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礬（fán）是各種金屬的硫酸鹽水合結晶，有時也指一大類通式為A2SO4·B2(SO4)3·24H2O（即AB(SO4)2·12H2O）的水合硫酸鹽復鹽（英文：Alum）。明礬（鉀鋁礬，KAl(SO4)2·12H2O）是最常見的礬。
[1] 當其中的三價陽離子為鋁離子時，該礬根據其一價陽離子命名；反之，當其中的一價陽離子為鉀離子時，該礬根據其三價陽離子命名。
化學性質
編輯礬被用於一系列工業用途，這是由於它們具有以下一些性質：它們易溶於水，並有一種淡淡的甜味；水溶液顯酸性並且能結晶為規則的八面體。當加熱時它們首先會液化，然後才失去結晶水，表面起泡，最終只留下無水粉末。它們的溶液顯酸性，並多具有凝血功能（膠體聚沉原理）。
用途
編輯工業
編輯Potassium alum is the common alum of commerce, although soda alum, ferric alum, and ammonium alum are manufactured.
Alum has been used at least since Roman times for purification of drinking water[2] and industrial process water. Between 30 and 40 ppm of alum[2][3] for household wastewater, often more for industrial wastewater,[4] is added to the water so that the negatively charged colloidal particles clump together into "flocs", which then float to the top of the liquid, settle to the bottom of the liquid, or can be more easily filtered from the liquid, prior to further filtration and disinfection of the water.
Alum solution has the property of dissolving steels while not affecting aluminium or base metals, and can be used to recover workpieces made in these metals with broken toolbits lodged inside them.[5] As considerable expense and/or effort may have gone into machining a specialist part, this can be a worthwhile excercise.
化妝品
編輯
- Alum in block form (usually potassium alum) can be used as a blood coagulant.[6]
- Styptic pencils containing aluminium sulfate or potassium aluminium sulfate are used as astringents to prevent bleeding from small shaving cuts.
- Alum may be used in depilatory waxes used for the removal of body hair or applied to freshly waxed skin as a soothing agent.
- Alum's antiperspirant and antibacterial properties[7][8] contribute to its traditional use as an underarm deodorant.[9] It has been used for this purpose in Europe, Mexico, Thailand (where it is called sarn-som), throughout Asia and in the Philippines (where it is called tawas). Today, potassium or ammonium alum is sold commercially for this purpose as a "deodorant crystal", often in a protective plastic case.[10]
烹調
編輯- Alum powder, found in the spice section of many grocery stores, may be used in pickling recipes as a preservative to maintain fruit and vegetable crispness.
- Alum is used as the acidic component of some commercial baking powders.
- Alum was used by bakers in England during the 1800s to make bread whiter.[11] The Sale of Food and Drugs Act 1875 prevented this and other adulterations.[12]
- In Nigeria, it is used in the removal of snail slime before cooking
阻燃劑
編輯- Solutions containing alum may be used to treat cloth, wood, and paper materials to increase their resistance to fire.
- Alum is also used in fire extinguishers to smother chemical and oil fires.[來源請求]
化學絮凝劑
編輯- Alum is used to clarify water by neutralizing the electrical double layer surrounding very fine suspended particles, allowing them to flocculate (stick together). After flocculation, the particles will be large enough to settle and can be removed.
- Alum may be used to increase the viscosity of a ceramic glaze suspension; this makes the glaze more readily adherent and slows its rate of sedimentation.
- Alum is an ingredient in some recipes for homemade modeling compounds intended for use by children. (These are often called "play clay" or "play dough" for their similarity to "Play-Doh", a trademarked product marketed by American toy manufacturer Hasbro).[來源請求]
醫藥
編輯- Alum has been used as an adjuvant to increase the efficacy of vaccines since the 1920s. See adjuvant for details on the mechanism.
- Alum can be used as a coagulant to help stop internal bleeding of organs. Its mechanism of action is believed to be due the same preservative properties for which it is used in food storage, by causing shrinkage of the pores and decreasing humoral secretions.[來源請求]
生產
編輯 |
以明礬石為原料
編輯In order to obtain alum from alunite, it is calcined and then exposed to the action of air for a considerable time. During this exposure it is kept continually moistened with water, so that it ultimately falls to a very fine powder. This powder is then lixiviated with hot water and sulfuric acid, the liquor decanted, and the alum allowed to crystallize. The alum schists employed in the manufacture of alum are mixtures of iron pyrite, aluminium silicate and various bituminous substances, and are found in upper Bavaria, Bohemia, Belgium, and Scotland. These are either roasted or exposed to the weathering action of the air. In the roasting process, sulfuric acid is formed and acts on the clay to form aluminium sulfate, a similar condition of affairs being produced during weathering. The mass is now systematically extracted with water, and a solution of aluminium sulfate of specific gravity 1.16 is prepared. This solution is allowed to stand for some time (in order that any calcium sulfate and basic ferric sulfate may separate), and is then evaporated until ferrous sulfate crystallizes on cooling; it is then drawn off and evaporated until it attains a specific gravity of 1.40. It is now allowed to stand for some time, decanted from any sediment, and finally mixed with the calculated quantity of potassium sulfate, well agitated, and the alum is thrown down as a finely divided precipitate of alum meal. If much iron should be present in the shale then it is preferable to use potassium chloride in place of potassium sulfate.
以鋁土礦等含鋁礦物為原料
編輯當使用粘土或鋁土礦為原料時，原料會被小心地煅燒，再使用逐漸加熱至沸騰的硫酸進行酸浸。此後，這一混合物將被靜置一段時間以得到清液，再與酸化了的硫酸鉀溶液按比例混合併結晶。
當使用冰晶石為原料時，它會被與碳酸鈣混合在一起並加熱，從而生成鋁酸鈉。生成的鋁酸鈉用水浸方式提取，氟化鈣和其他雜質則留在燒渣中。然後，通過向清液內通入二氧化碳或加入碳酸氫鈉的方式使鋁元素以氫氧化鋁的形式沉澱下來。最後，沉澱會被硫酸溶解，並加入適量的硫酸鉀以析出晶體。
種類
編輯許多三價金屬都能夠形成礬。礬的通式為AMIII(SO4)2·nH2O，其中A是鹼金屬離子或銨根離子，MIII是一個三價離子，結晶水數n通常是12。一般來說，對應的鹼金屬離子越大，礬越易生成。這一規則最早是由Locke在1902年提出[13]的，因為他發現如果一個三價離子不能與銫離子形成礬，那麼它就不會與其它任意一種鹼金屬離子或銨根離子形成礬。
Double sulfates with the general formula A
2SO
4·B
2(SO
4)
3·24H
2O, are known where A is a monovalent cation such as sodium, potassium, rubidium, caesium, or thallium(I), or a compound cation such as ammonium (NH+
4), methylammonium (CH
3NH+
3), hydroxylammonium (HONH+
3) or hydrazinium (N
2H+
5), B is a trivalent metal ion, such as aluminium, chromium, titanium, manganese, vanadium, iron(III), cobalt(III), gallium, molybdenum, indium, ruthenium, rhodium, or iridium.[14] Analogous selenates also occur. The specific combinations of univalent cation, trivalent cation, and anion depends on the sizes of the ions. For example, unlike the other alkali metals the smallest one, lithium, does not form alums, and there is only one known sodium alum. In some cases, solid solutions of alums occur.
礬可以以三種不同晶型結晶，它們分別被稱為α-礬，β-礬和γ礬。
鉀明礬
編輯
硫酸鋁鉀（KAl(SO4)2·12H2O)，即常見的明礬，有著絮凝劑、媒染劑、止血劑、防腐劑等多種用途。A common method of producing potash alum is leaching of alumina from bauxite, which is then reacted with potassium sulfate.
鈉明礬
編輯Soda alum, NaAl(SO
4)
2·12H
2O, mainly occurs in nature as the mineral mendozite. It is very soluble in water, and is extremely difficult to purify. In the preparation of this salt, it is preferable to mix the component solutions in the cold, and to evaporate them at a temperature not exceeding 60 °C. 100 parts of water dissolve 110 parts of sodium alum at 0 °C, and 51 parts at 16 °C. Soda alum is used in the acidulent of food as well as in the manufacture of baking powder.
銨明礬
編輯Ammonium alum, NH
4Al(SO
4)
2·12H
2O, a white crystalline double sulfate of aluminium, is used in water purification, in vegetable glues, in porcelain cements, in deodorants (though potassium alum is more commonly used), in tanning, dyeing and in fireproofing textiles.
鉻明礬
編輯
鉻明礬，KCr(SO4)2·12H2O，是一種鉻與鉀的硫酸復鹽，晶體呈紫色。它可用於鞣製、媒染。
在這類礬中，硒原子取代了硫原子的位置，使硫酸根變成了硒酸根（SeO42-）。由於硒酸根的特性，它們是強氧化劑。
硫酸鋁
編輯硫酸鋁，有時又被稱為造紙礬（Papermaker's Alum），是一種在工業上常被誤稱為礬的物質。 Although reference to this compound as alum is quite common in industrial communication, it is not regarded as technically correct. Its properties are quite different from those of the set of alums described above. Most industrial flocculation done with alum is actually aluminium sulfate.
溶解度
編輯The solubility of the various alums in water varies greatly, sodium alum being readily soluble in water, while caesium and rubidium alums are only sparingly soluble. The various solubilities are shown in the following table.
- 在溫度為T時，100份的水可溶解的量為：
| T | 銨明礬 | 鉀明礬 | 銣明礬 | 銫明礬 |
|---|---|---|---|---|
| 0 °C | 2.62 | 3.90 | 0.71 | 0.19 |
| 10 °C | 4.50 | 9.52 | 1.09 | 0.29 |
| 50 °C | 15.9 | 44.11 | 4.98 | 1.235 |
| 80 °C | 35.20 | 134.47 | 21.60 | 5.29 |
| 100 °C | 70.83 | 357.48 |
參見
編輯參考資料
編輯- ^ Austin, George T. Shreve's Chemical process industries. 5th ed. New York: McGraw-Hill. 1984: 357. ISBN 9780070571471.
- ^ 2.0 2.1 Samuel D. Faust, Osman M. Aly. Chemistry of water treatment 2nd ed. Chelsea, MI: Ann Arbor Press. 1999. ISBN 9781575040110.
- ^ Bratby, John. Coagulation and flocculation in water and wastewater treatment 2. ed. London: IWA Publ. 2006. ISBN 9781843391067.
- ^ Rice, J. K. The use of organic flocculants and flocculating aids in the treatment of industrial water and industrial waste water. Symposium on Industrial Water and Industrial Waste Water (ASTM International). June 1957, (207): 41–51.
- ^ http://www.model-engineer.co.uk/forums/postings.asp?th=91442&p=82#PostTop
- ^ [1] A Woman Rice Planter: Electronic Edition. Pringle, Elizabeth Waties Allston (pseud. Pennington, Patience),(1845-1921) p.18
- ^ Kanlayavattanakul, M.; Lourith, N. Body malodours and their topical treatment agents. International Journal of Cosmetic Science. 1 August 2011, 33 (4): 298–311. PMID 21401651. doi:10.1111/j.1468-2494.2011.00649.x.
- ^ Aguilar, T. N.; Blaug, S.M.; Zopf, L.C. A study of the antibacterial activity of some complex aluminum salts. Journal of the American Pharmaceutical Association. American Pharmaceutical Association. July 1956, 45 (7): 498–500. PMID 13345689.
- ^ Alumen, and the Several Varieties of it; Thirty-eight Remedies., Pliny the Elder, The Natural History, book 35, chapter 52; on the Perseus Digital Library at Tufts University. Last accessed 27 December 2011.
- ^ US patent 5399364,Francis Verdan,「Cosmetic assembly defined by encased stick of alum」,發行於1995-05-21
- ^ Church Pastoral-aid Society, London. Brown Bread. The Church of England magazine. January–June 1847, 22: 355.
- ^ Hassall, Arthur Hill. Adulterations detected; or, Plain instructions for the discovery of frauds in food and medicine. 1857.
- ^ J. Locke. On some double sulphates of thallic thallium and caesium. American Chemical journal. 1902, 27: 281.
- ^ Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford: Butterworth-Heinemann. ISBN 0-7506-3365-4.
外部連結
編輯
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