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D1832-04 – Standard Test Method Technical Guide
The ASTM D1832-04 (Reapproved 2009) standard, also designated as TAPPI Method T 659 wd-85, outlines a precise test method for determining the peroxide number of petroleum wax. This value serves as a critical marker for quantifying the oxidizing constituents that contribute to wax degradation.
🔬 Scope and Principle
The test method covers the determination of the peroxide number, defined as the milliequivalents of constituents per 1000 g of wax that will oxidize potassium iodide. The procedure involves dissolving a wax sample in treated xylenes, acidifying it with a specialized acetic acid solution, adding potassium iodide, and titrating the liberated iodine with standardized sodium thiosulfate.
| 📐 Parameter | 🎯 Specification / Value |
|---|---|
| Measured Property | Peroxide Number (meq/1000g wax) |
| Reaction Vessel | 250 mL borosilicate glass iodine flask |
| Primary Standard | Potassium Dichromate (K₂Cr₂O₇) |
| Endpoint Indication | Color change of added starch solution |
⚠️ Safety Alert: Xylenes, used as the primary solvent, are highly flammable and produce a harmful vapor. The standard mandates that xylenes must be treated to remove oxidizing impurities, typically by passing them through an activated alumina column shortly prior to use.
🧪 Reagent Preparation and Methodology
Reagent chemicals must conform to ACS specifications. The acetic acid used must pass the ½-hour test for substances reducing K₂Cr₂O₇. The potassium iodide solution must be freshly prepared and discharged of any iodine color, requiring blanketing with nitrogen or carbon dioxide during standardization to prevent atmospheric oxidation.
| 🧪 Reagent | ⚡ Preparation Details |
|---|---|
| Acetic Acid Solution | 4 mL HCl (sp gr 1.19) mixed with 996 mL glacial acetic acid |
| Potassium Iodide Solution | 120 g KI dissolved in 100 mL of distilled water |
| 0.1 N K₂Cr₂O₇ Solution | 2.452 g of purified K₂Cr₂O₇ dissolved and diluted to 500 mL |
| 0.01 N K₂Cr₂O₇ Solution | 100 mL of 0.1 N K₂Cr₂O₇ diluted with water to 1000 mL |
📊 Significance and Interpretation
The magnitude of the peroxide number is an indication of the quantity of oxidizing constituents present. Deterioration of petroleum wax results in the formation of peroxides and other oxygen-carrying compounds. The peroxide number measures those compounds that will oxidize potassium iodide. It is a critical measure for quality control and assessing raw material stability. Values are reported in inch-pound units, with SI unit conversions provided for reference only.
💡 Technical Tip: To ensure accurate results, the glacial acetic acid must rigorously pass the ½-hour test for substances reducing K₂Cr₂O₇. Furthermore, the KI solution must be blanketed with an inert gas (N₂ or CO₂) during standardization to prevent atmospheric oxygen from oxidizing the iodide, which would yield an erroneously high peroxide number.
❓ Frequently Asked Questions
🔍 What does the peroxide number specifically measure in a petroleum wax sample?
It indicates the milliequivalents of oxidizing constituents (such as peroxides) present per 1000 g of wax that are capable of oxidizing potassium iodide under the specific test conditions.
💡 Why is it essential to treat the xylenes solvent before use?
Untreated xylenes may contain their own oxidizing impurities. Using untreated xylenes would result in a background reaction with potassium iodide, artificially inflating the measured peroxide number.
⚡ What is the purpose of blanketing the flask with nitrogen or carbon dioxide?
The inert gas blanket prevents atmospheric oxygen from dissolving into the solution and oxidizing the potassium iodide, which would lead to a false positive or an elevated peroxide determination.
📌 What specific equipment is required for this test?
The primary apparatus is a 250-mL borosilicate glass iodine flask with a glass stopper. This allows the reaction and titration to occur within a sealed environment free from atmospheric interference.