The use of ultra high-performance liquid chromatography for studying hydrolysis kinetics of CL-20 and related energetic compounds

Ultra high-performance liquid chromatography (UHPLC) utilizes columns packed with sub-2-mum stationary-phase particles and allows operation with pressures of up to 15,000 psi to yield increased resolution, speed, and sensitivity versus conventional HPLC. This promising new technology was used for the analysis of energetic compounds (RDX, HMX and CL-20) and a selective method was developed on an Acquity UPLC. A fast UHPLC method was applied to determine alkaline hydrolysis reaction kinetics of major energetic compounds. Activation energies of alkaline hydrolysis reaction for CL-20, RDX and HMX were comparable to those in literature, however they were determined in a shorter amount of time due to the speed of analysis of the chromatographic method. The use of liophilic salts (KPF(6)) as mobile-phase additives for the enhancement of separation selectivity of energetic compounds was demonstrated.     

Study of Cu(II) biosorption by dried activated sludge: effect of physico-chemical environment and kinetics study

Biosorption is a recent technology used to remove heavy metal ions from aqueous solutions. The biosorption of copper ions from aqueous solution by dried activated sludge was investigated in batch systems. Effect of solution pH, initial metal concentration and particle size range were determined. The suitable pH and temperature for studied conditions were determined as 4.0 and 20 °C, respectively. The theoretical max biosorption capacity of activated sludge was 294 mg g⁻¹ at 20 °C for <0.063 mm particle size. The equilibrium data fitted very well to both Langmuir and Freundlich isotherm models. The pseudo first and second-order kinetic models were used to describe the kinetic data. The experimental data fitted to second-order kinetic model. The particle size and initial metal concentration were effected the biosorption capacity of dried activated sludge. An increase in the initial metal concentration increases of biosorption capacity, which also increases with decreasing particle size. Dried activated sludge has different functional groups according to the FT-IR results.     

二硝基乙腈钾与火药组分相容性的DSC法评估

为了了解二硝基乙腈钾(DNCK)与火药常用组分之间的相容性,采用差示扫描量热法（DSC）研究了DNCK与这些组分之间的相互作用。结果表明:DNCK与DAGR吸收药、DA吸收药、硝化棉（NC）、硝基胍（NQ）、叠氮硝胺（DIANP）、1,3-二甲基-1,3-二苯基脲（C2）、2-硝基二苯胺（2-NDPA）相容性良好;与六硝基六氮杂异戊兹烷（CL-20）和N 甲基-4-硝基苯胺（MNA）轻微敏感;与黑索今（RDX）、三羟甲基乙烷三硝酸酯（TMETN）和间苯二酚（Res）敏感;DNCK与奥克托今（HMX）和N-丁基硝氧乙基硝胺（BUNENA）混合体系的分解峰温较HMX和BUNENA单质组分分别提前了35.2 ℃和17.4 ℃,因此,与HMX和BUNENA不相容。     

RDX和HMX混合物中HMX的分离研究

根据HMX和RDX在不同溶剂中的溶解机理的差异,选用两种代表性物质对RDX和HMX混合物进行分离研究,确立以N,N-二甲基甲酰胺(DMF)为溶剂的分离RDX和HMX混合物的最佳工艺条件。最佳工艺条件为物料比14,溶解温度95～100℃,解离剂为水,解离温度90℃,解离时间2 h。运用高效液相色谱(HPLC)对分离得到的HMX进行了纯度测定,HMX纯度可达98%;通过偏光显微镜观察显示分离得到的HMX为β-晶型。分离得到的HMX在民用混合炸药中得到了再利用,可以替代直接生产的HMX。     

基于分子动力学的DNAN基熔铸炸药结合能和热分解反应性能研究

采用Compass力场对DNAN基熔铸炸药的结合能、溶度参数进行分子动力学模拟。计算结果表明:DNAN/RDX混合体系的溶度参数大于DNAN/HMX混合体系的溶度参数;当RDX团簇和HMX团簇的直径均大于15×10^-10 m时,DNAN/RDX混合体系的结合能远大于DNAN/HMX混合体系的结合能。基于ReaxFF-lg力场的分子动力学计算方法,对目标温度为2 000~3 500 K时DNAN/RDX混合炸药的热分解反应进行研究。结果表明:DNAN分子和RDX分子在高温下的初始分解反应路径均会受到影响;除了两种组分的硝基官能团发生脱落形成硝基官能团的初始反应路径不会受到影响之外,DNAN分子生成CH₂O碎片、RDX分子生成HONO和C₃H₃N₃碎片的反应路径均会受到抑制。     

Time resolved luminescence of quartz from Nigeria

Characteristics of luminescence lifetimes and luminescence intensity obtained from time resolved spectra of quartz from Nigeria are presented. The luminescence was pulse-stimulated at 11 μs width at 470 nm. Samples used consisted of unannealed quartz as well as samples annealed at 500 °C, 600 °C, 700 °C, 800 °C and 900 °C. The luminescence lifetimes and luminescence intensities were studied as a function of annealing temperature, irradiation dose and measurement temperature. It was found that there is a decrease, although non-monotonic, in the luminescence lifetime with change in annealing temperature from 20 to 900 °C. In addition, lifetimes extracted from time resolved spectra of unannealed samples as well as ones annealed at 500 °C and 600 °C are initially independent of irradiation dose but do later decrease with further irradiation. Regarding the luminescence intensity it was observed that in general, the intensity passes through a peak as the measurement temperature is increased from 20 to 200 °C with slight differences in the detailed pattern dependent on preheating. Activation energies for thermal quenching and thermal assistance evaluated from temperature-dependent changes of luminescence lifetime and luminescence intensity are given. The results are discussed in terms of a model consisting of three luminescence centres with probability of hole trapping during irradiation being highest for the luminescence centre associated with the least lifetime.     

Effect of negatively charged species on the growth behavior of silicon films in hot wire chemical vapor deposition

The deposition behavior of silicon in hot wire chemical vapor deposition was investigated, focusing on the generation of negatively charged species in the gas phase using a gas mixture of 20% SiH₄ and 80% H₂ at a 450 °C substrate temperature under a working pressure of 66.7 Pa. A negative current of 6–21 µA/cm² was measured on the substrate at all processing conditions, and its absolute value increased with increasing wire temperature in the range of 1400 °C–1900 °C. The surface roughness of the films deposited on the silicon wafers increased with increasing wire temperature in the range of 1510 °C–1800 °C. The film growth rate on the positively biased substrates (+ 100 V, + 200 V) was higher than that on the neutral (0 V) and negatively biased substrates (− 100 V, − 200 V, − 300 V). These results indicate that the negatively charged species are generated in the gas phase and contribute to deposition. The surface roughness evolved during deposition was attributed to the electrostatic interaction between these negatively charged species and the negatively charged growing surface.     

Sintering kinetics of 8Y–cubic zirconia: Cation diffusion coefficient

Zirconia ceramics, mainly of cubic phase, are used in different applications because of their particular electrical and structural properties.

After the forming stage, sintering leads to a material with suitable microstructural characteristics. The sintering process mainly depends on thermal cycle and on starting particle size and its distribution; it also depends on density and the microstructure of green material. Cubic zirconia has a high (2680 °C) melting temperature; however, effective sintering could be observed for temperatures higher than 900 °C (nanoparticles), and it may reach a final density of 96–98% the theoretical value at relative low temperatures.

The objective of this paper is to study the sintering kinetics of stabilized zirconia in its cubic phase with 8% molar of Y₂O₃ under fast firing rates up to nearly isothermal conditions. Samples were shaped from suspensions dispersed with ammonium polyacrylate by slip casting. Sintering was performed in the temperature range between 1200 °C and 1400 °C. The sintering kinetic process was followed by measuring density as a function of time. A sintering model was applied to fit the experimental data of the first steps of densification. It was observed that sintering obeys the same mechanism in the temperature and time ranges under study, which results in an activation energy of 170 kJ mol⁻¹. Sintering is controlled by Zr cation diffusion, for which a lattice diffusion coefficient of D_l = 8 × 10⁻¹² cm² s⁻¹ at 1400 °C was found, and the activation energy of the diffusion process was 223 kJ mol⁻¹.     

Experimental study on the performance of a room temperature magnetic refrigerator using permanent magnets

An investigation of a room temperature active magnetic refrigerator was carried out in this work. An experimental rig was built, in which two reciprocating regenerative beds packed with 1167.4 g of gadolinium were used, helium gas was used as a heat transfer fluid, and an average 1.5 T magnetic field was supplied by permanent magnets. With this apparatus, the influence of the gas pressure, the operating frequency and the temperature range were studied systematically. The lowest no heat load temperature of −2.79 °C at the cold end heat exchanger and a maximum no heat load temperature span of 42.28 °C were obtained. A maximum cooling power of 51.3 W was achieved over a temperature span of 18.16 °C. The results in this study provide useful data for future design and development of room temperature magnetic refrigerators.     

Low ductility at intermediate temperature of Ni–base superalloy M963

Tensile behavior of a cast Ni–base superalloy M963 under solution treatment and age treatment was studied in the temperature range from 20 to 1100 °C. Extensive TEM investigations were performed after tensile test to fracture. Furthermore, the fracture surfaces were studied in the SEM. The yield and tensile strengths under the two conditions initially increase with temperature and reach a peak at around 800 °C. Beyond this temperature, a sharp decrease of both yield and tensile strengths was observed. A ductility minimum was observed at 800 °C under solution treatment and disappeared under age treatment. With the increment of temperature, the following sequence of deformed substructure features was observed: dislocation pairs → connected slip bands within matrix channel under solution treatment and homogeneous interface dislocations under age treatment → homogeneous dislocation network within matrix channel. The fracture surface observation indicated that localized slip which leading to glide plane decohesion caused the poor ductility of M963 alloy.     

Ageing behavior of a Cu-bearing ultrahigh strength steel

On ageing at different temperatures a various combination of properties has been obtained for this Cu-bearing ultrahigh strength steel. A substantial increase in strength has been obtained at 450 °C, accompanied by a drop in percentage elongation, percentage reduction in area and toughness. At 550 °C temperature extensive -Cu precipitates have been observed. The increased strength value retained in the temperature range of 450–600 °C and a secondary hardening peak obtained at 600 °C is probably due to the formation of fine Mo carbide precipitates. The decrease in strength at 650 °C along with an increase in percentage elongation, percentage reduction in area and toughness is due to the coarsening of Cu particles and a partial recovery of matrix. At 700 °C most of the Cu precipitates become rod shaped and formation of fresh martensite with a dark contrast is observed at the lath boundaries.     

A novel technique to synthesize hydroxyapatite at low temperature

Hydroxyapatite (HAP), a well known biomaterial, was synthesized by a novel technique using agarose gel in a high alkaline medium at a relatively low temperature 85 °C. The XRD analysis of the as-synthesized material revealed the absence of either brushite or or β tricalcium phosphate phases. Sintering studies at 750 and 1200 °C revealed the conversion of HAP into pyrophosphate without leaving any additional phases. A considerable decrease in the transformation temperature of HAP phase to that of -calcium pyrophosphate (-CPP) phase was found compared to the reported values.     

Temperature effects of PTFE diffusers

Poly(tetrafluoroethylene) (PTFE) is the most commonly used diffuser material in ultraviolet irradiance measurements. The temperature sensitivities of five PTFE diffusers were measured over a broad temperature range. The transmittance change varied from −0.015%/°C to −0.1%/°C. At 19 °C there was an unexpected abrupt change in transmittance ranging from 1% to 3%. This change is due to the change of the crystal structure of PTFE at 19 °C. Temperature sensitivity decreases significantly the accuracy of high precision measurements, especially if the temperature of the diffusers is not stabilized.     

Diffusion bonding between commercially pure titanium and micro-duplex stainless steel

Diffusion-bonded joints between commercially pure titanium and micro-duplex stainless steel were prepared in the temperature range of 800–950 °C for 1.5 h under 3 MPa uniaxial load in vacuum. The diffusion bonds were characterized using light and scanning electron microscopy. The composition of the reaction products were determined by energy dispersive spectroscopy. Up to 850 °C, -Fe + λ and λ + FeTi phase mixtures were formed at diffusion interface; however -Fe + λ, λ + FeTi and FeTi + β-Ti phases mixtures were formed at 900 °C and above. The presence of these intermetallics was confirmed by X-ray diffraction technique. The maximum tensile strength of 96% of Ti and shear strength of 81% of Ti along with 6.9% ductility were obtained for the diffusion couple processed at 850 °C due to the finer width of intermetallic phases. With a rise in the joining temperature the bond strength drops owing to an increase in the width of reaction products.     

Internal friction associated with phase transformation of nanograined bulk Fe–25 at.% Ni alloy

The internal friction and modulus of a nanograined bulk Fe–25 at.% Ni prepared by an inert gas condensation and in situ warm consolidation technique were measured in temperature range −100 to 400 °C by means of a dynamic mechanical analyzer (DMA). An internal friction peak at around −75 °C associated with martensitic transformation was observed. During heating, an internal friction peak at about 200 °C accompanied with the decrease of modulus was also observed, which was proved by XRD that this may mainly be attributed to the reverse phase transformation of stress-induced martensite (SIM). Some abnormal features of modulus versus temperature were observed and discussed.     

Sorption and degradation of bisphenol A by aerobic activated sludge

Laboratory-scale batch experiments were conducted to investigate the sorption and degradation of bisphenol A (BPA) at μg/L range in an aerobic activated sludge system. The sorption isotherms and thermodynamics indicated that the sorption of BPA on sludge was mainly a physical process in which partitioning played a dominating role. The values of sorption coefficient K_oc were between 621 and 736 L/kg in the temperature range of 10–30 °C. Both mixed liquor suspended solid (MLSS) and temperature influenced BPA sorption on sludge. The degradation of BPA by acclimated activated sludge could be described by first-order reaction equation with the first-order degradation rate constant of 0.80 h⁻¹ at 20 °C. The decrease of initial COD concentration and the increase of MLSS concentration and temperature enhanced BPA degradation rate. The removal of BPA in the activated sludge system was characterized by a quick sorption on the activated sludge and subsequent biodegradation.     

Residential CO2 heat pump system for combined space heating and hot water heating

A theoretical and experimental study has been carried out for a residential brine-to-water CO₂ heat pump system for combined space heating and hot water heating. A 6.5 kW prototype heat pump unit was constructed and extensively tested in order to document the performance and to study component and system behaviour over a wide range of operating conditions. The CO₂ heat pump was equipped with a unique counter-flow tripartite gas cooler for preheating of domestic hot water (DHW), low-temperature space heating and reheating of DHW.

The CO₂ heat pump was tested in three different modes: space heating only, DHW heating only and simultaneous space heating and DHW heating. The heat pump unit gave off heat to a floor heating system at supply/return temperatures of 33/28, 35/30 or 40/35 °C, and the set-point temperature for the DHW was 60, 70 or 80 °C. Most tests were carried out at an evaporation temperature of −5 °C, and the average city water temperature was 6.5 °C. The experimental results proved that a brine-to-water CO₂ heat pump system may achieve the same or higher seasonal performance factor (SPF) than the most energy efficient state-of-the-art brine-to-water heat pump systems as long as: (1) the heating demand for hot water production constitutes at least 25% of the total annual heating demand of the residence, (2) the return temperature in the space heating system is about 30 °C or lower, (3) the city water temperature is about 10 °C or lower and (4) the exergy losses in the DHW tank are small.     

Equilibrium, kinetic and thermodynamic study of the biosorption of uranium onto Cystoseria indica algae

Biosorption equilibrium, kinetics and thermodynamics of binding of uranium ions to Cystoseria indica were studied in a batch system with respect to temperature and initial metal ion concentration. Algae biomass exhibited the highest uranium uptake capacity at 15 °C at an initial uranium ion concentration of 500 mg l⁻¹ and an initial pH of 4. Biosorption capacity increased from 198 to 233 mg g⁻¹ with an decrease in temperature from 45 to 15 °C at this initial uranium concentration. The Langmuir isotherm model were applied to experimental equilibrium data of uranium biosorption depending on temperature. Equilibrium data fitted very well to the Langmuir model C. indica algae in the studied concentration range of Uranium ions at all the temperatures studied. The saturation type kinetic model was applied to experimental data at different temperatures changing from 15 to 45 °C to describe the batch biosorption kinetics assuming that the external mass transfer limitations in the system can be neglected and biosorption is chemical sorption controlled. The activation energy of biosorption (E_A) was determined as −6.15 using the Arrhenius equation. Using the thermodynamic equilibrium coefficients obtained at different temperatures, the thermodynamic constants of biosorption (ΔG°, ΔH° and ΔS°) were also evaluated.     

CL-20基薄膜炸药的爆轰特性研究

采用重结晶方法细化的CL-20炸药进行CL-20基薄膜炸药制备。研究了CL-20基薄膜炸药的爆轰性能、熄爆厚度和拐角效应,并与HMX基薄膜炸药进行对比。研究结果表明:在装药相对密度为85%时,CL-20基和HMX基薄膜炸药的爆速分别为8 393 m/s和8 069 m/s;CL-20基和HMX基薄膜炸药的熄爆厚度分别为0.23 mm和0.41 mm;相比HMX基薄膜炸药,CL-20基薄膜炸药的熄爆厚度更小,传爆能力更强。     

III-Nitrides growth and AlGaN/GaN heterostructures on ferroelectric materials

The growth of III-nitrides on the ferroelectric materials lithium niobate (LN) and lithium tantalate (LT) via molecular beam epitaxy (MBE) using rf plasma source has been investigated. We have found that gallium nitride (GaN) epitaxial layers have a crystalline relationship with lithium niobate (tantalate) as follows: (0 0 0 1) GaN || (0 0 0 1) LN (LT) with [10−10] GaN || [11−20] LN (LT). The surface stability of LN and LT substrates has been monitored by in situ spectroscopic ellipsometry in the vacuum chamber. Three different temperature zones have been discerned; surface degas and loss of OH group (100–350 °C); surface segregation/accumulation of Li and O-species (400–700 °C); surface evaporation of O-species and Li desorption (over 750 °C). However, LT shows only surface degassing in the range of 100–800 °C. Therefore, congruent LN substrates were chemically unstable at the growth temperature of 550–650 °C, and therefore developed an additional phase of Li-deficient lithium niobate (LiNb₃O₈) along with lithium niobate (LiNbO₃), confirmed by X-ray diffraction. On the other hand, LT showed better chemical stability at these temperatures, with no additional phase development. The structural quality of GaN epitaxial layers has shown slight improvement on LT substrates over LN substrates, according to X-ray diffraction. Herein, we demonstrate AlGaN/GaN heterostructure devices on ferroelectric materials that will allow future development of multifunctional electrical and optical applications.