Screening of Wheat Germplasm with High Flour Whiteness and Analysis of Its Quality

为了挖掘面粉白度高、品质优的小麦种质,对1 248份小麦种质资源进行了面粉白度测定,并对面粉白度值超过80的小麦种质的籽粒硬度、淀粉RVA糊化特性以及面团揉混特性等有关品质性状进行了分析。筛选出面粉白度值≥80的小麦种质195个,其籽粒硬度指数分布范围为15～77;淀粉RVA糊化特性参数峰值黏度范围为1 030～3 407cP,稀懈值范围为629～1 522cP,回生值范围为5～1 546cP,糊化温度范围为65.3～88.2℃,最终黏度范围为755～3 870cP;面团形成时间范围为1.3～4.2min,衰落角范围为3～35度,沉降值范围为21～58.7mL。研究结果还表明,面粉中类胡萝卜素含量低,则面粉白度就高,仅靠延长面粉储存时间不会大幅度提高面粉白度。筛选出的14个高白度优异小麦种质可用于培育中强筋面粉高白度小麦新品种。     

Mechanical response of multicrystalline thin films in mesoscale field dislocation mechanics

A continuum model of plasticity, Phenomenological Mesoscopic Field Dislocation Mechanics (PMFDM), is used to study the effect of surface passivation, grain orientation, grain boundary constraints, and film thickness on the mechanical response of multicrystalline thin films. The numerical experiments presented in this paper show that a surface passivation layer on thin films introduces thickness dependence of the mechanical response. However, the effect of passivation decreases in films with impenetrable grain boundaries. The orientation of individual grains of the multicrystal also has a significant effect on the mechanical response. Our results are in qualitative agreement with experimental observations. A primary contribution of this work is the implementation of a jump condition that enables the modeling of important limits of grain boundary constraints to plastic flow, independent of ad-hoc constitutive assumptions and interface conditions.     

Damage simulation of brittle heterogeneous materials at the grain size level

Microstructure models at the grain size level open new potentials for the numerical investigation of micromechanical damage and fracturing. This paper presents a strategy to model heterogeneous brittle structures composed of binder and aggregate using the Discrete Element Method (DEM). A discretisation concept for both components was developed and implemented using spherical particles as discrete elements. The aggregate grains were modelled by clusters of these particles. Special routines were developed to generate specimens, to simulate laboratory tests and to analyse these simulations. Methods were developed to calibrate homogeneous and heterogeneous material by the determination of appropriate constitutive laws and their corresponding parameters. The simulation strategy allows to distinguish in detail between inter- and intra-granular microfracturing, between shear- and tensile-cracking and between microcracks within or between the different components of the heterogeneous material. Exemplarily, selected simulation results are presented for MgO-concrete.     

Microstructure-property relations in composite yttria-substituted zirconia solid electrolytes

A study of composite 8 mol% yttria stabilized zirconia (8YSZ) and 3 mol% yttria tetragonal zirconia polycrystal (3YTZP) solid electrolytes sintered under isothermal and two-step sintering cycles is reported. The nominal phase composition is retained for composites with up to 25 wt.% 3YTZP. These composites show a combination of beneficial effects with respect to pure 8YSZ, including slight improvement in sinterability, gains in bulk and grain boundary conductivity and also enhanced fracture toughness. Impedance spectroscopy revealed an enhancement of the specific grain boundary conductivity for samples with finer grain sizes, attained by increasing the fraction of 3YTZP or by hindering grain growth under two-step sintering cycles. This effect is rationalized in terms of a decrease of the grain boundary space-charge potential. The conductivity gains decrease with increasing temperature, but even at 700 °C the total ionic conductivity of ceramics with 25 wt.% 3YTZP is still higher than that of pure 8YSZ, whereas at 900 °C there is a performance loss of less than 10%. The improved mechanical and electrical performance in the intermediate temperature range represents an important advantage of the heterostructured electrolytes for low/intermediate temperature SOFC operation.     

Growth dynamics and thermal stability of Ni nanocrystalline nanowires

The growth dynamics and the thermal stability of a Ni nanocrystalline nanowire (NNW) model system fabricated using electrochemical deposition has been investigated using X-ray diffraction, scanning and transition electron microcopy, and differential scanning calorimetry (DSC). It has been found that the thermal stability of the Ni-NNW is dominated by the microstructure movement and the grain boundary rotation mechanism at temperature ranging from 400 to 600 °C. The Ni-NNW experiences the Rayleigh instability at temperature approaching the melting point. The observed fragment separation in the Rayleigh phase-transition is much greater than that expected theoretically.     

Innovative processing using ultrafine particulation

Anodic sites like grain-boundaries, micro-voids, micro-inclusions and other stress concentration points such as dislocations, vacancies, etc., take an active part in the galvanic interactions occurring on the surface of metals and alloys. This paper discusses the role of low concentration reinforcement of metals like Zn, Pb and Sn, alloy matrices like Cu-Zn, Cu-Mn, Zn-Al and Al-Zn and non-metals like polyaniline, along with the amorphous Ni-P-B class of current-assisted electroless deposits. It is assumed that ultrafine ceramic particulates in low concentration ranges (1–1.5 wt%) may cover the anodic defect sites such that these anodic boundaries start behaving cathodically as a network, within the already existing cathodic grain matrices, because they are predominantly more cathodic, compared to the grain boundaries, voids, etc. As such, there is a considerable reduction of surface dissolution and in the anodic current of the matrix. It has been shown that surface dissolution is a minimum for a critical threshold concentration of the particulates, above which there is drastic dissolution of the surface. It appears that particulates above that critical concentration cannot be accommodated within the available anodic sites, such that they are dispersed on the grain proper in a random fashion, creating stress spikes and subsequent enhanced matrix dissolution. It further appears that it will thus be possible either to decrease or increase the dissolution of the composite matrices for selective tailor-made applications, by changing the concentration of these ultrafine particulates around the threshold concentration. It has been shown that such a technique may eventually reduce the leaching of copper from conventional brass matrices and also reduce the dissolution of tin in the packaging industries. Grain boundary structures of the metallic matrices have also been correlated with the particulate trapping capacity and their corresponding galvanic stress factors. It has also been applied to amorphous Ni-P-B types of metal-metalloid coatings, for enhancement of surface corrosion resistance. Particulation of epoxy and epoxy-silicone classes of barrier with ultrafine SiC has revealed a more positive potential and lower galvanic currents. Reinforcement of the permalloy type Ni-Fe-Mo class barrier with fine Al₂O₃ particulates has indicated considerable improvement of the polarization resistance values. Received: 25 January 1999 / Accepted: 19 October 1999     

Continuous hydrothermal synthesis of nanometric BaZrO3 in supercritical water

Nanocrystalline barium zirconate (BaZrO₃) was synthesized using a hydrothermal synthesis process working in supercritical conditions and in a continuous way. By this method, we succeeded in the continuous and rapid production of nanopowders. As a preliminary work three barium precursors have been investigated: barium hydroxide (Ba(OH)₂), barium acetate (Ba(CH₃COO)₂) and barium nitrate (Ba(NO₃)₂). Two of them (Ba(CH₃COO)₂ and Ba(NO₃)₂) led to the pure perovskite phase. Then an experimental design has been conducted in order to determine the influence of the experimental parameters on the crystallinity and the grain size of the final product.     

Influence of Dislocation Pile-Up on Main Crack Propagation in Nanocrystals in the Hydrogen Environment

The influence of material micro-defects on the main crack growth under pure shear loading is studied theoretically.The mechanism behind the initiation of micro-cracks and crack propagation induced by dislocation accumulation near the grain boundary(GB)is mainly considered,and the influence of dislocation accumulation on the main crack propagation is analyzed.The research results reveal that the initiation of micro-cracks near the GB is prior to the propagation of the main crack.In a hydrogen environment,hydrogen can cause serious embrittlement of the crack tip and promote crack growth.The energy release rate in the main crack growth direction in the dislocation emission direction is the highest.Therefore,the main crack will eventually merge with the micro-cracks at the GB along the direction of the slip band,resulting in fracture of the crystal material.The research presented in this paper provides some new information for the first stage of crack propagation and contributes to the analysis of the mechanism of crystal metal fracture.