Cerium Oxide-Coated Zinc Oxide UV-A Shielding
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Solution Overview
Problem
Current ultraviolet shielding agents, such as zinc oxide and titanium oxide, are insufficient in blocking UV-A radiation, and cerium oxide alone is expensive and not effective due to indirect electronic transitions, while composite oxides with cerium oxide inside zinc oxide suffer from reduced UV shielding performance due to heat treatment that coarsens cerium oxide particles.
Innovation Solution
Cerium oxide-coated zinc oxide particles with a cerium oxide layer on the surface of zinc oxide particles, produced without high-temperature heat treatment, offering improved UV-A radiation shielding by maintaining the direct transition property of zinc oxide and forming a dense cerium oxide layer for enhanced absorption and scattering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If heat treatment at 350°C or more is performed to produce composite oxides with cerium oxide inside zinc oxide, then the particle shape and size of cerium oxide are changed, but the cerium oxide particles are coarsened to impair the function of cerium oxide as fine particle, resulting in insufficient ultraviolet shielding performance
Solution Approach 1:
The cerium oxide particles are prepared and coated on the zinc oxide particle surfaces before any heat treatment, ensuring that the fine particle structure is established in advance. The coating process is performed at low temperature to prevent coarsening, and the cerium oxide layer is formed as ultrafine particles that maintain their shielding function.
Solution Approach 2:
A thin cerium oxide coating layer is formed on the zinc oxide particle surfaces, creating a protective shell structure. This thin film approach allows the cerium oxide to maintain its fine particle characteristics while providing effective ultraviolet shielding, avoiding the coarsening problem associated with bulk composite oxides.
2Quantity of substance
If composite oxides comprising zinc oxide and cerium oxide are used, then the ultraviolet absorption property and light scattering property of zinc oxide is lost corresponding to a blending amount of cerium oxide, resulting in decreased ultraviolet shielding performance
Solution Approach 1:
Instead of uniformly blending cerium oxide throughout the zinc oxide bulk, the invention applies cerium oxide locally as a surface coating layer. This localized application preserves the bulk zinc oxide's excellent light scattering properties while adding ultraviolet absorption capability at the surface, avoiding the performance loss associated with bulk composite oxidation.
Solution Approach 2:
The invention creates a composite structure where cerium oxide coating layer is applied on zinc oxide core particles. This composite material approach combines the advantages of both materials: zinc oxide provides light scattering and baseline UV shielding, while the cerium oxide coating enhances UV-A absorption, achieving synergistic performance rather than compromising either material's properties.
3Reliability
If cerium oxide alone is used as ultraviolet shielding agent, then it can absorb ultraviolet at wavelength smaller than corresponding to original Eg value, but only ultraviolet at smaller wavelength than that corresponding to original Eg value is absorbed due to indirect transition, resulting in insufficient shielding performance for UV-A radiation
Solution Approach 1:
The invention merges cerium oxide and zinc oxide into a composite particle structure where cerium oxide coating layer is applied on zinc oxide particles. This combination allows the system to leverage cerium oxide's absorption capability while zinc oxide provides broad-spectrum scattering and absorption, achieving effective UV-A shielding that neither material can achieve alone.
Solution Approach 2:
By creating a composite material system with cerium oxide coating on zinc oxide particles, the invention combines the direct bandgap absorption of zinc oxide with the indirect bandgap absorption characteristics of cerium oxide. This composite structure achieves superior UV-A shielding performance by utilizing the complementary absorption mechanisms of both materials.
4Reliability
If zinc oxide particles are used as ultraviolet shielding agent, then they can reveal protection performance by scattering effect and absorption effect, but they are insufficient in blocking UV-A radiation
Solution Approach 1:
The invention applies cerium oxide specifically to the particle surfaces of zinc oxide, creating a localized enhancement layer. This surface coating approach concentrates the UV-A absorption capability at the particle boundaries where light interaction is most effective, while maintaining the bulk zinc oxide's light scattering properties that provide broad-spectrum protection.
Solution Approach 2:
The composite particle structure combines zinc oxide's excellent light scattering properties with cerium oxide's UV-A absorption capability. The zinc oxide core provides bulk scattering and UV-B protection, while the cerium oxide coating layer provides enhanced UV-A absorption, creating a multi-functional shielding agent that addresses both UV-B and UV-A protection needs.
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
The cerium oxide-coated zinc oxide particles demonstrate superior UV-A radiation shielding performance compared to bare zinc oxide, cerium oxide, and composite oxides, maintaining the physical properties of zinc oxide while improving UV-A protection without impairing light scattering.
Implementation Method 1
the electronic excitation of cerium oxide is indirect transition same as titanium oxide, so that it is anticipated that only ultraviolet at the smaller wavelength than that corresponding to original Eg value is absorbed
Implementation Method 2
The scattering effect depends on the reflection factor of the particle and the particle size
Implementation Method 3
The Eg of zinc oxide is 3.2 eV and electronic excitation thereof is direct transition so that zinc oxide can absorb effectively the light at the wavelength of 388 nm or less corresponding substantially to the Eg value
Data Source
AI summary
It is one of the objects of the present disclosure to provide zinc oxide particles having improved ultraviolet shielding performance especially in the region of UV-A radiation at 400 to 320 nm. A cerium oxide-coated zinc oxide particle comprising a matrix raw zinc oxide particle and a cerium oxide layer formed on the surface of the matrix particle, wherein a cerium oxide amount is 5 to 30 wt% relative to 100 wt% of the zinc oxide, a particle diameter of the cerium oxide-coated zinc oxide particles is 0.01 µm or more, and a specific surface area of the cerium oxide-coated zinc oxide particle is 5.0 m2/g or more.