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发表于 2013-11-17 11:48:01
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Background
Alumina is the most widely used oxide ceramic material. Its applications are widespread, and include spark plugs, tap washers, pump seals, electronic substrates, grinding media, abrasion resistant tiles, cutting tools, bioceramics, (hip-joints), body armour, laboratory ware and wear parts for the textile and paper industries. Very large tonnages are also used in the manufacture of monolithic and brick refractories. It is also used mixed with other materials such as flake graphite where even more severe applications are envisaged, such as pouring spouts and sliding gate valves.
Key Properties
The characteristics which alumina has and which are important for these applications are shown below.
· High compression strength
· High hardness
· Resistant to abrasion
· Resistant to chemical attack by a wide range of chemicals even at elevated temperatures
· High thermal conductivity
· Resistant to thermal shock
· High degree of refractoriness
· High dielectric strength
· High electrical resistivity even at elevated temperatures
· Transparent to microwave radio frequencies
· Low neutron cross section capture area
· Raw material readily available and price not subject to violent fluctuation
Annual Production
Annual production of alumina is some 45 million tonnes, of which 90% is used in the manufacture of aluminium metal by electrolysis.
Where Does Alumina Come From?
Most of the aluminium oxide produced commercially is obtained by the calcination of aluminium hydroxide (frequently termed alumina trihydrate or ATH). The aluminium hydroxide is virtually all made by the Bayer Process. This involves the digestion of bauxite in caustic soda and the subsequent precipitation of aluminium hydroxide by the addition of fine seed crystals of aluminium hydroxide.
Phases of Alumina
Aluminium oxide exists in many forms, a, c, h, d, k, q, g, r; these arise during the heat treatment of aluminium hydroxide or aluminium oxy hydroxide. The most thermodynamically stable form is a-aluminium oxide.
Aluminium Hydroxides
Aluminium forms a range of hydroxides; some of these are well characterised crystalline compounds, whilst others are ill-defined amorphous compounds. The most common trihydroxides are gibbsite, bayerite and nordstrandite, whilst the more common oxide hydroxide forms are boehmite and diaspore.
Commercially the most important form is gibbsite, although bayerite and boehmite are also manufactured on an industrial scale.
Aluminium hydroxide has a wide range of uses, such as flame retardants in plastics and rubber, paper fillers and extenders, toothpaste filler, antacids, titania coating and as a feedstock for the manufacture of aluminium chemicals, e.g. aluminium sulfate, aluminium chlorides, poly aluminium chloride, aluminium nitrate.
Commercial Grades of Alumina
Smelter Grade Alumina
Smelter or metallurgical grade alumina is the name given to alumina utilised in the manufacture of aluminium metal. Historically it was manufactured from aluminium hydroxide using rotary kilns but is now generally produced in fluid bed or fluid flash calciners. In the fluid flash processes the aluminium hydroxide is fed into a counter-current stream of hot air obtained by burning fuel oil or gas. The first effect is that of removing the free water and this is followed by removal of the chemically combined water; this occurs over a range of temperatures between 180-600oC. The dehydrated alumina is principally in the form of activated alumina and the surface area gradually decreases as the temperature rises towards 1000oC. Further calcination at temperatures > 1000oC converts this to the more stable a-form. The conversion to the a-form is typically of the order of 25% and the specific surface area is relatively high at >50m2/g due to the presence of transition aluminas.
Calcined Alumina
If aluminium hydroxide is heated to a temperature in excess of 1100oC, then it passes through the transition phases of alumina referred to above.
The final product, if a high enough temperature is used, is a-alumina. The manufacturing process is commercially undertaken in long rotary kilns. Mineralisers are frequently added to catalyse the reaction and bring down the temperature at which the a-alumina phase forms; fluoride salts are the most commonly used mineralisers.
These calcined alumina products are used in a wide range of ceramic and refractory applications. The main impurity present is sodium oxide. Various grades are produced which differ in crystallite size, morphology and chemical impurities.
The calcined grades are often sub-divided into ordinary soda, medium soda (soda level 0.15-0.25% wt%) and low soda alumina.
Low Soda Alumina
Many applications, particularly in the electrical/electronic areas, require a low level of soda to be present in the alumina. A low soda alumina is generally defined as an alumina with soda content of 漂流瓶的资料翻译，如有不对的还请指教。我也是软件翻译的。大体上看了一下，还可以。
背景
铝土是最用途广泛的氧化物陶瓷材料。 它的应用普遍， 并且包括火花塞， 轻拍洗衣机， 泵浦封印， 电子基体， 研的媒介， 磨蚀抗性瓦片， 切割工具， bioceramics， (臀部联接)， 身体装甲， 实验室商品和穿戴零件为纺织品和纸产业。非常大tonnages也用于整体和砖refractories制造。 也使用它混杂与其他材料例如片状石墨，更加严厉应用被想象， 例如倾吐的喷口和插板闸阀门。
关键物产铝土
关键物产铝土并且为这些应用是重要的特征如下所示。
高压缩强度
高坚硬
抗性对磨蚀
抗性对化学攻击由大范围化学制品甚而在高温；
高电介质强度
高电子抵抗力甚而在高温
透明对微波射频
低中子短剖面捕获区域
原料欣然可利用和价格不受猛烈波动[onlinetranslation支配]
每年铝土的生产每年生产是大约45百万吨， 其中90用于铝金属制造0is的由电析。
Where Does Alumina Come From?
商业被生产的大多数氧化铝由氢氧化铝的锻烧获得(频繁地被命名铝土trihydrate或ATH)。 氢氧化铝是由贝尔过程实际上所有做了。 这在苛性钠介入铝土矿和氢氧化铝的随后降雨雪的消化由氢氧化铝美好的晶种的加法。第一个作用是那取消自由水，并且这由化工联合的水的撤除跟随; 这发生在温度的范围在180-600°C之间。 被脱水的铝土主要地是以被激活的铝土的形式，并且表面逐渐减少，当温度上升往1000°C。
阶段铝土氧化铝存在以许多形式， a， c， h， d， k， q， g， r; 在氢氧化铝或铝oxy氢氧化的热治疗期间，这些升起。 最热力学上稳定的形式是铝氧化物。
氢氧化铝铝形成氢氧化的范围; 其中一些是很好被描绘的水晶化合物， 其他是不清楚的无定形的化合物。 最共同的trihydroxides是gibbsite， bayerite和nordstrandite， 更加共同的氧化物氢氧化形式是boehmite和水铝石。
商业最重要的形式是gibbsite， 虽然bayerite和boehmite在工业等级也被制造。
氢氧化铝有大范围用途， 例如火焰阻化剂在塑料和橡胶， 纸补白和增量剂， 牙膏补白， 抗酸剂， titania涂层和作为一种原料为铝化学制品制造， e.g. 铝硫酸盐， 氯化铝， 多氯化铝， 铝硝酸盐。
铝土商品级
精炼工等级铝土
精炼工或冶金成绩铝土是名字被给在铝金属制造运用的铝土。 历史上它从氢氧化铝是制作的使用回转炉，但一般现在被生产在流化床或流体一刹那calciners。 在流体闪光处理氢氧化铝被投向烧获得的一条逆流的小河空话燃料油或气体。 进一步锻烧在温度> 1000oC转换此成更加稳定的形式。 转换向形式特点是25 比表面区域是相对地高在>50m2/的0and等级 g由于转折aluminas出现。
被锻烧的铝土，如果氢氧化铝被加热到温度超出1100°C， 然后它穿过转折阶段铝土提到上面
最终产品， 如果使用一个高足够的温度， 是铝土。 制造过程在长的回转炉商业被承担。 Mineralisers频繁地增加摧化反应和减少铝土阶段形成的温度; 氟化物盐是通常半新mineralisers。
这些被锻烧的铝土产品用于大范围陶瓷和加工困难的应用。 主要杂质礼物是钠氧化物。 在晶子大小不同的各种各样的成绩导致， 形态学和化学制品杂质。
低苏打铝土
许多应用， 特别在电电子区域， 要求低级苏打是存在铝土。 低苏打铝土一般被定义作为铝土与
易反应的铝土
铝土是期限通常被给比低苏打焊接对一个充分地密集的身体在低温的相对地高纯度和小水晶大小(
表格铝土
表格铝土被重结晶或被焊接的铝土， 所谓，因为它的形态学包括大， 50-500毫米， 刚玉平的片剂形状的水晶。 它是通过成粒状生产的， 挤压， 或按被锻烧的铝土入形状然后加热这些形状到温度在他们的熔点之下， 1700-1850°C在立窑。
在锻烧以后， 被焊接的铝土形状球形，当他们是为有些应用，可以使用， e.g. 催化剂床， 或他们可以被击碎， 筛选和研导致大范围大小。 因为材料被焊接了它有特别低多孔性， 高密， 低渗透性， 好化工惰性， 高耐火度和为加工困难的应用是特别适当的
被熔化的铝土
被熔化的铝土在电电弧炉被做通过通过潮流在垂直的碳电极之间。 引起的热熔化铝土。 熔炉包括一根水冷的钢毛管，并且3-20吨批材料随时被熔化. 被熔化的铝土有高密， 低多孔性， 低渗透性和高耐火度。 结果这些特征， 用于研磨剂和refractories制造。
高纯度Aluminas
高纯度aluminas通常被分类和那些以99.99 0and纯净可以由路线制造从贝尔含水物开始使用连续活化作用和洗涤物， 或通过达到必要的程度的氯化物纯净。 更高的纯度被制造由锻烧的氨盐基铝硫酸盐或从铝金属. 在路线情况下通过氨盐基铝硫酸盐， 必要的程度纯净由连续再结晶获得。 特别是高纯度可以由铝被做通过起反应金属与酒精， 净化铝醇盐由蒸馏， 水解和锻烧较小路线介入服从超级纯净铝金属药丸在蒸馏水之下到火花放电。
应用包括综合性宝石石头制造例如红宝石和钇铝石榴石为lasers， 并且青玉为仪器窗口和lasers。 |
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