The possibility of lowering the mechanical strength of crystalline materials by suitably acting on their environment was highlighted as early as the 1930s by the research of the Russian physicist Rehbinder, who produced evidence that the shear strength of crystals was considerably lowered by the presence on the crystal surfaces of suitable chemical compounds. Subsequent investigations, mostly carried out in the USA, confirmed Rehbinder’s findings and gave them a sound theoretical interpretation that established the fundamentals of the new branch of technology called ‘mechanochemistry’. The diamond tool machines employed in quarrying and working of hard dimension stone appeared as promising devices for the application of mechanochemistry owing to the fact that diamond tools demolish the stone by just applying shear stresses on their surfaces. Several tests, carried out in the second half of the last  century in the authors’ laboratory with a bench machine that simulated the action of diamond tools on granite and orthogneiss specimens yielded encouraging results and provided a wealth of information on the factors affecting mechanochemical effects produced on various hard stones by a variety of chemical compounds. This laboratory phase was followed, from 1996 onwards, by test runs on commercial machines in machine factories and quarries, and finally a full application of sawing aids was performed in quarries operated in Sardinia by various companies. The chemical compounds, of which the sawing aids consist, are added to the flushing fluids and the water solutions or dispersions thus obtained are highly diluted to the order of 10-3 M. These solutions or dispersions therefore should be not harmful for the environment. However, should the environmental regulations be particularly strict, recycling of flushing fluids according to a simple flowsheet is described for hard dimension stones working plants. The productivity improvements of diamond tool machines on hard dimension stones range from 40% to more than 100%, depending on various factors on which the paper provides adequate details. Paper by G. Rossi, G. Loi, P. Trois and G. S.Andrissi.

The influence of the physico-chemical environment on certain mechanical properties of crystalline solids was discovered in the 1930s by the Russian physico-chemist P. A. Rehbinder [1] and the solid state physics and physicochemical fundamentals were studied by several researchers [2-21] who envisioned its major technological potential, naming this new branch of science and technology ‘mechanochemistry’. Shear strength of crystalline solids is significantly reduced when certain chemical compounds are adsorbed on their surfaces and this effect has been exploited in oil well drilling in the Soviet Union [22]. In actual fact, drilling tools, especially diamond bits, demolish the stone chiefly by applying shear stresses thereto [23] (Fig 1). The advent, in the late 1900s, of diamond impregnated tools – such as diamond discs and diamond wire that act on the rock in a manner that can be defined as ‘abrasion’ [24] – raised the interest of our Tool/Rock Interaction work Group (TRIG) that had been investigating the relationships between tools and rocks for several years. Research commenced in the 1970s culminated in the successful application of mechanochemistry to commercial dimension stone operations involving diamond disc and diamond wire machines. This paper describes TRIG’s work and the technological progress achieved.

Conclusions

The benefits of sawing aids in hard rock cutting machines can be seriously undermined by their improper use. Accurate monitoring of operation mode and of the influence of the most important parameters (flushing fluid composition, flow rate and temperature, cleanliness of the diamond tools, relative rock/tool velocity) is therefore very important and deserves due attention. Experience gained during plant operation can achieve further

savings in sawing aid costs. The authors believe it appropriate to conclude by quoting the concluding remarks of a paper published about forty years ago by two forerunners in this field [45]: “We believe that anything that helps to reduce costs in diamond drilling or sawing will benefit not only the users concerned but also the diamond industry as a whole by making diamond tools more economical and efficient and therefore capable of far wider applications.”