Development of multiphase bioceramics from a filler-containing preceramic polymer

Multiphase bioceramics based on wollastonite and wollastonite/hydroxylapatite (W/HAp) have been successfully prepared by the heat treatment of a filler-containing preceramic polymer. CaO-bearing precursors (Ca-carbonate, Ca-acetate, and CaO nano-particles) were dispersed in a solution of silicone resin, subsequently dried and pyrolysed in nitrogen. The reaction between silica, deriving from the oxycarbide (SiOC) residue of the silicone resin, and CaO “active filler” led to the formation of several calcium silicates, mainly consisting of wollastonite (CaSiO₃), in both low and high temperature forms. The phase assemblage of the final ceramic varied with the pyrolysis temperature (varying from 1000 to 1200 °C). HAp was additionally inserted, as “passive filler” (i.e. not reacting with SiOC), for the preparation of bioceramics based on W/HAp mixtures.     

Advanced ceramics from a preceramic polymer and nano-fillers

A commercial silicone resin (“silicone”) filled with ceramic nanoparticles has been employed for the preparation of mullite and β-SiAlON ceramics. Dense, pure, crack free mullite were prepared by the heating in air of a mixture of silicone resin and alumina nanoparticles in the temperature range 1200–1550 °C. The high reactivity of Al₂O₃ towards silica, coupled with nanometric size, led to a large volume fraction of mullite crystals even at low firing temperatures (1250 °C). β-SiAlON ceramics were prepared by the heating of a mixture of silicone resin and fillers consisting of Al₂O₃ nanoparticles and Si₃N₄ and AlN microparticles, in the temperature range 1450–1550 °C in nitrogen atmosphere. The formation of SiAlON was found to be preceded by the formation of intermediate alumino-silicate phases like mullite and sillimanite, successively reduced (due to the carbon content of the ceramic residue of silicone resins) and nitrided. Although some oxide contamination was still present after the high temperature treatment, a high β-SiAlON yield (about 80%) was achieved. The use of nano-filled silicones provides a promising route for the fabrication of advanced ceramic components by exploiting polymer processing techniques, with the achievement of complex shapes.     

Carbide-derived-carbons with hierarchical porosity from a preceramic polymer

Synthesis of carbon by extraction of metals from carbides has been successfully used to produce a variety of micro-porous carbide-derived carbons (CDCs) with narrow pore size distributions and tunable sorption properties. This approach is of limited use when larger mesopores are targeted, however, because the relevant synthesis conditions yield broad pore size distributions. Here we demonstrate the porosity control in the 3-10 nm range by employing preceramic polymer-derived silicon carbonitride (SiCN) precursors. Polymer pyrolysis in the temperature range 600-1400 °C prior to chlorine etching yields disordered or graphitic CDC materials with surface area in the range 800-2400 m² g⁻¹. In the hierarchical pore structure formed by etching SiCN ceramics, the mesopores originate from etching silicon nitride (Si₃N₄) nano-sized crystals or amorphous Si-N domains, while the micropores come from SiC domains. The etching of polymer-derived ceramics allows synthesis of porous materials with a very high specific surface area and a large volume of mesopores with well controlled size, which are suitable for applications as sorbents for proteins or large drug molecules, and supports for metal catalyst nanoparticles.     

聚合物陶瓷先驱体材料的合成与应用

概述了作为陶瓷先驱体的四种聚合物f聚碳硅烷(PCS)、聚硅氮烷(PSZ)、聚硼氮烷(PBZ)以及聚硅氧烷(PSO)]的合成与应用,介绍了国内外对该类材料研究的最新进展,并针对先驱体裂解转化陶瓷工艺所存在的局限性以及不足,提出了今后的发展方向.     

Ceramic foams and micro-beads from emulsions of a preceramic polymer

A commercially available solid silicone resin was dissolved in a solvent and emulsified via stirring in the presence of water and surfactant to form three different types of emulsions, namely water-in-oil (w/o), water-in-oil-in-water (w/o/w) and oil-in-water (o/w), by following different preparation procedures. After curing, thermosets possessing different morphologies, ranging from highly porous (monolithic) foams to porous micro-beads and solid micro-beads, formed. The samples kept their shape upon pyrolysis, and resulted in ceramic foams (via w/o) and porous micron sized (∼200 μm) spherical particles (via w/o/w) having more than 80 vol% of total porosity, while with o/w emulsification solid SiOC ceramic particles with an average diameter of ∼100 μm formed. Both surfactant and water altered the IR spectra for emulsion-derived thermoset samples, in comparison to the pure cured resin, but upon pyrolysis similar amorphous ceramics were obtained from all samples.     

The properties of a ceramic injection moulding suspension based on a preceramic polymer

A ceramic suspension incorporating fine sinterable silicon carbide powder in a polycarbosilane vehicle has been modified by additions of paraffin wax to make it suitable for plastic forming operations. The diluent enables higher volume fractions of ceramic to be incorporated and lowers the softening point of the suspension. The danger of temperature-induced crosslinking in processing machinery is alleviated.     

Oxidation resistant ceramic foam from a silicone preceramic polymer/polyurethane blend

Silicon oxycarbide (SiOC) ceramic foams, produced by the pyrolysis of a foamed blend of a methylsilicone preceramic polymer and polyurethane (PU) in a 1/1 wt.% ratio, exhibit excellent physical and mechanical properties. The proposed process allows to easily modify the density and morphology of the foams, making them suitable for several engineering applications. However, it has been shown that, due to residual carbon present in the oxycarbide phase after pyrolysis, the foams are subjected to an oxidation process that reduces their strength after high temperature exposure to air (12 h 1200°C). A modified process, employing the same silicone resin preceramic polymer but a much lower PU content (silicone resin/PU=5.25/1 wt.% ratio), has been developed and is reported in this paper. Microstructural investigations showed that carbon rich regions deriving from the decomposition of the polyurethane template are still present in the SiOC foam, but have a much smaller dimension than those found in foams with a higher PU content. Thermal gravimetric studies performed in air or oxygen showed that the low-PU containing ceramic foams display an excellent oxidation resistance, because the carbon-rich areas are embedded inside the struts or cell walls and are thus protected by the dense silicon oxycarbide matrix surrounding them. SiOC foams obtained with the novel process are capable to maintain their mechanical strength after oxidation treatments at 800 and 1200°C (12 h), while SiOC foams obtained with a higher amount of PU show about a 30% strength decrease after oxidation at 1200°C (12 h).     

Porous wollastonite-hydroxyapatite bioceramics from a preceramic polymer and micro- or nano-sized fillers

Wollastonite-hydroxyapatite ceramics have been successfully prepared by a novel method, corresponding to the thermal treatment in air of a silicone embedding micro- and nano-sized fillers. CaCO₃ nano-sized particles, providing CaO upon decomposition, acted as “active” filler, whereas different commercially available or synthesised hydroxyapatite particles were used as “passive” filler. The homogeneous distribution of CaO, at a quasi-molecular level, favoured the reaction with silica derived from the polymer, at only 900 °C, preventing extensive decomposition of hydroxyapatite. Open-celled porous ceramics suitable for scaffolds for bone-tissue engineering applications were easily prepared from filler-containing silicone resin mixed with sacrificial PMMA microbeads as templates. The pore size (in the range of 80-400 μm) and the open porosity percentage (40-50%) were evaluated by means of micro-computerized tomographic analysis. A preliminary assessment of the biocompatibility and cell activity of the produced ceramics was performed successfully by in vitro tests using human osteoblast cells.     

Joining of SiC ceramics via a novel liquid preceramic polymer (V-PMS)

A novel liquid preceramic polymer (V-PMS) was synthsized by modifying polymethylsilane (PMS) with 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane ([CH₃(CH₂CH)SiO]₄, D4Vi), for joining SiC ceramics under ambient pressure. The obtained V-PMS with a viscosity of 125 Pas at room temperature exhibits excellent thermal properties and bonding strength. The ceramic yield of V-PMS treated at 1200 °C under Ar atmosphere is 84.5%, which is 38.3% higher than the original PMS. The shear strengths of the SiC joints joined by V-PMS at 800 °C, 1000 °C and 1200 °C under N₂ atmosphere are 11.9 MPa, 34.5 MPa and 29.9 MPa, respectively. The excellent performances make the obtained V-PMS promising candidates for joining SiC ceramics in high-temperature applications.     

Lithium orthosilicate ceramics with preceramic polymer as silica source

Lithium orthosilicate ceramics powders were synthesized using a preceramic polymer as the source of silica. Stoichiometric, as well as batches lean and rich in lithium, were prepared by the said approach to understand the thermal stability of the orthosilicate phase at 1000 °C. All of the batches produced phase pure orthosilicate ceramics with sintered density up to 82%. However, different batches showed markedly different microstructural evolution with the lithium lean and stoichiometric compositions exhibiting formation of flower-like lithium metasilicate phase. The lithium rich composition showed no phase separation of the orthosilicate ceramic phase as confirmed by electron microscopy and x-ray diffraction. The high volatilization of the lithium species at high temperature was ascribed to the phase separation of the orthosilicate phase in the lithium lean compositions. The current report provides an alternative and novel method to fabricate lithium orthosilicate, and shows promise for application as tritium breeding blankets in fusion technologies.     

Synthesis,characterization, and ceramization of a carbon-rich SiCw-ZrC-ZrB2 preceramic polymer precursor

A precursor (PBSZ) for SiC_w-ZrC-ZrB₂ hybrid powder was synthesized by chemical reaction of phenol, paraformaldehyde, zirconium oxychloride, boric acid and tetraethylorthosilicate. Results show that zirconium, silicon and boron atoms have been successfully introduced into the branched structure. Decomposition of PBSZ is completed at 800 °C, and it gives amorphous carbon, SiO₂, B₂O₃ and ZrO₂ with a yield of 38% at 1200 °C. During the pyrolysis process, ZrB₂ and SiC form at about 1500 °C, followed by the appearance of ZrC when the amount of B₂O₃ is limited. Highly crystallized ZrB₂–ZrC–C powder with ZrB₂ and ZrC grains evenly distributed in the carbon matrix together with randomly distributed SiC whiskers are obtained after heat-treated at 1800 °C. Further heated at 1900 °C, ZrB₂ and ZrC grains grow from 200 to 500 nm, while SiC whiskers show a much smaller diameter size and tend to grow on the ZrB₂–ZrC–C block surface. The morphology difference is caused by the larger gas supersaturation and accommodation coefficient of the pore channels on the block surface. In addition, defects of the carbon matrix are cumulated to the highest at 1500 °C and the structure-ordered carbon is obtained after heat treated at 1900 °C.     

Novel crosslinking system with hydroxyl-containing polymer, alicyclic polyepoxide and polyalkoxysilane

The crosslinking system based on the reaction among alicyclic epoxide group, hydroxyl group and alkoxysilyl group in the presence of aluminum β-diketone chelate have been developed. Five kinds of reaction are possible, and the result of gas chromatography and infrared analyses indicated that the main reaction is the ring-opening reaction of alicyclic epoxide group with hydroxyl group and/or hydroxysilyl group. The acrylic resin obtained by free radical polymerization of these three kinds of functional monomers and non-functional monomers showed good curing property, and the film was superior in acid rain resistance and outdoor durability. The resin is suitable to use in automotive 2coat–1bake clear coat. The viscosity of this binder system was remarkably reduced by addition of a low molecular weight alicyclic polyepoxide compound and an alkoxysilane oligomer without affecting to its good curing property. Such a system made it possible to design novel high solid coatings. It was found that the crosslinking could be extended to the combination of a polyester polyol, an alicyclic epoxide compound and an alkoxysilane oligomer. In this case, it was necessary that the polyester polyol contained highly reactive terminal hydroxyl group in the branch chains.     

Preparation and characterisation of SiOC ceramics made from a preceramic polymer and rice bran

SiOC ceramics were prepared from a methyl silicone preceramic polymer and rice bran by a simple method. Dried rice bran powder was blended with a molten preceramic polymer (Silres 610) at various ratios by a Brabender-type static mixer. Composites were made from them by crosslinking at 250 °C in a hot press and porous ceramics were made by pyrolysing them at 900 °C. The produced porous ceramics were characterised by measuring their density, ceramic yield, volume shrinkage, hygroscopic expansion, and compressive strength. Additionally, the fabricated ceramics were examined by SEM, and FTIR. Ceramics made from Silres 610/rice bran 50/50 ratio showed the highest compressive strength (2.7 MPa) along with the highest ceramic yield (47.8%), but the lowest hygroscopic expansion, and volume shrinkage. On the other hand, the 20/80 ratio showed the lowest ceramic yield and compressive strength but the volume shrinkage higher than the 50/50 ratio. All ceramics showed negligible hygroscopic expansion.     

Facile obtainment of luminescent glass-ceramics by direct firing of a preceramic polymer and oxide fillers

Rare-earth (RE) doped glass-ceramics represent very interesting luminescent materials. The thermal annealing of the glass precursor causes the controlled precipitation of several crystalline phases, in which RE may be variously distributed, also with different oxidation states, e.g. Eu²⁺ and Eu³⁺. The present investigation demonstrates the feasibility of preparation of RE-doped alumino-boro-silicate glass-ceramics by direct firing in air (at 1000–1200 °C) of a preceramic polymer, filled with nano- and micro-sized particles, as an alternative to glass melting and annealing. In particular BaCO₃ or SrCO₃ micro-particles, mixed with nano-sized γ-Al₂O₃, were found to react with amorphous silica, available from the oxidative decomposition of a commercial silicone, yielding a strontium or a barium alumino-silicate phase. Boric acid micro-particles contributed both to the development of a liquid phase upon firing (promoting ionic interdiffusion) and to the formation of a La-borate phase, by interaction with La₂O₃ micro-particles. The blue and red luminescence of the obtained glass-ceramics is attributed to the incorporation of Eu²⁺ and Eu³⁺ ions, from nano-sized Eu₂O₃ filler, in alumino-silicate and borate phases, respectively.     

Synthesis of ordered mesoporous silicon oxycarbide monoliths via preceramic polymer nanocasting

Highly ordered mesoporous silicon oxycarbide (SiOC) monoliths have been synthesized using liquid poly(hydridomethylsiloxane) (PHMS) as starting preceramic polymer and mesoporous carbon CMK-3 as direct template. Monolithic SiOC-carbon composites were generated via nanocasting of PHMS into CMK-3, pressing without any additive, cross-linking at 150 °C under humid air and subsequent thermolysis at 1000 or 1200 °C under argon atmosphere. The carbon template was finally removed by the thermal treatment at 1000 °C in an ammonia atmosphere, as a result of the generation of monolithic SiOC ceramics with ordered mesoporous structures. The products were characterized by scanning electron and transmission electron microscopes, X-ray diffraction, Fourier transformation infrared spectrometer, X-ray photoelectron spectroscope and nitrogen absorption-desorption analyzer. The as-prepared SiOC monoliths exhibited crack-free, ordered 2-dimentional hexagonal p6mm symmetry with high specific surface areas. With increasing the calcination temperature, the ordered mesoporous structure was still remained and the specific surface area just had a slight reduction from 616 to 602 m² g⁻¹. Moreover, the porous SiOC monoliths possessed good compression strengths and anti-oxidation properties.     

Novel reagents for heat-activated polymer crosslinking

Summary The dipolar cycloaddition of nitrile oxides with species containing unsaturation is a very attractive means of forming crosslinks in polymer systems, since the reaction is rapid and yields thermally stable links. Latent nitrile oxide precursors can be prepared by reaction of an isocyanate and an alkyl nitroacetate. These precursors release alkanol and carbon dioxide when heated to liberate the highly reactive nitrile oxide species. An improved synthetic procedure was developed to afford novel crosslinking agents based on difunctional, trifunctional and aliphatic precursors. Further, application of these agents to polymer crosslinking has been demonstrated. Received: 20 April 2001/Revised version: 29 August 2001/Accepted: 29 August 2001     

Synthesis of a soluble preceramic polymer for ZrC using 2-hydroxybenzyl alcohol as carbon source

A preceramic polymer for ZrC was successfully synthesised by chemical reaction between zirconium oxychloride (ZrOCl₂·8H₂O) and 2-Hydroxybenzyl alcohol via a one-pot route. The molecular structure, thermal properties and pyrolysis behaviour of the precursor were investigated. The results indicated that the precursor might be Zr–O–Zr chain polymer with 2-Hydroxybenzyl alcohol as ligand. The precursor was air-stable and exhibited excellent solubility in common organic solvents. The conversions from precursor to ZrC powders were investigated by TG-DTA, X-ray diffraction, Scanning electron microscope, TEM and Raman spectrum. The precursor underwent a thermal decomposition in four steps, and ZrC powders were formed at 1300°C via carbothermal reduction reaction of ZrO₂ and carbon in argon with ceramic yield of 63.0%. The ZrC particles were fine and exhibited irregular polyhedron morphology with average size in the range of 100–300?nm.     

Development of a multimicroinjection molding system for thermoplastic polymer

A novel concept of microinjection molding system was designed and presented. The system was designed as a multimicroinjection module, which is matched with a vertical injection molding machine (IMM) and can be applied on commercial IMMs. A planetary gear pump was integrated in this system to complete the multi microinjection molding (MμIM). The module is fixed between the stationary platen and the mold of IMM. The plasticizing unit of the IMM provides the melt and initial pressure for the multi microinjection molding system. With this system, a commercial IMM could be upgraded to a precise microinjection machine and has the capability of precise metering for the microinjection molding. Melt flowing behavior was predicted through the 3D injection molding simulation and experiments were carried out to testify the performance of the MμIM. The injection molding performance was evaluated and the results revealed that the MμIM system could effectively realize the microinjection molding. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Detection of a new crosslinking and properties of liquid polysulfide polymer

Polysulfide polymer was found in the 19th century. At present, this polymer consists of the repetition of disulfide linkage and diethyl formal and has SH terminals. This liquid polymer (LP) is cured by lead dioxide. We studied polysulfide polymerization and elastomeric mechanical properties of cured LP. The condition of polymerization greatly influenced its elastomeric mechanical properties. These phenomena could not be explained from the point of residual unreacted chlorine or produced OH terminals. We found that additional crosslinking sites are produced during polymerization besides crosslinking agents trichloropropane (TCP) by using the Insensitive Nuclei Enhanced by Polarization Transfer (INEPT) method. We proposed their chemical structures and reaction scheme of their formation. TCP and also these additional crosslinking sites influence the modulus of cured LP. The sum of the intensity of their crosslinking sites by ¹³C‐NMR had good correlation with 300% modulus of cured LP. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 59–66, 1999