Characterization of molybdenum and tungsten phosphates compounds prepared using ammonium phosphate salt as flux

T T Chiweshe

doi:10.4314/bcse.v33i1.10

Abstract

Fusion of powdered molybdenum and tungsten oxide using ammonium phosphate salt as flux (ratio: 1:25 respectively) yielded soluble products which were unstable. The yellow (Mo) and purple-blue (W) solutions in deionized water, methanol and acetone decolorized within 3–5 hours. Infrared analysis of molybdenum and tungsten products revealed characteristic broad bands bearing two minor peaks in the region of 1040–1130 cm -1 which reflects the simultaneous existence of PO 2 and PO 3 groups. SEM-EDX quantitative analysis results showed percentage weight of the identified elements in the increasing order of Mo or W < P < O with molybdenum product having 7.1%wt (Mo), 37.2%wt (P) and 53.5%wt (O) whilst tungsten product had 10.3%wt (W), 24.7%wt (P) and 46.5%wt (O). The EDX results indicated the presence of polyphosphate products whilst the SEM images showed microscopic crystalline product of molybdenum and a hygroscopic product of tungsten. XRD patterns of both molybdenum and tungsten products corresponded to the standard (JCPDS) pattern of molybdenum oxide phosphate MoO 2 (PO 3 ) 2 and tungsten oxide phosphate (WO 2 (PO 3 ) 2 ), respectively. KEY WORDS : Molybdenum, Tungsten, Ammonium phosphate flux, Polyphosphates Bull. Chem. Soc. Ethiop. 2019 , 33(1), 103-112 DOI: https://dx.doi.org/10.4314/bcse.v33i1.10

Highlights

Preparation of chromium, molybdenum and tungsten-metaphosphates compounds using ammonium phosphate flux
Metaphosphates belong to a series of polyphosphates (general formula M(PO3)3 M = trivalent elements) which are characterized by a tridimensional network of isolated MO6 octahedral connected through a infinite number of repeated PO4 tetrahedral units
The resultant yellow and purple-blue solutions of molybdenum and tungsten decolorize after standing overnight at room temperature. The decolorization of both solutions was unexpected and pointed to the possible chemical similarities between the two products. These color changes were different from the chromium results, which suggest a possible shift in chemical properties of group VIB elements with ammonium phosphate flux

Summary

Introduction

Preparation of chromium, molybdenum and tungsten-metaphosphates compounds using ammonium phosphate flux Molybdenum and tungsten melts yielded yellow and purple-blue solutions respectively that were different from the solid chromium product. UV-vis determination of factors influencing decolourization of molybdenum and tungsten solutions using different solvents The resultant dark yellow and purple-blue melts of molybdenum and tungsten respectively were tested for solubility in polar and non-polar solvents.

Results

Conclusion