Papers by Keyword: Glassy Phase

Abstract: This project is devoted to the study of the felsite properties for the purpose of its application in the production of various types of fine ceramics: ceramic tiles, acid-resistant tiles, aluminosilicate proppants, etc. Felsite is a mixture of quartz (about 40%) and feldspars. In the compositions of ceramic masses, felsite can play the role of both nonplastic due to the quartz content, and flux due to the content of feldspars, that reduces the amount of mixture components. When felsite is fired, the melt appears at a temperature above 950°C. The felsite has a sintering effect when fired at a temperature of 1000°C. Glass phase enriched with SiO₂ ensures the absence of material deformation after firing. Also, glassy phase provides high-acid and chemical resistance of materials based on it. In addition, after firing above 1150°C, felsite has a light color, which is a great advantage in comparing it as a melt with other iron-alkali-containing materials. Ceramics based on felsite does not require the use of opacified glazes.

Abstract: During the operation of porcelain stoneware sometimes there is a type of defects associated with crumbling from the edge of tile. In addition, cracks occur when a small object is fallen and during transportation of the products. Compared to conventional ceramic floor tiles, porcelain stoneware has increased strength, which explains its high price. The brittle failure is most likely, due to the hardening of glassy phase of tiles during cooling stage of the firing process. As a rule, the quenching temperature depends on the chemical composition of the glassy phase formed during firing. Both the phase and chemical composition of porcelain stoneware, and the chemical composition of the glassy phase are determined.

Abstract: In this study, glassy phase is formed by SiO₂-K₂O addition to serve as amorphous grain boundary transition layer. SiC (SiO₂-K₂O) / Cu composite material were prepared by two-step coating method and hot pressing sintered below 770°C, 30MPa for 1.5h, using α-SiC as main reinforced phase, SiO₂-K₂O as grain boundary and Cu as matrix. The Cu-SiC volume ratio was 75:25. The SiO₂ contents were 5vol.%, 10vol.%, 15vol.%, 20vol.% and 25vol.% of the total volume of the SiC / Cu. XRD and SEM techniques were used to characterize the composite particles and the sintered compacts; Archimedes method, Vickers hardness tester, universal testing machine to test the apparent porosity of the composite materials, the Vickers hardness and the bending strength, respectively. The results showed that with increasing of glassy phase contents, the Vickers hardness and the bending strength first rise and then drop, at the same time, it shows the opposite tendency for the apparent porosity. The sintering samples with the SiO₂ content of 15vol.% have the optimum mechanical properties, the Vickers hardness reached 1.49 GPa, and the bending strength was close to 235 MPa.

Abstract: Glasses with two different compositions were added to yttria-stabilized zirconia TZP powder: a CAS glass and a bioactive glass. These additions allowed liquid phase sintering to occur at temperature as low as 1300 °C. The concentrations of each glass additions were of 1, 3, and 5 wt%. The prepared compositions were uniaxially pressed at 50 MPa and sintered at 1300oC for 2 hours. The sintered samples were characterized for their mechanical properties, by measuring four-point bending mechanical strength, Vickers microhardnesses, and fracture toughness ( K_Ic ). Vickers microhardness measured values ranged from 10 to 12 GPa, while fracture toughness, from 3.8 to 4.4 MPa.m^1/2. The flexural mechanical strength was situated between 302 and 408 MPa. The achieved mechanical properties, from sintered samples were possible due to glassy phase additions. These properties, associated to biocompatibility, enable such materials to be used in different applications, including bioceramics.

Abstract: TZP yttria-stabilized zirconia powder was mixed with two types of glasses as sintering additives: CAS glass and a bioactive glass. These additions were designed toward the material applications as bioceramics. The glassy phase was chosen to promote liquid phase sintering at lower temperature, when compared to pure material. This procedure contributed to reduce the fabrication costs while keeping the material biocompatibility. Each type of glass was added in concentrations of 1, 3, and 5 wt%. The prepared powders were uniaxially pressed at 50 MPa, and then sintered at 1300°C for two hours. The sintering behavior was evaluated by measuring the final sintered densities. It was found that the samples with bioactive glass additions were denser than those with CAS glass. Zirconia TZP powders without glassy additions would not sinter in this temperature. The microstructure of the sintered samples was characterized by SEM and XRD. The sintered ceramics exhibited both submicrometric and uniform grains. The analyzed grain sizes were slightly lower for the samples with CAS additions than for those with bioactive glass additions.

Abstract: The glassy phase in alumina ceramics is implied for Al₂O₃-SiO₂-CaO. The content of Al₂O3 and CaO can be measured by the common titration method for their total dissolution in 5% HNO₃ and that of SiO₂ can be measured by gravimetric method. Therefore, the glassy phase composition in alumina ceramics can be analysed. The content of each component is measured exactly by both powder method and sheet method.

Abstract: It is reported that a pitch gradient is formed in a side chain cholesteric liquid crystalline polymer (ChLCP) through a novel method. Heating up the ChLCP within the temperature range of the cholesteric (Ch) phase leads to the first availability of its planar texture. Then, the ChLCP film with the planar texture is cooled down to its glassy (G) state in line with the temperature difference between the upper and the bottom substrates. The SEM image indicates clearly a pitch gradient perpendicular to the substrates, and the results of transmission spectra show that the reflective bandwidth of the ChLCP film with the pitch gradient is greatly broadened.

Abstract: Two kinds of ultra high temperature ceramics (UHTC), ZrB2-20Vol.%SiC and ZrB2-15Vol.% SiC-5Vol.% SiCn (nano-size) were prepared by spark plasma sintering (SPS). The residual strength was used to characterize thermal shock resistance of ZrB2-SiC ceramics by quenching tests in the water. The mechanism of thermal shock damage of the ceramics was examined by SEM analysis. The results showed that the formed glassy phase has significant effect on thermal shock resistance of ZrB2-SiC ceramics. When the thermal shock temperature rises, the residual strength of ZrB2-SiC ceramics after thermal shock will decrease gradually. The formed glassy phase when quenched from the temperature of 1400°C can repair or heal the cracks and induce the higher residual strength. However, when the temperature increases to 1600°C, the residual strength of ZrB2-SiC ceramics decreases significantly due to the volatilization of the glassy phase. The residual strength of ZrB2-15Vol.% SiC-5Vol.% SiCn ceramic is higher than that of ZrB2-20Vol.%SiC ceramic, because nano SiC is easy to be oxidized and to induce the formation of more glassy phases and to improve the thermal shock resistance of the sample.