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Journal of Thermal Analysis and Calorimetry
Authors: V. Balek, L. Pérez-Maqueda, J. Poyato, Z. Černý, V. Ramírez-Valle, I. Buntseva, and J. Pérez-Rodríguez

Abstract  

The effect of grinding on thermal behavior of pyrophyllite and talc as commonly used ceramic clay minerals was investigated by DTA, TG, emanation thermal analysis (ETA), B.E.T. surface area (s.a.) measurements, X-ray diffraction (XRD) and scanning electron microscopy (SEM). A vibratory mill was used in this study, grinding time was 5 min. It was found that the grinding caused an increase in surface area and a grain size reduction of the samples. From TG and DTA results it followed that grinding caused a decrease of the temperature at which the structure bound OH groups released. The formation of high temperature phases was enhanced with the ground samples. For the ground talc sample the crystallization of non-crystalline phase into orthorhombic enstatite was observed in the range of 800°C. For ground pyrophyllite a certain agglomeration of grains was observed in the range above 950°C. Moreover, for both clays the ETA characterized a closing up of subsurface irregularities caused by grinding as a decrease of the emanation rate in the range 250–400°C. The comparison of thermal analysis results with the results of other methods made it possible to better understand the effect of grinding on the ceramic clays.

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Abstract  

The formation of carnallite type double salts by grinding mixtures of hydrated magnesium halide and alkali halides with the same anions was investigated by X-ray diffraction, infrared spectroscopy and thermal analysis. Carnallite (KMgCl3·6H2O), cesium-carnallite (CsMgCl3·6H2O), bromo-carnallite (KMgBr3·6H2O) and cesium-bromo-carnallite (CsMgBr3·6H2O) were formed by grinding mixtures of MgCl2·6H2O with KCl or CsCl and MgBr2·6H2O with KBr or CsBr, respectively. Hydrated solid solutions of magnesium in potassium or cesium halides were obtained from that portion of potassium and cesium halides which did not take part in the formation of the double salt.

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Abstract  

The effect of grinding on the physical properties and pharmaceutical performance of solid dispersions made of poly(ethylene) glycol 6000 (PEG6000) and temazepam or diazepam was studied using differential scanning calorimetry (DSC), X-ray powder diffraction and dissolution experiments. DSC-analysis of flash-cooled dispersions revealed that amorphous PEG present immediately after grinding crystallised upon aging mainly into the twice folded modification and to a small extent into the extended form. DSC-analysis of dispersions kept in the slab form for 1 month and subsequently ground, revealed that in the abscence of the grinding impulse crystallisation of PEG6000 takes place in the same way as in dispersions ground immediately after preparation and then aged for 1 month. Grinding solid dispersions immediately after preparation resulted in superior dissolution properties compared with solid dispersions kept in the monolith-slab form and subsequently ground. This difference in dissolution properties was found to be attributed to the drug and not to the polymer, more precisely, it was suggested that the drug particle size in ground dispersions was smaller than in dispersions kept in the slab form and subsequently ground. These findings suggest that grinding of solid dispersions immediately after preparation is the preparation method of choice instead of liquid filling of hard gelatin capsules resulting in monoliths.

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Abstract  

We have measured the contamination of samples of granite, quartz porphyry, greenstone and dolerite after grinding them in steel and cemented carbide grinding mills. The steel mill contaminated the granite with Fe. The cemented carbide mill contaminated all samples with W and Co, and the granite and quartz porphyry with Ta. Contamination during grinding is proportional to the free quartz content of the rock and to the grinding time.

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Ground roots of licorice with 3 particle sizes (fine particles <0.35 mm, medium: 0.35-8.0 mm, and coarse particles ?8.0 mm diameter) were exposed to 5, 10, 15 and 20 kGy of gamma radiation from a 60Co source. Microbial population of ground roots and the characteristics of their extracts (concentrations of glycyrrhizinic acid, total and inorganic dissolved solids), mineral ions (Ca++ and K+), pH and EC values were evaluated after irradiation. The results showed thatmicrobial count of fine particles of ground licorice roots were 106 g-1, that of coarse ones 105 g-1. The extract produced from coarse particles of ground roots had lower total and inorganic dissolved solids, mineral ions (Ca++ and K+), pH and EC values compared with those produced from fine particular ones. All sizes of licorice roots treated with gamma irradiation had significantly (P<0.05) lower microorganism counts than untreated (control) ones. The dose needed to reduce the microbial load to less than 10 bacteria per gram was 15 kGy for the fine particle and 10 kGy for the coarse ground root. Gamma irradiation decreased glycyrrhizinic acid concentrations in the extracts produced from coarse particle licorice roots.

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Grinding of drugs with pharmaceutical excipients at cryogenic temperatures

Part II. Cryogenic grinding of indomethacin-polyvinylpyrrolidone mixtures

Journal of Thermal Analysis and Calorimetry
Authors: T. Shakhtshneider, F. Danède, F. Capet, J. Willart, M. Descamps, L. Paccou, E. Surov, E. Boldyreva, and V. Boldyrev

Abstract  

The effect of cryogenic grinding on the indomethacin (IMC) and its mixtures with polyvinylpyrrolidone (PVP) was studied by powder X-ray diffraction and differential scanning calorimetry. Cryoground mixtures were shown to form glass solutions. PVP inhibits the crystallization of IMC from the amorphous state: the crystallization temperature of IMC in the mixtures with PVP increases, and the amorphous state is preserved longer on storage. The mixtures were characterized by Raman spectroscopy. Dissolution of the IMC in the cryoground mixtures is higher as compared to the pure form, also after a prolonged storage.

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Grinding of drugs with pharmaceutical excipients at cryogenic temperatures

Part I. Cryogenic grinding of piroxicam-polyvinylpyrrolidone mixtures

Journal of Thermal Analysis and Calorimetry
Authors: T. Shakhtshneider, F. Danède, F. Capet, J. Willart, M. Descamps, S. Myz, E. Boldyreva, and V. Boldyrev

Abstract  

The effect of cryogenic grinding on the piroxicam and its mixtures with polyvinylpyrrolidone (PVP) was studied by powder X-ray diffraction and differential scanning calorimetry (DSC). The crystallization of the amorphous piroxicam obtained during cryogrinding showed two events in a DSC curve (noticeable for pure piroxicam, and much more pronounced for the PVP-piroxicam mixtures). For the same measurement conditions, the intensity ratio of the peaks corresponding to the two events differed for the PVP-piroxicam mixtures of different drug-excipient ratios. The temperatures, at which these events were observed, increased with the increase in the PVP-concentration in the mixture. For the mixtures with a high relative content of PVP (≥60%), crystallization was not observed at all. Only one glass transition was revealed for the mixture containing 80% PVP suggesting that a molecular alloy was formed.

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Journal of Thermal Analysis and Calorimetry
Authors: M. Jiménez de Haro, L. Pérez Maqueda, E. Stepkowska, J. Ma Martínez, and J. Pérez-Rodríguez

Abstract  

Grinding and contact with water or salt solution increased the specific surface (ssa) but lowered the first dehydration effect (escaping up to 150C) and increased the second dehydration effect (150 to 500C). The dehydroxylation was moved to lower temperatures and was only ΔM(500-1100C)=3.70.3 % as compared to 5.5% in the parent vermiculite (V). Except ΔM(20-150C), the mass losses measured at the remaining T ranges, were consistent in the ground samples, thus the grinding for 2 min caused the homogenization of the crystal structure of vermiculite [ΔM(150-500C)=7.60.7%]. DTA curves after grinding and cation exchange indicate an important exothermal peak at 795-870C, its temperature depending on exchangeable cation. It indicates the formation of high temperature phases (enstatite, forsterite, spinel). The lowest temperature of the peak (795C) was observed in V-gr-Li, here lithium silicate was formed. The highest peak temperature (870C) was found in V-gr-K, where almost only forsterite developed. These exothermal peaks were very weak in unground V with various exchangeable cations.

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