Newsgroup: it.scienza.chimica
Titolo: Cosa c'e' in uno "scollatutto"?

https://i.postimg.cc/zGJKrKd0/IMG-20190104-174157.jpg
 
 
Cosa cavolo puo' sciogliere contemporaneamente molti tipi di colle?
 
--
Wakinian Tanka 

 ha scritto:

La scheda di sicurezza dice che contiene carbonato di propilene. 
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 La scheda di sicurezza dice che contiene carbonato di propilene. 
 
Grazie. 
 
--
Wakinian Tanka

 La scheda di sicurezza dice che contiene carbonato di propilene.
 
Il carbonato di propilene (in sigla PC) è un solvente aprotico polare 
eterociclico: lo si potrebbe definire metildiossaciclopentanone. Le sue 
caratteristiche più interessanti sono la bassa tossicità e 
infiammabilità, l'elevato momento di dipolo (4.9 D da confrontare con 
2.91 D dell'acetone) e il fatto che è "green" venendo prodotto con 
consumo e non con emissione di CO2. Vedere:
 
https://en.wikipedia.org/wiki/Propylene_carbonate
 
 
Per il suo effetto distruttivo sulla grafite, potrebbe forse essere 
un'alternativa al solfuro di carbonio come agente di pulizia del 
famigerato pentolino.
 
Anche il carbonato di etilene (EC) ha proprietà e usi molto simili:
 
https://en.wikipedia.org/wiki/Ethylene_carbonate
 
 
Bye,
 
   *GB*

    *GB*
 
 
-- 
1) Resistere, resistere, resistere.
2) Se tutti pagano le tasse, le tasse le pagano tutti
Soviet_Mario - (aka Gatto_Vizzato)
 

 incombustibilità no, in effetti.
 
Ci hai azzeccato. Punto di fiamma dell'EC: 150 °C
 
Bye,
 
   *GB*

 Sta scritta in quel link:
 
Al riguardo, vedasi questo del 2007:
 
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.462.366&rep=rep1&type=pdf
 
 
   New Insight into the Interaction between Propylene Carbonate-Based
   Electrolytes and Graphite Anode Material for Lithium Ion Batteries
 
   Sufficient understanding of surface chemistry for electrode and 
electrolytes during an electrochemical process is a crucial issue to 
further improve the performance of lithium ion batteries (LIB). In this 
study, we systematically investigate the interaction between propylene 
carbonate (PC)-based electrolytes and graphite anode material, which has 
been under dispute for a long time in the electrochemical community, and 
a new physical model is proposed to explain the poor compatibility of PC 
with graphite. With the aid of scanning electron microscopy, focused ion 
beam workstation, Raman spectroscopy, X-ray photoelectron spectroscopy, 
X-ray diffraction, and thermogravimetry-differential scanning 
calorimetry, the cumbersome but intriguing questions on the poor 
compatibility are addressed: (i) Does PC truly have the ability to 
co-intercalate into graphite materials? Our answer is yes. (ii) Where is 
the intercalation site? It is around the crystal boundary. (iii) Why 
does the co-intercalation occur for PC not ethylene carbonate - another 
kind of useful electrolyte in LIB, since both of them have a similar 
molecular structure? The methyl group in the PC molecule is the main 
wire-puller, which makes decomposition products of PC puffed and thus 
incompetent in inhibiting the subsequent co-intercalation. Finally, 
three feasible strategies to overcome the poor compatibility are summarized.
 
   [...] Currently, the most suitable solvents for liquid rechargeable 
LIB remain the mixtures of cyclic and linear alkyl carbonates such as 
propylene and ethylene carbonates (PC, EC) and dimethyl and diethyl 
carbonates (DMC, DEC), respectively.8 Both PC and EC demonstrate a wide 
electrochemical stability window, high ionic conductivity,9 and a 
similar cyclic molecular structure as shown in Figure 1, but there is a 
remarkable difference in the melting point for them: the former is 
approximately -49 °C, the latter approximately 39 °C.10 Obviously, the 
low-melting-point PC makes it easy to enlarge the application field of 
LIB, especially for the situation at a relatively low-working 
temperature. Unfortunately, the compatibility of PC with the graphite 
anode widely used in current LIB is very poor.11-15 In most cases, no 
reversible capacity can be delivered. Many researchers have attempted to 
investigate the reasons for this problem, because clarifying the 
interactions will make it helpful to understand the surface chemistry of 
electrode materials, to design optimum electrolyte solutions, and 
finally to develop high-performance LIB. Until now, two different 
physical models are documented to explain the destructive behavior of 
PC. Besenhard et al.16-17 considered that solvent molecules (e.g., PC) 
could co-intercalate into graphite to form a ternary graphite 
intercalation compound [Lix(solv)yCn], and its decomposition products 
among graphene layers caused graphite exfoliation. Nevertheless, Peled 
et al.18 emphasized the inability of PC-based electrolytes to form a 
stable solid electrolyte interphase (SEI) film on the surface of 
graphite. Aurbach et al.19-22 further attributed the failure of PC to 
its continuous reduction and decomposition accompanied by the production 
of gases (e.g., C3H6), and the decomposition products disconnect 
graphite particles from bulk electrode, finally leading to graphite 
deactivation because of electrical isolation. In brief, the first 
mechanism is a three-dimensional reaction process (i.e., 
co-intercalation), and the second is a surface reaction (i.e., reduction 
and decomposition). So far, each model can gain some support from a few 
experimental observations.
 
Poi anche quest'altro del 2013:
 
http://www.globalcis.org/jdcta/ppl/JDCTA3426PPL.pdf
 
 
   Unusual Interface Phenomena between Graphite and
   Propylene Carbonate-Based Electrolyte Solutions
 
   In the present study, the surface reactions occurring at the graphite 
negative electrodes of lithium secondary batteries in propylene 
carbonate (PC)-based media were examined. The electrode reactions were 
significantly affected by the electrolyte concentration. In a 
concentrated solution (3.27 mol kg^–1 LiClO4/PC), lithium ions were 
reversibly intercalated within graphite. In contrast, continual 
electrolyte decomposition and exfoliation of the graphene layers 
occurred in a low concentration solution (2.45 mol kg^–1 LiClO4/PC). In 
situ electrochemical atomic force microscopy revealed the formation of 
an effective surface film on the graphite surface after potential 
cycling in the 3.27 mol kg^–1 LiClO4/PC solution. The results of Raman 
analysis indicated the absence of free PC molecules in the concentrated 
solution, which suggested that ion–solvent interactions are an important 
factor for regulating the formation of stable surface films on graphite 
negative electrodes in PC-based solutions.
 
   Graphite, an allotrope of carbon, is a layered substance consisting 
of hexagonal sheets of sp2-carbon atoms (called graphene layers), weakly 
bonded together by van der Waals forces. Graphite is widely used as a 
negative electrode in lithium secondary batteries; lithium ion is 
intercalated between its layers to form lithium graphite intercalation 
compounds (Li-GICs) during charging and de-intercalated during 
discharging. These reactions at the graphite negative electrodes occur 
at extremely negative potentials below 0.25 V vs. Li+/Li. At such 
potentials, aqueous solutions cannot be used as electrolytes because of 
excessive hydrogen gas evolution; therefore, non-aqueous organic 
solutions are typically used as an electrolyte [1][2]. The liquid 
electrolyte media typically employed for lithium secondary batteries are 
ethylene carbonate (EC)-based solutions containing lithium salts such as 
LiClO4, LiPF6, LiBF4, etc. The development of lithium-containing 
EC-based solutions has permitted in-depth investigations of graphite as 
a negative electrode [3].
 
   Additionally, there has been considerable research directed toward 
propylene carbonate (PC)-based solutions in parallel with EC-based 
solutions. One of the major reasons for the interest in PC-based 
solutions is that they exhibit superior ionic conductivity to EC-based 
solutions at low temperatures [4]. Before the discovery and development 
of EC-based solutions, early attempts at electrochemical lithium 
intercalation within graphite were performed in PC-based solutions, 
which have been commonly used in primary lithium batteries. However, 
these attempts were unsuccessful because of poor compatibility between 
graphite and PC [5–7]. Instead of lithium intercalation, only continual 
solvent decomposition and graphene layer exfoliation processes were 
observed to take place when a graphite electrode was polarized to 
negative potentials in PC-based solutions.
 
   [...] In previous studies, it was reported that when a graphite 
electrode is polarized to a negative potential, solvent molecules as 
well as lithium ions are intercalated within the graphite. These 
molecules and ions then decompose between the graphene layers, which are 
accompanied by their characteristic features, e.g., exfoliation of the 
graphene layers or a large swelling (blister) 20–100 nm in height [12][13].
 
   [...] In a concentrated PC-based solution of 3.27 mol kg^–1 
LiClO4/PC, lithium ions were intercalated electrochemically into the 
graphite electrode to form Li-GICs, whereas solvent decomposition and 
the intensive exfoliation of graphene layers occurred in the relatively 
low-concentration solution, 2.45 mol kg^–1 LiClO4/PC. The graphite 
electrode showed a good reversible charge–discharge behavior in the 3.27 
mol kg^–1 LiClO4/PC solution similar to that observed in the EC-based 
solutions. In-situ ECAFM provided valuable information on surface film 
formation; the 3.27 mol kg^–1 LiClO4 / PC solution produced an effective 
surface film on graphite. The surface was noted to have two roles: 
suppressing the co-intercalation of PC molecules within the graphite and 
further electrolyte decomposition on the graphite surface.

 Ci hai azzeccato. Punto di fiamma dell'EC: 150 °C
 
non è poi molto in più, ma essendo più volatile è cmq un 
incremento significativo (perché di norma sarebbe l'inverso, 
maggiore volatilità a pari struttura e maggiore facilità a 
incendiarsi).
 
Però questa molecola ha meno carbonio e idrogeno, per cui la 
frazione combustibile è ridotta (il 70 % della massa è 
incombustibile nel senso che è già cenere : H2O, CO2) e solo 
il 30 % lo è. Siamo a livelli del vinile cloruro, anche se 
qui manca la forte azione inibitrice di fiamma del cloro 
(l'ossigeno è "trasparente" in questo senso perché non 
smorza la reattività dei radicali liberi che si formano, gli 
alogeni invece sono degli scavenger e una volta che 
l'elettrone dispari finisce su un alogeno la sua reattività 
si abbassa notevolmente e tende a troncare le catene 
reattive). Anche cineticamente il carbonato di etilene manca 
idrogeni "terziari", più facili da staccare e iniziare le 
suddette catene radicaliche, sicché riesce a spuntare quella 
manciata di gradi in più.
 
cmq mi segno di andare a cercare quel riferimento [8] appena 
avrò tempo. Mi piacerebbe capire come può il Propilene 
carbonato avere azione così nefasta sulla grafite. Sempre 
che la cosa sia spiegata in chiaro perché sulle formulazioni 
delle batterie ci sono un po' tanti brevetti e dettagli 
omessi (Ad es. se un elettrodo è a base grafite più additivi 
agglomeranti / adesivi, probabilmente glisserebbero sulla 
loro natura così da rendere poco copiabile la soluzione)


 the graphite surface.
 
si sbilanciano poco eh ... claro, su una pubblicazione se 
sgarri dopo ti fanno le pulci :)
 
 
grazie della documentazione !
A sproposito ... non trovo più sci-hub ... dove cavolo hanno 
mandato i server ? quello iraniano non funge più ...


 il responsabile" ?
 
Si, circa:
 
<<wire-puller
n. 1 burattinaio ( m.; f. -a) 
 
2 ( fig.) intrallazzatore ( m.; f. -trice), faccendiere ( m.; f. -a), maneggione ( m.; f. -a) >>
 
--
Wakinian Tanka

 server ?
 
In Svezia (finché dura):
 
https://sci-hub.se/
 
 
Infatti Elsevier, ACS e Springer Nature hanno convinto il Roskomnadzor a 
bloccarne l'accesso in Russia e Kazakistan (per cui anche in Iran).
 
Bye,
 
   *GB*


Anche questo, sperando che duri:
 
https://whereisscihub.now.sh
 
 
(ne mostra l'indirizzo corrente)
 
ciao
patrizio
 

 (ne mostra l'indirizzo corrente)
 
Buono a sapersi. Ma al momento l'unico indirizzo che funge è lo stesso 
che ho dato io: gli altri tre ivi riportati sono irraggiungibili.
 
Bye,
 
   *GB*

On Sunday, January 13, 2019 at 10:21:00 AM UTC+1, *GB* wrote:

Anche questo, sperando che duri:
 
https://whereisscihub.now.sh
 
 
(mostra l'indirizzo di schihub funzionante)
 
ciao
patrizio

 patrizio
