Uniform Pore Distribution Research Articles

Mesoscale simulation of granular materials under weak shock compaction–pore size distribution effects

This research established a systematic method to generate various pore-size distributions (PSDs) and studied the effect of PSDs on the shock compaction response of granular materials using two-dimensional mesoscale simulations under identical porosity. Simulations utilized various PSDs for three particle shapes (circle, ellipse, and square). Contacting particle configurations using three PSDs, characterized by spatially uniform distributed pores to heterogeneous distributed pores, and non-contacting particle configurations under a single case of PSD were tested. The PSD of generated particle sets was characterized using coordination number, mean diameter, and bimodality coefficient as statistical metrics. Mesoscale simulations showed that regardless of the conditions of pore distributions, shock compaction of granular materials consistently demonstrates a precursor, shock compaction front, and end. However, the shock compaction velocity of contacting particles was dependent on the PSDs despite the constant initial porosity. The compaction velocity was faster in particle configurations with relatively uniform pore distributions than in heterogeneous pore distributions, which our study demonstrated can be attributed to particle rearrangement during compaction. Circular-shaped particles had high sensitivity in shock compaction response to the various PSDs. Furthermore, a contacting particle configuration tended to propagate the shock compaction wave relatively faster than particles that were in a non-contact configuration. This study established the relative importance of considering PSD as a metric over the coordination number in studies of the shock compaction response of granular materials. Further, insights are provided on the evolving shock substructure to characterize the shock compaction response of granular materials.

Performance of yellow and pink oyster mushroom dyes in dye sensitized solar cell

A solar photovoltaic (PV) cell, is an electrical device that uses the PV effect to convert light energy into electricity. The application of oyster mushroom dyes in dye sensitized solar cell (DSSC) is a novel strategy to substitute the costly chemical production process with easily extractable, environmentally acceptable dyes. Both dyes of yellow and pink oyster mushrooms were extracted using the same process but dried into powder form using two techniques, warm drying and freeze drying. The characterization was carried out utilizing current-voltage (I-V) characterization for electrical properties, Ultraviolet-Visible (UV-Vis) spectrophotometer for optical properties, Field Emission Scanning Electron Microscopy (FESEM), and Atomic Force Microscopy (AFM) for the structural properties. It was found that freeze-dried pink and yellow oyster mushroom had shown the good properties for DSSC application as it produced energy bandgap which lies within the range of efficient dye sensitizer; 1.7 eV and 2.2 eV, the most uniform distribution of pores and a nearly spherical form in FESEM analysis, and AFM result obtained with the highest root mean square (RMS) roughness value (26.922 and 34.033) with stereoscopic morphologies. The data proved that mushroom dyes can be incorporated in DSSC with the optimization of drying method in the extraction process, dilution of dye and the layer of deposition on the glass substrate. The current density-voltage (J–V) characteristics of fabricated DSSC was characterized using Newport Oriel Sol3A solar simulator under AM 1.5 Sun condition (100 mW/cm2, 25 oC). From the result obtained by solar simulator, the fabricated FTO/TiO2/Pleurotus djamor dye/Pt indicated the Voc of 0.499 V and Jsc of 0.397 mA/cm2.

Preparation and Characterization of Ni-Mn-Ga-Cu Shape Memory Alloy with Micron-Scale Pores

Porous Ni-Mn-Ga shape memory alloys (SMAs) were prepared by powder metallurgy using NaCl as a pore-forming agent with an average pore size of 20–30 μm. The microstructure, phase transformation, superelasticity, and elastocaloric properties of the porous alloys were investigated. The prepared porous alloy had a uniform pore distribution and interconnected microchannels were formed. Cu doping can effectively improve the toughness of a porous alloy, thus improving the superelasticity. It was found that porous Ni-Mn-Ga-Cu SMAs have a flat stress plateau, which exhibits a maximum elongation of 5% with partially recoverable strain and a critical stress for martensite transformation as low as about 160 MPa. In addition, an adiabatic temperature change of 0.6 K was obtained for the prepared porous alloy at a strain of 1.2% at about 150 MPa. This work confirms that the introduction of porous structures into polycrystalline Ni-Mn-Ga SMAs is an effective way to reduce costs and improve performance, and provides opportunities for engineering applications.

Dual‐mode sensing biopolymer membrane impregnated with molybdenum for ethylene detection and monitoring of fruits

AbstractIn this study, a dual‐mode sensing biopolymer membrane employing chitosan (CS), polyvinyl alcohol (PVA), and ammonium molybdate (AM) was developed for optical and electrochemical detection of ethylene. The biopolymer composite was characterized by X‐ray diffraction (XRD), Fourier transform infra‐red (FTIR), and scanning electron microscopy (SEM).The relationship between ethylene concentration and optical/electrochemical response was investigated. XRD analysis showed enhanced ionic conduction, supported by SEM images showing uniform pore distribution within the synthesized membrane, facilitating effective gas interaction with Molybdenum. The increased FTIR peak intensities with higher amount of molybdenum in the membrane indicates enhanced molecular interactions. Applied to a microelectrode chip, the membrane exhibits a measurable electrochemical response with oxidation peak appearing in cyclic voltammogram as Molybdenum ions undergo reduction upon ethylene exposure. Colorimetric measurements, based on CIELAB values, reveals visible color shift with increasing ethylene concentrations, particularly at 10% molybdenum impregnation. Ionic conductivity and total color difference exhibit parallel variation with ethylene concentrations. X‐ray photoelectron spectroscopy confirms molybdenum oxidation state shift from +6 to +5 in the membrane upon ethylene interaction. The inexpensive colorimetric method enables direct color change visualization in practical applications. The resulting dual‐functional biopolymer membrane shows adaptability and versatility by responding to both optical and electrochemical signals.

Assessing Microstructural, Biomechanical, and Biocompatible Properties of TiNb Alloys for Potential Use as Load-Bearing Implants.

Titanium-Niobium (TiNb) alloys are commonly employed in a number of implantable devices, yet concerns exist regarding their use in implantology owing to the biomechanical mismatch between the implant and the host tissue. Therefore, to balance the mechanical performance of the load-bearing implant with bone, TiNb alloys with differing porosities were fabricated by powder metallurgy combined with spacer material. Microstructures and phase constituents were characterized with energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The mechanical properties were tested by uniaxial compression, and the corrosion performance was determined via a potentiodynamic polarization experiment. To evaluate a highly matched potential implant with the host, biocompatibilities such as cell viability and proliferation rate, fibronectin adsorption, plasmid-DNA interaction, and an SEM micrograph showing the cell morphology were examined in detail. The results showed that the alloys displayed open and closed pores with a uniform pore size and distribution, which allowed for cell adherence and other cellular activities. The alloys with low porosity displayed compressive strength between 618 MPa and 1295 MPa, while the alloys with high porosity showed significantly lower strength, ranging from 48 MPa to 331 MPa. The biological evaluation of the alloys demonstrated good cell attachment and proliferation rates.

Study on preparation and thermal insulation properties of curing foam

The thermal insulation performance of curing foam is a critical factor affecting fire extinguishing efficiency. In this study, sodium dodecyl sulfate was used as the foaming agent, and then combined with foam stabilizers, foam thickeners and inorganic powders to prepare the curing foam extinguishing agents. The result demonstrated that the addition of PEG and Xanthan gum could prolonge the 50 % drainage time of foam solution to 1.98 times compared with the foam solution without foam additives. The composite powders imparts an excellent thermal insulation and high-temperature stability to curing foam, especially the mass fractionratio of loess to cement equals to 4:6 and the water cement ratio is 0.7. Moreover, the thermal insulation tests showed that when the test temperature equalled 500 °C, the curing foam could reduce the temperature of the covered surface by 234.2 °C. Compared with the water-based foam, the thermal insulation performance was improved by 58.1 %. Finally, fire extinguishing test showed that the fire extinguishing time of curing foam is 0.47 s and 33.99 s shorter than that of water-based foam and water, respectively. The consumption of water-based foam and water fire extinguishing consumption is 1.46 times and 4.37 times that of curing foam, respectively. The excellent structural stability is due to the addition of Xanthan gum and PEG additives, which provide a more uniform distribution of bubbles and denser pores. At the same time, the mixture of loess and cement acts as a skeleton in curing foam thereby improving the stability of the integral structure and further preventing the heat transfer.

Analysis of porous alkali activated materials using bauxite residue as principal precursor

Bauxite residue is a red-hued and mineral-rich material that is released from the production of alumina during the Bayer process. There are large areas of land across the world dedicated to the storage of this underutilized material. The growing nature of the alumina-producing industry implies that the production of bauxite residue will increase, which necessitates solutions for valorizing bauxite residue. One area of research involves using bauxite residue as a precursor in preparation of porous alkali activated materials and the novelty of the study is to make porous alkali-activated material with bauxite residue. Porous AAMs have applications as industrial adsorbents and as insulating materials. This study focused on the pore analysis of AAMs prepared with a high proportion of bauxite residue and fly ash addition, using varying percentages of hydrogen peroxide and added water to form the pore structure, with hydrogen peroxide and water acting as a “green reagent”. The sample containing the highest percentage of added water displayed the highest open porosity, with the sample consisting of large millipores and the widest distribution of pore sizes out of all the samples. The samples containing only hydrogen peroxide displayed a uniform distribution of smaller pores as measured by nitrogen adsorption. The study describes a process to create highly porous AAMs in low temperatures using a limited number of constituents. Furthermore, it optimizes the variation of hydrogen peroxide and added water to tailor the pore character depending on the desired application of the material, with only as much as 3 % hydrogen peroxide needed for porosity. The porous alkali-activated bauxite residue has the potential to be used as insulating material in the building.

Enhancement in the Stability of Porous Silicon Using Electrochemical Grafting of Polymer 2,6 Dihydroxy Naphthalene

While there have been many advancements related to porous silicon, the reactivity of silicon with the ambient (particularly in environments with oxygen and humidity) has limited its use and integration in a wide variety of applications. Therefore, it is important to passivate the surface of nanostructured/porous silicon. To this end, there have been many reports in literature where passivation of bare (or unpassivated) porous silicon (UPSi) surface has been performed using gas phase techniques (thermal carbonization) and solution-based methods. In this work, we have studied the influence of the electrochemical deposition of polymer 2,6 dihydroxynaphthalene (2,6 DHN), in enhancing the stability of porous silicon surfaces.Porous silicon was synthesized by the electrochemical etching of pre-cleaned p-type silicon substrates with resistivity of about 0.001 Ω-cm to 0.005 Ω-cm, in a PTFE cell that we have fabricated, with 48% HF and ethanol mixture (7:3) as the electrolyte solution, at a current density of about 1.08 A/cm². The polymer solution used for electrodeposition was prepared as a solution of 1 mM 2,6-dihydroxy naphthalene (2,6-DHN) in 100 mL of 1x phosphate buffer solution, which was vacuum infiltrated in the synthesized porous silicon and electrodeposited on the same with the standard three electrodes chronopotentiometry method, at a constant current density of about 2 mA/cm² for 120 seconds. Electrodeposited porous silicon was kept on the hot plate for 10 min at 220℃, followed by a thermal treatment at 600℃, for 180 min, in the presence of N2 flow (1 L/min).The surface morphology of the unpassivated porous silicon (UPSi) and passivated porous silicon (PPSi) are shown in the insets of Fig. 1(a) and (b), respectively. This suggests the presence of an incredibly thin coating of the polymer on the pore walls. The pores in, both, unpassivated and passivated porous silicon samples (UPSi and PPSi) remained open and unobstructed, offering a uniform distribution of pores with sizes ranging between 5 nm and 20 nm.To perform a corrosion test of the UPSi and PPSi, we look at these layers after they have been exposed to 1 M NaOH aqueous solution, for different time durations. We have seen the formation of a spontaneous bubble on the surface of the UPSi sample during the test. To this end, we have observed visible and morphological changes of both UPSi and PPSi samples after the corrosion stability test for 5 seconds and 120 minutes, respectively, as seen in Fig. 1(a) to (h). Due to the very high internal area and the hydrogen-terminated surface, in an aqueous solution, UPSi is oxidized by water at room temperature and degrades. In comparison, the PPSi sample is stable for more than 120 minutes.Electrochemical characterisation of UPSi and PPSi was performed in a 10 mM NaCl aqueous electrolyte with a three-electrode cyclic voltammetry (C-V) setup. C-V measurements of the UPSi sample show strong redox reaction in the potential window of 0 V to 1 V, whereas, the PPSi sample shows a nearly constant charging current response in the potential window of -1 V to 1 V, as shown in Fig. 1(i). These results emphasize that the passivation of porous silicon using 2,6 DHN polymer makes it more stable and less reactive in an aqueous medium. Figure 1

Semi-quantitative analysis of the structural evolution of mesophase pitch-based carbon foams by Raman and FTIR spectroscopy

Graphitized carbon foams (GFms) were prepared using mesophase pitch (MP) as a raw material by foaming (450 °C), pre-oxidation (320 °C), carbonization (1 000 °C) and graphitization (2 800 °C). The differences in structure and properties of GFms prepared from different MP precursors pretreated by ball milling or liquid phase extraction were investigated and compared, and semi-quantitative calculations were conducted on the Raman and FTIR spectra of samples at each preparation stage. Semi-quantitative spectroscopic analysis provided detailed information on the structure and chemical composition changes of the MP and GFm derived from it. Combined with microscopic observations, the change from precursor to GFm was analyzed. The results showed that ball milling concentrated the distribution of aromatic molecules in the pitch, which contributed to uniform foaming to give a GFm with a uniform pore distribution and good properties. Liquid phase extraction helped remove light components while retaining large aromatics to form graphitic planes with the largest average size during post-treatment to produce a GFm with the highest degree of graphitization and the fewest open pores, giving the best compression resistance (2.47 MPa), the highest thermal conductivity (64.47 W/(m·K)) and the lowest electrical resistance (13.02 μΩ·m). Characterization combining semi-quantitative spectroscopic analysis with microscopic observations allowed us to control the preparation of the MP-derived GFms.

Study on the mechanical properties of micropore organic polymer membranes

Abstract Micropore organic polymer membranes are indispensable for membrane filtration with well-established selectivity and permeability. Pressure-driven conditions in harsh acidic or alkaline environments can influence the mechanical properties of these materials. Diminished mechanical properties may include a shortened membrane lifespan, reduced filtration effectiveness, and increased filtration cost. Understanding of the intricate mechanisms influencing the mechanical properties of organic polymer membranes remains incomplete. In this study, a comprehensive investigation was carried out to characterize the mechanical properties of different membrane materials with similar and varying pore size parameters. The influence of different methods of membrane preparation on the mechanical properties of these materials was also explored. Results showed that the PTFE membranes demonstrated excellent Young’s modulus and tensile strength, while PVDF membranes excelled in elongation at break. Organic filter membranes prepared by the phase transition method exhibited a more structured fiber filament arrangement, a smoother surface, reduced crack formation and extension, and uniform pore size and distribution when compared to materials prepared using the tensile method. The results of this study expanded our understanding of the factors that can influence the mechanical properties of organic filtration membranes.

Hierarchical Gradient Structural Porous Metamaterial with Selective Spectral Response for Daytime Passive Radiative Cooling

AbstractPorous photonic structures have greatly advanced large‐scale radiative cooling application owing to its satisfying optical properties, easy‐designation, and low cost. However, current reported porous radiative cooling materials mainly focuses on uniform or random pore distribution structure, which failed to achieve precise spectrum control for sunlight and mid‐infrared light, thereby weakening the radiative cooling performance. Herein, gradient structural porous metamaterials (GSPMs) are proposed and successfully constructed for maximizing cooling effectiveness based on step‐by‐step freeze‐casting technology. The designed GSPMs with gradient micro‐nano porous structure can wide‐range scatter entire solar spectrum while possess gradual refractive index transition to increase air‐medium interface absorption at mid‐infrared regions. Notably, solar reflectivity and mid‐infrared emissivity of GSPMs reach 97.3% and 97.6%, achieving maxinum cooling temperature of 8.7 °C and net cooling power of 94.1 W m−2, presenting a higher cooling effect than random porous materials. Moreover, GSPMs enable achieve compatibility with color aesthetic and cooling superiorities due to selective spectra response behavior, as well as can be applied in building materials, realizing efficient energy saving and CO2 emission reduction. This work proposed gradient porous structure can achieve highly efficient daytime radiative cooling, offering new possibilities in the structure design of next‐generation porous radiative cooling materials.

The potential of oil palm empty fruit bunches from Blitar Regency Indonesia as a filling material for NPK slow-release fertilizer

Abstract There is a clear gap between the mechanism of slow-release fertilizer (SRF) to promote plant growth and the prominent role of nanocomposites as filler materials for SRF synthesis. However, the production source of oil palm empty fruit bunches (OPEFB) is considered to influence its characteristics as a filler in new materials. This research aims to review the characteristics of OPEFB from Blitar Regency, East Java Province, Indonesia as a filling material for NPK-SRF fertilizer. The characteristics of OPEFB consist of analysis of nutritional content using proximate, nutritional content using Van Soest, morphology and topography using a scanning electron microscope (SEM), crystal phase using X-ray diffraction (XRD), and chemical compound composition using Fourier transformation infrared spectroscopy (FTIR). The identification results show that OPEFB has the potential to be used as a filler in NPK-SRF production. This can be seen from the high cellulose content (41.7%), with quite similar crystallinity index as native OPEFB fibers. The morphology of OPEFB shows a porous structure with a not uniform pore distribution, pore channel structure, and a not-quite-smooth pore surface. However, slight modifications to the cellulose from OPEFB need to be made, such as purifying it into a single nano-sized cellulose.

Study on comprehensive properties of mullite porous ceramics prepared from gangue based on sintering temperature

Based on coal gangue and clay with median particle diameters of 0.22 and 0.21 nm as the main raw materials, starch is used as the pore-forming agent, the mullite porous ceramics are prepared by the hydraulic forming method and the solid sintering method, and the sintering temperature and the amount of clay added are studied. The mechanism influence on the performance of mullite porous ceramics. Through thermogravimetric analysis (TG-DSC), flexural properties, X-ray diffractometer (XRD), scanning electron microscopy (SEM), mercury intrusion method and other technical methods, the thermal stability, mechanical strength, crystal phase composition, Performance indicators such as microscopic morphology and pore size are characterized. The results show that the mullite porous ceramics prepared under the conditions of sintering temperature of 1300 °C and clay content of 40 wt.% have the best performance, with a porosity of 34%, a bulk density of 1.79 g/cm3, and a volume shrinkage rate. 11.88%, flexural strength of 33.28 MPa, uniform pore distribution and more mature mullite crystals. The research results open a new way to explore the high-value utilization of coal-based wastes.

Experimental study of compression behavior and its correlation with the microstructure of a deep-water sediment

Understanding the volume change behavior of deep-water sediments is essential for the safety design of deep-water engineering structures. In this study, the volume change behaviors of marine sediments from the South China Sea were studied through oedometer and isotropic compression tests. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests have been conducted to investigate the microstructure evolution of two types of sediments under loads. The experimental results showed that the structural anisotropy of intact specimens is more pronounced in oedometer tests with the increase of stress, however, depolarization occurs in the isotropic consolidation test. The volume change after yield in the oedometer and isotropic consolidation tests comes from inter-aggregate pore variations associated with the adjustment of the soil fabric. The reconstituted specimen presents a more uniform distribution of pores than that of the intact specimen, and the macropores are more easily compressed for the reconstituted specimen than those of the intact specimen. With increasing stress, the oedometer compression and isotropic consolidation curves of intact specimens gradually approach those of the reconstituted specimen. The deformation mechanism under high stresses is that soil particles are reoriented and the variation of micropores.

Dissolution and Regeneration of Cellulose and Chitosan in Molten Salt Hydrate

The energy and environmental problems caused by current fossil resources are becoming more and more serious, and the development of renewable and sustainable materials has become a research hotspot. Chitosan and cellulose, as the two most abundant biomasses in nature, have the advantages of being non-toxic, harmless, and environmentally friendly. However, due to their high crystallinity, it is difficult to dissolve in water and common organic solvents. Molten salt hydrate has been discovered as a cost-effective and non-derivative solvent system for dissolving biomass. In this paper, the dissolution and regeneration of microcrystalline cellulose and chitosan in the molten salt system to prepare gel materials is investigated using lithium bromide molten salt as an example. First dissolve cellulose and chitosan, the total mass is unchanged according to the mixing ratio of the two are divided into multiple groups, dissolved in a mass fraction of 60% lithium bromide solution at 140°C into a hydrogel, gradient regeneration in water-ethanol-tert-butanol, to produce aerogel composites, the molten salt rotary evaporation back to use. Characterization tests show that the material has uniform distribution of nanoscale pores, pore size of about 50nm, porosity of 97.53%, strain 50% range can withstand up to 0.4MPa. 6mm thickness of the sample can be insulated at 150°C for up to 2h or more, the degree of adsorption of 2500mg/L copper sulfate solution reaches 22115.4mg/g. It has excellent thermal insulation and adsorption performance and has a wide range of application prospects in environmental protection, biomedical and other fields.

Study on meso-macroscopic ionic conductivity of hydrogels and construction of prediction model

The utilization of hydrogels in biological devices has seen a significant expansion, necessitating a thorough investigation into their conductivity. In this regard, we conducted a comprehensive examination of the impact of crosslinkers on pore radius and distribution. When the crosslinker proportion was augmented by a factor of 10, the pore radius exhibited a reduction of nearly 3.7 times, resulting in a more uniform pore distribution. Notably, our findings indicated a direct proportionality between conductivity and mesoscopic porosity, coupled with an inverse relationship with crosslinking density. To advance our understanding, we proposed an equivalent pore network model that omits considerations of curvature to predict the ionic conductivity of hydrogels. Intriguingly, as the proportion of crosslinker increased, the mesoscopic pores of hydrogels demonstrated a correlation with macroscopic features. Upon comparison with experimental data, the model exhibited a commendable alignment with the observed trends. Through mutual refinement with experimental results, a novel prediction equation emerged, yielding an average prediction error less than 2 %. Beyond trend prediction, our model achieved relative quantitative predictions, providing valuable insights for the regulation of conductivity in electronic biological devices. This research contributes to the advancement of knowledge in the field, offering a nuanced perspective on the interplay between crosslinkers, pore characteristics, and the conductivity of hydrogels.

The Preparation and Performance of Epoxy/Acetylene Carbon Black Wave-Absorbing Foam.

The epoxy foam material filled with an absorbing agent effectively absorbs electromagnetic waves. In this study, epoxy resin was used as the matrix, and acetylene carbon black was used as the magnetic absorbing agent to prepare an absorbing foam material (epoxy/CB). The microstructure of acetylene carbon black (CB) and its distribution in epoxy resin, as well as the effects of pre-polymerization time and CB content on the foam structure, were systematically characterized. Additionally, two dispersion methods, the hot-melt in situ stirring dispersion method and the three-roll milling dispersion method, were studied for their effects on the foaming process and absorbing properties of epoxy/CB. The results showed that with the prolongation of pre-polymerization time, the pore size decreased from 1.02 mm to 0.4 mm, leading to a more uniform pore distribution. Compared to the hot-melt in situ stirring dispersion method, the three-roll milling dispersion method effectively improved the dispersion of CB in epoxy resin, reducing the aggregate size from 300-400 nm to 70-80 nm. The pore diameter also decreased from 0.453 mm to 0.311 mm, improving the uniformity of particle size distribution. However, the absorbing material prepared with the three-roll milling dispersion method exhibited unsatisfactory absorption performance, with values close to 0 dB at mid-low frequencies and around -1 dB at high frequencies. In contrast, the absorbing material prepared with the hot-melt in situ stirring dispersion method showed better absorption performance at high frequencies, reaching around -9 dB.

Titania Nanoparticles Doped Electrospun Membranes

Electrospun membranes exhibit very promising properties, such as high surface area, high surface area-to-pore volume ratio, high pore interconnectivity, and uniform pore distribution. Nanoparticles are a promising alternative for improving the properties of the electrospun membranes. Titania nanoparticles, which are stable, resistant, and non-toxic, have various applications including water treatment, sensors, food additive and cosmetics. Due to the high hydrophilicity of titania nanoparticles, membrane fouling is reduced in titania nanoparticles doped membranes. Titania nanoparticle doped polyacrylonitrile (PAN) nanocomposite electrospun membranes were prepared by electrospinning method in this work. Compared to bare PAN electrospun membranes 0.05% titania nanoparticles doped electrospun membranes have thinner nanofibers, higher hydrophilicity and almost 2 times lower bovine serum albumin adsorption, which shows lower fouling tendency.

Research of foam concrete quality by two-stage foam injection method in comparison with classical foam concrete

The article presents a method of production of foam concrete, which involves two-stage injection of foam. The proposed method involves improving the pore structure of foam concrete, due to a more uniform distribution of pores throughout the volume of the material. Laboratory tests were carried out for two types of samples, represented by the proposed method of foam concrete production by two-stage foam injection with the use of modified additive in comparison with the classical foam concrete. The density of Type 1 samples varies from 410 to 793 kg/m3 (coefficient of variation from 5.12 to 7.31%), while the density of fiberboard samples lies within the range from 539 to 655 kg/m3 (coefficient of variation from 2.66 to 3.14%). The results of greater variation of densities by height in the Type 1 sample relative to the Type 2 sample indicate the influence of the technological process of foam concrete production on the quality of the pore structure of the material. The results of strength evaluation showed a large scatter of Type 1 samples in relation to Type 2 samples. The highest values of CM strengths are logically observed in the lower part of the sample and the lowest in the upper location: 44.04 and 32.33 kg/cm2 (coefficient of variation from 5.15 to 9.54%). For Type 2 samples, the same values are 55.18 and 44.44 kg/cm2, for the lower and upper locations, respectively (coefficient of variation from 2.79 to 5.35%). The results of thermal conductivity measurements of Type 1 samples range from 0.098 to 0.203 W/m0C (coefficient of variation from 4.59 to 11.88%), while the densities of Type 2 samples lie between 128 and 162 W/m0C (coefficient of variation from 3.38 to 3.55%).

Freezing pre-treatment improves radio frequency explosion puffing (RFEP) quality by altering the cellular structure of purple sweet potato [Ipomoea batatas (L) Lam.

Radio frequency explosion puffing (RFEP) is a novel oil-free puffing technique used to produce crispy textured and nutritious puffed snacks. This study aimed to investigate the effects of freezing at different temperatures (−20 °C, −40 °C, −80 °C) for14 h and freezing times (1 and 2 times) on the cellular structure of purple sweet potato and the quality of RFEP chips. The analysis of cell microstructure, conductivity, and rheology revealed that higher freezing temperatures and more freezing times resulted in increased damage to the cellular structure, leading to greater cell membrane permeability and decreased cell wall stiffness. However, excessive damage to cellular structure caused tissue structure to collapse. Compared with the control group (4 °C), the RFEP sample pre-frozen once at −40 °C had a 47.13 % increase in puffing ratio and a 61.93 % increase in crispness, while hardness decreased by 23.44 % (p < 0.05). There was no significant change in anthocyanin retention or color difference. X-ray microtomography demonstrated that the RFEP sample pre-frozen once at −40 °C exhibited a more homogeneous morphology and uniform pore distribution, resulting in the highest overall acceptability. In conclusion, freezing pre-treatment before RFEP can significantly enhance the puffing quality, making this an effective method for preparing oil-free puffing products for fruits and vegetables.