Papers by Keyword: Seeding

Abstract: This study explored the effects of formulation modifications of natural hydraulic lime (NHL) mortars exposed to hot temperature and high humidity conditions. The modified mortars were seeded by oyster shell powder, partially replacing the sand. The mortar samples underwent a curing period of 56 days with five observation days. The pH, carbonation depth, flexural strength, compressive strength, sorptivity, and morphology were studied. The results indicated that seeded mortars were more successful at setting and hardening high humidity settings. In addition, curing the mortars at higher temperatures hastened the hydration reaction significantly. The data indicate that seeded mortars can improve performance in several areas, notably carbonation rate (25%-45%), flexural strength (16%-60%), compressive strength (20%-55%), and sorptivity (18%-25%). The experimental protocol shows that the hardened mortar pore system is affected by the water-binder ratio, hydration level, relative humidity, and carbon dioxide concentration. The hydration of mortar greatly influences its strength. Using oyster shell powder as an aggregate substitute increased the performance of the mortars by microstructure and capillarity development. This circumstance is significant in our comprehension of modified lime mortars and seeding compounds, especially in hot-humid environments.

Abstract: Nanostructured zinc oxide (ZnO) particles were grown on paper substrate made from Abaca hybrid 7 pulp. Microwave irradiation technique was used at power levels (180 and 540W) and exposure times (5, 10, 20 and 25 minutes). Chemical transformations were observed using Fourier Transform Infrared (FTIR) Spectroscopy. The effects of the power levels and exposure times on the morphology of the nanostructures were determined using scanning electron microscopy. FTIR spectra proved the embedment of ZnO on the paper substrate. Power levels and exposure times affected the distribution, particle size and structure of the ZnO nanoparticles. Higher power level and longer exposure resulted to the formation of more ZnO with larger particles. Grainlike and flowerlike ZnO nanostructures were formed at lower and higher levels, respectively.

Abstract: The method to attach seed to crucible lid as well as seed quality is very important for obtaining high quality crystals. Therefore, modified seeding method was developed for improving adhesive layer between seed and graphite crucible lid. SiC single crystal grown with modified seeding method definitely exhibited lower micropipe density (MPD) and lower full width at half maximum (FWHM) values comparing with values from conventional seeding method. Etch pit density of SiC crystal was successfully decreased with using the modified seeding method.

Abstract: This paper reports a method for producing α-Al₂O₃ at low temperature from aluminum alkoxide using a combination of seeding of α-Al₂O₃ nanocryatallites and adding of inorganic alumina sol. An alkoxide alumina sol was obtained by hydrolyzing aluminum isopropoxide in water at 80°C and then peptizing the hydrolyzed aluminum isopropoxide using acetic acid at 80°C. An inorganic alumina sol was obtained by producing aluminum compound with a homogeneous precipitation method using aluminum nitrate and urea in aqueous solution and then peptizing the aluminum compound using acetic acid at room temperature. α-Al₂O₃ nanocrystallites were added to the alkoxide alumina sol containing the inorganic alumina sol. The addition of inorganic alumina sol provided successful fabrication of a crack-free α-Al₂O₃-seded alumina film by a spin-coating technique. The sol containing α-Al₂O₃ nanocrystallites was transformed to an α-Al₂O₃-seeded alumina gel by drying the sol at room temperature. The non-seeded alumina gel was crystallized into γ-Al₂O₃ at a temperature below 900°C. In contrast, the alumina seeded at 1% α-Al₂O₃ nanocrystallites content began to be transformed to α-Al₂O₃ by annealing at the temperature. The seeding and the adding promoted crystallization of the alumina gel into α-Al₂O₃. The promotion of crystallization was significant with an increase in α-Al₂O₃ nanocrystallites content by weight in the final seeded alumina gel.

Abstract: The effect of (i) heterogeneous nucleation by seeding or (ii) doping with neodymium on the formation of lanthanum hexaaluminate was studied during sol to gel conversion. The resultant dried gels were calcined at various temperatures starting from 1100°C to 1600°C for 2 h to study the phase evolution and microstructure.The combined effects of advanced sol gel processing and heterogeneous nucleation promoted the formation of lanthanum hexaaluminate phase at lower temperature (1200°C) than the conventional routes (1300°C). Lanthanum hexaaluminate phase was detected at 1200°C and 1300°C in seeded gel (SG) and unseeded gel (UG), respectively. Heterogeneous nucleation of SG decreases the temperature of formation of lanthanum hexaaluminate by 100°C. Single phase lanthanum hexaaluminate was formed at 1600°C in seeded gel whereas trace of lanthanum monoaluminate phase was still present in UG even at 1600°C.On the doped ones, randomly grown platelets of lanthanum magnesium hexaaluminate form a porous interlocking structure. Presence of various percentages of neodymium oxide significantly modifies the porous interlocking microstructure into self-reinforced, card-house like microstructure. Platelets of rare earth rich magnesium hexaaluminate were grown preferentially more than the stoichiometric rare earth magnesium hexaaluminate at elevated temperature greater than 1450°C. Rare earth rich magnesium hexaaluminate platelets formed the skeleton of a card house structure and the tiny platelets of stoichiometric rare earth magnesium hexaaluminate fill the rest. Lattice parameters of the hexagonal unit cell (c and a) decrease, relative density increases and pore size distribution remained almost unaltered with the increment of doping concentration.

Abstract: The preparation of a ZSM-5 zeolite membrane on porous stainless steel disk by hydrothermal synthesis with electrophoretic deposition (EPD) as a seeding method was investigated. Micron size ZSM-5 crystal powder was seeded by EPD on the support disk by using ZSM-5 powder dispersed in ethanol. The seeded amounts were easily controlled by the deposition time during EPD. The membrane after secondary growth had a low amount of zeolite in comparison with the in situ seeding method and the permeance of single gas such as He, N₂ and CO₂ was also low in comparison with that of the in situ seeding method.

Abstract: The compact MFI membrane supported on a mesoporous-layer-modified macroporous Al₂O₃ substrate has been prepared by the secondary growth method. SEM images indicate that the MFI membranes with the thickness of ca. 15 μm consist of highly intergrown crystals with remarkable integrity. The H₂ permeance of MFI membranes on mesoporous/macroporous substrate is 8-18 times larger than that on the macroporous substrate, and further the permselectivity of H₂/C₃H₈ maintains at the level of 20, which is 4 times higher than that of the corresponding Knudsen diffusion. More importantly, the real selectivity of the mixture of H₂/C₃H₈ on these membranes is 2-4 times higher than that of the corresponding Knudsen diffusion. The method is attractive for the practical application.

Abstract: A kind of straw returning and fertilization seeder was designed. The overall structure and key technologies were introduced. The structures and parameters of the key parts were determined. The teamwork machine has a reasonable and compact structure and wide applicability, which can realize straw chopping, tillage, soil preparation, seeding, fertilization and compacting.

Abstract: The highly intergrown NaA zeolite membranes on seeded ZrO₂ substrate were synthesized by microwave heating method. The preparation of seeds with the size of ca.60nm employed the vapor phase transformation method (VPT). The XRD patterns indicated that the pure NaA zeolite membranes formed on the seeded ZrO₂ substrate for varied synthesis times. However, the peak intensity of NaA zeolite membrane after 50min obviously decreased, suggesting that the NaA membrane could take place the dissolution at that time. The SEM images indicated that the NaA zeolite membranes for 15-30min had a good integrity and consisted of highly intergrown zeolite crystals, but the NaA membrane after 50min appeared some large defects, further verifying the result of XRD pattern. The gas permeability showed that the H₂/N₂ and H₂/C₃H₈ permselectivities on zeolite membrane attained 4.01 and 8.13, respectively, higher than those of the corresponding Knudsen diffusion. These results suggested that the diffusion of gases, at least in part, are affected by the pore size of zeolite and the function of molecular sieving can be embodied on the synthesized membrane.

Abstract: The NaA zeolite membranes with high permeance were synthesized by seeding and secondary growth both using vapor phase transformation method (VPT). The SEM image of seed layer on substrate indicated that the size of seeds was about 60nm. The XRD patterns showed that the formation of NaA zeolite membrane was after vapor phase transformation of 12h, and the pure NaA zeolite crystals formed on substrate. The SEM images showed that the NaA zeolite membrane consisted of compact polycrystalline crystals with an average size of ca. 2µm. The permeation results showed that the H2 permeance s of NaA membranes attained at the level of 10-6 mol/Pa·m2·s, and the maximum permselectivities of the H2/N2, H2/CO and H2/C3H8 were 4.15,4.78 and 10.1, respectively, which were higher than those of the corresponding Knudsen diffusion selectivities. However, the permeation of C3H8 suggested that there existed unwanted intercrystalline pores or defects in the membranes.