صفحة 1 من 2 1 2 الأخيرةالأخيرة
النتائج 1 إلى 7 من 9

الموضوع: crystallization

  1. #1
    عضو ذهبي الصورة الرمزية احمد الطريفي
    تاريخ التسجيل
    Jul 2011
    المشاركات
    369

    افتراضي crystallization


    Crystallization is the (natural or artificial) process of formation of solid
    crystalsprecipitating from a solution, melt or more rarely deposited directly from a gas. crystallization is also a chemical solid-liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs.

    Frost crystallization on a shrub

    عضو في نادي ماركا الأكاديمي


  2. #2
    عضو ذهبي الصورة الرمزية احمد الطريفي
    تاريخ التسجيل
    Jul 2011
    المشاركات
    369

    افتراضي رد: crystallization

    Process





    Time-lapse of growth of a citric acid crystal. The video covers an area of 2.0 by 1.5 mmmin. and was captured over 7.2


    The crystallization process consists of two major events,
    nucleation and crystal growth. Nucleation is the step where the solute molecules dispersed in the solvent start to gather into clusters, on the nanometer scale (elevating solute concentration in a small region), that becomes stable under the current operating conditions. These stable clusters constitute the nuclei. However when the clusters are not stable, they redissolve. Therefore, the clusters need to reach a critical size in order to become stable nuclei. Such critical size is dictated by the operating conditions (temperature, supersaturation, etc.). It is at the stage of nucleation that the atoms arrange in a defined and periodic manner that defines the crystal structure— note that "crystal structure" is a special term that refers to the relative arrangement of the atoms, not the macroscopic properties of the crystal (size and shape), although those are a result of the internal crystal structure.
    The crystal growth is the subsequent growth of the nuclei that succeed in achieving the critical cluster size. Nucleation and growth continue to occur simultaneously while the supersaturation exists. Supersaturation is the driving force of the crystallization, hence the rate of nucleation and growth is driven by the existing supersaturation in the solution. Depending upon the conditions, either nucleation or growth may be predominant over the other, and as a result, crystals with different sizes and shapes are obtained (control of crystal size and shape constitutes one of the main challenges in industrial manufacturing, such as for pharmaceuticals). Once the supersaturation is exhausted, the solid-liquid system reaches equilibrium and the crystallization is complete, unless the operating conditions are modified from equilibrium so as to supersaturate the solution again.
    Many compounds have the ability to crystallize with different crystal structures, a phenomenon called
    polymorphism. Each polymorph is in fact a different thermodynamic solid state and crystal polymorphs of the same compound exhibit different physical properties, such as dissolution rate, shape (angles between facets and facet growth rates), melting point, etc. For this reason, polymorphism is of major importance in industrial manufacture of crystalline products

    عضو في نادي ماركا الأكاديمي


  3. #3
    عضو ذهبي الصورة الرمزية احمد الطريفي
    تاريخ التسجيل
    Jul 2011
    المشاركات
    369

    افتراضي رد: crystallization

    Crystallization in nature


    Snowflakes are a very well known example, where subtle differences in crystal growth conditions result in different geometries.



    Crystallized
    honey


    There are many examples of natural process that involve crystallization.
    Geological time scale
    process examples include:
    • Natural (mineral) crystal formation (see also gemstone);
    • Stalactite/stalagmite, rings formation.
    Usual time scale process examples include:

    • Snow flakes formation (see also Koch snowflake);
    • Honey crystallization (nearly all types of honey crystallize

    عضو في نادي ماركا الأكاديمي


  4. #4
    عضو ذهبي الصورة الرمزية زهراء غانم
    تاريخ التسجيل
    Jul 2011
    الدولة
    الاردن - ماركا
    المشاركات
    936

    افتراضي رد: crystallization

    مشكور اخي احمد
    الحمـــــــــــــــــــــد لله رب العالمــــــــــــــــين

  5. #5
    عضو ذهبي الصورة الرمزية يارا حماد
    تاريخ التسجيل
    Dec 2011
    المشاركات
    385

    افتراضي رد: crystallization

    شكرا لكم

    عضو في نادي ماركا الأكاديمي


  6. #6
    عضو ذهبي الصورة الرمزية Raed
    تاريخ التسجيل
    Jul 2011
    الدولة
    الاردن - ابو نصير
    المشاركات
    1,052

    افتراضي رد: crystallization

    شكرا اخ عدنان

    عضو في نادي ماركا الأكاديمي


  7. #7
    عضو فعال الصورة الرمزية احمد بيروتي
    تاريخ التسجيل
    Dec 2011
    المشاركات
    31

    افتراضي رد: crystallization

    شكرا
    جزاكم الله خير الجزاء

    عضو في نادي ماركا الأكاديمي


صفحة 1 من 2 1 2 الأخيرةالأخيرة

معلومات الموضوع

الأعضاء الذين يشاهدون هذا الموضوع

الذين يشاهدون الموضوع الآن: 1 (0 من الأعضاء و 1 زائر)

الكلمات الدلالية لهذا الموضوع

المفضلات

ضوابط المشاركة

  • لا تستطيع إضافة مواضيع جديدة
  • لا تستطيع الرد على المواضيع
  • لا تستطيع إرفاق ملفات
  • لا تستطيع تعديل مشاركاتك
  •