Crystallization and void formation in ZnO–B2O3–SiO2–MgO sintered solder glasses

The evolution of crystallization and porosity changes with firing temperature were studied in ZnO–B2O3–SiO2–MgO glasses. Those glasses presintered at 610 °C to a low porosity were crystallized in the temperature range of 690–870 °C. The glasses were crystallized by a surface crystallization mechanism. The porosity increased with the crystallization temperature. In the temperature range of 710–790 °C, several crystalline phases, such as 3ZnO–B2O3, willemite (2ZnO–SiO2), 5ZnO–2B2O3, and another form of zinc silicate (2ZnO–SiO2), produced at relatively low temperatures, were produced, while above 800 °C only the 2ZnO–SiO2 phase co-existed with a glass phase. Only an observed density difference between the glass and the crystallized glass cannot be attributed to the void formation during the crystallization reaction. Due to the crystallization the composition of the remaining glass around the crystalline phases is expected to change. The depletion of a certain component in the remaining glass, probably the SiO2 due to the production of the 2ZnO–SiO2 phase, might result in the increase in the vapour pressure of the remaining glass and lead to the observed increase in porosity. Below 800 °C, at which temperature the crystallization rate is fast and only a small amount of the glass phase remained, the porosity remained constant after the completion of the crystallization. Contrarily at 860 °C the porosity continuously increased with firing time. This revised version was published online in November 2006 with corrections to the Cover Date.     

GROWTH INHIBITION OF CLOSTRIDIUM PERFRINGENS VEGETATIVE CELLS AND SPORES USING CHICKEN IMMUNOGLOBULIN Y

Egg yolk antibody (IgY) was isolated by the water dilution method from the egg yolk of chickens immunized with Clostridium perfringens vegetative cells and spores. Specific binding activity of IgY against C. perfringens vegetative cells and spores remained relatively high during the immunization period (up to 9 weeks). The titer of specific IgY against C. perfringens spores was 1.4-fold less than that of specific IgY against C. perfringens vegetable cells. The specific IgY powder (10 µg/mL) was found to inhibit the growth of C. perfringens vegetative cells or C. perfringens spores in a liquid medium. The difference of C. perfringens vegetative cell growth between the treatment and control groups was 8.9  ×  10⁶ colony forming units (cfu)/mL at 8 h of incubation and 9.95  ×  10⁷ cfu/mL at 24 h of incubation. Significant cfu reductions in C. perfringens spores were also observed with specific IgY powder at 24 h of incubation.

PRACTICAL APPLICATIONS

IgY antibody exerts an antimicrobial activity against pathogens by binding, immobilizing and consequently reducing or inhibiting the growth, replication or colony forming ability of pathogenic bacteria; thus, it is proved to be a viable alternative for antibiotics and preservatives. In this study, IgY against Clostridium perfringens can be used to replace chemical preservatives in food industries. Because IgY functions well at low temperature, it can be used to inhibit the growth of Clostridia which germinate in refrigerated storage conditions, thus preventing foodborne enterotoxicity caused by such bacteria. In practical applications, natural antimicrobial IgY antibody can be applied to meat products for the improvement of food safety.