Abstract: An NOx sensor has the sensor element made of an oxide, the resistance of which is varied in response to an NOx component in a gas to be measured, and a measuring portion for measuring a resistance variation of the sensor element and for detecting an NOx concentration in the gas to be measured. A catalyst is arranged at an upstream side of a flow of the gas to be measured with respect reach to the sensor element, which makes a partial pressure ratio of NO/NO.sub.2 reach to an equilibrium state and removes a CO component from the gas to be measured. A heater for adjusting a temperature is arranged at a position close to the sensor element, which maintains temperatures of the sensor element and the catalyst constant. An O.sub.2 sensor is arranged at a position close to the sensor element so that the measuring portion can detect accurately the concentration of Nox in the measurement gas by reference to the resistance of the sensor element.

Abstract: A fabric chemical sensor, a process and an apparatus is disclosed. The sensor, process and apparatus are for the detection, classification, identification and/or quantitation of one or more component chemicals of a chemical vapor via a resistance measurment made across sensor in response to exposure of the sensor to the chemical vapor.

Abstract: A sensor for hydrogen is disclosed comprising an electrically insulating substrate carrying a thin amorphous film of co-deposited nickel and zirconium and an overlying film of palladium wherein during the operation of the sensor, hydrogen in a sample gas is dissociated on the palladium film and diffuses into the nickel-zirconium film to change its electrical resistance in proportion to the amount of hydrogen in the sample to be analyzed.

Abstract: A halogenated hydrocarbon (HHC) detector is formed from a silent discharge (also called a dielectric barrier discharge) plasma generator. A silent discharge plasma device receives a gas sample that may contain one or more HHCs and produces free radicals and excited electrons for oxidizing the HHCs in the gas sample to produce water, carbon dioxide, and an acid including halogens in the HHCs. A detector is used to sensitively detect the presence of the acid. A conductivity cell detector combines the oxidation products with a solvent where dissociation of the acid increases the conductivity of the solvent. The conductivity cell output signal is then functionally related to the presence of HHCs in the gas sample. Other detectors include electrochemical cells, infrared spectrometers, and negative ion mobility spectrometers.

Abstract: A method for metering a reagent into a flowing medium includes adjusting a quantity of a reagent to be metered per unit of time into a flowing medium as a function of a thickness of a reaction zone in a catalytically active material. An apparatus for metering a reagent into a flowing medium includes a control unit, a device associated with the control unit for detecting a thickness of a reaction zone, and a metering device associated with the control unit for introducing a reagent into a flowing medium upstream of a catalytic converter as seen in flow direction of the medium. The control unit adjusts a quantity of the reagent to be metered into the flowing medium per unit of time by the metering device, as a function of a thickness of the reaction zone.

Abstract: A combustible gas sensor having a noble metal sensor element with a surface that is heated above a critical temperature at which the surface is able to dissociate oxygen in a gas stream and adsorb the oxygen onto its surface. The adsorbed oxygen present on the noble metal surface enhances the reactivity of the sensor element and permits it to react with combustible gases that otherwise would have little or no affinity for the sensor element. The balance of adsorbed oxygen and combustible gas species on the sensor surface cause a change in an electrical property that is used to determine the presence or identity of a combustible gas, or to derive a concentration measurement.

Abstract: A sensor is proposed for detecting nitrogen oxides (NO, NO.sub.2, N.sub.2 O.sub.4) in a test gas, having a semiconducting metal oxide layer (3) which is deposited on a ceramic substrate (10) and whose electrical resistance provides information about the concentration of nitrogen oxides (NO, NO.sub.2, N.sub.2 O.sub.4) in the test gas. The main components of the sensor are a converter layer (4) which is deposited on the metal oxide layer (3) and is made of a material which causes the oxidation of combustible components of the test gas and converts the nitrogen monoxide (NO) contained in the test gas into nitrogen dioxide (NO.sub.2) or dinitrogen tetroxide (N.sub.2 O.sub.4), which then reaches the metal oxide layer (3), as well as a heating device (5) which heats the metal oxide layer (3) and the converter layer (4). The converter layer is suitably constituted of titanium oxide (TiO.sub.2) and/or zirconium oxide (ZrO.sub.2) and/or silicon oxide (SiO.sub.2) and/or aluminum oxide (Al.sub.2 O.sub.

Abstract: A gas detecting device for a vehicle includes a casing which is formed therein with an air passage having an air inlet and an air outlet located above the air inlet. A filter is provided in the air passage below and downstream of a gas sensor. The filter has a lower end surface at a side of the air inlet and an upper end surface at a side of the gas sensor. The lower end surface of the filter works as an air-passing surface through which the air flows into the filter, while the upper end surface of the filter works as an air-passing surface through which the air flows out of the filter. A certain gap is provided between a lower portion of a side surface of the filter and an inner wall surface of the casing defining the air passage so that this lower portion of the filter also works as an air-passing surface through which the air flows into the filter. A labyrinth structure may be provided in the air passage between the air inlet and the filter for causing the air to meander at the labyrinth structure.

Abstract: A process for extracting extractable material from a base material in which it is present, while protecting against explosion of any solvent vapor in air includes heating by microwave radiation in a closed pressure-resistant and heat-resistant container, such base material, extractable material and organic extraction solvent, passing air near or into contact with the extraction container so that it will carry away from the container any escaping solvent vapor, and passing said air with the solvent vapor, if present, into contact with solvent detector which turns off a source of microwave radiation when the solvent vapor is present. Preferably the invented process will include passing the air, with any solvent vapor which may be present in it, to a flow detector, which will turn off the source of microwave radiation if flow ceases.

Abstract: P-type semiconductor 15 and n-type semiconductor 16 are formed as thick films or spray-coated onto electrodes 13 and 14 on top of substrates 11 and 12, with films of p-type semiconductor 15 and n-type semiconductor 16 being formed in such manner that they are in mutual contact. If a gas to be detected is introduced to the contact region while a bias voltage is being applied between the two electrodes, an output will be obtained in accordance with the concentration of flammable gas components in the gas being detected. In addition, if a film is formed from a material comprising a mixture of particles of p-type semiconductor and particles of n-type semiconductor, the bias voltage can be an AC voltage.

Abstract: To provide an oxygen sensor having a heater unit without being broken by vibration impact of a vehicle, the oxygen sensor includes a cylindrical oxygen detecting element with a closed bottom and a heater unit installed in an inside of the oxygen detecting element. The heater unit includes insulators, the heat generating body helically wound a surface thereof and lead wires. In the insulators, concave portions reaching lead holes are disposed. Lead wires are put through the lead holes from an outer circumferential surface. In the concave portions, the heat generating body and the lead wires are connected. The outer circumference of a winding portion of the heat generating body is preferably formed at a position more inwardly than the outer circumferential surface of the adjacent insulator.

Abstract: The disclosure where the hydrogen peroxide vapor 4a is supplied to a treatment vessel, and a subject 1 to be treated in the treatment vessel 2 is subjected to a sterilization treatment by contact with the hydrogen peroxide vapor 4a, the concentration of the hydrogen peroxide vapor 4a in the treatment vessel 2 is detected directly and accurately on a real-time basis by a semiconductor gas sensor 8.

Abstract: A thin film device having a selectively passivated surface is provided. An embodiment of the device is particularly suited to detection of chemical constituents by selective adsorption, where the selectively passivated surface is inert to the chemical constituent being detected. A method of fabrication of the device is also provided in which the selective passivation is achieved by selectively applying the metallic adhesive to the substrate. The migration of the metallic adhesive through the thin film layer is essentially normal to the surface of the substrate, thereby limiting the passivation of the thin film layer to the surface areas directly overlying the metallic adhesive.

Abstract: An improved sensor support subassembly for a chemical sensor in the testing of gaseous emissions. The sensor support subassembly of the present invention comprises means for slideably engaging a sensor unit with a gas intake manifold block. The sensor unit comprises a cylindrical base which forms the inlet to the sensor. The manifold block comprises a gas intake means, a gas channel and a U-shaped slot for slideably engaging the sensor unit's cylindrical base within the manifold block such that an air-tight passage is formed between the sensor inlet and the gas channel. The sensor support subassembly also provides a sealing means for ensuring an air-tight seal between the sensor unit and the manifold block. This slidable engagement scheme allows the sensor unit to be rotated about the axis of the cylindrical base, which in turn facilitates the use of a card-edge connector for making the electronic connections between the sensor and the sensor testing system power and data lines.

Abstract: A photoionization detector (PID) and an improved halogen specific detector are disclosed, for direct connection of the PID outlet to the halogen specific detector inlet. The tandem detector is used for detection of volatile organic compounds and the like. A jet assembly and seal between the PID and halogen specific detector provide a leak free and upswept dead volume-free connection between the two detectors.

Abstract: A device for selective detection of gas, enabling a first gas to be detected relative to a second gas, the device having a solid state sensor provided with an insulating substrate having a first face and a second face, a heater element deposited on the first face of said substrate, metal electrodes deposited on the second face of said substrate, and a semiconductor layer formed on said electrode and over the second face of said substrate. Detection is performed by simultaneously determining a voltage U representative of the resistance of the semiconductor element of the solid state sensor and the voltage difference S between a voltage representative of the temperature of the heater element of said solid state sensor and a voltage representative of the temperature of a heater element of a reference sensor, the voltage U and the voltage difference S each being compared with a different and predetermined threshold voltage in order to enable selective detection of gas.

Abstract: A biosensor for measuring alcohol concentration includes an insulating substrate and an amperometric device formed on the insulation substrate, having a plurality of conductive lines and connective pads and a plurality of electrodes. An enzyme immobilized layer is formed on one of the plurality of electrodes of the amperometric device and an enzyme paste is printed on the amperometric device. An outer membrane is formed on the substrate having the plurality of electrodes for forming an electrode system and an insulating membrane is formed on the substrate, except on the outer membrane.

Abstract: Detector of the filament type for determining a static or dynamic charactstic of an ambient medium, constituted by a resistive component intended to be heated by the Joule effect in the medium, and an interface region suitable for reacting with the medium by a physico-chemical process with an effect, depending on the characteristic to be determined, on the electrical characteristic of the interface region, in which there is a supporting member through which there is at least one aperture and at least one filament including the resistive component, composed of one or more thin films and a central portion located in the aperture and end portions via which the central portion is connected to the supporting member.

Abstract: A gas sensor for use in monitoring gases such as H.sub.2 S, NO.sub.2 or SO.sub.2 comprises a film or layer of non-protonated polyaniline as the gas sensing material.

Abstract: A gas detecting method and apparatus for selectively detecting a fuel gas having methane as a main component thereof and an incomplete combustion gas having carbon monoxide as a main component thereof. A low heat capacity, hot-wire semiconductor type gas sensor used has an oxide semiconductor formed mainly of valency-controlled tin oxide and acting as a sensitive section thereof. An inactive to gas combustion, heat resistant, quadrivalent metallic oxide is mixed into the sensitive section. The sensitive section is alternately switched between a fuel gas detecting temperature and an incomplete combustion gas detecting temperature.

Abstract: An electrochemical detection cell (320), which is usable either for potentiometric or electrolytic conductivity detection, has a capillary (305), which controls electrolyte flow. A gas stream containing detectable substances is input through a non-wettable plastic capillary (306). A reaction zone (310) through which both gas and liquid flow is internally wettable. Reference electrode (309) and either electrode (311) or (312) may be used for potentiometric detection. Sensor electrodes (311) and (312), both in the reaction zone, are used for conductivity detection. The electrolyte is fed through the capillary (305) gravimetrically from a reservoir, and the gas stream is supplied by a pyrolysis furnace. The mechanism of ionization in the gas phase ionization detector (GPELCD) is described.

Abstract: A combustible gas sensor having a noble metal sensor element with a surface that is heated above a critical temperature at which the surface is able to dissociate oxygen in a gas stream and adsorb the oxygen onto its surface. The adsorbed oxygen present on the noble metal surface enhances the reactivity of the sensor element and permits it to react with combustible gases that otherwise would have little or no affinity for the sensor element. The balance of adsorbed oxygen and combustible gas species on the sensor surface cause a change in an electrical property that is used to determine the presence or identity of a combustible gas, or to derive a concentration measurement.

Abstract: A method of determining an analyte in the gaseous or vapour phase and in which a bioreceptor or biomimic is retained at an electrode. The bioreceptor or biomimic is preferably retained at a support at the electrode which comprises a solid or gel matrix of an electrolyte, especially organic salt electrolytes. Electrochemical detection of analytes in this way has several advantages over existing methods which rely on solution monitoring. For example gas sensors can be prepared for monitoring an analyte by the occurrence of a reaction with a bioreceptor or biomimic, in addition to monitoring the presence of toxins due to inhibition of the bioreceptor or biomimic reaction. Furthermore, the invention enables gas or vapour analyte monitoring with increased sensitivity and speed and greater stability of the sensors can be achieved. The invention also relates to novel media for carrying out bioelectrochemical reactions.

Abstract: The invention relates to a method for determining small quantities of carbon monoxide and nitrogen oxides in gaseous mixtures containing oxygen with the aid of a sensor whose electrical resistance changes at a higher temperature with the carbon monoxide and nitrogen oxide concentrations. It makes use of the fact that, with suitable sensors, on the one hand the resistance-temperature curve of the one of the gases to be determined is clearly different from that of the reference mixture over a broad temperature range (gaseous mixture without the two gases to be determined) and, on the other hand, the resistance-temperature curves of the two gases to be determined approach one another in one part of this temperature range, or coincide, and maintain a clear distance from one another in another part of this temperature range.

Abstract: The cleanliness of water-rinsed surfaces originally carrying hazardous compositions is determined by using a surface active agent as a marker in said material prior to placing the composition into contact with the surface.

Abstract: A method and system for monitoring a concentration of volatile organic constituents in a test sample. A sparging vessel separates a volatile organic constituent sample from the test sample. A dryer dries the constituent sample to remove any vapor therein by mixing the constituent sample with a drying agent. A sorbent trap adsorbs the volatile constituents from the drying agent and concentrates the purged constituents. A microprocessor controlled director valve selectively directs the constituent sample from the dryer to the sorbent trap and from the sorbent trap to an organic vapor detector for determining the concentration of volatile constituents and for generating an electrical signal proportional to the total concentration of the volatile constituents in the sample.

Abstract: This invention is a self-contained NO.sub.x sensor assembly. It may be used to detect NO.sub.x levels in a flowing gas stream such as might be found in an exhaust gas from a combustion process and to produce a measurable electrical output related to the content of NO.sub.x measured. The NO.sub.x sensor assembly is of a configuration that may be detached from a mounting and replaced. The sensor assembly comprises two sensor elements one of which is made up of a catalyst on a temperature measuring device. The other is a gas stream ambient temperature measuring device. The catalyst is selected and configured so that it selectively reduces NO.sub.x and the resulting heat of the reaction raises the temperature of the allied temperature measuring device. The sensor assembly also contains a NO.sub.x reductant source. The sensor assembly may be placed in a moving vehicle for measuring NO.sub.x levels in its exhaust gas.

Abstract: In this invention, a first sensor senses an organic gas, liquid or vapor and includes a first support having a first support surface with a layer of material fastened to it. In the presence of liquid, gas or vapor, the material swells and expands so as to vary at least one of its dimensions. Such expansion develops a stress at an interface between the first support surface and the material, and strain sensitive resistors detect the stress and produce an output which varies as a function of the stress at the interface. One of a pair of piezoresistors is located where there is increased stress and the other piezoresistor is disposed where there is reduced stress. If desired, a second sensor similar in structure to the first but exposed only to a reference organic liquid, gas or vapor temperature compensates the first. In another embodiment of the invention, an organic chemical responsive sensor includes a first support having a first support surface and a first capacitor plate fastened to the first support.

Abstract: SnO.sub.2 gas sensors are described incorporating Bi.sub.2 O.sub.3 in an amount less than 35% but sufficient to confer hydrogen sensitivity and selectivity to the sensors described comprises 25% by weight Bi.sub.2 O.sub.3 and incorporates a platinum catalyst.

Abstract: A porous alumina coating layer covering an oxide semiconductor type or solid electrolyte type oxygen concentration sensor carrys a catalyst (Pt/Rh) for accelerating equilibration reaction of an unburnt gas in exhaust gas from an automobile engine. The deterioration of the catalyst activity can be prevented by incorporating a thermal stability improving agent into the alumina coating layer.

Abstract: An explosion proof microwave heated solvent extraction apparatus or system for extracting organic materials includes a pressure resistant microwave transmissive extraction container, which is preferably of reinforced polyetherimide lined with fluoropolymer, in a microwave radiation heated chamber, with a device for controlling a microwave radiation generator, such as a magnetron, in response to the presence of any solvent vapor in a collection container for rupture diaphragm discharged material from an extraction container or in exhaust gas from the chamber. The presence of the solvent in the collection container or exhaust gas is preferably detected by a semiconductor gas sensor which decreases its electrical resistance in the presence of solvent vapors, thereby increasing its voltage and thus controlling operation of the magnetron, turning it off when solvent vapor (and a potentially explosive gas mixture) is present.

Abstract: An apparatus and method for measuring the amount of gas adsorbed on or desorbed from a solid and for analyzing and surveying reactions of a gas with a solid are disclosed. Reactions can be of either a physical or chemical nature. Parameters of governing comprise a broad range of pressure, temperature, and the rate of gas flow. More particularly, the invention provides an apparatus and method for very accurate and rapid measurement of the amount of gas adsorbed on or desorbed from a solid and means to govern the reaction of a gas with a solid at pressures from high vacuum to high pressure.

Abstract: A surface ionization detector for detecting organic molecules such as illicit drugs and non-organo-nitrate explosives includes a heated surface and a collector electrode. A sample containing trace amounts of the organic molecules in ambient air is directed over the heated surface maintained at a temperature in the range of 500.degree. C. to 800.degree. C., thereby causing the molecules to decompose into fragments. A polarization voltage between 18 V and 24 V is applied to ionize the fragments which are then collected by the collector electrode. An electrometer connected to the collector electrode measures the current and a change in the current indicates the presence of ionized fragments, and thereby indicates the presence of the organic molecules. The temperature of the heated surface and the polarization voltage are optimized for detection of particular organic molecules.

Abstract: A elecret substrate (10), which is exposed to the environment so as to collect molecular contamination, lies at the bottom of a holder (20). Above the substrate a sensor head (100) is supported. Signals from the sensor head are relayed to an electrostatic voltmeter (130). The voltage reading at electrostatic voltmeter (130) is a function of the amount of polar molecule contamination on substrate (10).

Abstract: Apparatus for preconcentrating trace amounts of organic vapors in a sample of air for subsequent detection, comprising a metallic substrate; a thin film of fullerenes deposited on the metallic substrate for adsorbing the organic vapors on the thin film of fullerenes, thereby preconcentrating the organic vapors; and apparatus for heating the metallic substrate to a predetermined optimum temperature for desorbing the vapors from the thin film of fullerenes to form desorbed organic vapors for subsequent detection.

Abstract: An element for detection of NO.sub.x gas in which at least one titanium-containing oxide which is selected from the group of(a) titanium oxide,(b) a solid solution wherein at least one element from the group of aluminum (Al), gallium (Ga), indium (In), scandium (Sc), magnesium (Mg), yttrium (Y), neodymium (Nd), tantalum (Ta), antimony (Sb) and arsenic (As) is contained in the solid-solution state in the titanium oxide, and(c) an oxide which contains titanium and other metal element(s) and has a perovskite structure,and has such an oxygen deficiency that its nonstoichiometric parameter (.delta.) is in the range of 0.03 to 0.3. Thereby, NO.sub.x of an exhaust gas can be measured easily.

Abstract: The present invention relates to a method for storing chemical reagents in micro-reservoirs, a chemical sensor system and a chemical micro-reactor.

Abstract: A solid-state, multi-stage gas detector for detecting a selected gaseous species from a plurality of gaseous species. The multi-stage gas detector includes a first conductive layer, exposable to the plurality of gaseous species, which permits the selected gaseous species to diffuse therethrough and which interacts with at least one of the plurality of gaseous species such that its conductivity changes. A second conductive layer, electrically isolated from the first conductive layer, interacts with the selected gaseous species after it has passed through the first conductive layer such that the second conductive layer's conductivity changes in relation thereto. Electrodes are attached to the first conductive layer and to the second conductive layer for separate detection of conductivity changes within the conductive layers. Detector conductivity changes comprise detection information correlated to the selected gaseous species.

Abstract: A hydrogen sensor element comprises an essentially inert, electrically-insulating substrate having a thin-film metallization deposited thereon which forms at least two resistors on the substrate. The metallization comprises a layer of Pd or a Pd alloy for sensing hydrogen and an underlying intermediate metal layer for providing enhanced adhesion of the metallization to the substrate. An essentially inert, electrically insulating, hydrogen impermeable passivation layer covers at least one of the resistors, and at least one of the resistors is left uncovered. The difference in electrical resistances of the covered resistor and the uncovered resistor is related to hydrogen concentration in a gas to which the sensor element is exposed.

Abstract: A system for coulometric TCO.sub.2 analysis wherein a sample bottle is pressurized by a head space gas having a CO.sub.2 composition which approximates the dissolved CO.sub.2 concentration in the sample. The head space gas transfers to sample to a pipette. The sample is then transferred to a stripper where the sample is degassed. Two carrier gas lines flush the stripper and transfer the CO.sub.2 to a coulometer.

Abstract: A chemical sensor includes a diode or a transistor fabricated in diamond. A diamond-based diode chemical sensor includes a first diamond layer of first conductivity type and a second diamond or non-diamond layer of second conductivity type. A relatively highly doped region is formed in the first diamond layer, adjacent an electrical contact to reduce the frequency dependance of the sensor's capacitance/voltage characteristic. A diamond-based transistor sensor includes a controlling electrode such as a gate which is configured to allow a chemical external to the transistor to alter the characteristics of the transistor. Relatively highly doped regions are formed adjacent the transistor's controlling electrodes, such as the source and drain. A heater is thermally coupled to the sensor for heating the sensor to a predetermined operating temperature. A temperature monitor is also coupled to the sensor for monitoring the sensor temperature.

Abstract: A sensor which is selective to carbon monoxide relative to other reducing gases includes a Bi--Sr--Ca--Cu--O system metal oxide element.

Abstract: The invention relates to a sensor for the determination of carbon monoxide, especially in gas mixtures containing oxygen, on the basis of doped metal oxides whose electric conductivity is a function of the composition of the gas mixtures. Suitable metal oxides are those having n-type conductivity, the dopants used being other oxides of a metal having a maximum valency <4; oxides of a metal catalyzing the reaction of carbon monoxide with oxygen to give carbon dioxide, each in amounts from 0.01 to 0.2 mol %; and from 0.001 to 0.1 mol % of an oxide of a metal of the 5th subgroup of the Periodic Table of Elements. The sensors are notable for a small resistance-temperature coefficient while having high sensitivity and low hysteresis.

Abstract: A sensor detects analytes in a fluid medium by measuring the conductivity of a layer on a carrier with the layer contacting an electrode pair. The layer interacts with the analyte and is improved in that the sensor has a long-term stability and the indication provided by the sensor is completely reversible. The layer is a fullerene layer.

Abstract: In a system for detecting gaseous emissions (10), a housing (20) encases a mechanical member such as a flanged coupling (21) of a closed mechanical system which contains a fluid such as a gas (11) and receives gas (11) escaping through the flanged coupling (21). A sensor (26) extends through the housing (20) into a cavity (22) formed by the housing (20). A semipermeable membrane (28) forming the union between the sensor (26) and housing (20) allows gas (11) encased by the housing (20) to slowly pass from the housing (20) while preventing foreign matter from entering the housing.

Abstract: A machine for analyzing and displaying the concentration of a pressurized gas flowing through a delivery line in relationship to a reference gas. The machine includes a thermal conductivity detector which is connected to a microprocessor and a visual display. The microprocessor allows the machine operator to select any of a number of references and sample gas combinations for analysis.

Abstract: The present invention relates to a method for storing chemical reagents in micro-reservoirs, a chemical sensor system and a chemical micro-reactor.

Abstract: An ammonia sensor consisting of at least one pair of electrodes and an ammonia-sensing material comprising a polyaniline filling the space between the electrodes.

Abstract: An apparatus and method for the measurement of low levels of carbon dioxide in a sample employing membrane separation and ion-exchange technology. The difference in acid strength of carbonic acid and other acids is exploited by treating the sample with a weak base in a membrane separator (10). In this manner, the carbonic acid is distinguished from the stronger acids.

Abstract: This invention relates to processes and apparatus for detecting the overall nature of combustion gases using a detector comprising a semi-conducting film of a metallic phthalocyanine which is deposited between two electrodes on an insulating wafer and which is placed in contact with the combustion gases and maintained at a temperature higher than a determined threshold, for example higher than 40.degree. C. for a monoclinic copper phthalocyanine, in order to render the phthalocyanine insensitive to the water vapour contained in the combustion gases.