Aluminum metallization

The method of obtaining aluminum metal by the electrolysis of alumina dissolved in cryolite was discovered in 1886 by Hall in the U.S. and at about the same time by Heroult in France. Cryolite, a natural ore found in Greenland, is no longer widely used in commercial production, but has been replaced by an artificial mixture of sodium, aluminum, and calcium fluorides. 

Acetic acid, fp 16.635°C ((1), bp 117.87°C at 101.3 kPa (2), is a clear, colorless Hquid. Water is the chief impurity in acetic acid although other materials such as acetaldehyde, acetic anhydride, formic acid, biacetyl, methyl acetate, ethyl acetoacetate, iron, and mercury are also sometimes found. Water significantly lowers the freezing point of glacial acetic acid as do acetic anhydride and methyl acetate (3). The presence of acetaldehyde [75-07-0] or formic acid [64-18-6] is commonly revealed by permanganate tests biacetyl [431-03-8] and iron are indicated by color. Ethyl acetoacetate [141-97-9] may cause slight color in acetic acid and is often mistaken for formic acid because it reduces mercuric chloride to calomel. Traces of mercury provoke catastrophic corrosion of aluminum metal, often employed in shipping the acid. 

The principal use of AIF. is as a makeup ingredient in the molten cryoflte, Na.. AIF AI2O2, bath used in aluminum reduction cells in the HaH-Haroult process and in the electrolytic process for refining of aluminum metal in the Hoopes cell. A typical composition of the molten salt bath is 80—85%... 

Metallization layers are generally deposited either by CVD or by physical vapor deposition methods such as evaporation (qv) or sputtering. In recent years sputter deposition has become the predominant technique for aluminum metallization. Energetic ions are used to bombard a target such as soHd aluminum to release atoms that subsequentiy condense on the desired substrate surface. The quaUty of the deposited layers depends on the cleanliness and efficiency of the vacuum systems used in the process. The mass deposited per unit area can be calculated using the cosine law of deposition ... 

Examples of similar processes are the decomposition of precipitated aluminum trHiydroxide to alumina, which is the feed for the electrolytic production of aluminum metal, and the drying of wet sulfide concentrates in preparation for flash roasting (see Aluminumand aluminum alloys). 

Aluminum obtained by electrolysis of cryoHte baths contains iron [7439-89-6] and siUcon [7440-21-3] as impurities. Iron content may vary from 0.05 to 0.4% and siUcon from 0.05 to 0.15% depending on the raw materials and the age and condition of the reduction cell. Primary aluminum metal also contains small, usually not to exceed 0.05% in total, amounts of many other elements. Some of these trace impurities are Cu, Mn, Ni, Zn, V, Na, Ti, Mg, and Ga, most of which are present in quantities substantially below 100 ppm. 

Production of both monobasic aluminum diformate, (HO)Al(OOCH)2, and monobasic aluminum formoacetate, (HO)Al(OOCH) (OOCCH ), has declined. One reason could be the ready substitution of inexpensive aluminum formate solution (17—19) for soHd aluminum acetate in formoacetate in most of the common commercial appHcations. Monobasic aluminum formoacetate, mol wt 148.05, mp 350°C, is a fine crystalline powder, prepared from aluminum metal. It is used for fabric water repeUency and in the tanning of coUagen tape for surgical sutures (10). 

Economic Aspects. The North American demand for anhydrous aluminum chloride, estimated to be from 25,000 to 30,000 metric tons per year (9), is divided among the appHcations shown in Figure 2. In 1984 the anhydrous aluminum chloride demand was estimated at 40,000 tons in Western Europe and 9,000 tons in Japan (10). Pricing is heavily dependent on the cost of aluminum metal. The deHvered price of aluminum chloride during the first quarter of 1989 ranged from 0.32/kg for bulk tmddoads to 0.35/kg for small dmms. The North American demand for this catalyst has remained relatively constant over the last 20 years (10). 

The anodized surface is often subjected to additional treatment before the radiation-sensitive coating is appHed. The use of aqueous sodium siUcate is well known and is claimed to improve the adhesion of diazo-based compositions ia particular (62), to reduce aluminum metal-catalyzed degradation of the coating, and to assist ia release after exposure and on development. Poly(viQyl phosphonic acid) (63) and copolymers (64) are also used. SiUcate is normally employed for negative-workiag coatings but rarely for positive ones. The latter are reported (65) to benefit from the use of potassium flu o r o zirc onate. 

The head of the femoral component then articulates with an ion-bombarded, HDPE, high walled, acetabular liner which fits iato a screwed ia, machined, titanium, chromium—cobalt—molybdenum or vanadium—aluminum metallic alloy hydroxyapatite-coated acetabular shell/cup. Each of the separate parts of the modular system for total hip arthroplasty is manufactured ia several different sizes. 

The potential of the reaction is given as = (cathodic — anodic reaction) = 0.337 — (—0.440) = +0.777 V. The positive value of the standard cell potential indicates that the reaction is spontaneous as written (see Electrochemical processing). In other words, at thermodynamic equihbrium the concentration of copper ion in the solution is very small. The standard cell potentials are, of course, only guides to be used in practice, as rarely are conditions sufftciendy controlled to be called standard. Other factors may alter the driving force of the reaction, eg, cementation using aluminum metal is usually quite anomalous. Aluminum tends to form a relatively inert oxide coating that can reduce actual cell potential. 

The simple picture of the MOS capacitor presented in the last section is compHcated by two factors, work function differences between the metal and semiconductor and excess charge in the oxide. The difference in work functions, the energies required to remove an electron from a metal or semiconductor, is = —25 meV for an aluminum metal plate over a 50-nm thermally grown oxide on n-ty e siUcon with n = 10 cm . This work... 

Lithium—Aluminum/Metal Sulfide Batteries. The use of high temperature lithium ceUs for electric vehicle appUcations has been under development since the 1970s. Advances in the development of lithium aUoy—metal sulfide batteries have led to the Li—Al/FeS system, where the foUowing ceU reaction occurs. 

Further dechlorination may occur with the formation of substituted diphenyhnethanes. If enough aluminum metal is present, the Friedel-Crafts reactions involved may generate considerable heat and smoke and substantial amounts of hydrogen chloride, which reacts with more aluminum metal, rapidly forming AlCl. The addition of an epoxide inhibits the initiation of this reaction by consuming HCl. Alkali, alkaline-earth, magnesium, and zinc metals also present a potential reactivity hazard with chlorinated solvents such as methylene chloride. 

Chemical Raw Material. In addition to use as a catalyst raw material, clays are used or have been extensively studied as chemical raw material. For example, kaolin has been investigated as a raw material for aluminum metal production. Kaolin has a 38 to 40% alumina content and is available in the United States in large quantities whereas the higher alumina bauxite reserves are very limited. The Bureau of Mines has actively carried out research in the aluminum from ka olin area for many years. Activity increases whenever imports of bauxite are threatened by war or other trade intermptions (1,22,23). 

For example, chloride and duoride ions, even in trace amounts (ppm), could cause the dissolution of aluminum metallization of complimentary metal oxide semiconductor (CMOS) devices. CMOS is likely to be the trend of VLSI technology and sodium chloride is a common contaminant. The protection of these devices from the effects of these mobile ions is an absolute requirement. The use of an ultrahigh purity encapsulant to encapsulate the passivated IC is the answer to some mobile ion contaminant problems. 

Metal Preparation. Sheet-steel parts are formed by stamping, bending, and shearing. Many parts require welding (qv), which needs to be carried out in a uniform, smooth manner so that the welded joint can be enameled without defects. Cast-iron parts are formed by the usual cast-iron foundry methods however, additional care is given to prevent contamination of the surface. Surface contamination causes defects in the enamel, particularly bUsters and bubbles. Aluminum metal can be formed in sheets, extmsions, and as castings. 

Although insulators other than aluminum oxide have been tried, aluminum is still used almost universally because it is easy to evaporate and forms a limiting oxide layer of high uniformity. To be restricted, therefore, to adsorption of molecules on aluminum oxide might seem like a disadvantage of the technique, but aluminum oxide is very important in many technical fields. Many catalysts are supported on alumina in various forms, as are sensors, and in addition the properties of the oxide film on aluminum metal are of the greatest interest in adhesion and protection. 

The Alfol process (Figure 7-7) for producing linear primary alcohols is a four-step process. In the first step, triethylaluminum is produced by the reaction of ethylene with hydrogen and aluminum metal ... 

Zinc or aluminum metal spray Sprayed metal coatings are porous and should be sealed after application by applying a sealer coat (i.e. a thin coat such as an etch primer) or a thinned version of the final coating system. Oil-based systems should not be used. Metal spray coatings can have excellent durability without overcoating with paint and, particularly for aggressive conditions it is preferable to leave them with sealer only. 

Write balanced equations for foe reaction of aluminum metal with foe following nonmetals ... 

The Space Shuttle uses aluminum metal and ammonium perchlorate in its reusable booster rockets. The products of die reaction are aluminum oxide, aluminum chloride, nitrogen oxide gas, and steam. The reaction mixture contains 7.00 g of aluminum and 9.32 g of ammonium perchlorate. 

When water is added to a mixture of aluminum metal and sodium hydroxide, hydrogen gas is produced. This is the reaction used in commercial drain cleaners ... 

In Figure 5-12 is a set of core level spectra shown, which have been recorded between successive steps during the growth of an aluminum metallic overlayer on top of PPV [59]. The thickness of the aluminum layer for the lowest and highest coverage correspond to 2 and 20 A, respectively. 

Aluminum metal reacts with aqueous acidic solutions to liberate hydrogen gas. Write the two half-reactions and the net ionic reaction. 

If aluminum metal is mixed with a metal oxide such as ferric oxide, Fe203, and ignited, the oxide is reduced and large amounts of heat are evolved 2A1 (s) + FejOsfsJ —> 2FefsJ + AlsO/sJ... 

FIGURE 6.8 The thermite reaction is so exothermic that it melts the metal that it produces and is used to weld railroad tracks together. Here, aluminum metal is reacting with iron(lll) oxide. Fe20 causing a shower of molten iron sparks. 

A note on good practice Distinguish between amphoteric and amphiprotic. Aluminum metal is amphoteric (it reacts with both acids and bases), but it has no hydrogen atoms to donate as protons, and is not amphiprotic. 

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