Correlating cation coordination, stiffness, phase transition pressures, and smart materials behavior in metal phosphates

Abstract

In this study we present X-ray diffraction data on metal phosphates containing either high or low coordination number zinc or calcium. The experiments reveal that low-coordination zinc phosphate crystals are relatively soft at ambient conditions but stiffen dramatically with pressure, p, thereby exhibiting smart materials behavior. In comparison, high-coordination zinc and calcium phosphates have higher initial bulk moduli, K(0), and stiffen much less rapidly with increasing p. The investigated metal phosphate crystals all amorphize under compression when K reaches a value near 210 ± 40 GPa, the precise value depending on the chemical details. Our interpretation of this result is that elastic properties and structural instabilities are related to the motion of rigid phosphate units, which becomes more hindered as the material density increases, and that stiffening can occur independent of a change of cation coordination. These ideas are supported by ab initio simulations of zinc α-phosphate. The efficacy of low-coordination zinc phosphates as antiwear agents is discussed in the context of these results.

Chemical response of aldehydes to compression between (0001) surfaces of α-alumina

“…48 However, there are differences between the results of the present study in which the MeCHO molecules were subjected to uniaxial compression between (0001)-Al 2 O 3 surfaces and the earlier simulations of bulk MeCHO. First, the formation of C-O bonds occurred at lower P (17)(18)(19)(20)(21)(22) in the present work than it did in the earlier study (P ∼ 26 GPa). This was particularly true in the case of the MeCHO dimers formed on the lower surface [initially shown in Fig.…”

“…11,[14][15][16] However, tribochemical reactions can be useful in some cases, with studies suggesting that compression-induced changes in the coordination numbers of zinc atoms in protective films contribute to lubrication in autoa) Electronic mail: nicholas.mosey@chem.queensu.ca. mobile engines 17,18 and the tribochemical conversion of proteins into protective coatings contributes to the lubrication of artificial biological implants and joints. 19,20 Recent efforts have aimed at designing lubricants containing components that undergo desirable tribochemical reactions in response to the conditions experienced in sliding contacts.…”

Excellent melt lubrication of alkali metal polyphosphate glass for high temperature applications

“…ZDDP. [8][9][10][11] Remarkably, this tribolm shows an excellent adaptive tribology behaviour, which is intelligently responsive to the tribo-stressed conditioins. 10,11 Moreover, it can protect the substrate against further oxidation.…”

“…[8][9][10][11] Remarkably, this tribolm shows an excellent adaptive tribology behaviour, which is intelligently responsive to the tribo-stressed conditioins. 10,11 Moreover, it can protect the substrate against further oxidation. Alkali metal phosphates glasses, a class of thermoplastic polymers similar to epoxy resin based thermoset, 12,13 have been implemented in the formulation of ceramic restorative cements and more generally of bioactive functional materials, employed as active elements in laser engineering owing to itself useful optical properties, [14][15][16][17] owing to its exceptionally thermal stability and inability to oxidize, as well as high coefficient of thermal expansion.…”

“…10,11 Especially polyphosphate tribolms show the adaptive tribological behaviour in response to different extreme range of conditions, i.e. high loads, high speeds and temperatures, which is primarily related to the preferential alignment of the tribolm in structure and composition: a layered structure with a gradient composition from surface to the depth.…”