Cold Sintering

Cold sintering is done by mixing a sintering powder in a solvent and subjecting the mixture to pressure at relatively low temperatures. This is followed by evaporation of the solvent accompanied by densification.

During the process of cold sintering, the temperature is maintained below T0, where T0 is typically 200℃ above the boiling point of the solvent. The final product of cold sintering is generally very dense due to low temperature and may not require any post-processing.

Time for cold sintering is typically less. 

The following diagram shows cold sintering process visually.

Source: Patent Image

Cold sintering process (CSP) can be used for making:

  • Ceramic polymer composites
  • Solid electrolytes
  • Chemical vapor deposition (CVD) precursors
  • Instant coffee powder

Using cold sintering to manufacture ceramic polymer composites

A cold sintering process of inorganic compounds in conjunction with the polymerization of monomers and oligomers in a solvent can be used to produce ceramic polymer composites.

Cold sintering enables a large variety of ceramic polymer composites to be produced at low temperatures and intermediate pressures.

To make ceramic polymer composites using cold sintering, a mixture of inorganic compounds (e.g. metal oxides such as  MoO3, WO3, V2O3) is combined with a monomer (e.g. epoxide and  cyclic phosphazene) and a solvent(e.g. water or alcohol). Then the mixture is subjected to polymerization conditions to obtain a pre-ceramic polymer mixture.

This mixture is then heated and put under pressure, while maintaining a temperature below T0, which is 200℃ above the boiling point of the solvent.

More information about this process can be found in this patent.

Using cold sintering to manufacture solid lithium-ceramic electrolyte

A lithium salt-ceramic electrolyte can be prepared by applying pressure and heat to a mixture of lithium salt, a lithium-ceramic, and a solvent to form a lithium salt-ceramic composite.

The temperature during the sintering process is maintained below 250℃.

Sintering mixture is prepared by combining a lithium based ceramic and a lithium salt with a polar solvent that dissolves the lithium salt.

The lithium-based ceramic can be lithium-aluminum phosphate or lithium-titanium phosphate. The lithium salt can be an organic or inorganic salt.

The polar solvent has an aqueous medium such as over 90 wt% water. The mixture includes less than about 50 wt% of the polar solvent. The lithium salt is in an amount greater than 4 volume% relative to the mixture.

Refer to this patent for more information about this process.

Using cold sintering for making CVD precursors

A solid chemical vapor deposition (CVD) precursor can be prepared by cold sintering of a compacted form of a particulate precursor.

The solid precursor is volatilized to generate precursor vapor for a chemical vapor deposition (CVD) process. The solid precursor can be hafnium chloride, zirconium chloride, or pentakisdimethylamino tantalum (PDMAT).

The precursor is compacted at a temperature between 15 to 30℃.

More information about this process can be found in this patent.

Using cold sintering to make instant coffee powder

Instant coffee powder can be prepared by cold sintering followed by drying a powder mix of coffee, sugar and water under cold conditions to form pore-free coffee powder.

The processed powder contains ice sublimation voids throughout the volume of the powder particles. The powder has a porosity of at least 35% and an ice crystal pore volume of less than 2.5 mL/g. The ice crystal pore size is less than 3 micrometres.

This powder is used for making instant beverages. The prepared beverage has the same taste quality as that prepared from conventional fresh-brewed coffee. The prepared powder can be stored in a compressed form at room temperature.

Refer to this patent for more information about this process.

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