{"title":"SiBOC泡沫从甲基乙烯基硼硅氧烷使用尿素晶体作为孔模板和乙二胺作为胶凝剂","authors":"Anil Painuly, Benny K. George, K. Prabhakaran","doi":"10.1007/s41779-023-00886-8","DOIUrl":null,"url":null,"abstract":"<div><p>A simple urea crystal templating method is reported for the preparation of SiBOC ceramic foams, with rectangular rod-like pores, from methylvinylborosiloxane (MVBS) preceramic polymer solution. Pastes of urea crystals in concentrated MVBS solution were filled in open rectangular mold and set by cross-linking of MVBS using ethylenediamine (EDA) at room temperature. The cross-linking is due to the formation of adduct between electron-deficient boron in the polymer backbone and lone pair of electrons in amino groups of EDA. The gelation time of 60 wt.% MVBS solution in ethanol is modulated in the range of 240 to 3.25 h using EDA concentration in the range 0.33 to 10 wt.%. The gelled body is water-washed to leach out urea, followed by inert heat treatment at 1500 °C to produce SiBOC foam. The SiBOC ceramic foams of density 0.739 to 0.215 g cm<sup>−3</sup>, compressive strength 2.75 to 0.207 MPa, and thermal conductivity 0.262 to 0.073 W m<sup>−1</sup> K<sup>−1</sup> were achieved with urea concentrations of 50 to 88 vol.%. SEM micrographs show rectangular rod-like pores resulting from the urea particle template, which increases with an increase in urea concentration. XRD and TEM confirm SiBOC as amorphous, with the presence of a few nanocrystals of β-SiC and turbostratic carbon layers. The low thermal conductivity, excellent oxidation resistance, and reasonably high compressive strength make the prepared foams suitable candidate for high temperature thermal protection in aerospace.</p></div>","PeriodicalId":49042,"journal":{"name":"Journal of the Australian Ceramic Society","volume":"59 4","pages":"935 - 946"},"PeriodicalIF":1.9000,"publicationDate":"2023-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s41779-023-00886-8.pdf","citationCount":"0","resultStr":"{\"title\":\"SiBOC foams from methylvinylborosiloxane using urea crystals as a pore template and ethylenediamine as a gelling agent\",\"authors\":\"Anil Painuly, Benny K. George, K. 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The SiBOC ceramic foams of density 0.739 to 0.215 g cm<sup>−3</sup>, compressive strength 2.75 to 0.207 MPa, and thermal conductivity 0.262 to 0.073 W m<sup>−1</sup> K<sup>−1</sup> were achieved with urea concentrations of 50 to 88 vol.%. SEM micrographs show rectangular rod-like pores resulting from the urea particle template, which increases with an increase in urea concentration. XRD and TEM confirm SiBOC as amorphous, with the presence of a few nanocrystals of β-SiC and turbostratic carbon layers. 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引用次数: 0
摘要
本文报道了一种简单的尿素晶体模板法,以甲基乙烯基硼硅氧烷(MVBS)预陶瓷聚合物溶液为原料制备具有矩形棒状孔的SiBOC泡沫陶瓷。将浓缩的MVBS溶液中的尿素晶体填充在开模矩形中,并在室温下用乙二胺(EDA)对MVBS进行交联固化。交联是由于聚合物主链上的缺电子硼与EDA的氨基上的孤对电子之间形成加合物。60 wt.%的MVBS溶液在乙醇中的凝胶时间在240至3.25小时的范围内调节,使用EDA浓度在0.33至10 wt.%的范围内。将凝胶体水洗以滤出尿素,然后在1500°C下进行惰性热处理以产生SiBOC泡沫。当尿素浓度为50 ~ 88 vol.%时,SiBOC陶瓷泡沫的密度为0.739 ~ 0.215 g cm−3,抗压强度为2.75 ~ 0.207 MPa,导热系数为0.262 ~ 0.073 W m−1 K−1。SEM显微图显示,尿素颗粒模板形成的矩形棒状孔隙,随着尿素浓度的增加而增加。XRD和TEM证实SiBOC为非晶态,存在少量β-SiC纳米晶和涡层碳层。其导热系数低、抗氧化性能优异、抗压强度较高,是航空航天领域高温热防护的理想选择。
SiBOC foams from methylvinylborosiloxane using urea crystals as a pore template and ethylenediamine as a gelling agent
A simple urea crystal templating method is reported for the preparation of SiBOC ceramic foams, with rectangular rod-like pores, from methylvinylborosiloxane (MVBS) preceramic polymer solution. Pastes of urea crystals in concentrated MVBS solution were filled in open rectangular mold and set by cross-linking of MVBS using ethylenediamine (EDA) at room temperature. The cross-linking is due to the formation of adduct between electron-deficient boron in the polymer backbone and lone pair of electrons in amino groups of EDA. The gelation time of 60 wt.% MVBS solution in ethanol is modulated in the range of 240 to 3.25 h using EDA concentration in the range 0.33 to 10 wt.%. The gelled body is water-washed to leach out urea, followed by inert heat treatment at 1500 °C to produce SiBOC foam. The SiBOC ceramic foams of density 0.739 to 0.215 g cm−3, compressive strength 2.75 to 0.207 MPa, and thermal conductivity 0.262 to 0.073 W m−1 K−1 were achieved with urea concentrations of 50 to 88 vol.%. SEM micrographs show rectangular rod-like pores resulting from the urea particle template, which increases with an increase in urea concentration. XRD and TEM confirm SiBOC as amorphous, with the presence of a few nanocrystals of β-SiC and turbostratic carbon layers. The low thermal conductivity, excellent oxidation resistance, and reasonably high compressive strength make the prepared foams suitable candidate for high temperature thermal protection in aerospace.
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