Foaming Agent Research Articles

Study on the Structural Characteristics and Foaming Properties of Ovalbumin—Citrus Pectin Conjugates Prepared by the Maillard Reaction

This study explored the structural features and foaming properties of ovalbumin (OVA) and its glycosylated conjugates with citrus pectin (CP) formed through the Maillard reaction. The results demonstrated that OVA and CP were successfully conjugated, with the degree of grafting increasing to 43.83% by day 5 of the reaction. SDS-PAGE analysis confirmed the formation of high-molecular-weight conjugates. Fourier-transform infrared (FT-IR) and fluorescence spectroscopy further revealed alterations in the secondary and tertiary structures of OVA, including an enhanced β-sheet content, a reduced β-turn content, and the depletion of tryptophan residues. Moreover, the surface hydrophobicity of the OVA–CP conjugates significantly increased, enhancing foaming properties. Furthermore, the analysis of foaming properties exhibited that the Maillard reaction improved the foaming capacity of OVA to 66.22% and foaming stability to 81.49%. These findings highlight the potential of glycosylation via the Maillard reaction to significantly improve the foaming properties of OVA, positioning it as a promising novel foaming agent.

Shape Memory Polyurethane Foams With Tunable Mechanical Properties and Radiation Tolerance for Breast Repair and Reconstruction.

This study developed a shape memory polyurethane foam (SM-PUF) with tunable mechanical properties and exceptional radiation tolerance for potentially implanting tissue defects after mastectomy. The PUFs were synthesized via an insitu foaming strategy using water as a foaming agent, incorporating 4,4'-diphenylmethane diisocyanate (MDI) as the rigid segment and both polyoxytetramethylene glycol and polycaprolactone as the soft segment. The resultant PUFs possess an open-cell structure with a pore size of 30 ~ 800 μm, which achieves a compressive stress of 0.04 MPa under 70% compression strain and a tensile elongation of 667.9%. PUFs exhibit body temperature (37°C)-responsive softening and shape memory abilities, with recovery and fixation ratios reaching 88% and 98%, respectively. It was verified that PUFs can resist 40 Gy radiotherapy without changing their mechanical properties and biocompatibility. This study introduces an innovative approach to produce customizable foam for the reconstruction of implant prostheses for the breast.

Self-Compacting Mixtures of Fair-Faced Concrete Based on GGBFS and a Multicomponent Chemical Admixture—Technological and Rheological Properties

The use of superplasticizers in a self-compacting concrete mix without the addition of a foaming agent in practice leads to a well-known problem associated with increased air entrainment and promotes the formation of harmful large bubbles, high-void content, and ununiform appearance. This paper presents research on the properties of cement paste consisting of Ordinary Portland Cement (OPC), powder based on ground granulated blast furnace slag (GBBS), and superplasticizer. The methodology of this study was the estimation of flow diameter and flow time, as well as the evaluation of the rheological characteristics. The influence of ground granulated blast furnace slag and polycarboxylate plasticizer on the flowability and viscosity of cement paste was studied. The effect of superplasticizer (SP) based on polycarboxylate esters (PCE) anti-foaming agent (AFA) based on a glycol ester and air-entraining admixture (AEA) based on an amphoteric surfactant on flowability, viscosity, rheological properties and the strength of the cement paste was evaluated. It was found that the increase of slag content in cement paste (25%) with the presence of superplasticizer (0.64%) significantly changes the flowability and viscosity. It was stated that the addition of 0.04% anti-foaming agents increases flowability (20%) and reduces viscosity (44%) of cement paste. It was stated that the addition of small dosages of glycol ester-based anti-foaming agent (0.02 and 0.04%) significantly changes the rheological properties, decreases the shear yield stress by 2.1–2.8 times, the plastic viscosity by 2.4–2.6 times and apparent viscosity 1.6–2.5 times, improves the compressive strength at the age of 1 and 7 days by 2.5 and 1.4 times, respectively. The addition of air-entraining admixture led to a decrease in the plastic viscosity by 1.2–1.4 times. It was stated that the presence of air-entraining admixture assists in increasing the apparent viscosity by 1.7–2.4 times. It was shown that the presence of complex admixtures of various origins, purposes, and mechanisms of action would assist in predicting the behavior of concrete mixtures under the conditions of the building site and reduce the consumption of polycarboxylate esters due to the enhancing plasticizing effect of anti-foaming agent and air-entraining admixture.

The study of foaming agent concentration choice in EPB shield soil conditioning

The study of foaming agent concentration choice in EPB shield soil conditioning

Optimizing Glass Foam Production from Recycled Sources: Influence of Variation in Cullet Color and Spent Alkaline Battery Components

Glass foams present a compelling opportunity for upcycling glass waste, offering a favorable combination of low weight, thermal insulation, and mechanical strength. Prior works demonstrated the feasibility of producing glass foams from glass waste and foaming agents sourced from synthetic textile waste, manganese oxides, and spent alkaline battery cathodes. This work explores the optimization of the process, investigating the impact of glass composition of differently colored glasses on final properties and incorporating entire alkaline batteries, encompassing both cathode and anode components. By carefully adjusting the composition, foaming agent content, and process temperature, customizable properties are achieved. Increasing foaming agent content or utilizing transparent glass improves insulation but lowers density and mechanical properties. Lowering foaming agent content or using brown/green glass enhances density and strength at the expense of insulation. Temperatures beyond 900 °C increase crystalline content, boosting mechanical performance without affecting density. This innovative approach not only offers a pathway to sustainable insulation materials but also underscores the potential for minimizing environmental impact through the efficient upcycling of glass waste.

MICROSTRUCTURE AND WEAR BEHAVIOR CHARACTERIZATION OF STIR-CAST ALUMINUM 6063 ALLOY AND ITS FOAM: A COMPARATIVE STUDY

In this research work, aluminum 6063 alloy foam was synthesized through stir casting using varying amounts of titanium hydride as a foaming agent. A comparative microstructural and wear behavior analysis of stir-cast aluminum 6063 alloy and its foam is presented. The oxide and aluminide phases present as intermetallic compounds in the stir-cast aluminum 6063 alloy foam ensure the stability of the synthesized foam. In order to optimize the effect of wear parameters on the tribological properties of stir-cast aluminum 6063 alloy foam, the L933 orthogonal array (OA) was designed and modeled statistically. The tribological properties of stir-cast aluminum 6063 alloy and its foam were evaluated by pin-on-disc tests. The optimal tribological properties of the synthesized foam are 0.29 coefficient of friction, 8.6 N frictional force, and 0.00025 mm3/N-m specific wear rate. The tribological properties of stir-cast aluminum 6063 alloy foam are superior to those of aluminum 6063 alloy and comparable to other aluminum foams described in the literature.

Precipitation–Flotation Process for Molybdenum and Uranium Separation from Wastewater

The mining of molybdenum and uranium ores inevitably results in the generation of large volumes of wastewater containing low concentrations of metals, which poses significant threats to the environment. This study presents a novel precipitation–flotation process for the simultaneous separation of molybdenum and uranium from wastewater. A systematic investigation was conducted on the impacts of the type of precipitant, flotation reagent type, and flotation parameters on the experimental results. Ferric salt served better as a precipitant than aluminum salt and humic acid did, and sodium dodecyl sulfate (SDS) was more suitable than sodium dodecyl benzene sulfonate for acting as a surfactant and foaming agent. Under specific conditions, including a pH of 6.6, an Fe3+ dosage of 0.6 mmol·L−1, an SDS dosage of 40 mg·L−1, an air flow rate of 25 mL·min−1, and a flotation time of 10 min, the removal efficiencies of molybdenum and uranium reached 96.6% and 93.6%, respectively. After flotation, the molybdenum concentration, uranium concentration, chemical oxygen demand, and turbidity of the treated water all meet the emission standards. Furthermore, the metal removal mechanisms, including the particle size distribution, functional group structure, surface element composition, microstructure, and element distribution, were elucidated on the basis of characterization of the precipitation–flotation products.

Preparation of styrene‐phenylamine monomer copolymer nanospheres and its performance for stabilizing CO2 foam

AbstractImproving the stability of CO2 foam is a core concern in CO2 foam flooding oil recovery technology. Using hydrophobic nano‐SiO2 to enhance the stability of CO2 foam is a common approach, but hydrophobic nano‐SiO2 faces challenges, such as easy aggregation, difficult dispersion, and performance needs to improve. In this article, a novel dispersion of styrene‐phenylamine monomer copolymer (PSSN) nanosphere with primary amine groups on the surface was synthesized. The synthesis conditions of PSSN were optimized, and its performance for stabilizing CO2 foam was evaluated. The experimental results demonstrated that PSSN had better performance for stabilizing CO2 foam than that of hydrophobic nano‐SiO2 when using cocamidopropyl betaine (CAB) as the foaming agent. With the CAB concentration of 4000 mg/L and PSSN concentration of 100 mg/L in the brine having salinity of 8460 mg/L, the half‐life of CO2 foam at 90°C was 131 min, which was 43 min longer than that stabilized by hydrophobic nano‐SiO2 under the same conditions. This is for the first time that polystyrene microspheres with amine groups on the surface was used to stabilize CO2 foam. The study provides a new nanoparticle option for stabilizing CO2 foam.

Tuning the Interfacial Deformation of Gliadin-Flaxseed Gum Complex Particles for Improving the Foam Stability

Gliadin nanoparticle (GNP) is a promising foaming agent, but its application is hindered by the limited foam stability under low acidic conditions. Herein, we attempted to tune the foam stability of GNP by coating it with flaxseed gum (FG) and investigated the structure, interfacial behaviors, and foam functionality of gliadin-FG (GFG) particles at pH 4.5. Results showed that the formation of GFG complex particles was driven by an electrostatic interaction between positive charge patches on the surface of GNP (~17 mV) and negative charges in FG molecule (~−13 mV) at all tested ratios. The addition of appropriate amounts of FG (1:0.05) effectively improved the foam stability of GNP. This was because GFG with larger sizes and lower surface charge possessed higher rigidity after coating with FG. When they adsorbed at the air/water interface, their deformation process was slower than that of GNP, as indicated by interfacial dilatational rheology and cryo-SEM, and the covered particles seemed to be more closely distributed to form solid-like and dense interfacial films. Notably, the addition of FG at a higher ratio (1:0.3) promoted the foam stability of GNP by about five folds because the larger GFG with suitable flexibility and wettability could form a stiff interface layer with more significant elastic response, and the unabsorbed particles and FG could form a gel-like network structure in the continuous phase. These characteristics effectively prevented foam disproportionation and coalescence, as well as retard the drainage. Our findings demonstrate that coating GNPs with FG is an effective approach to improve their application in foamed foods.

Improving thermal insulation and thermal resistance properties of laterite‐based geopolymer foams by direct foaming

AbstractThis work aims to synthesize new foaming laterite geopolymer foam using laterite, sodium silicate solution, sand, and aluminium powder. The porosity rapidly increased with the addition of the foaming agent. The foam matrix had thermal conductivity values of 0.10 W/m K with 0.7% of Al powder and 0.64 W/m K with 0% of Al powder. For fire resistance, samples exposed to high temperatures (200°C and 500°C) showed increased flexural strength, linear shrinkage at 500°C, and a decrease at 900°C due to structural weakening under high thermal pressure and the appearance of new phases such as nepheline and akermanite in X‐ray diffraction analysis. The results also showed that a 30% increase in fine aggregate content increased the strength of the foam matrix, with flexural strength ranging from 5 to 9.1 MPa after 28 days of ambient curing. These laterite geopolymer foams have shown promising thermal insulation and mechanical qualities that are appropriate for building applications.

Production of lightweight geopolymer concrete with foam glass aggregate derived from cathode-ray glass waste

This work focused on producing an eco-friendly lightweight structure by recycling the cathode ray tube glass waste (CRT-GW)to prepare a foam glass aggregate (FGA) and using metakaolin to prepare a geopolymer binder (GP). The geopolymer binder replaces cement to decrease the release of gas generated during cement production. The silicon carbide (SiC) was used as a foaming agent at 1 wt% to prepare the FGA. The foaming temperature effect was investigated for the FGA characterization included: bulk density, volume expansion, apparent porosity, uniaxial compressive strength, and leaching tests for lead and barium. The foam glass aggregate was sintered at different temperatures 725 °C, 750 °C, 775 °C, and 800 °C. These temperatures were selected depending on heating microscopy analysis results, where the maximum expansion height was 119 % at 800 °C. The main characterization ranges of foam glass were: bulk density 0.58–1.26 g/cm3, volume expansion 8–77 (vol%), uniaxial compressive strengths 1.55–9.98 MPa, and thermal conductivity 0.063–0.097 W/m.K.The lightweight geopolymer (LWGP) was prepared with 30 vol% of FGA sintered at different temperatures and 70 vol% of GP. These samples hardened at room temperature. The bulk density and compressive strength were measured for the lightweight geopolymer samples after a curing time of 28 days. A higher compressive strength was 9.11 MPa with a bulk density of 1.21 g/cm3 for lightweight geopolymer-containing foam glass aggregate sintered at 775 °C.

Design and performance of a foamed ceramic prepared by sintering using boron carbide as a foaming agent

To meet the requirements of microwave penetration in military applications, the technical potential of preparing foamed ceramics (FCs) with low permittivity and reduced preparation costs by using desalted sea sands as the main raw material and boron carbide (B4C) as a foaming agent was investigated. The results of the orthogonal experiment demonstrate that the FCs prepared from a material system containing 3 wt% B4C, 2 wt% Fe2O3 and 4 wt% Na2CO3 exhibit the optimal overall performance. The performance of the FCs is strongly influenced by the sintering temperature, but less so by the sintering time. The FCs sintered at 1000 °C for 10 min have a high total porosity of 72 %, a high compressive strength of 9.7 MPa due to their homogeneous internal pore structure with small pore diameter, a high closed porosity of 71 % due to their dense smooth surface and intact pore walls, and a low permittivity of (2.09–2.25)+j(0.014–0.019) in the X–band due to their high porosity and simple composition, indicating that they are a promising multifunctional material for microwave penetration.

Adsorption behavior of in-house developed CO2-philic anionic surfactants

Incorporating CO2-philic functionalities into surfactant structure is proposed to address the drawbacks of conventional foaming agents such as premature rupture of lamellae in contact with oil, surfactant loss due to adsorption on rock or partitioning between oil and water, and salinity and temperature tolerance issues. Increased activity at the gas/water interface and less surfactant adsorption to the rock due to the presence of CO2-philic chains results in higher foam durability in the presence of oil. In the present paper, a comprehensive study on the adsorption of anionic CO2-philic surfactants onto sandstone rock surface is performed to understand adsorption mechanisms through the addition of CO2-philic tail groups in surfactant structure by observing the changes in concentration, static adsorption, and point of zero charge measurements. The static adsorption tests, Fourier Transform Infrared, and the X-ray Photoelectron Spectroscopy techniques were employed to investigate the interaction of surfactants with crushed Berea sandstone core sample at 90 °C. The static adsorption values of the S (single-tail), D (double-tail), and T (triple-tail) anionic surfactants were reported to be 0.53, 0.40, and 0.6 mg /g, respectively. The effect of alkali on the adsorption process of surfactants was also investigated and the adsorption of synthesized surfactants was found significantly low in alkaline conditions. A variety of analyses, including model fitting along with kinetics and thermodynamics studies at 30, 40, and 50 °C were performed to predict the adsorption behavior. The adsorption isotherm was found to best fit in Langmuir model. The process showed the best fit in the pseudo-second-order reaction kinetics model. The spontaneity of the adsorption process was verified by thermodynamic feasibility studies of the process.

Study on the Process of Preparing Aluminum Foam Sandwich Panel Precursor by Friction Stir Welding

In recent years, high-performance lightweight and multifunctional aluminum foam sandwiches (AFSs) can be successfully applied to spacecraft, automobiles, and high-speed trains. Friction stir welding (FSW) has been proposed as a new method for the preparation of AFS precursors in order to improve the cost-effectiveness and productivity of the preparation of AFS. In this study, the AFS precursors were prepared using the FSW process. The distribution of foaming agents in the AFS precursors and the structure and morphology of AFS were observed using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray energy dispersive spectroscopy (EDS). The effects of the temperature and material flow on the distribution of the foaming agent during the FSW process were analyzed through experimental study and numerical simulation using ANSYS Fluent 19.0 software. The results show that the uniform distribution of the foaming agent in the matrix and excellent densification of AFS precursor can be prepared when the rotation speed is 1500 r/min, the travel speed is 25 mm/min, the tool plunge depth is 0.2 mm, and the tool moves along the retreating side (RS). In addition, the experimental and numerical simulations show that increasing the welding temperature improves the uniformity of foaming agent distribution and the area of AFS precursor prepared by single welding, shortening the thread length inhibits the foaming agent from reaching the upper sandwich plate and moving along the RS leads to a more uniform distribution of the foaming agent. Finally, the AFS with porosity of 74.55%, roundness of 0.97, and average pore diameter of 1.192 mm is prepared.

Preparation of PVA/EG-WG gel foam and its inhibition of coal spontaneous combustion

In order to solve the shortcomings of existing gel foam such as poor stability, low strength and weak water retention capacity, a novel gel foam was prepared. The optimal ratio of this gel foam was determined in this experiment, and its inhibition performance and inhibition mechanism were analyzed. The results showed that the gel foam had the optimal performance when the mass fractions of foaming agent, foam stabilizer, gelling agent, cross-linking agent, Polyvinyl alcohol (PVA) and Ethylene glycol (EG) were 0.8 %, 1 %, 8 %, 2.2 %, 3 % and 7 %. After the gel foam action, the peak CO content in the oxidation process of coal samples decreased by 56.17 %, the average inhibition rate increased by 18.67 %, and the activation energy before and after the dry cracking temperature increased by 3.08 kJ and 9.20 kJ. The characteristic temperature points were greatly improved compared with those of the raw coal, which effectively slowed down the exothermic rate of coal oxidation. Compared with the traditional gel foam, PVA/EG-WG gel foam can achieve the effect of coal spontaneous combustion inhibition by means of inhibition and oxygen isolation, cooling and chemical reaction, etc.

Effect of the Addition of Egg White and Maltodextrin on the Characteristics of Dayak Onion Powder (Eleutherine palmifolia) by Foam Mat Drying Method

Dayak onion is a plant that has antioxidant content and chemical components that can be used as spices, flavor enhancers, fragrances, and food preservatives whose use is limited. Dayak onions that are easily damaged are processed into powder to make them more durable. The manufacture of powder products is carried out using the foam mat drying method with the addition of foaming agent, namely egg white, and foam stabilizer, namely maltodextrin. This study aims to determine the effect of the addition of egg whites and maltodextrin on the physicochemical and organoleptic characteristics of Dayak onion powder by the foam mat drying method. This study used a two-factor Complete Random Design (CRD) with three replicates. The observation data was processed using ANOVA at a confidence level of 5%, if there is a significant influence, a further DMRT test of 5% is carried out. The results showed that there was a significant interaction between the addition of egg white and maltodextrin in different moisture content, phenol content, and solubility. The best treatment was obtained with the addition of 8% egg white and 15% maltodextrin with 7.32% moisture content; 2.11% ash content; 51.08% antioxidant activity; 3.37 mg GAE/g phenol content; 46.65% solubility; 54.03 L; 21.00 a*; 11.43 b*; and color hedonic score 3.96 (quite red); aroma hedonic score 3.36 (slightly scented of Dayak onions); texture hedonic score 2.92 (slightly rough); 0.01% flavonoid content; and 9.35 ppm anthocyanin content.

Alkali activated materials from Tajogaite volcanic ash (La Palma, Spain): a green recovery after the 2021 eruption

The 2021 Tajogaite eruption was marked by intense pyroclastic fallout that covered a substantial portion of La Palma island, with maximum thicknesses in the central-western part. This, combined with lava flows, resulted in widespread damage to public and private properties. In this study, we investigated if volcanic ash from this eruption could serve as a raw material in the synthesis of alkali activated materials (AAMs) and contribute to the construction of eco-friendly buildings and the restoration of those damaged by the eruption. Volcanic ash-based AAMs were synthesized using NaOH and Na2SiO3 as alkaline solutions and by adding metakaolin to enhance ash reactivity and enable processing at ambient temperatures. Lightweight porous AAMs were also produced using H2O2 and metallic aluminum as foaming agents. Chemical, textural, physical, and mechanical analyses on the final products assessed their suitability as environmentally friendly materials to be used in the reconstruction of the island infrastructure, opening new perspectives on recovery actions that can be undertaken after disastrous eruptions. Of all the islands in the Canary Archipelago, La Palma has experienced the highest number of eruptions (8) in historical times, all of which showing considerable similarity in terms of eruptive mechanisms and composition to the most recent Tajogaite event. Although this study investigated fresh Tajogaite ash, similar perspectives can be envisaged for both other recent eruptions at La Palma and other similar volcanic scenarios worldwide.

Waste-to-resource: Employing lime mud as a foaming agent in glass foam manufacturing

The paper industry globally releases vast amounts of lime mud waste annually, raising environmental concerns. Composed mainly of calcium carbonate, lime mud has been utilized in various research works, including catalyst synthesis, cement production, and ceramic fabrication. This study investigates the use of lime mud as an eco-friendly foaming additive in the production of glass foam. Glass foams were prepared through a simple sintering method, utilizing glass cullet collected from households and incorporating different lime mud contents (0.5–2.0 wt%). The effects of lime mud concentration on the density, porosity, and pore size distribution of the glass foams were examined. Additionally, the thermal conductivity, compressive strength, and Weibull modulus were investigated in relation to the average porosity. The results revealed that the pore size distribution was dependent on the amount of lime mud, exhibiting three distinct distributions: a positively skewed distribution, a non-symmetric bimodal distribution, and a positively skewed distribution with a wide range. The Weibull modulus markedly decreased with increasing pore size. The compressive strength of the prepared glass foams ranged from 5.53±0.40–12.73±0.46 MPa, while the bulk density and porosity fell within the ranges of 0.41±0.02–0.70±0.04 g/cm3 and 72.12±1.45–85.38±0.98 %, respectively. The thermal conductivity could be as low as 0.07 W/m·K, approaching the upper limit for commercial glass foams used in thermal energy storage systems and meeting the requirements for Type I cellular glass thermal insulation classified by ASTM C552–16.

Performance Assessment on the Manufacturing of Zn-22Al-2Cu Alloy Foams Using Barite by Melt Route

A barium-rich Celestine (Sr,Ba)SO4 concentrate from the primary Mexican ore production was used as a thickening agent to produce closed-cell Zn-22Al-2Cu alloy foams, while calcium carbonate was used as a foaming agent. The microstructure and mechanical properties of the foams were analyzed by optical microscopy, scanning electron microscopy, and compression tests, respectively. The Zn-22Al-2Cu alloy foams showed a typical lamellar eutectic microstructure, constituted by a zinc-rich phase (η) and a (α) solid solution that was richer in aluminum, while a copper-rich (ε) phase was formed in the interdendritic regions. The SEM micrographs show the presence of small particles and aggregates that are randomly scattered in the cell walls and correspond to unreacted calcite and Celestine–Barian particles, especially for the higher barite addition. The compressive curves showed smooth behavior, wherein the particles at the cell walls did not affect the foam’s compressive behavior. The trial containing 1.5 wt. % of BaSO4 and 1.0 wt. % of CaCO3 showed a higher energy absorption capacity of 5.64 MJ m−3 because of its highest relative density and lowest porosity values. The Celestine–Barian concentrate could be used as a foaming agent for high melt-point metals or alloys based on the TGA results.

Operando visualization of porous metal additive manufacturing with foaming agents through high-speed x-ray imaging

Porous metals find extensive applications in soundproofing, filtration, catalysis, and energy-absorbing structures, thanks to their unique internal pore structure and high specific strength. In recent years, there has been an increasing interest in fabricating porous metals using additive manufacturing (AM), leveraging its unique advantages, including improved design freedom, spatial material control, and cost-effective small-batch production. In this study, we conducted pioneering operando visualization of AM porous metal using a laser powder bed fusion (L-PBF) setup combined with a high-speed synchrotron x-ray imaging system. Single track printing experiments using Ti6Al4V (Ti64) combined with titanium hydride (TiH2) and sodium carbonate (Na2CO3) as foaming agents, with varying mixing ratios were performed under different processing conditions. The results elucidate the dynamic development of porosity formation. The average pore size is significantly influenced by the particle size of foaming agents when pore coalescence is absent. For all foaming agent content tested in the current study, the number of pores is found to be more sensitive to changes in laser power than in laser scanning speed. Increasing linear energy density (increasing laser power or reducing laser scanning speed) promotes the foaming agent activation thereby porosity formation. However, high linear energy density skews pore distribution towards the surface despite forming deeper melt pools. In addition, the impact of additional factors including foaming agent’s laser absorptivity and decomposition kinetics with respect to AM time scales should be carefully considered to avoid ineffective activation of foaming agents during the AM of porous metals.