Pore-forming Agent Research Articles

Controllable preparation and properties of gel-casting porous mullite ceramics via lignin fiber assisted pore formation method

The preparation of high-strength porous mullite via gel-casting has emerged as a hot topic, but balancing high strength and high porosity remains challenging. Herein, we successfully prepared porous mullite with uniform pore size and high strength using natural lignin fibers as the pore-forming agent via gel-casting. Moreover, we investigated the properties of mullite slurries, as well as green bodies and sintered ceramics in details. The strong water transport capacity of the lignin fibers enabled the homogeneous dispersion of gel system and improved the flowability of slurry. The flexural strength of green body was significantly increased to 16.07 MPa by optimizing the lignin fiber content. Porous mullite ceramics sintered at 1400 °C exhibited a homogeneous microstructure with average pore size of 5.62 μm. Furthermore, mullite ceramics had a porosity of 64.73% at a total solid loading of 55 wt% and a lignin fiber content of 10 wt%, whereas the compressive strength remains high at 11.32 MPa. Permeability tests confirmed the presence of interconnected pores, its coefficients k1 and k2 increases with the total porosity of ceramics. This work provides new insights into designing the preparation of porous mullite ceramics with high performance.

A digital light processing 3D printing approach for tuning the interfacial properties of pore forming agents for porous ceramics

The utilization of pore forming agents (PFAs) in digital light processing (DLP) 3D printing to manufacture porous ceramics through their thermal decomposition has received a great deal of attention. Nevertheless, even though the inner PFA microstructure of a green body is an essential precondition for tailoring the properties of porous ceramics, the approaches established to date have only focused on post-processing. To address this gap, the present study demonstrates a novel DLP approach to elucidate how PFAs are formed in green bodies during DLP 3D printing. Specifically, complex UV light scattering patterns that are common in composite DLP 3D printing and often detrimental were exploited to modify the interface between PFA and the ceramic-polymer matrix. This was done through modulation of the size difference between ceramics and PFAs as well as the DLP's process parameters. Additionally, a method for inferring the interfacial properties of PFAs embedded in a green body through surface characterization is proposed.

Pore Forming Agent–Assisted Fabrication of Porous Platinum Vent Frits and Their Suitability Evaluation for Radioisotope Power Sources

Disc-shaped porous platinum sintered frits were fabricated employing a pore forming agent (PFA) via a powder-metallurgical process. Porous vent frits using several platinum-PFA compositions were prepared after characterizing the starting materials (platinum and PFA powders) for particle size (D50) and distribution (D10 to D90), morphology, Brunauer-Emmet-Teller surface area, density (apparent and tap), etc. The sintered platinum vent frits were extensively characterized to evaluate their suitability for application in terms of surface microstructure analysis by scanning electron microscopy, helium/air permeability parameters, and particulate filtration characteristics. This paper reports for the first time on the measurement of retention efficiency of vent frits for particulate sizes 0.3, 0.5, and 1 µm. The platinum frits made using 10 and 20 vol % PFA were found to be suitable as a vent hole filter for radioisotope power sources.

Effects of a hierarchical pore structure on the tribological properties of an oil-containing iron-based composite

Oil-containing materials depend on micropore structures to store lubricating oil. However, the micropore structure, an important component of such materials, is difficult to control. Herein, a porous iron-based oil-containing material was successfully prepared via powder metallurgy with TiH2 and polyamide 66 short fiber as dual pore formers. Scanning electron microscopy observations and analyses indicated that the complementary effect of dual pore formers enabled the formation of an interconnected hierarchical pore structure with two pore types, which not only provided abundant oil storage spaces but also facilitated the transfer of oil within the materials. Based on ring-on-block friction and wear tests, the iron-based oil-containing composite presented a low coefficient of friction (about 0.078) under a contact pressure of 1.2 MPa.

Boosting activity on copper functionalized biomass graphene by coupling nanocrystalline Nb2O5 as impressive rate capability for supercapacitor and outstanding catalytic activity for oxygen reduction

A novel and hierarchical porous but cross-linked copper-doped biomass graphene (Cu@HPBG) combined with Nb2O5 (denoted as Nb2O5/Cu@HPBG) is successfully fabricated on a large-scale using fig peels as biomass carbon and copper as the graphitization catalyst. During the synthesis process, basic copper carbonate serves dual functions of pore-forming agent, as well as homogeneous copper provider, and NH3 is employed as a defect-forming agent and N dopant. Owing to the porous hierarchical structure increased availability of contact interface and pseudo capacitance active sites provided by copper and Nb2O5, the assembled asymmetrical supercapacitor (ASC) employing Nb2O5/Cu@HPBG as positive electrode and HPBG as negative electrode can not only widen the stability window range of 0～1.9 V, but also deliver a maximum gravimetric energy density of 82.8 W h kg−1 at the power density of 950.0 W kg−1 and maintain a remarkable cycling stability of 97.1% after 15,000 cycles. Impressively, due to the synergistic enhancement of Cu@HPBG and Nb2O5, the resulting Nb2O5/Cu@HPBG hybrid displays more positive half wave potential (∼0.85 V) and a long-life stability than Pt/C electrode toward oxygen reduction reaction (ORR). Our research provides a feasible strategy to fabricate renewable biomass graphene electroactive composites for large-scale supercapacitor electrodes and efficient ORR catalysts toward energy applications.

Enhancing thermal insulation and mechanical strength of porous ceramic through size-graded MA Hollow Spheres

In this study, a series of porous ceramics were prepared using different ratios of small and large size MA hollow ceramic spheres as pore-forming agents, and their thermal insulation properties were investigated. The results showed that increasing the proportion of small size hollow ceramic spheres could effectively decrease the thermal conductivity and improve the compressive strength of the porous ceramics. The optimal porous ceramic was prepared with a ratio of 10∼50 of small and large size hollow ceramic spheres, which had a thermal conductivity of 0.368 W/(m·K) at 800 °C and a compressive strength of 22.43 MPa. Microscopic analysis indicated that the enhanced thermal insulation and mechanical properties were due to the improved pore structure and the enhanced bonding strength between the ceramic spheres and the matrix. The findings provide valuable insights for the development of high-performance thermal insulation materials.

Preparation of Coal Gangue-Based Porous Ceramics and Its Application on Pb2+ Cycling Adsorption

The presence of lead in wastewater poses a significant threat to human health. To address this issue, coal gangue-based porous ceramics (CGPC) were developed to remove Pb2+ in wastewater. Coal gangue (CG) waste from Lvliang City, Shanxi province in China was used as raw material, and porosity was introduced through the addition of a pore-forming agent and an extrusion molding process. Properties of CGPC were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area analysis, Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) to explore its adsorption mechanism. The researchers examined the impact of pH, dosage of adsorbent, initial concentration, duration of adsorption, and temperature on the adsorption efficiency of CGPC. The CGPC of best performance had a porosity of 32.91% and compressive strength of 20.5 MPa prepared at 800 °C under nitrogen atmosphere with 10 wt% Na2CO3 pore-forming agent and 8 wt% CaO-MnO2 combined fluxing agent. The removal rate of Pb2+ in simulated lead-containing wastewater with a concentration of 200 mg/L reached 99.63%, and the maximum adsorption capacity was 32.15 mg/g. The adsorption process of Pb2+ by CGPC involves chemical adsorption and ion exchange. After being regenerated for seven cycles with 1 mol/L NaOH as the desorption agent, the removal rate of Pb2+ by CGPC still had 72%.

Conversion of agricultural waste to porous hydrochar for non-metallic activation of persulfate to phenol degradation via non-radical-dominated processes: Singlet oxygen and electron transfer

Recently, non-radical oxidation was served as an efficient approach during pollutant degradation due to its excellent environmental applicability. However, designing a green and low-cost non-metallic catalyst to activate persulfate (PS) for removal of hazardous organic contaminants via non-radical-dominated processes is still challenging. Herein, porous hydrochar (PHC) was synthesized with agricultural waste of corn straw (CS) as precursor and KHCO3 as pore-forming agent, which contained mesoporous structures with defects, thus facilitating phenol adsorption (117.14 mg/g). Moreover, 20 mg/L of phenol could achieve 100% removal at a wide pH range (7.0–11.0) within 10 min by PHC/PS system. The radical pathways induced by O·H and O2·− had certain effect on phenol removal, while non-radical pathways (1O2 and electron transfer process) played dominant contributions. Among them, 1O2 was produced from the reaction between surface functional groups on PHC and PS, and electron transfer process occurred from phenol to PS via PHC as the conductor. Whether under the interference of co-existing substances or in different water matrixes, the degradation efficiency of phenol could reach above 80%, exhibiting the excellent adaptability of PHC/PS system. This study proposed a potential resource utilization method of agricultural waste to prepare non-metallic catalyst for effective water remediation.

W-doped Lanthanum Molybdenum Oxide/Lithium-Sodium-Potassium Carbonate Composite Membranes for Carbon Dioxide Permeation.

Single-phase tungsten-doped lanthanum molybdenum oxide (La2MoWO9) ceramic powders were synthesized using the complex polymerization technique. Porous ceramic pellets were obtained by thermally removing graphite, which served as a pore former. The porous pellets were then impregnated with molten eutectic lithium-sodium-potassium carbonates. The energy dispersive X-ray analysis and scanning electron microscopy (FEG-SEM) images of the external and fracture surfaces of the La2MoWO9-(Li,Na,K)2CO3 composite dual-phase membrane revealed the percolation of the carbonate mixture through the pores. Electrochemical impedance spectroscopy measurements conducted at temperatures below and above the melting point of the eutectic carbonate composition demonstrated the contributions of oxygen and carbonate ions to the ionic conductivity of the dual membrane. The electrical conductivity of the carbonate ions within the membrane was continuously monitored for over 1300 h with negligible degradation, implying that the membrane could be used for long-term monitoring of CO2 without aging effects. A comparison of FEG-SEM images taken before and after this endurance test suggested minimal fouling, indicating that the membrane could potentially replace similar zirconia- and ceria-based composite membranes.

Effect of boric acid coating on the electrical, thermal, mechanical and oxidation-resistant properties of coke derived carbon foam

In this study, carbon foams with high oxidative resistance were fabricated by employing a powder metallurgy route using semi-coke as a carbon precursor and ammonium bicarbonate as a pore-forming agent. The boric acid was used as an oxidative inhibitor. The effect of boric acid coating on the surface of carbon foam was extensively analyzed and compared with pure carbon foam. The oxidation resistance of boric acid-coated carbon foam (CF70BA) demonstrated very good thermal stability at 650 °C in the air for a period of 3 h, along with good compressive strength as compared to pure carbon foam. The resultant boric acid-coated carbon foam exhibit a high electrical conductivity of 437 S/cm and high thermal conductivity of 9.5 W/m.K. All the results revealed that this approach established a new simple and affordable concept for the development of lightweight carbon material with high oxidation resistance performance.

Regulating cathode surface hydroxyl chemistry enables superior potassium storage

Potassium vanadium fluorophosphate (KVPO4F) is regarded as a promising cathode candidate for potassium-ion batteries due to its high working voltage and satisfactory theoretical capacity. However, the usage of electrochemically inactive binders and redundant current collectors typically results in inferior electrochemical performance and low energy density, thus implying the important role of rational electrode structure design. Herein, we have reported a scalable and cost-effective synthesis of a cellulose-derived KVPO4F self-supporting electrode, which features a special surface hydroxyl chemistry, three-dimensional porous and conductive framework, as well as super flexible and stable architecture. The cellulose not only serves as a flexible substrate, a pore-forming agent, and a versatile binder for KVPO4F/conductive carbon but also enhances the K-ion migration ability. Benefiting from the special hydroxyl chemistry-induced storage mechanism and electrode structural stability, the flexible freestanding KVPO4F cathode exhibits high-rate performance (53.0% capacity retention with current densities increased 50-fold, from 0.2 C to 10 C) and impressive cycling stability (capacity retention up to 74.9% can be achieved over 1,000 cycles at a rate of 5 C). Such electrode design and surface engineering strategies, along with a deeper understanding of potassium storage mechanisms, provide invaluable guidance for better electrode design to boost the performance of potassium-ion energy storage systems.

Fabrication of PVDF ultrafiltration membrane using modified thermally induced phase separation: The role of amphiphilic and hydrophilic non-solvents

The use of amphiphilic pore formers and hydrophilic non-solvents has demonstrated its effectiveness in improving the surface porosity and permeability of polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes through the nonsolvent induced phase separation (NIPS) process in literatures. However, in the thermally induced phase separation (TIPS) process, few reports illustrated how the amphiphilic pore-former and water-soluble non-solvent interact with water-insoluble diluents. In this study, water-insoluble dimethyl phthalate (DMP) was used as the main diluent to rule out the effect of diluent outflow. The amphiphilic pore former polyethylene glycol 400 (PEG400) failed to open pores on the outer surface of the membranes because of its amphiphilic nature. On the contrary, UF membranes with a mean pore size of 55 nm could be obtained by adding hydrophilic triethylene glycol (TEG) to the dope with a satisfactory pure water permeability (PWP) of 262.6 L m−2 h−1 bar−1. Moreover, PEG400 can serve as a stabilizer for the TEG droplets during the phase separation if both were added to the polymer dope solution. The addition of both PEG400 and TEG could significantly increase the membrane's PWP to 645.4 L m−2 h−1 bar−1 with moderate enlargement of the mean pore size of the membrane to 84 nm. Additionally, the well-connected membrane structure resulted in the tensile strength of the membranes ranging from 3.07 to 6.65 MPa. This study expands the range of additives used in the TIPS process and demonstrates the different roles of amphiphilic and hydrophilic non-solvents in the TIPS process.

Preparing ceramic membranes for oil-in-water emulsions separation with oil-based drilling cutting pyrolysis residues (ODPRs) as raw material

Oil-based drilling cutting pyrolysis residues (ODPRs) are one of the solid wastes from pyrolysis of the oil-based drilling cuttings (OBDCs) that need to be recycled as raw materials to avoid the possible pollution. In this study, a facile low-cost ceramic membrane for oil-in-water emulsions separation was prepared with ODPRs incorporating with fly ash as raw material. CaCO3 in ODPRs would decompose acting as pore-forming agent, and anorthite was formed in resultant membranes. The obtained membrane with 30 wt% ODPRs and 70 wt% fly ash fired at 1050 °C possessed apparent porosity of 38.2%, mean pore size of 0.4 μm, flexural strength of 13.1 MPa, and Darcy permeability of 1.06 × 10−13 m2. Consequently, commendable filtration performance for oil-in-water emulsions was presented. In addition, the ceramic membrane showed favorable recyclability and corrosion resistance. Leaching test indicated that the membrane is safe for oil-in-water emulsion separation. Hereby, this paper confirmed the availability of ODPRs for preparing ceramic filtration membranes, and provided a new environmental conservation way to treat oil-in-water emulsions that was consistent with the sustainable development goals.

From weed to N/O/S co-doped honeycomb-like porous carbon for high-performance supercapacitors: a facile and friendly one-step carbonization

Recent research interest has increased in the production of heteroatoms-doped porous carbon with controlled morphology from biomass. However, there is still a significant challenge in resolving alkaline solutions that cause equipment corrosion and devising a simple and adaptable approach. In this study, N/O/S co-doped honeycomb-like porous carbons were synthesized from a widely cultivated annual weed (Hemistepta Iyrata Bunge) using a simple and eco-friendly method. The sodium hydroxide (NaOH)/urea system was utilized as the pore-forming agent and cellulose solvent, with urea as the nitrogen source. By varying the activation temperature, the as-prepared porous carbon has a high specific surface area (709 m2 g−1), a large total pore volume (0.44 cm3 g−1), and a high heteroatom content of 6.20 at% nitrogen and 8.12 at% oxygen. The prepared porous materials were evaluated as electrodes for supercapacitors. The product (HIB-PHC-750 °C) exhibited a high specific capacitance (353.6 F g−1 at 0.2 A g−1) at a carbonization temperature of 750 °C. Additionally, the HIB-PHC-750 °C-based symmetric device with a wide voltage range of 2.0 V possessed a desirable energy density of 44.22 Wh kg−1 at 500 W kg−1. Moreover, the HIB-PHC-750 °C also demonstrated outstanding cycling stability with 98.2 % capacitance retention after 10,000 cycles. This research provided a facile and favorable alternative method for preparing N/O/S co-doped honeycomb-like porous carbon for electrochemical energy storage devices.

Fabrication and petrophysical characterization of artificial carbonate rocks with multiscale porosity sintered in a CO2 atmosphere

Carbonate rock samples are used in research related to enhanced oil recovery, acid stimulation, calibration of well-logging tools, and validation of numerical petrophysical simulations. However, natural carbonates samples are extremely heterogeneous and have limited availability, compromising experimental analyses. Furthermore, the previous attempts to fabricate synthetic rock replicas were unable to produce samples with pure calcium carbonate composition and multiscale porosity. This paper presents the fabrication of artificial rock with pure calcite composition. Calcite powder was compacted with a pore former (ammonium bicarbonate) and sintered at 850 °C with CO2 atmosphere to avoid the decomposition of the CaCO3. Five groups of samples were produced: partially sintered, sintered with 5, 10, and 20% of the large porogen, and with 20% of the small porogen. The artificial rocks were characterized through X-ray diffraction, porosimetry, X-ray microtomography, scanning electron microscopy, mercury injection, permeability, nuclear magnetic resonance, mechanical compression, and acidizing core flooding experiments. The results revealed that the artificial rocks have a controlled bimodal porosity, with large pores induced by the pore formers (83–211 μm) and nanometric intrinsic pores and fractures. In addition, the samples presented a high mechanical resistance (40 to 126 MPa), similar to natural rocks, and could withstand water immersion and even the core flooding tests. The main drawback was the low permeability (0.05–0.06 mD) achieved, an aspect to be improved in future works. The reported methodology is a significant advance because it allows independently tuning the porosity and pore size distribution, controlling the resultant petrophysical properties in a reproducible way without compromising the chemical constitution, enabling several applications in research.

Influence of the content of polymethyl methacrylate on the properties of porous Si3N4 ceramics fabricated by digital light processing

Porous Si3N4 ceramics are highly regarded as ideal materials for radomes due to their unique characteristics. However, the slurry used for the preparation of porous Si3N4 ceramics suffers from a low cure depth, making it challenging to fabricate ceramic components using DLP technology. In this study, porous Si3N4 ceramics were prepared by combining DLP technology with pore-forming agent method. The addition of polymethyl methacrylate (PMMA) powders with lower refractive index than that of Si3N4 powders can improve the penetration depth of ultraviolet light in the Si3N4 slurry. A systematic study was conducted to investigate the influence of the addition of PMMA powders on the properties of Si3N4 slurries and porous Si3N4 ceramics. When PMMA powders were added at 10 wt%, the slurry with a lowest viscosity of 0.13 Pa s (the shear rate is 30 s−1) and cure depth of 40.0 μm (the exposure energy is 600 mJ/cm2) was obtained. With the increase of PMMA content, porous Si3N4 ceramics experienced a gradual decrease in both the flexural strength and bulk density, while the porosity increased from 14.41% to 27.62%. Specifically, when 20 wt% PMMA was added, the resulting porous Si3N4 ceramics had a lowest bulk density (2.41 g/cm3), a maximum porosity (27.62%), and a flexural strength (435.87 MPa). The study is of great significance in establishing an experimental foundation for fabricating porous Si3N4 ceramics by using DLP technology.

Direct-methane anode-supported solid oxide fuel cells fabricated by aqueous gel-casting

Direct methane Solid Oxide Fuel Cells (SOFCs) operated under catalytic partial oxidation (CPOX) conditions are investigated, focusing on the processing of the anode support and the anode deactivation caused by carbon deposition. Anode-supported SOFCs based on gadolinium-doped ceria (GDC) electrolyte, and NiO-GDC anode support were fabricated by the gel-casting method. Suitable aqueous slurries formulations of NiO–GDC were prepared, starting NiO-GDC nanocomposite powders, agarose as gelling agent and rice starch as pore former. Electrochemical and mechanical tests evidenced that the support of 550 ± 50 µm thickness and 10 wt% pore former is a good candidate for direct-methane SOFCs. The cells operating under stoichiometric conditions of CPOX reached a performance of 0.64 W·cm−2 at 650 ºC, a very close value to that measured under humidified hydrogen (0.71 W·cm−2). The best electrochemical stability of the cell is achieved at a CH4/O2 ratio of 2.5, showing no evidence of carbon deposition and reducing nickel re-oxidation significantly.

РАЗРАБОТКА ЛИТЕЙНОЙ ТЕХНОЛОГИИ ПОЛУЧЕНИЯ ПОРИСТОГО КОМПОЗИЦИОННОГО МАТЕРИАЛА НА ОСНОВЕ АЛЮМИНИЯ

The work is devoted to the development of technology for obtaining composite material based on aluminium alloy with a given morphology of pores by using hollow metal spheres as pore formers. In the course of work the following researches have been carried out: selection of material-former of hollow metal spheres forming the structure and physical and mechanical properties of porous aluminum; study of influence of binder type on uniformity of conductive coating on the surface of form-former; study of influence of electrolysis modes on continuity of metal coating on the surface of conductive layer of formformer; production of porous aluminum by foundry technology. It is shown that the use of hollow metallized spheres as a pore former allowed to reduce the density of the AK12 alloy prototype by 40%.

Effect of starch pore formers with different particle sizes on cordierite porous ceramics

Particulate matter (PM) from vehicle exhaust can be effectively removed by cordierite particulate filters. The pore size and distribution of the cordierite particulate filter are very important to PM trapping efficiency. The main factors affecting the pore formation of porous cordierite ceramics are the grain size of the feedstock, the size of pore-forming agent particles, the sintering process, etc. Talc, kaolin, silicon oxide, alumina, and boehmite were used as the raw materials, and the effects of starch pore formers of different particle sizes on the CTE, XRD, microstructure, pore size distribution, and mechanical strength of honeycomb cordierite were investigated.

A facile synthesis of hierarchical porous carbon derived from renewable lignin for high-performance supercapacitor

In this work, we proposed a facile one-pot pyrolysis method to conveniently manufacture lignin-derived carbon materials with graded porous construction for use in supercapacitors. The renewable lignin was selected as precursor, while the potassium citrate was used as a pore-forming agent. The properties of the prepared lignin-derived carbon (LAC) and the performance for supercapacitor application were thoroughly evaluated. The LAC at optimal preparation conditions shows a layered porous structure with a large specific surface area of 3174 cm2 g−1 and pore volume of 2.796 cm3 g−1, where the specific capacitance reach to 241 F g−1 at 1 A g−1 scan rate in 6 M KOH electrolyte solution. At the same time, the specific capacitance remains at 220 F g−1 even at an excessive scan velocity of 20 A g−1, while the capacitance retention is still close to 91.3%. The capacitance retention rate is stable above 95% after 10,000 charge/discharge cycles, which shows the desired long-time stability. All these results demonstrate the outstanding properties of the new prepared LAC material and the considerable application potential in the field of electrical energy storage.