Cleaning and Corrosion Control Flashcards
- A primary reason why ordinary or otherwise nonapproved cleaning compounds should not be used when washing aircraft is because their use can result in A— hydrogen embrittlement in metal structures.
B— hydrogen embrittlement in nonmetallic materials. C— a general inability to remove compound residues.
A— hydrogen embrittlement in metal structures.
Some nonapproved commercial cleaning compounds can cause a chemical reaction with some of the metals used in aircraft structure. This reaction releases hydrogen gas that can be absorbed into the metal and cause hydrogen embrittlement which weakens the metal and can cause cracking and failure.
- How may magnesium engine parts be cleaned?
A— Soak in a 20 percent caustic soda solution.
B— Spray with methyl ethyl ketone (MEK).
C— Wash with a commercial solvent, decarbonize, and scrape or grit blast.
C— Wash with a commercial solvent, decarbonize, and scrape or grit blast.
Magnesium engine parts are cleaned by washing them with a commercial solvent such as naphtha or Stoddard solvent, then soaking them in a decarbonizer that has been proven safe for magnesium. Any hard deposits that are not removed by this treatment can be removed with a scraper or with a grit blast.
- When an anodized surface coating is damaged in service, it can be partially restored by
A— applying a thin coat of zinc chromate primer.
B— chemical surface treatment.
C— use of a suitable mild cleaner.
B— chemical surface treatment.
An anodized coating is an electrolytically deposited film of oxide that covers the surface of the metal and keeps air and moisture away from it. If this coating is damaged, the metal can corrode.
Damaged anodized coating can be repaired by treating the damaged area with a chemical conversion coating material such as Alodine. This chemical treatment forms a hard oxide film on the surface much like the anodized surface.
8349-1.
For which of the following reasons would a water break test be conducted?
A— To make certain that a newly alodized aluminum surface is sufficiently coated.
B— To make certain that a bare metal surface is thoroughly clean.
C— To make certain that an anodizing coating has been sufficiently removed before an electrical bonding connection can be made.
B— To make certain that a bare metal surface is thoroughly clean.
Alodine can be applied to a surface after all traces of corrosion have been removed. The surface should be chemically cleaned until it supports an unbroken water film. Any breaks in the film of rinse water show that there some wax, grease, or oil on the surface, and further cleaning must be done.
- Select the solvent recommended for wipedown of cleaned surfaces just before painting.
A— Aliphatic naptha.
B— Dry-cleaning solvent.
C— Aromatic naptha.
A— Aliphatic naptha.
Aliphatic naptha is a petroleum product between gasoline and kerosine in its characteristics. It is well suited for use as a cleaning agent for removing fingerprints, dust, and oily deposits that have settled on a surface to prepare the surface for painting.
Dry-cleaning solvent, such as Stoddard solvent, leaves a slight residue on the surface that can interfere with the adhesion of the paint.
Aromatic naptha is a coal tar derivative that is toxic and attacks acrylics and rubber products. It is not suitable for wiping down a surface before painting.
- Nickel-cadmium battery cases and drain surfaces which have been affected by electrolyte should be neutralized with a solution of
A— boric acid.
B— sodium bicarbonate.
C— potassium hydroxide.
A— boric acid.
An area that has been affected by the electrolyte from a nickel-cadmium battery should be washed and neutralized with ammonia or a boric acid solution, allowed to dry thoroughly, then painted with an alkali-resisting varnish.
- Which of the following are acceptable to use when utilizing chemical cleaning agents on aircraft?
A— Cotton fiber wiping cloths when using a flammable agent and atomizing spray equipment.
B— Microfiber wiping cloths when using a flammable agent and atomizing spray equipment.
C— Synthetic fiber wiping cloths when using a flammable agent.
A— Cotton fiber wiping cloths when using a flammable agent and atomizing spray equipment.
When cleaning and/or depainting an aircraft surface with a flammable agent, use only a cotton wiping cloth or a natural bristle brush. Synthetic fibers like microfiber tend to create unsafe charges of static electricity that could ignite the flammable agent. Emulsion-type cleaning agents may be applied to a surface with atomizing spray equipment. After the agent has penetrated the dirt or exhaust residue, it should be scrubbed with a natural bristle brush and washed from the surface.
- Select the solvent used to clean acrylics and rubber.
A— Aliphatic naphtha.
B— Methyl ethyl ketone.
C— Aromatic naphtha.
A— Aliphatic naphtha.
Aliphatic naphtha is the only one of the three materials listed here that will not damage rubber or acrylic plastic.
Be sure that aromatic naphtha (a coal tar derivative) is not used.
- Fayed surfaces cause concern in chemical cleaning because of the danger of
A— forming passive oxides.
B— entrapping corrosive materials.
C— corrosion by imbedded iron oxide.
B— entrapping corrosive materials.
Fayed surfaces are the parts of a structure that are covered in a lap joint.
It is important when a structure is chemically cleaned that the fayed surfaces be protected so that corrosive materials do not seep between the sheets in the lap joints. This would cause corrosion to form in an area where it is hard to detect.
- Caustic cleaning products used on aluminum structures have the effect of producing
A— passive oxidation.
B— improved corrosion resistance.
C— corrosion.
C— corrosion.
Aluminum alloys such as those used in an aircraft structure are reactive metals. This means that they are likely to react with chemicals to form salts (corrosion). Many caustic cleaning products react with aluminum alloy and cause them to corrode.
- Fretting corrosion is most likely to occur
A— when two surfaces fit tightly together but can move relative to one another.
B— only when two dissimilar metals are in contact.
C— when two surfaces fit loosely together and can move relative to one another.
A— when two surfaces fit tightly together but can move relative to one another.
Fretting corrosion is a form of corrosion that forms between closely fitting assembled parts that have a slight amount of relative motion.
When sheets of aluminum alloy are riveted together, there should be no relative motion between the sheets or between the sheets and the rivets. But if there is a slight bit of movement, the protective oxide coating will be rubbed off of the metal and a new oxide coating will form. The material that has been rubbed off acts as an abrasive and accelerates the wear.
- The rust or corrosion that occurs with most metals is the result of
A— a tendency for them to return to their natural state.
B— blocking the flow of electrons in homogenous metals, or between dissimilar metals.
C— electron flow in or between metals from cathodic to anodic areas.
A— a tendency for them to return to their natural state.
Corrosion is a natural phenomenon which attacks metal by chemical or electrochemical action and converts it into a metallic compound, such as an oxide, hydroxide, or sulfate. Corrosion occurs because of the tendency for metals to return to their natural state. Noble metals like gold and platinum do not corrode since they are chemically uncombined in their natural state.
- Which of the following are the desired effects of using Alodine on aluminum alloy?
A— A smooth painting surface and increased corrosion resistance.
B— Relieved surface stresses.
C— A slightly rough surface and increased corrosion resistance.
C— A slightly rough surface and increased corrosion resistance.
Alodine is a conversion coating used to prepare aluminum alloys for painting. It etches the surface providing a microscopically rough surface and forms an oxide film on the surface to increase the corrosion resistance.
- Which of the listed conditions is NOT one of the requirements for corrosion to occur?
A— The presence of an electrolyte.
B— Electrical contact between an anodic area and a cathodic area.
C— The presence of a passive oxide film.
C— The presence of a passive oxide film.
passive oxide film is used as a corrosion preventive.
There are four conditions that must exist before corrosion can occur:
1. The presence of a metal that will corrode, the anode. 2. Presence of a dissimilar conductive material, the cathode, which has less tendency to corrode.
3. Presence of a conductive liquid, the electrolyte.
4. Electrical contact between the anode and cathode.
- The lifting or flaking of the metal at the surface due to delamination of grain boundaries caused by the pressure of corrosion residual product buildup is called A— brinelling.
B— granulation.
C— exfoliation.
C— exfoliation.
Exfoliation corrosion is a severe form of intergranular corrosion that normally forms in extruded metal.
When metal is extruded, its grain structure is basically arranged in a series of layers. If an extrusion is improperly heat-treated, the grains are enlarged to the extent that intergranular corrosion can form along the grain boundaries within the metal.
Severe intergranular corrosion in an extruded material causes it to delaminate (the layers of the metal to push apart). The surface of the metal lifts or flakes off.
