Platinum Ribbon Research Articles

Stapedectomy Technique

This article reviews the evolution of the author's stapedectomy technique from total footplate removal with single loop wire prosthesis and Gelfoam seal to small fenestra stapedectomy with platinum ribbon piston prosthesis and blood seal. The author concludes that the microdrill is effective, safe, and cost effective for performing this procedure. Since using this technique, the author has had no cases of sensorineural hearing loss and few complaints of dizziness or vertigo.

Traveling temperature fronts on catalytic ribbons

Ignition and extinction fronts were observed on a thin platinum ribbon heated by a constant electrical current during ammonia oxidation in air. At a fixed ammonia concentration, propagation velocity of the ignition fronts increased with increasing current, while extinction fronts' speed increased as the current was decreased. A relatively wide range of currents exists in which the velocity of the extinction front is extremely small, but the front velocity vanishes only at one current value.

Temperature patterns on a catalytic ribbon heated by a constant electrical current: propylene oxidation

This paper discusses how temperature variations of the reaction rate of the oxidation of propylene in air on a platinum ribbon heated by a constant electrical current revealed that the ribbon remained at a constant high temperature for most of the time, but boundary movement of this region caused temporal variations in the reaction rate. The oscillation of the reaction rate decreases with increasing current, occurs at a higher frequency and decays exponentially as compared to the local temperature. The oscillation time interval probability density function is widely spread around two modes. 36 refs., 12 figs.

Catalytic oxidation of methane on platinum thin films

The kinetics of methane catalytic oxidation on platinum thin films have been studied in order to improve the lifetime and sensitivity of methane calorimetric sensors. The samples are placed in a quartz reactor and are heated up to 830 °C in isothermal conditions under a mixture of 1% methane in air with a flow rate of a few tens of cm 3/min. The gas phase is analysed by mass spectrometry. The behaviour of thin platinum ribbons and of evaporated thin films has been compared. An Arrhenius plot of the reaction rate yields an activation energy of about 30–35 kcal/mole for platinum ribbons, which is consistent with previous determinations. After heating the obtained platinum films at a temperature higher than 730 °C in the reactive mixture, their activity becomes of the same order of magnitude as that of clean platinum ribbons.

Spatiotemporal temperature patterns on an electrically heated catalytic ribbon

Oscillatory and chaotic variations in the overall reaction rate were observed during the oxidation of propylene in air on a thin platinum ribbon, the average temperature (resistance) of which was kept at a preset value via electrical heating. A thermal image showed that back and forth movement of a high-temperature wave on the ribbon and the dynamic change in the length and temperature of the ignited zone were the cause of the variation in the overall reaction rate

Surface adsorption and gas consumption in restricted flow, thermally driven, gas sensors

The operation of a new type of thermally cycled gas sensor is examined. Taguchi-type tin oxide semiconductor gas sensors are mounted within a small chamber, along with a platinum ribbon, and access to the outside atmosphere is restricted to a narrow opening. During the thermal cycling of either the sensor heater voltage or the platinum ribbon current, gas will 'breathe' in and out of the chamber. The outside atmosphere contains the reducing gas to be tested mixed in normal air. When cycling the sensor temperature, gas will enter as the tin oxide cools, and adsorb onto the surface. When the tin oxide is reheated the adsorbed gas will quickly oxidise, producing a sharp rise in conductance. Increasing the rate of bulk gas consumption in the enclosed chamber, by increasing the constant current supplied to the platinum ribbon, the authors are able to examine this process in more detail. In other experiments the sensor heater is kept at a constant voltage and the gas is drawn in by cycling the platinum ribbon current. In this case low-temperature surface adsorption does not take place and direct comparison of gas consumption rates can be made. They examine the response of the TGS Hash 812 and the TGS Hash 813 to ethanol, propane and carbon monoxide gas.

Design of platinum hot wire gas sensors

The design characteristics of lower-power platinum gas sensors are studied. These sensors work by the detection of the positive ions produced during the catalytic oxidation of organic vapours on hot platinum wires and ribbons. These sensors are selective to long-chain hydrocarbons. A prototype sensor design is presented, which uses a small piece of platinum ribbon welded to a ceramic header with a wire mesh cathode to collect the positive ions. The ionic current is measured with a battery-run picoammeter circuit biased to float at −120 V. The ribbon is heated resistively with a standad power supply. At the operating temperature of 800 °C, the power consumption is about 2 W. The prototype is capable of detecting iso-octane vapour down to a concentration of 2 ppm. Platinum ribbon was used rather than wire as the wire had a greater tendency to melt due to thermal runaway in the resistive heating process. It was observed that the number of positive ions produced by the catalytic process decreased during long-term measurements. Scanning electron micrographs showed this to be due to facetting of the platinum surface. A few seconds' exposure at 1300 °C restored the surface and the ionic response. Thus periodic thermal cycling is necessary for the prototype sensor.

Chaos during the oxidation of carbon monoxide on platinum—experiments and analysis

Experiments were conducted on the oxidation of carbon monoxide on a polycrystalline platinum ribbon in a gradientless, isothermal system. Qualitatively reproducible aperiodic oscillations were observed at two different states, and recently developed methods to identify the existence of a strange attractor, and thus deterministic chaos in phase space, were applied to the experimental data. These methods included Fourier power spectral analysis, Poincaré sections, Poincaré maps and the dimension and the Kolmogorov entropy of the attractor—all of which yielded results suggesting that the observed aperiodic behaviour is deterministic chaos and that a minimum of four state variables are necessary to model the system.

Diaphragm pacing by electrical stimulation of the phrenic nerve.

Sophisticated techniques for electrical stimulation of excitable tissue to treat neuromuscular disorders rationally have been developed over the past 3 decades. A historical review shows that electricity has been applied to the phrenic nerves to activate the diaphragm for some 200 years. Of the contemporary methods for stimulating the phrenic nerve in cases of ventilatory insufficiency, the authors prefer stimulation of the phrenic nerve in the thorax using a platinum ribbon electrode placed behind the nerve and an attached subcutaneously implanted radiofrequency (RF) receiver inductively coupled to an external RF transmitter. Instructions are given for implanting the electrode-receiver assembly, emphasizing atraumatic handling of the phrenic nerve and strict aseptic techniques. Diaphragm pacing is conducted with low frequency electrical stimulation at a slow repetition (respiratory) rate to condition the diaphragm muscle against fatigue and maintain it fatigue-free. Candidates for diaphragm pacing are those with ventilatory insufficiency due to malfunction of the respiratory control center or interruption of the upper motor neurons of the phrenic nerve. In the Yale series, there were 77 patients treated by diaphragm pacing; 63 (82%) started before 1981 and thus were available for follow-up for at least 5 years; 33 (52%) were paced for 5 to 10 years, and 15 (24%) were paced for 10 to 16. Long term stimulation of the phrenic nerves to pace the diaphragm is an effective method of ventilatory support in selected cases.

Diaphragm pacing by electrical stimulation of the phrenic nerve

Sophisticated techniques for electrical stimulation of excitable tissue to treat neuromuscular disorders rationally have been developed over the past 3 decades. A historical review shows that electricity has been applied to the phrenic nerves to activate the diaphragm for some 200 years. Of the contemporary methods for stimulating the phrenic nerve in cases of ventilatory insufficiency, the authors prefer stimulation of the phrenic nerve in the thorax using a platinum ribbon electrode placed behind the nerve and an attached subcutancously implanted radiofrequency (RF) receiver inductively coupled to an external RF transmitter. Instructions are given for implanting the electrode-receiver assembly, emphasizing atraumatic handling of the phrenic nerve and strict aseptic techniques. Diaphragm pacing is conducted with low frequency electrical stimulation at a slow repetition (respiratory) rate to condition the diaphragm muscle against fatigue and maintain it fatigue-free. Candidates for diaphragm pacing are those with ventilatory insufficiency due to malfunction of the respiratory control center or interruption of the upper motor neurons of the phrenic nerve. In the Yale series, there were 77 patients treated by diaphragm pacing; 63 (82%) started before 1981 and thus were available for follow-up for at least 5 years; 33 (52%) were paced for 5 to 10 years, and 15 (24%) were paced for 10 to 16. Long term stimulation of the phrenic nerves to pace the diaphragm is an effective method of ventilatory support in selected cases. (Neurosurgery 17:974-984, 1985)

Polarization (ellipsometric) measurements of liquid condensate deposition and evaporation rates and dew points in flowing salt/ash-containing combustion gases

An optical polarization (“ellipsometric”) technique is developed for measuring rapidly growing and evaporating transparent liquid condensate films (e.g., boric oxide) on solid surface exposed to flowing combustion product gases at film thicknesses well below the onset of complications due to run-off. To demonstrate the validity of optical techniques both ellipsometric and optical interference techniques were first used to measure, under similar geometric, flow, and thermal conditions, the growth rate of solid molybdenum trioxide films on molybdenum, with excellent agreement being obtained. Moreover, our new polarization results for the B 2O 3( l) deposition rate from BCl 3-seeded propane/air flames agree well with the results of our earlier interference measurements, and also with theoretical chemical vapor deposition predictions. While previously unable to measure interferometrically B 2O 3( l) evaporation rates, these rates (from platinum ribbons into seeded/propane air flames) are here estimated using the polarization technique. It appears that, compared with the interference method, the polarization technique places less stringent requirements on surface quality, which may justify the added optical components needed for such measurements. We conclude that the complementary real-time optical methods of polarization (ellipsometry) and interference hold considerable promise for application to rapid remote measurement of condensation and evaporation rates in high temperature (e.g., combustion product) flow environments at film thicknesses below the onset of complications in interpretation due to liquid film run-off.

Optical experiments on thermophoretically augmented submicron particle deposition from “dusty” high temperature gas flows

Using a real-time laser-reflectivity method and platinum ribbon targets we have obtained, and here report, experimental data on the initial deposition rate of MgO(s) particles of approximately 0.7 μm diameter from otherwise “clean” combustion products as a function of target temperature (about 950 K – 1450 K and mainstream gas temperature (about 1500 K – 1600 K). These preliminary data are used to demonstrate the dominant role of thermophoresis (particle drift down a temperature gradient) and to assess the utility of recently developed theoretical methods for predicting and correlating the temperature dependence of thermophoretically augmented convective-diffusion “dust” deposition rates from flowing hot gases. While additional aspects of this theoretical approach remain to be tested, it is already evident that engineering predictions of small particle (or heavy vapor) mass transfer rates in the presence of energy transfer must include the thermophoretic mechanism, and that temperature “contrast” or the ratio T(surface)/T(gas) can, therefore, play as decisive a role in determining mass transfer (deposition or “fouling”) rates as the mainstream submicron dust loading itself.

Subgrain rotation during in-situ annealing of Al-6 wt% Ni in the HVEM

Recently a series of commercial aluminum alloys has been developed (based on eutectic compositions), which contain a high volume fraction (∼10%) of second phase [1,2]. This paper describes the behavior of one such alloy, when thinfoil specimens (75% defd.) were annealed in-situ in the HVEM.The eutectic alloy studied was Al-6 wt% Ni. The alloy heat treatment and particle (Al3Ni) dispersion parameters are given in Table 1. Three-mm discs were punched from as-deformed material. Thin foil specimens were prepared by standard jet polishing techniques. In-situ annealing was carried out in the AEI EM7 high voltage electron microscope at 500 kV, using a platinum ribbon heating stage [3].

Optical methods and results of dew point and deposition rate measurements in salt/ash‐containing combustion gases—B2O3(I) deposition rates by interference methods and comparisons with theory

AbstractThis study is focused on deposition rate processes leading to inefficiency and “hot corrosion” in fossil‐fuel‐fired furnaces and engines. The inorganic compounds which deposit on heat exchanger surfaces and blades are formed in combustion product gases when the fuel and/or ingested air contains inorganic impurities. An improved understanding of the coupled thermodynamic, kinetic, and transport processes governing the deposition rate of inorganic oxides and salts from hot gases containing these compounds (or their precursors) can suggest more efficient test strategies and control measures. Accordingly, an optical interference method for accurately measuring the growth rate of deposits well before the onset of run‐off under laboratory burner conditions has been developed.To demonstrate the technique and provide data suitable for theoretical model development, a deliberately simple chemical system and target geometry are used. BCl3(g) is introduced into a premixed C3H8‐air flat flame at atmospheric pressure. The growth rate of B2O3(I) on an electrically heated platinum ribbon is then measured interferometrically over a range of fuel/air ratios and seed levels. However, the very existence of B2O3(I) deposition at the present seed levels and surface temperatures (about 1,200–1,300 K) clearly demonstrates the importance of kinetic restrictions on B2O3(I) gasification reactions. Optically measured film growth rates are obtained at film thicknesses small enough to neglect condensate run‐off, hence they yield vapor deposition rates directly. These deposition rates are found to be in good agreement with the predictions of a recently developed multicomponent mass‐transfer boundary layer (BL) theory, with a constrained equilibrium ((HBO2)3 precluded) boundary condition. Remarkably, at a constant value of the BCl3 flow rate, the Pt ribbon temperature above which there is no B2O3 condensate (i.e., the so‐called dew point) is observed to depend on the fuel/air ratio. Whereas previous equilibrium‐based deposition models cannot embrace such phenomena, a semi‐quantitative argument, based on the nonequilibrium chemistry of B2O3 precursor formation and (HBO2)3‐formation barriers, explains these potentially significant trends. These encouraging results suggest a more general applicability for the optical methods and chemically frozen (CF) BL theory described herein, and demonstrate the important role of heterogeneous and homogeneous kinetic barriers in determining dew points and deposition rates in combustion systems.

On energy transfer and catalytic reaction of 1-butene on platinum

Single collision energy transfer catalytic reaction of 1-butene of polycrystalline platinum at temperatures up to 1040 °C has been studied with a modulated molecular beam mass spectrometer. The free radicals, C4H7 and C3H5, which has previously been reported as strong evidence for catalytic reaction by platinum, are not evolved. In collision with the heated surface, 1-butene molecules acquire considerable internal energy, which lowers the appearance potentials for the radical ions. By studying appearance potential curves for C4H+7 and C3H+5 from 1-butene heated in a molecular beam oven, as well as by the platinum ribbon, and using time-of-flight measurements to determine translational energy accommodation, several aspects of the energy transfer process have been investigated. A possible explanation for the disparate results on free radical production by 1-butene on heated platinum is presented.

Study of H 2 and CO coadsorption on platinum

Coadsorption of H 2 and CO has been studied on a recrystallized platinum ribbon using TDS and ESD techniques. TDS spectra are presented corresponding to sample exposure to H 2 CO mixture ratios of 11 and 3. The presence of CO in the dosing gas is shown to be responsible for the appearance of a high temperature peak in the mass 2 TDS spectra. ESD O ion energy distributions are presented which exhibit a double peak structure when both hydrogen and carbon monoxide are adsorbed on the platinum surface. The results are interpreted as evidence for the existence of a surface species containing both H and CO.

Oszillationen der reaktionsgeschwindigkeit bei der reaktion von NO MIT CO an platin im Knudsengebiet

The reduction of NO by CO on a polycrystalline platinum ribbon is studied in a open system at pressures less than 5 × 10 −4 Torr (6.7 × 10 −2 Pa). In the temperature range 440 < T/K < 520 one can initiate sustained oscillations of the reaction rate in an oxidizing atmosphere (1 < p NO / p CO < 4). At constant feed of gas to the reactor this can be obtained by a temperature jump, at constant temperature of the catalyst these oscillations may be created by the variation of the partial pressure of one of the reactants. As the oscillations arise isothermally under Knudsen conditions they cannot be due to the coupling of transport phenomena and reactions at the catalyst surface. The interaction between adsorbed gases and the surface structure must play the determinant roll.

Surface Stress Curves for Platinum

Electrocapillary‐type curves were measured for platinum ribbon electrodes in aqueous salt solutions using an extensometer instrument previously developed. A surface stress maximum was observed which varied with pH with a slope of about −50 mV/pH. This surface stress maximum is attributed to formation of a surface platinum hydride. Immediately positive of this maximum is a region about 0.15–0.4V wide in which platinum exhibits classical electrocapillary behavior. At potentials more positive than this region, the surface stress decreases rapidly due to formation of surface oxides. A surface stress maximum is found for the oxide surface at +1.8V.

Die kinetik der reaktion zwischen no und co an polykristallinem platin bei niedrigen drucken: I. Messmethode und experimenteller Befund

The reaction between NO and CO on a polycrystalline platinum ribbon under stationary conditions is followed by mass-spectrometry using isotopically labelled 13CO. At temperatures from 300 to 1100 K the ratio of the partial pressure of reactants varies between 0.1 < P NO P CO < 10, the value of total pressure in the reactor being 1.75 × 10 −4 or 4.2 × 10 −3 Torr. The main reaction to N 2 and CO 2 is accompanied by the parallel reaction to N 2O and CO 2 which attains under certain conditions up to 50% of the total reaction. The pronounced temperature dependence of the reaction rate leads to maximum values between 500 and 650 K, the corresponding values of the reaction probabilities are as high as 0.3.

A tilting high temperature gas reaction chamber for the JEM 7A T.E.M.

A gas reaction chamber has been designed and constructed for the JEM 7A transmission electron microscope which is based on a notably successful design by Hashimoto et. al. but which provides specimen tilting facilities of ± 15° aboutany axis in the plane of the specimen.It has been difficult to provide tilting facilities on environmental chambers for 100 kV microscopes owing to the fundamental lack of available space within the objective lens and the scope of structural investigations possible during dynamic experiments has been limited with previous specimen chambers not possessing this facility.A cross sectional diagram of the specimen chamber is shown in figure 1. The specimen is placed on a platinum ribbon which is mounted on a mica ring of the type shown in figure 2. The ribbon is heated by direct current, and a thermocouple junction spot welded to the section of the ribbon of reduced cross section enables temperature measurement at the point where localised heating occurs.