• Journal of Sensor Science and Technology
• /
• v.29 no.6
• /
• pp.388-393
• /
• 2020

In this study, a PbS quantum dots (QDs)-based H₂ gas sensor with a Pd electrode was proposed. QDs have a size of several nanometers, and they can exhibit a high surface area when forming a thin film. In particular, the NH₂ present in the ligand of PbS QDs and H₂ gas are combined to form NH₃⁺, subsequently the electrical characteristics of the QDs change. In addition to the resistance change owing to the reaction between Pd and H₂ gas, the resistance change owing to the reaction between the NH₂ of PbS QDs and H₂ gas increases the current signal at the sensor output, which can produce a high output signal for the same concentration of H₂ gas. Using the XRD and absorbance properties, the synthesis and particle size of the synthesized PbS QDs were analyzed. Using PbS QDs, the sensitivity was significantly improved by 44%. In addition, the proposed H₂ gas sensor has high selectivity because it has low reactivity with heterogeneous gases such as C₂H₂, CO₂, and CH₄.

• Journal of the Korean Ceramic Society
• /
• v.26 no.5
• /
• pp.712-718
• /
• 1989

PMN ceramics with excess MgO addition in the range of 0 to 70m/o were prepared, and their electrical properties, such as dielectric constant, tan$\delta$, diffuseness coefficient, remanent polarization, coercive field and electrical conductivity were measured. Dielectric constant and remanent polarization increased with up to 5m/o excess MgO and then decreased presumely due to the precipitation of second phase, etc. Electrical conductivity slightly increased with the addition of excess MgO.

• Journal of the Korean Ceramic Society
• /
• v.38 no.11
• /
• pp.1046-1054
• /
• 2001

Effects of B$_2$O$_3$and CuO addition on the microwave dielectric properties of the PbWO$_4$-TiO$_2$ceramics were investigated in order to use this material as an LTCC material for fabrication of a multilayered RF passive components module. We found that PbWO$_4$could be used as an LTCC material because of its low sintering temperature (8$50^{\circ}C$) and fairy good microwave dielectric properties($\varepsilon$$_{r}$=21.5, Q$\times$f$_{0}$=37200 GHz and $\tau$$_{f}$ =-31 ppm/$^{\circ}C$). In order to stabilize $\tau$$_{f}$ of PbWO$_4$, TiO$_2$was added to the PbWO$_4$and the mixture was sintered at 8$50^{\circ}C$. A near zero $\tau$$_{f}$ value (+0.2 ppm/$^{\circ}C$) was obtained with 8.7 mol% TiO$_2$addition. $\varepsilon$r and Q$\times$f$_{0}$ values were 22.3 and 21400 GHz, respectively. It was believed that the decrement of Q$\times$f$_{0}$ value with TiO$_2$addition was resulted from increasing grain boundary. In order to improve Q$\times$f$_{0}$, various amounts of B$_2$O$_3$and CuO were added to the 0.913PbWO$_4$-0.087TiO$_2$mixture. The optimum amount of CuO was 0.05 wt%. At this addition, the 0.913PbWO$_4$-0.087TiO$_2$ceramic showed $\varepsilon$$_{r}$=23.5, $\tau$$_{f}$ =-2.2ppm/$^{\circ}C$, and Q$\times$f$_{0}$=32900 GHz after sintered at 8$50^{\circ}C$. In case of B$_2$O$_3$addition, the optimum amount range was 1.0~2.5 wt% at which we could obtain following results; $\varepsilon$$_{r}$=20.3~22.1, Q$\times$f$_{0}$=48700~54700 GHz, and $\tau$$_{f}$ =+2.4~+8.2ppm/$^{\circ}C$.

• Transactions on Electrical and Electronic Materials
• /
• v.5 no.3
• /
• pp.109-112
• /
• 2004

In this study, in order to develop the low temperature sintering ceramics for ultrasonic vibrator, Pb(Sb$\_$$\frac{1}{2}$/Nb$\_$$\frac{1}{2}$/) O$_3$-Pb(Ni$\_$1/3/Nb$\_$2/3/)O$_3$-Pb(Zr$\_$0.48/Ti$\_$0.52/)O$_3$ ceramics were manufactured as a function of the amount of CuO addition, and their dielectric and piezoelectric characteristics were investigated. With increasing CuO addition, the grain size and density increased up to 0.3 wt% CuO addition. Taking into consideration electromechanical coupling factor(k$\_$p/) of 0.53, mechanical quality factor(Q$\_$m/) of 423, dielectric constant($\varepsilon$$\_$r/) of 1,759 and piezoelectric constant(d$\_$33/) of 362pC/N, it could be concluded that 0.5 wt% CuO added composition ceramic sintered at 920$^{\circ}C$ was suitable for ultrasonic vibrator application.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.28 no.5
• /
• pp.332-337
• /
• 2015

We have studied the effects of Ag on the characteristics of $Sn_{60}Pb_{40}Ag_x$ (wt%) solder for photovoltaic ribbon. Ag atoms in the solder formed an alloy phase of $Ag_3Sn$ after reacting with some part of Sn atoms, while they did not react with Pb atoms, but decreased the mean size of Pb solid phase. The enhancement of peel strength between solar cell and ribbon is an important part in the developments of long-lifespan solar module. The peel strength of the solder ribbon of $Sn_{60}Pb_{40}$ (wt%) was $169N/mm^2$, and it was largely enhanced by adding a small amount of Ag atoms. The maximum peel strength was $295N/mm^2$ in the solder ribbon of $Sn_{60}Pb_{40}Ag_2$ (wt%). This result is caused by the high binding energy of 162.9 kJ/mol between Ag atoms in the solder and Ag atoms in Ag sheet.

• Bulletin of the Korean Chemical Society
• /
• v.21 no.1
• /
• pp.56-60
• /
• 2000

The mechanism of a matrix modification for the trace determination of volatile lead and bismuth by an electro-thermal atomic absorption spectrophotometry was studied by a X-ray diffractometry (XRD). For the investigation of structures, the ash products of the elements were produced by using a palladium as a matrix modifier with or without aluminum or nickel as an auxiliary modifier. The same charring conditions as in the analysis of samples were applied together with much concentrated solution of analytical elements and modifiers in a graphite furnace to get a large amount of the product for XRD. The XRD patterns showed PbPd3 for lead and BiPd3 for bismuth. These mean that the reaction procedures through the charring and atomization were changed from $Pb^{2+}$ ${\rightarrow}$ PbO ${\rightarrow}$$Pb^0$ to $Pb^{2+}$ ${\rightarrow}$ PbO ${\rightarrow}PbPd_3$ ${\rightarrow}$ Pb o for lead and from $Bi^{3+}$ ${\rightarrow}$ BiO ${\rightarrow}$ Bi o to $Bi^{3+}$ ${\rightarrow}$ BiO ${\rightarrow}$ $BiPd_3$ ${\rightarrow}$ $Bi^0$ for bismuth by the addition of modifiers. The volatile elements were stabilized by the formation of palladium alloys through a charring process. Charring temperatures were raised about 500 $^{\circ}C$ by the alloying and the atomization was also stabilized for the enhancement of sensitivities.

• Applied Chemistry for Engineering
• /
• v.4 no.2
• /
• pp.273-283
• /
• 1993

Addition of various acids or organic compounds to the electrolyte solution during the electrodeposition of $PbO_2$ on titanium madras substrate strongly affected performance of the deposited $PbO_2$ layer. Results of X-ray diffractometry ascertained that ${\beta}-PbO_2$ was deposited in acidic electrolyte. Among additives used in this experiment, $PbO_2$ with a high oxygen overvoltage was electrodeposited when sodium lauryl sulfate was added, and $PbO_2$ with a lower chlorine overvoltage was electrodeposited when polyethylene glycol was added to the electrolyte solution. The oxygen and chlorine overvoltage of $PbO_2$ was strongly dependent on the stirring provided during the electrodeposition experiment. It was observed by the SEM results that the $PbO_2$ grains deposited when stirring was not provided during the electrodeposition have larger than $PbO_2$ grains deposited by stirring. In the $PbO_2$ deposition under acidic electrolyte, the oxygen overvoltage increased with larger $PbO_2$ grains and the chlorine overvoltage decreased with smaller $PbO_2$ grains. The optimal current efficiency of $PbO_2$ in the presence of perchloric acid was observed at $Pb(NO_3)_2$ 560g/l, $65{\sim}70^{\circ}C$, and pH>1.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2005.05a
• /
• pp.64-64
• /
• 2005

• Journal of the Korean Ceramic Society
• /
• v.31 no.8
• /
• pp.841-848
• /
• 1994

The sintering behavior of La-modified PbTiO3 ceramics was investigated in order to improve the poor sinterability of PbTiO3. Addition of La improved the sinterability. It was confirmed that this improvement was due to the decrease in tetragonality ratio c/a of crystal lattice. The variations of dielectric constant and pyroelectric coefficient were measured with temperature. It was observed that with the increase of La content, Curie temperature decreased and dielectric constant at room temperature increased. La-modified PbTiO3 ceramics had smaller pyroelectric figure of merits than those of pyroelectric materials in use. The effects of grain size on dielectric and pyroelectric properties were also investigated. The change of grain size had effect on maximum dielectric constant and pyroelectric coefficient, but is had little effect on pyroelectric figure of merit at room temperature. The closer examination near ferro-paraelectric phase transition temperature revealed that the behavior of phase transition approached a more relaxor character with the increase of La content and the decrease of grain size.

• The Korean Journal of Food And Nutrition
• /
• v.11 no.5
• /
• pp.521-527
• /
• 1998

Removabilities of heavy metals(Cd and Pb) by the tea materials (barley-tea, corn-tea, jasmin-tea, brown rice-green tea, black-tea, cassia tora-tea, persimmon peel-tea, and rice-tea) in the tea-water were studied in the various conditions ; particle size of tea (20, 40, 70 mesh), concentration of heavy metal (25, 50, 100 ppm) and extraction temperature(20, 30, 50, 100$^{\circ}C$). The removabilities by the tea solids were increased as the particle size decreased, concentration of heavy metal increased, and extracting temperature increased. Of the nine kinds of tea, Cd and Pb removability by jasmin-tea was highest. In addition, heavy metal removability by cassia tora tea was better than that of other tea as extraction temperature was increased.