| 171. |
- Johari, G P, et al.
(författare)
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In situ transformation of amorphous ices at high pressures
- 2007
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Ingår i: Physical Review B. ; 76, s. 134103-1
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Tidskriftsartikel (refereegranskat)abstract
- By using thermal conductivity and its change with temperature and pressure as a criteria for in situ structural transformation of the crystalline and amorphous solid forms of water, we report two findings: (i) transformation of high-density amorph (HDA) directly to cubic ice on slow depressurization and (ii) slow transformation or dilation of metastable HDA at 130 K to a low-density amorph (LDA) even when the pressure was increased from 0.2 to 0.3 GPa, and then gradual reversion by collapse of the LDA to HDA on further pressurization to 0.5 GPa. We also discuss implications of these findings for the current understanding of the transformations of metastable ices under pressure, particularly of those studied in situ.
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| 172. |
- Johari, G. P., et al.
(författare)
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Instability and thermal conductivity of pressure-densified and elastically altered orientational glass of Buckminsterfullerene
- 2018
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 148:14
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Tidskriftsartikel (refereegranskat)abstract
- We report on the temperature, pressure and time (T, p and t)- dependent features of thermal conductivity, k, of partially ordered, non-equilibrium state of C60-OG, the orientational glass of Buckminsterfullerene (at T below the orientational freezing temperature Tog) made more unstable (i) by partially depressurizing its high-p formed state to elastically expand it, and (ii) by further pressurizing that state to elastically contract it. The sub-Tog effects observed on heating of C60-OG differ from those of glasses, because phonon propagation depends on the ratio of two well-defined orientational states of C60 molecules and the density of the solid. A broad peak-like feature appears at T near Tog in the k-T plots of C60-OG formed at 0.7 and heated at 0.2 GPa, which we attribute to partial overlap of the sub-Tog and Tog features. A sub-Tog local minimum appears in the k -T plots at T well below Tog of C60-OG formed at 0.1 GPa and heated at 0.5 GPa, and corresponds to the state of maximum disorder. Although Buckminsterfullerene is regarded as an orientationally-disordered crystal, variation of its properties with T and p is qualitatively different from other such crystals. We discuss the findings in terms of the nature of its disorder, sensitivity of its rotational dynamics to temperature and the absence of the Johari-Goldstein relaxation. All seem to affect the phenomenology of its glass-like transition.
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| 173. |
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| 174. |
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| 175. |
- Johari, G. P., et al.
(författare)
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Structural relaxation and thermal conductivity of high-pressure formed, high-density di-n-butyl phthalate glass and pressure induced departures from equilibrium state
- 2017
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 146:23
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Tidskriftsartikel (refereegranskat)abstract
- We report a study of structural relaxation of high-density glasses of di-n-butyl phthalate (DBP) by measuring thermal conductivity, κ, under conditions of pressure and temperature (p,T) designed to modify both the vibrational and configurational states of a glass. Various high-density glassy states of DBP were formed by (i) cooling the liquid under a fixed high p and partially depressurizing the glass, (ii) isothermal annealing of the depressurized glass, and (iii) pressurizing the glass formed by cooling the liquid under low p. At a given low p, κ of the glass formed by cooling under high p is higher than that of the glass formed by cooling under low p, and the difference increases as glass formation p is increased. κ of the glass formed under 1 GPa is ∼20% higher at ambient p than κ of the glass formed at ambient p. On heating at low p, κ decreases until the glass to liquid transition range is reached. This is the opposite of the increase in κ observed when a glass formed under a certain p is heated under the same p. At a given high p, κ of the low-density glass formed by cooling at low p is lower than that of the high-density glass formed by cooling at that high p. On heating at high p, κ increases until the glass to liquid transition range is reached. The effects observed are due to a thermally assisted approach toward equilibrium at p different from the glass formation p. In all cases, the density, enthalpy, and entropy would change until the glasses become metastable liquids at a fixed p, thus qualitatively relating κ to variation in these properties.
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| 176. |
- Johari, G.P., et al.
(författare)
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Vibrational and relaxational properties of crystalline and amorphous ices
- 2007
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Ingår i: Thermochimica Acta 461, issue 1-2. - : Elsevier BV. ; , s. 14-43
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Konferensbidrag (refereegranskat)abstract
- Pure water forms 15 crystalline ices at different temperatures and pressures, and its solutions containing small molecules form three crystallographically distinct clathrates. Its vapours deposited on a substrate at T< 100K produce a porous amorphous solid and pure water vitrifies (T-g = 136 K) when hyperquenched in micron-size droplets. At a temperature below 140 K, hexagonal and cubic ice collapse when pressure exceeds similar to 1 GPa to a similar to 30% denser amorphous solid, which on heating at ambient pressure transforms to an amorphous solid with density similar to that of hexagonal ice. In this essay, we describe (i) the thermal conductivity of the ices and clathrates and the thermal conductivity and heat capacity of water's amorphous solids, their thermodynamic paths and their transformations, and (ii) the dielectric relaxation time of ultraviscous water formed on heating the amorphous solids. We also describe the characteristics of pressure collapse and subsequent amorphization of hexagonal and cubic ices that occurs over a period of several days according to a stretched exponential kinetics and a pressure-, and temperature-dependent rate constant. This process is attributed to the production of lattice faults during deformation of the ice and the consequent distribution of the Born instability pressures. This ultimately produces a kinetically unstable high-energy amorphs in the same manner as random deformation of crystals produces kinetically unstable high-energy amorphs, with density and properties depending upon their temperature-pressure-time history. On heating at 1 GPa pressure, the pressure-amorphized solid relaxes to a lower energy state, becoming ultraviscous water at 140 K. But on heating at ambient pressure, it irreversibly transforms slowly to a low-density amorph that differs from glassy water and vapour-deposited amorphous solid.
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| 177. |
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| 178. |
- Johari, Gyan P, et al.
(författare)
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Water's polyamorphic transitions and amorphization of ice under pressure
- 2004
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Ingår i: Journal of Chemical Physics. - : API. - 0021-9606 .- 1089-7690. ; 120:13, s. 6207-6213
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Tidskriftsartikel (refereegranskat)abstract
- Transformations of water’s high density amorph (HDA) to low density amorph (LDA) and of LDA’s to cubic ice (Ic) have been studied by in situ thermal conductivity κ measurements at high pressures. The HDA to LDA transformation is unobservable at p of 0.07 GPa, indicating that, for a fixed heating rate, an increase in pressure increases the temperature of HDA to LDA transformation and decreases that of LDA to ice Ic, causing thereby the two transformations to merge, and HDA appears to convert directly to ice Ic. Thus either LDA forms but converts extremely rapidly to ice Ic, or LDA does not form. At a fixed p and T, in the range of pressure amorphization of hexagonal ice, κ continues to decrease with time. Therefore, the amorphization of ice Ih is kinetically controlled. When HDA at 1 GPa was heated from 130 to 157 K and densified to very HDA, its κ increased by 3%. Our findings and a scrutiny of earlier reports show that a reversible transition between HDA and LDA does not occur at ∼135 K and ∼0.2 GPa. Since there is no unique HDA, it is difficult to justify the conjecture for a second critical point for water.
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| 179. |
- Jonsson, Ove, et al.
(författare)
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TIMFIE-provtagning för tidsintegrerad haltbestämning av växtskyddsmedel, PFAS, läkemedel och metaller i ytvatten : En pilotstudie
- 2022
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- TIMFIE (Time Integrating, Micro Flow, In situ Extraction) är en enkel och billig tidsintegrerad provtagningsmetod som här användes för bestämning av ett stort antal organiska ämnen från vitt skilda substansgrupper. Tekniken bygger på kontinuerlig fastfasextraktion i fält under en till två veckor och den efterföljande bestämningen av organiska ämnen är kvantitativ och baseras på helvatten, dvs. med partikelbunden fraktion inkluderad.Förutom organiska ämnen som växtskyddsmedel, PFAS och läkemedel mättes i detta projekt även metallhalter och löst organiskt kol (DOC) i det uppsamlade, filtrerade vattnet. Merparten av de studerade metallerna och DOC påverkades dock negativt av fastfaskolonnerna som används för extraktion av de organiska ämnena. En separat TIMFIE utan kolonner ska därför användas vid bestämning av metaller. En fältstudie med veckovisa TIMFIE-provtagningar i tolv provpunkter fördelade på fem regioner utfördes i samarbete med länsstyrelserna i Gotland, Östergötland och Dalarna samt med en avfallsanläggning i Mälardalen. Totalt analyserades 47 TIMFIE-prover för drygt 200 organiska ämnen och 21 metaller, samt ytterligare 8 TIMFIE-prover endast för metaller.I framtiden kommer två olika TIMFIE-provtagare att användas i studier där både organiska och oorganiska ämnen bestäms. Fortsatt arbete med att även inkludera näringsämnen i det oorganiska analyspaketet pågår och möjligheten att göra dessa bestämningar på ett återskapat helvatten undersöks.
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| 180. |
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