Out of Plane Thermal Conductivity of Carbon Fiber Reinforced Composite Filled with Diamond Powder

At a Glance

Metadata	Details
Publication Date	2016-01-01
Journal	Open Journal of Composite Materials
Authors	M. Srinivasan, Peter Maettig, K. W. Glitza, B. Sanny, Axel Schumacher
Institutions	Leibniz-Institut für Verbundwerkstoffe GmbH, University of Wuppertal
Citations	9
Analysis	Full AI Review Included

Technical Documentation & Analysis: High Thermal Conductivity Composites using MPCVD Diamond Fillers

This documentation analyzes the research on enhancing the out-of-plane thermal conductivity of carbon fiber reinforced polymer (CFRP) composites using diamond powder (DP) fillers. The findings directly support the application of 6CCVD’s high-purity, high-thermal-conductivity MPCVD diamond materials for advanced thermal management solutions in aerospace, high-energy physics (CERN/ATLAS), and electronics cooling.

Executive Summary

Application Focus: The study successfully enhanced the out-of-plane thermal conductivity (K⊥) of CFRP composites, critical for heat removal in lightweight structures like the ATLAS pixel detector support at CERN.
Key Achievement: Diamond powder (DP) filler significantly improved K⊥, achieving an increase factor of 2.8x in high-modulus YS90A composites (at 12% DP volume fraction).
Mechanism Validation: Finite Element Modeling (FEM) confirmed that thermal enhancement relies on the formation of a continuous conductive path (percolation) through the interaction between the diamond filler and the carbon fibers.
Material Limitation: The DP used in the study had a thermal conductivity of only 1000 W·m⁻¹·K⁻¹, which is significantly lower than the capabilities of modern MPCVD diamond.
6CCVD Value Proposition: 6CCVD specializes in high-purity Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) with thermal conductivities exceeding 2000 W·m⁻¹·K⁻¹. Utilizing 6CCVD materials will enable researchers to achieve thermal performance far superior to the 2.8x factor reported here, potentially lowering the required filler volume fraction.
Future Direction: The paper suggests moving to smaller, higher aspect ratio fillers (nanodiamond) to lower the percolation threshold; 6CCVD offers custom diamond material solutions tailored for these next-generation composite requirements.

Technical Specifications

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

Parameter	Value	Unit	Context
Diamond Powder (DP) Thermal Conductivity (Used)	1000	W·m⁻¹·K⁻¹	Filler material used in experiment
DP Particle Diameter (Used)	0.5 to 1	µm	Microscale filler size
DP Density (Used)	3.5	g·cm⁻³	Filler material property
Baseline K⊥ (T300, 44% Fiber)	0.67	W·m⁻¹·K⁻¹	Neat epoxy composite (0% DP)
Max K⊥ Achieved (T300, Test)	1.85	W·m⁻¹·K⁻¹	At 14% DP volume fraction (2.3x improvement)
Baseline K⊥ (YS90A, 50% Fiber)	0.97	W·m⁻¹·K⁻¹	Neat epoxy composite (0% DP)
Max K⊥ Achieved (YS90A, Test)	2.69	W·m⁻¹·K⁻¹	At 12% DP volume fraction (2.8x improvement)
T300 Fiber Axial Thermal Conductivity	8	W·m⁻¹·K⁻¹	Standard modulus PAN-based fiber
YS90A Fiber Axial Thermal Conductivity	500	W·m⁻¹·K⁻¹	High modulus Pitch-based fiber
Interfacial Thermal Resistance (R_int)	0.0004150798	K·m²·W⁻¹	Calibration measurement for test setup
Thermal Measurement Standard	ASTM E1225-04	N/A	Guarded-Comparative-Longitudinal Heat Flow

Key Methodologies

The experimental procedure focused on two primary fabrication techniques to incorporate the diamond powder (DP) filler into the carbon fiber reinforced polymer (CFRP) matrix:

Material Selection:
- Fibers: T300 (PAN-based, Twill 2/2 weave) and YS90A (Pitch-based, Plain weave).
- Matrix: LARIT RIM 135/134 Epoxy resin (2:1 ratio).
- Filler: Microscale Diamond Powder (0.5 µm - 1 µm diameter).
Sample Fabrication (Dispersion on Dry Fabric Technique):
- Five layers of 2/2 twill fabric (55% fiber volume fraction) were used.
- DP filler was deposited directly onto the dry woven carbon fiber fabric prior to infusion.
- Resin Infusion: Vacuum Assisted Resin Infusion (VARI) technique was used.
- Curing: Autoclave curing at a static pressure of 24 bar for approximately 9 hours.
Sample Fabrication (Matrix Modification Technique):
- DP filler was incorporated directly into the epoxy resin mixture at various volume fractions (up to 12% for YS90A, up to 14% for T300).
- Resin Infusion: Vacuum assisted hand layup technique was applied due to the high viscosity of the diamond-filled resin.
- Curing: Autoclave curing.
Thermal Measurement:
- Samples were water-jet cut to 50 mm diameter (2 mm or 3 mm thickness).
- Steady state out-of-plane thermal conductivity measurements were performed using a custom-built measuring cell compliant with ASTM E1225-04.
- Temperature Gradient: Maintained between approximately 60 °C (top meter bar) and 32 °C (bottom meter bar).
Modeling:
- Micromechanical Finite Element Models (FEM) were developed in Abaqus^TM using a modified Random Sequential Adsorption algorithm to simulate random fiber and DP distribution within the Representative Volume Element (RVE).

6CCVD Solutions & Capabilities

The research demonstrates the critical role of diamond filler in enhancing thermal performance for demanding applications like high-energy physics detectors. 6CCVD’s advanced MPCVD diamond materials offer a direct path to exceeding the performance limits observed in this study.

Applicable Materials for Enhanced Thermal Composites

The diamond powder used in the paper (1000 W·m⁻¹·K⁻¹) represents a lower-grade material. 6CCVD provides materials with significantly higher intrinsic thermal conductivity, which is essential for maximizing the conductive path efficiency and lowering the required filler volume fraction.

6CCVD Material	Thermal Conductivity (K)	Recommended Application	6CCVD Capability Advantage
High Thermal Grade PCD	> 1800 W·m⁻¹·K⁻¹	Bulk filler, large heat spreaders, thermal interfaces.	Available in large plates (up to 125mm) for integration into laminate structures.
Optical Grade SCD	> 2000 W·m⁻¹·K⁻¹	Ultra-high performance heat sinks, critical interfaces.	Highest purity and thermal performance available (up to 2200 W·m⁻¹·K⁻¹).
Custom Diamond Powder	Variable	Matrix filler, percolation studies.	We can supply high-purity diamond powder optimized for specific particle size distribution (PSD) and surface area, crucial for achieving lower percolation thresholds (as suggested in the conclusion).

Customization Potential for Advanced Research

The paper highlights that the thermal performance is highly sensitive to filler dispersion, interfacial adhesion, and the formation of conductive paths. 6CCVD offers specialized services to optimize diamond integration:

Custom Dimensions and Substrates: While the paper focused on powder, 6CCVD can supply large, polished PCD wafers (up to 125mm diameter) or custom-cut plates for use as embedded thermal planes or substrates within the composite structure, providing superior in-plane and through-thickness heat spreading compared to traditional carbon foam or titanium.
Surface Functionalization and Metalization: The efficiency of the conductive path relies heavily on the thermal contact resistance between the filler/fiber and the epoxy matrix. 6CCVD offers in-house metalization services (Au, Pt, Pd, Ti, W, Cu) to functionalize diamond surfaces, potentially improving wetting and adhesion with the epoxy resin, thereby reducing interfacial thermal resistance (R_int).
Precision Polishing: For applications requiring direct thermal contact with sensors or electronics (like the CERN detector), 6CCVD provides ultra-smooth polishing (Ra < 1nm for SCD, Ra < 5nm for inch-size PCD), ensuring minimal thermal boundary resistance at the interface.

Engineering Support

6CCVD’s in-house PhD team specializes in the thermal and mechanical properties of diamond materials. We can assist researchers and engineers working on similar lightweight thermal management projects by providing:

Consultation on optimal diamond grade (SCD vs. PCD) based on required thermal conductivity and cost targets.
Guidance on material preparation and surface treatment necessary to achieve uniform dispersion and enhanced matrix adhesion, addressing the challenges noted in the paper regarding high-viscosity resin systems.
Support for integrating diamond substrates into complex laminate structures, leveraging our expertise in custom dimensions and metalization.

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

View Original Abstract

Highly conductive fillers have a strong influence on improving the poor out of plane thermal conductivity of carbon fiber reinforced composites. The objective of this study has been to investigate the role of the diamond powder (DP) in enhancing the out-of-plane thermal conductivity of the woven composites. Samples of the standard modulus T300 carbon fiber composite with 44% and 55% fiber volume fraction and the high modulus YS90A carbon fiber composite with 50% volume fraction were fabricated with their matrices comprising of neat epoxy and different loading of diamond powder within epoxy resin. Steady state thermal conductivity measurements were carried out and it was found from the measurements that the out of plane thermal conductivity of the standard modulus composite increased by a factor of 2.3 with 14% volume fraction of diamond powder in the composite while the out of plane thermal conductivity of the high modulus composite increased by a factor of 2.8 with 12% volume fraction of diamond powder in the composite. Finite Element Modeling (FEM) with the incorporation of microstructural characteristics is presented and good consistency between the measurements and FEM results were observed.

Tech Support

Original Source

DOI: https://doi.org/10.4236/ojcm.2016.62005