摘要:

A 1.5‐GHz superconducting niobium triaxial cavity has been fabricated to study residual surface resistance of superconducting materials at 2 K. Unlike many other structures where the entire test samples have to be placed in strong magnetic field locations, we have the edge of a 25.4 mm or larger diameter sample outside of the strong field region, a procedure which will greatly reduce edge effects and image current losses between the thin film and substrate. A calorimetric method is used to measure the sample losses, and is designed to resolve a 10‐&mgr;K temperature change using 16 carbon resistor sensors. A detection limit of 0.05‐&mgr;W power dissipation has been determined with a calibration heater, which corresponds to a surface resistance of 0.02 n&OHgr; at a maximum cavity magnetic field of 250 G. Initial cavity testing was performed in a magnetically unshielded cryostat, yielding a 2.2‐&mgr;&OHgr; residual resistance which was measured by both the rf measurement and the calorimetric measurement.

ISSN:0034-6748    

DOI:10.1063/1.1143979

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A canal surface viscometer has been designed and constructed to measure the in‐plane steady shear viscosity (&eegr;s) of monolayers at the air/water interface. The technique involves forcing a monolayer to flow through a canal to another monolayer under a constant surface pressure gradient and measuring the area flow rate. The instrument incorporates a feedback electronic system to maintain the surface pressure on each side of the canal to about 0.1 dyn/cm during monolayer flow. The canal design is modified from that of an earlier design in the literature to eliminate artifacts that give rise to systematic variabilities as reported. Specifically, it is demonstrated that the glass‐paraffin canal design used in the past produces ill reproducible results in contrast to an all Teflon canal, which gives rise to consistently reproducible surface viscosity data. A comparison is made between &eegr;svalues obtained from the canal viscometer and the knife‐edge ring surface viscometer, another technique reported in the literature. The comparison reveals the importance of controlling key experimental variables which can have an order‐of‐magnitude effect on the surface viscosity data.

ISSN:0034-6748    

DOI:10.1063/1.1143980

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A new microcomputer‐controlled instrument has been developed for making measurements of thermomechanical behavior of polymeric fibers and yarns under conditions relevant to high‐speed industrial fiber processing. The instrument can apply extension and/or twist, and rapid heating or cooling in the temperature range 20–300 °C, while tension and torque are measured. Particular novel features are: a temperature control device providing heating or cooling at rates up to 103K/s; a new form of high‐sensitivity torque transducer with resolution of 10−9Nm; and computer integration of extension, twist, and temperature. The instrument provides an unprecedented degree of flexibility in the design of thermomechanical tests. It is suitable not only as a versatile research tool for material property measurements relevant to processes such as spinning, heat setting, and thermobonding of fibers, but also as a convenient tester for use in quality control on fibers and yarns.

ISSN:0034-6748    

DOI:10.1063/1.1143981

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A transient one‐dimensional heat‐flow technique for absolute determination of thermal conductivity of solids has been developed. A commercial thermistor, pressed into contact with the front surface of a bar‐shaped test specimen typically 5–20 mm long, is used simultaneously as a constant heat source and as a sensor of the temperature increase. The measurement time is typically 5–10 s. Measurements on stainless‐steel and graphite standards from NIST indicate that the technique is accurate to within 3% in the thermal conductivity range 10–100 W m−1 K−1at room temperature.

ISSN:0034-6748    

DOI:10.1063/1.1143982

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A Holometrix, Inc., R‐Matic model R‐41 Heat Flow Meter Apparatus (HFMA) is evaluated by measurements on homogeneous materials and anisotropic composite materials. The former class of materials includes: foams, calcium silicate boards, fiberglass batts, and loose‐fill fiberglass. Materials in the latter class are polystyrene with gas‐filled panels and batts with powder‐filled evacuated panels. Thermal models of the anisotropic composite materials allow design of composite test specimens and help in the interpretation of test results by computation of apparent thermal conductivities (k). The HFMA includes a dedicated computer for test control, data acquisition, and data analysis. Thus, the computer helps obtain the conditions needed to conduct accurate and repeatable steady‐state tests to meet ASTM C 518 with minimum operator involvement. Thekvalues from this HFMA and three other HFMAs (model R‐20 and R‐21 units) exhibit imprecisions of 2.2% (two standard deviations) for specimens of foam insulation. Such performance requires proper calibrations of good quality heat flux transducers and use of correct thermocouple thermometry practices. For six lots of fiberglass batt insulation, this HFMA and a HFMA model R‐21 yieldkvalues as a function of density with two standard deviations of 4.5%. Test results from this HFMA for three specimens of loose‐fill fiberglass insulation providekvalues as a function of density with two standard deviations of 5.1%. Because these levels of imprecision (2.2%–5.1%) include material differences, they illustrate the limits of error of the model R‐41 HFMA.

ISSN:0034-6748    

DOI:10.1063/1.1143983

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Measurements of the optical constants and thermal radiative properties of high‐temperature solid tungsten and molten aluminum have been made using a new instrument that includes two independent optical systems and surface control and analysis capability. The two optical systems, one for measuring the complex index of refraction by ellipsometry, the other for measuring the normal spectral emissivity by direct comparison to an integral blackbody cavity, operate over the wavelength range 0.4–10 &mgr;m with sample temperatures between 940 and 1630 K. The surface science capabilities of the instrument permit the preparation of high‐purity samples of known compositioninsitu. The apparatus includes two 5‐keV argon‐ion sputter guns, an ultrahigh vacuum pumping system, and an Auger spectrometer. The two sputter guns allow surface cleaning to occur while optical measurements are being made, or while Auger spectroscopy is determining the surface composition of solid or liquid samples. The ellipsometric optical system uses a novel radiation source (a carbon composite element), refractive optics (calcium fluoride), interference filters for spectral selection, and both calcite and wire grid polarizers to cover the extended wavelength range. The system for measuring the normal spectral emissivity uses reflective optics and an integral blackbody cavity that is located in the wall of the crucible holding the liquid sample. The use of two measurement techniques gives independent determinations of the normal spectral emissivity and thus allows reliable estimation of experimental errors.

ISSN:0034-6748    

DOI:10.1063/1.1143984

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

This study reports the construction and working of a sintered diamond anvil high‐pressure cell for performing electrical resistance measurements using a four‐probe method at cryogenic temperatures. The apparatus has been designed to minimize the pressure shift during the cooling cycle from room temperature to 1.2 K. Pressure is calibrated using the pressure dependence of the superconducting transition temperature (Tc) of Bi to 50 GPa. The usefulness of the apparatus is demonstrated by electrical resistance andTcmeasurements on Se and Zr up to 60 GPa.

ISSN:0034-6748    

DOI:10.1063/1.1143985

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The new apparatus described enables making simultaneously absolute measurements of physisorption, bulk density, and adsorption kinetics of multicomponent gas mixtures as a function of pressure up to 30 MPa. The method which combines the dynamic and the gravimetric methods is self‐sufficient because it does not require complementary data. An in‐line high‐pressure chromatographic device directly measures the time evolution of the effluent flow composition (breakthrough curves). Results of adsorption, density, and adsorption kinetics at high pressures of the equimolar Ar‐CH4mixture on activated carbon are reported.

ISSN:0034-6748    

DOI:10.1063/1.1143986

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A high‐temperature reactor system is developed for studying ultrafast gas‐solid reactions. Time‐resolved measurements of the reaction kinetics and changes in particle properties can be obtained with this system in the time scale 10–100 ms. The reactor system consists of an electrical furnace and ceramic reactor tubes, a pulse powder feed system, injection and collection probes, and a cascade impactor forinsituparticle size classification. The feed system injects solids as short pulses and is capable of handling powders of size 1 &mgr;m or less. Hot jet impaction technique is used for rapid heating of the powder to the reaction temperature. The injection and collection probes are equipped with optical systems that are interfaced with a microcomputer data acquisition system, perform particle injection/sampling, reaction quenching, and optical solids monitoring. The most unique feature of the reactor system is its ability, using the probe combination, to directly measure residence times as low as 10 ms for the solids sampled from the high‐temperature environment. Sample results are shown for the decomposition of limestone at 975 °C.

ISSN:0034-6748    

DOI:10.1063/1.1143987

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The wetted surfaces of the high‐temperature, high‐pressure Raman cell (400 °C and 1 kbar) were constructed of inert materials (i.e., sapphire or quartz and platinum with gold seals) and designed to allow spectroscopic measurements to be made with small volumes (<0.5 cm3at temperature) of corrosive solutions. This design permits solution to be forced slowly through the cell at experimental temperatures and pressures for cases where the solute may be unstable thermally over prolonged periods of time. The entire pressure‐generating equipment, temperature controller and readout, solution separation vessels, and cell can be mounted on a cart for convenient transport to various laboratories. Raman spectra of bichromate/dichromate solutions were obtained from ambient conditions to 300 °C and 1 kbar in order to test the capabilities of this apparatus and to allow comment on the controversy surrounding the existence of HCrO−4raised by recent Raman studies of the aqueous chromate system at ambient conditions.

ISSN:0034-6748    

DOI:10.1063/1.1143988

出版商:AIP    

年代:1993

数据来源: AIP