A novel fabrication method for glass foams with small pore size and controllable pore structure

In this paper, a novel fabrication method for glass foams has been introduced based on colloidal suspension foaming method using waste glass as starting materials. It is demonstrated for the first time that foam stabilization via in‐situ hydrophobization of waste glass particles is possible. The fabrication conditions for stable glass particle‐stabilized foams are optimized by investigating the influences of pH value, concentration of propyl gallate and ball milling time, respectively. It is demonstrated that this is a versatile method for fabrication of stable foamed glass suspension and final glass foams with small pore size of dozens of microns, which is much smaller than that of most glass foams in previous literatures. This novel method enables both closed pore structure and open pore structure simply by tailoring solid loading of glass suspension. A “sieve‐like” hierarchical pore structure can be achieved by adjusting sintering temperature. The glass foams with controllable structure could be applied in thermal insulation fields for closed pores, and in catalyst loading, filtration, and separation fields for open pores and hierarchical pore structure.     

A novel method of strong and tough Si3N4 ceramic from the particle-stabilized foam

The brittleness of Si₃N₄ ceramics has always limited its wide application. In this paper, Si₃N₄ ceramics were prepared based on foam. Combining the unique honeycomb structure of the ceramic foams and the self-toughening mechanism of Si₃N₄, the strengthening and toughening of Si₃N₄ ceramics can be further achieved by adjusting the microstructure of Si₃N₄ ceramic foams. The powder particles are self-assembled by particle-stabilized foaming to form a foam body with a honeycomb structure. It was pretreated at different temperatures (1450–1750°C). The microstructure evolution of foamed ceramics at different pretreatment temperatures and the conversion rate of α-Si₃N₄ to β-Si₃N₄ at different pretreatment temperatures were explored. Then the foamed ceramics with different microstructures are hot-press sintered to prepare Si₃N₄ dense ceramics. The effects of different microstructures of foamed ceramics on the strength and toughness of Si₃N₄ ceramics were analyzed. The experimental results show that the relative density of Si₃N₄ ceramics prepared at a particle pretreatment temperature of 1500°C is 97.8%, and its flexural strength and fracture toughness are relatively the highest, which are 1089 ± 60 MPa and 12.9 ± 1.3 MPa m^1/2, respectively. Compared with the traditional powder hot-pressing sintering, the improvement is 21% and 33%, respectively. It is shown that this method of preparing Si₃N₄ ceramics based on foam has the potential to strengthen and toughen Si₃N₄ ceramics.     

A new method of preparing superabsorbent PVF porous foam through the simultaneous acidification of water glass solution–aspect of environmental protection

To reduce the wastewater pollution problem, silica particles that have resulted from simultaneous sulfuric acidification of water glass solution serve as the pore‐forming agent for preparing superabsorbent PVF/SiO₂ foam in this study. This is a departure from the traditional porous PVF/starch foam's manufacture method. The pore structure of PVF/SiO₂ foam is very different from that of PVF/starch foam. The effect of the concentration of these pore‐forming agents on the pore structure, mechanical modulus, and water adsorption capacity of PVF/starch and PVF/SiO₂ foams are investigated in this study. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39894.     

A novel polyurethane prepolymer as toughening agent: Preparation,characterization, and its influence on mechanical and flame retardant properties of phenolic foam

A novel phosphorus‐ and silicon‐containing polyurethane prepolymer (PSPUP) was synthesized by the chemical reaction of phenyl dichlorophosphate with hydroxy‐terminated polydimethylsiloxane (HTPDMS) and subsequently with toluene‐2,4‐diisocyanate. The structure of PSPUP was confirmed by Fourier transform infrared spectroscopy and ¹H nuclear magnetic resonance. Afterward, a series of phenolic foams (PF) with different loadings of PSPUP toughening agent were prepared. The apparent density and scanning electron microscopy results showed that the addition of PSPUP can increase the apparent density of phenolic foam. The compressive, impact and friability test results showed that the incorporation of PSPUP into PF dramatically improved the compressive strength, impact strength, and reduced the pulverization ratio, indicating the excellent toughening effect of PSPUP. The limiting oxygen index of PSPUP modified phenolic foams remained a high value and the UL‐94 results showed all samples can pass V0 rating, indicating the modified foams still had good flame retardance. The thermal properties of the foams were investigated by thermogravimetric analysis under air atmosphere. Moreover, the thermal degradation behaviors of the PF and PSPUP/PF were investigated by real‐time Fourier transform infrared spectra. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

A novel method for the preparation of porous zirconia ceramics with multimodal pore size distribution

This work presents a new route of processing porous ceramic materials by vacuum induction melting of metallic ternary alloys from the system Ni–Zr–Y. Following internal oxidation results in an interpenetrating network of nickel and oxide phase consisting of yttria and zirconia. After dissolution of the metallic nickel matrix the oxide phase remains as a stable porous ceramic material with a multimodal pore size distribution. The porosity, pore size distribution and specific surface area can be controlled by alloy composition, solidification conditions and oxidation parameters.     

Fabrication and thermal conductivity of highly porous alumina body from platelets with yeast fungi as a pore forming agent

A highly porous alumina body was fabricated by heating a green clinker body consisting of platelets and yeast fungi as a pore forming agent. Four kinds of alumina platelets were used. When green clinker bodies of platelet aggregates (A11) with 10 and 30 mass% of yeast fungi were heated at 1500 °C for 2 h, their porosities reached 72% and 78%, respectively. In contrast, when the green clinker bodies composed of platelets with an average size of 10 µm and an aspect ratio of 25–30 (SERATH①), and 20 mass% of yeast fungi were heated at 1400 °C for 2 h, the porosity of the resultant porous alumina body was also approximately 72%. However, the room temperature thermal conductivities of the porous alumina bodies with 72% porosity derived from A11 and SERATH① were 0.86 and 0.50 W m⁻¹ K⁻¹, respectively. The decrease in the thermal conductivity of the porous alumina body produced from SERATH① is caused by the long path route for heat transfer.     

A unified interaction model for multiphase flows with the lattice Boltzmann method

The lattice Boltzmann method (LBM) has been increasingly adopted for modelling multiphase fluid simulations in engineering problems. Although relatively easy to implement, the ubiquitous Shan–Chen pseudopotential model suffers from limitations such as thermodynamic consistency and the formation of spurious currents. In the literature, the Zhang–Chen, Kupershtokh et al., the β-scheme, and the Yang–He alternative models seek to mitigate these effects. Here, through analytical manipulations, we call attention to a unified model from which these multiphase interaction forces can be recovered. Isothermal phase-transition simulations of single-component in stationary and oscillating droplet conditions, as well as spinodal decomposition calculations, validate the model numerically and reinforce that the multiphase forces are essentially equivalent. Parameters are selected based on the vapour densities at low temperatures in the Maxwell coexistence curve, where there is a narrow range of optimal values. We find that expressing the model parameters as functions of the reduced temperature further enhances the thermodynamic consistency without losing stability or increasing spurious velocities.     

一种新型发泡剂的泡沫稳定性研究

对阳离子表面活性剂CHLB(一种新型发泡剂),采用Waring-Blender搅拌法进行了泡沫性能研究。结果表明,该发泡剂在体系中的最佳浓度为0.90%,具有较好的耐盐性,泡沫性能受上沙溪庙组地层岩屑的影响较小,所能容忍的水侵量约为泡沫基液的2倍,能够承受一定的柴油污染。     

A preliminary study of the dynamics of phase separation in oligomeric polystyrene-polybutadiene blends

We report here the preliminary results of a study of the kinetics of spinodal decomposition in an oligomeric blend, polystyrene with polybutadiene using small angle light scattering. The data are compared with the theoretical predictions of Cahn-Hilliard and van-Aartsen. The results corroborate the position of the critical point as determined by the pulse induced critical scattering technique.     

Factors that enable the formation of porous strut morphology in “Swiss Cheese” viscoelastic polyurethane foam technology

Several factors were investigated that affect porous strut morphology in the Highly Porous Supersoft Viscoelastic Foam. Porous strut morphology and high air permeability of the Swiss‐Cheese TDI VE technology were found to be enabled by the combination of immiscible polyether polyols mixed with a third, highly hydrophobic polyol of high equivalent weight that is immiscible with either of the first two polyether polyols. Completely “punctured through” pores in struts were observed more frequently in foam samples where an isocyanate index of 90 versus 100 was employed. When isocyanate index is fixed to 90, it was found that a poly(1,2‐butylene oxide) (“PBO”) monol level of ≥3.0 parts per hundred polyol (pphp) was needed to see the first signs of a “punctured” pore strut morphology. Studies show that a “high‐Eq.Wt.‐hydrophobic‐polyol‐leaving‐voids” model is consistent with observed results. Hydrophobic polyols that allowed the formation of porous strut morphology included BO‐4000 monol (Eq.Wt. ～ 4000) and PBD‐10000 diol (Eq.Wt. ～ 5000). The use of these hydrophobic polyols also yielded air flows that were significantly higher than those obtained with the “standard” viscoelastic foam formulations that were prepared at the same isocyanate index. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44449.     

Effects of pore structure on thermal conductivity and strength of alumina porous ceramics using carbon black as pore-forming agent

In the present work, carbon black (CB) works as a pore-forming agent in the preparation of alumina porous ceramics. The pore structures (i.e. mean pore size, pore size distribution and various pores size proportions) were characterized by means of Micro-image Analysis and Process System (MIAPS) software and mercury intrusion porosimetry. Then their correlation and thermal conductivity as well as strength were determined using grey relation theory. The results showed that the porosity and mean pore size increased against the amount of CB, whereas the thermal conductivity, cold crushing strength and cold modulus of rupture reduced. The <2 μm pores were helpful for enhancing the strength and decreasing the thermal conductivity whereas the >14 μm pores had the opposite effects.     

Capillary rise properties of porous mullite ceramics prepared by an extrusion method using organic fibers as the pore former

Porous mullite ceramics with unidirectionally oriented pores were prepared by an extrusion method to investigate their capillary rise properties. Rayon fibers 16.5 μm in diameter and 800 μm long were used as the pore formers by kneading with alumina powder, kaolin clay, China earthen clay and binder with varying Fe₂O₃ contents of 0, 5 and 7 mass%. The resulting pastes were extruded into cylindrical tubes (outer diameter (OD) 30–50 mm and inner diameter (ID) 20–30 mm), dried at room temperature and fired at 1500 °C for 4 h. The bulk densities of the resulting porous ceramics ranged from 1.31 to 1.67 g/cm³, with apparent porosities of 43.2–59.3%. The pore size distributions measured by Hg porosimetry showed a sharp peak at 10.0 μm in the sample without Fe₂O₃ and at 15.6 μm in the samples containing Fe₂O₃; these pores, which arose from the burnt-out rayon fibers, corresponded to total pore volumes ranging from 0.24 to 0.34 ml/g. SEM showed a microstructure consisting of unidirectionally oriented pores in a porous mullite matrix. Prismatic mullite crystals were well developed on the surfaces of the pore walls owing to the liquid phase formed by the Fe₂O₃ component added to color the samples. The bending strengths of the tubular samples ranged from 15.6 to 26.3 MPa. The height of capillary rise, measured under controlled relative humidities (RH) of 50, 65 and 85%, was greater in the ceramics containing Fe₂O₃ than in those without Fe₂O₃, especially in the thinner samples. The maximum capillary rise reached about 1300 mm, much higher than previously reported. This excellent capillary rise ability is thought to be due to the controlled pore size, pore distribution and pore orientation in these porous mullite ceramics.     

A strategy for the preparation of closed‐cell and crosslinked polypropylene foam by supercritical CO2 foaming

We report the preparation of a closed‐cell polypropylene (PP) foam material by supercritical carbon dioxide foaming with the assistance of γ‐ray radiation crosslinking. Styrene–ethylene–butadiene–styrene (SEBS) copolymer was added to PP to enhance radiation crosslinking and nucleation. Radiation effects on the foaming of the PP/SEBS blend with different ratios were investigated. A significant improvement in the foaming of the crosslinked PP/SEBS blend was achieved as compared to pristine PP. The cell density of the crosslinked PP/SEBS foam greatly increased at a dose of 10 kGy and a high closed‐cell ratio was obtained. The tensile strength of the crosslinked PP/SEBS foams (10 kGy) was improved from 14 to 20.7 MPa compared to pristine PP foam (0 kGy). In addition, the crosslinked PP/SEBS blend exhibited a wider foaming temperature window (10 °C) as compared to the non‐crosslinked ones (4 °C). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45809.     

(CO2 + 2‐propanol) mixture as a foaming agent for polystyrene: A simple thermodynamic model for the high pressure VLE‐phase diagrams taking into account the foam vitrification

The equation of state model developed by Lacombe and Sanchez (J Phys Chem 1976, 80, 2352) is used in the form proposed later by Sanchez and Stone (Polymer Blends, Vol. 1: Formulation, 2000; Chapter 2) to correlate experimental vapor‐liquid equilibrium (VLE) data for the three binaries and the ternary systems. Experimental data from the binary systems carbon dioxide‐isopropyl alcohol (CO₂‐IPrOH), isopropyl alcohol‐polystyrene (IPrOH‐PS), and carbon dioxide‐polystyrene (CO₂‐PS) are used to calculate VLE properties for the ternary system CO₂‐IPrOH‐PS. Two‐dimensional VLE‐phase diagrams were calculated and used to describe from a thermodynamic point of view the pressure, volume, and temperature values that characterize a thermoplastic foam evolution process, from the extruder to the foaming die. For different initial mixture CO₂ + IPrOH concentrations, pressure reduction produces liquid foaming until the vitrification curve arrests the final foam volume expansion. The dependence of the vitreous transition with the system CO₂ + IPrOH concentration while foaming is represented by the Chow (Macromolecules 1980, 13, 362) equation. The calculation procedure is proposed as a design tool to reduce the amount of experimental data usually needed as a requirement previous to the design stage. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2663–2671, 2007     

溶胶-凝胶法碳源对多孔炭材料孔隙结构的影响

以正硅酸乙酯(TEOS)为模板硅源,β-环状糊精和可溶性淀粉分别为碳前驱体,运用溶胶-凝胶法制备了多孔炭材料。利用低温N2等温吸脱附、X射线衍射、高倍扫描电子显微镜等对所得炭材料的结构进行了测试与表征,结果表明,β-环糊精为碳源的样品主要孔径分布在2~3 nm;以可溶性淀粉为碳源的样品孔径呈双峰分布,即孔径集中在3.7 nm和5~20 nm,但由于炭化温度较低,所得的炭材料仍为无定形结构。     

Characteristics of microbubbles generated by porous mullite ceramics prepared by an extrusion method using organic fibers as the pore former

Porous mullite ceramics with unidirectionally oriented pores were prepared by an extrusion method using rayon fibers as the pore formers and the characteristics of microbubbles generated by these porous ceramics were investigated. The 1200 mm long ceramics were tubular and of thick or thin types of 20–30 mm inner diameter and 30–50 mm outer diameter, respectively. The thin and thick samples had porosities of 47 and 49% and average pore radii of 7.8 μm. The gas permeabilities of the thick and thin samples were 4.1 × 10^?14 and 5.4 × 10^?14 m², respectively. Microbubbles were generated by introducing N₂ gas through the ceramic tube by immersing it into water. The minimum pressure (bubble point pressure) for generation of microbubbles was 20 kPa, much lower than for other bubble-forming methods. The average microbubble radii ranged from about 70 to 105 μm at flow rates of 0.15–0.25 L/min in the thin sample and 0.3–0.7 L/min in the thick sample. These bubble sizes are much smaller than calculated for a Fritz-type bubble such as generally formed by bubbling from pores and/or orifices. However, the present bubble sizes agree well with the calculated value based on nanobubbles, indicating that bubble formation occurs by mixing the gas with water in small pores. Since microbubbles enhance the dissolution rate of a gas phase in water, they are potentially useful for improving water environments, especially oxygen-deficient water. The effectiveness of gas dissolution in water was confirmed by determining the dissolution behavior of CO₂ gas using these porous ceramics.     

A new analysis method for the determination of the pore size distribution of porous carbons from nitrogen adsorption measurements

A new analysis method has been developed for the determination of the pore size distribution of porous carbons from nitrogen adsorption measurements. The method is based on a molecular model for the adsorption of nitrogen in porous carbon. It allows, for the first time, the distribution of pore sizes to be determined over both the micropore and mesopore size ranges using a single analysis method. In addition to carbons, this method is also applicable to a range of adsorbents, such as silicas and aluminas.     

A new method for the investigation of porous structures using mercury porosimetry

The influence of wetting angle hysteresis on volume hysteresis and retention of mercury in porous solids was considered. Although different explanations are possible (as explained in the paper), the resulting effect for cylindrical pores in the examined sample of active carbon was that the advancing angle θ_A = 162°, and the effective value of the receding angle θ_R = 90°. The rise of the mercury volume (V_m) intruded in the second run after the preceding reduction of pressure (p) to zero corresponds with a formation of spherical caps at the orifice of pores. The dependence of V_m on p in such a case has been called local hysteresis and it has been used to evaluate the true θ_A, the number of pores with a radius corresponding to the pressure of intrusion and their mean length.     

Glass foam of macroporosity using glass waste and sodium hydroxide as the foaming agent

Glass foams using float glass waste and sodium hydroxide were produced. The influence of the sodium hydroxide amount in the foam formulation was studied. Titanium dioxide was used as a strengthening agent. The variations of temperature, heating rate and sintering time were investigated during the synthesis process. Open porosity was estimated using mercury porosimetry. The morphology of the glass foams was evaluated using scanning electron microscopy, phase formation was studied using X-ray diffraction, and chemical composition was estimated using X-ray fluorescence. As a result, glass foams with macroporosity were obtained. Since the glass foams used glass waste as reactant, the results suggest the development of an alternative route for glass recycling.