Characterization of the calcination process of yttria

A complete characterization of the calcination of precipitates obtained from a continuous operation was carried out in this study. The precipitate was obtained by reacting yttrium nitrate and ammonia solutions in a MSMPR reactor. It precipitated out as yttrium hydroxide nitrate hydrate, which has the general form Y₂(OH)_6-x(NO₃)_x·y H₂O. This compound decomposed in consecutive steps with the last reaction occurring at 525°C.The calcination process was characterized by chemical analysis, X-ray diffraction analysis, DTA and TG. In addition, the physical characteristics of calcined powders, such as specific surface area, particle size distribution, pore volume distribution, X-ray crystallite size and conversion were measured as a function of calcination temperature and time. Finally, the kinetics of the reduction of surface area, the growth of crystallite size and conversion were also examined.     

The 4051-Angstroms band of C3 (A 1Piu-X 1Sigmag +, 000-000): perturbed low-J lines and lifetime measurements

Rotational analyses have been carried out at high resolution for the 000-000 and 000-100 bands of the A (1)Pi(u)-X (1)Sigma(g) (+) transition of supersonic jet-cooled C(3). Two different spectra have been recorded for each band, using time gatings of 20-150 and 800-2300 ns. At the shorter time delay the spectra show only the lines observed by many previous workers. At the longer time delay many extra lines appear, some of which have been observed previously by [McCall et al.Chem. Phys. Lett. 374, 583 (2003)] in cavity ring-down spectra of jet-cooled C(3). Detailed analysis of these extra lines shows that at least two long-lived states perturb the A (1)Pi(u), 000 state. One of these appears to be a (3)Sigma(u) (-) vibronic state, which may possibly be a high vibrational level of the b (3)Pi(g) state, and the other appears to be a P = 1 state with a low rotational constant B. Our spectra also confirm the reassignment by McCall et al. of the R(0) line of the 000-000 band, which is consistent with the spectra recorded towards a number of stars that indicate the presence of C(3) in the interstellar medium. Fluorescence lifetimes have been measured for a number of upper-state rotational levels. The rotational levels of the A (1)Pi(u) state have lifetimes in the range of 230-190 ns, decreasing slightly with J; the levels of the perturbing states have much longer lifetimes, with some of them showing biexponential decays. An improved value has been obtained for the nu(1) vibrational frequency of the ground state, nu(1) = 1224.4933 +/- 0.0029 cm(-1).     

Studies on the Chemical Synthesis of Nanosized Nickel Powder and its Stability

The synthesis of nanosized nickel colloids is investigated by using nickel chloride as the precursor, hydrazine as the reducing agent and palladium as the nucleation agent. High purity nickel can be obtained when the reaction temperature is above 80^°C. At a lower reaction temperature, nickel hydroxide is also present in the precipitate form. Starting concentration of nickel ion is a dominant factor in affecting colloidal sizes, while other parameters such as reaction temperature and quantity of poly(vinyl pyrrolidone) (PVP) exhibit only minor effects. Although PVP has some dispersion power, it is not capable of preventing nickel colloids from gradual agglomeration. Our study shows that the subsequent addition of poly(acrylic acid) (PAA) after synthesis can help to stabilize the nickel suspension. This stabilized suspension can then be de-stabilized by changing pH to lower than 4 and vice versa. This reversible stabilization–de-stabilization process is likely due to the behaviour of PVP–PAA complex in the aqueous solutions.     

Study on the microfiltration of Escherichia coli-containing fermentation broth by a ceramic membrane filter

Microfiltration (MF) of a fermentation broth containing Escherichia coli is reported in this article. We used a ceramic membrane filter (zirconia on sintered carbon) having a nominal pore size of 0.2 μm. Our results indicate that the filtration resistance was mainly caused by the cake formed on the membrane surface. Both transmembrane pressure (TMP) and fluid sweeping velocity influenced this cake resistance. Resistances due to membrane itself and due to internal pore blockage by E. coli were less important and insensitive to both TMP and fluid sweeping velocity. Preliminary results also showed that the cell density could be significantly increased when we connected such a ceramic filter on-line with our fermentation system. In particular it was found that the gas bubbles entrained in the broth side of the filter could increase the filtration flux by as much as 80%.