Hard anodized aluminum

H. Shih, D. Outka, and J. Daugherty, "Specification for Hard Anodized Aluminum... 

They have good corrosion resistance. Therefore, one can do without expensive surface treatments. However, it is possihie to chrome plate, nickel plate, or hard anodize aluminum plates after machining (electrical discharge machining [EDM]). 

Nonreactive materials include glass, stainless steel, ceramic, enamel, and hard anodized aluminum. Reactive materials include (non-stainless) steel, cast-iron, copper, and aluminum. These materials conduct heat evenly and are excellent for boiling water, frying burgers, or making stock. But if you re working with acidic or alkaline ingredients, stick to nonreactive cookware. 

The previous paragraph assumes that the ethanol will be dry (containing no water) and contain only very small amounts of contaminants such as chloride and sulfate ions that would greatly increase the corrosivity of ethanol. Ethanol produced for fuel purposes in the past has contained up to 5 volume percent water and ion concentrations that made it much more corrosive than pure ethanol [3.7]. For an ethanol fuel with these corrosion characteristics, it was found that aluminum and steel could be coated with cadmium, hard chromium, nickel, or anodized aluminum to make them compatible. Coatings such as zinc, lead, and phosphate were found to be inadequate to prevent corrosion [3.7]. 

The most commonly used hard templates are anodic aluminum oxide (AAO) and track-etched polycarbonate membranes, both of which are porous structured and commercially available. The pore size and thickness of the membranes can be well controlled, which then determine the dimension of the products templated by them. The pores in the AAO films prepared electrochemically from aluminum metals form a regular hexagonal array, with diameters of 200 nm commercially available. Smaller pore diameters down to 5 nm have also been reported (Martin 1995). Without external influences, capillary force is the main driving force for the Ti-precursor species to enter the pores of the templates. When the pore size is very small, electrochemical techniques have been employed to enhance the mass transfer into the nanopores (Limmer et al. 2002). 

Anode elements are commonly prebaked low ash carbon blocks, since any ash residue ends up in the electrolyte. These are electrically connected to copper or aluminum bus bars (heavy electrical conductors) suspended over the cell, which also provide mechanical support and a means for vertical adjustment of the anode elements. An anode variant is the Soderberg paste option, which uses powdered petroleum coke formed into a paste with hard pitch. Electrical contact is established and mechanical adjustment provided by using specially shaped steel pins (Fig. 12.3). As the baked portion of this anode (Fig. 12.3) is gradually consumed, the paste approaches the molten electrolyte and the volatile components in the paste vaporize to leave a hard baked working anode element. Either type of anode element is consumed at the rate of 1-2 cm/day during normal operation, requiring periodic vertical adjustment to maintain an anode-aluminum metal pool spacing of about 5 cm. 

CAS 89-08-7 EINECS/ELINCS 201-881-6 Uses Electrolytic bath additive for production of hard anodic oxide coatings on aluminum and aluminum-based alloys colored coalings are abrasion resist, and attractive for architectural and other uses Features Colors depend on base metal composition, current dens., voltage, film thickness and electrolyte composition, particularly sulfate and aluminum contents Properties 49-51% act. 

In general, template method is classified by soft and hard templates. Whereas anodic aluminum oxide (AAO) membrane, track-etched polycarbonate (PC) and zeolite can be used as hard templates, soft templates include surfactant, cyclodextrin, liquid crystal, etc. Compared with soft and hard templates, template-free method represents the fabrication technique of conducting polymer nanomaterials without the template, which is discussed in this section [115]. 

The initial temperature rise was lower for the nail test (137.5 °C) compared to the controlled anode-alnmimim short test (251.4 °C) for the same SOC condition. This is due to multiple-layer short and multiple kinds of short (including the anode-aluminum) that would have occurred during nail penetration. Based on infrared scanning for the entire cell [22], it was estimated that about 45% of the cell area showed 80 °C or above within 2 s of controlled anode-aluminum internal short while for the nail penetration test, it was only 15%. Chances of thermal runaway are more for a single-layer anode-aluminmn internal short than compared to a multilayer short incurred due to nail penetration. Anode-cathode short was foimd out to be much safer compared to anode-aluminum short as the cell showed a maximum temperature of 71 °C even after 30 s of continuous hard shorting. 

Micro-hardness on surface and through the anodized aluminum layer. 

Many acidic solutions can be used for anodizing aluminum, but sulfuric acid solutions are surely the most common. Chromic, oxalic, and phosphoric acids are also used relatively often for specific applications [28]. The "standard" sulfuric acid anodizing bath (Type 11) produces the best oxides for coloring. The solution consists of approximately 15 percent sulfuric acid and the anodizing bath is maintained at 20°C. As the anodizing temperature is increased, the oxide becomes more porous and improves in its ability to absorb color however, it also loses its hardness and its luster, due to the dissolution action of the acid on the oxide surface. 

The relatively low abrasion and wear resistance of aluminum can be compensated by an appropriate surface treatment so that sufficient life times can be achieved. Hard anodizing, chemical nickel plating, chrome plating, and special chemical coatings, which facilitate demolding, have proven their worth. 

Hard anodizing is suitable for aluminum alloys. It enables the production of extremely hard surfaces (about 350 HV). In contrast to the coatings, the anodic oxide layer is formed from the metal itself (which is why there are no adhesion problems). 

A hard template can restrict the growth of nanomaterials by spatial confinement. To grow ID nanomaterials, anodic aluminum oxide (AAO) is a commonly used hard template with uniform hex-agonally ordered channels. Assisted by the capillary driving force, the precursors diffuse into the channel. After precipitation by a base or simple hydrolysis by heating, the ID nanostructure can form. ... 

In special cases where the surface hardness must be increased or chemical corrosion resistance is necessary (e.g. plasma etching with chlorine), anodized aluminum surfaces can be useful. Alloying elements, impurities, and heat treatment can influence the nature and quality of the anodized coating - typically, the more pure the aluminum alloy, the better the anodized layer. To build up a thick anodized layer on aluminum, it is necessary for the electrolyte to continuously corrode the oxide, producing a porous oxide layer. ASTM Specification B-580-73 designates seven thicknesses (up to 50 microns) for anodization. 

Anodized coatings on SiC/aluminum composites provide satisflictoiy corrosion protection, but they are not as effective as anodized coatings are for unieinfor-ced aluminum because the structure of the anodized layer is affected by the SiC particulates (the particulates interfere with the formation of a continuous barrier layer). TaUe 3 shows a comparison of pitting times and crevice times for sulfriric acid-an ized samples with a hot water seal with those of hard anodized SiCyahiminum. The corrosion resistance of the hard aiaxlized SiC/aluminum is less than that of the conventional anodized SiC/aluminum because the area fraction of the continuous barrier layer for hard anodized SiC/ahiminum is less than that for conventionally anodized SiC/alimiinum. 

---