Effect of Environment on Crystallinity and Chemical Stability in Solid-State of Ground Cephalotin Sodium During Storage

Effects of environmental conditions on the crystallinity and the decomposition point (Dp) of ground cephalotin sodium during storage were investigated by X-ray diffraction and differential thermal analysis (DTA). The X-ray diffraction peaks of ground products increased after storage at 0% and 75% relative humidity (R.H.), at 35° C. The crystallinity of ground product increased at 75% R.H. and 0% R.H., 35°C, but that of ground product at 0% R.H., -30°C was not changed. The Dp measured by DTA of the ground product increased from 189.5°C to 197°C after 4 days at 75% R.H., but the Dp of the ground product at 0% R.H., -30°C for 4 days was 190.1°C. Relation between the Dp and the crystal Unity of ground cefalotin sodium was a straight suggesting that the thermal stability of cefaiotin sodium in the solid-state depends on the degree of crystallinity.     

The effect of repeated microwave heating,fill level and temperature on the impact resistance of a polypropylene syrup bottle

The effect of repeated microwave heating, fill level/and storage temperature on the impact resistance of microwavable polypropylene bottles containing syrup was studied. Bottles filled with syrup at 100%, 75%, 50%, and 25% levels were subjected to drop tests after storage at 8°C, 20°C/and 40°C and after several reheatings in a conventional microwave oven following the label directions. The degree of crystallinity of the polypropylene was also evaluated using modulated DSC. A decrease in impact resistance and an increase in the degree of crystallinity of the package material was observed after the bottles were repeatedly heated in the microwave oven. Impact orientation, product fill level and storage temperature also significantly affected the impact resistance of the bottles. The bottle impact resistance may be insufficient for the intended use. Copyright © 2000 John Wiley & Sons, Ltd.     

CO impurities effect on LaNi4.7Al0.3 hydrogen storage alloy hydrogenation/dehydrogenation properties

LaNi_4.7Al_0.3 alloy was prepared by vacuum induction melting in high purity helium atmosphere, and the ingot was pulverized into 200–400 mesh powder after annealing. X-ray diffraction (XRD) and scanning electron microscopies (SEM) were utilized to study the alloy morphology and phase structure. X-ray photoelectron spectroscopy (XPS) was used for surface analysis. The poisoned alloy was tested at 30 °C in the mixture gas by thermogravimetric and differential thermal analyses (TG + DTA). The hydrogen storage properties were studied by the pressure-composition-temperature test. The activated sample was completely deactivated after only 3 hydriding/dehydriding cycles in hydrogen containing 300 ppm CO at 30 °C, but hydrogen storage capacity did not degrade when tested at 80 °C. Additionally, two different steps appeared in the absorption processes. Combined with XRD, XPS and TG + DTA results, an explanation for this phenomenon is given.     

Dehydration and Hydration Ktnetics,Phase Change,Solubility and Dissolution Behavior of Fenoprofen Calcium

Abstract

The role of water of hydration on the crystal structure, the solubility and the rate of dissolution of fenoprofen calcium dihydrate was examined. The rate of dehydration of fenoprofen calcium dihydrate at 0% relative humidity (R.H.) increased from 0.0400 to 0.7488 fraction dehydratedhour over a temperature range of 50°C to 80 °C and appeared to occur by a combination of diffusion and nucleation processes. The enthalpy of dehydration was 21.897 kcal/mole. Hydration of dehydrated fenoprofen calcium occurred rapidly at 100% R.H. X-ray powder diffraction analysis showed that the upon dehydration fenoprofen calcium dihydrate underwent a change in its crystal structure to form anhydrous fenoprofen calcium. The rate of dissolution of fenoprofen calcium dihydrate tablets at 37°C was not significantly different than that of tablets containing anhydrous fenoprofen. The enthalpies of solution (δH_sol) of fenoprofen calcium dihydrate and anhydrous fenoprofen calcium were 2.0504 and 3.5583 kcaYmole respectively. The transition temperature at which the dihydrate and anhydrous fenoprofen had equal solubilities was approximately 59.91 °C.     

Thermal effects induced by grinding in dolomite

Differential Scanning Calorimetry (DSC) curves of ground samples of dolomite show an exothermic peak at $\text{ca}$. 300°C. Analysis of the released energy, ΔH, shows that the maximum is reached at 35 h of milling ($\text{ca}$. 5 J/g) with a subsequent declination as grinding time progresses. No significant loss of specific surface is observed when the ground samples are heated at temperatures above the peak, and therefore the exothermic peak cannot be ascribed to a surface reordering. On the other hand, a recovery of crystallinity, as shown by the intensity of the X-ray diffraction lines and changes in crystallite size and microstrains calculated from the variance of the (104) line profiles, takes place between 200 and 300°C, the interval of temperature at which the exothermic peak appears. Thus, the energy released during heating is due to a restoration of ground dolomite crystallinity.     

A convenient thermal decomposition-co-reduction synthesis of nanocrystalline tungsten disilicide

Nanocrystalline WSi₂ was synthesized by a thermal decomposition-co-reduction route via the reaction of anhydrous tungsten hexachloride and sodium fluorosilicate with metallic potassium in an autoclave at 650°C. X-ray powder diffraction pattern indicated that it was tetragonal WSi₂. Transmission electron microscope image showed that it consisted of particles with an average diameter of about 50 nm. TGA and DTA indicated that it had good thermal stability below 600°C in air.     

Microcrystalline silicon films fabricated by bias-assisted hot-wire chemical vapor deposition

Microcrystalline silicon films (μc-Si:H) were deposited on stainless steel substrates by bias-assisted hot-wire chemical vapor deposition. The effect of substrate bias and substrate temperature on the crystallinity of μc-Si:H films was studied by Raman spectroscopy, X-ray diffraction and scanning electron microscopy. The results show that both the Raman peak position and the crystalline fraction of the μc-Si:H films deposited at 200 °C were obviously improved by introducing ?800 V substrate bias. The films deposited at 200 °C with ?800 V substrate bias show strongly sharpened Si (111) peak together with Si (220) and Si (311) peaks, which was different from a weak Si (111) peak for those deposited without substrate bias. By increasing the substrate temperature from 200 to 300 °C, while keeping the substrate bias at ?800 V, the crystallinity of the silicon films was further improved, and μc-Si:H films with crystalline fraction of 74 % was obtained.     

Effect of crystallinity on the mechanical properties of starch/synthetic polymer blends

Crystallization behaviour of starch and maleated blends was studied at 50°C over a period of 20 weeks using wide angle X-ray diffraction (WAXS). The variation of mechanical properties (tensile and flexural) and stress relaxation behaviour of the blends stored at 50°C and −10°C were studied over the same period. The starch content in the blends was 70% by weight. The synthetic polyolefins used in the blends were two grades of ethylene-co-vinyl acetates (EVA) containing 28% and 18% VA, two grades linear low-density polyethylene (melt index of 40 and 20) and high density polyethylene. An increase in the tensile properties of all the blends was observed in the first 5 weeks for samples kept at both temperature conditions. Blend samples kept at 50°C had higher tensile strengths than the ones at −10°C. Flexural strength remained constant over the duration of time. Freshly moulded specimens relaxed faster than the samples aged at either temperature. X-ray diffraction patterns showed that the starch was completely melted and had lost its crystallinity. Also, starch blends with EVA did not show any crystalline structure. The crystallinity in the starch blends with polyethylene was mainly due to the crystallinity of the synthetic polymer. The X-ray patterns of pure synthetic polymers were not found to be different from their functionalized counterparts. Crystal intensity was found to decrease for all the polyethylene blends. The effect of crystallinity on the mechanical properties is discussed. This revised version was published online in November 2006 with corrections to the Cover Date.     

Polycrystalline silicon films fabricated by rapid thermal annealing

Poly-crystalline silicon (poly-Si) films were fabricated by rapid thermal annealing (RTA) of amorphous silicon films which were deposited on quartz by hot wire chemical vapor deposition. An insertion of Cr layer can significantly suppress the peeling of Si films during the RTA process. The effect of RTA parameters on the structural properties of poly-Si films was investigated by Raman spectroscopy, X-ray diffraction and scanning electron microscopy. The results show that the crystallinity of the poly-Si films is increased with the increase of RTA temperature and duration. A sharp peak at about 520?cm^?1 is observed in the Raman spectra of poly-Si films annealed at 900 and 1,100?°C for 15?s indicating the excellent crystallinity of the poly-Si films fabricated by RTA. Poly-Si films with high crystalline fraction of 97.3?% were obtained by RTA at 1,100?°C for 20?s.     

Synthesis and characterization of boron suboxide powder produced at ambient pressure condition

Boron suboxide (B₆O)?based materials have shown good properties which make them good candidates for cutting tool and other applications where abrasive wear resistance is important. The objective of this study was to optimize the production of B₆O at ambient pressure by varying reaction temperature and time. B₆O powders were produced from the reaction between boric acid and amorphous boron powders at the reaction temperatures between 300°C and 1400°C for 6 h. The powders produced were characterized in terms of particle size, phase analysis and composition, product yield, as well as morphology. Increase in temperature increased both the yield as well as the particle size of the produced powders. X-ray diffraction (XRD) pattern obtained also showed improved crystallinity of the produced powder as the temperature increases. Scanning electron microscopy (SEM) images of the synthesized powder at higher temperature clearly showed improved crystallinity (star-like crystals) as the reaction temperature was increased. The B₆O powders synthesized at 1300°C for 6 h had the optimum yield of over 95%.     

The effect of heat treatment on textural evolution of ferrihydrite

Thermal treatment in air of synthetic ferrihydrite has been carried out at up to 400°C. The product was characterised by means of X-ray powder diffraction, transmission electron microscopy, thermal analysis and nitrogen adsorption isotherms. Three stages may be distinguished during the course of this reaction:

• 1.(i) original sample (r.t.); mesoporous ferrihydrite with cylindrical shape mesopores and high surface area;
• 2.(ii) 200°C mesoporous protohematite or pseudohematite with slit-shape mesopres;
• 3.(iii) 200°C mesoporous hematite with slit-shaped mesopores and significant decrease in suface area as a consequence of internal sintering within the microcrystals increasing its crystallinity as the temperature increases.

     

Effect of annealing on aqueous stability and elastic modulus of electrospun poly(vinyl alcohol) fibers

Electrospun poly(vinyl alcohol) (PVA) fibers rapidly dissolve in water. Their aqueous stability can be improved by annealing using a combination of controlled temperature and treatment time. The increase in aqueous stability of the PVA fibers is associated with an increase in PVA crystallinity and is defined by X-ray diffraction and the ratio of the Fourier transform infrared spectroscopy band intensities at 1141 and 1425 cm⁻¹. A ratio of intensity of these two infrared bands ≥2.5 or ~75% and above in the degree of crystallinity as determined by X-ray diffraction indicates fiber stability in water. Annealing treatment also results in an increase in the stiffness of the fibers. At a treatment temperature of 135 °C for 4 h, the elastic modulus of the fiber increased by 80%. This information is useful when these fibers are being considered for applications in an aqueous environment such as membrane filter or tissue scaffold.     

Processing of cardanol resin with CSP using compression molding technique

This paper exhibits the synthesis of a cardanol-based polymeric resin (CR) from cashew nut shell liquid as a composite matrix along with coconut shell (CS) as reinforcement utilizing poly-condensation technique. In the proposed method, the provincially gathered CSs are dried in an oven in order to expel dampness content. With an average diameter ranging from 25 to 75 µm, the dried CSs are then grated into small particles and in the compression molding method these particles are made into two sets for untreated and treated (5% NaOH) biocomposites with varying concentration of 0%, 10%, 20%, 30%, and 40%. The thermal properties are assessed by thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) whereas the chemical formulation is reckoned by the assistance of Fourier transforms infrared spectroscopy. The microstructures of the composites are portrayed by scanning electron microscopy to scrutinize the morphological and surface characteristics of CR and CS. The TGA and DTA results revealed that the treated CS particle at 25 and 75 µm thermal stability (484° and 459°) with untreated CS particle (466°C and 449°C) at 30% particle loading condition. The 25-µm CS particles are thermally more stable than 75 µm particles. Veritably it is unveiled that, a polymeric matrix composite combined with untreated and treated CS particles might be a good alternative remembering the ultimate goal to nab an eco-friendly product.     

Preparation of hydroxyapatites via the MSO4 sulphates (M = Ca,Sr, Pb and Eu)

Hydroxyapatites of Ca, Sr and Pb have been prepared by a reaction of the sulphates of these metals with sodium phosphate arsenate or vanadate respectively in a strongly basic solution. X-ray diffraction and IR spectroscopy proved the formation of hydroxyapatites. DTA and TG data indicate the presence of one water molecule in Ca₅(PO₄)₃OH lost at 110°C.     

Photonic response and temperature evolution of SiO2/TiO2 multilayers

The microstructural and optical reflectivity response of photonic SiO₂/TiO₂ nanomultilayers have been investigated as a function of temperature and up to the material system’s melting point. The nanomultilayers exhibit high, broadband reflectivities up to 1350 °C with values that exceed 75% for a 1 μm broad wavelength range (600–1600 nm). The optimized nanometer sized, dielectric multilayers undergo phase transformations from anatase TiO₂ and amorphous SiO₂ to the thermodynamically stable phases, rutile and cristobalite, respectively, that alter their structural morphology from the initial multilayers to that of a scatterer. Nonetheless, they retain their photonic characteristics, when characterized on top of selected substrate foils. The thermal behavior of the nanometer sized multilayers has been investigated by differential thermal analysis (DTA) and compared to that of commercially available, mm-sized, annealed powders. The same melting reactions were observed, but the temperatures were lower for the nm-sized samples. The samples were characterized using X-ray powder diffraction before DTA and after annealing at temperatures of 1350 and 1700 °C. The microstructural evolution and phase compositions were investigated by scanning electron microscopy and energy-dispersive X-ray spectroscopy measurements. The limited mutual solubility of one material to another, in combination with the preservation of their optical reflectivity response even after annealing, makes them an interesting material system for high-temperature, photonic coatings, such as photovoltaics, aerospace re-entry and gas turbines, where ultra-high temperatures and intense thermal radiation are present.

     

Preparation of a hyperbranched polycarbosilane precursor to SiC ceramics following an efficient room-temperature cross-linking process

Room-temperature cross-linking of a hyperbranched polycarbosilane (HBPCS) with divinylbenzene (DVB) in the presence of the cyclohexanone peroxide–cobaltous naphthenate (CHP–CN) initiator system was studied. According to the Fourier transform infrared spectroscopy (FT-IR) and ¹H nuclear magnetic resonance (¹H NMR) results, the cross-linking reaction occurred via the vinyl polymerization. The GPC analysis confirmed the molecular weight of the cross-linked HBPCS significantly increased. Thermal behaviors of cross-linked HBPCS and original HBPCS were investigated by thermal gravimetric analysis-differential thermal analysis (TGA–DTA). The TGA results indicated that the ceramic yield of HBPCS remarkably increased by the cross-linking treatment. For the HBPCS/10 wt% DVB system, the maximum of reaction degree of HBPCS was obtained, which might be responsible for the highest ceramic yield of 70.1 wt% at 1000 °C. However, the ceramic yield of the non-crosslinked HBPCS was only 45 wt% at 1000 °C. The evolution of crystal structure of SiC as a function of pyrolysis temperature was traced by means of X-ray diffraction (XRD) and FT-IR. With the pyrolysis temperature increasing, the β-SiC peaks became sharper and the grain size also grew larger. As the DVB content increased, the intensity of β-SiC peaks significantly reduced, indicating smaller β-SiC grain size.     

Dissolution and Absorption of Nipedipine from Nifedipine-Polyvinylpyrrolidone Coprecipitate

Attempt was made to develop the solid dosage form of nifedipina which showed good absorption rate and total bioavailability. Nifedipine is a poorly water-saluble drug, whom bioavailability is low when administered orally in the crystalline form. Solutions of nifedipine were well absorbed from the gastrointestinal tract. The dissolution rate of PVP-nifedipine coprecipitates exhibited rapid dissolution rate. X-ray diffraction data suggested the lack of crystallinity in the coprecipitate. The relation between the dissolution rates and average molecular weights of PVP was studied. Nifedipine in the copretipitate was chemically stable to heat and humidity, but the dissolution rate of nifedipine from the coprecipitate stored at 21° and 75% R.H. markedly decreased. X-ray diffraction data revealed that it might be due to the transformation of amorphous form of nifedipine to crystalline form under higher relative humidity. The gastrointestinal absorption of nifedipine in beagle dogs after oral administration of the coprecipitate was increased than that after oral adniniatration of the physical mixture.     

Effect of Humidity on The Formation and Stability of Acetaminophen-β-Cyclodextrin Inclusion Complexes

Abstract

The effect of humidities (75% RH and 100% RH) on the inclusion complex formation and crystallizing behavior of physical mixture and ground mixture of acetaminophen with α-cyclodextrin, β-cyclodextrin or microcrystalline cellulose at 30 °C were studied by DSC thermal analysis, X-ray diffractometer, IR spectrophotometer. The change of water content in the physical mixture and ground mixture when stored at 30 °C, 75% RH or 100% RH was determined. The results indicate that the inclusion complex formation and crystallizing behavior of these mixtures were dependent on the relative humidity and types of cyclodextrins. The physical mixture of acetaminophen and β-cyclodextrin stored at 30 °C and 100% RH was transformed to crystalline inclusion complex, but stored at 75% RH still exhibited a behavior of physical mixture. The ground mixture of acetaminophen and β-cyclodextrin was converted amorphous inclusion complex to crystalline inclusion complex whether stored at 75% RH or 100% RH. However, physical mixture and ground mixture of acetaminophen and α-cyclodextrin or microcrysatlline cellulose when stored at 75% RH or 100% RH belonged to a crystalline physical mixture.     

Effect of the rigid segment content on the properties of segmented polyurethanes conjugated with atorvastatin as chain extender

Segmented polyurethanes were prepared with polycaprolactone diol as soft segment and various amounts of 4,4´-Methylenebis(cyclohexyl isocyanate) and atorvastatin, a statin used for lowering cholesterol, in order to obtain SPU with different content of rigid segments. Polyurethanes with 35% or 50% of rigid segment content were physicochemically characterized and their biocompatibility assessed with L929 fibroblasts. High concentrations of atorvastatin were incorporated by increasing the content of rigid segments as shown by FTIR, Raman, NMR, XPS and EDX. Thermal and mechanical characterization showed that polyurethanes containing atorvastatin and 35% of rigid segments were low modulus (13?MPa) semicrystalline polymers as they exhibited a glass transition temperature (T_g) at ?38?°C, melting temperature (T_m) at 46?°C and crystallinity close to 35.9% as determined by DSC. In agreement with this, X-ray diffraction showed reflections at 21.3° and 23.6° for PCL without reflections for atorvastatin suggesting its presence in amorphous form with higher potential bioavailability. Low content of rigid segments led to highly degradable polymer in acidic, alkaline and oxidative media with an acceptable fibroblast cytotoxicity up to 7 days possibly due to low atorvastatin content.     

Effect of Storage Conditions on the Hardness,Disintegration and Drug Release from Some Tablet Bases

Abstract

The effect of storage at relatively high temperature and humidity on tablets prepared from different bases was studied for up to eight weeks. Drug release from tablets was followed by measuring the concentration of a marker (amaranth) in the dissolution medium. Lactose and mannitol based tablets showed an increase in hardness and disintegration time, and a decrease in the initial rate of drug release. Sorbitcl based tablets, stored under 50°C/50% relative humidity (R.H.), showed a decrease in hardness and slower disintegration and dissolution. When stored under 40°C/90% R.H., the tablets were completely deformed within three days. Tricalcium phosphate and cellulose-based tablets did not show any storage related changes in hardness, disintegration or drug release.