Hydrogen embrittlement, microcracking and piezonuclear reactions in the metal electrodes of an electrolytic cell

Formation and propagation of fractures in solid materials are main topics in the discipline of Fracture Mechanics. The study of the propagation of fractures is also vital in Structural Mechanics as an important indicator of the level of damage of a generic structure. When focusing on metal materials, hydrogen embrittlement (HE) is one of the most relevant factors making the material itself more sensitive to propagation of cracks. This is a remarkable issue also in metallurgic processes. Moreover, any environment rich in hydrogen is a risk for the metal: for instance, either electrolytic environments or any situation that leads to an increment in both cathodic and anodic polarizations. The effect of HE reduces the threshold stress intensity factor as free Hydrogen (H) atoms hosted in the metal lattice cause the solid to become more brittle and less resistant to crack formation and propagation. As regards to Ni- and Fe-based alloys, H absorption into the crack tip fracture process zone increases the stress intensity and the crack growth rate. The knowledge of such features is the key to study the topics reported in this thesis. In fact, the first part of Chapter 1 will describe useful details about HE. The aim of this work is to investigate the mechanical features involved in crack propagation and arguing in what terms they are connected to nuclear effects observed during compression experiments and other failure phenomena involved in electrolysis. The second part of Chapter 1 reports some literature of experimental results about nuclear emissions detected during compression tests on brittle rocks, carried out in the Fracture Mechanics Laboratory at the Department of Structural, Geotechnical and Building Engineering (DISEG) of the Politecnico di Torino (Turin, Italy). From the experimental data collected and the nuclear emissions detected a hypothesis of piezonuclear fission reactions is drawn. Such would be the idea of specific nuclear reactions triggered by stress relief caused by cracks and fractures in the material under compression. Results of chemical composition analyses on external and fractured surfaces of the specimens are reported. Comparing the proportions of the chemical changes measured on the specimens to the evolution of the abundance of the Earth Crust elements, a connection between the laboratory scale and the Earth scale is presented. From a different perspective, the piezonuclear effect could be interpreted as an original experimental proof of nuclear reactions induced in solid materials through mechanical processes. Features like this one are studied in the research field of Nuclear Science of condensed matter, also known as cold fusion research. That is, nuclear reactions are induced by means of processes involving relatively low energy, such as chemical electrolysis. In Chapter 2, part of the literature concerning nuclear effects in condensed matter is presented. Various experimental data indicating the occurrence of anomalous nuclear reactions at relatively low energies are mentioned. Accordingly, the author of this thesis followed a two-year laboratory campaign, investigating possible nuclear effects occurring during electrolysis experiments. Chapter 3 and 4 describe the experimental activity carried out using an electrolytic cell with different metal electrodes. In details, Chapter 3 describes the laboratory experiments conducted on nickel-iron anode and cobalt-chromium cathode. Chapter 4 reports details of the second part of the laboratory campaign: nickel anode and palladium cathode were used. The set-up of the laboratory rig is described as well as the equipment for the measurements. The measures were taken focusing on alpha particle and neutron emission, as well as on the chemical composition of the electrodes before and after the electrolysis. The appearance of micro-cracks on the surface of nickel and palladium electrodes is one of the key aspects observed after the experiments. After illustrating the results of the laboratory research, a strict connection between micro-cracks, neutron emission and compositional changes is considered as the evidence of non-traditional nuclear reactions implicating the fission of nickel and palladium into lighter elements. Numerous are the hypotheses behind the jungle of experimental data in the literature, nonetheless, a unified theory has not been established yet. In the attempt of providing a contribution to the theoretical explanation, Chapter 5 focuses the attention on describing the nucleus of an atom through a lattice model. The model described in this chapter was proposed by Professor Norman D. Cook of the Kansai University (Osaka, Japan). In the latter the author of the thesis spent five months of his PhD course to study and broaden his knowledge of the model itself. Also numerical simulations are reported considering the fission of different lattices corresponding to different elements. The results of the simulations provide a first attempt to predict what fragments would form from the geometrical rupture of the nuclear lattices investigated: that is iron, nickel, and palladium. Such prediction might be in support of the experimental activity related to fracture and electrochemical processes, when trying to reproduce nuclear effects in condensed matter. This thesis intends to pose a closure to the research developed in a three year PhD course; thus, the conclusions outlined at the end are drawn under the light of what has been experienced by the author in the past three years. On the other hand, one of the purposes of what is written below is to provide the support to any further research intended to be developed in the field of Fracture Mechanics and Nuclear Science of Condensed Matter. For this reason a plausible mechanical interpretation to nuclear-like effects observed in fracture and electrolysis processes is considered.