995 resultados para Hot deformation


Relevância:

20.00% 20.00%

Publicador:

Resumo:

Solid molecular dispersions of bicalutamide (BL) and polyvinylpyrrolidone (PVP) were prepared by hot melt extrusion technology at drug-to-polymer ratios of 1:10, 2:10, and 3:10 (w/w). The solid-state properties of BL, physical mixtures of BL/PVP, and hot melt extrudates were characterized using differential scanning calorimetry (DSC), powder X-ray diffractometry (PXRD), Raman, and Fourier transform infrared (FTIR) spectroscopy. Drug dissolution studies were subsequently conducted on hot melt extruded solid dispersions and physical mixtures. All hot melt extrudates had a single Tg between theTg of amorphous BL and PVP indicating miscibility of BL with PVP and the formation of solid molecular dispersions. PXRD con?rmed the presence of the amorphous form of BL within the extrudates. Conversely, PXRD patterns recorded for physical mixtures showed sharp bands characteristic of crystalline BL, whereas DSC traces had a distinct endotherm at 1968C corresponding to melting of crystalline BL. Further investigations using DSC con?rmed solid-state plasticization of PVP by amorphous BL and hence antiplasticization of amorphous BL by PVP. Experimentally observed Tg values of physical mixtures were shown to be signi?cantly higher than those calculated using the Gordon–Taylor equation suggesting the formation of strong intermolecular interactions between BL and PVP. FTIR and Raman spectroscopy were used to investigate these interactions and strongly suggested the presence of secondary interaction between PVP and BL within the hot melt extrudates. The drug dissolution properties of hot melt extrudates were enhanced signi?cantly in comparison to crystalline BL and physical mixtures. Moreover, the rate and extent of BL release were highly dependent on the amount of PVP present within the extrudate. Storage of the extrudates con?rmed the stability of amorphous BL for up to 12 months at 208C, 40% RH whereas stability was reduced under highly humid conditions (208C, 65% RH). Interestingly, BL recrystallization after storage under these conditions had no effect on the dissolution properties of the extrudates.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Deformation localisation is the main reason for material failure in cold forging of titanium alloys and is thus closely related to the production yield of cold forging. In the study of the influence of process parameters on dynamic compression, considering material constitutive behaviour, physical parameters and process parameters, a numerical dynamic compression model for titanium alloys has been constructed. By adjusting the process parameters, the severity of strain localisation and stress state in the localised zone can be controlled thus enhancing the compression performance of titanium alloys.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

The relationship between microstructure and deformation and damage behaviour during dynamic compression in Ti-3Al-5Mo-5V alloy has been studied using several experimental techniques, including optical microscopy, scanning electron microscopy and microhardness measurements. It was found that the deformation behaviour during dynamic compression was closely related to deformation parameters. After dynamic deformation, the deformation shear band that formed in the titanium alloy had microhardness similar to that of the matrix. However, the microhardness of the white shear band was much higher than the matrix microhardness. The effects of deformation parameters, including deformation rate and deformation degree, on deformation localisation were investigated. Based on the results from the present work, the microstructure and deformation processing parameters can be optimised. In addition, treatment methods after dynamic compression were explored to restore alloy properties. Using post-deformation heat treatment, the microstructure and property inhomogeneity caused by shear bands could be largely removed.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

This article is concerned with understanding the behavior of polyethylene terephthalate (PET) in the injection stretch blow molding (ISBM) process where it is typically biaxially stretched to form bottles for the packaging industry. A comprehensive experimental study was undertaken, analyzing the behavior of three different grades of PET under constant width (CW), simultaneous (EB), and sequential (SQ) equal biaxial deformation. Experiments were carried out at temperature and strain rate ranges of 80–110C and 1 /s to 32 /s, respectively, to different stretch ratios. Results show that the biaxial deformation behavior of PET exhibits a strong dependency on forming temperature, strain rate, stretch ratio,deformation mode, and molecular weight. The tests were also monitored via a high speed thermal image camera which showed an increase in temperature between 5C and 15C observed depending on the stretch conditions.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

We have searched for HDS emission in a small number of hot cores. Using observations of (H2S)-S-34, we have derived upper limits to the [HDS]/[H2S] abundance ratio. The upper limits, which are close to 10(-3) can be interpreted in two ways, depending on whether grain surface reactions contribute to the formation of H2S. If grains do not dominate, then the H2S observed is formed in hot, post-shocked gas and a ratio close to the cosmic [D]/[H] ratio is expected for [HDS]/[H2S]. This scenario is consistent with our upper limits and with the relatively low abundance ratio found for [HDO]/[H2O] in hot cores but does not seem to account for all of the molecular [D]/[H] ratios observed in hot cores. If grains do dominate the formation of HBS, then the observed upper limit to the ratio is consistent with the formation of 'hot core ices' at a temperature of 60-80 K, close to the temperature at which cometary ices are thought to form.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

We compare the results of our JCMT spectral line survey of molecular gas towards ultracompact HII regions with the predictions of models of sulphur chemistry in hot cores. We investigate the range of evolutionary models that are consistent with the observed physical conditions and chemical abundances, and see to what extent it is possible to constrain core ages by comparing abundances with the predictions of chemical models. The observed abundance ratios vary little from source to source, suggesting that all the sources are at a similar evolutionary stage. The models are capable of predicting the observed abundances of H2S, SO, SO2, and CS. The models fail to predict the amount of OCS observed, suggesting that an alternative formation route is required. An initial H2S abundance from grain mantle evaporation of similar to 10(-7) is preferred.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

We have observed the 3-2 transitions of DCN and (HCN)-N-15 in a number of hot molecular cores previously surveyed by us with the interesting result that the DCN/HCN ratio is low, a few times 10(-3), in the hot cores. The abundance ratio of DCN/HCN is derived both 'on-core' and 'off-core' and, in general is larger at the 'off-core' positions. Comparision with chemical models of these sources indicates that DCN liberated from evaporated ices can be destroyed rapidly in the hot gas by reaction with atomic hydrogen, which works to reset the the initial DCN/HCN ratio in the ice to the gas-phase atomic D/H ratio. The low DCN/HCN abundance ratio we measure can be reached in less than 10(4) years, consistent with previous estimates of the core ages, if the activation energy of the reaction is less than 500 K.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

This paper presents the results of a model of the chemistry of deuterium-bearing molecules in hot molecular cores. It is found that because hydrogen- and deuterium-bearing molecules are destroyed by the same reactions at about the same rates, the initial fractionation present in ice mantles persists for over 10(4) yr. This is the case for a wide range of physical conditions, so it is safe to infer the fractionation on grain surfaces from observations of deuterated molecules in hot cores. The implications of the observed abundances of deuterium-bearing species in Orion are then discussed.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Hot molecular cores in star-forming regions are known to have gas-phase chemical compositions determined by the evaporation of material from the icy mantles of interstellar grains, followed by subsequent reactions in the gas phase. Current models suggest that the evaporated material is rich in hydrogenated species, such as water, methane and methanol. In this paper, we report the detection of 14 rotational transitions of ethanol in the submillimetre spectrum of the molecular cloud associated with the ultra-compact H II region G34.3+0.15. We derive a rotation temperature of 125 K and a beam-averaged column density of 2.0x10(15) cm(-2), corresponding to a fractional abundance on the order of 4x10(-9). This large abundance, which is a lower limit due to the likelihood of beam dilution, cannot be made by purely gas-phase processes, and we conclude that the ethanol must be formed efficiently in the grain surface chemistry. Since it has been argued previously that methanol is formed via surface chemistry, it appears that alcohol formation may be a natural by-product of surface reactions.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Hot molecular cores in star-forming regions are known to have gas-phase chemical compositions determined by the material evaporated from the icy mantles of interstellar grains, followed by subsequent reactions in the gas phase. Current models suggest that the evaporated material is rich in hydrogenated species. In this paper, we consider the chemistry induced in a hot core by the release of phosphine, PH3 from interstellar grains. We find that PH3 is rapidly destroyed by a series of reactions with atomic hydrogen and is converted, within 10(4) yr, into atomic P, and PO and PN, with P atoms being the most abundant species. Other P-bearing molecules can be formed in the hot gas, but on time-scales that are long compared to those of the hot cores.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

We have modeled the gas phase chemistry of warm molecular material around protostars that is seeded with evaporating grain mantles. We show that the release of simple molecules into the gas drives ion-molecule and neutral chemistries which can account for many of the complex 0-bearing and N-bearing molecules observed in hot cores. Initial grain mantle components and secondary product molecules are identified, and the observational consequences are discussed.