Materials synthesis in the liquid phase, or wet-chemical synthesis, utilizes a solution medium in which the target materials are generated from a series of chemical and physical transformations. Although this route is central in organic chemistry, for materials synthesis the low operational temperature range of the solvent (usually below 200 °C, in extreme 350 °C) is a serious restriction. Here, salt melt synthesis (SMS) which employs a molten inorganic salt as the medium emerges as an important complementary route to conventional liquid phase synthesis. Depending on the nature of the salt, the operational temperature ranges from near 100 °C to over 1000 °C, thus allowing the access to a broad range of inorganic crystalline materials and carbons. The recent progress in SMS of inorganic materials, including oxide ceramic powders, semiconductors and carbon nanostructures, is reviewed here. We will introduce in general the range of accessible materials by SMS from oxides to non-oxides, and discuss in detail based on selected examples the mechanisms of structural evolution and the influence of synthetic conditions for certain materials. In the later sections we also present the recent developments in SMS for the synthesis of organic solids: covalent frameworks and polymeric semiconductors. Throughout this review, special emphasis is placed on materials with nanostructures generated by SMS, and the possible modulation of materials structures at the nanoscale in the salt melt. The review is finalized with the summary of the current achievements and problems, and suggestions for potential future directions in SMS.

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Salt melt synthesis of ceramics, semiconductors and carbon nanostructures

Ultralight ceramic aerogels with the property combination of recoverable compressibility and excellent high-temperature stability are attractive for use in harsh environments. However, conventional ceramic aerogels are usually constructed by oxide ceramic nanoparticles, and their practical applications have always been limited by the brittle nature of ceramics and volume shrinkage at high temperature. Silicon carbide (SiC) nanowire offers the integrated properties of elasticity and flexibility of one-dimensional (1D) nanomaterials and superior high-temperature thermal and chemical stability of SiC ceramics, which makes it a promising building block for compressible ceramic nanowire aerogels (NWAs). Here, we report the fabrication and properties of a highly porous three-dimensional (3D) SiC NWA assembled by a large number of interweaving 3C-SiC nanowires of 20–50 nm diameter and tens to hundreds of micrometers in length. The SiC NWA possesses ultralow density (∼5 mg cm–3), excellent mechanical properties o...

Ultralight, Recoverable, and High-Temperature-Resistant SiC Nanowire Aerogel.

Green concrete: Prospects and challenges

Proliferating energy consumption, particularly of fossil fuels, has led to an increasing generation of pollutants; many of these harmful products have been of serious environmental concern. While e...

Advanced Hydrodesulfurization Catalysts: A Review of Design and Synthesis

Hierarchically pore-structured porous diatomite ceramics containing 82.9∼84.5% porosity were successfully prepared for the first time via foam-gelcasting using diatomite powder as the main raw material. Sizes of mesopores derived from the raw material and macropores formed mainly from foaming were 0.02∼0.1 μm and 109.7∼130.5 μm, respectively. The effect of sintering temperature, additive content and solid loading of slurry on pore size and distribution, and mechanical and thermal properties of as-prepared porous ceramics were investigated. Compressive strength of as-prepared porous ceramics increased with sintering temperature, and the one containing 82.9% porosity showed the highest compressive strength of 2.1 ± 0.14 MPa. In addition, the one containing 84.5% porosity and having compressive strength of 1.1 ± 0.07 MPa showed the lowest thermal conductivity of 0.097 ± 0.001 W/(m·K) at a test temperature of 200 C, suggesting that as-prepared porous ceramics could be potentially used as good thermal insulation materials.

Foam-gelcasting preparation, microstructure and thermal insulation performance of porous diatomite ceramics with hierarchical pore structures

Effects of pore structure on thermal conductivity and strength of alumina porous ceramics using carbon black as pore-forming agent

Microstructure and mechanical properties of MgOC refractories containing graphite oxide nanosheets (GONs)

Effect of particle size of fly ash on the properties of lightweight insulation materials

Synthesis of silicon carbide whiskers using reactive graphite as template

Microstructures and mechanical properties of Al 2 O 3 -C refractories with Al, Si and SiO 2 as the additives fired in the temperature range from 800 to 1400 °C are investigated when multi-walled carbon nanotubes (MWCNTs) were used as the carbon source to partially or totally replace graphite flake in the materials. The results showed that the mechanical properties such as cold modulus of rupture (CMOR), modulus of elasticity ( E ) of all the specimens increased in the firing temperature range from 800 to 1200 °C, but decreased dramatically at 1400 °C. Compared with specimens with only graphite flake, specimens containing 0.05 wt% MWCNTs possessed better mechanical properties. However, they got deteriorated with the further increase of MWCNTs amount from 0.1 to 1 wt%. The differences in mechanical properties were closely associated with the microstructures of Al 2 O 3 -C refractories. In comparison with specimens having only graphite flake, the improvement of mechanical properties of specimens containing MWCNTs was attributed to strengthening and toughening mechanism of MWCNTs as well as formation of larger amount of ceramic phases in the matrix at 800 and 1000 °C, respectively. At 1200 and 1400 °C, the improvement was mainly associated with the quantity and morphology of SiC whiskers induced from MWCNTs in the specimens. However, with the increase of MWCNTs amount, the mechanical properties of the materials got deteriorated because of agglomeration of MWCNTs and their influence on the morphology of ceramics phases.

Yuanbing Li

Papers

Effects of pore structure on thermal conductivity and strength of alumina porous ceramics using carbon black as pore-forming agent

Microstructure and mechanical properties of MgOC refractories containing graphite oxide nanosheets (GONs)

Effect of particle size of fly ash on the properties of lightweight insulation materials

Synthesis of silicon carbide whiskers using reactive graphite as template

Microstructures and mechanical properties of Al2O3-C refractories with addition of multi-walled carbon nanotubes