Developments in the theory and application of chemomechanical effects

Westwood, A. R. C.; Ahearn, J. S.; Mills, J. J.

doi:10.1016/0166-6622(81)80050-9

Cited by 115 publications

(29 citation statements)

References 47 publications

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“…[629][630][631][632][633][634] The enhanced breakage and milling efficiency may result from the lowering of solid strength due to decrease in interfacial tension (Rebinder effect), increased mobility and annihilation of dislocation and/ or surface charge (chemo-mechanical effect) and retardation of sealing of freshly created cracks. 629,630,[639][640][641][642] The phenomena of aggregation and agglomeration (see section 1.4) responsible for coarsening of size distribution during milling and mechanical activation are affected by the presence of water. 629,630,634 In the presence of a polar liquid like water, molecular dense aggregates decompose to give primary particles and fine milling rather than mechanical activation is promoted.…”

Section: Role Of Water In Mechanochemistrymentioning

confidence: 99%

Hallmarks of mechanochemistry: from nanoparticles to technology

et al. 2013

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The aim of this review article on recent developments of mechanochemistry (nowadays established as a part of chemistry) is to provide a comprehensive overview of advances achieved in the field of atomistic processes, phase transformations, simple and multicomponent nanosystems and peculiarities of mechanochemical reactions. Industrial aspects with successful penetration into fields like materials engineering, heterogeneous catalysis and extractive metallurgy are also reviewed. The hallmarks of mechanochemistry include influencing reactivity of solids by the presence of solid-state defects, interphases and relaxation phenomena, enabling processes to take place under non-equilibrium conditions, creating a well-crystallized core of nanoparticles with disordered near-surface shell regions and performing simple dry time-convenient one-step syntheses. Underlying these hallmarks are technological consequences like preparing new nanomaterials with the desired properties or producing these materials in a reproducible way with high yield and under simple and easy operating conditions. The last but not least hallmark is enabling work under environmentally friendly and essentially waste-free conditions (822 references).

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Section: Role Of Water In Mechanochemistrymentioning

confidence: 99%

Hallmarks of mechanochemistry: from nanoparticles to technology

et al. 2013

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“…Many important practical applications involve the coupling between mechanic and chemical effects with the competition between several characteristic time scales. Application of stress may act as a catalyst of chemical reactions [5] or, reciprocally, chemical reactions may lead to bond weakening [6] and thus promote failure. A dramatic example is the aging of present aircrafts due to repeating loading in a corrosive environment [7].…”

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confidence: 99%

Critical ruptures

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The fracture of materials is a catastrophic phenomenon of considerable technological and scientific importance. Here, we analysed experiments designed for industrial applications in order to test the concept that, in heterogeneous materials such as fiber composites, rocks, concrete under compression and materials with large distributed residual stresses, rupture is a genuine critical point, i.e., the culmination of a self-organization of damage and cracking characterized by power law signatures. Specifically, we analyse the acoustic emissions recorded during the pressurisation of spherical tanks of kevlar or carbon fibers pre-impregnated in a resin matrix wrapped up around a thin metallic liner (steel or titanium) fabricated and instrumented by Aérospatiale-Matra Inc. These experiments are performed as part of a routine industrial procedure which tests the quality of the tanks prior to shipment and varies in nature. We find that the seven acoustic emission recordings of seven pressure tanks which was brought to rupture exhibit clear acceleration in agreement with a power law "divergence" expected from the critical point theory. In addition, we find strong evidence of log-periodic corrections that quantify the intermittent succession of accelerating bursts and quiescent phases of the acoustic emissions on the approach to rupture. An improved model accounting for the cross-over from the non-critical to the critical region close to the rupture point exhibits interesting predictive potential. * Corresponding author: D. Sornette, University of California, Los Angeles, 3845 Slichter Hall, Box 951567 Los Angeles, CA 90095-1567. Tel.: +1 (310) 825 28 63 Fax.: +1 (310) 206 3051-e-mail: sornette@moho.ess.ucla.edu. Plan of the studyIn this paper, we first present in section 2 a brief review of the "critical rupture" concept with an emphasis on the role of heterogeneity. Section 3 describes the experimental systems and the properties of the acoustic emission time series that we analyse with three theoretical formulas derived from the critical rupture concept. We present a brief justification for these three power laws. Section 4 gives the results obtained on the acoustic emission energy release rate on seven systems. Section 5 analyses the cumulative energy releases of these seven systems. Section 6 describes the relative merits of the three power law formulas for the prediction of the critical pressure of rupture and section 7 concludes.2 Review of the "critical rupture" concept BackgroundThe damage and fracture of materials is of enormous technological interest due to their economic and human cost. They cover a wide range of phenomena like, e.g., cracking of glass, aging of concrete, the failure of fiber networks in the formation of paper and the breaking of a metal bar subject to an external load. Failure of composite systems are of utmost importance in naval, aeronautics and space industry [1]. By the term composite, we refer to materials with heterogeneous microscopic structures and also to assemblages of macro...

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“…These were observed by Westbrook and co-workers [10,11] and Westwood and co-workers [12][13][14] in a number of ceramic systems. For instance, Hanneman and Westbrook [10] investigated the time dependence of the hardness of a range of materials measured in a range of solvents and reported even a short-term softening of about 10-20% in the presence of adsorbed water layers on various ceramic materials including zinc oxide and alumina.…”

Section: Previous Microindentation Studiesmentioning

confidence: 66%

“…dislocations and vacancy clusters etc.). However, such effects have been shown to be several orders of magnitude too small to explain the observed hardness changes [13].…”

Section: Previous Microindentation Studiesmentioning

confidence: 99%

“…Despite this, a variety of mechanisms have been proposed to explain these observations as discussed in detail by Westwood et al [13]:-(1) Adsorption creating differences in the way that changes in surface charges might interact electrostatically with charged near-surface structural defects (e.g. dislocations and vacancy clusters etc.).…”

Section: Previous Microindentation Studiesmentioning

confidence: 99%

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The origins of chemomechanical effects in the low-load indentation hardness and tribology of ceramic materials

et al. 2015

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We have used high-resolution techniques (nanoindentation, atomic force microscopy) to further isolate and identify environmental effects previously reported as possibly affecting both the microindentation response of a range of ceramic materials and their tribological behaviour. In order to make meaningful comparisons, these new experiments have been conducted alongside conventional Knoop and Vickers microhardness experiments conducted under identical conditions on the same samples. A range of polycrystalline, single crystal and amorphous ceramic materials have been studied including some only available as coatings. Our results show that thin adsorbate-modified layers (of dimensions ~1nm) are almost invariably present on all the materials studied but their presence is not directly identifiable by nanoindentation in most cases even if it does affect friction response. However, in crystalline materials, (1012 sapphire and ZnO), we have been able to distinguish a further softening effect seen as a thicker layer (tens of nm) and believed associated with an adsorption-induced near-surface band-structure change affecting the motion of charged dislocations. This produces a measurable softening that is clearly evident in nanoindentation tests but less clear in microindentation tests. Finally, we present conclusions on the suitability of indentation testing for studying these phenomena, together with the implications of chemomechanical effects for influencing tribological performance and, thus, materials selection.

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Developments in the theory and application of chemomechanical effects

Cited by 115 publications

References 47 publications

Hallmarks of mechanochemistry: from nanoparticles to technology

Hallmarks of mechanochemistry: from nanoparticles to technology

Critical ruptures

The origins of chemomechanical effects in the low-load indentation hardness and tribology of ceramic materials

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