Thermal conductivity and bending strength of SiC composites reinforced by pitch-based carbon fibers

In this work, pitch-based carbon fibers were utilized to reinforce silicon carbide (SiC) composites via reaction melting infiltration (RMI) method by controlling the reaction temperature and resin carbon content. Thermal conductivities and bending strengths of composites obtained under different preparation conditions were characterized by various analytical methods. Results showed the formation of SiC whiskers (SiCw) during RMI process according to vapor—solid (VS) mechanism. SiCw played an important role in toughening the Cpf/SiC composites due to crack bridging, crack deflection, and SiCw pull-out. Increase in reaction temperature during RMI process led to an initial increase in thermal conductivity along in-plane and thickness directions of composites, followed by a decline. At reaction temperature of 1600 °C, thermal conductivities along the in-plane and thickness directions were estimated to be 203.00 and 39.59 W/(m·K), respectively. Under these conditions, bending strength was recorded as 186.15±3.95 MPa. Increase in resin carbon content before RMI process led to the generation of more SiC matrix. Thermal conductivities along in-plane and thickness directions remained stable with desirable values of 175.79 and 38.86 W/(m·K), respectively. By comparison, optimal bending strength improved to 244.62±3.07 MPa. In sum, these findings look promising for future application of pitch-based carbon fibers for reinforcement of SiC ceramic composites.

Thermal Insulation Blocks Made of Sunflower Pith Particles and Polysaccharide-Based Binders: Influence of Binder Type and Content on Their Characteristics

Co-product of sunflower cultivation, pith of stem has a little exploited insulating potential. Blocks in which pith particles are glued together using a starch-based binder have already been obtained. However, they are highly water-sensitive. Replacing this binder with others has been considered here. Polysaccharide-based binders were tested, chosen for their more hydrophobic character: sodium alginate, chitosan, Citrus pectin, and a modified starch. Like starch, these binders are physically binding. They are first solubilised in water (except chitosan, dissolved in 2% acetic acid). The solution is then mixed with pith particles before cold compression molding for 90 s. A 10% binder content was initially considered. The blocks were all cohesive with a dry density from 36 to 42 kg/m3). Their performances were assessed through water absorption capacity and resistance via capillary absorption tests on wet sponges, mechanical test and thermal conductivity. Chitosan and pectin-based blocks show the best properties, particularly concerning water resistance and mechanical properties. The pectin-based block has improved its elastic modulus by 40% compared to a starch-based block. The pectin-based block in its case absorbs 2.7 times less water than starch. Finally, thermal conductivities of pectin and chitosan-based pith blocks are in the same order of magnitude as for starch (39.8-40.1 mW/m.K), and close to values from commercial materials (e.g., polystyrene). Pectin and chitosan were also tested at three rates (5%, 10% and 15%). A significant improvement in the blocks' compressive strength was observed with the increase in binder rate, while thermal conductivities varied little.

Thermal Conductivity Determination of Ga-In Alloys for Thermal Interface Materials Design

Thermal interface material (TIM) that exists in a liquid state at the service temperature enables efficient heat transfer across two adjacent surfaces in electronic applications. In this work, the thermal conductivities of different phase regions in the Ga-In system at various compositions and temperatures are measured for the first time. A modified comparative cut bar technique is used for the measurement of the thermal conductivities of GaxIn1−x (x = 0, 0.1, 0.214, 0.3, and 0.9) alloys at 40, 60, 80, and 100 °C, the temperatures commonly encountered in consumer electronics. The thermal conductivity of liquid and semi-liquid (liquid + β) Ga-In alloys are higher than most of the TIM’s currently used in consumer electronics. These measured quantities, along with the available experimental data from literature, served as input for the thermal conductivity parameter optimization using the CALPHAD (calculation of phase diagrams) method for pure elements, solution phase, and two-phase region. A set of self-consistent parameters for the description of the thermal conductivity of the Ga-In system is obtained. There is good agreement between the measured and calculated thermal conductivities for all of the phases. Due to their ease of manufacturing and high thermal conductivity, liquid/semi-liquid Ga-In alloys have significant potential for TIM in consumer electronics.

Thermal Conductivity of Polybutadiene Rubber from Molecular Dynamics Simulations and Measurements by the Heat Flow Meter Method

Thermal conductivities of polybutadiene rubbers crosslinked by 2.4 and 2.8 phr of sulfur have been found to be functions of temperature via molecular dynamics (MD) simulations using the Green–Kubo method. From an analysis of the heat flux autocorrelation functions, it has been revealed that the dominant means of heat transport in rubbers is governed by deformations of polymeric chains. Thermal conductivities of rubber samples vulcanized by 2.4 and 2.8 phr of sulfur have been measured by the heat flow meter method between 0 ∘C and 60 ∘C at atmospheric pressure. The temperature dependencies of the thermal conductivities of rubbers and their glass transition temperatures derived from MD simulations are in good agreement with the literature and experimental data. Details are discussed in the paper.