ASTM D6845-22 PDF

Full title and description

Standard Test Method for Silica, Precipitated, Hydrated—CTAB (Cetyltrimethylammonium Bromide) Surface Area. Designation: ASTM D6845-22. This method describes a CTAB (cetyltrimethylammonium bromide) adsorption/turbidity titration procedure to determine the specific surface area of precipitated hydrated silicas used for rubber and related applications. The reported surface area excludes area contained in micropores too small to admit CTAB molecules and therefore reflects the surface available for interaction with rubber macromolecules.

Abstract

ASTM D6845-22 defines a laboratory test for measuring the CTAB-accessible specific surface area (reported in m2/g) of precipitated hydrated silicas. The method uses CTAB adsorption combined with a turbidity titration end point to quantify surface area that is relevant to rubber compounding and other applications where the accessible external surface controls performance. The procedure includes specimen preparation, reagent and apparatus requirements, stepwise test procedure, calculation of results, precision statements, and applicability/limitations (not intended for microporous silicas that exclude the CTAB molecule).

General information

• Status: Active
• Publication date: November 1, 2022
• Publisher: ASTM International
• ICS / categories: 71.100.55 (Silicones / silica materials)
• Edition / version: D6845-22 (2022)
• Number of pages: 4

Scope

This test method covers measurement of the specific surface area of precipitated (hydrated) silicas excepting area contained in micropores too small to admit hexadecyltrimethylammonium bromide (CTAB) molecules. It is intended primarily for characterization of rubber-grade precipitated silicas and other hydrated silicas where CTAB-accessible surface is the relevant parameter. SI units are the standard. The standard notes safety responsibilities for users and states its development in accordance with internationally recognized standardization principles.

Key topics and requirements

• Principle: adsorption of CTAB onto silica surface and endpoint determination by turbidity titration.
• Reagents and materials: CTAB reagent preparation, solvents, and standards for calibration.
• Apparatus: turbidity/turbidimeter or comparable photometric equipment, titration setup, sample drying/conditioning equipment.
• Sample preparation: drying, dispersing, and handling to ensure representative test portions.
• Procedure: step-by-step titration and measurement sequence, including blank and control determinations.
• Calculation and reporting: conversion of adsorption/turbidity data to specific surface area (m2/g) and required report elements.
• Precision and bias: statements on repeatability/reproducibility and known method limitations.
• Limitations: does not measure micropore surface inaccessible to CTAB; not a full replacement for gas-adsorption BET where micropore area is required.

Typical use and users

Primary users are quality control and R&D laboratories in precipitated silica manufacturers, rubber and tyre compounders, filler suppliers, and materials testing labs. Typical uses include acceptance testing, batch-to-batch quality control, specification compliance for rubber-grade silicas, formulation work for elastomers, and comparative characterization alongside other surface-area methods.

Related standards

ASTM D6845-22 revises and replaces earlier edition D6845-20. It is referenced by other ASTM standards concerned with rubber and filler testing. For complementary surface-area methods, practitioners commonly compare CTAB results with gas-adsorption (BET) methods such as ISO 9277. Users should review the normative references listed in the full ASTM text for cross-references and cited procedural standards.

Keywords

CTAB, cetyltrimethylammonium bromide, precipitated silica, hydrated silica, surface area, CTAB surface area, turbidity titration, rubber-grade silica, specific surface area, m2/g.

FAQ

Q: What is this standard?

A: ASTM D6845-22 is a standard test method that specifies how to measure the CTAB-accessible specific surface area of precipitated hydrated silica using CTAB adsorption and turbidity titration.

Q: What does it cover?

A: It covers measurement of the surface area accessible to the relatively large CTAB molecule, excluding micropore area too small for CTAB, and provides procedure, apparatus, reagents, calculations, and precision information for rubber-grade silicas.

Q: Who typically uses it?

A: Quality control and R&D labs at silica suppliers, rubber and tyre manufacturers, compounders, and materials testing laboratories use this method to characterize filler surface properties relevant to elastomer formulations.

Q: Is it current or superseded?

A: The current edition is D6845-22 (published November 1, 2022) and it supersedes D6845-20. Status is active.

Q: Is it part of a series?

A: It is a stand‑alone ASTM test method but is commonly used alongside other ASTM and international surface-area and filler characterization standards (for example, gas-adsorption/BET methods) and is referenced by related ASTM standards in rubber and filler testing.

Q: What are the key keywords?

A: CTAB, cetyltrimethylammonium bromide, precipitated silica, hydrated silica, CTAB surface area, turbidity titration, specific surface area, rubber-grade silica.