Papers by Keyword: Chemical Durability

Abstract: Inorganic foams offer several unique properties such as low thermal conductivity, fire resistance, or UV stability. Inorganic foam specimens were synthesized from fly ash and aluminium powder through an alkali-activation process. Depending on mix proportions, bulk densities ranged between 400 and 800 kg/m³. Thermal treatment at 80°C for 12 hours accelerated curing process. Compressive strength was found in the range 4.5-9.0 MPa, flexural strength 0.6-1.7 MPa, Young's modulus 0.6-1.1 GPa, thermal conductivity 0.14-0.16 W/m/K and thermal capacity around 1100 J/kg/K. Exposing the foams to temperature 800°C led to a small decrease of compressive strength while exposure to 1100°C sintered the foam to higher strength of 13 MPa. Volumetric shrinkage 20% occurred at 1100°C without further disintegration. Residual compressive strength was determined after exposure to NaCl, HCl, Na₂SO₄, MgSO₄, H₂SO₄. The highest reduction to 20% occured in both acids with pH=2 after one year of exposition. Digitized microstructures entered finite element analysis to validate a stress-strain diagram.

Abstract: In alkaline earth aluminoborosilicate glasses CaO-B₂O₃-Al₂O₃-SiO₂, the changes of structure and properties caused by variations in the ratio Al₂O₃/B₂O₃ were investigated. The structure was investigated by Fourier transform infrared spectroscopy. The dielectric constant and tangent loss were measured at 1 MHz. Chemical durability was evaluated by weight losses of glass samples after immersion in HCl and NaOH solutions. The results indicated that the fraction of four-coordinated boron atoms (N₄), chemical durability and dielectric properties increased with increasing Al₂O₃/B₂O₃ replacements.

Abstract: In alkaline earth aluminoborosilicate glasses containing P₂O₅, the changes of structure and properties caused by variations in the ratio P₂O₅/B₂O₃ were investigated. The structure was investigated by Fourier transform infrared spectroscopy and nuclear magnetic resonance. The dielectric constant and tangent loss were measured at 1 MHz. Chemical durability was evaluated by weight losses of glass samples after immersion in water. The results indicated that the fraction of four-coordinated boron atoms (N₄), chemical durability and dielectric properties increased with increasing P₂O₅/B₂O₃ replacements.

Abstract: In alkaline earth aluminoborosilicate glasses CaO-B₂O₃-Al₂O₃-SiO₂, the changes of structure and properties caused by variations in the ratio SiO₂/B₂O₃ were investigated. The structure was investigated by Fourier transform infrared spectroscopy. The dielectric constant and tangent loss were measured at 1 MHz. Chemical durability was evaluated by weight losses of glass samples after immersion in HCl and NaOH solutions. The results indicated that the fraction of four-coordinated boron atoms (N₄), chemical durability and dielectric properties increased with increasing SiO₂/B₂O₃ replacements.

Abstract: In the paper, a series of Na2O-CaO-Al2O3-SiO2 system glasses following similar compositions to the soda-lime-silicate float glasses and possessing more excellent physi-chemical properties were prepared with different Al2O3/SiO2 ratio. The structure of glasses have been studied by IR and density tests. The investigation of Al2O3/SiO2 on the performance was carried out by bending strength tests, linear dilatometry and chemical durability tests in aqueous and alkaline environment. The results showed that the number of no bridging oxygens decreased with increasing the Al2O3/SiO2 ratio, the glass network structure and density increased, which leading to enhance the bending strength, thermo-stability and chemical durability of glass.

Abstract: In this paper, optical, the chemistry stability, and glass transformation, softening temperature were studied on Bi2O3-SiO2-ZnO-B2O3 system glass doped with 2wt.%、4wt.%、6wt.% and 8wt.%TiO2. The results showed that glass surface has no stripes and defects with transmittance between 20%-50%. Moreover, with the increasing of Ti content, the results of the experiments indicated that the metal oxides TiO2 could enhance the glass chemical stability most clearly, and regulate the glass transformation temperature.

Abstract: Bioglass Ceramics having molar composition 40SiO2-(44-X)CaO-10MgO-6P2O5-XCaF2 (where X = 0 to 8%) were prepared by conventional melting process in an electric globar furnace at 1400±10°C. Controlled crystallizations were carried out to convert the bioglasses to their corresponding ceramics. Nucleation and crystallization regimes were carried out by differential thermal analysis. The crystalline phases termed hydroxy fluoroapatite, akermanite and wollastonite were identified by using x-ray diffraction analysis. The investigation of bioactivity for the prepared glass and glass ceramics was done by infrared absorption and infrared reflection spectra after immersion in simulated body fluid (SBF) for different periods at 37.8°C. Scanning electron microscope (SEM) analysis was carried out to investigate the surface texture. Micrographs show the formation of HCA layer on the surface of the bioglass ceramics samples after 7 days of SBF treatment. The surfaces of the samples were completely covered with irregular and needle-like aggregates of Ca–P layer. The released ions were estimated by atomic absorption spectroscopy. The chemical durability of these materials was determined by pH measurement methods and it was found that pH of the solution increases up from 1 to 7 days. Further, pH decreases with increasing time period, from 15 to 30 days in SBF solution.

Abstract: The effect of deposition parameters such as sputtering power, nitrogen flow rate and thickness of TaN_x on the optical performance and chemical durability of composite Tantalum nitride /Ag/ tantalum nitride (TaN_x/Ag/TaN_x) films was investigated. When the configuration of composite film was TaN_x (60nm)/Ag (12nm)/TaN_x (60nm) accompanying with the sputtering power 120W and the nitrogen flow rate 50sccm, the visible light transmittance of composite film could reach up to 80% at the wavelength of 550nm and the emissivity was 0.087. In addition, the chemical durability of the coatings was evaluated and the results indicated that the low-e coating presented very good chemical durability.

Abstract: Hydroxyapatite powder is produced using combustion synthesis method. The powder was produced using a low-temperature processing method involving time as short as 15 minutes. As silver is known to have anti-bacterial properties, silver-doped hydroxyapatite was also produced by the same method. Both the powders were fully crystalline. XRD indicated the presence of an additional phase of CaO in both the samples. FT-IR indicated the presence of hydroxide, phosphate and carbonate groups. Silver addition tends to control the reactions of powder with a test Tris buffer environment and maintain a stable pH for a longer period of 500-hour duration.

Abstract: Glass fiber is commonly used as thermal insulation for the equipment in nuclear power plants. In case of LOCA (Loss Of Coolant Accident), the insulation can be damaged by the jet impact and carried to the screens of the emergency systems needed to cool the reactor. In this case, the fibers can be strongly corroded by particular cooler solutions and their behavior under this environment can modify the head loss of the screens. The pH value of coolant solution can be stabilized respectively by borate or phosphate buffering systems depending of the plants. A new type of small scale laboratory equipment allowing simultaneous study of the chemical durability of glass fibers and hydrodynamic conditions on the glass fiber bed placed on the screen was developed and tested. The results obtained for leaching of glass fibers in sodium borate and sodium phosphate solutions show the significant difference between the saturation levels of Ca, Al, and Si in tested leaching solutions. The observed difference in leaching chemistry caused significant differences in the head loss value and its time development. This preliminary conclusion opens a new research field to improve the NPPs but it has to be substantiated by additional records and sensitivity studies including uncertainties analysis.