Moderate Porosity Research Articles

Copper Aluminum Spinels Doped with Cerium as Catalysts for NO Removal

Cu-Ce(Mn)-Al oxide catalysts to NO removal in the broad temperature range were synthesized and tested. The precursor of copper aluminium spinel was obtained with the coprecipitation method. By this method, Cu–Al spinels with various amounts of manganese and cerium were synthesized as well. These oxides crystallized in the structure of inverse spinel; however, Ce doping caused the appearance of additional CeO2 phase as determined by XRD. The samples were mesoporous solids with moderate surface area and porosity measured by low temperature sorption of nitrogen. The addition of another metal to Cu–Al spinel caused an increase of activity in selective catalytic reduction of nitrogen oxide with ammonia. The presence of manganese caused the formation of a higher amount of N2O by-product. The catalytic activity increased with the cerium concentration. For the sample with the atomic ratio Ce0.15Cu0.18, ca. 90% of NO conversion was registered between 200 and 350 °C. As examined with XPS spectroscopy, such conversion was attained due to the good dispersion of copper on the catalyst surface. This copper was placed mainly in spinel octahedral positions which enable its easier reduction. The spinel structure causes the presence of cerium as the trivalent cation important in redox cycles with the participation of copper.

Modelling heterogeneous dust particles: an application to cometary polarization

ABSTRACT In this work, we introduce a comet dust model that incorporates multiple dust morphologies along with inhomogeneous mixture of silicate minerals and carbonaceous materials under power-law size distribution, to replicate the standard polarization-phase curve observed in several comets in the narrow-band continuum. Following the results from Rosetta/midas and COSIMA, we create high porosity hierarchical aggregates (HA) and low porosity (<10 per cent) Solids in the form of agglomerated debris. We also introduce a moderate porosity structure with solids in the core, surrounded by fluffy aggregates called fluffy solids (FS). We study the mixing combinations, (HA and Solids), (HA and FS), and (HA, FS, and Solids) for a range of power-law index n= 2.0 to 3.0 for different sets of mixing percentage of silicate minerals and carbonaceous materials. Polarimetry of the short period comets 1P/Halley and 67P/Churyumov-Gerasimenko match best with the polarization resulting from the combination of HA and Solids while the combinations (HA and FS) and (HA, FS, and Solids) provide the best-fitting results for the long period comets C/1995 O1 (Hale-Bopp) and C/1996 B2 (Hyakutake). The best-fitting model results also recreate the observed wavelength dependence of polarization. Our dust model agree with the idea that the long period comets may have high percentage of loose particles (HA and FS) compared to those in the case of short period comets as the short period comets experience more frequent and/or higher magnitude of weathering.

A "Thermodynamically Stable" 2D Nickel Metal-Organic Framework over a Wide pH Range with Scalable Preparation for Efficient C2 s over C1 Hydrocarbon Separations.

The design and construction of "thermodynamically stable" metal-organic frameworks (MOFs) that can survive in liquid water, boiling water, and acidic/basic solutions over a wide pH range is highly desirable for many practical applications, especially adsorption-based gas separations with obvious scalable preparations. Herein, a new thermodynamically stable Ni MOF, {[Ni(L)(1,4-NDC)(H2 O)2 ]}n (IITKGP-20; L=4,4'-azobispyridine; 1,4-NDC=1,4-naphthalene dicarboxylic acid; IITKGP stands for the Indian Institute of Technology Kharagpur), has been designed that displays moderate porosity with a BET surface area of 218 m2 g-1 and micropores along the [10-1] direction. As an alternative to a cost-intensive, cryogenic, high-pressure distillation process for the separation of hydrocarbons, MOFs have recently shown promise for such separations. Thus, towards an application standpoint, this MOF exhibits a higher uptake of C2 hydrocarbons over that of C1 hydrocarbon under ambient conditions, with one of the highest selectivities based on the ideal adsorbed solution theory (IAST) method. A combination of two strategies (the presence of stronger metal-N coordination of the spacer and the hydrophobicity of the aromatic moiety of the organic ligand) possibly makes the framework highly robust, even stable in boiling water and over a wide range of pH 2-10, and represents the first example of a thermodynamically stable MOF displaying a 2D structural network. Moreover, this material is easily scalable by heating the reaction mixture at reflux overnight. Because such separations are performed in the presence of water vapor and acidic gases, there is a great need to explore thermodynamically stable MOFs that retain not only structural integrity, but also the porosity of the frameworks.

Synthesis of N-containing porous aromatic frameworks via Scholl reaction for reversible iodine capture

Abstract The effective capture of radioactive volatile iodine (131I and 129I) from nuclear waste stream is of vital significance. In this work three kinds of porous organic frameworks (POFs) knitting with N-containing building units were constructed via cost-effective and maneuverable Scholl reaction. The obtained PAFs exhibited moderate porosity and satisfying thermal stability. With coexistence of open porous structure, the electron-rich amino group featured with π-π interactions was found to improve the affinity to iodine, and the iodine uptake capacities were 408 wt%, 335 wt% and 268 wt% when the prepared POFs of P-DPDA, P-TPB and P-PC were employed for the adsorption experiments. The results were superior to most of the porous adsorbents including zeolite, metal-organic frameworks (MOFs) and porous organic polymers (POPs). Iodine adsorption capacities of 289.50 mg g−1 (for P-DPDA), 194.63 mg g−1 (for P-TPB) and 259.69 mg g−1 (for P-PC) in organic solution were achieved, and the adsorbed iodine molecules could be released to ethanol. Such promising and cost-effective materials can be envisaged for application in the field of nuclear waste management.

Reservoir variations and heterogeneities under valley‐monadnock palaeo‐geomorphology in hinterland area of the Junggar Basin, northwestern China: Sedimentary characteristics and diagenetic alterations

Palaeo‐geomorphology can exert significant effects on reservoir quality via controlling the distribution of depositional facies and diagenetic alterations. However, little attention has been paid to the studies of the reservoir variations and heterogeneities under distinctive valley‐monadnock palaeo‐geomorphology. Taking the Lower Cretaceous Qingshuihe Formation (K1q) in the Junggar Basin as an example, this study improves the current understanding of reservoir potential within topography of this kind by examining the link between depositional facies, diagenesis and their impact on reservoir quality. In total, nine types of lithofacies can be identified in the K1q reservoirs, which can be further grouped into lowstand systems tract (LST) gravelly braided river and debris flow deposits and transgressive systems tract (TST) sandy braided river delta deposits. These reservoirs are rich in rock fragments and characterized by moderate porosity and moderate to low permeability with development of intergranular and dissolution pores. Generally, detrital composition has a greater impact on reservoir quality of the LST conglomerates than on that of the TST sandstones. However, texture maturity only shows positive correlation with physical properties of the sandstone reservoirs. The mechanical compaction was responsible for the major destruction of the initial porosity. However, the large heterogeneities in calcite cements account for the extremely heterogeneous reservoir quality. Calcite cements formed during eodiagenesis usually show poikilotopic fabric and preferentially concentrated inthe basal coarser units/facies within inidividual fining‐upward successions. Consequently, the upper finer units/facies became more favourable for the secondary dissolution and oil charging processes during mesodiagenesis. In contrast, the amounts of authigenic quartz and clay minerals are relatively low. Nevertheless, the contents of different authigenic clay minerals show a variety of relationships with the reservoir quality. The valley‐monadnock topography spatially controls the scales of the LST and TST reservoirs. The simultaneously evolutionary processes between the back‐filling of the valleys and weathering of the monadnocks resulted in the prolonged residence time and large area of depositional water contacting with the weathering crust. This may give rise to the formation of alkaline pore fluids and facilitate the nucleation and growth of eogenetic carbonate cements and grain‐coating chlorite. Furthermore, the reservoir quality generally displays an increasing trend from the monadnock to the valley thalweg due to the increase of hydrodynamic strength and the less influence of mélange debris flow deposits.

Petrophysical and acoustic assessment of carbonate rocks, Zahle area, central Lebanon

Transport and acoustic measurements have been conducted on fifteen rock samples collected from central Lebanon to characterize the rock properties and to assess the impact of lithology, pore types, pore sizes, and textural parameters on the storage capacity and elastic characteristics. The spontaneous imbibition of selected samples was examined by detecting the moving capillary front across a sample. The coefficient of capillarity derived from the spontaneous imbibition is positively correlated with permeability. Seismic velocities in the studied rocks vary widely and are positively correlated with the rock density. Matrix-supported rocks with a larger proportion of micropores have lower seismic wave velocities, whereas the grain-supported carbonates exhibit low to moderate porosity and higher acoustic velocities. The elastic properties of the studied carbonates indicate a granular, rather than a crystalline, texture for the majority of the studied rocks. The widely variable elastic behavior of basically carbonate rocks implies that seismic reflection profiles in carbonate sequences may contain seismic reflections that do not result from non-carbonate intercalations but which result mainly from variable porosity, pore types, and shapes in the carbonate rocks themselves. This study provides important information on the textural, petrophysical, and elastic properties of carbonate rocks which are crucial for the assessment and understanding of the seismic reflection sections in subsurface carbonate reservoirs.

Reservoir Potential Evaluation of the Middle Paleocene Lockhart Limestone of the Kohat Basin, Pakistan: Petrophysical Analyses

The Lockhart Limestone is evaluated for its reservoir potential by utilizing wireline logs of Shakardara-01 well from Kohat Basin, Pakistan. The analyses showed 28.03% average volume of shale (Vsh), 25.57% average neutron porosity (NPHI), 3.31% average effective porosity (PHIE), 76% average water saturation (Sw), and 24.10% average hydrocarbon saturation (Sh) of the Lockhart Limestone in Shakardara-01 well. Based on variation in petrophysical character, the reservoir units of the Lockhart Limestone are divided into three zones i.e., zone-1, zone-2 and zone-3. Out of these zones, zone-1 and zone-2 possess a poor reservoir potential for hydrocarbons as reflected by very low effective porosity (1.40 and 2.02% respectively) and hydrocarbon saturation (15 and 5.20%), while zone-3 has a moderate reservoir potential due to its moderate effective porosity (6.50%) and hydrocarbon saturation (52%) respectively. Overall, the average effective porosity of 3.31% and hydrocarbon saturation of 24.10% as well as 28.03% volume of shale indicated poor reservoir potential of the Lockhart Limestone. Lithologically, this formation is dominated by limestone and shale interbeds in the Shakardara-01 well. Cross-plots of the petrophysical parameters versus depth showed that the Lockhart Limestone is a poor to tight reservoir in Shakardara-01 well and can hardly produce hydrocarbons under conventional drilling conditions.

Reservoir Potential Evaluation of the Middle Paleocene Lockhart Limestone of the Kohat Basin, Pakistan: Petrophysical Analyses

The Lockhart Limestone is evaluated for its reservoir potential by utilizing wireline logs of Shakardara-01 well from Kohat Basin, Pakistan. The analyses showed 28.03% average volume of shale (Vsh), 25.57% average neutron porosity (NPHI), 3.31% average effective porosity (PHIE), 76% average water saturation (Sw), and 24.10% average hydrocarbon saturation (Sh) of the Lockhart Limestone in Shakardara-01 well. Based on variation in petrophysical character, the reservoir units of the Lockhart Limestone are divided into three zones i.e., zone-1, zone-2 and zone-3. Out of these zones, zone-1 and zone-2 possess a poor reservoir potential for hydrocarbons as reflected by very low effective porosity (1.40 and 2.02% respectively) and hydrocarbon saturation (15 and 5.20%), while zone-3 has a moderate reservoir potential due to its moderate effective porosity (6.50%) and hydrocarbon saturation (52%) respectively. Overall, the average effective porosity of 3.31% and hydrocarbon saturation of 24.10% as well as 28.03% volume of shale indicated poor reservoir potential of the Lockhart Limestone. Lithologically, this formation is dominated by limestone and shale interbeds in the Shakardara-01 well. Cross-plots of the petrophysical parameters versus depth showed that the Lockhart Limestone is a poor to tight reservoir in Shakardara-01 well and can hardly produce hydrocarbons under conventional drilling conditions.

Rock‐physics forward modelling to predict seismic behaviour: A case study for exploration target in Mahanadi basin, East Coast of India

ABSTRACTOne of the major aspects of rock‐physics forward modelling is to predict seismic behaviour at an undrilled location using drilled well data. It is important to model the rock and fluid properties away from drilled wells to characterize the reservoir and investigate the root causes of different seismic responses. Using the forward modelling technique, it is possible to explain the amplitude responses of present seismic data in terms of probable rock and reservoir properties. In this context, rock‐physics modelling adds significant values in the prospect maturation process by reducing the risk of reservoir presence in exploration and appraisal phases. The synthetic amplitude variation with offset gathers from the forward model is compared with real seismic gathers to ensure the fidelity of the existing geological model. ‘Prospect A’ in the study area has been identified from seismic interpretation, which was deposited as slope fan sediments in Mahanadi basin, East Coast of India. The mapped prospect has shown class‐I amplitude variation with offset response in seismic without any direct hydrocarbon indicator support. The existing geological model suggests the presence of an excellent gas reservoir with proven charge access from the fetch area, moderate porosity and type of lithology within this fan prospect. But, whether the seismic response from this geological model will exhibit a class‐I amplitude variation with offset behaviour or ‘dim spot’ will be visible; the objective of the present study is to investigate these queries. A rock‐physics depth trend analysis has been done to envisage the possibilities of class‐I reservoir in ‘Prospect A’. Forward modelling, using a combination of mechanical and chemical compaction, shows the synthetic gas gathers at ‘Prospect A’, which are class I in nature. The study has also depicted 2D forward modelling using lithology and fluid properties of discovery well within similar stratigraphy to predict whether ‘dim spot’ will be seen in seismic. The estimated change in synthetic amplitude response has been observed as ∼5% at contact, which suggests that the changes will not be visible in seismic. The study connects the existing geological model with a top‐down seismic interpretation using rock‐physics forward modelling technique to mature a deep‐water exploratory prospect.

Hydrocarbon reservoir development in reef and shoal complexes of the Lower Ordovician carbonate successions in the Tazhong Uplift in central Tarim basin, NW China: constraints from microfacies characteristics and sequence stratigraphy

The analyses of hydrocarbon reservoirs in the high-frequency reef and shoal facies of the Lower Ordovician carbonate successions in the Penglaiba Formation (O1P) and Yingshan Formation (O1–2Y) in the Tazhong (Katake) Uplift in central Tarim basin showed three types of hydrocarbon reservoirs: type 1 associated with synsedimentary facies, type 2 developed by hot active basinal dissolution fluids [mesogenetic fluids, geothermal/hydrothermal fluids and thermochemical sulfate reduction-related fluids] and tectonic activity, and type 3 are hypogenic–epigenetic karst reservoirs formed by meteoric and mesogenetic dissolution fluids. Porosity and permeability development in the reef and shoal facies in the highstand system tracts (HST) of the third-order sequence cycles (SQ1–SQ3) correlates well with regression peaks in O1P and O1–2Y, mostly related to multiphase tectonic activity, long-term exposure, denudation and dissolution in near-surface to shallow burial settings. The carbonate successions in the O1P and O1–2Y are composed of seventeen microfacies (MF-1 to MF-17) deposited on a shallow marine platform. Six main groups of microfacies associations (MFA-1 to MFA-6) were recognized, with each microfacies association corresponding to the transgressive system tracts and HST of SQ1–SQ4 in O1P and O1–2Y. The microfacies represent specific sedimentary environment including platform interior and platform margin deposited under particular hydrodynamic conditions. Tectonics and frequent relative sea-level fluctuation associated with rapid transgression and slow regression favored the deposition of the large-scale vertical stacking, high-frequency reef and shoal facies across the carbonate platforms in this uplift. The hydrocarbon reservoirs in this study have relatively moderate porosity and low permeability, and are somewhat potential reservoirs for hydrocarbon exploration in the Tazhong Uplift.

Sintering and final properties of kaolinite‐magnesite tapes for the manufacture of cordierite‐mullite ceramics

AbstractThe present work aims at studying the effect of the sintering temperature and magnesite addition on the structure and final properties of silicate ceramics tapes. A kaolinitic clay from Algeria was selected and mixed with different magnesite contents (≤12 mass%). Tape casting process was used to produce the green tapes in an aqueous system with optimized amount of surfactants. The green tapes were fired from 1000°C to 1200°C using a dwelling time of 30 minutes. The effect of the dwelling time was investigated for a firing temperature of 1200°C namely: 30 minutes, 1 hour 30 minutes and 3 hours for samples with 6 and 12 mass% of magnesite. Regarding firing conditions, crystalline phases, thermal conductivity, porosity, and flexural strength were analyzed. The results showed that increasing the sintering temperature to 1200°C tended to significantly decrease the total porosity of samples, which led to the improvement of the stress to rupture values. Specimens with 6 and 12 mass% sintered during 3 hours exhibited highest stress to rupture values (≈117 MPa) and lowest thermal conductivity (<0.2 W.m−1.K−1) and moderate open porosity (27%). The as‐obtained ceramics appeared promising for further utilization in refractory industry, thanks to the presence of both cordierite and mullite phases.

NATURAL STATE MODELLING OF SALAK GEOTHERMAL FIELD

The Awibengkok geothermal field, also known as Salak, is a liquid-dominated field. The commercial Awibengkok reservoir is a moderate-to-high temperature (240–312 ◦C) geothermal resource with high fracture permeability, moderate porosity, and moderate-to-low matrix permeability, and can generate electricity up to 377 MW. This field fracture-controlled reservoir has benign chemistry and low-to-moderate non-condensable gas content. The geothermal reservoir is associated with youngvolcanism and intrusions in a highland area in the west of Salak Mountain and east of the Cianten caldera, a collapsed andesitic stratocone. In this paper, numerical method for calculation is used for modelling and reservoir simulation. A simulator is used to build the model. The model was built until it reached the natural state. The method used for model calibration is through pressure and temperature matching of two wells P-T logging data. One of the well is located on the western region of Salak geothermal field, while the other is located on the eastern region. Salak geothermal field model would reach natural state with simulation time up to millions of years. The model state the field is a liquid-dominated field and has steam caps in western and eastern area. The material on those two areas are different, thus the initial conditions are different. The temperature is higher in the western area. The gas saturation vary between 0.127 to 0.5 and there is a caprock with permeability 9mD.

Gravity Wave Trapping by Series of Horizontally Stratified Wave Absorbers Away From Seawall

AbstractThe fluid oscillation between the rigid wall and stratified wave absorber is analyzed in the context of the linearized water wave theory. The stratified wave absorber is composed of multiple horizontal layers considering higher porosity in the surface layer, moderate porosity in the middle layer, and zero porosity in the bottom layer. The study examined the wave motion through multiple horizontally stratified wave absorbers on solving the multilayer dispersion relation. The eigenfunction expansion method is used to form the system of analytical equations using the property of orthogonal mode-coupling relation with continuity of dynamic pressure and velocity at each of the interfaces. The free spacing available between leeward porous wave absorber and the rigid wall is termed as “trapping chamber.” The effect of the trapping chamber on wave reflection and fluid force experienced by a rigid wall is discussed. The analytical results formulated for the physical problem are validated with the available experimental and numerical results. The wave trapping is examined and compared for three types of seawalls such as vertical wall, permeable wall, and stepped wall. The change in trapping chamber length shows the harmonic peaks and troughs in the trapping coefficients and the harmonic oscillations help in the design and development of the stratified porous wave absorbers for the protection of marine infrastructure.

Embedded Manganin Gauge Measurements and Modeling of Shock Initiation in HMX‐Based PBX Explosives with Different Particle Sizes and Porosities

AbstractA series of shock initiation experiments on the explosive PBXC03 (87 % HMX, 7 % TATB, and 6 % Viton by weight) with different particle sizes and porosities under various shock loadings have been performed, and it is found that the particle size and the porosity of the explosives have much influence on the shock initiation characteristics. That is, the smaller the particle size, the more difficult the explosive to be ignited but the faster the detonation grows once the explosive is ignited. It is also found that the detonation grows the fastest in the explosive with moderate porosity. Moreover, a modified mesoscopic reaction rate model based on the experimental results and the pore collapse hot‐spot ignition mechanism is developed, which allows for a separate reaction mechanism evaluation at different reaction stages for the shock initiation and detonation growth processes in the explosives. The calculated pressure‐time histories and Pop‐Plots for PBXC03 are founded to be all in good agreement with the experimental data. The modified mesoscopic reaction rate model shows its potentiality for quantitatively predicting the effects of the mesostructure of PBXs on the shock initiation and detonation growth processes with a high degree of confidence.

Porosity-Induced Selective Sensing of Iodide in Aqueous Solution by a Fluorescent Imidazolium-Based Ionic Porous Framework.

Developing a chemosensor for rapid, sensitive, and visual detection of iodide (I-) by a simple synthetic strategy is still challenging. Herein, we report a highly efficient iodide sensor by simply introducing ionic imidazolium groups into the porous network. This sensor, that is, a fluorescent ionic porous framework (IPF), was prepared by the quaternization reaction of octa((benzylchloride)ethenyl)silsesquioxane and 1,4-bis(1H-imidazole-1-yl)benzene and exhibited moderate porosity with a Brunauer-Emmett-Teller surface area of 379 m2 g-1 and blue fluorescence when excited by UV light. The IPF suspension in water can detect I- with high sensitivity and selectivity among various anions and quick response by fluorescence quenching. In contrast to no response toward I- by the linear model compound and the enhanced sensing performance with an increment of porosity, this finding indicates that the porosity of IPF is important for the detection of I- and an inducement of the sensing process. A fluorescent paper sensor was further developed, which shows high efficiency for the visual detection of I- similar to the abovementioned sensor, suggesting its potential in convenient and on-site sensing of I-. In addition, the paper sensor is recyclable with a remarkable fluorescence resuming ratio of 83% after 10 times cycle detection. Moreover, the developed sensor is used for the analysis of real samples. This work represents the first example of the detection of I- by an ionic porous polymer. Compared with conventional iodide sensors, the present sensor does not require unique structures to form the pseudocavity during sensing I- and can easily achieve high efficiency by incorporating ionic hydrogen bond donors into the porous network, indicating the importance of porosity and the feasibility of replacing the pseudocavity with a real cavity (or pore). More iodide sensors with high efficiency can be designed and fabricated by this novel and simple strategy.

Quantitative characterization of diagenetic reservoir facies of the Karamay alluvial fan in the Junggar Basin, western China

The distribution of the remaining oil in developed oilfields is primarily influenced by the existing diagenetic reservoir facies (DRFs), which encompass the effects of both the sedimentary environment and the local diagenetic processes on the reservoir quality. We divided the Lower Karamay Formation reservoir samples into nine DRFs according to characteristics such as porosity, permeability, diagenetic intensity, and rock type. After applying the sequential indicator simulation methodology, we were able to create three-dimensional (3D) geological models of the DRFs. Based on these models, we can see that, during phases A and B of eodiagenesis, the prevailing DRF is a sandstone/sandy conglomerate that is moderately to weakly dissolved, moderately cemented, and characterized by moderate porosity and permeability values. The highest quality DRF, which emerged during the early stage of mesodiagenesis, is a sandstone/sandy conglomerate that is weakly compacted/cemented, moderately-to-strongly dissolved, and characterized by very high porosity and permeability values. By providing high-quality analyses of the DRFs in Block 6 of the Karamay oilfield, we provided vital information that allowed the operation to more efficiently target and extract oil from reservoir units that are already in production.

Petrophysical and acoustic characteristics of Jurassic and Cretaceous rocks from Central Lebanon

We conducted several petrophysical and acoustic measurements on 49 core samples collected from the Jurassic and Cretaceous strata exposed at west central Lebanon to evaluate their petrophysical and elastic properties and study the effects of the depositional conditions, sediment composition, and subsequent diagenetic processes on the measured parameters. First, these rocks were petrographically studied to identify their facies, porosity, and the main diagenetic features. In addition, these rocks were investigated under the scanning electron microscope (SEM) and by the X-ray diffraction (XRD) analysis to identify their mineralogy. The petrophysical measurements were performed on the core samples where porosity, permeability, bulk, and grain densities were first determined, followed by measuring the seismic wave velocities under dry and water-saturation conditions. Both carbonates and siliciclastics are encountered in the studied formations. The SEM and XRD analyses revealed that the main constituting minerals are quartz, calcite and dolomite. The studied rocks have generally low to moderate porosity and very low permeability with averages of 0.05, and 0.31 mD, respectively. The bulk density is moderate to high and varies narrowly between 2.03 and 2.79 with an average of 2.64 g/cm3, whereas the average grain density is 2.77 g/cm3. The average primary and secondary wave velocities (Vp and Vs) are 4263, and 2323 m/s, respectively, with an average Vp/Vs of 1.83. Water-saturation has significantly impacted the elastic properties of the studied rocks. From the obtained measurements, we further calculated the elastic coefficients of the studied rocks and constructed several relationships between the measured properties to investigate their mutual interdependence and evaluate the effects of porosity, rock composition, depositional and diagenetic processes on the rock characteristics. We found that some samples, mainly carbonates, deviate significantly from the expected porosity-velocity and density-velocity trends. Originally present micro- and intercrystalline pores and characteristic diagenetic processes in these carbonate rocks, and possibly coring-induced microcracking in few samples, may account for the observed outliers.

Relationship between Brittleness Index and Crack Initiation Stress Ratio for Different Rock Types

Brittleness and crack initiation stress (σci) are important rock mechanical properties and intrinsically related to rock deformation and failure. We establish the relationship between σci and uniaxial tensile strength (σt) based on the Griffith stress criterion of brittle failure and introduce brittleness indexes B1–B4 based on the ratio of uniaxial compressive strength (σc) to σt. The crack initiation stress ratio (K) is defined as the ratio of σci to crack damage stress. The relationship between brittleness index and K is obtained from laboratory mechanics tests including uniaxial compression and Brazilian splitting tests. The results show that B1 and B2 have an inversely proportional and variant inversely proportional relationship with K, respectively, whereas no apparent relationship is observed between B3 and B4 and K. The fitting of experimental data from igneous, metamorphic, and sedimentary rocks shows that B1 and B2 have a power and linear relationship with K, respectively, whereas no functional relationship is observed between B3 and B4 and K. We collected 70 different types of uniaxial compression test data for igneous, metamorphic, and sedimentary rocks and obtained laws that are consistent within each rock type. The experimental data are used to verify K estimations using a specified constant α based on the experimental data. According to results of the limestone tests, α = 3 for σc < 60 MPa (high porosity), α = 5 for 60 MPa ≤ σc ≤ 90 MPa (moderate porosity), and α = 8 for σc > 90 MPa (low porosity) as well as for igneous and metamorphic rocks. Estimates of K for 127 different rock types using the newly defined brittleness index are in good agreement with the experimental results. This study provides an important new brittleness index calculation method and a simple and reliable method for estimating K.

Fe and N co-doped carbon derived from melamine resin capsuled biomass as efficient oxygen reduction catalyst for air-cathode microbial fuel cells

Cathode oxygen reduction reaction (ORR) performance is crucial for power generation of microbial fuel cells (MFCs). The current study provides a novel strategy to prepare Fe/N-doped carbon (Fe/N/C) catalyst for MFCs cathode through high temperature pyrolyzing of biomass capsuling melamine resin polymer. The obtained Fe/N/C can effectively enhance activity, selectivity and stability toward 4 e– ORR in pH neutral solution. Single chamber MFC with Fe/N/C air cathode produces maximum power density of 1166 mW m−2, which is 140% higher than AC cathode. The improved performance of Fe/N/C can be attributed to the involvement of nitrogen and iron species. The excellent stability can be attributed to the preferential structure of the catalyst. The moderate porosity of the catalyst facilitates mass transfer of oxygen and protons and prevents water flooding of triple-phase boundary where ORR occurs. The biomass particles encapsulated in the catalyst act as skeletons, which prevents catalyst collapse and agglomeration.

Series-parallel resistance method based thermal conductivity model for rock-soil with low or high porosity

The estimation of the underground rock-soil thermal conductivity from different depths is of great importance for the studies on the performance prediction and evaluation of geothermal utilization systems. Based on the authors’ previous work on the prediction of rock-soils with moderate porosities (0.2146 <n < 0.4764), this study presents a series-parallel thermal resistance method based thermal conductivity model for the rock-soils with different constituents and water contents at low (n < 0.2146) or high porosity (n> 0.4764). The arrangement of different phases in the cubic cell element is introduced, and the thermal resistance for each part is theoretically derived to achieve the expression of the effective thermal conductivity. After verified by 74 experimentally measured and predicted results of rock-soil sample thermal conductivities in the existing work, the newly proposed method is validated to be successful to predict the rock-soil thermal conductivity with an average RMSE of 0.1289, which implies that the present model configured with two hemispheres and cylindrical water framework and based on the series-parallel resistance method provides an accurate prediction on the thermal conductivity of the rock-soils with different constituents and water contents at low or high porosity.