Solution deposition precursors prepared by solution deposition method are the precursors of the final products. In the solution deposition method, one or more suitable soluble metal salts should be selected and prepared into solution according to the composition of the final material, making each element in ionic or molecular states. It is also necessary to select a suitable precipitator or use evaporation, sublimation, hydrolysis and other operations to precipitate or crystallize the metal ions evenly. Finally, the precipitation or crystallization is dehydrated or heated to obtain the required final material. The solution deposition method has the advantages of simple equipment, easy access to raw materials and high purity, which is generally used in the preparation of metal oxides and multi-component composite nano powder materials.

Applications:

• Optics field: Solution deposition precursors can be used in the optics field, such as optical thin film, liquid tuned laser, new optical glass and the others, which is benefit for creating new materials that are uniform at the atomic level.
• Electronic products field: Due to simple, low temperature treatment and controllable performance, solution deposition precursors are widely used in electronic products field for information storage, dielectric material, ion conduction and the others.
• Catalysis field: Solution deposition precursors can be applied in catalysis field to obtain high specific surface catalysts. This type catalysts have high selectivity in molecular recognition.
• The others: Solution deposition precursors also have other applications, including mechanics, thermology and the others.

Classification:

According to the states of the final products, solution deposition precursors can be divided into precursors of powder materials, membrane materials and the others.

• Solution deposition precursors of powder materials: Many powder materials are obtained by further treatment of solution deposition precursors. For example, Nickel-Cobalt-Manganese ternary cathode material is a kind of important powder material, which is obtained by sintering the solution deposition precursor by selecting appropriate sintering condition.

Figure 1. An example of solution deposition precursor of powder material.

• Solution deposition precursors of film materials: Many film materials require liquid deposition methods to obtain solution deposition precursors, including SiO₂ film, TiO₂ film, iron oxide film and the others. Among them, TiO₂ thin film is an important semiconductor photovoltaic material that has been widely applied in solar cells.

Figure 2. An example of solution deposition precursor of film material.

• The others: In addition to the two mentioned kinds, the solution deposition precursors also include the precursors of bulk materials and fibrous materials.

Production processes:

The preparation processes of solution deposition precursors can be divided into precipitation method, hydro-thermal method, sol-gel method and hydrolysis method.

• Precipitation method: This process mainly includes precipitation formation and solid-liquid separation, the precipitation separation is the key step of the process. The precipitation method can be divided into direct precipitation method, co-precipitation method and homogeneous precipitation method.
• Hydro-thermal method: This method can obtain ultrafine powder precipitates by chemical reactions in high temperature and pressure water. A large number of metal oxide and metal composite oxide ceramic powders with particle sizes ranging from several nanometers to several hundred nanometers can be prepared, which are usually unavailable or difficult to obtain.

Figure 3. The process of hydro-thermal method.

• Sol-gel method: This method can prepare homogeneous sol of metal oxide or metal hydroxide by decomposition or polymerization of metal alcohol salt, and then condense into transparent gel, which can be dried and heat-treated to obtain the required material.

Figure 4. The process of sol-gel method.

• Hydrolysis method: The products of hydrolysis reaction are usually hydroxides, hydrates and other precipitations. Ultrafine powder materials with high purity can be obtained by hydrolysis and dehydration.

References:

1. Sun Z, Jiao L, Fan Y, et al. Industrialization of tailoring spherical cathode material towards high-capacity, cycling-stable and superior low temperature performance for lithium-ion batteries[J]. RSC Advances, 2016:97818-97824.
2. Xie B, Zhang H, Zhang Q, et al. Enhanced energy density of polymer nanocomposites at a low electric field through aligned BaTiO₃ nanowires[J]. Journal of Materials Chemistry A, 2017, 5(13).