Quantitative Examination of Porous Rust on Steel

Development of porous structure during air drying of agricultural plant products

ABSTRACTThis study investigated the use of sulfate‐based stabilizers to stabilize the surface of Q420qNH weathering steel (WS) and their effect on rust layer formation and corrosion resistance. Dry/wet cyclic corrosion tests (CCT) were used to examine the effects of the various treatment regimens. The results demonstrated that sulfate‐based stabilizers accelerated the formation of α‐FeOOH, thereby enhancing the corrosion resistance of WS in simulated marine atmospheres. Particularly, the A1 stabilizer consisting of the CuSO4, FeSO4, NaHSO3, and Cr2(SO4)3 solution system shows better applicability under the simulated marine atmosphere. Specifically, after 8+64CCTs, the corrosion rate of sample A1 decreased by 54%, while the proportion of α‐FeOOH, the α/γ* value, and the self‐corrosion potential (Ecorr) increased by 15%, 0.55, and 0.29 V, respectively. The rust layer of Q420qNH WS primarily consists of γ‐FeOOH, α‐FeOOH, Fe3O4, and γ‐Fe2O3. Surface stabilization treatment with sulfate‐based stabilizers promoted the enrichment of Cu and Cr in the cracks, facilitating the filling of these defects and enhancing the stability and corrosion potential of the rust layer.

Comparison of transport characteristics and textural properties of porous material; the role of pore sizes and their distributions

<p>Hydrocarbon exploration is extending from the shallowly buried to deeply buried strata with increasing demands for fossil fuels. The variable storage and percolation capacities that intrinsically depend on the pore geometry restrict the hydrocarbon recovery and displacement efficiency and trigger studies on the micro-scale pore structure, fluid flow capacity, and their controlling factors. Minerals within sandstone are the results of the coupling control of depositional factors and diagenetic alternations, which determine the microscopic pore geometry and subsequently affect the fluid flow capacity. In order to investigate the impacts of mineralogy on the pore structure and fluid flow capacity, integrated analyses including porosity and permeability measurements, casting thin section (CTS), scanning electron microscopy (SEM), pressure-controlled mercury porosimetry (PCP), rate-controlled mercury porosimetry (RCP), nuclear magnetic resonance (NMR), and X-ray diffraction (XRD) are conducted on the deeply buried sandstone samples in the Jurassic Sangonghe Formation of the Junggar Basin. Microscopic pore structure is characterized by the combination of SEM, CTS, PCP, and RCP and fractal theory. Fluid flow capacity is evaluated by the innovative application of film bound water model in NMR and mineralogy is quantitatively measured by XRD. The results indicate that the deeply buried sandstone is rich in quartz (54.2%), feldspar (25.1%), and clay (14.2%), with dominant kaolinite (5.04%) and chlorite (5.38%) cementation. The reservoir has a wide pore-throat diameter distribution with three peaks in the ranges 0.01–1, 10–80, and 200–1000 μm. Pores are tri-fractal and can be divided into micropores, mesopores, and macropores, with average porosity contributions of 50.11, 21.83, and 28.04%, respectively. The movable porosity of deeply buried sandstone ranges from 1.75 to 8.24%, primarily contributed by intergranular (avg. 2.34%) and intragranular pores (avg. 2.56%). Most of the fluids are movable in intergranular pores but are irreducible in intragranular pores. Correlation analyses between mineralogy and pore structure suggest that quartz provides preservation to intergranular porosity, which increases pore size and macropores porosity and reduces heterogeneity of the pore system. The influence of feldspar reverses and becomes poor owing to the simultaneous clay precipitation and complex roles of feldspar dissolution in microporosity. Chlorite, kaolinite, and illite, all act as destructions to intergranular porosity. They enhance the mesopores and micropores porosities, reduce the pore size, and increase the microscopic heterogeneities of the macropores, micropores, and whole pore system. The relationships between mineralogy and fluid flow capacity indicate that quartz is favorable for the fluid flow capacity, but feldspar and clay play negative roles. The reversed impacts of quartz and feldspar lay in their opposite controls on pore size. However, both pore size and hydrophilia should be taken into account when considering the effects of clay minerals. These negative effects are associated with types, contents, and hydrophilic degrees of clay minerals, in which I/S and illite exhibit the strongest negative impacts. The fluid flow in the intergranular and intragranular pores is generally enhanced by higher quartz content, but reduced by higher clay content. Irreducible fluids in the intergranular and intragranular pores are determined by chlorite and kaolinite contents, respectively.</p>

Stereolithographic 3D printing is of paramount interest for researchers studying porous media because it is possible to use resins with a wide range of physical and chemical properties. Currently, these properties can be designed and adjusted to model the interaction of solids with fluids occupying the pore space, which is not feasible with natural materials. This ability enables replicating the pore network geometry of natural rocks as well as tuning the wettability of pore network surfaces. This study presents analysis of uncured liquid resins and porous rock models 3D-printed in those resins to establish the accuracy of the stereolithographic 3D printer in repeatedly printing the same pore network, as well as the fidelity of transport properties (e.g., porosity, pore sizes, wettability) to the model design. Viscosity of uncured resins was measured to predict the physical properties of the resulting cured models. A digital model of Fontainebleau sandstone was 3D-printed at three magnifications (15-, 23-, and 30-fold) from the original tomographic volume of 1 mm3 and in six resins (black, gray, clear, white, green, and yellow). The models were validated using the following techniques: helium pycnometry (for porosity); mercury porosimetry (for pore-throat size); and drop shape analyzer (for contact angles). Validation tests showed that green resin had the highest accuracy in replicating the rock’s pore network. White, yellow, and gray resins produced models with moderate accuracy with respect to their transport properties. Black and clear resins had the lowest accuracy and would need further analysis of their physical and chemical properties to be useful in reservoir rock replication.

One of the main problems in coal utilization is the inability to properly characterize its complex pore structure. Coals typically have micro/ultramicro pores but they also exhibit meso and macroporosity. Conventional pore size techniques (adsorption/condensation, mercury porosimetry) are limited because of this broad pore size range, microporosity, reactive nature of coal, samples must be completely dried, and network/percolation effects. Small angle scattering is limited because it probes both open and closed pores. Although one would not expect any single technique to provide a satisfactory description of a coal`s structure, it is apparent that better techniques are necessary. Small angle scattering could be improved by combining scattering and adsorption measurements. Also, the measurement of NMR parameters of various gas phase and adsorbed phase NMR active probes can provide pore structure information. We will investigate the dependence of the common NMR parameters such as chemical shifts and relaxation times of several different nuclei and compounds on the pore structure of model microporous solids, carbons, and coals. In particular, we will study the interaction between several small molecules ({sup 129}Xe, {sup 3}He, {sup 2}H{sub 2},{sup 14}N{sub 2}, {sup 14}NH{sub 3}, {sup 15}N{sub 2},{sup 13}CH{sub 4}, {sup 13}CO{sub 2}) and the pore surfaces in coals.

Shale oil is an unconventional kind of oil and gas resource with great potential. China has huge reserves of shale oil, and shale oil resources are abundant in the third submember of the Triassic Chang 7 member in the southern Ordos Basin. At present, this area is in the initial stage of shale oil exploration and development. The reservoir pore is one of the key factors affecting oil accumulation, drilling safety, and oil production. It is also an important reservoir parameter that must be defined in the exploration stage. In general, the clay content in the shale section is high, and is prone to hydration. In order to study the effect of fluid on the pore type, structure, and distribution of shale oil reservoirs, experiments using X-ray diffraction, a porosity–permeability test, mercury porosimetry, rock casting thin section, and scanning electron microscopy were carried out. The experimental results show that the content of clay and quartz is very high in the studied formation. The pore porosity and permeability of the rock is highly heterogeneous because of the obvious stratigraphic bedding and interbeds. Microstructural observation of rocks shows that the main pore types are intergranular pores, intragranular pores, intercrystalline pores, and organic pores. Crack types are dissolution cracks, contraction cracks of organic matter, and abnormal pressure structural cracks. After hydration, the porosity of rock will increase in varying degrees, and pore size, pore content in different sizes, and pore structure will also change. The results show that the pores of tuff mainly changes at the initial stage of hydration, and the pore change of tuff is the most obvious within 6 hours of soaking in clear water. The influence of hydration on the pore of shale is greater than that of tuff, but the main change stage is later than tuff, and the pore change of shale is the most obvious within 12 to 24 hours of soaking in clear water. The soaking experiment of water-based drilling fluid (WBM-SL) shows that it can plug a certain size of holes and cracks and form a protective layer on the rock surface, thus effectively reducing hydration. In actual construction, multisized solid particles should be allocated in drilling fluid according to the formation pore’s characteristics, and the stability of the protective layer should be guaranteed. This can reduce the accident of well leakage and collapse and is conducive to the efficient and safe development of shale oil.

Membrane pore structure analysis via nmr spinlattice relaxation experiments

The influences of RE, Cr, P and P-RE elements on atmospheric corrosion resistance behaviors of weathering angle steels in a simulated industrial atmosphere were investigated by periodic immersion wet/dry cyclic corrosion test. According to weight loss test and rust analysis results, the corrosion rate is relatively faster in the initial stage of the corrosion since the compositions of rust layer are mainly γ-FeOOH and Fe3O4. Then, γ-FeOOH and Fe3O4 gradually transform to α-FeOOH and the corrosion rate reduces. The increasing amount of α-FeOOH with enhanced corrosion resistance is related to the addition of phosphorus element and the enrichment of copper, chromium and nickel elements in inner rust layer. Besides, rare earth can reduce the content of chromium and work with phosphorus to improve atmospheric corrosion resistance of steel. Consequently, weathering angle steel containing phosphorus and rare earth elements exhibits high corrosion resistance, and the electrochemical measurement on it indicates that the anodic process is inhibited and the evolution of resistance increases with the prolongation of immersion time.

High-pressure water injection, as an important measure for coal and gas outburst prevention, is still under-researched, especially its mechanism on the coal pore structure. The anthracite samples taken from no. 3 coal seam in Xinjing coal mine were dried and injected with high-pressure water, after which their pore characteristics were studied by using mercury porosimetry (MP) and low-pressure N2 gas adsorption (LP-N2GA). The results of MP showed that after the water was injected into the coal samples, the pore volume and the pore size of samples increased, but the specific surface area (SSA) remained almost unchanged. It could be concluded from LP-N2GA experiments that after the high-pressure water injection, the SSA of coal samples reduced greatly, but their pore size increased significantly. Through detailed analysis, the mechanism of high-pressure water injection on the coal pore structure is described as follows: the pores within the samples fracture after high-pressure water injection and the diameter of pores becomes bigger, resulting in increases in both the pore volume and the pore size. In addition, water molecules injected will stay at the end of micropores, so there is almost no change in the SSA, as indicated by MP testing results. However, the SSA of coal samples decreased significantly in the LP-N2GA testing. This is because it is really difficult to evaporate water molecules staying in the micropores by heating because of the strong interaction between water and coal. This study is helpful to further understand the mechanism of high-pressure water injection on preventing coal and gas outburst at the microlevel.

Corrosion behaviour of weathering steel in diluted Qinghai salt lake water in a laboratory accelerated test that involved cyclic wet/dry conditions

Determination of pore connectivity by mercury porosimetry

Effect of metal oxide on surface area and pore size of water-dispersible colloids from three German silt loam topsoils

With the development of imaging technology, tools to quantitatively describe pore structure, morphology, and connectivity have been widely applied on low permeable rocks; however, it is still questionable to what extent this information can be used to predict permeability. Applicability and comparability of different techniques are discussed here for the Middle Ordovician Cobourg limestone (Canada), a rock dominated by calcite grains of variable sizes (µm–cm) and heterogeneously distributed quartz, dolomite, pyrite, and meshy clay minerals. Absolute porosities determined by helium pycnometry (HP) in literature are approximately 1.6% (±0.9%), and gas permeabilities range from 10−20 to 10−19 m2. Porosities obtained from BIB-SEM are much smaller compared to those from HP (16–69% of HP). Pores found in clays are smaller, slit-shaped, and more densely spaced when compared to those in calcite minerals. Connectivity between pores could not be resolved with 3D micro-CT or FIB-SEM reconstructions, which have a resolution limit of 8 µm and 10 nm, respectively. However, assuming the pores to be connected, laboratory-derived permeability data could be fitted using a simple capillary bundle model, including information about the visible pore size distributions obtained from BIB-SEM images and a tortuosity range of 8 to 15.

Production of oil and gas from unconventional source rocks (shales) has increased significantly in recent years, reflecting a shift in the focus of the oil and gas industry from conventional to unconventional oil/gas resources. An improved insight into the pore structure characteristics of these important porous materials will enable a better understanding and further optimization of the production behavior from such vast hydrocarbon resources. In particular, characterization of porosity and permeability of shales is the key to accurately estimating the initial oil and gas in place and fluid flow through these rocks. However, evaluating the pore structure of shales presents technical challenges due to the presence of a range of pores, from the nanometer to the micrometer size. Characterization of the entire range of pore sizes requires an all-inclusive study employing a variety of techniques. Such an integrated approach is followed in this work to understand the pore structure of Monterey shale samples as...