Temperature Thermometry Research Articles

Stable Isotope Characterization of the Thermal Profile and Subsurface Biological Activity during Oxidation of the Great Australia Deposit, Cloncurry, Queensland, Australia

The application of stable isotope thermometry and phase relations was used to examine the thermal evolution of oxidation and secondary mineralization at the Great Australia Cu-Au-Co deposit, Cloncurry, Queensland, Australia. Results show that early secondary mineralization consisted of djurleite crystallization at temperatures <93°C, followed by calcite mineralization at 66° to 75°C. The secondary mineralization paragenesis continued with azurite that formed at about 51°C, followed by malachite crystallization at 41° to 38°C, and malachite after azurite at 34°C. The final stage of secondary mineralization consists of calcite that formed at 25° to 30°C, followed by goethite. The general trend observed is for early oxidation and supergene enrichment at apparent temperatures less than 93°C and between 66° and 75°C, cooling to ambient surface temperatures late in the period of mineralization. A correlation is observed between decreasing isotope thermometry temperatures and increasing δ 13C values as oxidation and supergene enrichment progressed. This is interpreted to result from exothermic sulfide oxidation and associated subsurface thermophilic bacterial oxidation within the oxidation front. Over the period of oxidation and supergene enrichment, temperatures decreased and δ 13C values increased, recording in the secondary minerals the passing of the oxidation front and a diminishing subsurface bacterial carbon source.

An investigation of closure temperature of the biotite Rb-Sr system: The importance of cation exchange

Factors controlling closure in the biotite Rb-Sr system were investigated in a detailed study of an amphibolite-facies metacarbonate from the central Swiss Alps. Oxygen isotope data suggest that the rock cooled as a closed system. Calcite-dolomite thermometry temperatures of ∼450°C to 500°C and feldspar thermometry temperatures of ∼300°C to 400°C provide evidence of extensive Ca-Mg and Na-K exchange during cooling. Biotite in the sample is 90 mol.% phlogopite and has high Rb (∼900 ppm) compared to Sr (∼0.3 ppm), giving precise Rb-Sr ages. Carefully separated and sized phlogopite shows a range of Rb-Sr ages that do not simply decrease with grain size as predicted by current models of closure temperature. Rb-Sr ages decrease from 18.1 Ma to 16.6 Ma with a decrease in mean grain diameter from 1.16 mm to 0.74 mm, but grains with mean diameter of 0.54 mm show an increase again to 17.6 Ma. This contrasts with Ar-Ar data for single phlogopites, which do show a decrease in age with decreasing grain size. The Rb-Sr age pattern is due to Rb-loss during cooling, which is most pronounced in the finest fraction. The phlogopites are restricted to a 2-cm-thick layer in calcite marble; 87Sr/ 86Sr of the calcite decreases away from the phlogopite band over 4 cm, indicating that the calcite was moving towards Sr-isotope equilibration with the phlogopites over this distance and that the phlogopite was not equilibrating with an “infinite reservoir.” Ion microprobe traverses across grains of different minerals reveal systematic core-rim variations in major and trace element concentrations. In particular, Sr decreases from calcite core to rim, but increases from core to rim in K-feldspar, whereas Rb decreases from core to rim in phlogopite but also increases from core to rim in K-feldspar. These gradients are interpreted as indicating the direction of transport of elements during cooling as a result of cation exchange reactions; calcite and phlogopite were sources for Sr and Rb, respectively, whereas K-feldspar acted as a sink for both elements. This chemical equilibration was taking place at the same time as isotopic equilibration during cooling, and was equally important in controlling the apparent ages recorded by the mica grains. In contrast, closure temperature calculations for geochronological systems based on classic Dodson-type models assume parent and daughter element concentrations are homogeneous across grains and do not change with time, only isotopic exchange is modeled. Closure in mica Rb-Sr systems will depend both on the factors that control isotopic exchange (grain size, mode, 87Sr diffusion coefficients) and those that control chemical exchange (grain size, mode, Rb and Sr diffusion coefficients, Rb and Sr contents of phases and their partition coefficients).

Frontiers in refrigeration and cooling: how to obtain and sustain ultralow temperatures beyond nature's ambience

The investigation of matter at very low temperatures close to absolute zero is a powerful and important subject as it provides the unique possibility for studying physical properties, e.g. phase transitions, in an environment where most of the unavoidable disturbances present at higher temperatures are almost completely frozen out. In particular, the improvement of the standard cooling techniques for mK- and μK temperatures, i.e. 3He– 4He dilution refrigeration and adiabatic nuclear refrigeration, respectively, opens up a temperature range for the study of liquid and solid matter several orders of magnitude below the minimum temperature existing in nature (background temperature of the universe, ∼2.7 K). In this paper, some important contributions obtained at the ultralow temperature facility at the University of Bayreuth will be discussed: (1) the achievement of a minimum electronic temperature of T el=1.5 μK by adiabatic nuclear refrigeration of platinum, (2) the progress in improving the thermal coupling between different materials at low temperatures, and (3) recent developments in low temperature thermometry.

Low temperature thermometry in high magnetic fields. VII. Cernox™ sensors to 32 T

This article describes the behavior of Cernox™ zirconium oxynitride film temperature sensors from Lake Shore Cryotronics, Inc. in magnetic fields up to 32 T at temperatures between 2 and 286 K. Results from a number of sensors with different dimensionless temperature sensitivities and from different production batches are analyzed and compared with previous results on carbon-glass sensors that extend to 19 T. In that field range, the Cernox™ sensors appear to be a real alternative to carbon glass. Furthermore, the magnitude of their uncorrected error, ΔT/T, is smaller than other sensors at most temperatures in fields less than 20 T, and their temperature correctabilities appear to apply to off-the-shelf sensors with dimensionless temperature sensitivities in the range of −0.74 to −1.9. The sensors show a negligible (&amp;lt;0.05%) orientation dependence of their ΔR/R at 78 K; at 4.2 K, that dependence can be as high as ∼0.7% at 20 T.

Low Temperature Thermometry in High Magnetic Fields

The calibration and reproducibilty of various commercial and homemade thermometers have been investigated over a temperature range from 20 mK to 4.2 K and magnetic field strength from 0 to 16 Tesla. The performance of resistance thermometers made of different materials varies widely as a function of magnetic field. One type (Scientific Instruments RO600) is found to have a relatively small magneto-resistance, which is predictable to better than 1% down to 100 mK, making calibration in a magnetic field unnecessary for many applications. This was not true of homemade ruthenium oxide and Cernox (Lakeshore Cryotronics). A new type of sensor, thin film doped germanium on a GaAs substrate, was also investigated and found to be useful at higher fields and low temperature.

Phosphor thermometry at cryogenic temperatures

The temperature dependence of the lifetimes of two phosphors, La2O2S:Eu and Mg4FGeO6:Mn, is presented from 300 to 11 and 140 to 8 K, respectively. Emission from the D35 state of La2O2S:Eu reveals a strong temperature dependence from 11 to about 130 K, where the signal becomes too weak to measure accurately. Emission from the F24 state of Mg4FGeO6:Mn changes throughout the temperature range measured. Both of these materials are used for higher temperature thermometry applications. This work illustrates their utility down to liquid helium temperatures.

NEONATAL INFRARED AXILLARY THERMOMETRY. 1450

Neonatal body temperature(T) thermometry has evolved from rectal(R) mercury-in-glass thermometers to tympanic infrared thermometers. Infrared measurement of axillary skin(AX) T(Lightouch, Exergen Corp.) is now available. It is rapid, safe, and avoids the physical limitations of tympanic measurement, but clinical accuracy is unknown. We measured simultaneous infrared AXT and RT(by thermistor) in 16 term neonates under radiant warmers(RWs), at admission to a triage nursery(Term1). Ts were repeated when in cribs, at discharge from triage(Term2). We also measured AXT and RT in 12 non-ventilated preterm neonates, mean(range) weight 1242(1020-1490)g, age 14.5(5-25) days, in air servo controlled incubators initially(Prem1) and after 30 seconds of complete arm abduction(Prem2). Paired t values, significance, and correlations are shown in the table. Additionally, 2 premature infants studied under RWs at NICU admission(age 20 min) had AXTs 0.5 and 1.2 °C higher than their RTs. Infrared AXT and RT correlated poorly in term neonates under RWs. Correlation was better later in cribs, but AXT and RT were not interchangeable. Initial AXT and RT of premature infants in incubators were similar by paired t test, probably because air T was close to RT. Infrared axillary thermometry requires more study. Modifying AXTs by using correlation data could improve clinical usefulness. The thermal environment may influence clinical usefulness. The infrared thermometer(Lightouch) was supplied by the Exergen Corp.(Newton, MA).

Empirical tests of carbon isotope thermometry in granulites from southern California

Abstract ‘Peak’metamorphic carbon isotope fractionations between calcite and graphite (ΔCal–Gr) in marbles and calc‐silicates from the Cucamonga granulite terrane (San Gabriel Mountains, California) range from 3.48 to 2.90%. The data are used to test three previously published calibrations of the calcite–graphite carbon isotope thermometer. An empirical calibration of the calcite–graphite carbon isotope thermometer gives temperatures of 700–750°C; a theoretical–experimental calibration of the system gives temperatures of 760°–870°C; an experimental calibration gives temperatures of 870–1300°C. Temperatures calculated using the empirical calibration are in agreement with those calculated from garnet‐based cation exchange thermometry when uncertainty is considered. Temperatures calculated using the theoretical–experimental calibration overlap the upper range of cation exchange thermometry temperatures and range to 50°C higher. The experimental calibration yields temperatures from 50 to 480°C higher than those from cation exchange thermometry. Moreover, temperatures from the experimental calibration are also inconsistent with mineral and melt equilibria in the granulite phase assemblage.Despite the better agreement between cation exchange thermometry and the empirical calibration of the calcite–graphite system, temperatures calculated using the theoretical–experimental calibration may be real peak metamorphic temperatures. If retrograde diffusion partially reset garnet‐based cation exchange thermometers by c. 50°C, then the cation exchange temperatures are consistent with those from the theoretical–empirical calibration. Thermometric evidence from biotite dehydration melting equilibria is consistent with either the empirical calibration if melting was fluid‐present, or the theoretical–experimental calibration if melting was fluid‐absent.

New dielectric material for low temperature thermometry in high magnetic fields

Dielectric experiments on the incommensurate solid solution (Pb0.45Sn0.55)2P2Se6 for T=1.2–200 K reveal a strong temperature dependence of the real part of the dielectric constant for T&amp;lt;45 K. The relative dielectric sensitivity d ln(ε′)/dT≊2–8 K−1 is found to be 2–3 times higher in comparison to widely used glass-ceramic temperature sensors. Moreover, the dielectric constant has a very good time stability and is insensitive to magnetic fields up to 20 T (dT/dB&amp;lt;10−4 K/T). These characteristics make this material a very promising candidate for applications in capacitive temperature sensors for low temperature thermometry in high magnetic fields.

Thick platinum films as low temperature thermometers

Resistance measurements of thick platinum films between 4.2 and 300 K are reported. The thick films were prepared by standard screen-printing techniques. The properties of the films make them suitable for low temperature thermometry. In the temperature range 77–300 K experimental data are fitted using a quadratic fit with an error in temperature of less than 0.2%.

Survival of Salmonella Species Heated by Microwave Energy in a Liquid Menstruum Containing Food Components

Common food constituents were examined to determine the protective influence they may exert on a mixture of Salmonella species heated by microwave energy. A model system was developed, wherein combinations of sucrose, sodium chloride, caseinate and corn oil, all at 1.0% (w/v) concentrations, were added to 0.3mM phosphate buffer (pH 6.8), producing a total volume of 100 ml. Salmonella-inoculated solutions were heated for 47 sec in a 700 watt microwave oven. Temperatures at localized areas were monitored by fluorescent fiberoptic (fluoroptic) thermometry as the solutions heated, and by mercury thermometer after heating. The mean final temperature achieved for the various combinations of solutes was not significantly different and varied only by 4°C as measured by a mercury thermometer. However, solutions containing NaCl afforded the Salmonella spp. up to 170 times the protection of the phosphate buffer control. This protective effect occurred although the mean final temperature of NaCl-containing solutions would be as high as those solutions lacking salt. Fluoroptic thermometry temperature profiles revealed that surface temperatures were higher when NaCl was present in solution, due to decreased depth of penetration of the microwaves. This re-sulted in decreased temperatures at greater depths. Of the solutes evaluated, only NaCl appears to confer a significant protective effect.

Thermometry below 1K using NMR frequency pulling

At very low temperatures, nuclear magnetic resonance frequency decreases with decreasing temperature in an ordered magnetic medium. This phenomenon (frequency pulling) is caused by a coupled motion of the electronic magnetization and the nuclear magnetization. Application of the NMR frequency pulling to low temperature thermometry is discussed.

A nuclear demagnetization cryostat for thermometry

A single-stage nuclear demagnetization cryostat is reported with 33 moles of copper in a magnetic induction of 8 T developed for the investigation of low temperature thermometry. The lowest temperature measured with a Pt NMR thermometer was 130 μK, and the time dependent heat leak approached 0.3 nW after 80 days.

Digital bridge for ultralow temperature thermometry

A transparent replacement for the usual set of precision ratio transformers within ultralow temperature thermometry systems is described. This new device uses digital electronics to both lower costs and to provide local intelligence for greater flexibility. The device has been used in our experiments on superfluid 3He without the difficulties usually attendant with interfacing computers to ultralow temperature apparatuses.

A nuclear demagnetization cryostat for thermometry

A single-stage nuclear demagnetization cryostat is reported with 33 moles of copper in a magnetic induction of 8 T developed for the investigation of low temperature thermometry. The lowest temperature measured with a Pt NMR thermometer was 130 μK, and the time dependent heat leak approached 0.3 nW after 80 days.

高温技術と高温度の測定講座 Ｉ レーザ計測の基礎

高温技術と高温度の測定講座 Ｉ レーザ計測の基礎

Growth of Optical Quality Sapphire Single Crystal Fibers

AbstractVoid-free sapphire single crystal fibers with diameters of 110 μm and 60 μm and lengths of over 2 m have been grown by the laser-heated pedestal growth method. The growth dynamics of the floating zone was studied and shows the features expected from a simple theoretical model. Optical losses have a minimum of 0.5 dB/m in the near infrared at 1064 nm. An absorption band centered at 400 nm results in losses of up to 20 dB/m in the visible. The fibers have potential applications in high temperature thermometry and in delivery systems for laser surgery. Absorption losses of 0.88 dB/m with a damage threshold higher than 1.2 kJ/cm2 at 2936 nm made tissue ablation feasible with fibers several meters in length.

Application of magnetization measurements in iron to high temperature thermometry

It is proposed to use iron whiskers as elements for magnetic thermometers. The sharpness and reproducibility of the large second harmonic response that occurs just as the centre of the whisker saturates depends upon temperature through Ms(T). As a thermometer the whisker has a built-in fixed point which is reproducible to parts in 106. A one point calibration is needed to determined the demagnetizing factor. Suggestions are made for incorporating magnetic thermometers into thermocouples and resistance thermometers.

Low temperature thermometry using inexpensive silicon diodes

Low temperature thermometry using inexpensive silicon diodes

Status of carbon resistors for low temperature thermometry

Carbon resistor brand identification and availability problems are discussed.