Gas Porosity Research Articles

Effects of zirconium diboride addition on porosity reduction in laser metal deposition of tungsten carbide–cobalt cermet material

Laser metal deposition of tungsten carbide–cobalt (WC-Co) cermet material is a promising means of improving the wear resistance of metal products. However, laser metal deposition of WC-Co has constraints on its practical use because a clad bead of WC-Co often includes numerous gas pores. Earlier studies have found CO gas generation in a molten pool by reaction of carbon and oxygen to be the main cause of gas porosity in a WC-Co clad bead. Preventing the gas reaction is important to obtain clad beads with few pores. The addition of elements with strong affinity for oxygen, such as aluminum, was found to be effective for porosity reduction in a clad bead. However, the addition of highly reactive pure aluminum particles on WC-Co powder presents some difficulties for industrial use. For this study, zirconium diboride (ZrB2), a chemically stable compound, was used as an additive to WC-Co powder. After WC-Co powder with adhered ZrB2 particles was prepared using a wet granulation process, laser metal deposition was conducted. Zirconium stemming from the dissolution of ZrB2 in the molten pool was found to have the effect of trapping oxygen elements as solid zirconium oxides. Consequently, gas generation in the molten pool by the reaction of carbon and oxygen was restrained. Clad beads having few pores and fine microstructures were obtained. Observations of the molten pool behavior taken using a high-speed camera indicated that ZrB2 addition drastically improves process stability compared to processes using conventional WC-Co powder.

Effect of Microgravity on the Metal Droplet Transfer and Bead Characteristics in the Directed Energy Deposition-Arc Process

Abstract Directed energy deposition-arc (DED-arc) is a viable method of metal 3D printing for manufacturing in-space under microgravity conditions. This study investigates the effect of reduced gravity on the droplet transfer in a gas metal arc welding (GMAW)-based DED-arc process. Single bead deposited using GMAW welding process under microgravity and standard terrestrial gravity (1 g) are compared. Microgravity was simulated in a drop tower where the experimental capsule was subjected to 2.5 s of free-fall. The experimental setup for GMAW welding process, including high-speed cameras and sensors, was present within the experimental capsule. Droplet frequency and diameter were measured and compared between microgravity and 1 g using the images obtained. Further, the impact of reduced gravity on weld bead geometry and the distribution of gas porosity was investigated. Microhardness analysis was also conducted on both 1 g and reduced gravity samples to assess variations in material hardness. A statistically significant difference in droplet diameter and frequency was found. This difference is attributed to the reduction in gravitational force. Upon analyzing the weld bead geometry, noticeable variations are detected in the contact angles and the reinforcement of beads formed under different gravity conditions. These differences are attributed to alterations in convection within the molten weld pool. The blowhole analysis revealed a noticeable trend, wherein reduced gravity facilitated the coalescence of gas porosity, resulting in larger diameters due to alterations in weld pool convection. There were no statistically significant changes observed in both microhardness and surface finish.

Experimental study on characteristics of gas seepage in broken coal and rock

AbstractThe characteristics of gas seepage in broken coal and rock composed of different particle sizes and grades were investigated in this study. On the basis of Darcy's law and non‐Darcy seepage theory, equations of gas permeability in the nonlinear seepage of broken coal and rock, as well as the porosity of broken coal and rock, under triaxial compression were determined. The stress loading path of gas seepage in broken coal and rock was developed. The characteristics of gas seepage in broken coal and rock composed of different particle sizes and grades were analyzed, and the results showed that the gas permeability after compression was proportional to the particle size of the broken coal and rock. Under triaxial compression, the gas permeability of the broken coal and rock composed of graded‐particle sizes was lower than that of the broken coal and rock composed of different single‐particle sizes. The gas permeability of the broken coal was lower than that of the broken rock mass, and the gas permeability and porosity of the broken coal and rock can be described by the exponential decay function. At a constant porosity, the gas permeability of the broken coal and rock was proportional to the size grading index under triaxial compression. The coefficient of viscosity and gravity of the flow are key factors influencing the flow permeability in broken coal and rock. This study provides a reference for on‐site practice such as the efficient extraction of gas in goafs.

Investigation of individual lack-of-fusion defects in the fatigue performance of laser-powder bed fusion Ti6Al4V alloys: A finite element analysis

Laser-Powder Bed Fusion (L-PBF) techniques have revolutionized the production of Ti6Al4V alloys across various industries. However, the widespread adoption of L-PBF Ti6Al4V alloys is impeded by their inadequate fatigue performance, particularly in high cycle regimes. A significant contributing factor to this limitation is the presence of internal defects inherent to the L-PBF process, act as sites for fatigue crack initiation. Previous investigations have focused on the fatigue performance of L-PBF Ti6Al4V alloys with gas porosities, while research on lack-of-fusions (LOFs) which are recognized as the most detrimental defects, remains limited. In order to deepen our understanding of the factors influencing the reduced fatigue performance observed in L-PBF Ti6Al4V alloys associated with inherent LOFs, this study employed three-dimensional (3D) finite element analysis approaches. Such approaches allow to assess fatigue indicator parameters to evaluate fatigue life and predict fatigue crack propagation. A 3D average Smith-Watson-Topper method has been proposed, which is able to rationally estimate the fatigue life of L-PBF Ti6Al4V. In addition, a novel finite element method has been developed to accurately calculate stress intensity factors along irregular shaped crack front of a notch-like feature embedded on a LOF. Additionally, parametric studies were conducted to gain further insights into the influence of LOFs on fatigue performance. The results shown the presence of embedded humps and notch-like features, and their topologies play key roles in the fatigue performance of LOF predominated L-PBF Ti6Al4V alloys.

Substantial gas enrichment in shales influenced by volcanism during the Ordovician–Silurian transition

The substantial gas enrichment in shales of the Ordovician–Silurian transition was associated with the development of the most favorable source rock. While organic matter enrichment has been linked to intensive volcanism, it remains a challenge to precisely evaluate the impact of the volcanism on substantial gas enrichment containing the largest gas storage capacity. This study focused on consecutive borehole shale samples from the Wufeng–Longmaxi formations during the Ordovician–Silurian transition in southern China. We conducted a comprehensive analysis, integrating the major geological volcanism with high-resolution analysis, including QEMSCAN, argon-ion SEM, thin-section examination, XRD mineralogy, TOC, Hg concentration, petrophysical properties and nanopore structure analysis (low-pressure CO2/N2 gas adsorption, porosity and permeability). The results link the significant shale gas enrichment in Wufeng–Longmaxi formations to intensive volcanism across the Ordovician–Silurian transition. We identified the most favorable shale intervals in the lower Longmaxi Formation, aligning with the peak period of volcanism. This period showed synchronous spikes in Hg, Hg/TOC, and TOC contents. Shale deposited during this favorable paleoenvironment exhibited the highest values of TOC, porosity, permeability, specific surface area, pore volume, maximum gas adsorption capacity, leading to the largest amount of gas content and substantial gas enrichment. Our work, therefore, provides new insights into identifying the most favorable shale gas resources. This knowledge assists in accurate predictions of the stratigraphic ‘sweet spot’ intervals for large shale gas storage capacity, providing crucial information for engineering explorations and developments in shale formations.

The Influence of Post-Treatment on Micropore Evolution and Mechanical Performance in AlSi10Mg Alloy Manufactured by Laser Powder Bed Fusion.

Gas-induced porosity is almost inevitable in additively manufactured aluminum alloys due to the evaporation of low-melting point elements (e.g., Al, Mg, and Zn) and the encapsulation of gases (e.g., hydrogen) during the multiple-phase reaction in the melt pool. These micropores are highly unstable during post-heat treatment at elevated temperatures and greatly affect mechanical properties and service reliability. In this study, the AlSi10Mg samples prepared by LPBF were subjected to solution heat treatment at 560 °C for 0.5 and 2 h, followed by artificial aging at 160 °C, 180 °C and 200 °C, respectively. The defect tolerance of gas porosity and associated damage mechanisms in the as-built and heat treated AlSi10Mg alloy were elucidated using optical, scanning electron microscopic analysis, X-ray micro computed tomography (XCT) and room temperature tensile testing. The results showed the defect tolerance of AlSi10Mg alloy prepared by LPBF was significantly reduced by the artificial aging treatment due to the precipitation of Mg-Si phases. Fracture analysis showed that the cooperation of fine precipitates and coarsened micropores assists nucleation and propagation of microcracks sites due to stress concentration upon tensile deformation and reduces the tensile elongation at break.

Analysis of Factors Influencing Tight Sandstone Gas Production and Identification of Favorable Gas Layers in the Shan 23 Sub-Member of the Daning-Jixian Block, Eastern Ordos Basin

The Daning-Jixian Block harbors abundant tight sandstone gas resources. However, significant variations in gas production exist among the different wells within the block. A comprehensive study was conducted on key factors such as sedimentary strata and petrophysical characteristics to elucidate their impact on gas reservoir productivity. Linear regression equations were employed to classify the favorable reservoirs within the study area. The analysis revealed that within the first 6 months of production from the Shan 23 gas layer, daily gas production ranged from 2576.19 to 156,078.17 m3/d, averaging 24,037.9 m3/d. Over the first year, average daily production varied from 2185.05 to 136,806.99 m3/d, averaging 23,469.23 m3/d, indicating relatively stable production from the Shan 23 layer alone. In the dominant central area of the underwater distributary channel delta front in Shan23, the sand body exhibits a superimposed cutting type, resulting in high production rates. Conversely, the sand bodies on the periphery gradually transition to superimposed and isolated types, leading to decreased production. Through a correlation analysis of gas layer thickness, porosity, permeability, and initial gas well production, it was determined that gas production from the wells within the same layer is primarily influenced by gas layer thickness, porosity, and permeability. Gas saturation demonstrates a minimal impact on production according to single-factor analysis. The evaluated factors such as the gas productivity coefficient, energy storage coefficient, and enrichment coefficient exhibited similar distribution patterns across the study area. The high-value areas for the gas productivity coefficient, energy storage coefficient, and enrichment coefficient are concentrated in distributary channel zones and delta lobes. In contrast, regions with underdeveloped skeletal sand bodies generally display lower values for these parameters. The linear relationships between these parameters and the average gas production were calculated to further classify the favorable reservoirs in the study area. This study aimed to establish a scientific basis for the efficient development of the tight sandstone gas reservoirs within the Daning-Jixian Block.

Evolution of gas permeability and porosity of sandstone under stress loading and unloading conditions

Evolution of gas permeability and porosity of sandstone under stress loading and unloading conditions

CO2 transport through swelling organic-rich nanoporous media: Insights on gas permeability from coarse-grained pore-scale simulations

Sorption-induced swelling reduces porosity and permeability in porous media, impacting long-term CO2 storage injectivity. This study employs an innovative coarse-grained model to couple fluid flow with sorption-induced solid deformation at the pore-scale. Our model preserves the advantages of molecular dynamics in simulating complex fluid-solid interaction under nano-confinement while extending the time and length scales. Adjusting the gas-solid interaction energy controls solid swelling and gas slippage at pore walls. Gas permeability curves demonstrate a linear decline with the increasing gas-solid interaction energy in both swelling and non-swelling nanoporous media, with the former experiencing a greater drop. Surprisingly, in the regime of weak gas-solid interactions, swelling is not yet initiated and the porosity and permeability of flexible porous media increase, possibly due to gas flow-induced pore throat opening. Nanoporous media with lower initial porosity experience a greater permeability decline during swelling. The relationship between permeability and porosity changes shows a linear increase characterized by different slopes with varying initial porosities. These findings provide valuable insights into the complex interactions among gas transport, solid deformation, and porosity changes in nanoporous media, with implications for understanding and optimizing gas production and CO2 storage in realistic geological environments.

Experimental and numerical investigations of cake baking in mold

This article deals with the in-mold cake baking process. The methodology relies on numerical and experimental investigations to validate a multiphysics developed model. This numerical model is next exploited to enhance the comprehension of the physical processes that occur during a typical cake baking phase. Based on the governing equations for heat and mass transport and under few assumptions (deformable porous medium, local thermodynamic equilibrium, ideal gas mixture …), the problem consists in solving a system of five coupled partial derivative equations. Temperature, moisture content, total gas pressure, porosity and displacement are used as state variables in this study. The swelling of the dough caused by the increase in total gas pressure is predicted by a viscoelastic model. This thermo-hydro-mechanical model is implemented in a finite element code. Moreover, an experimental laboratory set-up was developed to continually acquire temperatures, water losses and gas pressure inside the product. The browning kinetic is also studied. Furthermore, the cake deformation is tracked by camera. The numerical model is validated based on the conducted experiments. Different operating conditions are tested to verify the robustness of the model. Finally, a sensitivity analysis is performed to understand the impact of estimated parameters on the outputs of the developed model.

Nanotube-mediated storage of methane and hydrogen: Insights from molecular simulation

We investigate the storage of methane (CH4) and hydrogen (H2) within single-walled nanotubes carbon, boron nitride (BN), and molybdenum disulfide (MoS2) nanotubes using Grand Canonical Monte Carlo (GCMC) algorithm. We observed that BN nanotubes exhibit the highest weight adsorption capacity for CH4 at 298 K, reaching up to 0.441 g/g at 8 MPa, closely aligning with the Department of Energy (DOE) target of 0.5 g/g. In contrast, MoS2 nanotubes, despite their larger radius, demonstrated the lowest weight adsorption capacity due to their higher atomic mass, with a value of 0.096 g/g at the same pressure. Volumetric adsorption capacity for CH4 was notably highest in (10,10) BN nanotubes, achieving 244 cm3/cm3 at 8 MPa, although this was still below the DOE target of 330 cm3/cm3. For hydrogen storage at 77 K, (30,30) BN nanotubes outperformed the 2025 DOE benchmarks of 5.5 wt% and 0.04 kg/L, with a weight adsorption of 12.19 wt% and a volumetric adsorption of 0.051 kg/L at 8 MPa, respectively. The adsorption heat within nanotubes showed a complex relationship with adsorption quantity, highlighting the interplay between fluid-wall and fluid-fluid interactions. The study also examines the impact of material structure on gas release, revealing a linear relationship between gas release and porosity or pore volume. The Ideal Adsorbed Solution Theory (IAST) was validated for predicting CH4/H2 mixture separations on amorphous carbon materials, and further reveals that the (30,30) BN nanotubes identified as the most suitable candidate for CH4/H2 separation, offering a balance of high CH4 adsorption capacity (20.2 mmol/g) and selectivity of 15 at 8 MPa.

Modeling and validation of hydrogen porosity formation in aluminum laser welding

Laser welding is used to weld aluminum alloy 1100 for battery cell manufacturing in the automotive industry. However, these welds can have porosity that can decrease their performance in the battery packs. One type of porosity is gas porosity, commonly understood to be due to hydrogen entrapment in the weld during solidification. Hydrogen is dissolved in the molten aluminum at elevated temperatures during laser heating and can be entrapped in the weld pool upon solidification. When welding anodized aluminum, the amount of hydrogen porosity is increased because the anodized oxide layer is broken up and the broken-up oxide can act as heterogeneous nucleation sites for hydrogen pores. A cellular automaton model has been developed to predict the nucleation and growth of hydrogen porosity during laser welding. This model has been validated with microstructure analysis, LECO® hydrogen analysis, and X-ray micro-computed tomography. This model can be used by welding engineers to reduce porosity and control weld quality during laser welding of aluminum alloys.

Numerical simulation of melt flow and heat transfer in casting filling process based on SPH

There is a great influence of the melt filling process on the quality of castings. Smoothed particle hydrodynamics (SPH) that materials are approximated by free particles rather than by fixed grids is applied to accurately predict fluid flows involving complex free surfaces. In this paper we present a mathematical model of melt flow and heat transfer by using SPH method. A novel approach is used in the governing equations to ensure stable numerical schemes and homogeneous particle distributions. The SPH heat equation takes into account the thermal release during phase transition and is more suitable for alloy solidification. The solid wall boundary conditions are slightly modified to satisfy the filling simulations. Several case studies are carried out to predict significant details about the filling order and flow structures in the mold cavity. The velocity and temperature distributions during different stages of melt filling are also given. The results show that this proposed model allows us to understand the predisposition of defects such as gas porosity and weld lines in the castings. These predictions can be used as inputs for improving process parameters, venting and cooling systems design.

The practice of using chill vents in construction injection molding forms

Options for improving the quality of castings during injection molding are considered. The variants of the design and placement of the chill vents in the mold are presented. The practical experience of using chill vents in order to improve the ventilation system of the mold to ensure a reduction in the defect of the gas sink molds and porosity is described.

Gas prediction in tight sandstones based on the rock-physics-derived seismic amplitude variation versus offset method

Estimating gas enrichments is a key objective in exploring sweet spots within tight sandstone gas reservoirs. However, the low sensitivity of elastic parameters to gas saturations in such formations makes it a significant challenge to reliably estimate gas enrichments using seismic methods. Through rock physical modeling and reservoir parameter analyses conducted in this study, a more suitable indicator for estimating gas enrichment, termed the gas content indicator, has been proposed. This indicator is formulated based on effective fluid bulk modulus and shear modulus and demonstrates a clear positive correlation with gas content in tight sandstones. Moreover, a new seismic amplitude variation versus offset (AVO) equation is derived to directly extract reservoir properties, such as the gas content indicator and porosity, from prestack seismic data. The accuracy of this proposed AVO equation is validated through comparison with the exact solutions provided by the Zoeppritz equation. To ensure reliable estimations of reservoir properties from partial angle-stacked seismic data, the proposed AVO equation is reformulated within the elastic impedance inversion framework. The estimated gas content indicator and porosity exhibit favorable agreement with logging data, suggesting that the obtained results are suitable for reliable predictions of tight sandstones with high gas enrichments. Furthermore, the proposed methods have the potential to stimulate the advancement of other suitable inversion techniques for directly estimating reservoir properties from seismic data across various petroleum resources.

Effect of tracheid cell structure on gas permeability and porosity in conifer species

Effect of tracheid cell structure on gas permeability and porosity in conifer species

Looking beyond X-ray: Neutron tomography analyses of Late Bronze Age weapons from the Somló Hill

Three spearheads and an arrowhead from the Somló Hill (Veszprém County, Hungary) Urnfield site are selected for X-ray radiography and neutron tomography analyses. The four weapons can be dated to the late phase of the Urnfield period between Ha B1 and Ha B2 and originate from different contexts: spearheads Nos. 1–2 from Hoard I, spearhead No. 3 from Hoard III, and an arrowhead (No. 4) as a stray find. Macroscopic characteristics of these newly discovered weapons attest to different stages of production and use, from as-cast to finished, used and heavily used products. The applied methods provide information on the inside of the objects, with special attention to the quality of the casting and traces of repair. Neutron tomography potentially offers an unbiased and quantifiable evaluation of the objects’ porosities and their levels from a modern industrial perspective. All three spearheads from Somló Hill showed different levels of porosity inside, the morphological characteristics of which suggest that they were probably caused by gas porosity. The long spearhead No. 1 from Somló Hill also shows traces of a misrun defect repaired by the cast-on technique. Traces of production and use suggest that except for one spearhead (No. 3), which was cast almost solid and showed high levels of porosity together with other types of defects, such as flashes and incomplete casting, all other studied objects were finished products used for combat and hunting.

Mechanistic analysis of acid gas storage and oil recovery in naturally fractured reservoirs using single matrix block approach

AbstractThe objective of this study is to assess the storage of acid gas, containing CO2 and H2S, in a depleted naturally fractured reservoir (NFR) using single matrix block (SMB) approach. The acid gas dissolution in oil is considered by Peng‐Robinson equation of state and compositional simulation. The PHREEQC package is used to determine acid gas solubility in formation brine. Three types of acid gases with different compositions are used for this study and their swelling behavior and miscibility in relation to the reservoir oil are analyzed. An SMB model, with a matrix block surrounded by fractures, is constructed, and validated for simulation of a real experiment. The simulation is conducted for synthetic and real reservoir fluids when the oil is in its residual saturation. A sensitivity analysis is performed to study the effects of key parameters, such as acid gas composition, reservoir pressure, permeability, porosity and matrix height on the storage capacity and oil recovery factor. The matrix has a volume of 27 m3 and about half of acid gas storage is achieved in the first 5 years while the simulations are run for 30 years. The results show that up to 90% of remained oil is recoverable, and more than 0.67 kmol of acid gas per cubic meter of matrix is stored whether matrix contains a real oil or a synthetic one. Higher storage is achieved for higher matrix porosities and heights and large H2S proportion in acid gas. In all cases about 10% of acid gas is trapped in water and the remaining 90% is dissolved in oil. The mineral trapping was more active in CO2‐rich acid gases. While about 10 kg of the matrix rock was dissolved in the acidic brine when the acid gas contained H2S, the amount of the dissolved minerals in acidic brine resulted from the injection of CO2‐rich acid gas was more than 16 kg. Finally, this study gives a comparative analysis of the storage performance of acid gas mixture and pure CO2. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

Optimizing Factors affecting gas porosity in GDC of Al-Si (A356) Alloy using Taguchi’s DOE

Aluminium alloys find extensive use in various applications because of its advantage of strength-to-weight ratio,. However, the casting process introduces susceptibility to defects, and managing all parameters proves to be a complex task. Casting rejections often stem from one or more defects, with mold parameters, filling, and solidification processes being key contributors. When the molten metal of the Al-Si (A356) alloy is exposed to the atmosphere in a holding furnace, it develops an oxide layer on its surface. Turbulence in the molten metal leads to the formation of a double oxide layer, also known as bifilms. Gas entrainment occurs due to the turbulent movement of metal, resulting in the entrapment of gas in the molten metal and ultimately causing gas porosity in the final casting. Gas entrapment during the filling process leads to gas porosities during the solidification phase.This study aims to comprehend the factors influencing the formation of gas entrapment during the casting of the aluminium alloy Al-Si (A356). The experimental investigation utilizes Taguchi’s Design of Experiments (DOE) to explore the impacts of parameters such as pouring temperature (PoT), degassing time (DgT), and volume in the holding furnace (VoH) on the formation of gas porosity in casting [8].An experimental setup was created to produce tensile test rods and reduced pressure test (RPT) samples. The results were validated using the mechanical properties of the tensile test samples and the density of the Reduced Pressure Test (RPT) samples. Better the mechanical properties, fewer will be the defects in castings. Taguchi’s DOE is applied to analyse the results. The experimental findings indicate that a pouring temperature at level 1 (710°C), degassing time at level 1 (10 minutes), and volume in the holding furnace at level 1 (>450 kg) yield favourable castings. Confirmatory tests were conducted to validate the results, and they aligned with the experimental data.

Numerical modelling of heat and mass transfer during cake baking

This article deals with the development of a numerical multiphysics model to study heat and mass transfer phenomena as well as the swelling during the baking of a cake contained in mold. The aim of this study is to provide an effective numerical tool, experimentally validated, for a better understanding of mechanisms leading to the desired end product. Based on the governing equations for heat and mass transport and under few assumptions (homogenous medium, local thermodynamic equilibrium, ideal gas mixture…), the problem consists in solving a system of five coupled partial derivative equations. Temperature, moisture content, total gas pressure, porosity and displacement are used as state variables in this study. The swelling of dough caused by the increase of total gas pressure is predicted by a viscoelastic model. This thermo-hydro-mechanical model is implemented in finite elements code. Moreover, an experimental laboratory set-up was developed in order to continually acquire temperatures, water losses, deformation and to correctly apprehend the boundaries conditions. The numerical results are then compared with experimental data. They are overall in good agreement. Various operating conditions are tested to check the robustness of predictions.