Ceramic oxides, measurement

The sample block cell 13 h consists of an aluminum oxide block which can be removed from the base plate. The thermocouples serving for DTA and temperature measurement are reinforced up to the hot junction by ceramic oxide capillary tubes. The sample cell can be mounted in either of two alternative positions, according to the quantity of test substance used. The DTA thermocouples extend into either the large or the small hole. 

Ardizzone, S. and Bassi, G., Components of the measured surface charge of low temperature ceramic oxides, 7. Electroanal. Chem., 300, 585,1991. 

Chapter 200, by Peter M. Allenspach and M. Brian Maple, reviews some aspects of the low-temperature heat capacity of the ceramic oxide superconductors. These measurements yield valuable information about the electronic, lattice, magnetic, crystalline electric field and hyperfine nature of the various rare-earth cuprate materials, and in that respect compliment other physical property studies, such as neutron diffraction, inelastic neutron scattering, and various spectroscopic measurements. The authors review the heat-capacity properties of the stoichiometric RBaCu307 compoimds and oxygen-deficient materials, and show that there are significant differences. The heat capacities of other lanthanide cuprates, such as RBa2Cu40g and R2B4CU7O14+X, are also discussed. 

Semiconducting Ceramics. Most oxide semiconductors are either doped to create extrinsic defects or annealed under conditions in which they become non stoichiometric. Although the resulting defects have been carefully studied in many oxides, the precise nature of the conduction is not well understood. Mobihty values associated with the various charge transport mechanisms are often low and difficult to measure. In consequence, reported conductivities are often at variance because the effects of variable impurities and past thermal history may overwhelm the dopant effects. 

The sensor usually consists of a coil of wire made from the material that is wound on a former and the whole sealed to prevent oxidization, although a film of the metal deposited on a ceramic substrate can also be used. The resistor is connected in a Wheatstone bridge network (Figure 17.17), using fixed resistors in the other three arms. The instrument connected across the bridge is calibrated directly in terms of temperature. The range is limited by the linearity of the device and the upper temperature, which can be measured, must be well below the melting point of the material. 

Two types of continuous flow solid oxide cell reactors are typically used in electrochemical promotion experiments. The single chamber reactor depicted in Fig. B.l is made of a quartz tube closed at one end. The open end of the tube is mounted on a stainless steel cap, which has provisions for the introduction of reactants and removal of products as well as for the insertion of a thermocouple and connecting wires to the electrodes of the cell. A solid electrolyte disk, with three porous electrodes deposited on it, is appropriately clamped inside the reactor. Au wires are normally used to connect the catalyst-working electrode as well as the two Au auxiliary electrodes with the external circuit. These wires are mechanically pressed onto the corresponding electrodes, using an appropriate ceramic holder. A thermocouple, inserted in a closed-end quartz tube is used to measure the temperature of the solid electrolyte pellet. 

Primary clay is also known as residual clay, indicating that they are either the in situ residue of one type of weathered rock or the transported residue of many types of rocks most primary clay deposits occur, however, in situ, at the location where the clay particles were formed. The clay is usually quite pure and colorless or white, but very small relative amounts of minerals mixed with the clay, such as quartz and/or iron oxides, may impart to it a yellow, brown, or green color. Primary clay is also characterized by the extreme fineness of its particles, which usually measure below 2 micrometers (0.002 mm) in diameter. The more than 20 different types of primary clay minerals can be distinguished by their chemical composition, which varies widely, and by their physical properties. Primary clays that have been used for making ceramic objects are listed in Table 55. 

Fig. 12.75Section through zirconium oxide cell 1, zirconium oxide tube 2, NTC resistor 3, dosing electrodes 4, ceramic spacer 5, measuring electrodes 6, thermal insulation 7, heating coil 8, thermocouple Source Own files... 

Thermistor basedflow-through calorimetric sensors. Enzyme thermistors make the most widely developed type of heat measurement-based sensors. The thermistors are normally used as temperature transducers in these devices. Thermistors are resistors with a very high negative temperature coefficient of resistance. They are ceramic semiconductors made by sintering mixtures of metal (manganese, nickel, cobalt, copper, iron) oxides. Like the two previous groups, thermistor sensors do not comply strictly with the definition of "sensor" as they do not consist of transducers surrounded by an immobilized enzyme rather, they use a thermistor at the end of a small... 

Archaeomagnetism can be considered a branch of Paleomagnetism specifically devoted to the dating of archaeological materials from the measurement of the remanent magnetization achieved by the iron oxide impurities present in clay after cooling of the ceramic artifact. This recording mechanism primarily provides information on the direction of the Earth s field at the time the artifact was fired or the kiln was last used. 

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