Performance Study of Diamond Powder-Filled Sodium Silicate-Based Thermal Conductive Adhesives

At a Glance

Metadata	Details
Publication Date	2023-05-24
Journal	Materials
Authors	Ming Chen, Z. C. Zhou, Xu Wang, Yangchun Zhao, Yongmin Zhou
Institutions	Nanjing Tech University
Citations	2
Analysis	Full AI Review Included

Executive Summary

This study introduces a high-performance, inorganic thermal conductive adhesive (TCA) system based on sodium silicate and surface-modified diamond powder, designed to overcome the limitations of traditional organic TCAs (poor high-temperature resistance and low thermal conductivity).

Core Innovation: Utilization of sodium silicate as an inorganic matrix combined with high-thermal-conductivity diamond powder (1 µm) as the filler.
Surface Engineering: Diamond filler was modified using 3-aminopropyltriethoxysilane (APTES) coupling agent to enhance dispersion and improve interfacial bonding with the sodium silicate matrix.
Peak Thermal Performance: The adhesive achieved a maximum thermal conductivity of 10.32 W/(m·K) at a 50% diamond mass fraction.
Peak Mechanical Performance: The maximum tensile shear strength reached 1.83 MPa at a 60% diamond mass fraction, nearly double that of comparable industry products.
Optimal Balance: The ideal filler content range for balancing both high thermal conductivity and strong adhesion was determined to be 50% to 60% diamond mass fraction.
Structural Analysis: SEM confirmed that optimal filler loading (50%) created effective, continuous thermal conduction pathways, while excessive loading (80%) led to voids and reduced matrix connectivity, severely degrading performance.

Technical Specifications

Parameter	Value	Unit	Context
Matrix Material	Sodium Silicate	Mass Fraction	34% solute in solution
Filler Material	Diamond Powder	Particle Size	1 µm
Filler Modification Agent	3-aminopropyltriethoxysilane (APTES)	N/A	Silane coupling agent
Peak Thermal Conductivity (TC)	10.32	W/(m·K)	Achieved at 50% diamond mass fraction
Peak Tensile Shear Strength	1.83	MPa	Achieved at 60% diamond mass fraction
Optimal Performance Range	50-60	wt%	Balance of TC and adhesion
Modification Reaction Temp.	70	°C	Condensation reflux reaction (3 hours)
Adhesive Curing Temp.	50	°C	Curing time 1 hour
Diamond Intrinsic TC (Reference)	2000	W/(m·K)	High thermal conductivity of bulk diamond
Tensile Shear Test Speed	20	mm/min	Electronic universal testing machine (WY-10TB)

Key Methodologies

The preparation involved a two-step process: surface modification of the diamond filler followed by compounding with the sodium silicate matrix.

1. Diamond Powder Surface Modification

Dispersion: 1 g of diamond powder was dispersed in 30 mL of anhydrous ethanol via stirring at room temperature in a three-necked flask.
Coupling Agent Preparation: 3-aminopropyltriethoxysilane (APTES) was mixed with water at a ratio of 1:2 (silane:water) and added to the diamond dispersion.
Reaction: A condensation reflux reaction was performed in a constant temperature magnetic stirrer at 70 °C for 3 hours.
Purification: The modified powder was repeatedly washed with anhydrous ethanol and filtered until the filtrate was clear.
Drying: The filter cake was dried in a vacuum drying oven at 70 °C to obtain modified diamond particles.

2. Thermal Conductive Adhesive Preparation

Mold Preparation: Disc-shaped graphite molds were coated with liquid paraffin and pre-baked in a drying oven at 80 °C for 3 hours.
Compounding: Colloids were prepared by mixing the modified diamond powder (at varying mass fractions, 10% to 80% of dry weight) with the 34% sodium silicate solution.
Mixing: The mixture was stirred magnetically for 1 hour.
Curing: The colloid was poured into the treated mold and cured in a drying oven at 50 °C for 1 hour.
Sample Preparation: Cured samples were cooled, demolded, and polished to a thickness of < 5 mm for thermal conductivity testing.

3. Characterization Techniques

Morphology: Scanning Electron Microscopy (SEM) was used to analyze diamond surface modification and the cross-sectional structure of the cured adhesives.
Composition: Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD) confirmed the presence of the silane coupling agent elements (O, Si, N) and verified that no new phases were formed during compounding.
Performance:
- Tensile shear strength was measured using an electronic universal testing machine (WY-10TB).
- Thermal conductivity was measured using a thermal conductivity tester (DM3615).

Commercial Applications

This high-performance, inorganic TCA system is ideal for applications requiring superior heat dissipation and mechanical stability, particularly in environments where organic materials typically fail due to high temperatures or aging.

High-Power Electronics: Assembly and installation of heat sinks for CPUs, GPUs, and power modules in computers, mobile phones, and tablets.
Automotive Industry: Heat dissipation for engines and electronic control modules, where high thermal stability is critical.
LED Lighting: Thermal management for high-brightness LED arrays, improving reliability and lifespan.
Industrial Equipment: Use in fields requiring robust thermal interface materials to improve equipment reliability and stability under continuous thermal load.
Aerospace/Defense: Applications requiring materials with good anti-aging performance and relatively high intrinsic thermal conductivity compared to organic polymers.

View Original Abstract

With the development of miniaturized, highly integrated, and multifunctional electronic devices, the heat flow per unit area has increased dramatically, making heat dissipation a bottleneck in the development of the electronics industry. The purpose of this study is to develop a new inorganic thermal conductive adhesive to overcome the contradiction between the thermal conductivity and mechanical properties of organic thermal conductive adhesives. In this study, an inorganic matrix material, sodium silicate, was used, and diamond powder was modified to become a thermal conductive filler. The influence of the content of diamond powder on the thermal conductive adhesive properties was studied through systematic characterization and testing. In the experiment, diamond powder modified by 3-aminopropyltriethoxysilane coupling agent was selected as the thermal conductive filler and filled into a sodium silicate matrix with a mass fraction of 34% to prepare a series of inorganic thermal conductive adhesives. The thermal conductivity of the diamond powder and its content on the thermal conductivity of the adhesive were studied by testing the thermal conductivity and taking SEM photos. In addition, X-ray diffraction, infrared spectroscopy, and EDS testing were used to analyze the composition of the modified diamond powder surface. Through the study of diamond content, it was found that as the diamond content gradually increases, the adhesive performance of the thermal conductive adhesive first increases and then decreases. The best adhesive performance was achieved when the diamond mass fraction was 60%, with a tensile shear strength of 1.83 MPa. As the diamond content increased, the thermal conductivity of the thermal conductive adhesive first increased and then decreased. The best thermal conductivity was achieved when the diamond mass fraction was 50%, with a thermal conductivity coefficient of 10.32 W/(m·K). The best adhesive performance and thermal conductivity were achieved when the diamond mass fraction was between 50% and 60%. The inorganic thermal conductive adhesive system based on sodium silicate and diamond proposed in this study has outstanding comprehensive performance and is a promising new thermal conductive material that can replace organic thermal conductive adhesives. The results of this study provide new ideas and methods for the development of inorganic thermal conductive adhesives and are expected to promote the application and development of inorganic thermal conductive materials.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma16113937

References

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