An electron microscopy study of graphite growth in nodular cast irons

Growth of graphite during solidification and high-temperature solid-state transformation has been investigated in samples cut out from a thin-wall casting which solidified partly in the stable (iron–graphite) and partly in the metastable (iron–cementite) systems. Transmission electron microscopy has been used to characterize graphite nodules in as-cast state and in samples having been fully graphitized at various temperatures in the austenite field. Nodules in the as-cast material show a twofold structure characterized by an inner zone where graphite is disoriented and an outer zone where it is well crystallized. In heat-treated samples, graphite nodules consist of well-crystallized sectors radiating from the nucleus. These observations suggest that the disoriented zone appears because of mechanical deformation when the liquid contracts during its solidification in the metastable system. During heat-treatment, the graphite in this zone recrystallizes. In turn, it can be concluded that nodular graphite growth mechanism is the same during solidification and solid-state transformatio

Efficient and Selective Transport of Silver(I) Cation Across a Bulk Dichloromethane Membrane Using 1,13-Bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane as a Carrier

Abstract: 1,13-Bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (Kryptofix 5) was used as a highly efficient carrier for the transport of silver(I) cation through a dichloromethane (DCM) bulk liquid membrane. In order to achieve the highest transport efficiency of Ag + cation across the bulk liquid membrane system, the influence of different parameters was studied. These include: the nature of various organic solvents as liquid membrane phase, concentration of the carrier in the membrane phase, concentration of picric acid as counter anion in the source phase, type of various stripping agents in the receiving phase, concentration of thiosulfate anion (S 2 O 3 2-) as a suitable stripping agent, pH of the source and receiving phases, volume of the receiving phase and equilibrium time of transport which were optimized. In the optimum procedure conditions, the transport of a 3×10 -4 M solution of silver(I) cation was observed (88.03 ± 0.82%) after 4 hours

Thermodynamic studies of the complexation of 18-crown-6 and dibenzo-24- crown-8 with potassium ion in mixed non-aqueous solvents

568-574<span style="font-size:14.0pt;font-family: " times="" new="" roman","serif";mso-fareast-font-family:"times="" roman";mso-ansi-language:="" en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">The formation constant of 1:1 complexes of 18-crown-6 (18C6) with potassium ion in dimethylformamide (DMF)-methanol (MeOH), DMF-nitrobenzene (NB), DMF- benzonitrile (BN) binary solvents and dibenzo-24-crown-8 (DB24C8) with potassium ion in DMF-MeOH binary mixtures have been determined conductometrically at different temperatures. The values of thermodynamic parameters <span style="font-size:14.0pt;font-family:HiddenHorzOCR; mso-hansi-font-family:" times="" new="" roman";mso-bidi-font-family:hiddenhorzocr;="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">(∆ <span style="font-size: 14.0pt;font-family:" arial","sans-serif";mso-fareast-font-family:"times="" new="" roman";="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">H°<span style="font-size: 14.0pt;font-family:" arial","sans-serif";mso-fareast-font-family:"times="" new="" roman";="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa;="" mso-bidi-font-style:italic"="" lang="EN-US">C <span style="font-size:14.0pt; font-family:" times="" new="" roman","serif";mso-fareast-font-family:"times="" roman";="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">and <span style="font-size:14.0pt;font-family:HiddenHorzOCR; mso-hansi-font-family:" times="" new="" roman";mso-bidi-font-family:hiddenhorzocr;="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">(∆ S<span style="font-size: 14.0pt;font-family:" arial","sans-serif";mso-fareast-font-family:"times="" new="" roman";="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">°<span style="font-size: 14.0pt;font-family:" arial","sans-serif";mso-fareast-font-family:"times="" new="" roman";="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa;="" mso-bidi-font-style:italic"="" lang="EN-US">C) for complexion reactions have been determined from temperature dependence of formation constants. In all cases, the complexes are enthalpy stabilized but with very few exceptions entropy destabilized and the results show that both parameters are very sensitive to solvent composition. The origins of the enthalpies and entropies of the complexation are discussed in terms of the solvent composition and the structural features of the ligand. The stability of complexes is strongly affected by the nature of solvent and solvent composition. The stability constants of complexes increase with increase in the concentration of solvent with lower donocity (smaller Gutman Donor Number) in binary mixtures. In addition, it has been found that the variation of stability constant<span style="font-size:14.0pt; font-family:HiddenHorzOCR;mso-hansi-font-family:" times="" new="" roman";mso-bidi-font-family:="" hiddenhorzocr;mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:="" ar-sa"="" lang="EN-US"> (log <span style="font-size: 14.0pt;font-family:" arial","sans-serif";mso-fareast-font-family:"times="" new="" roman";="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">K°f) of 18C6- K+ complex versus the solvent composition is linear in DMF-BN and DMF-NB binary mixtures, but a nonlinear behaviour is observed for 18C6-K+  and of DB24C6-K+  complexes in DMF-MeOH binary systems.</span