Thermal Stability Of Foams Research Articles

Investigation on thermal stability of highly stable fluorine-free foam co-stabilized by silica nanoparticles and multi-component surfactants

Nanoparticles (NPs) have shown promising applications in developing the novel environmental-friendly firefighting foams. Hydrophilic silica NPs, siloxane surfactant (CoatOsil-77), and hydrocarbon surfactant (BS-12) were used to prepare mixed foam dispersions. The adsorption between surfactant molecules and NPs, and foamability of the mixed dispersions were analyzed. Thermal stability of foam was evaluated by using foam drainage, coarsening, and volume decay under thermal radiation. The strengthening mechanism of NPs on thermal stability of foam was analyzed. Results indicate that the intense interaction exists between NPs and surfactants. The presence of NPs with a concentration below 1 wt% leads to the deterioration of foam stability by accelerating foam drainage and coarsening, while a concentration of NPs above 1.5 wt% enhances foam stability. The foam coarsening, drainage, and foam volume decay were obviously delayed by NPs under thermal radiation. This research can give theoretical guidance for NP application in invention of fluorine-free firefighting foams.

Study of the thermal stability of foam of different expansion ratio

Introduction. Currently, the industry produces a wide range of foam generators to produce fire-extinguishing foams, and the foams they produce differ significantly in their expansion ratio and, consequently, fire resistance. Since heat fluxes have the main destructive effect on the foam, the purpose of this paper is to establish the patterns of destruction of foam of different expansion ratio when heated.Methods of research. The foam with expansion ratio from 7.5 to 80 was used for the tests. It was obtained by mechanical beating of 6 % solution of foaming agent PO-6RZ. The thermal stability of the foam was studied when the heat flow from the gas burner flame affects the foam layer. During the experiment, the change in the height of the foam column in time was recorded.Results and Discussion. The results of measurements, presented in the form of dependence of foam layer destruction rate on time, quantity of released liquid phase on 1 m2·s, dependence of foam layer destruction rate on its density allowed revealing a number of patterns. The destruction rate of foam with an expansion ratio of up to 30 remains constant throughout the entire duration of thermal exposure. As the foam expansion ratio increases, the rate of destruction at the initial stage of heat flux exposure increases. With a foam expansion ratio of more than 50, there is initially a sharp increase in the rate of destruction, which subsequently decreases as the foam column decreases. In the conditions of the experiment, the best characteristics were shown by the foam with an expansion ratio of 50, because in the foam with a smaller expansion ratio the syneresis makes a significant contribution to its destruction, and the foams with a larger expansion ratio are destroyed by the mechanical effect of convective flame flows.Conclusion. The study of the foam destruction patterns under thermal impact allowed establishing the fact that its destruction is limited by the rate of impoverishment of the upper layers with liquid.

Construction of Polyurethane-imide/Graphene Oxide Nanocomposite Foam with Gradient Structure and Its Thermal Mechanical Stability

Graphene oxide (GO)@Fe3O4 nanohybrid with ferromagnetism was prepared and polyurethane-imide copolymer (PUI)/GO@Fe3O4 nanocomposite foams with gradient structure were first fabricated under a magnetic field. Fe3O4 nanoparticles intercalated into GO layers with high grafting ratio, resulting in complete exfoliation of GO in matrix. For the composite foam, the average cell size, cell wall thickness and apparent density gradually decreased along magnetic field direction, forming gradient cell structure in foam. Both mechanical property and thermal stability of foam were remarkably improved by addition of GO@Fe3O4. Compared with A region, in B region with enriched distribution of GO@Fe3O4, the compressive strength and modulus increased by 12.5 and 7.0%, respectively. The thermal degradation temperature, storage modulus, and Tg were obviously improved, indicating enhancement of thermal mechanical stability of PUI along magnetic field, revealing formation of gradient distribution of thermal mechanical property ...

Thermal stability of foam during steam drive

A fine-long tube model was established for carrying out the thermal degradation experiments of steam foam to determine the foam stability in steam chamber. The real core sand from the Yulou oil layer of Block Jin45 of Liaohe Oilfield was packed in the model, and the experiment lasting for twenty days was conducted under the typical reservoir pressure and saturated steam temperature. The analysis on the experimental results and theoretical calculation results indicate that the thermal degradation reaction model of the added foam is the first-order reaction, and the degradation rate constants at the temperatures of 200 °C, 250 °C, and 300 °C are 9.35×10−8 s−1, 17.80×10−8 s−1, and 24.53×10−8 s−1 respectively. The foam thermal degradation rate kinetic model was deduced, which can be used to calculate the foam thermal degradation rate and half-life at any temperature condition. The half-lives of the added foam are 370 d, 160 d, 83 d, 49 d and 31 d at the temperatures of 100 °C, 150 °C, 200 °C, 250 °C and 300 °C respectively, which indicates that the production performance of most heavy oil reservoirs developed by steam drive in China can be improved by injecting foam agent. But in terms of the deep and high-pressure heavy oil reservoirs, the foam stability is poor when the saturated steam temperature is over 300 °C.

Effect of hard segments on the thermal and mechanical properties of water blown semi-rigid polyurethane foams

Water blown semi-rigid polyurethane foams with different ethylene glycol (EG) content were prepared. EG is used as chain extender to vary hard segments content of semi-rigid polyurethane foams. The effect of EG on foam molding process, hard segment structure and the relationship between structure and thermal, mechanical properties of foams has been investigated. Results indicate that the addition of EG contributes to preparing flawless foams, and reduces the apparent density of foams due to the increase in cell size. Fourier transform infrared analysis (FTIR) displays the existence of hydrogen bonds among polyurea segments, which is influenced by reactant activity. Dynamic mechanical analysis (DMA) manifests different phase mixing and soft domains Tg of foams with different EG content. Soft domains Tg is dependent on the purity of soft domains controlled by urethane hard segments and dissolved urea groups. Thermo gravimetric analysis (TGA) illustrates that thermal stability of foams is associated with hard segments content in foams. Mechanical tests demonstrate that improvements of mechanical properties of foams can be achieved by modifying foam formulation to increase microphase separation of polyurea segments.

Boron–carbon–nitrogen foam surfaces for thermal physisorption applications

A surface chemical treatment of highly porous carbon foams was adopted to synthesize boron–carbon–nitrogen (B–C–N) foams for thermal energy storage and release using an adsorption/desorption cycle with lightweight hydrocarbons. Microwave treatment in boric acid and urea was used to modify carbon foams with a B–C–N surface. Depending on the initial carbon foam state, B–C–N surface layers were produced with both amorphous and crystalline structures. The resultant B–C–N foams were characterized by TEM, XPS, XRD, FESEM and Raman measurements to quantify their stoichiometry, structure, and morphology. Adsorption enthalpy with methanol and thermal stability of foams was analyzed with DSC and TGA respectively. Thermal conductivity was measured by a transient laser flash technique. Results indicate that the crystalline graphitic carbon foam produces superior B–C–N surfaces compared to amorphous carbon foam. The crystalline B–C–N foams are found to provide the highest adsorption capacity, better thermal and oxidation stability.

Preparation and Characterization of Lignin-Phenolic Foam

In this paper, lignin could partly replaced phenol to prepare lignin-phenolic(LPF) foam.The effects of amount of lignin on mechanical properties, thermal stability, fire-retardant and micro-structure of LPF foam. The results indicated that the addition of lignin decreased the brittleness and flexibility of foam, and the foam hole became larger in diameter and distributed more unevenly. When the lignin replacement amount was lower, the foam had regular foam hole structure and even distribution of foam hole, the size of foam hole increased with an increase of lignin content, SEM observations were in accordance with the early research of the mechanical properties of foams. And the addition of lignin slightly affected the fire-retardant and thermal stability of foam. When lignin replacement amount was 30% and 40%, the critical oxygen index of foam was even slightly higher than the pure PF foam.

Impact of proteins–κ-carrageenan interactions on foam properties

Foaming properties of κ-carrageenan (κ-C)+β-lactoglobulin (β-lg), native and denatured soy protein and the thermal stability of foams were investigated. Apparent viscosity measurements were used to obtain the gelation rate and maximum viscosity of foams. Gelling and melting temperatures of the solutions determined by dynamic rheology were related to the thermal stability of foams. Foam expansion of the mixed κ-C+ protein solutions followed the same order as the pure protein solutions (β-lg>DSP>NSP). However, the presence of κ-C reduced foam expansion due to the higher viscosity of the systems. No liquid drainage or collapse was observed while apparent viscosity was measured. DSP induced a greater synergistic effect with κ-C, reflected in a faster gelling rate and increased foam stability. The thermal stability of foams stored at temperatures between 5°C and 45°C showed significant differences when they were pre-gelled at 5°C. A large increase in foam stability was observed at 25°C, which is above the average T gel and below the melting temperatures of the systems. The kinetic analysis of the process revealed that different mechanisms were involved in the drainage of pre-gelled or non-gelled foams.