Foaming conditions of high density polyethylene–natural rubber blends

Abstract

Foams made from high density polyethylene (HDPE) and natural rubber (NR) blends, using azodicarbonamide as a chemical blowing agent, have been investigated to establish a relationship between the structure and physical properties. The blends of HDPE, NR, epolene wax, chemical blowing agent, and necessary ingredients were prepared on a two roll mill. Subsequently, foamed structures of the blends were obtained by a single stage compression moulding. Results indicate that foaming process variables, i.e. heating time, blowing agent loading, ratio of HDPE/NR, crosslinking agent loading, and ratio of HDPE/NR at a fixed crosslinking agent loading, affect the physical properties of the foams. Attempts were made to relate such properties as foam density, hardness, tensile strength, elongation at break, tear strength, flexural strength, elastic modulus, and gel content to the foam structure. The foam structure was investigated using optical microscopy, in terms of the average cell size and its distribution.     

Evaluation of plasma sprayed alumina–40 wt% titania and partially stabilized zirconia coatings on high density graphite for uranium melting application

Ceramic coatings have been proposed on high density graphite crucibles for the application of uranium consolidation and distillation of molten salt in pyrochemical reprocessing of metallic fuels. Towards this, uranium melting experiments were carried out on plasma sprayed partially stabilized zirconia (PSZ) and Al₂O₃–40 wt% TiO₂ (A40T) coated high density graphite samples at 1350 °C using induction heating system for evaluating the compatibility of these coatings with molten uranium. The coated high density graphite samples were characterized before and after uranium melting test by scanning electron microscopy attached with energy dispersive X-ray spectroscopy, X-ray diffraction and Raman spectroscopy. Microstructural observations revealed that no significant reaction layer or product was formed between uranium and PSZ coating, while uranium significantly adhered to A40T coating. PSZ coating offers better stability and protection to high density graphite crucibles from the chemical attack by molten uranium.     

A review of high energy density lithium–air battery technology

Today’s lithium (Li)-ion batteries have been widely adopted as the power of choice for small electronic devices through to large power systems such as hybrid electric vehicles (HEVs) or electric vehicles (EVs). However, it falls short of meeting the demands of new markets in these areas of EVs or HEVs due to insufficient energy density. Therefore, new battery systems such as Li–air batteries with high theoretical specific energy are being intensively investigated, as this technology could potentially make long-range EVs widely affordable. So far, Li–air battery technology is still in its infancy and will require significant research efforts. This review provides a comprehensive overview of the fundamentals of Li–air batteries, with an emphasis on the recent progress of various elements, such as lithium metal anode, cathode, electrolytes, and catalysts. Firstly, it covers the various types of air cathode used, such as the air cathode based on carbon, the carbon nanotube-based cathode, and the graphene-based cathode. Secondly, different types of catalysts such as metal oxide- and composite-based catalysts, carbon- and graphene-based catalysts, and precious metal alloy-based catalysts are elaborated. The challenges and recent developments on electrolytes and lithium metal anode are then summarized. Finally, a summary of future research directions in the field of lithium air batteries is provided.     

Mechanisms of TiB2 and graphite nucleation during TiC–B4C high temperature interaction

Reactive hot pressing of TiC–B₄C precursors was undertaken at 1800 °C to produce TiB₂ with carbon inclusions. Atomic mechanisms of titanium diboride nucleation, as well as sponge-like carbon inclusions and submicron platelets of graphite precipitation have been investigated. Precursor grain size, green body composition and synthesis time were varied to analyze phase transformation. The carbon left after B₄C high temperature decomposition is shown remaining as graphite sponge-like inclusions. Ab-initio calculations confirm that the boron atoms accumulation on (111) TiC plains leads to tensile stress. The developed stress cleaves TiC grains and enhances further reaction. Most of carbon expelled from TiC during its transformation into TiB₂ forms graphite submicron platelets.     

Multi-synergy ablative effects of laminated SiO2–graphite/SiO2/Cu composite irradiated by high power laser

Faced with the challenge of ultra–high–temperature ablation problems, multi-synergy and efficient energy dissipation method is a feasible solution. A structure-modified silica-graphite composite with multiple copper layers was prepared by hot-pressing. The ablation behaviors and mechanisms were analyzed in detail. During the laser ablation, the designed composite exhibits excellent ablation resistance with a multi-synergy effects strategy. As ablation time increases, the ablation mechanisms change from reflection and horizontal thermal diffusion to reaction and horizontal thermal diffusion and vertical heat insulation. Moreover, the gap generated by the reaction volume contraction can further insulate against heat transfer in the vertical direction. The rate of increase of back-surface temperature can be further reduced. This multi-synergy effects strategy and designed structure accompanied with appropriate materials can greatly enhance the ablation resistance ability of the composite.     

Electrical properties of high density PZT and PMN–PT/PZT thick films produced using ComFi technology

To achieve high actuation forces in piezoelectric film actuators and transducers it is desirable to have relatively thick films. Sol-gel derived films are often limited in the maximum thickness that is obtainable due to the increased probability of cracking and delamination during processing. Composite film (ComFi) technology combines conventional sol-gel processing with ceramic powder processing to enable thick (>2 μm) ferroelectric films to be deposited onto silicon substrates at temperatures as low as 710 °C. Ten micrometre thick films have been fabricated using three different piezoelectric powders [hard doped PZT, soft doped PZT and PMN–PT(85–15)]. The resultant films have high densities with relative permittivities of 800, 900 and 1800, respectively. The d₃₃ piezoelectric coefficients were found to be lower than corresponding values for the bulk material. This has been attributed to a combination of small grain size and the clamping effects of the rigid substrate. Hysteresis loop measurements show that greater fields are required to achieve a similar degree of polarisation to that of the bulk material. This indicates that the presence of the substrate also affects the ability to pole the material so further reducing the observed piezoelectric coefficient.     

Morphology and dynamic mechanical properties of high density polyethylene/petroleum resin/polyethylene–octylene elastomer blends

Summary  In this work a study of the synthesis and characterization of several associative water-soluble polymer families, consisting of acrylamide (AM), N-isopropylacrylamide (NIPAM) and N,N-dihexylacrylamide (DHAM) is presented. Three different polymer structures: telechelic (with hydrophobic groups at the chain ends), multisticker (with hydrophobic groups along the polymer chain) and combined (with hydrophobic groups along the chain as well as at the chain ends) were prepared via free radical solution polymerization, using a hydrophobic initiator derived from 4,4’-azobis(4-cyanopentanoic acid) (ACVA) containing linear chains of 12 carbon atoms (C₁₂). The viscoelastic properties of these different families of associative polymers were investigated using steady-flow experiments in aqueous solution. The structures as a function of surfactant (sodium dodecylsulfate, SDS) concentration and temperature were investigated. It was observed that the viscosity remains fairly constant up to a certain temperature (“breaking point”) and then decreases with increasing temperature. The breaking point occurs at 40 °C in the case of the telechelic polymers, at 50 °C for the multisticker polymers and at 60 °C for the combined polymers.     

Factors influencing the resistivity–temperature behavior of carbon black filled isotactic polypropylene/high density polyethylene composites

The relationship between morphology and resistivity–temperature behavior of carbon black (CB) filled isotactic polypropylene/high density polyethylene (iPP/HDPE) composites was investigated. The positive temperature coefficient intensity for all composites studied in this paper was lower than one and the negative temperature coefficient (NTC) effect was obvious. The factors influencing resistivity–temperature behavior include the CB contents, types of the polymer matrices and their composition, which determine the phase morphology and thus the conductive network. The types of iPP and HDPE influenced the NTC effect, while the morphology of the composites mainly influenced the initial volume resistivity of the composites.     

Synthesis of micro-nano hierarchical structured LiFePO₄/C composite with both superior high-rate performance and high tap density

Efforts were made to synthesize LiFePO(4)/C composites showing both high rate capability and high tap density. First, monoclinic phase FePO(4)·2H(2)O with micro-nano hierarchical structures are synthesized using a hydrothermal method, which are then lithiated to LiFePO(4)/C also with hierarchical structures by a simple rheological phase method. The primary structures of FePO(4)·2H(2)O are nanoplates with ～30 nm thickness, and the secondary structures of the materials are intertwisted micro-scale rings. The LiFePO(4)/C materials lithiated from these specially structured precursors also have hierarchical structures, showing discharge capacities of more than 120, 110, and 90 mAh g(-1) at rates of 5 C, 10 C and 20 C, respectively, and high tap density of 1.4 g cm(-3) as cathode materials for lithium ion batteries. Since tap density is an important factor that needs to be considered in fabricating real batteries in industry, these hierarchical structured LiFePO(4)/C moves closer to real and large-scale applications.     

Nitrogen and phosphorus co-doped activated carbon induces high density Cu+ active center for acetylene hydrochlorination

This work aims to solve the problems of low reaction activity of Cu-based catalysts and agglomeration of active centers in acetylene hydrochlorination.Cu-based catalysts supported by NAP co-doped activated carbon(AC) with different content(mCu-xNP/AC) were manufactured and applied in the acetylene hydrochlorination reaction.It was found that the doping of carriers N and P induced the transformation of Cu²⁺ to Cu⁺,and the catalytic activity was markedly improved.Under the op...     

Excellent thermal stability,high efficiency and high power density of (Sr0.7Ba0.3)5LaNb7Ti3O30–based tungsten bronze ceramics

A series of (1-x)(Sr_0.7Ba_0.3)₅LaNb₇Ti₃O₃₀–x(Bi_0.5Na_0.5)TiO₃ (x = 0.1–0.4) ceramics with tungsten bronze structure were prepared by solid state reaction. Phase composition, microstructure and energy storage properties were studied. When x = 0.3, excellent thermal stability satisfying the X7R specification was obtained and its energy storage as well as charge-discharge performances were further evaluated. Release energy density (W_re) of 0.77 J/cm³ and an energy storage efficiency of 97.3 % were detected at a low electric field of 20 kV/mm. Under the electric field of 10 kV/mm, the change of W_re in the temperature range of −55 °C to 125 °C is less than 15 % compared to room temperature. Short discharge period (∼0.17 μs), high power density (61.2 MW/cm³) and high discharge energy density (2.45 J/cm³) were evaluated by charge-discharge tests. Excellent thermal stability, high energy storage efficiency and high power density indicate that 0.7(Sr_0.7Ba_0.3)₅LaNb₇Ti₃O₃₀–0.3(Bi_0.5Na_0.5)TiO₃ ceramic is a promising pulse capacitor for working over a wide temperature range.     

Achieving ultrabroad temperature stability range with high dielectric constant and superior energy storage density in KNN–based ceramic capacitors

Multilayer ceramic capacitors (MLCCs) had become an important component of many electronic devices on account of its miniaturization, high capacitance and reliability. To satisfy the requirements of MLCCs, the temperature–insensitivity and dielectric properties of the dielectric ceramics were urgent to be enhanced. In our work, (1–x)K_0.5Na_0.5NbO₃–xBi(Li_0.5Nb_0.5)O₃ (abbreviated to KNN–xBLN) were successfully synthesized by traditional solid state reaction method. On the one hand, the doping BLN induced the diffused phase transition and broadened the dielectric anomaly peaks, which improved the temperature insensitivity of KNN-based ceramics. On the other hand, the nanosized grains and dense microscopy boosted the breakdown electric field. Ultimately, the KNN–0.175BLN samples presented the excellent dielectric properties with high dielectric constant (1735) and low dielectric loss (1.9%) at room temperature with a wide temperature stability range (–62 – 300 °C), which exhibited the wider temperature stability range than X9R specification. Meanwhile, the x = 0.175 samples also achieved a high recoverable energy storage density of 3.71 J/cm³ under the breakdown electric field of 360 kV/cm. The designed KNN–based dielectric materials were expected to be applicable to the energy storage capacitor with standed high operating temperature.     

The origin of the electric and dielectric behavior of expanded graphite–carbon nanotube/cyanate ester composites with very high dielectric constant and low dielectric loss

High performance expanded graphite (EG)–multiwalled carbon nanotube (MWCNT)/cyanate ester (CE) composites with very high dielectric constant, low dielectric loss and low percolation threshold were developed. In order to understand the electric and dielectric behavior of EG–MWCNT/CE composites, EG/CE and MWCNT/CE binary composites were also prepared for comparison. Results show that the ternary composites have greatly different electric and dielectric properties from the binary composites. The percolation threshold of the EG–MWCNT/CE composite is much lower than that of either the EG/CE or MWCNT/CE composite. With the same content of conductive fillers, the EG–MWCNT/CE composite shows a much higher dielectric constant than EG/CE and MWCNT/CE composites. In addition, to obtain the same dielectric constant, the dielectric loss of the EG–MWCNT/CE composite is lower than that of either binary composite. The difference is attributed to the synergistic effect between EG and MWCNT. The addition of EG not only improves the dispersion of MWCNTs in the resin matrix, but also helps to form conductive networks. An equivalent circuit model is proposed.     

水中总磷酸盐（Phosphate salt）的测定方法

水中总磷酸盐的含量高低,决定了对水污染程度（因为磷酸盐是使藻类植物生成必须的营养元素）。在工业中,水是常用的溶剂、冷却剂,为了使水中钙（Calcium）、镁（Magnesium）等离子降低,需要加入一定量的多磷酸盐,降低水的硬度,使其达到工艺要求。用钼酸钠显色,进行比色分析。     

Spatial-five coordination promotes the high efficiency of CoN4 moiety in graphene-based bilayer for oxygen reduction electrocatalysis: A density functional theory study

The searching of highly efficient catalysts for oxygen reduction reaction(ORR) has attracted particular attention. In this work, we construct the graphene-based bilayers BG/X that consists by the CoN₄ embedded graphene as the upper layer and the X modified graphene as the bottom layer(X = Si, P, S). The interfacial bonding between CoN₄ site and the X dopant is spontaneously formed due to the strong pd hybridization, which changes the Co ligand from the planar-four N₄     

Mechanochemical-molten salt synthesis of α-Al2O3 platelets

The polyaluminium chloride (PACl) precursor was used for a simple and scaled-up mechanochemical-molten salt synthesis of α-Al₂O₃ platelets. PACl, as a low temperature α-Al₂O₃ precursor, was firstly mechanically activated by high-energy ball milling for 5 min, followed by a next 5 min ball milling in the presence of a NaCl–KCl salt mixture. The starting formation temperature of the α-Al₂O₃ phase was 600 °C. In the subsequent annealing in the temperature range of 660–1000 °C, the α-Al₂O₃ phase with a well developed plate-like morphology was obtained. The products were characterized by X-ray powder diffractometry, scanning electron microscopy (SEM), and thermal analysis (DTA, TG) and solution ²⁷Al NMR spectroscopy.     

Hydrogen and oxygen evolution on graphite fiber—epoxy matrix composite electrodes

The electrochemical behavior of three graphite fiber—epoxy matrix composite materials containing various fiber orientations and fiber loadings was studied. Cyclic voltammetry was used to detect surface functionalities and to determine the electrochemically active surface areas of each material in 1 N H₂SO₄ and 30 weight percent (w/o) KOH.Hydrogen and oxygen evolution were studied on each electrode in 1 N H₂SO₄ and 30 w/o KOH, respectively. Tafel slopes for the hydrogen evolution reaction on the composite electrodes ranged from 0.14 to 0.18 V decade⁻¹ while exchange current densities ranged from 4 to 11 × 10⁻⁷ A cm⁻². Tafel slopes for the oxygen evolution reaction on the composite materials were high, ranging from 0.25 to 0.28 V decade⁻¹. Exchange current densities for the oxygen evolution reaction ranged from 2 to 5 × 10⁻⁷ A cm⁻². In general, fiber orientation and volume percent loading in the limited range studies had no noticeable effect on the kinetic behavior for the gas evolution reactions studied.     

Bulk graphite nozzle recession—an analysis based on the carbon-steam reaction

Bulk graphite gasification rates (Zone I) have been measured between 1123–1323 K at $\text{H}{}_2\text{O}\text{H}{}_2$ ratios which encompass those found in the exhaust gases resulting from the firing of a typical aluminized solid propellant. These Zone I rates are extrapolated on an Arrhenius plot to a temperature (≈3200 K) which is thought to exist at the surface of a graphite nozzle through which propellant combustion gases pass. The extrapolated rate is higher than that predicted for Zone III kinetics or found experimentally by other investigators. It is concluded that graphite recession under rocket motor conditions is in the intermediate region between Zones II and III. That is, gasification occurs not only at the exterior graphite surface but also in pores close to the exterior surface.     

A heterogeneous double chamber electro-Fenton with high production of H2O2 using La–CeO2 modified graphite felt as cathode

Hydrogen peroxide synthesis by electro-reduction of O₂ to substitute the current anthraquinone process has attracted a great deal of attention. Low oxygen utilization rate and low hydrogen peroxide production remain obstacles to electro-Fenton application. In situ H₂O₂ generated by electrochemical reaction depends on the electrochemical performance of the cathode and the structure of the reactor. Here, novel graphite felt(GF) modified by La-doped CeO₂(...