Composite microcrystals of the nitramines(NAs)viz.,RDX,HMX,BCHMX,and CL-20 with electrically conductive polyaniline(PANi)are a charge transfer complexes in coagglomerated composite crystals(CACs).The activation energi...Composite microcrystals of the nitramines(NAs)viz.,RDX,HMX,BCHMX,and CL-20 with electrically conductive polyaniline(PANi)are a charge transfer complexes in coagglomerated composite crystals(CACs).The activation energies of thermolysis,E_(a),of the pure NAs and their PANi-CACs were determined using the Kissinger method,and decomposition processes are discussed.Except for the RDX/PANi CACs,all the other CACs show higher E_(a) values for decomposition compared to their pure NA counterparts.For all CACs,relationships are specified between the E_(a) values,on the one hand,and the squares of the detonation velocities,enthalpies of formation,spark energy and impact sensitivities,on the other.The relationships between their low-temperature heats of decomposition,ΔH,from DSC,and their enthalpy of formation,logarithm of impact sensitivity,electric spark energy,as well as detonation energy,are described.The PANi favorably influences the density of the corresponding CACs;surprisingly close linear correlations were found,and explained,between these densities and the E_(a) values.This presence of PANi strongly increased the electrical spark sensitivity of the CACs in comparison to the base NAs.Based on the results obtained,it can be noted in particular the exceptional desensitization of HMX to impact and the increased sensitivity to electrical spark by coating its crystals with polyaniline.展开更多
Synergistic interplays involving multiple active centers originating from TiO2 nanotube layers(TNT)and ruthenium(Ru)species comprising of both single atoms(SAs)and nanoparticles(NPs)augment the alkaline hydrogen evolu...Synergistic interplays involving multiple active centers originating from TiO2 nanotube layers(TNT)and ruthenium(Ru)species comprising of both single atoms(SAs)and nanoparticles(NPs)augment the alkaline hydrogen evolution reaction(HER)by enhancing Volmer kinetics from rapid water dissociation and improving Tafel kinetics from efficient H*desorption.Atomic layer deposition of Ru with 50 process cycles results in a mixture of Ru SAs and 2.8-0.4 nm NPs present on TNT layers,and it emerges with the highest HER activity among all the electrodes synthesized.A detailed study of the Ti and Ru species using different high-resolution techniques confirmed the presence of Ti^(3+)states and the coexistence of Ru SAs and NPs.With insights from literature,the role of Ti^(3+),appropriate work functions of TNT layers and Ru,and the synergistic effect of Ru SAs and Ru NPs in improving the performance of alkaline HER were elaborated and justified.The aforementioned characteristics led to a remarkable performance by having 9mV onset potentials and 33 mV dec^(-1) of Tafel slopes and a higher turnover frequency of 1.72 H2 s^(-1) at 30 mV.Besides,a notable stability from 28 h staircase chronopotentiometric measurements for TNT@Ru surpasses TNT@Pt in comparison.展开更多
Dill(Anethum graveolens),an annual species,was used to study the impact of metallic pollution potentially spreading fromthe nickel smelter dump in Dolna Streda(Slovakia)by monitoring 55 elements.Despite the proximity ...Dill(Anethum graveolens),an annual species,was used to study the impact of metallic pollution potentially spreading fromthe nickel smelter dump in Dolna Streda(Slovakia)by monitoring 55 elements.Despite the proximity of this dump(1 km),only soil Ni(54.8 mg/kg)or Pb(47.3 mg/kg),but not Cr,Mn,Fe or Co(main elements of the dump’s sludge)was elevated in given garden soil compared to two control sites.Mainly flowers and/or leaves contained significantly higher amounts of Ni,Cr,Pb,Cu,As,Sb,Sn,V,W,and some rare earth elements at the site close to the dump.Correlation between elements in organs and soil was significant mainly in stem or root but the bioaccumulation factor was typically low(<0.02)for most elements.A positive finding was that the 2022/2024 comparison revealed a decline in most elements in dill leaves,even at the dump site,which may reflect a decrease in the content of air PM particles.Soluble phenols were less accumulated in plants close to the nickel smelter dump,but flavonols showed the opposite trend,and free amino acids were positively correlated with many elements in the stem and root.An evaluation of commercial dill samples revealed variability(e.g.,up to 0.7 mg Cd/kg dry weight)but subsequent NCA and PCA analyses clearly separated the dump locality from other samples.However,significant differences in the content of Cd,Ni,Pb,As,and other elements encourage precise control of commercially available dill dry matter.展开更多
Fractions of β-HMX(β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane) have been used to demonstrate the mutual relationship between friction and impact sensitivities.Inclusion of an additional twelve nitramines into this sce...Fractions of β-HMX(β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane) have been used to demonstrate the mutual relationship between friction and impact sensitivities.Inclusion of an additional twelve nitramines into this scenario resulted in a series of partial relationships,which were determined from the molecular structure of these substances.It was also found that there is a relation between increasing heats of fusion of the nitramines studied and their decreasing friction sensitivities.Comparison of friction sensitivity with heats of fusion,ΔHm,tr of the studied nitramines shows that the increase in ΔHm,tr values is more or less connected with a decrease in friction sensitivity.展开更多
Calcium tungstate phosphors activated by the Ln3＋ ions （Ln-Pr, Nd, Tb, Yb） were synthesized by a traditional high-temperature solid-state method. The crystal structures and morphologies of the products were charact...Calcium tungstate phosphors activated by the Ln3＋ ions （Ln-Pr, Nd, Tb, Yb） were synthesized by a traditional high-temperature solid-state method. The crystal structures and morphologies of the products were characterized by scanning electron microscopy （SEM）, X-ray powders diffraction （XRD） and infrared spectra （FT-1R）. The samples were fotmd to show luminescence properties （down-conversion, DC, at excitation wavelength 254 nm and up-conversion, UC, at excitation wavelength 980 nm）. CaWO4 doped with Tb3＋/yb3＋ showed green DC and UC luminescence characteristic of Tb（Ⅲ） ion in the range of 470-660 nm, cor- responding to the 5D4→7F6,5,4,3,2 electronic transition. CaWO4 doped with Pr3＋/Yb3＋ showed week blue, green and red （DC and UC） luminescence of Pr（Ⅲ） ion, in the wavelength region of 450-700 nm. Emission peaks were ascribed to the 3P1→3H4,5,6, 3P0→3H4,5,6, 3P1→3F2 and 3P0→3F2 transitions, respectively. CaWO4 doped with Nd3＋/yb3＋ phosphor emitted orange UC luminescence at 450-690 nm （2p3/2→4I15/2, 4G7/2→419/2,11/2,13/2） and strong near-infrared UC luminescence at 720-900 nm （4F7/2＋4S3/2→4419/2, 4F5/2＋2H3/2→419/2, 4F3/2→4I9/2） which is the characteristic of Nd（Ⅲ） ion.展开更多
Information about the forty nine nitraminic plastic bonded explosives(PBXs)and different nitramines were collected.Fillers of these PBXs are nitramines 1,3,5-trinitro-1,3,5-triazinane(RDX)and β-1,3,5,7-tetranitro-1,3...Information about the forty nine nitraminic plastic bonded explosives(PBXs)and different nitramines were collected.Fillers of these PBXs are nitramines 1,3,5-trinitro-1,3,5-triazinane(RDX)and β-1,3,5,7-tetranitro-1,3,5-tetrazocane(β-HMX),cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5-d]imidazole(bicyclo-HMX,BCHMX)and e-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane(e-HNIW,CL-20)which are bonded by polyfluoro-elastomers,polydimethyl-siloxane,poly-glycidyl azide,polyisobutylene,polystyrene-butadiene,poly-acrylonitrile-butadiene and hydroxyl-terminated polybutadiene in addition to a melt cast compositions based on 2,4,6-trinitrotoluene.For thirty two of these PBXs the relationships are specified and analyzed between heats of their combustion and relative explosive strengths;by means of these relationships it might be possible to estimate,which groupings in the macromolecule of binder could be liable to their primary fission in the PBXs initiation.Similarly,for forty two of these explosives,the relationships are described and analyzed between their enthalpies of formation and impact sensitivities;here is especially attention paid to PBXs filled by BCHMX.Specific rate constants from Vacuum Stability Test(VST)of four nitramines and twenty PBXs are introduced into relationships with their enthalpies of formation.Regarding to all the mentioned cases,increasing of energy content of the studied explosives leads to increase of the relative explosive strength or initiation reactivity,respectively.Exception with the opposite trend,the outputs of VST are for BCHMX,where in PBXs are matrices with the esteric plasticizers or the energetic poly-glycidyl azide.Admixture of RDX or HMX,respectively,into the BCHX PBXs gives ternary PBXs whose thermal stability,in the sense of applied VST,is higher comparing to the original binary explosives.展开更多
More detailed analysis of a mutual relationship of impact sensitivity(detected by sound) and crystal lattice free volume, △V, for the 18 nitramines shows that its course is not unequivocal. For a part of the studied ...More detailed analysis of a mutual relationship of impact sensitivity(detected by sound) and crystal lattice free volume, △V, for the 18 nitramines shows that its course is not unequivocal. For a part of the studied compounds this sensitivity has increased with increase of the AV values, but for fairly big number of nitramines the relationship works in the opposite direction, especially for data of 1,3,5-trinitro-1,3,5-triazinane, 1,3,5,7-tetranitro-1,3,5,7-tetrazocane. and β-and ε-polymorphs of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane. Initiation reactivity of technical ε-polymorph of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane gives the impression by disorderliness in distribution of the actions of forces in its crystal lattice in comparison with its RS(reduced sensitivity) or chemically pure analogue. Limitations of partial shapes of the mentioned relationship by the molecular-structural similarity, and already published information about the decisive factors governing the crystal structure, signalizes a higher influence of the intermolecular interactions in a crystal lattice in comparison with influence of the crystal lattice free volume for initiation of the crystalline EMs.展开更多
The relationship between friction sensitivity(FS) and the crystal lattice free space per molecule, △V. of thirteen nitramines is described by a linear equation, divided into a number of the partial relationships with...The relationship between friction sensitivity(FS) and the crystal lattice free space per molecule, △V. of thirteen nitramines is described by a linear equation, divided into a number of the partial relationships with strong limitations by their molecular structure characteristics. Increasing FS due to raising of the △V values is not clearly confirmed. The influence of the △V values on friction sensitivity of nitramines is similar to that of their aza atoms which influence the mutual orientations of nitro groups in neighboring molecules. The dipole-dipole interaction of the oxygen and nitrogen atoms of nitro groups in neighboring nitramine molecules has a major effect on their own FS. In accordance with this interaction, a directly proportional relationship was derived between FS and the intrinsic gas phase molecular volume, V_(int), of the nitramines mentioned, which is divided also into several straight lines according to relatively tight molecular structure similarity. The relationships found again confirm a level of disorder in the distribution of the forces in the crystal lattice of the "common" quality of ε-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, in comparison with its reduced sensitivity(RS) or chemically pure analogue.展开更多
Preparation of cast double-propellant grains depends on the ability of nitrocellulose powder to swell and coalesce into a coherent mass when treated with a suitable solvent.The cast double-base process has been develo...Preparation of cast double-propellant grains depends on the ability of nitrocellulose powder to swell and coalesce into a coherent mass when treated with a suitable solvent.The cast double-base process has been developed into a highly versatile technique for manufacturing solid rocket charges.Propellants manufactured by this process provide a wide range of energies and burning rates.Successful preparation of cast double-base propellant grains has been performed using compatible casting liquid with the casting powder.BuNENA was used as an energetic plasticizer for manufacturing of casting powder.Burning rate measurements have been performed using closed bomb SV-2to investigate the burning behavior along a wide range of operating pressure.Plateau burning had been detected in pressure range(50-70)×105 Pa for the composition included BuNENA.DTA and TGA thermal analysis were conducted to evaluate the thermal behavior of the prepared cast double-base propellants.Results from DTA were used to calculate the apparent activation energy.展开更多
cis-1,3,4,6-Tetranitrooctahydroimidazo-[4,5-d]imidazole(BCHMX) is a relatively available bicyclic nitramine in the present. Due to the high energetic content of its molecule(deformation of valence angles) it has heat ...cis-1,3,4,6-Tetranitrooctahydroimidazo-[4,5-d]imidazole(BCHMX) is a relatively available bicyclic nitramine in the present. Due to the high energetic content of its molecule(deformation of valence angles) it has heat of formation higher than β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane(β-HMX) by nearly three times. As a result, it has heat of explosion and relative explosive strength exceed that of β-HMX including their corresponding PBXs. However, penetration abilities of PBXs based on HMX are higher than those based on BCHMX. The relatively high initiation reactivity of BCHMX could be modified in a wide range by its incorporation in a suitable polymeric matrices. Regarding to the performance, coating of BCHMX crystals by 5 wt% Viton A produces the maximum performance while the mixture of BCHMX with polydimethylsiloxane(PDMS) seems to be the optimum composition for the development of PBX with low sensitivity.展开更多
The relationship between the crystal lattice free volume,ΔV,and impact sensitivity,E_(dr),of ten nitramines has been analyzed. It was found that this relationship is not uniquely determined,i. e. it is not given only...The relationship between the crystal lattice free volume,ΔV,and impact sensitivity,E_(dr),of ten nitramines has been analyzed. It was found that this relationship is not uniquely determined,i. e. it is not given only by their own ΔV values but fundamentally by the type and intensity of the intermolecular forces in the nitramine crystals. Also,relationships between the E_(dr)values,on the one hand,and bulk modulus,K,and shear modulus,G,on the other,have been the subject of discussion not only for pure cyclic nitramines but also for their PBXs,bonded by a poly-fluoro binder. The closest linear correlation exists between the E_(dr)values and dimensionless K·G^(-1) ratio which indicates the plasticity range. A similar relationship is valid also for the ΔV values. Relationships of the E_(dr) and / or ΔV values with the shear modulus or to the K·G^(-1) ratio reflect an unusual behavior of ε-HNIW to which the published morphological instability of this particular HNIW version might also be related.展开更多
The friction sensitivities(FS) of five linear and eight cyclic nitramines have been determined.These FS values were compared with the respective detonation velocities,D,and with the dimensionless ratio created by rela...The friction sensitivities(FS) of five linear and eight cyclic nitramines have been determined.These FS values were compared with the respective detonation velocities,D,and with the dimensionless ratio created by relating the heat of explosion,Qreal,to the activation energy,Ea,of non-autocatalyzed thermal decomposition of the explosives concerned.For the nitramaines studied,these comparisons show a general trend of FS decreasing with increasing energy content.展开更多
Powder metallurgy is a powerful method for the preparation of materials with superior properties.This work aimed to investigate the effect of powder size on the microstructure,mechanical,and corrosion properties of ad...Powder metallurgy is a powerful method for the preparation of materials with superior properties.This work aimed to investigate the effect of powder size on the microstructure,mechanical,and corrosion properties of advanced WE43(Mg-4Y-3REE-Zr)alloy prepared by spark plasma sintering(SPS).At the same time,the effect of HF pre-treatment of the powder on the properties of final compacted products is studied.Smaller powder particles yielded microstructure with more interfaces formed by Y_(2)O_(3),or MgF_(2) and YF_(3).These interfaces work as barriers against corrosion,which greatly improves corrosion resistance.The suggested pre-treatment of powder in HF further reduced the corrosion rate of the compacted materials.On the contrary,fragile interfaces of YF_(3) decreased mechanical properties as the crack primarily propagates through these interfaces.The original powder containing the mixture of all powder fractions exerted the best combination of mechanical properties.Powder size has also shown to affect ignition temperature.The highest ignition temperature was measured for the finest powder fraction.展开更多
The linear,directly proportional,equations between the Arrhenius parameters(E_α,and log A)of the thermal decomposition and the crystal lattice free space per molecule,△V,of 22 nitramines are described.It is shown th...The linear,directly proportional,equations between the Arrhenius parameters(E_α,and log A)of the thermal decomposition and the crystal lattice free space per molecule,△V,of 22 nitramines are described.It is shown that,because of a significant limitation by the molecular structural characteristics of such compounds,they are divided into a number of partial relationships.These partial relationships divide the nitramines into a group of substances relating to dimethyl nitramine and a sub-group related to e-HNIW.These directly proportional equations mean that an increase in the△Vvalues is related to an increase in the thermal stability of the corresponding nitramines.A comparison with similar published dependencies for the impact and friction sensitivities,on the one hand,and with the relationship between the E_a values and the sum of the negative and positive extremes of molecular surface electrostatic potentials,on the other,confirms the well-known fact that intermolecular interaction in the nitramines studied plays a decisive role in the thermal reactivity of such compounds.The crystal lattice free space manifests itself here perhaps only in the solid state thermal decomposition of RDX,HMX and DINGU.This study again confirms a level of disorder in the distribution of the forces in the crystal lattice of the"common"quality of e-HNIW,compared with its"reduced sensitivity(RS)"or pure analogues.展开更多
The friction sensitivity(FS) of five linear and eight cyclic nitramines has been determined.Arrhenius parameters of non-autocatalyzed thermal decomposition of these nitramines were used for comparison of the FS values...The friction sensitivity(FS) of five linear and eight cyclic nitramines has been determined.Arrhenius parameters of non-autocatalyzed thermal decomposition of these nitramines were used for comparison of the FS values with thermal reactivity.Generally,increasing values of activation energies of non-autocatalyzed decomposition of the studied nitramines are connected with decreasing FS values.A similar trend was found in the relation between FS and hypothetical initiation temperature for 5% conversion of the nitramines after 50 μs of their thermolysis,however,if in the given series of nitramines their initiation reactivity is predominantly determined by the energy content of their molecules and closer similarity of their molecular structures,then the above-mentioned trend may be opposite.The found relationships were used for prediction and verification of the activation energy of non-autocatalyzed thermal decomposition of 2,5-dinitro-2,5-diazahexane.展开更多
A new tetragonal,scheelite-type Pb_(1-3 x)■_xEU_(2 x)(MoO_4)_(1-3 x)(WO_4)_(3 x)(0< x ≤0.1970 and ■ denotes A-site vacancies) solid solution was synthesized via solid state reaction method. The X-ray diffraction...A new tetragonal,scheelite-type Pb_(1-3 x)■_xEU_(2 x)(MoO_4)_(1-3 x)(WO_4)_(3 x)(0< x ≤0.1970 and ■ denotes A-site vacancies) solid solution was synthesized via solid state reaction method. The X-ray diffraction(XRD) and scanning electron microscopy(SEM) results confirm the formation of single, tetragonal scheelite-type phases(space group I4_1/a) with the average crystallite size in the range of ～20-100 μm. Substitution of Pb^(2+) with Eu^(3+) is relatively easy despite the large difference in ionic radii, and the formation of vacancies is necessary to compensate the excess positive charge in PbMoO_4 framework. A change in lattice parameters(both a and c as well as lattice parameter ratio c/a) and progressive deformation of MoO_4 and WO_4 tetrahedra with increasing Eu concentration are observed. Thermal stability of Eu-doped materials strongly depends on the concentration of Eu3+ ions. The Pb_(1-3 x)■_xEu_(2 x)(MoO_4)_(1-3 x)(WO_4)_(3 x) solid solution for x=0.0098 shows the highest melting point(1057 ℃) which is slightly higher than that of pure PbMoO_4(1040 ℃). The UV-vis diffuse reflectance spectroscopy(DRS) and the Tauc plots were used to extrapolate the optical indirect band gap(E_g) of doped materials. Eu-doped ceramics are insulators(E_g > 3 eV) and their band gap nonlinearly decreases with increasing dopant concentration.展开更多
A well-known ternary plastic explosive,Czech Semtex 1H,contains a mixture of PETN and RDX softened by SBR.In this work,BCHMX was used to replace PETN in Semtex 1H to form Sem-BC+RDX.In addition,another mixture based o...A well-known ternary plastic explosive,Czech Semtex 1H,contains a mixture of PETN and RDX softened by SBR.In this work,BCHMX was used to replace PETN in Semtex 1H to form Sem-BC+RDX.In addition,another mixture based on BCHMX and HMX as energetic fillers bonded by the polymeric matrix of Semtex 1H(Sem-BC+HMX)was studied.The particle size distribution of each individual explosive was determined to obtain the optimum mixing conditions.Friction and impact sensitivities were determined.The velocity of detonation was reported practically and the detonation properties were calculated by EXPLO5 code.The explosive strength of each sample was measured by the ballistic mortar test.The conclusion confirms that the velocity of detonation of Sem-BC+HMX was the highest in comparison with the prepared samples.Sem-BC+RDX has the least impact and frictions sensitivities.Sem-BC+RDX has higher detonation velocity,detonation properties and explosive strength than Semtex 1H.Addition of BCHMX in Semtex 1H as a replacement for PETN is the candidate to produce a high performance advanced Czech plastic explosive.展开更多
Gd3+-,Pr3+-or Sm3+-doped Co-Zn(Co0.5Zn0.5Fe2 O4)magnetic ferrites(i.e.,Co0.5Zn0.5Gd0.1Fe1.9O4,Co0.5Zn0.5Pr0.1Fe1.9O4 and Co0.5Zn0.5Sm0.1Fe1.9O4)were prepared using a facile sol-gel approach,and the structure,surface m...Gd3+-,Pr3+-or Sm3+-doped Co-Zn(Co0.5Zn0.5Fe2 O4)magnetic ferrites(i.e.,Co0.5Zn0.5Gd0.1Fe1.9O4,Co0.5Zn0.5Pr0.1Fe1.9O4 and Co0.5Zn0.5Sm0.1Fe1.9O4)were prepared using a facile sol-gel approach,and the structure,surface morphology and chemical composition of the products were studied by means of scanning electron microscopy(SEM),energy dispersive X-ray analysis(EDX),X-ray diffraction(XRD),UVvisible diffuse reflectance spectroscopy(DRS),photoluminescence(PL)spectroscopy,Fourier transform infrared spectroscopy(FT-IR)and vibrating sample magnetometer(VSM)spectroscopy.XRD patterns show the Co-Zn product is composed of cubic spinel phases with few impurities or secondary phases,and the average crystallite sizes of the samples are determined to be approximately^51—80,~99—181,~68—103 and^83—133 nm.Also the coercivity and remnant and saturation magnetizations,evaluated by vibrating sample magnetometer(VSM),are found to increase linearly with the incorporation of Gd3+,Pr3+and Sm3+in the product formulation.The CO1-xZnxFe2-yRyO4 photocatalyst sample is found to display a red shift in its absorption,and exhibits outstanding photocatalytic effects in the degradation of MO under ultraviolet(UV)light.This is attributed to the reduction of the band gap of cobalt-zinc ferrite due to the presence of rare earth ions.Further in vitro evaluations of the cytotoxic effects of the synthesized nanoparticles were performed on a HeLa cell line.展开更多
Porous carbon materials have exhibited a series of promising applications in supercapacitors and other research fields,yet still confronting the complicated synthetic procedures and massive usage of toxic reagents.Her...Porous carbon materials have exhibited a series of promising applications in supercapacitors and other research fields,yet still confronting the complicated synthetic procedures and massive usage of toxic reagents.Herein,we propose a green and one-pot method to produce heteroatomdoped hierarchical porous carbon materials in large-scale without any toxic reagents employed.Eventually,the as-prepared nitrogen-doped porous carbon(NPC)displays a high specific surface area of 2018 m^(2)g^(-1)together with abundant heteroatom dopants(14.8 wt%O and 1.03 wt%N).The potassium carbonate template can be recycled via a simple rinsing and re-precipitation process.Furthermore,the as-prepared nitrogen-doped porous carbon delivers a high specific capacitance of 361 F g^(-1)at 0.5 A g^(-1)and excellent rate capability of 240 F g^(-1)at 20 A g^(-1)(66.5%capacitance retention).Finally,considering the low-price raw materials and facile green synthesis procedure,the present approach can be easily scalable to prepare biomass-derived heteroatoms doped porous carbon,which is not only applicable for supercapacitor but also for other research fields.展开更多
基金funding from the Student Grant Project no.SGS_2022_003 of the Faculty of Chemical Technology at the University of Pardubice Czechia.
文摘Composite microcrystals of the nitramines(NAs)viz.,RDX,HMX,BCHMX,and CL-20 with electrically conductive polyaniline(PANi)are a charge transfer complexes in coagglomerated composite crystals(CACs).The activation energies of thermolysis,E_(a),of the pure NAs and their PANi-CACs were determined using the Kissinger method,and decomposition processes are discussed.Except for the RDX/PANi CACs,all the other CACs show higher E_(a) values for decomposition compared to their pure NA counterparts.For all CACs,relationships are specified between the E_(a) values,on the one hand,and the squares of the detonation velocities,enthalpies of formation,spark energy and impact sensitivities,on the other.The relationships between their low-temperature heats of decomposition,ΔH,from DSC,and their enthalpy of formation,logarithm of impact sensitivity,electric spark energy,as well as detonation energy,are described.The PANi favorably influences the density of the corresponding CACs;surprisingly close linear correlations were found,and explained,between these densities and the E_(a) values.This presence of PANi strongly increased the electrical spark sensitivity of the CACs in comparison to the base NAs.Based on the results obtained,it can be noted in particular the exceptional desensitization of HMX to impact and the increased sensitivity to electrical spark by coating its crystals with polyaniline.
基金support from the European Union Horizon 2020 program(project HERMES,nr.952184)the Ministry of Education,Youth and Sports of the Czech Republic for supporting CEMNAT(LM2023037)+1 种基金Czech-NanoLab(LM2023051)infrastructures for providing ALD,SEM,EDX,XPS,TEM,and XRDCzech Science Foundation(project 23-08019X,EXPRO).
文摘Synergistic interplays involving multiple active centers originating from TiO2 nanotube layers(TNT)and ruthenium(Ru)species comprising of both single atoms(SAs)and nanoparticles(NPs)augment the alkaline hydrogen evolution reaction(HER)by enhancing Volmer kinetics from rapid water dissociation and improving Tafel kinetics from efficient H*desorption.Atomic layer deposition of Ru with 50 process cycles results in a mixture of Ru SAs and 2.8-0.4 nm NPs present on TNT layers,and it emerges with the highest HER activity among all the electrodes synthesized.A detailed study of the Ti and Ru species using different high-resolution techniques confirmed the presence of Ti^(3+)states and the coexistence of Ru SAs and NPs.With insights from literature,the role of Ti^(3+),appropriate work functions of TNT layers and Ru,and the synergistic effect of Ru SAs and Ru NPs in improving the performance of alkaline HER were elaborated and justified.The aforementioned characteristics led to a remarkable performance by having 9mV onset potentials and 33 mV dec^(-1) of Tafel slopes and a higher turnover frequency of 1.72 H2 s^(-1) at 30 mV.Besides,a notable stability from 28 h staircase chronopotentiometric measurements for TNT@Ru surpasses TNT@Pt in comparison.
基金supported by the Slovak grant agency VEGA(project no 1/0003/21)analyses of foreign co-authors also by internal sources(grant no.SGS_2025_001)of their workplaces.
文摘Dill(Anethum graveolens),an annual species,was used to study the impact of metallic pollution potentially spreading fromthe nickel smelter dump in Dolna Streda(Slovakia)by monitoring 55 elements.Despite the proximity of this dump(1 km),only soil Ni(54.8 mg/kg)or Pb(47.3 mg/kg),but not Cr,Mn,Fe or Co(main elements of the dump’s sludge)was elevated in given garden soil compared to two control sites.Mainly flowers and/or leaves contained significantly higher amounts of Ni,Cr,Pb,Cu,As,Sb,Sn,V,W,and some rare earth elements at the site close to the dump.Correlation between elements in organs and soil was significant mainly in stem or root but the bioaccumulation factor was typically low(<0.02)for most elements.A positive finding was that the 2022/2024 comparison revealed a decline in most elements in dill leaves,even at the dump site,which may reflect a decrease in the content of air PM particles.Soluble phenols were less accumulated in plants close to the nickel smelter dump,but flavonols showed the opposite trend,and free amino acids were positively correlated with many elements in the stem and root.An evaluation of commercial dill samples revealed variability(e.g.,up to 0.7 mg Cd/kg dry weight)but subsequent NCA and PCA analyses clearly separated the dump locality from other samples.However,significant differences in the content of Cd,Ni,Pb,As,and other elements encourage precise control of commercially available dill dry matter.
基金the project of the Ministry of Education,Youth and Sports of the Czech Republic,No.MSM 0021627501
文摘Fractions of β-HMX(β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane) have been used to demonstrate the mutual relationship between friction and impact sensitivities.Inclusion of an additional twelve nitramines into this scenario resulted in a series of partial relationships,which were determined from the molecular structure of these substances.It was also found that there is a relation between increasing heats of fusion of the nitramines studied and their decreasing friction sensitivities.Comparison of friction sensitivity with heats of fusion,ΔHm,tr of the studied nitramines shows that the increase in ΔHm,tr values is more or less connected with a decrease in friction sensitivity.
文摘Calcium tungstate phosphors activated by the Ln3＋ ions （Ln-Pr, Nd, Tb, Yb） were synthesized by a traditional high-temperature solid-state method. The crystal structures and morphologies of the products were characterized by scanning electron microscopy （SEM）, X-ray powders diffraction （XRD） and infrared spectra （FT-1R）. The samples were fotmd to show luminescence properties （down-conversion, DC, at excitation wavelength 254 nm and up-conversion, UC, at excitation wavelength 980 nm）. CaWO4 doped with Tb3＋/yb3＋ showed green DC and UC luminescence characteristic of Tb（Ⅲ） ion in the range of 470-660 nm, cor- responding to the 5D4→7F6,5,4,3,2 electronic transition. CaWO4 doped with Pr3＋/Yb3＋ showed week blue, green and red （DC and UC） luminescence of Pr（Ⅲ） ion, in the wavelength region of 450-700 nm. Emission peaks were ascribed to the 3P1→3H4,5,6, 3P0→3H4,5,6, 3P1→3F2 and 3P0→3F2 transitions, respectively. CaWO4 doped with Nd3＋/yb3＋ phosphor emitted orange UC luminescence at 450-690 nm （2p3/2→4I15/2, 4G7/2→419/2,11/2,13/2） and strong near-infrared UC luminescence at 720-900 nm （4F7/2＋4S3/2→4419/2, 4F5/2＋2H3/2→419/2, 4F3/2→4I9/2） which is the characteristic of Nd（Ⅲ） ion.
基金supported by means of the financial resources of Students Grant Projects No. SGS_2018_002 of the Faculty of Chemical Technology at the University of Pardubice
文摘Information about the forty nine nitraminic plastic bonded explosives(PBXs)and different nitramines were collected.Fillers of these PBXs are nitramines 1,3,5-trinitro-1,3,5-triazinane(RDX)and β-1,3,5,7-tetranitro-1,3,5-tetrazocane(β-HMX),cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5-d]imidazole(bicyclo-HMX,BCHMX)and e-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane(e-HNIW,CL-20)which are bonded by polyfluoro-elastomers,polydimethyl-siloxane,poly-glycidyl azide,polyisobutylene,polystyrene-butadiene,poly-acrylonitrile-butadiene and hydroxyl-terminated polybutadiene in addition to a melt cast compositions based on 2,4,6-trinitrotoluene.For thirty two of these PBXs the relationships are specified and analyzed between heats of their combustion and relative explosive strengths;by means of these relationships it might be possible to estimate,which groupings in the macromolecule of binder could be liable to their primary fission in the PBXs initiation.Similarly,for forty two of these explosives,the relationships are described and analyzed between their enthalpies of formation and impact sensitivities;here is especially attention paid to PBXs filled by BCHMX.Specific rate constants from Vacuum Stability Test(VST)of four nitramines and twenty PBXs are introduced into relationships with their enthalpies of formation.Regarding to all the mentioned cases,increasing of energy content of the studied explosives leads to increase of the relative explosive strength or initiation reactivity,respectively.Exception with the opposite trend,the outputs of VST are for BCHMX,where in PBXs are matrices with the esteric plasticizers or the energetic poly-glycidyl azide.Admixture of RDX or HMX,respectively,into the BCHX PBXs gives ternary PBXs whose thermal stability,in the sense of applied VST,is higher comparing to the original binary explosives.
基金financial support from the Students Grant Projects No. SGSFCHT_2016002 of the Faculty of Chemical Technology at the University of Pardubicefinancial support The State Administration of Foreign Experts Affairs, Peoples Republic of China
文摘More detailed analysis of a mutual relationship of impact sensitivity(detected by sound) and crystal lattice free volume, △V, for the 18 nitramines shows that its course is not unequivocal. For a part of the studied compounds this sensitivity has increased with increase of the AV values, but for fairly big number of nitramines the relationship works in the opposite direction, especially for data of 1,3,5-trinitro-1,3,5-triazinane, 1,3,5,7-tetranitro-1,3,5,7-tetrazocane. and β-and ε-polymorphs of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane. Initiation reactivity of technical ε-polymorph of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane gives the impression by disorderliness in distribution of the actions of forces in its crystal lattice in comparison with its RS(reduced sensitivity) or chemically pure analogue. Limitations of partial shapes of the mentioned relationship by the molecular-structural similarity, and already published information about the decisive factors governing the crystal structure, signalizes a higher influence of the intermolecular interactions in a crystal lattice in comparison with influence of the crystal lattice free volume for initiation of the crystalline EMs.
基金financial support from the Students Grant Projects No. SGSFCHT_2016002 of the Faculty of Chemical Technology at the University of Pardubicefinancial support of the Chinese State Administration of Foreign Experts Affairs
文摘The relationship between friction sensitivity(FS) and the crystal lattice free space per molecule, △V. of thirteen nitramines is described by a linear equation, divided into a number of the partial relationships with strong limitations by their molecular structure characteristics. Increasing FS due to raising of the △V values is not clearly confirmed. The influence of the △V values on friction sensitivity of nitramines is similar to that of their aza atoms which influence the mutual orientations of nitro groups in neighboring molecules. The dipole-dipole interaction of the oxygen and nitrogen atoms of nitro groups in neighboring nitramine molecules has a major effect on their own FS. In accordance with this interaction, a directly proportional relationship was derived between FS and the intrinsic gas phase molecular volume, V_(int), of the nitramines mentioned, which is divided also into several straight lines according to relatively tight molecular structure similarity. The relationships found again confirm a level of disorder in the distribution of the forces in the crystal lattice of the "common" quality of ε-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, in comparison with its reduced sensitivity(RS) or chemically pure analogue.
文摘Preparation of cast double-propellant grains depends on the ability of nitrocellulose powder to swell and coalesce into a coherent mass when treated with a suitable solvent.The cast double-base process has been developed into a highly versatile technique for manufacturing solid rocket charges.Propellants manufactured by this process provide a wide range of energies and burning rates.Successful preparation of cast double-base propellant grains has been performed using compatible casting liquid with the casting powder.BuNENA was used as an energetic plasticizer for manufacturing of casting powder.Burning rate measurements have been performed using closed bomb SV-2to investigate the burning behavior along a wide range of operating pressure.Plateau burning had been detected in pressure range(50-70)×105 Pa for the composition included BuNENA.DTA and TGA thermal analysis were conducted to evaluate the thermal behavior of the prepared cast double-base propellants.Results from DTA were used to calculate the apparent activation energy.
基金financial support from the Students Grant Projects No. SGSFCHT_2016002 of the Faculty of Chemical Technology at the University of Pretoria
文摘cis-1,3,4,6-Tetranitrooctahydroimidazo-[4,5-d]imidazole(BCHMX) is a relatively available bicyclic nitramine in the present. Due to the high energetic content of its molecule(deformation of valence angles) it has heat of formation higher than β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane(β-HMX) by nearly three times. As a result, it has heat of explosion and relative explosive strength exceed that of β-HMX including their corresponding PBXs. However, penetration abilities of PBXs based on HMX are higher than those based on BCHMX. The relatively high initiation reactivity of BCHMX could be modified in a wide range by its incorporation in a suitable polymeric matrices. Regarding to the performance, coating of BCHMX crystals by 5 wt% Viton A produces the maximum performance while the mixture of BCHMX with polydimethylsiloxane(PDMS) seems to be the optimum composition for the development of PBX with low sensitivity.
文摘The relationship between the crystal lattice free volume,ΔV,and impact sensitivity,E_(dr),of ten nitramines has been analyzed. It was found that this relationship is not uniquely determined,i. e. it is not given only by their own ΔV values but fundamentally by the type and intensity of the intermolecular forces in the nitramine crystals. Also,relationships between the E_(dr)values,on the one hand,and bulk modulus,K,and shear modulus,G,on the other,have been the subject of discussion not only for pure cyclic nitramines but also for their PBXs,bonded by a poly-fluoro binder. The closest linear correlation exists between the E_(dr)values and dimensionless K·G^(-1) ratio which indicates the plasticity range. A similar relationship is valid also for the ΔV values. Relationships of the E_(dr) and / or ΔV values with the shear modulus or to the K·G^(-1) ratio reflect an unusual behavior of ε-HNIW to which the published morphological instability of this particular HNIW version might also be related.
基金the project of the Ministry of Education,Youth and Sports of the Czech Republic No.MSM 0021627501
文摘The friction sensitivities(FS) of five linear and eight cyclic nitramines have been determined.These FS values were compared with the respective detonation velocities,D,and with the dimensionless ratio created by relating the heat of explosion,Qreal,to the activation energy,Ea,of non-autocatalyzed thermal decomposition of the explosives concerned.For the nitramaines studied,these comparisons show a general trend of FS decreasing with increasing energy content.
基金The authors wish to thank the Czech Science Foundation(Project No.GA19-08937S)specific university research(A2_FCHT_2020_027 and A1_FCHT_2020_003)for the financial support of this research.
文摘Powder metallurgy is a powerful method for the preparation of materials with superior properties.This work aimed to investigate the effect of powder size on the microstructure,mechanical,and corrosion properties of advanced WE43(Mg-4Y-3REE-Zr)alloy prepared by spark plasma sintering(SPS).At the same time,the effect of HF pre-treatment of the powder on the properties of final compacted products is studied.Smaller powder particles yielded microstructure with more interfaces formed by Y_(2)O_(3),or MgF_(2) and YF_(3).These interfaces work as barriers against corrosion,which greatly improves corrosion resistance.The suggested pre-treatment of powder in HF further reduced the corrosion rate of the compacted materials.On the contrary,fragile interfaces of YF_(3) decreased mechanical properties as the crack primarily propagates through these interfaces.The original powder containing the mixture of all powder fractions exerted the best combination of mechanical properties.Powder size has also shown to affect ignition temperature.The highest ignition temperature was measured for the finest powder fraction.
基金support from the Students Grant Projects No.SGSFCHT_2016002 of the Faculty of Chemical Technology at the University of Pardubicefinancial support came from the Chinese State Administration of Foreign Experts Affairs
文摘The linear,directly proportional,equations between the Arrhenius parameters(E_α,and log A)of the thermal decomposition and the crystal lattice free space per molecule,△V,of 22 nitramines are described.It is shown that,because of a significant limitation by the molecular structural characteristics of such compounds,they are divided into a number of partial relationships.These partial relationships divide the nitramines into a group of substances relating to dimethyl nitramine and a sub-group related to e-HNIW.These directly proportional equations mean that an increase in the△Vvalues is related to an increase in the thermal stability of the corresponding nitramines.A comparison with similar published dependencies for the impact and friction sensitivities,on the one hand,and with the relationship between the E_a values and the sum of the negative and positive extremes of molecular surface electrostatic potentials,on the other,confirms the well-known fact that intermolecular interaction in the nitramines studied plays a decisive role in the thermal reactivity of such compounds.The crystal lattice free space manifests itself here perhaps only in the solid state thermal decomposition of RDX,HMX and DINGU.This study again confirms a level of disorder in the distribution of the forces in the crystal lattice of the"common"quality of e-HNIW,compared with its"reduced sensitivity(RS)"or pure analogues.
基金the project of the Ministry of Education,Youth and Sports of the Czech Republic No.MSM 0021627501
文摘The friction sensitivity(FS) of five linear and eight cyclic nitramines has been determined.Arrhenius parameters of non-autocatalyzed thermal decomposition of these nitramines were used for comparison of the FS values with thermal reactivity.Generally,increasing values of activation energies of non-autocatalyzed decomposition of the studied nitramines are connected with decreasing FS values.A similar trend was found in the relation between FS and hypothetical initiation temperature for 5% conversion of the nitramines after 50 μs of their thermolysis,however,if in the given series of nitramines their initiation reactivity is predominantly determined by the energy content of their molecules and closer similarity of their molecular structures,then the above-mentioned trend may be opposite.The found relationships were used for prediction and verification of the activation energy of non-autocatalyzed thermal decomposition of 2,5-dinitro-2,5-diazahexane.
文摘A new tetragonal,scheelite-type Pb_(1-3 x)■_xEU_(2 x)(MoO_4)_(1-3 x)(WO_4)_(3 x)(0< x ≤0.1970 and ■ denotes A-site vacancies) solid solution was synthesized via solid state reaction method. The X-ray diffraction(XRD) and scanning electron microscopy(SEM) results confirm the formation of single, tetragonal scheelite-type phases(space group I4_1/a) with the average crystallite size in the range of ～20-100 μm. Substitution of Pb^(2+) with Eu^(3+) is relatively easy despite the large difference in ionic radii, and the formation of vacancies is necessary to compensate the excess positive charge in PbMoO_4 framework. A change in lattice parameters(both a and c as well as lattice parameter ratio c/a) and progressive deformation of MoO_4 and WO_4 tetrahedra with increasing Eu concentration are observed. Thermal stability of Eu-doped materials strongly depends on the concentration of Eu3+ ions. The Pb_(1-3 x)■_xEu_(2 x)(MoO_4)_(1-3 x)(WO_4)_(3 x) solid solution for x=0.0098 shows the highest melting point(1057 ℃) which is slightly higher than that of pure PbMoO_4(1040 ℃). The UV-vis diffuse reflectance spectroscopy(DRS) and the Tauc plots were used to extrapolate the optical indirect band gap(E_g) of doped materials. Eu-doped ceramics are insulators(E_g > 3 eV) and their band gap nonlinearly decreases with increasing dopant concentration.
文摘A well-known ternary plastic explosive,Czech Semtex 1H,contains a mixture of PETN and RDX softened by SBR.In this work,BCHMX was used to replace PETN in Semtex 1H to form Sem-BC+RDX.In addition,another mixture based on BCHMX and HMX as energetic fillers bonded by the polymeric matrix of Semtex 1H(Sem-BC+HMX)was studied.The particle size distribution of each individual explosive was determined to obtain the optimum mixing conditions.Friction and impact sensitivities were determined.The velocity of detonation was reported practically and the detonation properties were calculated by EXPLO5 code.The explosive strength of each sample was measured by the ballistic mortar test.The conclusion confirms that the velocity of detonation of Sem-BC+HMX was the highest in comparison with the prepared samples.Sem-BC+RDX has the least impact and frictions sensitivities.Sem-BC+RDX has higher detonation velocity,detonation properties and explosive strength than Semtex 1H.Addition of BCHMX in Semtex 1H as a replacement for PETN is the candidate to produce a high performance advanced Czech plastic explosive.
文摘Gd3+-,Pr3+-or Sm3+-doped Co-Zn(Co0.5Zn0.5Fe2 O4)magnetic ferrites(i.e.,Co0.5Zn0.5Gd0.1Fe1.9O4,Co0.5Zn0.5Pr0.1Fe1.9O4 and Co0.5Zn0.5Sm0.1Fe1.9O4)were prepared using a facile sol-gel approach,and the structure,surface morphology and chemical composition of the products were studied by means of scanning electron microscopy(SEM),energy dispersive X-ray analysis(EDX),X-ray diffraction(XRD),UVvisible diffuse reflectance spectroscopy(DRS),photoluminescence(PL)spectroscopy,Fourier transform infrared spectroscopy(FT-IR)and vibrating sample magnetometer(VSM)spectroscopy.XRD patterns show the Co-Zn product is composed of cubic spinel phases with few impurities or secondary phases,and the average crystallite sizes of the samples are determined to be approximately^51—80,~99—181,~68—103 and^83—133 nm.Also the coercivity and remnant and saturation magnetizations,evaluated by vibrating sample magnetometer(VSM),are found to increase linearly with the incorporation of Gd3+,Pr3+and Sm3+in the product formulation.The CO1-xZnxFe2-yRyO4 photocatalyst sample is found to display a red shift in its absorption,and exhibits outstanding photocatalytic effects in the degradation of MO under ultraviolet(UV)light.This is attributed to the reduction of the band gap of cobalt-zinc ferrite due to the presence of rare earth ions.Further in vitro evaluations of the cytotoxic effects of the synthesized nanoparticles were performed on a HeLa cell line.
基金supported by the National Natural Science Foundation of China(No.51303170)the National Science Centre,Poland within BEETHOVEN UMO-2016/23/G/ST5/04200。
文摘Porous carbon materials have exhibited a series of promising applications in supercapacitors and other research fields,yet still confronting the complicated synthetic procedures and massive usage of toxic reagents.Herein,we propose a green and one-pot method to produce heteroatomdoped hierarchical porous carbon materials in large-scale without any toxic reagents employed.Eventually,the as-prepared nitrogen-doped porous carbon(NPC)displays a high specific surface area of 2018 m^(2)g^(-1)together with abundant heteroatom dopants(14.8 wt%O and 1.03 wt%N).The potassium carbonate template can be recycled via a simple rinsing and re-precipitation process.Furthermore,the as-prepared nitrogen-doped porous carbon delivers a high specific capacitance of 361 F g^(-1)at 0.5 A g^(-1)and excellent rate capability of 240 F g^(-1)at 20 A g^(-1)(66.5%capacitance retention).Finally,considering the low-price raw materials and facile green synthesis procedure,the present approach can be easily scalable to prepare biomass-derived heteroatoms doped porous carbon,which is not only applicable for supercapacitor but also for other research fields.
