共查询到20条相似文献，搜索用时 45 毫秒
1.
应用X-射线衍射方法对不同水分含量的玉米淀粉颗粒的结晶度进行了研究。只有在玻璃态情况下,淀粉的无定型区域才产生X-射线衍射图样,衍射峰的强度、面积在某种程度上依赖于淀粉的含水量。玉米淀粉颗粒的X-射线衍射图形是由两部分组成的:微晶区域和无定型区域。随着水分含量的增加,样品的结晶度从小到大,并达到一个平衡值(约45%)。室温下,当水分含量处于低水平时(小于11.25%),玉米淀粉颗粒中的无定型区域处于玻璃态,衍射图形显示的是微晶区域和无定型区域两部分的衍射图形的综合。当水分含量处于较高水平时(大于18.55%),淀粉颗粒中的无定型区域处于橡胶态,其X-射线衍射图形仅由微晶区域形成。在较低水分含量时(小于18.55%),由于塑化作用的影响,增大含水量会导致更多的微晶的形成。当水分含量超过18.55%之后,再增大水分,就会导致微晶片层和剩余的无定型片层的同时分解。 相似文献
2.
Jeanloz R Ahrens TJ Lally JS Nord GL Christie JM Heuer AH 《Science (New York, N.Y.)》1977,197(4302):457-459
Transmission electron microscope (TEM) observations of an experimentally shock-deformed single crystal of natural peridot, (Mg(0.88)Fe(0.12))(2)SiO(4), recovered from peak pressures of about 56 x 10(9) pascals revealed the presence of amorphous zones located within crystalline regions with a high density of tangled dislocations. This is the first reported observation of olivine glass. The shocked sample exhibits a wide variation in the degree of shock deformation on a small scale, and the glass appears to be intimately associated with the highest density of dislocations. This study suggests that olivine glass may be formed as a result of shock at pressures above about 50 to 55 x 10(9) pascals and that further TEM observations of naturally shocked olivines may demonstrate the presence of glass. 相似文献
3.
Molecular dynamics simulations reveal the mechanism of the structural memory effect in alpha-berlinite (AlPO(4)), where a single crystal transforms to an amorphous solid by compression and then reverts to the original crystalline structure upon release of pressure. The enhanced oxygen coordination around the aluminum atoms in AlPO(4) at high pressure leads to a mechanical instability that causes the phase transformation. The difference in the structural memory behavior between AlPO(4) and isostructural alpha-quartz, for which the pressure-induced amorphized phase is recoverable, can be attributed to the presence of the PO(4) units, which remain essentially four-coordinated even when severely distorted. 相似文献
4.
为了研究证明含蜡原油流变曲线和微观蜡晶两者之间存在一定的关联,测试了广范围剪切速率下的含蜡原油流变曲线,确立了微观蜡晶和流变曲线之间的定性关系,并且取得以下认识：广范围剪切速率下的含蜡原油流变曲线能够一定程度地体现微观蜡晶特征,其中低剪切速率下的流变曲线能够体现蜡晶形态,高剪切速率下的流变曲线能够体现蜡晶结构;并非温度越低,剪切速率对粘度的影响程度越大,在高剪切速率下,有可能存在相反的情况;在低温条件下,剪切速率存在一个临界值,只有当剪切速率大于该值时,粘度才会出现较为明显的下降;温度越低,形成的蜡晶网格结构越稳定,需要较大的剪切应力,蜡晶网格结构才能破坏。该研究成果深化了对含蜡原油流变性的认识,具有一定的理论意义。（图6,表1,参15） 相似文献
5.
[目的]对铜尾矿废弃地中的氧化铁进行研究,探讨不同类型氧化铁对土壤形成过程的影响。[方法]以铜陵2处不同时间弃置的铜尾矿废弃地为对象,采用化学分析法研究了自然生态恢复过程中3类铁氧化物（无定形氧化铁、游离氧化铁和络合态氧化铁）的含量。[结果1尾矿废弃物无定形氧化铁含量为（1．73±0．77）～（9．68±2．94）g/kg,氧化铁活化度为（4．80±3．85）％-（91．94±4．34）％;游离氧化铁、晶质态氧化铁含量和游离度分别为（9．10±1．57）～（42．77±12．69）、（2．50±0．57）～（42．05±13．46）g／kg和（8．17±1．77）％～（20．02．±5．38）％;成土时间较短的杨山冲铜尾矿废弃地不同发育层尾矿中3种氧化铁含量差异较小,而弃置时间较长的铜官山尾矿废弃地随深度增加无定形氧化铁逐渐降低,游离氧化铁和络合态氧化铁逐渐增加。相关分析表明：2处尾矿废弃地pH值与无定形氧化铁含量及氧化铁活化度呈极显著正相关．而与游离氧化铁含量、铁游离度、晶质态氧化铁含量和络合态氧化铁含量呈极显著负相关;有机质含量与无定形氧化铁含量和氧化铁活化度呈极显著负相关,而与游离氧化铁含量、游离度及晶质态氧化铁含量呈极显著正相关.目前,铜陵铜尾矿废弃地尚处于成土过程的初期阶段,大量问题仍有待于进一步研究。[结论]探索了自然生态恢复过程中尾矿废弃地中铁氧化物的形态、含量变化特征及其影响因素,为进一步揭示铜尾矿及类似尾矿废弃物的成土过程、成土机制等理论研究提供参考。 相似文献
6.
Zeng Q Sheng H Ding Y Wang L Yang W Jiang JZ Mao WL Mao HK 《Science (New York, N.Y.)》2011,332(6036):1404-1406
Glass lacks the long-range periodic order that characterizes a crystal. In the Ce(75)Al(25) metallic glass (MG), however, we discovered a long-range topological order corresponding to a single crystal of indefinite length. Structural examinations confirm that the MG is truly amorphous, isotropic, and unstrained, yet under 25 gigapascals hydrostatic pressures, every segment of a centimeter-length MG ribbon devitrifies independently into a face-centered cubic (fcc) crystal with the identical orientation. By using molecular dynamics simulations and synchrotron x-ray techniques, we elucidate that the mismatch between the large Ce and small Al atoms frustrates the crystallization and causes amorphization, but a long-range fcc topological order still exists. Pressure induces electronic transition in Ce, which eliminates the mismatch and manifests the topological order by the formation of a single crystal. 相似文献
7.
T Ishikawa S Kajii K Matsunaga T Hogami Y Kohtoku T Nagasawa 《Science (New York, N.Y.)》1998,282(5392):1295-1297
A sintered silicon carbide fiber-bonded ceramic, which consists of a highly ordered, close-packed structure of very fine hexagonal columnar fibers with a thin interfacial carbon layer between fibers, was synthesized by hot-pressing plied sheets of an amorphous silicon-aluminum-carbon-oxygen fiber prepared from an organosilicon polymer. The interior of the fiber element was composed of sintered beta-silicon carbide crystal without an obvious second phase at the grain boundary and triple points. This material showed high strength (over 600 megapascals in longitudinal direction), fibrous fracture behavior, excellent high-temperature properties (up to 1600 degreesC in air), and high thermal conductivity (even at temperatures over 1000 degreesC). 相似文献
8.
The melting of pure ice single crystals can be inhibited by the presence of an antifreeze glycopeptide isolated from an Antarctic fish. This inhibition effect exhibits crystallographic dependence and can result in superheating of the crystal by heat conduction across the ice-solution interface. The antifreeze molecules inhibit melting in a manner more or less symmetrical to their well-known effect of inhibiting freezing. The melting effect is best expressed at concave ice interfaces, whereas the freezing effect is best expressed at convex ones. Both are restricted to orientations near (1010) with the particular antifreeze that was used. 相似文献
9.
We report microstructural and isotopic analyses of two presolar Al2O3 grains. Aluminum oxide is important cosmically, because its presence has been detected in the infrared spectra of the circumstellar envelopes of O-rich asymptotic giant branch stars and because it is predicted to be the first solid to condense in these stellar environments. The two grain structures, one corundum and the other amorphous, confirm that asymptotic giant branch stars produce both phases. The variation in structure and Ti content demonstrates that Al2O3 can condense in the absence of TiO2 seed clusters but that Ti may be important in determining the crystal structure. 相似文献
10.
Oppenlander GC 《Science (New York, N.Y.)》1968,159(3821):1311-1319
Through control of the crystallization process many polymers can be made to exhibit a broad spectrum of structural possibilities, ranging from a state of high disorder to one of high order. Emphasis has been placed on bulk-crystallized polymers which normally fall near the center of this spectrum. This was done in part because polymers are most commonly fabricated in this manner, and also because the amount of attention given in recent years to crystals grown from dilute solution has tended to obscure important aspects of the structure of bulk-crystallized polymers. Differences in the structure of the interlamellar regions account most reasonably for many of the variations in mechanical properties that crystalline polymers can be made to display. The interlamellar amorphous model, proposed here as a structural model for bulk-crystallized polymers, largely neglects the lamellae themselves, because so little is known about the structure of the lamellae of bulk-crystallized polymers and how variations in lamellar structure can affect properties. This model is intended, therefore, as both a working hypothesis to aid further investigation and as an outline to be filled in as more is learned about the supramolecular structure of crystalline polymers (31). 相似文献
11.
The mechanisms of the phase transformations between the spinel (gamma) and modified spinel (beta) polymorphs of Mg(2)SiO(4) have been studied experimentally between 15 and 20 gigapascals and 800 degrees to 950 degrees C. The gamma to beta transformation occurs by a shear mechanism, whereas the beta to gamma transformation involves grain-boundary nucleation and interface-controlled growth. These contrasting mechanisms are a consequence of the number of independent slip systems that are available in the respective crystal structures. This result leads to the prediction that in subduction zones and perhaps also rising plumes in the Earth's mantle, the gamma to beta transformation should be accompanied by a transient reduction in strength. 相似文献
12.
James OB 《Science (New York, N.Y.)》1969,165(3897):1005-1008
Jadeite (high-pressure sodium aluminum pyroxene) has been identified in a shock-phase assemblage of oligoclase. The shock assemblage consists of minute particles with high refractive indices that contain at least two phases: one (identified by x-ray) is a jadeite that is nearly pure NaAlSi(2)O(6); the other has the chemical composition of oligoclase minus jadeite and appears to be largely amorphous. 相似文献
13.
We report the growth of binary colloidal crystals with control over the crystal orientation through a simple layer-by-layer process. Well-ordered single binary colloidal crystals with a stoichiometry of large (L) and small (S) particles of LS2 and LS were generated. In addition, we observed the formation of an LS3 superstructure. The structures formed as a result of the templating effect of the first layer and the forces exerted by the surface tension of the drying liquid. By using spheres of different composition, one component can be selectively removed, as is demonstrated in the growth of a hexagonal non-close-packed colloidal crystal. 相似文献
14.
Schaefer DW 《Science (New York, N.Y.)》1989,243(4894):1023-1027
Concepts borrowed from polymer science have been applied to tailor the properties of inorganic materials, especially those derived from amorphous precursors. Fractal geometry can be used to characterize macromolecular precursors and to relate their structures to kinetic growth processes. Within the silica system, for example, it is possible to manipulate the conditions of solution polymerization to yield a variety of macromolecules from branched chains to smooth colloidal particles. 相似文献
15.
转Bt基因植物中杀虫蛋白的酶联免疫检测技术研究Ⅰ.Bt菌HD-1的杀虫晶体蛋白抗原制备 总被引：4，自引：2，他引：2
研究了培养时间对苏云金杆菌(Bacillusthuringiensis)HD-1菌株孢晶混合物的产量、杀虫晶体蛋白裂解液的种类和处理温度与时间对杀虫晶体蛋白提取率及纯度的影响。结果表明BtHD-1菌株在Bt生长繁殖平板培养基上,30℃下培养41～55h均可获得大量孢晶混合物。采用50mmol/LNa2CO3裂解液处理孢晶混合物,可获得纯度高的130kD杀虫晶体蛋白,而用40mmol/LNaOH提取的杀虫晶体蛋白中含有较多杂蛋白。所研究的处理温度和时间对杀虫晶体蛋白提取量和组成无明显影响。这些结果为杀虫晶体蛋白抗原的制备提供了依据。 相似文献
16.
L Wang B Liu H Li W Yang Y Ding SV Sinogeikin Y Meng Z Liu XC Zeng WL Mao 《Science (New York, N.Y.)》2012,337(6096):825-828
Solid-state materials can be categorized by their structures into crystalline (having periodic translation symmetry), amorphous (no periodic and orientational symmetry), and quasi-crystalline (having orientational but not periodic translation symmetry) phases. Hybridization of crystalline and amorphous structures at the atomic level has not been experimentally observed. We report the discovery of a long-range ordered material constructed from units of amorphous carbon clusters that was synthesized by compressing solvated fullerenes. Using x-ray diffraction, Raman spectroscopy, and quantum molecular dynamics simulation, we observed that, although carbon-60 cages were crushed and became amorphous, the solvent molecules remained intact, playing a crucial role in maintaining the long-range periodicity. Once formed, the high-pressure phase is quenchable back to ambient conditions and is ultra-incompressible, with the ability to indent diamond. 相似文献
17.
Temperature (T)- and frequency (omega)-dependent conductivity measurements are reported here in amorphous niobium-silicon alloys with compositions (x) near the zero-temperature metal-insulator transition. There is a one-to-one correspondence between the frequency- and temperature-dependent conductivity on both sides of the critical concentration, thus establishing the quantum-critical nature of the transition. The analysis of the conductivity leads to a universal scaling function and establishes the critical exponents. This scaling can be described by an x-, T-, and omega-dependent characteristic length, the form of which is derived by experiment. 相似文献
18.
Hotspots, basalts, and the evolution of the mantle 总被引：2，自引：0，他引：2
Anderson DL 《Science (New York, N.Y.)》1981,213(4503):82-89
The trace element concentration patterns of continental and ocean island basalts and of mid-ocean ridge basalts are complementary. The relative sizes of the source regions for these fundamentally different basalt types can be estimated from the trace element enrichment-depletion patterns. Their combined volume occupies most of the mantle above the 670 kilometer discontinuity. The source regions separated as a result of early mantle differentiation and crystal fractionation from the resulting melt. The mid-ocean ridge basalts source evolved from an eclogite cumulate that lost its late-stage enriched fluids at various times to the shallower mantle and continental crust. The mid-ocean ridge basalts source is rich in garnet and clinopyroxene, whereas the continental and ocean island basalt source is a garnet peridotite that has experienced secondary enrichment. These relationships are consistent with the evolution of a terrestrial magma ocean. 相似文献
19.
X-ray diffraction studies confirm that, with few exceptions, each skeletal element of echtinoderms is a single crystal of magnesium-rich calcite and that a relation exists between the shape of the element and the crystallographic a- and c-axes. The exceptions incluide the teeth of echinoids, and the calcareous ring as well as the anal teeth of holothurians. The tubercles of an echinoid plate begin their growth as parts of the single crystal of the plate; under the mechanical action of the spines that are attached to them, they become partly polycrystalline, as shown by scanning electron microscopy and by x-ray powder diffraction. The interface between inorganic crystalline and organic amorphous matter in the skeletal element appears to be the first example reported in nature of a periodic mninimal suirface. 相似文献
20.
We present a blueprint for a three-dimensional photonic band gap (PBG) material that is amenable to large-scale microfabrication on the optical scale using glancing angle deposition methods. The proposed chiral crystal consists of square spiral posts on a tetragonal lattice. In the case of silicon posts in air (direct structure), the full PBG can be as large as 15% of the gap center frequency, whereas for air posts in a silicon background (inverted structure) the maximum PBG is 24% of the center frequency. This PBG occurs between the fourth and fifth bands of the photon dispersion relation and is very robust to variations (disorder) in the geometrical parameters of the crystal. 相似文献