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D3906-19 – Standard Test Method Technical Guide
📜 Introduction and Scope
ASTM D3906-19 describes a test method for determining the relative X-ray diffraction intensities of faujasite-type zeolite-containing materials. It covers synthetic Y and X zeolites, their modifications such as cation exchange forms, dealuminized, decationated, and ultrastable variants. These zeolites exhibit cubic symmetry with unit cell parameters typically between 24.2 and 25.0 Å (2.42 and 2.50 nm). Samples include zeolite preparations and catalysts or adsorbents containing these zeolites.
The XRD intensity is defined as the integral intensity — either the area of counts under the peak or the product of peak height and width.
| 🟦 Parameter | 📏 Specification |
|---|---|
| Crystal Symmetry | Cubic |
| Unit Cell Parameter | 24.2 to 25.0 Å |
| Reference Standard | NaY (or modified Y/X as secondary standard) |
⚙️ Test Procedure and Calculations
The XRD patterns of the sample and reference NaY are obtained under identical conditions. For sufficiently strong patterns, intensities of eight peaks are compared to calculate % XRD intensity/NaY. For samples with lower zeolite content, the intensity of the (533) peak at 23.5° using Cu Kα radiation is compared. The ratio, expressed as a percentage, is labeled “% XRD intensity/NaY.”
⚠️ Requires that the zeolite in the sample be the same as the reference and that X-ray absorption be identical for both zeolite and non-zeolite phases to equate the ratio to percent zeolite.
📊 Importance in Catalysis and Adsorption
Y and X zeolites are critical in fluid catalytic cracking (FCC), hydrocracking, and adsorption applications such as desiccation, sulfur compound removal, and air separation. This X-ray procedure provides a number related to percent zeolite, widely used in technology, research, and specification compliance.
❓ Frequently Asked Questions
🔍 What is the scope of D3906-19?
It covers determination of relative XRD intensities for faujasite-type zeolites, including Y, X, and their modified forms.
💡 How is XRD intensity defined?
As integral intensity — either the area under the peak or the product of peak height and width.
⚡ When does % XRD intensity/NaY equal percent zeolite?
When the sample zeolite matches the reference and X-ray absorption is uniform across zeolite and non-zeolite components.
📌 Which peak is used for low zeolite content?
The (533) peak at 23.5° with Cu Kα radiation is used for such samples.