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SiC/Al2O3 composite powders with SiC nanowires were synthesized using a one-step combustion synthesis method taking silica fume (SiO2), aluminum powder (Al) and carbon black (CB) as raw materials, while ferrocene (C10H10Fe) was used as the catalyst. The calculated results for the relationship between the equilibrium phase and temperature of the Al–SiO2–C system show that SiC and Al2O3 are the only equilibrium phases in the system. In addition, the effects of C10H10Fe on the combustion synthesis process and products were studied. It was found that with increasing catalyst content, the amount of residual Si in the products first decreases and then increases, the combustion temperature first increases and then decreases, and the nanowire content continues to increase. For an optimal amount of C10H10Fe of 0.75 wt%, almost no residual Si is observed in the product, while the combustion temperature (Tc) is high (2104 K), the SiC nanowire content is relatively high, and the nanowire aspect ratio is large. In addition, two growth mechanism models for SiC nanowires: VS and VLS were validated.

The key characteristics of the porous carbon materials and ceramic composites derived from citrates are directly affected by the pyrolysis mechanism of parent citrates and the microstructural revolution during the process. The pyrolysis mechanism of magnesium citrate nonahydrate (MCN) and the microstructural evolution during its pyrolysis were investigated by analysing the C/MgO nanocomposite powders from MCN pyrolyzed in carbon embedded condition and flowing argon atmosphere. The pyrolysis process of MCN was composed of the following stages: (1) MCN dehydrated to magnesium citrate at about 150 °C; (2) magnesium citrate decomposed into itaconic acid magnesium and MgO at about 300 °C; (3) itaconic acid magnesium decomposed into carbon, MgO and CH4 at around 500 °C; (4) CH4 was pyrolyzed and graphene was deposited on MgO. The carbon produced in stage (3) was turbostratic while that derived from the pyrolysis-deposition of CH4 was few-layered-graphene. The MgO nano grains produced in stage (2) precipitated and agglomerated while those derived from itaconic acid magnesium were much smaller in size. In carbon embedded condition, the few-layered-graphene not only deposited on the MgO aggregates surface but also inserted into the MgO nano grain boundaries, which suppressed the growth and sintering of MgO nano grains.

Our previous investigations indicate that the thermal shock resistance (TSR) of hydratable magnesium carboxylate (HMC) bonded Al2O3–MgO castables is superior to castables bonded with calcium aluminate cement as a result of the in-situ formation of micro-sized spinel (MgAl2O4). In the present study, to further enhance the TSR of HMC bonded castables, the submicron alumina powders were added into the castables to decrease the size of the spinel particle through a reaction of submicron alumina with nano magnesia pyrolyzed from HMC. The effects of submicron alumina powders on the TSR, slag corrosion resistance, and microstructure of HMC bonded castables were investigated. The results show that the size of the in-situ spinel particle decreases from approximately 2 μm to approximately 0.8 μm and the spinel gradually transforms into the aluminum-rich spinel after adding submicron alumina powders. The residual strength retention ratio of the samples raises from 37.5% to 50.0%, and the thermal stress damage resistance index (R՛՛՛՛) of the samples increases from 3.1 m to 7.2 m with the increase in the amount of submicron alumina to 2.0 wt% after thermal shock. The microcracks in the castables matrix of sample 2A are more and shorter than those of sample 0A after thermal shock. This is attributed to the fact that the resistance of microcracks propagation in the castables is enhanced via smaller spinel with uniform distribution. Besides, the penetration index of the castables decreases from 20.8% to 9.8% with the increase of submicron alumina content powders to 2.0 wt%. This is because the submicron alumina powders decrease the porosity of the castables, and the smaller size of the aluminum-rich spinel has a stronger adsorption capacity for Fe2+ ions.

A novel electromagnetic wave (EMW) absorber was prepared by combustion synthesis. Boron carbide (B4C) powders with different grain sizes using a molten-salt-assisted combustion technique with B2O3, CB (carbon black), and Mg powders as starting materials, and NaCl as an additives. The effects of the NaCl content on the phase compositions and the microstructure of the products were characterized. A combustion front quenching method was used to elucidate the mechanism for the B4C powders synthesis. The dielectric, and EMW absorbing properties in the X-band were also investigated. The results showed that the addition of NaCl significantly reduced the grain size of B4C powders. Nanoscale B4C powders with cubic polyhedral structures were synthesized using 6 wt% NaCl (labeled as N-6). According to the quenching test results can be obtained that the first step in the combustion synthesis was melting B2O3 into a glassy substance. At the same time, Mg melted and formed a liquid pool into which the NaCl dissolved, followed reduction of the B2O3 to B. The formed B eventually reacted with CB to form B4C, and the B4C particles precipitated from the matrices. The N-6 sample exhibits optimal dielectric and EMW absorbing properties, because of a high specific surface area that enhances interfacial and space charge polarization.

C/MgO composite powders were prepared by combustion synthesis using magnesium oxalate and magnesium powders as raw materials. The phase composition and microstructure of the composite powders were investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy/energy dispersive spectroscopy (FESEM/EDS), high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. The synthetic mechanism was explored through TG-FTIR and combustion front quenching techniques. It was found that the C/MgO composite powders contained a large quantity of MgO nanofibers. When the molar ratio of magnesium oxalate and magnesium was 1:4, the carbon content of the product reached a maximum of 9.45 wt %. In the composite powders, cubic MgO particles were encapsulated by a thin carbon layer, and there was a tiny gap between MgO and the carbon layer; a large number of MgO nanofibers with aspect ratios of 80–100 were found. The cubic MgO particles of the products are the direct decomposition of MgC2O4, and the MgO nanofibers are the reaction product of gaseous Mg and CO2/CO at high temperature. Meanwhile, the carbon deposited on the MgO particles can inhibit the grain growth of MgO particles and result in the refinement of MgO particles. The uniform dispersion of carbon and the weak C/MgO interface combine, making the composite powders a potential additive for low-carbon MgO–C refractories with excellent thermal shock resistance.

The potential of hydratable magnesium carboxylate compounds (HMC) combined with MgO powder as a binder of castables was evaluated. The green mechanical and thermal shock resistance properties of HMC-bonded castables (HMCC) and calcium aluminate cement-bonded castables (CACC) were compared. The green mechanical strength of the HMCC reached the mechanical strength of the CACC. The residual strength ratio of the HMCC is higher than that of the CACC and increases first and then decreases with the MgO/HMC ratio. The residual strength ratio's highest value is 56.8% (MgO/HMC ratio is 2/3), which is 1.8 times that of CACC. Interestingly, the microcracks in the HMCC after thermal shock are radial, while those in CACC are linear. The micromechanical testing on the matrix of castables after thermal shock showed that the ratio of the energy for crack initiation to the work of fracture of the HMCC is lower than that of the CACC, but its fracture toughness is higher than that of the CACC, indicating that the microcracks in the HMCC initiate easily but propagate hardly.

To develop a novel high-temperature microwave absorber, B4C/Al2O3/CNTs composite powders were prepared by a combustion synthesis method. The experiment results show that the products are mainly composed by B4C, α-Al2O3, and residual CNTs. The better crystallinity B4C particles had a grain size about 0.5–1.0 μm and embedded in the Al2O3 matrix, while the CNTs cracked and dispersed in the composite powders. The results of combustion synthesis process illustrated that as CNTs increase, the product zone decreased, and the combustion temperature (Tc), the adiabatic combustion temperature (Tad), and the combustion wave velocity (VC) decreased. The dielectric permittivity of prepared composite powders has been determined in the X band. The results show that the dielectric real part e´ and dielectric loss tanδ have a growing tendency with the increase of the CNTs. The dielectric real part (e′) and the loss tangent (tanδ) reached the highest, when the molar excess coefficient of CNTs was 0.2 (CS-2). The different mass ratios of CS-2 and paraffin binder were combined to test their dielectric properties. The results show that both e′ and tanδ increased with the increase of the CS-2, while the impedance matching ratio decreased.

To improve the dispersity and oxidation resistance of nano carbon black (CB) in low carbon MgO-C refractories, B 4 C/Al 2 O 3 /C composite powders were prepared by a combustion synthesis method using B 2 O 3 , CB and Al powders as the raw materials. The phase compositions and microstructures of the synthesized products were characterized by X-ray diffraction (XRD), Raman spectroscopy, and a scanning electron microscopy/energy dispersive spectrometry (SEM/EDS). The results show that an 80 wt% excess of CB is the maximum amount of CB that can be added under the condition of a self-propagating combustion wave, and the phase compositions of the products are B 4 C, α-Al 2 O 3 and CB. B 4 C particles with uniform sizes and cubic polyhedral structures are embedded in the Al 2 O 3 matrix. The combustion-synthesized B 4 C/Al 2 O 3 /C powders and mechanically mixed B 4 C/Al 2 O 3 /C powders were added to the low carbon MgO-C refractories, and their corresponding properties were compared. The apparent porosity (AP) of the refractories with the synthesized powders (labelled as M3) is lower than those of the refractories with mechanically mixed powders (labelled as M2) and without composite powders (labelled as M1). The oxidation ratio and slag erosion depth of M3 were lower than those of M2 and M1. The thickness of the decarburized layer of M3 was 10.2% and 22.4% less than that of M2 and M1, respectively. The penetration depth of M3 was 12.0% and 27.9% less than that of M2 and M1, respectively. The thermal shock resistance of M3 was better than that of M2 and M1. The residual strength ratio of M3 was 15.8% and 17.2% more than that of M2 and M1, respectively. These results suggest that the combustion-synthesized B 4 C/Al 2 O 3 /C composite powders can be used as new and promising additives for low carbon MgO-C refractories.

The poor water dispersion and oxidation resistance of carbon has restricted the widely industrial application of carbon containing castables. High aspect ratio network-like carbon nanotubes containing calcium aluminate cement composite powders were synthesized by carbon-bed sintering method using calcium acrylate and activated alumina as raw materials, and nickel nitrate as catalyst. Meanwhile the effects of catalyst content on the structure and morphology of carbon nanotubes were also studied. The synthesized products were characterized by X-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy. The results indicated that the phase compositions of composite powders were similar to that of commercial Secar71. The length of carbon nanotubes was ca. 25 μm, and the diameter of carbon nanotubes was 55 nm. The aspect ratio of carbon nanotubes is ca. 450. The formation process and mechanism of carbon nanotubes was studied by thermogravimetric analysis coupled with Fourier transform infrared spectroscopy. The growth temperature of carbon nanotubes was 700 °C , and the growth of carbon nanotubes agrees with vapour–solid (V–S) model. In addition, the thickness of floating layer, floating ratio and oxidation ratios of the synthesized product were lower than those of the same carbon containing Secar71 cement (S71CB) composite powders, implying that the water dispersion and oxidation resistance of carbon nanotubes were improved because the high aspect ratio network-like carbon nanotubes were not easily separated from calcium aluminate cement and the carbon nanotubes were encased in calcium aluminate cement.