International
Tables for
Crystallography
Volume H
Powder diffraction
Edited by C. J. Gilmore, J. A. Kaduk and H. Schenk

International Tables for Crystallography (2018). Vol. H, ch. 3.7, p. 310

Section 3.7.2.4.3. Valve deposit from a piston aviation engine

J. A. Kaduka,b,c*

aDepartment of Chemistry, Illinois Institute of Technology, 3101 South Dearborn Street, Chicago, IL 60616, USA,bDepartment of Physics, North Central College, 131 South Loomis Street, Naperville, IL 60540, USA, and cPoly Crystallography Inc., 423 East Chicago Avenue, Naperville, IL 60540, USA
Correspondence e-mail: kaduk@polycrystallography.com

3.7.2.4.3. Valve deposit from a piston aviation engine

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Applying a commercial search/match program to the diffraction pattern of a deposit from a valve in a gasoline-powered aircraft engine easily identified quartz and corundum. The specimen was scraped from the valve seat and micronized. The corundum represents abrasion from the elements of the micronizing mill, as it was not present in the pattern of the as-scraped sample. Metal particles were visibly present in the deposit, so one could reasonably guess the presence of both ferrite and austenite (Fig. 3.7.7[link]; files maso04.gsas, maso04.rd and padv.prm). A Rietveld refinement using these four phases was carried out.

[Figure 3.7.7]

Figure 3.7.7 | top | pdf |

The four phases identified in a valve deposit from an aircraft engine by automated search/match methods and guessing based on the appearance of the sample. The pattern has had the background and Kα2 peaks removed.

Six peaks picked from the difference plot were entered into SIeve+ and a Hanawalt search was carried out. No chemically reasonable simple compounds were near the top of the hit list, so extra information was sought. An XPS analysis indicated the presence of Pb, Br, Fe, P, O and C (and H assumed). Aviation gasoline is still leaded, and ethylene dibromide is sometimes added as a lead scavenger. The result of a `just' chemistry search using these seven elements (6543/328 660 entries) was applied as a filter to the Hanawalt search. Near the top of the hit list was PbBr2. Although apparently surprising, this phase is reasonable given our chemical knowledge. Lead bromide was added to the Rietveld refinement. Further analysis of the difference pattern using the same techniques indicated the presence of cohenite, Fe3C, from the steel, and Fe3Fe4(PO4)6, the reaction product of the steel with a phosphate fuel additive. The final Rietveld refinement yielded a quantitative analysis of 26.5 (4) wt% austenite (γ-Fe, stainless steel), 47.9 (4) wt% ferrite (α-Fe, carbon steel), 17.7 (4) wt% quartz (sand/dirt), 2.9 (2) wt% PbBr2, 2.6 (2) wt% Fe3Fe4(PO4)6 and 2.2 (2) wt% cohenite (Fig. 3.7.8[link]).

[Figure 3.7.8]

Figure 3.7.8 | top | pdf |

The seven phases identified in the valve deposit from an aircraft engine.








































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