Investigation of Accelerated Degradation Methods to Cause Blisters for Non-Defective Vinyl Ester Resin Glass Flake Organic Coatings

Organic coatings are applied as a corrosion prevention measure, but their effectiveness may degrade over time. In this study, the acceleration effects of typical degradation methods in non-defective vinyl ester resin organic coatings containing glass flakes such as high-temperature immersion and immersion in chemical accelerators are clarified using physiochemical techniques. Immersion in an acetic acid (AcOH) aqueous solution causes resin swelling, and the behaviors are quantitatively evaluated through gravimetric, thickness, and electrochemical impedance spectroscopy (EIS) measurements. Furthermore, a combined process of immersion in hydrofluoric acid and an AcOH aqueous solution reduces the electrical properties and eventually blisters the thick coating surface. This result suggests that an appropriate combination of the resin swelling and the glass degradation (glass dissolution and/or formation of the gap between glass and resin) decrease mechanical properties of the glass flake coating and causes blisters. In order to help the health diagnosis of the visually non-defective aged glass flake coating, the relationship between the electrical characteristic values and the invisible degradation by accelerated tests is finally indicated.

Forty years of durability assessment of nuclear waste glass by standard methods

Standard methods to assess the durability of vitrified radioactive waste were first developed in the 1980’s and, over the last 40 years, have evolved to yield a range of responses depending on experimental conditions and glass composition. Mechanistic understanding of glass dissolution has progressed in parallel, enhancing our interpretation of the data acquired. With the implementation of subsurface disposal for vitrified radioactive waste drawing closer, it is timely to review the available standard methodologies and reflect upon their relative advantages, limitations, and how the data obtained can be interpreted to support the post-closure safety case for radioactive waste disposal.

Basalt - fluid interactions at subcritical and supercritical conditions: An experimental study

<p><b>To investigate the interaction between fluids and basalt at subcritical, near-supercritical, and supercritical hydrothermal conditions (350-400˚C/500 bar), eight experiments have been conducted. These used a continuous-flow, high temperature and pressure hydrothermal apparatus. The basalt was reacted with three fluids: distilled water; geothermal brine; and natural seawater. Two further experiments used only seawater as a control to determine its behaviour without the influence of basalt.</b></p> <p> With distilled water, the fluid chemistry results show elevated SiO2, K, Cl, SO4, and H2S in solution for the first 12 days of both experiments. This is due to volcanic glass dissolution. After glass was removed, fluid composition was controlled by the remaining rock minerals. At 400˚C, the secondary mineral assemblage at the bottom of the Reactor (fluid entry point) is composed of grossular, wollastonite, anorthite, and chlorite. These results show the effectiveness of distilled water, which lacks any alkali cations, at removing Na and K rapidly from the rock. At the top of the Reactor (fluid exit point) the secondary minerals are anorthite and celadonite. At 350˚C, the secondary mineral assemblage at the bottom is anorthite and chlorite, while celadonite is the dominant secondary mineral at the top. In both experiments, celadonite replaces solely olivine. The formation of celadonite through reaction with distilled water shows that it can be formed by the interaction of deuteric water and basalt without addition of other components.</p> <p> The geothermal brine contains high concentrations of SiO2, K, SO4, Na, Cl and has an acidic pH. At 400˚C, fluid chemistry displays elevated SiO2 concentrations for approximately two weeks due to glass dissolution. At 350˚C, SiO2 concentration is initially high after temperature increase, but decreases gradually over the remainder of the experiment. At 400˚C, the secondary mineral assemblage at the bottom of the Reactor is composed of anhydrite and biotite, while at the top of the Reactor, smectite is the only secondary mineral. At 350˚C, anhydrite and smectite are found at the bottom, while only smectite is found at the top. The lack of biotite at 350˚C suggests this mineral’s precipitation kinetics are too slow to outcompete chlorite precipitation.</p> <p> The seawater-only experiments were conducted as controls to determine its behaviour during heat-up and provide the input solution composition for the seawater-basalt experiments. Both seawater-only experiments (377˚C and 342˚C) show the precipitation of anhydrite, caminite and brucite due to their retrograde solubilities. The effluent solutions are greatly depleted in Ca, Mg and SO4.</p> <p> In the seawater-basalt experiments at near-supercritical (400˚C) and subcritical conditions (350˚C), elevated SiO2 concentrations due to glass dissolution are not observed. This is attributed to rapid secondary mineral precipitation. Fluid chemistry and mass balance calculations show almost complete removal of SO4, and in particular, Mg, from the seawater while Ca shows a considerable loss from the rock. Three mineralization fronts were identified: (1) glass dissolution; (2) chloritization; and (3) anhydrite precipitation. In both experiments, there is a switch from chloritization to smectitization. This is accompanied by a decrease in Mg/Fe ratio in smectite. This mineral was also found at the top of both experiments, but its composition was more reflective of the rock.</p> <p>In terms of reactivity, the order of phases from most to least reactive is glass – olivine – clinopyroxene – plagioclase – Fe-Ti oxide. For the aluminosilicate phases this is attributed their respective Al contents. The seawater-basalt experiments also emphasise the fast rate of reaction at which Mg is fixed by the rock, which is conjectured to take less than a few hours.</p> <p>Considering all experiments, the distilled water results show a rock control on fluid chemistry while in the remaining basalt experiments, the chemistry is largely controlled by the fluid.</p> <p>Temperatures calculated using standard Na/K geothermometer did not estimate, in most cases, values close to the experimental temperature. This is due to the inability of the rock to sufficiently adjust the Na/K ratio given the secondary mineral assemblages that form.</p> <p> </p>

Basalt - fluid interactions at subcritical and supercritical conditions: An experimental study

<p><b>To investigate the interaction between fluids and basalt at subcritical, near-supercritical, and supercritical hydrothermal conditions (350-400˚C/500 bar), eight experiments have been conducted. These used a continuous-flow, high temperature and pressure hydrothermal apparatus. The basalt was reacted with three fluids: distilled water; geothermal brine; and natural seawater. Two further experiments used only seawater as a control to determine its behaviour without the influence of basalt.</b></p> <p> With distilled water, the fluid chemistry results show elevated SiO2, K, Cl, SO4, and H2S in solution for the first 12 days of both experiments. This is due to volcanic glass dissolution. After glass was removed, fluid composition was controlled by the remaining rock minerals. At 400˚C, the secondary mineral assemblage at the bottom of the Reactor (fluid entry point) is composed of grossular, wollastonite, anorthite, and chlorite. These results show the effectiveness of distilled water, which lacks any alkali cations, at removing Na and K rapidly from the rock. At the top of the Reactor (fluid exit point) the secondary minerals are anorthite and celadonite. At 350˚C, the secondary mineral assemblage at the bottom is anorthite and chlorite, while celadonite is the dominant secondary mineral at the top. In both experiments, celadonite replaces solely olivine. The formation of celadonite through reaction with distilled water shows that it can be formed by the interaction of deuteric water and basalt without addition of other components.</p> <p> The geothermal brine contains high concentrations of SiO2, K, SO4, Na, Cl and has an acidic pH. At 400˚C, fluid chemistry displays elevated SiO2 concentrations for approximately two weeks due to glass dissolution. At 350˚C, SiO2 concentration is initially high after temperature increase, but decreases gradually over the remainder of the experiment. At 400˚C, the secondary mineral assemblage at the bottom of the Reactor is composed of anhydrite and biotite, while at the top of the Reactor, smectite is the only secondary mineral. At 350˚C, anhydrite and smectite are found at the bottom, while only smectite is found at the top. The lack of biotite at 350˚C suggests this mineral’s precipitation kinetics are too slow to outcompete chlorite precipitation.</p> <p> The seawater-only experiments were conducted as controls to determine its behaviour during heat-up and provide the input solution composition for the seawater-basalt experiments. Both seawater-only experiments (377˚C and 342˚C) show the precipitation of anhydrite, caminite and brucite due to their retrograde solubilities. The effluent solutions are greatly depleted in Ca, Mg and SO4.</p> <p> In the seawater-basalt experiments at near-supercritical (400˚C) and subcritical conditions (350˚C), elevated SiO2 concentrations due to glass dissolution are not observed. This is attributed to rapid secondary mineral precipitation. Fluid chemistry and mass balance calculations show almost complete removal of SO4, and in particular, Mg, from the seawater while Ca shows a considerable loss from the rock. Three mineralization fronts were identified: (1) glass dissolution; (2) chloritization; and (3) anhydrite precipitation. In both experiments, there is a switch from chloritization to smectitization. This is accompanied by a decrease in Mg/Fe ratio in smectite. This mineral was also found at the top of both experiments, but its composition was more reflective of the rock.</p> <p>In terms of reactivity, the order of phases from most to least reactive is glass – olivine – clinopyroxene – plagioclase – Fe-Ti oxide. For the aluminosilicate phases this is attributed their respective Al contents. The seawater-basalt experiments also emphasise the fast rate of reaction at which Mg is fixed by the rock, which is conjectured to take less than a few hours.</p> <p>Considering all experiments, the distilled water results show a rock control on fluid chemistry while in the remaining basalt experiments, the chemistry is largely controlled by the fluid.</p> <p>Temperatures calculated using standard Na/K geothermometer did not estimate, in most cases, values close to the experimental temperature. This is due to the inability of the rock to sufficiently adjust the Na/K ratio given the secondary mineral assemblages that form.</p> <p> </p>

Dissolution of simplified nuclear waste glass and formation of secondary phases

Immobilization of high-level and intermediate-level nuclear wastes by vitrification in borosilicate glass is a well-established process. There is a consensus between the waste management agencies of many countries and many experts that vitrified nuclear waste should be disposed of in a deep geological waste repository and therefore its long-term behavior needs to be taken into account in safety assessments. In contact with water, borosilicate glass is metastable and dissolves. In static dissolution experiments, often a surface alteration layer (SAL) forms on the dissolving glass, and later sometimes secondary phases form. Based on boron or lithium release rates, commonly three stages of glass dissolution are defined as a function of the reaction progress: (I) initial dissolution, described by a congruent glass dissolution at the highest rate, (II) residual dissolution, characterized by a glass dissolution rate several orders of magnitude lower than the initial one, and (III) resumption of glass alteration with initial rates. Microscopically, the formation of a complex SAL has been identified as a prerequisite for the slower dissolution kinetics of stage II. Stage III is typically observed under specific conditions, i.e., high temperature and/or high pH driven by the uptake of Si and Al into secondary phases. Different glass dissolution models explaining the mechanisms of the SAL formation and rate-limiting steps have been proposed and are still under debate. In this article different aspects of glass dissolution from recent studies in the literature and our own work are discussed with a focus on the microscopic aspects of SAL formation, secondary phase formation and the resumption of glass dissolution. Most of the experiments in the literature were performed under near-neutral pH conditions and at 90 ∘C, following standard procedures, to understand the fundamental mechanisms of glass dissolution. The example of interaction of glass and cementitious materials as discussed here is relevant for safety assessments because most international concepts include cement e.g., as lining, for plugs, or as part of the general construction of the repository. The aim of the investigations presented in this paper was to study the combined effect of hyperalkaline conditions and very high surface area/volume ratios (SA/V=264000m-1) on the dissolution of international simplified glass (ISG) and the formation of secondary phases at 70 ∘C in a synthetic young cement water containing Ca (YCWCa). The new results show that the SA/V ratio is a key parameter for the dissolution rate and for the formation of the altered glass surface and secondary phases. A comparison with similar studies in the literature shows that especially on the microscopic and nanoscale, different SA/V ratios lead to different features on the dissolving glass surface, even though the SA-normalized element release rates appear similar. Zeolite and Ca-silicate-hydrate phases (CSH) were identified and play a key role for the evolution of the solution chemistry. A kinetic dissolution model coupled with precipitation of secondary phases can be applied to relate the amount of dissolved glass to the evolution of the solution's pH.

Recycling of Nonwoven Polyethylene Terephthalate Textile into Thermal and Acoustic Insulation for More Sustainable Buildings

The construction and building sector is responsible for a large share of energy and material used during the life cycle of a building. It is therefore crucial to apply a circular economy model within the process wherever possible to minimize the impact on the environment. In this paper, the possibility of producing thermal and acoustic boards from industrial nonwoven waste textile is studied and presented. The nonwoven polyester textile obtained directly from the production line in the form of strips and bales was first shredded into smaller fractions and then in the form of pile compressed with a hot press to form compact thermal insulation boards. The first set of specimens was prepared only from waste polyester nonwoven textile, whereas the second set was treated with sodium silicate in order to check the material’s reaction to fire performance. The experimental work was conducted to define the acoustic properties, reaction to fire behavior and thermal conductivity of the produced specimens. The obtained results show that the thermal conductivity coefficient of specimens without added water glass dissolution is near to the values of conventional materials used as thermal insulation in buildings. The reaction to fire testing proved that the addition of water glass actually propagates the progressive flame over the entire product. It can be concluded that the presented thermal insulation can be used as an adequate and sustainable solution for building construction purposes.

The fate of Si and Fe while nuclear glass alters with steel and clay

The French concept developed to dispose high-level radioactive waste in geological repository relies on glassy waste forms, isolated from the claystone host rock by steel containers. Understanding interactions between glass and surrounding materials is key for assessing the performance of a such system. Here, isotopically tagged SON68 glass, steel and claystone were studied through an integrated mockup conducted at 50 °C for 2.5 years. Post-mortem analyses were performed from nanometric to millimetric scales using TEM, STXM, ToF-SIMS and SEM techniques. The glass alteration layer consisted of a crystallized Fe-rich smectite mineral, close to nontronite, supporting a dissolution/reprecipitation controlling mechanism for glass alteration. The mean glass dissolution rate ranged between 1.6 × 10−2 g m−2 d−1 to 3.0 × 10−2 g m−2 d−1, a value only 3–5 times lower than the initial dissolution rate. Thermodynamic calculations highlighted a competition between nontronite and protective gel, explaining why in the present conditions the formation of a protective layer is prevented.