WARNING
Refer to the supplier's Safety Data Sheet (SDS) or equivalent for health hazard data. Exposure
Refer to the supplier's Safety Data Sheet (SDS) or equivalent for health hazard data. Exposure to silica flour (ground quartz) can cause silicosis; other material may cause adverse health effects
a.
The main mineral constituents of dust derived from soils and sediments are quartz, feldspars, calcite
The main mineral constituents of dust derived from soil and sediments are quartz, feldspar, calcite (carbonate), dolomite, micas, chlorite, and a variety of heavy oxides and amorphous inorganic material and organic matter. Dust can also include mixed layer clays consisting of kaolinite, illite, and smectite. In arid regions, soluble salts are common components of dust and include calcite, gypsum, and halite, as well as the mineral opal and the clay palygorskite. In some regions, the dust-related problems with materiel such as fouling, interference of moving parts, increased electrical conductivity, and corrosion can be more pronounced if there are more reactive constituents in the natural dust. Using a dust material with a chemical composition close to that of the dust in the region being considered may give a realistic simulation of some of these effects on materiel in the blowing dust test. For example, mixed layer clays swell upon contact with fluids such as lubricants, and can cause parts to stick or seize. Carbonates can enhance the formation of scale on metal alloys and can cause shorting in electrical assemblies. These compounds can also cause corrosion in humid conditions. Other components such as soluble salts will result in both corrosion and abrasion resulting in electrical and physical malfunctions.
b. For tests to realistically represent these potential failure modes, natural dust from the region should be used, or a test dust that contains a close approximation of the components in the natural dust. When it may not be practical to obtain the natural material from the region of interest, the material closest in composition should be used for the test. These test dust materials should be chosen with deliberate consideration of these reactive properties as much as possible. If necessary, compounds can be mixed in with the more inert dust materials to achieve the necessary dust composition and a more realistic test outcome. Although the silica (quartz) content is generally the primary component of natural dust, it is usually less than 80 % of the sample mass. Silica is chemically non-reactive, but it can be abrasive and will cause wear and erosion of surfaces. Some regional dust may also contain a greater amount of clay-sized particles.
c.
Particle size distribution must also be considered. A particle size distribution of 100 percent by weight less than 150 µm, with a median diameter (50 percent by weight) of 20 ±5 µm has been used in prior testing and is recommended.
d. If dust from a region of interest or its analog is not available, a blowing dust test procedure may be conducted using the following dust compositions, by weight. The dust compositions are given in decreasing order of similarity to real world conditions.
(1) Red china clay has been used as a surrogate for dust commonly found worldwide and contains:
| CaCO3, MgCO3, MgO, TiO2, etc. | 5 percent |
| Ferric oxide (Fe2O3) | 10 ±5 percent |
| Aluminum oxide (Al2O3) | 20 ±10 percent |
| Silicon dioxide (SiO2) | remaining percentage (50 to 80 %) |
(2) Silica flour, although not truly representative of dust found in the natural environment (except for particle size), has been widely used in dust testing and contains 97 to 99 percent (by weight) silicon dioxide. A 140 mesh Silica Flour (about 2 percent retained on a 140 mesh (106 microns) sieve) has a particle size distribution of 100 percent by weight less than 150 \mu m, with a median diameter (50 percent by weight) of 20 \pm 5 \mu m. ASTM D185-07, Standard Test Methods for Coarse Particles in Pigments, provides a method for particle size measurements by sieve analysis. If particle size measurements are carried out using techniques other than sieve analysis, it must be demonstrated that the same results are produced. This type of dust is readily available and should produce comparable
MIL-STD-810H
METHOD 510.7
results to prior tests. Silica dust (ground quartz) has been found to provide adequate effects with regard to penetration or binding and abrasion. This is an inert compound that does not produce the effects that result from exposure to natural dust containing reactive components.
- (3) Other materials used for dust testing are less desirable and may have a particle size distribution that falls below that in paragraph 4.1.1.4c above. However, use unique dust compositions if the compositions are known. Ensure material to be used is appropriate for the intended purpose and regions of the world being simulated; e.g., for dust penetration, ensure the particle sizes are no larger than those identified for the region. These materials for dust testing include talcum powder (talc) (hydrated magnesium silicate), fire extinguisher powder (F.E.) (composed mainly of sodium or potassium hydrogen carbonate with a small amount of magnesium stearate bonded to the surface of the particles in order to assist free-running and prevent clogging. F.E. must be used in dry conditions to prevent corrosive reaction and formation of new chemicals (paragraph 6.1, reference c)), quartz (a constituent of many dusts occurring in nature), and undecomposed feldspar and olivine (that have similar properties to quartz).