The Thermal Decomposition of NiC2O4·2H2O: An In situ TP-XRD and TGA/FT-IR Study

Abstract

Nickel(II) Oxalate Dihydrate / Thermal Decomposition / Temperature Programmed-XRD / TGA-FTIRThe non-isothermal decomposition of NiC 2 O 4 · 2H 2 O was investigated under a dynamic inert atmosphere using a temperature-programmed X-ray diffractometer (TP-XRD) and a thermogravimetric analyzer coupled to a Fourier-transform infrared spectrometer (TGA-FTIR). Both solid and gaseous products were analyzed in situ. The XRD pattern of the dehydration product did not match data for NiC 2 O 4 reported in the JCPDS file. The thermal decomposition of the dehydration product (NiC 2 O 4 ) took place in two sub-steps, both of which involved CO 2 evolution. Metallic nickel was the final product.

Thermal Decomposition of Nickel Oxalate Dihydrate: A Detailed XPS Insight

“…The occurrence of C 2 O 3 − * anions was demonstrated 44 in experiments on dissociative electron attachment to maleic anhydride C 4 H 2 O 3 . According to theoretical calculations, 45 47 Although we prefer to refrain from speculations about possible structural properties of a NiC 2 O 3 (or/ and Ni 2 C 4 O 7 ) intermediate, we note here that Shen et al, 22 when heating Ni oxalate to 305−335 °C in Ar, detected by in situ XRD some intermediate phase, which coexisted along with metallic nickel and could not be fit with any JCPDS file patterns.…”

“…It is generally agreed that the thermal decomposition of nickel oxalate dihydrate proceeds via two stagesdehydration and decomposition, albeit some substages are being considered, 22 too. The dehydrated product is commonly accepted to be anhydrous nickel oxalate NiC 2 O 4 , which can exhibit an amorphous structure 48 (for thermal decomposition in vacuum), a predominantly crystalline one, 21,26 a disordered β-NiC 2 O 4 structure 27 (for decomposition in air), or coexist with less-crystalline hydrated oxalate.…”

“…12,14−16 The effect of four different atmospheres on thermal decomposition of Ni oxalate was studied in detail. 16,17 In most of the studies, the thermal decomposition of Ni oxalate was performed in N 2 6,8,11,12,14−23 or in air; 10,12−14,16−21,24−27 besides, other environments such as vacuum, 9,11,17,24 Ar, 22,28 He, 26 CO 2 , 11,16,25 H 2 , 16,17,28 O 2 , 23 N 2 + CH 4 , 6 and self-generated atmosphere 29 were also used. For all of these studies, the dehydration step was found to be endothermic.…”

“…It was found that the temperatures and activation energies of dehydration and decomposition were dependent on the heating rate, ,,− mass of the sample, and temperature of preparation of Ni oxalate . Typically, when increasing the heating rate, dehydration and decomposition occurred at higher temperatures whatever the environmental atmosphere. ,− The effect of four different atmospheres on thermal decomposition of Ni oxalate was studied in detail. , In most of the studies, the thermal decomposition of Ni oxalate was performed in N 2 ,,,,− or in air; ,− ,− ,− besides, other environments such as vacuum, ,,, Ar, , He, CO 2 , ,, H 2 , ,, O 2 , N 2 + CH 4 , and self-generated atmosphere were also used. For all of these studies, the dehydration step was found to be endothermic.…”

“…As to the final product in inert atmospheres, considerable controversy persists. In the majority of studies performed in N 2 , Ni metal was reported as the only product of decomposition, ,, though Ni+NiO ,, or even NiO , was also claimed to have formed. The formation of Ni+NiO was also reported to occur in He, Ar, or in the presence of the oxalate-related gaseous decomposition products, CO and CO 2 .…”