Bernard Bonnetot

Boron nitride matrices and coatings from boryl borazine molecular precursors

Thermal treatment of 2,4,6-[(NHPr i ) 2 B(NPr i )] 3 B 3 N 3 H 3 in vacuo led to a polyborazine in which the borazine rings are mainly linked by –N–B–N– bridges. Pyrolysis of up to 1400 °C resulted in the formation of high crystallinity hexagonal boron nitride which has been characterised by ESCA, powder X-ray diffraction and FTIR spectroscopy. Precursor has been used to prepare carbon fibres/BN microcomposites by dipping bundles of fibres into a solution of followed by pyrolysis up to 1200 °C. Optical micrographs and SEM analysis have shown that the BN matrices were compact and displayed good adherence properties onto graphite substrates. By contrast, BN coatings obtained from a polymer derived from B(NHPr i ) 3 displayed poor adherence properties. These results are related to the hydrocarbon chain ratio of each preceramic polymer. The effectiveness of the BN protective coatings in preventing oxidation has been measured by isothermal gravimetry in air. As expected, by considering the quality of the coatings, those obtained from showed the most interesting properties.

Conversion of B(NHCH3)3 into boron nitride and polyborazine fibres and tubular BN structures derived therefrom

The reaction of ammonia with tris(methylamino)borane B(NHCH 3 ) 3 1 or with a B(NHCH 3 ) 3 derived polyborazine 2 led to completely different processes. Compound 1 reacted spontaneously with NH 3 to give mainly the borazine (CH 3 NH) 3 B 3 N 3 H 3 and subsequently a BN prepolymer which was not processible. A polymer 2 obtained by heating 1 under argon could be spun into crude polyborazinic fibres. When 2 was heated under ammonia in order to obtain carbon free BN, it was partially dissociated into 1,3,5-trimethyl-2,4,6-tri(amino)borazine (NH 2 ) 3 B 3 N 3 (CH 3 ) 3 3. The borazine 3 was fully characterised by multinuclear NMR spectroscopy, FTIR and mass spectrometry. The structure of 3 has been confirmed by a single crystal X-ray diffraction analysis. An illustration of the formation of 3 was the formation of BN tubes from crude fibres. These results were explained by the TGA curves of the polymer 2 under ammonia or nitrogen.

Replacement of the nitrogen of [1-N2B10H9]− by amines or nitriles, a route to hydrophobic monoanions

Abstract Starting from closo-[B 10 H 10 ] 2− hydrophobic monoanions [R 1 R 2 R 3 N–B 10 H 9 ] − {R=H, C 6 H 5 CH 2 , C 6 H 5 , CH 3 , C 18 H 37 (CH 3 ) 2 } could be obtained by a multistep process in which the displacement of nitrogen from [1-N 2 B 10 H 9 ] − by amines was the key step. Attempts at direct synthesis employing bulky tertiary amines were unsuccessful: no reaction occurred at 120°C and at 150°C [1-N 2 B 10 H 9 ] − decomposed to [B 20 H 18 ] 2− . Pd{P(C 6 H 5 ) 3 } 2 Cl 2 used as a catalyst produced a favourable effect, but the [R 1 R 2 R 3 N–B 10 H 9 ] − ions were present in too low concentration to be isolated from the reaction mixtures. A more suitable route to monoanions carrying three bulky organic groups attached to the amino nitrogen consisted in preparing amino derivatives from the appropriate primary or secondary amines and reacting these intermediate products with alkylhalides in alkaline aqueous propanol solution. The displacement of N 2 by nitriles produced [1-RCNB 10 H 9 ] − monoanions {R=CH 3 , (C 6 H 5 ) 2 CH} which proved to be thermally stable, but were easily hydrolysed to [1-RCONH 2 B 10 H 9 ] − monoanions.

CONVERSION OF TRIS(ISOPROPYLAMINO)BORANE TO POLYBORAZINES. THERMAL DEGRADATION TO BORON NITRIDE

Abstract Thermolysis of tris(isopropylamino)borane (1) and its reaction with ammonia were investigated. Compound 1 exhibited good thermal stability resulting in almost complete evaporation during its thermogravimetric analysis under Ar up to 1000°C. Refluxing of 1 for 42 h at 250°C produced its conversion into the expected B,B′,B′-tris(isopropylamino)-N,N′,N″-triisopropylborazine (2), and into the new intermediate [(NHPri)2B]2NPri (3), both found in low concentrations. Reaction of 1 with ammonia at room temperature resulted in spontaneous transamination, cyclization and polycondensation reactions leading first to B,B′,B″-tris(isopropylamino)borazine (4), and subsequently to polyborazines. In spite of the high carbon content of 1, its pyrolysis at 1000°C under NH3 led to the formation of boron nitride containing less than 1% carbon.

Interaction sous haute pression entre l'aluminium solide et le carbure de silicium: High pressure interaction between solid Al and SiC

Abstract Two-phased mixtures were prepared from either Al and SiC powders or Al4C3 and Si powders. These mixtures were heated for 5–8 h under a pressure of 1800–2000 MPa in the temperature range 805–860 K and then quenched. The resulting pellets were examined using X-ray powder diffraction, optical metallography and scanning electron microprobe. At temperatures lower than 830 ± 7 K, no reaction occurs between Al and SiC whereas Al4C3 and Si react to form solid Al and SiC. At temperatures higher than 845 ± 7 K, both Al4C3Si and AlSiC mixtures react, resulting in a three-phased equilibrium involving Al4C3, SiC and a liquid phase AlSi.

Si3N4BN composites obtained from aminoboranes as BN precursors and sintering aids

Abstract The Si 3 N 4 -BN composite ceramic has been elaborated by combining Si 3 N 4 fine powder with boron nitride provided by the thermolysis of a molecular precursor. The properties of this new type of sample has been compared with those of composite ceramics obtained by the classical hot-pressing method using Si 3 N 4 -BN powders and sintering aids (Y 2 O 3 , Al 2 O 3 ). Giving the best ceramic yield, tris (methylamino) borane (TMB) has been used as BN precursor and sintering aid. Boron nitride formed from TMB thermolysis was poorly crystallized when the hot-pressing was run up to a temperature lower than 1800 °C. The density of the composite ceramic samples obtained from molecular precursors was higher than expected, this could be related to the sintering activation properties of the precursor. Moreover the problems due to the BN platelets orientations were removed. The Vickers hardness was clearly improved for samples without BN platelets, however the bending strength was not increased. The precursor improved some properties of the composite and could be considered as a sintering activator avoiding oxide addition as sintering aid.

Catalytic curing agents

SummaryThe BY3 (Y=F, Cl, Br, I, NCS, H) adducts with the tertiary amines N,N-dimethyl-n-octylamine (DMOA) and N,N-dimethyl-benzylamine (DMOA) were prepared, characterized and tested as catalytic curing agents for epoxy (DGEBA) and epoxy-isocyanate resins.Evaluation of the storage stability and reactivity of the resins showed that the BBr3, BCl3, BI3 and B(NCS)3 adducts were good latent catalysts. No correlation could be found between the temperature of decomposition of the catalysts in an inert atmophere or in contact with air and the catalytic properties. Consequently the reaction medium was involved in the activation process.

Catalytic curing agents: A study of boron halide and boron isothiocyanate complexes with tertiary amines as catalytic curing agents for epoxide and epoxy-isocyanate mixtures

Summary The BY3 (Y= F, CI, Br, I, NCS, H) adducts with the tertiary amines N,N-dimethyl-n-o ctylamine (DMOA) and N,N-dimethyl-ben zylamine (DMOA) were prepared, characterized and tested as catalytic curing agents for epoxy (DGEBA) and epoxy-isocyanate resins. Evaluation of the storage stability and reactivity of the resins showed that the BBr3, BC13, BI3 and B(NCS)3 adducts were good latent catalysts. No correlation could be found between the temperature of decomposition of the catalysts in an inert atmosphere or in contact with air and the catalytic properties. Consequently the reaction medium was involved in the activation process.

A New Synthetic Approach to Boron Triisothiocyanate-Tertiary Amine Adducts and Related Species

Abstract The reaction of the adduct BDMA.BC13 (BDMA = N.N dimethylbenzylamine) with KNCS in refluxing, toluene, with tetraglyme added, was found as a very convenient route to BDMA.B(NCS)3. Further, according to the stoichiometry, either mixed species BDMA.BC1n(NCS)3-n(n = 1,2) or K+|B(NCS)4|−, were also obtained. The same reaction was applied to KF and KNCO as well as to other tertiary alkylamines.

STUDY OF TRICHLOROBORANE AND TRIS(ISOTHIOCYANATO)- BORANE ADDUCTS WITH 1,4-DIAZABICYCLO[2,2,2]OCTANE AND THEIR PROPERTIES AS POLYMERIZATION CATALYSTS OF EPOXY RESINS

1,4-diazabicyclo(2,2,2) octane (Dabco) was reacted with boron trichloride giving the symmetric adduct Dabco(BCl3)2 but the more stable unsymmetrical adduct, DabcoBCl3, was obtained by redistribution of BCI3 between Dabco(BCl3)2 and Dabco. In spite of a low solubility in organic solvents Dabco(BCl3)2 reacted with KNCS to form Dabco[B(NCS)3]2 as ultimate product under solid / liquid phase transfer catalysis conditions. When the same reaction was carried out in the presence of Dabco the formation of unsymmetrical adducts Dabco[BCIx(NCS)3-x] prevailed. Similar mixtures were obtained by reacting DabcoBCIß with KNCS. Dabco(BCl3)2 can be classified as a latent catalyst of polymerization of epoxy resin, the polymerization is initiated at a temperature 30 °C higher than with Dabco and through a different mechanism.