Silicon Oxycarbide Composites Research Articles

Adsorption of CO2 on mechanochemically synthesized silicon oxycarbide composites

The present study explores the mechanochemical synthesis of porous silicon oxycarbide composites using commercial activated carbon and hydrated silica as precursors without additional functionalization, aiming to be used as effective adsorbents for carbon dioxide removal from gas streams. By adjusting the hydrated silica/activated carbon mass ratio, a set of materials were prepared with varying surface areas (256–662 m2/g), pore volumes (0.28–0.45 cm3/g), and surface functional groups concentrations (0.824–0.996 mmol/g). The optimal silicon oxycarbide composite (hydrated silica/activated carbon mass ratio of 1.5) demonstrated the CO2 adsorption capacity of 3.41 mmol/g at 25 °C and 1 bar, which can be attributed to the composite’s well-developed porosity and high surface functionality. In addition, the adsorbent exhibited high CO2/N2 selectivity of 15.2 along with stable cycling performance. These findings indicate that mechanochemically synthesized silicon oxycarbide composites have a considerable potential in the field of CO2 capture.

Silicon oxycarbide composites reinforced with silicon nitride and in situ formed silicon carbide

Dense SiOC-Si3N4 composites have been obtained employing mixtures with 10 % of Si3N4 (SN10) or 5 % Si3N4- and an extra amount of carbon-5 % carbon nanofibers- (SN5N5) using spark plasma sintering (SPS). SPS produces densification at 1300/1400 °C and delays the carbothermal reaction of SiO2/Si3N4 up to 1600 °C. It is observed the formation of a percolating network of SiC nanodots/nanowires widespread all over the matrix decorated with graphene-like carbon generated by Joule heating during SPS. The evolution of the Cfree is studied by conventional/non-conventional Raman parameters. In this sense, SN5N5–16 and SN10–17 show a Cfree phase composed by large highly tortuous and ordered graphene layers with the highest degree of interconnection and crystallinity determinant for understanding the highest thermal and electrical conductivities (1.91 WmK−1 and 33.6 Sm−1). Finally, this material displays a low coefficient of thermal expansion (1.26×10−6 K−1), remarkable resistance against oxidation to 1400 °C and high absorptance (95.8 %).

Preparation of polymer-derived SiOC-Cu ceramic composites and their tribological performance

Cu-containing silicon oxycarbide (SiOC) ceramic composites have been prepared by thermal pyrolysis of polymeric precursors and subsequent spark plasma sintering at 1600 °C. The resulting composites consist of SiO2, SiC, free carbon, and Cu-Si alloys. The microstructure of the composites has been identified via optical microscope and SEM. The mechanical properties, including the Vickers hardness, nano-indentation hardness, and Young’s modulus, of the SiOC composites have been assessed via indentation methods. The effects of Cu content on the tribological properties of the composites have additionally been investigated under different sliding frequencies against Al2O3 spheres at room temperature. It is shown that the introduction of the Cu-Si alloys is effective in reducing the friction coefficient of the material system, which decreases linearly from 0.27 of monolithic SiOC to 0.15 of SiOC with 7 wt% Cu content at 1 Hz. Raman spectroscopy has highlighted the friction-driven evolution of the free carbon phase in the SiOC ceramics. Finally, a correlation between the sliding frequency, Cu-Si content, and tribological properties of SiOC is established.

Механохимический синтез пористых кремнийоксиуглеродных композитов

The work is devoted to investigation of the process of mechanochemical synthesis of porous silicon oxycarbide composites. The synthesis was carried out by mechanical treatment of several mixtures of activated carbon and white soot with different mass ratios. Samples were investigated using such methods as X-ray diffraction, infrared spectroscopy, low-temperature nitrogen adsorption/desorption and potentiometric titration. Synchronous thermal analysis including thermogravimetric analysis and differential scanning calorimetry was performed. The results of X-ray diffraction analysis showed that no new phases were formed in the process of mechanochemical synthesis, and the structure of composites obtained can be characterized as highly amorphous. The possibility of activated carbon and white soot to be chemically bonded with the formation of silicon oxycarbides, which act as a binder in the composite structure, during intensive supply of mechanical energy to raw materials was proved. Thermal stability of silicon oxycarbides formed and the amount of free carbon that was not bonded with silicon dioxide were estimated by synchronous thermal analysis. It was established that the initial mixture composition significantly affects the surface chemistry of composites synthesized, which is expressed by a change in concentration of different surface functional groups. A possible mechanism of solid phase interaction between activated carbon and white soot resulting in the formation of Si–O–C bonds was proposed. Investigation of porous structure of composite materials obtained showed that the specific surface area and pore volume become lower with an increase in white soot concentration in the initial mixture. It is possible to adjust the porous structure of composites by changing the activated carbon to white soot mass ratio.

Further insights into the electrical and thermal properties of carbon enriched silicon oxycarbide composites

Cheap, abundant and easily-obtained carbon fillers such as graphite (GR), carbon black (CB), lamp black and active carbon were successfully incorporated into a silicon oxycarbide (SiOC) matrix using attrition milling followed by spark plasma sintering to obtain dense crack-free bulk composites. Carbon-enriched SiOC composites (C-SiOC) showed enhanced electrical (σ) and thermal (k) conductivities. Values as high as 667 Sm-1 for σ and an increase of 63% for k compared with SiOCs were obtained when GR flakes were incorporated into the SiOC. Very interesting values were also achieved (250 Sm-1 and a 46% increase) when CB was used, due to the formation of a percolating network of highly-interconnected tortuous graphene-like carbon domains which promoted phonon/electron transport.Raman parameters such as the tortuosity index, 3D ordering of graphene layers and the I2D/IG ratio, in conjunction with AB stacking, were crucial for understanding the electronic and/or phonon transport.

Mechanochemical synthesis of adsorbents based on silicon oxycarbide composites

In the work, an attempt was made to mechanochemically synthesize silicon oxycarbide composites from activated carbon and silica. Structure of the composites was studied using powder X-ray diffraction and IR spectroscopy. Formation of silicon oxycarbides was confirmed by presence of Si-O-C bond. Influence of the raw materials ratio on structural and chemical properties of resulting composites was revealed. With an increase of silica share in the initial mixture, a decrease in specific surface area and pore volume was noted, as well as an increase of the concentration of surface functional groups. Samples of the composites were tested in processes of sorption of methyl orange and fluoride ions. It was established that adsorption capacity for methyl orange decreased, while that for fluoride ions significantly increased comparing to activated carbon.

Strong and Thermostable Boron-Containing Phenolic Resin-Derived Carbon Modified Three-Dimensional Needled Carbon Fiber Reinforced Silicon Oxycarbide Composites with Tunable High-Performance Microwave Absorption Properties

This paper focuses on the preparation of boron-containing phenolic resin (BPR)-derived carbon modified three-dimensional (3D) needled carbon fiber reinforced silicon oxycarbide (SiOC) composites through a simple precursor infiltration and pyrolysis process (PIP), and the influence of PIP cycle numbers on the microstructure, mechanical, high-temperature oxidation resistance. The electromagnetic wave (EMW) absorption properties of the composites were investigated for the first time. The pyrolysis temperature played an important role in the structural evolution of the SiOC precursor, as temperatures above 1400 °C would cause phase separation of the SiOC and the formation of silicon carbide (SiC), silica (SiO2), and carbon. The density and compressive strength of the composites increased as the PIP cycle number increased: the value for the sample with 3 PIP cycles was 0.77 g/cm3, 7.18 ± 1.92 MPa in XY direction and 9.01 ± 1.25 MPa in Z direction, respectively. This composite presented excellent high-temperature oxidation resistance and thermal stability properties with weight retention above 95% up to 1000 °C both under air and Ar atmosphere. The minimal reflection loss (RLmin) value and the widest effective absorption bandwidth (EAB) value of as-prepared composites was −24.31 dB and 4.9 GHz under the optimization condition for the sample with 3 PIP cycles. The above results indicate that our BPR-derived carbon modified 3D needled carbon fiber reinforced SiOC composites could be considered as a promising material for practical applications.

Precursor infiltration and pyrolysis cycle-dependent microwave absorption and mechanical properties of lightweight and antioxidant carbon fiber felts reinforced silicon oxycarbide composites

High-performance microwave absorption materials combined with good oxidation resistance and mechanical properties are highly desirable in some extreme situations. Herein, three-dimensional (3D) needled carbon fiber felts reinforced silicon oxycarbide (SiOC/CFs) composites with excellent electromagnetic (EM) wave absorption, good oxidation resistance and mechanical properties were successfully prepared through a simple precursor infiltration and pyrolysis (PIP) process. Notably, the EM wave absorption, oxidation resistance and mechanical performances strongly depend on the PIP cycles through adjusting the content of SiOC to control the porosity and density of the composites. A substantial enhancement of EM wave absorption performance of composites is achieved via incorporation of SiOC with different PIP cycles, resulting from the matched characteristic impedance and enhanced loss ability. The minimum reflection loss (RLmin) of pure carbon fiber felts is −8.4 dB, whose value is decreased to −62.9 dB for the composites with 1 PIP cycle, and to −49.9 dB for the composites with 2 PIP cycles, respectively. The results indicate that the as-prepared SiOC/CFs composites with superior EM wave absorption, great oxidation resistance and mechanical properties could be considered as a great potential for the applications in harsh environments.

Graphene-reinforced silicon oxycarbide composites prepared by phase transfer

In order to compensate for cracking, brittleness and low electrical conductivity of polymer-derived silicon oxycarbide (SiOC), graphene was successfully introduced into a SiOC matrix by phase transfer of graphene oxide (GO) from an aqueous (GO dispersed in water) to organic phase (copolymer as SiOC precursor in diethyl ether). Spark plasma sintering (SPS) was used to fully densify composites to ∼2.3g/cm3. The prepared materials were comprehensively characterized and exhibited significant enhancement in the mechanical properties, electrical conductivity and electrochemical performance. Self-assembled lamellar structure of graphene in the SiOC-matrix was achieved, leading to anisotropy in the properties of the composites. The fracture toughness of the SiOC-2vol%GO composite was increased by ∼91%, at the expense of a slight decrease in the flexural strength, compared to the SiOC-matrix. Moreover, the composites exhibited three orders higher electrical conductivity than the SiOC-matrix. The electrical conductivity in the perpendicular direction (σ┴ = 3 × 10−1S/cm) of SiOC-2vol%GO composites was two orders of magnitude higher than that in the parallel direction (σ‖ = 4.7 × 10−3S/cm), owing to the self-assembled lamellar graphene in the SiOC-matrix. The SiOC-2vol%GO composites further showed better electrochemical performance of oxygen reduction reaction (ORR) than pure graphene, exhibiting an onset potential (∼0.75 V vs RHE) and more positive half-wave potential (∼0.6 V vs RHE).

Preparation of Silicon Oxycarbide Composites Toughened by Inorganic Fibers via Pyrolysis of Precursor Siloxane Composites

The optimization of silicon oxycarbide (SiOC) synthesis (sol-gel/pyrolysis) is described, starting from methyltriethoxysilane, dimethyldiethoxysilane, tetraethoxysilane, ethyltriethoxysilane and propyltriethoxysilane. Variation of final elemental composition was tested via change of monomer ratios and combinations. The main aim was to achieve low weight losses during cure and pyrolysis and high micromechanical properties. Gas chromatography and mass spectroscopy was used to analyse the by-products of cure and pyrolysis, indicating a prominent role of cyclosiloxane and polyhedral oligomeric silsesquioxane (POSS) oligomers. Best results were obtained with high contents of methyltriethoxysilane in the monomers mixture.

IR Laser‐Induced Carbothermal Reduction of Silica

AbstractPulsed IR‐laser irradiation of silica in the presence of gaseous hydrocarbons (benzene or ethyne) results in carbothermal reduction of silica by hydrocarbon decomposition products and allows deposition of amorphous solids which were analyzed by FTIR, Raman, X‐ray photoelectron and Auger spectra and by electron microscopy and revealed as nanosized carbon–silicon oxycarbide composites containing crystalline silica domains. The reported IR laser‐induced process is the first approach to deposition of nanosized carbon–silicon oxycarbide composites. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

IR laser-induced carbothermal reduction of silicon monoxide

Pulsed IR laser irradiation of silicon monoxide in the presence of gaseous hydrocarbons (benzene or ethyne) results in carbothermal reduction of silicon monoxide by hydrocarbon decomposition products and allows deposition of nanosized carbon–silicon oxycarbide composites which were identified by FTIR, Raman and X-ray photoelectron spectroscopy and by electron microscopy.

Effect of fiber surface state on mechanical properties of C f/Si–O–C composites

Three-dimensional braided carbon fiber reinforced silicon oxycarbide composites (3D-B C f/Si–O–C) were fabricated via a polysiloxane infiltration and pyrolysis route. The effects of fiber surface state on microstructure and mechanical properties of C f/Si–O–C composites were investigated. The change of carbon fiber surface state was achieved via heat treatment in vacuum. The results showed that heat treatment decreased carbon fiber surface activity due to the decrease of the amount of oxygen and nitrogen atoms. The C f/Si–O–C composites fabricated from the carbon fiber with low surface activity had excellent mechanical properties, which resulted from perfect interfacial bonding and good in situ fiber strength. The flexural strength and fracture toughness of the C f/Si–O–C composites from the treated fiber were 534 MPa and 23.4 MPa m 1/2, respectively, which were about 7 and 11 times more than those of the composites from the as-received carbon fiber, respectively.

Processing and characterization of three-dimensional carbon fiber-reinforced Si–O–C composites via precursor pyrolysis

The cure and pyrolysis of hydrogen-containing polysiloxane (PSO) and divinylbenzene (DVB) were investigated in this paper. It was found that (chloroplatinic acid) H 2PtCl 6 was an effective catalyst for the cure of DVB/PSO. The mass ratio of DVB/PSO had great effect on ceramic yield. The cured DVB/PSO with a mass ratio of 0.5:1 had the highest ceramic yield (76%) at temperature up to 1000 °C, and its pyrolyzates consisted of 38.3 wt.% silicon, 27.4 wt.% oxygen, and 34.3 wt.% carbon of which 26.3 wt.% was free carbon. The structures of the products pyrolyzed at different temperatures were characterized by FTIR. Three-dimensional braided carbon fiber-reinforced silicon oxycarbide composites (3D-B C f/Si–O–C) were fabricated via precursor infiltration and pyrolysis using DVB/PSO as precursor. The results showed that the mechanical properties of 3D-B C f/Si–O–C could be increased if the first pyrolysis was assisted by hot-pressing. The flexural strength and fracture toughness of the composite, which was hot-pressed at 1600 °C for 5 min with a pressure of 10 MPa in the first pyrolysis cycle and treated subsequently with six cycles of vacuum infiltration and pyrolysis under atmospheric pressure, were 502 MPa and 23.7 MPa m 1/2, respectively. The high mechanical properties were mainly attributed to the desirable interfacial structure.