Synthesis and microwave absorption properties of Fe–C nanofibers by electrospinning with disperse Fe nanoparticles parceled by carbon

The Fe–C nanofibers were achieved using electrospinning technique. The microstructure was characterized by field emission scanning electron microscope and high resolution transmission electron microscopy equipped with energy-dispersive X-ray analysis. The results indicated that magnetic Fe nanoparticles uniformly dispersed along nanofibers and were parceled by carbon matrix. For the Fe–C nanofibers/paraffin composite, a minimum reflection loss (RL) value of −44 dB was observed at 4.2 GHz. Moreover, the frequency range with RL peak value below −10 dB was achieved in a wide frequency range from 2.2 to 13.2 GHz. The excellent microwave absorption properties were due to the combination of complex permeability and permittivity resulting from magnetic Fe particles and lightweight carbon.     

Advanced visible-light photocatalytic property of biologically structured carbon/ceria hybrid multilayer membranes prepared by bamboo leaves

Biologically structured carbon/cerium dioxide materials are synthesized by biological templates. The microscopic morphology, structure and the effects of different oxidation temperatures on materials are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) ultraviolet-visible light spectrum (UV–Vis) and X-ray Photoelectron Spectroscopy (XPS). Moreover, by splitting water under visible light irradiation, the hydrogen production is measured to test the photocatalytic property of these materials. The results show that materials made with bamboo biological templates which are immersed in 0.1 mol L^?1 of cerium nitrate solution, then carbonizated in nitrogen (700 °C) and oxidized in air (500–600 °C), can obtain the biological structure of bamboo leaves. The product is in the composition of hybrid multilayer membrane, which one is carbon membrane form plant cell carbonation and another is ceria membrane by nanoparticle self assembly. The best oxidation temperature is 550 °C and the band gap of carbon/cerium dioxide materials synthesized at this optimum oxidation temperature could be reduced to 2.75 eV. After exposure to visible light for 6 h, the optimal hydrogen production is about 302 μmol g^?1, which is much higher than that of pure CeO₂.     

Comparative 27Al NMR and LAXS studies on rapidly quenched aluminosilicate glasses

Aluminium site occupancies deduced from ²⁷Al NMR measurements of several aluminosilicate glasses of composition 35–60 mol% Al₂O₃ were used to calculate the mean coordination number, assuming two polyhedral models. In the models the 30 ppm Al NMR resonance was assigned to fivefold coordinated Al or to distorted tetrahedral units, respectively. Comparison of these mean coordination numbers with those derived from pair distribution functions (PDF) from X-ray scattering data of these glasses support the model in which the 30 ppm Al NMR peak is assigned to distorted tetrahedral units. This conclusion is also supported by simulations of the PDF line profiles using the NMR site occupancies and mean polyhedral bond lengths.     

Graphitization of highly porous carbons derived from poly(p-phenylene benzobisoxazole)

We studied the development of graphitization in carbonaceous materials derived from poly(p-phenylene benzobisoxazole) (PBO) pre-activated with carbon dioxide to burn-off degrees of 15 and 51 wt.%. The activated materials were subsequently heat-treated at various temperatures comprised between 1600 and 2700 °C. The changes in porous texture, structure and nanostructure were characterized by gas adsorption analysis, X-ray diffraction, Raman spectroscopy and high-resolution transmission electron microscopy. The two sets of materials pre-activated to different degrees of burn-off exhibited similar changes as a function of the heat treatment temperature. Quite unexpectedly, the presence of porosity generated by physical activation of PBO chars does not affect their graphitizability. The materials seem to retain a sufficiently large degree of the order acquired during the spinning of the PBO fibres to allow the remaining bi-periodic structural units to re-arrange, allowing subsequent graphitization.     

Hydrothermal synthesis of dumbbell-shaped ZnO microstructures

Dumbbell-shaped ZnO microstructures have been successfully synthesized by a facile hydrothermal method using only Zn(NO₃)₂·6H₂O and NH₃·H₂O as raw materials at 150 °C for 10 h. The results from X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) show that the prepared ZnO samples exhibit dumbbell-shaped morphology and hexagonal wurtzite structure. The length of ZnO dumbbells is about 5–20 μm, the diameters of the two ends and the middle part are about 1–5 μm and 0.5–3 μm, respectively. The dumbbell-shaped ZnO microstructures may be formed by self-assembly of ZnO nanorods with 1–5 μm in length and 100–200 nm in diameter. The photoluminescence (PL) spectrum of dumbbell-shaped ZnO microstructures at room temperature shows three emission peaks at about 362, 384 and 485 nm.     

Controllable synthesis of porous CxNy nanofibers with enhanced electromagnetic wave absorption property

Porous C_xN_y nanofibers are controllably synthesized by a simple two-step method. The prepared samples possess uniform micropores and a chemical composition of C_0.73 N_0.27 with a surface area of 329 m² g⁻¹. The obtained C_xN_y nanofibers exhibit remarkable electromagnetic (EM) wave absorption properties when compared with conventional one-dimensional carbon materials. The minimum reflection loss (RL) reaches −36 dB at 2.7 GHz when the ratio of the C_xN_y absorbent added in paraffin matrix is only 1:3. The bandwidth of the RL below −10 dB covers 7.7 GHz (8.1–15.8 GHz) at the sample thickness of 2.5 mm. A possible EM wave loss mechanism was proposed in detail. The multiple reflection and dielectric loss could govern the excellent EM absorption leading the product to a probable application in stealth materials.     

Carbon-based piezoresistive polymer composites: Structure and electrical properties

Piezoresistive polymeric composites were prepared by melt mixing of polypropylene (PP) with expanded graphite (EG) (10–15 wt%) and/or multiwalled carbon nanotubes (MWCNTs) (1–2 wt%). The composites were extruded at a temperature of 185 °C, by adopting 2.5–10 rpm screw speeds, and fibres with diameters of 0.2, 1.5 and 3 mm, were obtained. An integrated piezoresistive sensor device was obtained by hot pressing the extruded fibres into two sandwiched PP panels.Structure and morphology of the carbon fillers (EG and MWCNTs) and of the fibres, were investigated by means of X-ray diffraction, optical microscopy, scanning electron microscopy (conventional and conductive SEM) and atomic force microscopy. Piezoelectric properties of fibres and sensor devices were detected through a set up made by a dynamometer, a potentiometer and a digital multimeter. It was shown, that mechanical deformations, due to the applied loads, affect remarkably the resistivity of the materials.     

Structural and morphological transformation of NaX zeolite crystals at high temperature

Nearly perfect crystalline zeolite structures could be used as proton exchangeable membranes for fuel cells, potentially offering major advantages over current separation and catalytic processes. They could also be employed as host materials for semiconductor clusters from 1 to 20 nm in diameter to create electronic and optical properties specific to the form of nano-crystals. Well-shaped NaX zeolite octahedral crystals of a large size of 30 μm were synthesized by a hydrothermal method in a mother solution having a 3.5Na₂O:Al₂O₃:2.1SiO₂:593–2000H₂O composition. Thermal treatment of NaX zeolite crystals resulted in the formation of an intermediate amorphous phase at temperature above 800 and 900 °C and a crystalline phase of aluminium silicate (T < 1000 °C). Environmental scanning electron microscopy (ESEM), high resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, DTA/TGA and BET analysis were used to characterize the initial materials and the obtained products after various heat treatments.     

Synthesis of glass-ceramics using glass cullet and vitrified industrial by-products

This study concerns the recycling of inorganic waste materials for the production of glass-ceramics and the evaluation of the developed physical properties. Four industrial by-products were selected due to their mass production: (i) two high calcium lignite fly ashes, (ii) slag derived from the production of Fe–Ni and, (iii) steel slag. In order to examine the role of the SiO₂ in the crystallization process, glass cullet and Egyptian sand were added. Thermal treatment, at 1450 °C, enables the production of glasses using mixtures of these materials at appropriate proportions. The crystallization was achieved by heating at 900, 950 and 1000 °C. The produced materials were examined concerning their structure by X-ray diffraction and scanning electron microscopy (SEM-EDS). The results showed that the crystalline phase is greatly depending on the structure of the raw material and the thermal process, influencing accordingly the hardness of the final products.     

The use of egg shells to produce Cathode Ray Tube (CRT) glass foams

Cleaned Cathode Ray Tube (CRT) (panel and funnel) waste glasses produced from dismantling TV and PC colour kinescopes were used to prepare glass foams by a simple and economic processing route, consisting of a direct heating of glass powders at relatively low temperatures (600–800 °C). This study reports on the feasibility of producing glass foams using waste egg shells as an alternative calcium carbonate-based (95 wt%) foaming agent derived from food industry. The foaming process was found to depend on a combination of composition, processing temperature and mixture of raw materials (glass wastes). Hot stage microscopy (HSM), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize foams and evaluate the foaming ability and the sintering process. The experimental compositions allowed producing well sintered glass foams with suitable properties for some functional applications with environmental benefits such as: (1) reduced energy consumption because of the low heat treatment temperatures used; and (2) materials produced exclusively from residues.     

The steeple spire of the Parma Cathedral: An analysis of the glazed bricks and mortars

In October 2009, a terrible lightning struck the steeple spire of the Parma Cathedral, causing a fire. The fire-fighting operation made possible the discovery of the original spire ceiling made up by dichromatic glazed bricks, white and black, dating from the 14th century. Original materials presented a relevant decay, both for the high temperatures reached during the fire and for lack of maintenance. The research presents the first study of glazed bricks of the 14th century in Po Valley (Italy) with the purpose of collect chemical, mineralogical and petrographic data on the dichromatic glazed bricks. Brick samples with different kind of glazes and mortars exposed at different condition of fire were analyzed. The following techniques were used in the study: X-ray powder diffraction, optical microscopy, scanning electron microscopy analysis, inductively coupled plasma atomic emission spectroscopy and Raman spectroscopy. Glazes, applied on to Ca-rich paste, have a high lead content (41–57 wt%), with an high amount of tin (19–24 wt%) for the white opacified glazes and manganese (about 4.0 wt%) for the black ones. Typological and historical analysis allowed us to define the production technique of bricks and glazes. Mortars are mainly composed of lime binder and carbonate aggregate.     

Corrosion behaviour of carbon materials exposed to molten lithium chloride–potassium chloride salt

The corrosion behaviour of four carbon materials namely low density graphite, high density graphite, glassy carbon and pyrolytic graphite were investigated in molten LiCl–KCl electrolyte medium at 600 °C for 2000 h under high pure argon atmosphere. Structural and microstructural changes in the carbon materials after exposure to molten chloride salt were investigated from the weight change and using scanning electron microscopy, atomic force microscopy, X-ray diffraction and laser Raman spectroscopic techniques. Microstructural analysis of the samples revealed the poor corrosion resistance of high density and low density graphite and severe attack was observed at several places on the surface. On the other hand, glassy carbon and pyrolytic graphite were relatively inert, while pyrolytic graphite showed the best corrosion resistance to molten salt attack. In the order of increasing corrosion resistance to molten salt, the carbon materials were found to follow the sequence: low density graphite < high density graphite < glassy carbon < pyrolytic graphite.     

Inorganic polymers from laterite using activation with phosphoric acid and alkaline sodium silicate solution: Mechanical and microstructural properties

Geopolymers from laterite, an iron-rich soil available in developing countries, have great potential as building materials. In this work, laterite from Togo (Africa) was used to prepare geopolymers using both phosphoric acid and alkaline sodium silicate solution. Microstructural properties were investigated by scanning electron microscopy, X-ray powder diffraction and mercury porosimetry, whereas thermal properties were evaluated by thermal analyses. The local environment of iron was studied by X-ray Absorption Spectroscopy (XANES region). The mechanical properties were determined. Modulus of Rupture and Young's modulus fell in the ranges 3.3–4.5 MPa and 12–33 GPa, respectively, rendering the materials good candidates for construction purposes. Heating above 900 °C results in weight-gain, presumably due to iron redox reactions. X-ray Absorption Spectroscopy data evidence changes in the chemical and structural environments of iron following thermal treatment of geopolymers. These changes indicate interaction between the geopolymer structure and iron during heating, possibly leading to redox properties.     

Electrochemical energy storage performance of heterostructured SnO2@MnO2 nanoflakes

In this work, we report synthesis of SnO₂@MnO₂ nanoflakes grown on nickel foam through a facile two-step hydrothermal route. The as-obtained products are characterized by series of techniques such as scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The as-obtained SnO₂@MnO₂ nanoflakes are directly used as supercapacitor electrode materials. The results show that the electrode possesses a high discharge areal capacitance of 1231.6 mF cm⁻² at 1 mA cm⁻² and benign cycling stability with 67.2% of initial areal capacitance retention when the current density is 10 mA cm⁻² after 6000 cycles. Moreover, the heterostructured electrode shows 41.1% retention of the initial capacitance when the current densities change from 1 to 10 mA cm⁻², which reveals good rate capability. SnO₂@MnO₂ nanoflakes products which possess excellent electrochemical properties might be used as potential electrode materials for supercapacitor applications.     

Preparation of multi-walled carbon nanotube incorporated MIL-53-Cu composite metal–organic framework with enhanced methane sorption

Multi-walled carbon nanotubes (MWCNTs) incorporated MIL-53-Cu composite MOF material (MWCNT@MIL-53-Cu) has been synthesized by adding purified multi-walled carbon nanotube (MWCNT) in situ during the synthesis of MIL-53-Cu. Resulting sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmet–Teller (BET), and FT-IR analysis. Methane sorption capacities of MIL-53-Cu were observed to increase from 8.52 to 13.72 mmol g^?1 at 298 K and 35 bar. The increment in the methane uptake capacities of composite MOF materials was attributed to the decrease in the pore size and enhancement of micropore volume of MIL-53-Cu by multi-walled carbon nanotube incorporation.     

Continuous hydrothermal synthesis of ZnGa2O4:Mn2+ nanoparticles at temperatures of 300–500 °C and pressures of 25–35 MPa

Mn²⁺ doped ZnGa₂O₄ particles were continuously synthesized in subcritical and supercritical water using a flow hydrothermal reaction system. Zn, Ga and Mn nitrates were used as the starting materials. The syntheses were carried out at temperatures from 300 to 500 °C, at pressures from 25 to 35 MPa, at KOH concentration of 0.04 M, and for residence times from 0.13 to 1.13 s. X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric differential thermal analysis (TG-DTA) and photoluminescent spectroscopy were used to characterize the samples. Single phase of ZnGa₂O₄ was achieved at residence times of less than 1 s. The crystallite sizes were in the range from 12 to 21 nm which tend to increase with an increase in the reaction temperature and with a decrease in the reaction pressure. Green emission was observed for the annealed samples under reducing conditions whereas as-synthesized samples did not exhibit photoluminescence.     

Adsorption of toluene on mesoporous materials from waste solar panel as silica source

The adsorption of toluene was tested with MCM-41 and mesoporous silica materials (S-MCM) synthesized from waste solar panel. X-ray powder diffraction (XRD), nitrogen adsorption–desorption analysis, Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM) were applied to characterize the prepared samples. In addition, the adsorption capacities of MCM-41 and S-MCM were almost the same which was observed according to the breakthrough experiments. The adsorption capacity of toluene in S-MCM was 57, 104, 200 and 277 mg g^− 1 for initial toluene concentrations of 250 to 1500 ppm respectively. The effects of the operation parameters, such as contact time and initial concentration on adsorption performance, were also tested in this study.     

Impact of nanotube density and alignment on the elastic modulus near the top and base surfaces of aligned multi-walled carbon nanotube films

The mechanical compliance of vertically aligned carbon nanotube (VACNT) films renders them promising as interface materials that can accommodate thermal expansion mismatch. Here we study the relationship between the detailed morphology and elastic modulus of multi-walled VACNT films with thicknesses ranging from 98 to 1300 μm. A systematic analysis of scanning electron micrographs reveals variations in nanotube alignment and density among samples and within different regions of a given film. Nanoindentation of both top and bottom film surfaces using an atomic force microscope with spherical indenters with radii between 15 and 25 μm provides evidence of the modulus differences. The top surface is shown to have a higher modulus than the base, with out-of-plane modulus values of 1.0–2.8 MPa (top) and 0.2–1.4 MPa (base). The indentation data and microstructural information obtained from electron microscopy are interpreted together using an open cell foam model to account for differences in nanotube alignment and density, which are generally lower at the base and yield predictions that are consistent with the modulus data trends. This work shows that microstructure analysis complements property measurements to improve our understanding of nanostructured materials.     

Fabrication and characterization of bone china using synthetic bone powder as raw materials

The synthetic bone powder was studied as a raw materials for bone china, completely replacing natural bone ash raw materials. The physical and thermal properties of samples obtained by the two bone powders were tested and comparatively studied. Performance tests included pyroplastic deformation, flexural strength, bulk density, sintering shrinkage, water absorption, transmittance, thermal expansion coefficient and the thermal shock resistance. The phase composition and morphology were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results indicated that using synthetic bone powder could shorten the preparation time, reduce the sintering temperature and result in high-quality bone china. The pyroplastic deformation decreased from 9.14% to 7.92%, the three-point flexural strength increased from 123 MPa to 191 MPa, the light transmittance (at a 2-mm thickness) increased from 6.7% to 11.2%, the thermal expansion coefficient decreased from 8.24×10⁻⁶ °C⁻¹ to 7.69×10⁻⁶ °C⁻¹, and the thermal shock resistance increased from 140 °C to 180 °C. A continuous interface layer without cracks was produced by using the synthetic bone powder.     

Core–shell BaMoO4@SiO2 nanospheres: Preparation,characterization, and optical properties

Core–shell BaMoO₄@SiO₂ nanospheres were prepared in reverse microemulsions and exhibited enhanced photoluminescence (PL) intensity as compared to that of the uncoated BaMoO₄. Characterization was performed using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX), and X-ray powder diffraction (XRD). It was found that the silica shell could increase the PL intensity, but the shell is not the thicker the better. The PL emission can be decomposed into three individual Gaussian components: two UV emissions at 308 nm and 369 nm and a visible emission at 448 nm. Such short emission wavelengths can be attributed to quantum size effect of the small BaMoO₄ cores (～16 nm).