Browsing by Author "Maguire, John F."
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- Hypotheses in phase transition theories: “What is ‘liquid’?”Publication . Maguire, John F.; Woodcock, LeslieTheories predicting thermodynamic properties that describe liquid phase transitions and critical phenomena have resulted in the award of three Nobel prizes in physics: (i) “Continuity of Gaseous and Liquid States” hypothesis of van der Waals [1910], (ii) “Critical Point Universality” hypothesis embodied in the renormalization group (RG) theory of Wilson [1982], and (iii) “Topological Defect Melting” hypothesis that 2D-crystal-liquid states exhibit ‘hexatic’ phases in KTHNY theory [Kosterlitz et al. 2016]. All three hypotheses are invalidated by the reality of experimental results and raise a fundamental question first posed by Barker and Henderson in 1976: “What is liquid”. A single Gibbs phase, that includes triple-point (Tt) liquid, extends over the whole fluid density range to temperatures above the Boyle temperature (TB). Below TB, above the critical temperature Tc, predominantly gas- and liquid-like states are bounded by a narrow colloidal ‘supercritical mesophase’ with constant rigidity (ω = (dp/dρ)T). The liquid phase also becomes colloidal at the onset of pre-freezing growth and percolation of crystallites in a narrow density range below freezing density for all T > Tt. Whereas the Boyle line (RT = p/ρ) defines a crystalline ground state, a rigidity line, RT = ω, interpolates to an amorphous ground-state akin to random close packing (RCP) at T = 0. All states of gas, liquid, and crystals, are present in the stable ‘liquid phase’ and, are represented in thermodynamic p-T states all along the rigidity line. For 2D liquid–crystal coexistence in constrained computer models, the KTHNY theory describes a non-equilibrium fracture process. Hetero-phase fluctuations, leading to percolation transitions, have been misconstrued as “hexatic” in 2D, as also have 2-phase coexistence states, that are homogeneous in the absence of gravity.
- On the thermodynamics of aluminum cladding oxidation: water as the catalyst for spontaneous combustionPublication . Maguire, John F.; Woodcock, LeslieA recent article (Casey et al. in J Failure Anal Prev 22:1252–1259, 2022) finds a thermodynamic explanation for the catastrophic effect of water as an extinguisher in aluminum-clad tower block fires (Entropy 22: 14, 2020) to be ‘‘unsubstantiated hypotheses’’ and ‘‘suppositions unsupported by data’’. The article by Casey et al., however, is misleading because it is based upon a false premise that it is the hydrolysis of solid aluminum panels that produce hydrogen (H2), which was not detected in their experiments. The combustion of aluminum (Al) to alumina (Al2O3) reaction is highly exothermic to the extent that it can be explosive, but the reaction is inhibited, for all temperatures of solid and liquid Al, below the melting point of alumina (2250 C), by the formation of a thin nanometre skin of alumina that prevents combustion. In tower block infernos of Al-plastic cladding materials, there cannot be production of detectable hydrogen gas, as wrongly assumed by Casey et al., who only investigate the laboratory hydrolysis reaction of solid aluminum in cladding samples, and not the combustion conditions at temperatures exceeding 1500 C. Here we show that H2 is an intermediate in the Al-combustion mechanism of cladding fires, and that water (H2O) is the catalyst. This is one of two possible reaction mechanisms that enable combustion by circumventing direct oxidation of Al. For cladding with adjacent plastic insulation material, water provides an alternative mechanism via methane and the carbide Al4C3 as intermediates, also with H2O as the catalyst.
- Thermochemistry of Grenfell Tower fire disaster: catastrophic effects of water as an 'extinguisher' in aluminium conflagrationsPublication . Maguire, John F.; Woodcock, LeslieWe review the thermochemistry of combustion reactions involved in the Grenfell Tower fire that occurred during the early hours of 14thJune 2017. London Fire Brigade (LFB), having advised all the occupants to stay in their apartments, attempted to extinguish the fire with water. The Grenfell Tower 24-storey block had recently been re-clad with an insulationto meet energy saving targets.It comprised an aluminum exterior façade, and a polymer composite thermal insulator ‘sandwich filler’, mainly polyethylene, with narrow air gaps inbetween polymer and aluminium sheets.The renovated window frames were also made of aluminum coated with a powdered polyester. Here, we highlight the scientific thermochemical reasonswhy water should never be used on aluminum fires; not least because a mixture of aluminium and water is a NASA rocket fuel! When the plastic insulation initially catches fire and burns with limited oxygen (O2 in air) to carbon(C), seen as an aerosol (black smoke) and black residue, the heat of reaction melts the aluminum(Al)and increases its fluidity and volatility, hence also its reactivity,whence it rapidly reacts with the carbon product of polymer combustion to form aluminum carbide (Al4C3). The heat of formation of Al4Cl3 is so great that it becomes white hot sparks like fireworks. At very high temperatures, both molten Al and Al4C3 aerosol react violently with water to give alumina fine dust aerosol(Al2O3)+ hydrogen (H2) gas and methane (CH4) gas, respectively, with white smoke and residues. These highly inflammable gases, with low spontaneous combustion temperatures, instantaneously react with the oxygen in air accelerating the fire out of control. Adding water to an aluminum fire is like adding “rocketfuel” to the existing flames. The timeline of events and photographic evidence corroborates this scientific explanation why a 4th-floor kitchen-appliance fire became a major tower-block inferno within 12minutes of applying water as a would-be extinguisher. A CO2-foam/powderextinguisher, as deployed in the aircraft industry against aluminum+plastic fires by smothering, might have contained the fire in its early stages. Thermochemistry of Grenfell Tower Fire Disaster
- Thermodynamics of tower-block infernos: effects of water on aluminum firesPublication . Maguire, John F.; Woodcock, LeslieWe review the thermodynamics of combustion reactions involved in aluminum fires in the light of the spate of recent high-profile tower-block disasters, such as the Grenfell fire in London 2017, the Dubai fires between 2010 and 2016, and the fires and explosions that resulted in the 9/11 collapse of the World Trade Center twin towers in New York. These fires are class B, i.e., burning metallic materials, yet water was applied in all cases as an extinguisher. Here, we highlight the scientific thermochemical reasons why water should never be used on aluminum fires, not least because a mixture of aluminum and water is a highly exothermic fuel. When the plastic materials initially catch fire and burn with limited oxygen (O2 in air) to carbon (C), which is seen as an aerosol (black smoke) and black residue, the heat of the reaction melts the aluminum (Al) and increases its fluidity and volatility. Hence, this process also increases its reactivity, whence it rapidly reacts with the carbon product of polymer combustion to form aluminum carbide (Al4C3). The heat of formation of Al4Cl3 is so great that it becomes white-hot sparks that are similar to fireworks. At very high temperatures, both molten Al and Al4C3 aerosol react violently with water to give alumina fine dust aerosol (Al2O3) + hydrogen (H2) gas and methane (CH4) gas, respectively, with white smoke and residues. These highly inflammable gases, with low spontaneous combustion temperatures, instantaneously react with the oxygen in the air, accelerating the fire out of control. Adding water to an aluminum fire is similar to adding "rocket fuel" to the existing flames. A CO2-foam/powder extinguisher, as deployed in the aircraft industry against aluminum and plastic fires by smothering, is required to contain aluminum fires at an early stage. Automatic sprinkler extinguisher systems should not be installed in tower blocks that are at risk of aluminum fires.