Crack propagation driven by crystal growth

Crystals that grow in confinement may exert a force on their surroundings and thereby drive crack propagation in rocks and other materials. We describe a model of crystal growth in an idealized crack geometry in which the crystal growth and crack propagation are coupled through the stress in the surrounding bulk solid. Subcritical crack propagation takes place during a transient period, which may be very long, during which the crack velocity is limited by the kinetics of crack propagation. When the crack is sufficiently large, the crack velocity becomes limited by the kinetics of crystal growth. The duration of the subcritical regime is determined by two non-dimensional parameters, which relate the kinetics of crack propagation and crystal growth to the supersaturation of the fluid and the elastic properties of the surrounding material

Allocation in LCAs of biorefinery products: implications for results and decision-making

In Life Cycle Assessments (LCAs) of biorefinery products, a common challenge is the choice of method for allocating environmental burdens of multifunctional processes (feedstock cultivation and biorefinery processes), a choice which can substantially influence LCA results and hence decision-making. The aim of this paper is to explore how this choice influences results and in which decision contexts the choice is particularly important. To do this, we tested six allocation methods in a case study of a biorefinery using pulpwood as feedstock. Tested methods included: main product bears all burden, substitution, traditional partitioning methods (based on economic value and exergy), a hybrid method combining elements of substitution and partitioning, and an alternative hybrid method developed by us, which allocates less environmental burden to co-products with a high potential to mitigate environmental burdens. The methods were tested in relation to decision contexts and LCA questions of relevance for biorefineries.</br></br> The results indicate that the choice of allocation method deserves careful attention, particularly in consequential studies and in studies focussed on co-products representing relatively small flows. Furthermore, the alternative hybrid allocation method is based on a logical rationale – favouring products with higher substitution potential – and has some other potential benefits. However, in cases where the scales of co-product flows are of different orders of magnitude, the method yields extreme results that could be difficult to interpret. Results also show that it can be important with consistent allocation for both cultivation and biorefinery processes, particularly when substitution is applied

Reaction-induced fracturing during olivine serpentinization: A mechanistic investigation at the interface scale

Serpentinization of the Earth's impermeable upper mantle is one of the most fundamental metamorphic hydration reactions. It governs lithospheric weakening, geochemical subduction zone input and possibly even the formation of life-essential building blocks. Serpentinization relies on fluid pathway generation due to low initial permeability and the large positive solid volume change associated with hydration. Although these pathways can be produced as a tectonic stress response, there is substantial evidence that the volume increase during olivine serpentinization itself generates stresses sufficient to fracture the rock. Nonetheless, the actual fracturing mechanism during olivine serpentinization is largely unexplored. Unconstrained batch experiments (Okamoto et al. 2011, this study) produce comparable hierachial fracture patterns to those found in natural samples demonstrating that no external forces (e.g., tensile stress) are required for fracturing to take place. Combining this with the observation that fluid-mediated mineral replacement advances via an interface-coupled dissolution-reprecipitation mechanism (e.g., Putnis 2009) without solid-state diffusion into the dissolving mineral indicates that classical (stress) corrosion cracking mechanisms cannot describe fracturing during olivine serpentinization. By uniting micro- and nanostructural characteristics ubiquitous to serpentinized olivine grains with a coupled diffusion-reaction-deformation model and crack growth theory this study explores the sub-critical fracturing mechanism at the interfacial scale. We present a new multistep reaction process and test the feasibility of a molecular wedge-assisted fracturing mechanism based on the following ubiquitously identified features: (1) no rotation of grain domains during fragmentation, (2) isotropic fracture orientation distribution with a uniform average width of individual finite length serpentine veins, (3) cumulative fragment area distribution with a log-normal scaling behavior following a hierachical fracturing model, (4) etch pit development at olivine-lizardite reaction interfaces, (5) crack initiation at these surface perturbations and (6) amorphous layer formation during olivine dissolution prior to serpentine nucleation (e.g., Rumori et al. 2004). Based on these observations we propose an entirely self-propagating reaction-driven fracturing process, where fractures nucleate at dissolution-induced surface perturbations assisted by a molecular wedge of amorphous 'gel', followed by further olivine dissolution and serpentine (±brucite) reprecipitation coupled with the force of crystallization. This process results in the observed hierarchical fracture network. Our results suggest that the mechanical force needed to advance serpentinization at the grain-scale does not rely on external forces but is due to interface-coupled, chemomechanical feedback during olivine re-equilibration in the presence of a fluid phase. Nevertheless, the influence of tectonic forces will need to be accounted for at larger scales

The LCA modelling of chemical companies in the industrial symbiosis perspective: Allocation approaches and regulatory framework

The application of industrial symbiosis to chemical processes is made possible by considering physical by-products as new sources in spite of potential waste. The by-product acts as a substitution of raw materials in symbiotic chemical companies, possibly taking into account geographical proximity. While advantages appear evident in terms of reduced cost savings and resource consumption, benefits related to other environmental impacts seem to be less clear. This chapter deals with different case studies of industrial symbiosis and how these are treated according to literature, regulatory approaches and main guidelines. Once the different approaches and their range of applications are presented, the chapter describes the main barriers and strengths in the application of these rules to the chemical sector. Finally, the identified approaches are applied to a specific case of industrial symbiosis in the chemical sector by illustrating how the single data can be calculated and can quantitatively change. This chapter aims to guide the LCA practitioner through an agile set of rules in modelling industrial symbiosis in an LCA perspective and to provide a quantitative evaluation of the effects that a modelling choice may produce with respect to another