Mixture Of Polymorphs Research Articles

Convenient Route to Heterometallic Group 4-Zinc Precursors for Binary Oxide Nanomaterials.

In this study, simple and efficient synthetic routes to a family of uncommon group 4-zinc heterometallic alkoxides were developed. Single-source molecular precursors with the structures [Cp2TiZn(μ,η-OR)(THF)Cl2] (1), [Zr3Zn7(μ3-O)(μ3,η2-OR)3(μ-OH)3(μ,η2-OR)6(μ,η-OR)6Cl6] (2), and [Hf3Zn7(μ3-O)(μ3,η2-OR)3(μ-OH)3(μ,η2-OR)6(μ,η-OR)6Cl6] (3) were prepared via reduction of Cp2TiCl2 with metallic zinc or protonolysis of the metal-cyclopentadienyl bond in Cp2M'Cl2 (M' = Zr or Hf) in the presence of 2-methoxyethanol (ROH) and Zn(OR)2. This synthetic route enables the creation of compounds with well-defined molecular structures and therefore provides precursors suitable for obtaining group 4-zinc oxides. Precursors 1-3 were characterized by elemental analysis, nuclear magnetic resonance and infrared spectroscopies, and single-crystal X-ray diffraction. Compound 1 decomposed at 800-900 °C to give a mixture of binary metal oxides (i.e., Zn2Ti3O8, ZnTiO3, or Zn2TiO4) and common polymorphs of TiO2 and ZnO. After calcination at 1000 °C, only TiO2 and the high-temperature-stable phase Zn2TiO4 were observed. Thermolysis of compounds 2 and 3 gave mixtures of ZnO and ZrO2 or HfO2, respectively. The obtained ZnO-ZrO2 and ZnO-HfO2 mixed oxide materials have constant phase compositions across a broad temperature range and therefore are attractive host lattices for Eu3+ for applications as yellow/red double-light-emitting phosphors. It was established that Eu3+ ions were successfully introduced into the ZnO and ZrO2/HfO2 lattices. It was revealed that Eu3+ ions prefer to occupy low-symmetry sites in ZrO2/HfO2 rather than in ZnO.

Templating effect of single-layer graphene supported by an insulating substrate on the molecular orientation of lead phthalocyanine.

The influence of single-layer graphene on top of a SiO2/Si surface on the orientation of nonplanar lead phthalocyanine (PbPc) molecules is studied using two-dimensional grazing incidence X-ray diffraction. The studies indicate the formation of a mixture of polymorphs, i.e., monoclinic and triclinic forms of PbPc with face-on (lying down) and edge-on (standing up) PbPc orientations, respectively. The formation of monoclinic fractions is attributed to the presence of the graphene layer directing the π interactions between the highly delocalized macrocycles. The competing interfacial van der Waals forces and molecule–molecule interactions lead to the formation of a small fraction of triclinic moieties. The nanoscale electrical characterization of the thin PbPc layer on graphene by means of conducting atomic force microscopy shows enhanced vertical conductance with interconnected conducting domains consisting of ordered monoclinic crystallites through which the charge transfer occurs via tunneling. These results show the importance of a templating layer to induce the formation of a required phase of PbPc suitable for specific device applications.

Preparation and in vitro antitumor effects on MDA-MB-231 cells of niclosamide nanocrystals stabilized by poloxamer188 and PBS.

Niclosamide (NLM) has prominent antitumor activities on various kinds of cancer. In this study, we developed a novel niclosamide nanocrystals (NLM-NCs) stabilized by phosphate buffered saline (PBS) and poloxamer188 (P188). The formed NLM-NCs displayed 12,039 times solubility improvement (2.769mg/mL) than that of free NLM and desired storage stability. Transmission electron microscope (TEM) observation illustrated NLM-NCs were needle-like shape. Differential scanning calorimetry (DSC) and X-ray powder diffraction (XRPD) analysis indicated that NLM-NCs were not anhydrate or any monohydrate but probable a polymorphic mixture. In vitro release evaluation manifested more than 95% NLM released in 48h from NLM-NCs. In comparison to free NLM, NLM-NCs showed stronger cytotoxic effect on MDA-MB-231 cells and promoted cellular uptake. Wound healing assays indicated that NLM-NCs could inhibit cell migration and also decrease the expression of CD44 which is a marker of breast cancer stem cells. Overall, NLM-NCs were of raised solubility, feasible storage stability and desired killing effect for MDA-MB-231 cell, which revealed the impacts of NLM crystal form on its nanocrystals and provided a novel idea for the design of NLM antineoplastic formulation.

Dynamic Crystallization Pathways of Polymorphic Pharmaceuticals Revealed in Segmented Flow with Inline Powder X-ray Diffraction.

Understanding the transitions between polymorphs is essential in the development of strategies for manufacturing and maximizing the efficiency of pharmaceuticals. However, this can be extremely challenging: crystallization can be influenced by subtle changes in environment, such as temperature and mixing intensity or even imperfections in the crystallizer walls. Here, we highlight the importance of in situ measurements in understanding crystallization mechanisms, where a segmented flow crystallizer was used to study the crystallization of the pharmaceuticals urea: barbituric acid (UBA) and carbamazepine (CBZ). The reactor provides highly reproducible reaction conditions, while in situ synchrotron powder X-ray diffraction (PXRD) enables us to monitor the evolution of this system. UBA has two polymorphs of almost equivalent free-energy and so is typically obtained as a polymorphic mixture. In situ PXRD analysis uncovered a progression of polymorphs from UBA III to the thermodynamic polymorph UBA I, where different positions along the length of the tubular flow crystallizer correspond to different reaction times. Addition of UBA I seed crystals modified this pathway such that only UBA I was observed throughout, while transformation from UBA III into UBA I still occurred in the presence of UBA III seeds. Information regarding the mixing-dependent kinetics of the CBZ form II to III transformation was also uncovered in a series of seeded and unseeded flow crystallization runs, despite atypical habit expression. These results illustrate the importance of coupling controlled reaction environments with in situ XRD to study the phase relationships in polymorphic materials.

Scandium extraction from multicomponent systems by crystallization of complex sulfates

Red mud generated from alumina production is one of the most promising scandium resources. Leaching for concentrating scandium and other valuable metals is often performed with the use of acid solutions in specially selected conditions. Different precipitants can be employed for selective precipitation of scandium in the form of poorly soluble compounds. A new method for the crystallization of ammonium scandium sulfates from sulfuric solutions was carried out in this study. Depending on the ammonium cation concentration, precipitation is possible in the form of NH4Sc(SO4)2 or (NH4)3Sc(SO4)3. The solubility values for NH4Sc(SO4)2 and (NH4)3Sc(SO4)3 in water established by the isothermal saturation method were 9.02 and 12.89 g/l Sc2O3, respectively. Complete precipitation of the most promising gravimetric form of scandium represented by NH4Sc(SO4)2 was achieved at 5-6 M H2SO4 and 0.5 M NH4 +. The product of crystallization from sulfuric solution used for treating poor scandium concentrate produced from red mud is a mixture of polymorphs of the composition NH4Sc(SO4)2. Co-precipitated impurities of Al, Fe, Ti, Zr etc. are separated after repeated dissolution and precipitation of ammonium scandium sulfate under analogous conditions. The recrystallization product after calcination at 1000°C contains 99% Sc2O3.

A Nitrogen- and Self-Doped Titania Coating Enables the On-Demand Release of Free Radical Species.

For potential applications such as suppressing the onset of peri-implant infections, a doped titania coating was developed to induce free radical release because of its ability for microbial elimination. The coatability of the sol–gel precursor is robust since the suspension’s rheology can be modified to attain uniform and complete surface coverage. The coating is composed of a mixture of anatase and rutile polymorphs doped with nitrogen (N3–), and it contains substoichiometric Ti2+ and Ti3+ species. Nitrogen doping results in a 0.4 eV band gap shift, while the defects induce photocurrent generation under visible light excitation up to 650 nm. Greater currents were observed in the nitrogen-doped titania at wavelengths above 450 nm vis-à-vis its (singularly) self-doped counterparts. The (photo)electrochemical behavior and photoactivity of the coating were evaluated by assessing redox species formation in a background aqueous solution. In the absence of any illumination, the coating behaved as an insulator and inhibited the activities of both oxidative and reductive species. On the other hand, under illumination, the coating enhances oxidation processes and inhibits reduction reactions within a near-field region wherein release of free radicals occurs and is constrained (delimited).

Do the bridging angle affect the luminescent properties of [(CO)3(phen)Re(µ-OH)Re(phen)(CO)3]+?. An experimental and computational study on three polymorphs

The reaction of [ReIBr(CO)3(THF)]2 with phenanthroline in solution leads to the diimine rhenium(I)tricarbonyl [(phen)Re(CO)3Br] and the dimer [(CO)3(phen)Re(µ-OH)(phen)Re(CO)3]+Br− (1+Br−) as a by-product (~5% yield). This latter bimetallic compound crystallizes as a mixture of three polymorphs, with variable amount of solvent: 1+Br−·CHCl3 (triclinic and orthorhombic) and 1+Br−·2(CHCl3) (triclinic). Rietveld analysis showed 38, 54 and 8% of 1+Br−·CHCl3 (triclinic), 1+Br−·CHCl3 (orthorhombic) and 1+Br−·2(CHCl3) (triclinic) respectively. The 1+ cation shows two [ReI(phen)(CO)3]+ units connected by means of a central hydroxyl group. Noteworthy, the bridging Re–O–Re angle varies between 130.9(7)° to 140.7(2)° along the polymorphic series. UV–Vis spectrum for the 1+ shows a broad absorption band around 390 nm in CH2Cl2 which has been attributed to has MLCT character (Re(dπ) → π*(phen)) as confirmed by DFT. Excitation at 405 nm in solution leads to emission at 595 nm (DCM), 605 nm (DMF) and 625 nm (CH3CN). The emission follows a mono-exponential law of decay and has lifetime of 405.8 ns (DCM). The solid-state polymorphic mixture absorbs around 460 nm. Excitation of the solid at 320 nm leads to emission with a maximum at 575 nm, which follow a bi-exponential law of decay with two components, a short one τ1 of 27.0 ns and longer one τ2 of 178.5 ns. These results suggest that the emitting state does not vary as function of the molecular geometry.

The effect of the natural degradation process on the cellulose structure of Moroccan hardwood fiber: a survey on spectroscopy and structural properties

<p>The aim of this work is to study the effect of natural degradation on the cellulose structure conformation changes of 2 ageing Moroccan hardwoods (400 and 500 years) compared to recent one considered as a reference; and to provide information on the polymorphs content variability from two-phases material (crystalline and amorphous) influenced by a long time of ageing and environmental degradation effects. In order to investigate the effects of both natural degradation conditions and a long time of exposure on cellulose structure conformation (examined samples) with estimating their content (crystalline and amorphous cellulose), three combined techniques XRD, ATR-FTIR and FT-Raman spectroscopy were used. XRD results associated with the crystallographic planes and Miller indices provide information on the presence of a mixture of celluloses polymorphs (crystalline cellulose I, II, I<sub>b</sub> and amorphous phase). The decrease in crystallinity-index values from recent to aged ones (38 to 19.5%) confirms well the occurred alteration of crystalline cellulose fibres and their evolution towards a high content of the amorphous form. The prominent regression in the intensities of three FTIR fingerprint cellulose regions evolving towards an overall increase in the intensities of C=O area (1733-1630 cm<sup>-1</sup>) is a sign on the introduced changes on cellulose conformation and cellulose fibres degradation more accentuated in the case of the very aged sample (500 years). Similar results were confirmed by combining FT-Raman spectroscopy as a vibrational technique. No work has been done on this genus of degraded Moroccan hardwood and the relevance of this study is to investigate the compositional content and structural conformation, to determine the variability in the forms of both crystalline and amorphous cellulose phases with estimating the evolution of their polymorphism, and to monitor the degree of crystalline cellulose fibres deterioration.</p>

The effect of the natural degradation process on the cellulose structure of Moroccan hardwood fiber: a survey on spectroscopy and structural properties

The aim of this work is to study the effect of natural degradation on the cellulose structure conformation changes of 2 ageing Moroccan hardwoods (400 and 500 years) compared to recent one considered as a reference; and to provide information on the polymorphs content variability from two-phases material (crystalline and amorphous) influenced by a long time of ageing and environmental degradation effects. In order to investigate the effects of both natural degradation conditions and a long time of exposure on cellulose structure conformation (examined samples) with estimating their content (crystalline and amorphous cellulose), three combined techniques XRD, ATR-FTIR and FT-Raman spectroscopy were used. XRD results associated with the crystallographic planes and Miller indices provide information on the presence of a mixture of celluloses polymorphs (crystalline cellulose I, II, Ib and amorphous phase). The decrease in crystallinity-index values from recent to aged ones (38 to 19.5%) confirms well the occurred alteration of crystalline cellulose fibres and their evolution towards a high content of the amorphous form. The prominent regression in the intensities of three FTIR fingerprint cellulose regions evolving towards an overall increase in the intensities of C=O area (1733-1630 cm-1) is a sign on the introduced changes on cellulose conformation and cellulose fibres degradation more accentuated in the case of the very aged sample (500 years). Similar results were confirmed by combining FT-Raman spectroscopy as a vibrational technique. No work has been done on this genus of degraded Moroccan hardwood and the relevance of this study is to investigate the compositional content and structural conformation, to determine the variability in the forms of both crystalline and amorphous cellulose phases with estimating the evolution of their polymorphism, and to monitor the degree of crystalline cellulose fibres deterioration.

Full Gamut Wall Tunability from Persistent Micelle Templates via Ex Situ Hydrolysis.

The predictive self-assembly of tunable nanostructures is of great utility for broad nanomaterial investigations and applications. The use of equilibrium-based approaches however prevents independent feature size control. Kinetic-controlled methods such as persistent micelle templates (PMTs) overcome this limitation and maintain constant pore size by imposing a large thermodynamic barrier to chain exchange. Thus, the wall thickness is independently adjusted via addition of material precursors to PMTs. Prior PMT demonstrations added water-reactive material precursors directly to aqueous micelle solutions. That approach depletes the thermodynamic barrier to chain exchange and thus limits the amount of material added under PMT-control. Here, an ex situ hydrolysis method is developed for TiO2 that mitigates this depletion of water and nearly decouples materials chemistry from micelle control. This enables the widest reported PMT range (M:T = 1.6-4.0), spanning the gamut from sparse walls to nearly isolated pores with ≈2 Å precision adjustment. This high-resolution nanomaterial series exhibits monotonic trends where PMT confinement within increasing wall-thickness leads to larger crystallites and an increasing extent of lithiation, reaching Li0.66 TiO2 . The increasing extent of lithiation with increasing anatase crystallite dimensions is attributed to the size-dependent strain mismatch of anatase and bronze polymorph mixtures.

Challenging identification of polymorphic mixture: Polymorphs I, II and III in olanzapine raw materials

Olanzapine (OLZ), a drug for the treatment of schizophrenia, presents in more than 60 crystal forms. Polymorphs I, II and III were reported, however, the preparation conditions for pure II and III have not been reported. Polymorph IV was reported but this form is actually polymorph II described at different temperature. The diversity of solid forms of OLZ, the change in the nomenclature found in the literature and the presence of polymorphic mixture in samples, increase the difficulty for a correct solid state characterization. Therefore, the goal was the polymorphic identification of three OLZ raw materials, highlighting the limitation of conventional techniques (typically used in analytical control) and the necessity to use a combination of advanced ones to solve this challenge. The samples were studied by conventional techniques such as powder X-ray diffraction, thermoanalytical techniques, infrared spectroscopy. In apart from that, synchrotron powder X-ray diffraction (SPXRD) and solid state nuclear magnetic resonance (ss-NMR) were used. All samples were in accordance with the pharmacopoeia criteria. However, the conventional techniques were not specific for the complete polymorphic identification. Therefore, a combination of advanced techniques (SPXRD and ss-NMR) was necessary to identify the mixture of polymorphs (I, II and III) in all samples.

Alumina Polymorphism in the Circumstellar Dust Shells of Asymptotic Giant Branch Stars

Abstract Many emission features remain unidentified in the infrared spectra of asymptotic giant branch (AGB) stars. In particular, features at ∼11, 20, 28, and 32 μm have been noted in mid-infrared spectra of oxygen-rich AGB stars. Here, I present models of dust excess emission in 36 spectra of 24 AGB stars from the Short Wavelength Spectrometer on board the Infrared Space Observatory and the Infrared Spectrograph on the Spitzer Space Telescope. The models include opacities of grains composed of mixtures of various polymorphs of alumina obtained by preparing bayerite and boehmite at high temperatures, and these dust components provide satisfactory fits to the 11, 20, 28, and 32 μm features. Though not a direct conclusion from this study, the presence of grains of the various polymorphs of aluminas in circumstellar dust shells around AGB stars suggests that corundum may have a role in giving rise to the 13 μm feature.

Quantitation of polymorphic impurity in entecavir polymorphic mixtures using powder X-ray diffractometry and Raman spectroscopy

Entecavir was used for the treatment of chronic hepatitis B through inhibiting hepatitis B virus. The anhydrous form of entecavir (ENT-A) often appeared as impurity polymorph in the manufacturing process of entecavir monohydrate (ENT-H) such as granulation, drying and compression. Since different crystal forms might affect drug bioavailability and therapeutic effect, it was vital to control the ENT-A content of the drug product. The work aimed to develop useful methods to assess ENT-A weight percentage in ENT-H. Powder X-ray diffractometry (PXRD) and Raman spectrometric methods were applied. Binary mixtures with different ratios of pure ENT-H and pure ENT-A were scanned using PXRD and Raman to obtain spectra. Then peak heights and peak areas versus weight percentage were used to construct calibration curves. The best linear regression analysis data for PXRD and Raman method were found to be R2 = 0.9923 and R2 = 0.9953, in the weight ratio range of 2.1–20.2% w/w% of ENT-A in binary mixtures. Limit of detection (LOD) of ENT-A was 0.38% and limit of quantitation (LOQ) was 1.15% for PXRD method. LOD and LOQ for Raman method were 0.48% and 1.16%. The results showed that PXRD and Raman methods: both were precise and accurate, and could be used for measurement of ENT-A content in the selected weight percentage range. Partial least squares (PLS) algorithm with four data pre-processing methods: including multiplicative scatter correlation (MSC), standard normal variate (SNV), first and second derivatives were applied and evaluated using prediction errors. The best performance of PLS was R2 = 0.9958 with RMSEC (0.44%) and RMSEP (0.65%). Multivariate analysis for Raman spectra showed similar good results with univariate analysis, and would be an advantageous method when there were overlapped peaks in the spectra. In summary, the proposed PXRD and Raman method could be developed for the quality control of ENT-H. And Raman was a more promising method in industrial practice due to its slightly better precision, accuracy and time-saving advantage.

Correlating Voltage Profile to Molecular Transformations in Ramsdellite MnO2 and Its Implication for Polymorph Engineering of Lithium Ion Battery Cathodes

Transition metal oxides are the primary choice for cathode materials in lithium ion batteries. These oxides occur as different polymorphs that have varied structures, stabilities, and affinities for Li+, and consequently, it is desirable to develop heuristics for the choice of the optimal polymorph. MnO2 is the most extensively used cathode material for lithium ion battery, and it exists in more than ten polymorphic forms. Among them, ϒ-MnO2, the most electrochemically active polymorph, is a mixture of pyrolusite and ramsdellite polymorphs. Here we have focused on the less explored ramsdellite MnO2 (R-MnO2). Highly crystalline R-MnO2 has been synthesized, and the experimentally obtained discharge features are compared with the calculations based on density functional theory followed by cluster expansion to obtain molecular insights into the intercalation process. R-MnO2 shows voltage fading beyond x = 0.5 (in LixMnO2). Computational results suggest that change in Li environment from tetrahedral to octahedral beyond x = 0.5 (in LixMnO2) causes the voltage fading. This change in Li environment is also correlated with experimentally obtained Mn 2p, O 1s, and valence band XPS spectra. The shift in the d-band center, plotted for valence band spectra at different lithium concentrations, is adduced for the migration of lithium ion from the tetrahedral site to the less favorable octahedral site beyond x = 0.5. Volume expansion of about 20% at full lithiation is accompanied by Jahn–Teller distortion of MnO6. Further, computations reveal the diffusional energy barrier to be 200 meV in the limit of dilute Li concentration (x = 0.125) and 481 meV in the limit of dilute vacancy concentration (x = 0.875). A structural rationale for the energy barrier is developed. The experimental and computational studies provide insight into the lithiation mechanism in R-MnO2 and are relevant to rationalize the high performance of the intergrowth structure of ϒ-MnO2. We discuss a wider implication of the study by correlating the voltage profile with structural changes in MnO2 polymorphs, which gives general design principles to make better cathodes through polymorphic engineering.

Antisolvent Crystallization of Polymorphs of L‐Histidine

AbstractAntisolvent crystallization is the most common method to study solvent effects on polymorphic crystallization. L‐Histidine (L‐his) served as a model substance. Acetonitrile, acetone, and methanol were selected as antisolvents, with water as solvent. The formation of L‐his polymorphs in antisolvent crystallization as a function of supersaturation, antisolvent volume fraction, and temperature was studied. The solubility of polymorph A of L‐his decreased with increasing volume fraction of antisolvent and increased with higher temperature. The metastable polymorph B of L‐his was obtained at higher antisolvent volume fraction and supersaturation. At lower antisolvent volume fraction and supersaturation, a mixture of polymorphs A and B was detected.

Structural characterization of (Sm,Tb)PO4 solid solutions and pressure-induced phase transitions

Sm1-xTbxPO4 solid solutions were synthesized and extensively characterized by powder X-ray diffraction, vibrational spectroscopy, and X-ray absorption spectroscopy. At ambient conditions solid solutions up to x = 0.75 crystallize in the monazite structure, whereas TbPO4 is isostructural to xenotime. For x = 0.8 a mixture of both polymorphs was obtained. Moreover, a phase with anhydrite structure was observed coexisting with xenotime, which was formed due to mechanical stress. Selected solid solutions were investigated at pressures up to ∼40 GPa using in situ high pressure synchrotron X-ray diffraction and in situ high pressure Raman spectroscopy. SmPO4 and Sm0.5Tb0.5PO4 monazites are (meta)stable up to the highest pressures studied here. TbPO4 xenotime was found to transform into the monazite structure at a pressure of about 10 GPa. The transformation of Sm0.2Tb0.8PO4 xenotime into the monazite polymorph commences already at about 3 GPa. This study describes the reversibility of the pressure-induced (Sm,Tb)PO4 xenotime-monazite transformation.

Catalytic wet air oxidation of bisphenol A aqueous solution in trickle-bed reactor over single TiO2 polymorphs and their mixtures

In this study, two series of TiO2 polymorphs (anatase (A and A1), rutile (R and R1), brookite (B and B1)) and nanocomposite mixtures of TiO2 polymorphs (anatase A/rutile R (AR), anatase A/TiO2-B polymorph (ATB), anatase A1/rutile R1/brookite B1 (ARB)) were synthesized and tested in the process of catalytic wet air oxidation (CWAO). The goal was total removal of the endocrine-disrupting chemical bisphenol A and its intermediates from a model aqueous solution. TiO2 polymorphs A1, B1 and R1 were prepared with a similar synthesis procedure and from the same TiO2 precursor to investigate the influence of catalyst preparation on their performance. To discover which is the main driving property of the catalyst that enables enhanced BPA degradation and mineralization in the CWAO process, different surface, textural and morphological characterization techniques (XRD, SEM, UV–vis-DRS, FT-IR, TG and N2 sorption) were used. CHNS elemental analysis was applied to reveal which of catalysts is suitable for use in a long-term CWAO process.Characterization and catalytic tests of solids examined show that the key factor enabling enhanced activity in the CWAO process is high BET specific surface area of the catalysts. It was found that low specific surface area of a solid can be compensated either by the presence of an appropriate crystallinity, or improved charge separation. Catalysts A, A1 and ATB showed encouraging results of BPA degradation and mineralization in the CWAO process and would also be appropriate for long-term use, since negligibly small amounts of carbonaceous deposits were accumulated on the surface of these solids during tests performed in the period of 40 h.

Polymorphism in the co-crystallization of the anticonvulsant drug carbamazepine and saccharin using supercritical CO2 as an anti-solvent

1:1 Co-crystals of carbamazepine (CBZ) and saccharin (SAC) were obtained for the first time through the supercritical anti-solvent (SAS) technique based on using supercritical CO2 as anti-solvent. The capability of SAS to produce the desired polymorphic form (two polymorphs are known) was assessed. Operational conditions investigated were temperature (40.0 and 60.0 °C), pressure (10.0 and 15.0 MPa), solvent choice and coformer concentration in the organic solution (CBZ: 30 and 15 mg/mL; SAC: stoichiometric ratio). Co-crystals were characterized in terms of crystallinity and coformers interactions. No homocrystals were present. Using methanol, at 40.0 °C polymorph I was obtained with yields up to 65%; whilst at 60.0 °C a mixture of polymorphs was obtained. Mixtures of polymorphs were also obtained in the ethanol and dichloromethane experiments at the studied conditions while the dimethylsulfoxide experiments failed to produce any co-crystal polymorph. For comparison purposes, pure CBZ and SAC were also processed by SAS.

Changes in Polymorph Composition in P25-TiO2 during Pretreatment Analyzed by Differential Diffuse Reflectance Spectral Analysis

Elucidating structural and compositional polymorph changes of multiphase semiconductors in a quick and quantitative manner is important for their manufacturing and applications in catalysis alike. Derivative peak fitting of diffuse reflectance UV–visible spectra (DPR) is presented as an inexpensive, fast, and quantitative method to estimate both the composition of a multiphase semiconductor sample as well as the band gap energies of each component semiconductor in the mixture. Degussa P25 TiO2, a widely used catalyst support and semiconductor photocatalyst, is a mixture of anatase and rutile polymorphs. The as-received P25 samples were subjected to grinding, sieving, and calcination or a combination of these operations. Samples were analyzed via DPR, X-ray diffraction (XRD), and Raman spectroscopy to quantify the percentage of anatase and rutile polymorphs present in each sample. Compositional measurements from DPR were in good quantitative agreement with XRD and Raman analysis. The application of in situ...

Study on the Failure Mechanism of the Polymorphic Mixture for Remanufactured Machinery Parts

The polymorphic mixture failure mode for multiple heterogeneity of remanufactured (RM) machinery parts makes it difficult to assess their lifetime. The Weibull distribution failure model of RM parts (substrate, coating layer, bonding surface and sudden failure) is constructed with failure time statistics of the parts in service, the latter is used to characterize the failure patterns of RM parts. In view of the multiple heterogeneity of RM parts, the Kaplan–Meier type decoupling method is used to analyze four sets of failure statistics, and each state of the Weibull failure function of the above parts is solved. It reveals the in-service failure mechanism of polymorphic mixtures for multiple heterogeneity of RM machinery parts. The validity and feasibility of the model are verified by the case study. Research results provide the theoretical basis for the design and preparation of a RM alloy powder and the improvement of RM technology. Moreover, the method for lifetime prediction and failure time evaluation of RM parts is proposed and validated.