Precipitation Of Bi Research Articles

Effects of the Various Preparation Procedures of Dragendorff Reagent on Sensitivity for Thin Layer Chromatography

The effects of the various preparation procedures of the Dragendorff reagent on sensitivity for thin layer chromatography (TLC) were examined. The sensitivity to various compounds was different depending on the preparation procedures of the Dragendorff reagent. The reagent with the highest sensitivity to most of the compounds tested was the one prepared with bismuth subnitrate and concentrated hydrochloric acid. However, color spots were disappeared relatively in a short time after the reagent was sprayed on the compounds. The reagent with the second highest sensitivity was the one prepared with precipitation of Bi(OH)3 from bismuth subnitrate, although the procedure was complicated and time-consuming. Consequently, to simplify the preparation procedure of the reagent, we modified it to the procedure without precipitation of Bi(OH)3 from bismuth subnitrate. The reagent was also prepared from commercially-manufactured Bi(OH)3 or BiI3. The modified Dragendorff reagents showed almost the same sensitivity to most of the compounds tested as the one prepared with precipitation of Bi(OH)3 from bismuth subnitrate, and would be useful for practical TLC analysis.

Investigations on microhardness of Sn–Zn based lead-free solder alloys as replacement of Sn–Pb solder

The microhardness of the Sn–Zn based solder pastes have been compared with the Sn–Pb solder paste. Two types of solder such as Sn–9Zn and Sn–8Zn–3Bi have been investigated along with Sn–37Pb solder for reference. The variation of microhardness with reflow temperature from 220 to 250 °C shows two different characteristics for eutectic and non-eutectic solder pastes. Hardness of Sn–37Pb and Sn–9Zn (eutectic) decreases with increasing reflow temperature while the microhardness of Sn–8Zn–3Bi (non-eutectic) increases with the increasing reflow temperature. Microstructural characterization at 220 and 250 °C shows grain coarsening in Sn–37Pb and Sn–9Zn solders, which cause the hardness to drop a little. For Sn–8Zn–3Bi, with increasing temperature the amount of hard Bi segregation increases which is the main cause of the rise in hardness. SEM images show the formation of Pb rich islands in Sn–37Pb, formation of Zn rod from spheroids in Sn–9Zn and precipitation of Bi rich phase in Sn–8Zn–3Bi are the important features that contribute to the different hardness nature. Again the effect of cooling rate on hardness was also studied and compared among these three solder pastes. The result shows that the Sn–9Zn is the most sensitive to cooling rate. With the change in cooling rate, the hardness increase in Sn–9Zn is greater (58% after water cooling) than in Sn–37Pb (30%) and Sn–8Zn–3Bi (33%). The hardness profile along the distance from the centre shows that the hardness gradient is also found highest on Sn–9Zn solder paste whereas similar trendlines were found in Sn–37Pb and Sn–8Zn–3Bi solder. SEM images of air- and water-cooled microstructures show preferential Zn formed at the edge in Sn–9Zn solder while Pb rich islands at the centre (for Sn–37Pb) and precipitation of Bi at the edge (for Sn–8Zn–3Bi) was found along with grain refinement.

Partial melting and HIP processing of Bi(2223): bulk and tapes

A detailed investigation of the equilibrium between the Bi,Pb(2223) phase and the melt was carried out by in-situ high temperature neutron powder diffraction both on sintered bulk samples and Ag-clad tapes. Stability, decomposition and re-formation of Bi,Pb(2223), as well as the evolution of secondary phases, were studied and the effect of the oxygen partial pressure was investigated. Bi,Pb(2223) melts incongruently to (Sr,Ca)/sub 14/Cu/sub 24/O/sub 41/, (Sr,Ca)/sub 2/CuO/sub 3/, and a Bi,Pb-rich liquid, and no precipitation of Bi(2212) was observed at this stage. Direct formation of the Bi,Pb(2223) phase from the melt was observed, opening up the possibility of processing Ag-sheathed tapes from a partial melting route. The possibility of reforming the Bi,Pb(2223) phase from the melt proved to be extremely sensitive to temperature and strongly dependent on the Pb-losses. The study of the mass losses due to Pb-evaporation was complemented by thermogravimetric analysis which proved that the Pb-losses are responsible for moving away from the equilibrium and therefore hinder the Bi,Pb(2223) to reversibly form from the melt. Hot isostatic pressure has proved to be an effective remedy for preventing volatile elements from evaporating and for increasing the density of the tapes. The first annealing stage of the Ag-Bi,Pb(2223) processing was performed under isostatic pressure after making the Ag-sheath airtight. Positive effects of pressure on filament density, formation kinetics and critical current were observed at 10 MPa. We have extended our search for an alternative processing route to the Pb-free Bi(2223) phase. High purity Bi(2223) bulk samples and Ag-sheathed tapes were successfully prepared from pre-reacted powders. Very large Bi(2223) grains (up to /spl sim/500 /spl mu/m) were observed to grow at the Ag-ceramic interface.

Polarographic determination of Pb, Tl, Bi and Sb in ethylenediamine in presence of mannitol

Pb, Tl, Bi and Sb yield well defined polarograms in 1 M ethylenediamine in presence of 3% mannitol, with half-wave potentials at − 0.71 V, − 0.51 V, − 0.60 V and − 1.10 V, respectively. Only Pb and Tl develop maxima which can be suppressed by 0.02% gelatin. Presence of mannitol prevents the precipitation of Pb, Bi, and Sb in the alkaline solution. Simultaneous determinations of Pb/Tl, Bi/Sb, and Pb/Sb can be carried out.