Silica, nitrogen, and nitrogen-plus-silica co-doped titania powders were synthesized via sol-gel method. Nitrogen, silica, and co-doping shifted the anatase-to-rutile phase transition toward higher temperatures. Silica was found to enter the anatase lattice, and nitrogen was presumed to enter thetitania crystal structure as well. Nitrogen doping and SiO2/N-co-doping shifted the light absorption toward the visible region.
COBISS.SI-ID: 1879143
A model organic pigment (β copper phthalocyanine) was encapsulated by silica using water glass as a precursor. It is shown that the thickness, porosity anduniformity of silica shells (coatings) around individual pigment particles depend significantly on pH and temperature of synthesis. It is further demonstrated that the obtained silica shells can serve as an efficient protection against the highly reactive products of photocatalysis. The degree of protection depends not only on the thickness of silica shells but also on their porosity.
COBISS.SI-ID: 1856615
The patina that covers bronze often has an aesthetic and/or historical value. It should therefore be protected from corrosion in aggressive urban environments. In the present study, two green chemically obtained bronze patinas were examined, as well as an electrochemical patina that resembles the natural patina. Different protective systems were applied to the samples azole-based inhibitors in an ethanol solution, azole-based inhibitors in polymer coating or wax coating. The efficiency of these protective systems during immersion in simulated urban rainwater was monitored by electrochemical impedance spectroscopy. The results showed that the protection of patinated bronzes by the inhibitor/ethanol system was long-lasting and most effective for electrochemically patinated bronze. Protective properties of investigated inhibitor/Paraloid B44 systems were found to depend on inhibitor present in the coating as well as on properties of the patina layer on which it was applied. For all types of patina BTA/Paraloid B44 coating exhibited better protecting properties than MTI/Paraloid B44 coating. Carnaubawax was found to provide stabile and effective protection, especially for nitrate patinated bronze.
COBISS.SI-ID: 1906535
Patinas form spontaneously on copper and high copper alloys when exposed to humidity and air. They usually protect the underlying metal from corrosion. Bronze is often chemically patinated by artists to achieve an antique appearance. However, in the case of chemical patinations on bronze, there is a lack of studies about their change over time during exposure to different types of environments. Recent types of bronze, brown patina and two green type patinas (green chloride and green nitrate patina) applied over a brown patina, were selected for testing. The aim of the present study was to monitor the transformation process of chemically formed patinas and of the bronze itself after exposure to simulated urban acid rain, for a period of 35 days. The structures of the patina and corrosion products were characterized by scanning electron microscopy (SEM) and Raman spectroscopy. Three differently coloured patinas were scraped off from the bronze statue of the poet France Prešeren, two green type patinas and one brown type, to predict the probable influences of the environment, the base alloy and previously used patination techniques.
COBISS.SI-ID: 1903207
In this paper, a possibility of using a frequency spectrum of ultrasonic P-waves to monitor the formation of structure of cement pastes at early ages is studied. A new parameter, labelled as a TG parameter, is defined as a dimensionless ratio between maximum amplitudes of two dominant frequency ranges that appear in a frequency spectrum of received ultrasound signals. Four stages and three characteristic points can be identified on the TG-vs.-time graphs, indicating that the development of the frequency spectrum is closely related to the setting phenomena. By comparing the TG parameter with the P-wave velocity and temperature evolutions in time, important milestones in the process of formation of microstructure were identified, such as the time of reduced workability and a period of intensive setting. The combined use of P-wave velocity and TG parameter results in a comprehensive ultrasonic method that gives a more complete picture of setting.
COBISS.SI-ID: 1920103