Degree Of Amorphization Research Articles

Morphological and thermal characterization of zirconia/hydroxyapatite composites prepared via sol-gel for biomedical applications

The thermal behavior of pure ZrO2 and hydroxyapatite (denoted as Z and HAp, respectively), as well as three composites with different content of Z and HAp (Z90HAp10, Z70HAp30 and Z50HAp50) prepared via sol-gel method has been studied by thermogravimetry (TG) and first-order derivative of TG up to 1200 °C under inert gas atmosphere. Dehydration, loss of alcohol and acetylacetone and a multi-step thermal decomposition processes has been identified by analyzing the gases evolved in each step by Fourier transform infrared spectroscopy (FTIR). Fresh samples of Z-rich composites undergo an abrupt ejection of material from the crucible around 200 °C with noticeable increase of the sample temperature. During the occurrence of this phenomenon FTIR spectra demonstrated the evolution of gases (CO, CO2, acetone and ethylene) due to the simultaneous decomposition of acetylacetone and ethanol, not present in the samples calcined at 120 °C. As far as the structural study is concerned, pure Z crystallizes at 1000 °C in the monoclinic system, but the presence of HAp in the composite materials enables the crystallization of Z in the tetragonal phase. Finally, the amorphization degree increases with increasing the content of Z in all the composites treated at 600 and 1000 °C.

Heavy-ion irradiation effects on U3O8 incorporated Gd2Zr2O7 waste forms

In this research, the heavy-ion irradiation effects of U-bearing Gd2Zr2O7 ceramics were explored for nuclear waste immobilization. U3O8 was designed to be incorporated into Gd2Zr2O7 from two different routes in the form of (Gd1-4xU2x)2(Zr1-xUx)2O7 (x = 0.1, 0.14). The self-irradiation of actinide nuclides was simulated by Xe20+ heavy-ion radiation under different fluences. Grazing incidence X-ray diffraction (GIXRD) analysis reveals the relationship between radiation dose, damage and depth. The radiation tolerance is promoted with the increment of U3O8 content in the discussed range. Raman spectroscopy testifies the enhancement of radiation tolerance and microscopically existed phase evolution from the chemical bond vibrations. In addition, the microstructure and elemental distribution of the irradiated samples were analyzed as well. The amorphization degree of the sample surface declines as the U content was elevated from x = 0.1 to x = 0.14.

A novel copper precursor for electron beam induced deposition.

A fluorine free copper precursor, Cu(tbaoac)2 with the chemical sum formula CuC16O6H26 is introduced for focused electron beam induced deposition (FEBID). FEBID with 15 keV and 7 nA results in deposits with an atomic composition of Cu:O:C of approximately 1:1:2. Transmission electron microscopy proved that pure copper nanocrystals with sizes of up to around 15 nm were dispersed inside the carbonaceous matrix. Raman investigations revealed a high degree of amorphization of the carbonaceous matrix and showed hints for partial copper oxidation taking place selectively on the surfaces of the deposits. Optical transmission/reflection measurements of deposited pads showed a dielectric behavior of the material in the optical spectral range. The general behavior of the permittivity could be described by applying the Maxwell–Garnett mixing model to amorphous carbon and copper. The dielectric function measured from deposited pads was used to simulate the optical response of tip arrays fabricated out of the same precursor and showed good agreement with measurements. This paves the way for future plasmonic applications with copper-FEBID.

Room temperature ferromagnetism and its origin for amorphous MoSe2 nanoflowers

Amorphous MoSe2 has been fabricated hydrothermally, and the degree of amorphousness was tuned by post-annealing procedures. Large room temperature ferromagnetism (RTFM) has been achieved for the amorphous MoSe2 which weakens during crystallization and phase transition from the 1T to the 2H structure. Theoretical calculations indicate that the amorphous MoSe2 exhibits higher magnetization compared with the crystalline 1T and 2H phases and that the magnetization mainly originates from the d orbitals of Mo atoms. This study provides insights into the RTFM for the amorphous transition metal dichalcogenides (TMDs) and provides amorphousness as a new option to tailor the magnetization of the TMDs for future spintronic applications.

Leaching behaviour of mechano-chemically activated bio-oxidised refractory flotation gold concentrates

In this paper, the leaching behaviour of mechano-chemically activated, refractory, bio-oxidised flotation gold concentrates has been investigated. In particular, the effect of activation parameters (e.g., milling time and speed, and ball to pulp ratio) and cognate physico-chemical changes on the impact of the refractory mineral components in the ore was studied. The results showed that mechano-chemical activation led to reduction in the average particle size and increased surface area and reagent consumption in tandem with remarkable mineral amorphisation of the bio-oxidised products. The gold yield increased by a maximum of ~1.8 times after 24 h of cyanide leaching, irrespective of the magnitude of milling speed, milling time, ball to pulp ratio and the degree of mineral amorphisation. Furthermore, the increase in reagent consumption was consistent with increasing mineral particle stress and exposure of reactive gangue mineral phases (e.g., sulphate minerals), a factor that least influenced the gold yield. It appears that the improvement in gold extraction efficacy was due to gold surface cleaning, creation of pores/crevices that are linked to gold sites, and disintegration of gold-gangue mineral agglomerates that encapsulated gold particles. The findings were consistent with the nature of refractoriness and necessary for understanding ways of mitigating gold refractoriness in bio-oxidised flotation concentrates.

Quantification of microwave-induced amorphization of celecoxib in PVP tablets using transmission Raman spectroscopy

In this study, the influence of drug load on the microwave-induced amorphization of celecoxib (CCX) in polyvinylpyrrolidone (PVP) tablets was investigated using quantitative transmission Raman spectroscopy. A design of experiments (DoE) setup was applied for developing the quantitative model using two factors: drug load (10, 30, and 50% w/w) and amorphous fraction (0, 25, 50, 75 and 100%). The data was modeled using partial least-squares (PLS) regression and resulted in a robust model with a root mean-square error of prediction of 2.5%. The PLS model was used to study the amorphization kinetics of CCX-PVP tablets with different drug content (10, 20, 30, 40 and 50% w/w). For this purpose, transition Raman spectra were collected in 60 s intervals over a total microwave time of 10 min with an energy input of 1000 W. Using the quantitative model it was possible to measure the amorphous fraction of the tablets and follow the amorphization as a function of microwaving time. The relative amorphous fraction of CCX increased with increasing microwaving time and decreasing drug load, hence 90 ± 7% of the drug was amorphized in the tablets with 10% drug load whereas only 31 ± 7% of the drug was amorphized in the 50% CCX tablets. It is suggested that the degree of amorphization depends on drug loading. The likelihood of drug particles being in direct contact with the polymer PVP is a requirement for the dissolution of the drug into the polymer upon microwaving, and this is reduced with increasing drug load. This was further supported by polarized light microscopy that revealed evidence of crystalline particles and clusters in all the microwaved tablets.

Disordering of the Crystal Structure of Cellulose Under Mechanical Activation

The present paper describes the study of the effect of mechanochemical activation on the amorphization process of individual α-cellulose and native cellulose being a constituent part of the lignocellulosic material in the form of partially crystalline fibrils. In processing the powder X-ray diffraction data the following methods are used to determine the degree of crystallinity of cellulose: Segal’s, Rietveld’s, and Lorentzian deconvolution. It is demonstrated that mechanical activation of individual α-cellulose in an AGO-2 laboratory planetary ball mill with a shock-shear action results only in grinding and amorphization, while the degree of amorphization increases propotionally to the duration of the power supply. When α-cellulose is treated in an RM-20 flow-through centrifugal roller mill with a shear action, particle agglomeration is observed together with amorphization. When a lignocellulosic material (wheat straw) is treated in a centrifugal roller mill, considerable amorphization occurs only at high energies, and no particle agglomeration is observed.

Selective extraction of aluminum from coal-bearing kaolinite by room-temperature mechanochemical method for the preparation of γ-Al2O3 powder

Coal-bearing kaolinite (CBK) is a solid waste generated during coal production. Despite being a potential source of aluminum, CBK presents a great challenge in terms of Al recovery. To tackle this challenge, we used a room-temperature mechanochemical method based on mechanical grinding and sulfuric acid treatment. Ground samples were characterized by X-ray diffraction, thermogravimetry and Fourier transform infrared spectroscopy to reveal that the degree of kaolinite amorphization increased with grinding time, mirrored by the concomitantly increasing Al extraction efficiency. An extraction efficiency of 100% was obtained after 12-h grinding (resulting in complete kaolinite amorphization) and 2-h leaching with 3M sulfuric acid and the leached aluminum could be readily recovered from the leaching liquor as Al2(SO4)3·18H2O using ethanol as a precipitant. Thermal decomposition of the Al2(SO4)3·18H2O at 900°C could produce γ-Al2O3 powder with a purity of 97.56% and a surface area of 206.9m2·g−1.

Implementation of pulse timing discriminator functionality into a GeSbTe/GeCuTe double layer structure.

The functionality of a pulse timing discriminator, which is commonly required in optical communication systems and artificial neuromorphic engineering, was implemented into chalcogenide phase-change materials. GeSbTe (GST) and GeCuTe (GCT), which exhibit opposite refractive index behavior in their respective crystalline and amorphous phases, were employed. A GST/GCT double layer enabled the order of arrival of two counter-propagating femtosecond pulses to be encoded as a difference in the degree of amorphization of the GCT layer, i.e., either a brighter or darker contrast of the amorphized area with respect to the crystalline background. Nonthermal ultrafast amorphization contributed to a picosecond time resolution in the discrimination of the pulse arrival order.

Influence of PVP molecular weight on the microwave assisted in situ amorphization of indomethacin

In situ amorphization is an approach that enables a phase transition of a crystalline drug to its amorphous form immediately prior to administration. In this study, three different polyvinylpyrrolidones (PVP K12, K17 and K25) were selected to investigate the influence of the molecular weight of the polymer on the degree of amorphization of the model drug indomethacin (IND) upon microwaving. Powder mixtures of crystalline IND and the respective PVP were compacted at 1:2 (w/w) IND:PVP ratios, stored at 54% RH and subsequently microwaved with a total energy input of 90 or 180kJ. After storage, all compacts had a similar moisture content (∼10% (w/w)). Upon microwaving with an energy input of 180kJ, 58±4% of IND in IND:PVP K12 compacts was amorphized, whereas 31±8% of IND was amorphized by an energy input of 90kJ. The drug stayed fully crystalline in all IND:PVP K17 and IND:PVP K25 compacts. After plasticization by moisture, PVP K12 reached a Tg below ambient temperature (16±2°C) indicating that the Tg of the plasticized polymer is a key factor for the success of in situ amorphization. DSC analysis showed that the amorphized drug was part of a ternary glass solution consisting of IND, PVP K12 and water. In dissolution tests, IND:PVP K12 compacts showed a delayed initial drug release due to a lack of compact disintegration, but reached a higher total drug release eventually. In summary, this study showed that the microwave assisted in situ amorphization was highly dependent on the Tg of the plasticized polymer.

A novel Ni-S-W-C electrode for hydrogen evolution reaction in alkaline electrolyte

Ni-S-W-C electrode, a novel efficient electrocatalyst for hydrogen evolution reaction (HER) in alkaline solution, has been prepared by pulse electrodeposition. The electrode shows excellent electrocatalytic activity with low overpotential of 262mV (at 10mA/cm2) and high exchange current density of 3.13×10-2mA/cm2, and exhibits much better HER activity than that of Ni-S, Ni-S-C, and Ni-S-W electrodes. The remarkable enhancement in electrocatalytic performance of Ni-S-W-C electrode is attributed to addition of tungsten and carbon. WS2 is formed in Ni-S-W-C electrode after the addition of tungsten, and is an efficient catalyst for hydrogen evolution with very low overpotential. The increased amorphization degree by carbon-doped is also benefit to improve HER electrocatalytic performance of Ni-S-W-C electrode.

Amorphous NiCoPt/Ce<sub>2</sub>O<sub>3</sub> Nanoparticles as Highly Efficient Catalyst for Hydrogen Generation from Hydrous Hydrazine

Hydrous hydrazine is a promising hydrogen carrier material because of its high content of hydrogen (8.0 wt.%) and easy recharging as a liquid. Amorphous Ni8.1Co1.0Pt0.9/Ce2O3 nanoparticles with low precious-metal content were synthesized by a facile co-reduction method at room temperature under ambient atmosphere. The increased degree of amorphization was attributed to the introduction of Ce2O3. The resultant Ni8.1Co1.0Pt0.9/Ce2O3 nanocomposite was employed as an efficient nanocatalyst towards the decomposition of hydrous hydrazine to H2, and exhibited excellent catalytic activity and 100% H2 selectivity. Turnover frequency (TOF) value catalyzed by amorphous Ni8.1Co1.0Pt0.9/Ce2O3 is 93.75 h-1, which is much higher than Ni8.1Co1.0Pt0.9 (4.39 h-1) at 298 K. The development of the improved catalytic performance and low-cost catalyst with amorphous structure is believed to strongly promote the practical application of hydrous hydrazine as a hydrogen storage material.

An explorative analysis of process and formulation variables affecting comilling in a vibrational mill: The case of praziquantel

Praziquantel, a BCS II class anthelmintic drug used for the treatment of schistosome infections, was coground in a vibrational mill with different polymers (linear and crosslinked povidone, copovidone and sodium starch glycolate). An explorative analysis of formulation variables (drug-polymer wt ratio and polymer type) and process parameters (type of grinding media, grinding time and frequency) was carried out with the help of an experimental screening design. The influence of the above mentioned factors on three PZQ characteristics (residual crystallinity, water solubility enhancement and drug recovery) was studied. The variation of carrier amount proved to be by far the most important variable affecting all the experimental responses. A lower impact and, in some cases, rather null effect, had the variation of the process variables. All coground systems were characterized by a high amorphous degree and a solubility significantly higher than the API. A very promising product was obtained by processing at 20Hz for 4h, using 3 spheres of 15mm as grinding media, i.e. a coground having a 50% API content, showing a 4.6-fold greater solubility at 20°C than pure praziquantel. This product maintained the same antischistosomal activity of pure API and was both physically and chemically stable for at least 6 months.

Neutron damage of hexagonal boron nitride: h-BN

Hexagonal boron nitride (h-BN) was neutron damaged at an integral flux of 2.40 × 1012 n cm−2 s−1 for 1, 2, 3 and 4 h. The h-BN samples undergo a transition from sp2 to sp3 hybridization as a consequence of the neutron induced damage with the formation of cubic boron nitride (c-BN) spots, as suggested both by FT–IR and Raman spectroscopy. In addition to c-BN, also a certain degree of amorphization is achieved by h-BN already at the lowest neutron fluence of 8.64 × 1015 n cm−2 as clearly evidenced by Raman spectroscopy. The Wigner or stored energy to the radiation-damaged h-BN samples was studied by DSC and also in this case there was a clear evidence that the neutron damage was partly irreversible and insensitive to the thermal annealing up to 630 °C. Electron spin resonance (ESR) was employed to further study the structural defects induced by the neutron bombardment of h-BN. Two kinds of paramagnetic defective structures centered on 11B atoms were identified.

Amorphization model of nanostructured composite solid electrolytes

In the last decades, extensive research has been undertaken to find solid electrolytes that might increase the power and safety of promising electrochemical devices such as lithium batteries, supercapacitors, and solid oxide fuel cells. It is mainly based on the screening of advanced functional suprastructures and developing special synthesis procedures to obtain nanosized materials, allowing one to increase ionic conductivity. That’s why special attention is paid to composite solid electrolytes. In this work we use the accumulated knowledge on the physical chemistry of metals and alloys to describe the amorphization effects. It is known that amorphization at the interphase boundaries (interfaces) and grain boundaries noticeably increases (sometimes by orders of magnitude) the ionic transfer rate and, therefore, affects the functional properties of nanostructured composite solid electrolytes. In the theoretical model proposed, we have attempted to elucidate the reasons, inducing the amorphization effects which are observed upon the crystallization of inorganic eutectics and composite formation. We have especially used the approximation of rigid discs, considered, unit-cell volumes. In the context of the theory, describing the amorphization as an excess molar volume arising upon the crystallization of metals and alloys, we have established that the degree of amorphization depends not only on the synthesis conditions, but also on the incommensurability of crystal unit cells in the components. The findings can be useful in the elaboration of novel inorganic materials for various applications.

A study of thermo-electric power and transport properties of polypyrrole/ash (paddy husk) nano-composites

The polypyrrole (PPy)/ash (paddy husk) (PH ash) nano-composites were synthesized in the presence of ammonium persulphate (oxidizing agent) with different compositions, viz. 15, 30, 45 and 60 wt% of ash in the pyrrole, by chemical polymerization (oxidation) method. The Powder X-ray diffraction patterns showed that the PPy/PH ash nano-composites exhibited a high degree of amorphousness with only a low degree of crystalline structure. Scanning electron micrographs revealed that the particle sizes of the nano-composites increased when compared with the pure PPy and ash particles, and they had spherical as well as elongated forms. The PPy/PH ash nano-composite (45 wt%) showed the highest conductivity which may be due to the increased chain length of pure PPy which facilitated the hopping of the charge carriers and the larger number of charge carriers to hop between the favorable localized sites. Hence, the composites might be good semiconductors. The results of Seebeck coefficient and thermo-electric power factor experiments of the nano-composites demonstrated a strong dependence on the weight percent of ash in pure PPy. These nano-composites showed the behavior of thermo-electric materials. The nano-composites have also shown good dielectric behavior. So, the composites might be good materials of dielectric.

Characterization of the Diamond Wire Sawing Process for Monocrystalline Silicon by Raman Spectroscopy and SIREX Polarimetry

A detailed approach to evaluate the sub-surface damage of diamond wire-sawn monocrystalline silicon wafers relating to the sawing process is presented. Residual stresses, the presence of amorphous silicon and microcracks are considered and related to diamond wire velocity and cutting ability. In particular, the degree of amorphization of the wafer surface is analyzed, as it may affect the etching performance (texturing) during solar cell manufacture. Raman spectroscopy and Scanning Infrared Stress Explorer (SIREX) measurements are used independently as non-destructive, contactless optical characterization methods to provide stress imaging with high spatial resolution. Raman mappings show that amorphous silicon layers can occur inhomogeneously across the surface of diamond wire-sawn wafers. The Raman and SIREX results reveal a connection between a higher fraction of the amorphous phase, a more inhomogeneous stress distribution and a lower peak maximum of the stress difference on wafers, depending on both the wire wear and the wire velocity. SIREX line scans of the in-plane difference of the principal stress components ∆σ taken across the sawing grooves show significant differences in magnitude and periodicity. Furthermore, the results are compared with the microcrack depth from the same investigation areas. The possibility to optimize the diamond wire sawing processes by analyzing the sub-surface stress of the wafers is offered by complementary use of both Raman and SIREX measurements.

Structural, Magnetic, and Mössbauer Investigation of Ordered Iron Nitride with Martensitic Structure Obtained from Amorphous Hematite Synthesized via the Microwave Route

Amorphous hematite synthesized by a simple and fast microwave route was used to obtain Fe16N2 fine particles by reducing in 5% H2/Ar gas flow, followed by long time nitridation in ammonia gas flow at temperatures below 200 °C. Depending on nitridation temperature, various amounts of metallic iron were present along with the α″-Fe16N2 main phase. A small amount of iron oxide was observed by Mossbauer spectroscopy, but it was undetected by X-ray diffraction due to its high degree of amorphization. Increased amounts of Fe3N and Fe4N phases were observed at a nitridation temperature above 150 °C, which had a detrimental effect on the magnetic properties. Structural information and phase composition were extracted from Rietveld refinement of the XRD data. Values of the magnetization at saturation measured at 40 kOe and 25 °C of 222 emu/g for α″-Fe16N2 and 192 emu/g for metallic iron were obtained via magnetic measurements, Rietveld, and Mossbauer analysis.

Time and temperature mediated evolution of CDHA from ACP nanoparticles in deep eutectic solvents: Kinetic and thermodynamic considerations

Calcium phosphate (CP) nanoparticles were synthesized in choline chloride-urea deep eutectic solvent (DES). The effect of synthesis time and temperature on crystallinity, particulate properties, and elemental/chemical purity of the CP nanoparticles were investigated by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier transform infra-red spectroscopy. The results confirmed the formation of amorphous calcium phosphate (ACP) nanoparticles (at 25°C for 10min) with spherical morphology, mean diameter of 29nm, and high elemental-structural purity. The increase of synthesis time from 10min to 48h at 25°C had no significant influence on the phase transformation of ACP nanoparticle so that the nanoparticles showed high degree of amorphization after 48h. The crystallization of particles rapidly rose upon increase of the synthesis temperature so that the nanoparticles of calcium-deficient hydroxyapatite (CDHA) with percent crystallinity of ~97% were obtained in choline chloride-urea DES at 150°C after 24h. Kinetic and thermodynamic studies revealed that upon increase of temperature from 25 to 150°C, the rate constant and Gibbs free energy for growth of CP crystals in the DES rises from 8.70×10−4 to 1.37×10−3min−1 and 3.22×10+2 to 4.57×10+2KJ·mol−1, respectively.

Effect of Amorphization Degree on Mechanical and Microstructural Properties of Portland Cement Paste

AbstractThis paper shows that besides the particle size reduction, prolonged high-energy ball milling of portland cement leads to mechanically induced phase transformation from the crystalline to t...