Porosity Of Samples Research Articles

Thermal effect on the geo-engineering characteristics of a rock salt.

Rock salt caverns are considered one of the best hosts to store oil, natural gas, radioactive and toxic wastes due to their low permeability, self-healing characteristics and wide distribution on the Earth. Stored nuclear waste in rock salts will radiate for many years. Therefore, the thermal energy and also temperature in the host environment will increase depending on time. In this study, P-wave velocity (Vp), Brazilian tensile strength (σt), uniaxial compression strength (σc) of Çankırı rock salt were investigated under different temperatures ranging from 20°C to 250°C since the temperature is a factor that causes changes in some physical and geo-mechanical properties of rocks. The acoustic emission technique was utilized during uniaxial compression strength tests, to monitor the crack accumulation. Additionally, X-ray micro-computed tomography technique was employed to observe the microstructure and determine the porosity of rock salt samples depending on the temperature. The Vp and the σt of Çankırı rock salt decrease with increasing temperatures of samples whereas the σc increases. The ductility of rock salt tends to increase with augmented temperature and the axial strain at the ultimate stress level is 2.96% at 20°C whereas it reaches up to 6.29% at 250°C. The AE activity of rock salt generates at the early stages of loading and AE count prominently increases with the increasing temperature of samples. Therefore, the stress levels of crack initiation (σi) and crack damage (σcd) thresholds were reached earlier than the previous one with each temperature increment. According to X-ray micro-CT images of rock salts, the number of cracks increased markedly in thermally treated rock salt samples and therewith the porosity increases from 1.12% to 2.73% with an increase in temperature from 50°C to 250°C.

Full-Scale Experimental Study on the Effect of CO2 Flooding on Storage-Seepage Capacity of Tight Sandstone Reservoirs.

In the CO2 flooding stage of tight sandstone reservoirs, the CO2-crude oil-rock interaction causes asphaltene deposition and mineral dissolution effect, which would affect the reservoir performance and reservoir physical property. To reveal the variation law of reservoir performance and percolation capacity in the CO2 flooding stage, the core samples of typical tight sandstone reservoirs with different permeability levels were selected. An indoor physical flow simulation experiment of CO2 flooding was then performed. The change in reservoir performance characteristics in the CO2 flooding stage of the tight sandstone reservoir was quantitatively evaluated, and the evolution law of reservoir macroscopic seepage ability during the CO2 flooding process was revealed. The experimental results show that the damage degree of CO2-crude oil-rock interaction on reservoir foundation performance is negatively correlated to the initial permeability of the reservoir. The lower the initial permeability of core samples, the greater would be the damage degree of the experimental process on the effective porosity and permeability of rock samples. However, in reservoirs with relatively high permeability (0.5-0.6 mD), the physical properties of rock samples improved after CO2 flooding with an average increase in effective porosity and permeability by 4.54 and 10.23%, respectively. The damage degree of reservoir effective porosity is slightly affected by CO2 injection pressure, while the damage degree of permeability has a significant negative correlation with injection pressure. In the high-pressure miscible flooding stage of 30 MPa, the organic matter deposition caused by the interaction of CO2-crude oil-rock causes the highest degree of damage to the permeability of rock samples (up to 33.33%). Moreover, the flooding efficiency in the CO2 flooding stage of a tight sandstone reservoir is positively correlated with the reservoir permeability and CO2 injection pressure. In the near-miscible flooding stage to miscible flooding stage, the flooding efficiency increases rapidly. After entering the miscible flooding stage, the growth rate in flooding efficiency decreases gradually with the increase in injection pressure.

Design of apple snacks – A study of the impact of calcium impregnation method on physicochemical properties and structure of apple tissues during convective drying

Calcium impregnation methods (at atmospheric pressure, AI, or under vacuum, VI) followed by air drying at 60 °C were used for producing healthy apple snacks. This study compared the effect of the impregnation method on the ultrastructure features and physicochemical properties (desorption isotherm, density, porosity and shrinkage, thermal transitions, rheological behaviour, colour) of fortified apples along convective drying. Calcium concentration in AI and VI dried apples were ≈ 3600 and ≈ 5200 ppm respectively, which implied, considering a portion of dried apple of 50 g, 18% and 26% of the recommended intake for adults. Calcium incorporation did not affect the desorption behaviour but induced browning of apple tissues. Drying resulted in a great increase in porosity of AI samples and a noticeable compaction of the VI tissues. Impregnated tissues at aw ≤ 0.47 exhibited distinctive mechanical properties: AI apples were characterized by very high stiffness and lower resistance to rupture, while VI apples appeared stronger and moderately stiff. Industrial relevance textThis study will help to develop large-scale commercial production of calcium fortified apple snacks with distinctive characteristics. High quality and content of nutrients, easy industrialization and storage and a long shelf life are important aspects of these healthy snacks. They constitute a valuable functional shelf-stable product, that also can help feeding the population during natural disasters and wars, as well as reducing food insecurity in vulnerable groups as part of the diet. On the other hand, the use of apples not meeting the organoleptic requirements for direct consumption, or not processed into juice, drink, or cider as raw material, looks of particular interest for diversifying the production within the framework of sustainable production.

A universal model for the permeability of sintered materials

Sintered materials are used as permeable filters and flow controllers, for which a validated and general model of porosity and permeability is required. Here, we prepare samples built from mono- and polydisperse glass bead populations sintered for known times at high temperature, and then measure the sample porosity and permeability. We supplement our new dataset with published permeability data for sintered systems including high-temperature in situ determinations of permeability during sintering. We test a range of mathematical models for the change in permeability with porosity as sintering progresses from a value for the initial granular particle packing geometry, down to the percolation threshold at low porosity. We find good agreement between our datasets and a preferred theoretical approach – a percolation theory model – with no explicit requirement for empirical adjustment. However, we propose semi-empirical steps that generalize this theory to a universal description across all porosities. Finally, we quantify the inertial component of fluid transport at high flow rates through these materials. Our model framework is made available via a user-friendly downloadable spreadsheet which takes particle size distribution as an input and provides permeability as an output.

Effect of Wet-Dry Cycles on the Mechanical Performances and Microstructure of Pisha Sandstone

The effects of the wet-dry cycles on the chemical compositions, microstructure, and mechanical properties of Pisha sandstone were experimentally investigated in the current study. A series of uniaxial compression tests were conducted to validate the deterioration of the mechanical property of specimens after wet-dry cycles. In addition, the evolutions of the mineral compositions and microstructure characteristics were confirmed by X-ray diffraction (XRD) and scanning electron microscope (SEM). Experimental results indicated that with the increase of wet-dry cycles, the mechanical properties of Pisha sandstone gradually decrease. After five wet-dry cycles, the uniaxial compressive strength, elastic modulus, and fracture energy of specimens were reduced by 41.06%, 62.39%, and 31.92%, respectively. The failure mode of the specimen changes from inclined shear failure to peel failure. Compared to the initial specimens, the relative content of primary minerals after five wet-dry cycles declined by 5.94%, and the relative content of clay minerals after five wet-dry cycles increased by 54.33%. Additionally, the porosity of samples exhibits a positive correlation with wet-dry cycles. Compared to the initial specimens, the porosity of specimens after five wet-dry cycles increased by 176.32%. Finally, a prediction model of the correlation between uniaxial compressive strength and porosity is proposed and verified.

Application of the container waste glass in foamed glass production

We report on foamed glass production from container glass cullet, foaming couple carbon/Mn3O4, and crystallization inhibitors (fluxing agents, aluminum oxide and phosphates) under an oxygen-free atmosphere. We study the influence of the content of the inhibitors on the density, porosity, crystallinity, and thermal conductivity of the foamed samples. We observe that the amounts of fluxing agents determined to effectively decrease the crystallization (5 wt%) prevent effective foaming and were thus decreased. By decreasing the content of the fluxing agent to 2 wt%, the densities of the foamed samples are decreased. With the addition of phosphates to the mixtures, crystalline content, open porosity and thermal conductivity are decreased. However, the obtained foamed samples remain mainly open porous with density and thermal conductivity in the ranges 140–168 kg m−3 and 57–66 mW m−1K−1, respectively.

Estimation of soil porosity in mine tailing using parameters from instrumented oedometer test

In the geological field, unexpected tailing failures have recently occurred and caused critical damage. The objective of this study was to evaluate the porosity of mine tailing using compressibility and elastic wave velocities from an instrumented oedometer test. Three samples (MS1, MS2, MS3) were obtained from the mine tailing at different depths, and their properties were assessed. The oedometer test was conducted from 0 to 1280 kPa for MS1, MS2 (with various initial stresses), and MS3, and the elastic wave velocities were measured during each loading and unloading step. The specific gravity, X-ray fluorescence, and X-ray diffraction test results revealed a portion of hematite (Fe2O3) in all the samples. According to the instrumented oedometer test, the compressibility and elastic wave velocities of the samples varied with respect to the sampling depth and stress conditions. In particular, the α factor and β exponent from the shear wave velocity followed the empirical relationship of general soil types. Empirical porosity evaluation methods reliably estimated the sample porosity at shallow depths by using the parameters from the instrumented oedometer tests. Thus, the in situ porosity at a mine tailing can be effectively evaluated if the profiling of elastic velocities in the field is available.

Analysis of Fluid Flow Pathways in the Mount Meager Volcanic Complex, Southwestern Canada, Utilizing AMT and Petrophysical Data

AbstractDefining the spatial distribution of geological structures and rock properties is important for understanding how fluid flow is controlled in a geothermal reservoir. Here, we present a procedure to examine the potential fluid pathways. By combining 3‐D resistivity models derived from audio‐magnetotelluric (AMT) data with available rock properties (porosity and permeability) and fluid sample data (fluid resistivity, salinity, and temperature), we investigated the relationship between electrical resistivity and fluid flow in an active volcanic system. Different petrophysical models and empirical relations are evaluated to determine the relationship between the fluid flow system at Mount Meager, British Columbia, and the resistivity model. In addition, we utilized porosity and permeability measured in the laboratory to define the porosity‐permeability relationship. The porosity of the volcanic core samples showed a range of 2.6%–23.2% and the permeability was in a range of 0.001–5,186.57 mD. The results showed the potential of 3‐D inversion of AMT data to map the fluid pathways at Mount Meager. These pathways are correlated with loss circulation zones in boreholes and can account for porosity up to 8.5%, which using the porosity‐permeability relationship translates to permeability of the order 0.249 mD. Not only are the fault and fracture zones important for reservoir exploitation, but they also provide permeability for the circulation of meteoric water. Our studies suggest that a set of fractures with 0.1 m spacing and 20 mm aperture can keep 40% fluid in pores and transmit fluid with possible permeability of 666 mD.

Experimental study on the evolution of pore structure of coal samples under freeze–thaw

To investigate the effect of freeze–thaw on damage and pore structure characteristics, some coal samples were freeze-thawed by freeze–thaw test machines. The evolution law of the pore structure of coal samples under freeze–thaw cycles, the porosity, and the bound and free fluid volume of coal samples under freeze–thaw were studied by low nuclear magnetic resonance, the complexity of the pore structure of coal samples under different freeze–thaw cycles was analyzed by fractal dimension, and the influence mechanism of freeze–thaw on the pore structure of coal samples was discussed. The results indicate that: (1) freeze–thaw could damage the pore and fracture structure and reduce the wave velocity of coal samples, and the wave velocity of coal samples after 120 freeze–thaw cycles decreased 66.5% compared with that of before the freeze–thaw cycle. (2) Freeze–thaw can effectively promote the development of pore and fracture. With the increase in freeze–thaw cycles, the proportion of micropores of coal samples decreases, while the proportion of mesopores and macropores gradually increases. (3) The freeze–thaw cycle can promote the increase in the coal sample porosity, and the increment of total, residual, and effective porosity is 3.47%, 1.94%, and 1.53%, respectively, after 120 freeze–thaw. (4) The fractal dimension of total, adsorption, and seepage pore of coal samples all decrease with the increase in freeze–thaw cycles, indicating that liquid nitrogen can reduce the complexity of the pore structure and weaken the heterogeneity of the pore structure.

Effect of skull porosity on ultrasound transmission and wave mode conversion at large incidence angles.

Transcranial ultrasound imaging and therapy depend on the efficient transmission of acoustic energy through the skull. Multiple previous studies have concluded that a large incidence angle should be avoided during transcranial-focused ultrasound therapy to ensure transmission through the skull. Alternatively, some other studies have shown that longitudinal-to-shear wave mode conversion might improve transmission through the skull when the incidence angle is increased above the critical angle (i.e., 25° to 30°). The effect of skull porosity on the transmission of ultrasound through the skull at varying incidence angles was investigated for the first time to elucidate why transmission through the skull at large angles of incidence is decreased in some cases but improved in other cases. Transcranial ultrasound transmission at varying incidence angles (0°-50°) was investigated in phantoms and ex vivo skull samples with varying bone porosity (0% to 28.54%±3.36%) using both numerical and experimental methods. First, the elastic acoustic wave transmission through the skull was simulated using micro-computed tomography data of ex vivo skull samples. The trans-skull pressure was compared between skull segments having three levels of porosity, that is, low porosity (2.65%±0.03%), medium porosity (13.41%±0.12%), and high porosity (26.9%). Next, transmission through two 3D-printed resin skull phantoms (compact vs. porous phantoms) was experimentally measured to test the effect of porous microstructure alone on ultrasound transmission through flat plates. Finally, the effect of skull porosity on ultrasound transmission was investigated experimentally by comparing transmission through two ex vivo human skull segments having similar thicknesses but different porosities (13.78%±2.05% vs. 28.54%±3.36%). Numerical simulations indicated that an increase in transmission pressure occurs at large incidence angles for skull segments having low porosities but not for those with high porosity. In experimental studies, a similar phenomenon was observed. Specifically, for the low porosity skull sample (13.78%±2.05%), the normalized pressure was 0.25 when the incidence angle increased to 35°. However, for the high porosity sample (28.54%±3.36%), the pressure was no more than 0.1 at large incidence angles. These results indicate that the skull porosity has an evident effect on the transmission of ultrasound at large incidence angles. The wave mode conversion at large, oblique incidence angles could enhance the transmission of ultrasound through parts of the skull having lower porosity in the trabecular layer. However, for transcranial ultrasound therapy in the presence of highly porous trabecular bone, transmission at a normal incidence angle is preferable relative to oblique incidence angles due to the higher transmission efficiency.

Density-Based Optimization of the Laser Powder Bed Fusion Process Based on a Modelling Framework

One of the main challenges encountered in the Laser-based Powder Bed Fusion (L-PBF) Additive Manufacturing (AM) process is the fabrication of defect-free parts. The presence of defects severely degrades the mechanical performance of AM parts and especially their fatigue strength. The most popular and reliable method to assess the ability of the employed process parameters for the fabrication of full-density parts is the process windows map, also known as printability map. However, the experimental procedure for the design of the printability maps and the identification of the optimum-density process parameters is usually time-consuming and expensive. In the present work, a modelling framework is presented for the determination of a printability map and the optimization of the L-PBF process based on the prediction and characterization of melt-pool geometric features and the prediction of porosity of small samples of 316L SS and Ti-6Al-4V metal alloys. The results are compared with available experimental data and present a good correlation, verifying the modelling methodology. The suitability of the employed defect criteria for each material and the effect of the hatch-spacing process parameter on the optimum-density parameters are also presented.

Investigation of Micro CT based method for porosity estimation of sintered-wick heat pipes

The use of sintered-wick heat pipes in heat exchanger performance-related studies gained popularity owing to the simplicity and affordability of heat pipes. Evaluation of the system performance may be based on various arrangements and numbers of heat pipes applicable to the literature. Wick porosity and permeability are critical parameters for the investigation of wick capillary pumping, which will ultimately determine heat pipe performance. Despite the significance of these parameters to thermal performance, they are difficult to obtain, as the methods for obtaining these parameters before installing the heat pipes are time-consuming and destructive. This study aims to investigate the feasibility of Micro Tomography (Micro CT) to observe the porosity of copper sintered-wick heat pipes. Visual data from three heat pipe samples, namely HP1, HP2, and HP3 are quantified and analyzed. Analysis of the average porosity of HP1 and HP2 samples showed a similar value of 47.6 and 48.1%, respectively; however, the value of porosity along the length of the scanned area shows a bigger range of 42–54%. The accuracy of Micro CT was tested by testing three porosity samples with designed porosity of 26%, 22.3%, and 16.6% which were 3D printed using atomic diffusion additive manufacturing technology. Each sample was designed with pore shapes hexagonal, circular, and elliptical, respectively. Micro CT visualization and analysis showed the porosity reduction of the 3D printed porosity samples compared to the CAD design. Due to the smallest reduction of porosity after the sintered process, the 3D printed sample with a hexagonal pore shape, and the designed porosity of 26%, this sample was recommended for sintered wick fabrication using this technology and to test the accuracy of Micro CT.

Experimental Study on the Dissolution Characteristics and Microstructure of Carbonate Rocks under the Action of Thermal-Hydraulic-Chemical Coupling.

Microdamage in a rock induces a change in the rock's internal structure, affecting the stability and strength of the rock mass. To determine the influence of dissolution on the pore structure of rocks, the latest continuous flow microreaction technology was used, and a rock hydrodynamic pressure dissolution test device simulating multifactor coupling conditions was independently developed. The micromorphology characteristics of carbonate rock samples before and after dissolution were explored using computed tomography (CT) scanning. To conduct the dissolution test on 64 rock samples under 16 groups of working conditions, 4 rock samples under 4 groups were scanned by CT under working conditions, twice before and after corrosion. Subsequently, the changes in the dissolution effect and pore structure before and after dissolution were quantitatively compared and analyzed. The results show that the dissolution results were directly proportional to the flow rate, temperature, dissolution time, and hydrodynamic pressure. However, the dissolution results were inversely proportional to the pH value. The characterization of the pore structure changes before and after sample erosion is challenging. After erosion, the porosity, pore volume, and aperture of rock samples increased; however, the number of pores decreased. Under acidic conditions near the surface, carbonate rock microstructure changes can directly reflect structural failure characteristics. Consequently, heterogeneity, the presence of unstable minerals, and a large initial pore size result in the formation of large pores and a new pore system. This research provides the foundation and assistance for predicting the dissolution effect and evolution law of dissolved pores in carbonate rocks under multifactor coupling, offering a crucial guide for engineering design and construction in karst areas.

Preparation of a Polyaniline-Modified Hybrid Graphene Aerogel-Like Nanocomposite for Efficient Adsorption of Heavy Metal Ions from Aquatic Media.

This paper considers the synthesis of a novel nanocomposite based on reduced graphene oxide and oxidized carbon nanotubes modified with polyaniline and phenol-formaldehyde resin and developed through the carbonization of a pristine aerogel. It was tested as an efficient adsorbent to purify aquatic media from toxic Pb(II). Diagnostic assessment of the samples was carried out through X-ray diffractometry, Raman spectroscopy, thermogravimetry, scanning and transmission electron microscopy, and infrared spectroscopy. The carbonized aerogel was found to preserve the carbon framework structure. The sample porosity was estimated through nitrogen adsorption at 77 K. It was found that the carbonized aerogel predominantly represented a mesoporous material having a specific surface area of 315 m2/g. After carbonization, an increase in smaller micropores occurred. According to the electron images, the highly porous structure of the carbonized composite was preserved. The adsorption capacity of the carbonized material was studied for liquid-phase Pb(II) extraction in static mode. The experiment results showed that the maximum Pb(II) adsorption capacity of the carbonized aerogel was 185 mg/g (at pH 6.0). The results of the desorption studies showed a very low desorption rate (0.3%) at pH 6.5 and a rate of about 40% in a strongly acidic medium.

Investigation of the Microstructure Characteristics and Deformation Mechanisms of the Carbonaceous Slate under Hydromechanical Coupling

Carbonaceous slate inevitably possesses microscopic pores, microcracks, cleavages, and bedding planes in complex geoenvironment during the diagenesis processes. The microstructure of carbonaceous slate changes apparently under the effects of underground water infiltration, tectonic stress, and engineering disturbance, which induces the large deformation of rock mass and influences the stability of geotechnical engineering projects. To investigate the microstructure characteristics and reveal deformation mechanisms of carbonaceous slate under the influence of water pressure and stress, the variations of the pore size distribution(PSD), connectivity of pores, and porosity of samples during water injection and triaxial compression were studied using multiple methods. The results indicated that voids include plate-like micropores and microcracks, which are discontinuous without external stress. The micropores with a size of less than 1 μm dominate in number. The flaky particles were extruded and bent at a confining pressure, which caused the intermediate pores to form and altered the PSD of the samples. Hence, the connectivity dramatically improved and resulted in increased permeability. Water with dissolved clay minerals and small particles could move between micropores and microcracks during the water injection process. The elastic deformation of the particles recovered, and the intermediate pores disappeared when the imbalanced forces on two sides of the particles were narrowed. Pore water pressure affected the effective stress state and decreased the cohesion and stiffness of the rock. In the lower stress state, the porosity had a certain range of decrease (about 0.2%) mainly due to micropore compression, while the microcrack sprouted and expanded with the increase of compressive stress, resulting in the extension of porosity. The interaction of the stress and water seepage on the slate reduced the rock strength and favored the deformation, leading to a large macrodeformation of the soft rock in the long run.

Creep Characteristics and Creep Model of Coal Based on Pore Water Pressure

Anthracite in a specific area of Shanxi Province is the subject of this essay’s research. In the creep studies, different porosity intervals and pore water pressures were employed to evaluate the mechanical properties of creep under various test paths. The conventional Burges model was coupled in series with the nonlinear viscous elements and plastic elements. The key parameters in the equation are fitted, and a creep model is created to describe the nonlinear viscosity-elastic-plastic characteristics of coal under the influence of pore water pressure with varying porosities. The creep tests used varied porosity intervals, pore water pressures, and test paths to study the mechanical properties of creep. The conventional Burges model was coupled in series with the nonlinear viscous element and plastic element. To represent the nonlinear viscosity-elastic-plastic properties of coal under the effect of pore water pressure with variable porosities, the main parameters in the equation are fitted, and a creep model is developed. The results show that the porosity and strength of the coal sample are negatively correlated. In comparison to coal samples with a porosity of 5–10%, the uniaxial compressive strength of coal samples with a porosity of 10–15% and 15–20% reduced by 9.6% and 22.3%. Throughout the creep process, instantaneous strain rises with porosity, and changes in pore water pressure and porosity have an effect on instantaneous creep under low-stress loading, resulting in different creep curve starting strain values. The duration from stress loading to the accelerated creep stage in the failure stage and the time from the deceleration creep stage to the accelerated creep stage are both gradually shortened with an increase in porosity and pore water pressure. For regression analysis and parameter identification, a creep constitutive model was developed to describe the creep characteristics of coal samples with varying porosity under varying pore water pressure. The creep parameters of the new constitutive model were obtained, and they could very well reflect the creep characteristics of specimens with varying porosity intervals under the influence of pore water pressure.

Boiling Heat Transfer Characteristics of Porous Microchannel with Pore-Forming Agent

Traditional microchannel needs to face the flow-reversal difficulty in high heat fluxes due to limited space. It results in large pressure and temperature fluctuation. Porous microchannels arouse more interest to provide a new solution to this problem. Flow boiling experiments in porous microchannels with PFA were investigated. Porous microchannels were sintered by 10 μm (or 30 μm) spherical copper particles with pore-forming agent (Na2CO3, 60–90 μm). Porous microchannels were composed of 23 parallel porous microchannels with 600 μm in width and 1200 μm in depth.The addition of PFA (pore-forming agent) could increase the sample porosity. For Q10 series, sample porosities increase from 20.4% to 52.9% with the PFA percentage change from 0% to 40%, while for the Q30 series they increase from 26.6% to 47.5%. Experimental results showed the boiling heat transfer coefficient (HTC) reached the maximum at the moderate porosity for both Q10 and Q30 series. Too large or too small porosity would degrade boiling heat transfer performance. It demonstrated that there existed an optimal range of PFA content for sintered microchannels. PFA content has a minor effect on the average pressure drop and would not cause the rapid increase in flow resistance. Visual observation disclosed that the sample porosity would affect the pressure instability significantly. The sample with moderate porosity showed periodic pressure fluctuation and could establish rhythmical boiling. Particle size also exerted a certain influence on the boiling heat transfer performance. Q30 series could achieve higher HTC and CHF (Critical heat flux) than Q10 series. This is attributed to the larger ratio of layer-thickness-to-particle-size (δ/d) for Q10-series samples.

Contribution to the characterization of the Nevado del Ruiz geothermal conceptual model based on rock properties dataset

The assessment of the geothermal resources available in a specific area requires a detailed knowledge of the thermal and hydraulic properties of host rock formations. These properties were quantified with rock samples mainly collected at the intersection between Nereidas, Cueva-Pirineos, and La Tosca-El Descanso faults, to the West of the Nevado del Ruiz volcano (Colombia), to improve the characterization of this volcanic geothermal system. The geological formations analyzed in this study are the Cajamarca Complex, PRE-Ruiz lava flows, Andesites unit, and volcanic member of the Quebradagrande Complex. A 3D geological conceptual model for the study area and a geological cross-section are presented. 113 laboratory measurements allowed to quantify thermal conductivity (TC) and diffusivity (TD), heat capacity (HC), porosity, and permeability of the rock samples collected. The Cajamarca Complex is the lithology with the highest TC (2.9 W m−1 K−1), but with the lowest primary permeability (0.038mD) and porosity (3.4%). Regarding extrusive igneous rocks, the Andesites unit present significative porosity (10.7%), and the PRE-Ruiz lava flows show a low TC (1.5 W m−1 K−1). The results of 6 petrographic analyses of thin sections of the PRE-Ruiz lava flows and Cajamarca Complex helped to justify the values of their thermal properties. Quartz-filled veinlets and garnet are identified in the volcanic member of the Quebradagrande Complex. Both minerals indicate that fluids might have circulated at high temperature. It is the first time that garnet is identified in rock samples of this region; since it can be the result of high temperature hydrothermal alteration mineral, its origin must be confirmed, and its identification provides new insights about the geothermal resources in the area. The conceptual model, the thin section results, and the quantification of rock properties are relevant public data for future geothermal development. All data reported in this manuscript are disclosed as supplementary material, providing a significant scientific contribution in the form of an open dataset that can be used as a basis for future hydrothermal modelling of the Nevado del Ruiz geothermal system, where is the most advanced geothermal development project in Colombia, and other similar geothermal systems.

Exploring the link between ultrasonic and strength behavior of cementitious mine backfill by considering pore structure

Understanding the porosity/pore linkage and strength properties of cementitious mine backfill (CMB) is essential for the design of underground mining filling. Adoption of new production techniques in parallel with the development of technology in the mining sector has also increased the orientation to easier and less costly applications for evaluating CMB performance. This study aimed to evaluate the strength development of CMB and the change in its pore structure by using ultrasonic pulse velocity (UPV) technique. The influence of two types of pyritic tailings (low pH and high pH) obtained because of diverse production techniques on the quality of filling specimens was also investigated. The link between the microstructure formation (e.g., MIP), mechanical (e.g., UCS) and ultrasonic (e.g., UPV) characteristics of backfilling was explored by using a fixed ratio of fly ash-slag as a cement substitute (cement/slag-fly ash: 70/30). Filling samples were prepared at constant solid content (74 wt%), different curing times (3–90 days), and binder ratios (3–5-7 wt%). The results revealed that the total porosity of CMBs decreased with increasing age and binder ratio. One could also observe that the total porosity of the fill samples containing high pH tailings was lower (up to 56 %) compared to those containing low pH tailings. The acidic nature of low pH tailings negatively affected the aged strength of CMBs, destructing its microstructure. However, it was observed that the negative effects of low pH added backfills decreased in slag substitution and high binder dosages. Excellent correlation curves (power fitting) were found between UPV and UCS according to the variables used (e.g., different types of processing tailings and mineral additives). The measured and calculated UCS values were largely (R2 = 94.8 %) consistent. Finally, this study provides a complete report to support operationally low cost, easy and feasible fill design for underground metallic mines.

Microstructural and wear properties of WC-12Co cemented carbide fabricated by direct energy deposition

The microstructural and wear properties of WC–12Co (wt.%) cemented carbide bulk material manufactured by additive manufacturing direct energy deposition (DED) process were investigated and compared to those of WC-12Co coating material fabricated by high-velocity oxygen fuel (HVOF) thermal spray process. The feedstock powder, DED and HVOF materials were analyzed using scanning electron microscopy/energy dispersive x-ray analysis (SEM/EDAX), X-ray diffraction (XRD) and an electron back-scattered diffraction (EBSD) technique. WC and α-Co phases were observed in the initial WC-12Co cemented carbide powder feedstock. After the DED process, WC phase growth and M12C phase were identified. However, the amount of M12C phase decreased after the HVOF process. The DED material had relatively higher porosity (BD: 11.58%; PD: 10.23%) as compared with HVOF (porosity: 1.66%). The hardness of the HVOF sample was measured as 1429 ± 49 HV, which was much higher than that of the DED (BD:1373 ± 68 HV, SD1: 1352 ± 62 HV) sample, due to the existence of porosity in the DED sample. A pin-on-disc tribometer was used to measure wear rates and coefficients of friction. The wear-worn surfaces were analyzed using SEM with an energy-dispersive spectrometer. The wear test results indicated that the DED material exhibited a lower wear rate (higher wear resistance) and a lower friction coefficient than those of the HVOF material. The difference in the wear behaviour of the DED and HVOF materials could be explained in terms of differences in WC size, the extent of reaction and decarburization during spraying, and the formation of the high oxide content.