The foaming mechanism of mixtures of fly ash (FA) and incinerated ash of sewage sludge was investigated in relationship with the chemical states of iron in the sintered bodies. The FA content was 20mass% of the total weight of the mixtures. The mixtures were pressed in a discus body (3cm in diameter), which was fired at 1000∼1100°Cfor 1 h in air or nitrogen. In the case of firing in nitrogen, the lowest apparent density for each fired body with 20mass% FA was 0.82 g cm-3. The large foaming was observed during firing in nitrogen but not during firing in air above 1050°C. The results of diffuse reflectance spectra and electron spin resonance measurements indicated that most of the ferric oxide in the samples fired above 1050°C in nitrogen atmosphere was reduced to ferrous oxide. The large forming was probably due to the evolution of oxygen from iron (III) oxide and the oxidation of residual carbon inside the samples after melting of the surface at high temperatures in nitrogen.
Zeolite is a microporous aluminosilicate material with uniform pore size of less than 2 nm and chemical, mechanical, and thermal stability. In general zeolite is synthesized from silica, alumina, mineralizer (alkali metal hydroxide and fluoride) and water. On the other hand, the production volume of various kinds of high-quality glass which are utilized for high-tech products such as liquid crystal displays and plasma displays is rapidly increasing. We tried to synthesize zeolite from an aluminoborosilicate glass which is used in LCD panel glass substrate and mainly composed of silica and alumina. By using only aluminoborosilicate glass powders, zeolite was synthesized at synthesis temperature higher than 423K and the synthesized samples had GIS type zeolite or ANA type zeolite related structure according to XRD analysis. We investigated the effect of Si/Al ratio and NaOH concentration to zeolite synthesis. In the range of Si/Al was 5.0 to 7.5, GIS type zeolite which has tetragonal structure was synthesized with 0.2M NaOH and 1.0M NaOH, though, by using only aluminoborosilicate glass powder, cubic GIS type zeolite has synthesized. It is because crystal structure of GIS type zeolite depends on chemical composition. In the case of Si/Al = 10.0, ANA type zeolite was synthesized with dilute NaOH solution and GIS type zeolite was synthesized with concentrated NaOH solution. From SEM observation, the products had the surface structures specific to zeolite. It was thought that zeolite was successfully synthesized from the aluminoborosilicate glass by hydrothermal processing. And kind of zeolite synthesized depended on Si/Al ratio and concentration of NaOH solution.
ZrO2 porous ceramic was prepared by a unidirectional freeze casting using aqueous slurries containing urethane latex binder. The effects of solid loading, binder content and cooling rate on the pore size distributions of sintered bodies were investigate by scanning electron microscopy and mercury intrusion porosimetry. Porous ZrO2 ceramic with continuously long-ranged pore structure was obtained by the unidirectional freezing of the aqueous ZrO2 slurry, followed by sublimation of ice and firing at 1400°C for 1h in air. The solid loading of the slurry scarcely affected the pore size of sintered bodies. However, the pore volume decreased and the thickness of pore wall increased with increasing solid content in the slurry. Binder content largely influenced the strength of green bodies. At low binder content, green bodies became weaker, and therefore many cracks were generated bodies. The effect of cooling rate on the sintered body was small, but pore size decreased with increasing cooling rate. These results show that the pore size and volume can be controlled by modifying the cooling rate of the slurries and slurry concentration.
Yttria-stabilized tetragonal zirconia (Y-TZP) and fine-grained alumina deform plastically at high temperatures and the mechanisms have been studied. Y-TZP shows superplastic behavior with extensive grain boundary sliding. On the other hand, Al2O3 possibly deforms by diffusional creep which is limited by interface reaction. Thus, a number of studies about deformation of ceramic materials have been reported, however, its mechanism has not yet been fully clarified. In this study, sintered Y-TZP-Al2O3 composite samples were prepared, and in order to examine its behaviors in a wide range of stress (∼2 to 350MPa), the specimens were used for three kinds of deformation tests : constant cross head speed compressive test, constant load compressive test and bending creep test. The results of strain rate έ vs true stress σ on a logarithmic scale, which generally determines stress exponent n, revealed four stages of flow (region I∼IV) exhibiting a sigmoidal curve. This indicates that the behaviors change from diffusional creep with n∼1 in region I at low stresses through a transition state with n >3 in region II at intermediate stresses and to superplasticity with n∼2 in region III at high stresses. The decrease in n with increasing stress from ∼2 in region III to ∼1.5 in region IV implies that diffusional creep tends to be dominant at higher stress. Furthermore, the increase in n from ∼2 in region III to >3 in region II suggests the occurrence of a threshold stress σ0 for superplastic flow. From the results of έ vs σ0 with different grain sizes, as the grain size is larger, the stress exponent n in region II seems to decrease gradually with increasing grain size, suggesting that threshold stress σ0 decreases with grain size.
The feasibility of recycling scallop shell as an adsorbent was evaluated. Crushed shells were encased in plaster, which acts as a source of calcium. The effects of shell particle size and volume fraction in consolidated body on phosphorus removal capacity were investigated. The crystalline phase precipitated on the scallop shell surface after immersing in KH2PO4 aqueous solution with hydrated gypsum was characterized by powder X-ray diffraction and thermogravimetry-differential thermal analysis. The phosphorus removal capacity of the shell powder -plaster composite increased with increasing the volume fraction of shell powder up to 30vol/%. However, there was little difference in phosphorus removal efficiency between samples containing 30vol/% and 50vol/% shell powder, and these samples removed more than 90% of 50ppm phosphorus in 10 days. Small particle size of shell powder was effective for phosphorus removal. By the use of the shell powder below 0.125mm, more than 80% of 50ppm phosphorus was removed in 4days. The results of XRD and TG-DTA showed that DCPD(CaHPO4・2H2O) precipitated on the surface of the scallop shell and grew with increasing immersion time. It was concluded that the phosphorus removal would proceed through the precipitation of DCPD seed crystals and its growth on the surface of scallop shell.
Ceria-zirconia-terbia solid solutions were synthesized by co-precipitation method. The powders were characterized by XRD, colorimetric assessment and UV-Vis diffuse reflectance. A solid solution phase structure was obtained for all of the samples heated at 900°C and belongs to cubic fluorite structure or distorted fluorite structure. It was found that the lattice size decreased with increasing Zr content in the range x = 0 to 0.8 in ZrxCe1-xO2 and ZrxCe0.99-xTb0.01O2-δ. Diffuse reflectance spectra of the ZrxCe1-xO2 solid solutions in the UV region showed the broad shoulder-type band at 320-350 nm, which was assigned to interband transitions in CeO2 and additionally broader band in higher wave length region in solid solution. It was observed that ZrxCe1-xO2 powder became deeper yellow depending on Zr content, and that the doping of Tb resulted in warm colour in CeO2-ZrO2 based solid solution. The powders in the system of ZrxCe1-xO2 and ZrxCe0.99-xTb0.01O2-δ were possible pigments with environmental friendly properties toward future ceramic application.
Corrosion fatigue is one of the most important issues involved in operating compressors in gas turbine power plants securely. To address this issue, we investigated corrosion pit growth as well as crack growth behavior initiated from corrosion pits. We also developed a method for evaluating corrosion fatigue life under service conditions. Although we did not observe any obvious relationship between operative stress and corrosion pit sizes of operated compressor blades, our investigation results suggested that corrosion pit growth was dependent on operational time. We therefore calculated and propose an estimation curve for corrosion pit growth. Under a corrosive environment with highly concentrated Na+, Cl-, and SO42-, the fatigue limit decreased to 40% of in-air strength. It also tended to decrease in inverse proportion to artificial defect size. We calculated crack growth threshold stress range σth from the relationship between stress and artificial defect size and found that the crack growth threshold stress intensity factor range ΔKth was 2.4MPa √m under a corrosive environment. We also measured operative stress in compressor blades under service conditions and calculated equivalent stress σeq from stress frequency distribution. We found out that corrosion pit size corresponding to crack initiation was 0.58mm from obtained σeq and ΔKth and developed an evaluation diagram for calculating operational time from our estimation curve for corrosion pit growth. Our results suggest that we can measure operative stress to evaluate corrosion fatigue life quantitatively and formulate allowable stress.