Physico Chamical On Some Binary_metal Oxides And Sulphides:

Abdullah Ahmed Ahmed El Bellihi

A sum8~ry of important results and conclusions of various parts of the present dissertation is given below.In the first part of the present studY,the kinetics of formation of some oxide and sulphide spinels wereinvestigated. stoichiometric mixtures of CUO-FeZ03 ,Cuo-CrZo3 and CU3-CrZs3were prepared by the co-precipitation method from solutions of A.R. salts and calcination at differenttemperatures.The actual amount o~ each metal in each mixture was determined by chemical analysis and the variousprepared samples were characterized and stUdied by differential thermal analysis-thermogravimetry(DTA-TG),infrared spectral analysis(IRA),X-ray diffraction (XRD)and electron microscopy(E:’1) techniques. the kinetics of the solid-solid spinel formationreactions were followed in the temperature range 500-8000C for CUO-FeZ0and CuO-CrZC systems and 200-3000C for CuS-CrZs3 system using a titrimetric tecnnique.Kineticanalysis of the reactions were discussed in view of solidstate reaction models based on diffusion of reactants througncontinueous product layer,pnase boundary reactions,flrst-orderreactions &~d rancom nucleation ffiodels.Yinetic analysis ofdata by linear regression analysis according to various t hecrct i.caI uode Ls sr.,Y.’:te.ahat the spinel f’or-natLo n reactions are best described by the tnree-aimensional diffusioncontrolled,Jander’s eqUation(D3l,t~o-dimensional diffusion process(D2l and Ginstling-BrounshLein three-dimensionalcontrolleu equ~~i8n(D lwhich gave the highest correlation coefficient tnan the other models Kinetic analysis was carried out in the range ofweight fraction (C(lvalues in the range 0.06(OC<0.470.18(0«0.70 and 0.16 «()(’(O.41 for CUFe24 ,CuCr20and CuCr2S4 ,respectively.It was found that the CuFe20 4 and CuCr2S4’ . formation are increased with the temperature of calcination. The activation energies of spinel formationwere calculated according to the two-dimensional diffusion .controlled(D2),three-dimensional diffusion Jander’s equation (D3)and the three-dimensional diffusion-controlled Ginstling -Brounshtein equation(D).The activation energies of thespinel formation are 59.4 = 1.5 , 97.6 = 3.5 and 24.6 = 1.6-1 kJ.mol for CuFe204 ’ CUCr204 and CuCr2S spimel,respictively.The variation in activation energy of the spinel formation reaction was explained on thebases of the energy required for the metal ion to diffuse through the crystal lattice. The radiusof Cr(III) is larger than Fe(III) end this increases the activation of Cucr204 than CuFe20 .On the other h3nd, the rela ’::viely mu ch lower acti va tion energy for the formation 0 fCuSr2s4 spinel is understood in view of the fact that metal ( 141 )sulp}lides have lower melting point and h6Dce hister ~obilityand lower energy for diffusion of the metal ions in the lattice.In the second part, the electrical conductivity of CuC-Fe2 C 3 stems were investigated.The electrical properties of solids are sensitive to a largenumber of variables of which chemical composition,irradiationand thermal treatments have important effects.The electricalconductivity was followed for all samples calcined for 5 hrs.in the temperature range 500-800°C for CuO-Fe203 and CUO-Cr 2 3and in the range 200-3000C for CUS-Cr2S3 system. The electrical conductivity ( ~ ) was carried out in the temperature range from room temperature up to 350°C.Results showed that Fe203 and CuFe204are n-type semiconductQ~S, CuO , CrP-type semiconductors w~ileCuS , Cr 2Swhich shows a break (Tb) at about 200°C. The break in copperferrite is due to the conversion of the conduction characterfrom P-type to n-type. The activation energies for theelectrical conductivity were calculated according to linearregression analysis and lie in the range of 29.3 - 33.2 and62.3 _ 80.0 kJ. mol -1 for cuO-Fe203 nuxtur e below and above,06/01/2013To,respectively; 19.8 - 2 .0 kJ.xol for CUO-Cr203 and4.Z - 5.7 kcT.mol-1 for CUS-Cr2S3 mixture.- thi~d part , the H202 deco~positicn in aqueous solution over the oxide and sulphide systems were carriedout. The reactivity of 22°2 decomposition in aqueous solution serves as a convenient test for investigation of the properties of various catalytic systems. The first-order reaction rate constant were measured in the range 30 - 50°Cfor samples calcined in the temperature range 500 - 800°C for the oxide samples , and in the range ZOO - 300°C for the sulphide samples.It was found that ,the hydrogen peroxide decompositionrate constant decreases with increasing the calcination temperature for the oxide samples,while it increases withincreasing calcination temperature for sulphide samples. ForCUO-Fe3 system it was found that the reactivity of CuO ishigher than that of both FeZ0and CuO-FeZO, mixture. Thisis due to CuO is P-type semiconductor whereas FeZ03is n-type.For cuO-crty of CuO is more than thatfor crz0 cuO-CrZo3mixture for samples calcined below7000C,while for samples calcined above 700°C the reactivityof CrZ3 is the higher. This is due to the presence of CuOas P-type with active Cu+ j CuZ+ centers at low temperaturewhile at temperature above 700°C Cr20,is P-type with./ crZ+j Cr3+ and Cr5+ / Cr6+ active centers. For CuS-CrZSsystem the reactivity of CuS is more higher than that of crZ S 3 and CuS-Cr ZSixture for samples calcined at ZOOoC,and aCDve 200°C the reactivity of Cr~3< is more higher c than that of both CuS and CU3-Cr2S3.Th results werediscussed in view of an electronic and a chain reaction mechanism involving the hydroxyl and the perhydroxylradicals as chain carriers. Such a mechanism could explainthe kinetics of the decomposition reaction using differentcatalysts and under various conditions.