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الكلية كلية الصيدلة
القسم فرع الصيدلانيات
المرحلة 2
أستاذ المادة ظافر قحطان سعيد الامين الماشطة
5/27/2011 2:27:24 PM
Free-flowing powders are characterized by "dustibility," a term meant to signify the opposite of stickiness. Lycopodium shows the greatest degree of dustibility; if it is arbitrarily assigned a dustibility of 100%, talcum powder has value of 57%, potato starch 27%, and fine charcoal 23%. Finely powdered calomel has a relative dustibility of 0.7%. These values should have some relation to the uniform spreading of dusting powders when applied to the skin, and stickiness, a measure of the cohesiveness of the particles of a compacted powder, should be of some importance in the flow of powders through filling machines and in the operation of automatic capsule machines.
Poorly flowing powders or granulations present many difficulties to the pharmaceutical industry. The production of uniform tablet dosage units has been shown to depend on several granular properties. As the granule size was reduced, the variation in tablet weight fell, The minimum weight variation was attained with granules having a diameter of 400 to 800 mm. As the granule size was reduced further, the granules flowed less freely and the tablet weight variation increased. The particle-size distribution affects the internal flow and segregation of a granulation. To improve flow characteristics, materials termed glidants are frequently added to granular powders. Examples of commonly used glidants are magnesium stearate, starch, and tale.
Compaction: Compressed tablets
It was found that when powders were compacted under a pressure of about 5 kg/cm2, the porosities of the powders composed of rigid particles (e.g., sodium carbonate) were higher than the porosities of powders in closest packing. Hence, these powders were dilatant, that is, they showed an unexpected expansion, rather than contraction, under the influence of stress. In the case of soft and spongy particles (e.g., kaolin), however, the particles deformed on compression, and the porosities were lower than after tapping the powder down to its condition of closest packing. Similar experiments might be conducted to determine the optimum condition for packing powders into capsules on the manufacturing scale.
The behavior of powders under compression is significant in pharmaceutical tableting. Although basic information can be obtained from the literature on powder metallurgy and the compression of metallic powders, it is pointed out that not all the theories developed for the behavior of metals will necessarily hold when applied to nonmetals.
The strength of a compressed tablet depends on a number of factors, the most important of which are compression force and particle size.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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