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Minearalogy of selected world soil samples, with implications regarding the abrasion/corrosion potential of environmental dust on military ordnance and a hypothesis for the Southeast Asia problem.

01 Mar 1973-

Abstract: Fifty-four representative soil samples from all over the world were selected for heavy mineral analysis from those provided by the Naval Weapons Center, China Lake, California. Data thus obtained, in conjunction with mineralogical, chemical, and abrasion investigation data from the literature, is presented in support of a discussion of the relationship between the mineralogical and chemical content to abrasion/corrosion potential of environmental dust. Crushed quartz is the most representative material for dust abrasion testing, but not for total dust damage potential prediction. It is quartz (not laterite) together with the phenomena of 'Differential A Aeration Cell' corrosion/erosion-corrosion and possible thermochemical contributions, that is believed to be responsible for the extensive damage to military ordnance due to dust contamination experienced in Southeast Asia.

Summary (6 min read)

GENERAL

  • During the last decade, overhaul and replacement costs of both military and commercial machinery due to dust erosion (a form of mechanical abrasion caused by solid air-borne particles), possibly accelerated by dust induced corrosion, have been extreme.
  • The service life of helicopter gas turbine engines has been reduced in some cases to 10% of the norm during dusty terrain operation.
  • This failure of machinery to withstand the severe environments of some operational areas after haying survived current test specifications is sufficient indication that a more thorough knowledge of the actual sand and dirt environments and of dust abrasion/corrosion phenomena is essential to the development of representative test criteria and adequate methods of minimizing the problem.

PURPOSE AND SCOPE

  • Concentration of heavy minerals (those with specific gravity greater than that of Bromoform, 2.85) [Table I ], which contain most of the species which are harder than quartz (MOH hardness 7), does occur under dynamic conditions in nature such as on beaches and in stream beds.
  • This process of concentration could occur in windy, dusty areas of the world, such as deserts or freshly cleared, unprepared, lateritic areas such as experienced in Southeast Asia.
  • The initial hypothesis was that anomalous surficial concentrations of heavy minerals harder than quartz (possibly corundum, with MOH hardness 9; diamond, the hardest mineral on the MOH scale, having a hardness value of 10) could possibly be the cause of this excessive dust erosion experienced in Vietnam, and also other areas could possess the same potential.
  • The remaining purpose was three-fold: MINERAL 1. II.

BACKGROUND

  • Mechanical abrasion has been an area of extensive interest and investigation over the past few years, most recently with regard to the dust erosion phenomenon.
  • Holding specific variables constant (positions of vulnerable surfaces relative to the ground or dust), the abrasion process is believed to be governed by three parameters: particle and surface characteristics and the environment, both contact and ambient [Compton and Steward, 1968; Finnie, 1971].
  • The literature, including available pedological sources, indicates that quartz is both the most common and most erosive mineral species occurring naturally in dust [Goodwin, Sage, and Tilly, 1970].
  • There are inconsistencies contained in the literature.
  • A great deal remains to be learned about abrasion/corrosion and associated environmental relationships.

SAMPLE COLLECTION

  • Over 240 soil samples were collected by NWC with the help of personnel stationed around the world [Kuletz and Schafer, 1971] .
  • Top priority was given to the Southeast Asia area because of the United States involvement in Vietnam and the highly erosive problem commensurate with the region.
  • Desert soils were given high priority as well due to the associated high dust potential.
  • In general, assuming the samples to be representative of the region from which they were taken, a good statistically random world-wide sampling was carried out, since most areas have dry periods and thus some dust potential.

Yuma, Arizona

  • A quart size paint can with a polyethylene bag inner liner was used as the sample container.
  • Personnel were instructed simply to scoop some soil into the bag, seal with the accompanying wire, secure the top of the can with the fiberglass tape provided, and send to NWC, China Lake, California [Fig. 2].
  • Soils are heterogeneous (irregular and patchy) and it is quite possible to sample an anomalous patch vice an area characteristic of an isopedological region.
  • It is most important that the samples be representative, not merely for accurate mineralogical data, but to determine the source (parent rocks) and, through a knowledge of drainage basins (plus geological heuristics), to extrapolate to broader geographic regions.

SAMPLE PREPARATION

  • Prior to opening in the United States, the samples were subjected to a rigorous sterilization treatment in order to eliminate any possibility of bacteriological contamination.
  • Since 170-180°C (338-356°F) for not less than two hours is the recommended sterilization environment, the temperature within the ovens was maintained between 350-400°F and the samples were cooked overnight as a safety precaution.
  • This dry heat treatment method was employed because it was convenient, economical, and effective [Kuletz and Schafer, 1971].
  • Thus, upon receipt from NWC, mechanical dispersion (breakingup of the samples) was often necessary using a mortar and pestle before proceeding with the preparation technique.

Soil Sample Container

  • Each sample (100 g) was then given a preliminary separation using a U.S. Standard #18 mesh screen (1000 ^openings) to remove pieces of thermally altered polyethylene, pebbles, roots, twigs, and the like, which were not considered soil material.
  • Next, since many soil materials have constituents, such as organic matter, carbonates and sulfates of calcium and magnesium, and the hydrous oxides and hydroxides of iron and aluminum, which militate against their breakdown into individual mineral grains, a rather thorough washing procedure was employed.
  • The organics were removed first (oxidized to water soluble species) using "Hypochlorite" .
  • After washing by sedimentation and decantation, the sesquioxides were rendered soluble by the "Dithionite" treatment.
  • The chemistry of this treatment is illustrated by the following step-wise reactions:.

THIOSULFATE

  • Corundum, on the other hand, even though a sesquioxide, is highly resistant to hydration and acid attack [Cotton and Wilkinson, 1962].
  • After a final washing, heavy mineral separations were conducted [Krumbein and Petijohn, 1938] on the remaining sand size separates (the silt and clay sizes having been washed out, since particle sizes finer than 60^are generally of only long-term abrasive interest), using Bromoform with specific gravity 2.85.
  • In a few cases, such as with the Antarctic samples, a high percentage of rock fragments necessitated a heavy mineral separation of only the fine sand fraction (125-62 x).
  • Finally, the magnetic minerals were separated out with a small hand magnet and reported as a percentage of the heavy minerals.

SAMPLE ANALYSIS

  • As a part of the analysis, each original soil sample was assigned a standard (dry) color code according to the Munscll Soil Color Comparison Technique [Munsell Soil Color Charts, 1971].
  • Due to the sterilization treatment, the color of the samples is probably slightly lighter than the in situ color.

Microscopic Method

  • The heavy mineral separates were manually sieved and the 250-125 u and 125-63 H fractions were mounted on slides using "Lakeside 70" resin.
  • The slides are being studied by Professor R. S. Andrews for qualitative and quantitative mineralogical content and will be the subject of a later report.

X-Ray Diffraction Method

  • Since statistical sampling, mean crystallite dimension, and preferred orientation are not serious considerations, it was utilized in the present study as a corroborative qualitative refinement to the microscopic analysis.
  • That is, even though the amphibole and garnet groups are fairly distinctive under the microscope, it is more difficult to determine which sub-species is actually present.
  • The portion of the 250-125^and 125-63^heavy separate fractions remaining after the slide preparation were utilized in the x-ray analysis.
  • Assuming that the diffractometer is properly calibrated and aligned (and all instrumental factors affecting diffraction profiles at an optimum), in order for the angular positions to be reliable and for the peak intensities to be at a maximum (with little broadening), a number of precautions were observed in the preparation and mounting of the powder [Klug and Alexander, 1954].
  • Following sufficient grinding, the samples were then dry mounted on one of two aluminum sample holders [Fig. 3 ], depending on the amount of sample.

RESULTS OF MINERALOGICAL ANALYSIS

  • The mineralogical analyses performed in this study confirm what the literature and a knowledge of geology and weathering phenomena had suggested (i.e., the heavy mineral portion of the sand fraction of most world soil epipedons is very small) and/or indicate that better sampling techniques are required in order to ever observe anomalous heavy mineral concentrations.
  • More likely than not, the former is as accurate an asseveration as the latter.
  • Traces of heavy minerals harder than quartz (zircon, topaz, tourmaline, garnet, spinel, corundum, etc.) were observed in most of the samples, but most of the heavy separate constituents were softer (riebeckite, MOH hardness 4, being the most common species) [Table IV ].
  • Those samples containing a large amount of heavy minerals [Table III , locations 13b, 46, and 52] generally had a high volcanic glass and/or magnetic content, excepting the contact met amorphic beach Anaco, Venezuela 3.

Corrosion Aspect

  • In general, in an oxygenated atmosphere, the epipedons of world soils that have a dust potential are chemically inert regarding machinery; they do not react directly with the metal surfaces, considering that iron, stainless steel, aluminum, brass, bronze, and magnesium are the most common metals in use.
  • Extremely acid soils (pli 4.0 and lower) can cause rapid corrosion of most bare metals, but this degree of acidity is uncommon, being limited to histosols and soils made acidic by large accumulations of plant materials such as pine needles in a coniferous forest.
  • The only mechanism by which dust contributes to corrosion is of a galvanic nature in the form of a "Differential Aeration Cell" [Uhlig, 1967], assuming that the dust has adhesive and hygroscopic properties (e.g. -Kaolinite) .
  • The process is self-sustaining since the rust [FefOH^/FefOH) ,] is quite hygroscopic.
  • Surface pitting results, with a decrease in surface continuity and strength and an increase in abrasion potential due to the roughened surface.

Erosion-Corrosion Aspect

  • One of the most characteristic features of ordnance and support equipment is that they are mobile and possess moving parts.
  • Erosion-corrosion results when these protective shields are damaged or worn away, leaving a bare metal or alloy surface open to attack at a rapid rate [Tomashov, 1967].
  • Thus, using the following equation: a maxiumum rise in temperature of a mere 30°C was calculated.
  • E = 1/2-M-V, Further, once the dust particles have been ingested, the associated elevated temperatures and pressures characteristic of some equipment could cause accelerated failure due to the extreme nature of the environment alone or again, to the chemical alteration of the particles themselves.
  • Of more interest though are the clay minerals (kaolinite, montmorillinite, illite, etc. , all approximately MOH hardness 2) and the hydrous sesquioxides.

Regarding corrosion and erosion-corrosion

  • All will undergo endothermic dehydration in the 100-600°C temperature range.
  • In the case of the latter, the X-Fe"0" or tf-Al^O, thus formed will have MOH hardness approximately equal to 6 and 7, respectively.

World-Wide Dus t Abrasion/Corrosion Potential of Soil Orders

  • Generally speaking, most areas on earth have dry periods of some finite length, no matter how short.
  • Therefore, even though dry, desertlike regions are generally associated with the most adverse dust conditions, most areas possess some relative dust potential.
  • The aridosols and psammentic entisols of desert regions have been included in potential rank 1 since they are dry most of the year, have a high free-silica content, and represent approximately 20% of the surface of the earth [Foth and Turk, 1972] , more than any other soil order.
  • Dry portions of sandy beaches are also in this category.

SOUTHEAST ASIA PROBLEM

  • As stated in the introduction, the dust problem in Vietnam has been excessive.
  • The nature of the dust in both areas is most pertinent.
  • The occurrence of brake drums actually falling off [Kuletz and Schafer, 1971] is probably a manifestation of erosion-corrosion and is more prevalent in the wet vice the dry season (dust contamination still a contributing factor), with no thermochemical acceleration.

APPLICABILITY OF CURRENT DUST TEST SPECIFICATIONS

  • Quartz is definitely a representative test abrasive, but it is not satisfactory in regard to dust-induced corrosion prediction since naturally occurring clay minerals, for instance, are much more strongly adhesive and hygroscopic.
  • It is the belief of this author that the determination of a pedologically more realistic world-wide "Standard Dirt" for dust testing is unwarranted.
  • It is simply necessary to be cognizant of these areas of high dust abrasion/corrosion potential and to faithfully take the necessary precautions [i.e., periodic and regular fresh water washdowns, strict utilization of engine and nacelle covers, etc.).

SUMMARY

  • Investigation described in this report has provided additional knowledge as to the general character of world dust (particularly in the vicinity of military bases) .
  • It is the belief of this author that the heavy mineralogy of world soil epipedons is not a contributing factor regarding dust abrasion potential.
  • That quartz, although probably not a satisfactory indicator of corrosion due to dust ingestion, is the most common and most abrasive mineral constituent of dust, there is little doubt.
  • Lastly, a hypothesis is presented for the excessive dust erosion problem experienced in Vietnam.
  • Contrary to popular belief, the erosive species is believed not to be laterite (primarily a mixture of 1:1 clay minerals and the hydrous sesquioxides of iron and aluminum), but rather the relatively coarser, more angular, and more readily available quartz grains.

RECOMMENDATIONS

  • Concerning the current research effort being conducted by the Naval Weapons Center, it is felt that further acquisition of soil samples and associated dust environment characteristic investigation be terminated.
  • Aside from the collection of dust particles emitted from the tail pipes of jet engines in order to investigate the possibility of thermochemical alteration of these particles, all further research should be directed toward a prevention or minimization of the problem; i.e., the development of (1) materials with higher abrasion/corrosion THERMOMETERS OTTAWA SAND.

Oxalic Acid-Magnesium Ribbon Method

  • If carbonates have not been removed, treat with appropriate amount of hydrochloric acid [Brewer, 1969].
  • (This is best achieved by bending a stirring rod into a loop at one end and wrapping the Mg ribbon around the loop.
  • Stirring then introduces the ribbon and it is simply removed by removing the stirring rod.).

Remove sesquioxides

  • Separate into size fractions Mount portion of remaining separate on slides for microscopic analysis 8.
  • Finally, grind remaining portion to required specifications for x-ray analysis Fifty-four representative soil samples from all over the world were selected for heavy mineral analysis from those provided by the Naval Weapons Center, China Lake, California.
  • Data thus obtained, in conjunction with mineralogical , chemical, and abrasion investigation data from the literature, is presented in support of a discussion of_ the relationship between the mineralogical and chemical content to abrasion/corrosion potential of environmental dust.

Soil Preparation Apparatus

  • Crushed quartz is the most representative material for dust abrasion testing, but not for total dust damage potential prediction.
  • It is quartz (not laterite) , together with the phenomena of "Differential Aeration Cell" corrosion/erosioncorrosion and possible thermochemical contributions, that is believed to be responsible for the extensive damage to military ordnance due to dust contamination experienced in Southeast Asia.

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Citations
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01 Aug 1971
Abstract: : The report describes the techniques of sampling and analyses of worldwide soil samples. The results demonstrate that there are considerable differences between the actual sand and dirt environment and that specified in the Military specification. Field reports show that many military and military- support items did not perform as expected even though they had fulfilled the specification requirements. Therefore, the Military Specification on Sand and Dirt should be revised to conform to the actual environmental test conditions.

1 citations


References
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01 Jan 1954

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01 Jan 1938

742 citations



Journal ArticleDOI
01 Oct 1969-Wear
Abstract: Erosion caused by solid particles, such as sand grains, can occur under a variety of service situations but has received little disciplined study before about 1960. The parameters influencing the extent of the erosion are associated with the impact conditions and the properties of the impacting particles and target surface, Their effects are briefly reviewed and it is concluded that further work is required to elucidate the mechanisms of erosion and relate material properties to erosion resistance.

103 citations


Journal ArticleDOI
01 Jul 1966-Wear
Abstract: An investigation has been carried out to study the variation of the volume of wear of different metals with variation of the mean diameter of abrasive particles (35–710 μ), the load (0.5–6 kg), the velocity of abrasion (0.032–2.50 m/sec) and the length of abrasion path (1.5–6 m). The investigation was conducted under normal laboratory conditions of the environment. From the results of the experiments an empirical formula relating volume of wear to different parameters was derived. An attempt has been made to explain the various aspects of the relationship of volume of wear with the different parameters.

82 citations


Frequently Asked Questions (1)
Q1. What are the contributions mentioned in the paper "Mineralogy of selected world soil samples, with implications regarding the abrasion/ corrosion potential of environmental dust on military ordnance and a hypothesis for the southeast asia problem" ?

Fifty-four representative soil samples from all over the world were selected for heavy mineral analysis from those provided by the Naval Weapons Center, China Lake, California. Data thus obtained, in conjunction with mineralogical, chemical, and abrasion investigation data from the literature, is presented in support of a discussion of the relationship between the mineralogical and chemical content to abrasion/corrosion potential of environmental dust. Crushed quartz is the most representative material for dust abrasion testing, but not for total dust damage potential prediction.