Amorphous Compounds Research Articles

Large Transmittance Change Induced by Exciton Accumulation under Weak Continuous Photoexcitation

Excited‐state absorption of materials is caused by instantaneous accumulation of excitons when irradiated with a high‐intensity laser pulse. If excitons can be accumulated by irradiation with weak continuous incoherent light at room temperature (RT) in air, then excited‐state absorption can be obtained over a large area, which is potentially useful for a variety of optical applications. Here, photoresponsive transmittance control using long‐lived RT triplet excitons is demonstrated. Host–guest glass films composed of a secondary amino‐substituted deuterated aromatic carbon material as a guest and an amorphous hydroxyl steroidal compound as a host form guest‐based triplet excitons with an RT lifetime of longer than 1 s upon photoexcitation and the triplet excitons of the guest exhibit a large absorption coefficient over the whole visible region. Efficient accumulation of the triplet excitons of the guest triggered by photoexcitation causes a large decrease in the transmittance of the host–guest films. The transmittance of one of the host–guest films decreases from 98% to 30% over the whole visible range and from 92% to 13% at the wavelength of maximum triplet–triplet absorption of the guest as the power of UV photoexcitation is increased from 10−1 to 103 mW cm−2.

In-situ defect repairing in hydroxyapatite/phytic acid hybrid coatings on AZ31 magnesium alloy by hydrothermal treatment

To improve the corrosion resistance of AZ31 magnesium alloy, a crack-free hydroxyapatite/phytic acid (HA/PA) hybrid coating was synthesized on AZ31 substrate via a chemical conversion deposition to form precursor coating, and followed by a hydrothermal treatment in the saturated CaO solution. During the hydrothermal treatment, the phosphate and calcium ions diffused to the interface of the precursor coating/solution to form amorphous CaP compound and subsequently crystallized into HA particles that repaired the defects in the precursor coating and exhibited a high bonding strength of 24.3 ± 1.7 MPa between the hybrid coating and the magnesium alloy substrate. Electrochemical measurements in simulated body fluid (SBF) revealed that the HA/PA hybrid coating could effectively provide protection for magnesium (Mg) alloy on account of the stable barrier properties.

High-Throughput Raman Spectroscopy Screening of Excipients for the Stabilization of Amorphous Drugs.

Low aqueous solubility of active pharmaceutical ingredients (APIs) is an enduring problem in pharmaceutical development, and it is becoming increasingly prevalent among new drug candidates. It is estimated that about 40% of drugs in the development pipeline and approximately 60% of the drugs coming directly from discovery suffer from poor aqueous solubility and slow dissolution, thereby reducing their bioavailability and efficacy and thus preventing their commercialization. It is well known that utilizing the amorphous form of a drug can be a useful approach to improve the dissolution rate and solubility of poorly water-soluble APIs. Amorphous compounds are thermodynamically unstable, but they can be stabilized by combining them with a carrier polymer (excipient) to form a solid dispersion. High-throughput Raman spectroscopy was used in this study to identify excipients that promote formation and stabilization of the amorphous drug form in solid dispersions. Four model APIs were used as poorly soluble drug candidates: ketoprofen, danazol, griseofulvin, and probucol. The Raman signals of excipients were generally negligible, and therefore Raman bands from the drugs were used with minimal spectral pre-processing. By comparing Raman spectra collected from the APIs in the crystalline and molten state, appropriate spectral features and regions were identified for the development of semi-quantitative methods to determine the amorphous content for each API. It is demonstrated that methods based on peak intensity ratio, peak width, peak distance, and classical least squares can all be effective methods for the screening of excipients. Interesting excipient-dependent phase transformation behavior was also observed for probucol.

EFFECT OF NANOSTRUCTURE OF THE PLATING ALLOY CO-NI-CR ON THE COATING MICROHARDNESS

The article reviews application of the methods of X-ray diffraction, electron microscopy, micro-roentgen-spectral analysis to study the structure and to prove a presence of nanostructures in the electrodeposition of the alloy Co-Ni-Cr. It was shown that the nanostructures obtained owe their origin to introduction of a residue of chromium amorphous hydroxide compounds.

Atomic mobility in the overheated amorphous GeTe compound for phase change memories

AbstractAbstractauthoren Phase change memories rest on the ability of some chalcogenide alloys to undergo a fast and reversible transition between the crystalline and amorphous phases upon Joule heating. The fast crystallization is due to a high nucleation rate and a large crystal growth velocity which are actually possible thanks to the fragility of the supercooled liquid that allows for the persistence of a high atomic mobility at high supercooling where the thermodynamical driving force for crystallization is also high. Since crystallization in the devices occurs by rapidly heating the amorphous phase, hysteretic effects might arise with a different diffusion coefficient and viscosity on heating than on cooling. In this work, we have quantified these hysteretic effects in the phase change compound GeTe by means of molecular dynamics simulations. The atomic mobility in the overheated amorphous phase is lower than in supercooled liquid at the same temperature and the viscosity is consequently higher. Still, the simulations of the overheated amorphous phase reveal a breakdown of the Stokes–Einstein relation between the diffusion coefficient and the viscosity, similarly to what we found previously in the supercooled liquid. Evidences are provided that the breakdown is due to the emergence of dynamical heterogeneities at high supercooling.

Dissolution performance of binary amorphous drug combinations—Impact of a second drug on the maximum achievable supersaturation

An increased number of amorphous formulations of poorly water soluble drugs are being introduced into the market due to their higher transient solubility and thus faster absorption and higher bioavailability. While most amorphous drug products contain a single drug substance, there is a growing trend towards co-formulating compounds in the same dosage form to improve patient compliance. The purpose of the present work was to evaluate the dissolution behavior and maximum achievable solution concentrations of amorphous solid dispersions of co-formulated ritonavir and lopinavir, and to compare the results with individual amorphous solid dispersion formulations. Dispersions of ritonavir and lopinavir were prepared in polyvinylpyrrolidone (PVP) or hydroxypropylmethylcellulose acetate succinate (HPMCAS) at a 20% (w/w) total drug loading, both alone and in combination, at three different lopinavir:ritonavir weight ratios. Amorphous films containing both drugs, but no polymer, were also prepared. The dissolution behavior of the dispersions and the amorphous films in non-sink conditions was evaluated, using ultracentrifugation to separate any colloidal material from molecularly dissolved drug. Nanoparticle tracking analysis was used to characterize colloidal material formed during the dissolution process. Results from the dissolution study revealed that, although supersaturated solutions resulted following dissolution, the maximum achievable concentration of each drug, when present in combination, was dramatically lower than when the individual dispersions were dissolved. The maximum achievable solution concentration for systems containing both drugs was found to decrease as the mole fraction of the drug in the amorphous phase decreased. The type of polymer used to formulate the dispersion also appeared to influence the dissolution behavior whereby the HPMCAS dispersions dissolved rapidly, resulting in the generation of a nanodroplets, while the PVP dispersions did not produce as many colloidal species. These results highlight the need to consider potential decreases in achievable supersaturation for formulations containing more than one amorphous compound.

The effect of MgO on the biodegradation, physical properties and biocompatibility of a Mg/HA/MgO nanocomposite manufactured by powder metallurgy method

Recently, magnesium-hydroxyapatite composites have shown the potential to serve as biodegradable metal matrix composite implants that can repair load-bearing defects in osseous tissue. However, the mechanical properties and corrosion resistance of magnesium-hydroxyapatite composites have been restricted by the significant agglomeration of HA particulates. In this study, the bio-corrosion properties of a Mg/HA-based composite were improved by the addition of different amounts of hydroxyapatite (HA) and periclase (MgO) nanopowders to pure magnesium and fabrication of the Mg/HA/MgO nanocomposites using a blend-cold press-sinter powder metallurgy (PM) technique. X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, atomic force microscopy and field-emission scanning electron microscopy were used to characterize the compositions of the corrosion products and the surface morphologies of the corroded specimens. Based on the electrochemical test, the corrosion resistance of the nanocomposites is shown to increase from 0.25 kΩ cm2 to 1.23 kΩ cm2 with the addition of 10 wt% MgO; however, the ultimate compressive strength decreased from ∼237 to ∼198 MPa. During immersion test in SBF solution, the growth of the Mg(OH)2 nanorods on the Mg-12.5HA-10MgO and Mg-5HA-15MgO (wt%) nanocomposites increased the contact angle between the SBF solution and the substrate; as a result, the corrosion rate decreased compared to that of the Mg-27.5HA-10MgO and Mg-20HA-5MgO (wt%) nanocomposites. The corrosion products formed on the nanocomposites surface are shown to be primarily Mg(OH)2, HA, Ca3(PO4)2 and amorphous CaP compounds. The cell culture results indicated that the Mg/HA/MgO nanocomposites remained biocompatible with osteoblasts by increasing of MgO amount.

Pair distribution function analysis of amorphous compounds using TEM electron diffraction

Pair distribution function analysis of amorphous compounds using TEM electron diffraction

Formation of NbB2/mullite composites by combustion synthesis involving metallothermic reduction of Nb2O5 and B2O3

NbB2/mullite composites were fabricated by self-propagating high-temperature synthesis (SHS) involving metallothermic reduction of Nb2O5 and B2O3 by Al and Si. Two reactant mixtures formulated as 13/11Nb2O5+26/11B2O3+6Al+xSi with x=2.0–3.0 and 13/9Nb2O5+52/27B2O3+52/27B+6Al+ySi with y=2.0–3.0 were prepared to study the effect of in situ formed SiO2 on combustion behavior and phase conversion. For comparison, test samples with pre-added SiO2 were employed and they were composed of 6/5Nb2O5+B2O3+14/5B+6Al+2SiO2, within which Al was the only reducing agent. When compared with combustion of the SiO2-added sample, the SHS process of the Si-adopted sample was more exothermic and effective in reduction of B2O3. Moreover, metallothermic reduction of B2O3 was greatly improved for the samples with excess Si and their final products were NbB2/mullite composites with negligible minor phases. However, due to incomplete reduction of B2O3 in the SiO2-added sample, the resulting product consisted of mullite, three boride phases (NbB, Nb3B4, and NbB2), and an amorphous compound.

CT patterns of pleuro-pulmonary damage caused by inhalation of pumice as a model of pneumoconiosis from non-fibrous amorphous silicates.

The aim of this article is to correlate the radiological features of pleuro-pulmonary damage caused by inhalation of pumice (an extrusive volcanic rock classified as a non-fibrous, amorphous, complex silicate) with exposure conditions. 36 subjects employed in the pumice quarries were evaluated for annual follow-up in a preventive medical surveillance program including spirometry, chest CT lasting from 1999 to 2014. They were only male subjects, mean age 56.92±16.45years. Subjects had worked in the quarries for an average of 25.03±9.39years. Domestic or occupational exposure to asbestos or other mineral dusts other than pumice was excluded. Subjects were also classified as smokers, former smokers and nonsmokers. Among the 36 workers examined, we identified four CT patterns which resulted to be dependent on exposure duration and intensity, FVC, FEV1 and FEF25-75, but not on cigarette smoking. The most common symptoms reported by clinical examination were dyspnoea, cough and asthenia. In no case it was proven an evolution of CT findings during follow-up for 10years. Liparitosis, caused by pumice inhalation, can be considered a representative example of pneumoconiosis derived by amorphous silica compounds, which are extremely widespread for industrial manufacturing as well as for applicative uses, such as nano-materials. Moreover, being pumice free of quartz contamination, it can represent a disease model for exposure to pure non-fibrous silicates.

Ion exchange synthesis of lanthanum zirconate

We have studied the formation of lanthanum zirconate through ion exchange in aqueous solutions of lanthanum and zirconyl chlorides and the AV-17-8 anion exchanger. The results demonstrate that the ion exchange leads to the formation of hydrosol of an amorphous lanthanum zirconium compound in the form of spherical particles about 4 nm in diameter. Heat treatment of the hydrosol at 700°C leads to crystallization of lanthanum zirconate with the fluorite structure, which transforms into the pyrochlore structure at higher temperatures.

A facile preparation of ceramic coatings on Ti alloys for thermal protection systems

In order to reduce the effects of solar energy on the instruments and the apparatus in the outer space, two different kinds of ceramic coatings were prepared on Ti6Al4V alloys by plasma electrolytic oxidation (PEO) in zirconate electrolytes. The phase composition, microstructure, thickness, and roughness of coatings were examined by XRD, SEM, EDS, thickness measurement gauge, and roughness measuring instrument, respectively. The infrared emissivity and solar absorbance of the ceramic coatings were studied with the UV–vis–NIR spectrophotometer and infrared reflectometer. The results show that ZrO2 coatings are dense and deep gray–green, and mainly composed of m-ZrO2, t-ZrO2. In addition, a small amount of TiO2, ZrTiO4, and the amorphous compound containing P exists in the coating. The intrinsic solar absorbance and emissivity of ZrO2 coatings are 0.92 and 0.76, respectively. The KZr2(PO4)3 coating is rough, thick, and white with the main crystalline of KZr2(PO4)3. The intrinsic solar absorbance and emissivity of the KZr2(PO4)3 coating are 0.62 and 0.91, respectively. For both coatings, the absorbance decreases while the emissivity increases due to an increase in the real surface area of the coatings by increasing thickness and roughness of the coatings as the PEO time progresses. The porous structure of the KZr2(PO4)3 is proved to be ideal for high emissivity and low absorbance materials with the lowest solar absorbance (0.239), the highest infrared emissivity (0.99), and a corresponding balance temperature of the coating of 276K.

Effect of sludge addition to coal on Na, K and S volatilisation in ashing process and ash fusibility

The effect of the addition of three types of sludge (L, O and F) on both the Na, K and S volatilisation and the slagging behaviour of a bituminous coal (H) was studied. Na, K and S volatilise in the coal, the sludges and their blends partially, and there exist linear relationships between their contents in ashes and the ratio sludge ash/blend ashes for each coal–sludge blend ash series. However, in blends with F (treated with FeCl3 and lime), S relationship is not linear due mainly to the following effects: a) sulphur retention by CaO to form CaSO4, and b) decrease of free CaO due to the formation of ferrites, silicates and phosphates. To determine the slagging tendency, the ash fusion temperatures (AFTs) were related with ash chemical and mineral composition by using the slagging factor, the base/acid ratio, the Fe2O3/CaO ratio, the P2O5 content, and the ternary equilibrium phase diagram SiO2–Al2O3–CaO. Sludge addition to coal produces a decrease in AFTs that depends on the percentage of sludge added, the sludge phosphorus content and additives (FeCl3 and/or lime), the fact that ash composition is near to those of the eutectics, and the formation of Si and P amorphous compounds.

Materials, Techniques, and Conservation of Historic Stained Glass “Grisailles”

A grisaille is a brown‐blackish paint applied onto the inner surface of stained glass to draw the contours and details of the figures and to produce the effect of shades and volumes. Grisailles were traditionally made of finely ground oxides of iron but also of copper, zinc, lead, or manganese mixed with a flux such as lead ground glass and a binder and fixed onto the flat glass by firing. The grisailles have typical layer thickness varying between 10 and 100 μm and are formed by a complex mixture of pigment particles, crystalline, and amorphous reaction compounds, aging, and weathering compounds. The high brilliance, collimation, energy selection, and monochromacity of the SR beam are ideal to obtain micro‐XRD patterns from thin cross sections of the grisailles. The analyses are complemented with SEM‐EDX and LA‐ICPMS. A selection of grisailles from several cathedrals and buildings in Spain, Avila, Burgos, Alcalá de Henares, and in particular from Segovia, dating from early 16th to the 20th century and belonging to several master glaziers are studied. Changes in the methods of production and materials in the different historical periods are obtained and also related to the conservation state of the materials.

Magnetocaloric effect and refrigeration cooling power in amorphous Gd7Ru3 alloys

In this paper, we report the magnetic, heat capacity and magneto-caloric effect (MCE) of amorphous Gd7Ru3 compound. Both, temperature dependent magnetization and heat capacity data reveals that two transitions at 58 K and 34 K. MCE has been calculated in terms of isothermal entropy change (ΔSM) and adiabatic temperature change (ΔTad) using the heat capacity data in different fields. The maximum values of ΔSM and ΔTad are 21 Jmol−1K−1 and 5 K respectively, for field change of 50 kOe whereas relative cooling power (RCP) is ∼735 J/kg for the same field change.

Predicting Crystallization of Amorphous Drugs with Terahertz Spectroscopy.

There is a controversy about the extent to which the primary and secondary dielectric relaxations influence the crystallization of amorphous organic compounds below the glass transition temperature. Recent studies also point to the importance of fast molecular dynamics on picosecond-to-nanosecond time scales with respect to the glass stability. In the present study we provide terahertz spectroscopy evidence on the crystallization of amorphous naproxen well below its glass transition temperature and confirm the direct role of Johari-Goldstein (JG) secondary relaxation as a facilitator of the crystallization. We determine the onset temperature Tβ above which the JG relaxation contributes to the fast molecular dynamics and analytically quantify the level of this contribution. We then show there is a strong correlation between the increase in the fast molecular dynamics and onset of crystallization in several chosen amorphous drugs. We believe that this technique has immediate applications to quantify the stability of amorphous drug materials.

SYNTHESIS AND STRUCTURE OF BIS(XYLARATO )GERMANATES OF MAGNESIUM, CALCIUM AND BARIUM

A procedure for the synthesis of the heterometallic germanium(IV) and magnesium, calcium and barium complexes with xylaric acid (H5Xylar) [Ge(μ-HXylar)2{Mg(Н2О)2}2]·4H2O(І), [Ge(μ-HXylar)2{Ca(Н2О)2}2]·3H2O(ІІ), [Ge(μ-HXylar)2{Ba(Н2О)4}2]·3H2O(ІІІ) were developed and the complexes isolated for the first time in the solid state. The first stage of synthesis portions of GeО2 (2.092 g, 0.02 mol) and xylaric acid С5H8О7 (7.2 g, 0.04 mol) were inserted in hot water (500 ml), heated (рН 1,5-2) and concentrated on a water bath to 150 ml (~4.5 h). Then the resulting solution was cooled to room temperature and MgCO3 (І), СаСO3 (ІІ) or ВаCO3 (ІІІ) added to рН=5. The heteronuclear coordination compounds were characterized by elemental analysis, powder X-ray diffraction, thermogravimetry, IR spectroscopy. Complexes I-III are X-ray amorphous compound with the molar ratio Mg(Ca, Ba) : Ge : ligand = 2 : 1 : 2. A study of the thermal stability of complexes has shown that its thermolysis is stepwise. Analysis of the IR spectra of complexes І-III showed that spectrums does not contain bands at 3590-3650 cm-1 and ν(С=О) = 1720 cm-1 typical of stretching vibrations of free OH and COOH. Bands detected at ν(С–О)~1000-1139 cm-1 typical of alkoxides, and nas(СОО–)~1678-1684 and ns(СОО–)~1356-1413 cm-1 of carboxylate ions. The scheme of structure of compounds I-IІІ was offered.

Corrosion Behavior of High Performance Offshore Platform Steel with Chromium and Nickel Addition in the Environment Containing Chloride Ions

The characterization of corrosion products formed on a high performance offshore platform steel in the environment containing chloride ions has been investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), electron probe microanalysis (EPMA) and electrochemical impedance spectroscopy (EIS). The results reveal that the corrosion process can be divided into the initial stage and the later stage. The main constituents of rust layers are α-FeOOH, β-FeOOH, γ-FeOOH, Fe3O4 and large amounts of amorphous compounds. With increasing corrosion time, the mass fraction of α-FeOOH and Fe3O4 increased, while that of γ-FeOOH and β-FeOOH changed slightly. The enrichment of Cr and Ni at the inner/outer interface, especially the side of inner rust, can be observed in the later corrosion stage of Cr-Ni steel, which can promote the formation of compact inner rust layer, impeding the transmission of corrosion mediums and slowing down the electrochemical reaction process.

Photoinduced mass transport in low molecular organic glasses and its practical application in holography

In this paper we present the synthesis and optical properties of amorphous low molecular compound 4-((4-(bis(5,5,5-Triphenylpentyl)amino)phenyl)diazenyl)benzoic acid. The surface relief gratings formation by polarization holography method on these thin films (thicknesses are 200–1700nm) was shown. The dependence of the surface relief modulation on various parameters: recording exposure dose, the polarization state of the recording beams, the grating period and the film thickness of the material was demonstrated. Values of surface tension at the air-film before and after irradiation of the substance by polarized radiation were measured.The efficiency of surface relief formation in different medium was compared. The possibility of practical application of 4-((4-(bis(5,5,5-Triphenylpentyl)amino)phenyl)diazenyl)benzoic acid in the holography as a non-etching photoresist was showed.

The mechanism of uranium transformation from U(VI) into nano-uramphite by two indigenous Bacillus thuringiensis strains

The mechanism of uranium transformation from U(VI) into nano-uramphite by two indigenous Bacillus thuringiensis strains was investigated in the present work. Our data showed that the bacteria isolated from uranium mine possessed highly accumulation ability to U(VI), and the maximum accumulation capacity was around 400mg U/g biomass (dry weight). X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR) analyzes indicated that the U(VI) was adsorbed on the bacterial surface firstly through coordinating with phosphate, CH2 and amide groups, and then needle-like amorphous uranium compounds were formed. With the extension of time, the extracellular crystalline substances were disappeared, but some particles were appeared in the intracellular region, and these particles were characterized as tetragonal-uramphite. Moreover, the disrupted experiment indicated that the cell-free extracts had better uranium-immobilization ability than cell debris. Our findings provided the understanding of the uranium transformation process from amorphous uranium to crystalline uramphite, which would be useful in the regulation of uranium immobilization process.