#تذكر_انّ لأخر صفحات شيت الباودر 🤍
-Particle size separation:
شن يصير فيها بالزبط ؟ operation in which particles of suitable size are selected and others are rejected because it is too small or too large
-ل تصنيف ال powders لنطاقات منفصلة particle size،استعادة environmental pollution،منع-circuit grinding،ازالة fine powder
وتحسين المظهر ومنع الفصل
-Mechanical sieves of this type usually use a mechanical cylindrical sieve with a high speed rotor inside the cylinder so that particles are thrown outwards by centrifugal forces
-Standards for powders based on sieving
These standards are provided in BP and BPC. The BP stated that the degree of coarseness or fineness of a powder is differentiated and expressed by reference to the nominal mesh aperture size of the sieves used
-Elutriation:
-Elutriation is a process of fractionation of fine particles according to their size by manipulatingوتكون في سائل متحرك اهم حاجه
-Powder properties
Particle Properties:
Adhesion (الالتصاق) occurs between different surfaces, while cohesion (التماسك) happens between similar particles. These forces are influenced by Van der Waals forces, surface tension, and electrostatic charges. Cohesion helps prevent unwanted powder flow.
Measurement of Adhesion/Cohesion:
Since direct measurement is difficult, cohesion is determined by the stress required to shear a powder bed under zero normal load.
Shear Cell (خلية القص):
Powder is packed into two segments with a lid on top. By applying different loads, the force needed to shear the bed is measured, and shear stress is calculated.
-Factors Affecting Cohesion:
1. Particle size (حجم الجسيمات): Smaller particles have higher cohesion due to surface effects.
2. Particle density (كثافة الجسيمات): Denser particles are less cohesive because they flow more under gravity.
3. Surface nature (طبيعة السطح): Surface free energy influences cohesion and is reduced by gas or water vapor absorption.
Powder Flowability:
It refers to how well a powder moves within equipment. Flowability depends on multiple factors, including physical properties like density, cohesion, and wall friction. In the pharmaceutical industry (الصناعة الدوائية), it affects processes such as powder transfer, storage, blending, and tablet production.
-Definition (زاوية الاستقرار):
It is the angle formed between a conical heap of powder and the horizontal surface. Particles begin to slide when the inclination angle is large enough to overcome friction. If the angle is too high (>50°), powder flow is poor, while angles near 25° indicate good flowability.
Determination (تحديد الزاوية):
The simplest method is allowing powder to flow through a funnel onto a horizontal surface and measuring the heap angle.
Disadvantages (العيوب):
1. Works only for free-flowing powders.
2. Results may vary due to falling powder impact.
Alternative Methods (طرق بديلة):
Filling an open-ended cylinder and removing it vertically to form a heap.
Using a controlled shutter system to prevent cone distortion.
-Bulk and Tapped Density Measurement Summary
Definition (الكثافة الظاهرية والمضغوطة):
Bulk density (الكثافة الظاهرية): Density of powder in its poured state.
Tapped density (الكثافة المضغوطة): Maximum density achieved after mechanical tapping.
Importance (الأهمية):
Comparing bulk and tapped densities helps assess interparticle interactions affecting powder flow (تدفق ).
A more consolidated powder bed has higher resistance to flow.
Measurement (القياس):
A mechanical tapping device (جهاز الطرق الميكانيكي) is used to determine tapped density.
Compressibility (قابلية الانضغاط):
Carr Index = ((Df - D0) / Df) × 100
Lower compressibility (%) means better powder flow.
Particle Shape Effect (تأثير شكل الجسيمات):
• Spherical particles stabilize quickly.
• Non-spherical particles need more tapping due to arches and void-filling (تعبئة الفراغات بين الجسيمات الصغيرة والكبيرة).
هكي نكونوا كملنا آخر صفحات الباودر وكملنا معاها ملخصات التكنو 1 ربي يفتحها عليكم ويوفقكم في امتحانكم وتصفوها كلكم وتروحوا مجبورين الخاطر يارب🤍🤍🤍.
