In-situ interfacial tribochemistry toward eliminating red-scale of silicon steel in friction process

Tribochemistry and Lubrication of Alkaline Glass Lubricants in Hot Steel Manufacturing

“…As presented in Figure 2, this tribofilm contains a 5 nm short-chain polyphosphate layer on the top, above a 5 nm long-chain polyphosphate layer below, which adheres to the oxide surface through a short-chain layer [21]. However, this polyphosphate film was mainly covering the valley area of the worn surface and was chemically inhomogeneous at the submicron level [19,21]. Interestingly, Na and P existed not only in the top sodium layer, but they were also found in the grain boundary of iron oxide layer [19].…”

“…However, this polyphosphate film was mainly covering the valley area of the worn surface and was chemically inhomogeneous at the submicron level [19,21]. Interestingly, Na and P existed not only in the top sodium layer, but they were also found in the grain boundary of iron oxide layer [19]. The phosphate glass was also beneficial for the pickling of silicon steel surfaces, with a quicker scale removal and a thinner fayalite layer than an unlubricated one [19].…”

“…Interestingly, Na and P existed not only in the top sodium layer, but they were also found in the grain boundary of iron oxide layer [19]. The phosphate glass was also beneficial for the pickling of silicon steel surfaces, with a quicker scale removal and a thinner fayalite layer than an unlubricated one [19].…”

“…Potassium/sodium (K/Na) polyphosphate begins melting at 600 • C and demonstrates exceptional friction-and wear-reducing ability on steel tribopairs from 600 • C to 900 • C. Friction was lowered by more than 50%, while the wear rate reduction varied with temperature, but often fell in the range of 30-90% [18,19]. On the rubbing surface, the tribofilm structure was characterized by two layers of K/Na polyphosphate sandwiching a thick iron oxide layer [19]. The complex tribofilm structure was a result of thermal diffusion and tribochemical reactions between composite polyphosphate and iron oxides.…”

“…Using energetic synchrotron radiation, the fine chemical structure of the K/Na polyphosphate tribofilm was studied in detail, showing a long chain-short chain hierarchy as a function of tribofilm depth. As a result of this tribochemical reaction, iron oxide was disintegrated and digested into the polyphosphate network to form ferric orthophosphate (FePO 4 ), as well as iron and sodium mixed phosphates, such as (NaFePO 4 ) [20] and Na 3 Fe 2 (PO 4 ) 3 [19]. The digestion of iron oxide is accountable for the excellent wear resistance of polyphosphate tribofilm.…”