Lcsm

Patrice Berthod

Several possible consequences of high temperature oxidation for the subsurface microstructure of carbidescontaining alloys

Many refractory cast alloys are strengthened by carbides to achieve sufficient mechanical properties for high temperature applications. When they are oxidized at high temperature their subsurface microstructures are changing. Carbides generally disappear from surface over a depth increasing with temperature yes?

and time while, sometimes, carbides undergo modifications in an area separating carbidefree zone and bulk (coarsening, stoichiometry change, precipitation of new ones). In some cases, a change of matrix in iron alloys can also be encountered in the zone affected by oxidation, due to local chemical changes. The aim of this work is to list the types of subsurface modifications (concerning carbides only) induced by high temperature oxidation, and to attempt to correlate them to the identity of the base elements, the initial carbide density and the exposure temperature.

In addition to the development of oxides layer over the external surface and sometimes internal oxides growth, oxidation at high temperature promotes several subsurface microstructure modifications. Among them there are sometimes curious phenomena concerning deeper carbides, obviously induced by a not outward but inward diffusion of carbon released by disappearing carbides, but also a more frequent growing carbidefree zone. If the latter may be considered as not desirable for the alloy surface because of a decrease in hardness and probably in wear resistance, this carbidefree zone can be considered as an especially refractory skin which can prevent emergence of molten alloy areas in case of sudden significant increase of temperature in service. The subsurface modifications which were considered are illustrated below: existence or not of an outer zone (1) in which carbides have disappeared, modification of the already existing interdendritic carbides, about their qualitative surface fraction or their apparent composition (2) and existence of new carbides precipitated in matrix in a zone separating the carbidefree zone and the unmodified bulk (3).

It appears that almost all alloys display a carbidefree zone ("cfz"). Its depth increases when T increases and decreases when the C content increases, and tends to be higher for Fe alloys than for Ni alloys, and higher for Co alloys than for Fe alloys.

About the coarsening of carbides (or their change of stoichiometry) in an area separating the cfz and the unaffected bulk, the Ni alloys concerned by these phenomena are mainly the ones with the low or medium C contents, and for the lowest T. This does not seem occurring in the Co alloys, and only at the highest T for the Fe alloys.

New secondary carbides precipitated in matrix, also in an area between the cfz and the bulk, in rare cases. This occurred in Fe30Cr-0.4C at 1200°C and for the Ni30Cr0.2C at 1000°C.

The development of the cfz shows that almost all C quitted this part of subsurface, generally into gaseous oxidized species, but sometimes it diffused a little deeper in alloy where it promoted the carbide coarsening (or stoichiometry change for carbonrichest carbides) or the precipitation of new carbides. Image analysis for specifying the carbides fractions versus the depth may lead to the distributions of C content, and then of the local solidus temperature, thanks to thermodynamic calculations (ThermoCalc).

The cfz with very low or zero C and the intermediate zone with a higher C content than in bulk, have their own solidus temperatures: a low one for the carbideenriched zone (when it exists) and a high one for the carbidefree zone, when compared to the bulk one.


Inrae
email: frederic.jean@inrae.fr

Long-term monitoring of leaf phenology for two forest tree species located at their hot and dry, southern margin

Introduction

The effect of climate change on European temperate tree species is characterized by a significant advance in budbreak dates¹ and contrasting responses regarding leaf senescence dates². These phenological responses are under the control of several environmental determinants some of which seem to play an increasingly important role, such as the need for cold to lift the dormancy necessary for budburst³ or the water stress causing early leaf senescence⁴. The dataset presented here shows the interest of long-term monitoring for two species located at the southern margin of their distribution area where environmental constraints are particularly pronounced (Fig. 1).

Phenological observations

Leaf phenology observations at the individual scale were conducted for two major European forest tree species, European beech (Fagus sylvatica L.) and silver fir (Abies alba Mill.). Observations were carried out over 14 consecutive years on 772 trees (Table 1) distributed along two altitudinal transects located on Mount Ventoux (Fig. 3), a mountain in French south-eastern Alps (Fig. 2).

Results

Silver fir: Over the observation period (2006 to 2019; Fig. 5), the linear regression analyze allow to detect a significant (p-value <2e-16) year effect on the budburst dates (budburst date = 1.382*Year -2.645e+03) which explains 25 % of the budburst date variation (R² = 0.2474). The positive slope indicates a significant increasingly late budburst trend (β = +1.382). When we include the classes of altitude in the analyze, the results of the linear ANCOVA model indicate a significant difference in the equality of the slopes (p-value <4.238e-14) : the altitude*year interaction is significant (p-value = 1.355e-05) and means that the influence of altitude on budburst dates varies from year to year.

European beech: Over the observation period (2012 to 2019), the linear regression of the year on the senescence dates gives a significant negative slope (β = -0.9841; p-value = 2.11e-09) , indicating an increasingly early senescence trend. Also, we observed a larger within-population variability at low than at high altitude (Fig. 6). Finally, the linear mixed model considering two fixed effects (altitude and year) and one random effect (observed trees) gives no significant effect of the altitude on the senescence dates (p-value = 0.1503). However, we observed a significant interaction between altitude*year (p-value = 1.026e-06), which means that depending on the year, the rank of the senescence date varies according to altitude. Indeed, some years the senescence begins at 1100 and others at 1350m.

Sites

Fig. 3 :

 3 Fig.3: Transects studied on Mount Ventoux. One transect is located on the north side of the mountain (from 968 m to 1522 m) and includes both species (picture A), and the other transect is located on the south side (from 875 m to 1537 m) and includes only beech (picture B)

Fig. 2 :

 2 Fig.2: Beech and silver fir in France. Area of presence of beech alone in green, silver fir alone in red and both species in brown.

Fig. 5 :

 5 Fig.5: Variation of the date of budburst (Day of the Year when a stage BBCH7 is observed) between 2006 and 2019 period for silver fir. The vertical bars represent standard errors.

Fig. 6 :

 6 Fig.6: Variation of the date of the leaf senescence (Day of the year when a stage BBCH95 is observed) between 2012 and 2019 at two elevations for European beech. The linear regression dashed lines for 1100m and 1350m are respectively in red and blue. The vertical bars represent standard deviation.

Fig. 1 :

 1 Fig.1: Decline of silver fir (Abies alba Mill.) stands on Mount Ventoux

Table 1 : Total number of trees observed and total number of observations over the period (2006-2019) by species, phenophase and exposure.

 1

Acknowledgements: UEFM (Marianne CORREARD, Olivier GILG, Mehdi PRINGARBE, Franck REI, Jean THEVENET, Norbert TURION) for Methodology and Investigation, URFM (Sylvie ODDOU-MURATORIO, Bruno FADY, Ivan SCOTTI, Caroline SCOTTI-SAINTAGNE, Philippe CLASTRE, Olivier MARLOIE, William BRUNETTO, Christian PICHOT) for Data Curation, Conceptualization, Investigation, Formal analysis, Writing and Review & Editing) and TEMPO network (https://tempo.pheno.fr/soere-tempo_eng/) for its support in the continuous improvement of phenology observation methods and the elaboration of associated protocols.


R Moury

A Gigante

H Hagemann

An alternative approach to the synthesis of NaB 3 H 8 and Na 2 B 12 H 12 for solid electrolyte applications

Keywords: Octahydrotriborate, dodecaborate, solid electrolyte, hydrogen storage

Alkaline or alkaline earth octahydrotriborate M(B 3 H 8 ) x and dodecahydro-closo-dodecaborate M x B 12 H 12 (M = Li, Na, Mg or Ca with x = 1 or 2) have recently attracted a lot of interest for hydrogen storage and solid electrolyte applications. Nevertheless, their syntheses are still a roadblock for large scale applications. In this paper we propose a novel approach for their syntheses starting from the cheapest borohydride NaBH 4 . The process involves first the solvothermal synthesis of tetrabutylammonium octahydrotriborate (C 4 H 9 ) 4 NB 3 H 8 (TBAB 3 H 8 ) being the basis for the syntheses of the others boranes. Starting from TBAB 3 H 8 , we have synthesized pure and unsolvated NaB 3 H 8 by salt metathesis reaction with sodium tetraphenylborate. Then, we have successfully obtained Na 2 B 12 H 12 by solvothermal decomposition of NaB 3 H 8 . This approach has shown to be quantitative and reproducible, which could lead to the development of these boranes in real life applications.

Introduction

Boron-hydrogen based materials have attracted a lot of interest since their discovery a hundred years ago. In the late 1990s, alkaline and alkaline earth borohydrides have been proposed as solidstate hydrogen storage materials due to their stability and high gravimetric hydrogen content [START_REF] Mcwhorter | Moderate temperature dense phase hydrogen storage materials within the US Department of Energy (DOE) H 2 storage program: trends toward future development[END_REF][START_REF] Arndt | [END_REF][START_REF] Moussa | Boron-based hydrides for chemical hydrogen storage[END_REF] leading to a wealth of experimental and theoretical studies [START_REF] Cerny | inorganic metal borohydrides and their relation to metal oxides[END_REF][START_REF] Fu | Synthesis of lithium octahydrotriborate and investigation on its thermal decomposition[END_REF]. To date, it appears that there remain important issues concerning reversibility and acceptable kinetics for efficient hydrogen storage applications. However, it was recently demonstrated that the system Mg(B 3 H 8 ) 2 -MgH 2 can be fully rehydrogenated to form Mg(BH 4 ) 2 under moderate conditions [START_REF] Chong | Reversible dehydrogenation of magnesium borohydride to magnesium triborane in the solid state under moderate conditions[END_REF][START_REF] Chong | Inorganic Chemistry. Selective reversible hydrogenation of Mg(B 3 H 8 ) 2 /MgH 2 to Mg(BH 4 ) 2 : pathway to reversible borane-based hydrogen storage?[END_REF]. Lately, a new possible application of boron-hydrogen based compounds has emerged as ionic conductor. For instance, sodium [START_REF] Udovic | Chemical Communicationa. Sodium superionic conduction in Na 2 B 12 H 12[END_REF], lithium and mixed salt sodium lithium dodecahydro-closo-dodecaborate [START_REF] He | Synthesis of a Bimetallic Dodecaborate LiNaB 12 H 12 with Outstanding Superionic Conductivity[END_REF] have shown superionic conductivity for the HT-phase, above 10 -1 S.cm -1 . Moreover, NaB 3 H 8 was also proposed as liquid anodic fuel [START_REF] Pylypko | Journal of Power Sources. A preliminary study of sodium octahydrotriborate NaB 3 H 8 as potential anodic fuel of direct liquid fuel cell[END_REF] or hydrogen storage material through hydrolysis [START_REF] Huang | International Journal of Hydrogen Energy. High-capacity hydrogen release through hydrolysis of NaB 3 H 8[END_REF]. Consequently, octahydrotriborate (for hydrogen storage and liquid anodic fuel) and dodecahydro-closododecaborate (for solid state ionic conduction) salts are also worthy to be studied in depth.

In view of future applications, it is desirable to develop new synthetic approaches to compounds with B 3 H 8 -or B x H x 2-ions avoiding the use of dangerous (toxic, flammable etc) chemicals such as Na/Hg, B 2 H 6 etc. which have been reported previously [START_REF] Hough | The sodium-diborane Interaction[END_REF][13][START_REF] William | Metal Boron Hydrides. BORAX TO BORANES[END_REF][START_REF] Nainan | Inorganic and Nuclear Chemistry Letters[END_REF][START_REF] Dewkett | Journal of Inorganic and Nuclear Chemistry. A simplified preparation of B 3 H 8 salts[END_REF][START_REF] Hill | Reduction of borane THF by alkali metal (potassium, rubidium, cesium) and ytterbium mercury amalgams to form salts of [B 3 H 8 ] -; a simple procedure for the synthesis of tetraborane[END_REF]. Further, in order to keep the price of the final product as low as possible, it is necessary to start with the cheapest borohydride available, i.e. NaBH 4 .

In this paper, we propose an alternative method to prepare NaB 3 H 8 by the use of a simple and fast cation exchange, involving sodium tetraphenylborate (NaBPh 4 ) and TBAB 3 H 8 . The latter was synthesized using mechano-chemical and solvothermal techniques. One of the interests to start with TBAB 3 H 8 as precursor for Na 2 B 12 H 12 synthesis is its high stability in ambient conditions. Finally, we show that the thermal decomposition of NaB 3 H 8 or mixture of TBAB 3 H 8 and NaBH 4 in diglyme leads to the formation of Na 2 B 12 H 12 among other boranes.

Background on existing synthesis

Table 1 provides a non-exhaustive list of procedures found in the literature to synthesize NaB 3 H 8 . It can be seen from this table that, for most of the syntheses, unfriendly, toxic, unstable, not readily available and expensive chemicals were used (Na/Hg, B 2 H 6 , BH 3 , B 4 H 10 and BF 3 O(C 2 H 5 ) 2 ), which hinder any large scale applications. Other methods were developed by using oxidizing agents as CuCl for instance. Nevertheless, Pylypko et al. reported the systematic failure of the procedure [START_REF] Pylypko | Journal of Power Sources. A preliminary study of sodium octahydrotriborate NaB 3 H 8 as potential anodic fuel of direct liquid fuel cell[END_REF]. Iodine was also used, but the presence of I -in solution make the isolation of pure B 3 H 8 -complicated [START_REF] Nainan | Inorganic and Nuclear Chemistry Letters[END_REF]. Weidong et al. used Na/NaCl fine powder for their synthesis which can be highly flammable [START_REF] Wu | International Journal of Hydrogen Energy. An improved synthesis of unsolvated NaB 3 H 8 and its application in preparing Na 2 B 12 H 12[END_REF]. It can also be seen from the table that for each synthesis involving BH 3 , disproportion into NaB 3 H 8 and NaBH 4 is observed which lowers the conversation to NaB 3 H 8 . Recently, Hansen et al. [START_REF] Hansen | Coordination Chemistry Reviews[END_REF] summarized the different synthetic routes to prepare Na 2 B 12 H 12 , most of which involve B 2 H 6 , or B 10 H 14 which are again toxic and overpriced [22,[START_REF] Muetterties | Inorganic Chemistry. Chemistry of Boranes. VIII. Salts and Acids of B 10 H 10 -2 and[END_REF]. Another route has been proposed using the thermal decomposition of NaB 3 H 8 in diglyme leading to the disproportion of NaB 3 H 8 into Na 2 B 12 H 12 and NaBH 4 [START_REF] Ellis | A convenient preparation of B 12 H 12 -2 salts[END_REF]. Furthermore, direct thermal decomposition of NaB 3 H 8 in a tubular furnace at 500°C was also reported [START_REF] Wu | International Journal of Hydrogen Energy. An improved synthesis of unsolvated NaB 3 H 8 and its application in preparing Na 2 B 12 H 12[END_REF]. However the yield for this reaction is fairly low, about 10%.

Results and discussion a. Preparation of TBAB 3 H 8

The goal of this work was to synthesize Na 2 B 12 H 12 starting from NaBH 4 . Our strategy was to first synthesize B 3 H 8 -anion in a reproducible, safe, scalable and cheap way and then use it as a building block to get Na 2 B 12 H 12 . To reach this purpose, we first tried to reproduce the synthesis proposed by Bürchner et al. [START_REF] Bürchner | Synthesis and Characterization of Boranate Ionic Liquids[END_REF]. The synthesis involves two steps, first a salt metathesis between TBABr and NaBH 4 in dichloromethane (DCM) (Equation 1), and second a reduction of DCM by NaBH 4 (Equation 2). They used ultrasonic bath to improve NaBH 4 solubilization in DCM. Nevertheless with our ultrasonic bath we were never able to obtain TBAB 3 H 8 . This led us to divide the synthesis in two independent parts, first the salt metathesis and second the reduction of DCM by BH 4 -.

TBABr + NaBH 4  TBABH 4 + NaBr (1)

TBABH 4 + 2 NaBH 4 + 2CH 2 Cl 2  TBAB 3 H 8 + 2 CH 3 Cl + 2NaCl (2)
For the salt metathesis (Equation 1), a mechano-chemical synthesis was used (see SI for details). A quantitative conversion was achieved within 1h. Fig. 1 shows a comparison of infrared spectra of both precursors (NaBH 4 and TBABr) with the final product TBABH 4 . The changes of the B-H stretching modes (around 2300 cm -1 ) confirm that NaBH 4 has reacted and that the borohydride ion is in a different environment [25]. For step (2), a solvothermal technique was used, using a homemade autoclave (Fig. S1), in order to:

i) perform safely the synthesis in a closed and robust system;

ii) keep all gaseous active species which could be formed inside the reactor (B 2 H 6 for instance), hence also to increase the yield if such species are formed;

iii) and increase the boiling point of DCM hence increase NaBH 4 solubility.

We found that a temperature of 80°C with a reaction time of 16h were optimal for TBAB 3 H 8 synthesis. This procedure was found to be highly reproducible with almost quantitative conversion (>80%) (see SI for details).

To gain insight into the reaction mechanism of the formation TBAB 3 H 8 , ex-situ sampling of the liquid phase at different reaction time (12, 24, 30, 36 and 48 hours) were performed, for this particular experiment, a reaction temperature of 60°C was chosen in order to slow down the reaction and identify the intermediates. Samples were then analyzed by 11 B NMR (Fig. 2).

The ex-situ measurements show the complete conversion of BH 4 -(δ = -38.8ppm, J B-H = 82 Hertz) into B 3 H 8 -(δ = -30ppm, J B-H = 33.2 Hertz) by increasing the reaction time. Nevertheless, several intermediate compounds are formed. The quartet at -11.4 ppm, was attributed to a BH 3 adduct due to its multiplicity. Another signal centered at -20.5 ppm was recorded, however, by increasing the resolution and using proton decoupled 11 B NMR, it can be seen that this signal is a combination of 3 signals at: -19.6, -21.5 and -22.3 ppm (Fig. S2). The proton coupled 11 B NMR spectra (Fig. S2) reveals that the signal at -19.6 ppm is a quartet which we assigned to another BH 3 adduct. The other two signals at -21.5 and -22.3 ppm are too much overlapping to establish their multiplicity.

Bürchner et al. [START_REF] Bürchner | Synthesis and Characterization of Boranate Ionic Liquids[END_REF] reported the formation of [Cl-BH 3 ] -(quartet at -15.2 ppm) and B 2 H 7 -(quartet of doublet at -25.4 ppm) during the synthesis of B 3 H 8 -. In our conditions, we found two quartets, then we propose also the formation of tributylamine borane (TBA-BH 3 ) by losing one butyl chain into butane. To support our assumption we performed 11 B NMR on commercial triethylamine borane in the same conditions and we found a quartet at -12.6 ppm which is close to our signal at -11.4 ppm. Hence we suggest, in our conditions, the following attribution: the quartet at -19. -to form TBAB 3 H 8 releasing hydrogen and another Na + in solution which must precipitate with Cl -. Consequently, the releasing of Na + and Cl -in solution followed by their precipitation drive the reaction to the formation of TBAB 3 H 8 . The rate limiting step is the solubilization of NaBH 4 in DCM. Our method allows to increase the solubility of NaBH 4 in DCM and speed up the reaction.

b. Formation of NaB 3 H 8

It is known from the literature that tetraphenylborate anion in sodium tetraphenylborate (NaBPh 4 ) precipitates with any kind of ammonium cation in aqueous or alcoholic solution leading to the formation of tetrabutylammonium tetraphenylborate [START_REF] Crane | Identification of amines as tetraphenylborates[END_REF]. Hence NaBPh 4 was used to perform the cation exchange (Equation 3). This procedure was found to be quantitative, reproducible and fast leading to unsolvated NaB 3 H 8 (Fig. 3). The IR spectra of our products NaB 3 H 8 and TBAB 3 H 8 agree with the literature [START_REF] Pylypko | Journal of Power Sources. A preliminary study of sodium octahydrotriborate NaB 3 H 8 as potential anodic fuel of direct liquid fuel cell[END_REF][START_REF] Bürchner | Synthesis and Characterization of Boranate Ionic Liquids[END_REF].

c. Synthesis of Na 2 B 12 H 12

At first, we attempted to prepare TBA 2 B 12 H 12 from a mixture of TBAB 3 H 8 and NaBH 4 (1:3 molar ratio) in diglyme using the solvothermal technique. At the end of the reaction the solid residue was filtered out. The liquid phase was analyzed by 11 B NMR (Fig. S3). The proton decoupled 11 . Moreover, Fig. S5 only shows the presence of diglyme, but no tetrabutylammonium, consequently, the solid is Na 2 B 12 H 12 complexed with diglyme. Thus this route does not allow the formation of TBA 2 B 12 H 12 . Our results suggest a complex mechanism involving first a metathesis between TBAB 3 H 8 and NaBH 4 to give NaB 3 H 8 and TBABH 4 , then the decomposition of NaB 3 H 8 into Na 2 B 12 H 12 by dehydrocoupling. The lower solubility of Na 2 B 12 H 12 in diglyme compare to the other boranes eases its separation.

The second route for Na 2 B 12 H 12 synthesis is similar, however, NaB 3 H 8 was used as starting material. The solid residue was filtered off and the liquid analyzed by 11 B NMR (Fig. S6). The spectrum, display 3 signals at -15.4, -17.1 and -29.3 ppm corresponding to Na 2 B 12 H 12 , Na 2 B 11 H 11 and Na 2 B 10 H 10 respectively. After self-precipitation of Na 2 B 12 H 12 at room temperature, the solid was separated and dried, the 11 B NMR spectrum reveals pure Na 2 B 12 H 12 but IR spectra shows the presence of diglyme which is coordinated to the sodium (Fig. S7). This route provides an efficient way to obtain in a fairly good yield solvated sodium dodecahydro-closo-dodecaborate. The yield cannot be calculated accurately due to the presence of an unknown number of diglyme molecules per formula unit.

Conclusion

In this work we have shown that TBAB 3 H 8 , NaB 3 H 8 and Na 2 B 12 H 12 can be obtained in a quantitative, safe and reproducible way. The use of mechano-chemistry combined with solvothermal synthesis have proved to be efficient approach to obtain this boranes. For all three synthesis the boron containing precursor was the cheapest borohydride on the market which makes this process attractive. Furthermore, the strategy of converting NaBH 4 into TBAB 3 H 8 in order to synthetize higher borane was shown to be interesting, due to the stability of TBAB 3 H 8 in ambient conditions without requiring special handling procedures. This precursor could also be used to synthesize other alkaline or alkaline earth octahydrotriborate or dodecahydro-closo-dodecaborate compounds. Work in this direction is under way in our laboratory.

Fig. 1 -

 1 Fig. 1 -Comparison of room temperature ATR-FTIR spectra of NaBH 4 , TBABr and TBABH 4 .

  6 ppm is due to [Cl-BH 3 ] -, the second quartet at -11.4 ppm to TBA-BH 3 and the last two signals at -21.5 and -22.3 ppm correspond to B 2 H 7 -formation (bridging and terminal hydrogen). With these results, we propose the following mechanism. First, TBABH 4 attacks CH 2 Cl 2 to form TBA-BH 3 , TBA[Cl-BH 3 ] and CH 3 Cl. Then, the anions Cl -in solution must combine readily with some Na + ions from NaBH 4 and precipitate. This precipitation allows to solubilize progressively more of NaBH 4 . Then, the BH 4 -released from the precipitation of NaCl can combine with TBA-BH 3 and/or TBA[Cl-BH 3 ] to form TBAB 2 H 7 which reacts with another BH 4

Fig. 2 -

 2 Fig. 2 -11 B NMR of reaction mixtures TBABH 4 + 2NaBH 4 at 60 °C after different reaction times.

NaBPh 4 (Fig. 3 -

 43 Fig. 3 -IR spectra of solid NaB 3 H 8 and TBAB 3 H 8 .

  B NMR spectra shows the presence of 5 signals, the 3 mains signals are assigned to: tributylamine borane (TBA-BH 3 ) at -11.7 ppm, B 12 H 12 at -15.4 ppm and unreacted TBAB 3 H 8 at -30 ppm. The two minor signals at -17.1 and -29.3 ppm could be due to B 11 H 11 2-and B 10 H 10 2-respectively [28-30]. The solid was allowed to self-precipitate in diglyme and analyzed 11 B (Fig. S4) and 1 H NMR (Fig. S5) revealing the presence of pure B 12 H 12 -2

Table 1 .

 1 Non exhaustive list of published NaB 3 H 8 synthesis

	Reactants	Solvent	Reaction

2 Cl 2  TBAB 3 H 8 + 2CH 3 Cl + 2NaCl + NaBr + H 2

[START_REF] Bürchner | Synthesis and Characterization of Boranate Ionic Liquids[END_REF]

Na/NaCl, NaBH 4 , CuCl THF NaBH 4 + CuCl  BH 3 -THF + NaCl + Cu BH 3 -THF + Na/NaCl  NaB 3 H 8 + NaBH 4

[START_REF] Wu | International Journal of Hydrogen Energy. An improved synthesis of unsolvated NaB 3 H 8 and its application in preparing Na 2 B 12 H 12[END_REF]

Acknowledgments

This work was supported by the Swiss National Science Foundation (project Sinergia CRSII2_160749). The authors thank Ms M. Pupier for providing the NMR spectra, Prof. Umit Demirci for providing a sample of NaB 3 H 8 for spectroscopic comparisons, and Prof. Radovan Cerny allowing to use the ball milling instruments and Mr. P. Barman for constructing the autoclaves.