Pore Generation Research Articles

Volumetric Additive Manufacturing of SiOC by Xolography.

Additive manufacturing (AM) of ceramics has significantly contributed to advancements in ceramic fabrication, solving some of the difficulties of conventional ceramic processing and providing additional possibilities for the structure and function of components. However, defects induced by the layer-by-layer approach on which traditional AM techniques are based still constitute a challenge to address. This study presents the volumetric AM of a SiOC ceramic from a preceramic polymer using xolography, a linear volumetric AM process that allows to avoid the staircase effect typical of other vat photopolymerization techniques. Besides optimizing the trade-off between preceramic polymer content and transmittance, a pore generator is introduced to create transient channels for gas release before decomposition of the organic constituents and moieties, resulting in crack-free solid ceramic structures even at low ceramic yield. Formulation optimization alleviated sinking of printed parts during printing and prevented shape distortion. Complexsolid and porous ceramic structures with a smooth surface and sharp features are fabricated under the optimized parameters. This work provides a new method for the AM of ceramics at µm/mm scale with high surface quality and large geometry variety in an efficient way, opening the possibility for applications in fields such as micromechanical systems and microelectronic components.

Amylopectin induces chain porous carbon skeleton boosting high performance of Na3V2(PO4)3

Poor conductivity and stability seriously hinder the development of Na3V2(PO4)3 (NVP). In current work, we use a facile hydrothermal method to dissolve low-cost amylopectin in urea as an additional carbon source for in-situ modification of NVP. The unique amylopectin, as structure guide agent, induces the formation of one-dimensional chain structure to cross each other. The gas produced in the urea decomposition process promotes the generation of pores on the one-dimensional chain structure. Finally, one-dimensional chain porous carbon skeleton is constructed. Plentiful defects and active sites are formed in the N-doped carbon derived from urea, effectively promoting the ionic conductivity at interface of NVP grains. Notably, amylopectin can induce the O atom in NVP bulk to escape from the crystal and combine with the N atom in carbon layer to form an N–O bond, thus generating abundant oxygen vacancy inside the NVP bulk. This special effect can reduce the resistance of Na+ transport in the crystal and enhance the connect bonds between the active particles and coated carbon substrate. Thus, both the ionic conductivity and the structural stability can be significantly improved. Moreover, the ex-situ SEM/TEM/XRD/XPS/CV/EIS measurements after cycling all demonstrate the optimized crystal structure and unique morphology can be perfectly maintained during the prolonged cycling process. The optimized NVP/C,N-0.25 sample reveals 116.3 mA h g−1 at 0.1 C. Even at 80 C, it still releases 74.4 mA h g−1 and maintains 51.2 mA h g−1 after 12,000 cycles, corresponding to a low decay rate of 0.0026 % per cycle.

Hot Hydrogen Testing of W-Coated UN Kernels in a Mo30W Matrix

Ceramic uranium mononitride (UN) is being considered as a reactor fuel for nuclear thermal propulsion. To avoid or reduce the dissociation of UN at the high temperatures needed, embedding it in a metallic matrix (cermet) has been proposed. To assess the viability of this concept, hot hydrogen testing of tungsten-coated UN kernels embedded in a Mo-30 wt% W (Mo30W) alloy matrix has been performed at temperatures from 1800°C to 2300°C. Both the isolated kernels and kernels consolidated by spark plasma sintering in the Mo30W matrix were tested. In addition to direct observations and mass loss measurements, the samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDS) after each run. The decomposition of UN started at 1800°C despite the coating and matrix, and increased at 2000°C. Uranium seeped through the tungsten grain boundaries of the coating at all temperatures. The consolidated sample expanded irregularly at 2000°C through the formation of voids, and SEM/EDS analysis showed uranium-containing veins in the matrix consisting of U2Mo according to the XRD data. The observed pore generation at 2000°C was explained by the formation of water vapor from residual oxides and diffused hydrogen. At 2200°C and above, both the kernels and the consolidated samples melted through the formation of uranium or low–melting point uranium-molybdenum alloys.

Experimental and molecular dynamics study on thermal‐mechanical properties of epoxy shape memory polymers

AbstractExperimental and molecular dynamics simulations were employed to investigate epoxy shape memory polymers' thermal‐mechanical properties and shape memory characteristics, utilizing polyether amine and modified hexanediamine as curing agents following the material prerequisites for variable stiffness fixtures. Glass transition temperature and Young's modulus of epoxy shape memory polymers are characterized by dynamic mechanical analysis. The consistency of the glass transition temperature between the simulation model and the experimental findings verified the accuracy of the molecular dynamics simulation. The uniaxial tensile simulation revealed that non‐bond energy predominantly exerts its influence in stretch. After reaching the yield stress, the weight fraction of the curing agent affects the generation of internal pores, with the yield stress of systems exhibiting substantial pores being minor. Systems characterized by a higher weight fraction of curing agents are more prone to pore formulation. Simulation of shape memory properties demonstrates that the entropy resulting from differences in molecular weight impacts the simulated system's shape fixation ratio and shape recovery ratio.

Influence of plasma breakdown on pores and fractures in bituminous coal: A new characterization method of breakdown energy

Plasma technology has a potential application prospect in the field of coal seam permeability enhancement. However, the relationship between plasma breakdown energy and the improvement effect of coal pores and fractures is lack of in-depth research. This study proposed a novel method for characterizing the plasma breakdown energy, and three testing techniques, namely, particle size distribution, mercury intrusion porosimetry (MIP) and low-field nuclear magnetic resonance (NMR), were utilized to examine the pore and fracture distribution of coal samples obtained from Jiulong Mine under varying breakdown energy conditions. The influence between breakdown energy and pores and fractures development is revealed. The results show that: (1) The degree of coal sample fragmentation increases with the increase of plasma breakdown energy. (2) Different breakdown energy induced the development of different pore distribution patterns. At lower breakdown energy, an increase in the volume of macropores dominates. As the breakdown energy increases, there is a rapid increase in the volume of mesopores, a slight increase in minipores, and the least increase in micropores, indicating that plasma treatment primarily improves pores with diameters greater than 100 nm. The test results of the three techniques were mutually verified. (3) Compared with capacitance energy and voltage, the effective breakdown energy obtained by the integral method has a more significant linear relationship with the particle size distribution, total pore volume, and average pore diameter, indicating that the effective breakdown energy is more suitable for characterizing the crushing effect of plasma. During the plasma breakdown process, the expansion stress and thermal stress formed by the effective breakdown energy exceeded the local tensile strength of coal, leading to the generation and development of pores and fractures, which in turn led to the rupture of the coal body. The larger the breakdown energy, the larger the crushing circle formed around the ion channel, the finer the coal is crushed, and the more pore fractures are developed. These nascent pores and fractures provide channels for gas transport, which is extremely favorable for coal mine gas extraction. The research conclusions provide theoretical support for the application of plasma in fracturing and permeability enhancement in coal seams.

Universal Synthesis of Amorphous Metal Oxide Nanomeshes.

Constructing the pore structures in amorphous metal oxide nanosheets can enhance their electrocatalytic performance by efficiently increasing specific surface areas and facilitating mass transport in electrocatalysis. However, the accurate synthesis for porous amorphous metal oxide nanosheets remains a challenge. Herein,a facile nitrate-assisted oxidation strategy is reported for synthesizing amorphous mesoporous iridium oxide nanomeshes (a-m IrOx NMs) with a pore size of ∼4nm. X-ray absorption characterizations indicate that a-m IrOx NMs possess stretched Ir─O bonds and weaker Ir-O interaction compared with commercial IrO2. Combining thermogravimetric-fourier transform infrared spectroscopy with differential scanning calorimetry measurements, it is demonstrated that sodium nitrate, acting as an oxidizing agent, is conducive to the formation of amorphous nanosheets, while the NO2 produced by the in situ decomposition of nitrates facilitates the generation of pores within the nanomeshes. As an anode electrocatalyst in proton exchange membrane water electrolyzer, a-m IrOx NMs exhibit superior performance, maintaining a cell voltage of 1.67V at 1Acm-2 for 120h without obvious decay with a low loading (0.4mgcatalyst cm-2). Furthermore, the nitrate-assisted method is demonstrated to be a general approach to prepare various amorphous metal oxide nanomeshes, including amorphous RhOx, TiOx, ZrOx, AlOx, and HfOx nanomeshes.

Montmorillonite pigment effects on the water barrier properties of paper coated with latexes synthesized through surfactant and Pickering emulsion methods

Pigments are often added to improve the barrier performance of dispersion coatings on paper, but they only are beneficial up to a limited pigment volume concentration (PVC). In this study, the use of montmorillonite (MMT) as pigment was explored in latex emulsions synthesized using surfactant and Pickering emulsion methods to explore the origins of this limitation. MMT was used to synthesize dispersion coatings for paper consisting of poly(styrene-co-butylacrylate) latex and compared with those synthesized using sodium dodecyl sulfate (SDS) surfactant. The Pickering, surfactant, and commercial coating systems with MMT decreased the water vapor transmission rate (WVTR), reaching minimum values at 1.2 %, 2 %, and 0.4 % PVC, respectively. At higher PVC values, the WVTR of all systems increased, which was attributed to the MMT pigments creating pathways for water transport. Moreover, similar pore volumes were found in all the latex films, indicating that the decrease in barrier properties as PVC increased was not caused by pore generation. The hydrophilicity of the MMT pigment was found to contribute to the observed minimum and lower barrier properties with increasing PVC. This work demonstrates that addition of pigments to the latex can be beneficial to improve paper barrier properties up to a certain level beyond which the pigments form percolation networks along the interfaces between MMT and the polymer, reducing the barrier properties.

Arc erosion behaviors of the densified Ag-SnO2 contact materials containing sub-micron and nano In2O3 additives

The effects of In2O3 additive size on the physical properties and arc erosion behaviors of the densified Ag-SnO2 materials were investigated. Arc resistance mechanism was analyzed based on the microscopic morphology characterization. Results revealed that the physical properties of the Ag-SnO2(In2O3) materials were significantly improved after densification. Relative density and electrical conductivity of the materials reached above 99.5% and 71%IACS, respectively. The densified Ag-SnO2 material containing sub-micron In2O3 showed the low and stable break arc energy. The mass loss of the cathode was dramatically decreased by 65.4%. Importantly, the generation of pores and micro-cracks on the surface of electrodes were significantly restrained and the contact resistance became more stable. By comparison, the nano In2O3 additive less than 100 nm effectively suppressed not only the splash of molten Ag on the surface of cathode but also the aggregation of SnO2 particles on anode. The arc erosion products were obviously decreased, resulting in an enhancement of arc-erosion resistance of Ag-SnO2(nano In2O3) materials. Compared with that without additive, the mass loss of the Ag-SnO2 material which contains nano In2O3 obviously decreased from 2.3 to 1.4 mg. The optimal mass fraction of nano In2O3 in the Ag-SnO2 contact materials was 1 wt%.

Corrosion-resistant behavior and structural optimization of Ti/Cr, Ti/Cu, Cr/Cu, Ti/Cr/Cu multimetallic layer coatings in simulated seawater

This article is based on the sacrificial anode cathodic protection principle and the optimization method of multilayer structure. According to the standard electrode potential of metals, starting from the corrosion-resistant passive film formed by the metal itself, Ti/Cr, Ti/Cu, Cr/Cu, and Ti/Cr/Cu coatings were prepared on a 316L stainless steel substrate using magnetron sputtering technology. The corrosion performance of the coatings was studied to explore the interaction patterns between them. The results showed that in artificial seawater, the Cr/Cu, Ti/Cu, and Ti/Cr metal bilayer film coatings exhibited an increasing impedance arc radius and widening phase angle plateau in the electrochemical impedance spectroscopy. In the polarization curve, the self-corrosion current, the self-corrosion potential and polarization resistance are all better than the substrate. In the static immersion test, the weight loss rate of the metal multi-layer film gradually decreased, with all samples showing a lower weight loss rate in the second week compared to the first week, ranging from 27% to 52%. By further designing the microstructure of the coating to mitigate the contradiction between hardness and toughness, and reduce the generation of pores, the corrosion performance of the new Ti/Cr/Cu coating is significantly improved. The coating can repair surface defects of the material, fill in micro and nano gaps, and enhance the cathodic protection effect of sacrificial anodes.

Elution-free hollow-fiber membranes of block copolymers for hemodialysis balancing protein retaining and toxin clearance

Hemodialysis has been used as the primary treatment for patients with end-stage renal disease, however, the current hemodialysis membranes still need complicated modifications to enhance the hemocompatibility and overcome the additive leaching issue. Herein, we prepare hemodialysis hollow-fiber membranes (HFMs) via the melt spinning and selective swelling of the block copolymers of polysulfone (PSF) and polyethylene glycol (PEG), PSF-b-PEG. PSF-b-PEG is first melt-extruded to form dense hollow fibers, and then soaked in selective solvents to transform the PEG microdomains into nanopores following the mechanism of selective swelling-induced pore generation, thus producing HFMs with three dimensionally interconnected porosities. As neither additives nor involatile solvents are involved in the manufacturing process of the HFMs, no elution of any organic matters could be detected for the HFMs during hemodialysis. The HFMs possess a symmetrical structure ensuring tight selectivity, and hydrophilic PEG chains are enriched on the pore surfaces, thus endowing the membranes with enhanced hydrophilicity and durable biocompatibility. We systematically investigate the effect of PEG contents and swelling conditions on pore sizes, porosities, surface properties, and consequently the hemodialysis performance. The optimized HFMs reject >99 % serum albumin while clear ∼70 % middle molecular toxins such as lysozyme and 93–95 % small molecular toxins including urea, phosphate and creatinine. This work provides a strategy to prepare elution-free hemodialysis membranes by taking advantage of selective swelling of block copolymers to balance high protein retaining and high clearance of middle and small molecular toxins, and demonstrates their superiority in hemodialysis performance and safety than conventional membranes.

Leaf-like ZIF-L as self-sacrificed template via acid induced removal for stronger negatively charged PES membranes based on RTIPS method

In this paper, ZIF-L was blended with citric acid (CA) and polyethersulfone (PES) to prepare a casting solution. A novel negatively charged ultrafiltration (UF) membrane (ZIF-L/CA/PES) was obtained using the reverse thermally induced phase separation (RTIPS) method. The hydrophilic carboxyl groups present in CA not only imparted high hydrophilicity and negative charge to the membrane surface, enhancing the membrane’s selectivity and contamination resistance, but also created an acidic environment to attack the Zn atoms in ZIF-L by the ionized H+ from CA, resulting in the generation of micro-defective pores and an improvement in permeability. Additionally, the results showed that membranes generated through the RTIPS process exhibit uniform porous surfaces and spongy cross-sections, enhancing membrane performance. The optimized membranes demonstrated the capability to achieve a pure water flux of up to 2267 L/m2h with 93.1 % humic acid (HA) retention, and a remarkable membrane flux recovery rate of 75.8 %, suggesting the crucial roles played by CA and ZIF-L in the separation process. In conclusion, hydrophilic anti-fouling UF membranes with a high negative charge and excellent permeation selectivity were fabricated by establishing micro-defective channels through the incorporation of carboxylic acid and ZIF-L, combined with the RTIPS process.

Porosity generation via spatially uncoupled dissolution precipitation during plagioclase replacement in quartz undersaturated fluids

The replacement of feldspars is commonly characterized by pseudomorphism and reaction-induced pore generation. However, the effects of compositions of feldspars and fluids on porosity generation during alteration are still poorly understood. In this study, we conducted a series of hydrothermal experiments on plagioclase replacement by 2 M KCl or NaCl aqueous solutions at 600 °C and 150 MPa for 1–8 days, using plagioclase with different compositions (anorthite, An96Ab4; labradorite, An66Ab33Or1; albite, An1Ab99) with or without quartz. Albite replacement by K-feldspar was not affected by the presence of quartz, whereas anorthite was unaltered in the quartz-absent fluid. The replacement of labradorite by KCl(aq) showed different results: in the presence of quartz, labradorite was altered by K-feldspar, whereas in the absence of quartz, alteration proceeded significantly with the generation of large pores hosted by secondary anorthite coupled with euhedral K-feldspar overgrowth. Such textural relationship and oxygen isotope-labeled experiments reveal that silica-deficient fluid enhances the uncoupled dissolution reprecipitation process. The Si and Al ions in the reacted aqueous solution diffused outside the labradorite grains and encountered K+-rich solutions to grow K-feldspar. The experiments with polycrystalline rocks composed of amphibole + labradorite using 2 M KCl aqueous solution indicated the replacement of labradorite grains by anorthite and K-feldspar overgrowth, as found in single-crystal experiments. Our results indicate that the silica concentration in the fluids has different influences on the saturation indices of albite, anorthite, and K-feldspars in saline fluids, which significantly affect the replacement textures and porosity generation in crustal rocks.

Operando scanning electron microscopy platform for in situ imaging of fluid evolution in nanoporous shale.

Fluid-solid interactions in nanoporous materials underlie processes fundamental to natural and engineered processes, including the thermochemical transformation of argillaceous materials during high-level nuclear waste disposal. Operando fluid-solid resolution at the nanoscale, however, is still not possible with existing optical and electron microscopy approaches that are constrained by the diffraction limit of light and by vacuum-fluid incompatibility, respectively. In this work, we develop an operando scanning electron microscopy (SEM) platform that enables the first direct in situ imaging of dynamic fluid-solid interactions in nanoporous materials with spatio-temporal-chemical resolutions of ∼2.5 nm per pixel and 10 fps, along with elemental distributions. Using this platform, we reveal necessary conditions for thermochemical pore and fracture generation in shales and measure their surface wetting characteristics that constrain the feasibility of high-level nuclear waste containment. Notably, we show that low heating-rate conditions typical of radioactive decay produce hydrocarbon liquids that wet fracture and pore surfaces in a self-sealing manner to impede aqueous radionuclide advection.

Pore Structure and Fractal Characteristics of the Middle and Upper Permian Dalong and Gufeng Shale Reservoirs, Western Hubei Province, South China

The Middle and Upper Permian Dalong and Gufeng Formations in South China have recently been considered as potential gas-producing shales. However, their pore structure characteristics remain poorly understood. To investigate the pore structure and fractal characteristics of the pores in these two formations, a suite of shale samples from the Dalong and Gufeng Formations in the western Hubei Province, South China were analyzed by multiple techniques, namely, TOC content, X-ray diffraction (XRD) mineralogy analysis, optical microscopy observations, major elemental analysis, field emission-scanning electron microscopy (FE-SEM), and low-pressure gas adsorption measurements (N2 and CO2). The identified major shale lithofacies include siliceous mudstone, carbonaceous mudstone, argillaceous-siliceous mixed mudstone, and calcareous-siliceous mixed mudstone. SEM images show that the dominant pore types include the pores between brittle minerals, slit-shaped pores between clay sheets, and secondary organic matter (OM) pores within solid bitumen. The pore size distribution is dominated by micropores and mesopores (<30 nm), which are the major contributors to total pore volume and surface area for the Dalong and Gufeng Formations. Based on the Frenkel–Halsey–Hill (FHH) method, fractal dimensions (D1, D2) calculated from the nitrogen adsorption data have a range of from 2.489 to 2.772 (D1) and from 2.658 to 2.963 (D2), and are higher in the Gufeng Formation (average TOC = 8.3 wt.%) due to a higher TOC content comparing to the Dalong Formation (average TOC = 6.2 wt.%). The pore development and fractal characteristics are primarily controlled by organic matter (OM), carbonate minerals, and clay minerals for both the Dalong and Gufeng Formations. Shale samples with high TOC content, low carbonate content, and high clay content tend to develop more heterogeneous micropores and mesopores, which is ascribed to the generation of clay-related and OM-hosted pores, along with the destruction of primary pores by pore-filling carbonate cements.

Reformation of coal reservoirs by microorganisms and its significance in CBM exploitation

The study investigates the variations in surface morphology and micro-nano-scale pore structure of coal matrix during the process of biodegradation. Comprehensive reservoir characterization techniques, including field emission scanning electron microscope, mercury intrusion porosimetry, and low-temperature N2 adsorption, are employed on four anthracite samples. The significance of the relationship between coal reservoir bio-reformation and coalbed methane (CBM) exploitation is proposed. The main findings indicate that organic matter on the surface of the coal matrix can undergo biodegradation, resulting in the generation of new pores. Microbial metabolism does not alter pore type but only modifies pore size and volume of coal. After microbial degradation, there is an increase in average pore width, while both Brunauer-Emmett-Teller specific surface area and Barrett-Joyner-Halenda pore volume decrease. Furthermore, bioconversion leads to a reduction in both surface and volume dimensions of coal, resulting in a smoother coal matrix surface and simplified complexity of its pore structure. This benefits desorption, migration, and exploitation of CBM. These findings further reinforce the pivotal role of microbial-enhanced coalbed methane production technology in improving CBM production and promoting the clean utilization of coal resources.

Pretreatment of pine needles via torrefaction, oxidation and hydrothermal carbonization at 250 °C impacts subsequent pyrolysis and activation in distinct ways

Thermal pretreatment of biomass in varied medium (i.e. nitrogen, air or water) might further impact pyrolysis and activation in distinct ways. Herein, hydrothermal carbonization (HTC) or torrefaction of pine needles in nitrogen or air at 250 °C and further pyrolysis/activation of pretreated samples was conducted. The results indicated yield of solid followed the method of pretreatment: torrefaction > oxidation > HTC, due to significant oxidation of aliphatics in the pretreatment in air and structural reconstruction in HTC. Additionally, pretreatment in air remarkably increased overall production of biochar (35.1 %), owing to enhanced resistivity to cracking. HTC released nearly half of organics, leading to remarkably lower overall yields of biochar than that in blank experiment (24.7 % versus 30.6 %), but increased thermal stability of biochar through enhancing aromatic degree. Additionally, pretreatment in air removed some H species via oxidation but not nitrogen species while the HTC was the opposite while induced leaching of inorganics. In-situ IR characterization indicated conversion of aliphatic -OH to phenolic -OH in nitrogen-pretreatment, oxidation of ether bridging bond between benzene rings in air-pretreatment and formation of thermally carbonyls via HTC. During activation, all the pretreatments reduced specific surface area of activated carbon, following the order: blank (1351.1 m2 g−1) > torrefaction in N2 (1314.7 m2 g−1) > oxidation in air (1293.8 m2 g−1) > HTC (1218.2 m2 g−1). Oxidation or aromatization reactions in the pretreatment increased aromatic degree of the feedstock, making pore generation via cracking more difficult. Besides, pretreatments also changed morphologies of resulting biochar or activated carbon in distinct ways.

Study on the effect of Ar–He shielding gas on the weld formation, microstructure and mechanical properties of 5083 aluminum alloy weld

In this paper, the ER5356 aluminum alloy wire was used for cold metal transfer (CMT) welding of the 5083-H111 base metal with 20 mm thickness. The effects of four shielding gases, which were 100%Ar, 75%Ar+25%He, 50%Ar+50%He and 100%He on the weld formation, microstructure and mechanical properties were investigated using optical microscope, scanning electron microscope (SEM), x-ray diffraction (XRD) and mechanical testing. The results showed that with the increase of He in the shielding gas, the weld penetration and width increased, and the porosity in the weld zone decreased significantly; the microstructure changed from coarse dendrites to fine equiaxed crystals, and the microstructure was gradually refined; the tensile strength of deposited metal increased from 220 MPa to 270 MPa, with an increase of 22.7%, the tensile fracture was quintessential ductile fracture, and the hardness increased from 64.2 HV to 68.4 HV. The addition of He in the shielding gas can effectively inhibit the generation of pores and promote the β-Al3Mg2 phase in the weld microstructure, thus improving the mechanical properties of the deposited metal.

Preparation of Ordered Nanostructures by Anodization of Ag Substrate with Depression Patterns

Nanostructures composed of Ag oxides are key materials with various potential applications such as sensors, catalysts, and batteries. We successfully fabricated nanohole array structures with an ordered arrangement of pores by anodizing a Ag substrate with a depression pattern in an ethylene glycol solution containing NH4F and KOH. Under these anodization conditions, each depression acts as a starting point for pore generation in the early stages of anodization. In addition, ordered nanopillar array structures were obtained by anodizing Ag substrates with depression patterns in ethylene glycol solution containing NH4F and CH3COONa. This is because the depressions formed by Ar ion beam irradiation act as masks during anodization, and the depressions remain during anodization, forming a nanopillar array structure. This is the first report on the fabrication of nanohole and nanopillar array structures by the anodization of a Ag substrate. In addition, this is the first report to show that ordered nanohole and nanopillar array structures can be fabricated by changing the electrolyte used for anodization. The Ag oxide nanostructures obtained by this process are expected to be applicable to various functional devices.

Underwater wet laser welding of duplex stainless steel under various water depths

Reports on experiments of underwater wet laser welding (UWLW) are scarce because of the poor forming quality of weldments. To address the key manufacturing challenges such as failure of welding with water depth exceeding 7 mm and the generation of pores and cracks which caused by the rapid water cooling, a specific self-designed flux assisted welding at different water depths (0–30 m) was innovatively proposed in this study. The microstructure, phase distribution, and properties of underwater wet laser welded duplex stainless steel joints were examined. The welding process successfully produced joints free from pores or cracks, even when performed within a 15 m water depth. In conjunction with thermodynamic calculation, the evolution process of welds and the effect of nickel from the flux on phases structure were analyzed. As the water depth increases and the welding speed decreases, the number of pores inside welds increase significantly, and no cracks are found. The penetration of all welds made in deep water is obviously smaller than that of shallow water and increased heat input does not seem to contribute to the increase of weld penetration. With the increase of water depth, a large amount of coarsened austenite consisted of columnar grains and cellular grains appear in weld zone. Texture and dislocation of the weld made in shallow water were investigated. Many dislocations including edge dislocations and dislocation entanglements arranged in austenite phase, while seldom dislocations appear in ferrite phase.

Role of delignification in water state changes during water absorption and air drying of wood characterized with LF-NMR

ABSTRACT Delignification, recently much used in wood modification and functional material preparation, is closely related to wood-water interactions. To attain more information on the role of delignification in wood, this study characterized the water state changes during water-absorption and air-drying process with LF-NMR. By adjusting delignification time, lignin was removed about 15%, 34%, and 61%, respectively. Water absorption increased after delignification, and free water was generated more and faster than bound water. This was because delignification changed wood-water interaction environments suggested by SEM and FTIR analysis. Specifically, delignification increased hygroscopic polysaccharide percentage and sorption site concentration. New pore generation and enlargement after delignification provided more water exchanging paths and accommodation. Besides, delignified wood had higher and faster moisture decrease, and wood air drying was facilitated because of enriched water exchanging paths and higher initial moisture gradient difference in water-saturated delignified wood. Therein, free water decreased more and faster than bound water. The T 2s of bound water and free water were both shortened after delignification, indicating water had tighter intermolecular interaction with delignified wood. The study provided new insight for understanding the role of lignin in water state changes during wood-water interactions and may facilitate better preparation of functional material and wood modification.