Chemical Origin of Sodium Phosphate Interactions on Iron and Iron Oxide Surfaces by First Principle Calculations

Abstract

Density functional theory calculations of chemical interactions of lubricant additives sodium pyrophosphate (Na4P2O7) and orthophosphate (Na3PO4) on nascent iron Fe(110) and iron oxide Fe2O3(0001) surfaces have been carried out. Comparisons of adsorption behaviors of the two lubricant additives on different surfaces have been implemented on the basis of the thermodynamics of adsorption and electronic structure analyses. The results indicate that sodium phosphates chemically adsorb on iron and iron oxide surfaces by forming Fe–O bonds and stick on the surfaces through Fe–O–P linkages. The stronger binding of Na3PO4 than that of Na4P2O7 on both Fe(110) and Fe2O3(0001) surfaces is consistent with its better antiwear performance observed by the experiments. It is found that Fe–O bonds formed during the phosphate adsorption are stable covalent bonds that are as strong as P–O bonds of the Fe–O–P linkages. However, the binding of Fe–O–P on Fe surface is caused by a donor–acceptor mechanism; in contrast, the donation/back-donation interaction mechanism on the Fe2O3 surface. This study provides an in-depth understanding of the early stage of the tribochemical reaction between polyphosphates and metal/oxide surfaces.

Depolymerization of sodium polyphosphates on an iron oxide surface at high temperature

“…The bond distance and bond overlap population change from 1.53 Å, 0.35 |e| into 1.55 Å, 0.31 |e|. The Fe 2 O 3 surface will reduce the strength of P-O terminal bond if the terminal oxygen atom contributes to P-O-Fe linkage which is consistent with Ta et al25 for short chain length sodium phosphate cluster Na 4 P 2 O 7 . In the case of adsorbed cluster structures, one oxygen atom of each PO 4 tetrahedron forms an interaction with one iron atom on the substrate.…”

“…In addition, these values are also observed in the studies of Belelli et al 17 and Acelas et al 18 25 In additional, the ELF value of cluster adsorption has been displayed in Fig. 6 for more information about Fe-O-P linkage interactions.…”

“…4a and 4b, respectively. Na 4 P 2 O 7 adsorption structure has been obtained from the study by Ta et al 25 A variety of oxygen types have been noted in Fig. 5a.…”

Understanding the tribological impacts of alkali element on lubrication of binary borate melt

“…The depolymerization reaction actively accommodates abrasive particles upon which the anti-wear capacity thrives. [13][14][15] On steel pair lubricated by borate, the boron oxides highly concentrates in the form of a compact and robust boundary lm to withstand direct asperity contacts. 7 Although the tribological behaviors of network-forming constituents have been understood in some extent, there remain unanswered questions surrounding the roles of alkali elements in melt lubrication.…”

Enhanced phosphate removal under an electric field via multiple mechanisms on MgAl-LDHs/AC composite electrode

“…Numerous adsorbents have been investigated for selective phosphate removal through specific (via inner-sphere complexation) and nonspecific interactions (via electrostatic affinity/outer-sphere complexation) of phosphate with the functional groups of the adsorbents [8]; these adsorbents include lanthanum oxide and hydroxide [9][10][11], iron oxides and hydroxides [12,13], magnesium oxide and hydroxide [14,15], aluminum hydroxides [16], and cobalt-containing spinel oxides [17], and Bayoxide® E33 [18]. Among them, layered double hydroxide (LDH) is one of the most widely used options and phosphate contained LDHs recently shows potential application in slow release phosphate fertilizer [19][20][21].…”