• 한국안전학회지
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• 제18권3호
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• pp.101-108
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• 2003

Polymeric positive temperature coefficient(PTC) composites have been prepared by incorporating carbon black(CB) into high density polyethylene(HDPE), polyphenylene sulfide(PPS) and polybutylene terephthalate(PBT) matrices. A PTC effect was observed in the composite, caused by the large thermal expansion due to He consecutive melting of HDPE, PPS and PBT crystallites. This theory is based upon the premise that the PTC phenomenon is due to a critical separation distance between carbon particles in the polymer matrix at the higher temperature. The influence of PTC characteristics of the PPS/CB composite can be explained by DSC result. HDPE, one of prepared composition, exhibit the higher performance PTC behavior that decreaseing of negative temperature coefficient(NTC) effect and improved reproducibility by chemically crosslinking. Also, PBT/CB and PPS/CB composites exhibit the higher PTC peack temperature than HDPE/CB PTC composite, individually $200^{\circ}C$ and $230^{\circ}C$. These PTC composite put to good use in a number of safety application, such as self$.$controlled heater, over-current protectors, auto resettable switch, high temperature proctection sensor, etc.

• Human Ecology Research
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• 제57권3호
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• pp.383-393
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• 2019

This study examined the association among practical teaching competence (PTC) and teaching efficacy (TE), and explored the mediation effects of theoretical teaching competence (TTC) between the PTC and TE of Practical Arts (Technology and Home Economics Education) teachers. Data were collected from the 301 survey responses completed by elementary, middle, and high school teachers. All teachers showed high levels of PTC, TTC, and TE. Elementary school teachers perceived higher PTC than middle and high school teachers. PTC, TTC, TE showed significant effect in regards to teacher's age and teaching career. Using multiple regression analysis, this study found that TTC fully mediated PTC and TE of elementary school teachers. For middle and high school teachers, there was a partial mediation effect of TTC in the relationship between PTC and TE. This study suggests that teacher education programs should develop a program that can enhance teaching efficacy by cultivating TTC and support teachers who want to strengthen competence, and more practical opportunities to practice teaching.

• 한국산학기술학회논문지
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• 제15권2호
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• pp.666-671
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• 2014

최근 디젤 차량과 같은 내연기관의 고효율화에 따라, 보조난방 열원으로서 PTC 히터의 사용이 증가하는 추세이다. 디젤 차량의 시동 초기에는 냉각수의 온도가 난방으로 직접 사용하기에 충분히 높지 않으므로, 동절기 난방을 위해 보조난방 열원은 필수적이다. 본 연구에서는 스크린 인쇄 전극공정을 바탕으로 한 PTC 소자를 제작하였고, 이를 활용한 PTC 소자 모듈 및 히터를 설계 및 제작하였다. PTC 소자 모듈의 방열핀 접촉형상 및 전열소자의 크기 변경에 따른 난방성능 변화를 열유동 해석을 통해 분석하였고, 난방성능 실험을 수행하여 PTC 히터의 난방성능 및 효율 특성을 살펴보았다. PTC 히터 시작품의 경우, 기존 PTC 히터와 동등한 수준 이상의 난방성능 및 효율을 나타내었으며, 향후 이를 바탕으로 PTC 소자와 히터에 대한 공정개선 및 성능증대 연구를 수행할 계획이다.

• 센서학회지
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• 제9권1호
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• pp.76-82
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• 2000

본 연구에서는 내부전극 접합기술을 이용하여 적층구조의 PTC 서미스터를 제작하였다. 적층구조 PTC 서미스터는 저항, 소형, 대전류 등의 특징을 갖는다. PTC 특성을 조사하기 위하여 첨가제효과, 전압-전류특성, 온도특성, 복합임피던스 특성 등을 측정하였다. 적층구조 PTC서미스터는 저항의 온도특성과 전압-전류특성에서 높은 비선형성을 나타내었다. 적층수가 증가함에 따라 상온저항이 감소되는 특성이 결정립의 효과에 기인됨을 알았다. 전류의 스윗칭 변화는 적층구조가 갖는 열용량의 크기에 비례하였으며, 적층수가 증가할수록 스윗칭 시간이 증가하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 추계학술대회 논문집 전기물성,응용부문
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• pp.140-145
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• 2001

In order to apply for silane crosslinking process to PTC products, especially. self-regulating heater, silane crosslinked samples were compared with radiation crosslinked sample in terms of PTC characteristic and PTC stability. Silane crosslinked samples have lower PTC intensity than radiation crosslinked sample. It can be explained that multiple networks of silane crosslink restrict the movement of molecules in the composite as the sample is heating. As a result of heat cycles at $140^{\circ}C$, the changes of volume resistivity and PTC intensity for radiation crosslinked sample were higher than those of silane crosslinked samples. Whereas, in the case of heat cycles at $85^{\circ}C$, which is limiting temperature for self-regulating heater, both silane and radiation crosslinked samples show stable results without pronounce changes of resistivity up to five cycles.

• 한국전기전자재료학회논문지
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• 제26권2호
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• pp.98-103
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• 2013

The alumina substrates that Ni electrode was printed on and the multi-layered PTCR thermistors of which composition is $(Ba_{0.998}Ce_{0.002})TiO_3+0.001MnCO_3+0.05BN$ were fabricated by a thick film process, and the effect of re-oxidation temperature on their resistivities and resistance jumps were investigated, respectively. Ni electroded alumina substrate and the multi-layered PTC thermistor were sintered at $1150^{\circ}C$ for 2 h under $PO_2=10^{-6}$ Pa and then re-oxidized at $600{\sim}850^{\circ}C$ for 20 min. With increasing the re-oxidation temperature, the room temperature resistivity increased and the resistance jump ($LogR_{290}/R_{25}$) decreased, which seems to be related to the oxidation of Ni electrode. The small sized chip PTC thermistor such as 2012 and 3216 exhibits a nonlinear and rectifying behavior in I-V curve but the large sized chip PTC thermistor such as 4532 and 6532 shows a linear and ohmic behavior. Also, the small sized chip PTC thermistor such as 2012 and 3216 is more dependent on the re-oxidation temperature and easy to be oxidized in comparison with the large sized chip PTC thermistor such as 4532 and 6532. So, the re-oxidation conditions of chip PTC thermistor may be determined by considering the chip size.

• Macromolecular Research
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• 제12권1호
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• pp.53-62
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• 2004

We have prepared polymer composites of low-density polyethylene (LDPE) and ionomers (Surlyn 8940) containing polar segments and metal ions by melt blending with carbon black (CB) as a conductive filler. The resistivity and positive temperature coefficient (PTC) of the ionomer/LDPE/CB composites were investigated with respect to the CB content. The ionomer content has an effect on the resistivity and percolation threshold of the polymer composites; the percolation curve exhibits a plateau at low CB content. The PTC intensity of the crosslinked ionomer/LDPE/CB composite decreased slightly at low ionomer content, and increased significantly above a critical concentration of the ionomer. Irradiation-induced crosslinking could increase the PTC intensity and decrease the NTC effect of the polymer composites. The minimum switching current (Ι$\sub$trip/) of the polymer composites decreased with temperature; the ratio of Ι$\sub$trip/ for the ionomer/LDPE/CB composite decreased to a greater extent than that of the LDPE/CB composite. The average temperature coefficient of resistance (${\alpha}$$\sub$T/) for the polymer composites increased in the low-temperature region.

• 전기의세계
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• 제31권6호
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• pp.437-444
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• 1982

Although several kinds of conduction mechanism of PTC thermistor have been reported, there were few satisfying results. In this paper, the reported conduction mechanism theories were scrutinized and analyzed by using the experimental results. PTC thermistors for this study were manufactured by adding Sb$\_$2/O$\_$3/, AI$\_$2/O$\_$3/, TiO$\_$2/, and SiO$\_$2/ to BaTiO$\_$3/, and by sintering it at different temperatures. In order to analyze the conduction mechanism, R-T characteristics and its frequency dependence of specimens were measured. And also, the structures of specimens were studied. Especially this paper emphasized the explanation of the resistivity characteristics as the grain growth state of PTC thermistor specimens with respect to soaking temperature. According to the results, the resistivity of PTC thermistor whose grain was formed by semiconducting, was independent to the grain size at room temperature. For small and uniform grain size, the slope of the resistivity near the Curie temperature and the resistivity above the Curie temperature became greater and PTCR effect was improved.

• 한국세라믹학회지
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• 제43권11호
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• pp.673-679
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• 2006

The discovery of ferroelectric barium titanate (BaTiO$_3$) in 1942 began the present era of dielectrics-based electronic ceramics. Ferroelectric barium titanate has a high dielectric constant and after the recognition of BaTiO$_3$ as a new ferroelectric compound, various attractive electrical properties have been extensively studied and reported. Since then, pioneering work on valence-compensated semiconduction led to the discovery of the positive temperature coefficient (PTC) of the resistance effect found in doped BaTiO$_3$. Significant progress has since followed with respect to understanding the PTC phenomena, advancing materials capabilities, and developing devices for sensor and switching applications. In this paper, the theoretical aspects of the various PTC models are discussed and the future trends of practical applications for PTC devices are briefly mentioned.

• Carbon letters
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• 제2권3_4호
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• pp.159-164
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• 2001

In this study, the effects of carbon black (CB) content and anodic oxidation treatment with $AgNO_3$ on positive temperature coefficient (PTC) behavior of CB/HDPE nanocomposites were investigated. Also, the addition of elastomer as a toughing agent was studied. The 20~50 wt% of CB, 0~5 wtt% of elastomer, and 1 wt% of $AgNO_3$-filled HDPE nanocomposites were prepared using the internal mixer in 60 rpm at $160{\circ}C$ and the compression-molded at $180{\circ}C$ for 10 min. As a result, the room temperature resistivity and PTC intensity of the composites were dependent, to a large extent, on the content of CB, addition of elastomer, and surface chemical properties that were controlled in the relative arrangements of the carbon black aggregates in a polymeric matrix. Moreover, the composites with relatively low room temperature resistivity and suitable PTC intensity could be achieved by treatment of $AgNO_3$. Consequently, it was noted that PTC effect was due to the deagglomeration or the breakage of the conductive networks caused by thermal expansion or crystalline melting of the polymeric matrix.