Surface Micropore Research Articles

Study on Boiling Heat Transfer Characteristics of Composite Porous Structure Fabricated by Selective Laser Melting.

Surface porosity is an important means of enhancing boiling heat transfer. In this paper, two kinds of composite porous structures of surface micropore + square channel and framework micropore + square channel were prepared by selective laser melting technology using AlSi10Mg as the powder material. The effect of composites with different pore forms on boiling heat transfer was investigated in pool boiling experiments. It was found that controlling the thickness of the powder layer manufactured by selective laser melting can change the surface roughness of the sample, and the sandblasting treatment reduced the surface roughness of the samples. The average heat transfer coefficient of the rough surface composite porous structure sample was increased by 40% compared to the sandblasted sample. The micropores on the surface of the sample and inside the framework significantly enhanced the heat transfer coefficient of the composite porous structure. The presence of surface micropores increased the heat transfer area and the vaporization core density of the composite porous structure and exhibited excellent heat transfer coefficient improvement in the low heat flux region. The framework microporous composite porous structure can form effective gas-liquid diversion at high heat flux and obtain higher heat transfer performance. The large channel in the composite porous structure is the key control factor of the critical heat flux.

Hygrothermal aging effects on fiber-metal-laminates with engineered interfaces

This short work is to communicate the influence of hygrothermal aging on the mechanical performances of fiber-metal-laminates (FMLs) with various ingenious metal surface treatments, namely, nano-scale electrochemical sculpture (NES), the conventional surface polishing (PS) and NaTESi anodizing (NaTESi). The specimens with different edge conditions were prepared using milling or wire-electrode cutting and subjected to hygrothermal aging treatment in a climatic test chamber at 60 °C and 96% relative humidity. Interlaminar shear and flexural testing results showed that the wire-electrode cutting method produced edges with exposed fibers and spalling resin after hygrothermal aging, while the milling cutting method resulted in edges with a micro-porous and defective surface, but without exposing fibers or spalling resin. The degree of reduction in interlaminar shear strength (ILSS) and flexural strength varied depending on the surface treatments and machining methods used. After undergoing hygrothermal aging, the wire-electrode cutting method causes a greater decrease in ILSS compared to the milling cutting method. This reduction is particularly pronounced in specimens with weaker interfacial bonding strength, in which the ILSS of wire-electrode cut FMLs-PS decreased by 32.5%, while that of FMLs-NES decreased by 17.8%.

3D Carbon Microspheres with a Maze-Like Structure and Large Mesopore Tunnels Built From Rapid Aerosol-Confined Coherent Salt/Surfactant Templating.

Hierarchically porous carbons with tailor-made properties are essential for applications wherein rich active sites and fast mass transfer are required. Herein, a rapid aerosol-confined salt/surfactant templating approach is proposed for synthesizing hierarchically porous carbon microspheres (HPCMs) with a maze-like structure and large mesopore tunnels for high-performance tri-phase catalytic ozonation. The confined assembly in drying microdroplets is crucial for coherent salt (NaCl) and surfactant (F127) dual templating without macroscopic phase separation. The HPCMs possess tunable sizes, a maze-like structure with highly open macropores (0.3-30µm) templated from NaCl crystal arrays, large intrawall mesopore tunnels (10-45nm) templated from F127, and rich micropores (surface area >1000 m2 g-1 ) and oxygen heteroatoms originated from NaCl-confined carbonization of phenolic resin. The structure formation mechanism of the HPCMs and several influencing factors on properties are elaborated. The HPCMs exhibit superior performance in gas-liquid-solid tri-phase catalytic ozonation for oxalate degradation, owing to their hierarchical pore structure for fast mass transfer and rich defects and oxygen-containing groups (especially carbonyl) for efficient O3 activation. The reactive oxygen species responsible for oxalate degradation and the influences of several structure parameters on performance are discussed. This work may provide a platform for producing hierarchically porous materials for various applications.

The Adsorption of Eriochrome Black T onto the Activated Carbon Produced from Pepper Stalks

The aim of this paper is to present the evaluation of the adsorption of Eriochrome Black T (EBT) on the activated carbon (trH-BS) produced from pepper stalk by activating with 50% phosphoric acid solution (H3PO4) and then by carbonizing at 650 oC for 30 min. in atmosphere of nitrogen (N2) was presented. The isotherm of trH-BS was Type IV, representing micro, meso and macroporous structures. The micropore volume and micropore surface area values of trH-BS were 0.39 cc/g and 1107.294 m2/g, respectively. Also, its meso and macropores had a volume of about 15-17 cc/g and an average surface area of 400 m2/g. The adsorption energy was 18.156 kJ/mol and the BET surface area was 756.257 m2/g. Depending on Langmuir parameters, monolayer capacity was determined as 55,56 mg/g. the enthalpy change was calculated as 30.78 kJ/mol. The structure of trH-BS was clarified structurally and morphologically and the formations like nano rod were seen at Scanning Electron Microscopy (SEM) images. By using trH-BS, the adsorption of EBT from the aqueous medium was investigated using 5 different parameters. As a result, it was found that the adsorbents obtained from pepper stalks are suitable for use in EBT adsorption with a ratio of about 50% under suitable conditions.

Liquids with Permanent Macroporosity.

Permanent macropores (>50 nm) had not been reported in the liquid state until a recent report by Tao Li and co-workers describing a synthetic strategy to form a porous liquid with dual micro-macroporosity. This is prepared by producing hierarchically porous particles that are surface coated and fluidised by dispersion. Surface micropores enable permanent porosity by steric exclusion of the fluid phase. The material has a considerable water uptake capacity (27 % w/w) due to large (480 nm) unoccupied macropores. This also enables switching of thermal conductivity on uptake of water. These are new properties translated from porous solids to the liquid state.

Liquids with Permanent Macroporosity

AbstractPermanent macropores (>50 nm) had not been reported in the liquid state until a recent report by Tao Li and co‐workers describing a synthetic strategy to form a porous liquid with dual micro‐macroporosity. This is prepared by producing hierarchically porous particles that are surface coated and fluidised by dispersion. Surface micropores enable permanent porosity by steric exclusion of the fluid phase. The material has a considerable water uptake capacity (27 % w/w) due to large (480 nm) unoccupied macropores. This also enables switching of thermal conductivity on uptake of water. These are new properties translated from porous solids to the liquid state.

Characterization, factors, and fractal dimension of pore structure of fly ash-based geopolymers

Fly ash-based geopolymer is a new cementitious material with environmentally friendly characteristics. Generally, the mechanical properties of cementitious materials are influenced by their pore structure. The variation in the pore structural characteristics of the geopolymers with various influencing factors was investigated in this study. A smaller activator modulus and liquid-solid ratio lead to a finer pore structure, while higher activator concentrations also result in a finer pore structure. However, the densification of pore structure does not follow a monotonic relationship with the conserving temperature. Increasing the conserving temperature within a certain range decreases the most probable pore diameter and porosity. Nevertheless, excessive temperature increase has the opposite effect. Furthermore, the fractal dimension was introduced to characterize the pore structure comprehensively. The results show that a lower pore volume, a larger pore-specific surface area, and a smaller most probable pore diameter contribute to increasing pore surface fractal dimension. Further, compared to porosity, the microporous pore surface fractal dimension shows a better linear correlation with compressive strength.

Nanocatalyst for carbon monoxide oxidation based on palladium(II), copper(II) salts, and carbon fiber material

The phase composition, textural, and activity of catalysts for the carbon monoxide low-temperature oxidation based on two series of non-woven carbon fiber material samples CFM-I and CFM-II, and K2PdCl4, Cu(NO3)2, KBr basic components were studied in this work. Catalysts and CFMs were studied by XRD, nitrogen and water vapor adsorption/desorption, and atomic absorption spectrophotometry methods. It has been found that the basic components K2PdCl4 and Cu(NO3)2 deposited on a microporous carbon surface undergo changes and form an X-ray amorphous Pd0 phase and a paratacamite—Cu2(OH)3Cl nanocrystalline phase. The catalysts were tested at carbon monoxide initial concentrations of 300 mg/m3 with an effective contact time of the catalyst with the gas–air mixture from 0.12 to 0.50 s. Catalysts provide air purification from CO to concentrations below MPCCO (20 mg/m3) and can be used in respiratory devices. The maximum catalytic activity is observed when the content of palladium in the catalyst is 1.70⋅10−4 mol/g and the content of copper (ІІ) is 4.68⋅10−4 mol/g.

Enhancement in pool boiling performance of GNP/Cu-Al2O3 nano-composite coated copper microporous surface

An experimental analysis of pool boiling is conducted on the GNP/Cu-Al2O3 (GNP-graphene nano particle) nanocomposite coated copper surfaces at atmospheric pressure using DI (distilled water) as boiling fluid. A two-step electro-deposition technique is used for fabrication of these micro/nano porous coated surfaces. A modified surface structure is formed due to this deposition and various surface morphology parameters such as surface structure, roughness, wettability are analysed. Results show the enhancement in BHTC (boiling heat transfer coefficient) and CHF (Critical heat flux) in nano composite coated surfaces compare to the bare copper surface. The maximum CHF of 2415 (kW/m2) and BHTC of 171.28 (kW/m2K) is found in the NCCS (nano-composite coated superhydrophilic) surfaces which are 122% and 239% more than the bare copper surfaces. The boiling performance is augmented mainly because of the improvement in roughness, wettability and also for the high thermal conductivity of the GNP/Cu- Al2O3 nano coating. Quantitative study of the bubble dynamics like active nucleation site density, bubble emission frequency, departure diameter of bubbleand their impact on heat transfer performance in the case of NCCS surfaces is performed with high-speed visualization.

Enhanced SO2 adsorption performance on nitrogen-doped biochar: Insights from generalized two-dimensional correlation infrared spectroscopy

Nitrogen-doped biochar is considered as a renewable, cost-effective, and promising SO2 adsorbent. However, it is difficult to improve the physicochemical properties of biochar synergistically and clarify the adsorption mechanism. Therefore, in this study, a one-step high-temperature CO2-NH3 modification method was proposed for biochar to improve its SO2 adsorption, and the in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (in situ DRIFTS) was used to reveal the interface reaction mechanism between SO2 and nitrogen-doped biochar. The results showed that when the modification temperature exceeded 700 °C, CO2 and NH3 exhibited significant thermal activation and nitrogen doping on biochar simultaneously. Under a modification temperature of 800 °C (BCAN-800), the microporous surface area and nitrogen content of modified biochar reached the highest value of 563.83 m2/g and 6.63 wt%. The SO2 adsorption capacities of BCAN-800 were up to 201.89 mg/g and 145.68 mg/g at 30 °C and 120 °C, respectively. The results of in situ DRIFTS showed that dimeric and bridge hydrogen bonds were the main SO2 adsorption sites on nitrogen-doped biochar at 30 °C. With the increase of adsorption temperature, nitrogen-containing groups as the main adsorption site could combine with SO2 to form sulfamide (60 °C), which eventually existed in a more stable form of SO42−/R-O-SO2-OR′ (120 °C).

Adsorption of CO2, CO, H2, and N2 on Zeolites, Activated Carbons, and Metal-Organic Frameworks with Different Surface Nonuniformities

The single-component adsorption of CO2, CO, N2, and H2 at 25 and 35 °C was studied using microporous faujasite-framework zeolites (NaY and NaX), activated carbons (GCN and MSP), and metal–organic frameworks (A100 and Z1200) as starting points for the separation of CO2 from syngases produced by gasifying biomass-based solid wastes. The indicated adsorption isotherms and uptake of the adsorbates strongly depended on the adsorbates themselves as well as on the adsorbents because of significant differences in the surface features, such as surface nonuniformity, and in the molecular properties. The selectivity of CO2 to the other gases also varied with the adsorbents due to the distinctive energetic characteristics. The surfaces of the zeolites were the most energetically heterogeneous ones, yielding higher CO2 uptake at low pressures, while the two activated carbons and A100 had moderate surface heterogeneities, and MSP showed the highest CO2 uptake at high pressures, such as 6 bar, at which the micropore volume and surface area are important. Z1200, which has highly homogeneous surfaces and no high-affinity-binding sites, exhibited the lowest CO2 adsorption capacity regardless of equilibrated pressure. The surface nonuniformities of the six sorbents were consistent with the calculated isosteric heats of CO2 adsorption. CO2 could be reversibly adsorbed on NaY and MSP but not on GCN, with some metal impurities, although all these adsorbents showed a fully reversible process for CO adsorption. The estimated working capacity for CO2 adsorption at 25 °C was 0.78–6.50 mmol/g, depending on the sorbents used. The highest value was disclosed for MSP, the surface energetic heterogeneity of which was between that of zeolites and Z1200. Such a high working capacity bodes well for use in our later applications.

Exploring the Charge Storage Dynamics in Donor-Acceptor Covalent Organic Frameworks Based Supercapacitors by Employing Ionic Liquid Electrolyte.

Two donor-acceptor type tetrathiafulvalene (TTF)-based covalent organic frameworks (COFs) are investigated as electrodes for symmetric supercapacitors in different electrolytes, to understand the charge storage and dynamics in 2D COFs. Till-date, most COFs are investigated as Faradic redox pseudocapacitors in aqueous electrolytes. For the first time, it is tried to enhance the electrochemical performance and stability of pristine COF-based supercapacitors by operating them in the non-Faradaic electrochemically double layer capacitance region. It is found that the charge storage mechanism of ionic liquid (IL) electrolyte based supercapacitors is dependent on the micropore size and surface charge density of the donor-acceptor COFs. The surface charge density alters due to the different electron acceptor building blocks, which in turn influences the dense packing of the IL near its pore. The micropores induce pore confinement of IL in the COFs by partial breaking of coulomb ordering and rearranging it. The combination of these two factors enhance the charge storage in the highly microporous COFs. The density functional theory calculations support the same. At 1 A g-1 , TTF-porphyrin COF provides capacitance of 42, 70, and 130 F g-1 in aqueous, organic, and IL electrolyte respectively. TTF-diamine COF shows a similar trend with 100 F g-1 capacitance in IL.

Development of Hydrogen-Oxygen Fuel Cells Based on Anion-Exchange Electrolytes and Catalysts with Reduced Platinum Content.

Studies have been carried out to optimize the composition, formation technique and test conditions of membrane electrode assemblies (MEA) of hydrogen-oxygen anion-exchange membranes fuel cells (AEMFC), based on Fumatech anion-exchange membranes. A non-platinum catalytic system based on nitrogen-doped CNT (CNTN) was used in the cathode. PtMo/CNTN catalysts with a reduced content of platinum (10-12 wt.% Pt) were compared with 10 and 60 wt.% Pt/CNTN at the anode. According to the results of studies under model conditions, it was found that the PtMo/CNTN catalyst is significantly superior to the 10 and 60 wt.% Pt/CNTN catalyst in terms of activity in the hydrogen oxidation reaction based on the mass of platinum. The addition of the Fumion ionomer results in minor changes in the electrochemically active surface area and activity in the hydrogen oxidation reaction for each of the catalysts. In this case, the introduction of ionomer-Fumion leads to a partial blocking of the outer surface and the micropore surface, which is most pronounced in the case of the 60Pt/CNTN catalyst. This effect can cause a decrease in the characteristics of MEA AEMFC upon passing from 10PtMo/CNTN to 60Pt/CNTN in the anode active layer. The maximum power density of the optimized MEA based on 10PtMo/CNTN was 62 mW cm-2, which exceeds the literature data obtained under similar test conditions for MEA based on platinum cathode and anode catalysts and Fumatech membranes (41 mW cm-2). A new result of this work is the study of the effect of the ionomer (Fumion) on the characteristics of catalysts. It is shown that the synthesized 10PtMo/CNTN catalyst retains high activity in the presence of an ionomer under model conditions and in the MEA based on it.

Promotion effect of cerium in ZSM-22 zeolite on the hydroisomerization of n-hexadecane

The study fabricated ZSM-22 zeolites with Ce/Al molar ratios ranging from 0 to 1, which were subsequently loaded with Pt to perform n-hexadecane hydroisomerization. Various methods, such as XRD, 29Si NMR, FTIR, UV–Vis, XPS, and H2-TPR, confirmed the direct evidence of Ce incorporation into the zeolite framework, and the framework Ce content was of a volcanic nature. Furthermore, the study observed successful manipulation of textural and acidity properties of the samples through variation of the Ce content, as shown by N2-physisorption, NH3-TPD, and Py-IR. Increasing Ce content led to retardation of micropore diffusion due to lower micropore volume and surface area, as well as an increase in the distribution of weak Brønsted acid sites, which suppressed outside-of-pore cracking reactions. These changes rendered improved i-hexadecane selectivity and catalyst stability for Pt/ZSM-22. At a Ce/Al molar ratio of 0.5 with a WHSV of 12 h−1, the high selectivity to monobranched isomers resulted in a yield exceeding 75 wt%.

Modeling of monolayer water adsorption on surface of cement minerals by molecule simulation and adsorption isotherm

The performance of water on the pore surface governs the mechanical properties and durability of cementitious materials and structures. As a fundamental mechanism, the interaction between water and cementitious mineral micropore surfaces behaves differently under various circumstances, which can be investigated by molecular simulation methods in detail. Molecular simulations based on Grand Canonical Monte Carlo method were performed to obtain the water vapor adsorption isotherms on the surface of tricalcium silicate (C3S) and calcium hydroxide (CH), which are selected as typical cement mineral and hydration product respectively. The adsorption behavior of C3S and CH is compared by the adsorption energy and adsorption isotherm model. The condensation processes were explained by the Kelvin equation. The critical pore sizes of C3S and CH for condensation are 19 Å and 15 Å respectively. Beyond the critical pore size, water adsorption shows monolayer adsorption performance. The water adsorption process on the surface includes three stages: rapid adsorption, stable adsorption and slightly condensed adsorption, which are related to the surface interaction of minerals with water molecules. The Langmuir model is more suitable for the CH with homogeneous surface, while the Freundlich model is more suitable for the C3S model with nonhomogeneous surface. The adsorption heat of the first layer of water film and adsorption energy on the surface of CH are higher.

Highly microporous and mesoporous nanomaterials derived from Agave sisalana waste for supercapacitors

AbstractNanostructured electrodes with large surface area are essential for studying charge storage mechanisms in supercapacitors. Biomass‐based carbonaceous porous electrodes have proven to be good candidates for supercapacitor application. In this study, micropore and mesopore dominated carbon materials derived from Agave sisalana sisal waste were prepared through carbonization and chemical activation with ZnCl2. Scanning electron microscopy, energy‐dispersive X‐ray, transmission electron microscopy, Raman spectroscopy, and X‐ray diffraction studies show that the microstructure and composition of the as‐prepared microporous carbon materials are influenced by adjusting the ZnCl2 to the carbon mass ratio. Sorption studies demonstrated a high Brunauer–Emmett–Teller (BET) surface area of 1464 m2 g−1, type I isotherms for low temperature, type IV at 900 °C, and 99% micropore content in all the samples. The fabricated electrodes exhibited high specific capacitances of 497 F g−1at 5 mV s−1, which is indicative of our carbon materials’ strong potential for use in the production of high‐performance supercapacitors. Specific capacitance increased with increasing micropore surface areas.

A Multiscale Strategy for Constructing Finned Microporous Superhydrophobic Surface for Highly‐Efficient Condensation Heat Transfer Enhancement Enabled by Lifespan Regulation of Droplets

AbstractSpontaneous droplet jumping on micro‐/nano‐structured superhydrophobic surfaces has been exploited as an efficient means for enhancing steam condensation heat transfer. However, the good performance of such surfaces quickly decays with raising the degree of subcooling, due to the mismatch between the characteristic length scales and droplet sizes when they grow up. Herein, a novel strategy for multiscale droplet regulation is proposed by combining sub‐millimeter fin structure with a hierarchical microporous superhydrophobic surface. A superior condensation heat transfer performance is attained on such hierarchical superhydrophobic finned tube (F‐SHB), in comparison to the baseline case of superhydrophobic non‐finned (SHB) tube under well‐controlled test conditions. Although the droplet jumping is not as vigorous as that on the SHB tube, the finned geometry of the F‐SHB tube leads to a condensation heat transfer enhancement even under high degrees of subcooling up to 36 K, because of the accelerated departure of large droplets by imposing Laplace force gradient in the presence of V‐shaped sub‐millimeter fins. This multiscale enhancement strategy is shown to enable a cascading regulation over the entire lifespan of condensate droplets. The fabrication of F‐SHB tubes is facile and easy to be scaled up, showing great potential in practical steam condensation applications.

Enhanced Embedding of Cations into Titanium Surfaces by AC Plasma Electrolytic Oxidation for Osteointegrated Implants

Titanium and its alloys represent the gold standard for osteointegrated implants, but their characteristic bioinertness still hinders their optimal integration within the host tissues. This limitation can be overcome by introducing osteoinductive functionalities on their surface. Plasma electrolytic oxidation (PEO) has emerged as a cost‐effective and rapid electrochemical method for generating bioactive titanium dioxide (TiO2) coatings, but the incorporation of pro‐osteogenic cations with this technique is typically passive and, in turn, characterized by a low efficiency. Here, alternate current (AC) PEO is investigated as a flexible solution to incorporate zinc into TiO2 coatings by exploiting the active transport of cations during the cathodic phase of the process. The resulting microporous surfaces show a greater zinc incorporation and an increased presence of rutile domains compared to conventional direct current (DC) PEO coatings, without, however, yielding significant morphological differences. In vitro assays with human mesenchymal stem cells (hMSCs) reveal an increased metabolic activity of cells adhering onto AC PEO surfaces. In addition, the increased expression of osteogenic differentiation markers (RUNX2 and osteocalcin) indicates significant surface‐driven osteoinductive effects, particularly for coatings grown by applying a short cathodic spike. Taken together, these aspects make Zn‐doped AC PEO surfaces a promising solution for osteoinductive orthopedic and dental applications.

Secondary Instabilities in Supersonic Boundary Layers over Microporous Surfaces

Secondary Instabilities in Supersonic Boundary Layers over Microporous Surfaces

Sequestration and utilization of carbon dioxide to improve engineering properties of cement-based construction materials with recycled brick powder: a pathway for cleaner construction

The research explores the possibility of utilizing carbon dioxide to modify the properties of recycled brick powder (RBP) and enhance the engineering performances of RBP-mortar. The RBP, crushed to the size range of 0.075 to 4 mm, is carbonated by exposing to 5% CO2 for 4 h and characterized for phase composition, porosity and micro-structure. The non-carbonated RBP (RBP) and pre-carbonated RBP (Carb-RBP) are applied to replace 25% and 75% of manufactured sand (M-sand) in cement mortars maintained at similar flow level (110 – 113%), which are then cured under three conditions - (i) ambient condition (N), (ii) 4 h of steam curing followed by moist and dry curing (STC), and (iii) accelerated CO2 curing (5% CO2 of 99% purity) for 4 h followed by moist curing and dry curing (CC). Physico-chemical characterizations suggest that Carb-RBP has higher micro-pore volume and surface area contributed by pores in the size range of 1 nm to 3 nm than RBP. After carbonation, the reactivity of RBP in alkaline environment is increased due to CO2-induced breakdown of calcium and alumino-silicate minerals into calcium carbonate and silica gel. Due to addition of 25% and 75% RBP and Carb-RBP, hydration kinetics is accelerated by 4 – 4.50 h compared to control due to nucleation of hydration products on the surfaces of RBP. Faster precipitation of hydration products, more micro-pore sites in RBP and higher porosity due to increased water demand enhance the carbon sequestration in RBP-mortars and Carb-RBP mortars by 30–82% compared to control (0% RBP). Use of Carb-RBP to replace 25% of M-sand offer similar compressive strength as control and 19 – 21% higher strength than mortars with RBP (non-carbonated). CO2 curing also reduces the total shrinkage of mortars with recycled brick powder by 12 – 17% compared to ambient curing and steam curing due to densification by calcium carbonate crystals. The findings from this research strongly suggests a significant reduction in embodied carbon of Portland cement-based construction materials by utilizing a combined approach of carbon sequestration and replacement of fine aggregates by recycled brick powder.