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D1366-86 – Standard Test Method Technical Guide
This standard practice, designated ASTM D1366-86 (Reapproved 2019), provides a standardized framework for reporting the fineness characteristics of pigments. Originally approved in 1955, it is under the jurisdiction of ASTM Subcommittee D01.31 on Pigment Specifications and has been approved for use by agencies of the U.S. Department of Defense.
📐 Scope and Applicable Methods
ASTM D1366–86 is designed to apply to well-known methods for determining particle size characteristics in the subsieve range. These methods include microscopic, sedimentation, and turbidimetric techniques, and partially applies to absorption and permeability methods.
The standard explicitly excludes laminar (plate-like) pigments and composite pigments that exhibit a definite bimodal distribution from its scope.
⚠️ Exclusion Notice: Laminar plate-like pigments and composite pigments with a definite bimodal distribution are not considered within the scope of this practice.
⚙️ Key Parameters and Definitions
The practice requires the reporting of fineness characteristics in the following three specific parameters:
- Particle Size Parameter (SSD): The Specific Surface Diameter. It is defined as the diameter of a sphere having the specific surface characteristic of the pigment. The formula is
SSD = Σ(d³f) / Σ(d²f), where d is the mean class size (µm) and f is the frequency. - Coarseness Parameter (CP): The diameter, expressed in micrometres, below which 99.5 % of the pigment falls.
- Dispersion Parameter (DP): A parameter descriptive of the uniformity of the particle size distribution, calculated as the ratio of the micrometre size range within which 50 % of the pigment lies to the median particle size.
| 🟦 Parameter | 📐 Symbol | 📏 Definition / Formula |
|---|---|---|
| Particle Size Parameter | SSD | SSD = Σ(d³f) / Σ(d²f) |
| Coarseness Parameter | CP | Diameter (µm) below which 99.5% of the pigment falls. |
| Dispersion Parameter | DP | Ratio of the 50% size range to the median particle size. |
💡 Shape Factor Guidance: Report the SSD whether or not the effect of shape has been considered in the calculations. As the effect of shape is better understood, it may figure more prominently in future calculations, but in the meantime, it can be ignored.
📊 Methods and References
The following table summarizes the applicability of common analytical methods to this reporting practice.
| 🔬 Method Type | 🎯 Applicability | ⚡ Reference Standard |
|---|---|---|
| Optical Microscopy | Fully applicable | ASTM E20 (Withdrawn 1994) |
| Sedimentation | Fully applicable | — |
| Turbidimetric | Fully applicable | — |
| Absorption / Permeability | Partially applicable | — |
❓ Frequently Asked Questions
🔍 What does the acronym SSD stand for in ASTM D1366?
SSD stands for Specific Surface Diameter. It is the diameter of a sphere having the specific surface characteristic of the pigment.
💡 What is the Coarseness Parameter (CP)?
The CP is defined as the diameter, expressed in micrometres, below which 99.5% of the pigment falls.
⚡ What types of pigments are excluded from this practice?
Laminar (plate-like) pigments and composite pigments having a definite bimodal distribution are excluded from the scope of this practice.
📌 What is the purpose of the Dispersion Parameter (DP)?
The DP is a parameter descriptive of the uniformity of the particle size distribution, specifically the spread of particle sizes around the median.