Improvement of the cycling performance of LiMn[2]O[4] as cathode material for lithium batteries by Cr, Al, Co and Ni substitution

The main advantages of LiMn[2]O[4] spinel system are low cost, high cathode potential versus lithium and lack of toxic metals such as cobalt or nickel present in LiCoO[2] and LiNiO[2] cathode materials whereas the main drawback of the system is the fading capacity during cycling as compared to LiCoO[2] and LiNiO[2]. To improve the structural and electrochemical properties of LiMn[2]O[4], as cathode material for lithium secondary batteries, Co, Cr, AI and Ni ions were substituted for manganese ions. LiMn[2]O[4], and LiM[gamma]Mn[2-gamma]O[4] [M = Al, Co, Cr and Ni; gamma = 1/6] samples were prepared by solid state reactions. The X-ray powder diffraction patterns of the substituted samples are almost identical to the parent sample. A well defined highly pure spinel was characterized for all samples without observation of extra phases for substituted samples. The electrochemical performance of the prepared samples was evaluated through cyclic voltammetry and galvanostatic charge/discharge operations. The first discharge capacities of the substituted spinels are lower than that of LiMn[2]O[4], but better cycling performance and capacity retention was observed for the substituted spinels compared to the parent LiMn[2]O[4],. The improvement in the cycling performance of LiM[gamma]Mn[2-gamma]O[4][M = Co, Cr, Ni and Al; gamma = 1/6] compared to that of parent LiMn[2]O[4] is attributed to the stabilization of the spinel structure by the substituted metal cations

Studies on the dissolution of phosphate ore in mineral acids

The dissolution of Abou-Tartor phosphate ore in sulphuric acid, phosphoric-sulphuric acid mixture and hydrochloric acid was studied. The effects of time, temperature, acid/ore ratio and shaking were investigated. The results indicated that the dissolution of the ore in sulphuric acid was rather difficult; but the dissolution in H3PO4- H2SO4 mixture [76.1: 54.5 g] gave good result from 100 g of the ore at an acid/ore ratio of 1.4 after 30 min, at 70 degree and a shaking rate of 100-200 rhm. The optimum condition of the dissolution in HCl/ore ratio of 27: 1 was 80 min, at 25 degree and a rate of shaking of 120 rhm. The obtained results showed that the dissolution of Abou- Tartor phosphate ore in HCl is more preferable than other mineral. acids

Thermal and spectroscopic characterization of Pd [II] and Pt [IV] thiobarbiturate complexes

Pd [II] and Pt [IV] thiobarbiturate complexes [Ligaud: 2-thiobarbituric acid; Abbreviation, HTBA] were synthesized as solid phases. Chemical and thermogravimetric analyses, together with IR and electronic absorption spectra of the ligand and the two complexes were carried out. IR vibrational bands support M-S and M-N bondings in the Pd [II] and Pt [IV] ions are tetra-and hexa-coordinated, as deduced from their electronic absorption bands characteristic of square planar and octahedral configurations, respectively. Results of thermogravimetric analysis were in agreement with the general molecular formulae: Pd [TBA]2 and Pt [TBA]4 [HTBA]2 proposed by chemical analysis. The TG and DTG curves of both the Pd [II] complex and the Pt [IV] complex showed three thermal dissociation steps ending with a final step at>790 and >772 omicron, respectively. The thermal stability of the studied compounds was found to have the order: Pt [TBA]4 [HTBA]2> HTBA>pd [TBA]2

Ligand exchange within some Co [III] ethylenediamine complexes in moltin tetrabutylammonium bromide

The behaviour of some prepared Cis- and trans-Co [III] ethyl-enediamine complexes of the type [Co en2, AB]X, where AB=Br[2], Cl2, [NCS] Cl, [NCS] Br, N3 Cl and X =Br, Cl, NO3, SCN and C1O4 was investigated at low concentrations [0.5 mole percent] in molten tetrabutylammonium bromide. The measured ligand-field bands of frozen mixtures were characteristic of octahedrally coordinated Co [III] in trans- [Co en- Br2]+ species indicating that bromide would eventually substitute ligands A and/or B. Addition of KS CN to the corresponding melt led to the formation of a compound [[C4H9][4]N][2] [Co [NCS]4] which showed a spectrum related to tetra-hedrally coordinated Co [II]