Porous silica ceramics with closed-cell structure prepared by inactive hollow spheres for heat insulation

New composite metal foams are processed using powder metallurgy (PM) and gravity casting techniques. The foam is comprised of steel hollow spheres, with the interstitial spaces occupied by a solid metal matrix (Al or steel alloys). The cyclic compression loading of the products of both techniques has shown that the composite metal foams have high cyclic stability at very high maximum stress levels up to 68 MPa. Under cyclic loading, unlike other metal foams, the composite metal foams do not experience rapid strain accumulation within collapse bands and instead, a uniform distribution of deformation happen through the entire sample until the densification strain is reached. This is a result of more uniform cell structure in composite metal foams compared to other metal foams. As a result, the features controlling the fatigue life of the composite metal foams have been considered as sphere wall thickness and diameter, sphere and matrix materials, and processing techniques as well as bonding strength between the spheres and matrix.

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The Processing and Structure of Steel Matrix Syntactic Foams Prepared by Infiltration Casting

Materials Science Forum ◽

10.4028/www.scientific.net/msf.933.129 ◽

2018 ◽

Vol 933 ◽

pp. 129-135

Author(s):

Quan Zhan Yang ◽

Yan Peng Wei ◽

Zhi Quan Miao ◽

Peng Gao ◽

Bo Yu

Keyword(s):

Metal Matrix ◽

Heat Insulation ◽

Hollow Spheres ◽

Syntactic Foam ◽

Average Diameter ◽

Steel Matrix ◽

Syntactic Foams ◽

Minimum Diameter ◽

Microstructure Characteristics ◽

Multifunctional Properties

Metal matrix syntactic foams are consisting of metal matrix and hollow spheres in closely or randomly packed, which own multifunctional properties with lightweight, damping, heat insulation, energy absorption and have a vast application prospect. Steel matrix can extend the potential of syntactic foams as a materials class to several new fields of application. In this paper, the hollow alumina spheres were introduced into the steel matrix by infiltration casting, the minimum diameter of hollow spheres for infiltration is analyzed in theory, the steel matrix syntactic foams were successfully prepared, which contain two different sphere types with average diameter sizes 3.97mm and 4.72mm, and the average densities of syntactic foams were calculated to be 4.39 (spheres occupy 43.7% of the volume) and 3.74 g/cm3 (spheres occupy 52.1% of the volume), respectively. The microstructure characteristics of the steel matrix syntactic foam were analyzed by means of scanning electron microscopy and energy spectrum.

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Microstructural and Chemical Analysis of Polyurethane and Polyisocyanurate Foam Insulations

10.32920/ryerson.14651922.v1 ◽

2021 ◽

Author(s):

Umberto Berardi

Keyword(s):

Thermal Conductivity ◽

Thermal Performance ◽

Cell Structure ◽

Polymer Degradation ◽

Chemical Characterization ◽

Aging Behavior ◽

Blowing Agent ◽

Closed Cell ◽

Physical Attributes ◽

Cell Foam

For some closed cell foam insulation products, the thermal conductivity increases at low temperatures, contrary to single thermal resistance values provided by manufacturers. This phenomenon has been demonstrated in various polyurethane and polyisocyanurate insulations. The reduction in thermal performance has been attributed to the diffusion of air and blowing agent through the foam and to the condensation of blowing agent. Aging processes such as freeze-thaw cycling, moisture accumulation, and polymer degradation further increase thermal conductivity. The initial cell structure plays a role in dictating the thermal performance. To further understand the loss of thermal performance in closed cell foams, microstructure and chemical characterization was performed in this study. The aging behavior of foam insulations was analyzed by imaging foams with SEM and by measuring foam. Changes in the polymer physical attributes were identified and compared to increases in thermal conductivity. This project also used gas chromatography and quantified changes in pentane concentration in polyisocyanurate foams that have undergone aging

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Enhancement of Mechanical and Thermal Characteristics of Polyurethane-Based Composite with Silica Aerogel

Materials Science Forum ◽

10.4028/www.scientific.net/msf.951.63 ◽

2019 ◽

Vol 951 ◽

pp. 63-67 ◽

Cited By ~ 1

Author(s):

Jae Hyeok Ahn ◽

Jeong Hyeon Kim ◽

Jeong Dae Kim ◽

Seul Kee Kim ◽

Kang Hyun Park ◽

...

Keyword(s):

Silica Aerogel ◽

Heat Insulation ◽

Porous Silica ◽

Thermal Characteristics ◽

Weight Percent ◽

Polyurethane Foams ◽

Mechanical And Thermal Properties ◽

Efficient Alternative ◽

Insulation Performance ◽

Compressive Tests

Synthesis of polyurethane foams (PUF) with silica aerogel nanoparticles is an efficient alternative to improve the mechanical and thermal properties of the foam owing to the outstanding thermal insulation properties of porous silica aerogel nanoparticles. Silica aerogel was added into polyurethane foams at different weight percent (0, 1, 3, 5 wt.%) to observe the changes in the material properties. To confirm the applicability of the synthesized PUF to the heat insulating material, compressive tests were carried out at ambient and cryogenic temperature (20, -163°C) and the thermal conductivities were measured according to wt.%. In addition, the cell microstructure was identified using FE-SEM to analyze the effect of silica aerogels on the foam morphologies. As a result of the experiment, it was confirmed that the mechanical strength and the heat insulation performance were improved in the polyurethane foam containing 1 wt.% of silica aerogel.

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Preparation and Properties of 3-Pentadecyl-phenol In-Situ Modified Foamable Phenolic Resin

10.20944/preprints201809.0596.v1 ◽

2018 ◽

Author(s):

Tiejun Ge ◽

Kaihong Tang ◽

Yang Yu ◽

Xiapeng Tan

Keyword(s):

Molecular Structure ◽

Phenolic Resin ◽

Bending Strength ◽

Cell Structure ◽

In Situ Modification ◽

Phenolic Foam ◽

Closed Cell ◽

Ft Ir ◽

Limited Oxygen

In this present study, 3-pentadecyl-phenol was selected as a modifier to prepare a foamable phenolic resin with excellent performance, which was successfully prepared by in-situ modification. Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (1H NMR, 13C-NMR) were used to test and characterize the molecular structure of the modified resin. The results showed that 3-pentadecyl-phenol successfully modified the molecular structure of phenolic resin with a reduction in resin gel time. The effect of changing the added amount of 3-pentadecyl-phenol on the mechanical properties, microstructure and flame retardancy of the modified foam was investigated. The results showed that when the amount of added 3-pentadecyl-phenol was 15% of the total amount of phenol, this resulted in the best toughness of the modified foam, which could be increased to 300% compared to the bending deflection of the unmodified phenolic foam. The cell structure showed that the modified phenolic foam formed a more regular and dense network structure and the closed cell ratio was high. Furthermore, the compressive strength, bending strength, and limited oxygen index were improved, while the water absorption rate was lowered. However, the foam density could be kept below 40 mg/cm3, which does not affect the load.

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Composite Foams Prepared through Hollow Glass Microspheres Assisted Bubbling

Advanced Composites Letters ◽

10.1177/096369351302200102 ◽

2013 ◽

Vol 22 (1) ◽

pp. 096369351302200

Author(s):

Zhenguo An ◽

Jingjie Zhang

Keyword(s):

Heat Insulation ◽

Cell Structure ◽

Nucleating Agent ◽

Glass Microspheres ◽

Insulation Property ◽

Hollow Glass Microspheres ◽

Hollow Glass ◽

Foaming Process ◽

Composite Foams ◽

Ammonium Hydrogen

Composite foamy structures were prepared through hollow glass microspheres (HGM) assisted bubbling of silicone rubber with ammonium hydrogen carbonate as the blowing agent. The presence of HGM not only favoured the foaming process (acted as nucleating agent for the formation of minute bubbles at the initial stage of the bubbling), but also bring heterogeneous close-cell bubbles with stable inorganic shells into the foamy structure, which played an important part in the improvement of the heat insulation property of the product. Compared to the foamy structures without HGM, The composite foamy structures possessed improved heat insulation and sound absorbing properties. This work provides an additional strategy to fabricate composite foams with tailored cell structure and properties.

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Preparation and Properties of the 3-pentadecyl-phenol In Situ Modified Foamable Phenolic Resin

Polymers ◽

10.3390/polym10101124 ◽

2018 ◽

Vol 10 (10) ◽

pp. 1124 ◽

Cited By ~ 5

Author(s):

Tiejun Ge ◽

Kaihong Tang ◽

Yang Yu ◽

Xiapeng Tan

Keyword(s):

Molecular Structure ◽

Phenolic Resin ◽

Bending Strength ◽

Cell Structure ◽

In Situ Modification ◽

Phenolic Foam ◽

Closed Cell ◽

Ft Ir ◽

Limited Oxygen

In this present study, 3-pentadecyl-phenol was selected as a modifier to prepare a foamable phenolic resin with excellent performance, which was successfully prepared by in situ modification. Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (1H NMR, 13C NMR) were used to test and characterize the molecular structure of the modified resin. The results showed that 3-pentadecyl-phenol successfully modified the molecular structure of phenolic resin with a reduction in the resin gel time. The effect of changing the added amount of 3-pentadecyl-phenol on the mechanical properties, microstructure, and flame retardancy of the modified foam was investigated. The results showed that when the amount of added 3-pentadecyl-phenol was 15% of the total amount of phenol, this resulted in the best toughness of the modified foam, which could be increased to 300% compared to the bending deflection of the unmodified phenolic foam. The cell structure showed that the modified phenolic foam formed a more regular and dense network structure and the closed cell ratio was high. Furthermore, the compressive strength, bending strength, and limited oxygen index were improved, while the water absorption rate was lowered. However, the foam density could be kept below 40 mg/cm3, which does not affect the load.

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