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 2:07:30 PM
Methods for determining surface area
The surface area of a powder sample can be computed from a knowledge of the particle-size distribution obtained using one of the methods discussed previously. Two methods are commonly available that permit direct calculation of surface area. In the first, the amount of a gas or liquid solute that is adsorbed onto the sample of powder to form a monolayer is a direct function of the surface area of the sample. The second method depends on the fact that the rate at which a gas or liquid permeates a bed of powder is related.
Adsorption method
Particles with a large specific surface are good adsorbents for the adsorption of gases and of solutes from solution. In determining the surface of the adsorbent, the volume in cubic centimeters of gas adsorbed per gram of adsorbent can be plotted against the pressure of the gas at constant temperature to give a type II isotherm.
An instrument used to obtain the data needed to calculate surface area and pore structure of pharmaceutical powders is the Quantasorb QS-16. Absorption and desorption of nitrogen gas on the powder sample is measured with a thermal conductivity detector when a mixture of helium and nitrogen is passed through a cell containing the powder. Nitrogen is the absorbate gas; helium is inert and is not adsorbed on the powder surface. Quantasorb and similar instruments have replaced the older vacuum systems constructed of networks of glass tubing. These required long periods of time to equilibrate and were subject to leakage at valves, and breaks in the glass lines. The sensitivity of the new instrument is such that small powder samples can be analyzed. Quantasorb s versatility allows the use of a number of individual gases or mixtures of gases as adsorbates over a range of temperatures. The instrument can be used to measure the true density of powdered material and to obtain pore-size and pore-volume distributions.
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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