At What Temperature Does Salt Melt?

Pure table salt, sodium chloride (NaCl), melts at about 801 °C (1,474 °F). That is hot enough to glow a dull red and far beyond the reach of any kitchen stove or backyard grill. But “salt” is a much bigger category than the stuff in your shaker, and different salts melt at wildly different temperatures, from well below zero to over a thousand degrees Celsius. Understanding why reveals something useful about how matter holds itself together and why engineers deliberately melt salts for applications ranging from solar power plants to next-generation nuclear reactors.

Why Table Salt Needs So Much Heat

Sodium chloride is an ionic compound, meaning it is built from positively charged sodium ions and negatively charged chloride ions locked into a rigid crystal lattice. Each ion is surrounded by neighbors of the opposite charge, and the electrostatic attraction between them is strong. To melt the crystal, you have to pump in enough energy to break those ions free from their fixed positions so they can flow past one another as a liquid. That takes a lot of thermal energy, which is why the melting point sits at 801 °C.

The size of the ions matters. Smaller ions pack more charge into a tighter space, creating a higher surface charge density and stronger electrostatic pull between neighbors. That is part of why sodium chloride, with its relatively small sodium and chloride ions, melts at a higher temperature than salts built from larger ions like cesium or rubidium.¹ Conversely, salts made from very large, irregularly shaped ions can have such weak lattice forces that they remain liquid at room temperature. These “ionic liquids” are technically molten salts, just ones that happen to be molten at comfortable temperatures.

A Quick Tour of Other Common Salts

Table salt gets most of the attention, but the word “salt” covers any compound formed by pairing a positively charged ion with a negatively charged one. Their melting points span an enormous range. Calcium chloride, which is often spread on icy roads, melts at roughly 772 °C. Potassium chloride, widely used as a salt substitute for people watching their sodium intake, melts at about 770 °C. Magnesium chloride comes in a bit lower, around 714 °C. These are all in the same ballpark as NaCl because the ions are similar in size and charge.

Move to salts with different anions and the numbers shift. Sodium nitrate melts at about 308 °C, and potassium nitrate at around 334 °C, both far lower than the chlorides. Sodium hydroxide (lye) melts near 318 °C. Jump to fluoride salts and some melt even higher than NaCl. Lithium fluoride, for example, melts at roughly 845 °C. The pattern holds: the smaller and more tightly packed the ions, the more energy it takes to break the lattice apart.

Melting Salt Versus Dissolving Salt

One of the most common mix-ups is confusing melting with dissolving. When you stir table salt into a glass of water, the crystal lattice breaks apart and the ions disperse into the liquid, but the salt has not melted. The water molecules pry the ions away from each other by surrounding them with a shell of polar molecules, a process that happens at room temperature. True melting, by contrast, means the solid salt itself becomes a liquid without any solvent involved, and that requires the extreme heat described above.

The confusion is understandable because both processes result in the crystal disappearing. But from a practical standpoint, the distinction matters. When you dissolve salt in water, the resulting solution has entirely different properties from molten salt. A saltwater brine conducts electricity modestly and freezes below 0 °C. Molten sodium chloride at 801 °C is a clear, dense liquid that conducts electricity aggressively and is used in industrial electrochemistry to produce pure sodium metal and chlorine gas.

Why Salt Lowers the Freezing Point of Water

Salt’s most familiar everyday job is melting ice on roads and sidewalks, and this has nothing to do with the 801 °C melting point. When you throw rock salt onto ice, the salt dissolves into the thin film of liquid water on the ice surface. The dissolved ions interfere with the water molecules’ ability to re-form an orderly ice crystal, which means the mixture stays liquid at temperatures that would normally freeze pure water. This is freezing-point depression, and it works with any dissolved substance, but salt is cheap and effective.

There is a limit, though. A salt-water mixture can only stay liquid down to about −21 °C (roughly −6 °F). That temperature is the eutectic point of the NaCl-water system, and below it, no liquid exists at all. Instead, the mixture solidifies into ice plus a crystalline salt-water compound called hydrohalite.² This is why road salt becomes useless during the coldest stretches of winter in places like Minnesota or northern Canada. At −25 °C, salt on the road does essentially nothing. Municipalities in those areas often switch to calcium chloride or magnesium chloride brines, which have eutectic points closer to −50 °C, or use sand for traction instead.

Even above the eutectic point, road salt does not instantly create a puddle. Research with frozen saltwater samples showed that between about −21 °C and −5 °C, ice surfaces were only partially wetted, with liquid patches or channels covering anywhere from roughly 11% to 85% of the surface depending on salt concentration and temperature.² So road salt’s effectiveness is not an on-off switch. It works best closer to 0 °C and becomes progressively less helpful as temperatures drop.

Eutectic Mixtures and the Art of Lowering Melting Points

If you blend two or more salts together, the mixture often melts at a temperature lower than either pure salt would on its own. The lowest possible melting point for a given combination is called the eutectic temperature, and finding the right blends is a major area of research for engineers who want salts that flow at relatively manageable temperatures.

Two factors help push the eutectic temperature down. First, using ions of very different sizes introduces disorder into the crystal lattice, making it harder for the mixture to freeze into a single neat structure. Second, adding more components increases the overall configurational disorder. A binary blend of two salts has a lower eutectic temperature than either pure salt, a ternary blend of three can go lower still, and quaternary or more complex mixtures keep pushing the floor down.³ Researchers have recently used machine learning to screen millions of possible combinations, from two-component to six-component blends, to identify promising low-melting mixtures without having to melt each one in a lab.

This is not just an academic exercise. The commercial salt mixture known as Hitec (a blend of sodium nitrate, potassium nitrate, and sodium nitrite) melts at about 142 °C and has been used in industry for decades. Newer formulations that add lithium nitrate to the mix have achieved melting points up to 65 °C lower than Hitec while remaining thermally stable up to at least 600 °C.⁴ That wider gap between melting and decomposition temperature is valuable because it means the salt can operate across a bigger temperature range, storing more heat per unit of material.

Molten Salt in Solar Power Plants

Concentrated solar power (CSP) plants use mirrors to focus sunlight and generate heat, often reaching well above 500 °C. The challenge is storing that heat so electricity can be generated after the sun goes down. Molten nitrate salts have become the go-to solution. The salt absorbs heat during the day, is pumped into insulated tanks, and then releases that heat at night to drive a steam turbine.⁵

The reason nitrate salts won this role over, say, molten sodium chloride is practical. NaCl’s 801 °C melting point means you would need to keep everything above that temperature just to prevent the salt from solidifying in the pipes, which is an engineering nightmare. Nitrate salts melt at a few hundred degrees, well within the operating range of CSP plants, and they remain stable at the upper end of that range. Quaternary nitrate mixtures, blending four different nitrate salts, are now being developed to push the melting point even lower and improve heat-transfer efficiency.⁶ The goal is a salt that stays liquid across the widest possible temperature window, minimizing the risk of freezing during cool desert nights while still being able to absorb intense daytime heat.

Molten Fluoride Salts in Nuclear Reactors

A different family of salts, fluorides, has attracted interest for a completely different high-temperature application: nuclear reactors. Molten salt reactors dissolve nuclear fuel directly into a fluoride salt mixture, which acts as both the fuel carrier and the coolant. The appeal is that these systems operate at low pressure (unlike conventional water-cooled reactors) and can run at very high temperatures, improving thermal efficiency.⁷

Fluoride salts like lithium fluoride-beryllium fluoride (FLiBe) melt at around 459 °C and remain liquid to very high temperatures. That liquid range and their excellent ability to absorb heat make them attractive coolants. The concept was demonstrated at Oak Ridge National Laboratory in the 1960s, and after decades of dormancy, several companies and government programs are now developing commercial molten salt reactor designs. The chemistry of the molten salt is a core engineering constraint: the mixture has to dissolve the right amount of fuel, resist corrosion of the reactor vessel, and stay liquid across the full operating range without decomposing or becoming too viscous.

Industrial Uses of Molten Salts

Beyond energy, molten salts show up in several industrial processes where extremely high temperatures and good electrical conductivity are needed. One longstanding example is the Hall-Héroult process for producing aluminum: alumina (aluminum oxide) is dissolved in molten cryolite, a fluoride salt, at around 960 °C, and an electric current is passed through to separate the aluminum metal. Without the molten salt acting as a solvent and conductor, the process would not work at industrially feasible temperatures.

Newer applications are still emerging. A recent study described an electrochemical method for extracting iodine and sodium alloys from iodide salts by splitting them in a molten salt bath at 630 °C. The process uses a liquid metal cathode to keep the products from reacting with each other, yielding high-purity iodine vapor and sodium alloys that can be used directly or refined further.⁸ Heat treatment of metals is another area: salt baths provide extremely uniform heating, which matters when you need to anneal steel at a precise temperature for just a few seconds.

Supercooling and the Oddities of Measuring Melting Points

Measuring the melting point of a salt sounds straightforward: heat it until it liquefies, note the temperature. In practice, the reverse direction, cooling, reveals a quirk called supercooling. A molten salt can sometimes remain liquid below its official melting point if it cools slowly and no impurity or disturbance triggers crystallization. Research on salts like potassium thiocyanate and calcium chloride found that the degree of supercooling depended heavily on how fast the sample was cooled and how much material was in the container.⁹ A small droplet cooled quickly could remain liquid well below its expected freezing point, while a large batch cooled slowly would crystallize on schedule.

This matters for any application where molten salt is stored or transported. In a solar thermal storage tank, for instance, if the salt supercools rather than crystallizing at the expected temperature, the system might behave unpredictably when it is time to release the stored heat. Engineers account for this by designing systems with nucleation aids or minimum circulation rates that prevent deep supercooling.

Salt Vapor on Jupiter’s Moon Io

Salt melting is not just an Earth problem. Jupiter’s moon Io, the most volcanically active body in the solar system, has volcanoes that blast sodium chloride and potassium chloride gas into its thin atmosphere. Observations from a large radio telescope array detected NaCl and KCl vapor at high temperatures, roughly 500 to 1,000 K (about 230–730 °C), confirming a volcanic origin for these gases.¹⁰ The ratios of the two salts in the atmosphere suggest that Io’s subsurface magma reaches about 1,300 K (roughly 1,030 °C), hot enough to vaporize both salts but preferentially outgassing KCl over NaCl.

These volcanic NaCl emissions contribute to the sodium clouds and plasma torus that surround Io and extend along its orbit around Jupiter.¹¹ The sodium chloride itself makes up only a tiny fraction of Io’s overall atmospheric composition, around 0.3% when averaged across the entire disk, but it is concentrated near volcanic vents. Once ejected, NaCl molecules are quickly broken apart by sunlight, releasing individual sodium and chlorine atoms into the surrounding space environment. It is a strange thought: the same compound sitting in your salt shaker is being blasted out of alien volcanoes and shredded by ultraviolet light hundreds of millions of miles away.

When “Salt” Means Something Totally Different

If you search for the melting point of salt in a chemistry context rather than a cooking context, you might run into ionic liquids, which are salts that are already liquid at or near room temperature. These are typically made from large, asymmetrical organic ions that do not pack efficiently into a crystal. Their melting points can be below 100 °C, and many are liquid at 25 °C. They are used as specialty solvents, in batteries, and in chemical synthesis. Calling them “salts” is chemically correct, but their behavior could not be more different from the rigid, high-melting crystals most people picture when they hear the word.

At the other extreme, some refractory salts have melting points above 2,000 °C. Thorium dioxide (sometimes loosely classified as a salt) melts around 3,300 °C. These materials are used in high-temperature ceramics and nuclear applications. The range, from room-temperature ionic liquids to ceramics that survive conditions hotter than lava, shows just how broad the “salt” category really is. The 801 °C melting point of table salt sits comfortably in the middle of that spectrum, high enough to be impressive but far from the upper limit of what ionic compounds can withstand.