<i>In</i><i>Situ</i> Densification Behavior in the Pyrolysis Consolidation of Amorphous Si‐N‐C Bulk Ceramics from Polymer Precursors

Wan, Julin; Gasch, Matthew J.; Mukherjee, Amiya K.

doi:10.1111/j.1151-2916.2001.tb00982.x

Cited by 35 publications

(34 citation statements)

References 8 publications

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“…the total amount of porosity) and not to the cell size. [22] While the transient porosity which forms upon pyrolysis in the polymer-to-ceramic conversion temperature interval (roughly 600 to 800°C) is in the micro-and meso-range (< 2 nm and between 2 and 50 nm, respectively), and tends to be removed upon further heating (due to pore shrinkage aided by the formation of active radicals and viscous flow), [23] the macro-porosity generated by this process cannot be eliminated, due to its much larger length scale, and thus remains within the resulting ceramic body. Occasionally, some cracks were observed in the structure of some of the produced porous ceramic monoliths, caused by stresses originating from several factors, including the large volume of gas released and a possible non homogeneous distribution of the two silicone precursors (PDMS and silsequioxane) within the unfired, dense body.…”

Section: Resultsmentioning

confidence: 99%

A Direct Method for the Fabrication of Macro‐Porous SiOC Ceramics from Preceramic Polymers

Vakifahmetoğlu

Colombo

2008

Adv Eng Mater

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Cellular ceramics, possessing both open or closed porosity, find use in several demanding engineering applications because of their favorable set of properties.[1] Several processing methods have been proposed for their fabrication, including the replication of the structure of polymeric foams, direct blowing, the use of sacrificial fillers, extrusion through special dies (for honeycombs), solid freeform techniques, the mimicking of natural templates (e.g. wood) or the assemblage of fibers or hollow bodies.[2,3] Preceramic polymers, in particular silicones, have been successfully used for obtaining ceramic components (such as foams and membranes) possessing a large amount of porosity, in the micro-, meso- and macro-size scale.[4, and references therein] However, some of the fabrication methods have some limitations: for instance, direct foaming techniques often lead to a gradient in the porosity amount and pore size along the main expansion axis;[5,6] the infiltration of a silicone resin within organic sacrificial fillers requires a burn out step that has to be carried out in a very controlled fashion in order to produce components without defects (besides often requiring warm pressing – depending on the rheological characteristics of the preceramic polymer – to obtain a well controlled morphology), thus limiting the size and shape of the component that can be produced;[7] the use of supercritical CO2 is regulated by the diffusion within the solid polymer, and works well only for components of limited thickness.[8] In recent years, it has been shown that blending preceramic polymers with different characteristics (molecular weight, molecular architecture, ceramic yield) allows to produce cellular ceramics.[9,10] This paper further explores this possibility, with the specific aim of directly developing a large amount of porosity within the resulting ceramic body during a one-step pyrolysis treatment

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Section: Resultsmentioning

confidence: 99%

A Direct Method for the Fabrication of Macro‐Porous SiOC Ceramics from Preceramic Polymers

Vakifahmetoğlu

Colombo

2008

Adv Eng Mater

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“…Over the past years, the effects of pore-opening and pore shrinkage [2][3][4][5]14,[17][18][19] as well as the effect of addition of thermally-labile polymer on porous structure have been reported. For instance, Kusakabe et al 4 and Li et al 5 prepared SiCbased membranes by pyrolyzing PCS mixed with thermallylabile polymer, polystyrene PS to further increase H 2 permeance.…”

Section: 15mentioning

confidence: 99%

Structural Evolution during Conversion of Polycarbosilane Precursor into Silicon Carbide-Based Microporous Membranes

Suda¹,

Yamauchi²,

Uchimaru³

et al. 2006

J. Ceram. Soc. Japan

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Silicon carbide-based microporous ceramic membranes for hydrogen separation were prepared via pyrolysis of polycarbosilane as a polymeric precursor. To prepare membranes with excellent hydrogen separation performance, effects of hydrosililation cross linking, addition of thermally-labile polymer as well as pyrolysis conditions on the structural evolution during conversion of the polycarbosilane precursor into the silicon carbidebased microporous membranes, have been investigated. The results of the activation energy for possible reactions, change in functional groups, and nitrogen adsorption and gas permeance measurements suggested that the cross-linking reaction between triple bond and Si-H bond gave three dimensional networks, resulting in smaller micropore and larger surface area. The size of the gases evolved during pyrolysis was also suggested to have relationship with the micropore structure.

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“…19,[66][67][68][69] This approach takes advantage of the transient porosity generated upon heat treating a preceramic polymer in the temperature range at which the polymer-to-ceramic conversion occurs (generally 400-800 • C). 4,70 The build-up of internal pressure in the component, provoked mainly by the decomposition of the organic moieties in the preceramic polymer (with generation typically of CH 4 and H 2 gas) leads to porosity (with pore size typically below 50-100 nm). This (micro-)porosity is however transient, because it is eliminated (and thus the SSA value is drastically reduced) when the pyrolysis temperature leading to the completion of the ceramization process is increased, according to a densification mechanism based on surface reaction/pyrolysis accommodated by viscous flow.…”

Section: Resultsmentioning

confidence: 99%

Engineering porosity in polymer-derived ceramics

Colombo

2008

Journal of the European Ceramic Society

209

123

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InSitu Densification Behavior in the Pyrolysis Consolidation of Amorphous Si‐N‐C Bulk Ceramics from Polymer Precursors

Cited by 35 publications

References 8 publications

A Direct Method for the Fabrication of Macro‐Porous SiOC Ceramics from Preceramic Polymers

A Direct Method for the Fabrication of Macro‐Porous SiOC Ceramics from Preceramic Polymers

Structural Evolution during Conversion of Polycarbosilane Precursor into Silicon Carbide-Based Microporous Membranes

Engineering porosity in polymer-derived ceramics

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