The CH stretching features on diamonds of different origins

Surface CH stretching features on diamonds from various sources have been explored using Fourier transform infrared spectroscopy and Raman spectroscopy. The exploration encompasses the samples of natural, meteoritic, and synthetic diamond crystallites produced by high-pressure/high temperature, and detonation methods. To obtain the infrared spectra, the diamond samples are first surface-cleaned by oxidation and then hydrogenated using atomic hydrogen created by hot tungsten filaments under vacuum. Sharp and distinct features, corresponding to the CH stretch of tertiary C on C(111)-1 × 1, are observed at 2835 cm^− 1 for samples of different origins, but the peak shape depends on the surface morphology. For meteoritic and detonation-synthesized diamonds, however, the 2835 cm^− 1 peak is completely missing. We attribute this observation to a domain size effect, where the sizes of the C(111)-1 × 1 facets created on these two diamond samples (3 and 5 nm in diameter, respectively) by H-etching are too small to yield the characteristic CH stretching feature. This study gives a detail analysis on the IR spectra of the CH stretching feature on various diamond and diamond films.     

Mineralizer-Assisted Solvothermal Synthesis of Manganese Sulfide Crystallites

Manganese sulfide (MnS) crystallites with varying morphology and polymorph can be synthesized via a solvothermal process assisted by mineralizers. It was found that KOH or KNO₃ as a mineralizer played a key role in the crystallization and development of different kinds of MnS crystallites. Adding KOH in the solvothermal process resulted in the formation of α-MnS crystallites, but γ-MnS could be produced by introducing KNO₃ as a mineralizer. The morphology control was also available.     

Morphology of nascent polyoxymethylene obtained by polymerization of trioxane in nitrobenzene solution

The morphology of the crystal structure of nascent polyoxymethylene (POM) obtained by cationic polymerization of trioxane in nitrobenzene was investigated by optical and electron microscopy. It was found that the morphology depends on temperature and conversion of polymerization at constant initial monomeric concentration (1.5 mol/l). Morphological changes were observed near the equilibrium concentration of trioxane in nitrobenzene (1.5 mol/l, 35°C). At lower temperatures (10–30°C), thin lamellar crystallites, organized in spherulites, are formed by successive polymerization and crystallization. At higher temperatures (40–90°C), thick crystallites organized in oval structures are formed by simultaneous polymerization and crystallization. Peculiarities of crystal formation of POM, obtained by simultaneous and successive polymerization and crystallization, are discussed.     

Powder Characteristics of Pb(Mg1/3Nb2/3)O3 Prepared by Molten Salt Synthesis

Lead magnesium niobate (Pb(Mg_1/3Nb_2/3)O₃, PMN) was prepared by a molten salt synthesis method. Powder characteristics were greatly influenced by the processing parameters, such as amount of salt, species of salt, and the presence of excess PbO. Grown in sulfate salts, PMN crystallites showed faceted morphology with a bimodal particle-size distribution in which the smaller particles were in the submicrometer range. The presence of excess PbO in the sulfate salts greatly influenced the faceted morphology and resulted in rounded PMN crystallites. The possible origin of particle morphology changes due to the processing parameters is discussed.     

Effect of pH of Medium on Hydrothermal Synthesis of Nanocrystalline Cerium(IV) Oxide Powders

Well-crystallized cerium(IV) oxide (CeO₂) powders with nanosizes without agglomeration have been synthesized by a hydrothermal method in an acidic medium by using cerium hydroxide gel as a precursor. The relationship between the grain size, the morphology of the CeO₂ crystallites, and the reaction conditions such as temperature, time, and acidity of the medium was studied. The experiments showed that with increasing reaction temperature and time, the CeO₂ crystallites grew larger. The crystallites synthesized in an acidic hydrothermal medium were larger and had a more regular morphology than the ones synthesized in a neutral or alkaline medium when the reaction temperature and time were fixed. The CeO₂ crystallites synthesized in an acidic medium were monodispersed; however, there was vigorous agglomeration among the grains synthesized in a neutral or alkaline medium. It was demonstrated that the hydrothermal treatment was an Ostwald ripening process and the acidity (pH) of the used hydrothermal medium played a key role in the dissolution of smaller grains. It is proposed that the dissolution process can control the kinetics of the growth of larger grains.     

Initial stages of tin electrodeposition from sulfate baths in the presence of gluconate

Tin electrodeposition in its initial stages in acid sulfate/gluconate baths was studied with varying tin and gluconate concentrations using potential-controlled electrochemical techniques. The deposit morphology was observed by scanning electron microscopy (SEM). A comparison with tin electrodeposition from acid sulfate baths in the absence of gluconate was also carried out. Use of a highly acidic bath leads to nonuniform deposits, even in the presence of gluconate; at pH 4 deposits are uniform, brilliant and suitable for finishing applications. Tin crystallites have a well defined morphology which depends on bath agitation conditions. In the absence of agitation, the crystallites have the same tetragonal shape as in a sulfate bath without gluconate.     

Strong effects of Tween 20 additive on the morphology and performance of poly(vinylidene fluoride) hollow‐fiber membranes

Poly(vinylidene fluoride) (PVDF) hollow‐fiber membranes were prepared from a Tween 20/water/triethyl phosphate/PVDF system. The effects of Tween 20 on the morphology and properties of the membranes were explored. Field emission scanning electron microscopy imaging indicated the presence of skinlike layers on both surfaces of the membranes. In the cross section, a bicontinuous morphology comprised of interlocked crystallites was observed. As the dosage of Tween 20 was raised, the size and quantity of nanopores on the surfaces increased, and the morphology of the crystallites in the cross section changed from sheaflike to sticklike. Tween 20 was removed almost completely during the membrane‐formation process, as validated by Fourier transform infrared–attenuated total reflection and ¹H‐NMR spectrometry. Dextran filtrations were preformed to demonstrate the potential applications of these membranes in separation processes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44600.     

Preferential precipitation of calcium hydroxide on alkali-resistant glass fibres

Carbon discs 12.5 mm diameter were coated with roughly equal areas of Portland cement (PC) and Alkali Resistant Glass (ARG); PC and Blastfurnace slag; PC and Fly Ash (FA): and with combinations of PC, ARG and BFS and PC, ARG and FA. The dry materials were separated by blank strips of carbon. The reaction was started by wetting the dry components with water. The discs were then stored at 100 percent relative humidity until they were examined in the SEM.

Calcium Hydroxide (CH) released into solution by hydration of PC could thus precipitate on ARG or BFS or FA or on the blank areas of carbon.

In all cases CH displayed a remarkable affinity for ARG in distinct preference to BFS and FA which are also known to attract deposits of CH.

Further the morphology of CH deposited on glass suggested that any tendency of the fibre to move relative to the matrix would result in principal compressive stress perpendicular to the fibre axis. This would reduce the longitudinal strength.

Embrittlement of Glass Reinforced Concrete with age is attributed to the affinity of CH with ARG and the morphology of CH precipitate.     

Strain-induced crystallization I. Limiting extents of strain-induced nuclei

This paper points out that interpretations from stress changes alone during oriented crystallization have led to widely different proposed chain conformations and consequently very different crystallization mechanisms for strain-induced crystallization (SIC). Many of the proposals, including the one by Keller and Machin which takes into account some electron microscopy and X-ray observations, show varying degrees of incompatibility with existing stress relaxation, kinetic or morphological data on SIC. Another problem lies in the difficulty with proper interpretation of observed morphology on samples which have been Subjected to additional thermally-induced crystallization (TIC) after SIC, especially, in the absence of prior characterization of SIC crystallites, the finding of a fibrillar-to-lamellar transformation in stretched polymers upon additional TIC (Part H) also indicates that the generally-observed oriented lamellar morphology has a much more subtle origin than-that depicted by most crystallization models. Part I discusses our previously published morphological data on the characteristics of SIC crystallites from the melt, which includes: (a) their melting point elevation, (T_m » T°_m), (b) their nearly perfect crystalline orientation function (f_c ～ 1), (c) their fast rates of crystallization (t_1/2 < 1 sec), and (d) their fibrillar morphology and limited dimensions along the fibrillar stretch axis (～100Å). Examples of morphology of SIC from the glass and from stirred solution are also included to show the overall similarity of fibrillar morphology brought about by stretching.     

Morphological analysis of linear low density polyethylene films by atomic force microscopy

Atomic force microscopy has been used to investigate the morphology of hexene linear low density polyethylene (LLDPE) blown film in the undrawn and drawn states. The morphology of the undrawn film, which is biaxially oriented due to the nature of the extrusion process, is composed of crystallites, which consist of aggregates of lamellae. Elongation of the film caused these crystallites to undergo deformation, resulting in the gradual formation of a fibrillar structure in the draw direction. The transformation of these crystallites into fibrils corresponded with an initial increase in the surface roughness, until 250% elongation. Further extension of the film to 450% caused the surface roughness to reach a plateau. The changes observed in the surface roughness and morphology indicate that drawing of the film caused the crystallites to tilt and slip, rupturing crystalline blocks, which then develop into a fibrillar structure. Further extension of these initial fibrillar structures resulted in a more oriented fibrillar morphology. Wide‐angle x‐ray scattering clearly showed the orientation of the crystals with respect to the draw direction throughout the film. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 777–784, 2002     

Attenuated total reflectance Fourier transform infra-red studies of crystalline-amorphous content on polyethylene surfaces

Intensity ratios of the bands due to CH₂ bending and rocking normal vibrations, used as a measure of the surface crystallinity in polyethylene, are examined by attenuated total reflectance Fourier transform infra-red (ATR FT_i.r.) spectroscopy. This study shows that the ATR optical dispersions and the orientation of surface crystallites have a substantial effect on the crystallinity measurements. It appears that improper analysis of strong, overlapping i.r. bands in the ATR spectra may generate systematic errors. While the optical effects associated with ATR measurements can be accounted for and corrected by the use of the Kramers-Kronig transform and Fresnel's equation, determination of the crystallinity gradients and orientation of the crystallites requires detailed polarization studies and theoretical considerations.     

Bi4Ge3O12（BGO）微晶粒的水热法制备

以Ｂｉ２Ｏ３和ＧｅＯ２粉为起始物料，经水热反应制得Ｂｉ４Ｇｅ３ｏ１２（ＢＧＯ）微晶粒。晶粒粒度为５－２０μｍ；结晶完好的晶粒呈多面体状。文中对所用前驱物的形式、水热反应的物理－化学条件与产物物相，晶粒形貌关系作了总结。     

Crystallization of poly(3‐hydroxybutyrate) with stereocomplexed polylactide as biodegradable nucleation agent

Crystallization kinetics behavior and morphology of poly(3‐hydroxybutyrate) (PHB) blended with of 2–10 wt% loadings of poly(L ‐ and D ‐lactic acid) (PLLA and PDLA) stereocomplex crystallites, as biodegradable nucleating agents, were studied using differential scanning calorimetry, polarizing‐light optical microscopy (POM), and wide‐angle X‐ray diffraction (WAXD). Blending PLLA with PDLA at 1:1 weight ratio led to formation of stereocomplexed PLA (sc‐PLA), which was incorporated as small crystalline nuclei into PHB for investigating melt‐crystallization kinetics. The Avrami equation was used to analyze the isothermal crystallization of PHB. The stereocomplexed crystallites acted as nucleation sites in blends and accelerated the crystallization rates of PHB by increasing the crystallization rate constant k and decreasing the half‐time (t_1/2). The PHB crystallization was nucleated most effectively with 10 wt% stereocomplexed crystallites, as evidenced byPOM results. The sc‐PLA complexes (nucleated PHB crystals) exhibit much small spherulite sizes but possess the same crystal cell morphology as that of neat PHB based on the WAXD result. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Sintering and recrystallization of small metal particles. Loss of surface area by platinum-black fuel-cell electrocatalysts

Operation of high-surface-area platinum-black electrodes in hot concentrated phosphoric acid produces a loss of surface area with time, giving consequent loss of performance.

The loss of surface area is the result of sintering produced by surface migration of platinum atoms on the individual crystallites to sites of lower surface energy. As the sintering process is a surface phenomenon, potential changes cause changes in the surface tensions of the metal crystallites giving rise to variations in sintering rate. The rate of sintering is greatest at low potentials and smallest at high.

Carbon monoxide and phosphoric acid impurities adsorbed on the surfaces of the platinum crystallites retard the sintering at low potentials. Similar adsorption-induced changes in physical properties of materials (Rebinder effects) have been observed with ionic solids, but in only a few instances is this effect known to operate on metals. The presence of a strongly adsorbed molecule on the metal surface alters the inter-atomic bonding between the surface metal atoms and illustrates the dependence of the sintering mechanism on the mobility of the surface atoms. Changes in crystallite morphology accompany the sintering process and are considered to be the result of a surface rearrangement of ad-atoms or clumps with elimination of the [100] faces.

The activation energy for the sintering process is 25 ± 2 kcal/mole at 0·5 V and is not significantly changed by adsorbed carbon monoxide on the platinum.     

Development of stress-crystallized morphology during melt-spinning of polypropylene fibers

Melt-spinning of isotactic polypropylene was performed in an effort to assess how the flow field that exists within a filament affects final as-spun fiber morphology. It was concluded that the molten filament deforms chiefly by elongational flow, with some small amount of shearing flow bearing localized near the filament periphery. The resulting crystal texture is mostly comprised of lamellae oriented perpendicular (chain direction parallel) to the fiber axis, but a minority population of crystallites whose orientation is orthogonal (chain direction perpendicular) to the primary population is also present in these fibers. Post-drawing steps initially cause crystallites to rotate toward the axial direction, while the chains within them undergo intralamellar slip and become better oriented parallel to the fiber axis. At larger extensions, lamellar crystallites are pulled into microfibrillar units.     

Bismuth Titanate from Mechanical Activation of a Chemically Coprecipitated Precursor

Most of the chemistry-based preparation routes for bismuth titanate (BIT) involve calcination at elevated temperatures in order to realize precursor-to-ceramic conversion. In a completely different approach using an amorphous BIT hydroxide precursor, nanocrystalline particles of layered perovskite BIT are synthesized by mechanical activation, skipping the detrimental crystallite coarsening and particle aggregation encountered at high temperatures. Mechanical activation leads to nucleation and steady growth of BIT crystallites in the amorphous precursor matrix, while Bi₂O₃ is involved as an intermediate transitional phase. The activation-derived BIT particles demonstrate a rounded morphology of ∼50 nm in size. This is in contrast to the BIT derived from calcination of the coprecipitated precursor at 600°C that is dominated by coarsened platelike particles. The former is sintered to a density of >95% theoretical at 875°C for 2 h, leading to a dielectric constant of ∼1260 when measured at 1 MHz and the Curie temperature of 646°C.     

Structural aspects of the oxidative coupling of methane

A comparative study of the structure and catalytic performance for methane oxidation is reported for two samples of MgO. MgO prepared by thermal decomposition of the basic carbonate is found to give higher selectivities to C₂ hydrocarbons in contrast to MgO obtained from burning metal ribbon in air. Additionally, the two oxides were found to exhibit different morphologies; MgO (ribbon residue) consisted mainly of single MgO crystallites with regular cubic structure, whereas MgO (ex basic carbonate) comprises of agglomerates of smaller MgO crystallites. The combination of the catalytic and structural studies demonstrate that the morphology of MgO is an important factor in the methane coupling reaction.     

Spontaneous Assembly in Organic Thin Films Spread on Aqueous Subphase: A Scanning Force Microscope (SFM) Study

Structure, morphology, and mechanical properties of mono- and several-layer structures of amphiphiles or pure n-alkane crystallites generated by spontaneous self-assembly on aqueous subphase have been analyzed by scanning force microscopy (SFM). Pure-component and heterogeneous mixtures of molecules were allowed to spread and self-assemble without compression on an aqueous subphase. The self-assembled films were transferred to an atomically smooth mica substrate by drainage for measurement using SFM. Results were compared with a variety of techniques including cryo-transmission electron microscopy, grazing incidence X-ray diffraction, X-ray reflectivity, and reflectance/absorption infrared spectroscopy. Whereas the collaborative techniques provide spatially-averaged information, we find that the SFM accesses both individual crystallites and amorphous material, thus providing unique information on the morphology, number of layers, and complementary structural features.     

Structure and stability analyses of collagen hydrolysate coacervates triggered by ethanol in aqueous solution

The coacervation of collagen hydrolysate (CH) in aqueous solution was triggered by ethanol as poor solvent which has a significant effect on the aggregation and rearrangement of CH macromolecules. In this work, the static coacervation was performed to investigate the influences on coacervates morphology. CH concentration and ethanol temperature had significant influences on coacervates morphology. Treatment for the CH solution of high concentration by lower temperature ethanol (<25°C) tended to form the microspheres morphology. High temperature ethanol was not conducive to CH coacervation, while enhanced the CH solubilization in water-ethanol. By directly mixing CH solution and ethanol under agitation, dispersed nanospheres could be successfully obtained in suspension. The turbidity and absorbance tests were carried out to further study the CH coacervation behaviors. The stability of milky suspension induced by ethanol was evaluated by a self-built light transmittance measurement. The result showed that the absorbance and turbidity of CH suspension increased with increasing the V_EtOH ratio and CH concentration. The milky suspension with high V_EtOH would turn clear gradually due to the CH solubilization in water–alcohol. The maximum absorbance presented at pH around 7 where the charges of CH molecules were negative. The coacervation behaviors of CH were very different from that of collagen and gelatin, owing to its lower molecular weight.     

Deformation of Polyether‐Polyester Thermoelastoplastics: Mechanothermal and Structural Characterisation

The complex investigation of copoly(ether‐ester) based on poly(butylene terephthalate) (PBT) and poly(tetramethylene oxide) (PTMO) reveals its microphase separated nanodomain structure. Initial morphology includes the stacks of crystalline blocks of α‐PBT embedded in amorphous matrix with the different degree of continuity of the crystalline network. Two types of amorphous regions can be distinguished, the PTMO‐rich phase and the other one containing the PTMO and PBT segments. Reduction of PBT content and proper decrease of its fragments length results in dramatic change in crystalline ordering, the crystallites became smaller and distorted, and more and more PBT segments are included in the amorphous phase. The initial reversible stage of deformation is controlled mostly by elastic deformation of amorphous phase, highly constrained by the network of crystallites. The further stretching results in plastic deformation and reorganisation of the crystalline blocks of PBT and a new crystalline morphology arises. Moreover, at large deformations the soft blocks of PTMO can crystallise and form very distorted paracrystalline regions. Finally, at high enough stress (≈25–30 MPa) the transition from α to β crystalline form in PBT crystal lattice occurs due to conformational changes in the tetramethylene segments. After large deformation, both the morphology and the polymer conformations are far from the equilibrium state. Annealing of the stretched samples at high temperature results in partial recovery of material properties, however the morphology is still far from the initial one even after such annealing.