انت هنا الان : شبكة جامعة بابل > موقع الكلية > نظام التعليم الالكتروني > مشاهدة المحاضرة
الكلية كلية الصيدلة
القسم فرع الصيدلانيات
المرحلة 2
أستاذ المادة ظافر قحطان سعيد الامين الماشطة
5/27/2011 2:25:31 PM
bulk density, rb, is defined as the mass of a powder divided by the bulk volume. a standard procedure for obtaining bulk density or its reciprocal, bulk specific volume, has been established. a sample of about 50 cm3 of powder that has previously been passed through a u.s. standard no. 20 sieve is carefully introduced into a 100-ml graduated cylinder. the cylinder is dropingped at 2-sec intervals onto a hard wood surface three times from a height of 1 inch. the bulk density is then obtained by dividing the weight of the sample in grams by the final volume in cm3 of the sample, contained in the cylinder.
the bulk density of a powder depends primarily on particle-size distribution, particle shape, and the tendency of the particles to adhere to one another. the particles may pack in such a way as to leave large gaps between their surfaces, resulting in a light powder or powder of low bulk density. on the other hand, the smaller particles may sift between the larger ones to form a heavy powder or one of high bulk density.
the interspace or void porosity of a powder of porous granules is the relative volume of interspace voids to the bulk volume of the powder, exclusive of the intraparticle pores. the interspace porosity is computed from a knowledge of the bulk density and the granule density and is expressed by the equation
where vb = w/rb is the bulk volume and vg = w/rg is the granule volume, that is, the volume of the particles plus pores.
the total porosity of a porous powder is made up of voids between the particles as well as pores within the particles, the total porosity is defined as
where vb is the bulk volume and vp is the volume of the solid material. this equation is identical with that for nonporous powders [equation (19-26)]. as in the previous cases, vp and vb can be expressed in terms of powder weights and densities:
where w is the mass ("weight") of the powder, r is the true density, and rb is the bulk density. substituting these relationships into equation (19-31) gives for the total porosity
example: the weight of a sodium iodide tablet was 0.3439 g and the bulk volume was measured by use of calipers and found to be 0.0963 cm3. the true density of sodium iodide is 3.667 g/cm3. what is the bulk density and the total porosity of the tablet?
in addition to supplying valuable information about tablet porosity and its evident relationship to tablet hardness and disintegration time, bulk density can be used to check uniformity of bulk chemicals and to determine the proper size of containers, mixing apparatus, and capsules for a given mass of the powder.
in summary, the differences among the three densities (true, granule, and bulk) can be understood better by reference to their reciprocals: specific true volume, specific granule volume, and specific bulk volume.
the specific true volume of a powder is the volume of the solid material itself per unit mass of powder. when the liquid used to measure it does not penetrate completely into the pores, the specific volume is made up of the volume per unit weight of the solid material itself and the small part of the pore volume within the granules that is not penetrated by the liquid. specifi
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 .
|