ブログ について Quartz Heaters Enhanced for Hightemperature Oxalic Acid Use

When industrial processes require handling high-concentration oxalic acid (10-20%) at temperatures reaching 80-100°C, quartz heating elements face a brutal survival test. What appears as simple chemical erosion is actually a sophisticated chelating attack that can rapidly degrade even chemically resistant materials.

Oxalic acid (H₂C₂O₄), as a dicarboxylic acid, possesses exceptional chelating power due to its molecular structure. At high temperatures, quartz (SiO₂) corrosion follows a dual mechanism:

• Proton-assisted hydrolysis: Hydrogen ions (H₃O⁺) from oxalic acid first attack quartz's siloxane bonds (Si-O-Si), converting them to reactive silanol groups (Si-OH).
• Chelation dissolution: Oxalate ions (C₂O₄²⁻) then bind with silicon atoms, forming stable five- or six-membered ring complexes—silicon oxalates. These water-soluble compounds systematically strip silicon atoms from the surface, exposing fresh quartz layers for continued attack.

Compared to non-chelating acids at equivalent concentrations, oxalic acid demonstrates significantly higher destructive power due to its lower activation energy.

Experimental data reveals that high-purity quartz corrodes at 0.0015-0.003 mm/h in 15% oxalic acid at 95°C. This means a standard 2.0 mm-thick quartz sheath could develop perforation risks after approximately 1,000 hours of continuous operation—a concerning timeline for 24/7 industrial processes that demands rigorous lifespan management.

Gas-induced pitting: Thermal decomposition of oxalic acid generates CO₂ bubbles that adhere to quartz surfaces, creating localized hot spots and chemical gradients that accelerate pitting corrosion.

The rare earth paradox: In rare earth extraction processes, RE³⁺ ions present a double-edged sword—they may catalyze oxalic acid decomposition (increasing corrosion) while simultaneously forming insoluble rare earth oxalates that deposit as scale. While this scale can temporarily protect underlying quartz, it severely reduces heat transfer efficiency, potentially causing dangerous overheating.

To maintain precise temperature control (±2°C) while extending equipment life, consider these strategies:

• Optimal wall thickness: While thicker walls (2.0-2.5 mm) prolong lifespan, they reduce heat transfer efficiency by up to 32% compared to thinner designs. Prioritize scheduled replacement over excessive thickening.
• Precision filtration: Install 5-10 µm filters to remove suspended crystals.
• Chemical maintenance: Regular cleaning with 5-10% hydrochloric acid or fresh oxalic acid removes surface deposits.
• Surface pretreatment: High-temperature oxalic acid exposure creates a protective silicon oxalate film that slows initial corrosion.
• Flow optimization: Maintain surface velocities exceeding 1 m/s to disrupt boundary layers and remove bubbles/impurities.

For extreme environments like rare earth processing where scaling proves uncontrollable, alternative materials like PTFE-lined systems, titanium, or silicon carbide may prove more viable than quartz.