What is Antimony trioxide?
Antimony trioxide (Sb₂O₃) has a molecular weight of 291.5, a density of 5.1 g/cm³, a melting point of 656°C, and a boiling point of 1425°C. It can sublime under high vacuum at 400°C. Antimony trioxide is a white crystalline powder, industrially known as antimony white. It is slightly soluble in water, dilute sulfuric acid, and dilute nitric acid, but soluble in hydrochloric acid, concentrated sulfuric acid, strong alkalis, and tartaric acid solutions.
High-quality antimony trioxide itself has low toxicity. However, inferior grades may exhibit slight toxicity, primarily due to excessive arsenic trioxide (As₂O₃) content. Exposure may cause symptoms such as itching of the hands and arms among operators.
The clarification mechanism of antimony trioxide is similar to that of arsenic trioxide. It is a versatile clarifying agent with a relatively high density. It transitions from a higher oxide to a lower oxide at a relatively low temperature and performs particularly well in glasses containing high amounts of lead oxide (PbO) or barium oxide (BaO).
The Usage of Antimony trioxide
Due to its volatility, Sb₂O₃ is not used alone as a clarifying agent. It is typically combined with oxidizers such as sodium nitrate (NaNO₃) or potassium nitrate (KNO₃).
In soda-lime silicate glass, a combination of 0.18% to 0.5% Sb₂O₃ with 4 to 8 times its weight of sodium nitrate is used as a clarifying agent. At lower temperatures, it reacts with oxygen released from the decomposition of sodium nitrate to form antimony pentoxide (Sb₂O₅). At slightly higher temperatures, Sb₂O₅ decomposes, releasing oxygen. This highly active oxygen diffuses into gas bubbles of various types within the glass melt, causing the bubbles to expand in volume and rise out of the melt, thereby promoting glass clarification. The chemical reactions are as follows:
2Sb₂O₃ + O₂ (from NaNO₃) → 2Sb₂O₅
2Sb₂O₅ → 2Sb₂O₃ + O₂]
In soda-lime silicate glass, if 0.2% antimony trioxide is used together with 0.2% arsenic trioxide (As₂O₃), the clarification effect is enhanced. This is because Sb₂O₅ releases oxygen at lower temperatures, while arsenic pentoxide (As₂O₅) releases oxygen at higher temperatures. This ensures the clarifying agent is active throughout the entire melting temperature range, helping to prevent the formation of secondary bubbles. However, when the Sb₂O₃/As₂O₃ combination is used in lead glass, excessive amounts can easily form arsenate and antimonate crystals, causing opacification in the glass.
For the production of solar patterned glass, the chemical composition and physical properties of the antimony oxide powder used must meet or exceed the requirements for Grade Sb₂O₃ 99.50 specified in the Chinese National Standard GB/T 4062-2013.
An important consideration when using antimony trioxide is that glass containing Sb₂O₃ may develop a faint yellowish tint upon exposure to ultraviolet light or sunlight. (In contrast, glass containing arsenic trioxide may turn dark brown).
Why Does Antimony Trioxide Need Ultrafine Grinding?
Ultrafine grinding of antimony trioxide is essential to optimize its flame retardant performance. The finer the particle size, the larger the surface area, which improves the dispersion and reactivity in polymer and textile matrices. Typical quality specifications for antimony trioxide powders include high purity (~99.8%), whiteness (~96.5%), and an average particle size below 4 microns for effective application. Achieving consistent ultrafine particle size distribution enhances synergistic fire resistance effects when combined with halogenated flame retardants, reducing the amount of additive needed and improving cost efficiency and performance.
Why Use Air Jet milling for Antimony Trioxide?
Luft Strahlfräsen (Air jet milling) is especially suitable for antimony trioxide pulverization due to several technical advantages:
It enables dry processing, which reduces contamination and environmental concerns related to wet milling.
The process allows simultaneous grinding and classification, achieving precise particle size distribution.
Air jet mills can reach ultrafine particle sizes efficiently, suited for the <5 micron requirements typical in flame retardant applications.
The technology generates less heat during pulverization, reducing the risk of thermal degradation or changes to product chemistry.
Its closed-circuit system improves safety when handling potentially toxic powders like antimony trioxide dust.
Critical Considerations in Antimony Trioxide Air jet milling
When milling antimony trioxide in an air jet mill, attention should be given to:
Dust control and worker safety: Antimony trioxide is suspected of carcinogenicity, so effective containment and dust extraction systems are paramount.
Particle size control: Precise classifier adjustments ensure the product meets specifications, typically targeting a narrow size range around 2-3 microns.
Feedstock quality: Consistent feed size and moisture content optimize milling efficiency and product uniformity.
Wear resistance: The abrasive nature of mineral powders requires durable grinding and classification components to maintain performance.
Process parameters: Optimizing airflow velocity, classifier speed, and grinding pressure balances throughput and ultrafine fineness.
EPIC Pulvermaschinen
EPIC-Pulver Machinery’s air jet mill systems are engineered to meet the demanding standards of the antimony trioxide industry. Our airflow mills can achieve:
Particle sizes consistently in the 1-3 micron range with narrow distribution for superior flame retardant synergy.
High throughput capacities with energy-efficient grinding technology.
Robust dust control and safety systems ensuring compliance with occupational health regulations.
Wear-resistant internal components optimized for abrasive mineral powders.
Customizable process controls allowing customers to optimize parameters for specific product requirements.
Customers have seen improved product quality, reduced additive dosage in end applications, and overall processing cost savings using EPIC’s air jet mills for antimony trioxide powder production.