Thermal Analysis of Sulphamethoxazole - Sugar Physical Mixes

Abstract

Differential scanning calorimetry and hot stage microscopy have been used to study the interactions between sulphamethoxazole and the sugars maltose, glucose, sucrose and mannitol. Only the sulphamethoxazole-mannitol system appeared to be stable and presented a eutectic containing 90.3% sulphamethoxazole. Heats of fusion for sulphamethoxazole, mannitol and their eutectic were 33.4, 73.6 and 39.9 cal g respectively.     

A Sustained Release Drug Delivery System Using Calcium Alginate Beads

Calcium alginate beads impregnated with sulphamethoxazole as model drug were prepared and characterized. Scanning electron microscope was used to examine their surface with and without the drug. The bead average diameter was 1.25mm and the sulphamethoxazole uptake by the beads was about half of the incorporated quantity. The release behaviour was followed using USP dissolution method. The effect on release of factors such as sodium alginate, calcium chloride concentration, pH, hydration and compression were studied. Sodium alginate concentrations had no pronounced effect on the release. The release was found to be a function of calcium chloride concentration. The higher the concentration the lower the release. The smaller the water content the lower the release from the beads. Compression of the beads yields a deformed beads with an increase in their release. Plain calcium alginate beads were not suitable for sulphamethoxazole loading. Sulphamethoxazole diffusion through calcium alginate film was determined. The dissolution patterns were discussed. The system may offer a simple and efficient sustain release preparation.     

Dissolution of Sulphamethoxazole From Polyethlene Gylcols and Polyvinlpyrrolidone Solid Dispersions

Solid dispersions of sulphamethoxazole have been prepared by fusion and solvent methods using polyethylens glycols 6000 and 9000, and polyvinylpyrrolidone (mol.wt. 40,000) as water-soluble carriers. Coprecipitates with the latter were superior to other carriers in releasing the drug into solution. Melts with the solvent method. Solubility of the drug increased also with the former produced faster rates of dissolution of sulphamethoxazole than the coprecipitate from the solvent method. Solubility of the drug increased also with corresponding increase in the concetrations of these carriers.     

A Sustained Release Drug Delivery System Using Calcium Alginate Beads

Abstract

Calcium alginate beads impregnated with sulphamethoxazole as model drug were prepared and characterized. Scanning electron microscope was used to examine their surface with and without the drug. The bead average diameter was 1.25mm and the sulphamethoxazole uptake by the beads was about half of the incorporated quantity. The release behaviour was followed using USP dissolution method. The effect on release of factors such as sodium alginate, calcium chloride concentration, pH, hydration and compression were studied. Sodium alginate concentrations had no pronounced effect on the release. The release was found to be a function of calcium chloride concentration. The higher the concentration the lower the release. The smaller the water content the lower the release from the beads. Compression of the beads yields a deformed beads with an increase in their release. Plain calcium alginate beads were not suitable for sulphamethoxazole loading. Sulphamethoxazole diffusion through calcium alginate film was determined. The dissolution patterns were discussed. The system may offer a simple and efficient sustain release preparation.     

Dissolution of Sulphamethoxazole From Polyethlene Gylcols and Polyvinlpyrrolidone Solid Dispersions

Abstract

Solid dispersions of sulphamethoxazole have been prepared by fusion and solvent methods using polyethylens glycols 6000 and 9000, and polyvinylpyrrolidone (mol.wt. 40,000) as water-soluble carriers. Coprecipitates with the latter were superior to other carriers in releasing the drug into solution. Melts with the solvent method. Solubility of the drug increased also with the former produced faster rates of dissolution of sulphamethoxazole than the coprecipitate from the solvent method. Solubility of the drug increased also with corresponding increase in the concetrations of these carriers.     

In Vitro and Invivo Evaluation of Some Fast Release Dosage Forms of Hydrochlorothiazide

The utilization of ternary sugar solid dispersion and solvent deposition systems for increasing the dissolution rate of hydrochlorothiazide (hot) were investigated. The dispersion systems were prepared by the fusion method using various combinations of mannitol and sorbitol, and urea and polyethylene glycol 4000 (peg 4000) were used for comparison. An 1:2 mixture of sorbitol-mannitol was found to be an excellent carrier. The dissolution rate of this sample was closely comparable to that of hot-peg 4000 solid dispersions. Drug-urea eutectic mixtures were inferior to both the sugar and polymer dispersions. Solvent deposition systems of hot with microfine cellulose and potato starch gave higher dissolution rates at the initial sampling times. It is proposed that solid dispersion systems of this drug may prove to be valuable. Tablets fabricated from fast-release hot granules showed better in vivo results than a marketed tablet. A linear relationship was observed between in vitro-in vivo data of some of the products.     

In Vitro and Invivo Evaluation of Some Fast Release Dosage Forms of Hydrochlorothiazide

Abstract

The utilization of ternary sugar solid dispersion and solvent deposition systems for increasing the dissolution rate of hydrochlorothiazide (hot) were investigated. The dispersion systems were prepared by the fusion method using various combinations of mannitol and sorbitol, and urea and polyethylene glycol 4000 (peg 4000) were used for comparison. An 1:2 mixture of sorbitol-mannitol was found to be an excellent carrier. The dissolution rate of this sample was closely comparable to that of hot-peg 4000 solid dispersions. Drug-urea eutectic mixtures were inferior to both the sugar and polymer dispersions. Solvent deposition systems of hot with microfine cellulose and potato starch gave higher dissolution rates at the initial sampling times. It is proposed that solid dispersion systems of this drug may prove to be valuable. Tablets fabricated from fast-release hot granules showed better in vivo results than a marketed tablet. A linear relationship was observed between in vitro-in vivo data of some of the products.     

Microstructural Evolution of Rapidly Solidified Co-Mo and Ni-Mo Eutectic Alloys

Droplets of Co-37.6 wt pct Mo and Ni-47.7 wt pct Mo eutectic alloys were rapidly solidified during containerless processing in a 3 m drop tube. A kind of anomalous eutectic appears in these two eutectic alloys when undercooling is beyond 56 and 61 K, respectively. The two eutectic phases in anomalous eutectic were observed to grow in dendrite manner. The formation of anomalous eutectic is ascribed to the cooperative dendrite growth of the two independently nucleated eutectic phases. Current dendrite and eutectic growth theories are applied to describe the observed processes.     

Microstructure and fracture toughness of the Bridgman directionally solidified Fe-Al-Ta eutectic at different solidification rates

Fe-Al-Ta eutectic composites were obtained by a modified Bridgman directional solidification technique at different solidification rates.Solidification microstructure transforms from regular eutectic to eutectic colony with the increase of the solidification rate.The solid/liquid interface of Fe-Al-Ta eutectic evolves from planar interface to cellular interface with the increase of the solidification rate.In addition,threepoint bending method was adopted to study the room-temperature fracture toughness of the as-cast Fe-Al-Ta eutectic alloy and the Fe-Al-Ta eutectic composites.Moreover,the fracture morphologies,the crack propagation path and the strengthening mechanism of Fe-Al-Ta eutectic were discussed.     

高温共晶点灌注方法研究

在高温共晶点研制过程中,目前常用的灌注方法包括直接共晶法和预共晶法两种,但直接共晶法存在效率低下的不足,预共晶法存在粘附问题。本文对高温共晶点灌注方法进行研究,设计了两种填充配件,一种为采用长石墨衬套的直接共晶坩埚;另一种为具有特殊结构的预共晶坩埚。经试验验证,前者可明显提高直接共晶法的灌注效率,后者有效避免了预共晶法的共晶体粘结问题,二者均达到了设计目的,为高温共晶点研制技术的完善发展起到了促进作用。     

Preferred growth orientation and microsegregation behaviors of eutectic in a nickel-based single-crystal superalloy

Abstract

A nickel-based single-crystal superalloy was employed to investigate the preferred growth orientation behavior of the (γ + γ′) eutectic and the effect of these orientations on the segregation behavior. A novel solidification model for the eutectic island was proposed. At the beginning of the eutectic island’s crystallization, the core directly formed from the liquid by the eutectic reaction, and then preferably grew along [100] direction. The crystallization of the eutectic along [110] always lagged behind that in [100] direction. The eutectic growth in [100] direction terminated on impinging the edge of the dendrites or another eutectic island. The end of the eutectic island’s solidification terminates due to the encroachment of the eutectic liquid/solid interface at the dendrites or another eutectic island in [110] direction. The distribution of the alloying elements depended on the crystalline axis. The degree of the alloying elements’ segregation was lower along [100] than [110] direction with increasing distance from the eutectic island’s center.     

Preferred growth orientation and microsegregation behaviors of eutectic in a nickel-based single-crystal superalloy

A nickel-based single-crystal superalloy was employed to investigate the preferred growth orientation behavior of the (γ + γ′) eutectic and the effect of these orientations on the segregation behavior. A novel solidification model for the eutectic island was proposed. At the beginning of the eutectic island’s crystallization, the core directly formed from the liquid by the eutectic reaction, and then preferably grew along [100] direction. The crystallization of the eutectic along [110] always lagged behind that in [100] direction. The eutectic growth in [100] direction terminated on impinging the edge of the dendrites or another eutectic island. The end of the eutectic island’s solidification terminates due to the encroachment of the eutectic liquid/solid interface at the dendrites or another eutectic island in [110] direction. The distribution of the alloying elements depended on the crystalline axis. The degree of the alloying elements’ segregation was lower along [100] than [110] direction with increasing distance from the eutectic island’s center.     

Formation and magnetic properties of Fe-B-Si metallic glasses

The equilibrium solidification behaviour of Fe-rich Fe-B-Si alloys has been characterized in terms of primary and secondary crystallization, and correlated to metallic glass formation and properties. A eutectic trough extends from the binary eutectic on the Fe-B edge of the ternary composition diagram toward the binary eutectic on the Fe-Si edge. Metallic glass forming compositions closely follow the path of the eutectic trough, extending from the Fe-B edge to compositions containing approximately 20 at% Si. The relative ease of glass formation and the thermal stability of the glassy state are maximized at compositions along the eutectic trough. The magnetic coercive forces of both as-cast and annealed metallic glasses are minimized along the eutectic trough.     

Effect of low voltage pulsed magnetic field on microstructure and wear behaviour of eutectic Al–Si alloys

Abstract

Effect of discharging frequency of low voltage pulsed magnetic field (LVPMF) on the morphology and size of eutectic Si in eutectic Al–Si (Al–12Si) alloys has been investigated, and some characteristic parameters the characterised the microstructure of the eutectic Si phase were obtained. Dry sliding wear behaviour of eutectic Al–Si alloys without and with LVPMF treatment were also tested using a pin-on-disc wear testing machine, and scanning electron microscopy and energy dispersive spectroscopy X-ray of worn surfaces were carried out to determine the governing mechanisms in the eutectic Al–Si alloys without and with LVPMF treatment. The results show that the eutectic Si became smaller with the increase in discharging frequency. Fine short rod-like or rounded particle-like eutectic silicon with 2·3 μm in length, 0·6 μm in the width, and 3·8 in aspect ratio was formed in eutectic Al–Si alloy treated by 6 Hz LVPMF. The wear resistance of eutectic Al–Si alloys increased with the increase in discharging frequency. The adhesive wear was observed in eutectic Al–Si alloy without LVPMF treatment under normal load of 80 N. However, mainly abrasive was observed in eutectic Al–Si alloy with 6 Hz LVPMF treatment.     

铝硅合金中共晶硅的变质机理:杂质诱发共生成对孪晶

为探讨铝硅合金中共晶硅的变质机理,根据杂质诱发共生成对孪晶的理论,对共晶硅的变质机理进行了分析.结果表明:杂质原子诱发的共生成对孪晶之一使得共晶硅在平行于{111}晶面的方向以TPRE的机制生长,而共生成对孪晶中的另一处与原{111}晶面夹角为109.5°的孪晶,则使得共晶硅垂直于{111}晶面方向的生长也按照TPRE机制进行;共生成对孪晶大大加快了共晶硅垂直于{111}晶面方向的生长,并大大降低{111}晶面厚度方向的生长速度与平行于{111}晶面的生长速度的差异,从根本上改变了共晶硅生长时的各向异性特点,使得共晶硅以各向同性方式生长,最终长成纤维状.     

Phase growth patterns for Al_2O_3/GdAlO_3 eutectics over wide ranges of compositions and solidification rates

Phase selection and growth characteristics of directionally solidified Al₂O₃/GdAlO_3(GAP)faceted eutectic ce ramics are investigated over wide ranges of compositions and solidification rates to explore the eutectic coupled zone.Through the obse rvation of the quenched solid-liquid interface,the competitive growth of primary faceted Al₂O₃phase,prima ry non-faceted GAP phase and Al₂O₃/GAP eutectic with diffe rent morphologies is detected.Microstructure transitions from wholly eutectic to primary Al₂O₃(GAP)dendrite plus eutectic and then to wholly eutectic are found in Al₂O₃-2 O mol%Gd₂O₃hypoeutectic(Al₂O₃-26 mol%Gd₂O₃hypereutectic)ceramics with the increase of solidification rate.The dendrite growth of faceted Al₂O₃and non-faceted GAP phases are well predicted by KGT model,which have introduced appro p riate dimensionless supersaturationΩto characterize the anisotropic growth of dendrites.Based on the maximum interface temperature criterion,the competitive growth of primary phase and eutectic is analyzed theoretically and the predicted coupled zone of Al₂O₃/GAP eutectic ceramics is in good agreement with the experimental results.Besides,the influence of microstructure with these different morphologies on the flexural strength of Al₂O₃/GAP eutectic ceramics is studied.     

DNAN/DNTF二元共熔物在热和机械刺激下的安全性研究

为了获取DNAN/DNTF二元共熔物安全性的变化规律,利用机械感度仪和DSC测试得到了DNAN、DNTF及二元共熔物的机械感度和热分解曲线,并采用Materials Studio软件对二元共熔物进行了分子动力学模拟。结果表明,二元共熔物的机械感度和热感度均随DNTF含量的提高而变差。DNTF引发键N—O的最大键长均随DNTF含量的增加而变大,共熔物的结构稳定性变差,与共熔物机械和热刺激下的安全性变化趋势一致。DNTF引发键N—O的最大键长可以作为DNAN/DNTF二元共熔物机械感度和热安全性相对大小的理论判据。     

Microbeam analysis studies of the copper-silver interface

Copper-silver bimetallic samples have been examined by microbeam analytical techniques. Composition studies have concentrated on the interface region between the two metals. In this region two distinct phases characteristic of a eutectic structure were observed by backscatter electron imaging in the SEM. X-ray microanalysis has shown that the eutectic is composed of a copper-rich and a silver-rich phase. The crystal structure and composition of the constituent phases of the eutectic material have been confirmed by electron diffraction studies of a thinned foil of the eutectic composition. The surface structure of ion-beam etched eutectic material has been examined at high resolution. The silver-rich constituent of the eutectic is found to etch preferentially. The surface composition of the eutectic has been explained in terms of this ion-beam-induced surface structure.     

激光双面区熔Al2O3/Y3Al5O12共晶自生复合陶瓷的制备与表征

采用激光区熔凝固技术制备大尺寸Al2O3/Y3Al5O12(YAG)共晶自生复合陶瓷,考察双面区熔条件下大尺寸氧化物共晶陶瓷的熔化及凝固成形规律,采用扫描电镜、能谱和X射线衍射对其凝固组织特征进行了表征和分析.研究结果表明:在优化的凝固工艺下,激光双面区熔增加了熔凝层的厚度,获得了熔凝层厚度8.2 mm,长度65.0 mm,致密度达98.5%±1%的Al2O3/YAG共晶陶瓷;共晶熔凝层厚度随激光扫描速率的减小而增加,随激光功率的增大而增大,并且致密度随着激光功率的增大呈现先增大后减小的趋势;双面区熔后的Al2O3/YAG共晶陶瓷微观组织由均一分布、相互交织的Al2O3和YAG共晶相组成,共晶层片间距较小(1.0~3.5μm),且与凝固速度满足Jackson-Hunt公式;共晶间距随扫描速率的增大逐渐减小;双面区熔界面处共晶组织生长具有连续性,界面结合良好;共晶陶瓷的Vickers硬度为(18.6±1.0)GPa.     

Sustained Release from Precirol® (Glycerol Palmito-Stearate) Matrix. Effect of Mannitol and Hydroxypropyl Methylcellulose on the Release of Theophylline

The release of theophylline embedded in a Precirol® (glycerol palmitostearate) matrix containing varying amounts of mannitol and/or hydroxypropyl methyl cellulose 4000 (HPMC) was studied. The results indicated that HPMC or mannitol when incorporated alone, the drug release followed the diffusion-controlled matrix model where the quantity of drug released was proportional to the square root of time. The release rate was found to increase with increase in the amount of HPMC or mannitol in the matrix. When both mannitol and HPMC were incorporated in the matrix, the mechanism of release changed from the Higuchi model to a first-order release. A linear relationship was found between the fraction of HPMC or mannitol in the matrix and the rate constant. An optimum combination of Precirol®, mannitol and HPMC was found for a 12 hour theophyll ine sustained release preparation