NH4Cl Electrolyte Research Articles

Interfacial chemistry and particle interactions and their impact upon the dewatering behaviour of iron oxide dispersions

The influence of interfacial chemistry and particle interactions on sedimentation and electroosmosis (EO) of coagulated iron oxide dispersions has been investigated. Both pH and ionic strength of NH 4Cl electrolyte had a profound effect on the particle electrokinetic zeta potential and dispersion rheological behaviour (shear yield stress), impacting strongly on the dewatering behaviour. In the absence of NH 4Cl, the zeta potential decreased with increasing dispersion pH, with an isoelectric point (iep) observed at pH 5.6. Upon NH 4Cl addition, specific adsorption of NH 4 + ions onto particles at pH>6 occurred and led to a significant reduction in particle zeta potential, accompanied by a shift in iep to higher pH (>7.5) and/or charge reversal. The shear yield stress was large where the zeta potential was low and small where the zeta potential was high. Fast dewatering rate was achieved by pH modification and NH 4Cl addition, however, these had no substantial impact upon the dispersion consolidation behaviour. Dewatering rates correlated strongly with both particle zeta potential and shear yield stress, the latter being highest at pH where the zeta potential was low and, hence, interparticle attraction was at a maximum (repulsion minimized). The consolidation of concentrated dispersions (60 wt.% solid) to a “spadeable” paste consistency (85 wt.% solid) by electroosmosis was achieved for moderately charged particles at 5×10 −3 M NH 4Cl and pH values away from the iep using moderate power consumption. The results exemplify clear links existing between interfacial chemistry, particle interactions and dewaterability of iron oxide tailings, which may be optimized to facilitate tails compaction.

What is the limiting factor of the cycle-life of Zn–polyaniline rechargeable batteries?

The factors affecting the cycle-life of Zn–polyaniline (PANI) rechargeable batteries are studied by means of electrochemical and surface analyses of electrodes. The PANI polymeric film is prepared by cyclic voltammetery in an aqueous solution, and is tested as the positive electrode (cathode) of a secondary battery containing a 1.0 M ZnCl2 and 0.5 M NH4Cl electrolyte. The battery is charged and discharged by a constant current. The capacity variation of Zn–PANI rechargeable batteries is studied as a function of cycle number, and the relation between capacity loss and performance of the zinc anode and polymeric cathode is examined. The behaviour of the zinc electrode is evaluated from Tafel plots. The capacity decreases with charge–discharge cycling. The cathode (PANI) is degraded electrochemically under charge conditions, and the cycle-life of the Zn–PANI rechargeable battery is limited by the anode (zinc). The polarization resistance (Rp) of the anode increases with cycling. As a result, the battery capacity is limited by the anode Rp. Surface analysis of the anode reveals that a solid phase containing the chlorine element is formed on the anode surface. The cycle-life of the Zn–PANI battery is limited by zinc passivation, which is possibly related to the formation of the solid phases ZnCl2·3NH4Cl and ZnCl2·2NH4Cl on the anode surface.

Electrolyzed Water as an Alternative for Environmentally Benign Semiconductor Cleaning

The present semiconductor cleaning technology is based upon RCA cleaning [W. Kern and D.A. Puotinen, Cleaning Solutions Based on Hydrogen Peroxide for use in Silicon Semiconductor Technology (RCA Rev., 1970) pp. 187–206], a high-temperature process that consumes vast amounts of chemicals and ultrapure water (UPW) [T. Futatsuki, T. Imaoka, Y. Yamashita, and K. Mitsumori, J. Electrochem. Soc., 142, 966 (1995)]. Therefore, this technology gives rise to many environmental issues, and some alternatives such as electrolyzed water (EW) are being studied. In this work, intentionally contaminated Si wafers were cleaned using electrolyzed water. The electrolyzed water was generated by an electrolysis system that consists of anode, cathode, and middle chambers. Oxidative water and reductive water were obtained in the anode and cathode chambers, respectively. When a NH4Cl electrolyte was supplied in the middle chamber, the oxidation–reduction potential and pH for anode water (AW) and cathode water (CW) were +1050 mV and 4.8, and −750 mV and 10.0, respectively. AW and CW deterioriated after electrolysis but maintained their characteristics for more than 40 min, which was sufficient for cleaning. Their deterioration was correlated with CO2 concentration changes dissolved from air. Contact angles of UPW, AW, and CW on DHF-treated Si wafer surfaces were 65.9°, 66.5°, and 56.8°, respectively, which characterizes clearly the electrolyzed water. To analyze the amount of metallic impurities on Si wafer surface, inductively coupled plasma, mass spectroscopy was introduced. AW was effective for Cu removal, while CW was more effective for Fe removal. To analyze the number of particles on Si wafer surfaces, we used the particle measurement Tencor 6220. The particle distributions after various particle removal processes maintained the same pattern. Overflow of EW during cleaning particles resulted in the same cleanness as that obtained with the RCA cleaning process. The roughness of patterned wafer surfaces after EW cleaning was similar to that of as-received wafers. Regardless of process sequence in this work, RCA consumed about 9 l of chemicals, while EW consumed only 400 ml HCl electrolyte or 600 ml NH4Cl electrolyte to clean 8-in. wafers. It was thus concluded that EW cleaning technology would be very effective for releasing environmental safety, and health issues in the next generation of semiconductor manufacturing.

Environmentally-benign cleaning for giga DRAM using electrolyzed water

ABSTRACTA present semiconductor cleaning technology is based upon RCA cleaning technology which consumes vast amounts of chemicals and ultra pure water(UPW) and is the high temperature process. Therefore, this technology gives rise to the many environmental issues, and some alternatives such as functional water cleaning are being studied. The electrolyzed water was generated by an electrolysis system which consists of anode, cathode, and middle chambers. Oxidative water and reductive water were obtained in anode and cathode chambers, respectively. In case of NH4Clelectrolyte, the oxidation-reduction potential and pH for anode water(AW) and cathode water(CW) were measured to be +1050mV and 4.8, and -750mV and 10.0, respectively. AW and CW were deteriorated after electrolyzed, but maintained their characteristics for more than 40 minutes sufficiently enough for cleaning. Their deterioration was correlated with CO2 concentration changes dissolved from air. It was known that AW was effective for Cu removal, while CW was more effective for Fe removal. The particle distributions after various particle removal processes maintained the same pattern. In this work, RCA consumed about 9 chemicals, while EW did only 400ml HCl electrolyte or 600ml NH4Cl electrolyte. It was hence concluded that EW cleaning technology would be very effective for eliminating environment, safety, and health(ESH) issues in the next generation semiconductor manufacturing.

Influence of methylcellulose-coated paper separators on the corrosion, polarization and impedance characteristics of zinc in concentrated ammonium chloride solution. II. Comparison of data obtained in flooded electrolyte and battery environments

An attempt has been made to determinein situ the corrosion rate of the zinc anode in Leclanche batteries devoid of ZnCl2 in the electrolyte using steady-state polarization and a.c. impedance techniques. Previously obtained corrosion data for zinc immersed in flooded NH4Cl electrolyte has been used as a point of reference with which to compare thein situ data and hence gauge its legitimacy. It is shown that in the case of cells containinguncoated paper separators, good agreement between the two sets of data is obtained, thus demonstrating thatin situ corrosion rate measurements can be made. This allows the effects of ionic composition, zinc alloying constituents, amalgamation level, electrolyte impurities, and the role of oxygen, etc, to be determined in the battery environment. However, the anode polarization and impedance characteristics of ZnCl2-free cells containing methylcellulose-coated paper separators do not reflect corrosion processes. In fact the electrochemical data is almost indistinguishable from that obtained in ZnCl2-containing cells. It is postulated that the presence of the methylcellulose layer permits the zinc ion concentration to build up adjacent to the anode causing the cathodic hydrogen evolution process to be electrochemically masked by zinc deposition. The electrochemical characteristics therefore reflect zincexchange processes only. Neither the presence of the separator coating itself nor the restricted volume of electrolyte appear to be unilaterally responsible for the anomalous behaviour of ZnCl2-free cells, but rather a combination of these two conditions is necessary. Thus considerably restricted diffusion and the near absence of convection would appear to be the important factors which dictate the observations.