Sodium-Ion Conductivity and Humidity-Sensing Properties of Na2O-MoO3-P2O5 Glass-Ceramics

A series of glass-ceramics were prepared by heat-treatments of 40Na2O-30MoO3-30P2O5 (in mol%) glass in a temperature range from 380 (Tg) to 490 °C (Tc) and for 1–24 h. The prepared glass-ceramics contain from 2 to 25 wt.% of crystalline NaMoO2PO4. The sodium-ion conductivity in these materials decreases up to one order of magnitude with an increase in the degree of crystallization due to the immobilization of sodium ions in crystalline NaMoO2PO4. The transport of sodium ions in these materials occurs primarily through the dominant continuous glassy phase, and it is weakly affected by the sporadically distributed crystalline grains. However, the prepared glass-ceramics exhibit high proton conductivity in a humid atmosphere and remarkable humidity-sensing properties; this could be related to crystalline NaMoO2PO4, which provides sites for water adsorption. The glass-ceramic prepared at 450 °C for 24 h shows the best humidity-sensing performance among all samples, showing an increase in proton conductivity for more than seven orders of magnitude with the increase in relative humidity from 0% to 95%. Under a highly humid atmosphere (95% relative humidity and 25 °C), the proton conductivity of this glass-ceramic reaches 5.2 × 10−3 (Ω cm)−1. Moreover, the electrical response of these materials on the change in the relative humidity is linear and reversible in the entire range of the relative humidity, which indicates that they are novel promising candidates for application as humidity sensors.

The Effect of Adding Sodium Carbonate on the Electrical Conductivity of Aluminum Paste

Base metal pastes have been widely used in the preparation of ZnO varistor electrodes, and it is important to accurately grasp the relevant mechanisms affecting the conductivity of aluminum electrodes. In this paper, the effect of adding sodium carbonate on the conductive property of aluminum paste was assessed, and the microscopic mechanism during aluminum electrode sintering explored. The results show that adding sodium carbonate can reduce the softening point of glass powder and enhance its fluidity. Sodium carbonate, glass, and aluminum oxide film react together; consequently, the aluminum oxide film is partially dissolved by reaction to produce defects, and there is tight contact at the interface between the aluminum powder particles. The sodium ions will displace the aluminum ions in the alumina, conferring the alumina film with a certain ionic conductivity. At the same time, sodium ions are doped into the aluminum lattice, which causes the aluminum lattice to swell. After sintering, the structure of aluminum electrode is compact and its electrical conductivity is significantly improved. This study is a valuable reference for the theoretical research and the potential applications of aluminum paste.

Electrical Properties of Pure and Modified Copper Tartrate Single Crystals

The present paper reports the electrical properties of pure and sodium modified copper tartrate single crystals. Single crystal growth of these materials followed by their characteristics has already been published somewhere else. Having achieved the growth of pure and sodium modified copper tartrate single crystals and established their basic characteristics, it is thought worthwhile to have an understanding of their electrical properties and their modification on replacement of some copper ions in the lattice of copper tartrate by sodium ions. The electrical properties are studied by measuring electrical conductivity in the temperature range from 80 to 300 K. The study reveals that conductivity is a function temperature in these crystals. Moreover both pure and modified copper tatrate single crystal are semiconducting but the conductivity of pure modified copper tatrate single crystal is more than that of pure a copper tatrate single crystal. The results have been explained in terms variable range hopping model.

Visualization of Spatial Charge in Thermally Poled Glasses via Nanoparticles Formation

It is shown for the first time that the vacuum poling of soda-lime silicate glass and the subsequent processing of the glass in a melt containing silver ions results in the formation of silver nanoparticles buried in the subanodic region of the glass at a depth of 800–1700 nm. We associate the formation of nanoparticles with the transfer of electrons from negatively charged non-bridging oxygen atoms to silver ions, their reduction as well as their clustering. The nanoparticles do not form in the ion-depleted area just beneath the glass surface, which indicates the absence of a spatial charge (negatively charged oxygen atoms) in this region of the vacuum-poled glass. In consequence, the neutralization of the glass via switching of non-bridging oxygen bonds to bridging ones, which leads to the release of oxygen, should occur in parallel with the shift of calcium, magnesium, and sodium ions into the depth of the glass.

Precipitation to remove calcium ions from stabilized human urine as a pre-treatment for reverse osmosis

Concentration of Ca(OH)2 stabilized urine by reverse osmosis (RO) has the potential to cause CaCO3 scaling on the membranes. The aim of this research was to determine whether the addition of carbonate salts could be used to precipitate CaCO3 prior to RO concentration and how to accurately dose the salts. Dosing of NaHCO3 or Na2CO3 reduced the calcium concentration to <0.18 mmol L−1, whilst maintaining a pH > 11. This is the pH threshold for enzymatic urea hydrolysis in urine, but above the operating pH range of most membranes. However, the pH could be decreased by adding an acid. Measuring conductivity as a proxy for the calcium concentration was found to be an effective method to determine the dose of salt required. Simulations with other carbonate producing salts (KHCO3, Mg­CO3, and NH4HCO3) were also shown to be effective. However, NH4HCO3 ($0.53 m−3 urine) was the only other salt comparable in cost to NaHCO3 ($0.49 m−3 urine) and resulted in a final pH within the normal operating range of membranes. The addition of NH4HCO3 would add extra N to the urine rather than sodium ions when dosing NaHCO3. The choice of salt will ultimately depend on what liquid fertilizer composition is desired.