E. Gottardi

Thermal expansion and thermal conductivity of Torlon at low temperatures

We measured the expansion coefficient of Torlon 4203 (polyamide-imide) as a function of temperature between 4.2 and 295 K. The thermal expansion is lower than that of most polymers. The thermal conductivity k between 0.1 and 5 K was also measured: below 1 K, a quadratic dependence on temperature of k was found, as predicted by the tunnelling model, while the behaviour shown by our data above 1 K suggests the presence of a plateau.

Low temperature thermal conductivity of Kevlar

Abstract We measured the thermal conductivity of a Kevlar cord, 0.8 mm in diameter, in the 0.1–2.5 K temperature range. The data were fitted with a power-law: k=(3.9±0.2)×10 −5 T 1.17±0.04 W/cm K . Our results are in good accordance with the existing data at T>2 K .

Low temperature thermal conductivity of Kapton and Upilex

Abstract We measured the thermal conductivity of Kapton HN and Upilex R in the lengthwise direction of a single layer of material. The temperature range was investigated 0.1–9 K for Upilex and 0.2–5 K for Kapton. For both conductivities, we found a linear dependence on temperature that can be ascribed to the presence of crystalline units inside the solids.

Thermal expansion and thermal conductivity of glass-fibre reinforced nylon at low temperature

Abstract We measured the expansion coefficient of glass-fibre reinforced nylon as a function of temperature between 4.2 and 300 K. The linear thermal expansion is about half that of unfilled nylon throughout the temperatures investigated. The thermal conductivity in the 0.2–5 K temperature range is very close to that of unfilled nylon and can be represented by the fit curve k =2.42×10 −5 T 1.77 .

Low-temperature thermal properties of polypropylene

Abstract We have studied the low temperature thermal properties of a polypropylene copolymer (PP): thermal conductivity (between 0.1 and 4 K), specific heat (between 0.06 and 1 K) and thermal expansion (from 4.2 K to room temperature). Both the thermal conductivity and the specific heat temperature data were interpreted using the tunnelling model for phonon scattering. The measured thermal properties show that PP is suitable for use as thermal insulating support material in cryogenic devices.

Dielectric properties of Stycast 1266 over the 0.07-300 K temperature range

Abstract We used Stycast 1266 in a high-pressure, low-temperature transducer. In order to ascertain the dependence of capacitance and loss on temperature, we measured the temperature behaviour of the dielectric constant and the dissipation factor of Stycast 1266 at 1 KHz between 0.07 and 300 K. We found a smooth decrease of the dielectric constant with decreasing T. The temperature dependence below 1 K is well explained by the tunneling model. The loss tangent showed very low values (always less than 5×10−5), with a peak around 260 K that can be ascribed to dielectric relaxation processes.

Thermal conductivity of manganin below 1 K

Abstract We carried out thermal conductivity measurements of Manganin wire having a composition of Cu 84%, Ni 4%, Mn 12% (sample 1) in the 0.1 ÷ 1K temperature range, and of Manganin wire having a composition of Cu 86%, Ni 2%, Mn 12% (sample 2) in the 0.05 ÷ 0.25K range. The measurements were performed in a low-power dilution refrigerator. For sample 1, the fit on the data gives a dependence on T: k = (0.79 ± 0.01)T1.22±0.02 mW/cmK; for sample 2, the fit leads to k = (0.95 ± 0.04)T1.19±0.02 mW/cmK. The difference in thermal conductivity in the overlapping temperature range depends on the different ratio of the Cu Ni content of the samples. A similar sensitivity to a small difference in the composition has also been found for other Cu alloys.

Low temperature thermal conductivity of polyamide-imide

Abstract Thermal conductivity of polyamide-imide Torlon 4203 was measured at temperatures between 0.1 K and 1 K . The measurements were carried out in a dilution refrigerator using a steady state technique. The fit on the data gave a temperature dependence of the conductivity: k = α · T n , with n = 2.23 ± 0.01 and α = (7.72 ± 0.08) · 10 −5 W / cmK n +1 . A quadratic dependence on T of the conductivity can be explained, within the framework of the tunneling model, as being due to the resonant scattering of phonons by two level systems.

A simple method for measuring the low temperature thermal conductivity in thin wires

A new method is presented for measuring the low-temperature thermal conductivity of thin electrically-conducting samples. The proposed two-probe technique is useful mainly in the case of non free-standing samples of medium and high thermal resistivity. The method is simple: a resistance bridge is used both for measuring the temperatures and for heating the sample. The limits of this method are discussed. The thermal conductivities below 0.3 K of a normal alloy (manganin) and a superconducting alloy (Al/Si 1%), both which we obtained using this method, are presented.

The influence of impurity concentration and magnetic fields on the superconducting transition of high-purity titanium

Abstract The influence of impurity concentration c and applied magnetic field H on the superconducting transition of high-purity commercial titanium samples was investigated. The superconductive transition temperature TC was found to be very sensitive to the impurity concentration ( dT C dc ≈ −0.6 mK/w.ppm) and to the applied magnetic field (( dT C dH ) ≈ −1.1 mK/G) . A linear dependence of TC decrease on impurity concentration, as theoretically predicted by various authors, was observed. In the purest sample, a linear decrease of TC on the applied magnetic field was found. The run-to-run and sample-to-sample reproducibility of the transition of the same sample was evaluated, and its suitability as a thermometric reference point below 1K was discussed.