Foam Pressure Research Articles

A new two-step process to prepare microcellular epoxy foams based on kinetic analysis

The foaming behavior of a diglycidyl ether of bisphenol-A (DGEBA) epoxy resin–anhydride hardener system at varying accelerator (tertiary amine) concentration, using chemical foaming agent (CFA), was investigated. The microstructure of foams revealed a smaller cell size, higher cell density, and more homogeneous distribution of cells at higher curing rate by varying accelerator contents, whereas not the same by varying foaming temperatures. The curing of epoxy system was studied by a differential scanning calorimetry, while the decomposition process of CFA was investigated by the foaming pressure measurement. Kinetics data showed that the addition of CFA in epoxy system produced obvious influence on the curing process of epoxy mixture; meanwhile, the decomposition reaction of CFA in epoxy system showed an autocatalytic behavior, which can be well predicted by Sestak–Berggren equation. Reaction rate constants of the curing of epoxy foaming system (k t ) and the degradation of CFA (k d ) were calculated, and the competition between these two simultaneously occurring reactions was expressed by the kinetic parameter k t /k d . The high specific value of k t /k d , which can be tuned by both accelerator concentration and foaming temperature, indicated that the curing rate was much higher than degradation rate of CFA. By further accelerating the curing rate in the foaming stage, a new two-step method was introduced to fabricate microcellular epoxy foam at relatively low viscosity.

CFD Simulation of Pipeline Transport Properties of Mine Tailings Three-Phase Foam Slurry Backfill

A three-dimensional backfill pipeline transport model is developed using the computational fluid dynamics (CFD) technique, which is applied to study the pipeline transport properties of three-phase foam slurry backfill (TFSB). Based on rheological property tests and CFD simulations, the foam phase, pressure, and velocity in the pipeline system are investigated using the CFD mixture method for different bubble volume fractions and bubble diameters. The simulation results indicate that TFSB can maintain a steady state during pipeline transport, experience a markedly reduced pipeline transport resistance, and exhibit better liquidity than conventional cement slurry. Furthermore, as the bubble volume fraction increases, the resistance of the pipeline decreases and the fluidity improves. By contrast, the bubble diameter has little effect on the transport properties of TFSB. The combined results of CFD simulations, slump tests, and strength tests indicate that, when the bubble volume fraction is 15–20 vol %, TFSB can satisfy the necessary strength requirements and exhibit self-flowing transport. The CFD technique provides an intuitive and accurate basis for pipeline transport research and has the potential for wider application in studies of mine backfill.

Diffusion and desorption of CO2 in foamed polystyrene film

ABSTRACTBased on the existence of the pores in foamed polystyrene (PS), foamed‐non‐Fickian diffusion (FNFD) model was proposed, for the first time, to regress the desorption data obtained by gravimetric method. Results showed that FNFD model could accurately describe the diffusion behavior of CO2 out of foamed PS, and well predict the solubility of CO2 in foamed PS. The characterization of scanning electron microscopy indicated that there were abundant pores in the foamed PS, and the pores store most of CO2, which would diffuse in the pores, adsorb to the wall of the pores, penetrate across walls of the pores, diffuse in the matrix of PS, and desorb out of PS. The mass of CO2 in the pores of foamed PS was expressed as a function of foaming pressure and temperature according to foaming kinetics. Results showed that the values calculated by this function agreed well with the values obtained from the FNFD model. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45645.

Hybrid Foam Pressure Sensor Utilizing Piezoresistive and Capacitive Sensing Mechanisms

The development of flexible and stretchable sensing for future applications, e.g., strain, force, and pressure, requires novel foam and foam-like structures with properties such as fast relaxation times, a wide linear response range, good sensitivity to different stimuli and repeatability, without compromising low-cost, simple and effective manufacturing methods, and excellent mechanical properties. We present a new type of hybrid foam pressure sensor that utilizes a combination of piezoresistive and capacitive sensor elements. The hybrid foam sensor shows a maximum pressure sensitivity of 0.338 kPa−1 and a linear response of 0.049 kPa−1 in the piezoresistive and capacitive sensor elements, respectively, in the pressure ranges of 80 kPa). Simultaneously, both the sensor elements can be used for impact measurements across a wide range of pressures up to ≥240 kPa. Thus, the concept of the hybrid foam sensor could be utilized widely for sensing of pressures, impacts, or even bending in various applications, e.g., wearable electronics.

Carbon foams prepared from coal tar pitch for building thermal insulation material with low cost

Abstract A new approach is provided to resolve the large-scale applications of coal tar pitch. Carbon foams with uniform pore size are prepared at the foaming pressure of normal pressure using coal tar pitch as raw materials. The physical and chemical performance of high softening point pitch (HSPP) can be regulated by vacuumizing owing to the cooperation of vacuumizing and polycondensation. Results indicate that the optimum softening point and weight ratio of quinoline insoluble are about 292 °C and 65.7%, respectively. And the optimum viscosity of HSPP during the foaming process is distributed in the range of 1000–10000 Pa·s. The resultant carbon foam exhibits excellent performance, such as uniform pore structure, high compressive strength (4.7 MPa), low thermal conductivity (0.07 W·m− 1·K− 1), specially, it cannot be fired under the high temperature of 1200 °C. Thus, this kind of carbon foam is a potential candidate for thermal insulation material applied in energy saving building.

Rheological properties study of foam fracturing fluid using CO2 and surfactant

In this study, the macro properties of a CO2 fracturing fluid were studied experimentally. A detailed experimental investigation has been conducted on the rheology of the CO2 clean-fracturing fluid by using a large scale experiment system. A fluid model using Fluent software was adopted to simulate the gasdistribution andfully developed state of the CO2 fracturing fluid. The experimental results show that the CO2 fracturing fluid is shear thinning and the rheological properties can be described by the power-law model. As well, the character of this fluid differs greatly from that of single phase non-Newtonian fluid because of its formation of foam and the structure of its external phase. It was also found that the viscosity of CO2 fracturing fluid was proportional to the increment of foam quality and pressure, which, however, was inversely proportional to the increase of temperature and shear rate. Moreover, through analysis of the effects of different factors on the rheology characteristics, correlations of its rheological parameters were obtained.

Design and Research of New Syntactic Foam Pressure Parts

With the development of materials and technology, new composite materials which can meet the requirement of new technology are produced, especially in some harsh conditions where traditional materials cannot meet the needs. In this paper, a new type of syntactic foam pressure part is studied, simulate and calculate the impact of load stress and breaking type by finite element analyze. The results of experiment are same as the calculation. A method is established in this paper to provide a reference and research ideas for the similar products.

Foaming of poly(vinylidene fluoride-co-hexafluoropropylene) using supercritical carbon dioxide

Abstract This work studied the foaming behavior of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) in supercritical carbon dioxide (scCO 2 ). The effects of foaming temperature, foaming pressure, saturation time, depressurization time on the foam structure and crystallinity of samples were investigated. The foaming ability varies with different combinations of the foaming temperature and foaming pressure. However, a lower foaming temperature and a higher foaming pressure are more favorable for obtaining uniform foam than a higher foaming temperature and a lower foaming pressure. At a given foaming temperature and saturation time, increasing the foaming pressure leads to the decreased crystallinity and an increase in the melting temperature.

Silica nanoparticles as a high-performance filtrate reducer for foam fluid in porous media

Abstract During the fracturing operations for oils and gases, not only the oil and gas reservoirs, but also the nearby civil aquifers are often polluted by the invasion of fracturing fluid filtrates. In this study, we investigated the potential of silica nanoparticles as a high-performance filtrate reducer for a foam fluid in a porous media. First, the three factors affecting filtration reduction using nanoparticles, i.e., surface rheology, foam slipping, and foam stability, were described. Then, the foam filtration through a porous media in the core was measured using a dynamic fluid-loss device, and the effects of foam quality, pressure drop, and core permeability on the performance of the filtrate reducer were evaluated. The difficulty of bubbles flowing from a throat to a pore in a porous media was described by resistance gradient coefficient Cf, which is a combination of surface tension and viscoelastic modulus and increases by adding nanoparticles. Nanoparticles improve the roughness of the SiO2/sodium dodecyl benzene sulfonate foam film surface, thus increasing the slipping resistance Fslip when foams flow on the wall of a throat in a porous media. For the foams in a porous media, the diffusion of bubbles decreased in the presence of nanoparticles, and the growth rate of gas bubble size also decreased, thus increasing the foam resistance to gas channeling. The results of core filtration tests indicate that the fluid-loss-control properties increased with foam quality ranging from 0 to 85%, and the negative effects of pressure drop and permeability increase to foam filtration were weakened by adding SiO2 nanoparticles. Thus, silica nanoparticles can be used as a high-performance filtrate reducer for a foam fluid in a porous media.

Preparation and characterization of carbon foam derived from coal pitch

Carbon foams with high mechanical strength and low thermal conductivity were produced using precursors obtained after thermo-oxidation treatment of purified coal-tar by self-foaming. The structure and properties of obtained foams were studied. The results indicate that foaming precursor pre-treated by varying temperature and time, and the varying foaming conditions significantly affect the foaming process, foam structure and foam mechanical properties. Foam formation can happened at relatively low pressure and fast heating rate during the foaming process because of the resultant pitches. The properties of resultant foams were studied. The influence of foaming temperature, foaming time, foaming pressure on the foaming process were discussed. And at the same time the pre-treating temperature and time of coal pitch on the foaming process were also discussed in this paper.

Evaluation of Appropriate Material Models in LS-DYNA for MM-ALE Finite Element Simulations of Small-Scale Explosive Airblast Tests on Clay Soils

This study conducted finite element simulations of a small scale, explosive airblast on clay soil in LS-DYNA using multi-material arbitrary Lagrangian–Eulerian methods. An explosive mass of 100.9 g with a 7.6 cm blast height was simulated in this study under two-dimensional conditions. The study compared four different material models to evaluate their ability to simulate explosively-induced airblast loads on cohesive soils. Material models included the Soil and Foam pressure dependent strength model, the Pseudo Tensor pressure dependent strength model, the FHWA Drucker–Prager model and the Two-Invariant Geologic Cap model. Crater dimensions were measured from the simulations and compared to the results of airblast experiments performed in another study. Three material models ran to completion with the exception of the Geologic Cap model, which terminated early in the calculation due to plasticity algorithm errors caused by the large strain increments. While the remaining three models somewhat over-predicted crater depth, the diameter dimensions and crater volumes from the Soil and Foam and particularly the Pseudo Tensor model compared very well to the experimental data. The crater shape from the FHWA model did not match particularly well with experimental results and was larger than the experimental crater. A simplified, pressure dependent strength model such as Soil and Foam model or the Pseudo Tensor model is therefore recommended for modeling small-scale airblast events on cohesive soils. The Pseudo Tensor model compared particularly well to experimental results and predicted crater dimensions very well. Additional studies with the Geologic Cap model implementing smoothed particle hydrodynamics are recommended which may resolve the errors associated with large strain increments.

Microfluidic comparative study of foam flow between a classical and a pH sensitive surfactant

Abstract Comparative study between foams made of a pH sensitive surfactant, nonaoxyethylene oleylether carboxylic acid (AKYPO ® RO 90 VG) and a classical foaming surfactant, sodium dodecyl sulphate (SDS) was realised using simple microfluidic devices in the scope of Enhanced Oil Recovery (EOR). The influence of injecting fluid parameters such as gas and foaming liquid pressure was investigated and discussed in terms of foam morphology, and lamellae stability and curvature radii. The increasing stability of AKYPO ® foam film lamellae by increasing pH is classically explained by the electrostatic repulsive interaction of the double layer in foam film. In other hand, the addition of dodecanol (DOH) on SDS solution seems to have no effect on foam regime and lamellae stability except for high DOH concentration where the foam film shape becomes double bump. The behaviour difference between AKYPO ® and SDS lays on the lamellae shape and stability domain. While SDS lamellae stay unchanged with increasing pressure ratio between the gas and the liquid, AKYPO ® lamellae curvature radius increases which could be related to surfactants solubilities and structure. These results pointed out the relevance of solution physicochemical parameters on foam stability and flowing and help the understanding of flowing foam in EOR context.

Simulation Blowing Agent Performance, Cell Morphology, and Cell Pressure in Rigid Polyurethane Foams

A series of over 30 differential equations were solved to model experimental data on urethane foam formation. Methyl formate and C5–C6 hydrocarbons were used as physical blowing agents, and water was used as a chemical blowing agent. The rate of evaporation of the physical blowing agents was estimated using an overall mass-transfer coefficient times the difference in activity in the gas phase inside the bubbles and in the resin walls of the bubbles. The rate of CO2 diffusion was expressed as the overall mass-transfer coefficient times the rate of CO2 generation. The overall mass-transfer coefficient was found to decrease to near zero as the gel point of the resin was approached. Only one fitted parameter was used for the overall mass-transfer calculation for all blowing agents. The simulation results for foam height agree with the experimental data. Bubble growth and bubble pressure were simulated for the first time as compared to the available literature.

Coal tar pitch based carbon foam for thermal insulating material

Coal tar pitch was used as raw material for carbon foam. After oxidized and modified, coal tar pitch can be foamed at an atmospheric foaming pressure. Thus, this kind of carbon foam is easy to produce in large scale with low cost. Importantly, owing to the uniform pore structure, high compressive strength and low thermal conductivity, the resultant carbon foam can be used as thermal insulation material applied in energy saving building. A new approach was provided to resolve the large-scale applications of coal tar pitch.

Aluminium Foam and Magnesium Compound Casting Produced by High-Pressure Die Casting

Nowadays, fuel consumption and carbon dioxide emissions are two of the main focal points in vehicle design, promoting the reduction in the weight of vehicles by using lighter materials. The aim of the work is to evaluate the influence of different aluminium foams and injection parameters in order to obtain compound castings with a compromise between the obtained properties and weight by high-pressure die cast (HPDC) using aluminium foams as cores into a magnesium cast part. To evaluate the influence of the different aluminium foams and injection parameters on the final casting products quality, the type and density of the aluminium foam, metal temperature, plunger speed, and multiplication pressure have been varied within a range of suitable values. The obtained compound HPDC castings have been studied by performing visual and RX inspections, obtaining sound composite castings with aluminium foam cores. The presence of an external continuous layer on the foam surface and the correct placement of the foam to support injection conditions permit obtaining good quality parts. A HPDC processed magnesium-aluminium foam composite has been developed for a bicycle application obtaining a suitable combination of mechanical properties and, especially, a reduced weight in the demonstration part.

Supercritical CO2 foaming of pressure-induced-flow processed linear polypropylene

Linear polypropylene is very difficult to foam due to its low melt strength and high crystallinity. Pressure-induced flow (PIF) has been demonstrated to be able to improve the foamability of linear PP under a very high pressure. In this study, we report a systematic evaluation to optimize PP foaming process using supercritical CO2. PP was firstly processed by means of PIF at optimized conditions. For CO2 foaming of PP, the effect of foaming pressure and saturation time was investigated in detail. A threshold foaming pressure of 13.8MPa was found to be needed to achieve low-density foams. Comparing to commercially available EPP and high melt strength PP foams, the PIF PP foams possess much higher compressive strength and thermal stability at lower densities.

Cyclic olefin copolymer–silica nanocomposites foams

A cyclic olefin copolymer (COC) matrix was melt compounded with various amounts of fumed silica nanoparticles (1, 3 and 5 vol%) and the resulting materials were foamed through supercritical carbon dioxide. Foams were produced at four different foaming pressures (90, 110, 130, and 150 bar), keeping all other processing parameters constant. The main physical properties of both bulk and foamed samples were investigated in order to assess the role of both nanofiller content and foaming pressure. It was observed that the density values of the foamed materials decreased as the foaming pressure increased and that the presence of nanofillers leads to slightly denser materials. Both scanning and transmission electron microscopy evidenced the presence of filler aggregates on the bulk composites. These aggregates resulted to be elongated along the cell wall direction upon foaming. Dynamic mechanical thermal analysis, quasi-static tensile tests, and creep tests evidenced a positive effect played by nanosilica in improving the stiffness, the strength, and the creep stability of the polymer matrix for all foaming pressures. The application of a theoretical model for closed-cell foams highlighted how the stiffening effect provided by the nanosilica networking is mostly effective at elevated filler amounts and reduced foaming pressure values.

Mechanical behaviour of cyclic olefin copolymer/exfoliated graphite nanoplatelets nanocomposites foamed through supercritical carbon dioxide

A cycloolefin copolymer matrix was melt mixed with exfoliated graphite nanoplatelets (xGnP) and the resulting nanocomposites were foamed by supercritical carbon dioxide. The density of the obtained foams decreased with the foaming pressure. Moreover, xGnP limited the cell growth during the expansion process thus reducing the cell diameter (from 1.08 to 0.22 mm with an XGnP amount of 10 wt% at 150 bar) and increasing the cell density (from 12 to 45 cells/mm 2 with a nanofiller content of 10 wt% at 150 bar). Electron microscopy observations of foams evidenced exfoliation and orientation of the nanoplatelets along the cell walls. Quasi-static compressive tests and tensile creep tests on foams clearly indicated that xGnP improved the modulus (up to a factor of 10 for a xGnP content of 10 wt%) and the creep stability.

On the nature of pressure dependence in foams

Present study explores the physical background of pressure dependence observed in the yield behavior of solid foams by analyzing the partition of strain energy and stress distribution in the struts that make up the foam. To this end, transversely isotropic Kelvin foam models of three different relative densities are utilized in FE analysis to probe the yield surface along various biaxial and triaxial stress paths for a wide range of mean stress. From a macroscopic viewpoint, it is observed that in addition to well-documented quadratic dependence of yielding on mean stress there also exists a linear pressure dependence, which has not been properly addressed in the literature. Partition of strain energy at the time of macroscopic yielding into bending and stretch modes of deformation within struts provides a unique tool with which the dominant deformation mode that drives yielding can be identified as a function of the stress path followed. Analysis of FE results indicates that positive mean stress, as compared to negative mean stress, provides a strong configurational stability in deformation kinematics that limits bending mode and promotes the stretch mode of deformation in struts. Increasing the fraction of strain energy stored in stretch mode effectively increases the critical strain energy of yielding and, thereby, delays the onset of microscopic yielding. Negative mean stress, on the other hand, results in a weak configurational stability where bending mode is more prominent. Furthermore, it seems that the degree of this already weak stability quickly decays with the magnitude of negative mean stress and completely disappears when (and if) the stabilizing effect of joint stiffness is exceeded. We conclude that this contrasting behavior is the main source of (i) linear pressure dependence observed in the yield behavior as well as (ii) the stronger effect of linear pressure in low-density foams.

Formation mechanism and tuning for bi-modal cell structure in polystyrene foams by synergistic effect of temperature rising and depressurization with supercritical CO2

Polystyrene (PS) foams are fabricated using supercritical carbon dioxide (Sc-CO2) as a physical foaming agent in a batch foaming process. It is demonstrated that a bi-modal cell structure (BMCS) is obtained by the synergistic effect of temperature rising and depressurization using a varying-temperature mode (VTM). The formation mechanism for the BMCS is revealed. Cell nucleation occurs in the supercritical CO2-saturated polymer both in temperature rising and depressurizing stages. The nuclei formed in the former stage develop into large cells, whereas the ones formed in the latter stage evolve into small cells. The effects of foaming temperature, saturation temperature, second saturation time and foaming pressure in the VTM on the cellular structure of PS foams were investigated. The results showed that no BMCS is formed when the foaming temperature is only 10°C higher than saturation temperature. By manipulating the foaming parameters, the BMCS PS foams with a wide range of mean diameters (50.0–713.7μm) and densities (2.1×103–3.6×106cells/cm3) for the large cells, and a wide range of foam density (0.09–0.73g/cm3) are obtained.