• Composites Research
• /
• v.37 no.5
• /
• pp.422-426
• /
• 2024

Due to the rapid miniaturization and increased power density of electronic devices, a significant amount of heat is generated during operation. This has led to a surge in demand for thermal management materials, such as thermal interface materials (TIMs) with high thermal conductivity. Among the various types, paste-type TIMs, mixtures of liquid silicone polymers and thermal fillers, can effectively fill the rough surfaces between heat sources and heat sinks, thereby ensuring efficient heat dissipation. However, thermal pastes generally exhibit poor long-term stability due to issues like filler/resin phase separation under extreme conditions of repeated heating, cooling, and prolonged compression. Consequently, research on high-performance thermal pastes with excellent long-term stability is actively underway. This paper aims to introduce various strategies for producing silicone oil based thermal pastes that achieve both high thermal conductivity and superior long-term stability.

• Journal of the Korea Institute of Building Construction
• /
• v.18 no.1
• /
• pp.51-57
• /
• 2018

The objective of the present study is to examine the feasibility on the development of high-insulation concrete using aerogels with hydrophilic surface treatment. To prevent the segregation and enhance the dispersibility of agerogels in the cement pastes, the substrate of aerogels was modified to be hydrophobic property using surfactant. The modified aerogels were added from 0% to 100% of the cement volume at the interval of 25% under the constant cement content. Some cement pastes showed segregation phenomenon and flocculation of aerogels during mixing phase. The addition of aerogels decreased the compressive strength of cement pastes but enhanced the thermal conductivity. The thermal conductivity of pastes with 100% aerogels was lower by 43% when compared with that measured in the conventional paste. To improve the compressive strength and insulation capacity of concrete containing aerogels, a reliable surface treatment method of aerogels needs to be further investigated.

• Korean Journal of Materials Research
• /
• v.22 no.8
• /
• pp.390-396
• /
• 2012

Ag pastes added to Bi-oxide frits have been applied to the electrode material of Si solar cells. It has been reported that frits induce contacts between the Ag electrodes and the Si wafer after firing. During firing, the control of interfaces among Ag, the glass layer, and Si is one of the key factors for improving cell performance. Specifically, the thermo-physical properties of frits considerably influence Ag-Si contact. Therefore, the thermal properties of frits should be carefully controlled to enhance the efficiency of cells. In this study, the interface structures among Ag electrodes, glass layers, and recrystallites on an $n^+$ emitter were carefully analyzed with the thermal properties of lead-free frits. First, a cross-section of the area between the Ag electrodes and the Si wafer was studied in order to understand the interface structures in light of the thermal properties of the frits. The depth and area of the pits formed in the Si wafer were quantitatively calculated with the thermal properties of frits. The area of the glass layers between the Ag electrodes and Si, and the distribution of recrystallites on the $n^+$ emitter, were measured from a macroscopic point of view with the characteristics of the frits. Our studies suggest that the thermophysical properties should be controlled for the optimal performance of Si solar cells; our studies also show why cell performance deteriorated due to the high viscosity of frits in Ag pastes.

• Journal of the Korea Institute of Building Construction
• /
• v.18 no.5
• /
• pp.413-418
• /
• 2018

This fundamental study is to examine the significance and limitation of the fumed silica addition to enhance the early compressive strength gain and thermal conduction resistance of cement pastes. The fumed silica content varied from 0% to 1.6% of the cement content by wt% at an interval of 0.4%. Test results showed that the addition of fumed silica is favorable to enhancing the early strength gain of the cement pastes, indicating that 1-day compressive strength corresponded to 45% of the 28-day strength. This high-early strength gain rate is comparable to the trend commonly observed in steam-cured cement concrete. However, the addition of fumed silica little influenced the thermal conduction resistance of cement pastes.

• Journal of Surface Science and Engineering
• /
• v.49 no.2
• /
• pp.218-224
• /
• 2016

Thermal radiation pastes were prepared by dispersing carbon materials as fillers with a content of 1 weight percent in an acrylic resin. The kind of fillers was as follows; $25{\mu}m$ graphite, $45{\mu}m$ graphite, $15{\mu}m$ carbon nanotube(CNT), a 1:1 mixture of $25{\mu}m$ graphite and $15{\mu}m$ CNT, and a 1:1 mixture of $45{\mu}m$ graphite and $15{\mu}m$ CNT. Thermal emissivity was measured as 0.890 for the samples with graphite only, 0.893 for that with CNT only, and 0.892 for those containing both. After coating prepared pastes on a side of 0.4 mm thick aluminium plate and placing the plate over an opening of a box maintained at $92^{\circ}C$ with the coated side out, the temperatures on the uncoated side of the plates were measured. The samples containing graphite and CNT showed the lowest temperatures. The paste with mixed fillers was coated on the back side of the PCB of an LED module and thermal analysis was carried out using Thermal Transient Tester (T3ster) in a still air box. The thermal resistance of the module with coated PCB was measured as 14.34 K/W whereas that with uncoated PCB was 15.02 K/W. The structure function analysis of T3ster data revealed that the difference between junction and ambient temperatures was $13.8^{\circ}C$ for the coated case and $18.0^{\circ}C$ for the uncoated. From the infrared images of heated LED modules, the hottest-spot temperature of the module with coated PCB was lower than that of the uncoated one for a given period of LED operation.

• Computers and Concrete
• /
• v.32 no.6
• /
• pp.567-576
• /
• 2023

In this study, a 3D microstructure-based model is established to simulate the effective thermal conductivity of cement paste, covering varying influencing factors associated with microstructure and thermal transfer mechanisms. The virtual cement paste divided into colloidal C-S-H and heterogeneous paste are reconstructed based on its structural attributes. Using the two-level hierarchical cement pastes as inputs, a lattice Boltzmann model for heat conduction is presented to predict the thermal conductivity. The results suggest that due to the Knudsen effect induced by the nanoscale pore, the thermal conductivity of air in C-S-H gel pore is significantly decreased, maximumly accounting for 3.3% thermal conductivity of air at the macroscale. In the cement paste, the thermal conductivities of dried and saturated cement pastes are stable at the curing age larger than 100 h. The high water-to-cement ratio can decrease the thermal conductivity of cement paste.

• 한국신재생에너지학회:학술대회논문집
• /
• 2010.06a
• /
• pp.61.2-61.2
• /
• 2010

Ag thick-film has usually been used for the front electrode of Si solar cells with the outstanding electrical properties. Ag paste consists of Ag powers, vehicles, frits and additives. Ag paste has broadly been screen-printed on the front side of Si wafer with the merits of low cost and simplicity. The optimal contact formation between Ag electrodes and Si wafer in the front electrode during a fast firing has been considered as the key factor for high efficiency. Although the content of frit in Ag pastes is less than 5wt%, it can profoundly influence the contact formation between Ag and Si under the fast firing. In this study, the effects of lead-free frits on the contacts between Ag and Si were studied with the thermal properties and compositions of various frits. Our experimental results showed that the electrical properties of cells were related to the interface structures between Ag and Si. It was found that current path of electrons from Si to Ag would be possible through the tunneling mechanism assisted by tens of nano-Ag recrystals on $n^+$ emitter as well as Ag recrystals penetrated into $n^+$ emitter layers. These preliminary studies will be helpful for designing the proper frits for the Ag pastes with considering the properties of various Si wafers.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.26 no.2
• /
• pp.144-150
• /
• 2013

A New Ag-pastes were developed for integrating the high efficiency mono-Si solar cell. The pastes were the mixture of 84 wt% Ag, 2 wt% glass frit, 11 wt% solvent of buthyl cabitol acetate, and 3 wt% additives. After fabricating the Ag-pastes by using a 3-roll mill, they were coated on a $SiN_x$/n+/p- stacks of a commercial mono-Si solar cell. And the post-thermal process was also optimized by varying the process conditions of peak temperature. The optimized solar cell efficiency on a 6-inch mono-Si wafer was 18.28%, which was the one of the world best performances. It meaned that the newly developed Ag-paste could be adopted to fabricate a commercial bulk Si solar cell.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.24 no.3
• /
• pp.245-249
• /
• 2011

Carbon nanotubes (CNTs) have been significantly used for the field emitters for display applications. However, the lifetime of CNT emitters which are formed by screen printing technique is not guaranteed yet, because the constituents in CNT paste affect the lifetime of CNTs. The CNT pastes for screen printing are normally composed of organic vehicles (nitro cellulose, ethyl cellulose, etc) and additives (glass frits, indium tin oxide (ITO), etc) with CNTs. In this study, the effects of constituents in CNT pastes on the lifetime and emission characteristics of CNTs were investigated by thermal and electrical analysis. Use of glass frits worsened the lifetime and electron emission of CNTs. However, an addition of ITO to CNT paste rather improved the lifetime of CNTs. Degradation of CNTs was small when nitro cellulose was used in CNT paste as an organic vehicle.

• Korean Journal of Food Science and Technology
• /
• v.40 no.3
• /
• pp.271-276
• /
• 2008

In this study, volatile compounds were isolated from traditional and commercial fermented soybean pastes according to different heating temperatures (room temperature, $50^{\circ}C$, $100^{\circ}C$) using headspace-solid phase microextraction (HS-SPME). The compounds were then analyzed by gas chromatography-mass spectrometry (GC-MS). A total of 51 volatile components, including 18 esters, 3 alcohols, 6 acids, 8 pyrazines, 5 volatile phenols, 6 aldehydes, and 5 miscellaneous compounds, were identified. Esters and acids such as ethyl hexadecanoate, acetic acid, and 2/3-methyl butanoic acid were the largest groups among the quantified volatiles. By applying principal component analyses to the GCMS data sets, differences were observed in the volatile components of the soybean pastes as to the different heating temperatures. A large variation was shown between the volatile components of the traditional and commercial soybean pastes by increasing the heating temperature. Commercial samples had significantly higher levels of longer chain ethyl esters, aldehydes, and thermal degradation products such as maltol and 2-acetyl pyrrole, while traditional samples showed higher concentrations of acids and pyrazines.