Thermal films

Ljungberg, N., Colombini, D. and Wesslen, B. 2005. Plasticization of polyjlactic add) with oligomeric malonate esteramides dynamic mechanical and thermal film properties. Journal of Applied Polymer Science 96 992-1002. 

Zinc poly(thio)phosphate thermal films have been recently recognized to be precursor reaction products in the formation of polyphosphate glasses tribofilm (Bascom et al., 1959 Bovington and Dacre, 1984 Fuller et al., 1997 Martin, 1999 Varlot et al. 1999 Willermet et al. 1991). 

The thermal film made of long-chain zinc polyphosphates is formed on the surface. When friction increases, the process of transformation of phosphorus compounds into short-chain phosphate glasses is observed and iron sulfide abrasive particles are eliminated by tribochemical acid-base reactions. Under very severe wear conditions (nascent metal surface creation), an iron sulfide is formed, which will be mixed with the phosphate glasses tribofilm. 

A Cameron-Plint friction machine generated tribofilms with two-layer structure a zinc polyphosphate thermal film overlying a mixed short-chain phosphate glass, containing iron sulfide precipitates. A tribochemical reaction between the zinc polyphosphate and the iron oxides species is proposed on the basis of the hard and soft acid and base HSAB principle (Martin, 1999 Martin et al., 2001). 

At lower temperature, thermally generated film has more similarity to tribofilm. The thermal films, as in the case of the tribofilms, contain mostly a mixture of short-and long-chain polyphosphates. The chemical states of phosphorus and sulfur in each neutral and basic pair were very comparable. The aryl phosphate films contain long-chain polyphosphate throughout the film, whereas the alkyl phosphate films are composed of long-chain polyphosphates in the bulk. Also, the aryl polyphosphate films contain more unchanged ZDDP. 

The (P) L-edge XANES spectra of tribofilms and thermal films generated from the neutral di-isopropyl ZDDP along with the model compounds (zinc metaphosphate and zinc pyrophosphate) are very similar and compare well with model compounds. The surface may also play an important role in catalysis of the thermal decomposition and provide oxygen for phosphate formation. There is also... 

Table 4.2. Chemical characterization of tribochemical and thermal films generated from zinc dialkyldithiophosphates (ZDDPs) using (P) L-edge and (S) L-edge XANES spectroscopy (Fuller et al., 1997)...

Thermal film in oil solution Mixture of short and long chain polyphosphates. Sulfur is absent at 200°C present as sulfate at low temp. Mixture of polyphosphates. Above 200°C, sulfur is absent in the film present as sulfate at low temp. Mixture of polyphosphates. Above 200°C, sulfur is absent in the film present as sulfate at low temp. 

The XANES data suggest (for a thermal film generated at 100°C, 48-108 h) that it is more likely that the surface adsorbed species in Fig. 4.4, spectrum [B], is a rearranged ZDDP, known as LI-ZDDP (linkage isomer of ZDDP). 

Fig. 4.4. Phosphorus (P) K-edge XANES spectra of a thermo-oxidative tribofilm generated at 100°C (48-108 h heating time) for model compounds ZDDP, disulfide and Zn orthophosphate. The surface adsorbed species of the thermal film [B] is a rearranged ZDDP (linkage isomer, LI-ZDDP). A shoulder in the thermo-oxidative tribofilm indicates that there is some orthophosphate present (Fuller et al., 1998)...

Peak a of the thermal film (spectrum B) is shifted by 1.2 eV to higher energy from peak a of the ZDDP (spectrum A) and peak a of the disulfide (spectrum C), and yet peak a of the thermal peak (spectrum B) does not correspond to peak b of the zinc orthophosphate (spectrum D), revealing that this species is a phosphate or the original ZDDP. 

Figure 4.4 Reprinted from Tribol. Int., Vol. 31, M.L.S. Fuller, M. Kasrai, G.M. Bancroft, K. Fyfe and K.H. Tan, Solution decomposition of zinc dialkyl dithiophosphate and its effect on antiwear and thermal film formation studied by X-ray absorption spectroscopy, pp. 627-644. Copyright 1998, with permission from Elsevier.

Light-triggered thermal film decomposition followed by DNA release... 

Fig. 7 (PLL/HA)24/PLL film with embedded DNA before (a, c) and after (b, d) irradiation with IR light. PLL in the film is labeled with FITC (a, b), and DNA is labeled with EtBr (c, d). Scale bars 5 pm. (e) Suggested mechanism of DNA release induced by the distortion of the DNA-doping PLL interaction as a result of partial thermal film decomposition in vicinity of nanoparticle aggregates. Reproduced from [98]...

Earlier, we reviewed silicon dioxide (thermal) films deposited with added phosphorus to serve as a getter for mobile ion impurities, as a final passivation film. Plasma-enhanced silicon nitride can also be doped with phosphorus.6 Some of the film characteristics have been reviewed, and it was found that the films with 2 to 3% P had the best electrical quality. No measurements of stress or H2 content were reported, so it is not clear that these would be use-able films. 

The ability of the plasma BPSG film to passivate against sodium penetration was compared to the thermal film. Evidence was found of some sodium penetration in the plasma films, and none in the thermal ones. 

It has been established that the process of enzymatic destmction of chitosan (CHT) film specimens obtained from acetic acid solution experiences the influence of the prehistory of film formation, including the concentration of acetic acid used for films preparation and the thermal film modification. 

Fig. 16 (a) Spectra taken at 1.2 V versus Ag/AgCl from thermal film... 

To evaluate liquid hydrogen properly as a coolant, more experimental information is required concerning the heat-transport mechanism through the thermal film for both subcritical and supercritical conditions. For this report, subcritical pressures 30-70 psi and a narrow range of bulk temperatures are included in the experimental conditions. The heat-transfer characteristics of hydrogen were measured in an electrically heated vertical tube. The tube was instrumented for surface temperature and pressure-drop measurements. The temperature difference between the wall and bulk fluid was varied from approximately 40° to 1000°R. The maximum heat flux was 0.8 Btu/in. -sec. 

The approximate film thickness (including a carbon overlayer) can be calculated from the attenuation by the overlying film of the electrons emitted from the metallic iron present in the steel beneath the surface film. It was found to be 5.0 0.2nm after the 5N test. This film thickness is significantly smaller than that reported in most other studies. This may be due to the fact that most of these studies have been carried out at temperatures above 80 °C. At these temperatures, but not below, a thick thermal film is formed on the surface. Under the conditions applied in this study, the contact temperature and the tribochemical reaction form a thin phosphate film, but the thermal activation is insufficient to form a thick polyphosphate film. 

The Fe2p XPS signal has not been detected in the thermal films formed from either pure ZnDTP and its solution in PAO on iron-coated germanium ATR crystals. This indicates there is no formation of polyphosphates associated with iron by thermochemical reaction of ZnDTP on iron surfaces, under the experimental conditions used in this work. 

Fig. 3. In situ ATR FTIR spectra of thermal films formed at room temperature and at 150°C and of tribofilms formed during tribotests at room temperature and at 150°C. Iron-coated (lOnm) germanium ATR crystal. Baseline correction was applied. The spectrum collected on undiluted ZnDTP deposited on the iron-coated Ge crystal without sliding or heating is shown for comparison. The normal load was 7N, the Hertzian contact area 0.1 mm, average apparent contact pressure 34MPa, mean sliding velocity 24mm/min.

Composition The composition of the reaction layer changed with the applied load and temperature (see Table 1). While on the tribotracks and the thermal films at 150 °C the amount of oxygen was about three times that of phosphorus, far more oxygen was present in the non-contact areas at 30 and 80 °C. Compared to the ZnDTP molecule, where a S P ratio of 2 1 is present, a depletion of sulphiu was found in the tribotracks and non-contact areas, while on the baU the deposited material behind the tribological contact at 80 °C was enriched in sulphiu . Small amounts of oxidized stdphur species were found in the non-... 

The tribological films formed in this study were thicker than those formed in the constant-load test, while the thermal films had similar thicknesses [11]. This is likely to be due to the longer time of tribostress only five turns per annulus were applied in the constant-load test, while 1000 turns were carried out with the oscillating-load test applied in this work. Short-chain poly(thio)phosphates with 2-6 phosphate units were found at all temperatures in the tribotracks, which corresponds to results obtained with constant loads [11, 65] and is in agreement with proposals made in the literature [22, 35]. At 150 °C, the thermal film... 

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