New Approach for Macro Porous RB‐SiC Derived from SiC/Novolac‐type Phenolic Composite

Shimamura, Akihiro; Fukushima, Manabu; Hotta, Mikinori; Ohji, Tatsuki; Kondo, Naoki

doi:10.1111/jace.13978

Cited by 13 publications

(11 citation statements)

References 35 publications

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“…However, loading of silicon sufficient for siliconization of carbon produced from the pitch is very difficult due to the high carbon yield (80–90 wt%) of the pitch. Shimamura et al reported a reaction bonding approach for the preparation of SiC foams from novolac phenolic resin and SiC powder . In this, carbon–SiC composite foams were obtained by carbonization of novolac resin–SiC powder composite foam bodies prepared by the foaming of novalac resin–SiC powder compacts using hexamethylenetetramine as a blowing agent.…”

Section: Introductionmentioning

confidence: 99%

Low‐Density Open Cellular Silicon Carbide Foams from Sucrose and Silicon Powder

et al. 2016

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Open cellular SiC foams with low densities were prepared by thermo‐foaming and setting (130°C–150°C) of silicon powder dispersions in molten sucrose followed by pyrolysis and reaction sintering at 1500°C. The bubbles generated in the dispersion by water vapor produced by the –OH condensation was stabilized by the adsorption of silicon particles on the air‐molten sucrose interface. The composition of a sucrose‐silicon powder mixture for producing SiC foam without considerable unreacted carbon was optimized. The sucrose in the thermo‐foamed silicon powder dispersion leaves 24 wt% carbon during the pyrolysis. The sintering additives such as alumina and yttria promoted the silicon‐carbon reaction. SiC nanowires with diameters in the range of 35–55 nm and length >10 μm observed on the cell walls as well as in the fractured strut region were grown by both vapor–liquid–solid and vapor–solid mechanisms. Large SiC foam bodies without crack could be prepared as the total shrinkage during pyrolysis and reaction sintering was only ~30 vol%. The relatively low compressive strength (0.06–0.41 MPa) and Young's modulus (14.9–24.2 MPa) observed was due to the large cell size (1.1–1.6 mm) and high porosity (93%–96%).

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Section: Introductionmentioning

confidence: 99%

Low‐Density Open Cellular Silicon Carbide Foams from Sucrose and Silicon Powder

et al. 2016

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“…We previously reported that blowing was observed above a novolac-HMT content of 60 vol%, while pore coarsening occurred at 80 vol%. 15) The content of the novolac-HMT was thus fixed at 60 vol% in this study. The mixed alumina powder was blended with novolac-HMT powder (SP1101 novolac type with 9 wt.% of curing agent: HMT, D 50 = 24.8¯m; Asahi Organic Chemicals Industry Co. Ltd., Tokyo, Japan) at a volume ratio of 40:60 (mixed alumina:novolac-HMT) for one hour under dry conditions by a V-type mixer.…”

Section: Experiments and Characterizationmentioning

confidence: 99%

Fabrication and characterization of porous alumina with denser surface layer by direct foaming

Shimamura

Fukushima

Hotta

et al. 2017

J. Ceram. Soc. Japan

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Porous alumina with a denser surface layer is fabricated from an alumina/novolac composite body containing hexamethylenetetramine (HMT) that is used as a blowing agent and a curing agent for the novolac resin. A gas blown from HMT leads to the formation of pores up to submillimeter inside the alumina/novolac composite body. On the other hand, the denser surface layer without large pores is formed by the gas released from the surface during blowing. The blowing condition for the alumina/ novolac composite body is examined as a function of heat-treatment temperature in order to investigate the formation of the pore and the surface layer. Porous alumina with the denser surface layer is obtained through de-binding and sintering of the body. This paper also describes the microstructure and mechanical strength of the sintered porous alumina, and advantages of the denser surface layer.

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“…We have previously proposed a direct-foaming approach for porous ceramics from ceramic/novolacHexaMethyleneTetramine (HMT) composite, 9), 10) and using this approach we have fabricated porous alumina with the relatively dense surface layer. 11) In this study, HMT was used as a blowing agent and as a curing one for the novolac resin.…”

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confidence: 99%

Fabrication and characterization of porous alumina with a surface layer composed of alumina platelet by direct-foaming method

Shimamura

Fukushima

Hotta

et al. 2017

J. Ceram. Soc. Japan

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Porous alumina with the surface layer was fabricated from an alumina platelet/novolac-HexaMethyleneTetramine (HMT) composite. HMT was used as a blowing agent as well as a curing one for the novolac binder. When the alumina platelet/novolac composite was heated with covering its surface with filter papers, a porous structure formed inside the composite due to blowing from HMT. On the other hand, the blowing gas near the surface was evolved outward through the filter paper, which resulted in the formation of the surface layer composed of the aligned alumina platelets. Effect of the surface layer on the mechanical strength was examined by three-point bending measurement. The bending strength of the obtained porous alumina increased by 94% compared to the porous alumina without the surface layer.©2017 The Ceramic Society of Japan. All rights reserved.Key-words : Alumina, Porous, Platelets [Received November 7, 2016; Accepted January 29, 2017] Porous ceramics have numerous industrial applications, including structural components, thermal insulators, absorbents, and filters, 1)6) due to a variety of specific properties, such as their heat and corrosion resistance, lightness, and low thermal conductivity. 7),8) Among these specific properties, the lightness is one of the most important properties in the porous ceramics. While increasing porosity reduces the weight, it also degrades mechanical strength, which is critically important where the porous ceramics is used as structural materials.We have previously proposed a direct-foaming approach for porous ceramics from ceramic/novolacHexaMethyleneTetramine (HMT) composite, 9),10) and using this approach we have fabricated porous alumina with the relatively dense surface layer. 11) In this study, HMT was used as a blowing agent and as a curing one for the novolac resin. A gas blown from HMT led to the formation of a porous structure in the alumina/ novolac composite with the expansion of the composite body, while it also resulted in swelling of the surface. This problem can be solved by covering the surface with a proper sheet and constraining the swelling using a mold during blowing. When using a plastic sheet for this purpose, coarse pores formed on the surface because the blowing gas accumulated around the surface, which led to degradation of mechanical strength. Instead, when employing a paper filter for the sheet, relatively dense layer was obtained since the blowing gas near the surface was released to the outside and to keep the surface flat, improving the mechanical strength 30% compared to that of porous alumina without the surface layer.It has been known that dense alumina with microstructure of aligned platelets exhibits excellent mechanical property when stress is applied in the alignment direction. 12)17) Therefore, if the surface layer composed of aligned alumina platelets parallel to the surface can be fabricated, then we can anticipate increase of the mechanical strength. However, to the best of our knowledge, there have been no studies on controlling mi...

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New Approach for Macro Porous RB‐SiC Derived from SiC/Novolac‐type Phenolic Composite

Cited by 13 publications

References 35 publications

Low‐Density Open Cellular Silicon Carbide Foams from Sucrose and Silicon Powder

Low‐Density Open Cellular Silicon Carbide Foams from Sucrose and Silicon Powder

Fabrication and characterization of porous alumina with denser surface layer by direct foaming

Fabrication and characterization of porous alumina with a surface layer composed of alumina platelet by direct-foaming method

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