Is silver iodide flammable? (A Comprehensive Overview)

This article will answer the following question: “Is silver iodide flammable?”. We will show relevant safety information about the compound and its proprieties.

Is silver iodide flammable?

No. Silver Iodide can’t catch fire. It’s an inorganic salt that cannot catch fire. No flames would appear on top of it if reaches high temperatures, and no heat.

What is silver iodide?

Silver iodide is an inorganic salt that has the formula AgI.

Naturally, the compound is mostly a bright and yellow solid, but also contains metallic silver impurities, which come from a photosensitive chemical reaction between silver iodide and sunlight. This ability makes the compound useful for photography purposes.

Silver Iodide is a crystalline material that can also be used for weather modification applications such as cloud seeding or anti-hail systems. 

What is iodine?

We can’t talk about silver iodide without depicting iodine itself.

Iodine is a chemical element from the periodic table.

It exists in many forms. We usually don’t encounter it in its pure form, only in salts or in a liquid solution. Commercially available forms of iodine are not pure forms of it. Silver iodide is an example.

Iodine is solid and has the formula I2 in its pure crystalline form, but it can also be a gas and present the same formula. It also exists as Iodide (I), iodate (IO3), some kinds of acid, and periodate anions (IO4, IO6−5, and others).

Iodine’s primary use is as a nutrient for us and livestock. We require Iodine in our bodies so it can synthesize thyroid hormones. The lack of it may lead us to disinvolve goiter and prejudice the central nervous system development in fetuses and infants.

Knowing that iodine deficiency is prejudicial, some governments request that manufacturers supplement table salt with a little iodine, but enough to prevent diseases.

Around 88% of all households worldwide use iodized salt, but it’s still a problem in some underdeveloped countries.

Some forms of salts considered gourmets, such as Himalayan Pink Salt, Kosher salt, Smoked salts, and others, may not have iodide added to their formulation.

If you mainly consume a salt that doesn’t contain iodine, consider speaking to a doctor about starting iodine supplementation.

Industrially, iodide anion is used as a catalyst in the production of acetic acid, and in organic chemistry to synthesize certain polymers.

Silver iodide properties

The compound is mostly a bright and yellow solid, but may contain metallic silver impurities (in a chemistry context, impurities don’t mean something bad or inferior, but simply something that diverges from purity).

Overall properties:

  • Chemical formula: AgI
  • Molar mass: 234.77 g/mol
  • Appearance: yellow, crystalline solid
  • Odor: odorless
  • Density: 5.675 g/cm3, solid
  • Melting point: 558 °C (1,036 °F; 831 K)
  • Boiling point: 1,506 °C (2,743 °F; 1,779 K)
  • Solubility in water: 3×10−7g/100mL (20 °C)
  • Solubility product (Ksp): 1.5 × 10−16
  • Magnetic susceptibility (χ): −80.0·10−6 cm3/mol

Silver iodide has a low water solubility, something common for silver salts.

Is iodine flammable? Is it a fire hazard?

No. Any pure form of iodine is not flammable.

Part of the reason that makes a fuel catch fire is the combustion reaction. When something reacts with oxygen, this reaction liberates energy from the fuel chemical bondings. 

The fire appears as a combination of heat and light.

This same reaction can also have another name: oxidation.

Although it’s not like any other oxidation, it’s a reaction that happens in a gas state. Even if the fuel is liquid, it gotta become airborne so the reaction can happen.

What makes it possible is heat, especially once the fire has already started.

But iodine is already an oxidation agent, it already acts chemically similar to oxygen. This means that a reaction between iodine and the air’s oxygen wouldn’t happen normally and that no energy would be generated by it.

Summarizing: iodine can’t catch fire because the chemical reaction that generates the flames can’t happen. Iodine and oxygen gas can’t react with each other under normal circumstances.

Iodine can still become airborne by reaching a vapor form if it’s heated. It doesn’t generate flames but unleashes toxic vapors.

Why iodine is used as an oxidizing agent?

An oxidant is a compound that can accept electrons from a donor.

Species like oxygen and iodine tend to receive electrons, that’s why they form anions instead of cations.

Oxidizing agents are species that can receive electrons hard because they have high reactivity.

These compounds often have good antimicrobial properties. This happens because microorganisms can suffer oxidation. Life forms are all carbon-based and are made from organic matter.

Likewise, fuel sources are made of organic matter, and can suffer combustion (oxidation). This means that fire, oxidation, fuels and oxidizing agents have a really close relation.

Silver iodide, although, doesn’t present such oxidizing properties. Silver iodide is considered an insoluble salt, poorly reactive, and can’t participate in a lot of chemical reactions.

What are the silver iodide hazards?

NFPA 704

Many government and non-governmental organizations establish systems, codes, and categories to express the overall hazards substances have.

The NFPA 704 is a standard maintained by the National Fire Protection Association, based in the U.S.

Also known as Safe Square and Fire Diamond, it uses a diamond with four divisions and colors. Each is rated on a scale of 0 to 4, known as Degrees of Hazard.

The four divisions have one color each. The red on top indicates flammability, the blue on the left indicates the level of health hazard, and the yellow on the right is for chemical reactivity. The white at the bottom contains codes for special hazards. 

This image summarizes the relevant hazards attributed to silver iodide. It does not present any health effects and is not known for being reactive, which happens for most iodine salts.

The health hazard is considered average. The compound can be irritating in case of skin or eye contact, ingestion, and inhalation, but only if it’s directly applied to someone.

Overall, the substance is not considered very hazardous.

Pictograms

There are also exist simpler kinds of hazard pictograms. Below we present some of them. Their purpose is simply to expose generally the kinds of hazards a certain substance can present.

Silver iodide pictograms

Silver iodide, although, only presents hazards to the environment.

It can be very toxic to aquatic life, presenting acute toxicity, but also can induce long-term hazards.

Silver iodide alone is not considered hazardous for any of the other conditions presented in the previous topic.

Is silver iodide flammable at all?

No. Silver iodide is a salt that can’t burn and won’t ignite. An attempt of burning it wouldn’t generate any flames, and the compound would not react with the air’s oxygen.

Anything can heat and have its temperature felt risen a lot, but not everything will burn because of that. Although, things can decompose if they reach too high a temperature.

There are three ways in which the thermal decomposition of organic matter happens: oxidation, pyrolysis, and evaporation/ vaporization.

All three happen at once during a fire. How fire will look depends on how these three events happen. 

For example, in a blue flame from an oven, oxidation is almost the only thing that happens, because the fuel is already vaporized (it is a gas), and its chemical composition is simple (the carbon chains are small), so the oxidation happens pretty quick.

In a fireplace, although, we can see many more yellow and red flames, smoke, fumes, and all kinds of byproducts from incomplete combustion. This happens because the chemical reactions are much more complex since the fuel has a very different composition.

When wood burns, the solid material is constantly being stimulated to a vapor-like state and suffers all kinds of breakdowns before finally reacting with oxygen (combustion). All these chemical reactions lead to many byproducts, many of which are toxic to us.

Silver iodide, although, doesn’t suffer a reaction with oxygen like that. A chemical reaction with oxygen gas and silver iodide wouldn’t be profitable for it, so AgI chooses to stay as a salt.

Most strong salts can’t participate in a combustion reaction, can’t suffer pyrolysis (a breakdown through intense heat), and can’t evaporate. Because of that, we can assure you that silver iodide won’t burn.

Conclusion

Silver iodide is an inorganic salt that doesn’t present any kind of flammability. It won’t burn, oxidize, or catch fire, and no flames would arise from it. Its melting point is also very high, around 558 °C (1,036 °F).

Frequently Asked Questions (FAQS): Is silver iodide flammable?

Why is silver iodide used for cloud seeding?

When silver iodide is used in supercooled clouds, at a temperature below the freezing point of water, the compound can form nuclei around the cloud, forcing the water droplets to evaporate.

This water vapor then attaches to the ice crystals, which quickly become droplets, hence condensing to allow raindrops to form.

is silver iodide harmful?

Silver iodide is considered a pollutant agent, hence a harmful substance to the environment. 

It is considered to be toxic to aquatic life, with long-lasting effects to it.

silver iodide is soluble in water?

Silver iodide is poorly soluble in water. It is considered an exception among salts, which tends to be highly soluble in water, especially when one of their forming species is a strong ion (meaning that it can solubilize easily, which is the case for chloride).

Citations

https://en.wikipedia.org/wiki/Silver_iodide

https://en.wikipedia.org/wiki/Photosensitivity
https://pubchem.ncbi.nlm.nih.gov/compound/6432717
https://en.wikipedia.org/wiki/Iodine
https://commons.wikimedia.org/wiki/File:GHS-pictogram-pollu.svg

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