Metal Oxide Solid Solution via Supercritical Water Synthesis
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Solution Overview
Problem
Current methods for preparing metal oxide solid solutions in nano size face challenges such as long reaction times, high energy consumption, and post-process treatment of by-products, while also struggling to maintain high specific surface area and thermal resistance, especially when exposed to high temperatures.
Innovation Solution
A method involving the continuous reaction of a reactant mixture containing water and at least two water-soluble metal compounds under subcritical or supercritical conditions, between 200 to 700°C and 180 to 550 bar, without sintering, to produce metal oxide solid solutions with controlled crystallite size and high specific surface area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional methods (firing, mechanochemical synthesis, hydrothermal synthesis) are used to prepare metal oxide solid solutions, then metal oxide solid solutions can be produced, but the reaction time is long and energy consumption is high
Solution Approach 1:
The invention utilizes the phase transition of water from liquid to supercritical state (above 374°C and 22.1 MPa) to enable rapid chemical reactions. The supercritical water environment allows metal salts to dissolve and react instantly, forming metal oxide solid solutions in seconds without prolonged heating or mechanical processing, thereby dramatically reducing reaction time and energy consumption.
2Temperature
If metal oxide solid solutions are exposed to high temperature, then thermal resistance is improved, but crystallite size increases and specific surface area decreases
Solution Approach 1:
The invention changes the physical-chemical parameters of the reaction medium to supercritical state, enabling metal oxide solid solutions to be formed with controlled crystallite sizes (1-100 nm) directly in the supercritical water environment. This parameter change allows the material to maintain high specific surface area even after thermal treatment, as the supercritical formation process creates a stable nanostructure that resists sintering.
3Ease of manufacture
If metal oxide solid solutions are prepared by conventional methods, then metal oxide solid solutions can be produced, but impurities are incorporated into the products
Solution Approach 1:
The invention uses supercritical water as an inert reaction medium that eliminates contamination from furnace atmospheres, mechanical milling media, and hydrothermal synthesis additives. The supercritical water environment is chemically inert toward the metal salts, allowing pure metal oxide solid solutions to form without incorporating impurities from the reaction environment, while maintaining process simplicity through direct injection of metal salt solutions into the supercritical water reactor.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enables the production of metal oxide solid solutions with superior UV light shielding effects, reduced catalytic activity, and maintained specific surface area even at high temperatures, suitable for applications in UV light shielding and oxygen storage.
Implementation Method 1
reacting a reactant mixture containing water and at least two water-soluble metal compounds at 200 to 700°C under a pressure of 180 to 550 bar in a continuous manner
Data Source
AI summary
Disclosed is a method for preparing a metal oxide solid solution in nano size. The metal oxide solid solution is prepared by reacting a reactant mixture containing water and at least two water-soluble metal compounds at 200 to 700° C. under a pressure of 180 to 550 bar in a continuous manner, wherein the reactant mixture contains the metal compounds at an amount of 0.01 to 30% by weight in total and the solid solution has a crystallite size of 1 to 1,000 nm. The metal oxide solid solution is, in particular suitable as a UV light shielding agent or as an oxygen storage component.