Effect of the microporous structure of ammonium perchlorate on thermal behaviour and combustion characteristics

Ammonium perchlorate(AP)is the component with the highest content in composite propellants,and it plays a crucial role in propellant performance.In view of the effects of low-temperature AP thermal decomposition on thermal safety and combustion characteristics,porous ammonium perchlorate(PAP)samples with different mass losses were first prepared by thermal convection heating,and the structures were characterized and analysed.Second,the effects of decomposition degree on the thermal decomposition characteristics of PAP were studied by DSC-TG.Finally,the combustion characteristics of AP/Al binary mixtures were tested with high-speed photography and in a sealed bomb.The results showed that low-temperature decomposition of AP resulted in formation of porous structures for AP particles.The pores first appeared near the surfaces of the particles and began from multiple points at the same time.The pores increased in size to approximately 5 mm and then expanded,and finally,the AP particles were full of pores.After partial decomposition,the crystal structure of AP remained unchanged,but the low and high decomposition temperatures decreased obviously.The decomposition rate accelerated.Due to the porous structure of PAP,the combustion rate of the AP/Al system increased obviously with increasing decomposition of AP.The relationship between the combustion rate and the mass loss was approximately linear under open conditions,and it was exponential for a high-pressure environment.A computational model of the combustion process for the AP/Al binary system was established to explain the effects of pore structure and pressure on the combustion process.

ADSORPTION OF 2,4-D ON MODIFIED HYPERCROSSLINKED POLYSTYRENE(NDA-99)AND XAD-4 RESIN

The adsorption behavior of pesticide 2,4-dichlorophenoxyacetic acid(2,4-D)in aqueous solution has been investigated using a hypercrosslinked polystyrene adsorbent(NDA-99)modified by dimethylamine group as well as a nonionic macroporous adsorbent(XAD-4).The Langmuir and Freundlich isotherm models were employed to fit the experimental data to describe adsorption mechanism.It shows that NDA-99 resin exhibits an adsorption affinity for 2,4-D higher than XAD-4 resin owing to its exceptional micropore structure and the amine group of the hypercrosslinked matrix. Further studies indicate that the hydrogen bonding interaction and the stronger π-π conjugation play a significant role in the course of the adsorption of 2,4-D on NDA-99 resin,which is in agreement with the IR spectroscopic results and the ΔE values of HOMO(the highest occupied molecular orbit)of adsorbent and LUMO(the lowest unoccupied molecular orbit)of adsorbate calculated from the MINDO/3 model.

Semi-interpenetrating network anion exchange membranes based on quaternized polyvinyl alcohol/poly(diallyldimethylammonium chloride)

The semi-interpenetrating network anion exchange membranes(AEMs)based on quaternized polyvinyl alcohol(QPVA)and poly(-diallyldimethylammonium chloride)(PDDA)are synthesized.The chemical cross-linking structure is formed between hydroxyl groups of QPVA and aldehyde groups of glutaraldehyde(GA),which makes PDDA more stable embed in the QPVA matrix and also improves the mechanical properties and dimensional stability of AEMs.Due to the phase separation phenomenon of AEMs swelling in water,a microporous structure may be formed in the membrane,which reduces the transmission resistance of hydroxide ions and provides a larger space for the transfer of hydroxide ions,thus improving the conductivity.The ring structure of PDDA is introduced as a cationic group to transfer hydroxide ions,and shields the nucleophilic attack of the hydroxide ions through the steric hindrance effect,which improves alkaline stability.The hydroxide conductivity of semi-interpenetrating network membrane(QPVA/PDDA0.5-GA)is 36.5 mS cm^(-1) at 60℃.And the membrane of QPVA/PDDA0.5-GA exhibits excellent mechanical property with maximum tensile strength of 19.6 MPa.After immersing into hot 3 mol L^(-1) NaOH solutions at 60℃ for 300 h,the OHconductivity remains 78%of its initial value.The semi-interpenetrating network AEMs with microporous structure exhibit good ionic conductivity,mechanical strength and alkaline durability.

A fibrous hypercrosslinked sorbent prepared on PP-ST-DVB matrix via post-crosslinking reaction

A fibrous sorbent possessing abundant micropore structure was firstly prepared via post-crosslinking reaction on the PP-ST-DVB original fiber. Its micromorphology and sorptive properties were investigated, and the results demonstrated that the novel fibrous hypererosslinked sorbent has narrow pore-size distribution, small average porous radius （1.90 nm）, high specific surface area （362.31 m^2/g）, and fine sorptive properties for small organic molecules.

Microstructure controlled synthesis of Ni,N-codoped CoP/carbon fiber hybrids with improving reaction kinetics for superior sodium storage

Transition-metal phosphides(TMPs)-based hybrid structure have received considerable attention for efficient sodium storage owing to their high capacity and decent reversibility.However,the volume expansion&the poor electronic conductivity of TMPs,the poor-rate capability,and fast capacity decay greatly hinder its practical application.To address these issues,a low-cost and facile strategy for the synthesis of Ni,N-codoped graphitized carbon(C)and cobalt phosphide(CoP)embedded in carbon fiber(Ni-CoP@CN⊂CF)as self-supporting anode material is demonstrated for the first time.The graphitized carbon and carbon fiber improve the electrical conductivity and inhibit the volume expansion issues.In addition to that,the microporous structure,and ultrasmall sized Ni-CoP offer a high surface area for electrolyte wettability,short Na-ion diffusion path and fast charge transport kinetics.As a result,outstanding electrochemical performance with an average capacity decay of 0.04%cycle^(−1)at 2000 mA g^(−1),an excellent rate capability of 270 mAh g^(−1)@2000 mA g^(−1)and a high energy density of~231.1 Wh kg^(−1)is achieved with binder-free self-supporting anode material.This work shows a potential for designing binder-free and high energy density sodium-ion batteries.

Tuning filament composition and microstructure of 3D-printed bioceramic scaffolds facilitate bone defect regeneration and repair

It is still a challenge to optimize the component distribution and microporous structures in scaffolds for tailoring biodegradation(ion releasing)and enhancing bone defect repair within an expected time stage.Herein,the core–shell-typed nonstoichiometric wollastonite(4%and 10%Mg-doping calcium silicate;CSiMg4,CSiMg10)macroporous scaffolds with microporous shells(adding~μ10 μm PS microspheres into shell-layer slurry)were fabricated via 3D printing.The initial mechanical properties and bio-dissolution(ion releasing)in vitro,and osteogenic capacity in vivo of the bioceramic scaffolds were evaluated systematically.It was shown that endowing high-density micropores in the sparingly dissolvable CSiMg10 or dissolvable CSiMg4 shell layer inevitably led to nearly 30%reduction of compressive strength,but such micropores could readily tune the ion release behaviour of the scaffolds(CSiMg4@CSiMg10 vs.CSiMg4@CSiMg10-p;CSiMg10@CSiMg4 vs.CSiMg10@CSiMg4-p).Based on the in rabbit femoral bone defect repair model,the 3D μCT reconstruction and histological observation demonstrated that the CSiMg4@CSiMg10-p scaffolds displayed markedly higher osteogenic capability than the other scaffolds after 12weeks of implantation.It demonstrated that core–shell bioceramic 3D printing technique can be developed to fabricate single-phase or biphasic bioactive ceramic scaffolds with accurately tailored filament biodegradation for promoting bone defect regeneration and repair in some specific pathological conditions.

HYDROTHERMAL SYNTHESIS OF NANO-METER MICROPOROUS ZINC FERRITE

Nano-meter microporous zinc ferrite was prepared by a hydrothermal method, using triethylamine as a template. Adsorption curves showed that the product had a microporous structure. The effects of precursor pH, reaction temperature and reaction time on the preparation were studied, yielding optimal conditions: pH=11, 448 K, 360 min. The morphology of zinc ferrite as observed by TEM, showed that zinc ferrite was well-crystallized and well-dispersed with little conglomeration.

Pollens derived magnetic porous particles for adsorption of low-density lipoprotein from plasma

Adsorption of low-density lipoprotein from plasma is vital for the treatment of dyslipidemia.Appropriate adsorbent material for efficient and selective adsorption of low-density lipoprotein is highly desired.In this work,we developed pollens-derived magnetic porous particles as adsorbents for this purpose.The natural pollen grains were modified to obtain high surface porosity,a large inner cavity,magnet responsiveness,and specific wettability.The resultant particles exhibited satisfying performance in the adsorption of a series of oils and organic solvents out of water.Besides,the particles were directly utilized to the adsorption of low-density lipoprotein in plasma,which showed high selectivity,and achieved an outstanding adsorption capacity as high as 34.9%within 2 h.Moreover,their salient biocompatibility was demonstrated through simulative hemoperfusion experiments.These features,together with its abundant source and facile fabrication,makes the pollens-derived magnetic porous particles excellent candidate for low-density lipoprotein-apheresis and water treatment applications.

Impacts of temperatures and phosphoric-acid modification to the physicochemical properties of biochar for excellent sulfadiazine adsorption

The textural properties and surface chemistry of phosphoric acid-modified biochars(PABCs)prepared at different pyrolysis temperatures(500-700℃)were studied based on the results obtained from XRD,SEM,BET,FT-IR,Raman,XPS and elements analyses.PABCs prepared at higher temperatures tended to possess a bigger proportion of microporous structure.The adsorption capacity and initial rate of PABCs for sulfadiazine(SDZ)were notably improved to 139.2 mg/g and 9.66 mg/(g min)as calculated from the Langmuir model.The adsorption equilibrium time was only one quarter of that without modification.The H_(3)PO_(4) modification was advantageous to produce phosphate and break functional groups to form disordered carbon structure abundant of micropores.The enhancement in the adsorption of SDZ was due to the confinement effect of hydrophobic cavities from the mircoporous structure and theπ-πelectron-donor-acceptor interaction.Specially,PABCs exhibited stable adsorption capacities at a wide pH range(3.0-9.0)or relatively high concentrations of coexisting ions.