Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D1648-86 – Standard Test Method Technical Guide
📜 Scope and Chemical Composition
ASTM D1648 – 86 (Reapproved 2020) provides the standard specification for basic lead silicochromate pigment, a corrosion-inhibiting pigment commonly utilized in protective coatings. This specification defines two distinct types of this pigment based on particle size distribution and sets forth the requirements for their chemical composition and physical properties. Both types consist of a silica core coated with lead silicates and lead chromates. The values stated in SI units are regarded as the standard, while values in parentheses are provided for information only.
⚙️ Particle Size Grades and Property Requirements
Particle size is the primary differentiator between the two pigment types. Type 1 is characterized by major amounts of particles in the 6.5 to 28 µm range, with a maximum Specific Surface Diameter (SSD) of 8.5 µm. Type 2 is a fine grade where the maximum size is essentially below 1.0 to 2.5 µm, with a maximum SSD of 2.0 µm. The following table summarizes the key physical requirements for both grades.
| 🟦 Property | 📏 Type 1 Requirements | 📐 Type 2 Requirements |
|---|---|---|
| Major Particle Size Range | 6.5 – 28 µm | Essentially below 1.0 – 2.5 µm |
| Coarse Particles (Retained on 45-µm No. 325 Sieve) | Less than 0.3 % | Less than 0.1 % |
| Maximum Specific Surface Diameter (SSD) | 8.5 µm | 2.0 µm |
| Mass Color and Character of Tint | Shall match an agreed-upon reference sample | |
| Oil Absorption | Equal within agreed tolerances to a reference sample | |
🔬 Important Note on Reference Standards: The mass color, character of tint obtained by mixing with a white pigment, and oil absorption of the pigment must conform to a mutually agreed-upon reference sample between the purchaser and the seller to ensure batch consistency and performance.
🧪 Sampling Procedures and Test Methods
Two samples must be taken at random from different packages for each lot, batch, or day’s pack. When no markings distinguishing units of production appear, samples shall be taken from different packages in the ratio of two samples for each 5000 kg (10,000 lb), with a minimum of two samples taken for shipments under 10,000 lb. At the option of the purchaser, the samples may be tested separately or blended into a composite sample for testing.
Testing must be performed according to the following ASTM methods, unless alternative procedures are mutually agreed upon by the purchaser and the seller:
- Chemical Analysis: Conducted in accordance with Test Methods D1844.
- Ignition Loss: Determined using Test Methods D1208 at an ignition temperature of 450 to 550°C.
- Particle Size by Microscopy: Determined following Practice E20.
⚡ Tighter Tolerances: Where closer control within a specific grade is required, the fineness requirements (e.g., sieve retention or SSD limits) shall be as agreed upon by the purchaser and the seller per Section 3.4.3 of the standard.
❓ Frequently Asked Questions
🔍 What are the specific particle size parameters for Type 1 pigment?
Type 1 is a coarser grade characterized by major amounts of particles in the 6.5 to 28 µm range. It must have less than 0.3% coarse particles retained on a 45-µm (No. 325) sieve and a maximum Specific Surface Diameter (SSD) of 8.5 µm.
💡 How are sampling quantities determined for a large shipment without unit markings?
Samples must be taken from different packages in the ratio of two samples for every 5000 kg (10,000 lb) of pigment in the shipment. For a 20,000 kg shipment, this requires eight individual samples taken at random.
⚡ Which ASTM method is specified for the chemical analysis of this pigment?
The standard explicitly requires chemical analysis to be conducted in accordance with ASTM D1844, which details the Test Methods for Chemical Analysis of Basic Lead Silicochromate.
📌 What distinguishes Type 2 Basic Lead Silicochromate from Type 1?
Type 2 is a fine-grade pigment where the maximum particle size is essentially below 1.0 to 2.5 µm. It has stricter limits on coarse particles, with less than 0.1% retained on a 45-µm sieve, and a significantly lower maximum Specific Surface Diameter (SSD) of 2.0 µm.