An engine stand
was constructed of box section mild steel. This was designed to hold
the engine in the most appropriate position for placement in the treatment
tank, keeping dimensions and volumes to a minimum. The devised treatment
method called for the engine to remain on the stand during the entire
treatment. Large lifting eyes were included in the design so that at
no time would the hoist cables be in contact with treatment solutions.
A tank of mild
steel sheet and box section reinforcing was designed and purpose built
for this treatment (fig. 7.). The outside of the tank was protected
with a coating of zinc anti-corrosion paint over which was applied several
layers of outdoor gloss enamel.
|Figure 7: Treatment tank showing
the stainless steel anode and the PVC frame and flooring.
No surface treatment
of the inside of the tank was undertaken other than descaling and degreasing.
The rationale for this was that the base of the tank is isolated from
the engine stand using rigid 7 mm PVC sheeting and the light gauge stainless
steel mesh (the anode) is isolated from the walls of the tank by means
of a frame constructed of 40 and 50 mm PVC tubing (fig.7.).
During the electrochemical
process the tank is independently cathodically protected using an applied
voltage. This was intended to prevent the dissolution of ferrous ions
from the surface of the tank which would interfere with the chemical
reactions. Further, the tank surface itself is protected from corrosion.
The structure of
the engine was examined using sophisticated industrial X-radiographic
equipment known as MINAC. This miniaturised system allows penetration
of approximately 1 metre of concrete and can generate 4 MeV of power.
As several cylinders
of the engine had become detached due to the impact of the crash, it
was decided that a comprehensive structural examination was required.
Cracks and breaks held together by only corrosion products, if present,
could cause complications during the treatment process. The examination
revealed however, that all major structural components were intact.
An endoscopic examination
of the inside of the engine was conducted to ascertain as to whether
it was visually apparent that the corrosion products present inside
the engine were of similar nature to those present on the outside. It
should be noted that the engine was recovered from deep mud in which
it had been “embedded” for some forty five years. Thus, it was possible
that certain chemicals such as fuel, oil and combustion products sealed
within the engine, may have initiated different chemical reaction paths.
The examination was videotaped for subsequent detailed inspection. Results
indicated that no unexpected reactions had taken place. Some signs of
original lubricants were present, although none was sampled.
Any treatment of
a composite object must be based on the results obtained from the detailed
analysis of the various alloys, corrosion products and other materials
which comprise the object. Analytical investigations were undertaken
in which metal samples were examined by x-ray fluorescence spectroscopy
and corrosion products were examined by x-ray diffraction analysis.
Electron microscopy with Energy Dispersive Xray Analysis was also used
to examine some samples. Due to the limitations of time and access to
analytical facilities however, more comprehensive investigations could
have been completed.
Of most interest
to note was that no Al-Cu alloy appeared to be present (unlike the Pratt
and Whitney engine). The composition of the cylinder head air-flow baffles
was quite unusual, being an Al-Si alloy which was in very good condition.
Inlet pipes are of almost pure aluminium, being comparable to the modern
2000 series designation. Significant amounts of magnesium corrosion
products were also present, together with a small amount of residual
magnesium alloy metal.
It was also apparent
that a number of aluminium components manifested various applied surface
treatments. Some wrought sheet appears to be covered with a chromate
conversion coating and other intricate components appear to be anodised.
These all appeared to be in remarkably good condition. Preliminary analytical
investigations (Appendix 1) indeed indicated
the presence of chromium but more sophisticated analytical techniques
are required to distinguish the true nature of these coatings.
Examination of Organic Material.
|Figure 8: Some of the components which
appear to be anodised.
Materials present on the
engine include a semi-rigid plastic wrapping for electrical cables
(fig. 8), reinforced rubber oil hose (fig. 9) and O ring gasket
seals all in varying degrees of degradation. Although an infrared
spectrum of the plastic material was obtained (Appendix
2) using a Perkin Elmer 1750 FTIP, at the time of publication,
no further analysis has been undertaken to characterise these.
||Figure 9: Semi rigid plastic wrapping
Two parts of the
engine, which have become separated from the bulk, a piston and an air-cleaner,
were selected as specimens to be used to test the effectiveness of ultrasonic
agitation during the treatment (fig. 10). A 12 litre “Sonoclean” ultrasonic
bath was used during a pretreatment in a citric acid solution buffered
to pH 5.4.
10: Items which had become detached from the engine, used to test
the effectiveness of ultrasonic agitation --- a piston and an
PH was monitored,
as was the nature and appearance of the concretions and corrosion products.
For example, after 4 days of treatment of the aircleaner most encrustations
became quite soft, changing from solid to mud-like consistency, which
could be easily removed. Interestingly, the pH of the solution rose
from pH 5.41 to 8.61 probably due to the dissolution of ferrous ions.
At this point the treatment was discontinued and the object thoroughly
washed and dried.
These results proved
most satisfactory. As with the Australian project, the usefulness of
the technique was demonstrated. The high cost of an ultrasonic unit
of sufficient size and power to be effective in the treatment of the
engine as a whole proved to be inhibitive.