Synthesis and Characterization of NiFe2O4 Nanoparticles via Solid‐State Reaction

NiFe₂O₄ nanoparticles were synthesized via solid‐state reaction. The effects of the reaction parameters, namely dispersant content, calcination temperature and annealing time on particle size and morphology were investigated. Magnetic properties of NiFe₂O₄ nanoparticles were tested. The formation mechanism of nanoparticles by solid‐state reaction was also discussed. The results indicated that the synthesized nickel ferrite particles were of nanometer size with different morphologies by slight variation of the reaction conditions. The solid‐state reaction technique is a simple, convenient, inexpensive and effective preparation method of NiFe₂O₄ in high yield.     

Catalyzed Solid‐State Polyamidation

Summary: The current study is focused on key experiments on catalyzed SSP, examining the effect of selected phosphonates on the overall process rate. Catalyst incorporation was achieved through melt blending in a single screw extruder, providing a suitable and homogenous starting material for the reaction in the solid phase. More specifically, the post‐polycondensation runs were performed in a fixed bed reactor under flowing nitrogen at 160 and 200 °C. The additives used were found to catalyze the reaction in the solid phase, resulting even in tripling the solution relative viscosity after 4 h of SSP. Differences in the catalytic performance of the added materials were observed and correlated to the catalysts properties and morphology. An indicative potential catalysis mechanism is suggested, in which reactivity enhancement through partial attachment of the phosphorus compounds on the polyamide chain is the key step. Finally, the kinetics of the process were examined based on a power‐law rate expression, which was further modified so as to relate the apparent SSP rate constant with the phosphorus concentration.

SSP rate constants as a function of catalyst content.     

Penicillin Acylase‐Catalyzed Solid‐State Ampicillin Synthesis

The ability of immobilized penicillin acylase from E. coli to retain a remarkable catalytic activity in solid‐state systems has been demonstrated. Stabilization of immobilized penicillin acylase by inorganic salt hydrates allowed us to exploit nearly the whole catalytic activity of the enzyme at a very low water content. Using this technique, enzymatic synthesis of ampicillin in solid‐state systems was performed with high yields (up to 70% starting from equimolar mixture of reagents) and rates comparable to the corresponding values in homogeneous solutions and heterogeneous systems, “aqueous solution‐precipitate”. Peculiarities of the enzymatic solid‐state acyl transfer process, such as absence of the clear‐cut maximum on the ampicillin accumulation curves and dependence of the synthetic efficiency on the enzyme loading, have been observed. The space‐time yield of solid‐state enzymatic ampicillin synthesis was shown to be up to ten times higher compared to the homogeneous solutions and heterogeneous “aqueous solution‐precipitate” systems.     

Fabrication of Transparent Dysprosium Aluminum Garnet (Dy3Al5O12) Ceramics via a Solid‐State Reaction Method

Polycrystalline, transparent Dy₃Al₅O₁₂ ceramics were firstly fabricated by a solid‐state reaction method using high‐purity Dy₂O₃ and Al₂O₃ powders. The fully dense Dy₃Al₅O₁₂ ceramic with an average grain size of less than 10 μm was obtained by vacuum sintering at 1820°C for 6 h. The in‐line transmittance of the optimized sample reaches 80% in the visible region. Scanning electron microscopy reveals that no secondary phases and almost no pores are observed at grain boundaries or triple junctions, and the fracture mode of the ceramic is mainly transgranular. The Dy₃Al₅O₁₂ ceramic is promising for magneto‐optical applications. Verdet constant of the Dy₃Al₅O₁₂ transparent ceramic is as high as ?0.41 min·(Oe·cm)^?1.     

Nanocatalysis in Polyamide 6.6 Solid‐State Polymerization

Solid‐state polymerization (SSP) of a poly(hexamethyleneadipamide) (PA 6.6)/clay nanocomposite system was studied. SSP runs were performed in a fixed‐bed reactor, at temperatures 160–200 °C and reaction times up to 8 h. The influence of clay presence on the PA 6.6 SSP rate constant was herewith quantified for the first time to prove significant acceleration of the SSP process. A catalysis mechanism was suggested, according to which the positive effect of clay is of a synergistic origin attributed to nucleated crystal morphology, that increased the concentration of reactive end groups in the amorphous regions, to chain extension performed by clay SiOH groups, and to thermal protection of the polyamide matrix due to the presence of the nanoparticles.

     

Sinterability of β-Calcium Orthophosphate Powder Prepared by Spray-Pyrolysis

Mixed solutions of Ca(NO₃)₂ and (NH₄)₂HPO₄ with Ca/P = 1.50 were spray-pyrolyzed at 600°C to produce β-calcium orthophosphate (β-Ca₃(PO₄)₂) powder; the spray-pyrolyzed powder was ground and then calcined at 600°C for 1 h. The best crystalline β-Ca₃(PO₄)₂ powder was obtained from the solution with 1.80 mol.L^–1 Ca(NO₃)₂, 1.20 mol.L^–1 (NH₄)₂HPO₄. The resulting powder was composed of primary particles with sizes of <0.5 μm. Dense β-Ca₃(PO₄)₂ ceramics with a relative density of 96.1% could be fabricated by firing this compressed powder at 1070°C for 5 h.     

Crystallinity and Property Enhancements in Neat Polylactic Acid by Chilled Extrusion: Solid‐State Shear Pulverization and Solid‐State/Melt Extrusion

Polylactic acid (PLA) is a biopolymer of significant interest to both industry and the scientific community, but an incomplete understanding of the practical processing‐structure‐property relations is limiting its application range. The study applies alternative, chilled extrusion technologies called solid‐state shear pulverization (SSSP) and solid‐state/melt extrusion (SSME) to neat, commercial PLA, and investigates the effect of the resulting morphological features upon the thermomechanical behavior. Although conventional, heated twin‐screw extrusion leads to significant thermal degradation of PLA chains, which in turn facilitates crystal growth due to enhanced chain mobility, chilled SSSP imparts chain defects and branching, which serve as heterogeneous nucleation sites in the polymer and promotes the formation of a rigid amorphous phase. A hybrid SSME process brings unique interplay of both chain architecture effects, resulting in a synergistic thermomechanical behavior involving the α' crystal polymorph formation. POLYM. ENG. SCI., 59:E286–E295, 2019. © 2019 Society of Plastics Engineers     

Characterization of Solid‐State Reaction of Barium Carbonate and Titanium Dioxide by Spatially Resolved Electron Energy Loss Spectroscopy

A mixture of ultrafine submicrometer‐sized BaCO₃ powder and TiO₂ (rutile) powder was calcined in air at 700°C, 800°C, and 900°C, and then quenched to liquid nitrogen temperature in each case. The cross‐sectional quenched specimens were characterized by spatially resolved electron energy‐loss spectroscopy (SR‐EELS). The energy‐loss near‐edge structures (ELNES) were sequentially extracted at 1.3 to 5.3 nm in width from SR‐EELS image obtained from the rectangularly cut SR‐EELS slit aperture put on the synthesized BaTiO₃ layer and TiO₂ rutile powder. The ELNES of Ti‐L_2,3 edges and Ba‐M_4,5 edges clearly show fine structure changes from the surface of BaTiO₃ layer to the TiO₂ bulk region reflected from crystallinity of synthesized BaTiO₃, lattice distortion of TiO₂ caused by Ba diffusion, and lattice misfit between BaTiO₃ and TiO₂ without formation of Ba₂TiO₄ and other titanate phases.     

Magnetic Properties of Mixed Valence La(AgSr)MnO3 Manganites Obtained by Solid‐State Reaction Method

In this work, we present a systematic study on the effect of monovalent and divalent cation inclusion on the magnetic properties of the manganites series La_0.80(Ag_1?xSr_x)_0.20MnO₃ (x = 0.0–1.0) synthesized by the solid‐state reaction method. The decreasing Sr:Ag proportion across the compositional series was verified by X‐ray photoelectron spectroscopy. Concerning magnetic properties, the hysteresis curves manifested an initial paramagnetic response at x = 0.0, followed by a progressive ferromagnetic behavior with an optimum Ag:Sr ratio at x = 0.75, for which an enhanced saturation magnetization of 51 Am²/kg and a Curie temperature of 336 K were recorded. Results are explained on the basis of the effect of the increasing unit cell volume on the double exchange interaction between magnetic Mn³⁺– Mn⁴⁺ atoms.     

Iminium Salts in Solid‐State Syntheses Giving 100% Yield

Numerous reaction types in the field of iminium salts are performed in the gas‐solid and solid‐solid techniques in order to reach 100% yield. The stoichiometric runs are waste‐free and do not require costly workup. Frequently, iminium salts were avoided, as acid catalysis was dispensable. Thioureas and α‐halogenated ketones give a variety of 2‐aminothiazoles via thiuronium salts in quantitative yield. A new intramolecular solid‐state thermal condensation is reported. Enaminoketones are synthesized quantitatively from anilines and 1,3‐diketones without catalysis and those can be used for quantitative solid‐state 4‐cascade reactions. Solid paraformaldehyde is used to produce methylene imines and internally trapped methylene iminium salts. Benzoylhydrazones are produced again without catalysis in the solid state. Vacuum and ball‐mill techniques are particularly useful in the production of highly sensitive iminium salts. Hexahydro‐1,3,5‐triazines cyclorevert upon exposure to HCl gas to give solid arylmethylene iminium chlorides as new versatile reagents. These are used in arylaminomethylations of β‐naphthol and of themselves to give Troeger's bases in 3‐cascades. More direct are 4‐cascade Troeger's base syntheses by dissolving hexahydro‐1,3,5‐triaryltriazines in trifluoroacetic acid. Alkylations of imines with trimethyloxonium tetrafluoroborate and triphenylmethyl cation give highly sensitive quaternary iminium salts in the ball‐mill. The products are characterized by spectroscopic techniques and density functional theory (DFT) calculations at the B3LYP 6‐31G* level. Molecular movements in the crystal and surface passivation are investigated with atomic force microscopy (AFM) techniques.     

Gas‐Phase and Solid‐State Simultaneous Mechanism for Two‐Step Carbothermal AlON Formation

AlON powders were synthesized by two‐step carbothermal reduction nitridation method, which includes thermal treatment of Al₂O₃/C mixtures at 1200°C–1600°C for 2 h, followed by subsequent heating at 1750°C for 1.5 h in N₂ flow. The effects of soaking temperatures of the first step on phase compositions and morphologies of the final products were investigated. It is found that the variation in precalcination does not have impact on phase compositions of the final products, which are all single‐phase AlON. However, it impacts the AlON morphology significantly. Lower precalcining temperature results in severer agglomeration of AlON powder. Obvious terrace surface morphology was also observed on AlON particles with lower precalcination. Both the agglomeration and terrace‐like morphology are attributed to the gas‐phase reaction induced by the residual carbon in the AlON formation process. An AlON formation mechanism including simultaneous solid‐state reaction between Al₂O₃ and AlN, and gas‐phase reaction among Al (g), O₂ (g), and N₂ (g) with the presence of residual carbon is proposed based on the experiment, kinetics, and thermodynamics. The mechanism was further examined by carefully designed control experiments, which was confirmed to be both experimentally and theoretically valid.     

Solid‐State Sintering of Glasses with Optical Nonlinearity from Mesoporous Powders

Silica glasses dispersed with Pt nanoparticles and Ag nanoparticles are derived from solid‐state sintering of mesoporous silica SBA‐15 encapsulated with Pt nanoparticles and Ag nanoparticles, respectively. Using mesoporous powders for sintering is a facile method to lower synthesis temperature for glass making and to efficiently disperse noble metal nanoparticles in silica glass matrix. The included nanoparticles still play their functional roles in impacting on optical properties of the glass products prepared by this novel method. The glass dispersed with Pt nanoparticles exhibits brown color due to the interband electron transition of Pt nanoparticles. The coloring effect of surface plasmon resonance absorption from Ag nanoparticles colors the glass dispersed with Ag nanoparticles with yellow. Open‐aperture and closed‐aperture Z‐scan methods are applied to measure third‐order nonlinear absorption and refraction coefficient of the composite glasses, respectively, under femtosecond laser radiation at 880 nm wavelength. The glass dispersed with Pt nanoparticles behaves intense nonlinear absorption comparing with nonlinear refraction in magnitude, which could be attributed to interband electron transition by monophoton absorption of Pt nanoparticles. The glass dispersed with Ag nanoparticles shows stronger nonlinear refraction than saturated absorption. The dominant contribution to third‐order optical nonlinearity of silica glass dispersed with Ag nanoparticles is intraband transition of free electrons near the Fermi surface of Ag nanoparticles. This method may have potential applications for fabricating silica glasses dispersed with ultrafine functional particles, which are potentially applicative in the fields of photonics.     

Solid‐State Conversion of Single Crystals: The Principle and the State‐of‐the‐Art

Solid‐state conversion of single crystals from polycrystalline materials has the advantages of cost‐effectiveness, chemical homogeneity, and versatility over the conventional melt growth and solution growth methods, particularly for systems with high melting points, incongruent melting, high reactivity (volatility), and phase transformations at high temperature. Nevertheless, for commercial production, this technique has only been successful in a few limited systems, in particular ferroelectric systems. This is mostly because of the difficulty in controlling the microstructure, particularly suppressing grain growth in the polycrystal during its conversion. This article describes the principle and the current status of the solid‐state conversion of single crystals. We first introduce the recently developed principle of microstructural evolution to explain the basis of the microstructure control in polycrystals for solid‐state conversion. We then report recent technical developments in fabricating single crystals by the solid‐state single crystal growth (SSCG) method and their physical properties. The SSCG method is expected to be studied and utilized more widely in fabricating single crystals with complex compositions as a strong alternative to the melt growth and solution growth methods.     

Mechanoelectrical Conversion in Highly Ionic Conductive Solid‐State Polymer Electrolyte Membranes

A novel phenomenon of mechanoelectrical conversion in a flexible solid‐state polymer electrolyte membrane (PEM) is presented, hereafter denoted as flexoelectric effect. The flexoelectric coefficient (≈323 µC m^?1), that is, a measure of the converted mechanoelectrical energy, is the highest among all flexoelectric materials hitherto reported. It is proposed in this work that the flexoelectricity in PEMs operates based on electrical energy generation driven by ion polarization/depolarization across the PEM subjected to a pressure gradient during bending. Of particular interest is the phenomenon of polarity switching during bending, that is, reversal of the polarization direction with increasing succinonitrile (SCN) concentration (i.e., 10–20 wt%). The size disparity between the solvated cations and anions is attributed as the key factor in determining the polarization direction, which is responsible for the polarity switching. Of particular importance is that the present flexoelectric PEM itself is a key component of the solid‐state lithium ion battery and thus their integration opens up a new avenue for energy harvesting and storage devices.     

Reactive Energetic Plasticizers for Energetic Polyurethane Binders Prepared via Simultaneous Huisgen Azide‐Alkyne Cycloaddition and Polyurethane Reaction

Reactive energetic plasticizers (REPs) for use in glycidyl azido polymer (GAP) based polyurethane (PU) energetic binders were investigated. These REPs consisted of an activated terminal alkyne group that was expected to give rise to Huisgen azide‐alkyne 1,3‐dipolar cycloaddition within the specific pot life for a PU formulation to prevent the migration of plasticizers, and with a gem‐dinitro group as an energy resource. A quantitative miscibility investigation between the plasticizers and uncured GAP showed that REPs exhibited better miscibility than conventional energetic plasticizers. The plasticization effect of the REPs on the GAP prepolymer with respect to the reduction of the viscosity illustrated REPs can effectively reduce the viscosity of the GAP prepolymer from 6,015 cP to 150–240 cP at the processing temperature when 50 wt‐% of REP was added. A comparison of the click reactivity and activation energies (E_a) of REPs and GAP prepolymer elucidated that the reactivity of azide‐alkyne cycloaddition depended on the dipolarophilicity of REPs which could be controlled by adjusting the length of methylene spacer between electron‐withdrawing groups (EWG) and neighboring alkynes in REPs. Thermogravimetric analysis manifested REP/GAP‐based PU binders maintained the thermal stability of the control GAP‐based PU binder. The mechanical properties and impact insensitivity of the GAP‐based PU binders were also improved by the incorporation of REPs.     

Characterization of Nanocrystalline Forsterite Fiber Synthesized via the Sol–Gel Process

An alkoxide sol–gel route was developed to prepare forsterite fibers. Transparent precursor gel fibers were converted to the crystalline phase of forsterite by heating above 550°C. Fibers heated at 1100°C for 2 h showed a porous microstructure with nanocrystalline sizes of about 50–100 nm. The structural evolution of fibrous gel was characterized. Effects of water and ethanol content on microstructures and strengths of fired fibers are also discussed. Some properties of the fired fibers were investigated.