO2 coatings produced through plasma electrolytic oxidation in a solution containing 3 g L−1 potassium titanyl oxalate, (PTO), using a unipolar waveform with constant current density. The surface and cross-section characteristics of PEO coatings including morphology, elemental distribution, and phase composition were evaluated using FESEM, EDS, and XRD techniques. Voltage-time response indicated the concentration of SMS and KOH had a significant effect on the duration of each stage of the PEO process. More cracks and pores were formed at the higher concent…