Rheology and gelation behavior of gel-cast cordierite-based glass suspensions

A cordierite-based glass suspension was shaped by gel-casting method. Effects of various parameters like pH, volume fraction of glass particles, gelling agents and dispersant on the rheology of the prepared slurries were investigated. The results demonstrated that using sodium tripolyphosphate (STPP) dispersant brings about a suspension of minimum viscosity. The bending strength of the dried gels was increased with the gelling agents. In addition, the utilization of cross linkers at a fixed concentration of monomer led to the gradual enhancement of the bending strength of the dried bodies. A bending strength of ∼11 MPa was obtained for the most promising dried gel cast bodies.     

Optimization of pullulan production using Ca‐alginate‐immobilized Aureobasidium pullulans by response surface methodology

BACKGROUND: The production of pullulan from synthetic medium by Aureobasidium pullulans P56 immobilized in Ca‐alginate beads was investigated using batch and repeated batch fermentation systems. RESULTS: The highest pullulan concentration (19.52 ± 0.37 g dm^?3) was obtained with 2.0‐2.4 mm beads prepared from 2% sodium alginate solution. Pullulan production was mainly accomplished by immobilized fungal cells since leaked cells in the fermentation medium comprised 17.4% of the total fungal population at the end of fermentation. The pullulan proportion was 84.5% of the total polysaccharide in the fermentation medium. Response surface methodology was used to investigate the effects of three fermentation parameters (initial pH, agitation speed and incubation time) on the concentration of pullulan. Results of the statistical analysis showed that the fit of the model was good in all cases. The maximum pullulan concentration of 21.07 ± 0.48 g dm^?3 was obtained at the optimum concentrations of process variables (pH 7.31, agitation speed 191.5 rpm, incubation time 101.2 h). The gel beads produced pullulan under the optimized conditions for six consecutive batch fermentations without marked activity loss and deformation. CONCLUSION: The results of this study suggest that the immobilization of A. pullulans cells in Ca‐alginate gel beads is suitable for batch and repeated batch production of pullulan. Copyright © 2007 Society of Chemical Industry     

Sintering Behavior and Machinability of Phlogopite Glass Ceramics Containing Fe2O3

Mica-based glasses in the SiO₂-Al₂O₃-MgO-K₂O-F system were prepared by a sintering method to investigate the effects of different amounts of hematite (Fe₂O₃) on thermal and sintering behaviors besides machinability of the glasses by means of differential thermal analysis (DTA), X-ray diffraction, and scanning electron microscope techniques. DTA analysis on fine and coarse glass powders indicated that the main crystallization mechanism in this system occurred in the bulk rather than the surface. Increasing Fe₂O₃ content to 5 wt.% improved machinability of the glass ceramic. Fe₂O₃ led to the disruption of the glass matrix and facilitated the nucleation of the crystalline phase. Precipitation of sellite (MgF₂) crystals as heterogeneous nucleating sites for potassium phlogopite crystals acted as a second contribution to the machinability of the 5 wt.% Fe₂O₃-containing sample. However, introducing more than 5 wt.% Fe₂O₃ to the base glass prohibited the nucleation of MgF₂, and as a result, large micas formed within the glass. This together with precipitation of cordierite aggregates in highly doped glass with Fe₂O₃ led to lower machinability in these samples.     

Effect of Ce, Sb, and Sn on Solarization and Crystallization of an X-Ray-Irradiated Photosensitive Glass

The effect of Ce, Sb, and Sn photosensitive elements, individually and in combination with each other, on solarization and crystallization of an X-ray irradiated and a nonirradiated lithium silicate-based glass were investigated. According to the results, considering the crystallization behavior of the nonirradiated glasses, they were divided into Ce-bearing and Ce-free groups, in which the former group showed a clearer solarization tendency that manifested as an appearance of an absorbance peak at 318 nm in the spectrophotometry experiment. However, the results showed that in the irradiated glasses, the presence of Sb was more important in terms of improvement in crystallization view. Antimony decreased the differential thermal analysis (DTA) crystallization peak temperature from 655°C to 594°C and, in combination with the two other elements, changed the surface crystallization mechanism to a bulk one. The reactions that seemed to be responsible for the above-mentioned observations were discussed by spectrophotometry, DTA, X-ray diffraction, and scanning electron microscopic methods.     

Synthesis and characterization of diopside glass–ceramic matrix composite reinforced with aluminum titanate

Glass–ceramic composites in the SiO₂–CaO–MgO–(Na₂O) system, reinforced with 5, 10 and 20 wt.% aluminum titanate were synthesized by pressureless sintering. Optimum sintering temperatures with maximum relative density were determined for each composition. The composites were fired above the crystallization peak temperature of glass–ceramic. Mechanical properties of glass–ceramic and sintered composites, such as fracture toughness, flexural strength and Vickers microhardness, were investigated. The sintered composites were characterized by scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS) and X-ray diffraction (XRD). The results showed that the composite containing 10 wt.% aluminum titanate has desirable behavior in comparison to the base glass–ceramic and the other compositions. It seems that crack deflection by aluminum titanate particles is the prevalent mechanism for improving mechanical characteristics.     

Batch and Continuous Production of Lactic Acid from Beet Molasses by Lactobacillus delbrueckii IFO 3202

Process variables were optimized for the production of lactic acid from pretreated beet molasses by Lactobacillus delbrueckii IFO 3202 for batch and continuous fermentations. In the batch fermentation, maximum yields (95·4% conversion, 77·1% effective) and maximum lactic acid volumetric productivity (4·83 g dm⁻³ h⁻¹) was achieved at 45°C, pH 6·0, 78·2 g dm⁻³ sugar concentration with 10 g dm⁻³ yeast extract. Various cheaper nitrogen sources were replaced with yeast extract on equal nitrogen bases in batch fermentation. Of all the nitrogen sources tested, yeast extract yielded the highest and malt sprouts yielded the second highest level of lactic acid. In the continuous fermentation, maximum lactic acid (4·15%) was obtained at a dilution rate of 0·1 h⁻¹. Maximum volumetric lactic acid productivity (11·20 g dm⁻³ h⁻¹) occurred at D = 0·5 h⁻¹ dilution rate. © 1997 SCI.     

Antimicrobial and antioxidant properties of burgers with quinoa peptide-loaded nanoliposomes

This study was aimed to examine the antioxidant (thiobarbituric acid reactive substances [TBARS], peroxide value [PV], and as well as antimicrobial (total bacterial count, Staphylococcus aureus [S. aureus], mold and yeast counts) activities and spoilage indices (total volatile base nitrogen [TVB-N]) of quinoa peptide-loaded liposomes incorporated into burger during 12 days of refrigerated storage. Among four prepared batches, the lowest TBARS, PV, and TVB-N values (0.281 ± 0.05 mg MDA/kg, 3.25 ± 0.34 mEq/kg and 18.65 ± 0.88%, respectively) were correlated with T3 treatment (5 mg/ml peptide). A significant different in the antimicrobial activity among each treatment after 12 days of storage was noted. At the end of refrigerated storage, the highest mean of total bacterial count, S. aureus, mold and yeast (8.36 ± 0.22, 4.19 ± 0.2, and 3.28 ± 0.05 log CFU/g, respectively) were observed in control group, while the lowest corresponded values (3.95 ± 0.2, 2.52 ± 0.25, and 1.52 ± 0.02 log CFU/g, respectively) were noted in T3 treatment. The results showed that the antimicrobial and antioxidant properties of the examined burgers were improved by incorporation of liposomes quinoa peptides encapsulated.     

Thermal and crystallization behavior of SiO2-PbF2 glass system in the presence of ErF3 and Al2O3

Oxyfluoride glass-ceramics have been introduced as one of the best bulk hosts for upconversion process of rare-earth ions. However, less attention to the technological topics in the process of glass crystallization has hindered the development of them in industrial scale applications. In this research, SiO₂–PbF₂ glasses were investigated to clarify the ambiguous role of rare-earth ions and alumina content in the microstructure and crystallization behavior. Results indicated that Er³⁺ addition caused a liquid-liquid phase separation via nucleation and growth mechanism, which led to single phase crystallization of β-PbF₂:Er³⁺ solid solution. Moreover, Er³⁺ had a significant effect on the crystallite size, size distribution, and PbF₂ crystallization temperature. On the other hand, increasing Al₂O₃ content enhanced the transparency and thermal stability of glass samples, whereas it reduced the amount of fluorine loss and increased the dissolution of Er³⁺ in fluoride crystalline structure. These results address some of the most controversial issues about crystallization behavior of rare-earth-doped oxyfluoride glasses.     

Floor tile glass-ceramic glaze for improvement of glaze surface properties

Simultaneous improvement of surface hardness and glossiness of floor tile glaze, without changing its firing temperature, was the main purpose of the present paper. Thus, various glazes in the system of CaO–MgO–SiO₂–Al₂O₃–ZrO₂ were prepared and their crystallization behaviors within a fast firing cycle were investigated. With increasing amounts of calcium and magnesium oxides to base glass, the optimum glass-ceramic glaze was obtained. The results showed that with increasing of CaO and MgO part weights in frit, the crystallization peak temperature was gradually decreased and the intensities of diopside and zirconium silicate were increased. The comparison of micro hardness for the optimum glass ceramic glaze derived in this work with a traditional one used in floor tile industries indicates an improvement of 21%. It was found that the glaze hardness not only depend on the amount and type of crystalline phases, but also on the residual glass composition. Furthermore, it was observed that the glaze micro hardness is only slightly affected by thermal expansion mismatch of body and glaze.