Ball Milling of Silica-Based Pyroclastic Scoriae: Measurement of Mechanochemical Reactivity by Radical Scavenging

Abstract

The present work concerns the mechanochemical reactivity of Pozzolane Rosse, a historical constituent of ancient Roman mortars and concretes. Suitably sieved Pozzolane Rosse powders were subjected to mechanical activation. Chemical behavior was investigated both during and after the mechanical treatment using an ethanol solution containing a free radical scavenger. Experimental findings indicate that the mechanical processing induces a decrease in scavenger concentration. The scavenger consumption is significantly larger when Pozzolane Rosse is exposed to the ethanol solution during the mechanical treatment, due to fracturing processes resulting in the increase of specific surface area of Pozzolane Rosse powder and to frictional processes between particles. The surface density of active sites is indirectly evaluated, and the emerging mechanochemical effects are discussed. Kinetic effects of the mechanical processing on the reaction between Pozzolane Rosse and calcium hydroxide in water are also evaluated. The accurate measurements of experimental observables and their interpretation based on a reliable kinetic model allowed a quantitative assessment of the mechanochemical reactivity of the material.

Chemical effects induced by the mechanical processing of granite powder

“…This suggested a very high reactivity for quartz surfaces excited by mechanical activation, eventually resulting in the formation of radicals. Similar results have been obtained for pozzolanas in the presence of H 2 O 58 .…”

The effect of ball mass on the mechanochemical transformation of a single-component organic system: anhydrous caffeine

“…Mathematically, any rate that is dependent upon the quantity of a reactant component can be described by a series of exponential equations. Relatively simple exponential functions have been previously derived for multi-component mechanochemical reactions, proving to describe a range of mechanochemical systems [ 48 , 53 , 54 ]. Typically, if only a single process is dominant, a single function can be employed of the form: where the conversion quantity, α, is dependent on an appropriate kinetic law, f(α) , and a ratio of required and available energies, τ .…”

“…This, in turn, reduces any limiting effects of mixing, even in the case of an originally single-phase system. Interestingly, the previous works on the kinetics of mechanochemical reactions have identified a rate-limiting step to be generation of new reactive interfaces, according to an exponential function [ 54 ]. When ball–particle interfaces are considered, the rate of contact formation depends on both ball surface area and the rate of comminution of the powder sample.…”

“…Relatively simple exponential functions have been previously derived for multi-component mechanochemical reactions, proving to describe a range of mechanochemical systems [48,53,54]. Typically, if only a single process is dominant, a single function can be employed of the form:…”

The Mechanism of Surface-Radical Generation and Amorphization of Crystalline Quartz Sand upon Mechanochemical Grinding

“…Such work has focused on understanding the effects of freshly fractured quartz dust and other silica polymorphs on the human respiratory system, a focal area in occupational health research. ,,,, One of the crucial features identified in the numerous EPR studies is related to the longevity of quartz or silica-based mechanoradicals. It is well noted that surface reactivity diminishes over time; however, mechanoradicals have been identified long after the mechanical energy input has ceased; in some cases, days to months following grinding. ,,, To this end, the level of understanding in the literature is limited to the spectroscopic data generated from EPR , and spin-trap studies that monitor the silica mechanoradicals in situ during mechanochemical treatment; ,, there are very few studies that comprehensively explore the transformations that occur to silica-based materials during mechanochemical activation. , As such, a detailed study examining the surface and bulk characterization of freshly fractured quartz sand would result in a better understanding of the transformations that occur during this process.…”