乾燥劑.....

乾燥劑的成分

（一）密封的乾燥劑
乾燥劑是為了使物品不易發黴、腐敗，可減少食品的體積、重量而便於運輸，不過乾燥食品在貯藏過程中，會吸濕引起品質變化，所以市售的乾燥食品常於包裝內放置乾燥劑。除食品外如：磁片、相機等物件也可放置在有乾燥劑的密封容器內保持乾燥。

（二）乾燥劑的成分
乾燥劑種類 常見的成分
可以和水反應的化合物氯化鈣、氧化鈣(生石灰)、磷酸酐
具有高吸水性的化合物矽膠、高分子聚合體、甘蔗纖維

（三）其他的乾燥劑
1.分子篩
化學成份為鋁矽酸鹽結晶體，獨特的單一孔徑多孔性微結構，以及對水分子的超強親和力，使分子篩在低濕度下的吸濕能力特別強，幾乎達到絕對乾燥的程度。最適合各類乾燥機、吸附塔、密閉包裝容器、藥品容器、製氧機、空調設備等應用場合。

2.活性氧化鋁
具有特殊的多孔性微結構，吸濕能力強。可以承受急遽的溫度變化，結構安定性佳、即使浸泡於水中也不會收縮、膨脹、軟化或分解，最常應用於乾燥機內的吸附床。
矽膠乾燥劑(Silica Gel Desiccant)的外觀是一顆顆直徑2-5mm無色或白色透明圓球。它的主要成份是SiO2,這是一種無毒的化學物質。
透過仔細控制條件的化學合成反應,SiO2會形成高比表面積的孔洞性結構(孔洞平均直徑約為20A2)。
而空氣中的水分子會藉由表面物理吸附機制,附著於孔洞性結構之中,由此而達成充份吸濕的功能。
一般在使用時,皆將矽膠乾燥劑以透氣性材料包裝成各種重量使用,並以內含乾燥劑重量多寡作為分類依據。

佢叫乾燥劑

Silica gel is a granular, porous form of silica made synthetically from sodium silicate. Despite the name, silica gel is a solid.
Silica gel is most commonly encountered in everyday life as beads packed in a semi-permeable plastic. In this form, it is used as a desiccant to control local humidity in order to avoid spoilage. Because of poisonous dopants, silica gel packets usually bear warnings for the user not to eat the contents, but to throw them away instead.
Chemistry
In chemistry, silica gel is used in chromatography as a stationary phase. In column chromatography the stationary phase is most often composed of silica gel particles of 40-63 μm. In this application, due to silica gel's polarity, non-polar components tend to elute before more polar ones, hence the name normal phase chromatography. However, when hydrophobic groups (such as C18 groups) are attached to the silica gel then polar components elute first and the method is referred to as reverse phase chromatography. Silica gel is also applied to aluminum or plastic sheets for thin layer chromatography.
Chelating groups have also been covalently bound to silica gel. These materials have the ability to remove metal ions selectively from aqueous media. Chelating goups can be covalently bound to polyamines that have been grafted onto a silica gel surface producing a material of greater mechanical integrity. Silica gel is also combined with alkali metals to form a M-SG reducing agent.