The influence of gel-casting parameters on the preparation of Si porous bodies (original) (raw)
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Le Journal De Physique Colloques, 1986
R6sum6-On a optimis6 les caractbristiques chimiques et morphologiques d e poudres de silicium ainsi que la porosit6 de ces poudres compact&es, de mani&re 5 obtenir du nitrure de silicium denze par frittage de RBSN. L'influence de la rbpartition granulom6trique sur la distribution de la taille des pores a 6t6 d6termin6e en faisant varier de mani6re syst6matique la r6partition granulo-m6trique par broyage & sec ou humide. L'influence de la micropo-rosit6 des poudres de Si compactbes sur la microporosit6 du RBSN a 6t6 analys6e.
Materials Science and Engineering: A, 2012
Porous Si 3 N 4 ceramics with high porosity prepared by gelcasting and pressureless sintering were used as frames for Si 3 N 4 -SiO 2 composites. Various contents of amorphous SiO 2 were introduced into porous Si 3 N 4 frames by repeating the sol-gel infiltration and sintering process. The sol-gel process resulted in the increase of density and the formation of well-distributed micro-pores with both uniform pore size and smooth pore wall. The mechanical properties and thermal shock resistance of Si 3 N 4 -SiO 2 composites were also largely improved. As the SiO 2 content increased from 0 to 25.9 vol%, the porosity of Si 3 N 4 -SiO 2 composites decreased from 49.3% to 22%, with the density of composites increased from 1.62 g/cm 3 to 2.18 g/cm 3 . The flexural strength and fracture toughness also increased from 92.6 MPa and 1.05 MPa m 1/2 to 148.1 MPa and 1.70 MPa m 1/2 , respectively. The dielectric constant increased from 2.65 to 3.61, but the dielectric loss did not increase much from 3.23 Â 10 À 3 to 3.84 Â 10 À 3 . The residual flexural strength of porous Si 3 N 4 ceramics retained to a DT of 700 1C, while the Si 3 N 4 -SiO 2 composites with 25.9 vol% of SiO 2 showed much better thermal shock resistance and had a DT of 900 1C.
Rheological properties of aqueous suspensions of Si3N4-Si-Al2O3-ZrO2 powders
1986
Resume -Le faqonnage est tres important dans la production des c6ramiyues puisque les defauts qui se produisent pendant cette phase de la fabrication demeurent aussi apr6s le frittage.Dans ce travail on Gtudie les proprietes rheologiques des suspensions des poudres de Si N -Si-A1 03-ZrO dans 3.4 Te but d'obtenir des barbotines de bonne qualite pour ?a proguction de ceramiques pour les hautes temperatures.
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008
Porous -Si 3 N 4 ceramics have a wide range of potential applications, including filters for hot gases or molten metals, bioreactor supports and lightweight structural components. In the present study, a new approach is taken for the production of porous -Si 3 N 4 ceramics based on compositional design. A low volume fraction of multiple sintering aids is employed, where each additive is designed to play one or more specific roles in the sintering behavior and microstructural development of -Si 3 N 4 (e.g. densification, ␣to -Si 3 N 4 transformation, anisotropic -Si 3 N 4 whisker growth, debonding aid). The primary aim of this work was to develop -Si 3 N 4 ceramics with a more porous microstructure than in prior work (ideally with 20-40 vol.% porosity), while developing high grain aspect ratios (i.e. >10:1) such that good mechanical performance can be expected. Compositions are based on various ratios of RE 2 O 3 :MgO, where RE = La, Nd, Y or Yb, with selected materials also prepared with small CaO additions. Sintering has been conducted in a nitrogen atmosphere (0.1 MPa), at temperatures between 1400 and 1700 • C. The influence of sintering aid composition and sintering temperature has been assessed. Particular attention was paid to microstructure development, including: densification behavior, retained pore size, the extent of ␣to -Si 3 N 4 transformation, and the evolution of -Si 3 N 4 grain aspect ratios. , etc.); oxides of this type will be subsequently referred to by the generic term "rare earth oxides" (RE 2 O 3 ). In this instance, a high viscosity Si-RE-O-N oxynitride glass phase is formed at the processing temperature, which retards densification but not the ␣to -Si 3 N 4 transformation. Sintering in this instance is observed to be diffusion controlled . This approach leads to materials with extremely fine scale porosity. The individual anisotropic -Si 3 N 4 grains form an interlocking network throughout the material, which provides good mechanical behavior. This general approach has been further refined, through the use of controlled seeding and texture development, including sinter-forging . Strengths in excess of 1 GPa can be achieved for these materials, in combination with high toughness, although the retained porosity content is typically less than 15 vol.% . 0921-5093/$ -see front matter
Production of high throughput nano-porous silicon (NPS) powder with different architectures
Materials Chemistry and Physics, 2018
In this study, a powder technology manufacturing route as a pioneering, low cost, simple and safe method is used for the fabrication of nano-porous silicon (NPS) powder. It is a promising one as its high throughput for different applications due to their supposed low toxicity and good compatibility. The NPS has been prepared using a combination between high energy ball milling technique and wet alkali chemical etching based technique through the utilization of commercial silicon powder; with high yield efficiency (86.3%). Preparation of several NPS shapes (nanorods, nanoplates, nanwalls, nanospheres and nanobelts) are fabricated, which could be used in different applications. The most significant reduction of the crystallite size was observed by increasing the milling time. Transformation of crystallographic plane of the commercial powder Si (400) to the NPS {(111), (220), (211), (312) and (400)} is resulted, using several concentrations of (KOH) as the etchant and wetting agent {npropanol (NPA)}.
Effect of processing variables on synthesis of β-Si 3N 4 particles
Journal of The European Ceramic Society, 2008
Synthesis of highly anisotropic rod-like -Si 3 N 4 particles with different morphological characteristics was accomplished using commercial ␣-Si 3 N 4 . A number of powder mixtures were prepared with additions of various oxides (Al 2 O 3 + RE 2 O 3 , being RE = Y, La or Yb) that were subsequently heat treated in a loose powder state in the temperature range of 1750-1950 • C and dwell times from 10 to 180 min under high pressure of N 2 (60 MPa) in a hot isostatic press. The obtained aggregated porous bodies were lightly crushed by hand using an alumina mortar and pestle and subsequently subjected to sequential chemical treatments to eliminate the glassy phases and possible residual crystalline compounds, and to separate the synthesized -Si 3 N 4 particles. Resulting -Si 3 N 4 particles were characterized by X-ray diffraction and examined by scanning and transmission electron microscopy. Morphological characteristics of the synthesized -Si 3 N 4 particles were determined through quantitative dimensional analysis. The effect of amount and chemical composition of oxide additives responsible for liquid phase formation as well as heat treatment parameters on -Si 3 N 4 particles size and morphology are established. Possible mechanisms of -Si 3 N 4 particles growth are discussed.
Journal of the European Ceramic Society, 2013
In this study, porous -Si 3 N 4 ceramics containing limited amount of Sm 2 O 3 and CaO as sintering aids were produced by addition of potato starch (10 and 20 vol.%) and partial sintering. Two different Si 3 N 4 powders, ␣and -, were used as starting materials. Scanning electron microscopy investigations revealed that development of elongated -Si 3 N 4 grains were much more pronounced when ␣-Si 3 N 4 starting powder was used. Even though porosity values of the compositions prepared by using ␣-Si 3 N 4 (∼57.0-58.4%) is significantly higher than the samples produced by -Si 3 N 4 (42.6%), no significant change was observed for the bending strength, fracture toughness and Weibull modulus. This indicates that microstructural features have a significant contribution to the mechanical properties of the porous materials in terms of bending strength and fracture toughness.
A novel method of fabricating porous silicon
Materials Science and Engineering: A, 2011
Porous silicon was fabricated using the spark plasma sintering technique. High porosity ∼10-50% and strength ∼50-60 MPa was obtained by tailoring the SPS variables. XRD and Raman investigations showed presence of pure silicon and exhibition of photoluminescence under visible light at wavelength ∼520 nm confirmed the presence of porous silicon.