Abstract:
In this work magnesium chromate (MgCr2O4)samples were produced by combustionmethod. Sample1 was prepared without adding ammoniahydroxide (pH = 0.96) during synthesis steps whilst sample 2 was prepared with ammonia hydroxide (pH = 8.62).Sample 1 was obtained in 2:10 h whilstsample 2 was produced in 45 min. Effect of pH upon structural properties wereinvestigated by X-rays diffraction (XRD) technique. Theresults confirm the formation of the cubic spinel structurewith average crystallite sizes of 13.0 nm and 8.0 nm for sample 1 and sample 2,respectively. The lattice parameters were calculated usingBragg’s law and found to be 8.30Å and8.33Å for sample 1 and sample 2, respectively.The X-rays densitiesvalues were 2.227× 106g/cm3 and 2.206× 106 g/cm3 for the sample 1 and sample 2, respectively.The obtainedmicrostrain values were0.007148 and 0.015206 for sample 1 and sample 2,respectively. The opticalproperties were studied using Ultra violate- Visible (Uv-Vis) absorption technique. The resultsshow that MgCr2O4 samples have a direct band gap of3.007 eV and 3.057 eV for the sample 1 and sample 2, respectively.It observed that the band gapof sample 2 was slightlygreater compared to sample 1. This associated with crystallite sizes of the samples. It can be concluded that control of pH can significantly reduce the duration ofcombustion synthesis method.
