Briefly describe the principle of molten salt method, what is molten salt?

The molten salt synthesis method usually uses one or several salts with low melting points as the reaction medium, and the reactants have a certain solubility in the molten salt, so that the reaction is carried out at the atomic level. After the reaction, the salts are dissolved with a suitable solvent, and the synthetic product can be obtained after filtration and washing.

Because the low melting point salt is used as the reaction medium, there is a liquid phase in the synthesis process, and the reactants have a certain solubility in it, which greatly accelerates the diffusion rate of ions, so that the reactants can be mixed at the atomic scale in the liquid phase, and the reaction is transformed from a solid-solid reaction to a solid-liquid reaction. Compared with the conventional solid-phase method, this method has the advantages of simple process, low synthesis temperature, short holding time, uniform chemical composition of synthesized powder, good crystal morphology and high phase purity. In addition, the salt is easy to separate, and can also be reused Molten salt synthesis method is a material synthesis method developed in modern times, using one or several salts with low melting point as the medium of reaction, using the characteristics of the synthesized reactants with a certain solubility in the molten salt, so that the reactants can be fully mixed at the atomic scale in the liquid phase of the molten salt, so that the synthesis reaction can be completed in a shorter time and at a lower temperature.

The molten salt method has the advantages of simple process, low synthesis temperature, short holding time, uniform chemical composition of synthesized powder, good crystal morphology, and high phase purity. Magnesium oxide powder was prepared by molten salt synthesis with lithium chloride (LiCl), potassium nitrate (KNO3) and sodium nitrate (Nan03) as reaction media, anhydrous magnesium chloride (MGC12), magnesium chloride hexahydrate (MGC12·6H2O) and calcium carbonate (CAC03) as reaction raw materials.

The reaction process and products were analyzed and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermogravimetric-differential scanning integrated thermal analyzer (TG-DSC). The results show that when the reaction temperature is 430, the MGO phase is formed in the reaction product, and with the increase of heat treatment temperature, the amount of MGO generation increases, and the crystallization degree is improved, and the product is mainly composed of MGO crystals after heat treatment. During the reaction of molten salt medium, Mg2+ ions and Ca2+ ions are replaced to form intermediate products such as dolomite and magnesium carbonate, and dolomite is finally converted into magnesium carbonate, and magnesium carbonate is decomposed to obtain magnesium oxide.

1. The salt tank heats the powdered solid molten salt above the melting point until the viscosity of the molten salt can be pushed by the liquid molten salt circulation pump, so that the whole system becomes a flowing and circulating state, and then sent to the furnace body to further heat exchange heat with the high-temperature flue gas to the working temperature required by the process heating equipment, so that it can be used for circulating heat supply in the flow state.

The working temperature of the common medium is 350-580, and the maximum working temperature can reach 600.

2. Classification. According to the different fuel heating methods, it can be divided into coal-fired type, oil-fired type, gas-fired type, biomass-fired type and electrically heated molten salt furnace; According to the different structural forms, it can be divided into cylindrical, square box and tube rack molten salt furnaces.

3. Application. It is widely used in solid alkali evaporation and concentration, melamine.

Production, aluminum hydroxide.

chemical units such as dissolution, waste liquid and waste oil high-temperature regeneration; It can also be applied to the heat storage unit of solar thermal power generation, which is to obtain clean and renewable green energy.

Key equipment for solar thermal utilization.

4. Technical parameters.

Operating temperature: 350 -580

Working medium: binary, ternary inorganic molten salt.

Design pressure: heating capacity: 300-36000kw

5. Features. 1. Low pressure and high temperature, strong safety, and heat conduction oil.

Higher operating temperatures can be obtained than at the same pressure;

2. The heating temperature is stable, and the load and temperature can be adjusted accurately;

3. System thermal efficiency.

high, generally higher than 92%;

4. Complete operation control and safety monitoring equipment, effectively reducing operation and maintenance costs;

5. Automatic control.

Mechanized, fully automatic control, proportional adjustment, PLC programmable or DCS man-machine dialogue integrated control technology;

6. Due to the different heating load and circulating flow, the molten salt furnace mostly adopts the form of two-layer or three-layer coil, the inner ring coil is the radiant heating surface, the middle ring coil and the outer ring coil are the convection heating surface, and the three-layer coil runs in parallel, with simple structure and easy to use.

Molten salts, melts formed after the melting of salts, such as alkali metals, halides of alkaline earth metals, nitrates, sulfates.

Molten salts are melts composed of metal cations and non-metal anions. There are more than 80 kinds of cations and more than 30 kinds of anions that can form molten salts, and more than 2,400 kinds of molten salts can be combined. Since metal cations can have several different valence states, and anions can also form different complexed anions, the number of molten salts will actually exceed 2400.

Molten salts are salts that are solid at standard temperature and atmospheric pressure, and present in the liquid phase after the temperature increases. Molten inorganic salts are often referred to as molten salts, but now they include oxide melts and molten organic compounds.

Molten Salt Composition:

1. Binary molten salt.

Binary molten salt (60% sodium nitrate + 40% potassium nitrate) is a mature heat storage medium that has been proven by practical cases to be suitable for CSP systems, but it cannot be used in the field of medium temperature heat utilization, mainly because its freezing point is too high, about 207 degrees Celsius. For medium-temperature heat utilization systems with an operating temperature of around 250 degrees Celsius, molten salt products with a lower freezing point must be used.

2. Ternary molten salt.

The ternary molten salt is a mixed nitrate composed of 53% potassium nitrate + 40% sodium nitrite + 7% sodium nitrate, with a melting point of 142 degrees Celsius and a gasification point of 500 degrees Celsius. Sodium nitrite will decompose slowly above 450 degrees Celsius, but the working temperature of the general medium temperature utilization system is within 250 350 degrees Celsius.

Molten salt is a melt formed by the melting of salts, which is an ionic melt composed of cations and anions. Molten salts are made up of cations and anions. The interaction forces between ions include electrostatic forces (which are long-range forces that obey Coulomb's law), short-range repulsive forces, and van der Waals forces.

As a primary approximation, the molten salt structure can be described using the electrostatic hard sphere model. That is, anions and cations are both charged hard spheres with a certain radius, and van der Waals forces are ignored or used as correction terms. Due to the electrostatic action, each ion in the molten salt is surrounded by a heterogeneous ion, and the results of X-ray diffraction experiments show that

Compared with the crystal structure, the closest distance between anion and cation in molten salt is slightly reduced instead of increasing, but the number of first nearest neighbors (coordination number) of each ion is significantly lower than that in the crystal. This indicates that there are irregularly distributed gaps or vacancies in the molten salt. The structure of the molten salt solution formed by the miscible mixture of the two molten salts is also generally similar.

According to the equation of potential energy of the interaction between ions, the movement and arrangement of ions in molten salt can be simulated by computer, and many physicochemical properties of molten salt or molten salt solution can be calculated.

Summary. I used to use electrically heated molten salt in a factory to process metal materials. There are two main methods of electrolytic heating of molten salt, one is resistance heating molten salt, and the other is arc heating molten salt.

The resistance heating molten salt method is to heat the molten salt through a resistance heater to make it reach the melting temperature, and then immerse the molten molten salt into the metal material, so as to realize the treatment of the metal material. The arc heating molten salt method is to heat the molten salt through an arc heater to make it reach the melting temperature, and then immerse the molten molten salt into the metal material, so as to realize the treatment of the metal material. Expansion:

The advantages of electric heating molten salt method are fast heating speed and high melting temperature, which can effectively improve the processing efficiency of metal materials and effectively reduce the pollution of metal materials.

I used to use electrically heated molten rock salt in a factory to process metal materials. There are two main methods of electrolytic heating of molten salt, one is resistance heating molten salt, and the other is arc heating molten salt. The resistance heating molten salt method is to heat the molten salt through a resistance heater to make it reach the melting temperature, and then immerse the molten molten salt into the metal material, so as to realize the treatment of the metal material.

The arc heating molten salt method is to heat the molten salt through an arc heater to make it reach the melting temperature, and then immerse the molten molten salt into the metal material, so as to realize the treatment of the metal material. Expansion: The advantages of electric heating molten salt method are fast heating speed, high melting temperature, blind cleaning can effectively improve the treatment efficiency of metal materials, and can effectively reduce the pollution of metal materials before grinding.

You've done a great job! Can you elaborate on that?

In response to your question, there are several ways to electrically heat molten salt:1Direct electric heating of molten salt:

The molten salt is put into a container and then heated with electricity to dissolve the molten salt, thus achieving the purpose of molten salt. 2.Electrically heated molten salt-water mixture:

The molten salt is mixed with water, and then heated with electricity to dissolve the molten salt, so as to achieve the purpose of local grinding of molten salt. YOU Min 3Electrically heated molten salt-oil mixture:

The molten salt and oil are mixed, and then heated with electricity to dissolve the molten salt, so as to achieve the purpose of molten salt. In addition, the advantages of electric heating molten salt are: it can save energy, the operation is simple, the temperature control is accurate, the operation is safe, the temperature can be traced to achieve high temperature, and the effect of rapid melting can be achieved.

1) as an electrolyte for the electrolysis of metals. The earliest application of molten salt began with the metal electrolysis of molten salt, and now the production of metal aluminum and the preparation of rare earth metals mainly use the molten salt electrolysis method, and some other metals such as alkali metals, alkaline earth metals, and high melting point metals also use the method of molten salt electrolysis. The production of metals by electrolysis of molten salts has:

The process flow is simple, the metal rate is high, the product quality is high, the mechanical slippery and the degree of automation is high. Today, molten salt electrolysis is the only method of industrial production of aluminum, and it cannot be replaced by other methods in recent decades.

2) Application in the nuclear industry. In the atomic energy industry, the molten salt mixture used in homogeneous reactors as a fuel solvent and heat transfer medium has many advantages, its operating temperature has a variable range, the addition of fuel is relatively easy, and the products of nuclear fission can be continuously removed. The most widely used in the nuclear industry is the LIF BEF2 molten salt system.

Molten salt is the molten liquid of salt, and the molten salt is usually referred to as the molten body of inorganic salt. Most of the inorganic salts in the molten state are ionic crystals, which are melted at high temperatures to form ionic melts, so the most common molten salts are composed of alkali metals or alkali socks earth metals and halides, silicates, carbonates, nitrates, and phosphates. Molten salts have many properties that are different from aqueous solutions, such as stability at high temperatures, low vapor pressure in a wide range, low viscosity, good electrical conductivity, high ion migration and diffusion velocity, high heat capacity, and the ability to dissolve various materials.

The principle of molten salt heating is to use the night trough electricity to heat the molten salt in the low-temperature tank to more than 500 and store it in the high-temperature tank, and the high-temperature molten salt is pumped out of the tank during the day, and the air and water are heated by the corresponding molten salt heat exchanger according to the different heat temperature and use, and the heating is carried out according to the user's needs. After the molten salt is exchanged, it flows into the low-temperature molten salt tank to form a complete cycle of molten salt heating-heating-heating-heat extraction-cooling, and realizes a circulating system that converts nighttime trough electrical energy into heat energy and stores it for use during the day. Its main materials and equipment:

Molten salt mold salt, cold salt tank, hot salt tank, molten salt pump, molten salt electric heater and molten salt-to-water heat exchanger.

The study of the physicochemical properties of molten salt and molten salt solution is not only helpful to understand the structure of molten salt and molten salt solution, but also provides a basis for finding molten salt systems that are technically useful in production. The selection of the right molten salt electrolyte is a key to the success of the molten salt electrolysis process. The melting point (phase equilibrium), density, surface tension or interfacial tension, viscosity, conductivity and other properties of molten salt systems have important effects on electrolytic production.

The study of molten salt phase diagram is important to understand the interaction between molten salts and to develop the molten salt electrolysis process. Commonly used methods for measuring molten salt phase diagrams are visual, variable temperature and differential thermal analysis. With the help of computer, the thermodynamic function is used to calculate the molten salt phase diagram, which has become an auxiliary means for the measurement of molten salt phase diagram.

The type of molten salt phase diagram is related to the type of molten salt interaction. Some molten salts with similar valence and ionic radius form a near-ideal solution in the liquid phase and a continuous solid solution after solidification. For example, potassium chloride-rubidium chloride.

When the valence type or ionic radius is quite different, a phase diagram with a low eutectic point is often formed. For example, potassium chloride lithium chloride. Some molten salt phase diagrams have stable or unstable intermediate compounds.

A small number of molten salt systems are incompletely miscible in liquid phase, forming a liquid phase layered system.

Except for molten salts with valence and ionic radii that tend to form near-ideal solutions, most molten salts have a non-zero heat of mixing. Many molten salt solutions can be theoretically used to calculate their thermodynamic properties.