Long-Term Corrosion of Eutectic Gallium, Indium, and Tin (EGaInSn) Interfacing with Diamond

At a Glance

Metadata	Details
Publication Date	2024-06-02
Journal	Materials
Authors	Stephan Handschuh‐Wang, Tao Wang, Zongyan Zhang, Fucheng Liu, Peigang Han
Institutions	Shenzhen Institutes of Advanced Technology, Shenzhen Technology University
Citations	5
Analysis	Full AI Review Included

Technical Documentation & Analysis: Long-Term EGaInSn/Diamond Interfacing

Reference Paper: Handschuh-Wang et al. (2024). Long-Term Corrosion of Eutectic Gallium, Indium, and Tin (EGaInSn) Interfacing with Diamond. Materials, 17, 2683.

Executive Summary

6CCVD analyzes this critical research confirming the superior long-term stability of CVD diamond coatings when interfaced with corrosive gallium-based liquid metals (EGaInSn/Galinstan). This validation is crucial for high-reliability thermal management systems (TIMs).

Corrosion Immunity: Diamond coatings (Nanocrystalline Diamond, NCD, and Boron-Doped Diamond, BDD) provided complete protection to underlying metal (Ti-alloy) and silicon substrates over a 4-year aging period.
Structural Integrity: Raman spectroscopy and SEM confirmed that the diamond coatings maintained their morphology and structure, showing no signs of corrosion or penetration by the liquid metal.
High Conductivity Validation: The study successfully utilized highly conductive BDD coatings (boron concentration ca. 2.8 x 10²¹ cm^-3), demonstrating the feasibility of using conductive diamond as a corrosion-resistant electrical contact or heat spreader.
Liquid Metal Failure Mechanism: The primary failure observed was the solidification of the liquid metal itself, attributed to atmospheric hydrolysis (reaction with humidity) forming GaOOH crystallites and subsequent dealloying, not diamond degradation.
Application Relevance: This research confirms that MPCVD diamond is the ideal, chemically inert interface material required to maximize the lifespan and reliability of liquid metal-enabled devices in high-power electronics, stretchable electronics, and wireless communication systems.

Technical Specifications

The following hard data points were extracted from the experimental methodology and results:

Parameter	Value	Unit	Context
Liquid Metal Composition	68.5% Ga, 21.5% In, 10% Sn	wt%	Eutectic Gallium, Indium, Tin (EGaInSn)
EGaInSn Melting Point	ca. 10.5	°C	Liquid metal property
EGaInSn Surface Tension	ca. 600	mN/m	High surface tension characteristic
Aging Duration	4	years	Long-term stability test duration
Average Storage Temperature	ca. 22	°C	Room temperature storage environment
Peak Storage Humidity (Summer)	ca. 80	%	Condition accelerating liquid metal hydrolysis
BDD Boron Concentration	ca. 2.8 x 10²¹	cm^-3	High doping level for metallic conductivity
NCD Crystallite Size	ca. 20	nm	Rough estimate for structured nanocrystalline diamond
Sub-Microcrystalline Size	ca. 500	nm	Boron-doped diamond morphology
Diamond Raman Shift (on Ti)	1335	cm^-1	Indicates compressive stress (-1.58 GPa)
Substrate Material	Ti₆Al₄V	Alloy	Used for corrosion protection test
Liquid Metal Solidification Product	GaOOH (Gallium Oxide Hydroxide)	Compound	Result of hydrolysis and dealloying

Key Methodologies

The diamond coatings were synthesized using Hot Filament Chemical Vapor Deposition (HFCVD), a technique closely related to 6CCVD’s Microwave Plasma CVD (MPCVD) capabilities, following specific seeding and growth recipes:

Substrate Preparation: Ti-alloy (Ti₆Al₄V) and Silicon (Si) substrates were mechanically ground and chemically cleaned (ultrasonication in water/ethanol). Si was oxidized in a Piranha-like solution (H₂O₂, NH₃H₂O, water) at ca. 80 °C.
Seeding (NCD/BDD): Electrostatic self-assembly was used, employing Detonation Nanodiamond (DND) particles stabilized by either TMAEMC (for smooth coatings, pH 3) or oxalic acid (for structured coatings, pH 5).
Nanocrystalline Diamond (NCD) Growth Parameters:
- Reaction Gases: Methane (32 sccm) and Hydrogen (800 sccm).
- Filament Temperature: ca. 2500 °C.
- Pressure: 1.5 kPa.
- Duration: 1 hour.
Boron-Doped Diamond (BDD) Growth Parameters:
- Reaction Gases: Methane (32 sccm), Hydrogen (400 sccm), and Boron Source (160 sccm of 0.1% Trimethyl Borane (TMB) in H₂).
- Filament Temperature: 2500 °C.
- Pressure: 2 kPa.
- Duration: 1 hour (yielding microcrystalline BDD).
Aging Test: 1-2 g of EGaInSn was deposited on the coated substrates using forced wetting. Samples were stored for 4 years at ambient conditions (average 22 °C, 60-80% humidity).

6CCVD Solutions & Capabilities

This research confirms that MPCVD diamond is the optimal material for high-reliability liquid metal interfaces. 6CCVD provides the custom materials and engineering expertise necessary to replicate and advance this technology for industrial applications.

Research Requirement	6CCVD Solution & Capability	Technical Advantage
Corrosion Resistance & Substrate Protection	Optical Grade SCD or High-Quality PCD	Provides an impermeable, chemically inert barrier against corrosive liquid metals (EGaInSn, EGaIn), ensuring long-term device reliability in thermal management systems.
High Electrical Conductivity (BDD)	Heavy Boron-Doped Diamond (BDD)	6CCVD guarantees precise boron doping control to achieve metallic-like conductivity (matching or exceeding the reported 2.8 x 10²¹ cm^-3) for conductive TIMs, electrochemical sensors, or electrical contacts.
Custom Dimensions & Scale-Up	PCD Wafers up to 125mm Diameter	Enables industrial scale-up for large-area heat sinks (e.g., network clusters, high-performance computing) far exceeding the 10x10 mm samples used in the study.
Structured/Nanocrystalline Coatings	Custom PCD/NCD Thickness and Morphology	We offer precise control over grain size (NCD/MCD) and thickness (0.1 µm to 500 µm) to optimize surface structure for specific wetting or adhesion requirements, including the structured coatings investigated.
Interfacial Bonding & Adhesion	Custom Metalization Services (Ti, W, Au, Pt, Pd, Cu)	For robust integration onto metal heat sinks (like Ti-alloys or Copper), 6CCVD offers in-house metalization capabilities to ensure strong, reliable interfaces between the diamond coating and the device structure.
Surface Finish Requirements	Ultra-Smooth Polishing (Ra < 1nm for SCD, < 5nm for Inch-size PCD)	Provides highly polished surfaces, which is critical for minimizing surface area exposure to humidity, potentially mitigating the liquid metal’s tendency to solidify via hydrolysis, and optimizing thermal contact resistance.

6CCVD’s ability to deliver custom SCD and PCD plates up to 500 µm thick, combined with our specialized BDD doping and metalization services, positions us as the ideal partner for engineers developing next-generation thermal interface solutions.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Thermal transport is of grave importance in many high-value applications. Heat dissipation can be improved by utilizing liquid metals as thermal interface materials. Yet, liquid metals exhibit corrosivity towards many metals used for heat sinks, such as aluminum, and other electrical devices (i.e., copper). The compatibility of the liquid metal with the heat sink or device material as well as its long-term stability are important performance variables for thermal management systems. Herein, the compatibility of the liquid metal Galinstan, a eutectic alloy of gallium, indium, and tin, with diamond coatings and the stability of the liquid metal in this environment are scrutinized. The liquid metal did not penetrate the diamond coating nor corrode it. However, the liquid metal solidified with the progression of time, starting from the second year. After 4 years of aging, the liquid metal on all samples solidified, which cannot be explained by the dissolution of aluminum from the titanium alloy. In contrast, the solidification arose from oxidation by oxygen, followed by hydrolysis to GaOOH due to the humidity in the air. The hydrolysis led to dealloying, where In and Sn remained an alloy while Ga separated as GaOOH. This hydrolysis has implications for many devices based on gallium alloys and should be considered during the design phase of liquid metal-enabled products.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma17112683

References

2023 - Heat dissipation design and optimization of high-power LED lamps [Crossref]
2022 - All-around diamond for cooling power devices [Crossref]
2022 - Liquid metal (LM) and its composites in thermal management [Crossref]
2022 - Diamond as the heat spreader for the thermal dissipation of GaN-based electronic devices [Crossref]
2021 - Critical Review on the Physical Properties of Gallium-Based Liquid Metals and Selected Pathways for Their Alteration [Crossref]
1972 - Thermal Conductivity of the Elements [Crossref]
2014 - Relative importance of grain boundaries and size effects in thermal conductivity of nanocrystalline materials [Crossref]
2011 - Nanocrystalline diamond [Crossref]
2019 - Diamond Etching Beyond 10 μm with Near-Zero Micromasking [Crossref]
2022 - Boron-Doped Diamond Electrodes: Fundamentals for Electrochemical Applications [Crossref]