Is the Crystalline Lattice Structure in Nanocrystalline Materials Different from the Perfect Crystal Lattice?

A thermodynamic analysis of the ultrafine crystallites in nanocrystalline materials was presented in this work.It was deduced that the structure of the nm-sized crystalline grains is different from the perfect crystal lattice,characterized by two possible structure changes;supersaturation of alloy ele- ments and crystal lattice distortion resulted from supersaturation of vacancies.Some experimental ev- idences in the literature,which are in agreement of the thermodynamic consideration,indicate that the structure changes in the nm-sized crystallite seems to be a consequential feature of the nanocrystalline materials.

Effects of Additive AlCl_3 on Crystal Phase, Particle Size and Microstructural Parameters of Nanocrystalline TiO_2 Prepared by HF-PCVD

Nanocrystalline TiO2 was prepared by high frequency plasma chemical vapor deposition (HF-PCVD). The effects of additive AlCl3 on crystal phase, particle size and microstructurai parameters of TiO2 nanocrystallites were investigated by X-ray diffraction(XRD) and transmission electron microscopy (TEM). The nanocrystallites obtained experimentally are mixture of anatase and rutile, the uniform diameters of particles are about 30 nm. The phase transformation from anatase to rutile was accelerated by AlCl3, and rutile content is increased from 26.7 wt pct to 53.6 wt pct with increasing of addition of AlCl3 from 0.0 wt pct to 5.0 wt pct. The particle size is reduced and the size distribution becomes very narrow. The crystal lattice constants have the trend to decrease, and celi volumes appear as shrinkable.

Crystal Growth Kinetics of Nanocrystalline ZnS under Surface Adsorption

The crystal growth mechanism, kinetics, and microstructure development play a fundamental role in tailoring the materials with controllable size and morphology. In this study, by introducing the strong surface adsorption of the concentrated NaOH, two-stage crystal growth kinetics of ZnS nanoparficles was observed. In the first stage, the primary particles grow into a size over a hundred times of the original volume and the growth is controlled by the crystallographically specific oriented attachment. The first stage data were fitted by the ＂multistep OA kinetic model＂ built based on the molecular collision and reaction. In the second stage, following the dispersal of nanoparficles, an abrupt transition from asymptotic to parabola growth kinetics occurs, which can be fitted by a standard Ostwald ripening volume diffusion model. The presence of surface adsorption causes the two-stage growth kinetics and permits an almost exclusive OA-based growth to dominate in the first stage.

Formation and Properties of Nanocrystalline (Fe_(0.99)Mo_(0.01))_(78)Si_9B_(13) Alloy

Polycrystalline Fe-Mo-Si-B alloys with grains sized from 15 to 200 nm were prepared by means of the crystallization method. A critical phenomenon was observed in the variations of microhardness and electrical resistivity with respect to the annealing temperature. The critical temperature is 893 K which corresponds to the average grain size of 45 nm.

Pressureless reactive sintering mechanism of nanocrystalline Bi_2O_3-Y_2O_3 solid electrolyte

The nanocrystalline Bi2O3-Y2O3 solid electrolyte material was synthesized by pressureless reactive sintering process with Bi2O3 and Y2O3 nano mixed powder as raw materials, which was prepared by a chemical coprecipitation process. The study on the behavior of nano δ-Bi2O3 formation and its grain growth showed that the solid solution reaction of Y2O3 and δ-Bi2O3 to form δ-Bi2O3 occurs mainly in the initial stage of sintering process, and nano δ-Bi2O3 crystal grains grow approximately following the rule of paracurve （（D-D0）^2=K.t） during sintering process. After sintered at 600℃ for 2 h, the samples could reach above 96% in relative density and have dense microstructure with few remaining pores, the δ-Bi2O3 grains are less than 100 nm in size.

Crystallization process and soft magnetic properties of nanocrystalline (Fe0.5 Co0.5 ) 86 Hf7 B6 Cu1 alloy used in elevated temperature applications

Nanocrystalline (Fe0.5 Co0.5 )86 Hf7 B6 Cu1 HITPERM alloy was investigated as the candidate of soft magnetic material for high temperature applications, compared with Fe86 Hf7B6 Cu1 NANOPERM alloy. Amorphous alloy ribbons were prepared by single-roller melt-spinning technology. Crystallization process of as-quenched ribbon was investigated using differential scanning calorimeter at different heating rates. The coercivity was determined from quasi-static hysteresis loop measured at room temperature using a computerized hysteresis loop tracer. X-ray diffraction with Cu Kα radiation was used to determine the structure. The vibrating sample magnetometer was usedto measure the magnetization as a function of temperature of the nanocrystllized alloys. That Co substitution for Fein alloy enhances the Curie temperature of amorphous alloy and the magnetization of nanocrystalline alloy at hightemperature. After annealing amorphous precursor, the optimum nanocrystalline alloy obtained shows the local minimum coercivity. The coercivity increases with the increasing annealing temperature corresponding to the formation of ferromagnetic phase in the secondary crystallization.

Effect of pH on Crystallization of Nanocrystalline Zirconia in a Microwave-hydrothermal Process

Nanocrystalline zirconia（ZrO） was synthesized using a microwave-hydrothermal process.The effect of pH on the crystallization of the ZrO2 powders was investigated.The phase and microstructure of ZrO2 powders were examined using X-ray diffraction（XRD）,Raman spectroscopy,and transmission electron microscopy（TEM）.Results show that pure m-ZrO2 can be obtained at low pH（pH＆lt;2）.Pure t-ZrO2 is formed at pH = 7 and 14.The size of the ZrO2 crystals is in the range of 8-26 nm and decreases with increasing pH.The formation of m-ZrO2 results from the precipitation of ZrO2 from solution.The t-ZrO2 is formed through the in-situ structural rearrangement of amorphous Zr（OH）xOy.The stabilization of t-ZrO2 is attributed to the small crystal size and the adsorption of hydroxy ions on the surfaces of the crystals.

Preparation and Study of the Crystallization Behavior of the Fe87Zr7B5-x Nanocristalline Soft-Magnetic Alloys

A series of materials of composition Fe87Zr7B6,Fe87Zr7B5Ag1,Fe87Zr7B5Cu1 have been prepared by the melt spinning method for different cooling speed to get completely or partly amorphous ribbons.It is proved that the crystallization process is composed of 2 steps.The first step is the precipitation of&-Fe only and the second step is the phase separation of&-Fe,Fe2Zr and Fe2B.All our own made materials have been used in the library monitoring system.Most of them showed a capability of triggling the alarm of the system.The triggling sensitivity at different positions and different sample geometry were investigated and the physical mechanisms were analyzed.

Crystallization Behavior and Magnetic Properties of(Fe0.6Co0.4)86Hf7B6Cu1 Alloy

Feo.eCoo.^seHfTBsCu! nanocrystalline alloy obtained in isothermal annealing process from amorphous precursor was investigated as candidate of soft magnetic materials for high temperature applications. Co substitution for Fe can enhance the curie temperature of amorphous alloy (Tc = 630 °C) and improve the magnetization of nanocrystalline alloy at high temperature ( = 1.56T at 550 °C). After annealing amorphous precursor at 550 °C for 1 hour, the optimum nanocrystalline alloy can be obtained which shows the local minimum coercivity ( = 16 A/m). The coercivity increases with the increase of annealing temperature corresponding to the formation of ferromagnetic phase in the secondary crystallization. Furthermore, additions of Hf and B elements reduce the melting temperature of the alloy studied comparing with the Fe-Co binary alloy.

Preparation and characterization of highly photoactive nanocrystalline TiO_(2)powders by solvent evaporation-induced crystallization method

Highly photoactive bi-phase nanocrystalline TiO2 photocatalyst was prepared by a solvent evaporation-induced crystallization (SEIC) method, and calcined at different temperatures. The obtained TiO2 photocatalyst was characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM) and BET surface areas. The photocatalytic activity was evaluated by the photocatalytic oxidation of acetone in air. The results show that solvent evaporation can promote the crystallization and phase transformation of TiO2 at 100°C. When calcination temperatures are below 600°C, the prepared TiO2 powders show bimodal pore size distributions in the mesoporous region. At 700°C, the pore size distributions exhibit monomodal distribution of the inter-aggregated pores due to the collapse of the intra-aggregated pores. At 100°C, the obtained TiO2 photocatalyst by this method shows good photocatalytic activity, and at 400°C, its photocatalytic activity exceeds that of Degussa P25. This may be attributed to the fact that the prepared TiO2 photocatalyst has higher specific surface areas, smaller crystallite size and bimodal pore size distribution.

Formation and crystallization behavior of Fe-based amorphous precursors with pre-existingα-Fe nanoparticles-Structure and magnetic properties of high-Cu-content Fe-Si-B-Cu-Nb nanocrystalline alloys

Structure,crystallization behavior,and magnetic properties of as-quenched and annealed Fe_(81.3)Si_(4)O_(13)Cu_(1.7)(Cu1.7)alloy ribbons and effects of Nb alloying have been studied.Three-dimensional atom probe and transmission electron microscopy analyses reveal that high-number-density Cu-clusters and Pre-existing Nano-sized a-Fe Particles(PN-a-Fe)are coexistence in the melt-spun Cu1.7 amorphous matrix,and the PN-α-Fe form by manners of one-direction adjoining and enveloping the Cu-clusters.Two-step crystallization behavior associated with growth of the PN-a-Fe and subsequent nucleation and growth of newly-formedα-Fe is found in the primary crystallization stage of the Cu1.7 alloy.The number densities of the Cu-clusters and PN-a-Fe in melt-spun Fe8_(1.3-x)Si_(4)B_(13)Cu_(1.7)Nb_(x)alloys are gradually reduced with enriching of Nb,and a fully amorphous structure forms at 4 at.%Nb,although smaller Cu-clusters still exist.After annealing,2 at.%Nb coarsens the average size(D_(α-F)e)of theα-Fe grains from 14.0 nm of the Nb-free alloy to 21.6 nm,and 4 at.%Nb refines the D_(α-Fe)to 8.9 nm.The mechanisms of theα-Fe nucleation and growth during quenching and annealing for the alloys with large quantities of PN-α-Fe as well as after Nb alloying have been discussed,and an annealing-induced oc-Fe growth mechanism in term of the barrier co-contributed by competitive growth among the PN-a-Fe and diffusion-suppression effect of Nb atoms has been proposed.A coercivity(HC)αDα-Fe^(3)correlation has been found for the nanocrystalline alloys,and the permeability is inverse with the H_(C).

Low Temperature Solvent Evaporation-induced Crystallization Synthesis of Nanocrystalline TiO_2 Photocatalyst

A novel and efficient methodology for obtaining highly active photocatalyst of bi phase TiO 2 with small particle size and high specific surface area was developed by solvent evaporation induced crystallization (SEIC) method at low temperature. The prepared TiO 2 powder was characterized with X ray diffraction (XRD), transmission electron microscopy (TEM) and BET surface areas. The photocatalytic activity was evaluated by the photocatalytic oxidation of acetone in air. The results showed that the photocatalytic activity of the TiO 2 powder prepared by this method approached that of Degussa P25. This may be attributed to the fact that the prepared TiO 2 powder had larger specific surface areas (265 m 2·g -1 ) and smaller crystallite size (about 5 nm), but relatively low crystallinity, as compared with Degussa P25.

Microstructure,magnetic domain and dynamic loss of surface-textured Fe-based nanocrystalline alloy

Heterogeneous coarse surface crystallites induced in the industrial Fe-rich nanocrystalline alloy is an obstacle for high-frequency and high-power commercial applications.Herein,the phase,crystal orientation,nanostructure and magnetic domain evolution of the surface-crystallized Fe-rich alloy were systematically investigated.Microstructure and inverse pole figures analysis confirms that the DOordered dendriticcrystallites bear<001>-oriented fiber texture before and after annealing at the free surface,while ultrafine nanocrystals are randomly oriented in the interior and wheel surface after annealing.As compared to zero magnetic-field-annealing,the transverse magnetic-field-annealing induces weakly oriented fiber texture and relatively uniform dendritic-crystallites at the surface,and uniform anisotropy in the interior and surface,which promotes smooth wall motion at the surface and magnetization rotation in the interior.This synergetic effect reduces the excess loss and leads reduction in dynamic loss at 1.0 T and10 kHz by 36%.

The Interfacial Defective Structure and Mechanical Property of Nanocrystalline Fe-based Alloys

Positron lifetime results showed that there are two kinds of interfacial defects in the nanocrystalline alloys obtained by crystallization of the amorphous alloy, namely free-volume-sized and nanovoid-sized defects. The former is smaller than a monovacancy; the latter is of the size of several monovacancies and is usually situated at the intersections of several interfaces. In comparison with the nanovoid-sized defect, though the free-volume-sized defect is a shallow trapping potential, the quantity can be as much as 90% of all defects. It should be noted that nanovoids can change remarkably in both size and concentration with grain growth. So it is imaginable that this type of defect will exert a great influence on the interfacial structure and properties of nanocrystalline materials. So far, reports in this aspect are still meager.

STM investigation of the nanostructure on nanocrystalline Fe_(73.5)Cu_1Nb_3Si_(13.5)B_9 prepared by amorphous crystallization

A new nanocrystalline alloy Fe73.5Cu1Nb3Si13.5B9 was cast initially as amorphous ribbons, and subsequent annealing above the crystallization temperature of the amorphous state created a homogeneous ultrafine grain structure of α-Fe（Si） solid solution with a typical grain diameter of 10—20 nm and a residual amorphous phase at the interface with a thickness of 4—5 atoms.

DTA (or DSC) Studies of the Effect of Cu, Nb on the Nanocrystalline Structure Formation After Crystallization of Fe-Si-B Amorphous Alloy

1 Introduction Many kinds of nanocrystalline alloys have been prepared after crystallization of the corresponding amorphous alloys and their typical compositions are Fe-M’-M'-Si-B, where M’=Cu and M'=Nb, Mo, V, Hf, Ta, etc. which are called the nanocrystalline structure formation(NSF) elements. They have become a new kind of soft magnetic alloys with excellent magnetic properties. So far, much significant progress has been achieved in

Influence of Temperature on the Inverse Hall-Petch Effect in Nanocrystalline Materials:Phase Field Crystal Simulation

The influence of temperature on the inverse Hall-Petch effect in nanocrystalline （NC） materials is investigated using phase field crystal simulation method. Simulated results indicate that the inverse Hall-Petch effect in NC materials becomes weakened at low temperature. The results also show that the change in microscopic deformation mechanism with temperature variation is the main reason for the weakening of the inverse Hall-Petch effect. At elevated temperature, grain rotation and grain boundary （GB） migration seriously reduce the yield stress so that the NC materials exhibit the inverse Hall-Petch effect. However, at low temperature, both grain rotation and GB migration occur with great difficulty, instead, the dislocations nucleated from the cusp of serrated GBs become active. The lack of grain rotation and GB migration during deformation is mainly responsible for the weakening of the inverse Hall-Petch effect. Furthermore, it is found that since small grain size is favorable for GB migration, the degree of weakening decreases with decreasing average grain size at low temperature.

Heterostructured crystallization mechanism and its effect on enlarging the processing window of Fe-based nanocrystalline alloys

The harsh melt-spinning and annealing processes of high saturation magnetization nanocrystalline softmagnetic alloys are the biggest obstacles for their industrialization. Here, we proposed a novel strategy to enlarge the processing window by annealing the partially crystallized precursor ribbons via a heterostructured crystallization process. The heterostructured evolution of Fe_(84.75)Si_(2)B_(9)P_(3)_(C0.5)Cu_(0.75)(at.%)alloy ribbons with different spinning rate were studied in detail, to demonstrate the gradient nucleation and grain refinement mechanisms. The nanocrystalline alloys made with industrially acceptable spinning rate of 25-30 m/s and normal annealing process exhibit excellent magnetic properties and fine nanostructure. The small quenched-in crystals/clusters in the free surface of the low spinning rate ribbons will not grow to coarse grains, because of the competitive grain growth and shielding effect of metalloid elements rich interlayer with a high stability. Avoiding the precipitation of quenched-in coarse grains in precursor ribbons is thus a new criterion for the composition and process design, which is more convenient than the former one with respect to the homogenous crystallization mechanism, and enable us to produce high performance nanocrystalline soft-magnetic alloys. This strategy is also suitable for improving the compositional adjustability, impurity tolerance, and enlarging the window of melt temperature,which is an important reference for the future development of composition and process.

纳米TiO_2粉晶的XRD研究

用溶胶－凝胶法制备了纳米了TiO2粉晶。对不同温度处理的系列粉末用X射线衍射进行了研究，发现所得粉晶随热处理温度的不同发生了从锐钛矿到金红石相的转变。对系列粉晶进行了X射线衍射点阵参量计算，结合所得到的晶粒度和微结构参数，发现纳米TiO2粉晶组元中存在着晶格畸变。而且随热处理温度的升高，粉末晶粒增大，锐钛矿相逐渐减少，金红石相逐渐增多，锐钛矿相与金红石相纳米粉晶的点阵参量呈现出了明显的变化，其晶格畸变与晶粒度和退火温度有较密切的关系，表现出尺寸效应和温度效应。

反相胶团软模板法制备氯化银晶体纳米线研究

The nanosystem has received considerable attention because of its peculiar pheno mena,which is different from macroscopy and microscopy. At present,the upsurge o f researching nanomaterials has shifted from nano particles to one dimensional na nosystem,such as nanowires,nanotubes,and so on.Seen from literatures, the repor ts on carbon nanotubes wer e more,on nanowires were less,and on transition metallic salt nanowires were noth ing .In this paper,AgCl nanocrystalline wires were successfully synthesized by Rever s e Micelle soft Templates, which will open a new way for the synthesis and applic ation of one dimensional nanomaterials.