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Flame-retardant composites for fireproof application of electromagnetic (EM) absorption are produced from the dispersion and formation of graphene nanosheets (GNS) and exfoliated manganese oxides (EMOs) in diphenyl amidophosphate (DAP)-modified epoxy resin. The DAP-modified composite can be a friendly type of high-performance EM absorbing material in practical application, because of its halogen-free merits and high reflection loss in EM absorbance. An overcharring phenomenon is discovered in the retardants with multicomponents embedded in a resin matrix. The flame retardancy of the DAP composite is exhibited from thermogravimetric analysis (TGA). Kinetics analysis presents the difference of composites before and after modification in thermal decomposition. Improvement of multicomponents wrapped system can result from dissociation of P–O bonds during the course of burning. A cone calorimeter is utilized to evaluate the combustion performance to learn about the retardancy of composites. Guarding against ov...

Waveguide configurations of hierarchical system are proposed as new microstructures for composites in absorbing enhancement. Supercritical fluid (SCF) one-pot exfoliation of layered graphite and manganese oxide mixing materials is developed to obtain a hierarchical system, containing graphene nanosheets (GNS) and exfoliated manganese oxides (EMO) in different sizes. Composites with GNS–EMO embedded in epoxy resin matrix are produced for a design of dielectric and magnetic loss integrated absorber. Volume fraction of GNS–EMO in composites is given for an optimal quantity of resin epoxy in fixation and formation. The effect of mixing ratios between electric and magnetic components is provided for the design of dielectric and magnetic loss integrated absorbers. Frequency shifting phenomena are revealed in the component adjusting course. Excluding the offsetting sizes, reflection loss of composites is enhanced as thickness increases. Synergistic effect of electric and magnetic coordinated materials demonstrates the superiority of micro-waveguide structures in GNS–EMO composite absorber.

Deoxidation of manganese oxides in supercritical N , N -dimethylformamide (SC-DMF) is revealed, contrasting to previous amounts of reports on supercritical water oxidation. Mn 3 O 4 and MnO can be produced by the reaction starting from layered manganese oxides (δ-MnO 2 ) in a uniform supercritical process. Time effect can give rise to the transition to Mn 3 O 4 under low temperature, but the prolonged time, under a temperature lower than 200 C, cannot cause this transition. Phase diagram is obtained, including three regions of MnO 2 , Mn 3 O 4 and MnO as the main material phase. The completion of transition accompanies with an oxygen loss course. Comparison between supercritical oxidation of water and supercritical deoxidation of organic DMF demonstrates the unique mechanisms of supercritical processing. In terms of the surface contacting fluid, deoxidation kinetics has a reciprocal law of growing size for manganese oxides. The new deoxidation procedure using organic solvent is proposed for the processing of metal oxides.

Trimanganese tetroxide (Mn3O4) nanosheets can evolve into various morphologies in supercritical N,N-dimethylformamide (SC-DMF), including particulate materials, triangle, rhombus, cube, and other regular polyhedrons. The obtained polyhedrons have sizes from hundred nanometers to several micrometers (1–3 μm), along with a growing course. The phases are changed from Mn3O4 to MnO, as the processing time increases. The growth of manganese oxides in SC-DMF has a rate of 28.7–61.5 nm·min− 1. The phenomena of accelerated growth for manganese oxides in supercritical fluid are discovered. The growth kinetics of manganese oxides is performed by the classical Lifshitz–Slyozov–Wagner (LSW) model. A mass transfer (MT) model of growth kinetics applicable to supercritical fluid surrounding is proposed. Solubility and diffusion, as main factors, are included in the proposed model. The theoretical model and the fitting curve are in accordance with experimental results. The growth of manganese oxides in SC-DMF satisfies the first-order kinetics, obeying the exponential law.

Titania nanosheets with {0 0 1} facets were produced by the supercritical N,N-dimethylformamide (SC-DMF) fluid exfoliation of the layered bulk titanate material. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) showed the starting titanate crystals with layered structure; SEM, atomic force microscopy (AFM) and transmission electron micrographs (TEM) demonstrated the obtained two-dimensional nanosheets with a thickness of 1.3 nm around and lateral dimensions of several microns; ultraviolet–visible (UV–vis) spectroscopy characterized the optic properties of the nanosheets with uniformity and the disassembly of layered structure. Absorbance peak is centered at 301 nm and the molar extinction coefficient is 1.01 × 102 mol−1 dm3 cm−1; thermogravimetric analysis (TGA) of the sediments revealed that the weight loss in the case of ice-cold water cooling was the least. The course of the SCF exfoliation was explained to be rapid intercalation and swollen exfoliation by thermal stress. Restacking of exfoliated nanosheets was shown by the in situ XRD technique, and ratios of the obtained single layers in the working conditions of furnace cooling, air cooling and ice-cold water cooling are increased up to 7.8%.

A novel method using supercritical N,N-dimethylformamide (SC-DMF) exfoliation is proposed for the preparation of trimanganese tetroxide (Mn3O4) nanosheets. The obtained Mn3O4 nanosheets have nanoscale thickness and lateral dimensions of hundreds of nanometers. The change in morphology from a bulk to a two-dimensional structure when exfoliated with SC-DMF is characterised. The exfoliated products can be uniformly dispersed in N,N-dimethylformamide (DMF), the dispersion has a molar extinction coefficient of approximately 5.52 × 102 mol−1 dm3 cm−1 at a peak wavelength of 266 nm. The fourier transform infrared (FTIR) spectra show that intercalation mainly occurs between 300 °C and 400 °C. Raman spectroscopy indicates that the phase transition from MnO2 to Mn3O4 takes place between 200 °C and 400 °C. X-ray diffraction (XRD) confirms that the phase transition between the manganese oxides begins at around 350 °C. The exfoliated products possess strong coercivity, approximately 7 kOe, at low temperatures. It is demonstrated that the exfoliated Mn3O4 products result from exfoliation and phase transition in SC-DMF. The exfoliated nanosheet materials can be easily cracked in the course of exfoliation and aggregate when collected, these phenomena are attributed to the fragility and magnetic properties of the material, respectively.