X-RAY DIFFRACTION PHASE ANALYSES OF MULLITE DERIVED FROM RICE HUSK SILICA

Ceramics (1-x)Ba(Fe1/2Nb1/2)O3−x(Na1/2Bi1/2)TiO3; 0≤x≤1.0 were prepared by conventional ceramic synthesis technique. Rietveld refinements of X-ray diffraction data of these ceramics were carried out using FullProf software and determined their crystal symmetry, space group and unit cell dimensions. Rietveld refinement revealed that Ba(Fe1/2Nb1/2)O3 has cubic structure with space group Pm 3¯ m and Na1/2Bi1/2)TiO3 has rhombohedral structure with space group R3c. Addition of (Na1/2Bi1/2)TiO3 to Ba(Fe1/2Nb1/2)O3 resulted in the change of unit cell structure from cubic to tetragonal (P4/mmm) for x = 0.75 and the X-Ray diffraction peaks slightly shift towards higher Bragg’s angle, suggesting slight decrease in unit cell volume. SEM studies were carried out in order to access the quality of the prepared ceramics which showed a change in grain shapes with the increase of (Na1/2Bi1/2)TiO3 content. FTIR spectra confirmed the formation of perovskite type solid solutions.

Non-lead ceramic samples of Ba0.06(Na0.5Bi0.5)0.94Ti1-x(Ni1/3Nb2/3)xO3; 0 ≤ x ≤ 1.0 were prepared by standard high temperature ceramic synthesis method. Rietveld refinements of X-ray diffraction data of these ceramics were carried out using FullProf software and determined their crystal symmetry, space group and unit cell dimensions. Rietveld refinement revealed that Ba0.06(Na0.5Bi0.5)0.94TiO3 has a monoclinic structure with space group P4/m while B0.06(Na0.5Bi0.5)0.94(Ni1/3Nb2/3)O3 has tetragonal (pseudo-cubic) structure with space group P4/mmm. Partial replacement of Ti4+ ion by pseudo-cation (Ni1/33+Nb2/35+)4+ resulted in the change of unit cell structure from monoclinic to tetragonal. SEM studies were carried out in order to access the quality of the prepared ceramics which showed a change in grain sizes with the increase of (Ni1/33+Nb2/35+)4+ content. FTIR spectra confirmed the formation of perovskite type solid solutions.

In this paper, the Minkowski fractal is used to design the geometry of a frequency selective surface (FSS) unit cell, which resembles the shapes found in nature. The proposed FSS unit cell has both angular and polarization stabilities of incident wave. For the miniaturization of FSS and decrease of resonance frequency, interdigital capacitances (IDCs) are devised in the FSS structure, which do not eliminate angular and polarization stabilities. The dimensions of the unit cell are 5 mm × 5 mm and miniaturized 0.095λ0×0.095λ0. The resonance frequency is specified as 5.75 GHz with 155 MHz bandwidth. An equivalent circuit is derived for the unit cell to evaluate its frequency responses. The effects of variations of the geometrical dimensions of the FSS unit cell on its performance are studied. A prototype model of proposed FSS is fabricated and measured. The performance of its full-wave computer simulation results and measured data are compared and are shown to be in good agreement.

Lithium aluminum silicate powders in the form of β-spodumene were synthesized through sol–gel technique by mixing boehmite sol, silica sol and lithium salt. The gel and oxide powders were characterized by thermogravimetry, differential thermal analysis (DTA), X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy and scanning electron microscopy. DTA, XRD and FTIR results confirmed that crystallization of β-spodumene took place at about 800 °C. The tiny crystallites with average size less than 1 μm appeared when the gel powders were sintered at 800 °C. A substantial increase of the crystal grain size was observed with increasing sintering temperatures.

Rietveld refinements and spectroscopic structural studies of a Na-free carbonate apatite made by hydrolysis of monetite

Hybrid compound 1-(2-fluro-4-bromobenzyl)-4-dimethylaminopyridium bis(maleonitriledithiolate) cuprate(II) [2F4BrBzDMAP]2[Cu(mnt)2] is prepared and characterized by X-ray diffraction. The compound crystallizes in the triclinic system with the space group P-1. The unit cell dimensions are a = 8.9813(11), b = 9.0794(12), c = 13.1082(17) A and α = 88.179(2)°, β = 81.397(2)°, γ = 70.736(1)° with Z = 1. The structure consists of two [2F4BrBzDMAP]+ cations and one [Cu(mnt)2]2– anion. The cations of the title compound stack into a one-dimensional column through p∙∙∙π and π∙∙∙π interactions, and the anions (A) and cations (C) are arranged alternatively into one 1D column in an ∙∙∙A–CC–A–CC–A∙∙∙ sequence through C–H∙∙∙N hydrogen bonds and S∙∙∙N interactions. The presence of functional groups is confirmed by the FT-IR spectrum, and optical absorption is ascertained by the recorded UV-Visible spectrum. The thermal stability of the compound is determined by thermogravimetric and differential thermal analyses. The variable-temperature magnetic susceptibility measurement shows that the compound exhibits a weak ferromagnetic coupling behavior when the temperature is lowered.

Nonlinear optical materials have been investigated recently due to their potential technological applications in information storage and communications. In this context, semi-organic crystals can effectively combine the desired nonlinear optical properties of amino acids with the promising mechanical and thermal properties of inorganic materials. In this work, we have synthesized and characterized a semi-organic crystal of the amino acid l-histidine and hydrofluoric acid and investigated the chemical interactions between the organic and inorganic moieties. The crystal of l-histidine bis(fluoride) has been produced by slow solvent evaporation and characterized by X-ray diffraction (XRD) crystallography and thermogravimetric and differential thermal analyses. The XRD conducted using the Rietveld method shows that the unit cell is orthorhombic with the P21212 space group and contains four l-histidine bis(fluoride) units. Both differential thermal analysis and temperature-dependent XRD show that the crystals are thermally stable up to 191°C and do not undergo phase transition. The computational Hirshfeld surface analysis of the crystal structure reveals the main intermolecular interactions. Density functional theory has been employed to calculate the ionic interaction energy and electrostatic potential maps and confirm the spontaneity of ionic association at 191°C. The combined experimental and computational results show that the thermal stability of the semi-organic l-histidine bis(fluoride) crystal makes it suitable for nonlinear optical applications in optical sensing and communication systems.Graphical abstract

A polyethylene terephthalate – Rice husk (PET-RH) composite was produced from waste plastic water bottle and rice husk. Burning rate test, scanning electron microscope (SEM), thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were employed to study the produced composite. The burning rate carried out on the composite revealed resistance to burning as result of the introduction of more PET material into the composite at varied proportions, it also revealed that to produce a more durable PET-RH composite, the ratio of PET to RH must be at optimum concentration to achieve a desired application. The SEM analysis revealed a well-structured morphology of the produced composite as there were less areas of fracture or unfilled fiber regions that could cause breakdown or fissure in the matrix of the composite. The TGA analysis of the produced composite revealed thermal stability of the PET-RH composite within the range 0 to 300 ℃ with a 20 % weight residue recorded in the temperature range 500 to 887 °C. The DTA analysis revealed and correlated with the results obtained from the TGA thermogram, whose initial drying was due to a 4 % loss in mass and a narrow endotherm which was visible at the 240 and 545 °C temperature range which corresponded to the pyrolytic stage visible in the TGA thermogram, this clearly suggested that the produced composite can serve in applications dependent on thermal resistant properties. Results so far obtained from this study suggested that the produced PET-RH composites exhibited good performance characteristics that could be likened to properties of conventional materials with the same matrix.

To solve the existing problems of silicon dioxide (SiO2) coating fabricated by the sol-gel method, such as complicated process, long production cycle, uncontrollable quality, etc., an improved electrophoretic deposition (EPD) combined with the sintering process was proposed to prepare SiO2 coating on a dark nickel (Ni)-coated Q235 steel substrate. Silica sol was prepared by basic catalysis, containing silica of ∼130 g L-1 with viscosities below 4 mPa s. Silica sol powder was characterized by the differential thermal analysis, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. EPD was applied to prepare SiO2 coating on the Ni adhesive layer, followed by the sintering process to improve the compactness. In addition, the effects of EPD and sintering parameters were also evaluated. Potentiodynamic polarization and electrochemical impedance spectra were utilized to assess the corrosion behavior of the coating. The results showed that the EPD coating demonstrated excellent wear resistance when deposited at 15 V for 40 s and sintered at 400 °C for 45 min, exhibiting ∼6 μm thickness and a compact morphology. It also showed superior corrosion resistance with icorr of 1.02 × 10-7 A cm-2, which was 2 orders of magnitude lower than that of dip-coating. Combining the EPD and sintering processes could shorten the fabrication period of SiO2 inorganic coating and also improve the mechanical and corrosion properties, providing guidance for inorganic ceramic fabrication and showing potential for practical applications.

Various phase changes which occur in crystals of hexamethylbenzene and beryllium oxyacetate have been investigated by X-ray methods.The crystal structure of hexamethylbenzene at high temperatures has been determined by single crystal oscillation method, (Cu Ka, λ=1.54 kX), in order to obtain some information about the anomalous volume change at high temperatures. It belongs to the orthorhombic system. The dimensions of the unit cell which contains four molecules of C6 (CH3) 6 are a=9.06 kX, b=15.70 kX and c=7.52 kX at 155°C. The space group was found to be D232h-Fmmm and the determined atomic parameters are shown in Table 2. Powder photographs were also taken at various temperatures, from which the change of the dimensions of the unit cell was deduced. The determined structure was discussed comparing with the structure at room temperatures which has been very accurately analyzed by Robertson and Brockway. The mechanism of the anomalous volume change was briefly discussed taking the thermal movements of the molecules into account.The crystal structures of different modifications of beryllium oxyacetate have been investigated by X-ray methods, (Cu Ka) . An attempt has been made to derive the expression for the change of the Bragg and diffuse reflections of X-rays associated with the transition about 40°C, from the viewpoint of the thermal movements of the acetate groups. It was shown that the derived intensity expression could account for the characteristic feature of the observed X-ray scattering.At 147°C the phase change of the first order occurs and when the temperature is raised above this point the substance assumes gradually the appearance of soft wax, though it melts sharply at 285°C. Powder photographs were taken at various temperatures. Most of the lines observed could be explained as due to a rhombohedral unit cell with dimensions a=9.72 kX. ar=54°20', containing one molecule in it. It will be noteworthy that this unit cell dimension is closely related to the cubic closest packing of spheres (rhombohedral lattice with ar=58°12') . This fact, combined with the observation that the X-ray intensity distribution in the powder photograph taken just below the melting point showed much resemblance to the liquid halo slightly above the melting point, suggests that the liquid state near the melting point may be considered to be cubic closest packing of molecules. Another modification of Be-oxyacetate can be obtained by sublimation, the crystal data of which are given.

Recently, a thin film of Bi4Ti3O12 (BTO) has been widely studied as one of candidate materials for applications of ferroelectric random access memory due to its large remnant polarization at room temperature. The crystal structure of BTO consists of pervoskite type units, Bi2Ti3O10 (An−1BnO3n+1 for n = 3), and interleaved Bi2O2 layers along the c-axis. In the Bi2Ti3O10 units, Ti ions are surrounded by oxygen octahedrons, and Bi ions occupy the outside of TiO6 octahedrons [1, 2]. Although the crystal structural information of BTO is essential to understand the remnant polarization at room temperature, the structural study of BTO has not been performed sufficiently because the difference between two kinds of crystal systems, monoclinic and orthorhombic, is subtle. This present work is focused on the structural refinement of BTO at room temperature using neutron powder diffraction data. The Rietveld refinement of Bi4Ti3O12 was carried out using neutron powder diffraction data, which provide a better refined results for a number of oxygen atoms in the unit cell, though Ti atom has a negative scattering length (−0.3438 × 10−12 m) for neutron radiation. The sample of BTO was prepared by a normal solidstate reaction using Bi2O3 and TiO2 as a starting material. The mixture was annealed at 1050 ◦C for 17 h. The second annealing process was carried out at 1150 ◦C for 48 h followed by intermediate regrinding. Neutron powder diffraction data were collected over scattering angles 0 ◦–160 ◦ using 1.8348 A neutron on the High Resolution Powder Diffractometer (HRPD) at Hanaro Center of Korea Atomic Energy Research Institute in Korea. The General Structure Analysis System (GSAS) program was used to do the Rietveld refinement [3]. The pseudo-Voigt function was used as a profile function among profile ones in GSAS program [4]. According to the report of the single crystal X-ray experiment [5], the phase of BTO at room temperature belongs to the monoclinic system with B1a1 space group. However, Hervoches et al. reported that BTO at room temperature has orthorhombic crystal system from the Rietveld refinement using neutron powder diffraction. Also, they mentioned that the deviation between orthorhombic and monoclinic system was too small to be detectable with neutron diffraction data [6]. When the reflections by the b-glide in the orthorhombic system with B2cb space group are not observed, it is difficult to discern the difference between the two crystal systems quantitatively because the final diffraction patterns for both crystal systems are almost identical. In order to start the Rietveld refinement, a reasonably approximated model of BTO for the actual structure based on the monoclinic and orthorhombic crystal system is required. As a starting model of BTO, two kinds of models based on the monoclinic and orthorhombic systems were used. The model based on the B1a1 space group (M-model) was built with crystallographic data taken from the single crystal X-ray diffraction [5]. The crystallographic data reported by Hervoches et al., were used to make the other one (O-model) [6]. The Rietveld refinement of BTO was performed by neutron powder diffraction data, which is powerful to determine atomic positions and occupancies factors of oxygen atoms. Because BTO contains a large number of oxygen atoms in the unit cell. The neutron scattering lengths for Bi, Ti and O atoms are 0.853 × 10−12 m, −0.3438 × 10−12 m and 0.5805 × 10−12 m, respectively. The initial refinement for the O-model was done by the unit-cell, the zero-point shift and background parameters. The zero-point shift was correct by neutron powder diffraction data of α-Al2O3 as a standard sample. A good match of the peak positions was achieved from the preliminary refinement, and then the peak profile parameters including the peak asymmetry were refined. A pseudo-Voigt function in this study was used as a profile function. It assumes that there is no defect for oxygen sites because the samples were prepared under air atmosphere. The final weighted and profile R-factors, Rwp and Rp, obtained from the O-model through the Rietveld refinement procedure showed 8.61% and 6.31%, respectively. Fig. 1 illustrates the Rietveld refinement patterns for the O-model. In the case of the same Rietveld refinement procedure applied to the M-model, all R-factors for M-model were lower than those for O-model. Among R-factors, the weighted R-factor, Rwp, was considerably decreased from 8.61% to 5.59%. The profile factor, Rp, which is a true quantity based on the discrepancies between observed and calculated intensities, was 4.17%. Also, the goodness-of-fit indicator, S(= Rwp/Re), was decreased from 2.15 to 1.40. The Rietveld refinement patterns of the M-model are shown

-Effect of Iron (iii) Oxide (Fe2O3), Nickel Oxide (NiO) nanoparticles (NPs) and their blends as biocatalysts on the yield and quality of bioethanol produced from co-fermentation of rice husks and banana peelshas been investigated. In this study, rice husks (RH) and banana peels (BP) were collected and prepared for characterization using proximate, ultimate and composition analysis techniques. Prepared samples were pretreated using acid pretreatment before enzymatic hydrolysis, co-fermentation and product analyses. Experiments were performed using the following blending ratios: 100wt.%RH:0wt.%BP, 70wt. %RH: 30wt. %BP, 50wt. %RH: 50wt. %BP, 30wt. %RH: 70wt. %BP and 0wt. %RH: 100wt.%BP. The Fe2O3 NPs, NiO NPs, and their blend (Fe2O3+NiO at 1:1) were added accordingly to sample blends. Untreated feedstocksamples without nanoparticles, butprepared using the same blending ratios, served as the control samples. Results revealed that the sample blend, 30wt. %RH: 70wt. %BP, treated with Fe2O3+NiO produced the highest yield of bioethanol (27.8 g/l). This could be associated with the combined effect of the nanoparticles and probably coupled with the co-fermentation effect of the blends of the two lignocellulosic biomass feedstocks. The least yield of bioethanol (23.2 g/l) was produced from the untreated sample blend, 100wt. %RH: 0wt. %BP, that contains only rice husks. The untreated sample blend, 0wt.%RH:100wt.%BP, containing banana peels alone gave a higher bioethanol yield (25.6 g/l) than sample blend with only rice husks, probably due to higher content of fermentable sugars and lower lignin level in banana peels than in rice husks. Bioethanol yields from feedstock samples treated with Fe2O3, NiO and Fe2O3+NiO NP respectivelywere observed to increase withthe increasing weight percentages of banana peels in the blends.The feedstock samples treated with Fe2O3 NPs gave higher yields of bioethanol than samples treated with NiO NPs alone. This suggested thatFe2O3 NPs is a better catalyst than NiO NPs in this specificreaction, enhancingenzymatic activities that facilitate conversion of sugars into bioethanol.

This study presents two routes to produce amorphous silica from an Egyptian rice husk under conditions optimized for least environmental impact and low cost. The first route includes thoroughly washing of the husk sample with water, dry milling and leaching with citric acid. The leaching process was applied in two stages, that is, at 323 K for 180 min and then at 353 K for 60 min. After washing and drying, the leached sample was subjected to a heat treatment in a muffles furnace at four sequential steps. The second route includes all the previously mentioned steps, except the citric acid leaching. The final products were characterized using x-ray fluorescence analysis, carbon content analysis, x-ray diffraction, differential thermal analysis, nitrogen adsorption, mercury intrusion, and scanning electron microscopy. The results show that the citric acid leaching has many advantages with respect to silica yield and porosity as well.

Synthesis, characterization, drug loading and in-vitro bioactivity studies of rice husk derived SiO2–P2O5–MgO–CaO–SrO bio-active glasses

Current cement-based building materials have a huge disadvantage that they are easily broken due to thermal decomposition at high temperature (over 500°C) of structures of hydrated cement. This is easily observed at construction works when burned, the cement-based mortar and concrete materials and plaster are susceptible to collapse causing damage to buildings or structures. More seriously, these accidents easily cause injuries or loss of life for residents and people working there. Therefore, research on fire resistance and structural stability at high temperatures of building materials is always an interested topic of many scientists. This study utilized resources of highly active alumino silicate materials such as coal bottom ash and rice husk ash to produce geopolymer using sodium silicate solution as an alkaline activator. The ash-based geopolymer has good engineering properties responding to requirements of ASTM C55 and C90 for lightweight concrete brick. It is interesting to note that the geopolymer product was tested for thermal properties at 1000°C such as heat resistance, volumetric shrinkage, mass loss. The experimental results show that the ash-based geopolymer material has high thermal stability with increasing significantly of compressive strength after heated at 1000°C. Moreover, the geopolymer was also carried out to characterize microstructure before and after exposed at high temperature using methods of X-ray diffraction (XRD), scanning electron microscope (SEM). Thermal analysis methods such as thermogravimetric (TG), differential thermal analysis (DTA), and dilatometry-thermal expansion (CTE) were used to evaluate microstructural stability of the geopolymer-based materials.