摘要:

An experimental technique for the study of short contact time gas–solid reactions is developed. The major components are a pulse powder feeder, an injection probe, and a collection probe. The feeder can inject small amounts of fine particles into the reactor as narrow pulses. The two probes also serve as optical solids monitors; an optical system consisting of fiber optic cables and miniature prisms is housed within each probe. With the combination of the two probes, residence time of the particles is determined directly and on‐line using photometric principles. With a cold model entrained flow reactor, it is demonstrated that solids with residence times as low as 4 ms can be successfully sampled from the reactor, with the residence time calculated to within 5% error. Methods for rapid heating of the injected powder and rapid quenching of the reaction of the sampled solids are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1143419

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An experimental system to determine the anisotropy ratio of thermal conductivity of polymer foils parallel to the sample surface is presented. This kind of measurement is important because the drawing of the foil orients the molecular chains making thermal conductivity parallel to the orientation higher than perpendicular to it. The measurement method is based on heating the foil with a dc‐supplied resistor and detecting the temperature by an infrared detector. The temperature of the foil is measured as a function of distance from the heat source in two separate measurements perpendicular to each other, i.e., rotating the sample 90° between the measurements, and the anisotropy ratio of thermal conductivities in these directions is obtained by using curve fitting. In this article the method has been applied on several plastic foils showing anisotropies ranging from 1 to 2.

ISSN:0034-6748    

DOI:10.1063/1.1143420

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An easily constructed zero‐crossing detection circuit, used in conjunction with common background fringe signal control techniques, vastly improves the dependability and accuracy of a fractional fringe interferometry system.

ISSN:0034-6748    

DOI:10.1063/1.1143421

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A versatile sample holder for ultrahigh vacuum is described allowing cooling and heating of the sample as well asinsiturotation around its surface normal which is perpendicular to the axis of rotation of the sample holder itself.

ISSN:0034-6748    

DOI:10.1063/1.1143422

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

For the correct interpretation of modulated photothermal radiometric signals both the absorptive and IR‐emmissive properties of the sample under test have to be taken into account. Therefore we derived a formula for layered samples and compared the theoretical predictions to measurements performed on a paint layer on brass.

ISSN:0034-6748    

DOI:10.1063/1.1143372

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A versatile low‐cost Czochralski system for pulling crystals from melt has been described. It is designed for low melting, transparent, and nonlinear optical materials. One of the most important novel feature of this crystal growth system is that the entire growth process including the solid–liquid interface can be viewed from any direction. Another is the use of an after‐heater to reduce excess heat loss from the surface of the melt.

ISSN:0034-6748    

DOI:10.1063/1.1143373

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The work function of dispenser cathode pellets has been determined by means of the retarding potential technique. A low‐energy electron gun was fabricated which delivers a collimated beam of electrons on the pellet surface at normal incidence. The set up is calibrated by employing samples of known work function such as gold and tungsten, prior to determining the work function of the cathode pellets. This set up provides a rapid determination of the work function of cathode pellets.  

ISSN:0034-6748    

DOI:10.1063/1.1143374

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A simple and inexpensive device to make electric or gas‐welded butt‐join thermocouples is described. It allows for junction bead size control by means of a spring‐loaded moveable block with adjustable travel. The device has been successfully tested with thermocouple wire diameters of 125, 250, and 375 &mgr;m and should also be able to accommodate smaller and larger wires with very minor modifications.

ISSN:0034-6748    

DOI:10.1063/1.1143375

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The Hall mobility in semi‐insulating GaAs has been measured by probing the Hall voltage dropped across the thickness of the sample optically. This is achieved by exploiting the linear electro‐optic (Pockels) effect in the material. The method only involves two electrical contacts to the sample which gives a distinct advantage over the conventional Hall or Van der Pauw techniques. It permits, in principle, the direct measurement of the time evolution of carrier populations, a useful corollary to transient photoconductivity. It also makes possible the measurement of a Hall voltage dropped across the width of a quantum well.

ISSN:0034-6748    

DOI:10.1063/1.1143376

出版商:AIP    

年代:1992

数据来源: AIP