PTC Thermistor Research Articles

Grain boundary characteristics of batio3PTC thermistor

Abstract A method to calculate physical parameters of grain boundaries of BaTio3 PTC thermistor is presented in this paper. Increasing temperature form 20°C to 200°C, the grain boundary parameters take a sudden change near 130°C., Capacitance of depletion layer decreases form 40 to 15 uF/cm2, while barrier height, charge density and depletion layer width increases from 0.05 to 0.03 eV, 3.5 to 8.5 uC/cm2, and 0.7 to 2.0 nm, respectively. From TEM observation, three types of grain boundaries have been identified. The calculated parameters are an average of al grain boundaries.

Inductively coupled plasma—atomic emission spectrometry (ICP-AES): an analytical technique for the chemical characterization of perovskite ceramic semiconductors

The possibilities of inductively coupled plasma-atomic emission spectrometry (ICP-AES) for the chemical characterization (dopants, impurities, and macroconstituents) of perovskite ceramic semiconductors (PTC thermistors, varistors, manganites, cobaltites) are shown. The dissolution of the samples is achieved by five methods: (a) decomposition with HCl in a Teflon-lined pressure vessel, (b) decomposition with HF + H 2SO 4 in a Teflon-lined pressure vessel, (c) decomposition with (NH 4) 2SO 4 + H 2SO 4 in a platinum dish, (d) fusion with Na 2CO 3 + Na 2B 4O 7 in a platinum crucible, (e) fusion with Li 2B 4O 7 in a graphite crucible. The spectral interferences and the inter-element effects are studied and corrected. The detection limits are comprised, approximately, between 0.00001% and 0.1%. High sensitivity and good precision are attained.

Phase change materials for thermal stabilization of composite thermistors

The objective of this investigation was to develop a triphasic PTC thermistor composite which incorporated a phase capable of absorbing heat at a critical temperature, and thus limiting deleterious effects associated with thermal runaway. The system chosen for study was pentaerythritol incorporated into a carbon black–polyethylene thermistor system. Pentaerythritol exhibits a first order tetragonal to cubic phase transition at 185 °C, with a 1.87 to 3.18 J/°C · g change in specific heat and a 425 J/cm3 heat of transition. Composites with room temperature resistivities as low as 0.1 Ω · m, a PTCR effect of up to six orders of magnitude, and reproducible temperature-cycling behavior were developed. The pentaerythritol introduced thermal delays up to 7 min at 185 °C and substantially increased the electrical and mechanical stability of the composites with temperature and voltage cycling. High fields imparted irreversible effects in these composites as reflected by an increase in the room temperature and high temperature resistivity.

The role of ferroelectric domains in PTC thermistors

Abstract The role of ferroelectric domains in positive temperature coefficient of resistivity (PTCR) barium titanate thermistors will be discussed. Domain related phenomena in this class of technologically important material are analyzed in terms of the grain boundary barrier layer model.

Formulation of silver loaded manganite based thermistor paste and application of percolation theory for sudden transition in conductance

A low cost thermistor paste using manganite (Mn1.5CoN0.5O4) as functional material, prepared by sintering manganese, cobalt, and nickel oxides, is formulated for use as planar temperature sensors. The paste contains glass frit as binder and silver metal (0% to 60% by weight) as conducting phase instead of RuO32. Thermistors are fabricated by screen printing of these pastes on alumina substrates and effect of addition of various percentages of silver on electrical properties like sheet resistivity and temperature coefficient of resistance (TCR) are measured in the temperature range of 25–200 °C. Up to 50% addition of silver the pastes show a negative TCR with thermistor constant in the range 3000–5000 K, and sheet resistivity of the order of 106 Ω/⧠, whereas the pastes with 55% and 60% silver show a drastic reduction in the value of sheet resistivity (20 Ω/⧠) and have positive TCR with thermistor constant of the order of 200–300 K. NTC thermistors have high sensitivity of 5%–7%/K and PTC thermistors have sensitivity of 1%–2%/K. This interesting result of NTC-PTC transformation in relation to silver concentration, along with the sudden change in the conductivity (of about 6 orders of magnitude) at a critical concentration of silver, is discussed in the paper. This has been explained on the basis of an effective medium theory (Springett model) and formation of some metallic silver complex.

Thermal and Electrical Characteristics of Thick Film Overcurrent Protector with Self‐recovery

A thick film overcurrent protector with self‐recovery has been developed using carbon black graft polymer. Carbon black graft polymer, henceforth called CG, is a thick film PTC thermistor material in which a polymer forms a three‐dimensional network structure around carbon blacks by graft‐copolymerising vinyl monomers. Since the CG material gives a large and stable positive temperature coefficient of resistance depending on the copolymer material, due to the difference of thermal expansion coefficient between carbon blacks and polymer, the stable thick film overcurrent protector with self‐recovery can be realised by using the CG material. The overcurrent protector utilises the dynamic current‐time characteristics of the CG element. When a very large current flows through the CG element, the temperature rises by self‐heating, and the resistance of the element increases dramatically; as a result it restrains the current at a lower level. Since this element is not destroyed after excess current flow, it can be used repeatedly, unlike a metal fuse. In this paper, the manufacturing process and thermal and electrical characteristics of the CG overcurrent protector are investigated, including an analysis of these characteristics.

The use of rare earths in ceramics

Three main areas are covered: ceramic tiles, electronic ceramics, engineering ceramics. In ceramic tiles praseodymium oxide in a zirconium silicate matrix is used as a yellow stain. Cerium oxide is used as an opacifier or to give esthetic effects in the glaze. In electronic ceramics barium titanate powder for capacitors and PTC thermistors are doped with lanthanides in order to modify both aging and Curie temperature. Yttrium is used to make ferrites for high frequencies and to stabilize zirconia in oxygen sensors for automative fuel control. Engineering ceramics are new materials which can replace metals. Among them PSZ (where yttrium is used to stabilize zirconia) and Si 3N 4 (where yttrium is used as a sintering agent) are the most promising materials. A survey is made of each sector with respect to final application, areas (U.S.A., Japan, Europe), nature of the rare earths and their function, volumes and major trends.

CR Low frequency tuned amplifier circuit with high selectivity

AbstractThe conductance of the reactance circuit used in the tuning circuit of the CR tuned amplifier is a function of frequency with negative minimum value. If the external parallel resistance to the tuning circuit is reduced so that a high selectivity is obtained, the conductance becomes negative at a frequency other than the resonance frequency and the circuit will oscillate. We have obtained a stable high‐gain tuned amplifier with high selectivity by selecting the values of resistor and capacitor in the voltage phase‐shift circuit so that the conductance of the tuning circuit is minimum at the resonance frequency. The amplifier with the resonance frequency of 10 kHz fabricated according to this design method exhibits the maximum selectivity of about 700 and the voltage gain of about 100 dB. These values agree well with the computed values. The rate of change of the resonance frequency for the temperature has been made rather small with the use of circuit components with small temperature coefficients. However, the rate of change of the gain (and hence selectivity) is extremely large. With the use of an ac resistive circuit with a positive temperature coefficient consisting of PTC thermistors and transistors, the rate has been reduced to the extent tolerable in the practical temperature range.

Present state and future development of instrumental techniques for solution thermochemical (thermometric) analysis

A review of instruments for thermochemical (thermometric) solution analysis is given, including new types of isoperibol reaction of bomb calorimeters, the design of which can influence the future development of thermochemical measuring techniques.The new type of Dithermanal (Vaskut-EMG, Hungary, and Herrmann- Morris, France) controls the individual steps of the thermochemical analysis, adding memory and computing capabilities. Similar programming units with microprocessors for bomb and/or reaction calorimetry have been developed by Parr Comp. and Leco Comp. (USA). The latest modification of the Technicon flow analyzer permits on-line analysis of solid samples. For thermochemical titrations, the Sanda titrator (USA) and Vaskut automatic titrator (Hungary) are available. In the USA, the Tronac isothermal or isoperibol calorimeters are widely used. At the Technical University of Brno, ČSSR, smaller table instruments with a water-bath are applied for different modes of solution thermochemical analysis, and also for the reactions of solid samples in liquids. For the measurement of very small temperature differences, PTC thermistors are used.The possibilities of the future development of measuring techniques are outlined.

New instruments and methods for enthalpimetric analysis and calibration

A review is given of recently developed instruments used in thermometric analysis and new methods of direct injection enthalpimetry. In the past two years, several types of Tronac (Orem, Utah) and Setaram (Lyon, France) calorimeters have been developed. A new mixing cell construction led to development of a flow instrument for automated thermometric analyses (Technicon, Tarrytown N. Y.). A new type of Hungarian instrument, Ditermanal (Orion, Budapest) permits arbitrary analyses. At the Technical University in Brno, small table twin isoperibol instruments allowing the direct analyses of solid samples have been developed. The use of PTC thermistors and a calibration device improved the accuracy of measurements. Many new methods of silicate and lime analysis, water determination, etc. have been elaborated.

Solderable low contact resistance metallizations for PTC thermistors : S. M. Marcus and F. K. Patterson. Proc. IEEE 28th Electron. Components Conf., Anaheim, 24–26 April 1978, p. 80

Solderable low contact resistance metallizations for PTC thermistors : S. M. Marcus and F. K. Patterson. Proc. IEEE 28th Electron. Components Conf., Anaheim, 24–26 April 1978, p. 80

A high sensitivity DC thermometric circuit using operational amplifiers and a hybrid combination of NTC and PTC thermistors

Equations predicting the response of thermometric circuits constructed from operational amplifiers with NTC and NTC—PTC hybrid thermistors are derived and tested. Sensitivities and time constants were determined experimentally and are compared with theoretical predictions. The circuit with the NTC—PTC hybrid is characterized by greater sensivity than a NTC circuit and greater linearity than a PTC circuit.

A low-frequency oscillator using PTC and NTC thermistors

A mathematical model and analysis method for discrete parameter thermistor networks are developed. Methods for predicting the static conditions and the stability and sensitivity of the equilibrium points are given. The dynamic behavior is discussed using numerical analysis methods. Experimental results have been obtained to verify the analysis methods for the case of oscillatory behavior. The analysis method is then used to predict the behavior of the oscillator as the applied voltage, thermal capacitance, dissipation factor, and ambient temperature are varied. It is concluded that the mathematical model and analysis methods predict the behavior of the discrete parameter thermistor networks. The temperature gradients in the elements in still air appear to be negligible, but caution must be used in applying the methods to those networks where the temperature gradients may not be negligible.