Formation Of Crystalline Phases Research Articles

Low-Cost and Eco-Friendly Hydroxyapatite Nanoparticles Derived from Eggshell Waste for Cephalexin Removal

This work describes the hydroxyapatite nanoparticle (HAP) preparation from eggshell waste and their application as an adsorbent for Cephalexin (Ceph) antibiotic removal from aqueous solutions. Chemical precipitation with phosphoric acid was used to evaluate the feasibility of calcium oxide for HAP preparation. The structural properties of HAP were characterized by X-ray diffraction, which revealed the formation of the hydroxyapatite crystalline phase formation. In addition, transmitting electron spectroscopy showed an irregular shape with a variation in size. The impact of various experimental conditions on the removal efficiency such as the solution’s pH, contact time, HAP mass, solution temperature, and Ceph concentration were studied. Experimental data showed that HAP could remove most Ceph species from aqueous solutions within 1 h at pH = 7 with 70.70% adsorption efficiency utilizing 50 mg of the HAP. The removal process of Ceph species by HAP was kinetically investigated using various kinetic models, and the results showed the suitability of the pseudo-second-order kinetic model for the adsorption process description. Moreover, the removal process was thermodynamically investigated; the results showed that the removal was spontaneous endothermic and related to the randomness increase. The data confirmed that HAP had high efficiency in removing Ceph antibiotics from an aqueous solution.

Forming zeolites and calcium silicate hydrates in Fe-rich, slag-based, porous inorganic polymers

This study provides insights on the formation of crystalline phases from Fe-rich slag-based porous inorganic polymers (porous IPs), cured under hydrothermal conditions. The porous IPs were synthesised using synthetic slags with different chemistries (from FeO-SiO2-CaO to FeO-SiO2-Al2O3-CaO systems) as solid precursors, and a sodium silicate-based alkaline activator. Chemical expansion was used to create the porous structure. After hardening, the porous monoliths were hydrothermally processed at different temperatures and respective steam pressures (150 °C, 4.8 bar; 200 °C, 15.5 bar and 250 °C, 39.7 bar) and for different durations (12–18 h). The presence of aluminium promoted the formation of the zeolite analcime within the first 12 h. The formation of crystalline calcium-silicate hydrates was promoted after a longer curing duration; however, just after the formation of analcime had taken place. Next to these phases, the Fe-rich smectite nontronite and calcium carbonates were detected.

Metal-Induced Crystallization in Metal Oxides.

ConspectusThe properties of a material depend upon its physical characteristics, one of these being its crystalline state. Next generation solid-state technologies will integrate crystalline oxides into thermal sensitive processes and composite materials. Crystallization of amorphous phases of metal oxides in the solid state typically requires substantial energy input to induce the amorphous to crystalline phase transformation. In the case of silica, the transformation to α-quartz in a furnace occurs above 1300 °C and that of titania, above 400 °C. These calcination processes are costly in energy but also often degrade complex material architectures or compositions.Thus, low temperature crystallization techniques are required that preserve macro- and mesostructures and complex elemental composition (e.g., organic-, metal-, and semiconductor-metal oxide hybrids/composites). Some solution-based techniques exist to directly fabricate crystalline metal oxides. However, these are not always compatible with the specificities of the system or industrial constraints. A postsynthetic, solid-state approach that reduces crystallization temperature in metal oxides is metal-induced crystallization (MIC).MIC is the introduction of catalytic amounts of a cation, which can be an s-block, p-block, or d-block cation, that migrates through the solid metal oxide lattice. The cation is thought to temporarily break metal oxide bonds, allowing [MOx] polyhedra to rotate and reform bonds with neighboring [MOx] groups in a lower energy crystalline phase. Depending on the system, the cation can favor or defavor the formation of a particular crystalline phase, providing a means to tune the purity and crystalline phase ratios. An advantage of MIC is that, although the crystallization occurs in the solid state, the crystallization process can be accomplished for particle suspensions in liquid media. In this case, the energy required to induce the crystallization can come from, for example, a microwave or an ultrasound bath. The crystallization of particles in suspension avoids aggregation from particle–particle sintering. In the case of thin films, the energy for crystallization typically comes from a laser or calcination.MIC is only recently being used as a low temperature metal oxide crystallization technique, despite being widely used in the semiconductor industry. Here, the mechanism and previous studies in MIC are presented for titania, silica, and other oxides. The beauty of this technique is that it is extremely easy to employ: cations can be incorporated into the system postsynthetically and then are often expelled from the lattice upon phase conversion. We expect MIC to enrich materials for photochromic, optoelectronic, catalyst, biological, and other applications.

Lithium extraction from β-LiAlSi2O6 using Na2CO3 through thermal reaction

• Heating of β-spodumene (mineral and synthetic) and sodium carbonate was studied. • NaAlSi 2 O 6 is produced by Li + substitution in β-spodumene after heating at 400 °C. • At high temperature (above 600 °C) NaAlSiO 4 is obtained. • Li 2 CO 3 is recovered from a mixture containing NaAlSi 2 O 6 with a yield of 70%. • β-spodumene displays similar thermal behavior regardless its origin. The aim of this study is to evaluate the role of Na 2 CO 3 in solid-state lithium extraction from β -spodumene (β -LiAlSi 2 O 6 ) under both dynamical and static heating conditions. Different samples of β -spodumene were used: one obtained from a mineral sample and another synthesized from oxides/carbonates reagents. Structural, chemical, microstructural and thermal analysis techniques were employed to analyze the samples before and after reaction. Experimental results show that lithium could be extracted from β -spodumene structure through sodium aluminosilicate phases formation under air atmosphere: NaAlSi 2 O 6 at low temperature (∼400 °C) and NaAlSiO 4 at high temperature (above 600 °C). The comparison between both β -spodumene samples reveals the formation of the same crystalline phases under both dynamical and static heating conditions, although mixtures of Na 2 CO 3 with synthetic β -spodumene show minor reactivity at low temperature. In addition, the study of different molar ratios of LiAlSi 2 O 6 :Na 2 CO 3 evidences that a major amount of NaAlSi 2 O 6 phase is obtained at 400 °C for the 2:1 mol ratio. Lithium can be recovered by additional dissolution and drying stages in the form of lithium carbonate Li 2 CO 3 reaching a high yield. These results are in agreement with thermodynamical calculations obtained for the LiAlSi 2 O 6 -Na 2 CO 3 system.

Effects on the properties of cementitious composites using waste glass powder (WGP) as a partial replacement for cement

The use of waste glass powder (WGP) as a supplementary cementitious material (SCM) rich in pozzolan as a partial replacement for cement has been a viable alternative, from the environmental and economic point of view, to solve problems caused by the high consumption of cement worldwide. Therefore, the objective of this study was to evaluate the effects of the use of WGP, when used as a partial cement substitute, in some properties of cementitious composites (pastes, mortars and concretes), in the fresh and hardened state. Through a systematic literature review, 23 experimental research articles obtained from the world-renowned Science Direct database were analyzed. The results obtained from this review indicate improvements in some properties of cementitious composites with WGP, such as increased compressive strength at advanced ages, increased thermal neutron shielding capacity, reduced penetration of sulfate and chloride ions, mitigation of alkali-silica reaction, reduced thermal conductivity, improved mechanical and chemical properties, including the formation of a new crystalline phase (devitrite) when exposed to high temperatures, reductions in air entrapment, water absorption and porosity. Regarding workability, there was no consensus, however, regardless of the substitution content, all composites were within the slump limits. Therefore, it can be concluded that the use of WGP in cementitious materials produces beneficial effects on some properties of cementitious composites.

Formation of Porous Structures and Crystalline Phases in Poly(Vinylidene Fluoride) Membranes Prepared by Nonsolvent Induced Phase Separation

Formation of Porous Structures and Crystalline Phases in Poly(Vinylidene Fluoride) Membranes Prepared by Nonsolvent Induced Phase Separation

Structural and Optical Properties of Dy3+ Doped with an Eulytite Type NaBaBi2(PO4)3 Phosphor for White Light Emitting Diodes

A series of NaBaBi(2-x)(PO4)3:xDy3+ eulytite type phosphors with varying doping concentrations were synthesized using a conventional solid-state reaction. The crystalline nature and phase formation of the phosphor were confirmed by the PXRD technique. FESEM was used to examine the surface morphology. UV-DRS measurements were used to quantify the band gap of the host and Dy3+ ion doped phosphors. The phosphors’ photoluminescence properties were thoroughly investigated. According to the excitation spectra, these phosphors show a strong absorption band in the near-ultraviolet (NUV) region, extending from 250 to 450 nm. Under the excitation of 352 nm, the peaks of the emission spectra of Dy3+ ions are located at 485 nm (blue), 575 nm (yellow) and 666 nm (red), corresponding to the magnetic dipole 4F9/2→6H15/2 transition, the electric dipole 4F9/2→6H13/2 transition and the 4F9/2→6H11/2 transition. The optimal concentration of Dy3+ doped phosphor is x = 0.075 and the major concentration quenching mechanism is accomplished by energy transfer between the nearest-neighbour ions. The critical transfer distance (Rc) is estimated to be about 19.01. The Commission International deI’Eclairage (CIE) of NaBaBi1.925(PO4)3:0.075Dy3+ phosphor was calculated to be (x = 0.341 and y = 0.374), which was very close to the “ideal white” (x = 0.33, y = 0.33). Present findings suggest that the phosphor might be a viable option for producing a white-light-emitting phosphor under NUV activation.

Определение толщины зародышевого слоя AlN, сформированного на поверхности Al-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-(0001) в процессе нитридизации, методами РФЭС и ИК-спектроскопии

The effect of different degrees of the sapphire surface nitridation process completion on the AlN buffer layer morphology has been studied. It was found that ~85% completion of the AlN crystalline phase formation promotes the growth of a two dimensional AlN buffer layer with a smooth surface morphology, regardless of the substrate temperature and ammonia flux. In contrast, during the AlN nucleation layer formation as a result of weak or excessive sapphire nitridation, a polycrystalline or three-dimensional AlN structures with a high density of inversion domains, respectively, were formed. Using independent methods of X-ray photoelectron spectroscopy and infrared spectroscopy of surface polaritons, the thickness of the AlN nucleation layer was determined at ~85% degree of the nitridation process completion, which amounted to ~1 monolayer.

Determination of the AlN nucleation layer thickness formed on the Al-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-(0001) surface during nitridation process by XPS and IR spectroscopy

The effect of different degrees of the sapphire surface nitridation process completion on the AlN buffer layer morphology has been studied. It was found that ~85% completion of the AlN crystalline phase formation promotes the growth of a two dimensional AlN buffer layer with a smooth surface morphology, regardless of the substrate temperature and ammonia flux. In contrast, during the AlN nucleation layer formation as a result of weak or excessive sapphire nitridation, a polycrystalline or three-dimensional AlN structures with a high density of inversion domains, respectively, were formed. Using independent methods of X-ray photoelectron spectroscopy and infrared spectroscopy of surface polaritons, the thickness of the AlN nucleation layer was determined at ~85% degree of the nitridation process completion, which amounted to ~1 monolayer. Keywords: ammonia molecular beam epitaxy, AlN, sapphire, reflection high-energy electron diffraction, nitridation, inversion domains, X-ray photoelectron spectroscopy, surface polaritons.

Amino Acid-Functionalized Graphene Oxide for Liquid Crystalline Phase Formation

Amino Acid-Functionalized Graphene Oxide for Liquid Crystalline Phase Formation

Modifications of the properties of a porcelain through the addition of niobium pentoxide (Nb2O5)

There is a gap in the literature regarding the influence of Nb2O5 on traditional ceramic masses. Thus, this work promoted the addition of different proportions of this oxide in a porcelain composition in order to verify its effect on physical and microstructural properties. It was found that the addition of Nb2O5 reduced the apparent porosity of the composition at lower temperatures. The composition containing 5% in weight reached the characteristics of a porcelain at 1220 °C and the others reached these properties at 1240 °C. In addition, the secondary mullite obtained was in the form of more refined needles, although this characteristic has not statistically influenced the mechanical strength and the pyroplasticity index. The addition of Nb2O5 caused darkening of the pieces due to the reduction of material absorption in the visible region. The results of chemical microanalysis by Energy Dispersive X-ray Spectroscopy (EDS) and X-ray diffraction (XRD) indicated that crystals of Nb2O5 was found to be dispersed in the glass phase, without the formation of a new crystalline phase.

Soft model of solidification with the order–disorder states competition

A theoretical model is proposed that describes the kinetics of the formation and evolution of competing phases, one of which is a disordered system of topologically stable excitations (vortices) and the second one is an ordered (crystalline) phase. This model is intended to be the simplest model which can demonstrate such important characteristics of solidification process as a sensitivity to the cooling speed, natural appearance of the relaxation times of kinetic phase transformations, and particular features of the rapidly solidified systems. The model was studied numerically showing the crucial properties relevant to the obtained in the experiments on the amorphization in metals. In the present work, we derive a general form of the system's Hamiltonian and stochastic dynamical equations to describe the rapid solidification and a competing formation of amorphous and crystalline phases. The numerical study of the formation of both phases shows the competition of inherited phases during the simultaneous growth from nuclei. The cooling speed has a significant impact on the regimes of the phase formation. We find that solidification during fast cooling leads to the preferred selection of the disordered phase, then the subsequent evolution leads to the aging and to continuous transition to a solid ordered phase. Also, it is shown that further cooling leads to the spinodal decomposition, and the mobility of phases plays a significant role in the dynamics of the defects migration.

Revealing the crystallization kinetics and phase transitions in Mg65Zn30Ca5 metallic glass by nanocalorimetry

As a potential candidate for biomedical applications, Mg65Zn30Ca5 (at%) metallic glass has attracted considerable attention. To guide the development of MgZnCa alloys with improved mechanical and biomedical properties, it is necessary to understand the phase transitions of this metallic glass. In this study, controlling phase transitions in Mg65Zn30Ca5 metallic glass is realized by nanocalorimetry. The underlying thermodynamic and kinetic features at heating rates ranging from 102 to 105 K s−1 are therefore revealed. Upon rapid heating, an intermediate amorphous phase is detected. This metastable phase facilitates the formation of the Mg7Zn3 crystalline phase with a remarkably reduced reaction temperature and activation energy. With the combination of nanocalorimetry and structural characterization, the continuous heating transformation (CHT) diagram for Mg65Zn30Ca5 metallic glass is plotted, and crystallization trajectories under various heating conditions are distinguished. Meanwhile, the crystallization kinetics covering seven orders of magnitude is estimated, giving the growth rate of the MgZn crystalline phase in the undercooled liquid with temperatures ranging from Tg to Tm. Accordingly, the maximum crystal growth rate and corresponding temperature are estimated at umax= 0.49 m s−1 and Tu,max= 563 K, respectively. With the decrease in undercooling, the transition from kinetics-controlled crystallization to thermodynamics-controlled crystallization is illustrated, causing divergence of the estimated growth rate from the experimental results.

Influence of Pb2+ doping in the optical and electro-optical properties of SnO2 thin films

Different types of doping incorporated to tin dioxide (SnO2) have been reported in order to control its bandgap aiming optoelectronic applications, such as transparent electrodes, solar cells and displays. In this work, the doping of SnO2 with lead in the oxidation state 2+ (Pb2 +) is investigated, in conjunction with the influence on the optical and electro-optical properties of thin films, deposited by sol-gel-dip-coating. It was observed that for an insertion up to 25 at% of lead, there is no formation of a secondary crystalline phase beyond the rutile phase of SnO2. Optical characterization data indicate two behavior tendencies: for doping level up to 1 at%, Pb2+ enters preferentially as interstitial impurity, whereas for higher doping it enters substitutional to Sn4+. For doping up to 1 at% the bandgap increases due to the Burnstein-Moss effect, in addition to a decrease in the capture energy for metastably photoexcited electrons. On the other hand, for doping above 1 at%, there is an increase in the Urbach energy, shifting the energy level of the valence band, leading to a decrease in the bandgap from 3.45 to 2.89 eV, which shows potential applicability in bandgap engineering. The higher doping level also increases the capture energy for photoexcited electrons and gives rise to the persistent photoconductivity effect at low temperatures, related to a large lattice relaxation around the dominant photoexcited defect.

Structure and Tribo-Mechanical Properties of MoSx:N:Mo Thin Films Synthesized by Reactive dcMS/HiPIMS

Modifying MoS2 thin films by additional elements shows great potential in order to adjust the property profile and to meet the increasing requirements regarding high wear resistance and low friction properties of industrial components. Within that context, MoSx:N:Mo thin films were deposited by a reactive hybrid dcMS/HiPIMS process. By systematically increasing the Mo target cathode power, an investigation of the structural and the mechanical properties was conducted to understand the evolution of the tribological behavior. A low Mo target cathode power of 1 kW is related to the formation of the preferential (002) MoS2 basal-plane and thus a low friction with µ = 0.2. With an increasing amount of Mo, the film loses its solid lubricant MoS2 properties and a nitride constitution of the thin film is developing due to the formation of crystalline Mo and MoN phases. Related to this transformation, the hardness and elastic modulus are increased, but the adhesion and the tribological properties are impaired. The film loses its plasticity and the generated film material is directly removed from the contact area during the sliding contact.

Structural and electrical studies of thermally annealed tungsten nitride thin film

Present work is focused on various properties of thermally annealed tungsten nitride (WN) film. Tungsten nitride thin films on silicon (100) substrates were deposited via reactive magnetron sputtering technique. Initially Ar/N2 flow ratio was optimized by varying N2 gas flow between 5 to 25 sccm. 20:5 (Ar:N2) was found to be the best for W2N phase formation. Using optimized condition, a set of WN deposited and then annealed at different temperatures i.e. 200°C, 400°C and 600°C for two hours each. Various characterizations have been done using X-ray diffraction, four probe resistivity and nano-indentation test. XRD results suggest formation of pure W2N crystalline phase of the films with face centered cubic structure. The resistivity result shows the decrease of resistivity value with increase in annealing temperature. Nano-indentation results showed hardness and elastic modulus values at 5mn load does not vary much with annealing at different temperatures. Structural, mechanical and electrical studies showed that the samples were stable up to 600°C. Thus, tungsten nitride thin films will contribute as a material suitable for long time exposure at elevated temperature for application of cutting tools. Copyright © 2017 VBRI Press.

Photo-response of polylactide-poly(methyl methacrylate) blends: Effect of ultraviolet irradiation

The applications of biodegradable polylactide (PLA) are dependent on its structural durability under service conditions. In this work, we analyze the temperature dependence of photo-stability of polylactide-poly(methyl methacrylate) (PLA/PMMA) blends after the irradiation of ultraviolet (UV) light. X-ray diffraction analysis of the UV-irradiated PLA reveals the crystalline phase formation at 55 °C, as confirmed by thermal analysis. The UV irradiation decreases the crystallization temperature of PLA. The thermal analysis and Fourier Transform Infra-Red (FT-IR) analysis illustrate the interaction between PLA and PMMA. We evaluate the photo-stability of the UV-irradiated PLA/PMMA blends from the temporal evolution of optical absorbance/transmittance of the blends. A first-order kinetic analysis is used to analyze the change of optical absorbance, controlled by the annihilation and generation of color centers. Two processes contribute to the photo-stability of the PLA/PMMA blends – one is annihilation-dominant for the blends with a large fraction of PMMA, and the other is generation-dominant for the blends with a large fraction of PLA. The combinational effect of UV irradiation and the interaction between PLA and PMMA determines the photo-stability of PLA/PMMA blends.

Influences of aluminum doping on the microstructures and electrical properties of tantalum nitride thin films before and after annealing

Ta–N–Al thin films were produced by reactive sputtering with two different TaAl alloys (Al 10 at.% and 20 at.%) for use as resistive materials for thin film chip resistors. Changing the N2 gas flow of the N2/Ar plasma and the Al ratio in TaAl alloy resulted in different microstructures and electrical properties of the Ta–N–Al thin film. The resistivity of the thin film sputtered by TaAl (Al 20 at.%) alloy was 1.23 times that sputtered by Ta under 20% N2/Ar. After deposition, rapid thermal processing was applied to anneal the thin films for 5 min at 600 °C, 650 °C, and 700 °C under N2 (99.995%) atmosphere, causing the Ta2N and TaN crystalline phase formation. Al in Ta–N–Al was observed to hinder Ta2N and TaN crystalline phase formation during annealing. It is crucial to dope Al ith Ta–N appropriately to obtain a near-zero temperature coefficient of resistance (TCR) after annealing. The TCR of Ta–N–Al thin film, sputtered by TaAl (Al 20 at.%) alloy, was substantially affected by the annealing temperature. However, the thin film sputtered by TaAl (Al 10 at.%) alloy under 16% N2/Ar can achieve a TCR of −1.8 ppm/°C and 1.4 ppm/°C after annealing at 600 °C and 650 °C, respectively.

Physicochemical and Mechanical Effects of Commercial Silver Diamine Fluoride (SDF) Agents on Demineralized Dentin.

To investigate the effects of four commercial silver diamine fluoride (SDF) agents on the chemical composition and microstructural properties of dentin, and its relation to the bond strength of two adhesives. Ninety human molars were randomly divided into sound dentin (negative control), demineralized dentin (positive control), and four experimental groups (n = 15) according to the SDF treatments (Cariestop [Biodinamica Quimica y Farmaceutica], RivaStar 1 [SDI], RivaStar 2 [SDI], and Saforide [Tokyo Seiyaku Kasei]). ATR-FTIR, x-ray diffraction, and SEM techniques were employed to characterize the compositional, crystalline, and microstructural properties of the samples. The microtensile bond strength test evaluated the bonding performance of two adhesives in demineralized dentin treated with SDF agents. Regarding the chemical composition, all SDF-treated groups showed a significantly higher phosphate:organic matrix ratio than the demineralized dentin group (p < 0.05). The XRD analyses revealed that the crystallite size for hydroxyapatite crystals increased on the surface areas (deep, medium, and superficial dentin) for all experimental groups compared to demineralized dentin (p < 0.05). SEM images showed that the behavior of the agents used differs on each surface treated. Bond strength values were adversely affected with both adhesive systems in the four experimental groups (p < 0.05). The application of SDF agents resulted in the formation of different crystalline phases of silver salts and the increase of mineralization of the pretreated demineralized dentin. However, SDF application showed a negative effect on the bond strength of the adhesives.

Structure, hirshfeld surface studies, optical and mechanical analysis on a third-order nonlinear optical crystal 2-amino-6-methylpyridin-1-ium 2-chloro-4-nitrobenzoate (2A6M2C4N)

Organic third order nonlinear optical material, 2-Amino-6-methylpyridin-1-ium 2-chloro-4-nitrobenzoate (2A6M2C4N) was effectively synthesized and single crystals were developed by slow cooling solution growth method. The crystallographic structure of the grown crystal has been confirmed through single crystal X-ray diffraction analysis and it uncovers that the title material belongs to Triclinic crystal system with centrosymmetric space group of P-1. The crystalline phase formation was ascertained from powder X-ray diffraction measurements. The functional groups present in the compound were confirmed by Fourier transform infrared analysis. Optical analysis explicit that the grown crystal possess good transmittance in the wave length region of 200–800 nm. Photoluminescence spectroscopy analysed by exciting the material at 320 nm supports that 2A6M2C4N crystal suits the requirements of optoelectronic devices. The thermal behaviour of 2A6M2C4N exploited by TG-DTA measurements show that it is stable up to 160.04 °C. Third order nonlinear optical properties such as nonlinear refractive index and third order nonlinear optical susceptibility were calculated by employing the z-scan technique. The HOMO-LUMO, molecular electrostatic potential (MESP) and contour map of the molecule was examined at B3LYP/6–311++G (d, p) level by using DFT calculations. The existence of the intermolecular interactions in the molecule were confirmed by Hirshfeld surface studies. • Novel third order nonlinear optical crystals 2A6M2C4N has been grown by slow cooling technique. • 2A6M2C4N belongs to triclinic crystal system with centrosymmetric space group P-1. • Intermolecular-interactions in 2A6M2C4N molecule were characterized by Hirshfeld surface analysis. • Third order nonlinear optical susceptibility (χ(3)) was calculated to be 2.918 × 10–11 esu.