Transitions and Phases of Polytetrafluoroethylene

Abstract

Behavior of transitions and the nature of high-pressure phase in polytetrafluoro ethylene are studied using methods of ultrasonic waves, thermal expansion, differential thermal analysis and X-ray diffraction. A phase diagram is obtained in pressure range from 1 atm. to 6,500 kg/cm2 and in temperature range from room temperature to 165°C. Three phases are found; phase I above 30°C, phase II below 20°C, both at 1 atm. and phase III above 5,000 kg/cm2. The triple point is located at 75°C and 5,000 kg/cm2. Pressure dependence of transition temperatures is obtained as 15 and 9 degrees per 1,000 kg/cm2 for the 20°C and 30°C transitions at low pressure, 9 degrees per 1,000 kg/cm2 for both transitions at intermediate pressure range from about 3,000 to 5,000 kg/cm2, -13 and 50 degrees per 1,000 kg/cm2 for the II–III and the III–I transitions, respectively. It is suggested that the high-pressure phase (phase III) may be a closely packed but disordered phase.

Effects of magnetic anisotropy on spin and thermal transport in classical antiferromagnets on the square lattice

“…Now, we will address possible experimental platforms to investigate the pronounced enhancement of the longitudinal spin-current conductivity σ s µµ associated with the KT transition. As the divergent peak in the σ s µµ (T ) curve toward T KT can commonly be seen in both ferromagnets and antiferromagnets only if an XY -type anisotropy exists, good candidate systems are quasi-twodimensional magnets having the signature of the KT transition such as the S = 1/2 square-lattice ferromagnet K 2 CuF 4 [38][39][40][41], the S = 1 honeycomb-lattice antiferromagnets BaNi 2 X 2 O 8 (X=As, P, V) [42][43][44][45][46][47][48], the S = 5/2 honeycomb-lattice antiferromagnet MnPS 3 [49][50][51], and the stage-2 NiCl 2 [52][53][54] and CoCl 2 [55][56][57] graphite intercalation which are respectively S = 1 and S = 1/2 triangular-lattice ferromagnets. In these compounds, a three-dimensional inter-layer coupling is extremely small, so that at first sight, the system may be regarded as a two-dimensional XY -type magnet.…”

“…Since the obtained value of B H ≃ 5.1 is comparable to b H ≃ 2π, it turns out that σ s xx ∝ ξ s , which is in good agreement with the analytical result in Eq. (40). To get insight into the origin of the rapid increase of σ s xx , we examine the temperature dependences of |j z s,x (0)| 2 and τ s like in the anisotropic cases of ∆ = 1.…”

The Basis of Thermal Analysis

“…Phase diagram of polytetrafluoroethylene after data fromHirakawa and Takemura (1969). The dotted line indicates where the average untwisting of the helical conforma tion is complete.…”

The Transition and Crystal Transformation of Poly[3,3-bis(chloromethyl)oxacyclobutane] under High Pressure

“…The pressure measurement was done with the Bourdon pressure gauge in the lower-pressure side of the intensifier and the pressure calibration was made by the observation of the well defined solid-state transition of poly(tetrafluoroethylene). 4 The thermal expansion measurement apparatus, shown in Figure 1, was inserted into the compound cylinder-type high-pressure vessel and six electrodes of differential transformer, two electric leads of inner sheathed heater (1.5 mm¢, Philips) and one sheathed chromel-alumel thermocouple (1 mm¢, Philips) were taken out from the pressure vessel using the previous technique. 17 The excellent characteristics of the differential transformer in dilatometric measurements under high pressure has been shown in a previous paper.…”

“…17 The excellent characteristics of the differential transformer in dilatometric measurements under high pressure has been shown in a previous paper. 4 In this study a modified apparatus for measurement under high temperature (inner heater) and measurement of thermal expansion of liquid (piston cylinder type) was used. For the sake of accu- As the pressure medium, silicon oil was used for most cases.…”