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D3926-05 – Standard Test Method Technical Guide
ASTM D3926-05 (Reapproved 2019) establishes standardized procedures for determining the weight percent of solids in aqueous slurries of titanium dioxide pigments. These test methods are essential for quality control in pigment manufacturing and application, providing a quick and reliable measurement of total solids content, which includes the pigment and all nonvolatile additives.
🔍 Scope and Significance of D3926-05
These test methods cover three distinct techniques for measuring solids content: Method A (Gravity-Convection Oven), Method B (Infrared Radiation Moisture Analyzer), and Method C (Microwave Drying System). All values stated in SI units are regarded as standard. The methods are designed to be a quick and reliable procedure for aqueous slurries of titanium dioxide pigments. It is the responsibility of the user to establish appropriate safety, health, and environmental practices prior to use.
The standard notes that measured percent solids include the pigment as well as nonvolatile additives. Care must be taken with highly treated TiO₂ products, as prolonged drying in the oven method or excessive heat in the infrared method can affect the aluminum and silica oxide treatments, potentially altering accuracy.
⚙️ The Three Standardized Test Methods
Method A (Oven): Slurry is weighed by difference into a tared aluminum foil dish, dried at 105°C ± 2°C for 60 to 65 minutes, cooled in a desiccator, and weighed gravimetrically. A high-velocity forced-draft oven is not suitable.
Method B (Infrared): Slurry is dried under infrared lamps for a specified time and temperature. Results are obtained directly from the unit’s display panel. Selection of time and temperature is critical for accuracy.
Method C (Microwave): A 2 to 4 g sample of slurry is placed between two glass fiber pads and dried in a microwave drying system. Results are obtained directly from the display panel. Overdrying is not a concern due to the short test duration.
| 🟦 Feature | 📐 Method A (Oven) | 📐 Method B (Infrared) | 📐 Method C (Microwave) |
|---|---|---|---|
| Sample Vessel | Aluminum foil dish | Instrument sample pan | Glass fiber pads |
| Sample Size | Weighed by difference | As per instrument | 2 to 4 g |
| Drying Conditions | 105 ± 2 °C / 60–65 min | IR lamps / Specified time/temp | Microwave / Short duration |
| Results | Gravimetric calculation | Direct from display panel | Direct from display panel |
⚠️ Critical Caution for Oven Method: The oven must be a gravity-convection type or a low-velocity forced draft. A high-velocity, forced-draft air change oven of the type used for baking finishes is not suitable. Oven temperature must be constantly monitored to ensure the 105 ± 2 °C tolerance is maintained.
📊 Key Technical Specifications and Apparatus
Compliance with D3926 requires specific laboratory apparatus. The analytical balance must be accurate to 0.1 mg with a 1-g optical readout range for fast weighing. The standard mandates that the accuracy of this optical scale be checked periodically using a known 1-g weight, and the zero adjustment must be checked at least every hour routinely.
| 🟦 Apparatus | 🎯 Specification |
|---|---|
| Laboratory Oven | 105 ± 2 °C; Gravity-convection or low-velocity forced draft only |
| Analytical Balance | Accuracy to 0.1 mg; 1 g optical readout range |
| Desiccator | Required for cooling oven-dried samples before weighing |
| Reagent Water | Per ASTM Specification D1193 |
💡 Technical Tip for Highly Treated TiO₂: For Method A, consider the solids dry after heating at 105 °C for exactly 60 to 65 minutes. Prolonged heating can alter the aluminum and silica oxide treatments. For Method B, careful selection of drying time and temperature is critical to avoid similar effects.
❓ Frequently Asked Questions
🔍 What is the purpose of ASTM D3926-05?
It specifies standard test methods for determining the weight percent of solids (pigment plus nonvolatile additives) in aqueous slurries of titanium dioxide pigments for quality control purposes.
💡 What are the three methods included in this standard?
The standard covers Method A (Gravity-Convection Oven), Method B (Infrared Radiation Moisture Analyzer), and Method C (Microwave Drying System).
⚡ Which oven type is explicitly prohibited for Method A?
An oven with a high-velocity, forced-draft air change, commonly used for baking finishes, is not suitable. Only gravity-convection or low-velocity forced draft ovens meeting the 105 ± 2 °C tolerance are permitted.
📌 Why must the balance’s optical scale be routinely checked?
The standard requires periodic accuracy checks using a known 1-g weight and hourly zero adjustments to maintain the required 0.1 mg accuracy for precise gravimetric results.