Synthesis of Al3BC from mechanically milled and spark plasma sintered Al-MgB2 composite materials

The aluminium-rich ternary aluminium borocarbide, Al₃BC was synthesised for the first time by solid-state reactions occurring during heat treatments after mechanical milling (MM) of pure aluminium with 15 or 50 at% MgB₂ powder mixtures in the presence of the process control agent (PCA).

The solid-state reactions in the Al–15 and 50 at% MgB₂ composite materials occurred between the MMed powders and process control agent (PCA) after heating at 773–873 K for 24 h. The products of the solid-state reaction induced Al₃BC, AlB₂, γ-Al₂O₃ and spinel MgAl₂O₄. MM processing time and heating temperatures in the Al–15 and 50 at% MgB₂ composite materials affected the selection of those intermetallic compounds. When MM processing time was increased for a given composition, the formation of the Al₃BC compound started at lower heat treatment temperatures. However, when the amount of MgB₂ was increased in the 4 h MM processing regime, the formation of the Al₃BC compound during heating was suppressed. As a result of the solid-state reactions in MMed powders the hardness was observed to increase after heating at 573–873 K for 24 h.

The fully dense bulk nano-composite materials have been successfully obtained through the combination of the MM and spark plasma sintering (SPS) processes for the 4 h or 8 h MMed powders of the Al–15 at% MgB₂ composite materials sintered under an applied pressure of 49 MPa at 873 K for 1 h.

Understanding ring strain and ring flexibility in six - and eight-membered cyclic organometallic group 14 oxides

A simple model was developed for the approximation of ring strain energies of homo- and heterometallic, six- and eight-membered cyclic organometallic group 14 oxides and the degree of puckering of their ring conformations. The conformational energy of a ring is modelled as the sum of its angular strain components. The bending potential energy functions for the various endocyclic M–O–M′ and O–M–O linkages (M, M′=Si, Ge, Sn) were calculated at the B3LYP/(v)TZ level of theory using H3MOM′H3 and H2M(OH)2 as model compounds. For the six-membered rings, the minimum total angular contribution to ring strain, ERSGmin was calculated to decrease in the order: cyclo-(H2SiO)3 (13.0 kJ mol−1)>cyclo-H2Sn(OSiH2)2O (7.0 kJ mol−1)>cyclo-H2Ge(OSiH2)2O (4.9 kJ mol−1)>cyclo-H2Si(OSnH2)2O (3.4 kJ mol−1)>cyclo-(H2SnO)3 (1.7 kJ mol−1)>cyclo-H2Si(OGeH2)2O (0.8 kJ mol−1)≈cyclo-H2Ge(OSnH2)2O (0.7 kJ mol−1)>cyclo-H2Sn(OGeH2)2O (0.1 kJ mol−1)≈cyclo-(H2GeO)3 (0 kJ mol−1). All of the six-membered rings were predicted to adopt (nearly) planar conformations (a=0.996<a<1). By contrast, all eight-membered rings were predicted to adopt strainless, but puckered conformations. The degree of puckering was predicted to increase in the order: cyclo-(H2SiO)4 (a=0.983)<cyclo-H2Sn(OSiH2O)2SiH2 (a=0.959)<cyclo-(H2SiO)2(H2SnO)2 (a=0.942)< cyclo-H2Si(OSnH2O)2SiH2 (a=0.935)<cyclo-(H2SnO)4 (a=0.916)<cyclo-(H2GeO)4 (a=0.885). The differences in ring strain and the degree of puckering were linked to the different electronegativities of Si, Ge and Sn. The results obtained are consistent with experimental ring strain energies; reactivities towards ring opening polymerizations or ring expansion reactions and observed ring conformations of cyclic organometallic group 14 oxides.

Properties of mechanically milled and spark plasma sintered Al–15 at.% MgB2 composite materials

Air-atomized pure aluminium powder with 15 at.% MgB₂ was mechanically milled (MMed) by using a vibrational ball mill, and MMed powders were consolidated by spark plasma sintering (SPS) to produce composite materials with high specific strength. Solid-state reactions of MMed powders have been examined by X-ray diffraction (XRD), and mechanical properties of the SPSed materials have been evaluated by hardness measurements and compression tests. Orientation images of microstructures were obtained via the electron backscatter diffraction (EBSD) technique.

The solid-state reactions in the Al–15 at.% MgB₂ composite materials occurred between the MMed powders and process control agent (PCA) after heating at 773–873 K for 24 h. The products of the solid-state reaction were a combination of AlB₂, Al₃BC and spinel MgAl₂O₄. Mechanical milling (MM) processing time and heating temperatures affect the characteristics of those intermetallic compounds. As the result of the solid-state reactions in MMed powders, a hardness increase was observed in MMed powders after heating at 573–873 K for 24 h. The full density was attained for the SPSed materials from 4 h or 8 h MMed powders in the Al–15 at.% MgB₂ composite materials under an applied pressure of 49 MPa at 873 K for 1 h. The microstructure of the SPSed materials fabricated from the MMed powders presented the bimodal aluminium matrix grain structure with the randomly distributions. The Al–15 at.% MgB₂SPSed material from powder MMed for 8 h exhibited the highest compressive 0.2% proof strength of 846 MPa at room temperature.

Mechanically alloyed and spark plasma sintered aluminium/precious metal oxide composite materials

Air-atomised pure aluminium powder with additions of 10 at.% of AgO, PtO₂ or PdO was mechanically alloyed (MAed) by using a vibrational ball mill, and MAed powders were consolidated into bulk materials by a spark plasma sintering (SPS) process. Mechano-chemical reactions among pure Al, precious metal oxide and stearic acid, added as a process control agent, during the mechanical alloying (MA) process and subsequent heat treatments were investigated by X-ray diffraction. The mechanical properties of MAed powders obtained under various heat treatment conditions and those of the SPS materials were evaluated by hardness tests. Mechano-chemical reactions occurred in Al/precious metal oxide composite powders during 36 ks of the MA process to form AlAg₂, Pt and Al₃Pd₂ for the Al-AgO, Al-PtO₂ and Al-PdO systems, respectively. Further solid-state reactions in MAed powders have been observed after heating at 373 K to 873 K for 7.2 ks. The hardness of MAed powders initially increased significantly after heating at 373 K and then generally decreased with increasing heating temperatures. The full density was obtained for the SPS materials under the conditions of an applied pressure of 49 MPa at 873 K for 3.6 ks. All the SPS materials exhibited hardness values of over 200 HV in the as-fabricated state.

Purification and characterization of a low molecular mass alkaliphilic lipase of Bacillus cereus MTCC 8372

A low molecular mass alkaliphilic extra-cellular lipase of Bacillus cereus MTCC 8372 was purified 35-fold by hydrophobic interaction (Octyl-Sepharose) chromatography. The purified enzyme was found to be electrophoretically pure by denaturing gel electrophoresis and possessed a molecular mass of approximately 8 kDa. It is a homopentamer of 40 kDa as revealed by native-PAGE. The lipase was optimally active at 55 °C and retained approximately half of its original activity after 40 min incubation at 55 °C. The enzyme was maximally active at pH 8.5. Mg ²⁺ , Cu ²⁺ , Ca ²⁺ , Hg ²⁺ , Al ³⁺ and Fe ³⁺ at 1 mM enhanced hydrolytic activity of the lipase. Interestingly, Hg ²⁺ ions synergized and Zn ²⁺ and Co ²⁺ ions antagonized the lipase activity. Among surfactants, Tween 80 promoted the lipase activity. Phenyl methyl sulfonyl fluoride (PMSF, 15 mM) decreased 98% of original activity of lipase. The lipase was highly specific towards p -nitrophenyl palmitate and showed a V _max and K _m of 0.70 mmol.mg ⁻¹ .min ⁻¹ and 32 mM for hydrolysis of p NPP.

Synthesis and characterization of nanocrystalline hexagonal boron carbo-nitride under high temperature and high pressure

A study of the synthesis of hexagonal boron carbo-nitride (h-BCN) compounds via a two-step high-temperature and high-pressure (HTHP) technique using melamine (C 3N 6H 6) and boron oxide (B 2O 3) as raw materials is presented. An amorphous BCN precursor was prepared at 1000K under vacuum in a resistance furnace and then single-phase h-BCN nanocrystalline was synthesized at 1600K and 5.1GPa in a multi-anvil apparatus. X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicated that the final products were pure h-BCN crystals with the lattice constants a ≤ 0.2510nm and c ≤ 0.6690nm. The average grain size was about 150nm. X-ray photoelectron spectroscopy (XPS) results confirmed the occurrence of bonding between C-C, C-N, C-B and N-B atoms. Raman scattering analysis suggested that there were three strong Raman bands centered at 1359, 1596 and 1617cm -1, respectively. The band at 1617cm -1 was considered to be consistent with the characteristic Raman peak of h-BCN.

RFID ownership transfer protocol based on cloud

RFID and Cloud computing are widely used in the IoT (Internet of Things). However, there are few research works which combine RFID ownership transfer schemes with Cloud computing. Subsequently, this paper points out the weaknesses in two protocols proposed by Xie et al. (2013) [3] and Doss et al. (2013) [9]. To solve the security issues of these protocols, we present a provably secure RFID ownership transfer protocol which achieves the security and privacy requirements for cloud-based applications. To be more specific, the communication channels among the tags, mobile readers and the cloud database are insecure. Besides, an encrypted hash table is used in the cloud database. Next, the presented protocol not only meets backward untraceability and the proposed strong forward untraceability, but also resists against replay attacks, tracing attacks, inner reader malicious impersonation attacks, tag impersonation attacks and desynchronization attacks. The comparisons of security and performance properties show that the proposed protocol has more security, higher efficiency and better scalability compared with other schemes.