Crystalline RuO2 Research Articles

A New Charge Storage Mechanism for Electrochemical Capacitors and Charge Storage Density Vs. Crystalline Structure of Metal Oxides

ABSTRACTThe hydrous ruthenium oxide (RuO2.xH2O) powders with different contents of H20 have been formed by a sol-gel process and have been annealed at different temperatures. It was found that the specific capacitance of RuO2.xH2O is strongly dependent on the crystalline structure. The specific capacitance of over 720 F/g was obtained in an amorphous RuO2.xH2O. This value is at least two times greater than ever reported of this type of material.The specific capacitance dropped rapidly as the amorphous phase transforms into the crystalline phase at high temperatures. In contrast to the crystalline phase the specific capacitance of an amorphous RuO2.xH2O was not dependent on the specific surface area. The charge storage mechanism in amorphous RuO2.xH2O is different from that in the crystalline RuO2. The current in the cyclic voltammetric curve of RuO2.xH2O is nearly constant and is symmetrical with the potential in a range of 1 volts. The resistivity of pellets made from these powders is in the order of 10−3 Ω-cm.

Vernetzung von CD-ROM-arbeitsplätzen beim ungarischen patentamt: Eine fallstudie : Vadász, Á. World Patent Information 16(1), pp. 46–49

The hydrolysis of ruthenium alkoxide/titanium tetraethoxide mixtures to gels and powders containing 30–40 mol% Ru was investigated. Basic or neutral conditions led to powders consisting of 2–10 nm diameter crystalline RuO2 nanoparticles embedded in a matrix of crystalline (anatase) and amorphous TiO2. Acid hydrolysis conditions gave gels containing smaller, amorphous RuO2 nanoparticles (1–3 nm). In all samples the RuO2 nanoparticles tended to clump into aggregates up to 0.5 μm across. Acid or neutral hydrolysis of ruthenium ethoxide gave samples which displayed lower surface Ru:Ti ratios as measured by XPS compared to the bulk (XRF), and also contained more low-valent Ru (as measured by XRF), probably due to incomplete hydrolysis of the precursors. These samples also contained more Ru metal after calcination (XRD). Calcination (450 °C) was accompanied by Ru-promoted combustion of organic material and led to crystalline (anatase) TiO2 and TixRu1−xO2 solid solution (rutile phase).

The influence of the preparation temperature of colloidal ruthenium dioxide on the photosensitized reduction of H + ions

Samples of colloidal RuO 2were prepared by thermal decomposition of RuCl 3 at 300, 400 and 500 °C. X-ray diffraction showed that they all consisted of stoichiometric and crystalline RuO 2. The specific surface area decreases strongly with increasing preparation temperature. Catalytic properties for the photochemical production of hydrogen were tested in an aqueous system containing a photosensitizer (ruthenium trisbipyridyl), an electron relay (methylviologen) and an electron donor (EDTA). In this solution the RuO 2 particles form aggregates which have approximately the same size for all preparation temperatures. The rate of hydrogen gas production was measured as a function of weight concentration of RuO 2. For RuO 2 samples prepared at 300°C and at 400°C identical curves were obtained; for the 500 °C sample the production rate is slightly lower only for low RuO 2 concentrations. The aclivation energies for hydrogen evolution are the same for all RuO 2 samples, and do not change upon addition of anthracene carboxylate, which changes the mechanism of the homogeneous reactions. It is concluded that the small variation in hydrogen production rate with preparation temperature of the catalyst is due to changes in mass transfer of methylviologen radicals to the catalytic surface. Differences in catalytic properties of the RuO 2 samples are negligible.

Surface-modified RuO2-based thick film resistors using Nd:YAG laser

An RuO2-based thick film resistor (TFR) is a cermet-type resistor which consists of RuO2 particles and glass. Paste containing organic vehicles is printed onto an insulating substrate, and subsequent firing at about 900 °C makes the cermet-type resistors. TFRs are widely utilized as electrical resistive materials in electric devices such as hybrid ICs (integrated circuits) [see, for example, R. W. Vest, Ceram. Bull. 65, 631 (1986)]. The features of an advanced laser application process to control the electrical resistivity of the TFRs were proposed. This new process is an application of surface-modification using laser beams. In this paper, a mechanism of the surface-modification of the TFR is considered using results of morphology observation, x-ray diffraction (XRD), and x-ray photoemission spectroscopy (XPS). The following points should be noticed. (1) In the surface-modifying process using normal mode pulse Nd:YAG laser beams, glass in the TFR is modified and supersaturated with ruthenium impurities because of rapid heating and rapid cooling rates in the irradiation process; the specific resistivity of the modified glass is extremely decreased, estimated at 10−3 Ω cm at most. (2) No new crystalline phase in the ruthenium-oxygen system is detected after the surface modification by results of x-ray diffraction (XRD) analysis. (3) The valence state of the ruthenium ions in the modified glass is more positively charged than that in crystalline RuO2 , while the valence states of lead and oxygen ions in the modified glass are more negatively charged than in as-fired glass before surface modification according to the results obtained by x-ray photoemission spectroscopy (XPS) analysis. It is suggested that if ruthenium ions introduce electrons into the modified glass and if these electrons behave as itinerant electron carriers in the modified glass, a decrease in the resistivity of TFR after the surface modification is quite reasonable for the results of XPS.